Automatic temperature and humidity regulation – Humidity control
Utility Patent
1999-12-14
2001-01-02
Tanner, Harry B. (Department: 3744)
Automatic temperature and humidity regulation
Humidity control
C062S078000, C062S176600, C454S187000, C055S385200
Utility Patent
active
06168085
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to systems for semiconductor fabrication, and more particularly concerns an improved system for controlling temperature and humidity in semiconductor manufacturing environments.
2. Description of Related Art
Processing of materials such as wafers, cassettes of wafers or substrates used in manufacturing integrated circuits has been conventionally carried out in a carefully temperature and humidity controlled, particulate free environment generally known as a “clean room.” Such environments are used to protect contaminant sensitive products such as wafers, masks, ceramic substrates, flat panel displays, and the like during processing. Since particulates, humidity and certain chemicals can contaminate and degrade the surface of semiconductor manufacturing materials, it is important to adequately purge and maintain the local manufacturing environment for such materials free of such contaminants. When photosensitive chemicals are deposited on wafers, some of these chemicals are not only sensitive to the temperature and humidity in the air around them, but they are also highly sensitive to very small amounts (parts per billion) of certain chemicals in the clean room air. Contaminants in the atmosphere can include vaporous amines, halogens, or radicals, such as ammonia, chlorine, bromine, arsine, and silane, for example. Maintenance of such “clean rooms” in a temperature and humidity controlled, contaminant free state can require a great deal of care and effort, particularly during processing of the materials.
As a more easily controlled alternative to “clean rooms,” a modular isolation chamber such as a minienvironment can be used to isolate and control the environment surrounding a wafer, cassette of wafers or substrates used in manufacturing integrated circuits, during storage, transport and processing of the materials.
While such systems can control the level of particulates in a minienvironment, temperature and humidity variations can be undesirable. Unfortunately, chemical filters such as a charcoal filter typically used for removing chemical contamination have an exothermic reaction to moisture, adding heat to the filtered air stream circulated through a minienvironment. In the past, temperature and humidity sensors have been placed in the air stream flow path upstream of the chemical filter for feedback control to the environmental control unit (ECU) of the sensed temperature and humidity of the air supplied, prior to filtration of the air stream. However, such a chemical filter induces a relatively long lag time between control of temperature and humidity in the air stream by the environmental control unit (ECU) and the actual conditions in the minienvironment ultimately being controlled, following filtration of the air stream supplied, making viable control at the point of process difficult or impossible to achieve. Essentially, it has been found that energy generated in the chemical filtration process is allowed to accumulate before a response can be detected, causing the environmental system to continually overshoot the temperature set point. The process value may never settle to an acceptable error. Slowing the rate of rise of the desired process temperature value can result in unacceptably slow rates of heating, with the final value taking from hours to days to reach. Apart from the exothermic reactions occurring in such filters, due to the long time cycle and time lag introduced into such systems by such filters, stabilization of temperature and humidity levels of such a minienvironment can take typically from 8 to 48 hours to reach a steady state following startup. Such systems with long lag times between an energy source and a point of process, such as the chemical filtration process for a semiconductor manufacturing environmental control system, typically can not be controlled accurately or efficiently with a single control loop having a single set point for a process parameter. It would be desirable to be able to improve the control of temperature to ±0.1° C. and humidity to ±0.5 percent at the point of process, with carbon filtration or chemical filtration, and to reach this level of control from startup in a much shorter time period.
There thus remains a need for a system and method of controlling temperature and humidity in semiconductor manufacturing environments to consistently condition and maintain desired levels of relative humidity, temperature, and chemical contaminants. The present invention meets these and other needs.
SUMMARY OF THE INVENTION
Briefly, and in general terms, the present invention provides for improved control of temperature and humidity of an environment for a process chamber for semiconductor manufacturing materials. A cascade control approach with first and second control loops is used to allow the output of the first control loop to determine the set point of the second control loop, limiting the energy introduced into the system, allowing an optimal rate of heating, with minimal overshoot, and allowing the control of the process parameters within desired limits to a specified temperature and humidity, typically within 1 to 3 hours.
The present invention accordingly provides for a system for controlling temperature and humidity of an environment for a process chamber for semiconductor manufacturing materials. The system comprises a environmental control unit for providing a supply of temperature and humidity controlled gaseous working fluid to the process chamber through a flow path, a filter disposed in the flow path between the environmental control unit and the process chamber, and a controller operatively connected to the environmental control unit for controlling the output of the environmental control unit. The environmental control unit preferably comprises a heater, a dehumidifier for removing humidity from the gaseous working fluid, and a humidifier to regulate the amount of moisture. In one presently preferred embodiment, the flow path recirculates gaseous working fluid from the chamber to the environmental control unit. In a presently preferred embodiment, the filter comprises a charcoal filter for removing chemicals from the gaseous working fluid.
A first sensor assembly is connected to the controller and to the flow path downstream of the filter for sensing the environmental parameter of the gaseous working fluid, and for sensing a controlled environmental parameter of the gaseous working fluid, and for providing a first sensed value of the controlled environmental parameter to the controller; and a second sensor assembly is connected to the controller and to the flow path upstream of the filter for providing a second sensed value of the controlled environmental parameter to the controller, for monitoring and controlling the parameter of the gaseous working fluid within the process chamber. In a presently preferred embodiment, both temperature and humidity are controlled environmental parameters.
The controller preferably includes means for determining a first control error output by comparing a desired process parameter set point for the controlled environmental parameter of the gaseous working fluid with the first sensed value, means for determining a second set point from the first control error, and means for generating a command output to the environmental control unit for controlling the environmental control unit responsive to the second set point.
The present invention also provides for a method for controlling temperature and humidity of an environment for a process chamber for semiconductor manufacturing materials. The steps of the method comprise providing a supply of temperature and humidity controlled gaseous working fluid to the process chamber through a flow path, providing a chemical filter in the flow path to the process chamber, sensing a controlled environmental parameter of the gaseous working fluid downstream of the filter, and providing a first sensed value of the controlled environmental parameter o
Fulwider Patton Lee & Utecht LLP
Semifab Incorporated
Tanner Harry B.
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