| CPC H01L 21/68714 (2013.01) [H01L 21/67259 (2013.01); H01L 21/6838 (2013.01)] | 20 Claims |
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1. A method comprising:
mounting a first wafer on a first wafer chuck and mounting a second wafer on a second wafer chuck;
bringing the second wafer into physical contact with the first wafer;
monitoring a first relative distance between the first wafer and the second wafer using a first distance sensor in a first area above the first distance sensor, and monitoring a second relative distance between the first wafer and the second wafer using a second distance sensor in a second area above the second distance sensor, wherein the first relative distance is smaller than the second relative distance, wherein each distance sensor measures intensity peaks at a plurality of interfaces to determine the respective relative distances, and wherein changes in the measured relative distances over time indicate propagation of a bonding wave between the first and second wafers;
independently controlling levels of applied vacuum of a first vacuum zone and a second vacuum zone on the second wafer chuck using feedback from the first distance sensor and the second distance sensor, wherein the first vacuum zone is above the first area and the second vacuum zone is above the second area, and wherein responsive to the changes in the measured relative distances indicating non-uniform bonding wave propagation, the level of applied vacuum of the first vacuum zone is increased and the level of applied vacuum of the second vacuum zone is decreased to compensate for detected variations in bonding wave velocity; and
removing the bonded first wafer and second wafer from the first wafer chuck.
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