Plasma etching method and plasma etching unit

The present invention is a plasma etching method including: an arranging step of arranging a pair of electrodes oppositely in a chamber and making one of the electrodes support a substrate to be processed in such a manner that the substrate is arranged between the electrodes, the substrate having a silicon film and an inorganic-material film adjacent to the silicon film; and an etching step of applying a high-frequency electric power to at least one of the electrodes to form a high-frequency electric field between the pair of the electrodes, supplying a process gas into the chamber to form a plasma of the process gas by means of the electric field, and selectively plasma-etching the silicon film of the substrate by means of the plasma; wherein a frequency of the high-frequency electric power applied to the at least one of the electrodes is 50 to 150 MHz in the etching step.

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Description
FIELD OF THE INVENTION

The present invention relates to a plasma etching method and a plasma etching unit of plasma-etching a silicon film formed on a substrate to be processed such as a semiconductor wafer, which has the silicon film and an inorganic-material film adjacent to the silicon film.

DESCRIPTION OF THE RELATED ART

In a manufacturing step of a semiconductor device, a multilayer film including a silicon film, such as a poly-silicon film, and insulating films is formed on a semiconductor wafer, and then a plasma-etching process is conducted in order to form a predetermined wiring pattern.

In order to conduct the plasma-etching process, various kinds of units are used. Among them, a capacitive-coupling type of parallel-plate plasma etching unit is used mainly. In the capacitive-coupling type of parallel-plate plasma etching unit, a pair of parallel-plate electrodes (upper electrode and lower electrode) are arranged in a chamber, a process gas is introduced into the chamber, and a high-frequency electric power is applied to at least one of the electrodes to form a high-frequency electric field between the electrodes. By means of the high-frequency electric field, plasma of the process gas is generated so that a plasma-etching process is conducted to a substrate to be processed.

In such a plasma processing unit, a high-frequency electric power of 13.56 to 40 MHz is applied to the lower electrode in order to conduct the etching process.

In such conditions, for example, when a silicon film such as a poly-silicon film is etched with a mask of an inorganic-material film such as an SiO2, the etching process is conducted under a relatively high pressure in order to enhance an etching selectivity with respect to the inorganic-material film.

However, when the etching process is conducted under the conventional relatively high pressure, although the etching selectivity of the silicon film with respect to the inorganic-material film is enhanced, an etching geometric control performance is not good. This problem is arisen not only in the case using the mask of the inorganic-material film, but also in another case wherein an inorganic-material film is formed as a base of the silicon film.

SUMMARY OF THE INVENTION

This invention is developed by focusing the aforementioned problems in order to resolve them effectively. An object of the present invention is to provide a plasma etching method and a plasma etching unit that can etch a silicon film adjacent to an inorganic-material film with a high etching selective ratio and a good etching geometric control performance.

According to a result of study by the inventors, in the etching process of the silicon film such as a poly-silicon film, plasma density is dominant, and ion energy contributes only a little. On the other hand, in the etching process of the inorganic-material film such as a SiO2 film or a SiN film, both the plasma density and the ion energy are necessary. Thus, if the plasma density is high and the ion energy is low to some extent, an etching selective ratio of the silicon film with respect to the inorganic-material film can be enhanced. In the case, the ion energy of the plasma indirectly corresponds to a self-bias electric voltage of an electrode at the etching process. Thus, in order to raise the etching selective ratio of the silicon film with respect to the inorganic-material film, finally, it is necessary to etch the silicon film under a condition of high plasma density and low bias.

On the other hand, in order to improve the etching geometric control performance, it is necessary to conduct the process under a low pressure. However, under the above conditions, a process under a lower pressure can achieve a high etching selective ratio. That is, if a high plasma density and a low self-bias electric voltage are achieved, the etching selective ratio of the silicon film with respect to the inorganic-material film can be enhanced under a lower pressure. Thus, a high etching selective ratio and a good etching geometric control performance may not be in conflict with each other.

According to a further result of study by the inventors, when the frequency of the high-frequency electric power applied to the electrode is high, a condition wherein the plasma density is high and the self-bias electric voltage is low can be generated.

The present invention is a plasma etching method comprising: an arranging step of arranging a pair of electrodes oppositely in a chamber and making one of the electrodes support a substrate to be processed in such a manner that the substrate is arranged between the electrodes, the substrate having a silicon film and an inorganic-material film adjacent to the silicon film; and an etching step of applying a high-frequency electric power to at least one of the electrodes to form a high-frequency electric field between the pair of the electrodes, supplying a process gas into the chamber to form a plasma of the process gas by means of the electric field, and selectively plasma-etching the silicon film of the substrate by means of the plasma; wherein a frequency of the high-frequency electric power applied to the at least one of the electrodes is 50 to 150 MHz in the etching step.

According to the present invention, since the frequency of the high-frequency electric power applied to the electrode is 50 to 150 MHz, which is higher than prior art, even under a condition of a lower pressure, a high plasma density and a low self-bias electric voltage can be achieved. Thus, the silicon film can be etched with a high etching selective ratio with respect to the inorganic-material film and with a good geometric control performance.

It is preferable that the frequency of the high-frequency electric power applied to the electrode is 70 to 100 MHz, in particular 100 MHz.

In addition, in the etching step, it is preferable that power density of the high-frequency electric power is 0.15 to 5 W/cm2.

In addition, in the etching step, it is preferable that plasma density in the chamber is 5×109 to 2×1010 cm−3.

In addition, in the etching step, it is preferable that a pressure in the chamber is not higher than 13.3 Pa.

In addition, the present invention is a plasma etching method comprising: an arranging step of arranging a pair of electrodes oppositely in a chamber and making one of the electrodes support a substrate to be processed in such a manner that the substrate is arranged between the electrodes, the substrate having a silicon film and an inorganic-material film adjacent to the silicon film; and an etching step of applying a high-frequency electric power to at least one of the electrodes to form a high-frequency electric field between the pair of the electrodes, supplying a process gas into the chamber to form a plasma of the process gas by means of the electric field, and selectively plasma-etching the silicon film of the substrate by means of the plasma; wherein in the etching step, the process gas includes at least one of an HBr gas and a Cl2 gas, plasma density in the chamber is 5×109 to 2×1010 cm−3, and a self-bias electric voltage of the electrode supporting the substrate to be processed is not higher than 200 V.

According to the present invention, under a condition wherein the plasma density in the chamber is 5×109 to 2×1010 cm−3 and the self-bias electric voltage of the electrode supporting the substrate to be processed is not higher than 200 V, plasma of the gas including at least one of an HBr gas and a Cl2 gas is generated, so that the silicon film can be etched with a high etching selective ratio with respect to the inorganic-material film and with a good geometric control performance.

In the above, the inorganic-material film may comprises at least one of a silicon oxide, a silicon nitride, a silicon oxinitride, and a silicon carbide.

In addition, it is preferable that the high-frequency electric power is applied to an electrode supporting the substrate to be processed. In the case, a second high-frequency electric power of 3.2 to 13.56 MHz may be applied to the electrode supporting the substrate to be processed, the second high-frequency electric power being overlapped with the high-frequency electric power. By overlapping the second high-frequency electric power of a lower frequency with the high-frequency electric power, plasma density and ion drawing effect can be adjusted so that an etching rate of the silicon film can be raised more while a high etching selective ratio with respect to the inorganic-material film can be assured.

It is preferable that a frequency of the second high-frequency electric power is 13.56 MHz. If the frequency of the second high-frequency electric power is 13.56 MHz, it is preferable that power density of the second high-frequency electric power is not higher than 0.64 W/cm2. In addition, if the second high-frequency electric power of 3.2 to 13.56 MHz is applied, it is preferable that a self-bias electric voltage of the electrode supporting the substrate to be processed is not higher than 200 V.

