WO1999048138A1

WO1999048138A1 - Large area uniform laminar gas flow dispenser

Info

Publication number: WO1999048138A1
Application number: PCT/US1999/003929
Authority: WO
Inventors: Robert P. Mandal
Original assignee: Applied Materials, Inc.
Priority date: 1998-03-18
Filing date: 1999-02-23
Publication date: 1999-09-23

Abstract

A gas flow dispenser in accordance with the present invention employs a multistage construction to disperse gas having highly uniform velocities and pressures across the dispensing face. A gas flow is introduced at a given pressure into the gas flow dispenser through a relatively small diameter source and enters first into a gas dispersing stage. The gas dispersing stage roughly spreads the gas flow over the entire cross-sectional area of the gas flow dispenser. After passing through the gas dispersing stage, the gas flow enters into a gas pressure equalization stage in which the gas flow encounters minimal impedance in a forward direction and essentially zero impedance in a lateral direction. This allows the gas pressure, and thus the gas flow rate, to equalize with minimal loss in gas pressure. Successive gas equalization stages can be used to further refine gas flow uniformity such that the gas flow exiting the gas flow dispenser achieves laminal flow within a few millimeters from the dispensing face of the gas flow dispenser.

Description

1

LARGE AREA UNIFORM LAMINAR GAS FLOW DISPENSER

FIELD OF THE INVENTION

This invention relates generally to semiconductor integrated circuit wafer processing, and more particularly to a gas dispenser to provide large area uniform laminar gas flow into semiconductor processing equipment.

BACKGROUND OF THE INVENTION Many types of semiconductor processing modules require gas flow dispensers (sometimes called "showerheads") with uniform areal flow across the dispensing face of the dispenser. Some advanced processing modules require gas flow dispensers which can accommodate flow rates in excess of 4 liters per second while maintaining laminar areal gas flow uniformity across the dispensing face.

Spin-cast chambers, in which polymer films such as photoresist films are formed onto the surface of a semiconductor wafer, are one type of advanced processing module that require such high performance gas dispensers. In spin-casting, an amount of a polymer fluid is applied to the center of a spinning wafer. Centrifugal forces cause the polymer fluid to spread towards the outer edges of the spinning wafer, coating the surface of the wafer with a polymer film as it spreads. However, solvent from the polymer fluid tends to evaporate as it spreads, causing the polymer fluid to become more viscous and the film to become more thick towards the edges. To overcome this problem, spin-cast chambers, such as the one described in U.S. Patent No. 5,472,502, incorporate a showerhead to dispense a gas mixture containing a low concentration of solvent vapors into the volume immediately adjacent to the semiconductor wafer surface. The presence of the solvent vapors slows the evaporation of solvent from the polymer fluid, thus maintaining the viscosity and uniformity of the polymer fluid as it spreads to the edges of the wafer.

During spin-casting, however, polymer fluids are highly susceptible to areal variances in gas flow velocities and pressures. Such areal variances diminish the uniformity of the polymer film's thickness across the substrate. For spin-cast photoresist films, for example, diminished film thickness uniformity in turn diminishes the accuracy and reproducibility of submicron feature critical dimensions and thus good integrated circuit yields. To achieve accurate and reproducible submicron feature critical dimensions, and thus good integrated circuit yields, requires film thickness uniformity on the order of less than 10 A variance for films of 7000-12,000 A thickness. This translates into a variance of no more than roughly one (short axis) molecular diameter in 1000.

Thus, advanced semiconductor wafer processing modules require extremely high uniform areal gas flow on both microscopic and macroscopic scales. The advent of 300mm diameter wafer processing places even greater demands on areal gas flow uniformity because the same level of film thickness uniformity is required over the significantly larger wafer surface area.

