WO2019005530A2 - Laser processing apparatus, methods of use and related arrangements - Google Patents

Abstract

A laser processing system can include a laser source configured to generate a beam of laser pulses at an average power of greater than 10 W and a turn mirror disposed in a path of the beam. The turn mirror can include a mirror configured to reflect a first portion of light within the laser pulses and transmit a second portion of the light within the laser pulses, and a mirror mount coupled to the mirror. The mirror mount is configured so as to not be present behind the mirror at a location where the mirror is irradiated with the laser pulses.

Description

LASER PROCESSING APPARATUS, METHODS OF USE AND RELATED

ARRANGEMENTS CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No. 62/524,863, filed June 26, 2017, which is incorporated by reference in its entirety.

BACKGROUND

L Technical Field

Embodiments described herein relate generally to a laser processing apparatus and components thereof, and to methods of using the same in a manner that facilitates accurate and reliable processing of workpieces.

II. Technical Background

Laser processing systems are used in a wide range of applications that encompass a variety of performance requirements such as wavelength, power, spot size, working distance, part handling, throughput, accuracy, yield, etc. In some cases, such as in certain semiconductor processing applications, via-drilling applications, etc., the accuracy of the system can be quite demanding and in a range of just a couple of microns or even submicron level. Systems with such high beam placement accuracy require that the laser' s beam pointing instability be quite small and, furthermore, that the beam path delivery optics also not cause additional beam motion instability. An example of something that can cause a laser beam to move undesirably is an unstable turn mirror. It is common practice for laser processing systems to use a lens to focus the laser beam to a small spot at the work surface of a workpiece to be processed (e.g., a semiconductor wafer, a printed circuit board, etc.). To first order, the lateral motion (Δ) of that spot at the work surface will be equal to the focal length (F) of the focusing lens multiplied by the change in beam angle (Θ) at the input to the lens (A=FO). In some systems, such as a microscope, the focal length of a focusing lens (e.g., a microscope objective) can be quite small at just a few millimeters. In other systems, such as laser processing systems those that use a scan lens, the lens focal length might be many tens or hundreds of millimeters. For a system with a 100 millimeter focal length lens, it only takes a beam angle change of 10 μΙ¾ά8 to move the focused spot laterally by 1.0 micron. Once other contributors to accuracy such as alignment and part placement are taken into account, an extra 1.0 micron of spot motion can put the entire system's accuracy requirement in jeopardy. In the case of a turn mirror, a laser beam will reflect at twice the mirror angle. Thus, it only takes a 5 μΚ-ad change in mirror angle to cause the beam angle to change by 10 μΚ^8. Unfortunately, it does not take very much of a disturbance to a mirror mount to impart such a small angle change. Mirror mounts that are adjustable can be more vulnerable to disturbances due to the greater number and variety of component piece parts that make up the mirror mount assembly. Disturbances can be in the form of vibrations, something pushing or pulling on the mount (e.g., a clean dry air purge hose), or even small temperature changes. As an example of a change due to temperature disturbance, consider that a common mirror diameter is one inch (25.4mm). If a disturbance were to cause the edge of the mirror to move (i.e., so as to tilt the mirror) just 0.127 microns, then the mirror angle change is 0.127um/25.4mm = 5 μΐ^ά.

Many mirror mounts exist that have a solid back side to it. The solid back can be beneficial. It can provide protection to the mirror since it will typically be made of a material like aluminum which will be less fragile than the mirror which is likely made from glass. It can also form a natural safety barrier to any stray light that leaks through the mirror. However, if the mirror mount is made of aluminum (a very common mirror mount material with CTE =

0.000023 m/m°C), and if the mirror mount was 5.5 mm thick, then it would only take a 1°C change in temperature on one edge of the mirror mount (with respect to the opposite edge of the mirror mount) to cause the aluminum to expand by 0.127 microns and thus impart a change in mirror angle by 5 μΐ^ά.

In a high accuracy laser processing system, it is important to know all the sources of heat and their potential for affecting the items in the beam path. The mechanisms by which a part is cooled can also affect its sensitivity to heat sources. One source of heat for many mirror mounts can be the laser beam itself. Although it can be quite common to require a mirror to have a reflectivity of 99.5% or even higher, there will still be a small amount of light that transmits through the mirror. For systems in which the laser beam power is < 1 W, the total amount of light transmitted is likely negligible. However, in higher power systems (e.g., in which the laser beam power is about 30 W or more), 0.5% of the power is 150 mW. If a 150 mW beam of laser light is transmitted through the mirror and hits the back of the mirror mount, then much of it can be absorbed by the mount, converted to heat, and cause the mount to increase in temperature on the order of one degree. Depending on the materials and geometry of the mirror mount assembly, orientation, and available cooling mechanisms the mirror will undergo a change in tilt, which can cause unwanted beam steering problems. One way to prevent a mirror from degrading the beam steering accuracy of a laser processing system due to beam heating is to turn the laser on and wait until thermal equilibrium is established. Subsequently, any alignment or processing can be performed. However, this can be disadvantageous because the time required to attain thermal equilibrium can be undesirably long (i.e., on the order of a few minutes to a few 10s of minutes) and would need to be performed every time the laser beam was turned on (even after being temporarily turned off).

