Polishing apparatus, polishing method, and semiconductor device fabrication method

Abstract

According to the present invention, there is provided a polishing apparatus comprising: a rotatable turntable; a polishing cloth attached on said turntable; a slurry supply pipe which supplies a slurry onto said polishing cloth; and a polishing member which presses an object to be polished against a surface of said polishing cloth, wherein said polishing cloth once stores the supplied slurry inside said polishing cloth, and discharges the slurry when pressed by said polishing member, thereby supplying the slurry to the surface of the object.

Description

CROSS REFERENCE TO RELATED APPLICATION

This application is based upon and claims benefit of priority under 35 USC §119 from the Japanese Patent Application No. 2003-353393, filed on Oct. 14, 2003, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

The present invention relates to a polishing apparatus, polishing method, and semiconductor device fabrication method including a polishing process.

In the recent semiconductor device fabrication field, new fabrication apparatuses have been developed as the degree of micropatterning of semiconductor elements and the density of element structures increase.

Among other fabrication apparatuses, a CMP (Chemical Mechanical Polishing) apparatus is essential in, e.g., CMP processes of a DRAM or high-speed logic LSI, i.e., a metal interconnection formation process, buried element isolation region formation process, and the like.

In these processes using the CMP apparatus, it is important to reduce the use amount of slurry which occupies most of the cost, in addition to improving the process performance such as the surface uniformity.

FIG. 10 shows polishing cloth 100 used in the conventional polishing technique.

A slurry is supplied on the polishing cloth 100 in the direction of an arrow 102. Since the polishing cloth 100 hardly has a function of storing the slurry inside it, the slurry radially scatters on the surface of the polishing cloth 100 as indicated by arrows 103. The polishing cloth 100 is adhered on a turntable (not shown) by a double-coated adhesive tape, and rotated in the direction of an arrow 101.

FIG. 11 is a longitudinal sectional view of the polishing cloth 100 and an object 111 to be polished in a conventional polishing apparatus.

As described above, a slurry supplied onto the surface of the polishing cloth 100 scatters in the direction of the arrow 103. The object 111 to be polished is rotated and pressed by a polishing member 112, and polished when the slurry enters a gap between the object 111 and polishing cloth 100.

In this state, the slurry can enter the gap between the polishing cloth 100 and object 111, so the object 111 can be polished although it is difficult to evenly supply the slurry onto the surface of the object 111.

FIG. 12 is a longitudinal cross sectional view of the polishing cloth 100 and the object 111 to be polished in another conventional polishing apparatus.

In this state, the pressure, indicated by an arrow 114, which presses a polishing member 113 into the shape of a ring is high, so almost no gap exists between the polishing cloth 100 and object 111. This makes it difficult to allow the slurry to enter in the direction indicated by the arrow 103, and obtain a satisfactory polishing performance.

In the conventional general slurry supply method as shown in FIG. 10, a slurry is dropped onto the polishing cloth 100 placed on the turntable, and supplied to the whole polishing cloth by the centrifugal force obtained by the rotation of the turntable, regardless of whether the polishing apparatus shown in FIG. 11 or 12 is used. Since most of the supplied slurry scatters on the polishing cloth as described above, less than half the supplied slurry effectively functions during polishing, and more than half the supplied slurry is wasted. If it is possible to allow a minimum necessary amount of slurry to effectively function, the use amount of slurry can be presumably reduced.

In the conventional slurry supply method, however, the supply amount of slurry inevitably varies in accordance with the distance from the slurry dropping position. Therefore, to polish the entire surface of a semiconductor wafer as the object 111 to be polished, an excess slurry must be supplied to ensure a high process performance, and this increases the cost.

Also, the reduction in use amount of slurry generally leads to various process performance deteriorations, e.g., not only the decrease in surface uniformity and polishing speed, but also the extension of erosion which worsens the flatness of the polishing surface and the increase in scratch.

