Electric heating – Heating devices – Combined with container – enclosure – or support for material...
Reexamination Certificate
1999-11-02
2001-11-06
Walberg, Teresa (Department: 3742)
Electric heating
Heating devices
Combined with container, enclosure, or support for material...
C219S411000, C118S724000, C392S416000
Reexamination Certificate
active
06313441
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to methods and apparatuses for providing thermal cycling for processing substrates. More particularly, it relates to a control system for variable ramp rate operation of a heater or integrated heating/cooling plate.
BACKGROUND OF THE INVENTION
Certain stages of semiconductor manufacturing require thermal cycling of the semiconductor substrate wherein the substrate is heated and then chilled. For example, the photoresist processing stage of semiconductor manufacturing requires heating to flow the photoresist material along the substrate surface, followed by cooling or chilling the substrate to set the photoresist. In order to produce high quality wafers suitable for state of the art integrated circuit applications, the temperature of the wafer during thermal cycling must be precisely controlled with respect to both the temporal temperature profile of the thermal cycles and the uniformity of the temperature across the substrate.
Conventional methods for heating and chilling wafers involve first baking the wafer at a temperature ranging typically between 70° C. and 250° C. for a period of time ranging typically between 30 seconds and 90 seconds. After baking the wafer, the wafer is then mechanically moved to a cold plate where it is chilled to a temperature ranging typically between 0° C. and 30° C. Disadvantages of the conventional methods for heating and chilling wafers include the inability to control temperature variations at the wafer surface during the transfer between plates and/or between processing stations, and the potential for wafer damage from physical mishandling or contamination during transfer.
Recent developments for heating and chilling wafers involve thermal cycling modules where a wafer is heated and chilled on one plate, thus eliminating the need to move the wafer between plates. In such a thermal cycling module, the wafer is placed on a thermal conduction plate which is thermally coupled to a heating and cooling device. The heating and cooling device is controlled by a controller which is programmed with the desired thermal cycling profile (e.g., heating to 80° C. for 10 seconds, increase temperature to 200° C. for 10 seconds, followed by cooling to 10° C. for 30 seconds, etc.) for processing the wafer.
To achieve precise temperature control at the wafer, a plurality of sensors (e.g., thermocouple sensors or infrared sensors) are generally connected as described in parent application Ser. No. 08/939,926, to provide feedback to the controller regarding the temperature at the wafer surface. While the programmed thermal cycling profile for a given wafer may have fixed temperature and duration values, the wafer temperature ramp rates for different stages of the thermal cycling profile, for different wafer-bearing plates, and for the processing of different wafers, can vary drastically resulting in quality variations in the wafers processed thereby.
Accordingly, a need exists for an improved control system for controlling wafer temperature ramp rates during processing within thermal cycling systems.
SUMMARY OF THE INVENTION
The present invention provides a heater and a control system coupled thereto which can adjust wafer temperature dynamically based on information from temperature sensors positioned proximate the wafer. The control and feedback system includes a program for controlling both the temperature of a thermally conductive heating/cooling plate, and the proximity of the wafer to the heating/cooling plate. Preferably the program also includes optional methods for increasing and/or decreasing the overall processing time. Specifically, a heater is provided in thermal contact with the substrate being processed, where thermal contact includes, but is not limited to the following: an arrangement in which the substrate is brought into physical contact with the top surface of the heater; an arrangement in which the substrate is disposed on a thermally conductive plate which is coupled so as to exchange heat with the heater; or, an arrangement in which the substrate is supported at a small distance above either the top surface of the heater or the top surface of the thermally conductive plate (e.g., by substrate lift pins). The substrate is supported by pins coupled to a pin actuator for adjusting the distance between the substrate and the top surface of the heater.
The heater comprises a heating mechanism which is connected, through heater actuator circuitry, to the controller. Additionally connected to the controller, and responsive to input therefrom, are the pin actuator for adjusting the distance between the substrate and the top surface of either the heater or the thermally conductive plate, and a pump operatively coupled to a fluid spray component for providing cooling fluid (e.g., water) to the bottom surface of the heater. Temperature sensors, disposed proximate to the substrate being processed (e.g., on the top surface of the heater or if a thermally conductive plate is employed, on the top surface of the thermally conductive plate), provide feedback to the controller which controls processing according to a pre-programmed thermal cycling profile and which adjusts processing in response to feedback from the temperature sensor.
In operation, the heater is calibrated by placing a calibration wafer having sensors attached thereto, on the heater and adjusting the variable components of the system (e.g., the heater actuator, the pin actuator and the pump operation) based on the wafer sensor readings to achieve a predetermined thermal cycling profile. To obtain a calibration signal the controller records the signals output to the variable components, in addition to the temperature sensed by the temperature sensors positioned on the heater, or thermally conductive plate. When obtaining a calibration signal, a user may specify a desired processing speed (e.g., fast, slow or standard speed), and the controller will adjust the variables accordingly. During production processing, the controller executes the calibration signal and makes any necessary adjustments thereto based on feedback from the sensors positioned on the heater or thermally conductive plate. Should the temperature sensed by the heater/plate sensors vary from that experienced during the calibration process, the controller adjusts the variable components so as to maintain the calibration temperature of the heater/plate.
Thus, the inventive control system allows wafer temperature to be precisely controlled, eliminating thermal cycling induced variations in wafer quality. Further, chamber throughput may be increased by selecting a fast operating speed which increases the wafer temperature ramp rate by initially raising the heater temperature above the desired substrate temperature, so as to quickly heat the substrate and/or by initially decreasing the heater temperature below the desired substrate temperature so as to quickly cool the substrate.
Other objects, features and advantages of the present invention will become more fully apparent from the following detailed description of the preferred embodiments, the appended claims and the accompanying drawings.
REFERENCES:
patent: 5156820 (1992-10-01), Wong et al.
patent: 6080969 (2000-06-01), Goto et al.
patent: 40-3135011 (1991-06-01), None
Bolandi Hooman
Schaper Charles D.
Young Douglas W.
Applied Materials Inc.
Dugan & Dugan
Fuqua Shawntina S.
Walberg Teresa
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