Laser processing apparatus including a beam analysis system and method for measuring and controlling beam characteristics

Abstract

Numerous embodiments of a laser processing apparatus are disclosed. In one embodiment, the laser processing apparatus includes a laser source operative to generate a beam of laser energy, an acousto-optic deflector (AOD) disposed in the beam path, a controller coupled to the AOD, and a beam analysis system operative to measure characteristics of the beam, generate measurement data representative of the beam characteristics, and transmit the measurement data to the controller operative to control operation of the AOD based on the measurement data. In another embodiment, the laser processing apparatus includes a system for characterizing cross-axis fluctuations of a galvanometer mirror, the system including a reference laser source configured to emit a reference laser beam, and a reflective surface formed on the galvanometer mirror and configured to reflect the reference laser beam to a sensor configured to output a signal representative of a position of the reference beam to the controller.

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of U.S. Provisional Patent Application No. 63 / 213,075, filed June 21, 2021, the contents of which are incorporated by reference in their entirety. [Background technology]

[0002] Technical Field TECHNICAL FIELD The embodiments described herein relate generally to laser processing devices, and more particularly to acousto-optic deflectors (AODs), their components, and techniques for operating the same, for processing a workpiece.

[0003] background Laser processing systems or devices are used in a wide variety of applications including printed circuit board (PCB) machining, additive manufacturing, and the like. For processing PCBs, precise control of ablation of PCB materials (e.g., metal, insulator, that used for via formation, etc.) is required, for example, when laser processing is used to form holes or vias. In some applications, it can be difficult to control the operation of the AOD used to diffract the laser processing beam while processing the workpiece. In particular, changes in laser spot size by chirping the AOD can be difficult to control, and characterization of the processing beam can be time consuming and may not provide the precise control required. To ensure proper / correct AOD chirp, precise timing of the laser pulse and acoustic wavefront as it passes through the AOD is required. Inaccurate timing between the control command for the AOD and the laser source can cause poor spot position displacement and poor spot quality, reducing the accuracy and feature quality of the entire system. Closed-loop control of this timing can improve overall system performance, including throughput and productivity. It is in light of these and other problems discovered by the inventors that the embodiments described herein were developed. Summary of the Invention [Means for solving the problem]

[0004] overview One embodiment of the present disclosure relates to what may be characterized as a laser processing apparatus including a laser source operative to generate a laser energy beam propagating along a beam path, an acousto-optic deflector (AOD) disposed in the beam path and operative to diffract the laser energy beam, a controller coupled to the AOD, and a beam analysis system operative to measure one or more characteristics of the laser energy beam, generate measurement data representative of the one or more measured beam characteristics, and transmit the measurement data to the controller operative to control operation of the AOD based at least in part on the measurement data.

[0005] Another embodiment of the present disclosure relates to a method of controlling laser beam characteristics, comprising generating a laser energy beam, directing (using an AOD) the laser energy beam along a beam path to a beam analysis system, measuring (using the beam analysis system) one or more characteristics of the laser energy beam, generating measurement data representative of the one or more measured beam characteristics, transmitting the measurement data from the beam analysis system to a controller, and outputting a control command from the controller to the AOD based at least in part on the measurement data.

[0006] Another embodiment relates to a method of controlling laser beam characteristics, comprising generating a laser energy beam, directing the laser energy beam along a beam path to a beam analysis system using at least one selected from the group consisting of a first AOD and a second AOD, measuring one or more characteristics of the laser energy beam (using the beam analysis system), generating measurement data representative of the one or more measured beam characteristics, transmitting the measurement data from the beam analysis system to a controller, and outputting a control command from the controller to at least one of the first AOD and the second AOD based on at least a portion of the measurement data of at least one of the first AOD and the second AOD.

