Coating apparatus – Intercontrol or safety interlock
Reexamination Certificate
1997-12-23
2001-02-06
Beck, Shrive (Department: 1762)
Coating apparatus
Intercontrol or safety interlock
C118S712000, C118S725000, C118S666000, C432S036000, C432S054000
Reexamination Certificate
active
06183562
ABSTRACT:
FIELD OF THE INVENTION
The field of the present invention involves semiconductor fabrication processing equipment. More particularly, the present invention pertains to a circuit for use with chemical vapor deposition machines.
BACKGROUND OF THE INVENTION
Semiconductor wafer fabrication involves many complex and highly precise processes. Many of these processes are highly dependent on the precise control of process temperature. Small variations in temperature can have detrimental effects on the resulting semiconductor devices. One such fabrication process is chemical vapor deposition. Chemical vapor deposition (CVD) is a widely used process for depositing thin films of a variety of materials. In addition to semiconductor electronics, applications of CVD include the deposition of protective coatings for other applications (e.g., optics, mechanical parts, etc.).
In a typical CVD process, a mixture of reactant gases (often diluted in a carrier gas) at room temperature are injected into a CVD reaction chamber. The gas mixture, as it approaches a deposition surface (e.g., a semiconductor wafer), is heated radiatively by thermal lamps, or alternatively, placed upon a heated substrate. Depending on the precise process temperature and operating conditions, the gas mixture typically undergoes homo geneous chemical reactions in the vapor phase before striking the deposition surface. Near the surface, thermal, momentum, and chemical concentration boundary layers form as the gas stream heats, slows down, and the chemical composition changes. Heterogeneous reactions of within the gas mixture subsequently occur at the deposition surface, forming the deposited material (e.g., thin film). The resulting reaction by-products are then transported out of the CVD reaction chamber.
The characteristics and the results of the CVD process very much depend on controlling the process temperature. High temperatures are often used (e.g., 280 C.). The precise operating temperature within the CVD chamber is typically regulated and maintained by an embedded computer system within the CVD machine. This computer system implements a software defined process for heating the CVD chamber, following a temperature profile during processing, and protecting the components comprising the CVD machine from being damaged by excessive heat.
There is a problem, however, in that under certain conditions, errors can occur with the embedded computer system and its software. The computer systems of CVD machines and their controlling software are thoroughly tested and exhaustively examined prior to use of the machines in a fabrication line. As such, any errors which may occur are usually of little or no consequence, since a typical CVD machine includes a variety of error handling routines to diagnose and fix such errors. On occasion, however, an error of sufficient severity may occur which results in the scrapping of wafers undergoing processing. Even worse, under certain conditions, a catastrophic error may occur which results in damage to the CVD machine itself. One such catastrophic error is thermal “lock up”.
Thermal lock up refers to a condition where the embedded computer system controlling the CVD machine malfunctions and looses the ability to shut off heating components (e.g., radiant thermal lamps within the CVD chamber). For example, in the case where a CVD machine is processing a wafer and following a process temperature profile, the embedded computer system modulates the heating elements, alternately turning them on and off, to achieve and maintain a desired temperature within the CVD chamber. If a malfunction occurs during a period when the heating elements are “on”, the embedded computer system may loose the ability to subsequently turn them “off”. For example, if the embedded computer system “locks up” (e.g., due to a software error or a power supply voltage glitch) after having commanded the heating elements on, the command to turn the heating elements off may not be issued. Consequently, the temperature within the CVD chamber “runs away,” increasing to the point at which some components within the CVD chamber are significantly damaged.
The cost of repairing the CVD machine can be very high. A modern CVD machine is an extremely accurate, complex device. In addition to the costs of repairing the CVD machine itself, however, are the costs associated with the machine's lost productivity. A typical wafer fabrication line involves the production of hundreds, and perhaps thousands, of semiconductor components daily. The interruption in production could be much more costly than the cost attributed to repairing of the CVD machine.
SUMMARY OF THE INVENTION
Accordingly, what is needed is a system which protects against thermal lock up in CVD machines. What is needed is a system which remains functional should the embedded systems within a CVD machine fail. What is needed is yet a system which is easily integrated with existing CVD machines in existing wafer fabrication lines. What is needed is a system which provides protection against thermal lock up without interfering with sensor inputs and outputs used by the embedded systems within the CVD machines. The present invention provides an advantageous solution which satisfies the above requirements.
The present invention provides a system which protects against thermal lock up in CVD (chemical vapor deposition) machines. The system of the present invention remains functional should the embedded systems within a CVD machine fail. The system of the present invention is easily integrated with existing CVD machines in existing wafer fabrication lines. In addition, the present invention provides protection against thermal lock up without interfering with sensor inputs and outputs used by the embedded systems within the CVD machines (e.g., a CVD machine's controller).
In one embodiment, the present invention includes a thermal protection system for a CVD machine. The system of the present invention includes a thermal sensor for providing a temperature signal corresponding to a CVD chamber temperature, a heating component for heating the CVD chamber, and a controller for regulating the CVD chamber temperature. The controller is coupled to receive the temperature signal and to control the heating component in response thereto. An interlock circuit is coupled between the heating component and the controller. The interlock circuit has an open state and a closed state. A comparison circuit is coupled to receive the temperature signal and coupled to control the interlock circuit, wherein the comparison circuit effects a comparison between the temperature signal and a reference and commands the interlock to the open state when the temperature signal exceeds the reference. In so doing, the comparison circuit protects the CVD chamber from an over-temperature condition.
In an alternate embodiment, the present invention includes a comparison circuit capable of easily retrofitting a pre-existing CVD machine. The comparison circuit of the present invention is coupled in parallel to a temperature signal of the CVD machine and has a high input impedance to avoid distorting the temperature signal. The comparison circuit is coupled to control an interlock between the CVD machine's controller and heating component. When the comparison circuit detects an over-temperature condition, the comparison circuit commands the interlock to the open state.
REFERENCES:
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patent: 5151871 (1992-09-01), Matsumura et al.
patent: 5562947 (1996-10-01), White et al.
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patent: 5595241 (1997-01-01), Jelinek
patent: 5640059 (1997-06-01), Kammiller et al.
patent: 5653806 (1997-08-01), Van Buskirk
Czaja Douglas A.
Pierce Tracy Lavalle
Beck Shrive
Chen Bret
Sony Corporation of Japan
Wagner , Murabito & Hao LLP
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