Systems and methods for laser ablation - Patents.com

Abstract

Described herein are various techniques for laser ablation of material from a workpiece. The ablation system includes a laser, a focusing system, and a computing device configured to control operation of the laser and the focusing system. The laser emits light that is received by the focusing system. The computing device controls operation of the laser and / or the focusing system such that the focusing system focuses the light emitted by the laser to a focal point on a surface of the workpiece. The focused light causes ablation of the workpiece at the focal point.

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority to U.S. Provisional Patent Application No. 63 / 332,309, entitled "SYSTEMS AND METHODS FOR LASER ABLATION," filed April 19, 2022, which is incorporated by reference in its entirety.

[0002] Government Interest Statement This invention was made with Government support under Contract No. DE-SC0021786 awarded by the U.S. Department of Energy. The U.S. Government has certain rights in this invention. [Background technology]

[0003] Microfabrication refers to a variety of techniques used to manufacture integrated circuits (ICs) and micro-electro-mechanical systems (MEMS). ICs and MEMS manufactured by traditional microfabrication techniques have feature sizes on the order of microns or nanometers. Traditionally, IC and MEMS microfabrication is a layer-by-layer process in which layers of semiconductors (and various other materials) are deposited, patterned using lithography tools, and then etched to define part of the final shape. In general, these traditional microfabrication techniques are limited to creating structures with shapes similar to two-dimensional extruded shapes, sometimes referred to as 2.5D.

[0004] Furthermore, these conventional microfabrication techniques are complex, time consuming, and costly. In one example, fabrication of a single layer of a device can include the steps of: 1) depositing a thin film on a substrate or wafer; 2) coating the thin film with a photoresist masking layer; 3) photolithographic patterning the photoresist masking layer; 4) etching the thin film layer through the photoresist masking layer; 5) stripping the photoresist masking layer; and 6) thoroughly cleaning the substrate or wafer before similarly depositing and patterning subsequent layers. Furthermore, these techniques are not readily available for some materials, limiting their use to certain classes of materials. Summary of the Invention

[0005] The following is a brief summary of the subject matter described in detail herein. This summary is not intended to be limiting on the scope of the claims.

[0006] Described herein are various techniques for laser ablation of micro-scale features on a workpiece. The laser ablation system includes a computing device, a laser, and a focusing system. The computing device is configured to control the operation of the laser, the focusing system, and / or other components of the laser ablation system. The laser is configured to output a light beam that is received and focused by the focusing system. The focusing system is configured to focus the beam to a small focal spot on or within the workpiece. In exemplary embodiments, the focal spot can have a spot width of less than 2 microns, 1 micron or less, or 500 nanometers or less. The laser ablation system can be configured such that the light beam has sufficient power to cause ablation of material from the workpiece at the focal spot, but insufficient power to cause ablation of material at locations along the beam that are not proximal to the focal spot. Thus, the laser ablation system can be precisely controlled to cause ablation at desired locations on or within the workpiece. Additionally, the laser ablation system can be utilized to form features on the workpiece, and such features can be less than 1 micron in size.

[0007] The above summary presents a simplified overview to provide a basic understanding of some aspects of the systems and / or methods discussed herein. This summary is not an extensive overview of the systems and / or methods discussed herein. It is not intended to identify key / critical elements or to delineate the scope of such systems and / or methods. Its sole purpose is to present some concepts in a simplified form as a prelude to the more detailed description that is presented later. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a functional block diagram of an exemplary laser ablation system. [Diagram 2]FIG. 2 shows the positions of the beams relative to the surface of the workpiece and their respective ablation regions. [Diagram 3] FIG. 3 is a diagram illustrating an exemplary confocal microscope system. [Figure 4] FIG. 4 is a functional block diagram of another exemplary laser ablation system. [Diagram 5] FIG. 5 is a functional block diagram of yet another exemplary laser ablation system. [Figure 6] FIG. 6 is a functional block diagram of yet another exemplary laser ablation system. [Figure 7] FIG. 7 is a conceptual diagram showing the overlap of laser beams within the bulk of a workpiece. [Figure 8] FIG. 8 is a functional block diagram of yet another exemplary laser ablation system. [Figure 9] FIG. 9 is a flow diagram illustrating a method for selective laser ablation. [Figure 10] FIG. 10 illustrates an exemplary computer system. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Various techniques relating to selective laser ablation are now described with reference to the drawings, in which like reference numerals are used to refer to like elements throughout. In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of one or more aspects. However, it may be apparent that such aspects may be practiced without these specific details. In other instances, well-known structures and devices are shown in block diagram form to facilitate the description of one or more aspects. Furthermore, it should be understood that a function described as being performed by a particular system component may be performed by multiple components. Similarly, for example, a component may be configured to perform a function described as being performed by multiple components.

[0010] Furthermore, the term "or" is intended to mean an inclusive "or" rather than an exclusive "or." That is, unless otherwise specified or clear from the context, the phrase "X utilizes A or B" is intended to mean any of the natural inclusive permutations. That is, the phrase "X utilizes A or B" is satisfied by either X utilizes A, X utilizes B, or X utilizes both A and B. Furthermore, the articles "a" and "an," as used in this application and the appended claims, should be construed generally to mean "one or more," unless otherwise specified or clear from the context that the singular form is intended.

[0011] Moreover, as used herein, the terms "component" and "system" are intended to encompass a computer-readable storage device configured with computer-executable instructions that, when executed by a processor, cause a particular function to be performed. The computer-executable instructions may include routines, functions, and the like. It should also be understood that a component or system may be localized on a single device or distributed across several devices. Moreover, as used herein, the term "exemplary" is intended to mean serving as an example or example of something and is not intended to indicate preference.