FIG. 13 shows the polishing speed and erosion as functions of the flow rate of slurry. As is apparent from this graph, when the slurry flow rate decreases, the polishing speed lowers, and the erosion increases.

By contrast, in the technique disclosed in patent reference 1 presented below, a slurry is supplied from below the polishing cloth, i.e., from the surface opposite to the polishing surface. In addition, to reduce the slurry supply amount, area control is performed by dividing a turntable into four portions, and the slurry is supplied upward to a wafer when it passes by. Patent reference 1: Japanese Patent Laid-Open No. 10-94965 Unfortunately, the control mechanism is complicated, and it is difficult to evenly supply the slurry to the entire surface of a wafer.

As described above, it is conventionally impossible to assure a high process performance with a simple arrangement without supplying any excess slurry, and this increases the cost.

SUMMARY OF THE INVENTION

According to one aspect of the present invention, there is provided a polishing apparatus, comprising:

• • a rotatable turntable;
  • a polishing cloth attached on said turntable;
  • a slurry supply pipe which supplies a slurry onto said polishing cloth; and
  • a polishing member which presses an object to be polished against a surface of said polishing cloth,
  • wherein said polishing cloth once stores the supplied slurry inside said polishing cloth, and discharges the slurry when pressed by said polishing member, thereby supplying the slurry to the surface of the object.

According to one aspect of the present invention, there is provided a polishing method, comprising:

• • attaching a polishing cloth on a turntable and rotating the polishing cloth; and
  • supplying a slurry onto the polishing cloth, and pressing an object to be polished against a surface of the polishing cloth by using a polishing member, thereby polishing the object,
  • wherein the slurry is once stored inside the polishing cloth, and discharged and supplied to a surface of the object when pressed by the polishing member.

According to one aspect of the present invention, there is provided a semiconductor device fabrication method, comprising:

• • obtaining an object to be polished by depositing a conductive film above an insulating film formed above a semiconductor substrate, so as to fill a recess formed in the insulating film;
  • attaching a polishing cloth on a turntable, and rotating the polishing cloth; and
  • supplying a slurry onto the polishing cloth, and pressing the object to be polished against a surface of the polishing cloth by using a polishing member, thereby polishing the object and removing the conductive film except for the conductive film in the recess,
  • wherein when the conductive film is removed, the slurry is once stored inside the polishing cloth, and discharged and supplied to a surface of the object while pressed by the polishing member.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a longitudinal cross sectional view showing the sectional structure of a polishing cloth used in a polishing apparatus according to the first embodiment of the present invention;

FIG. 2 is a longitudinal cross sectional view showing the movement of a slurry when an object to be polished is polished by using the polishing cloth shown in FIG. 1;

FIG. 3 is a perspective view showing an outline of the overall arrangement of the polishing apparatus shown in FIG. 1;

FIG. 4 is a graph showing the polishing speed and erosion as functions of the flow rate of slurry when polishing is performed using the polishing apparatus shown in FIG. 1;

FIG. 5 is a longitudinal cross sectional view showing an element section in a certain process when a semiconductor device is fabricated by using the polishing apparatus shown in FIG. 1;

FIG. 6 is a longitudinal cross sectional view showing the element section in another process when the semiconductor device is fabricated by using the polishing apparatus shown in FIG. 1;

FIG. 7 is a longitudinal cross sectional view showing the sectional structure of a polishing cloth used in a polishing apparatus according to the second embodiment of the present invention;

FIG. 8 is a longitudinal cross sectional view showing an example of the structure of a polishing member (top ring head) included in the polishing apparatus;

FIG. 9 is a longitudinal cross sectional view showing another example of the structure of the polishing member (top ring head) included in the polishing apparatus;

FIG. 10 is a perspective view showing the way a slurry is dropped onto polishing cloth used in a conventional polishing apparatus;

FIG. 11 is a longitudinal cross sectional view showing the movement of the slurry when polishing is performed using the conventional polishing apparatus;

FIG. 12 is a longitudinal cross sectional view showing the movement of the slurry when polishing is performed using another conventional polishing apparatus; and

FIG. 13 is a graph showing the polishing speed and erosion as functions of the flow rate of slurry when polishing is performed using the conventional polishing apparatus.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the present invention will be described below with reference to the accompanying drawings.