In addition, the present invention is a plasma etching unit comprising: a chamber configured to contain a substrate to be processed having a silicon film and an inorganic-material film adjacent to the silicon film; a pair of electrodes arranged in the chamber, one of the pair of electrodes being configured to support the substrate to be processed; a process-gas supplying system configured to supply a process gas into the chamber; a gas-discharging system configured to discharge a gas in the chamber; and a high-frequency electric power source configured to supply a high-frequency electric power for forming a plasma to at least one of the electrodes; wherein a frequency of the high-frequency electric power generated from the high-frequency electric power source is 50 to 150 MHz.

It is preferable that the frequency of high-frequency electric power generated from the high-frequency electric power source is 70 to 100 MHz, in particular 100 MHz.

Preferably, power density of the high-frequency electric power is 0.15 to 5 W/cm2.

In addition, it is preferable that a pressure in the chamber is not higher than 13.3 Pa.

In addition, preferably, the high-frequency electric power is applied to an electrode supporting the substrate to be processed.

In addition, preferably, the plasma etching unit further comprises: a second high-frequency electric power source configured to apply a second high-frequency electric power of 3.2 MHz to 13.56 MHz to the electrode supporting the substrate to be processed, the second high-frequency electric power being overlapped with the high-frequency electric power. In the case, preferably, a frequency of the second high-frequency electric power is 13.56 MHz. In addition, preferably, power density of the second high-frequency electric power is not higher than 0.64 W/cm2.

Herein, because of the Paschen's law, an electric-discharge starting voltage Vs takes a local minimum value (Paschen's minimum value) when a product pd of a gas pressure p and a distance d between the electrodes takes a certain value. The certain value of the product pd that corresponds to the Paschen's minimum value is smaller when the frequency of the high-frequency electric power is higher. Thus, when the frequency of the high-frequency electric power is high, in order to decrease the electric-discharge starting voltage Vs to facilitate and stabilize the electric-discharge effect, the distance d between the electrodes has to be reduced, if the gas pressure p is constant. Thus, in the present invention, it is preferable that the distance between the electrodes is shorter than 50 mm. In addition, when the distance between the electrodes is shorter than 50 mm, residence time of the gas in the chamber can be shortened. Thus, reaction products can be efficiently discharged, and etching stop can be reduced.

In addition, it is preferable that the plasma etching unit further comprises a magnetic-field forming unit configured to form a magnetic field around a plasma region between the pair of electrodes.

When the frequency of the applied high-frequency electric power is high, the etching rate may be higher in a central portion as a feeding position compared with in a peripheral portion. However, if a magnetic field is formed around a plasma region between the pair of electrodes, plasma confining effect can be achieved so that the etching rate on the substrate to be processed arranged in a processing space can be made substantially the same between in an edge portion (peripheral portion) of the substrate to be processed and in a central portion thereof. That is, the etching rate can be made uniform.

It is preferable that strength of the magnetic field formed around a plasma region between the pair of electrodes by the magnetic-field forming unit is 0.03 to 0.045 T (300 to 450 Gauss).

In addition, it is preferable that a focus ring is provided around the electrode supporting the substrate to be processed, and that when the magnetic-field forming unit forms a magnetic field around a plasma region between the pair of electrodes, strength of the magnetic field on the focus ring is not lower than 0.001 T (10 Gauss) and strength of the magnetic field on the substrate to be processed is not higher than 0.001 T.

When the strength of the magnetic field on the focus ring is not lower than 0.001 T, drift movement of electrons may be generated on the focus ring, so that the plasma density around the focus ring is raised to make the plasma density uniform. On the other hand, when the strength of the magnetic field on the substrate to be processed is not higher than 0.001 T, which substantially has no effect on the substrate to be processed, charge-up damage can be prevented.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic vertical sectional view showing a plasma etching unit of an embodiment according to the present invention;

FIG. 2 is a horizontal sectional view schematically showing a magnetic annular unit arranged around a chamber of the plasma etching unit of FIG. 1;

FIG. 3 is a sectional views showing a structural example of semiconductor wafer to which a plasma etching process according to the present invention is applied;

FIG. 4 is a sectional views showing another structural example of semiconductor wafer to which a plasma etching process according to the present invention is applied;

FIG. 5 is a schematic sectional view partly showing a plasma processing unit comprising a high-frequency electric power source for generating plasma and a high-frequency electric power source for drawing ions;

FIG. 6 is a graph showing relationships between the absolute value of a self-bias electric voltage |Vdc| and plasma density Ne, in respective cases wherein the frequency of the high-frequency electric power is 40 MHz or 100 MHz, when the plasma consists of argon gas;

FIG. 7A is a graph showing etching rates of a poly-silicon film at a wafer position, in respective cases wherein the high-frequency electric power is 500 W, 1000 W or 1500 W, when the frequency of the high-frequency electric power is 100 MHz;

FIG. 7B is a graph showing etching rates of a poly-silicon film at a wafer position, in respective cases wherein the high-frequency electric power is 500 W or 1000 W, when the frequency of the high-frequency electric power is 40 MHz;

FIG. 8 is a graph showing relationships between a high-frequency electric power and an etching rate of the poly-silicon film, in respective cases wherein the frequency of the high-frequency electric power is 40 MHz or 100 MHz;

FIG. 9 is a graph showing relationships between a high-frequency electric power and an etching rate of the SiO2 film, in respective cases wherein the frequency of the high-frequency electric power is 40 MHz or 100 MHz;

FIG. 10 is a graph showing relationships between a high-frequency electric power and an etching rate of the poly-silicon film and relationships between a high-frequency electric power and a ratio (an etching rate of the poly-silicon film/an etching rate of the SiO2 film) corresponding to an etching selective ratio, in respective cases wherein the frequency of the high-frequency electric power is 40 MHz or 100 MHz;

FIG. 11 is a graph showing relationships between an etching rate of the poly-silicon film and a ratio (an etching rate of the poly-silicon film/an etching rate of the SiO2 film) corresponding to an etching selective ratio, in respective cases wherein the frequency of the high-frequency electric power is 40 MHz or 100 MHz;

FIG. 12A is a graph showing relationships between a pressure in the chamber at the etching process and an etching rate of the poly-silicon film, in respective cases wherein the frequency of the high-frequency electric power is 40 MHz or 100 MHz;

FIG. 12B is a graph showing relationships between a pressure in the chamber at the etching process and an etching rate of the SiO2 film, in respective cases wherein the frequency of the high-frequency electric power is 40 MHz or 100 MHz;

FIG. 13 is a graph showing relationships between a pressure in the chamber and a ratio (an etching rate of the poly-silicon film/an etching rate of the SiO2 film) corresponding to an etching selective ratio, in respective cases wherein the frequency of the high-frequency electric power is 40 MHz or 100 MHz;

FIG. 14 is a graph showing relationships between a pressure in the chamber and an etching rate of the poly-silicon film and relationships between a high-frequency electric power and a ratio (an etching rate of the poly-silicon film/an etching rate of the SiO2 film) corresponding to an etching selective ratio, in respective cases wherein the frequency of the high-frequency electric power is 40 MHz or 100 MHz;

FIG. 15 is a graph showing relationships between an etching rate of the poly-silicon film and a ratio (an etching rate of the poly-silicon film/an etching rate of the SiO2 film) corresponding to an etching selective ratio, in respective cases wherein the frequency of the high-frequency electric power is 40 MHz or 100 MHz;

FIG. 16 is a graph showing relationships between the absolute value of a self-bias electric voltage |Vdc| and plasma density Ne, when the plasma consists of a HBr gas, in respective cases wherein the high-frequency electric power is 500 W, 1000 W, 1500 W or 2000 W, the frequency of the high-frequency electric power being 100 MHz, and the second high-frequency electric power is 0 W, 200 W or 600 W, the frequency of the second high-frequency electric power being 13.56 MHz;

FIG. 17 is a graph showing relationships between a high-frequency electric power and an etching rate of the poly-silicon film and relationships between a high-frequency electric power and a ratio (an etching rate of the poly-silicon film/an etching rate of the SiO2 film) corresponding to an etching selective ratio;

FIG. 18 is a graph showing relationships between a second high-frequency electric power and an etching rate of the poly-silicon film and relationships between a second high-frequency electric power and a ratio (an etching rate of the poly-silicon film/an etching rate of the SiO2 film) corresponding to an etching selective ratio; and

FIG. 19 is a graph comparatively showing relationships between an Ar-gas flow rate and a pressure difference ΔP of a central portion of the wafer and a peripheral portion thereof, in respective cases wherein an electrode gap is 25 mm or 40 mm, wherein the Ar gas is used as a plasma gas.