[0012] 1, an exemplary laser ablation system 100 is shown. The laser ablation system 100 includes a computing device 102, a laser 104, a collection system 106, and a workpiece 108. The computing device 102 includes a processor 110 and a memory 112. The memory 112 further includes process control components 114 that, when executed by the processor 110, are configured to control the operation of the laser 104 and / or the collection system 106.

[0013] The laser 104 outputs a light beam 116. The laser 104 may be a pulsed laser, such as a femtosecond laser, that produces high intensity and short duration light pulses. The beam 116 is received by a focusing system 106. The focusing system 106 comprises one or more optical elements that are collectively configured to focus the beam 116 to a focal point 118 on a surface of the workpiece 108 or within the body of the workpiece 108. The focusing system 106 is configured to focus the beam 116 such that the focal point 118 has a small diameter (e.g., less than 2 microns, 1 micron or less, or 500 nanometers or less). The focusing system 106 is further configured to focus the beam 116 such that the beam 116 has a shallow depth of focus (e.g., 10 microns or less, 5 microns or less, or 1 micron or less). In one example, the depth of focus is the Rayleigh length. In another example, the depth of focus is a confocal parameter. In an exemplary embodiment, collection system 106 includes one or more optical elements having a high numerical aperture, with the optical element having an overall high numerical aperture. In non-limiting examples, collection system 106 can have a numerical aperture of 0.15 or greater, 0.42 or greater, or 0.55 or greater.

[0014] In various exemplary embodiments, the focal point 118 of the beam 116 can be scanned laterally (e.g., along a planar surface of the workpiece 108) by the focusing system 106. For example, the focusing system 106 can include a galvanometer optical scanner, an acousto-optic deflector (AOD), or an electro-optic deflector (EOD), which can be controlled by the process control components 114 to deflect the propagation angle of the laser beam 116. In further embodiments, the laser ablation system 100 can include a stage 120 that can translate in one or more directions. In an exemplary embodiment, the stage 120 can be a three-axis stage that can translate along three orthogonal axes. In some embodiments, the stage 120 can be a six-axis stage that can translate along and rotate about three orthogonal axes. The workpiece 108 can be mounted on a stage 120, and the process control components 114 can scan the focal spot 118 across the surface of the workpiece 108 by controlling the stage 120 to move the workpiece 108 relative to the beam 116.

[0015] The shallow focal depth of the beam 116 provided by the focusing system 106 enables the system 100 to ablate extremely fine features on a workpiece at a precisely controlled depth. In a non-limiting example, the system 100 can selectively ablate a thin film of metal (e.g., less than 2 microns thick) deposited on a plastic substrate without damaging the plastic substrate, even though the power required to ablate the plastic substrate in a given area is much lower than the power required to ablate the metal film. To ablate fine features, an energy density of about 0.1 J / mm per laser pulse is typically required. 2 It requires a pulse width of about 100 nm, which may be higher or lower depending on the absorption of the material being ablated. The total power delivered to the workpiece depends on the total energy per pulse as well as the frequency of the pulses generating the laser beam.

[0016] As the beam 116 propagates away from the focal point 118, the power imparted by the beam 116 to the workpiece 108 decreases. The shallow focal depth imparted to the beam 116 by the focusing system 106 defines an ablation region within which the power imparted by the beam 116 to the workpiece 108 is sufficient to cause ablation of material of the workpiece 108 and outside of which the power imparted by the beam 116 is insufficient to cause ablation of material of the workpiece 108.

[0017] 2, a side view 200 of three beams 202-206 incident on an exemplary workpiece 208 is shown. Within each of the beams 202-206, a respective ablation region 210-214 is defined within which the power imparted by the beam to the material of the workpiece 208 is sufficient to ablate the workpiece 208. Outside of the ablation regions 210-214, the beams 202-206 have insufficient power per unit area to cause ablation of the material of the workpiece 208. As a result, ablation or lack thereof of the workpiece 208 depends on precise control of the location of the focal points of the beams 202-206. The first beam 202 has a focal point 216 located on the surface 218 of the workpiece 208. Thus, the ablation region 210 defined by the first beam 202 extends from the surface 218 into the workpiece 208 to a depth defined by the size of the ablation region 210. In exemplary embodiments, the height h of the ablation region may be 10 microns or less, 5 microns or less, or 1 micron or less.

[0018] As shown in FIG. 2, when the focal point of the beam is located above or below the surface 218 of the workpiece 208, ablation may not occur. For example, the beam 206 has its ablation region 214 located entirely above the surface 218 of the workpiece 208, and therefore the beam 206 has insufficient power per unit area in the workpiece 208 to cause ablation. The beam 204 has its ablation region 212 located entirely below the surface 218 of the workpiece 208. Whether the beam 204 causes ablation of the workpiece 208 depends on the absorption of the beam 204 by the workpiece 208. If the energy of the beam 204 is strongly absorbed by the workpiece 208 before reaching the ablation region 212, the beam 204 may not have enough energy within its normally defined ablation region 212 to actually cause ablation of the workpiece 208. Therefore, it should be understood that depending on other operating factors associated with the laser ablation systems described herein, ablation may or may not occur within the area of ​​the beam defined as the "ablation region."

[0019] From the above, it should be appreciated that precise control of the position of focal point 118 may be desirable in system 100. The laser ablation system may further include a conventional microscope and / or a confocal microscope for feedback control. For example, system 100 may further include a microscope 122. Microscope 122 may be a conventional microscope or a confocal microscope. Collection system 106 may be configured to receive a reflection of beam 116 from workpiece 108 and direct reflected beam 123 to microscope 122. Microscope 122 may include a detector 124 configured to output an indication of the light incident on detector 124 to computing device 102.

