Plasma Generator Apparatus
Embodiments of a plasma generator apparatus for ashing a work piece are provided. The apparatus includes a container adapted for continuous gas flow there through from an inlet end to an outlet end thereof. The container is fabricated of a dielectric material and adapted for ionization therein of a portion of at least one component of gas flowing therethrough. A gas flow distributor is configured to direct gas flow to a region within the container and a coil surrounds at least a portion of side walls of the container adjacent the region of the container to which the gas flow distributor directs gas flow. A radio frequency generator is coupled to the coil.
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The present technology relates generally to apparatus used in the fabrication of semiconductor devices, and more particularly, the present technology relates to plasma generator apparatus for generating plasma used in ashing and surface treatment procedures.
BACKGROUNDIn semiconductor manufacturing, plasma ashing is the process of removing the photoresist from an etched wafer. Plasma in this context is an ionized form of a gas. A gas ionizing apparatus, also referred to as a plasma generator, produces a monatomic reactive species of oxygen or another gas required for the ashing process. Oxygen in its monatomic or single atom form, as O rather than O2, is the most common reactive species. The reactive species combines with the photoresist to form ash which is removed from the work piece with a vacuum pump.
Typically, monatomic oxygen plasma is created by exposing oxygen gas (O2) to a source of energy, such as a RF discharge. At the same time, many charged species, i.e. ions and electrons, are formed which could potentially damage the wafer. Newer, smaller circuitry is increasingly susceptible to damage by charged particles. Originally, plasma was generated in the process chamber, but as the need to avoid charged particles has increased, some machines now use a downstream plasma configuration, where plasma is formed remotely and channeled to the wafer. This reduces damage to the wafer surface.
Monatomic oxygen is electrically neutral and although it does recombine during the channeling, it does so at a slower rate than the positively or negatively charged particles, which attract one another. Effectively, this means that when substantially all of the charged particles have been neutralized, the reactive neutral species remains and is available for the ashing process.
Current plasma generating apparatus present a variety of challenges during ashing procedures. Generally, plasma is generated using a coil, often copper, wrapped around a dielectric tube, such as quartz or aluminum/sapphire tube. The coil is energized with a radio frequency (RF) voltage from an appropriate RF generator. Plasma formation is initiated by capacitively coupling the electric field through the quartz to the rarefied gas inside the quartz tube. As the power level and current through the coil are increased, the plasma switches from a capacitively coupled mode to an inductively coupled mode. Significant voltages exist on the coil. Difficulties arise in trying to isolate the high voltage components to prevent these components from breaking down and arcing to cause damage to other components. In addition, the high voltages generate a high electric field across the quartz and can cause significant ion bombardment and sputtering on the inside of the quartz tube thus reducing its lifespan and increasing its maintenance needs. A reduction in the ion bombardment energy may be helpful.
In addition, as illustrated in schematic cross section in
Ion bombardment of the quartz cylinder 15 poses another significant challenge. When a small diameter plasma source 10 is used, the plasma density should be very high in order to generate enough O atoms to perform ashing at an acceptable rate. This high plasma density coupled with the high energy fields (E-fields) present in the coil 14 cause significant ion bombardment of the quartz container 15 and a reduced container lifespan. One method to ameliorate this effect is to place a Faraday shield 22 between the quartz container 15 and the coil 14, as illustrated in the schematic cross section of
In addition, present day plasma generator apparatus suffer from non-uniform plasma production. Generally, when an oxygen-containing gas flows through the container, plasma generation is initiated in the tube adjacent the coil. But since the E-field has limited penetration into the container, the peak area for energy dissipation is near the inner wall of the container. Due to this limited penetration of the E-field, the plasma forms a ring 25 inside the quartz container 15, as seen from above, and as schematically shown in
In addition, present day plasma generators are difficult to adapt to ashing larger wafers. If the quartz container 15 is increased in diameter, the peak plasma region remains approximately the same size and is still located near the wall. The hole 26 in the ring 25 increases in size dramatically as the diameter of the quartz container 15 is increased. The majority of the gas flows down the center of the quartz container 15 and is never directly ionized. Thus, few O atoms are produced in the central region of the quartz container 15. The efficiency of producing O atoms in larger diameter quartz containers is therefore expected to be low.
Accordingly, it is desirable to provide an improved plasma generation apparatus that is suitable for use in ashing procedures in semiconductor fabrication. It is also desirable to provide an apparatus that is able to provide a more uniform distribution of O atoms over a large diameter work piece, such as a 300 mm or larger wafer. It is further desirable to provide a plasma generator that does not require Faraday shields, but that also provides an acceptable quartz container lifespan. In addition, it is desirable to provide a plasma generation apparatus and/or process that converts oxygen more efficiently to O atoms. Other desirable features and characteristics of the present technology will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.
