Lateral temperature equalizing system for large area surfaces during processing

• US 7,195,693 B2
• Filed: 06/04/2003
• Issued: 03/27/2007
• Est. Priority Date: 06/05/2002
• Status: Active Grant

• Current Assignee: B/E Aerospace, Inc. (Raytheon Technologies Corporation d/b/a RTX)
• Original Assignee: Advanced Thermal Sciences Corporation (Raytheon Technologies Corporation d/b/a RTX)
• Inventors: Cowans, Kenneth W.
• Primary Examiner(s): Hassanzadeh; Parviz
• Assistant Examiner(s): DHINGRA, RAKESH KUMAR
• Application Number:
  US10/455,491
• Publication Number:
  US 20030228772A1
• Time in Patent Office: 1,392 Days
• Field of Search: 156/345, 118/724, 118/725, 219/158, 219/121.43, 432/152, 165/272
• US Class Current: 156/345.51
• 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. A method of maintaining the temperature level of a semiconductor wafer substantially uniform across the surface of a wafer being supported on the top surface of a pedestal with the wafer being 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 pedestal top surface and the wafer to extract heat from the heated wafer;

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

translating liquid by wicking action from the liquid sink upwardly through a plurality of wicking sites extending downwardly from the underside of the surface of the pedestal to below the surface of the vaporizable liquid and distributed below and throughout the area of the wafer; and

condensing vapor generated because of localized heating at the underside of the pedestal surface at a plurality of condensing sites distributed throughout and spaced apart from the wicking sites, the condensing sites extending from within the liquid sink to above the liquid sink.

2. A method as set forth in claim 1 above, wherein the liquid sink has limited vertical dimension.

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 semiconductor wafer of at least about 300 mm comprising the steps of:

positioning a semiconductor wafer in heat transfer relation on a support surface above a liquid heat sink disposed within the support including a vaporizable liquid and being coextensive with the wafer area;

extracting heat by vaporization from regions of the support surface adjacent heated regions of the wafer at proximate ones of a multiplicity of evaporative first sites extending downwards into the liquid heat sink and distributed throughout the liquid heat sink;

condensing vapor formed by local heating of the wafer at regions above the liquid sink at the closest ones of a plurality of condensing second sites contacting the liquid heat sink and distributed in interdigitated fashion among but separate from the evaporative first sites, and

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

5. A method of laterally equalizing the temperature of a

semiconductor wafer, to maintain the temperature of the wafer surface substantially uniform, as it is supported on its underside on the top surface of a pedestal and heated on its upper side as the pedestal is cooled below the wafer, the method comprising the steps of:

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

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

translating liquid from the liquid sink to below the upper surface of the pedestal by vertical wicking action up through a plurality of wicking paths a really distributed relative to the area of the wafer and extending downwards from the underside of the surface of the pedestal down into the liquid sink to form a plurality of local evaporative sites above the liquid sink and individually responsive to local wafer temperatures that are above the selected temperature level, and

condensing vapor generated locally in the evaporative sites due to local temperature increases in the wafer by lateral transport of vapor to adjacent ones of a plurality of spaced apart condensing sites distributed throughout the evaporative sites and spaced laterally apart from the evaporative sites, the condensing sites extending from within to above the liquid sink and providing lateral heat transfer from the evaporative sites to equalize the wafer temperature.