[0020] In an exemplary embodiment, the microscope 122 is a conventional microscope and the detector 124 is or can include an imaging sensor, such as a charge-coupled device (CCD) configured to output a two-dimensional image of the surface of the workpiece 108 proximate the focal point 118. In such an embodiment, the process control component 114 can determine a position of the focal point 118 on the workpiece 108 based on the image output by the detector 124 (e.g., by utilizing one or more image recognition algorithms or techniques). The process control component 114 can then control the position of the focal point 118 on or within the workpiece 108 based on the determined position of the focal point 118.

[0021] The process control components 114 can determine the position of the focal spot 118 in the x, y, and z directions. In other words, the process control components 114 can determine the x-y position of the focal spot 118 along the surface of the workpiece 108.

[0022] The process control component 114 can further determine 1) whether the focal point 118 is located on the surface 126 of the workpiece 108, or 2) whether the focal point 118 is located at a height above the surface 126 of the workpiece 108, or at a depth below the surface 126 of the workpiece 108. In an exemplary embodiment, the process control component 114 receives an image of the surface 126 in a region that includes the focal point 118. The image includes a depiction of the incident spot of the beam 116 on the surface 126 of the workpiece 108. The incident spot of the beam 116 is the area of ​​the surface 126 where the beam 116 strikes. When the focal point 118 of the beam 116 is not located on the surface 126 of the workpiece 108, the incident spot of the beam 116 is larger than the focal point 118. The process control component 114 can be programmed with an expected incident spot size at the surface 126 of the workpiece 108. The process control component 114 can determine whether the focal point 118 is located at the surface 126 based on the image of the surface 126 and the expected incident spot size.

[0023] In one example, the process control component 114 can utilize image processing to determine which pixels of the image of the surface 126 represent the incident spot of the beam 116. Based on such determination, the process control component 114 calculates the size of the incident spot. The process control component 114 compares the calculated size of the incident spot to the expected incident spot size. If the calculated size of the incident spot is larger than the expected incident spot size, the process control component 114 determines that the focal point 118 is not located at the surface 126. In response to determining that the focal point 118 is not located at the surface 126, the process control component 114 can control the stage 120, the focusing system 106, and / or the laser 104 to move the focal point 118 to the surface 126 of the workpiece 108.

[0024] It should be understood that the spot where ablation actually occurs (i.e., the ablation spot) may be smaller than the incident spot on the surface 126 of the workpiece 108 due to the non-uniform distribution of power imparted by the beam 116 across the incident spot. In an exemplary embodiment, the ablation spot size may be, for example, less than 2 microns, 1 micron or less, or 500 nanometers or less.

[0025] In another exemplary embodiment, the microscope 122 may be a confocal microscope, and the detector 124 may be configured to output to the computing device 102 an indication of the intensity of the reflected light 123 incident on the detector 124. In an embodiment in which the microscope 122 is a confocal microscope, the light 123 incident on the detector 124 tends to be at a maximum intensity when the focal point 118 is located on the surface of the workpiece 108.

[0026] 3, an exemplary confocal microscope system 300 is shown. The confocal microscope system 300 includes an objective lens 302, a pinhole 304 (e.g., formed in a plate 305), and a detector 306. The objective lens 302 receives light 308 (e.g., reflected light 123) reflected from a surface of the ablation workpiece and collects the light 308 through the pinhole 304. The detector 306 is configured to output a signal indicative of the intensity of the light 308 received by the detector 306.

[0027] When the focal point 118 is located on the surface 126 of the workpiece 108, the reflected light 123 will be collimated after reflecting back through the objective lens of the collection system 106. When the focal point 118 is not located on the surface 126 of the workpiece 108, the reflected light 123 will not be collimated after reflecting back through the objective lens of the collection system 106. The objective lens 302 and pinhole 304 of the confocal microscope system 300 are configured such that when the reflected light 308 is collimated (indicating that the focal point 118 is located on the surface 126 of the workpiece 108), the light 308 is collected through the pinhole 304, such that the light 308 is incident on the detector 306. When the reflected light 308 is not collimated, the light 308 is not suitably collected through the pinhole 304, and the light 308 is substantially prevented from reaching the detector 306 by the pinhole 304. Thus, when the focal point 118 is located on the surface 126 of the workpiece 108, the signal output by the detector 306 is maximized. Referring again to FIG. 1, in an embodiment in which the microscope 122 is a confocal microscope, the process control component 114 may determine that the focal point 118 is at the surface 126 of the workpiece 108 based on the signal output by the detector 124. For example, the process control component 114 may determine that the focal point 118 is at the surface 126 of the workpiece 108 based on the signal output by the detector 124 being maximized. In another example, the process control component 114 may determine that the focal point 118 is within a threshold distance of the surface 126 of the workpiece 108 based on the signal output by the detector 124 being above a threshold indicating that the reflected light 123 is being properly focused through a pinhole filter included in the microscope 122.

[0028] In various exemplary embodiments, system 100 may include microscope 122 and one or more additional microscopes (not shown). For example, microscope 122 may be or include a confocal microscope, and system 100 may further include a conventional microscope. In such embodiments, each of the confocal microscope and the conventional microscope may output data to computing device 102 indicative of a location of focal point 118 on or within workpiece 108.

[0029] In some embodiments, the process control component 114 can maintain the laser 104 in an "on" operational state while reducing the power of the laser 104 to stop ablation by the beam 118. In these embodiments, the microscope 122 continues to receive the reflected light 123 and the process control component 114 can determine the location of the focal spot 118 on or within the workpiece 108 based on the data output by the detector 124.

