Handling: hand and hoist-line implements – Utilizing fluid pressure – Venturi effect
Reexamination Certificate
1999-04-07
2001-02-06
Cherry, Johnny D. (Department: 3652)
Handling: hand and hoist-line implements
Utilizing fluid pressure
Venturi effect
C901S040000
Reexamination Certificate
active
06183026
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to handling of substrates in semiconductor manufacturing and, more particularly, to an improved end effector coupled to a robot mechanism for supporting substrates.
In semiconductor manufacturing, robots are commonly used to move wafers from one location to another. For instance, robots transfer wafers between different reaction chambers for carrying out different processes. Typically, a replaceable end effector or blade is mounted to a robot for supporting a wafer. Examples of wafer handling robot systems can be found in U.S. Pat. Nos. 5,292,303, 5,569,014, and 5,655,060, which are incorporated herein by reference in their entireties.
During processing, a wafer can reach temperatures that are significantly different from the temperature of the end effector. When the end effector comes in contact with the wafer, the temperature differential produces a temperature gradient in the wafer, which can introduce thermal stresses in the wafer and cause cracking and fracture of the wafer. This results in substantial economic loss, particularly for wafers made of GsAs which are more costly than silicon wafers.
SUMMARY OF THE INVENTION
The present invention provides an improved end effector that reduces the thermal stresses caused by temperature differentials between the end effector and the wafer in order to reduce cracking and fracture of the wafer. When two objects at different temperatures come in contact, conduction of heat occurs between them generally according to the following equation:
Q=−kA&Dgr;T
where Q is the heat conduction, k is the coefficient of conductivity or thermal conductivity of the material of the reference object, A is the contact area, and &Dgr;T is the temperature differential between the reference object and the other object.
One way to reduce thermal stresses caused by the contact of two objects at different temperatures is to minimize the heat conduction between them so as to reduce the temperature gradient in the objects. According to the above equation, the heat conduction can be decreased by reducing the thermal conductivity of at least one of the two objects, reducing the contact area, or reducing the temperature differential. Specific embodiments of the present invention decrease the heat conduction by reducing the thermal conductivity of the end effector or reducing the contact area between the wafer and the end effector, or both. This decreases the thermal stresses in the wafer and cracking and fracture of the wafer.
In accordance with an embodiment of the present invention, an end effector for handling a substrate comprises an end effector body having a proximal end portion and a distal end portion. The end effector body includes at least one aperture disposed between the proximal end portion and the distal end portion. A contact member is coupled with the proximal end portion of the end effector body for contacting a substrate over a contact surface area which is smaller in size than the surface of the substrate facing the contact member. The contact member spaces the substrate from the end effector body. The at least one aperture of the end effector body overlaps in position with a portion of the substrate when the substrate is in contact with the contact member. In a specific embodiment, the end effector body includes a plurality of apertures disposed between the proximal end portion and the distal end portion, at least some of which overlap in position with a portion of the substrate when the substrate is supported by the contact member.
In accordance with another embodiment of the invention, an end effector for handling a substrate comprises an end effector body having a proximal end portion and a distal end portion. The end effector body comprising a body material. A support member is coupled with the proximal end portion of the end effector body for supporting a substrate and spacing the substrate from the end effector body. The support member comprises a support member material having a thermal conductivity which is lower than the thermal conductivity of the body material. In a specific embodiment, the body material includes steel and the support member material includes ceramic which has a thermal conductivity of about ⅕ the thermal conductivity of steel.
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Cai Lihong
MacDonald Douglas
Cherry Johnny D.
Gasonics International Corporation
Townsend and Townsend / and Crew LLP
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