[0007] Another embodiment relates to a method of controlling a laser beam characteristic that includes generating a laser energy beam, directing (with an AOD) the laser energy beam along a beam path to a beam analysis system, the AOD operative to change a first characteristic of the laser energy beam thereby changing a second characteristic of the laser energy beam, measuring the second beam characteristic using the beam analysis system, generating measurement data representative of the measured second beam characteristic, transmitting the measurement data from the beam analysis system to a controller, and then transmitting a control command from the controller to the AOD operative to reduce a magnitude of the change in the second beam characteristic based at least in part on the measurement data.

[0008] Another embodiment of the present disclosure relates to a method of generating a plurality of laser pulses based on control commands sent from the controller to the laser source during a measurement step, generating an acoustic signal in the AOD based on AOD control commands sent from the controller to the AOD, the acoustic signal being configured to diffract at least one laser pulse of the plurality of laser pulses, measuring at least one characteristic of the plurality of diffracted laser pulses, adjusting a timing offset between the control commands and the AOD control commands during the measurement, generating measurement data representative of the at least one measured characteristic of each diffracted laser pulse, correlating at least one of the measurement data with a timing offset associated with each diffracted laser pulse, and then, during a workpiece processing step, generating a laser pulse and generating an acoustic signal in the AOD configured to diffract at least one laser pulse of the plurality of laser pulses, directing the at least one diffracted laser pulse at the workpiece, wherein the timing offset between the laser control commands and the AOD control commands corresponds to a timing offset that is correlated with the measurement data in the measurement step and has a predetermined relationship to the reference characteristic.

[0009] Another embodiment of the present disclosure relates to a method of, during a measurement step, generating a laser energy beam, generating an acoustic signal configured to diffract the laser energy beam into the AOD, measuring at least one characteristic of the diffracted laser energy beam, generating measurement data representative of the at least one measured characteristic of the diffracted laser energy beam, correlating at least one of the measurement data with a reference value of one or more system operating parameters associated with the diffracted laser energy beam, and subsequently, during a workpiece processing step, generating an acoustic signal configured to diffract the laser energy beam into the AOD and directing the laser energy beam to the workpiece, wherein the characteristic of the laser energy beam corresponds to at least one reference value of the system operating parameter correlated with the measurement data in the measurement step and having a predetermined relationship with the characteristic of the laser energy beam.

[0010] Another embodiment of the present disclosure relates to a method of correcting laser beam astigmatism, generating a laser energy beam, directing the laser energy beam along a beam path to a beam analysis system using a first AOD, measuring beam astigmatism of the laser energy beam using the beam analysis system, generating measurement data representative of the measured beam astigmatism of the laser energy beam using the beam analysis system, transmitting the measurement data to a controller, and outputting control commands from the controller to the second AOD operative to operate the second AOD to correct the measured beam astigmatism.

[0011] Another embodiment of the present disclosure relates to a system for characterizing cross-axis fluctuations of a galvanometer mirror, comprising a reference laser source configured to emit a reference laser beam, a reflective surface formed on the galvanometer mirror and configured to reflect the reference laser beam as a reflected beam, and an auxiliary sensor configured to receive the reflected beam at a reference spot and output a signal representative of a position of the reference spot to a controller.

[0012] Another embodiment of the present disclosure relates to a method for compensating for cross-axis wobble of a galvanometer mirror, comprising: emitting a reference laser beam from a reference laser source, the reference laser beam being incident on a reflective surface formed on a galvanometer mirror; receiving the laser beam reflected at a reference spot; and detecting the reflected laser beam using an auxiliary sensor configured to output a signal representative of the position of the reference spot to a controller; the controller receiving the signal representative of the position of the reference spot, calculating a compensation value for the cross-axis wobble, and outputting a command to the AOD system to compensate for the cross-axis wobble to operate the AOD system.

[0013] Another embodiment of the present disclosure relates to a beam analysis system comprising a token having a reflective surface configured to reflect at least a portion of an incident primary beam propagating along a beam path, and a plurality of apertures formed in the reflective surface, the token being formed of a material that is more transparent to the laser energy beam than the reflective surface, and further comprising a photodetector assembly positioned optically downstream of the token.