[0030] A laser ablation system including one or more microscopes may further include a beam splitter or spatial light modulator configured to provide a secondary beam that can be reflected from the workpiece to one or more microscopes to determine the location of the surface of the workpiece. For example, referring now to FIG. 4, another exemplary laser ablation system 400 is shown. The system 400 includes a computing device 102, a laser 104, a focusing system 106, a workpiece 108, a stage 120, and a microscope 122. The system 400 further includes a beam splitter 402 disposed between the laser 104 and the focusing system 106. The laser 104 emits a beam 116 toward the beam splitter 402. In the system 400, the beam 116 serves as a primary beam. The beam splitter 402 splits the primary beam 116 into a secondary beam 404 (e.g., transmitted by the beam splitter) and a tertiary beam 406 (e.g., reflected by the beam splitter 402). The secondary beam 404 is received by the focusing system 106, which focuses the secondary beam 404 to a focal point 118 on or within the workpiece 108.

[0031] The system 400 further comprises a mirror 408 and a second beam splitter 410. The mirror 408 receives the tertiary beam 406 from the first beam splitter 402 and directs the tertiary beam 406 to the second beam splitter 410. The second beam splitter 410 is configured to transmit the tertiary beam 406 towards the workpiece 108. The workpiece 108 reflects at least a portion of the light in the tertiary beam 406 as a reflected tertiary beam 412. The reflected tertiary beam 412 is received by the second beam splitter 410 and directed towards the microscope 122.

[0032] It should be understood that in other embodiments, a secondary light source may be used to determine the position of the surface 126 of the workpiece 108. Referring now to FIG. 5, yet another exemplary laser ablation system 500 is shown. The system 500 includes a computing device 102, a laser 104, a focusing system 106, a workpiece 108, a stage 120, and a microscope 122. The system 500 further includes a secondary light source 502 that emits secondary light 504. The secondary light source 502 may be a laser, or the secondary light source 502 may be another light source, such as a lamp, an LED, etc. The secondary light 504 is incident on the surface 126 of the workpiece 108. The system 500 further includes a beam splitter / mirror 206. The secondary light 504 is reflected from the surface 126 of the workpiece as reflected light 508. The reflected light 508 is directed by the beam splitter / mirror 506 to the microscope 122.

[0033] In some embodiments, the systems 100, 400, 500 can be configured to cause laser ablation within the workpiece 108 rather than at the surface of the workpiece 108. In these embodiments, the systems 100, 400 can create a damage surface in the workpiece 108 along which the workpiece 108 can be fractured to create a desired shape.

[0034] 1 , the workpiece 108 may be substantially transparent to the wavelengths of light present in the beam 116 emitted by the laser 104. The focusing system 106 may be configured to focus the beam 116 such that the focal point 118 is within the bulk of the workpiece 108 rather than at the surface of the workpiece 108. Until the beam 116 reaches the focal point 118, individual photons may have insufficient energy to cause ablation. At the focal point 118, the intensity of the beam 116 is high enough that multiphoton absorption (MPA) occurs and material is ablated at the focal point 118.

[0035] In embodiments in which the focal spot 118 is located within the bulk of the workpiece 108, it may be difficult to determine the location of the focal spot 118 such that the workpiece 108 is ablated in a desired manner. In these embodiments, the process control component 114 may reduce the power of the laser 104 below the ablation threshold of the workpiece 108. The process control component 114 may identify (e.g., based on the output of the detector 124 of the microscope 122) the location where the focal spot 118 is located on the surface of the workpiece 108. The process control component 114 may then control one or more of the collection system 104 or the stage 120 to move the focal spot a known distance in one or more directions to reach the desired ablation location within the workpiece 108.

[0036] In some embodiments, the laser ablation system may include optical elements configured to split the primary beam into multiple secondary beams, each of which performs ablation of the workpiece 108. By way of example, and referring now to FIG. 6, another exemplary laser ablation system 600 is shown. The system 600 includes a computing device 102, a laser 104, a workpiece 108, and a stage 120. The system 600 further includes a beam splitter 602, a focusing system 604, and a microscope 606. The process control component 114 of the computing device 102 controls the operation of the laser 104 as described above. The laser 104 emits a primary beam 608 toward the beam splitter 602. The beam splitter 602 splits the primary beam 608 into a plurality of N secondary beams 610-614, where N is a positive integer. The beam splitter can be or include any of a variety of optical components that can be collectively configured to split the primary beam 608 into multiple secondary beams 610-614. By way of example and not limitation, the beam splitter 602 can be or include a diffraction grating, a digital micromirror device (DMD), a holographic beam splitter, etc.

[0037] The secondary beams 610-614 are received by the focusing system 604 and each focused to a respective focal point on the workpiece 608. The focusing system 604 may be or include any of a variety of optical elements capable of receiving the multiple secondary beams 610-614 and focusing the beams to respective focal points on the workpiece 608. According to one example, the focusing system 604 may comprise a microlens array including a lens corresponding to each of the secondary beams 610-614. In such an embodiment, the beam splitter 602 may be configured to direct each of the beams 610-614 to a respective lens in the microlens array.

[0038] The laser 104 can be configured such that the primary beam 608 is sufficiently intense that each of the secondary beams 610-614 carries sufficient power to ablate the workpiece 108 at its focal point. Thus, each of the secondary beams 610-614 causes ablation at a different location on or within the workpiece.

[0039] The collection system 604 can be configured to direct the beams reflected from the surface of the workpiece 108 back towards the beam splitter 602. The beam splitter 602 can include one or more components configured to direct such reflections towards the microscope 606. Thus, the microscope 606 can receive multiple reflected beams 616-620. In various embodiments, the reflected beams 616-620 can be reflections of the secondary beams 610-614 from the surface of the workpiece 608. In other embodiments, the reflected beams 616-620 can be reflections of beams different than the secondary beams 610-614 used to perform the ablation of the workpiece 108. For example, the collection system 604 and / or the beam splitter 602 can include components similar to the beam splitters and mirrors 402, 408, 410 shown in FIG. 4. In another example, the system 600 can be modified to include secondary light sources and secondary optics similar to those described above with respect to FIG. 5. The detector 622 included in the microscope 606 can be configured to output data indicative of each of the reflected beams 616-620 to the computing device 102. Such data can be utilized by the process control component 114 for alignment and control purposes as described above. In an exemplary embodiment, the detector 622 can include multiple detectors, each of which receives light from a respective one of the reflected beams 616-620. In such an embodiment, the microscope 606 can be configured with separate collection optics for each of the reflected beams 616-620. For example, when the microscope 606 is a confocal microscope, the microscope 606 can include a respective pinhole aperture through which each of the beams 616-620 passes before hitting the detector 622.