Another way to solve the problem of degraded beam steering accuracy due to beam heating involves adding motors or other mechanisms to adjust the mirror tilt angle to compensate for beam heating, in real-time, when the laser is powered on. This has several disadvantages such as the need to provide some sort of indicator to know how much to adjust, in which axis to adjust, and for how long to perform the compensation adjustment. Yet another way to solve the problem of degraded beam steering accuracy due to beam heating (or reduce the severity thereof) involves the use of mirrors that have a reflectivity much higher than 99.5%. However, mirrors with very high reflectivity have a potential for higher cost and/or lead time. There is also potential for some lot to lot variation.

Sometimes, when processing a workpiece using a laser processing system (e.g., when a scribing or dicing a workpiece such as a semiconductor wafer), it can be important that the placement of a feature (e.g., a scribe/kerf) be well maintained for each of a series of workpieces to be processed. Errors in spot placement at the workpiece can arise from changes in system hardware, from problems with correctly aligning to the workpiece to be processed, or even from errors in creating the recipe used to process the workpiece. If errors are not detected, a workpiece can be damaged or lost entirely, sometimes at significant cost. Vision-based metrology is currently available for use with a number of laser processing systems, either as dedicated metrology tools, or incorporated within the systems themselves. Conventional vision- based metrology techniques typically utilize edge finding algorithms, often using low-angle lighting to help highlight edges, or simple image thresholding algorithms, to help identify specific visual changes in images of the die streets, which should represent the edge of a feature (e.g., a scribe or kerf) to formed in a workpiece (e.g., a semiconductor wafer). Other non-vision- based metrology techniques, such as laser triangulation sensors, can be used to measure height changes, and thus help determine the location of a feature (e.g., a scribe or kerf), but the resolution associated with such non-vision-based metrology techniques are often limited (e.g., in the case of laser triangulation sensors, by the spot sizes that can be produced by a laser triangulation system).

SUMMARY

One embodiment of the present invention can be broadly characterized as a laser processing system that includes a laser source configured to generate a beam of laser pulses at an average power of greater than 10 W and a turn mirror disposed in a path of the beam. The turn mirror can include a mirror configured to reflect a first portion of light within the laser pulses and transmit a second portion of the light within the laser pulses, and a mirror mount coupled to the mirror. The mirror mount is configured so as to not be present behind the mirror at a location where the mirror is irradiated with the laser pulses.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically illustrates an apparatus for processing a workpiece, according to one embodiment.

FIGS. 2 and 3 are perspective views taken from the back side of a turn mirror, which may incorporated within the apparatus shown in FIG. 1, according to some embodiments.

FIGS. 4 to 7 schematically illustrate an exemplary process for facilitating alignment of a workpiece within the apparatus shown in FIG. 1, according to one embodiment.

DETAILED DESCRIPTION

L Introduction

Example embodiments are described herein with reference to the accompanying drawings. Unless otherwise expressly stated, in the drawings the sizes, positions, etc., of components, features, elements, etc., as well as any distances therebetween, are not necessarily to scale, but are exaggerated for clarity.

The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting. As used herein, the singular forms "a," "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It should be recognized that the terms "comprises" and/or "comprising," when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. Unless otherwise specified, a range of values, when recited, includes both the upper and lower limits of the range, as well as any sub-ranges therebetween. Unless indicated otherwise, terms such as "first," "second," etc., are only used to distinguish one element from another. For example, one node could be termed a "first node" and similarly, another node could be termed a "second node", or vice versa. The section headings used herein are for organizational purposes only and are not to be construed as limiting the subject matter described.

Unless indicated otherwise, the term "about," "thereabout," etc., means that amounts, sizes, formulations, parameters, and other quantities and characteristics are not and need not be exact, but may be approximate and/or larger or smaller, as desired, reflecting tolerances, conversion factors, rounding off, measurement error and the like, and other factors known to those of skill in the art.

Spatially relative terms, such as "below," "beneath," "lower," "above," and "upper," and the like, may be used herein for ease of description to describe one element or feature's relationship to another element or feature, as illustrated in the FIGS. It should be recognized that the spatially relative terms are intended to encompass different orientations in addition to the orientation depicted in the FIGS. For example, if an object in the FIGS, is turned over, elements described as "below" or "beneath" other elements or features would then be oriented "above" the other elements or features. Thus, the exemplary term "below" can encompass both an orientation of above and below. An object may be otherwise oriented (e.g., rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein may be interpreted accordingly.

Like numbers refer to like elements throughout. Thus, the same or similar numbers may be described with reference to other drawings even if they are neither mentioned nor described in the corresponding drawing. Also, even elements that are not denoted by reference numbers may be described with reference to other drawings.

It will be appreciated that many different forms and embodiments are possible without deviating from the spirit and teachings of this disclosure and so this disclosure should not be construed as limited to the example embodiments set forth herein. Rather, these examples and embodiments are provided so that this disclosure will be thorough and complete, and will convey the scope of the disclosure to those skilled in the art. II. System Overview