DESCRIPTION OF THE PREFERRED EMBODIMENT

An embodiment of the invention will now be described with reference to the attached drawings.

FIG. 1 is a schematic sectional view showing a plasma etching unit used for carrying out the present invention. The etching unit of the embodiment includes a two-stage cylindrical chamber vessel 1, which has an upper portion 1a having a small diameter and an lower portion 1b having a large diameter. The chamber vessel 1 may be hermetically made of any material, for example aluminum.

A supporting table 2 is arranged in the chamber vessel 1 for horizontally supporting a wafer W as a substrate to be processed. The supporting table 2 may be made of any material, for example aluminum. The supporting table 2 is placed on a conductive supporting stage 4 via an insulation plate 3. A focus ring 5 is arranged on a peripheral area of the supporting table 2. The focus ring 5 may be made of any conductive material or any insulating material. When the diameter of the wafer W is 200 mmφ, it is preferable that the focus ring 5 is 240 to 280 mmφ. The supporting table 2, the insulation plate 3, the supporting stage 4 and the focus ring 5 can be elevated by a ball-screw mechanism including a ball-screw 7. A driving portion for the elevation is arranged below the supporting stage 4 and is covered by a bellows 8. The bellows 8 may be made of any material, for example stainless steel (SUS). The chamber vessel 1 is earthed. A coolant passage (not shown) is formed in the supporting table 2 in order to cool the supporting table 2. A bellows cover 9 is provided around the bellows 8.

A feeding cable 12 for supplying a high-frequency electric power is connected to a substantially central portion of the supporting table 2. The feeding cable 12 is connected to a high-frequency electric power source 10 via a matching box 11. A high-frequency electric power of a predetermined frequency is adapted to be supplied from the high-frequency electric power source 10 to the supporting table 2. A showerhead 16 is provided above the supporting table 2 and oppositely in parallel with the supporting table 2. The showerhead 16 is also earthed. Thus, the supporting table 2 functions as a lower electrode, and the showerhead 16 functions as an upper electrode. That is, the supporting table 2 and the showerhead 16 form a pair of plate electrodes.

Herein, it is preferable that the distance between the electrodes is set to be shorter than 50 mm. The reason is as follows.

Because of the Paschen's law, an electric-discharge starting voltage Vs takes a local minimum value (Paschen's minimum value) when a product pd of a gas pressure p and a distance d between the electrodes takes a certain value. The certain value of the product pd that corresponds to the Paschen's minimum value is smaller when the frequency of the high-frequency electric power is higher. Thus, when the frequency of the high-frequency electric power is high like the present embodiment, in order to decrease the electric-discharge starting voltage Vs to facilitate and stabilize the electric-discharge effect, the distance d between the electrodes has to be reduced, if the gas pressure p is constant. Thus, it is preferable that the distance between the electrodes is shorter than 50 mm. In addition, when the distance between the electrodes is shorter than 50 mm, residence time of the gas in the chamber can be shortened. Thus, reaction products can be efficiently discharged, and etching stop can be reduced.

However, if the distance between the electrodes is too short, pressure distribution on the surface of the wafer W as a substrate to be processed (pressure difference between in a central portion and in a peripheral portion) may become large. In the case, problems such as deterioration of etching uniformity may be generated. Independently on gas flow rate, in order to make the pressure difference smaller than 0.27 Pa (2 mTorr), it is preferable that the distance between the electrodes is not shorter than 35 mm.

An electrostatic chuck 6 is provided on an upper surface of the supporting table 2 in order to electrostaticly stick to the wafer W. The electrostatic chuck 6 consists of an insulation plate 6b and an electrode 6a inserted in the insulation plate 6b. The electrode 6a is connected to a direct-current power source 13. Thus, when the direct-current power source 13 supplies an electric power to the electrode 6a, the semiconductor wafer W may be stuck to the electrostatic chuck 6 by coulomb force, for example.

The coolant passage not shown is formed in the supporting table 2. The wafer W can be controlled at a predetermined temperature by circulating a suitable coolant in the coolant passage. In order to efficiently transmit heat of cooling from the suitable coolant to the wafer W, a gas-introducing mechanism (not shown) for supplying a He gas onto a reverse surface of the wafer W is provided. In addition, a baffle plate 14 is provided at an outside area of the focus ring 5. The baffle plate 14 is electrically connected to the chamber vessel 1 via the supporting stage 4 and the bellows 8.

The showerhead 16 facing the supporting table 2 is provided in a ceiling of the chamber vessel 1. The showerhead 16 has a large number of gas jetting holes 18 at a lower surface thereof and a gas introducing portion 16a at an upper portion thereof. Then, an inside space 17 is formed between the gas introducing portion 16a and the large number of gas jetting holes 18. The gas introducing portion 16a is connected to a gas supplying pipe 15a. The gas supplying pipe 15a is connected to a process-gas supplying system 15, which can supply a process gas for etching that consists of a reaction gas and a diluent gas.

As the reaction gas, any halogen gas may be used. As the diluent gas, an Ar gas, a He gas, or any other gas generally used in this field may be used.

The process gas is supplied from the process-gas supplying system 15 into the space 17 of the showerhead 16 through the gas supplying pipe 15a and the gas introducing portion 16a. Then, the process gas is jetted from the gas jetting holes 18 in order to etch a film formed on the wafer W.

A discharging port 19 is formed at a part of a side wall of the lower portion 1b of the chamber 1. The discharging port 19 is connected to a gas-discharging system 20 including a vacuum pump. A pressure of an inside of the chamber vessel 1 may be reduced to a predetermined vacuum level by operating the vacuum pump. A transferring port for the wafer W and a gate valve 24 for opening and closing the transferring port are arranged at an other upper part of the side wall of the lower portion 1b of the chamber vessel 1.

A magnetic annular unit 21 is concentrically arranged around the upper portion 1a of the chamber vessel 1. Thus, a magnetic field may be formed around a processing space between the supporting table 2 and the showerhead 16. The magnetic annular unit 21 may be caused to revolve around a center axis thereof (along an annular peripheral edge thereof) by a revolving mechanism 25.

The magnetic annular unit 21 has a plurality of segment magnets 22 which are supported by a holder not shown and which are arranged annularly. Each of the plurality of segment magnets 22 consists of a permanent magnet. In the embodiment, 16 segment magnets 22 are arranged annularly (concentrically) in a multi-pole state. That is, in the magnetic annular unit 21, adjacent two segment magnets 22 are arranged in such a manner that their magnetic-pole directions are opposite. Thus, a magnetic line of force is formed between the adjacent two segment magnets 22 as shown in FIG. 2, so that a magnetic field of 0.02 to 0.2 T (200 to 2000 Gauss), preferably 0.03 to 0.045 T (300 to 450 Gauss), is generated only around the processing space. On the other hand, in a region wherein the wafer is placed, a substantially non-magnetic field state is generated. The above strength of the magnetic field is determined because of the following reasons: if the magnetic field is too strong, a fringing field may be caused; and if the magnetic field is too weak, plasma confining effect can not be achieved. Of course, the suitable strength of the magnetic field also depends on the unit structure or the like. That is, the range of the suitable strength of the magnetic field may be different for respective units.

