WO2001064315A1

WO2001064315A1 - Centering ring diffuser/filter

Info

Publication number: WO2001064315A1
Application number: PCT/US2000/005179
Authority: WO
Inventors: Chris A. Tsourides
Original assignee: Mykrolis Corporation
Priority date: 2000-03-01
Filing date: 2000-03-01
Publication date: 2001-09-07
Also published as: AU2000237113A1

Abstract

A diffuser/filter is disclosed for use in process chamber applications. The diffuser is formed of a porous filtration material such as porous sintered metal, PTFE or ceramic. It has a pore structure that provides a flow/unit area filter value at a 9 LRV of from about 0.75 to about 6 SLPM/cm2. The diffuser is mounted in a centering ring that is located in the chamber at the entrance/exit for gases, or in a line to or from the chamber. It prevents the introduction of new particles into the chamber and prevents the stirring of settled particles within the chamber.

Description

CENTERING RING DIFFUSER / FILTER

This invention relates to a gas diffuser that has filtration capabilities. More particularly, it relates to a gas diffuser with filtration capabilities for use in a vacuum system.

Background of the Invention

The use of various process chambers is well known, especially in semiconductor manufacturing, fiber optics and the automotive industry. Typically, the chamber is a vacuum chamber and is used to treat a substrate in some manner.

In the semiconductor industry it is typically used to either grow or etch a semiconductor wafer. In either process, there is a support for the semiconductor wafer and associated equipment for either etching or growing the substrate of the wafer. Additionally, there are one or more gas inlets and outlets into the chamber. These openings are used to introduce process gas into the chamber as well as in the case of vacuum chambers to evacuate the chamber in order to form the vacuum and to re- pressurize the chamber such as upon completion of the process or the introduction of additional materials or the change in one process step to the next.

The chamber may contain various particulate materials, which may have been formed during the treatment process or introduced into the chamber through the process gas stream or with the transfer of materials into the system. These particulate materials can cause defects in the substrate if they land upon the surface before or during processing. Rather than attempt to remove these particles it has been the practice to allow them to settle with in the chamber and one simply tries not to disturb the particles and thus prevent them from becoming air borne and landing upon the substrate surface.

However, when one simply introduces or removes a gas through an opening, one moves the gas in a high velocity manner with a non-uniform flow. Various diffusers have been suggested to move the gas into or out of a chamber in a laminar gas flow at a reduced face velocity in order to reduce the disturbance of these particles within the chamber and thus reduce the potential for such particles to land on the surface of the substrate that is being treated. These diffusers have been made of various highly porous materials such as PTFE resin, ceramic or stainless steel. Typically these diffusers have had an average pore size of greater than 2 microns. Additionally, these devices have been mounted inside the chamber typically by use of various well-known fittings such as tube stub fittings to which the diffuser is welded, or by a mechanical, threaded device such as a Swagelok®-type fitting or a VCR®-type fitting.

These diffusers have several disadvantages. First, they are relatively large, are mounted within the chamber, use special fittings and take up valuable space within the chamber. Second, they have not significantly reduced the face velocity of the gas in the chamber and tend to stir some of the settled particles especially upon evacuation or pressurization of the chamber. Lastly, either they are highly porous that they are not capable of preventing the introduction of new particles contained within the gases which passes through them into the chamber or they are not very porous (porosity of 20 to 35%) which causes unacceptable pressure drops, long cycle times and overall poor performance. What is desired is a diffuser that provides better laminar flow and reduced face velocity and lower pressure drop while also providing significant filtration performance in order to reduce the introduction of particles into the chamber. Additionally, reduction in the amount of space consumed with the chamber for the diffuser is desired. The present invention provides such a device.

