GB2175131A

GB2175131A - Plasma reactor and method for removing photoresist

Info

Publication number: GB2175131A
Application number: GB08602734A
Authority: GB
Inventors: James F Battey; Perry A Diederich
Original assignee: Psi Star; PSI Star Inc
Current assignee: Psi Star; PSI Star Inc
Priority date: 1985-02-05
Filing date: 1986-02-04
Publication date: 1986-11-19
Also published as: GB2175131B; CA1281439C; JPS61191033A; GB8602734D0; DE3603355A1; FR2579059A1

Abstract

A plasma reactor comprises a working chamber 14 that has at least one entry port 24 and receives at least one article 20. The entry port also admits a working gas into the working chamber. At least one pair of electrodes 28e, 30e is positioned adjacent the working chamber entry port. The electrodes, which are connected to a generator, create an electric field Ee adjacent the entry port that converts the working gas into a working plasma for interacting with a material of the article. An electric field-free region downstream of the plasma generating region is provided in which the article is positioned. The plasma is constrained to pass in the vicinity of the article 20 by an apertured insert 40. <IMAGE>

Description

SPECIFICATION Plasma reactor and method for removing photoresist Technical Field This invention relates to plasma reactors, and more particularly, to plasma barrel reactors for removing the photoresist from semiconductor wafers or etching thin films such as aluminum, silicon dioxide or polysilicon on silicon wafers patterned with photoresist for etching.

Background Art The use of gas plasma for processing semiconductor wafers is common in the art. For example, various techniques are described in J. Hollahan and A. Bell, Techniques and Applications of Plasma Chemistry, Ch. 9 (1974).

Semiconductor components are fabricated on a semiconductive substrate or wafer. The material of the wafer is generally silicon. In manufacturing semiconductor devices, a photosensitive polymer, generally referred to as a photoresist, is used. After selective exposure to optical radiation and subseguent chemical development, the photoresist hardens where it has not been removed and protects the under- lying wafer from other chemicals. One method of removing photoresist from wafers after it has served its protective function is by using a gas plasma.

In general, the gas plasma used in removing photoresist is oxygen. More particularly, diatomic oxygen is first exposed to an electric field which transforms some of the diatomic oxygen into an oxygen plasma that contains some monoatomic oxygen, generally referred to as atomic oxygen. Atomic oxygen is capable of reacting with the photoresist by breaking its polymer chains such that the photoresist is removed from the semiconductor wafer by the combined action of the atomic oxygen and the molecular oxygen. The resultant by-products are gases such as H20, CO and CO2.

Prior art oxygen plasma reactors for removing photoresist, an example of which is shown in Figure 2A, consist of a cylindrical quartz reactor. A plurality of semiconductor wafers, each of which has a layer of photoresist on its surfaces, are positioned within the reactor.

Metal electrodes are positioned around the reactor, one of which is connected to a radiofrequency (RF) generator operating at 13.56 MHz or some harmonic of that frequency and the other is connected to the ground. The quartz reactor also includes a gas input manifold and an exhaust manifold.

Other prior art plasma reactors, not shown, include single-chamber reactor that has an electrode within the chamber, as best exemplified in U.S. Patent No. 4,230,515. In addition, prior art reactors include double-chamber reactor in which the plasma is generated in one chamber and the work such as photoresist removal is performed in a second chamber.

The plasma may be transported between the two chambers either through a narrow channel or through narrow tubes. The primary disadvantage of the doublechamber reactor is the likelihood of plasma degeneration before it could perform the removal of the photoresist, that is, atomic oxygen tends to recombine to diatomic oxygen on the walls of the channel or tubes.

In prior single chamber reactors with external electrodes, the electrodes are wrapped around the entire sides of the cylindrical reactor so that the electric field fills the whole volume of the reactor. However, due to the electrical skin effect of the RF discharge, the electric current produced tends to "hug" the reactor wall. This effect is analogous to the phenomena of high frequency current flowing near the surface or skin of a metal conductor.