[0040] In some embodiments, the collection system 604 may include a separate optical collection channel for each of the secondary beams 610-614. However, in various embodiments, the collection system 604 may include one or more optical components shared by the secondary beams 610-614. Stated differently, the secondary beams 610-614 may all be incident on a common optical component included in the collection system 604. Since each of the secondary beams 610-614 must be of sufficient intensity to cause ablation, the combined power of the secondary beams 610-614 may be sufficient to cause damage to the common optical component. Furthermore, within the bulk of the workpiece 108, the beams 610-614 may be close enough to each other to overlap away from their respective focal points.

[0041] For example, referring now to Figure 7, a cross-sectional view 700 of a workpiece 702 is shown in which a first laser beam 704 and a second laser beam 706 overlap within the workpiece 702. The first laser beam 704 has a focal point 708 where the intensity of the beam 704 is sufficient to cause ablation. The second laser beam 706 has a focal point 712 where the intensity of the beam 706 is sufficient to cause ablation. Thus, the beams 704, 706 cause ablation at the focal points 708, 712.

[0042] The laser beams 704, 706 overlap in a region 724 within the bulk of the workpiece 702. Although each of the beams 704, 706 may not individually have sufficient intensity to cause ablation, except at their respective focal points 708, 712, within the region 724, the overlap of the beams 704, 706 may provide sufficient intensity for ablation to occur. Thus, ablation of the workpiece 702 may also occur in the overlap region 724 of the beams 704, 706, even though it is desired that ablation occur only near the focal points 708, 712. Thus, when the beams 704, 706 are sufficiently close to each other, ablation may occur at unintended locations within the workpiece 702.

[0043] Various approaches can be utilized to mitigate these effects. Referring again to FIG. 6, to avoid unintended ablation in the bulk of the workpiece 108, the focusing system 604 can include a DMD that can selectively deflect one or more of the secondary beams 610-614 away from the workpiece 108. The process control component 114 can be configured to control the DMD so that the beams 610-614 do not overlap in the workpiece 108. In various embodiments, the process control component 114 can selectively deflect the secondary beams 610-614 to precisely control the geometry of the ablated features either in the workpiece 108 or on the surface of the workpiece 108. Furthermore, each of the beams 610-614 can strike multiple elements of the DMD. Thus, the process control component 114 can reduce the intensity of one or more of the beams 610-614 at the workpiece 108 by selectively deflecting a portion of the beam by a subset of the multiple elements of the DMD on which the beam strikes.

[0044] In a further example, the beam splitter 602 and / or collection system 604 can be configured to direct the beams 610-614 to positions at a distance at least as large as the maximum width of the beams 610-614 in the workpiece 108. In a non-limiting illustrative example, the beam 610 can be the widest of the beams 610-614 having a maximum width x1 in the workpiece 108. The process control component 142 can be configured to prevent any of the other beams 612-614 from simultaneously irradiating any position within the distance x1 of the beam 610. The width of each of the beams 610-614 in the workpiece 108 can depend on the focal depth of each of the beams 610-614 in the workpiece 108.

[0045] In further exemplary embodiments, the focusing system 604 may include an afocal system configured such that each of the secondary beams 610-614 traverses a different path length to reach their respective focal points. By way of example and not limitation, the afocal system may include a first beam expander that expands and spatially separates the beams 610-614. The afocal system may further include a second beam expander that returns the beams 610-614 to their original spatial arrangement. The beams 610-614 traverse different path lengths to their respective focal points due to the expansion of the beams 610-614 by the beam expander. In embodiments in which the laser 104 is a pulsed laser (e.g., a femtosecond laser), the peak intensities of each of the secondary beams 610-614 are offset in time from one another in a common optical component due to the different path lengths traversed by the secondary beams 610-614. Stated another way, the peak intensity of the first beam 610 may reach the common optical element at a first time, the peak intensity of the second beam 612 may reach the common optical element at a second time, and so on until the peak intensity of the Nth beam 614 reaches the common optical element at an Nth time. Thus, the common optical element does not receive the peak intensity of the primary beam 608. Furthermore, referring again to FIG. 7, although the combined intensity of beams 704, 706 in region 724 may be insufficient to cause ablation due to the temporal offset of beams 704, 706, beams 704, 706 maintain sufficient intensity at their focal points 708, 712 for beams 704, 706 to cause ablation.

[0046] In some embodiments, the ablation surface can be placed in a liquid to reduce redeposition of ablated material. By way of example, referring now to FIG. 8, another exemplary ablation system 800 is shown. The ablation system 800 includes a computing device 102, a laser 104, a collection system 106, a workpiece 108, a stage 120, and a microscope 122. The system 800 further includes a tank 802 that contains a liquid 804. The workpiece 108 and the stage 120 can be disposed within the tank 802 such that the workpiece 108 is submerged in the liquid 804. The liquid 804 can be substantially transparent to the beam 116 such that the beam 116 propagates through the liquid 804 to the surface of the workpiece 108. The liquid 804 can prevent the ablated material from being blown away toward the optical elements of the collection system 106. Additionally, the system 800 can include an acoustic wave generator 806 configured to propagate acoustic waves 808 through the liquid 804. The acoustic waves 808 can help prevent ablated material from redepositing on the surface of the workpiece 108 and can also help clean ablated material from high aspect ratio features ablated in the workpiece 108 by the beam 116. The acoustic wave generator 806 can be configured to generate ultrasonic waves (e.g., waves having a frequency between about 20 kHz and about 200 kHz) or megasonic waves (e.g., waves having a frequency between about 500 kHz and about 2 MHz).