Summarv of the Invention

The present invention is a diffuser, which has significant filtration capabilities and delivers gases with a laminar flow and reduced face velocity. The diffuser of the invention may be installed inside the gas or vacuum line or it may be mounted flush against the inside wall of the chamber thus reducing the amount of chamber space taken up by the diffuser. The present invention comprises a highly porous filtration disk or tube mounted to a ring-like structure such as a centering ring. This ring or tube may be mounted to a KF, NW, or ISO vacuum flange. The filtration disk/tube is formed of a porous material such as a sintered metal including but not limited to stainless steel, nickel, Inconel, Hastelloy or chromium or a ceramic or polymer such as PTFE. The filtration disk/tube has a particulate filtration efficiency (also known as log reduction i value (LRV)) of at least 3 as measured at the most penetrating particle size and a flow rate between 1 and about 200 SLPM and preferably a LRV of at least 9 for the most penetrating particle size at a flow rate between 1 and 90 SLPM. It has a flow/unit area of at least lSLPM/cm² at a LRV of 3, preferably a flow/unit area of at least lSLPM/cm² at a LRV of 9.

In the Drawings

Figure 1 shows a first embodiment of the present invention in a cross section view as mounted in a vacuum line adjacent the processing chamber.

Figure 2 shows a second embodiment of the present invention in a cross section view as mounted in a gas line adjacent the processing chamber.

Figure 3 shows a third embodiment of the present invention in a cross section view as mounted in a gas line adjacent the processing chamber.

Detailed Description of the Invention

In Figure 1, a first embodiment of the present invention is shown. In this embodiment, the diffuser 1 is mounted within the opening 2 of the gas line 3 for the chamber 4. The diffuser 1 is comprised of two components, the filtration material 5 and the support structure 6. The support structure has an inner circumference 7 to which the filtration material 5 is sealed. The support structure also has an outer circumference 8 that forms the attachment/sealing means of the diffuser 1 to the opening 2 of the gas line 3. In this embodiment, the sealing of the outer circumference 8 of the support structure 6 to the gas line wall 3 is by an O-ring 9, although a weld, solder or caulk may be used. This in conjunction with the sealing of the filtration material 5 to the inner circumference 7 of the support structure 6 ensures that a gas which flows through the gas line 3 to or from the chamber passes through the filtration material 5 of the diffuser 1. In this embodiment, the filtration material is shown as a flat disk of material. While it is preferred that the disk be flat, it may also be arched. Alternatively, it may be in the form of a tube having one end open and the other end closed. Such an embodiment is shown in Figure 2. All of the components of Figure 2 are identical to those of Figure 1 except for the shape of the filter media, which have been designed 5 A. In the embodiment of Figure 2, the end of the tube, which is closed, is shown as being closed with a solid cap 10 which is welded to the end of the tube.

In Figure 3 is shown an alternative design to the tube of Figure 2. In this embodiment, the end of the tube is porous as shown by 10A and is typically formed as part of the tube itself during its processing.

Additionally, while this embodiment refers to being mounted in a gas line for the chamber, the same device may also be added in other locations of the process chamber or its associated equipment where ever a gas is used such as at the pump, or the foreline or pump down line.

The filtration material of the present invention may be selected from the group of porous filtration materials such as porous sintered metal, including stainless steel, nickel, chromium, titanium, Hastelloy or Inconel, porous ceramics, or porous polymers such as PTFE resin sheets.

All of these filtration materials are available from a variety of sources. Preferred materials include stainless steel filter elements known as SF filter elements and nickel filter elements known as NF elements available from Millipore Corporation of Bedford, Massachusetts. A preferred plastic porous material is a PTFE porous filtration sheet known as WAFERGARD ® filters available from Millipore Corporation of Bedford Massachusetts.

Preferably, the material is a porous sintered metal. By porous sintered metal, it is meant a material formed of a plurality of metal particles, which have been loosely packed together and then sintered, together into a form stable shape. As these particles only sinter where they touch each other, they form spaces or pores between the particles. Preferred metals for such a material include stainless steel, nickel and chromium although other metals may be used so long as they are inert to the gases which flow through the gas line and the metals are capable of being formed into porous sintered metal products.

The shape of the particle is not critical to the present application provided it allows for the proper laminar flow and LRV. Typically these particles are in the form of dendritic particles, spherical particles, irregular particles or fibrous particles. The formation of such particles and such porous sintered metal filtration materials is well known, see US Patents US 5,487,771, US 5,814,272 and US 5,114,447, the teachings of which are incorporated herein in their entireties.