Thus, most of the atomic oxygen is produced near the walls of the reactor and is pumped out of the reactor without getting near the wafers. The only atomic oxygen that is involved with the removal process is that which diffused into the center of the reactor where the wafers are placed and then diffusing between the wafers.

Disclosure of the Invention In view of such deficiencies in the prior art, it is a major object of the present invention to provide a plasma reactor that is capable of maximizing the use of the products of the plasma in performing the desired chemistry. In the instance of photoresist removal, maximizing the reaction of the atomic oxygen with the photoresist.

In order to accomplish the above and still further objects, the present invention provides a plasma reactor that has a working chamber with at least one entry port, the entry port is adapted to receive a working gas into the working chamber. In addition, the working chamber is adapted to receive at least one article. An electrical energy generator is provided. At least one pair of electrodes are positioned adjacent the working chamber entry port. The electrodes, which are connected to the generator, create an electric field adjacent the entry port that converts the working gas into a working plasma for interacting with a material of the article. The position of the electric field adjacent the entry port leaves a substantially electric field-free region in the barrel chamber adjacent the article.

In addition, the plasma reactor of the present invention includes a plasma flow constraint member which is positioned within the working chamber. The constraint member permits the flow of the gas only through itself so as to enhance the interaction of the gas with the material of the article. More particularly, the constraint member includes at least one opening that is adapted to receive the article and to permit the passage of the gas.

It should be noted that as long as the material being processed is placed in the center of the electric field used to create the plasma, the species of interest will be generated and will flow around the sides of the material being processed without reacting with it to an appreciable extent. By generating the plasma upstream of the material being process, it is easy to force the species of interest to flow adjacent the material being processed. This must be done without passing the flow through narrow constrictions which will exterminate the species of interest.

In the preferred embodiment of the present invention, the material of the article that is removed by the working plasma is photoresist. In addition, the article is a semiconductor wafer. Last, the working plasma consists of oxygen.

Other objects, features, and advantages of the present invention will appear from the following detailed description of the best mode of a preferred embodiment, taken together with the accompanying drawings.

Brief Description of the Drawings Figure 1 is a perspective view of the plasma barrel reactor of the present invention Figure 2 is a partial, cross-sectional, and diagrammatical view of a prior art plasma reactor; Figure 3 is a partial, cross-sectional, and diagrammatical view of the plasma barrel reactor of Figure 1; and Figure 4 is a partial, cross-sectional, and diagrammatical view of the plasma flow constraint member of the plasma barrel reactor of Figures 1 and 3.

Best Mode for Carrying Out the Invention Referring to Figure 1, there is shown a plasma barrel reactor, generally designated 12.

Reactor 12 includes a generally barrel-like, cylindrical working chamber 14. Barrel chamber 14 may have a diameter from six to 12 inches; the diameter of chamber 14 is 12 inches in the preferred embodiment. The axial length of chamber 14 is approximately 21 inches. Chamber 14 has a plurality of entry ports 16 for receiving a working gas and a plurality of exhaust ports 18 for venting various gases and by-products of chamber 14.

There are four entry ports 16 and five exhaust ports 18 in the preferred embodiment. Moreover, entry ports 16, as best illustrated in Figure 3, are positioned diametrically opposite exhaust ports 18. Chamber 14, in the preferred embodiment, is made from a conventional inert material such as quartz.

Chamber 14 is adapted to receive a plurality of articles 20. Articles 20, as shown, are semiconductor wafers each of which has a layer of photoresist material on it when the wafers are placed in chamber 14.

Reactor 12 further includes an entry gas manifold 22 that is positioned adjacent chamber 14. Entry gas manifold 22 is a tube, also made of quartz that has a plurality of ports 24 each of which is in communication with one of the barrel chamber entry ports 16. Entry gas manifold 22 in the preferred embodiment has four ports 24. Entry gas manifold 22 is capable of transporting the working gas to barrel chamber 14.

A radio-frequency (RF) electrical energy generator, not shown, is provided. In the preferred embodiment, the frequency of the RF energy is 13.56 MHz.

In addition, reactor 12 includes a pair of entry port electrodes 28e and 30e which are positioned adjacent barrel chamber entry ports 16, as best shown in Figure 3. Each of the electrodes 28e and 30e, which are manufactured from a conductive metal such as copper, contains a slight curvature in its design such that it follows the curvature of chamber 14.

