Laser processing power output stabilization

Abstract

A Q-switched solid state laser system (24) operates in a pulse processing control system (10) that employs an autopulse mode and a pulse-on-position mode to stabilize the pulse-to-pulse laser energy delivered to a workpiece (20) that is moved by an X-Y positioner (18). In the autopulse mode, laser pulses are emitted at a near maximum PRF, but the pulses are blocked from reaching the workpiece by an external modulator (28, 32), such as an acousto-optic modulator ('AOM') or electro-optic modulator (also referred to as a Pockels cell). In the pulse-on-position mode, the laser emits a pulse in response to the positioner moving to a location on the workpiece that coincides with a commanded coordinate location. The processing control system delivers a stream of coordinate locations, some requiring processing, at a rate that moves the positioner and triggers the laser at about the near maximum PRF. The pulse processing control system sets the AOM to a transmissive state whenever a coordinate location requiring processing is commanded and otherwise sets the AOM to a blocking state. This pulse timing technique provides a nearly constant interpulse period for the laser, thereby improving its pulse-to-pulse energy stability at the near maximum PRF.

Description

technical field [0001] The present invention relates to lasers, and more particularly to a method and apparatus for providing laser pulses of uniform energy at high pulse repetition frequency ("PRF") in on-the-fly sample processing applications. Background technique [0002] Lasers are commonly used in a variety of industrial operations including inspection, machining, and micromachining of substrates such as electronic materials. For example, to repair a dynamic random access device ("DRAM"), a first laser pulse is used to remove the conductive connection of a bad memory cell in a DRAM device, and a second laser pulse is used to remove the resistive connection of a redundant memory cell to replace the Damaged storage unit. Because of the random distribution of bad memory cells that need to be disconnected, the delay time of workpiece positioning usually requires that the laser repair process can be carried out in a wide range of PRF, rather than under a constant PRF. This...

AI Technical Summary

Problems solved by technology

Unfortunately, the pulse-to-pulse energy levels of such UV lasers are particularly sensitive to variations in the PRF as well as the pulse period

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