The porous sintered metal filtration material may be in the form of a flat sheet or tube. When in the form of a flat sheet, it is preferred that the material be in a spherical or ovoid shape so as to create a uniform laminar flow through the diffuser. However, the use of other shaped sheets, such as square, rectangular or triangular sheets may occur so long as the laminar flow and flow/unit are maintained.

When in the form of a tube, one end of the tube must be closed in order to achieve filtration. The end may be porous or non-porous, with a porous end being preferred in order to achieve laminar gas flow. The porous end cap may be formed as part of the sintering process, which is preferred or it may be a porous cap, which is welded or otherwise secured to the end of the tube.

The porous sintered metal materials preferably have porosity ranging from about 35% to about 80%o, preferably at least 40% and more preferably between 40% and 80%. Regardless of the porosity, the filtration material must be able to remove most particles typically found in gas streams and prevent them from passing through the diffuser and into the chamber while providing the gas flow at a low pressure drop. Typically, filtration materials that are capable of removing particles of a diameter of 0.003 microns or greater are preferred. One method for defining the efficiency of a filter is the flow/unit area of filtration media (defined as the surface area of the filter, e.g. one surface when in the form of a sheet or flat disk and the average of the two outer surfaces when in the from of a tube), for a stated LRV. For example, one diffuser of the present invention, a nickel disk, has a surface area of 16.4cm² and archives a LRV of 9 at a flow of 70 SLPM resulting in a flow/unit area filter of 4.5 SLPM/cm². Preferably, the flow/unit area is measured at 9 LRV and for a device of the present invention is at least 0.75 SLPM/cm² at 9LRV. A range of suitable values is from about 0.75 to about 6 SLPM/cm² at 9LRV, preferably from about 1 to about 4.5 SLPM/cm² at 9LRV and more preferably from about 2 to about 4.5 SLPM/cm² at 9LRV.

Al alternative and less accurate method of defining filter efficiency is to give the LRV or log reduction value for a filter at a given flow rate and at its most penetrating particle size, see the article by Rubow, et.al., "Characteristics of Ultra-High Efficiency Membrane Filters in Gas Applications", Journal of Environment Sciences, Vol. 31 , pgs. 26-30 (May 1988). A filter capable of retaining of 99.9% particles at its most penetrating particle size is a LRV of 3. This value is typically determined by comparing the ratio of the number of particles impacting the upstream side of the filtration material with the number of particles, which actually pass through the material and are detected on the downstream side of the material. Therefore, a LRV of 3 would imply that a challenge of 10x3 particles of the most penetrating size were directed against the filtration material and only one particle was detected downstream of the filter. The log of that value is 3, thus resulting in the LRV of 3.

Typically this test is conducted by generating an aerosol of several million particles with a size distribution centered around the most penetrating particle size, passing this aerosol through the filter and counting the number of particles that pass with a condensation nucleus counter (CNC). Preferably, the filtration material will have a LRV of at least 3 and more preferably at least 6 and most preferably 9, for its most penetrating particle size at a flow of from about 1 to 200 SLPM, preferably at a flow of between about 1 and about 90 SLPM. The pressure drop of diffusers according the present invention vary between about 4 psid and about 25 psid at 9 LRV. It is preferred that the pressure drop be less than 20, more preferably between 5 and 20 psid. This allows for adequate laminar flow with good filtration properties.

The support structure typically is formed of the same material as the filtration material, namely metal, ceramic or plastic. However, the support structure may be formed of a material different from that of the filtration material so long as it is capable of forming a seal between its inner circumference and the filtration material and does not cause any adverse interactions between the two materials. Unlike the filtration material, the support structure should not be porous.

The filtration material may be sealed to the inner circumference of the support structure in a variety of ways, depending upon the select of the filtration material and the support structure.

For example, when using metal for both the filtration material and the support structure, the filtration material may be welded, soldered or chemically bonded to the metal surface of the support structure. Alternatively, the metal support structure may be formed of two pieces such that the filtration material is placed between the two pieces and the two pieces are then attached to each other via a weld, soldered line or chemical bonding. Additionally, when using a plastic filtration material with the metal support structure, one may heat bond or adhere the two together.