Electrodes 28e and 30e are capable of creating an electric field in barrel chamber 14 adjacent entry ports 16. This entry port electric field E, then converts the working gas to a working plasma. Moreover, the position of entry port electric field E, delineates a substantially electric field-free region FR in chamber 14 adjacent articles 20.

A pair of manifold electrodes 28m and 30m, which are positioned adjacent entry gas manifold 22, is also provided. Each of the manifold electrodes 28m and 30m is a generally vertically-extending plate that is positioned at either side of manifold 22, as best shown in Figure 3. Electrodes 28m and 30m are also manufactured from a conductive metal such as copper. Manifold electrodes 28m and 30m are capable of creating an electric field in manifold 22. The manifold electric field E, converts a portion of the working gas to the working plasma before the working gas enters chamber 14. The combined effort of the manifold electric field E, and the entry port electric field E efficaciously convert the working gas to the desired working plasma.

Although electrodes 28e and 28m and electrodes 30e and 30m are claimed and described as separate and discrete electrodes, electrodes 28e and 28m could be manufactured as a single electrode and electrodes 30e and 30m as a single electrode. In addition, manifold electrodes 28m and 30m need not be required in all instances. Although the manifold electric field Em generated by electrodes 28m and 30m does contribute to the efficacious conversion of the working gas to the working plasma, its elimination does not detract the overall conversion of the working gas to the working plasma made by the entry port electric field E, alone.

Reactor 12 also includes a plasma flow constraint member 40 that is positioned within barrel chamber 14. Constraint member 40 is a planar, board-like platform which has a plurality of openings 42. Openings 42 perform two functions the first of which is to receive wafers 20. Wafers 20 are first placed into a conventional wafer receptacle 44, which is generally referred to as a wafer boat. Each wafer boat 44 is capable of receiving a plurality of wafers, as best shown in Figure 4. The wafers in boat 44 are spaced apart sufficiently so as to permit the atomic oxygen to flow among them and react with the photoresist which are on the wafers. Boat 44, which is manufactured from an inert material such as quartz, is then received in opening 42.

The next, and more important, function of platform 40 is to restrict the flow of the working gas, and direct it only to wafers 20.

The working gas ceases to be a plasma when it leaves the electric field. In prior art reactor such as that shown in Figure 2, a substantially amount of the working gas or in this instance, plasma, may never come in contact with wafers 120. This is due to the fact there is sufficient space in chamber 114 to permit the free drift of plasma. In contrast, platform 40 is configured such that it divides chamber 14 into two regions, a working region 46 and an exhaust region 48. The only communication between these two regions is through openings 42. This design forces the working gas to pass only through openings 42, which are positioned immediately below wafers 20. This causes all of the plasma to flow through wafers 20 and react with the photoresist.Platform 42, which has dimensions of approximately 21 inches X 9 inches X 1/8 inch, is manufactured from a non-reactive material such as hard anodized aluminum. Platform 42 may also be manufactured from quartz.

Reactor 12 further includes an exhaust manifold 50 that is positioned adjacent chamber 14. Exhaust manifold 50 is a tube, also made of quartz, that has a plurality of ports 52 each of which is in communication with one of the barrel chamber exhaust ports 18. Exhaust manifold 50 of the preferred embodiment has five ports 52. Exhaust manifold 50 is capable of transporting away from chamber 14 any remaining working plasma along with gaseous by-products of the plasma-photoresist reaction.

In use, wafer boats 44 each of which that has a plurality of wafers 20 are first placed in openings 42 of platform 40. Chamber 14 is then evacuated to a moderate vacuum, approximately 1/1000 of an atomosphere. The evacuation is accomplished by a conventional pump, not shown, that is connected to exhaust manifold 50. Diatomic oxygen, the working gas, is admitted to chamber 14 via entry gas manifold 22. A source of diatomic oxygen, not shown, is connected to entry gas manifold 22.