Figure 1 A illustrates in cross-section a typical showerhead gas dispenser found in the prior art. The showerhead comprises a housing 10 with an inlet 12 for gas and a gas dispersing plate 14 having a plurality of holes 16a-c opposite the gas inlet 12. Gas 18 entering through the gas inlet 12 travels through the interior of the housing, as shown by the arrows 19a-c, and is dispersed through the plurality of holes 16a-c as an array of individual gas jets 20a-c. The individual streams of gas 20a-c have very high areal variances in gas flow velocities and pressures, making the prior art gas dispensers incapable of meeting the extreme demands of many advanced wafer processing modules. One way to minimize such areal variances, shown in Figure IB, is for the gas to pass through a semi-permeable (e.g., solvent-permeable) filter 22 before it exits through the plurality of holes 24a-c. However, the filter 22 can retain condensables, thereby preventing rapid flow rates and possibly contaminating the gas flow composition. Moreover, showerhead gas dispensers of this type can achieve areal flow uniformity only with an accompanying loss in pressure between the gas entering and the gas exiting the dispenser, which in turn limits the throughput of gas through this type of dispenser.

SUMMARY OF THE INVENTION

Therefore, a need exists for a gas flow dispenser which can accommodate relatively high gas flow rates while maintaining a high degree of gas flow uniformity across the dispersing face. It is a feature of this invention to provide high flow uniformity together with optional high flow rates.

It is another feature of this invention to provide high areal flow uniformity over a relatively large area. It is another feature of this invention to provide laminar flow within a few millimeters of the dispensing face.

It is another feature of this invention to provide adjustable levels of gas flow uniformity.

It is another feature of this invention to minimize the loss in pressure between the gas entering and the gas exiting the gas flow dispenser.

It is another feature of this invention to not trap condensables. It is another feature of this invention to minimize particle contamination to the gas flow.

It is another feature of this invention to be resistant to chemical corrosion. It is yet another feature of this invention to be reproducibly manufactured in a cost-effective manner.

In accordance with one aspect of the present invention, a gas flow dispenser comprises a first stage, providing a rough dispersal of gas flow from a small diameter source to the area desired, and at least one subsequent stage, providing equalization of gas pressure and thus gas flow without significant reduction in gas pressure. Successive stages, if used, further refine gas flow uniformity without significant loss in gas pressure, thereby dispensing gas with high flow uniformity while allowing high flow rates.

In accordance with another aspect of the present invention, a gas flow dispenser comprises a housing, into which is placed a gas dispersing plate followed by at least one gas flow equalization element. The gas dispersing plate is separated from the first gas flow equalization element by a spacer element, and successive gas flow equalization elements, if used, are similarly separated from one another by a spacer element. The gas flow equalization elements presents minimal impedance to forward gas flow and essentially zero impedance to lateral gas flow, allowing the gas pressure to equalize in the volume between the gas dispersing plate and the first gas flow equalization element and in the volume between successive gas flow equalization elements.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 A shows in cross-section a gas dispenser of the prior art.

Figure 1 B shows in cross-section another gas dispenser of the prior art. Figure 2 is a cross-sectional view of one embodiment of a gas flow dispenser assembled in accordance with the present invention.

Figure 3 A shows the plurality of holes of the gas dispersing plate in a symmetric pattern in accordance with one embodiment of the present invention.

Figures 3B and 3C are cross-sectional views of two embodiments of a gas dispersing plate.

Figure 4 shows one embodiment of a gas flow equalization element. Figure 5 shows a cross-sectional view of the gas flow equalization element shown in Figure 4.

DETAILED DESCRIPTION OF THE INVENTION

A gas flow dispenser in accordance with the present invention uses a multistage construction to disperse gas having highly uniform velocities and pressures across the dispensing face. The multistage construction imparts manufacturing flexibility, as each stage can be manufactured individually. The individual stages then can be assembled to meet specific processing requirements.

A gas flow is introduced at a given pressure into the gas flow dispenser through a relatively small diameter source and enters first into a gas dispersing stage. The gas dispersing stage roughly spreads the gas flow over the cross-sectional area of the gas flow dispenser. This rough dispersal typically spreads the gas flow unevenly, such that the gas pressure across the cross-sectional area of the gas flow dispenser has very little uniformity.