When the above magnetic field is formed around the processing space, strength of the magnetic field on the focus ring 5 is desirably not lower than 0.001 T (10 Gauss). In the case, drift movement of electrons (E×B drift) is generated on the focus ring, so that the plasma density around the wafer is increased, and hence the plasma density is made uniform. On the other hand, in view of preventing charge-up damage of the wafer W, strength of the magnetic field in a portion where the wafer W is positioned is desirably not higher than 0.001 T (10 Gauss).

Herein, the substantially non-magnetic state in a region occupied by the wafer means a state that there is not a magnetic field affecting the etching process in the area occupied by the wafer. That is, the substantially non-magnetic state includes a state that there is a magnetic field not substantially affecting the wafer process.

In the state shown in FIG. 2, a magnetic field whose density is not more than 0.42 mT (4.2 Gauss) is applied to a peripheral area of the wafer. Thus, plasma confining function can be achieved.

When a magnetic field is formed by the magnetic annular unit of the multi-pole state, wall portions of the chamber 1 corresponding to the magnetic poles (for example, portions shown by P in FIG. 2) may be locally whittled. Thus, the magnetic annular unit 21 may be caused to revolve along the peripheral direction of the chamber by the above revolving mechanism 25. Thus, it is avoided that the magnetic poles are locally abutted (located) against the chamber wall, so that it is prevented that the chamber wall is locally whittled.

Each segment magnet 22 is configured to freely revolve around a perpendicular axis thereof by a segment-magnet revolving mechanism not shown. Then, when the segment magnets 22 are caused to revolve, the state wherein the multi-pole magnetic field is substantially formed and the state wherein the multi-pole magnetic field is not formed can be switched. Depending on a process condition, the multi-pole magnetic field may be effective or not. Thus, when the state wherein the multi-pole magnetic field is formed and the state wherein the multi-pole magnetic field is not formed can be switched, a suitable state can be selected correspondingly to the process condition.

As the state of the magnetic field is changed depending on the arrangement of the segment magnets, when the arrangement of the segment magnets is changed variously, various profiles of magnetic field can be formed. Thus, it is preferable to arrange the segment magnets so as to obtain a required profile of magnetic field.

The number of the segment magnets is not limited to the above examples. The section of each segment magnet is not limited to the rectangle, but may have any shape such as a circle, a square, a trapezoid or the like. A magnetic material forming the segment magnets 22 is also not limited, but may be any known magnetic material such as a rare-earth magnetic material, ferrite magnetic material, an Arnico magnetic material, or the like.

The above plasma etching unit can be used for an etching process to a poly-silicon film adjacent to an inorganic-material film such as an SiO2 film or an SiN film. An operation for the etching process by means of the plasma etching unit is explained.

For example, as shown in FIG. 3, a wafer W to be etched has a structure wherein a poly-silicon film 32 is formed on a silicon substrate 31 and wherein an inorganic-material film 33 having a predetermined pattern as a hard mask is formed on the poly-silicon film 32. Alternatively, as shown in FIG. 4, a wafer W has another structure wherein an inorganic-material film 42 consisting of SiO2 as a gate oxide film is formed on a silicon film 41, wherein a poly-silicon film 43 as a gate is formed on the inorganic-material film 42, and wherein a resist film 44 having a predetermined pattern as a mask is formed on the poly-silicon film 43.

The inorganic-material film 33 consists of a material generally used as a hard mask. As a suitable example, it may be a silicon oxide, a silicon nitride, a silicon oxinitride, a silicon carbide, or the like. That is, it is preferable that the inorganic-material film 43 consists of at least one of the above materials.

In each of the above wafers W, the poly-silicon film 32 or 43 is etched. At first, the gate valve 24 is opened, the wafer W is conveyed into the chamber 1 by means of a conveying arm, and placed on the supporting table 2. After that, the conveying arm is evacuated, the gate valve 24 is closed, and the supporting table 2 is moved up to a position shown in FIG. 1. The vacuum pump of the gas-discharging system 20 creates a predetermined vacuum in the chamber 1 through the discharging port 19.

Then, a predetermined process gas, for example an HBr gas, is introduced into the chamber 1 through the process-gas supplying system 15, for example at a flow rate of 0.02 to 0.4 L/min (20 to 400 sccm). Thus, a pressure in the chamber 1 is maintained at a predetermined pressure. In this state, a high-frequency electric power whose frequency is 50 to 150 MHz, preferably 70 to 100 MHz, is supplied from the high-frequency electric power source 10 to the supporting table 2. In this case, power per unit area i.e. power density is preferably within a range of about 0.15 to about 5.0 W/cm2. Then, a predetermined electric voltage is applied from the direct current power source 13 to the electrode 6a of the electrostatic chuck 6, so that the wafer W sticks to the electrostatic chuck 6 by means of Coulomb force, for example.

When the high-frequency electric power is applied to the supporting table 2 as the lower electrode as described above, a high-frequency electric field is formed in the processing space between the showerhead 16 as the upper electrode and the supporting table 2 as the lower electrode. Thus, the process gas supplied into the processing space is made plasma, which etches the poly-silicon film on the wafer W.

During the etching step, by means of the annular magnetic unit 21 of a multi-pole state, a magnetic field as shown in FIG. 2 can be formed around the processing space. In the case, plasma confining effect is achieved, so that an etching rate of the wafer W may be made uniform, even in a case of a high frequency like this embodiment wherein the plasma tends to be not uniform. However, depending on the process condition, it is preferable that the magnetic field is not formed. In the case, the segment magnets 22 may be caused to revolve in order to conduct the etching process under a condition wherein a magnetic field is substantially not formed around the processing space.

When the above magnetic field is formed, by means of the electrically conductive or insulating focus ring 5 provided around the wafer W on the supporting table 2, the effect of making the plasma process uniform can be more enhanced. That is, if a plasma density at a peripheral portion of the wafer is high and an etching rate at the peripheral portion of the wafer is larger than that at a central portion of the wafer, by using a focus ring made of an electrically conductive material such as silicon or SiC, even a focus-ring region functions as the lower electrode. Thus, a plasma-forming region is expanded over the focus ring 5, the plasma process around the wafer W is promoted, so that uniformity of the etching rate is improved. In addition, if a plasma density at the peripheral portion of the wafer is low and an etching rate at the peripheral portion of the wafer is smaller than that at the central portion of the wafer, by using a focus ring made of an electrically insulating material such as quartz, electric charges can not be transferred between the focus ring 5 and electrons and ions in the plasma. Thus, the plasma confining effect may be increased so that uniformity of the etching rate is improved.

In order to adjust plasma density and ion-drawing effect, the high-frequency electric power for generating plasma and a second high-frequency electric power for drawing ions may be overlapped with each other. Specifically, as shown in FIG. 5, in addition to the high-frequency electric power source 10 for generating plasma, a second high-frequency electric power source 26 for drawing ions is connected to the matching box 11, so that they are overlapped. In the case, the frequency of the second high-frequency electric power source 26 for drawing ions is preferably 3.2 to 13.56 MHz, in particular 13.56 MHz. Thus, the number of parameters for controlling ion energy is increased so that an optimum processing condition can be easily set wherein an etching rate of the poly-silicon film is raised more while a necessary and sufficient etching selective ratio with respect to the inorganic-material film is assured.

