PHOTONIC MILLING USING DYNAMIC BEAM ARRAYS

• US 20090242522A1
• Filed: 09/22/2008
• Published: 10/01/2009
• Est. Priority Date: 03/31/2008
• Status: Active Grant

• Current Assignee: Electro Scientific Industries Incorporated (MKS Instruments Incorporated)
• Original Assignee: Electro Scientific Industries Incorporated (MKS Instruments Incorporated)
• Inventors: Baird, Brian W., Bruland, Kelly J., Hainsey, Robert
• Granted Patent: US 8,178,818 B2
• Time in Patent Office: Days
• US Class Current: 219/121.610
• CPC Class Codes: B23K 26/03 Observing, e.g. monitoring, the workpiece

Abstract

A laser processing system includes a beam positioning system to align beam delivery coordinates relative to a workpiece. The beam positioning system generates position data corresponding to the alignment. The system also includes a pulsed laser source and a beamlet generation module to receive a laser pulse from the pulsed laser source. The beamlet generation module generates a beamlet array from the laser pulse. The beamlet array includes a plurality of beamlet pulses. The system further includes a beamlet modulator to selectively modulate the amplitude of each beamlet pulse in the beamlet array, and beamlet delivery optics to focus the modulated beamlet array onto one or more targets at locations on the workpiece corresponding to the position data.

Claims

1. A laser processing system comprising:

a beam positioning system to align beam delivery coordinates relative to a workpiece, the beam positioning system generating position data corresponding to the alignment;

a pulsed laser source;

a beamlet generation module to receive a laser pulse from the pulsed laser source, and to generate from the laser pulse a beamlet array comprising a plurality of beamlet pulses;

a beamlet modulator to modulate the amplitude of each beamlet pulse in the beamlet array; and

beamlet delivery optics to focus the modulated beamlet array onto one or more targets at locations on the workpiece corresponding to the position data.

2. The system of claim 1, further comprising a photodetection module to:

sample the beamlet pulses in the beamlet array; and

determine a total energy for each beamlet pulse in the beamlet array.

3. The system of claim 2, wherein the photodetection module is further configured to provide an error correction compensation signal to the beamlet modulator to adjust successive beamlet amplitudes provided to a particular target on the workpiece.

4. The system of claim 2, wherein the photodetection module is further configured to:

determine that a sum of the pulse energies provided by a series of beamlet pulses delivered to a particular target on the workpiece meets or exceeds a predetermined threshold, and

control the beamlet modulator to prevent further beamlet pulses from reaching the particular target.

5. The system of claim 1, further comprising a system control computer to cooperate with the beam positioning system to provide the alignment by matching a workpiece target pitch with:

a pulse repetition frequency (PRF) of the pulsed laser source,

a beamlet array pitch, and

a relative velocity between the beam positioning system and the workpiece (stage velocity).

6. The system of claim 5, wherein the beamlet pitch is related to the workpiece target pitch and the PRF of the pulsed laser source through the relationship:

c×

(beamlet pitch)=d×

(workpiece target pitch),

wherein c and d are integers, wherein;

workpiece pitch=stage velocity/PRF,

and wherein the integers c and d are selected such that;

c/d=an integer value.

7. The system of claim 1, wherein the beamlet generation module comprises a discretely banded reflectivity plate comprising:

a first surface comprising a first plurality of respectively reflective bands; and

a second surface comprising a second plurality of respectively reflective bands;

wherein the first surface is configured to;

receive the laser pulse into the discretely banded reflectivity plate; and

successively reflect diminishing portions of the laser pulse received from the second surface back into the discretely banded reflectivity plate toward the second surface; and

wherein the second surface is configured to;

successively transmit a first part and reflect a second part of the diminishing portions of the laser pulse received from the first surface, the transmitted first part corresponding to respective beamlet pulses in the beamlet array.

