Thermal control system and method

Abstract

Improvements in systems and methods which employ a two-phase fluid, such as a refrigerant, as a saturable fluid in direct heat transfer relation to a thermal load, are realized by extraction of vapor from the saturated fluid before heat exchange. Moreover, automatic changing of the paths under command of a controller enables charges to be effected between different modes at higher rates than in other systems by employing the variety of modes available in the direct transfer system.

Description

REFERENCE TO PRIOR APPLICATIONS [0001] This invention relies for priority on previously filed application Ser. No. 11 / 057,383 of Kenneth W. Cowans et al, filed Feb. 15, 2005 and entitled “Thermal Control System and Method”, and on provisional application 60 / 733,078 filed Nov. 4, 2005 by Kenneth W. Cowans et al and entitled “Thermal Control System and Method”.BACKGROUND OF THE INVENTION [0002] The above mentioned utility application of Cowans et al discloses a system and method of temperature control in which the temperature of a load is varied by thermal exchange with a saturated fluid directly, without requiring an intervening heat transfer fluid. Typically the saturated fluid is a refrigerant used in pure gas phase, or pure liquid phase, or more often in a mixed or saturated phase. In accordance with the invention, the vaporizable refrigerant is processed through substantially conventional compression and condensation steps as provided by commercially available equipment. However,...

AI Technical Summary

Benefits of technology

[0005] In a transfer direct saturated fluid (TDSF) thermal control system, a number of local variations in control loops and components improve efficiency and stability across a range of load temperatures. Cooling efficiency, at very low temperatures, for example, is markedly improved at the load by extracting at least part of the vapor components in the condensed fluid after expansion before mixing with compressed gas. The lowered mass flow through the line then returning from the load to the compressor reduces the pressure drop in said return line. To this end, a vapor separator is disposed in the line transporting liquid / vapor product before the mixing junction, and the extracted vapor is fed back into the refrigerant returning from the load to compressor while a higher proportion of liquid is fed to the load. Thus heat transfer is more efficient without affecting the temperature of the mix.

[0007] A further feature of the system is the incorporation of a computer controlled solenoid bypass between the hot gas shunt that leads to the mixing circuit, and the return line from the load to the suction input of the compressor. This bypass is operated to remove some of the flow from the hot gas line when full hot gas flow might tend to make the loop gain of the servo system unstable and / or reduce the amount of cooling available at temperatures within the desired range. The result introduces a time delay in cooling the load to enable closer control of temperature.

[0008] Control circuit adaptations may be introduced to realize further benefits from the concept. Where fast reaction to commands requiring fast temperature changes are needed, temporary and short term commands can be utilized to shorten response times. If, for example, the active part of a thermal load comprises the surface of a wafer holding chuck in a semiconductor processing system, and the heat exchange region is physically spaced apart from the upper surface of the chuck, some time may be needed to bring the chuck surface to a specified temperature. By introducing control algorithms which bypass the need for accumulation of tracking data, the wafer can be much more rapidly stabilized at a target temperature, increasing yield rates and lowering costs.

Problems solved by technology

This bypass is operated to remove some of the flow from the hot gas line when full hot gas flow might tend to make the loop gain of the servo system unstable and / or reduce the amount of cooling available at temperatures within the desired range.

The result introduces a time delay in cooling the load to enable closer control of temperature.

Images