Patent Application
20060207976
1. Field of the Invention
The apparatus and methods relate to pulsed lasers and to micromachining with pulsed lasers.
2. Description of the Related Art
Many materials can be micromachined using lasers and in particular pulsed lasers. In a laser micromachining process, laser energy is directed into a medium so as to alter the physical or structural characteristics of the medium. Typically, a portion of the irradiated material is removed, for example, by ablation. Laser micromachining can be used, for example, to drill, cut, scribe, and mill materials so as to form structures including, for example, channels, grooves, or holes, or to form other features in the material.
In some micromachining processes, the laser energy comprises one or more laser pulses. However, when more than a single laser pulse is used, residual heat can accumulate in the bulk of the remaining material as successive pulses are incident upon the material. If the laser pulse repetition rate is sufficiently high, the accumulated heating can become severe enough to cause undesirable effects, such as melting, oxidation, or other changes to the atomic arrangements in and/or on regions of the material. These regions are known as Heat Affected Zones (HAZ), and they lead to imprecision in the micromachining process.
In some pulsed laser micromachining processes, a higher laser pulse repetition rate is necessary to make the micromachining process economically feasible. Accordingly, apparatus and methods are needed that enable pulsed laser micromachining at higher repetition rates.
Various embodiments of systems and methods to laser micromachine material with green femtosecond pulses are disclosed. One embodiment comprises a method comprising producing a visible light beam comprising femtosecond optical pulses having a wavelength between about 490 and 550 nanometers and micromachining a region of a surface by directing at least a portion of the visible light beam into the region of the surface.
Another embodiment comprises a system for micromachining. The system comprises a light source producing a beam of visible light comprising femtosecond pulses having a wavelength between about 490 and 550 nanometers, and material positioned in the beam such that the material is micromachined by the beam.
Another embodiment comprises a system for performing micromachining on an object. The system comprises a visible laser light source that outputs a visible light beam comprising femtosecond duration optical pulses having a wavelength between about 490 and 550 nanometers and illuminates a spatial region of the object with the visible light. The system further comprises a translation system for translating the beam or the spatial region, wherein the translation system is configured to alter the relative position of the beam and object such that the visible laser beam micromachines the object.
A system 10 configured to micromachine a material is shown in
The visible laser light source 12 comprises a laser configured to produce ultrashort pulses having pulse durations from about 100 fs to 20 ps. In one embodiment, the laser light source 12 comprises a Yb-doped fiber laser 14 that outputs light having a wavelength of approximately 1045 nanometers. An example Yb-doped, amplified fiber laser 14 comprises the FCPA μJewel available from IMRA America, Ann Arbor Mich. This fiber laser has a pulse repetition rate between about 100 kHz and 5 MHz and is capable of outputting ultrashort pulses having pulse durations between about 200 and 500 fs. The pulse duration may also be between 300 and 700 fs in some embodiments. Repetition rates and pulse durations outside these ranges may also be possible in other embodiments.
The visible laser light source 12 further comprises a frequency doubler 16 that receives the optical pulses from the Yb-doped fiber laser 14. One preferred embodiment of the frequency doubler 16 utilizes non-critically phase matched lithium triborate (LBO) as the nonlinear media as this can maximize conversion efficiency and output beam quality. The frequency doubler may also comprise nonlinear media such as beta-barium borate (BBO), potassium titanyl phosphate (KTP), bismuth triborate BiB3O6, potassium dihydrogen phosphate (KDP), potassium dideuterium phosphate (KD*P), potassium niobate (KNbO3), lithium niobate (LiNbO3) and may include appropriate optics to direct or focus the incident beam into the nonlinear medium, to increase conversion efficiency, and collimate the second harmonic output beam. In some embodiments, the frequency doubler produces a frequency doubled output at a wavelength of about 522 nm through second harmonic generation. This output from the frequency doubler 16 and from the visible laser light source 12 is shown as a beam 18 in
Other types of light sources and specifically other types of visible laser light sources 12 may be employed. Other types of lasers may be employed. For example, other types of fiber and non-fiber pulsed lasers may be employed. In some embodiments, for example, the light source 12 may comprise a solid state laser such as a Nd:YAG laser that outputs light at approximately 1064 nm. Frequency doubling and second harmonic generation may or may not be employed in different embodiments. In various preferred embodiments, ultrashort pulses, for example, femtosecond pulses less than one picosecond are useful. Certain pulsed fiber lasers may provide the ability to produce such ultrafast pulses at the suitable visible wavelength.