FIG. 1 schematically illustrates laser processing system, in accordance with one embodiment of the present invention, which is configured to process a workpiece. Generally the processing is accomplished, either in whole or in part, by irradiating the workpiece with laser radiation, to heat, melt, evaporate, ablate, crack, discolor, polish, roughen, carbonize, foam, or otherwise modify one or more properties or characteristics (e.g., chemical composition, crystal structure, electronic structure, microstructure, nanostructure, density, viscosity, index of refraction, magnetic permeability, relative permittivity, etc.) of one or more materials from which the workpiece is formed. Such materials may be present at an exterior surface of the workpiece prior to or during processing, or may be located within the workpiece (i.e., not present at an exterior surface of the workpiece) prior to or during processing. Specific examples of processes that may be carried out by the illustrated apparatus include via drilling, perforating, welding, scribing, engraving, marking (e.g., surface marking, sub-surface marking, etc.), cutting, laser-induced forward transfer, cleaning, bleaching, bright pixel repair (e.g., color filter darkening, modification of OLED material, etc.), decoating, surface texturing (e.g., roughening, smoothing, etc.), sintering, cladding or deposition, or the like or any combination thereof. Thus, features that may be formed on or within workpieces, as a result of the processing, can include openings, slots, vias (e.g., blind vias, through vias, slot vias), grooves, trenches, scribe lines, kerfs, recessed regions, conductive traces, ohmic contacts, resist patterns, indicia (e.g., comprised of one or more regions in or on the workpiece having one or more visually, textually, texturally, etc., distinguishing characteristics), or the like or any combination thereof. When formed as openings, vias, etc., such features can have any suitable or desirable shape (e.g., circular, elliptical, square, rectangular, triangular, annular, or the like or any combination thereof).

Workpieces that may be processed by the apparatus can be generically characterized as metals, polymers, ceramics, or composites. Specific examples of workpieces that may be processed include, panels of printed circuit boards (PCBs) (also referred to herein as "PCB panels"), PCBs, flexile printed circuits (FPCs), integrated circuits (ICs), IC packages (ICPs), light-emitting diodes (LEDs), LED packages, semiconductor wafers, electronic or optical device substrates (e.g., substrates formed of AI2O3, A1N, BeO, Cu, GaAS, GaN, Ge, InP, Si, S1O2, SiC, Sii-_xGe_x (where 0.0001 < x < 0.9999), or the like, or any combination or alloy thereof), articles formed of plastic, glass (e.g., either unstrengthened, or strengthened thermally, chemically, or otherwise), quartz, sapphire, plastic, silicon, etc., for microfluidic devices, touch sensors, components of electronic displays (e.g., substrates having formed thereon, TFTs, color filters, organic LED (OLED) arrays, quantum dot LED arrays, or the like or any combination thereof), coverslips, lenses, mirrors, screen protectors, etc., turbine blades, powders, films, foils, plates, molds, fabrics (woven, felted, etc.), surgical instruments, medical implants, consumer packaged goods, shoes, bicycles, automobiles, automotive or aerospace parts (e.g., frames, body panels, etc.), appliances (e.g., microwaves, ovens, refrigerators, etc.), device housings (e.g., for watches, computers, smartphones, tablet computers, wearable electronic devices, or the like or any combination thereof).

Accordingly, materials that may be processed include one or more metals (e.g., Al, Ag, Au, Cu, Fe, In, Mg, Pt, Sn, Ti, or the like, or combinations or alloys thereof), conductive metal oxides (e.g., ITO, etc.), transparent conductive polymers, semiconductors, ceramics, waxes, resins, inorganic dielectric materials (e.g., used as interlayer dielectric structures, such as silicon oxide, silicon nitride, silicon oxynitride, or the like or any combination thereof), low-k dielectric materials (e.g., methyl silsesquioxane (MSQ), hydrogen silsesquioxane (HSQ), fluorinated tetraethyl orthosilicate (FTEOS), or the like or any combination thereof), organic dielectric materials (e.g., SILK, benzocyclobutene, Nautilus, (all manufactured by Dow),

polyfluorotetraethylene, (manufactured by DuPont), FLARE, (manufactured by Allied

Chemical), or the like or any combination thereof), glass fibers, polymeric materials

(polyamides, polyimides, polyesters, polyacetals, polycarbonates, modified polyphenylene ethers, polybutylene terephthalates, polyphenylene sulfides, polyether sulfones, polyether imides, poly ether ether ketones, liquid crystal polymers, acrylonitrile butadiene styrene, and any compound, composite, or alloy thereof), leather, paper, build-up materials (e.g., ANJINOMOTO Build-up Film, also known as "ABF", etc.), glass fiber-reinforced epoxy resin laminates (e.g., FR4), prepregs, or the like or any composite, laminate, or other combination thereof.

Referring to FIG. 1, the laser processing system 100 includes a laser source 102 for generating laser pulses, a beam positioner 104, a workpiece positioner 108, a scan lens 110, a controller 112 and, optionally, a camera 114. Although not illustrated, the laser processing system 100 also includes one or more optical components (e.g., beam expanders, beam shapers, apertures, harmonic generation crystals, filters, collimators, lenses, mirrors, polarizers, wave plates, diffractive optical elements, or the like or any combination thereof) to focus, expand, collimate, shape, polarize, filter, split, combine, or otherwise modify, condition or direct laser pulses generated by the laser source 102 along one or more beam paths (e.g., beam path 116) extending between the laser source 102 and the scan lens 110. Laser pulses transmitted through the scan lens 110 propagate along a beam axis so as to be delivered to the workpiece 101. Laser pulses are typically delivered so as to be incident upon a region of the workpiece surface 101a that is to be processed. The region that is irradiated by a delivered laser pulse is herein referred to as a "process spot," "spot location" or, more simply, a "spot", and encompasses a region where the beam axis traverses the workpiece 101.