When using a plastic support structure, it may be injection molded to be outer periphery of the filtration material, or the filtration material may be adhered to the support structure. Alternatively, when both are plastic, the filtration material may be heat sealed, ultrasonically welded or friction bonded to the support structure. Additionally, when one seals a metal filtration material to a plastic support structure, one may heat the metal to a temperature above the melting point of the support structure and simply melt bond the filtration material into the support structure to form a seal. Ceramic filtration materials may be used with a plastics support structure and may be attached via injection molding, adhesive or in some case melt bonding. The ceramic material may actually be formed as one piece containing both the support structure and the porous filtration material. In this instance, it is preferred to then render the support structure portion of the ceramic device non-porous, such as by treating that portion with a glaze or filler.

The support stmcture is preferably formed of a flange or seal that is typically used in the semiconductor industry. Such flanges and seals are well known in the art. Preferred flanges include KF flanges, ISO flange and NW flange. These are available from various suppliers such as Millipore Corporation of Bedford, Massachusetts, Norcal of Yureka, California, Varian Corporation of Lexington, Massachusetts, and Key High Vacuum of Nesconset, New York.

The diffuser may be attached to the chamber in a variety of ways. When the diffuser is mounted within the gas line or gas line opening, it may simply be welded or adhered to the inner wall of the gas line or opening. When mounted to the wall of the chamber over the opening, it may be held in place by a threaded fixture formed on the surface of the diffuser and the wall of the chamber, welded or adhered in place or mechanically held in place with screws, rivets, or clamps. The method of attachment is not critical to the invention except that it should form a seal between the diffuser and the wall of the chamber, vacuum line, component opening (such as a pump air port), gas line or other opening (including exhaust lines,) such that all gas must flow through the filtration material.

The following example is provided as an illustration of the present invention and is not meant in any way to be limiting on the scope of the invention.

EXAMPLE 1 A diffuser according to the present invention and having a configuration of that of

Figure 1 was made. The support structure was a stainless steel NW centering ring having an inner diameter of 50 mm obtained from Millipore Corporation of Bedford, Massachusetts. A nickel filter having a surface area of 16.4 square centimeters was made according to the teachings of US Patent 5,487,771 and had a porosity of about 64%. The filter was welded to the inner circumference of the ring.

The flow/unit area at 9LRV was 4.5 SLPM/cm². The LRV was measured at a flow rate of 90 SLPM. The pressure drop was measured at 20 psi at 9 LRV.

EXAMPLE 2

A diffuser according to the present invention and having a configuration of that of Figure 2 was made. The support structure was a stainless steel NW centering ring having an inner diameter of 50 mm was obtained from Millipore Corporation of Bedford, Massachusetts. A nickel tube filter having a surface area of 28 cm² was made according to the teachings of US Patent 5,487,771 and had a porosity of about 62%. The closed end of the tube was formed as an integral part of the device and therefore was porous as well as the rest of the tube. The filter was welded to the inner circumference of the ring.

The flow/unit area at 9LRV was 2 SLPM/cm². The pressure drop was 10 psid at 9LRV.

EXAMPLE 3

A diffuser according to the present invention and having a configuration of that of Figure 1 was made. The support structure was a stainless steel NW centering ring having an inner diameter of 50 mm obtained from Millipore Corporation of Bedford, Massachusetts. A stainless steel flat disk filter having a surface area of 16.4 square centimeters was made according to the teachings of US Patent 5,487,771 and had a porosity of about 52%. The filter was welded to the inner circumference of the ring.

The flow/unit area at 9LRV was 0.75 SLPM/cm². The pressure drop was 5 psid at 9 LRV.

The present invention provides a diffuser that has excellent filtration capabilities and laminar flow characteristics and low-pressure drops. It occupies little or no space

Claims

within the chamber and provides for faster vent times of processing, cool down, transfer and load lock chamber with low particle disturbance.WHAT I CLAIM:

1. A diffuser for use on a gas line comprising a support structure having an outer solid portion, and an opening formed through the inner portion of the support structure, a porous filtration material sealed within the opening of the support structure such that all gas which passes through the line must pass through the filtration material and the filtration material having a flow/unit area value of at least 0.75 SLPM/cm² at 9 LRV.