The system 10 may include mirrors 20a, 20b that direct the beam 18 to other components of the system 10. The system 10 may comprise a power adjust assembly 22 configured to attenuate the average power and pulse energy in the beam 18. In some embodiments, the power adjust assembly 22 comprises a neutral density filter and may comprise a graduated neutral density filter. In other embodiments, the power adjust assembly 22 comprises a polarizer and a wave plate that is rotatable with respect to the polarizer.
In some embodiments, a feedback system 25 is used to monitor and control the power or pulse energy in the beam 18. The feedback system 25 comprises the mirror 20b, which is partially transmissive of the laser light beam 18. The feedback system 25 further comprises a controller 36 that is connected to the power adjust assembly and is configured to receive a portion of the light transmitted from the mirror 20b. The controller 36 may include an optical sensor or detector that is sensitive to light incident thereon. The controller 36 can monitor the transmitted light and suitably regulate the power adjust assembly 22 so as to control the average power and/or the pulse energy in the beam 18.
The system 10 directs the laser beam 18 onto a material 28 and, in particular, into a target region 30 in and/or on the material 28 so as to micromachine features or structures. This material 28 may comprise metal, semiconductor, or dielectric material. For example, the material 28 may include copper, aluminum, gold, and chrome. The material 28 may also comprise crystal or polymer. Additionally the material 28 may comprise glass or other dielectric materials. Some examples of material that may be employed include fluorine-doped silica glass and high bandgap crystalline materials such as quartz, sapphire, calcium fluoride, magnesium fluoride, barium fluoride, and beta barium borate. Also, the material 28 may comprise silica glass based dielectrics or “low-k” dielectrics commonly used to increase the performance of semiconductor devices, for example, microprocessors. The material 28 may comprise organic, inorganic, or hybrid materials. Additionally, the material 28 may comprise a combination of these materials. Other materials may be used.
Suitable materials 28 also include Coming Pyrex® glass, borosilicate glass, silicon carbide, crystalline silicon, zinc oxide, and nickel. Additionally, various nickel-chromium alloys such as, for example, Inconel® (Special Metals Corporation, New Hartford, N.Y.), e.g., Inconel® alloy 625, may be used. In certain embodiments, the material 28 may comprise nickel-titanium alloys such as, for example, shaped-memory or superelastic alloys such as nitinol (Nlckel TItanium Navel Ordnance Laboratory). Further, experiments indicate that such materials may be micromachined at lower levels of laser fluence when using green (e.g., 522-nm light) rather than infrared (e.g., 1045-nm light). In other micromachining process, indium-tin-oxide (ITO) may be used, and in particular transparent-conducting-oxide ITO may be used.
In some embodiments the system 10 is configured to remove portions of a thin film deposited on a substrate, such as, for example, a chrome film deposited on quartz. Certain embodiments of the system 10 may be configured to remove portions of the thin film without significant damage to the underlying substrate. In some embodiments, the thin film may comprise a multilayer stack of thin films such as, for example, alternating thin layers of metal and dielectric materials.
The system 10 further includes optics 26 disposed to receive visible light output from the visible laser light source 12. The optics 26 may include, for example, a microscope objective that focuses the beam 18 into the target region 30. In some embodiments, the optics 26 focuses the laser beam 18 to achieve a high fluence (energy per unit area) in the target region 30. Note that the drawing in
The optics 26 may have a numerical aperture (NA) less than about 1.0 and between about 1.0 and 0.4 in some embodiments. The reduced resolution due to use of lower numerical aperture optics, however, may be offset by using shorter wavelengths such as visible wavelengths. Moreover, the low NA focusing objective facilitates micromachining of three-dimensional features and structures due to the longer depth of focus relative, e.g., to oil-and water-immersed objectives with NA>1.0. The visible wavelength near about 520 nm is also more compatible with standard high magnification objectives used in visible microscopy than near infrared (NIR) wavelengths. As such, the insertion loss and beam aberration introduced by the objective is significantly reduced. Other types of optics 26 may be employed, and the optics may be excluded in certain embodiments.