[0014] Another embodiment of the present disclosure relates to a laser processing apparatus including a laser source operative to generate a beam of laser energy propagating along a beam path, an acousto-optic deflector (AOD) disposed in the beam path operative to deflect the beam passing therethrough in a first direction, a galvanometer mirror operative to deflect the beam passing therethrough in a second direction different from the first direction, and a controller coupled to the AOD and the galvanometer mirror operative to control operation of the galvanometer mirror to induce cross-axis fluctuations in the galvanometer mirror and to control operation of the AOD to correct the cross-axis fluctuations. [Brief description of the drawings]

[0015] [Figure 1] FIG. 1 is a schematic diagram of a laser processing apparatus according to an embodiment. [Diagram 2] FIG. 2 shows a schematic of a control diagram for an acousto-optic deflector according to one embodiment. [Diagram 3-4] 3 and 4 illustrate schematics of an exemplary characterization of a laser energy beam using a beam analysis system, according to one embodiment. [Diagram 5] FIG. 5 illustrates a schematic of an exemplary beam characterization tool according to one embodiment. [Figure 6] FIG. 6 shows a plan view of a token for use with the embodiment of the beam characterization tool in FIG. [Figure 7] FIG. 7 illustrates a schematic of an exemplary apparatus for measuring vibration modes of a galvanometer shaft according to one embodiment. [Figure 8]FIG. 8 illustrates a diagram of a photodiode configured to measure a reflected laser energy beam according to one embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] Detailed Description Hereinafter, examples of embodiments will be described with reference to the accompanying drawings. Unless explicitly stated, in the drawings, the sizes, positions, etc. of components, features, elements, etc. and the distances therebetween are not necessarily to scale and are exaggerated for ease of understanding. Like numbers refer to like elements throughout the drawings. Thus, the same or similar numbers may be described with reference to other drawings even if they are not mentioned or described in the corresponding drawings. Also, elements without reference numbers may be described with reference to other drawings.

[0017] The terms used in the specification are for the purpose of describing certain exemplary embodiments only and are not intended to be limiting. Unless otherwise defined, all terms (including technical and scientific terms) used in this specification have the same meaning as commonly understood by one of ordinary skill in the art. As used herein, the singular is intended to include the plural unless the content clearly indicates otherwise. Furthermore, it should be understood that the terms "comprises" and / or "comprising", when used herein, specify the presence of the stated features, integers, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof. Unless otherwise indicated, when a range of values ​​is described, the range includes the upper and lower limits as well as any subranges between the upper and lower limits of the range. Unless otherwise indicated, terms such as "first" and "second" are only used to distinguish elements from one another. For example, one node can be referred to as a "first node" and similarly another node can be referred to as a "second node" or vice versa.

[0018] Unless otherwise indicated, "about," "around," and the like mean that amounts, sizes, formulations, parameters, and other quantities and characteristics are not and need not be exact, but may be approximate and / or larger or smaller, as appropriate, or to reflect tolerances, conversion factors, rounding, measurement errors, and the like, and other factors known to those of skill in the art. Spatially relative terms such as "lower," "below," "lower side," "upper," and "above" may be used herein for ease of description in describing the relationship of an element or feature to another element or feature, as depicted in the figures. It should be understood that the spatially relative terms are intended to include different orientations in addition to those depicted in the figures. For example, an element described as being "lower" or "below" another element or feature would be oriented "above" the other element or feature if the object in the figure were inverted. Thus, the exemplary term "lower" may include both an upper and lower orientation. If the object is otherwise oriented (e.g., rotated 90 degrees or at another orientation), the spatially relative descriptors used herein may be interpreted accordingly.

[0019] Section headings used herein, unless specifically noted, are for organizational purposes only and should not be construed as limiting the subject matter described. It will be understood that many different forms, embodiments, and combinations are possible without departing from the spirit and teachings of the present disclosure, and the present disclosure should not be construed as being limited to the example embodiments described herein. Rather, these examples and embodiments are provided so that this disclosure will be complete and all-inclusive, and will fully convey the scope of the disclosure to those skilled in the art.