Although not illustrated, the system 100 includes one or more turn mirrors arranged in the beam path 116 (e.g., between the laser source 102 and the beam positioner 104). Any turn mirror can be provided as a fixed turn mirror or an adjustable turn mirror. The orientation of a fixed turn mirror generally remains fixed (or at least substantially fixed) once mounted within the system 100. The orientation of an adjustable turn mirror can be adjusted (e.g., so as to tip or tilt the mirror about one or more axes) by means of manually- adjustable screws, piezoelectric actuators, or the like or any combination thereof. Generally, a turn mirror includes, as components thereof, a mirror for reflecting the laser pulses (i.e., redirecting the beam path 116), and a mirror mount for coupling the mirror to the system 100.

A. Laser Source

In one embodiment, the laser source 102 is operative to generate laser pulses. As such, the laser source 102 may include a pulse laser source, a QCW laser source, or a CW laser source. In the event that the laser source 102 includes a QCW or CW laser source, the laser source 102 may optionally include a pulse gating unit (e.g., an acousto-optic (AO) modulator (AOM), a beam chopper, etc.) to temporally modulate beam of laser radiation output from the QCW or CW laser source. Laser pulses generated by the laser source 102 may be characterized as having one or more wavelengths in one or more of the ultra-violet (UV), visible (e.g., violet, blue, green, red, etc.), or infrared (IR) ranges of the electromagnetic spectrum, or any combination thereof. Laser light in the UV range of the electromagnetic spectrum may have one or more wavelengths in a range from 150 nm (or thereabout) to 385 nm (or thereabout), such as 157 nm, 200 nm, 334 nm, 337 nm, 351 nm, 380 nm, etc., or between any of these values. Laser light in the visible green range of the electromagnetic spectrum may have one or more wavelengths in a range from 500 nm (or thereabout) to 570 nm (or thereabout), such as 511 nm, 515 nm, 530 nm, 532 nm, 543 nm, 568 nm, etc., or between any of these values. Laser light in the IR range of the electromagnetic spectrum may have one or more wavelengths in a range from 750 nm (or thereabout) to 15 μιη (or thereabout), such as 700 nm to 1000 nm, 752.5 nm, 780 nm to 1060 nm, 799.3 nm, 980 nm, 1047 nm, 1053 nm, 1060 nm, 1064 nm, 1080 nm, 1090 nm, 1152 nm, 1150 nm to 1350 nm, 1540 nm, 2.6 μιη to 4 μιη, 4.8 μιη to 8.3 μιη, 9.4 μιη, 10.6 μιη, etc., or between any of these values.

If the beam of incident light includes a series of laser pulses, the laser pulses can have a pulse duration (i.e., based on the full-width at half-maximum (FWHM) of the optical power in the pulse versus time) that is in a range from 10 fs to 900 ms. It will be appreciated, however, that the pulse duration can be made smaller than 30 fs or larger than 900 ms. Thus, at least one laser pulse can have a pulse duration greater than or equal to 10 fs, 15 fs, 30 fs, 50 fs, 100 fs, 150 fs, 200 fs, 300 fs, 500 fs, 700 fs, 750 fs, 850 fs, 900 fs, 1 ps, 2 ps, 3 ps, 4 ps, 5 ps, 7 ps, 10 ps, 15 ps, 25 ps, 50 ps, 75 ps, 100 ps, 200 ps, 500 ps, 1 ns, 1.5 ns, 2 ns, 5 ns, 10 ns, 20 ns, 50 ns, 100 ns, 200 ns, 400 ns, 800 ns, 1000 ns, 2 μ8, 5 μ8, 10 μ8, 50 μ8, 100 μ8, 300 μδ, 500 μ8, 900 μ8, 1 ms, 2 ms, 5 ms, 10 ms, 20 ms, 50 ms, 100 ms, 300 ms, 500 ms, 900 ms, 1 s, etc., or between any of these values. Likewise, at least one laser pulse can have a pulse duration less than 1 s, 900 ms, 500 ms, 300 ms, 100 ms, 50 ms, 20 ms, 10 ms, 5 ms, 2 ms, 1 ms, 300 ms, 900 μ8, 500 μ8, 300 μ8, 100 μδ, 50 μ8, 10 μ8, 5 μδ, 1 μ8, 800 ns, 400 ns, 200 ns, 100 ns, 50 ns, 20 ns, 10 ns, 5 ns, 2 ns, 1.5 ns, 1 ns, 500 ps, 200 ps, 100 ps, 75 ps, 50 ps, 25 ps, 15 ps, 10 ps, 7 ps, 5 ps, 4 ps, 3 ps, 2 ps, 1 ps, 900 fs, 850 fs, 800 fs, 750 fs, 700 fs, 500 fs, 300 fs, 200 fs, 150 fs, 100 fs, 50 fs, 30 fs, 15 fs, 10 fs, etc., or between any of these values.

If the beam of incident light includes a series of laser pulses, the laser pulses can have an average power in a range from 5 mW to 50 kW. It will be appreciated, however, that the average power can be made smaller than 5 mW or larger than 50 kW. Thus, laser pulses can have an average power greater than or equal to 5 mW, 10 mW, 15 mW, 20 mW, 25 mW, 50 mW, 75 mW, 100 mW, 300 mW, 500 mW, 800 mW, 1 W, 2 W, 3 W, 4 W, 5 W, 6 W, 7 W, 10 W, 15 W, 18 W, 25 W, 30 W, 50 W, 60 W, 100 W, 150 W, 200 W, 250 W, 500 W, 2 kW, 3 kW, 20 kW, 50 kW, etc., or between any of these values. Likewise, laser pulses can have an average power less than 50 kW, 20 kW, 3 kW, 2 kW, 500 W, 250 W, 200 W, 150 W, 100 W, 60 W, 50 W, 30 W, 25 W, 18 W, 15 W, 10 W, 7 W, 6 W, 5 W, 4 W, 3 W, 2 W, 1 W, 800 mW, 500 mW, 300 mW, 100 mW, etc., or between any of these values.