In some embodiments of the system 10, the optics 26 are mounted on a focusing stage 24 that can be translated or moved to align and focus the beam so that a portion of the beam 18 with high fluence can be directed into suitable regions of the material 28. Other embodiments may use additional optics and/or mirrors to adjust the focus of the optics 26.
The system 10 further comprises a translation system 32 for moving the target region 30. The medium 28 may, for example, be mounted on a translation stage 34 that is translated or otherwise moved with respect to the laser beam 18. In other embodiments, the laser beam 18 may be translated, for example, using a mirror that can be rotated or tilted. The laser beam 18 may be translated or moved by moving other optical elements, for example, by shifting the microscope lens 26 or the focusing stage 24. Other configurations and arrangements for moving the beam 18 with respect to the medium 28 or otherwise moving the target region 30 may be employed. In certain preferred embodiments, the translation system 32 is configured so that large regions or many regions in the material 28 can be laser machined.
The visible light laser pulses incident on the material 28 alter the physical characteristics and/or structure of the material 28. Micromachining of the material 28 using ultrashort laser pulses allows for removal or ablation of the material without disadvantageously heating the remaining bulk matter. One reason that the bulk material is not significantly heated may be that the laser pulse duration, which is the time during which laser energy is deposited into the material, is less than a characteristic time in which energy is transferred from the material's electronic structure to its phononic structure. Therefore, provided the fluence is sufficiently high, the irradiated material is ablated before significant heating can occur in the surrounding material.
As referred to above, systems 10 such as described above offer many advantageous technical features. Use of frequency-doubled 1045-nanometer radiation, for example, provides numerous benefits. The shorter wavelength allows for tighter focusing due to the reduction in the diffraction limited spot size. Achieving high focal intensity/fluence with relatively low incident pulse energy is therefore possible.
For weakly-absorbing or transparent materials, an ablation threshold, which is the fluence at which absorbed laser energy is sufficient to break chemical bonds in the material so as to permit ablation to occur, has been found to be lower for shorter wavelength light. The lower ablation threshold allows micromachining to be performed at fluences that are sufficiently low such that significant heating of the surrounding material does not occur. Accordingly, the use of shorter wavelengths results in reduced formation of HAZ and higher quality micromachining. For example, experiments have shown that the laser-damage threshold of Pyrex® glass is lower for 522-nm ultrashort pulses than for 1045-nm ultrashort pulses, despite the fact that the material is transparent to both wavelengths.
Without subscribing to any particular theory or explanation, one possible reason for the lower ablation threshold at shorter wavelengths is that the shorter wavelength light is more effective at producing free electrons that can break bonds in the bulk of the material. Free electrons can be produced by a variety of processes such as, for example, photoionization processes in which incident light has sufficient energy to free an electron from a valence band in the material. Typically, the incident light energy must exceed a bandgap energy, which is the energy difference between an ionization band and the valence band. In a single-photon ionization process, a single photon with energy larger than the bandgap energy can ionize an electron. The rate at which single-photon ionization occurs generally depends linearly on the laser intensity/fluence. In a multi-photon ionization process, a number of photons, each having an energy below the bandgap energy, nonetheless can ionize an electron, because the sum of their energies exceeds the bandgap energy. The rate at which multi-photon ionization occurs depends nonlinearly on the laser intensity/fluence, and at a given fluence, the rate is larger if a smaller number of photons are involved in the process. Accordingly, the multi-photon ionization rate is larger for shorter wavelength light, because shorter wavelength photons have larger energies, and fewer shorter wavelength photons are needed to exceed the bandgap energy. Therefore, it is possible that multi-photon ionization may contribute toward the lower ablation threshold at shorter wavelengths. However, it is also possible that the multi-photon ionization process does not play a significant, or even any, role in lowering the ablation threshold and that other physical processes may be responsible in whole or in part for the lower ablation threshold at shorter wavelengths.