2. The diffuser of claim 1 wherein the filtration material is formed of a material selected from the group consisting of sintered porous metal, porous ceramic and porous PTFE resin sheets.

3. The diffuser of claim 1 wherein the filtration material is in a form selected from the group consisting of a disk or a tube with one end of the tube being closed.

4. The diffuser of claim 1 wherein the filtration materials is in a form of a tube with one end of the tube being closed, said closed end being porous.

5. The diffuser of claim 1 wherein the diffuser has a flow/unit area at 9LRV of from about 0.75 to about 6 SLPM/cm² and a pressure drop of from about 4 to about 25 psid. at 9 LRV.

6. The diffuser of claim 1 wherein the LRV is at least 9 as measured at the most penetrating particle size and at a flow of between 1 and 90 SLPM.

7. The diffuser of claim 1 wherein the filtration materials is a porous sintered metal selected from the group consisting of stainless steel, nickel, chromium, titanium, Hastelloy and Inconel.

8. The diffuser of claim 1 wherein the filtration material is a porous sintered metal selected from the group consisting of stainless steel, nickel and chromium and, said filtration material has a porosity of at least 35%.

i 9. The diffuser of claim 1 wherein the filtration material is a porous sintered metal selected from the group consisting of stainless steel, nickel and chromium and wherein the porous sintered metal is formed from particles selected from the group consisting of dentritic particles, spherical particles, irregular particles and fibrous particles.

10. The diffuser of claim 1 wherein the support structure is formed as a ring having an inner and outer circumference and the filtration material is sealed to the inner circumference of the ring in a fluid tight seal.

1 1. The diffuser of claim 10 wherein the filtration materials is in the form of a disk.

12. The diffuser of claim 10 wherein the filtration material is in the form of a tube having one closed end and wherein the open end of the tube is sealed to the inner circumference of the ring.

13. A diffuser for use on a processing chamber comprising a support structure having an outer solid portion and an opening formed through the inner portion of the support structure, a porous filtration material sealed within the opening of the support structure such that all gas which passes through the support structure must pass through the filtration material, the filtration material is formed of a material selected from the group consisting of sintered porous metal, porous ceramic and porous PTFE resin sheets, the filtration material is in a form selected from the group consisting of a disk or a tube with one end of the tube being closed and the filtration material having a flow/unit area of filter at 9 LRV of from about 0.75 to about 6 SLPM/cm².

14. In a processing chamber having a chamber with one or more openings into the chamber through which one or more gases may pass, the improvement comprising one or more diffusers, each of the diffusers being formed of a support structure having an outer solid portion, and an opening formed through the inner portion of the support structure, a porous filtration material sealed within the opening of the support structure such that all gas which passes through the support structure must pass through the filtration material and the filtration material having a flow/unit area value of from about 0.75 to about 6 SLPM/cm² at 9 LRV, said diffusers being mounted in or over the one or more opening through which the one or more gases pass into the chamber.

15. The diffuser of claim 13 wherein the filtration material is formed of a material selected from the group consisting of sintered porous metal, porous ceramic and porous PTFE resin sheets and the filtration material is in a form selected from the group consisting of a disk or a tube with one end of the tube being closed.

16. The diffuser of claim 13 wherein the LRV is at least 9 as measured at the most penetrating particle size and at a flow of between 1 and 200 SLPM.

17. The diffuser of claim 13 wherein the filtration material is a porous sintered metal selected from the group consisting of stainless steel, nickel, chromium, titanium, Inconel and Hastelloy.

18. The diffuser of claim 13 wherein the one or more diffusers are mounted within the one or more openings of the chamber.

19. The diffuser of claim 13 wherein the one or more diffusers are mounted within the chamber at the entrances of one or more openings of the chamber.

20. The diffuser of claim 14 wherein the one or more diffusers have a flow/unit area at 9 LRV of from about 1 to about 4.5 SLPM/cm².

21. The diffuser of claim 13 wherein the one or more diffusers have a flow/unit area at 9 LRV of from about 2 to about 4.5 SLPM cm².

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