Apparatus for sensing the presence of a wafer

In a wafer carrier of a type in which a plenum is bounded above by a piston plate and below by a resilient diaphragm, and in which a wafer is acquired by elevating the wafer into contact with the resilient diaphragm and then applying a vacuum to the plenum through a vacuum port and through a vacuum conduit connected to the vacuum port causing the resilient diaphragm to grip the wafer by a suction cup effect with the resilient diaphragm drawn into the plenum but not so far as to contact the piston plate, and in which in the absence of a wafer the application of the vacuum draws the resilient diaphragm farther into the plenum than when the wafer is present, the improvement comprising:

• an air port entering into the plenum;
• an air conduit connected to said air port and communicating with the plenum through said air port;
• an orifice connected to said air conduit for admitting air into said air conduit at a limited rate;
• and,
• means communicating with the vacuum conduit for sensing the pressure within the vacuum conduit;
• wherein the vacuum port is so located in the plenum that the vacuum port is covered and sealed by the resilient diaphragm only when vacuum is applied to the plenum in the absence of a wafer, but is not covered by the resilient diaphragm when the wafer is present.

In a wafer carrier of a type in which a plenum is bounded above by a piston plate and below by a resilient diaphragm, and in which a wafer is acquired by elevating the wafer into contact with the resilient diaphragm and then applying a vacuum to the plenum through a vacuum port and through a vacuum conduit connected to the vacuum port causing the resilient diaphragm to grip the wafer by a suction cup effect with the resilient diaphragm drawn into the plenum but not so far as to contact the piston plate, and in which in the absence of a wafer the application of the vacuum draws the resilient diaphragm farther into the plenum than when the wafer is present, the improvement comprising:

• an air port entering into the plenum;
• an air conduit connected to said air port and communicating with the plenum through said air port;
• an orifice connected to said air conduit for admitting air into said air conduit at a limited rate;
• and,
• means communicating with the vacuum conduit for sensing the pressure within the vacuum conduit;
• wherein said air port is so located in the plenum that said air port is covered and sealed by the resilient diaphragm only when vacuum is applied to the plenum in the absence of a wafer, but is not covered by the resilient diaphragm when the wafer is present.

In a wafer carrier of a type in which a plenum is bounded above by a piston plate and below by a resilient diaphragm, and in which a wafer is acquired by elevating the wafer into contact with the resilient diaphragm and then applying a vacuum to the plenum through a vacuum port and through a vacuum conduit connected to the vacuum port causing the resilient diaphragm to grip the wafer by a suction cup effect with the resilient diaphragm drawn into the plenum but not so far as to contact the piston plate, and in which in the absence of a wafer the application of the vacuum draws the resilient diaphragm farther into the plenum than when the wafer is present, the improvement comprising:

• an air port entering into the plenum;
• an air conduit connected to said air port and communicating with the plenum through said air port;
• an orifice connected to said air conduit for admitting air into said air conduit at a limited rate;
• and,
• means communicating with said air conduit for sensing the pressure within said air conduit;
• wherein the vacuum port is so located in the plenum that the vacuum port is covered and sealed by the resilient diaphragm only when vacuum is applied to the plenum in the absence of a wafer, but is not covered by the resilient diaphragm when the wafer is present.

In a wafer carrier of a type in which a plenum is bounded above by a piston plate and below by a resilient diaphragm, and in which a wafer is acquired by elevating the wafer into contact with the resilient diaphragm and then applying a vacuum to the plenum through a vacuum port and through a vacuum conduit connected to the vacuum port causing the resilient diaphragm to grip the wafer by a suction cup effect with the resilient diaphragm drawn into the plenum but not so far as to contact the piston plate, and in which in the absence of a wafer the application of the vacuum draws the resilient diaphragm farther into the plenum than when the wafer is present, the improvement comprising:

• an air port entering into the plenum;
• an air conduit connected to said air port and communicating with the plenum through said air port;
• an orifice connected to said air conduit for admitting air into said air conduit at a limited rate;
• and,
• means communicating with said air conduit for sensing the pressure within said air conduit;
• wherein said air port is so located in the plenum that said air port is covered and sealed by the resilient diaphragm only when vacuum is applied to the plenum in the absence of a wafer, but is not covered by the resilient diaphragm when the wafer is present.