In certain embodiments, the system 10 may be used to micromachine a dielectric material, while in other embodiments, the system 10 may be used to micromachine a thin layer disposed on a dielectric, without significantly damaging the dielectric. For example, in one embodiment, a thin film may be removed from a substantially transparent substrate (e.g., a glass or Pyrex® substrate), without substantial damage to the substrate material. The use of visible (e.g., green) wavelength light is advantageous, because it permits fine resolution features to be machined, because feature resolution is proportional to wavelength. Accordingly, shorter wavelengths permit smaller features to be machined. Further, in some micromachining processes, the shorter wavelength light can pass through the substrate without being substantially absorbed and without causing significant damage to the substrate.
As the wavelength decreases below the green portion of the spectrum, there is an increased likelihood of damage to the substrate. For wavelengths below about 400 nm, for example, many transparent materials begin to show an increase in linear absorption, which will increase likelihood of damage to the glass. Use of such shorter wavelengths reduces the ability of a system to remove a thin film without also damaging or removing portions of the substrate. Use of such shorter wavelengths also decreases the yield of the process and increases cost.
The ability to machine materials at lower operating fluences is advantageous, because it results in reduced HAZ (Heat Affected Zones) and thereby improves precision and quality. Once ablation begins in a material, various avenues exist for coupling energy into the material over longer time scales, which results in the generation of heat. For example, plasma that forms during the ablation process can absorb light, thus heating the plasma and the surrounding material. In addition, absorption due to molecular defect formation within the material (due to material interaction with intense ultrashort pulses) and absorption by residual debris from the ablation process can cause heating of the material during the laser machining. The negative effects of these absorption processes can be reduced if laser machining can be performed at lower operating fluences at shorter wavelengths.
Also, since substantially many optical objectives have been designed for biological microscopy, the performance of these microscope objectives (such as optical transmission and aberration correction) is improved or optimized for visible wavelengths. Accordingly, by using the second harmonic of the Yb-based laser, the resultant visible wavelength allows for simple integration into existing optical microscope systems. Micromachining can therefore be integrated in parallel together with a rudimentary inspection system.
Pulsed laser micromachining is a complex and challenging process. Techniques that may be well-suited for one class of materials may be inappropriate for another class. Accordingly, identifying a regime (e.g., wavelength, pulse duration, pulse repetition rate, pulse energy, laser power) wherein micromachining is possible appears to provide benefits such as, for example, improved quality machining (e.g., reduced formation of HAZ, cleaner cuts, etc.), use of smaller spot sizes, lower optical losses, higher focal intensity/fluences, and improved integration into existing microscope systems, etc., that might not otherwise available.
In one preferred embodiment, a laser source 200 such as schematically shown in
The oscillator 210 may comprise a pair of reflective optical elements that form an optical resonator. The oscillator 210 may further include a gain medium disposed in the resonator. This gain medium may be such that optical pulses are generated by the oscillator 210. The gain medium may be optically pumped by a pump source (not shown). In one embodiment, the gain medium comprises doped fiber such as Yb-doped fiber. The reflective optical elements may comprise one or more mirrors or fiber Bragg gratings in some embodiments. The reflective optical elements may be disposed at the ends of the doped fiber. Other types of gain mediums and reflectors as well as other types of configurations may also be used. The oscillator 210 outputs optical pulses having a pulse duration or width (full width half maximum, FWHM), τ, and a repetition rate, Γ.
The pulse stretcher 220 may comprise an optical fiber having dispersion. The pulse stretcher 220 is optically coupled to the oscillator 210 and disposed to receive the optical pulses output by the oscillator. In certain embodiments, the oscillator 210 and the pulse stretcher 220 are optical fibers butt coupled or spliced together. Other arrangements and other types of pulse stretchers 220 may also be used. The output of the pulse stretcher is a chirped pulse. The pulse stretcher 220 increases the pulse width, τ, stretching the pulse, and also reduces the amplitude of the pulse.