(1) FIRST EMBODIMENT

FIG. 1 shows the longitudinal cross sectional structure of polishing cloth 10 used in a polishing apparatus according to the first embodiment.

The polishing cloth 10 has a first layer 11 and second layer 12. The first layer 11 has a plurality of through holes 13 which extend from the upper surface to the lower surface in contact with the second layer 12. The second layer 12 is made of a porous material having open cells. The first and second layers 11 and 12 are formed by using a polymer material such as polyurethane.

When a slurry is dropped on the surface of the polishing cloth 10 in the direction of an arrow 14, it is supplied to the second layer 12 trough the through holes 13 in the first layer 11. In the second layer 12, the slurry is diffused toward the circumference as indicated by arrows 15 by the centrifugal force of the rotation of a turntable, and once stored.

In this state, as shown in FIG. 2, an object 21 to be polished is placed on the surface of the first layer 11, and a polishing member 22 presses the object 11 in the direction of an arrow 23, thereby discharging the slurry stored in the second layer 12. Consequently, the slurry is discharged in the direction of arrows 16 through the through holes 13 in the first layer 11, and supplied to the contact surface between the surface of the first layer 11 and the object 21.

FIG. 8 shows an example of the structure of the polishing member 22.

The object 21 to be polished is placed on the polishing cloth 10, and the polishing member having a housing 201 rotates the object 21 while pressing it. The housing 201 has a guide ring 205 for holding the object 21, an elastic sheet 204 which comes in contact with the rear surface of the object 21, and a hollow portion 203 which improves the uniformity of polishing by applying an air pressure in the direction of an arrow 211 to the rear surface of the object 21 via the elastic sheet 204. Also, a load necessary for polishing is applied to the inside of the housing 201 by applying an air pressure in the direction of an arrow 212.

FIG. 9 shows another example of the structure of the polishing member 22. The polishing member 22 shown in FIG. 9 can apply a more even pressure to the object 21 to be polished.

That is, the object 21 is placed on the polishing cloth 10, and the polishing member having a housing 221 rotates the object 21 while pressing it. The housing 221 has an airbag chamber 222, hollow chamber 223, and retainer ring 224. The airbag chamber 222 is formed by a membrane 235 which is made of hard rubber and comes in contact with the rear surface of the object 21, and a chucking plate 234. The airbag chamber 222 applies a load necessary for polishing when an air pressure is applied in the direction of an arrow 231. The hollow chamber 223 gives an air pressure for pressing the chucking plate 234 in the direction of an arrow 232. The retainer ring 224 retains the object 21 to be polished, and presses the surface of the polishing cloth 10 into the shape of a ring in a position separated from the outer circumference of the object 21 when an air pressure is applied in the direction of an arrow 233 inside the housing 221.

The pressure indicated by the arrow 231 is higher than that indicated by the arrow 233. This improves the uniformity of polishing.

FIG. 3 shows an outline of the overall arrangement of a polishing apparatus usable in the embodiment of the present invention.

The polishing cloth 10 is adhered by, e.g., a double-coated adhesive tape on a turntable 31 which rotates in the direction of an arrow 43. A semiconductor wafer is set as the object 21 to be polished.

A slurry 34 is dropped in a substantially central position on the polishing cloth 10 from a slurry supply pipe 33, and diffused in the polishing cloth 10 toward the periphery by the centrifugal force. The slurry 34 is once stored as it is spread over the entire region of the polishing cloth 10.

A top ring head 22 as a polishing member rotates the semiconductor wafer as the object 21 in the direction of an arrow 42 while pressing the wafer against the polishing cloth 10. Also, a dressing head 32 opposes the top ring head 22 on the other side of the central position of the turntable 31, and rotates as indicated by an arrow 41 to dress the polishing cloth 10.