A more complete understanding of the present technology may be derived by referring to the detailed description and claims when considered in conjunction with the following figures, wherein like reference numbers denote like elements throughout the figures and wherein:
The following detailed description is merely exemplary in nature and is not intended to limit the described embodiments or the application and uses of the described embodiments. Furthermore, there is no intention to be bound by any expressed or implied theory presented in the preceding technical field, background, brief summary or the following detailed description.
In accordance with an exemplary embodiment, a plasma generator apparatus includes means for diverting a portion of an incoming gas flow into a region of higher plasma density than another region of the apparatus. The region of higher gas density is located in a container of suitable dielectric material, such as a quartz container, and specifically within or proximate the strongest region of a plasma-generating energy field to which the container is subjected. Accordingly, a higher proportion of the incoming ionizable components in the gas flow is ionized (or “converted to plasma”) when sufficient appropriate excitation energy is applied.
Another embodiment provides symmetrical segmented coils for generation of an electrical field of a frequency that will generate ionization of a gaseous component in a plasma generator. The use of such coils, as explained below, reduces or eliminates the necessity for a Faraday shield. This results in significant cost savings. In addition, by reducing the creation of free radicals that are produced at high voltages there is reduced etching of the quartz tubes often used in the plasma generator. Thus, the symmetrical segmented coils increase the useful life of the quartz tubes.
An example embodiment of a plasma generator apparatus 100 with a conical upper portion is illustrated in
The plasma generator 100 includes an upper portion 110 that is conical (
The nozzle 114 shown in top view in
Referring to
Because a large proportion, or even a major portion, of the gas flow is directed by the nozzle 114 and the container inner walls 118 into region 130, region 130 is a zone of highest plasma density 130. Excitation energy is applied from the outside of the tubular container 125 directly into this region 130. This permits more efficient gas component ionization because it ameliorates the effect of the energy level diminishing (and ionization decreasing) as the energy penetrates farther into the container. Of course, the flowing of more gas through the region of highest power dissipation, region 130, increases the production of radicals and atoms as well, in this case O atoms.
A gas distributor plate 150 is disposed at the exit end 102 of the generator 100. This gas distributor plate 150 has a plurality of through holes, or is of a porous construction. It provides means to control the O atom flux that impinges upon the work piece being treated. As the gas impinges upon and travels through the gas distributor plate 150, some charged species are neutralized thereby reducing the potential for charged particle damage to the work piece 200.
In accordance with another exemplary embodiment, a diameter 120 of the tube 125 and a diameter 210 of work piece 200 are approximately the same. While equality of diameter is not necessary, embodiments may have equal diameters of tube 125 and work piece 200, or diameters that approximate equal size. This feature significantly or completely reduces the need to expand the tube 125 near its exit end 102 to approximate the work piece diameter to facilitate distribution of the gas flow. In general, it is preferable that a characteristic dimension of the apparatus, such as tube diameter in the example of a quartz cylinder, approximates a characteristic dimension of a work piece, such as the diameter of a circular work piece surface that is presented transverse to the direction of gas flow. In this regard, the plasma generation region is increased in size thereby allowing a reduction in overall plasma density while still increasing the O atom production generated in the flowing gas. Increasing the volume of the plasma reduces the plasma density in the region near the container wall. This in turn results in less ion bombardment and less container wall heating.
The plasma generator 100 may be used in conjunction with a Faraday shield 144, shown in
As a preliminary matter, the prior art of driving the induction circuit 160 is shown in
The effect may be further enhanced by dividing the coil into a plurality of symmetrical segments, as shown in
In accordance with an exemplary embodiment of the present invention, illustrated schematically in
While at least one example embodiment has been presented in the foregoing detailed description, it should be appreciated that a vast number of variations exist. It should also be appreciated that the example embodiment or embodiments described herein are not intended to limit the scope, applicability, or configuration of the invention in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing the described embodiment or embodiments. It should be understood that various changes can be made in the function and arrangement of elements without departing from the scope of the invention as set forth in the appended claims and the legal equivalents thereof.
Claims
1. A plasma generator apparatus for ashing a work piece, the apparatus comprising:
- (a) a container adapted for continuous gas flow there through from an inlet end to an outlet end thereof, the container comprising a dielectric material and further adapted for ionization of a portion of at least one component of gas flowing therethrough;
- (b) a gas flow distributor configured to direct gas flow to a region within the container;
- (c) a coil surrounding at least a portion of side walls of the container, the portion of the side walls adjacent the region of the container to which the gas flow distributor directs gas flow; and
- (d) a radio frequency generator coupled to the coil.