The pulse stretcher 220 is optically coupled to the amplifier 230 such that the amplifier receives the stretched optical pulse. The amplifier 230 comprises a gain medium that amplifies the pulse. The amplifier 230 may comprise a doped fiber such as a Yb-doped fiber is some embodiments. The amplifier 230 may be optically pumped. A same or different optical pump source may be used to pump the oscillator 210 and the amplifier 230. The amplifier 230 may be non-linear and may introduce self-phase modulation. Accordingly, different amplitude optical pulses may experience different amounts of phase delay. Other types of amplifiers and other configurations may be used.
The grating compressor 240 is disposed to receive the amplified optical pulse from the optical amplifier 230. Different types of grating compressors 240 are well known in the art. The grating compressor 240 may comprise one or more gratings that introduce dispersion and is configured to provide different optical paths for different wavelengths. The grating compressor 240, which receives a chirped pulse, may be configured to provide for phase delay of longer wavelengths (e.g., temporally in the front of the optical pulse) that is different than the phase delay of the shorter wavelengths (e.g., temporally in the rear of the optical pulse). This phase delay may be such that in the pulse output from the compressor, the longer and short wavelengths overlap temporally and the pulse width is reduced. The optical pulse is thereby compressed.
In one preferred embodiment, the laser source 200 comprises a Yb-doped, amplified fiber laser (e.g., a modified FCPA μjewel, available from IMRA America). Such a laser offers several primary advantages over commercial solid-state laser systems. For example, this laser source provides a variable repetition rate that spans a “unique range” from about 100 kHz to 5 MHz. The variable repetition rate facilitates the optimization of the micromachining conditions for different materials, e.g., different metals, different dielectrics, etc. Higher repetition rate than solid-state regeneratively amplified systems allow greater microprocessing speed. Additionally, higher pulse energy than oscillator-only systems allows greater flexibility in focal geometry.
In one embodiment of the laser source 200, the pulse is stretched with a length of conventional step-index single-mode fiber and compressed with the bulk grating compressor 240. The large mismatch in third-order dispersion between the stretcher 220 and compressor 240 is compensated via self-phase modulation in the power amplifier 230 through the use of cubicon pulses. The cubicon pulses have a cubical spectral and temporal shape. Under the influence of self-phase modulation in the power amplifier 230, the triangular pulse shape increases the nonlinear phase delay for the blue spectral components of the pulses while inducing a much smaller nonlinear phase delay for the red spectral components. The degree of this self-phase modulation depends on the intensity of the laser pulse within the power amplifier 230. Moreover, variation in the repetition rate will cause a change in the intensity and, thus, also alter the phase delay and dispersion.
For constant average power, Pavg, resulting in large part from constant pumping, Pavg=Epulse×Γ, where Epulse is the pulse energy (J) and Γ is the repetition rate (Hz). Thus for constant average power, increasing the repetition rate causes the pulse energy to decrease. Conversely, decreasing the repetition rate causes the pulse energy to increase. Given that the pulse energy changes with repetition rate, e.g., from 3 μJ at 100 kHz to 150 nJ at 5 MHz, the degree of self-phase modulation also changes. The change in self-modulation in the amplifier 230 causes the pulse width to change. To correct for this change in pulse width caused by the variation in repetition rate, the dispersion of the grating compressor 240 can be adjusted.
The storage device 256 may also comprise one or more local or remote devices such as, for example, disk drives, volatile or nonvolatile memory, optical disks, tapes, or other storage device or medium both those well known in the art as well as those yet to be devised. Communication may be via, e.g., hardwiring or by electromagnetic transmission and may be, e.g., electrical, optical, magnetic, or microwave, etc. A wide variety of configurations and arrangements are possible.