In the first embodiment, when pushed by the top ring head 22, the slurry 34 once stored in the polishing cloth 10 oozes out toward the upper surface in FIG. 3 and is supplied between the polishing cloth 10 and object 21.

Consequently, unlike in any conventional apparatus, it is possible to evenly supply the slurry to the surface in contact with the object 21 without wasting it by scattering it on the polishing cloth 10. Also, even when the retainer ring is pressed by a high pressure by using the head shown in FIG. 9, the slurry can be reliably supplied to the surface in contact with the object 21.

FIG. 4 shows the polishing speed and erosion as functions of the flow rate of slurry when the polishing apparatus according to the embodiment of the present invention is used. Unlike in the conventional apparatus shown in FIG. 13, both the polishing speed and erosion are maintained substantially constant regardless of the slurry flow rate.

Accordingly, this embodiment can reduce the cost by reducing the use amount of slurry with a simple arrangement without deteriorating the process performance.

Especially in a semiconductor wafer CMP process, very many additives are contained in a slurry in order to improve the polishing performance. Since this makes the slurry expensive, the cost can be largely reduced by reducing the use amount of slurry.

In order for the slurry to rapidly diffuse toward the periphery after it is dropped directly on the second layer 12 of the polishing cloth 10, the first layer 11 may also be removed in the shape of a circle, as shown in FIG. 1, immediately below the slurry supply pipe, i.e., in a central region 13a of the polishing cloth 10.

In the first layer 11 of the polishing cloth 10, fine holes having a diameter of, e.g., 10 μm to 10 mm evenly distribute at a density of 1 to 1,000 holes/cm². The first layer 11 is more desirably formed by a porous material having the linear through holes 13 as shown in FIG. 1.

This shape can be realized by molding a porous material such as a polymer-based material into fibers or a honeycomb shape, and forming the through holes 13 substantially parallel to each other.

Also, the second layer 12 can be obtained by molding, e.g., a generally used hard foamed polyurethane resin, such as a polymer-based material having open cells whose diameter is, e.g., 10 to 500 μm. However, the material is not limited to this material, and any material which can store the slurry and discharge it when pressed can be used. Examples are polystyrene-based and silicone-based polymers.

A method of forming a copper damascene interconnection will be explained below as a semiconductor device fabrication method using the polishing apparatus according to the first embodiment.

As shown in FIG. 5, an element (not shown) is formed by patterning in a surface portion of a semiconductor substrate 51. An interlayer insulating film 52 having a film thickness of, e.g., about 3,000 Å is formed on the surface of the semiconductor substrate 51. A recess 55 which is at least one of a trench and hole is formed in the surface of the interlayer insulating film 52.

On the entire surface including the inner surfaces of the recess 55, a Ta/TaN layer 53 having a film thickness of, e.g., about 300 Å is formed as a liner by sputtering.

In addition, a copper film 54 having a film thickness of, e.g., about 7,000 Å is deposited by sputtering and plating so as to cover the entire surface.

As shown in FIG. 6, of the copper film 54 and Ta/TaN layer 53, unnecessary portions except for the portions buried in the recess 55 are removed by CMP. The polishing apparatus according to the first embodiment described above is used in this CMP process.

The polishing conditions can be set, for example, as follows.

Two types of slurries A and B presented below are supplied onto the polishing cloth at a flow rate of 50 cc/min each.

• • Slurry A: Mixture of CMS7401+CMS7452 (manufactured by JSR (registered trademark))
  • Slurry B: BTS-12 (manufactured by HIROTA CHEMICAL INDUSTRY (registered trademark))

The polishing load is 400 g/cm², and the carrier/table rotational speeds are 100/100 rpm.

By performing the CMP process by using the polishing apparatus according to the first embodiment, good polishing characteristics can be obtained by using a minimum necessary slurry.