Laser pulses can be output by the laser source 102 at a pulse repetition rate in a range from 5 kHz to 1 GHz. It will be appreciated, however, that the pulse repetition rate can be less than 5 kHz or larger than 1 GHz. Thus, laser pulses can be output by the laser source 102 at a pulse repetition rate greater than or equal to 5 kHz, 50 kHz, 100 kHz, 250 kHz, 500 kHz, 800 kHz, 900 kHz, 1 MHz, 2 MHz, 10 MHz, 20 MHz, 50 MHz, 70 MHz, 100 MHz, 150 MHz, 200 MHz, 250 MHz, 300 MHz, 350 MHz, 500 MHz, 550 MHz, 700 MHz, 900 MHz, 2 GHz, 10 GHz, etc. Likewise, laser pulses can be output by the laser source 102 at a pulse repetition rate less than 10 GHz, 2 GHz, 1 GHz, 900 MHz, 700 MHz, 550 MHz, 500 MHz, 350 MHz, 300 MHz, 250 MHz, 200 MHz, 150 MHz, 100 MHz, 90 MHz, 70 MHz, 50 MHz, 20 MHz, 10 MHz, 2 MHz, 1 MHz, 900 kHz, 800 kHz, 500 kHz, 250 kHz, 100 kHz, 50 kHz, 5 kHz, etc. It another embodiment, the laser source 102 can be operated to generate one or more laser pulses on an on- demand basis rather than at any particular pulse repetition rate.

In addition to wavelength, pulse duration, average power and pulse repetition rate, laser pulses delivered to the workpiece 101 can be characterized by one or more other characteristics such as pulse energy, peak power, etc., which can be selected (e.g., optionally based on one or more other characteristics such as wavelength, pulse duration, average power and pulse repetition rate) to irradiate the workpiece 101 at the process spot at an optical intensity

(measured in W/cm²), fluence (measured in J/cm²), etc., sufficient to process the workpiece 101 or a component thereof.

Examples of types of lasers that may be used to generate the aforementioned beam of incident light may be characterized as gas lasers (e.g., carbon dioxide lasers, carbon monoxide lasers, excimer lasers, etc.), solid-state lasers (e.g., Nd:YAG lasers, etc.), rod lasers, fiber lasers, photonic crystal rod/fiber lasers, passively mode-locked solid-state bulk or fiber lasers, dye lasers, mode-locked diode lasers, pulsed lasers (e.g., ms-, ns-, ps-, fs-pulsed lasers), CW lasers, QCW lasers, or the like or any combination thereof. Specific examples of laser that may be used to generate the aforementioned beam of incident light include one or more lasers such as: the BOREAS, HEGOA, SIROCCO or CHINOOK series of lasers manufactured by EOLITE; the PYROFLEX series of lasers manufactured by PYROPHOTONICS; the PALADIN Advanced 355 or DIAMOND series (e.g., DIAMOND E-, G-, J-2, J-3, J-5 series) of lasers manufactured by COHERENT; the PULSTAR- or FIRESTAR-series lasers manufactured by SYNRAD; the TRUFLOW-series of lasers (e.g., TRUFLOW 2000, 2700, 3000, 3200, 3600, 4000, 5000, 6000, 7000, 8000, 10000, 12000, 15000, 20000), TRUCOAX-series of lasers (e.g., TRUCOAX 1000) or the TRUDISK-, TRUPULSE-, TRUDIODE-, TRUFIBER-, or TRUMICRO-series of lasers, all manufactured by TRUMPF; the FCPA μ JEWEL or FEMTOLITE series of lasers

manufactured by IMRA AMERICA; the TANGERINE and SATSUMA series lasers (and MIKAN and T-PULSE series oscillators) manufactured by AMPLITUDE SYSTEMES; CL-, CLPF-, CLPN-, CLPNT-, CLT-, ELM-, ELPF-, ELPN-, ELPP-, ELR-, ELS-, FLPN-, FLPNT-, FLT-, GLPF-, GLPN-, GLR-, HLPN-, HLPP-, RFL-, TLM-, TLPN-, TLR-, ULPN-, ULR-, VLM-, VLPN-, YLM-, YLPF-, YLPN-, YLPP-, YLR-, YLS-, FLPM-, FLPMT-, DLM-, BLM-, or DLR-series of lasers manufactured by IPG PHOTONICS (e.g., including the GPLN-100-M, GPLN-500-QCW, GPLN-500-M, GPLN-500-R, GPLN-2000-S, UPLN-355-M, UPLN-355-R, UPLN-355-QCW-R, etc.), or the like or any combination thereof.