[0047] In various embodiments described herein, the process control component 114 can control any of the systems 100, 400, 500, 600, 800 to create complex three-dimensional features on a non-planar surface of the workpiece 108. In a non-limiting example, referring again to FIG. 6, the process control component 114 can receive data from the detector 622 indicative of the three-dimensional surface of the workpiece 108 either during ablation with the secondary beams 610-614 or during pauses in ablation when the intensities of the beams 610-614 are kept low enough so that ablation does not occur. For example, the detector 622 can output data indicative of the depth of a point on the surface of the workpiece 608 at which each of the reflected beams 616-620 was received. In a further embodiment, the detector 622 can output an image of the ablated surface of the workpiece 108. Based on the depth of the spot and the image of the ablated surface, the process control component 114 can determine an approximate surface contour of the ablated surface of the workpiece 108 and the location of the focal points of the ablation beams 610-614 on the ablated surface. The process control component 114 can then control the operation of the beams 610-614 (e.g., by selectively turning the beams on or off using the beam splitter 602 or the DMD included in the focusing system 604) to cause the beams 610-614 to ablate complex three-dimensional micro-scale features of the non-planar surface of the workpiece 108.

[0048] 9, an exemplary method 900 for selective laser ablation is shown. Although the method is shown and described as a series of acts performed in a sequence, it should be understood and appreciated that the method is not limited by the order of the sequence. For example, some acts can occur in a different order than described herein. In addition, any act can occur simultaneously with another act. Furthermore, in some examples, not all acts may be required to practice a method described herein.

[0049] Additionally, the acts described herein may be computer-executable instructions that may be performed by one or more processors and / or stored on one or more computer-readable media. Computer-executable instructions may include routines, subroutines, programs, threads of execution, and / or the like. Additionally, results of the acts of the methods may be stored on a computer-readable medium, displayed on a display device, and / or the like.

[0050] Method 900 begins at 902 with light being emitted by a laser at 904. The laser may be, for example, a pulsed femtosecond laser. At 906, the light emitted by the laser is focused by a focusing system to a focal point on the workpiece that is desirably to be ablated. The focusing system focuses the light to the focal point such that ablation occurs at the focal point. The focusing system may focus the light to the focal point such that the size of the ablation spot (e.g., centered on the focal point) is less than 2 microns in diameter. At 908, method 900 ends.

[0051] Referring now to FIG. 10, there is shown a high level diagram of an exemplary computing device 1000 that may be used in accordance with the systems and methods disclosed herein. For example, the computing device 1000 may be used to control the operation of a system for laser ablation (e.g., system 100, system 400, system 500, system 600, or system 800). The computing device 1000 includes at least one processor 1002 that executes instructions stored in a memory 1004. The instructions may be, for example, instructions for performing a function described as being performed by one or more components described above, or instructions for performing one or more of the methods described above. The processor 1002 may access the memory 1004 via a system bus 1006. In addition to storing executable instructions, the memory 1004 may also store images of a workpiece, a computer-implemented definition of a pattern to be ablated from the workpiece, various ablation process parameters, and the like.

[0052] The computing device 1000 further includes a data store 1008 accessible by the processor 1002 via the system bus 1006. The data store 1008 may include executable instructions, computer-implemented ablation pattern definitions, and the like. The computing device 1000 also includes an input interface 1010 that allows an external device to communicate with the computing device 1000. For example, the input interface 1010 may be used to receive instructions from an external computing device, a user, and the like. The computing device 1000 also includes an output interface 1012 that couples the computing device 1000 with one or more external devices. For example, the computing device 1000 may display text, images, and the like via the output interface 1012.

[0053] It is contemplated that external devices communicating with the computing device 1000 via the input interface 1010 and the output interface 1012 may be included in an environment that provides virtually any type of user interface with which a user may interact. Examples of types of user interfaces include graphical user interfaces, natural user interfaces, and the like. For example, a graphical user interface may accept input from a user utilizing input devices such as a keyboard, mouse, remote control, and provide output to an output device such as a display. Furthermore, a natural user interface may enable a user to interact with the computing device 1000 in a manner that is not subject to the constraints imposed by input devices such as a keyboard, mouse, remote control, and the like. Rather, a natural user interface may rely on voice recognition, touch and stylus recognition, gesture recognition both on and adjacent to the screen, air gestures, head and eye tracking, voice and speech, vision, touch, gestures, machine intelligence, and the like.

[0054] Moreover, although shown as a single system, it should be understood that computing device 1000 may be a distributed system, such that, for example, several devices may communicate over network connections and collectively perform the tasks described as being performed by computing device 1000.

[0055] Various functions described herein may be implemented in hardware, software, or any combination thereof. If implemented in software, the functions may be stored on or transmitted over as one or more instructions or code on a computer-readable medium. A computer-readable medium includes a computer-readable storage medium. A computer-readable storage medium may be any available storage medium that can be accessed by a computer. By way of example, and not limitation, such computer-readable storage media may comprise RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium that can be used to carry or store desired program code in the form of instructions or data structures and that can be accessed by a computer. As used herein, disk and disc include compact disc (CD), laser disc, optical disc, digital versatile disc (DVD), floppy disk, and Blu-ray disc (BD), where disks typically reproduce data magnetically and discs typically reproduce data optically using a laser. Additionally, propagated signals are not included within the scope of computer-readable storage media. Computer-readable media also includes communication media, which includes any medium that facilitates transfer of a computer program from one place to another. A connection may be, for example, a communication medium. For example, if the software is transmitted from a website, server, or other remote source using coaxial cable, fiber optic cable, twisted pair, digital subscriber line (DSL), or wireless technologies such as infrared, radio, and microwave, the coaxial cable, fiber optic cable, twisted pair, DSL, or wireless technologies such as infrared, radio, and microwave are included in the definition of communication media. Combinations of the above should also be included within the scope of computer-readable media.