8. The system of claim 1, wherein the beamlet generation module comprises:

a first quarter wave plate to receive the laser pulse, and to convert the laser pulse from a linear polarization to a circular polarization;

a polarizing beamsplitter cube comprising a first channel, a second channel, and an output surface, the polarizing beamsplitter cube configured to transmit a first portion of the circularly polarized laser beam through the output surface as a first beamlet pulse in the beamlet array, and to transmit a second portion of the circularly polarized laser beam into the first channel;

a second quarter wave plate to transmit the second portion of the circularly polarized laser beam to a first mirror, and to receive a reflection from the first mirror to thereby convert the reflection from the first mirror into a p-polarized beam passed back to the polarizing beamsplitter cube, wherein the polarizing beamsplitter cube transmits the p-polarized beam through the second channel; and

a third quarter wave plate to transmit the p-polarized beam to a second mirror, to receive a reflection from the second mirror, and to transmit the reflection from the second mirror back to the polarizing beamsplitter cube, wherein the polarizing beamsplitter cube transmits the beam received from the third quarter wave plate through the output surface as a second beamlet pulse in the beamlet array.

9. The system of claim 1, wherein the beamlet generation module comprises at least one diffractive optical element.

10. The system of claim 1, wherein the pulsed laser source comprises:

a photonic oscillator to emit laser pulses at a first pulse repetition frequency, the first pulse repetition frequency providing a reference timing signal for coordination of the beam positioning system for the alignment of the beam delivery coordinates relative to the workpiece; and

a first optical modulator to select, at a second pulse repetition frequency that is lower than the first pulse repetition frequency, a subset of the laser pulses for amplification, wherein the selection of the laser pulses included in the subset is based on the first pulse repetition frequency and the position data.

11. The system of claim 10, further comprising a laser comb indexing module to adjust the alignment of the beam delivery coordinates based on the position data, the laser comb indexing module configured to:

select the second pulse repetition frequency such that the first pulse repetition frequency is an integer multiple n of the second pulse repetition frequency; and

offset an interpulse time between a first amplified pulse in the subset and a second amplified pulse in the subset by an integer multiple k of the photonic oscillator interpulse time based on the amount of beam delivery coordinate adjustment.

12. The system of claim 1, wherein the pulsed laser source comprises a tandem photonic amplifier including a fiber master oscillator.

13. The system of claim 12, wherein the fiber master oscillator is configured to output a laser pulse with a pulse duration in a range between approximately 100 femtoseconds and approximately 500 picoseconds.

14. The system of claim 1, wherein the pulsed laser source comprises a q-switched diode-pumped solid state laser.

15. The system of claim 1, wherein the pulsed laser source comprises a master oscillator power amplifier (MOPA).

16. The system of claim 15, further comprising a programmable pulsewidth element integrated with a master oscillator of the MOPA.

17. The system of claim 16, wherein the programmable pulsewidth element comprises a programmable bandpass filter.

18. The system of claim 1, wherein the pulsed laser source comprises a master oscillator regenerative amplifier.

19. A method for processing a workpiece with a laser, the method comprising:

generating a laser pulse;

generating, from the laser pulse, a beamlet array comprising a plurality of beamlet pulses;

modulating the amplitude of each beamlet pulse in the beamlet array; and

focusing the modulated beamlet array onto one or more target locations on the workpiece.

20. The method of claim 19, further comprising:

sampling the beamlet pulses in the beamlet array;

determining a total energy for each beamlet pulse in the beamlet array; and

generating an error compensation signal to adjust successive beamlet amplitudes provided to a particular target on the workpiece.

21. The method of claim 19, further comprising:

determining that a sum of the pulse energies provided by a series of beamlet pulses delivered to a particular target on the workpiece meets or exceeds a predetermined threshold, and

based on the determination, preventing further beamlet pulses from reaching the particular target.

22. The method of claim 19, matching a workpiece target pitch with:

a pulse repetition frequency (PRF) of a pulsed laser source,

a beamlet array pitch, and

a relative velocity between a beam positioning system and the workpiece.