Herein, according to a result of study by the inventors, in the etching process of the poly-silicon film, the plasma density is dominant, and the ion energy contributes only a little. On the other hand, in the etching process of the inorganic-material film, both the plasma density and the ion energy are necessary. Thus, as shown in FIGS. 3 and 4, in the etching process of the poly-silicon film adjacent to the inorganic-material film, in order to etch the poly-silicon film with a high etching selective ratio with respect to the inorganic-material film, the plasma density has to be high and the ion energy has to be low. That is, if the ion energy necessary for etching the inorganic-material film is low and the plasma density dominant for etching the poly-silicon film is high, only the poly-silicon film can be selectively etched. Herein, the ion energy of the plasma indirectly corresponds to a self-bias electric voltage of an electrode at the etching process. Thus, in order to etch the poly-silicon film with a high etching selective ratio, finally, it is necessary to etch the organic-material film under a condition of high plasma density and low self-bias electric voltage.

On the other hand, in order to improve the etching geometric control performance, it is necessary to conduct the etching process under a low pressure. However, when the above condition is satisfied, a process under a lower pressure can achieve a high etching selective ratio. That is, if a high plasma density and a low self-bias electric voltage are achieved, the etching selective ratio of the poly-silicon film with respect to the inorganic-material film can be enhanced even under a lower pressure. Thus, a high etching selective ratio and a good etching geometric control performance can not be in conflict with each other. For that purpose, it was found that the frequency of the high-frequency electric power to be applied to the electrode is 50 to 150 MHz, which is higher than prior art.

This is explained with reference to FIG. 6 as follows. FIG. 6 is a graph showing relationships between the absolute value of a self-bias electric voltage |Vdc| and plasma density Ne, in respective cases wherein the frequency of the high-frequency electric power is 40 MHz or 100 MHz. The transverse axis represents the absolute value of a self-bias electric voltage |Vdc|, and the ordinate axis represents the plasma density Ne. In the case, as the plasma gas, Ar was used for evaluation, instead of real etching gas. For each frequency, applied high-frequency electric power was changed, so that values of the plasma density Ne and the absolute value of a self-bias electric voltage |Vdc| were changed. That is, in the respective frequencies, if the applied high-frequency electric power is large, both the plasma density Ne and the absolute value of a self-bias electric voltage |Vdc| are large. Herein, the plasma density was measured by means of a microwave interferometer.

As shown in FIG. 6, in the case wherein the frequency of the high-frequency electric power is conventionally 40 MHz, when the plasma density is increased to enhance the etching rate of the poly-silicon film, the absolute value of a self-bias electric voltage |Vdc| is greatly increased. On the other hand, in the case wherein the frequency of the high-frequency electric power is 100 MHz that is higher than prior art, even when the plasma density is increased, the absolute value of a self-bias electric voltage |Vdc| is not so increased and controlled substantially not higher than 100 V. That is, it was found that a condition of high plasma density and low self-bias electric voltage can be achieved. That is, if the frequency is relatively low like a conventional art, when the etching rate of the poly-silicon film is increased in a real etching process under a low pressure, the inorganic-material film is also etched to the same extent and good selective-etching performance is not achieved. On the other hand, if the frequency is as high as 100 MHz, it was found that the poly-silicon film can be etched with a high etching selective ratio with respect to the inorganic-material film.

In addition, as seen from FIG. 6, in order to etch the poly-silicon film under a low pressure with a higher etching selective ratio by higher plasma density and lower self-bias electric voltage than prior art, when the plasma of Ar gas is formed, it may be thought preferable to form the plasma under a condition wherein the plasma density is not less than 1×1010 cm−3 and the self-bias electric voltage of the electrode is not higher than 100 V. Alternatively, the plasma density is not less than 5×1010 cm−3 and the self-bias electric voltage of the electrode is not higher than 200 V. Then, in order to satisfy such a plasma condition, it may be estimated that the frequency of the high-frequency electric power has to be 50 MHz or higher.

Thus, the frequency of the high-frequency electric power for generating plasma is set not less than 50 MHz, as described above. However, if the frequency of the high-frequency electric power for generating plasma is higher than 150 MHz, the uniformity of the plasma may be deteriorated. Thus, it is preferable that the frequency of the high-frequency electric power for generating plasma is not higher than 150 MHz. In particular, in order to effectively achieve the above effect, it is preferable that the frequency of the high-frequency electric power for generating plasma is 70 to 100 MHz.

It is preferable that a pressure in the chamber at the etching process is not higher than 13.3 Pa (100 mT). From a view of preventing any conflict between the etching selective ratio of the poly-silicon film with respect to the inorganic-material film and the etching geometric control performance, it is more preferable that a pressure in the chamber is not higher than 4 Pa (30 mT). If the etching geometric control performance is thought to be more important, it is further more preferable that a pressure in the chamber is not higher than 1.33 Pa (10 mT).

Next, in order to obtain a real etching rate of an poly-silicon film and an etching selective ratio with respect to an inorganic-material film, etching experiments for whole-surface formed films of an poly-silicon film and an inorganic-material film (SiO2) were conducted. The result is explained.

Herein, a 200 mm wafer was used as the wafer W, an HBr gas: 0.2 L/min (0.02 L/min only when the pressure is 0.133 Pa) was supplied as an etching gas, the gap between the electrodes was 27 mm, and the pressure in the chamber was 4 Pa.

FIG. 7A is a graph showing etching rates of a poly-silicon film at a wafer position, in respective cases wherein the high-frequency electric power is 500 W (1.59 W/cm2), 1000 W (3.18 W/cm2) or 1500 W (4.77 W/cm2), when the frequency of the high-frequency electric power is 100 MHz. FIG. 7B is a graph showing etching rates of a poly-silicon film at a wafer position, in respective cases wherein the high-frequency electric power is 500 W (1.59 W/cm2), 1000 W (3.18 W/cm2) or 1500 W (4.77 W/cm2), when the frequency of the high-frequency electric power is 40 MHz. FIG. 8 is a graph showing relationships between a high-frequency electric power and an etching rate of the poly-silicon film, in respective cases wherein the frequency of the high-frequency electric power is 40 MHz or 100 MHz. FIG. 9 is a graph showing relationships between a high-frequency electric power and an etching rate of the SiO2 film, in respective cases wherein the frequency of the high-frequency electric power is 40 MHz or 100 MHz. FIG. 10 is a graph showing relationships between a high-frequency electric power and an etching rate of the poly-silicon film and relationships between a high-frequency electric power and a ratio (an etching rate of the poly-silicon film/an etching rate of the SiO2 film) corresponding to an etching selective ratio, in respective cases wherein the frequency of the high-frequency electric power is 40 MHz or 100 MHz. FIG. 11 is a graph showing relationships between an etching rate of the poly-silicon film and a ratio (an etching rate of the poly-silicon film/an etching rate of the SiO2 film) corresponding to an etching selective ratio, in respective cases wherein the frequency of the high-frequency electric power is 40 MHz or 100 MHz.

As seen from these drawings, the etching rate of the poly-silicon film tends to be increased when the high-frequency electric power is increased. However, there is no great difference between those in the cases of 40 MHz and 100 MHz. In addition, at the same gas pressure and the same power, the etching rates of the poly-silicon film in the cases of 40 MHz and 100 MHz are at the same level, but the etching rate of the SiO2 film in the case of 40 MHz is higher than that in the case of 100 MHz. Thus, it was confirmed that the ratio corresponding to an etching selective ratio (an etching rate of the poly-silicon film/an etching rate of the SiO2 film) is higher in the case of 100 MHz than in the case of 40 MHz. That is, from the experimental result of the samples for estimation, at the pressure of 4 Pa, it was confirmed that the possibility of etching the poly-silicon film with a high etching selective ratio is higher in the case of 100 MHz than in the case of 40 MHz. If the power of the high-frequency electric power is increased too much, the etching rate of the poly-silicon film is increased but the etching selective ratio is decreased, because the etching rate and the etching selective ratio of the poly-silicon film are in a tradeoff relationship. Thus, it is preferable that the power density of the high-frequency electric power of 100 MHz is not higher than 5 W/cm2 (about 1500 W).