B. Beam Positioner

The beam positioner 104 is operative to diffract, reflect, refract, or the like, or any combination thereof, the beam of laser energy propagating along the beam path 116 from the output of the beam imaging system 104 so as to impart movement of the beam path 116 relative to the scan lens 110. Generally, the beam positioner 104 is configured to impart movement of the beam axis relative to the workpiece 101 along X- and Y-axes (or directions) such that process spots can be scanned, moved or otherwise positioned within a scan field that is projected onto the workpiece 101 (e.g., from the scan lens 110). Although not illustrated, the X-axis (or X- direction) will be understood to refer to an axis (or direction) that is orthogonal to the illustrated Y- and Z-axes (or directions).

The beam positioner 104 can be provided as a micro-electro-mechanical-system (MEMS) mirror or mirror array, an AO deflector (AOD) system, an electro-optic deflector (EOD) system, a fast-steering mirror (FSM) element (e.g., incorporating a piezoelectric actuator, electrostrictive actuator, voice-coil actuator, etc.), a galvanometer mirror system (e.g., including two

galvanometer mirror components, where one galvanometer mirror component is arranged to impart movement of the beam axis relative to the workpiece 101 along the X-direction and another galvanometer mirror component is arranged to impart movement of the beam axis relative to the workpiece 101 along the Y-direction), or the like or any combination thereof. D. Workpiece Positioner

The workpiece positioner 108 is operative to move the workpiece 101 relative to the scan lens 110 in the X-, Y- and/or Z-directions. Thus, to the extent that the workpiece positioner 108 moves the workpiece 101 in the X- and/or Y-directions, the workpiece positioner 108 is configured to move different regions of the workpiece 101 into and out the scan field projected by the scan lens 110. In one embodiment, the workpiece positioner 108 is provided as one or more linear stages (e.g., each capable of imparting translational movement to the workpiece 101 along the X-, Y- and/or Z-directions), one or more rotational stages (e.g., each capable of imparting rotational movement to the workpiece 101 about an axis parallel to the X-, Y- and/or Z-directions), or the like or any combination thereof. In one embodiment, the workpiece positioner 108 includes an X-stage for moving the workpiece 101 along the X-direction, and a Y- stage supported by the X-stage (and, thus, moveable along the X-direction by the X-stage) for moving the workpiece 101 along the Y-direction. The laser processing system 100 may optionally include a chuck (not shown) coupled to the workpiece positioner 108, to which the workpiece 101 can be clamped, fixed, held, secured or be otherwise supported. Although not shown, the laser processing system 100 may also include an optional base that supports the workpiece positioner 108.

As described thus far, the laser processing system 100 employs a so-called "stacked" positioning system, in which positions of the components such as the beam positioner 104, scan lens 110, etc., are kept stationary within the laser processing system 100 (e.g., via one or more supports, frames, etc., as is known in the art) relative to the workpiece 101, which is moved via the workpiece positioner 108. In another embodiment, and although not shown, one or more supplemental positioners (e.g., one or more linear, rotational stages, or the like or any

combination thereof) may be provided to move one or more components such as the beam positioner 104, scan lens 110, etc., and the workpiece 101 may be kept stationary (in which case, the workpiece positioner 108 may be omitted).

In yet another embodiment, the laser processing system 100 can employ a split-axis positioning system in which one or more components such as the beam positioner 104, scan lens 110, etc., are positioned by one or more supplemental positioners (not shown). In such an embodiment, one or more linear or rotational stages are arranged and configured to move one or more components such as the beam positioner 104, workpiece positioner 108, scan lens 110, etc., and the workpiece positioner 108 is arranged and configured to move the workpiece 101. Some examples of split-axis positioning systems that may be beneficially or advantageously employed in the laser processing system 100 include any of those disclosed in U.S. Patent Nos. 5,751,585, 5,798,927, 5,847,960, 6,706,999, 7,605,343, 8,680,430, 8,847,113, or in U.S. Patent App. Pub. No. 2014/0083983, or any combination thereof, each of which is incorporated herein by reference in its entirety.

In another embodiment, one or more components such as the beam positioner 104, scan lens 110, etc., may be carried by an articulated, multi-axis robotic arm (e.g., a 2-, 3-, 4-, 5-, or 6- axis arm). In such an embodiment, the beam positioner 104 and/or scan lens 110 may, optionally, be carried as an end effector of the robotic arm. In yet another embodiment, the workpiece 101 may be carried directly on an end effector of an articulated, multi-axis robotic arm (i.e., without the workpiece positioner 108). In still another embodiment, the workpiece positioner 108 may be carried on an end effector of an articulated, multi-axis robotic arm.

D. Scan Lens

The scan lens 110 (e.g., provided as either a simple lens, or a compound lens) is generally configured to focus laser energy directed along the beam path 116, so as to produce a beam waist. The scan lens 110 may be provided as an f-theta lens, a telecentric lens, an axicon lens, or the like or any combination thereof. In one embodiment, the scan lens 110 is provided as a fixed-focal length lens and is coupled to a lens actuator (not shown) configured to move the scan lens 110 (e.g., so as to change the position of the beam waist along the beam axis). For example, the lens actuator may be provided as a voice coil configured to linearly translate the scan lens 110 along the Z-direction. In another embodiment, the scan lens 110 is provided as a variable- focal length lens (e.g., a zoom lens, or a so-called "liquid lens" incorporating technologies currently offered by COGNEX, VARIOPTIC, etc.) capable of being actuated (e.g., via a lens actuator) to change the position of the beam waist along the beam axis.