The RF generator is then activated, causing electrodes 28e, 28m, 30e and 30m to generate electric fields in both entry gas manifold 22 and chamber 14. The electric fields produced, Ee and Em, decompose diatomic oxygen to monoatomic oxygen, the working gas. The electric field in manifold 22 converts a small portion of the working gas into plasma before the gas enters ports 16 of chamber 14. The remaining portion of the working gas is converted to plasma by the electric field that is adjacent entry chamber ports 16. The position of the entry port electric field Ee forces all of the working gas to pass through the field, enhancing the conversion of gas to plasma.

As the working gas travels through chamber 14, its route of travel is dictated by constraint platform 40. Instead of meandering around in chamber 14, which is the case for plasma in prior art chambers, it can only exit by passing through openings 42. Since wafers 20 are positioned immediately above openings 42, all of the plasma must pass through wafers 20.

Since this enhances the number of oxygenphotoresist interactions, the time for completing the entire photoresist removal process is reduced.

It will be apparent to those skilled in the art that various modifications may be made within the spirit of the invention and the scope of the appended claims.

Claims

1. A plasma reactor, comprising a working chamber having at least one entry port, said working chamber is adapted to receive at least one article; said entry port is adapted to receive a working gas into said working chamber; an electrical energy generator; at least one pair of electrodes positioned adjacent said working chamber entry port, said electrodes, which are connected to said generator, create an electric field adjacent said entry port that converts said working gas into a working plasma for interacting with a material of said article, whereby an electric field-free region downstream of the plasma generating region is provided in which said article is positioned.

2. The plasma reactor as claimed in Claim 1, wherein said electric field-free region is shaped so as to constrain the flow of said working plasma as it passes said article to be processed.

3. The plasma reactor as claimed in Claim 1 or 2, wherein said material of said article is photoresist.

4. The plasma reactor as claimed in Claim 3, wherein said article is a semiconductor wafer.

5. The plasma reactor as claimed in Claim 4, wherein said working plasma consists of oxygen.

6. The plasma reactor as claimed in Claim 1 or 2, wherein the material of said article is a thin film of aluminum, silicon dioxide, or polysilicon on silicon wafers patterned with photoresist ready for etching.

7. A plasma barrel reactor, comprising a generally barrel-like working chamber having at least one entry port, said barrel chamber is adapted to receive at least one article; said barrel chamber entry port is adapted to receive a working gas into said barrel chamber; an electrical energy generator; at least one pair of electrodes positioned adjacent said barrel chamber entry port, said electrodes, which are connected to said generator, create an electric field adjacent said entry port that converts said working gas into a working plasma for interacting with a material of said article, whereby the position of said electric field adjacent said entry port promotes the efficacious conversion of said working gas to said working plasma.

8. The plasma barrel reactor as claimed in Claim 7, wherein the position of said electric field adjacent said entry port delineates a substantially electric field-free region in said barrel chamber adjacent said article, downstream of the plasma generating region.

9. The plasma barrel reactor as claimed in Claim 7 or 8, wherein said material of said article is photoresist.

10. The plasma barrel reactor as claimed in Claim 9, wherein said article is a semiconductor wafer.

11. The plasma barrel reactor as claimed in Claim 10, wherein said working plasma consists of oxygen.

12. The plasma barrel reactor as claimed in Claim 7 or 8, wherein the material of said article is a thin film of aluminum, silicon dioxide, or polysilicon on silicon wafers patterned with photoresist ready for etching.

13. A plasma barrel reactor, comprising a generally barrel-like working chamber having at least one entry port, said barrel chamber is adapted to receive at least one article; an entry gas manifold positioned adjacent said barrel chamber, said entry gas manifold includes at least one port that communicates with said barrel chamber entry port, said entry gas manifold is adapted to transport a working gas to said barrel chamber; an electrical energy generator; at least one pair of electrodes positioned adjacent both said barrel chamber entry port and said entry gas manifold, said electrodes, which are connected to said generator, create an electric field that converts said working gas into a working plasma, said working plasma is adapted to interact with a material of said article.