On the other hand, in the case of 100 MHz, when the power density is decreased, the etching rate of the poly-silicon film is decreased and the etching selective ratio with respect to the SiO2 film is improved. If a base film of a film to be etched is a gate oxide film such as a SiO2 film, since the base film has usually a thickness of several nm, the etching rate of the SiO2 film has to be decreased to an order of 0.1 nm/min. For example, when the pressure condition is 1.33 Pa (10 mT) and the power density is 1.5 W/cm2 (about 500 W), the etching rate of the poly-silicon film is 100 nm/min, the etching selective ratio is 70, and the etching rate of the SiO2 film is 1.43 nm/min. Thus, in order to decrease the etching rate of the SiO2 film to the order of 0.1 nm/min, it is estimated that the power density has to be decreased to about 0.15 to 0.3 W/cm2 (about 50 to 100 W). Taking into account the above point, it is preferable that the minimum high-frequency electric power is not lower than 0.3 W/cm2, in particular not lower than 0.15 W/cm2 (about 50 W). In view of only the etching selectivity, it is preferable that the high-frequency electric power is not higher than 1.5 W/cm2 (about 500 W).

Next, other etching processes were conducted while the flow rate of the HBr gas was changed within a range of 0.02 to 0.2 L/min, the pressure in the chamber was changed within a range of 0.133 to 13.3 Pa, the high-frequency electric power was fixed to 500 W, and the other conditions were the same as the above.

FIG. 12A is a graph showing relationships between a pressure in the chamber at the etching process and an etching rate of the poly-silicon film, in respective cases wherein the frequency of the high-frequency electric power is 40 MHz or 100 MHz. FIG. 12B is a graph showing relationships between a pressure in the chamber at the etching process and an etching rate of the SiO2 film, in respective cases wherein the frequency of the high-frequency electric power is 40 MHz or 100 MHz. FIG. 13 is a graph showing relationships between a pressure in the chamber and a ratio (an etching rate of the poly-silicon film/an etching rate of the SiO2 film) corresponding to an etching selective ratio, in respective cases wherein the frequency of the high-frequency electric power is 40 MHz or 100 MHz. FIG. 14 is a graph showing relationships between a pressure in the chamber and an etching rate of the poly-silicon film and relationships between a high-frequency electric power and a ratio (an etching rate of the poly-silicon film/an etching rate of the SiO2 film) corresponding to an etching selective ratio, in respective cases wherein the frequency of the high-frequency electric power is 40 MHz or 100 MHz. FIG. 15 is a graph showing relationships between an etching rate of the poly-silicon film and a ratio (an etching rate of the poly-silicon film/an etching rate of the SiO2 film)-corresponding to an etching selective ratio, in respective cases wherein the frequency of the high-frequency electric power is 40 MHz or 100 MHz.

As seen from these drawings, at the same high-frequency electric power and the same pressure in the chamber, the etching rate of the poly-silicon film is a little higher and the etching selective ratio is also higher in the case of 100 MHz than in the case of 40 MHz. In addition, as the same high-frequency electric power, a high etching selective ratio can be achieved at a lower pressure in the case of 100 MHz than in the case of 40 MHz. In addition, as shown in FIG. 15, at the same high-frequency electric power and the same etching rate, the etching selective ratio is higher in the case of 100 MHz than in the case of 40 MHz. That is, in the case of 100 MHz, a high etching selective ratio can be achieved under a condition of a lower pressure, which is advantageous in the etching geometric control performance, so that both the high etching selectivity and the good etching geometric control performance can be achieved.

Regarding the effect of the pressure, in the both cases of 40 MHz and 100 MHz, when the pressure is higher, the etching rate and the etching selective ratio of the poly-silicon film are better. However, in view of the etching geometric control performance of the poly-silicon film, it was confirmed that a lower pressure is preferable, specifically not higher than 13.3 Pa.

Next, a real etching gas (HBr) was used and a high-frequency electric power of 100 MHz was applied to measure the absolute value of a self-bias electric voltage |Vdc| and plasma density Ne. The measurement results are explained.

FIG. 16 is a graph showing relationships between the absolute value of a self-bias electric voltage |Vdc| and plasma density Ne, when the plasma consists of a HBr gas and the frequency of the high-frequency electric power is 100 MHz. The transverse axis represents the absolute value of a self-bias electric voltage |Vdc|, and the ordinate axis represents the plasma density Ne. The plasma density was measured by means of a microwave interferometer.

Herein, the pressure in the chamber was 2.7 Pa (20 mTorr). In addition, the high-frequency electric power of 100 MHz was changed within a range of 500 to 2000 W so that the plasma density Ne and the absolute value of a self-bias electric voltage |Vdc| were changed. In addition, when the high-frequency electric power of 100 MHz was 500 W, a second high-frequency electric power of 0 W, 200 W or 600 W, whose frequency was 13.56 MHz, was overlapped with the high-frequency electric power.

As seen from FIG. 16, in the respective frequencies, when the applied high-frequency electric power is larger, both the plasma density Ne and the absolute value of a self-bias electric voltage |Vdc| are larger.

As shown in FIG. 16, in the case of the plasma of the real etching gas, compared with the plasma of the Ar gas (see FIG. 6), the plasma density tends to be a little lower. In addition, when the second high-frequency electric power of the lower frequency (13 MHz) is overlapped to increase the power, the self-bias electric voltage tends to be increased.

In addition, as seen from FIG. 16, when the second high-frequency electric power is not overlapped and the plasma density is increased, the absolute value of a self-bias electric voltage |Vdc| is not increased so much, but maintained at about 100 V or less. That is, it was found that the high plasma density and the low self-bias electric voltage can be achieved.

FIG. 17 is a graph showing relationships between a high-frequency electric power and an etching rate of the poly-silicon film and relationships between a high-frequency electric power and a ratio (an etching rate of the poly-silicon film/an etching rate of the SiO2 film) corresponding to an etching selective ratio, wherein the second high-frequency electric power is not overlapped.

When the high-frequency electric power is increased, the etching rate of the poly-silicon film is increased but the selective ratio is decreased. Thus, it is preferable that the high-frequency electric power is not higher than about 1500 W (about 4.77 W/cm2). On the other hand, when the high-frequency electric power is decreased, the etching rate is decreased but the selective ratio is increased. Thus, it is preferable that the high-frequency electric power is not lower than about 500 W (about 1.5 W/cm2).

As seen from FIGS. 16 and 17, it was confirmed that a necessary etching rate of the poly-silicon film can be achieved while the poly-silicon film can be etched with a high etching selective ratio with respect to the inorganic-material film, by means of the high frequency of 100 MHz.

In addition, as seen from FIGS. 16 and 17, it is thought preferable that the plasma density is 5×109 to 2×1010 cm−3 and the self-bias electric voltage of an electrode is not higher than 200 V, in order to etch the poly-silicon film with a high selective ratio and a required etching rate at a low pressure.

Herein, as a process gas, instead of the gas including an HBr, a gas including a Cl2 gas may be used. In the latter case, it was confirmed that a suitable range of the plasma density is the same as the above.

FIG. 18 is a graph showing relationships between a second high-frequency electric power and an etching rate of the poly-silicon film and relationships between a second high-frequency electric power and a ratio (an etching rate of the poly-silicon film/an etching rate of the SiO2 film) corresponding to an etching selective ratio, wherein the high-frequency electric power is fixed to 500 W and the second high-frequency electric power is overlapped with the high-frequency electric power.

