Transferring heat in loadlocks

• US 8,288,288 B1
• Filed: 06/16/2008
• Issued: 10/16/2012
• Est. Priority Date: 06/16/2008
• Status: Active Grant

• Current Assignee: Novellus Systems Incorporated (LAM Research Corporation)
• Original Assignee: Novellus Systems Incorporated (LAM Research Corporation)
• Inventors: Gage, Christopher, Chua, Lee Peng
• Primary Examiner(s): Ahmed, Shamim
• Application Number:
  US12/140,196
• Time in Patent Office: 1,583 Days
• Field of Search: 438/715, 34/15, 344/08
• US Class Current: 438/715
• CPC Class Codes: H01L 21/67109 mainly by convection
• CPC Class Codes: H01L 21/67201 characterized by the construction of the load-lock chamber

Abstract

Methods that increase the overall rate of heat transfer between a substrate and a heat sink or source, e.g., in a loadlock are provided. According to various embodiments, the methods involve varying the heat transfer coefficient of a heat transfer gas in the loadlock or other chamber. The heat transfer coefficient is varied to reduce the time-dependent variation of the rate of heat transfer. As a result, the overall rate of heat transfer is improved. In certain embodiments, the methods involve varying the gas pressure of a chamber in order to affect the rate of heat transfer to a wafer within a system. By manipulating the gas pressure accordingly, the rate of heat transfer is controlled throughout the heating or cooling cycle.

Claims

1. A method of transferring heat to or from a substrate in an air-tight chamber, said air-tight chamber containing a substrate support and a heat transfer element, said substrate support configured to support the substrate at a distance above the heat transfer element such that a thermally conductive heat transfer gas can flow between the supported substrate and the heat transfer element, the method comprising:

transferring heat between the wafer and the heating element to bring the wafer from a first temperature to a second temperature during a bulk heat transfer operation,

wherein transferring heat during the bulk heat transfer operation comprises varying the heat transfer coefficient of the thermally conductive heat transfer gas by varying the partial pressure of the thermally conductive heat transfer gas.

2. The method of claim 1 wherein the distance between the bottom surface of the substrate and the heat transfer element is between about 2-200 mils.

3. The method of claim 2 wherein the distance is between the bottom surface of the substrate and the heat transfer element is between about 2-15 mils.

4. The method of claim 1 wherein the thermally conductive gas is helium.

5. The method of claim 1 wherein the substrate is a partially fabricated semiconductor substrate.

6. The method of claim 1 further comprising, after the bulk heat transfer operation, venting or pumping down the chamber to bring it to a final pressure.

7. The method of claim 1 wherein the varying the partial pressure of the thermally conductive heat transfer gas during the bulk heat transfer operation comprises inletting the heat transfer gas to the chamber throughout the bulk heat transfer operation.

8. The method of claim 1 wherein varying the partial pressure of thermally conductive heat transfer gas during the bulk heat transfer operation comprises inletting a first amount of the thermally conductive heat transfer gas to the chamber to bring the partial pressure of the thermally conductive heat transfer gas to a first intermediate level, maintaining the partial pressure at the first intermediate level for a specified first time period, inletting a second amount of the thermally conductive gas to the chamber to bring the partial pressure to a second intermediate level and maintaining the partial pressure of the thermally conductive gas at the second level for a specified period of time.

9. The method of claim 1 wherein varying the partial pressure of the thermally conductive heat transfer gas comprises sequentially raising the partial pressure to a plurality of intermediate levels, wherein the partial pressure at each level is maintained for a specified period of time.

10. The method of claim 9 wherein the last of the plurality of sequential levels is greater than about 100 Torr and each of the other levels is below about 100 Torr.

11. The method of claim 1 wherein the rate of heat transfer varies by no more than about 30% during the bulk heat transfer operation.

12. The method of claim 1 wherein the rate of heat transfer varies by no more than about 20% during the bulk heat transfer operation.

13. The method of claim 1 wherein the rate of heat transfer varies by no more than about 10% during the bulk heat transfer operation.

14. A method of cooling a partially fabricated semiconductor device substrate in a loadlock during a vent cycle, said method comprising:

positioning the substrate in the loadlock such that the substrate is at distance d from a heat sink within the loadlock, wherein said substrate is at average temperature T₁ during introduction;

introducing a thermally conductive heat transfer gas to the loadlock;

cooling the substrate from T₁ to a temperature T₂ during a bulk heat transfer operation; and

varying the heat transfer coefficient of the thermally conductive heat transfer gas during the bulk heat transfer operation to thereby reduce the time-dependent variation of the rate of heat transfer from the substrate to the heat sink during the bulk heat transfer operation.

15. The method of claim 14 wherein the distance d is between about 5 and 50 mils.

16. The method of claim 14 wherein the varying the heat transfer coefficient comprises varying the partial pressure of the heat transfer gas.

17. The method of claim 16 wherein varying the partial pressure of the heat transfer gas comprises maintaining the partial pressure of the heat transfer gas at least one first intermediate level between 5 and 50 Torr for a period of time and maintaining the partial pressure of the heat transfer gas at at least one second intermediate level greater than 100 Torr for a period of time.

18. A method of cooling a partially fabricated semiconductor device substrate in a loadlock during a vent cycle from a temperature T₁ to a temperature T₂;

said method comprising;

positioning the substrate in the loadlock such that the substrate is at distance between 5 and 50 mils from the top surface of a pedestal having cooling channels within the loadlock;

sealing the loadlock so that it is air-tight;

introducing a small amount of helium into the loadlock to raise the chamber pressure within the loadlock to a level between about 5 and 30 Torr and maintaining the chamber pressure at that level for a time period;

introducing an amount of helium into the loadlock to raise the chamber pressure to a level between about 100-500 Torr and maintaining chamber pressure at that level for a time period sufficient such that the substrate is substantially cooled to the temperature T₂; and

introducing nitrogen into the loadlock to thereby raise the chamber pressure to atmospheric pressure.