After passing through the gas dispersing stage, the gas flow enters into a gas pressure equalization stage in which the gas flow encounters minimal impedance in a forward direction and essentially zero impedance in a lateral direction. This allows the gas pressure, and thus the gas flow rate, to equalize with minimal loss in gas pressure. Successive gas equalization stages can be used to further refine gas flow uniformity until the gas flow exiting the gas flow dispenser achieves laminar flow within a few millimeters from the dispensing face of the gas flow dispenser. A. Gas Flow Dispenser

Figure 2 illustrates in cross-section one embodiment of a gas flow dispenser of the present invention. The embodiment shown 28 has three stages — a gas dispersal stage and two successive gas pressure equalization stages. The gas flow 30 is introduced into the gas flow dispenser through an inlet 32 and enters into the gas dispersal stage. The gas dispersal stage comprises a gas dispersing plate 34 having a plurality of holes 36a-f. The entering gas flow 30 is dispersed through the plurality of holes 36a-f, as shown by the arrows 37a-f.

The dispersed gas flow 37a-f then enters into the first of two gas pressure equalization stages. As shown, each gas pressure equalization stage comprises a spacer element 38, 42 and a gas flow equalization element 40, 44. The first spacer element 38 serves to separate the first gas flow equalization element 40 from the gas dispersing plate 34. In the space defined by the first spacer element 38 between the gas dispersing plate 34 and first gas flow equalization element 40, the dispersed gas flow 37a-f encounters minimal impedance in the forward direction (i.e., in the direction of the arrows) and essentially zero impedance in the lateral direction (i.e., in the direction perpendicular to the arrows). Within this space, the gas pressure and consequently the gas flow will tend to equalize before passing through the first gas flow equalization element 40 into the second gas pressure equalization stage. The thicker arrows 4 la-f represent the increased areal gas flow uniformity of the gas flow leaving the first gas pressure equalization stage. The second gas pressure equalization stage comprises a spacer element 42 and a gas flow equalization element 44. The second spacer element 42 serves to separate the second gas flow equalization element 44 from the first gas flow equalization element 40. As in the first gas pressure equalization stage, the gas flow entering the second gas pressure equalization stage encounters minimal impedance in the forward direction and essentially zero impedance in the lateral direction. In the space defined by the second spacer element 42 between the first gas flow equalization element 40 and the second gas flow equalization element 44, the gas pressure and consequently gas flow rate are further equalized. The gas flow leaving the dispensing face 46 of the gas flow dispenser has even higher areal gas flow uniformity, as shown by the even thicker arrow 48.

The embodiment shown in Figure 2 uses two gas pressure equalization stages, but additional gas pressure equalization stages may be added to further refine the gas flow uniformity, or fewer gas pressure equalization stages may be used if a lower level of gas flow uniformity is acceptable. Gas pressure equalization stages may be added successively until the gas flow exiting the gas flow dispenser achieves uniform laminar flow across the cross-sectional area of the gas flow dispenser within a few millimeters of the gas flow dispenser.

To insure uniformity of gas flow across the entire surface of the wafer or substrate to be processed, the cross-sectional area of the gas flow dispenser should be at least equal to the surface area of the wafer to be processed. Thus, for 300mm diameter wafer processing, the gas flow dispenser should have a diameter of at least 300mm, advantageously greater than 300mm. B. Gas Dispersing Plate

Figures 3 A, 3B and 3C illustrate possible features of a gas dispersing plate 34. The plurality of holes may be laid out in a symmetric pattern 50, as shown in

Figure 3A.

Each of the plurality of holes may be fashioned so as to provide some measure of lateral direction to the gas flow within the gas dispersing plate, which would aid in dispersing the gas flow over the entire cross-sectional area of the gas flow dispenser. Figure 3B shows, in cross-section, one embodiment in which each hole has a conical- shape. Alternatively, as shown in cross-section in Figure 3C, each hole may be double- drilled such that the diameter of the exit orifice 52 is greater than the diameter of the inlet orifice 54.