As described above, in the embodiment of the compressor grating 240 shown in
Different configurations are possible. With reference to
Translation of the first retroreflector 272 as indicated by the arrow 252 alters the optical path distance traveled by the beam 248 between reflections from the grating 242 and thus alters the dispersion introduced to the beam 248 by the compressor grating 240. Other aspects of the operation of the grating compressor 240 shown in
Further, in some embodiments, an optical detector (e.g., a photodiode) may be included that monitors the repetition rate. The controller 254 may use this information from the optical detector. In other embodiments, the optical detector provides a measure of the pulse width and the controller 254 uses this information to automatically adjust the dispersion of the grating compressor 240. Thus, a feedback system that includes the optical detector and the controller 254 may be included to automatically adjust the dispersion of the grating compressor 240. Additional details regard using feedback to control the laser system 200 is disclosed in U.S. patent application Ser. No. 10/813,269 entitled “Femtosecond Laser Processing System with Process Parameters, Controls and Feedback,” (IM-110) filed Mar. 31, 2004, which is incorporated by reference herein in its entirety. Other variations in design are possible.
As described herein, this laser source 200 may be particularly useful for material micromachining. The combination of ultrashort pulse duration, relatively high pulse energy, and visible (e.g., green) wavelength makes possible high quality and high precision micromachining for a significant variety of laser machining processes. The high quality micromachining results from, for example, reduced formation of HAZ (Heat Affected Zones) and provides an ability to machine precise, controlled, repeatable cuts in the material over a wide range of laser fluences. The ability to use relatively low NA focal objectives simplifies the optical layout and provides long working distance and long depth of focus which are useful for micromachining three-dimensional structures.
Embodiments of the system 10 may be used to machine a variety of materials, including, for example, polymer compounds.
A direct comparison was also made between micromachining at green (522 nm) and at infrared (1045 nm) wavelengths to show the advantages of using shorter wavelengths. In this comparison experiment, PET (polyethylene terephthalate) was micromachined with 1045 nm and 522 nm femtosecond laser pulses at a 100 kHz repetition rate. The duration of the pulses was about 450 fs. In this experiment, the same 1045 nm laser 14 (see
Additionally, while the edges of the 1045-nm features appear smoother than the edges of the 522-nm features, the diameters of the 1045-nm features are different for the same fluence, which may indicate large-scale melting of the material. The “splatter” 540a, 540b surrounding the features 510a, 510b indicates melting on a smaller scale, and, although evident to some extent in both
In another experiment showing precise, high-quality laser micromachining with green ultrashort pulses, a portion of a thin chrome film 605 (having a 100-nm thickness) deposited on a quartz photomask 610 was removed using 522-nm ultrashort pulses. The pulse width was about 300 fs, and the pulse repetition rate was 100 kHz. The use of green light (e.g., 522 nm) is beneficial in that the quartz photomask 610 permits transmission of the incident laser light without incurring permanent and significant damage to the quartz material.
The micromachining methods utilizing the system 10 are not limited to the particular materials in the example results shown in
In another embodiment of the micromachining methods, visible laser light is used to machine a medium that comprises layers of different materials. For example, the medium may comprise a stack of alternating layers of various materials that include a wide range of absorption coefficients for the wavelength of the incident laser pulses. In some cases, the alternating layers may comprise metals and dielectrics. The combination of shorter illuminating wavelength (e.g., green light) and ultrashort pulse duration is advantageous compared to the separate cases of either longer illuminating wavelength (e.g., infrared) or longer illuminating pulse duration. In addition to the increased precision enabled by imaging or simple focusing of comparatively shorter-wavelength light, the ultrashort pulse duration enables machining of both metallic and dielectric layers with a minimal amount of potentially deleterious heating of the material adjacent to the machined regions.
Additionally, micromachining with comparatively shorter-wavelength light having ultrashort pulse duration enables controlled removal of material that can be repeated with similar results. For example, the micromachining process can be used to form openings, holes, channels, cuts, grooves, or other features, which have a size and shape that can be repeatably produced. The bottom, top, sides, edges, etc., of the opening, holes, channels, cuts, or grooves, etc., are substantially, regular, smooth, and repeatable. The bottoms, tops, sides, edges, etc., of the features may, for example, have ±10 nm RMS roughness or total variation of between about 20 nm and about 50 nm. Likewise, substantially straight channels can be formed ranging from about 5 micrometers to several centimeters in length and from about 100 nanometers to several hundred micrometers in width to within a tolerance of about 1% of the width of the channel on each side. Openings, holes, channels, cuts, grooves, etc., having other shapes are also possible. Accordingly, micromachining may include, for example, milling or cutting or drilling to provide sharp-edged, smooth, and uniform surfaces (e.g., edges, sides, bottoms, and tops) in microstructural features. Roughness may be less than about 100 nanometers RMS. Micromachining may also be used in scribing, and in grooving, in some embodiments. Advantageously, the micromachining is precise, controllable, and repeatable over a wide range of laser fluences.
