Refrigeration – Automatic control – Selective heating or cooling
Reexamination Certificate
2002-02-22
2004-08-17
Tanner, Harry B. (Department: 3744)
Refrigeration
Automatic control
Selective heating or cooling
C062S196400, C062S201000, C062S259200
Reexamination Certificate
active
06775996
ABSTRACT:
FIELD OF THE INVENTION
This invention pertains to controlling the temperature of process tools using thermal transfer fluids, and more particularly to meeting the needs of industries which require precise but selectable control of the temperature of units having different thermal loads, such as fabrication equipment using cluster tools for making high precision semiconductors.
BACKGROUND OF THE INVENTION
Temperature control units for industries which manufacture high precision products, such as multiple semiconductor chips on wafers, must meet a number of stringent and sometimes conflicting requirements. While the manufacture of semiconductors perhaps imposes greater demands than are encountered in most other industrial fields, this industry illustrates particularly well the extent and variety of the problems which might now be encountered with modern temperature control systems. Semiconductor fabrication installations usually include many so-called cluster tools disposed throughout a high cost facility. Wafers are processed using successive steps which demand both high energy usage and close temperature control during removal or addition of thermal energy. Examples of these steps include chemical and high energy deposition and etching procedures carried out in specialized chambers. To maintain the appropriate internal environment and the particular temperature conditions needed for a given process step, separate temperature control units are usually employed to provide a chilled or heated thermal transfer fluid for circulation through the operative process parts of a tool. The temperature control unit must not only maintain the thermal transfer fluid at a prescribed setting and also bring the fluid temperature to its setpoint within specified time limits, but also operate over long periods with very limited down time, be energy efficient and demand minimal floor space.
Preferred systems for such applications have included temperature control units as described in Kenneth W. Cowans U.S. Pat. No. 6,102,113 entitled “Temperature Control of Individual Tools in a Cluster Tool System”. These temperature control units provide multichannel capability for the control of several different process temperatures by delivery of pressurized refrigerant to chill thermal transfer fluid flows, or by regulated heating of thermal transfer fluids. For refrigerating the thermal transfer fluid, pressurized liquid refrigerant in each channel is passed through an expansion valve regulating flow to an evaporator/heat exchanger. For heating the thermal transfer fluid each channel includes a separate heat source. This temperature control unit employs a single refrigeration unit and single reservoir for the thermal transfer fluid, and uses a different pump in each channel for fluid recirculation. The system has proven to be extremely reliable, requires low floor space (footprint) and provides precise temperature control of the thermal transfer fluid, in both static and dynamic modes.
With time, however, and with the evolution of new cluster tool systems and other units for semiconductor fabrication, a number of additional and particular requirements have more recently been imposed. Thus further and different needs must now be met that necessitate greater flexibility, adaptability and performance, while the goals of long life, compactness and efficient operation remain. For example, some typical modern process tools include more than one unit, such as a process chamber, with each of these having a number of different subunits, each to be brought to and maintained at preset temperature levels. In some of these tools, there may be common settings for like subunits, while other subunits there may be no commonality among the desired settings. Holding temperature at the given levels may require substantial cooling capacity, or only moderate cooling capacity, or even the addition of heat energy. Thermal exchange capacity, usually expressed here in terms of kilowatts, is necessarily a function of both temperature and flow rate.
Overall, the requirements at a semiconductor fabricating facility may differ such that the specified temperature levels can vary from very cold (e.g. down to −40° C.), to within a moderate temperature range (e.g. 0° C. to 40° C.), or to a higher temperature (e.g. up to about 120° C. for semiconductor fabrication houses). Moreover, the thermal demand, in KW, may also be substantially different, meaning that the capacity of a compressor or pump, for example, may have to be high for one installation but can be much lower for another. Sometimes one control unit may have sufficient thermal capacity for a number of subunits. In other user environments the temperatures to be maintained may be at more extreme temperature limits, or there may be special needs for varying temperatures within specified time periods.
For most practical applications in the semiconductor fabrication industry, temperature is controlled by circulating a thermal transfer fluid through a cluster tool subunit and back to the temperature control unit, with the user specifying the temperature and flow rate needed. The thermal transfer fluid is typically an equal mixture of ethylene glycol and water, or a proprietary fluid, such as that sold under the trademark “Galden”. These both accommodate very wide differentials between freezing and boiling levels, and have viscosity characteristics which tolerate pumping force differences within the operating temperature limits.
To meet these varied requirements with a compact, low footprint unit is not enough, since it is also desirable to maintain the subunit temperatures while using minimal amounts of energy without losing the flexibility needed to meet temperature level and flow rate requirements for a substantial number of subunits. Cooling solely by air is seldom a viable option. The cheapest available temperature control medium is facilities (utilities) water, for example, which suffices for cooling down to a limited intermediate temperature range somewhat above that of the water itself. For greater chilling capacity, a pressurized refrigerant can be used, while for heating an external thermal energy source, such as an electrical heater, can be employed. Providing appropriate thermal energy solutions for a variety of coexisting needs and at the same time using a compact, high reliability and low energy demand configuration, however, presents problems that have not heretofore been satisfactorily resolved.
SUMMARY OF THE INVENTION
In a temperature control unit in accordance with the invention, separate modules of like or related form factors are received in a control chassis, there being at least two broadly distinguishable module types each having at least two different temperature control capabilities, and each with energy savings potential. The modules each have their own pump and reservoir for thermal transfer fluid, an energy efficient unit providing a cooling medium, a heat exchanger or exchangers for transfer of thermal energy between the cooling medium and the transfer fluid, and at least one element for heating the thermal transfer fluid. These modules themselves can be modified while remaining consistent with the defined form factor by the use of differently powered compressors, different capacity pumps, differently sized reservoirs, or more than one heat exchanger. Flow rates as well as thermal load capacities can be adapted or revised to service individual or multiple subunits.
This versatile module-based approach offers a variable array of functionalities to confront the individual needs of multiple operative subunits. Self contained refrigeration loops with thermal transfer fluid reservoirs and pumps enable extraction of heat from a substantial but accommodatable fluid volume in order to cool a process tool. Since the modules can be used in different combinations and internally varied as well, they can be both individually tailored and flexibly responsive to multiple needs on an overall basis. The heat removal rate requirements, which are changeable, of a variet
Advanced Thermal Sciences Corp.
Jones Tullar & Cooper PC
Tanner Harry B.
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