Measuring and testing – Instrument proving or calibrating – Fluid pressure
Reexamination Certificate
1999-08-23
2001-08-28
Raevis, Robert (Department: 2856)
Measuring and testing
Instrument proving or calibrating
Fluid pressure
Reexamination Certificate
active
06279373
ABSTRACT:
TECHNICAL FIELD
This invention relates generally to semiconductor processing and, more particularly, to a system and method for calibrating gas or liquid pressure during wafer processing.
BACKGROUND
Contamination of materials is a factor in many manufacturing processes, and is of particular concern in the fabrication of integrated circuits. In general, integrated circuit technology is based on the ability to form numerous transistor structures on a single semiconductor substrate. Typically, multiple integrated circuits will be formed on a single silicon wafer, the wafer providing the semiconductor substrate for the circuits. The intricacy of the circuits and the large number of steps involved in the fabrication make it essential that each of the process steps be tightly controlled and meet very stringent specifications to prevent any type of contamination. To increase the purity and hence the quality and reliability of manufacturing processes, most are done in sealed rooms or chambers, where the environment, including temperature, pressure and purity of liquids or gases introduced can be controlled. One of the biggest sources of contamination occurs when the product being manufactured is transferred from one area of the manufacturing process to the next, which necessitates opening a door or valve to introduce the material into the next chamber or room. When the door or valve is open, if there is a pressure differential between the chambers, the potential for contamination is increased. Processing fluid and/or gas will rush from the chamber with the higher pressure to the chamber with the lower pressure to equalize the pressure, bringing solids and liquids along with the gas, which may cause such problems as condensation and particulate contamination on the material being manufactured.
The solutions used to mitigate the above-identified problem have included: reducing the amount of time that the door or valve is opened to reduce the amount of contaminants that enter the chamber; making the transfer in two stages; utilizing an intermediate or transfer chamber into which only one of the other chambers is opened at a given time; placing calibrated pressure sensors in each chamber; and tying the pressure sensors into the valve-opening mechanisms in both chambers to obtain a desired, consistent pressure balance before the valve between the chambers is opened. However, these solutions, separately or in combination, do not always adequately resolve the aforementioned problems.
Even minimizing the time the door or valve is open will result in some contamination, especially if the pressure is not equalized between the two chambers before opening the door or valve. One of the biggest problems in equalizing the pressure is keeping the pressure sensors calibrated, as sensors tend to drift in calibration over time. If the pressure sensor in either chamber is out of calibration, the pressure between the two chambers will not actually be equal, and when the door or valve is open, the gas will rush from the higher to lower pressure chamber to equalize the pressure. The effective drift of the pressure sensors is actually doubled if the two sensors drift calibration in opposite directions. If a sensor has drifted, process overseers are generally unaware of the problem until a rush of gas between the chambers has occurred, resulting in contamination of a manufactured product. In order to re-calibrate sensors that have drifted, the manufacturing process generally has to be shut down, and the sensor taken off-line to be calibrated, resulting in production down-time.
U.S. Pat. No. 5,808,175 issued Sep. 15, 1998 to Shen-Yan Chang discloses a method of temporarily, manually mounting a second, in-line calibrated sensor to the same chamber for the purpose of monitoring or correcting the first sensor. However, Chang only utilizes the second sensor for comparison to the readings obtained from the first sensor for the same chamber, to determine if it needs replacing. If there is drift in the sensors used to read the pressure in different chambers, a situation may still occur wherein the pressure differential between two chambers is such that a rush of gas and contaminants occurs when the door or valve between the two chambers is opened.
It would, therefore, be desirable to be able to provide a method and apparatus wherein the pressure in the two chambers between which materials are being transferred can be kept equal so that there will not be a rush of gas between the two chambers when the door or valve is opened.
SUMMARY
The present invention overcomes the above outlined problems and a technical advance is achieved by a system and method that equalizes and calibrates the pressure of two or more chambers on either side of a valve (door) during operation. In one embodiment, the method is performed each time the valve is opened. When the valve is opened, the pressure in the chambers will equalize. After the pressure in the chambers has equalized, pressure readings from sensors mounted in each chamber are calibrated relative to each other.
In some embodiments, the pressure readings are sent to a control module The control module evaluates the readings taken from the sensors and adjusts them to match each other.
In some embodiments, there may be an intermediate, or transfer chamber between a process chamber and a loading chamber. The sensor readings from the process and loading chambers are adjusted to match the sensor readings of the transfer chamber. As a result, all the chambers will be calibrated with the transfer chamber, and therefore with each other.
Since calibration occurs every time the valve is open, the pressure differential between the chambers never becomes too great. As a result, there is little if any fluid flow (e.g., a flow processing gases and/or contaminants) between the chambers and a very clean chamber environment is maintained.
Also, because the relative calibration is done during actual use, the system does not have to be shut down to perform calibration routines. This, of course, results in increased productivity and cycle time.
REFERENCES:
patent: 4576035 (1986-03-01), Hooven et al.
patent: 5808175 (1998-08-01), Chang
patent: 1247700 (1986-07-01), None
patent: 1275-243-A1 (1986-12-01), None
patent: 1441-212-A1 (1988-11-01), None
Kenney Danny
Lindberg Keith
Globitech, Inc.
Jones Day Reavis & Pogue
Raevis Robert
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