(2) SECOND EMBODIMENT

The polishing cloth 10 used in the polishing apparatus according to the first embodiment described above has a two-layered structure having the first and second layers 11 and 12.

By contrast, in a polishing apparatus according to the second embodiment, the polishing cloth has an integrated structure such as polishing cloth 10a shown in FIG. 7. The overall arrangement of the apparatus except for this polishing cloth is the same as the first embodiment, so a detailed explanation thereof will be omitted.

In the polishing cloth 10a, a slurry dropped on the surface of the polishing cloth 10a enters the polishing cloth 10a in the direction of an arrow 14. This slurry is diffused toward the periphery as indicated by arrows 15 by the centrifugal force of the rotation of a turntable, and once stored.

When the polishing cloth 10a is pressed in the direction of an arrow 23 by a polishing member 22, the slurry oozes out in the direction of arrows 16, and is discharged to the surface of an object 21 to be polished.

Even when the polishing apparatus of the second embodiment using the polishing cloth 10a as described above is used, as in the first embodiment, the slurry is once stored in the whole of the polishing cloth 10a by permeation, and then evenly supplied to the surface of the object 21 to be polished.

In addition, according to the second embodiment, even when the head shown in FIG. 9 is used, since the slurry is uniformly supplied to that surface of the object to be polished, which is in contact with the polishing cloth, the slurry is reliably supplied to this surface irrespective of the pressure acting on the retainer ring.

A method of performing the CMP process shown in FIG. 6 by using the polishing apparatus according to the second embodiment will be explained below.

The polishing conditions can be set, for example, as follows.

A slurry C presented below is supplied onto the polishing cloth at a flow rate of 300 cc/min.

• • Slurry C: CMS8301 (manufactured by JSR (registered trademark))

The polishing load is 240 g/cm², and the carrier/table rotational speeds are 50/51 rpm.

In the second embodiment, as in the first embodiment described previously, a slurry is once stored in the whole of the polishing cloth, and then evenly supplied to the surface to be polished of the semiconductor substrate. Since the slurry is reliably supplied to the surface to be polished, good characteristics can be obtained.

As described above, the polishing apparatuses, polishing methods, and semiconductor device fabrication methods of the first and second embodiments make it possible to reduce the cost by reducing the slurry use amount without deteriorating the process performance.

Each of the above embodiments is merely an example, and hence does not limit the present invention. That is, these embodiments can be variously modified within the technical scope of the present invention.

For example, in the above embodiments, a copper film is used as a conductive film to be polished in the CMP process. However, it is also possible to use a film containing at least aluminum, tungsten, titanium, niobium, tantalum, silver, vanadium, ruthenium, platinum, silicon, or an oxide, nitride, boride, or alloy of any of these materials.

Claims

1. A polishing apparatus comprising:

a rotatable turntable;

a polishing cloth attached on said turntable;

a slurry supply pipe which supplies a slurry onto said polishing cloth; and

a polishing member which presses an object to be polished against a surface of said polishing cloth,

wherein said polishing cloth once stores the supplied slurry inside said polishing cloth, and discharges the slurry when pressed by said polishing member, thereby supplying the slurry to the surface of the object.

2. An apparatus according to claim 1, wherein when rotated by said turntable, said polishing cloth diffuses the supplied slurry toward a periphery inside said polishing cloth.

3. An apparatus according to claim 1, wherein

said polishing cloth has a stacked structure including first and second layers,

said first layer has a plurality of through holes extending from one surface to the other surface in contact with said second layer, and

said second layer is made of a porous material having open cells.

4. An apparatus according to claim 3, wherein

when the slurry is supplied to said one surface, said first layer supplies the slurry to said second layer from said other surface through the through holes,

said second layer once stores the slurry supplied from the through holes, and discharges the slurry when pressed by said polishing member, and

the discharged slurry oozes out to said one surface from the through holes in said first layer.