Advantageously, the gas dispersing plate is made of a rigid, chemically-resistant material. Suitable materials include polytetrafluoroethylene and polypropylene. C. Gas Flow Equalization Element

Figure 4 illustrates one embodiment of a gas flow equalization element 40, 44. Figure 5 illustrates the same embodiment in cross-section. This gas flow equalization element shown comprises a fabric 56 mounted onto an open supporting frame 58. A variety of methods may be used to secure the fabric 56 to the supporting frame

58. As shown in Figures 4 and 5, the fabric 56 is stretched over the supporting frame 58, and a wire segment 60 is pressed over the fabric and into a groove cut into the face of the supporting frame 58, securing the fabric 56 to the supporting frame 58.

The fabric 56 has a relatively open structure, such as in a screen or mesh, and comprises a non-porous material that will not trap condensables. The relatively open structure provides minimal impedance to gas flow in a direction peφendicular to the face of the gas flow equalization element, as the arrow 62 shows, whereas nothing provides any impedance in a direction parallel 64 to the face of the gas flow equalization element. Suitable non-porous materials include stainless steel, nichrome, and Kevlar. In one embodiment, the fabric 56 may comprise a 400 mesh stainless steel fabric, and the supporting frame 58 may comprise a stainless steel ring.

The gas flow equalization element can be treated with a vapor-deposited coating of a chemically-resistant mechanically-compliant adherent film, such as Parylene-F, Parylene-N, or polynaphthalene. Alternatively, the fabric can be treated with the vapor- deposited coating before it is secured to the supporting frame.

The embodiments disclosed herein only illustrate the principles of this invention and are not meant to limit the present invention in any way. Many other embodiments and modifications may be made without departing from the scope of the invention as defined in the claims.

Claims

WHAT IS CLAIMED IS:

1. A gas flow dispenser to dispense a gas flow over a given area, comprising: a gas dispersal stage to disperse said gas flow over said given area, wherein said gas flow enters into said gas dispersal stage through an inlet having a cross-sectional area less than said given area; and at least one gas pressure equalization stage following said gas dispersal stage, wherein said at least one gas pressure equalization stage presents minimal impedance to said gas flow in a forward direction and essentially zero impedance to said gas flow in a lateral direction, thereby allowing said gas flow to become highly uniform over said given area.

2. A gas flow dispenser, comprising: a gas dispersing plate having a plurality of holes therethrough; a first spacer element; at least one gas flow equalization element; a housing, into which is placed in series said gas dispersing plate followed by said first spacer element followed by a first gas flow equalization element; and where more than one gas flow equalization element is used, a plurality of spacer elements, wherein each of said gas flow equalization elements is separated from a subsequent gas flow equalization element following in series by one of said plurality of spacer elements.

3. The gas flow dispenser of claim 2, wherein said gas dispersing plate comprises a rigid chemically-resistant material.

4. The gas flow dispenser of claim 3, wherein said rigid chemically-resistant material is selected from the group consisting of polytetrafluoroethylene or polypropylene.

5. The gas flow dispenser of claim 2, wherein said plurality of holes is in a symmetric pattern.

6. The gas flow dispenser of claim 2, wherein each of said plurality of holes comprises an inlet orifice defining an inlet diameter and an exit orifice defining an exit diameter, said exit diameter being greater than said inlet diameter.

7. The gas flow dispenser of claim 6, wherein each of said plurality of holes is double-drilled through said gas dispersing plate.

8. The gas flow dispenser of claim 2, wherein each of said gas flow equalization elements comprises a fabric mounted onto an open supporting frame.

9. The gas flow dispenser of claim 8, wherein said fabric comprises a non-porous material.

10. The gas flow dispenser of claim 9, wherein said non-porous material is selected from the group consisting of stainless steel, nichrome, or Kevlar.