[0020] I. System Overview FIG. 1 is a schematic diagram showing a laser processing apparatus according to an embodiment of the present invention.

[0021] 1, a laser processing apparatus 100 (also referred to herein simply as "the apparatus") for processing a workpiece 102 can be characterized as including a laser source 104 for generating a beam of laser energy, one or more positioners (e.g., a first positioner 106, a second positioner 108, a third positioner 110, or any combination thereof), and a scan lens 112. The scan lens 112 and the second positioner 108 may be integrated into a scan head 120, which will be described in more detail below.

[0022] The laser energy transmitted through the scan lens 112 along the beam path 114 propagates along a beam axis 118 to impinge on the workpiece 102. The laser energy propagating along the beam axis 118 may be characterized as having a Gaussian spatial intensity profile or a non-Gaussian (or "shaped") spatial intensity profile (e.g., a "top hat" spatial intensity profile). Regardless of the type of spatial intensity profile, the spatial intensity profile may be characterized as the shape (i.e., cross-sectional shape, also referred to herein as "spot shape") of the laser energy beam propagating along the beam axis 118 (or beam path 114). Such shapes may be circular, elliptical, square, rectangular, triangular, hexagonal, ring-shaped, etc., or any shape. As used herein, the term "spot size" refers to the diameter or maximum spatial width of the laser energy beam impinging on a region of the workpiece 102 that is at least partially processed by the impinging laser energy beam at a location where the beam axis 118 intersects (also referred to as a "process spot," "spot location," or simply "spot"). For purposes of this description, the spot size is the distance from the beam axis 118 that the light intensity is 1 / e 2 The spot size of a laser energy beam is generally measured as the radial or transverse distance down to the beam waist. Generally, the spot size of a laser energy beam is smallest at the beam waist.

[0023] Generally, the positioners described above (e.g., first positioner 106, second positioner 108, and third positioner 110) are configured to change the relative position between the spot and the workpiece 102. It should be understood from the following description that when the apparatus 100 includes the first positioner 106 and optionally includes the third positioner 110, the inclusion of the second positioner 108 is optional. Similarly, it should be understood that when the apparatus 100 includes the first positioner 106 and optionally includes the second positioner 108, the inclusion of the third positioner 110 is optional.

[0024] A. Laser Source In one embodiment, the laser source 104 can generate laser pulses. Thus, the laser source 104 can include a pulsed laser source, a CW laser source, a QCW laser source, a burst mode laser, etc., or any combination thereof. If the laser source 104 includes a QCW or CW laser source, the laser source 104 can operate in a pulsed mode, or in a non-pulsed mode, but can further include a pulse gating unit (e.g., an acousto-optic (AO) modulator (AOM), a beam chopper, etc.) that temporally modulates the laser radiation output from the QCW or CW laser source. The laser source 104 can be operated in a "burst mode" in which multiple individual pulses can be grouped together in a burst envelope. Within the burst envelope, the power of each pulse and the time between each pulse can be adjusted to suit specific laser processing requirements. As such, the laser source 104 may be broadly characterized as capable of generating a beam of laser energy, which may be represented as a series of laser pulses, or as a continuous or quasi-continuous laser beam, which may then propagate along the beam path 114. Although some embodiments described herein refer to laser pulses, it should be understood that a continuous or quasi-continuous beam may alternatively or additionally be used where appropriate or desired.

[0025] In addition to wavelength, average power, and, if the laser energy beam is represented as a series of laser pulses, pulse duration and pulse repetition rate, the laser energy beam irradiated to the workpiece 102 may be characterized by one or more other characteristics, such as pulse energy, peak power, etc. Such characteristics may include the optical intensity (W / cm2) sufficient to process the workpiece 102 (e.g., to form one or more features). 2 (measured in J / cm) and fluence (J / cm 2 The laser beam may be selected (e.g., based on one or more other characteristics, such as wavelength, pulse duration, average power, pulse repetition rate, etc., as desired) to irradiate a process spot on the workpiece 102, such as at a wavelength of 100 nm (measured in Hz).