5. An apparatus according to claim 3, wherein

said second layer once stores the slurry directly dropped through the through hole formed in said first layer immediately below said slurry supply pipe, and discharges the slurry when pressed by said polishing member, and

the discharged slurry oozes out to said one surface from the through holes in said first layer.

6. An apparatus according to claim 3, wherein said first and second layers are made of a polymer-based material.

7. An apparatus according to claim 6, wherein said second layer is made of a material selected from the group consisting of a polyurethane-based material, polystyrene-based material, and silicone-based polymer material.

8. An apparatus according to claim 1, wherein said polishing member comprises a member which presses the surface of the polishing cloth on an outer peripheral side of the object to be polished.

9. A polishing method, comprising:

attaching a polishing cloth on a turntable and rotating the polishing cloth; and

supplying a slurry onto the polishing cloth, and pressing an object to be polished against a surface of the polishing cloth by using a polishing member, thereby polishing the object,

wherein the slurry is once stored inside the polishing cloth, and discharged and supplied to a surface of the object when pressed by the polishing member.

10. A method according to claim 9, wherein the slurry supplied onto the polishing cloth is diffused toward a periphery inside the polishing cloth by rotating the turntable.

11. A method according to claim 9, wherein when the slurry is to be supplied,

the polishing cloth having a stacked structure including first and second layers is used, the first layer having a plurality of through holes extending from one surface to the other surface in contact with the second layer, and the second layer being made of a porous material having open cells,

when the slurry is supplied onto the polishing cloth from the first layer of the stacked structure, the second layer once stores the slurry supplied from the through holes in the first layer, and discharges the slurry when pressed by the polishing member, and

the discharged slurry oozes out to the one surface from the through holes in the first layer, and thereby the slurry is supplied to the surface of the object to be polished.

12. A method according to claim 11, wherein when the slurry is to be supplied,

the slurry is directly dropped on the second layer through the through hole formed in a central region of the first layer.

13. A method according to claim 11, wherein said first and second layers are made of a polymer-based material.

14. A method according to claim 13, wherein said second layer is made of a material selected from the group consisting of a polyurethane-based material, polystyrene-based material, and silicone-based polymer material.

15. A semiconductor device fabrication method, comprising:

obtaining an object to be polished by depositing a conductive film above an insulating film formed above a semiconductor substrate, so as to fill a recess formed in the insulating film;

attaching a polishing cloth on a turntable, and rotating the polishing cloth; and

supplying a slurry onto the polishing cloth, and pressing the object to be polished against a surface of the polishing cloth by using a polishing member, thereby polishing the object and removing the conductive film except for the conductive film in the recess,

wherein when the conductive film is removed, the slurry is once stored inside the polishing cloth, and discharged and supplied to a surface of the object while pressed by the polishing member.

16. A method according to claim 15, wherein the slurry supplied onto the polishing cloth is diffused toward a periphery inside the polishing cloth by rotating the turntable.

17. A method according to claim 15, wherein when the slurry is to be supplied,

the polishing cloth having a stacked structure including first and second layers is used, the first layer having a plurality of through holes extending from one surface to the other surface in contact with the second layer, and the second layer being made of a porous material having open cells,

when the slurry is supplied onto the polishing cloth from the first layer of the stacked structure, the second layer once stores the slurry supplied from the through holes in the first layer, and discharges the slurry when pressed by the polishing member, and

the discharged slurry oozes out to the one surface from the through holes in the first layer, and thereby the slurry is supplied to the surface of the object to be polished.

18. A method according to claim 17, wherein said first and second layers are made of a polymer-based material.

19. A method according to claim 18, wherein said second layer is made of a material selected from the group consisting of a polyurethane-based material, polystyrene-based material, and silicone-based polymer material.

20. A method according to claim 15, wherein the conductive film contains at least a material selected from the group consisting of aluminum, copper, tungsten, titanium, niobium, tantalum, silver, vanadium, ruthenium, platinum, silicon, and an oxide, nitride, boride, and alloy of any of the materials.