Automated wafer lapping system

A wafer lapping system comprising:

• a wafer lapping machine including upper and lower lapping plates and multiple wafer carriers located generally on the lower lapping plate, the wafer carriers each having multiple openings therethrough for receiving wafers and holding the wafers in a position between the upper and lower lapping machine plates to constrain the wafers to move conjointly with the wafer carrier, the wafer lapping machine being constructed for relative motion between the wafer carrier and the upper and lower plates thereby to remove material from the wafers to achieve a target wafer thickness, the lapping machine including a controller for stopping the lapping action of the lapping machine when the target thickness of the wafers has been reached, the upper lapping plate being movable between a position over the lower lapping plate and a position spaced away from the lower lapping plate to expose the wafer carriers for loading and unloading wafers;
• a wafer thickness gauging device separate from the wafer lapping machine, the thickness gauging device being positioned for receiving wafers from the wafer lapping machine following lapping and gauging the thickness of lapped wafers, the thickness gauging device being electronically interconnected with the wafer lapping machine controller for signalling the wafer lapping machine controller to correct any deviations of the target thickness stored in the lapping machine controller and an actual target thickness of lapped wafers according to the measurement of the wafer thickness gauging device.

A wafer lapping system, comprising:

• a wafer holding station for holding a plurality of wafers to be lapped;
• a wafer lapping machine including upper and lower lapping plates and multiple wafer carriers located generally on the lower lapping plate, the wafer carriers each having multiple openings therethrough for receiving wafers and holding the wafers in a position between the upper and lower lapping machine plates to constrain the wafers to move conjointly with the wafer carrier, the wafer lapping machine being constructed for relative motion between the wafer carrier and the upper and lower plates thereby to remove material from the wafers to achieve a target wafer thickness, the upper lapping plate being movable between a position over the lower lapping plate and a position spaced away from the lower lapping plate to expose the wafer carriers for loading and unloading wafers;
• a wafer transport mechanism disposed in proximity to the wafer holding station and to the wafer lapping machine, the wafer transport mechanism being constructed for lifting wafers out of the holding station, transporting the wafers from the holding station to the wafer lapping machine and placing the wafers in respective ones of the openings in the wafer carriers on the lower lapping plate thereby to load the wafer carriers with wafers for lapping, and further constructed for unloading the wafers from the lapping machine after lapping;
• a controller for controlling the wafer transport mechanism;
• a wafer carrier orientation detector for detecting the orientation of the wafer carrier about a vertical axis passing through the center of the wafer carrier at a home position on the wafer lapping machine and providing a signal to the controller indicative thereof, the controller being configured to identify the location of each individual opening in the wafer carrier when the wafer carrier is loaded and to identify the location of each individual opening in the wafer carrier when unloading after lapping so that the identity of each wafer is maintained after lapping.

A method for automatic feedback control in wafer lapping, the method comprising the steps of:

• providing a wafer lapping machine including upper and lower lapping plates and multiple wafer carriers located generally on the lower lapping plate, the wafer carriers each having multiple openings therethrough for receiving wafers and holding the wafers in a position between the upper and lower lapping machine plates to constrain the wafers to move conjointly with the wafer carrier, the wafer lapping machine being constructed for relative motion between the wafer carrier and the upper and lower plates thereby to remove material from the wafers to achieve a target wafer thickness, the lapping machine including a controller for stopping the lapping action of the lapping machine when the target thickness of the wafers has been reached, the upper lapping plate being movable between a position over the lower lapping plate and a position spaced away from the lower lapping plate to expose the wafer carriers for loading and unloading wafers;
• providing a wafer thickness gauging device separate from the wafer lapping machine, the thickness gauging device being positioned for receiving wafers from the wafer lapping machine following lapping and gauging the thickness of lapped wafers;
• loading a first batch of wafers in the wafer carriers on the lapping machine;
• operating the lapping machine to lap the wafers to the target thickness as measured by the lapping machine and determined by the lapping machine controller;
• removing lapped wafers from the lapping machine;
• measuring the actual thickness of a predetermined number of the lapped wafers with the thickness gauging device;
• generating a signal representative of the average measured thickness of the predetermined number of lapped wafers measured with the thickness gauging device;
• generating a feedback signal representative of the deviation of the average measured thickness from an actual target thickness of the wafers;
• transmitting the feedback signal to the wafer lapping machine controller to recalibrate the lapping machine controller so that the target thickness corresponds with the actual target thickness.

A method for automatically lapping wafers comprising the steps of:

• (a) providing a wafer holding station for holding a plurality of wafers to be lapped;
• (b) providing a wafer lapping machine including upper and lower lapping plates and multiple wafer carriers located generally on the lower lapping plate, the wafer carriers each having multiple openings therethrough for receiving wafers and holding the wafers in a position between the upper and lower lapping machine plates to constrain the wafers to move conjointly with the wafer carrier, the wafer lapping machine being constructed for relative motion between the wafer carrier and the upper and lower plates thereby to remove material from the wafers to achieve a target wafer thickness, the lapping machine including a controller for stopping the lapping action of the lapping machine, the upper lapping plate being movable between a position over the lower lapping plate and a position spaced away from the lower lapping plate to expose the wafer carriers for loading and unloading wafers;
• (c) providing a wafer transport mechanism disposed in proximity to the wafer holding station and to the wafer lapping machine, the wafer transport mechanism having a controller to control the transport mechanism for lifting wafers in the holding station and transporting the wafers from the holding station to the wafer lapping machine thereby to load the lapping machine with wafers for lapping, and for unloading the wafers from the lapping machine after lapping;
• (d) providing a vision system including a camera disposed over a home position on the lower plate of the wafer lapping machine;
• (e) taking a picture with the camera of a first of the wafer carriers in the home position on the lower lapping plate to locate markings on the first wafer carrier;
• (f) determining the location of a first of the openings in the first wafer carrier using the markings as a reference;
• (g) loading wafers from the wafer holding station into the first wafer carrier with the wafer transport mechanism one at a time and one after another beginning with the first opening in the first wafer carrier and proceeding to the next adjacent one of the openings until all openings therein are filled;
• (h) indexing the wafer lapping machine to bring a second of the wafer carriers into the home position;
• (i) repeating steps (e)-(h) until all wafer carriers have been loaded with wafers;
• (j) operating the wafer lapping machine to lap the wafers;
• (k) bringing the first wafer carrier back to said home position;
• (l) taking a picture with the camera of the first wafer carrier in the home position to locate markings on the first wafer carrier;
• (m) determining the location of the first opening in the first wafer carrier using the markings as a reference;
• (n) unloading wafers from the first wafer carrier with the wafer transport mechanism one at a time and one after another beginning with the first opening in the first wafer carrier and proceeding to the next adjacent one of the openings until all openings therein are emptied of wafers;
• (o) indexing the wafer lapping machine to bring the second wafer carrier into the home position;
• (p) repeating steps (l)-(o) until all wafer carriers have been emptied of wafers.