E. Controller

Generally, the controller 112 is communicatively coupled (e.g., over one or more wired or wireless communications links, such as USB, Ethernet, Firewire, Wi-Fi, RFID, NFC,

Bluetooth, Li-Fi, or the like or any combination thereof) to one or more components of the laser processing system 100, such as the laser source 102, the beam positioner 104, workpiece positioner 108, the lens actuator, etc., and are thus operative in response to one or more control signals output by the controller 112.

Generally, the controller 112 includes one or more processors configured to generate the control signals upon executing instructions. A processor can be provided as a programmable processor (e.g., including one or more general purpose computer processors, microprocessors, digital signal processors, or the like or any combination thereof) configured to execute the instructions. Instructions executable by the processor(s) may be implemented software, firmware, etc., or in any suitable form of circuitry including programmable logic devices (PLDs), field-programmable gate arrays (FPGAs), field-programmable object arrays (FPOAs), application-specific integrated circuits (ASICs) - including digital, analog and mixed

analog/digital circuitry - or the like, or any combination thereof. Execution of instructions can be performed on one processor, distributed among processors, made parallel across processors within a device or across a network of devices, or the like or any combination thereof.

In one embodiment, the controller 112 includes tangible media such as computer memory, which is accessible (e.g., via one or more wired or wireless communications links) by the processor. As used herein, "computer memory" includes magnetic media (e.g., magnetic tape, hard disk drive, etc.), optical discs, volatile or non-volatile semiconductor memory (e.g., RAM, ROM, NAND-type flash memory, NOR-type flash memory, SONOS memory, etc.), etc., and may be accessed locally, remotely (e.g., across a network), or a combination thereof.

Generally, the instructions may be stored as computer software (e.g., executable code, files, instructions, etc., library files, etc.), which can be readily authored by artisans, from the descriptions provided herein, e.g., written in C, C++, Visual Basic, Java, Python, Tel, Perl, Scheme, Ruby, etc. Computer software is commonly stored in one or more data structures conveyed by computer memory.

Although not shown, one or more drivers (e.g., RF drivers, servo drivers, line drivers, power sources, etc.) can be communicatively coupled to an input of one or more components such as the laser source 102, the beam positioner 104, the workpiece positioner 108, the lens actuator, etc. In one embodiment, each driver typically includes an input to which the controller 112 is communicatively coupled and the controller 112 is thus operative to generate one or more control signals (e.g., trigger signals, etc.), which can be transmitted to the input(s) of one or more drivers associated with one or more components of the laser processing system 100. Thus, components such as the laser source 102, the beam positioner 104, the workpiece positioner 108, the lens actuator, etc., are responsive to control signals generated by the controller 112.

In another embodiment, and although not shown, one or more additional controllers (e.g., component- specific controllers) may, optionally, be communicatively coupled to an input of a driver communicatively coupled to a components (and thus associated with the component) such as the laser source 102, the beam positioner 104, the workpiece positioner 108, the lens actuator, etc. In this embodiment, each component- specific controller can be communicatively coupled and the controller 112 and be operative to generate, in response to one or more control signals received from the controller 112, one or more control signals (e.g., trigger signals, etc.), which can then be transmitted to the input(s) of the driver(s) to which it is communicatively coupled. In this embodiment, a component-specific controller may be configured as similarly described with respect to the controller 112.

In another embodiment in which one or more component- specific controllers are provided, the component- specific controller associated with one component (e.g., the laser source 102) can be communicatively coupled to the component- specific controller associated with one component (e.g., the beam positioner 104, etc.). In this embodiment, one or more of the component- specific controllers can be operative to generate one or more control signals (e.g., trigger signals, etc.) in response to one or more control signals received from one or more other component- specific controllers.

E. Camera

When included in the laser processing system 100, the camera 114 is generally configured to capture imagery of the workpiece 101 and transmit image data, representative of the captured imagery, to the controller 112. The camera 114 may be provided as a digital camera (e.g., a CCD camera, a CMOS camera, or the like or any combination thereof), and may be configured and arranged such that a field of view of the camera 114 lies completely outside the scan field. In another embodiment, the camera 114 is configured and arranged such that the field of view of the camera 114 lies completely within the scan field. In yet another embodiment, the camera 114 is configured and arranged such that the field of view of the camera 114 lies only partially within the scan field. When the field of view of the camera 114 lies completely outside the scan field (or only partially within the scan field), the workpiece positioner 108 may be configured to position any region of the workpiece 101, which is capable of being positioned within the scan field, within the field of view of the camera 114.

III. Embodiments Concerning Beam Stabilization

As mentioned above, it does not take very much of a disturbance to a mirror mount to impart such a small angle change. FIG. 2 illustrates an example of a tip/tilt adjustable mirror mount. Although it is known that the portion of the mirror mount that sits immediately behind the mirror will warm up when the mirror is irradiated with laser pulses, it is not known exactly which part or parts of the mirror mount will deform (e.g., due to the coefficient of thermal expansion of the mirror mount) and result in undesirable tilting of the mirror. It has also been observed in one case that, if the mirror mount was oriented such that heat was rising away from the mount (i.e., mirror pointing down) as opposed to rising away from the mount but being at least partially blocked by the mirror (i.e., mirror pointing up), that the amount of undesirable mirror tilting increased.