14. The plasma barrel reactor as claimed in Claim 13, wherein said material of said article is photoresist.

15. The plasma barrel reactor as claimed in Claim 14, wherein said article is a semiconductor wafer.

16. The plasma barrel reactor as claimed in Claim 15, wherein said working plasma consists of oxygen.

17. The plasma barrel reactor as claimed in Claim 13, wherein the material of said article is a thin film of aluminum, silicon dioxide, or polysilicon on silicon wafers patterned with photoresist ready for etching.

18. A plasma barrel reactor, comprising a generally barrel-like working chamber having at least one entry port, said barrel chamber is adapted to receive at least one article; an entry gas manifold positioned adjacent said barrel chamber, said entry gas manifold having at least one port that communicates with said barrel chamber entry port, said entry gas manifold is adapted to transport a working gas to said barrel chamber; an electrical energy generator; at least one pair of entry port electrodes positioned adjacent said barrel chamber entry port, said electrodes, which are connected to said generator, create an electric field in said barrel chamber adjacent said entry port that converts said working gas into a working plasma;; at least one pair of manifold electrodes positioned adjacent said entry gas manifold, said manifold electrodes, which are also connected to said generator, create an electric field in said manifold that converts a portion of said working gas into a working plasma before said working gas enters said barrel chamber, whereby said manifold electric field and said entry port electric field efficaciously convert said working gas to said working plasma for interacting with a material of said article.

19. The plasma barrel reactor as claimed in Claim 18, wherein the position of said electric field adjacent said entry port delineates a substantially electric field-free region in said barrel chamber adjacent said article, downstream of the plasma generating region.

20. The plasma barrel reactor as claimed in Claim 18 or 19, wherein said material of said article is photoresist.

21. The plasma barrel reactor as claimed in Claim 20, wherein said article is a semiconductor wafer.

22. The plasma barrel reactor as claimed in Claim 21, wherein said working plasma consists of oxygen.

23. The plasma barrel reactor as claimed in Claim 18 or 19, wherein the material of said article is a thin film of aluminum, silicon dioxide, or polysilicon on silicon wafers patterned with photoresist ready for etching.

24. A plasma reactor, comprising a working chamber having at least one entry port for receiving a working gas into said working chamber, said working chamber is adapted to receive at least one article; an electrical energy generator; at least one pair of electrodes positioned about said working chamber, said electrodes, which are connected to said generator, create an electric field that converts said working gas into a working plasma; a plasma flow constraint member positioned within said working chamber for restricting the flow of said working plasma, whereby said constraint member permits the flow of said working plasma only through itself so as to enhance the interaction of said working plasma with a material of said article.

25. The plasma reactor as claimed in Claim 24, wherein said plasma flow constraint member includes at least one opening which is adapted to receive said article and to permit the passage of said working plasma.

26. The plasma reactor as claimed in Claim 24 or 25, wherein said material of said article is photoresist.

27. The plasma reactor as claimed in Claim 26, wherein said article is a semiconductor wafer.

28. The plasma reactor as claimed in Claim 27, wherein said working plasma consists of oxygen.

29. The plasma barrel reactor as claimed in Claim 24 or 25, wherein the material of said article is a thin film of aluminum, silicon dioxide, or polysilicon on silicon wafers patterned with photoresist ready for etching.

30. A plasma barrel reactor, comprising a generally barrel-like working chamber having at least one entry port, said barrel chamber is adapted to receive at least one article; an entry gas manifold positioned adjacent said barrel chamber, said entry gas manifold having at least one port that communicates with said barrel chamber entry port, said entry gas manifold is adapted to transport a working gas to said barrel chamber; a radio-frequency electrical energy generator; at least one pair of entry port electrodes positioned adjacent said barrel chamber entry port, said electrodes, which are connected to said generator, create an electric field in said barrel chamber adjacent said entry port that converts said working gas into a working plasma;; at least one pair of manifold electrodes positioned adjacent said entry gas manifold, said manifold electrodes, which are also connected to said generator, create an electric field in said manifold that converts a portion of said working gas into a working plasma before said working gas enters said barrel chamber, whereby said manifold electric field and said entry port electric field efficaciously convert said working gas to said working plasma; and a plasma flow constraint member positioned within said barrel chamber for restricting the flow of said working plasma, whereby said constraint member permits the flow of said working plasma only through itself so as to enhance the interaction of said working plasma with a material of said article.