As seen from FIGS. 16 and 18, when the second high-frequency electric power of 13 MHz is overlapped to increase the electric power, the etching rate is increased and the self-bias electric voltage of an electrode is also increased. When the self-bias electric voltage is increased, the etching selective ratio tends to be decreased. However, until the self-bias electric voltage reaches 200 V, that is, the second high-frequency electric power reaches about 200 W (about 0.64 W/cm2), the etching selective ratio can be maintained within an allowable range.

Thus, by increasing the overlapped second high-frequency electric power (bias electric power), the etching rate can be enhanced while the etching selective ratio can be maintained at 10 or more.

In the above experiments, the gap between the electrodes was 27 mm. As described above, if the distance between the electrodes is too small, pressure distribution (pressure difference between at a central portion and at a peripheral portion) on the surface of the wafer W, which is a substrate to be processed, becomes so large that deterioration of the etching uniformity or the like may be generated. Thus, in practice, the distance between the electrodes is preferably 35 to 50 mm. This is explained with reference to FIG. 19.

FIG. 19 is a graph comparatively showing relationships between an Ar-gas flow rate and a pressure difference ΔP of a central portion of the wafer and a peripheral portion thereof, in respective cases wherein the electrode gap is 25 mm or 40 mm, wherein the Ar gas is used as a plasma gas. As shown in FIG. 20, the pressure difference ΔP is smaller when the gap is 40 mm rather than 25 mm. In addition, in the case of the gap of 25 mm, when the Ar-gas flow rate is increased, the pressure difference ΔP tends to be sharply increased. When the gas flow rate is higher than about 0.3 L/min, it exceeds 0.27 Pa (2 mTorr) as an allowable maximum pressure difference ΔP, at which deterioration of the etching uniformity or the like may not be generated. On the other hand, in the case of the gap of 40 mm, independently on the gas flow rate, the pressure difference is smaller than 0.27 Pa (2 mTorr). Thus, it can be expected that the allowable maximum pressure difference ΔP at which deterioration of the etching uniformity or the like may not be generated is ensured, independently on the gas flow rate, if the electrode gap is not less than about 35 mm.

The present invention is not limited to the above embodiment but may be variously modified. For example, in the above embodiment, the silicon film is the poly-silicon film. However, the silicon film may be a mono-crystal silicon film, an amorphous silicon film, or any other silicon film.

In addition, in the above embodiment, as the magnetic-field generating means, the annular magnetic unit in the multi-pole state is used wherein the plurality of segment magnets consisting of permanent magnets are arranged annularly around the chamber. However, the present invention is not limited to this manner if a magnetic-field can be formed around the processing space to confine the plasma. In addition, the peripheral magnetic field for confining the plasma may be unnecessary. That is, the etching process can be conducted under a condition wherein there is no magnetic field. In addition, the present invention can be applied to a plasma etching process conducted in a crossed electromagnetic field wherein a horizontal magnetic field is applied to the processing space.

In addition, in the above embodiment, the high-frequency electric power for generating plasma is applied to the lower electrode, but may be applied to the upper electrode. The layer structure of the substrate to be processed is not limited to those shown in FIGS. 3 and 4. In addition, the semiconductor wafer is taken as an example of the substrate to be processed. However, this invention is not limited thereto, but applicable to an etching process for a silicon film in another type of substrate to be processed.

Claims

1. A plasma etching method comprising:

an arranging step of arranging a pair of electrodes oppositely in a chamber and making one of the electrodes support a substrate to be processed in such a manner that the substrate is arranged between the electrodes, the substrate having a silicon film and an inorganic-material film adjacent to the silicon film, and
an etching step of applying a high-frequency electric power to at least one of the electrodes to form a high-frequency electric field between the pair of the electrodes, supplying a process gas into the chamber to form a plasma of the process gas by means of the electric field, and selectively plasma-etching the silicon film of the substrate by means of the plasma,
wherein, in the etching step, a frequency of the high-frequency electric power applied to the at least one of the electrodes is 50 to 150 MHz and a pressure in the chamber is not higher than 13.3 Pa.

2. A plasma etching method according to claim 1, wherein

the frequency of the high-frequency electric power applied to the at least one of the electrodes is 100 MHz in the etching step.

3. A plasma etching method according to claim 1, wherein

in the etching step, power density of the high-frequency electric power is 0.15 to 5 W/cm2.

4. A plasma etching method according to claim 1, wherein

in the etching step, plasma density in the chamber is 5×109 to 2×1010 cm−3.

5. A plasma etching method according to claim 1, wherein

the inorganic-material film comprises at least one of a silicon oxide, a silicon nitride, a silicon oxinitride, and a silicon carbide.

6. A plasma etching method according to claim 1, wherein

in the etching step, the high-frequency electric power is applied to an electrode supporting the substrate to be processed.

7. A plasma etching method according to claim 6, wherein

in the etching step, a second high-frequency electric power of 3.2 MHz to 13.56 MHz is applied to the electrode supporting the substrate to be processed, the second high-frequency electric power being overlapped with the high-frequency electric power.

8. A plasma etching method comprising:

an arranging step of arranging a pair of electrodes oppositely in a chamber and making one of the electrodes support a substrate to be processed in such a manner that the substrate is arranged between the electrodes, the substrate having a silicon film and an inorganic-material film adjacent to the silicon film, and
an etching step of applying a high-frequency electric power to at least one of the electrodes to form a high-frequency electric field between the pair of the electrodes, supplying a process gas into the chamber to form a plasma of the process gas by means of the electric field, and selectively plasma-etching the silicon film of the substrate by means of the plasma,
wherein
in the etching step, a frequency of the high-frequency electric power applied to the at least one of the electrodes is 50 to 150 MHz,
in the etching step, the high-frequency electric power is applied to an electrode supporting the substrate to be processed,
in the etching step, a second high-frequency electric power is applied to the electrode supporting the substrate to be processed, the second high-frequency electric power being overlapped with the high-frequency electric power, and
a frequency of the second high-frequency electric power is 13.56 MHz.

9. A plasma etching method according to claim 8, wherein

power density of the second high-frequency electric power is not higher than 0.64 W/cm2.

10. A plasma etching method according to claim 7, wherein

in the etching step, a self-bias electric voltage of the electrode supporting the substrate to be processed is not higher than 200 V.

11. A plasma etching method according to claim 1, wherein

a distance between the pair of electrodes is shorter than 50 mm.

12. A plasma etching method comprising:

an arranging step of arranging a pair of electrodes oppositely in a chamber and making one of the electrodes support a substrate to be processed in such a manner that the substrate is arranged between the electrodes, the substrate having a silicon film and an inorganic-material film adjacent to the silicon film, and
an etching step of applying a high-frequency electric power to at least one of the electrodes to form a high-frequency electric field between the pair of the electrodes, supplying a process gas into the chamber to form a plasma of the process gas by means of the electric field, and selectively plasma-etching the silicon film of the substrate by means of the plasma,
wherein
in the etching step, a frequency of the high-frequency electric power applied to the at least one of the electrodes is 50 to 150 MHz, and
in the etching step, a magnetic field is formed around a plasma region between the pair of electrodes to achieve a plasma confining effect.

13. A plasma etching method according to claim 12, wherein

strength of the magnetic field formed around the plasma region between the pair of electrodes is 0.03 to 0.045 T (300 to 450 Gauss).

14. A plasma etching method according to claim 13, wherein

when the magnetic field is formed around the plasma region between the pair of electrodes, strength of the magnetic field on a focus ring provided around the substrate to be processed is not lower than 0.001 T (10 Gauss) and strength of the magnetic field on the substrate to be processed is not higher than 0.001 T.

15. A plasma etching method according to claim 1, wherein

the silicon film comprises poly-silicon.