[0056] Alternatively or additionally, the functionality described herein may be implemented, at least in part, by one or more hardware logic components. For example, and without limitation, illustrative types of hardware logic components that may be used include Field-programmable Gate Arrays (FPGAs), Program-specific Integrated Circuits (ASICs), Program-specific Standard Products (ASSPs), System-on-a-chip systems (SOCs), Complex Programmable Logic Devices (CPLDs), etc.

[0057] Systems and methods are disclosed herein according to at least the following examples.

[0058] (A1) In one aspect, a method for laser ablation includes emitting light by a laser. The method also includes focusing the light emitted by the laser to a focal point on a surface of a workpiece by a focusing system, whereby the focused light causes ablation of the workpiece within an ablation spot having a diameter of less than 2 microns at the surface of the workpiece.

[0059] In some embodiments of the method of (A2)(A1), the focused light includes a beam that defines an ablation region, within the ablation region, the beam has sufficient intensity to cause ablation of material of the workpiece, and outside the ablation region, the beam does not have sufficient intensity to cause ablation of material.

[0060] (A3) In some embodiments of the method of (A2), the ablated region has a height along the beam of 10 microns or less.

[0061] (A4) In some embodiments of at least one of the methods of (A1)-(A3), the light collection system has a numerical aperture of 0.15 or greater.

[0062] (A5) In some embodiments of at least one of the methods of (A1)-(A4), the method also includes determining a position of the focal spot relative to a surface of the workpiece. The method further includes moving the position of the focal spot based on the determined position of the focal spot relative to the surface such that ablation continues to occur on the surface.

[0063] In some embodiments of the method of (A6)(A5), determining the position of the focal point relative to the surface is performed while the focused light is ablating the workpiece.

[0064] (B1) In another aspect, a laser ablation system includes a laser, a focusing system, and a computing device configured to perform acts including controlling operation of the laser and the focusing system such that the laser emits light focused by the focusing system to a focal point on a surface of a workpiece, the focused light causing ablation of the workpiece within an ablation spot having a diameter of less than 2 microns on the surface of the workpiece.

[0065] (B2) In some embodiments of the laser ablation system of (B1), the collection system has a numerical aperture for the collected light of 0.15 or greater.

[0066] (B3) In some embodiments of at least one of the laser ablation systems of (B1)-(B2), the diameter of the ablation spot is a first diameter and the focal point has a second diameter, the second diameter being larger than the first diameter.

[0067] (B4) In some embodiments of at least one of the laser ablation systems of (B1)-(B3), the laser ablation system further comprises a beam splitter that receives light emitted by the laser and splits the light into a plurality of beams, and a focusing system that receives the plurality of beams and focuses the beams to a plurality of respective focal points on the surface of the workpiece, whereby ablation occurs at the plurality of respective focal points and the focal points are included within the plurality of respective focal points.

[0068] In some embodiments of the laser ablation system of (B5)(B4), the laser is a pulsed laser. Further, the acts also include controlling at least one of the laser, a beam splitter, or a focusing system such that the beams in the plurality of beams are offset in time from one another.

[0069] (B6) In some embodiments of the laser ablation system of at least one of (B4)-(B5), the multiple beams are spaced apart such that the beams do not overlap within the body of the workpiece.

[0070] (B7) In some embodiments of at least one of the laser ablation systems of (B1)-(B6), the focused light includes a light beam, the light beam defining an ablation region where an intensity of the light beam is sufficient to cause ablation of the workpiece, and the ablation region has a height of less than 10 microns.

[0071] (B8) In some embodiments of at least one of the laser ablation systems of (B1)-(B7), the laser ablation system further includes a confocal microscope system. The confocal microscope system includes an objective lens that receives light reflected from the surface of the workpiece at a focal point. The confocal microscope system also includes a pinhole through which the objective lens focuses the light reflected from the surface of the workpiece. The confocal microscope system further includes a detector configured to receive light passing through the pinhole and output a signal indicative of the light impinging on the detector.

[0072] In some embodiments of the laser ablation system of (B9)(B8), the act further includes determining, based on the signal output by the detector, that the focus of the focused light is within a threshold distance of a surface of the workpiece.

[0073] (B10) In some embodiments of at least one of the laser ablation systems of (B1)-(B9), the laser ablation system also includes an imaging sensor, and the focusing system is further configured to receive light reflected from the surface of the workpiece at the focal point and focus the reflected light on the imaging sensor such that the imaging sensor outputs an image of the surface of the workpiece. The act also includes calculating a size of the focal point based on the image of the surface of the workpiece. The act further includes determining that the focal point is incident on the surface of the workpiece based on the calculated size of the focal point.

[0074] (B11) In some embodiments of the laser ablation system of at least one of (B1)-(B10), the focusing system is configured such that ablation of the workpiece does not occur at a depth greater than 5 microns from the position of the focal point.

[0075] (C1) In yet another aspect, a system for laser ablation includes a laser, a beam splitter, a focusing system, and a computing device configured to perform acts including controlling operation of the laser, the beam splitter, and the focusing system such that the laser emits a first light beam that is received by the beam splitter, such that the beam splitter splits the first light beam into a plurality of secondary light beams that are focused by the focusing system to respective focal points on a surface of a workpiece, and the focused light causes ablation of the workpiece within the focal points and respective ablation spots, each having a diameter less than 2 microns.

[0076] (C2) In some embodiments of the system of (C1), the beam splitter includes a digital micromirror device (DMD), the focusing system includes a microlens array, and the computing device controls operation of the DMD such that each of the secondary beams is directed to a respective lens in the microlens array.

