Ion beam scan control

Apparatus for scanning a semi-conductor wafer through an ion beam to controllably treat the wafer comprising:

• a) a wafer support mounted for movement along a generally linear travel path to scan a wafer supported by the wafer support through an ion beam;
• b) a motor having an output shaft for providing motion to the wafer support;
• c) a transmission that couples the output shaft of the motor to the wafer support and converts a rotational movement of the motor shaft to a linear scan of the wafer support to move a wafer through the ion beam at a controlled velocity;
• d) a linear encoder that provides signals related to the position of the wafer support as the wafer support moves along the generally linear path;
• e) a motor encoder that provides signals related to an orientation of the motor's output shaft;
• f) a programmable controller coupled to said linear encoder and said motor encoder for energizing the motor, said controller having a stored program for comparing a target wafer support position with a motor position sensed by the motor encoder to compute a motor energization signal based upon said motor position and target wafer support position;
• and
• g) a programmable controller communications interface for communicating a change in optimum wafer speed to the controller as the wafer is moved through the ion beam to adjust target wafer support positions used by the programmable controller in determining the motor energization signal.

A method of operating an ion implanter that includes an ion source for generating an ion beam, a movable wafer support for positioning wafers within the ion beam, a motor coupled to the wafer support by a transmission that converts rotary movement of a motor output shaft to translational movement of the wafer support through the ion beam, and a controller for activating the motor to provide a scan of the wafer through an ion beam impinging onto the wafers comprising the steps of:

• a) monitoring a position of the motor shaft to provide a first position signal and monitoring a position of the wafer support to provide a second position signal;
• b) comparing the first position signal with a target position signal to produce a position error signal for energizing the motor;
• c) determining instantaneous motor shaft velocity and wafer velocity based upon the first and second position signals as the motor scans the wafer through the ion beam;
• and
• d) modifying the position error signal with a damping correction factor based upon the shaft and wafer velocities to provide a modified position error signal and using the modified position error signal to energize the motor.

An ion implanter for scanning a semi-conductor wafer through an ion beam to controllably treat the wafer comprising a wafer support mounted for translational movement along a travel path to allow the ion beam to impinge upon a time-varying region of a wafer supported by the wafer support, a motor having an output shaft for providing motion to the wafer support, a transmission that couples the output shaft of the motor to the wafer support and converts a rotational movement of the motor shaft to a linear scan of the wafer support to move a wafer through the ion beam;

• a linear encoder for monitoring a position of the support and providing a first position signal;
• a shaft encoder for monitoring an orientation of the motor shaft and providing a second position signal;
• and a controller coupled to the linear and shaft encoders for monitoring the first and second position signals and activating the motor with energization signal based upon a difference between a target motor position and a sensed motor position to achieve a desired scanning speed;
• said controller including structure for modifying the energization signal by a damping factor based upon velocities of the motor shaft and wafer support calculated by the controller from said first and second position signals.

Apparatus for scanning a semi-conductor wafer through an ion beam to controllably treat the wafer comprising:

• a) a wafer support mounted for movement along a travel path to scan a wafer supported by the wafer support through an ion beam;
• b) a motor having an output shaft for providing motion to the wafer support;
• c) a transmission that couples the output shaft of the motor to the wafer support and converts a rotational movement of the motor shaft to a linear scan of the wafer support to move a wafer through the ion beam;
• d) a controller for energizing the motor having means for comparing a target wafer support position to a sensed motor position and producing a motor energization signal based upon a difference between the target wafer support position and the sensed motor position;
• said controller including means for limiting a rate of acceleration of said support as the motor begins and ends a linear scan of the wafer support relative to the ion beam.