1 1. The gas flow dispenser of claim 8, wherein said fabric comprises a 400 mesh stainless steel material and said open supporting frame comprises a stainless steel ring.

12. The gas flow dispenser of claim 2, wherein each of said gas flow equalization elements is treated with a vapor-deposited coating of a chemically-resistant mechanically-compliant adherent film.

13. The gas flow dispenser of claim 12, wherein said vapor-deposited coating comprises Parylene-F, Parylene-N, or polynaphthalene.

14. The gas flow dispenser of claim 8, wherein said fabric is treated with a vapor- deposited coating of a chemically-resistant mechanically-compliant adherent film.

15. The gas flow dispenser of claim 14, wherein said vapor-deposited coating comprises Parylene-F, Parylene-N, or polynaphthalene.

16. The gas flow dispenser of claim 2, wherein said gas dispersing plate, said first spacer element, each of said gas flow equalization elements, and each of said plurality of spacer elements have a common diameter.

17. The gas flow dispenser of claim 16, wherein said common diameter is greater than 300 mm.

18. The gas flow dispenser of claim 17, wherein said common diameter is between 320 mm and 340 mm.

19. A gas flow dispenser comprising: a gas dispersing plate having a plurality of holes therethrough, each of said plurality of holes having an inlet orifice and an exit orifice; 10

a first spacer element; at least one gas flow equalization element, each of said gas flow equalization elements comprising a fabric mounted onto an open supporting frame; a housing, into which is placed in series said gas dispersing plate followed by said first spacer element followed by a first gas flow equalization element such that said fabric of said first gas flow equalization element faces towards said exit orifice; and where more than one gas flow equalization element is used, a plurality of spacer elements, wherein each of said gas flow equalization elements is separated from a subsequent gas flow equalization element following in series by one of said plurality of spacer elements such that said fabric of each of said gas flow equalization element faces towards said exit orifice and is separated from said fabric of said gas flow equalization element following in series.

20. The gas flow dispenser of claim 19, wherein said gas dispersing plate comprises a rigid chemically-resistant material.

21. The gas flow dispenser of claim 20, wherein said rigid chemically-resistant material is selected from the group consisting of polytetrafluoroethylene or polypropylene.

22. The gas flow dispenser of claim 19, wherein said plurality of holes is in a symmetric pattern.

23. The gas flow dispenser of claim 19, wherein said inlet orifice defines an inlet diameter and said exit orifice defines an exit diameter, said exit diameter being greater than said inlet diameter.

24. The gas flow dispenser of claim 23, wherein each of said plurality of holes is double-drilled through said gas dispersing plate.

25. The gas flow dispenser of claim 19, wherein said fabric comprises a non-porous material.

26. The gas flow dispenser of claim 25, wherein said non-porous material is selected from a group consisting of stainless steel, nichrome, or Kevlar. 11

27. The gas flow dispenser of claim 19, wherein said fabric comprises a 400 mesh stainless steel material and said open supporting frame comprises a stainless steel ring.

28. The gas flow dispenser of claim 19, wherein each of said gas flow equalization elements is treated with a vapor-deposited coating of a chemically-resistant mechanically-compliant adherent film.

29. The gas flow dispenser of claim 28, wherein said vapor-deposited coating comprises Parylene-F, Parylene-N, or polynaphthalene.

30. The gas flow dispenser of claim 19, wherein said fabric is treated with a vapor- deposited coating of a chemically-resistant mechanically-compliant adherent film.

31. The gas flow dispenser of claim 30, wherein said vapor-deposited coating comprises Parylene-F, Parylene-N, or polynaphthalene.

32. The gas flow dispenser of claim 19, wherein said gas dispersing plate, said first spacer element, each of said gas flow equalization elements, and each of said plurality of spacer elements have a common diameter.

33. The gas flow dispenser of claim 32, wherein said common diameter is greater than 300 mm.

34. The gas flow dispenser of claim 33, wherein said common diameter is between 320 mm and 340 mm.