[0077] (C3) In some embodiments of at least one of the systems of (C1)-(C2), the light collection system has a numerical aperture of at least 0.15.

[0078] (D1) In another embodiment, a laser ablation system is configured to carry out at least one of the methods disclosed herein (e.g., any of methods (A1)-(A6)).

[0079] (E1) In yet another aspect, the present specification discloses the use of any of the systems described herein (e.g., any of the systems (B1)-(B11) or (C1)-(C3)).

[0080] (F1) In yet another aspect, the present specification discloses a method of making any of the systems described herein (e.g., any of the systems (B1)-(B11) or (C1)-(C3)).

[0081] The above description includes examples of one or more embodiments. Of course, it is not possible to describe every conceivable modification and variation of the above-described device or method for the purposes of describing the foregoing aspects, but one skilled in the art can recognize that many further modifications and substitutions of the various aspects are possible. Accordingly, the described aspects are intended to encompass all such changes, modifications, and variations that fall within the spirit and scope of the appended claims. Moreover, to the extent that the term "include" is used in either the detailed description or the claims, such term is intended to be as inclusive as the term "comprising," in the same manner that "comprising" is interpreted when used as a transitional term in the claims.

Claims

1. 1. A laser ablation system comprising: A laser, A light collecting system; a computing device configured to perform acts including controlling operation of the laser and the focusing system such that the laser emits light focused by the focusing system to a focal point on a surface of a workpiece, the focused light causing ablation of the workpiece within an ablation spot having a diameter of less than 2 microns on the surface of the workpiece; and A laser ablation system comprising:

2. 10. The laser ablation system of claim 1, wherein the focusing system has a numerical aperture for the focused light of 0.15 or greater.

3. 2. The laser ablation system of claim 1, wherein the diameter of the ablation spot is a first diameter and the focal spot has a second diameter, the second diameter being greater than the first diameter.

4. 2. The laser ablation system of claim 1, further comprising a beam splitter that receives the light emitted by the laser and splits the light into a plurality of beams, and a focusing system that receives the plurality of beams and focuses the beams to a plurality of respective focal points on the surface of the workpiece, whereby ablation occurs at the plurality of respective focal points and the focal points are included within the plurality of respective focal points.

5. the laser is a pulsed laser, and the act of:

5. The laser ablation system of claim 4, further comprising controlling at least one of the laser, the beam splitter, or the focusing system such that beams in the plurality of beams are offset in time from one another.

6. The laser ablation system of claim 4 , wherein the multiple beams are spaced apart such that the beams do not overlap within the body of the workpiece.

7. 2. The laser ablation system of claim 1, wherein the focused light comprises a light beam, the light beam defining an ablation region where an intensity of the light beam is sufficient to cause ablation of the workpiece, the ablation region having a height of less than 10 microns.

8. The confocal microscope system further comprises: an objective lens that receives light reflected from the surface of the workpiece at the focal point; a pinhole through which the objective lens focuses the light reflected from the surface of the workpiece; a detector configured to receive light passing through the pinhole and output a signal indicative of the light impinging on the detector; The laser ablation system of claim 1 , comprising:

9. 9. The laser ablation system of claim 8, wherein the acts further comprise determining, based on the signal output by the detector, that the focal point of the focused light is within a threshold distance of the surface of the workpiece.

10. and an imaging sensor, the light collection system further configured to receive light reflected from the surface of the workpiece at the focal point and to collect the reflected light onto the imaging sensor such that the imaging sensor outputs an image of the surface of the workpiece, the act of: calculating a size of the focal spot based on the image of the surface of the workpiece; 10. The laser ablation system of claim 1, further comprising: determining that the focal spot is incident on the surface of the workpiece based on the calculated size of the focal spot.

11. The system of claim 1 , wherein the focusing system is configured such that no ablation of the workpiece occurs at a depth greater than 5 microns from the location of the focal point.

12. 1. A method for laser ablation, comprising: emitting light with a laser; focusing the light emitted by the laser to a focal point on a surface of a workpiece with a focusing system, whereby the focused light causes ablation of the workpiece within an ablation spot having a diameter of less than 2 microns at the surface of the workpiece.

13. 13. The method of claim 12, wherein the focused light comprises a beam defining an ablation region, within the ablation region, the beam has sufficient intensity to cause ablation of material of the workpiece, and outside the ablation region, the beam does not have sufficient intensity to cause ablation of the material.

14. The method of claim 13 , wherein the ablated region has a height along the beam of 10 microns or less.

15. The method of claim 12 , wherein the light collection system has a numerical aperture of 0.15 or greater.

16. determining a position of the focal point relative to the surface of the workpiece; moving the position of the focal spot based on the determined position of the focal spot relative to the surface such that ablation continues to occur on the surface. The method of claim 12 further comprising:

17. The method of claim 16 , wherein the step of determining the position of the focal point relative to the surface is performed while the focused light is ablating the workpiece.

18. 1. A system for laser ablation, comprising: A laser, A beam splitter; A light collecting system; and a computing device configured to perform acts including controlling operation of the laser, the beam splitter, and the focusing system such that the laser emits a first light beam that is received by the beam splitter, such that the beam splitter splits the first light beam into a plurality of secondary light beams that are focused by the focusing system to respective focal points on a surface of a workpiece, and the focused light causes ablation of the workpiece within the focal points and respective ablation spots, each having a diameter of less than 2 microns.

19. 20. The system of claim 18, wherein the beam splitter comprises a digital micromirror device (DMD), the focusing system comprises a microlens array, and the computing device controls operation of the DMD such that each of the secondary beams is directed to a respective lens in the microlens array.

20. 20. The system of claim 18, wherein the light collection system has a numerical aperture of at least 0.15.

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