[0026] B. First Positioner The first positioner 106 is disposed, positioned, or located in the beam path 114 and operates to diffract, reflect, refract, or the like, or any combination of the laser pulses generated by the laser source 104 to deflect or move the beam path 114 (e.g., relative to the scan lens 112) and, in turn, deflect or move the beam axis 118 relative to the workpiece 102. Generally, the first positioner 106 is adapted to move the beam axis 118 relative to the workpiece 102 along an X-axis (or X-direction), a Y-axis (or Y-direction), or a combination thereof. Although not shown, the X-axis (or X-direction) will be understood to mean an axis (or direction) that is orthogonal to the illustrated Y-axis (or Y-direction) and Z-axis (or Z-direction).

[0027] In the embodiments disclosed herein, the first positioner 106 is provided as one or more AO deflector (AOD) systems that operate to deflect the beam path 114 by diffracting the incident laser beam. Diffraction of the incident laser beam produces a diffraction pattern that typically includes zero and first order diffraction peaks, and may also include other diffraction peaks of higher orders (e.g., second order, third order, etc.). As known in the art, the portion of the laser energy beam diffracted at the zero order diffraction peak is referred to as the "zero order" beam, the portion of the laser energy beam diffracted at the first order diffraction peak is referred to as the "first order" beam, and so on. Generally, the zero order beam and other order diffracted beams (e.g., first order beam, etc.) propagate along different beam paths as they exit the AOD system. The laser energy in the zero order beam (and other higher order beams other than the first order beam) may be absorbed in a suitable or desired manner in one or more beam dumps (not shown), and the laser energy in the first order beam may propagate along the beam path 114. AOD in an AOD system An AO deflector (AOD) system typically includes an AOD crystal formed from materials such as crystalline germanium (Ge), gallium arsenide (GaAs), pyrosite (PbMoO4), tellurium dioxide (TeO2), quartz, vitreous SiO2, arsenic trisulfide (As2S3), lithium niobate (LiNbO3), or the like, or any combination thereof.

[0028] C. Second Positioner The second positioner 108 is disposed in the beam path 114 and operates to diffract, reflect, refract, or the like, or any combination thereof, of the laser pulses generated by the laser source 104 and passed through the first positioner 106 to deflect or move the beam path 114 (e.g., relative to the scan lens 112) and thereby deflect or move the beam axis 118 relative to the workpiece 102. Generally, the second positioner 108 may move the beam axis 118 relative to the workpiece 102 along an X-axis (or X-direction), a Y-axis (or Y-direction), or a combination thereof. In view of the above, the second positioner 108 may be provided as an AOD system, a galvanometer mirror scanning system, a rotating polygon mirror system, a deformable mirror, a microelectromechanical system (MEMS) reflector, or the like, or any combination thereof.

[0029] D. Third Positioner In the illustrated embodiment, the third positioner 110 includes one or more linear stages (e.g., capable of imparting translational movement to the workpiece 102 along the X, Y, and / or Z directions, respectively), one or more rotational stages (e.g., capable of imparting rotational movement to the workpiece 102 about axes parallel to the X, Y, and / or Z directions, respectively), or any combination thereof, arranged and configured to effect relative movement between the workpiece 102 and the scan lens 112 and, as a result, relative movement between the workpiece 102 and the beam axis 118. In accordance with embodiments described herein, although not shown, the third positioner 110 includes one or more stages configured and adapted to effect relative movement between the scan lens 112 and the first positioner 106.

[0030] In view of the configurations described herein, it should be understood that movement of the process spot relative to the workpiece 102 (e.g., by the first positioner 106 and / or the second positioner 108) can be superimposed on movement of the workpiece 102 or the scan lens 112 by the third positioner 110.

[0031] In the illustrated embodiment, the third positioner 110 is operable to move the workpiece 102. However, in other embodiments, the third positioner 110 may be positioned and operable to move one or more components, such as the scan head 120 and optionally the first positioner 106, while keeping the workpiece 102 stationary.

