Lateral temperature equalizing system for large area surfaces during processing

• US 20030228772A1
• Filed: 06/04/2003
• Published: 12/11/2003
• Est. Priority Date: 06/05/2002
• Status: Active Grant

• Current Assignee: B/E Aerospace, Inc. (Rtx Corporation)
• Original Assignee: Advanced Thermal Sciences Corporation (Rtx Corporation)
• Inventors: Cowans, Kenneth W.
• Granted Patent: US 7,195,693 B2
• Time in Patent Office: Days
• US Class Current: 438/795
• CPC Class Codes: H01J 2237/2001 Maintaining constant desired temperature
• CPC Class Codes: H01J 2237/32 Processing objects by plasma generation
• CPC Class Codes: H01J 37/32724 Temperature
• CPC Class Codes: H01L 21/67109 mainly by convection

Abstract

In many processes used in fabricating semiconductors the wafer is seated on the top surface of a pedestal and heated in a high energy process step, such as plasma etching. The pedestal, chuck or platen may be cooling but the wafer gradually heats until the process can no longer continue. Where large, e.g. 300 mm diameter, wafers are being processed the temperature level across the wafer is difficult to maintain substantially constant. In this system and method the lateral temperature distribution is equalized by a heat sink structure in a chamber immediately under the wafer support on top of the pedestal. A number of spatially distributed wicking posts extend downwardly from a layer of wicking material across the top of the chamber, into a pool of a vaporizable liquid. At hot spots, vaporized liquid is generated and transported to adjacent condensation posts extending up from the liquid. The system thus passively extracts heat to equalize temperatures while recirculating liquid and assuring adequate supply. The free volume above and within the liquid, and the short distances between posts, assure adequate heat transfer rates.

Claims

1. The method of maintaining the temperature level of a semiconductor wafer substantially uniform across the surface of a wafer supported on the top surface of a pedestal and heated on its upper side while the pedestal is cooled below the wafer, the method comprising the steps of:

circulating a gaseous medium between the top surface and the wafer to extract heat from the heated wafer;

maintaining a liquid sink of vaporizable liquid below the upper surface of the pedestal, the liquid vaporizing at a selected temperature level;

translating liquid by wicking action from the liquid sink through a plurality of wicking sites on the underside of the surface of the pedestal; and

condensing vapor generated at the underside of the pedestal surface at a plurality of spaced apart sites extending above the liquid sink.

2. A method as set forth in claim 1 above, wherein the liquid sink has limited vertical dimension, and wherein the plurality of sites at the underside of the surface of the pedestal extends into the liquid sink and wherein the condensing sites are distributed throughout the wicking sites.

3. A method as set forth in claim 1 above, wherein the liquid comprises a vaporizable liquid in the class including ammonia, H₂O and alcohol.

4. A method of equalizing the temperature variations across a 300 mm semiconductor wafer comprising the steps of:

positioning a semiconductor wafer in heated transfer relation on a support surface above a liquid heat sink involving a vaporizable liquid;

extracting heat by vaporization from regions of the support surface adjacent heated regions of the wafer at proximate ones of a multiplicity of distributed sites contacting the liquid;

condensing vapor formed above the liquid sink at the closest ones of a plurality of distributed condensing sites, and

passively continuing the process of locally evaporating and condensing to equalize the lateral temperature variations of the wafer as the process continues, to equalize lateral temperature variations in the wafer.

5. A wafer supporting pedestal for maintaining the temperature across a semiconductor wafer substantially uniform as the wafer is heated on its upper side and pedestal is cooled beneath the wafer, comprising:

a pedestal compartment adjacent the underside of the top surface supporting the wafer, the compartment defining a shallow open volume below the top surface and including a sink of vaporizable liquid in the open volume;

a surface of wicking material disposed on the underside of the top surface of the volume, and including a plurality of distributed wicking elements extending into vaporizable liquid, but not contacting the bottom of the volume;

a condensing surface comprising a plurality of elements protruding up from the bottom of the volume to above the liquid level, but without contacting the top surface of the volume, and

the lateral distances between the dependent and protruding elements each being respectively selected with respect to the transport distance and pressure of the liquid undergoing wicking action to minimize wicking transport distances.

6. An apparatus as set forth in claim 5 above, wherein the pedestal is configured to receive a semiconductor wafer of approximately 300 mm in diameter, and wherein the liquid is a vaporizable liquid from the class including ammonia, H₂O and alcohol.

7. An apparatus as set forth in claim 6 above, wherein the pedestal includes a gas cooling system interjecting gas between the upper surface of the pedestal and the adjacent under surface of the wafer, and wherein the pedestal includes a cooling system in operative relation to the pedestal body below the compartment.

8. An apparatus as set forth in claim 7 above, wherein the upper surface of the compartment comprises a plurality of depending wicking posts extending from the top surface of the housing into the liquid, the top surface of the compartment is covered with a wicking material and wherein the protruding elements also comprise condensing posts of wicking material interdigitized among the wicking posts.

9. An apparatus as set forth in claim 8 above, wherein the apparatus includes strength posts extending from the bottom of the housing into the top surface of the pedestal for withstanding interior pressures.

10. A structure providing a lateral heat distribution function for maintaining the temperature of a semiconductor wafer substantially uniform in the lateral direction during a heating process, comprising:

a chamber having a roof and a floor for providing a substantially compact temperature equalizer for contact with a wafer supporting surface that is in heat conductive engagement across the area of a semiconductor wafer;

a plurality of like modular members having heads with hexagonal outlines nested together to form a wall covering the upper side of the chamber, each hexagonal element having a depending post, and the hexagonal elements and posts each being of a wicking material;

a second plurality of elements, each having hexagonal heads and of like configuration so that they fit together to form a planar base structure covering the floor of the chamber each of the second hexagonal elements including an upstanding condensing post, the elements and posts being of wicking material, and nested together to provide a wall covering the bottom of the chamber;

a locking element having a substantially planar body for sandwiching between the upper and lower assemblies, which nest together into a interdigitated structure, the locking element having a plurality of openings for receiving the upstanding condensing posts of the lower structure and a plurality of spring elements for engaging the tips of the depending posts to urge them into engagement with the upper surface of the interior, the locking elements each holding a different one of the upper hexagonal heads out of contact with adjacent condensing posts and the hexagonal heads of the second elements, and

a vaporizable liquid in the chamber to a level wetting both the depending posts and upstanding posts.