A solution to the heating problem discussed above with respect to FIG. 2 is to provide a turn mirror having a mirror mount that is not present immediately behind the a region of the mirror that is intended or expected to be irradiated with laser pulses. FIG. 3 illustrates an example of such a mirror mount. With this approach, any laser light that is transmitted through the mirror will heat up a region of the mirror mount that is not immediately behind the irradiated region of the mirror and/or will propagate until it strikes some other part that is further away from the beam path 116. Thus, a mirror mount such as the mirror mount shown in FIG. 3 can reduce the risk of undesirable tilting of the mirror. Further, turn mirrors such as those shown can be quite simple and less inexpensive compared to an automated beam steering system. In one embodiment, turn mirrors such as those shown in FIG. 3 can be used in system 100 when the laser source 102 generates a beam of laser pulses at an average power of greater than or equal to 10 W, 20 W, 30 W, 40 W, etc., or between any of these values.

IV. Embodiments Concerning Workpiece Alignment

As mentioned above, when laser scribing or dicing a workpiece such as a semiconductor wafer, it can be important to ensure that the placement of a feature (e.g., a scribe, kerf, etc.) is well maintained for each and every workpiece. In one embodiment (e.g., in which the system 100 includes camera 114), a Z-stacking technique (also known as extended-focus-depth technique) can be used to accurately determine the position of a feature in the workpiece. Z- stacking is a vision-based method that is used in both photography and microscopy to provide images with a depth-of-focus that appears far beyond the traditional optical capability. With Z- stacking, a number of images are collected using the camera 114, through a range of focal distances (see, e.g., FIG. 4), without otherwise changing the position of the workpiece with respect to the camera 114. This is referred to as a "Z-stack." For each pixel in the images, the local image gradient is calculated by any suitable technique. This is done for the same pixel location across all images in the Z-stack (see, e.g., FIG. 5). The "best focus" for an image, or region within an image, can often be determined by a peak in image gradient (i.e. the contrast between visible features of an image is highest when in focus). Thus, by comparing the image gradient for the same pixel location across all images in the Z-stack (see, e.g., FIG. 6), it is possible to determine which image within the stack provides best focus for the pixel location being analyzed. By interpolating between data points, it is possible to achieve results that have a resolution beyond that provided by the spacing of the Z-stack. When this same analysis is performed for all pixels across the image, you can determine the best image in the stack for all pixel locations, allowing you to build a composite image, where each pixel represents the best focus for that location across the Z-stack. For many applications, this increased depth-of-field image is the main output. However, knowing which image in the Z-stack represents best focus for a particular pixel, means that you know the height of that location (i.e., the height of that location, as measured along the Z-axis), and if that information is known for all pixels in the image, you can construct a height/profile map of the scene (see, e.g., FIG. 7). Once a height map has been produced, the scribe edges can be found by looking at higher gradient areas in the height data (i.e., regions that have steeper slopes). Knowing that the kerf edges should be roughly linear, and knowing what a typical scene may look like (for example, when examining an intersection, both horizontal and vertical kerf edges are present) can also aid in identifying the edges. The images processed using the technique described can be collected using the same cameras and illuminators used for other typical system activities, such as vision alignment. No additional hardware is required. This is beneficial from a cost point of view.

Although computationally intensive, one of the main benefits of the Z- stacking technique described above is that the detection of an edge of a feature (e.g., of a scribe or kerf) is carried out using only the height data. The visual content of the scene (e.g., having regions which may be bright or dark) is not used in the analysis; the only important aspect of the visual content is how it changes with position within the Z-stack, which impacts the quality of the height data collected. This means that the same algorithm may be used for different product types (that may have significant visual differences), without requiring parameter changes or tuning.

V. Conclusion

The foregoing is illustrative of embodiments and examples of the invention, and is not to be construed as limiting thereof. Although a few specific embodiments and examples have been described with reference to the drawings, those skilled in the art will readily appreciate that many modifications to the disclosed embodiments and examples, as well as other embodiments, are possible without materially departing from the novel teachings and advantages of the invention. Accordingly, all such modifications are intended to be included within the scope of the invention as defined in the claims. For example, skilled persons will appreciate that the subject matter of any sentence, paragraph, example or embodiment can be combined with subject matter of some or all of the other sentences, paragraphs, examples or embodiments, except where such combinations are mutually exclusive. The scope of the present invention should, therefore, be determined by the following claims, with equivalents of the claims to be included therein.

Claims

WHAT IS CLAIMED IS:

1. A laser processing system, comprising:

a laser source configured to generate a beam of laser pulses at an average power of greater than 10 W; and

a turn mirror disposed in a path of the beam, the turn mirror comprising:

a mirror configured to reflect a first portion of light within the laser pulses and transmit a second portion of the light within the laser pulses; and

a mirror mount coupled to the mirror, wherein the mirror mount is not present behind the mirror at a location where the mirror is irradiated with the laser pulses.

2. The laser processing system of claim 1, wherein the average power is greater than 18 W.

3. The laser processing system of claim 2, wherein the average power is greater than 25 W.

4. The laser processing system of claim 3, wherein the average power is equal to 30 W.

5. The laser processing system of claim 3, wherein the average power is greater than 30 W.

6. The laser processing system of any one of claims 1 to 5, further comprising:

a scan lens arranged within a beam path along which the beam of laser pulses is propagatable; and

beam positioner arranged within the beam path between the laser source and the scan lens.

7. The laser processing system of claim 6, wherein the beam positioner includes a galvanometer mirror system.

8. The laser processing system of claim 6, wherein the beam positioner includes an acousto- optical deflector system.

9. The laser processing system of claim 6, wherein the turn mirror is oriented to face downwards.