Electro Scientific Industries, Inc.

Xiaoyuan Peng

William J Jordens

Wensheng Ren

Brian W Baird

David Martin Hemenway

David Barsic

Andrew Edwin Hooper

Qi S Wang

Kelly Bruland

Yasu Osako

Daragh Finn

Lynn Sheehan

Jim Dumestre

Tailored laser pulse shapes are used for processing workpieces. Laser dicing of semiconductor device wafers on die-attach film (DAF), for example, may use different tailored laser pulse shapes for scribing device layers down to a semiconductor substrate, dicing the semiconductor substrate, cutting the underlying DAF, and/or post processing of the upper die edges to increase die break strength. Different mono-shape laser pulse trains may be used for respective recipe steps or passes of a laser beam over a scribe line. In another embodiment, scribing a semiconductor device wafer includes only a single pass of a laser beam along a scribe line using a mixed-shape laser pulse train that includes at least two laser pulses that are different than one another. In addition, or in other embodiments, one or more tailored pulse shapes may be selected and provided to the workpiece on-the-fly. The selection may be based on sensor feedback.

Methods and systems for laser processing a workpiece using a plurality of tailored laser pulse shapes

Two pulsed lasers () or sets of lasers propagate beams of pulses () having orthogonally related polarization states. A beam combiner () combines the orthogonal beams to form a combined beam propagating along a common beam path () to intersect an optical modulator () that selectively changes the polarization state of selected pulses of either beam to provide a composite beam () including similarly polarized pulses from the orthogonal beams. The composite polarized beam has a composite average power and a composite repetition rate that are greater than those provided by either laser. The optical modulator can also selectively control the polarization states of pulses from either laser to pass through or be blocked by a downstream polarizer (). Additional modulators may facilitate pulse shaping of the pulses. The system is scalable by addition of sets of single lasers or pairs of lasers with beam combiners and modulators.

Combining multiple laser beams to form high repetition rate, high average power polarized laser beam

A laser processing system provides a burst of ultrafast laser pulses having a selectively shaped burst envelope. A burst pulse laser includes a high repetition rate ultrafast laser to deliver a pulse train with each pulse in the train having an independently controlled amplitude. The respective amplitudes of each ultrafast pulse in a group define a 'burst envelope.' In addition to independently controlling the amplitude of each ultrafast pulse within the burst envelope, the system may also provide selective control of spacing between each ultrafast pulse and/or the overall temporal width of the burst envelope. Thus, the system provides selective shaping of the burst envelope for particular laser processing applications.

Pulse temporal programmable ultrafast burst mode laser for micromachining

Embodiments of laser systems advantageously use pulsed optical fiber-based laser source () output, the temporal pulse profile of which may be programmed to assume a range of pulse shapes. Pulsed fiber lasers are subject to peak power limits to prevent an onset of undesirable nonlinear effects; therefore, the laser output power of these devices is subsequently amplified in a diode-pumped solid state photonic power amplifier (DPSS-PA) (). The DPSS PA provides for amplification of the desirable low peak power output of a pulsed fiber master oscillator power amplifier () to much higher peak power levels and thereby also effectively increases the available energy per pulse at a specified pulse repetition frequency. The combination of the pulsed fiber master oscillator power amplifier and the diode-pumped solid state power amplifier is referred to as a tandem solid state photonic amplifier ().

Tandem photonic amplifier

Laser pulse shaping techniques produce tailored laser pulse spectral output. The laser pulses can be programmed to have desired pulse widths and pulse shapes (such as sub-nanosecond to 10 ns-20 ns pulse widths with 1 ns to several nanoseconds leading edge rise times). Preferred embodiments are implemented with one or more electro-optical modulators receiving drive signals that selectively change the amount of incident pulsed laser emission to form a tailored pulse output. Triggering the drive signal from the pulsed laser emission suppresses jitter associated with other stages of the link processing system and substantially removes jitter associated with pulsed laser emission build-up time.

Laser micromachining using programmable pulse shapes

A programmable laser pulse combines electrical modulation of the pulse frequency and optical modulation of the pulse shape to form laser pulses of prescribed pulse shapes. A prescribed pulse shape features high peak power and low average power. The laser system disclosed also allows for power-scaling and nonlinear conversions to other (shorter or longer) wavelengths. The system provides an economical reliable alternative to using a laser source with high repetition rates to achieve shaped pulses at a variety of wavelengths. The combinatorial scheme disclosed is inherently more efficient than existing subtractive methods.

Generating laser pulses of prescribed pulse shapes programmed through combination of separate electrical and optical modulators

High-power, diode-pumped solid state (DPSS) pulsed lasers are preferred for applications such as micromachining, via drilling of integrated circuits, and ultraviolet (UV) conversion. Nd:YVO(vanadate) lasers are good candidates for high power applications because they feature a high energy absorption coefficient over a wide bandwidth of pumping wavelengths. However, vanadate has poor thermo-mechanical properties, in that the material is stiff and fractures easily when thermally stressed. By optimizing laser parameters and selecting pumping wavelengths and doping a concentration of the gain medium to control the absorption coefficient less than 2 cmsuch as the pumping wavelength between about 910 nm and about 920 nm, a doped vanadate laser may be enhanced to produce as much as 100 W of output power without fracturing the crystal material, while delivering a 40% reduction in thermal lensing.

Laser with gain medium suppressing higher order modes to provide lasing output with high beam quality

Anisotropic crystals such as Nd:YVO, Nd:YLF, and Nd:GdVOhave become preferred gain materials for many laser applications. The anisotropic gain medium without ancillary compensation ensures there is no degradation of laser modes when passing through the gain medium. An optical power amplifier that incorporates an anisotropic gain medium achieves power scaling with multiple passes while also maintaining good mode matching between the laser and the pump during each pass. Preferred embodiments implement for multiple passes of a seed laser beam through an anisotropic gain medium with substantially zero angular beam displacement during each pass. The multi-pass system provides an economical, reliable method of achieving high TEMpower to meet the demands of micromachining, via drilling, and harmonic conversion applications.

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Portland, OR, United States of America

Xiaoyuan Peng