2. The apparatus of claim 1, further comprising a gas diffuser at an outlet of the container.
3. The apparatus of claim 1, wherein the container is cylindrical and the gas flow distributor comprises a circular baffle plate axially centered in a cylindrical container to direct gas flow towards side walls of the container.
4. The apparatus of claim 1, wherein the container comprises a cylindrical lower portion capped with a domed or conical upper portion.
5. The apparatus of claim 4, wherein the gas flow distributor comprises a nozzle located proximate an apex of the domed or conical upper portion, the nozzle directing gas flow along inner walls of the domed or conical upper portion.
6. The apparatus of claim 5, further comprising a Faraday shield interposed between the coil and the at least a portion of the side walls of the container.
7. The apparatus of claim 5, wherein the nozzle comprises a hemisphere with a plurality of through holes, the through holes directing gas flowing therethrough to at least a portion of the side walls surrounded by the coil.
8. The apparatus of claim 5, wherein the nozzle comprises a tube extending axially into the container, the tube comprising a plurality of through holes in a side wall thereof, the through holes directing gas flow to the portion of the side walls of the container surrounded by the coil.
9. The apparatus of claim 1, wherein the coil comprises a symmetrical coil.
10. The apparatus of claim 9, wherein the symmetrical coil comprises at least about 2 segments.
11. The apparatus of claim 1, wherein a largest dimension of the container, transverse to gas flow in the container, approximates a dimension of a surface of a work piece, the surface to be treated by the apparatus.
12. An apparatus for ashing a work piece, the apparatus comprising:
- (a) a container configured for flow there through from an inlet end to an outlet end, the container comprising side walls adapted for ionization of a portion of at least one component of the gas flowing through the container;
- (b) a gas flow distributor adapted to direct gas flow to a region within the container;
- (c) a segmented coil surrounding at least a portion of side walls the container, the portion adjacent the region of the container to which the gas flow distributor directs gas flow, the segmented coil free of any Faraday shield interposed between the segmented coil and the portion of the side walls;
- (d) a radio frequency generator coupled to the segmented coil; and
- (e) a diffusion plate at an exit end of the container to direct gas flow onto a surface of a work piece to be ashed.
13. The apparatus of claim 12, wherein the container is cylindrical and the gas flow distributor comprises a circular baffle plate axially centered in a cylindrical container to direct gas flow towards side walls of the container.
14. The apparatus of claim 12, wherein the container comprises a cylindrical lower portion capped with a domed or conical upper portion.
15. The apparatus of claim 12, wherein the gas flow distributor comprises a nozzle located proximate an apex of the domed or conical upper portion, the gas flow distributor directing gas flow along inner walls of the domed or conical upper portion to the portion of the side walls of the container surrounded by the segmented coil.
16. The apparatus of claim 14, wherein the container and the dome-shaped or cone-shaped upper portion are comprised of quartz.
17. The apparatus of claim 15, wherein the gas flow distributor comprises a hemispherical nozzle with a plurality of through holes.
18. The apparatus of claim 15 wherein the gas flow distributor comprises a tube extending axially into the container, the tube comprising a plurality of through holes in a side wall thereof, the through holes directing gas flow along inner walls of the domed or conical upper portion to the portion of the side walls of the container surrounded by the segmented coil.
19. The apparatus of claim 12, wherein the segmented coil comprises at least 2 segments.
20. A plasma generator apparatus for ashing a work piece, the apparatus comprising:
- (a) a container of larger diameter configured for continuous gas flow there through from an inlet end to an outlet end, the container comprising side walls of a dielectric material adapted for containing charged particles produced by radio frequency discharge into a gas, the container having a domed-shaped or cone-shaped upper portion;
- (b) a gas flow distributor proximate the dome-shaped or cone-shaped upper portion of the container, the gas flow distributor adapted to direct gas flow to a region within the container;
- (c) a diffusion plate proximate an outlet end of the container to direct gas flow from inside the container onto a surface of a work piece to be treated;
- (d) a symmetrical coil comprising at least 2 segments, the symmetrical coil surrounding at least a portion of the side walls of the container, the portion of the side walls adjacent the region within the container to which the gas flow distributor directs gas flow; and
- (e) a radio frequency generator coupled to the symmetrical coil.
Type: Application
Filed: Dec 27, 2006
Publication Date: Jul 3, 2008
Applicant: Novellus Systems, Inc. (San Jose, CA)
Inventors: James A. Fair (Mountain View, CA), Vincent Decaux (San Francisco, CA), Anirban Guha (Milpitas, CA), David Cheung (Foster City, CA), John Keller (Newburgh, NY), Peter Jagusch (Los Gatos, CA)
Application Number: 11/616,324
International Classification: C23C 16/00 (20060101);