16. A plasma etching method comprising:

an arranging step of arranging a pair of electrodes oppositely in a chamber and making one of the electrodes support a substrate to be processed in such a manner that the substrate is arranged between the electrodes, the substrate having a silicon film and an inorganic-material film adjacent to the silicon film, and
an etching step of applying a high-frequency electric power to at least one of the electrodes to form a high-frequency electric field between the pair of the electrodes, supplying a process gas into the chamber to form a plasma of the process gas by means of the electric field, and selectively plasma-etching the silicon film of the substrate by means of the plasma,
wherein in the etching step, the process gas includes at least one of an HBr gas and a Cl2 gas, plasma density in the chamber is 5×109 to 2×1010 cm−3, a self-bias electric voltage of the electrode supporting the substrate to be processed is not higher than 200 V, and a pressure in the chamber is not higher than 13.3 Pa.

17. A plasma-etching-condition confirming method comprising:

an arranging step of arranging a pair of electrodes oppositely in a chamber and making one of the electrodes support a substrate to be processed in such a manner that the substrate is arranged between the electrodes, the substrate having a silicon film and an inorganic-material film adjacent to the silicon film, and
a plasma-forming step of applying a high-frequency electric power to at least one of the electrodes to form a high-frequency electric field between the pair of the electrodes, and supplying an Ar gas into the chamber to form a plasma of the Ar gas by means of the electric field,
wherein in the plasma-forming step, a confirming step is carried out to confirm that plasma density in the chamber is not lower than 1×1010 cm−3 and that a self-bias electric voltage of the electrode supporting the substrate to be processed is not higher than 100 V.

18. A plasma etching unit comprising:

a chamber configured to contain a substrate to be processed having a silicon film and an inorganic-material film adjacent to the silicon film,
a pair of electrodes arranged in the chamber, one of the pair of electrodes being configured to support the substrate to be processed,
a process-gas supplying system configured to supply a process gas into the chamber,
a gas-discharging system configured to discharge a gas in the chamber, and
a high-frequency electric power source configured to supply a high-frequency electric power for forming a plasma to at least one of the electrodes,
wherein a frequency of the high-frequency electric power generated from the high-frequency electric power source is 50 to 150 MHz, and a pressure in the chamber is not higher than 13.3 Pa.

19. A plasma etching unit according to claim 18, wherein

the frequency of high-frequency electric power generated from the high-frequency electric power source is 100 MHz.

20. A plasma etching unit according to claim 18, wherein

power density of the high-frequency electric power is 0.15 to 5 W/cm2.

21. A plasma etching unit according to claim 18, wherein

the high-frequency electric power is applied to an electrode supporting the substrate to be processed.

22. A plasma etching unit according to claim 21, further comprising

a second high-frequency electric power source configured to apply a second high-frequency electric power of 3.2 MHz to 13.56 MHz to the electrode supporting the substrate to be processed, the second high-frequency electric power being overlapped with the high-frequency electric power.

23. A plasma etching unit comprising:

a chamber configured to contain a substrate to be processed having a silicon film and an inorganic-material film adjacent to the silicon film,
a pair of electrodes arranged in the chamber, one of the pair of electrodes being configured to support the substrate to be processed,
a process-gas supplying system configured to supply a process gas into the chamber,
a gas-discharging system configured to discharge a gas in the chamber, and
a high-frequency electric power source configured to supply a high-frequency electric power for forming a plasma to at least one of the electrodes,
wherein a frequency of the high-frequency electric power generated from the high-frequency electric power source is 50 to 150 MHz,
the high-frequency electric power is applied to an electrode supporting the substrate to be processed,
a second high-frequency electric power source configured to apply a second high-frequency electric power to the electrode supporting the substrate to be processed is provided, the second high-frequency electric power being overlapped with the high-frequency electric power, and
a frequency of the second high-frequency electric power is 13.56 MHz.

24. A plasma etching unit according to claim 23, wherein

power density of the second high-frequency electric power is not higher than 0.64 W/cm2.

25. A plasma etching unit according to claim 18, wherein

a distance between the pair of electrodes is shorter than 50 mm.

26. A plasma etching unit comprising:

a chamber configured to contain a substrate to be processed having a silicon film and an inorganic-material film adjacent to the silicon film,
a pair of electrodes arranged in the chamber, one of the pair of electrodes being configured to support the substrate to be processed,
a process-gas supplying system configured to supply a process gas into the chamber,
a gas-discharging system configured to discharge a gas in the chamber, and
a high-frequency electric power source configured to supply a high-frequency electric power for forming a plasma to at least one of the electrodes,
wherein a frequency of the high-frequency electric power generated from the high-frequency electric power source is 50 to 150 MHz, and
a magnetic-field forming unit configured to form a magnetic field around a plasma region between the pair of electrodes is provided, the magnetic field achieving a plasma confining effect.

27. A plasma etching unit according to claim 26, wherein

strength of the magnetic field formed around the plasma region between the pair of electrodes by the magnetic-field forming unit is 0.03 to 0.045 T (300 to 450 Gauss).

28. A plasma etching unit according to claim 27, wherein

a focus ring is provided around the substrate to be processed, and
when the magnetic-field forming unit forms the magnetic field around the plasma region between the pair of electrodes, strength of the magnetic field on the focus ring is not lower than 0.001 T (10 Gauss) and strength of the magnetic field on the substrate to be processed is not higher than 0.001 T.

29. A plasma etching unit comprising:

a chamber configured to contain a substrate to be processed having a silicon film and an inorganic-material film adjacent to the silicon film,
a pair of electrodes arranged in the chamber, one of the pair of electrodes being configured to support the substrate to be processed,
a process-gas supplying system configured to supply a process gas into the chamber,
a gas-discharging system configured to discharge a gas in the chamber, and
a high-frequency electric power source configured to supply a high-frequency electric power for forming a plasma to at least one of the electrodes,
wherein when a gas including at least one of an HBr gas and a Cl2 gas is used as the process gas, plasma density in the chamber is 5×109 to 2×1010 cm−3, a self-bias electric voltage of the electrode supporting the substrate to be processed is not higher than 200 V, and a pressure in the chamber is not higher than 13.3 Pa.

30. A plasma etching unit comprising:

a chamber configured to contain a substrate to be processed having a silicon film and an inorganic-material film adjacent to the silicon film,
a pair of electrodes arranged in the chamber, one of the pair of electrodes being configured to support the substrate to be processed,
a process-gas supplying system configured to supply a process gas into the chamber,
a gas-discharging system configured to discharge a gas in the chamber, and
a high-frequency electric power source configured to supply a high-frequency electric power for forming a plasma to at least one of the electrodes,
wherein when an Ar gas is used as the process gas, plasma density in the chamber is not lower than 1×1010 cm−3, a self-bias electric voltage of the electrode supporting the substrate to be processed is not higher than 100 V, and a pressure in the chamber is not higher than 13.3 Pa.

31. A plasma etching method according to claim 1, wherein

in the etching step, the pressure in the chamber is not higher than 4 Pa.

32. A plasma etching method according to claim 1, wherein

in the etching step, the pressure in the chamber is not higher than 1.33 Pa.

33. A plasma etching unit according to claim 18, wherein

the pressure in the chamber is not higher than 4 Pa.

34. A plasma etching unit according to claim 18, wherein

the pressure in the chamber is not higher than 1.33 Pa.
Patent History
Publication number: 20050039854
Type: Application
Filed: Oct 7, 2004
Publication Date: Feb 24, 2005
Inventors: Shoichiro Matsuyama (Nirasaki-Shi), Masanobu Honda (Nirasaki-Shi), Kazuya Nagaseki (Nirasaki-Shi), Hisataka Hayashi (Yokohama-Shi)
Application Number: 10/959,585
Classifications
Current U.S. Class: 156/345.440; 156/345.430