Abrading – Precision device or process - or with condition responsive... – With indicating
Reexamination Certificate
1999-02-16
2001-08-28
Ostrager, Allan (Department: 3725)
Abrading
Precision device or process - or with condition responsive...
With indicating
C451S009000, C451S269000
Reexamination Certificate
active
06280291
ABSTRACT:
FIELD OF THE INVENTION
The present invention is related to sensing devices and, more particularly, to wafer sensing devices for use with equipment used in fabricating integrated circuits.
BACKGROUND INFORMATION
Equipment or machines used in processing wafers to fabricate integrated circuits are typically automated to reduce exposure of personnel to chemicals, speed production and reduce costs. The machines often have several stations to perform various processes on the wafer and include automated wafer handling devices to move wafers between stations in a machine. Accordingly, each station and wafer handling device includes some sort of wafer holder. It is important that each station and wafer handling device be able to detect or sense whether a wafer is present in its wafer holder. Fast and accurate wafer sensing is needed to optimize the performance of the machine.
Conventional wafer sensors typically use optical sensing methods. For example, a light beam may be directed so as to impinge on a wafer present in the wafer holder. In a through beam system, a wafer present in the wafer holder would block transmission of the light beam to a light sensor. The light sensor would then indicate a wafer is present if the light beam is blocked, and would indicate the absence of a wafer if the light beam is detected. In a reflective beam system, presence of a wafer in the wafer holder would reflect a transmitted light beam to a light sensor. Thus, in this type of sensor, the light sensor would indicate the presence of the wafer if the reflected beam is detected, and would indicate the absence of a wafer if the reflected beam is not detected.
However, these optical systems are not effective in a wet environment due to refraction of the light beam by fluid in the wet environment. For example, in some types of processing machines, the wafers are kept wet when being transferred to one or more stations. Typically, in these types of systems, the processing machines wet the wafers with deionized (DI) water to keep slurry or other chemicals from drying and staining the surface prior to the controlled drying step. It can also help reduce scratching when the wafer is transferred to the wafer holder. As a result, a thin film of the DI water is formed on the wafer upon which the wafer rests in the wafer holder. This film of DI water helps reduce the risk of the wafer holder scratching the wafer. However, the DI water can cause refraction of the light beams used by optical wafer sensors, which tends to cause inaccurate sensing by the optical wafer sensors.
Another type of conventional wafer sensor uses a vacuum technique to sense the presence of a wafer. In this type of wafer sensor, holes are formed in the wafer holder through which a vacuum is drawn. A wafer present in the wafer holder would block the holes, allowing a vacuum to be formed in the holes. This vacuum would then be detected by a vacuum pressure transducer or switch. However, because air is compressible, the time required to detect the vacuum could take several seconds. This relatively long sensing time tends to undesirably reduce machine through-put. In addition, wafer warpage or particles on the wafers may prevent complete blockage of the holes, thereby preventing the vacuum from forming and causing inaccurate wafer sensing. Liquids may also enter the vacuum system and decrease reliability of wafer retention. Accordingly, there is a need for a fast, accurate wafer sensor for use in a wet environment.
SUMMARY
In accordance with the present invention, a wafer sensor is provided that uses a hydrodynamic pressure differential technique. In one embodiment, the wafer sensor includes a wafer holder, a liquid distribution system, and a pressure sensor. The wafer holder has a series of holes and is configured such that when a wafer is placed in the wafer holder, the wafer covers the holes thereby restricting the flow of liquid from the liquid distribution system through the holes. The pressure sensor has a predetermined threshold and is configured to sense the pressure of the fluid in the supply ducts supplying the holes. When no wafer is present in the wafer holder, the fluid flows essentially unrestricted through the holes in the wafer holder, resulting in a relatively low pressure of the liquid in the supply ducts. In contrast, when the wafer holder holds a wafer, the restricted flow through the holes causes an increase in pressure of the liquid in the supply ducts. This increased pressure triggers the pressure sensor, thereby indicating the presence of the wafer in the wafer holder. The liquid distribution system of the present invention advantageously allows the wafer sensor to avoid the refraction problems of conventional optical wafer sensing systems when used in a wet environment. Further, because a liquid is essentially incompressible, the response time of the wafer sensor is fast relative to conventional systems that use an evacuated air method of sensing.
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Gromko Robert Dean
Lisi Edmund Terry
Hong William
Ostrager Allan
SpeedFam-IPEC Corporation
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