31. The plasma barrel reactor as claimed in Claim 30, wherein the position of said electric field adjacent said entry port delineates a substantially electric field-free region in said barrel chamber adjacent said article, downstream of the plasma generating region.

32. The plasma barrel reactor as claimed in Claim 31, wherein said plasma flow constraint member is a generally planar, board-like platform that includes at least one opening that is adapted to receive said article and to permit the passage of said working plasma.

33. The plasma barrel reactor as claimed in Claim 30, 31 or 32, wherein said material of said article is photoresist.

34. The plasma barrel reactor as claimed in Claim 33, wherein said article is a semiconductor wafer.

35. The plasma barrel reactor as claimed in Claim 34, wherein said working plasma consists of oxygen.

36. The plasma barrel reactor as claimed in Claim 30 or 31, wherein the material of said article is a thin film of aluminum, silicon dioxide, or polysilicon on silicon wafers patterned with photoresist ready for etching.

37. A method of interacting a working plasma with an article which is positioned within a working chamber comprising the steps of positioning said article in a working position within said chamber; introducing a working gas into said chamber remote from said working position; establishing an electric field for converting said working gas into said working plasma for interacting with a material of said article; and confining said electric field to a region immediately adjacent where said working gas is introduced into said working chamber, whereby said working plasma interacts with said material of said article in said working position that is substantially electric field-free.

38. The method of interacting a working plasma with an article as claimed in Claim 37, wherein said material of said article is photoresist.

39. The method of interacting a working plasma with an article as claimed in Claim 38, wherein said article is a semiconductor wafer.

40. The method of interacting a working plasma with an article as claimed in Claim 39, wherein said working plasma consists of oxygen.

41. The method of interacting a working plasma with an article as claimed in Claim 37, wherein the material of said article is a thin film of aluminum, silicon dioxide, or polysilicon on silicon wafers patterned with photoresist ready for etching.

42. A method of interacting a working plasma with an article which is positioned within a working chamber comprising the steps of positioning said article in a working position within said chamber; introducing a working gas into said chamber remote from said working position; establishing an electric field for converting said working gas into said working plasma for interacting with a material of said article; and restricting the flow of said working plasma so as to enhance the interaction of said working plasma with said material of said article.

43. The method of interacting a working plasma with an article as claimed in Claim 42, wherein said material of said article is photoresist.

44. The method of interacting a working plasma with an article as claimed in Claim 43, wherein said article is a semiconductor wafer.

45. The method of interacting a working plasma with an article as claimed in Claim 44, wherein said working plasma consists of oxygen.

46. The method of interacting a working plasma with an article as claimed in Claim 42, wherein the material of said article is a thin film of aluminum, silicon dioxide, or polysilicon on silicon wafers patterned with photoresist ready for etching.

47. A method of interacting a working plasma with an article which is positioned within a working chamber comprising the steps of positioning said article in a working position within said chamber; introducing a working gas into said chamber remote from said working position; establishing an electric field for converting said working gas into said working plasma for interacting with a material of said article; confining said electric field to a region immediately adjacent where said working gas is introduced into said working chamber, whereby said working plasma interacts with said material of said article in said working position that is substantially electric field-free; and restricting the flow of said working plasma so as to enhance the interaction of said working plasma with said material of said article.

48. The method of interacting a working plasma with an article as claimed in Claim 47, wherein said material of said article is photoresist.

49. The method of interacting a working plasma with an article as claimed in Claim 48, wherein said article is a semiconductor wafer.

50. The method of interacting a working plasma with an article as claimed in Claim 49, wherein said working plasma consists of oxygen.

51. The method of interacting a working plasma with an article as claimed in Claim 47, wherein the material of said article is a thin film of aluminum, silicon dioxide, or polysilicon on silicon wafers patterned with photoresist ready for etching.

52. A plasma reactor as claimed in Claim 1 with reference to the accompanying drawings.