[0032] In one embodiment in which the third positioner 110 includes a Z stage, the Z stage may be positioned and configured to move the workpiece 102 along the Z direction. In this case, the Z stage may be carried by or may carry one or more of the other stages described above for moving or positioning the workpiece 102, or any combination thereof. In another embodiment in which the third positioner 110 includes a Z stage, the Z stage may be positioned and configured to move the scan head along the Z direction. Moving the workpiece 102 or the scan head along the Z direction can change the spot size at the workpiece 102.

[0033] E. Scan lens In general, the scan lens 112 (e.g., provided as either a simple lens or a compound lens) is typically configured to focus a laser energy beam directed along a beam path to generate a beam waist that may be located at or near a desired process spot. The scan lens 112 may be provided as an f-theta lens, a telecentric lens, an axicon lens (in which case a series of beam waists are generated resulting in multiple process spots offset from one another along the beam axis), or the like, or any combination thereof. The scan lens 112 may be provided as a non-telecentric lens (as shown), an f-theta lens, a telecentric lens, an axicon lens (in which case a series of beam waists are generated resulting in multiple process spots offset from one another along the beam axis 118), or the like, or any combination thereof.

[0034] In one embodiment, the scan lens 112 is provided as a fixed focal length lens and is coupled to a scan lens positioner (e.g., a lens actuator, not shown) capable of moving the scan lens 112 (e.g., to vary the position of the beam waist along the beam axis). For example, the lens actuator may be provided as a voice coil capable of linearly translating the scan lens 112 along the Z direction. In this case, the lens actuator may now be considered as a component of the third positioner 110 described above. By varying the position of the beam waist along the beam axis 118, the spot size at the workpiece 102 may be varied.

[0035] As mentioned above, in one embodiment, the scan lens 112 and the second positioner 108 are integrated into a common scan head 120. Thus, in embodiments in which the apparatus 100 includes a lens actuator, the lens actuator may be coupled to the scan lens 112 (e.g., to allow movement of the scan lens 112 relative to the second positioner 108 within the scan head 120). Alternatively, the lens actuator may be coupled to the scan head 120 and operable to allow movement of the scan head itself, in which case the scan lens 112 and the second positioner 108 move together. In either case, the lens actuator may be considered herein as a component of the third positioner 110 described above. In other embodiments, the scan lens 112 and the second positioner 108 are integrated into different housings (e.g., such that the housing in which the scan lens 112 is integrated is movable relative to the housing in which the second positioner 108 is integrated).

[0036] F. Controller Generally, the apparatus 100 includes one or more controllers, such as controller 122, for controlling or facilitating the control and operation of the apparatus 100. In one embodiment, the controller 122 is communicatively coupled (e.g., via one or more wired or wireless communication links) to one or more components of the apparatus 100, such as the laser source 104, the first positioner 106, the second positioner 108, the third positioner 110, the lens actuator, the scan lens 112 (if provided as a variable focal length lens), and the fixture, such that these components operate in response to one or more control signals output by the controller 122.

[0037] For example, the controller 122 may control the operation of the first positioner 106, the second positioner 108, or the third positioner 110, or any combination thereof, to effect relative motion between the beam axis 118 and the workpiece 102 and to effect relative motion between the process spot and the workpiece 102 along a path or trajectory (also referred to herein as a "process trajectory") within the workpiece 102. It will be appreciated that any two of these positioners, or all three of these, may be controlled such that two positioners (e.g., the first positioner 106 and the second positioner 108, the first positioner 106 and the third positioner 110, the second positioner 108 and the third positioner 110) or all three positioners simultaneously effect relative motion between the process spot and the workpiece 102 (thereby effecting a "compound relative motion" between the beam axis and the workpiece).