For the case of dielectric layers that are generally optically transparent for wavelengths greater than an ionization bandgap of the material, λg, the use of shorter wavelength light permits micromachining at lower fluences, which generally results in superior quality and precision in the machining process due to reduced material heating and HAZ formation. For example, during micromachining of transparent materials, material defects and debris generated. Such defects and debris can absorb light, which can result in heating, melting, or burning of the surrounding material. If the machining of the transparent material is performed at a lower fluence, there will be less energy to cause heating in the regions near the machined portions. As described above, one possible (although not required) explanation for the decreased heating is that the ablation threshold is lower for shorter wavelength (e.g., green) light, because, for example, multi-photon ionization processes occur at an increased rate at shorter wavelengths. For example, experiments show that many transparent materials have a lower ablation threshold with green (e.g., 522 nm) light than infrared (e.g., 1045-nm) light. Accordingly, lower fluences may be used with green light, which will cause less material heating than, for example, infrared light.
In certain embodiments, the system 10 is configured to dice a processed semiconductor wafer into individual components, e.g., individual “chips.” In these embodiments, laser micromachining of the semiconductor wafer is advantageous, as compared to the use of a wafer dicing saw, because laser micromachining avoids significant damage to the individual “chips.” For example, many “low-k” dielectrics tend to crack and chip if they are cut with a wafer dicing saw blade, and these cracks can propagate to and damage the individual “chips.” Laser micromachining with ultrashort visible pulses advantageously avoids this cracking and chipping, because, for example, no physical saw blade comes into contact with the semiconductor wafer.
In other embodiments, the system 10 can be configured to cut glass, crystal, sapphire, calcium fluoride, and other dielectric materials into smaller pieces. For example, such embodiments may be used for “scribe and break” processes, in which a groove is machined on the surface of a sheet of material, and the sheet is subsequently cleaved (e.g., by mechanical, thermal, or other methods). Such embodiments may also be used to cut other materials such as, for example, metals and semiconductors.
In certain embodiments, the system 10 can be used to pattern grooves in a dielectric material, such as glass or crystal. These embodiments may be used, for example, to fabricate microfluidic circuits in which grooves in the material are used to channel fluids. Additionally, embodiments may use groove cutting for various “scribe and break” processes so as to break a larger sheet of material into smaller pieces in a controlled fashion. For example, such embodiments may be used to machine glass, and in particular borosilicate glass, which may be used for flat panel displays, including cell phones, laptops, televisions, displays, and personal digital assistants.
As described above, the configuration of the micromachining system may be different and variations in micromachining methods are possible. One example alternative embodiment is shown in
Other variations in the apparatus and method described herein are possible. For example, components may be added, removed, or arranged or configured differently. Similarly, processing steps may be added, removed, reordered, or performed differently.
Embodiments of the system 10 may be used in a variety of micromachining processes. For example, a beam of visible ultrashort laser pulses may be used to drill, cut, scribe, groove, mill, etch, and weld a variety of materials including, for example, many metals, semiconductors and dielectrics (e.g., glasses and crystals). The system 10 may be used in processes such as, for example, micropatterning, microfluidics, microelectromechanical systems (MEMS), lithography, semiconductor fabrication, thin film removal, “scribe and break” processing, bearing surface structuring, and via-hole drilling. Many other processes are possible.
While certain embodiments of the invention have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the present invention. Accordingly, the breadth and scope of the present invention should be defined in accordance with the following claims and their equivalents.
This application claims priority to U.S. Patent Application No. 60/646,101 filed Jan. 21, 2005, entitled “LASER MATERIAL MICROPROCESSING WITH GREEN FEMTOSECOND PULSES,” (Attorney Docket No. IMRAA.033PR), which is hereby incorporated by reference herein in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 60646101 | Jan 2005 | US |