[0038] G. Beam Analysis System The apparatus 100 may include a beam analysis system 130 operable to measure one or more characteristics of the laser energy beam. The beam analysis system 130 may be used to measure various beam characteristics including beam diameter, spot size, spot position, beam circularity, beam astigmatism, focal height, beam waist size, beam waist position (e.g., along the X, Y, or Z direction), beam axis position, spatial energy distribution, pulse repetition rate, average power, peak power, and the like, or any combination thereof. The measurements of the beam characteristics listed above may be used by the controller 122 to calculate laser beam parameters such as beam astigmatism and focal height (e.g., beam waist height compared to known data). The beam analysis system 130 may generate measurement data representative of these measured beam characteristics and may transmit the measurement data (e.g., as one or more measurement signals) to the controller 122. In some embodiments, the measurement data transmitted to the controller 122 is representative of the pulse timing or number of pulses emitted by the laser source 104. The controller 122 may then interpret, apply, or process the measurement data to control the operation of one or more positioners (e.g., the first positioner 106, the second positioner 108, the third positioner 110, or any combination thereof).

[0039] The beam analysis system 130 may be mounted on the third positioner 110 (as shown in FIG. 1 ), or may be mounted on various other structures or stages as needed or advantageous. For example, the third positioner 110 may include one or more linear stages (e.g., as described above), and the beam analysis system 130 may be mounted on the same linear stage (e.g., on a side thereof) or on a fixture coupled to the third positioner 110. In one embodiment, the beam analysis system 130 is provided as a camera-based beam profiler configured to measure Rayleigh scattered light from the laser energy beam to a photodetector. In another embodiment, the beam analysis system 130 is provided as a knife edge feature located optically upstream from the photodetector such that the amount of optical power passing through the knife edge and incident on the photodetector can be measured and correlated to a known position of the knife edge in one or more axes or directions. In another embodiment, the beam analysis system 130 is provided as a camera-based beam profiler configured to focus the beam directly or through an attenuating filter onto a photodetector positioned directly along the beam axis 118. In another embodiment, the beam analysis system 130 is provided as a rotating slit beam profiler. In each of these configurations of the beam analysis system 130, the beam is measured at the plane of the photodetector (i.e., the detector plane shown in FIG. 2).

[0040] II. Chirp AOD in General In general, the controller 122 may control the operation of one or more AODs of the first positioner 106 by applying a chirp RF signal to one or more ultrasonic transducer elements of the AOD to vary the shape (i.e., “spot shape”) or vary the size (i.e., “spot size”) of the spot impinged on the workpiece 102 by laser energy propagating along the beam axis 118. When applied to the AOD, the chirp RF signal has the effect of producing a chirp acoustic waveform (i.e., an acoustic waveform having an instantaneous frequency that changes over time, also referred to as a “chirp acoustic signal”) that propagates through the AOD crystal. In contrast, a “non-chirp” acoustic waveform, or “non-chirp acoustic signal,” refers to an acoustic waveform that has a substantially constant instantaneous frequency. A first order beam diffracted by a chirp acoustic signal may be referred to as a “chirp beam,” “chirp first order beam,” or the like. The rate of change of frequency of the RF signal is referred to as the “chirp rate” (e.g., measured in MHz / μs). The applied RF signal may be chirped linearly, or non-linearly, or in any other desired or suitable manner. A change in the instantaneous frequency of the chirped acoustic waveform has the effect of applying a single-axis (astigmatic) focusing term (or cylindrical lens effect) to the primary beam within the AOD crystal, changing the collimation of the primary beam exiting the AOD (i.e., diverging or converging with respect to the incident beam, depending on the sign of the chirp rate).

[0041] III. EMBODIMENTS RELATING TO A LASER PROCESSING APPARATUS WITH A BEAM ANALYSIS SYSTEM As described above, the beam analysis system 130 may be incorporated into the laser processing apparatus 100 to measure various beam characteristics. Measurement data generated by the beam analysis system 130 may be provided as feedback to the system controller 122. The controller 122 may process the feedback to modify the control commands sent to one or more AODs of the first positioner 106 and / or the laser source 104. For example, if an AOD (e.g., the first AOD) is driven to generate a chirped primary beam, thereby changing one beam characteristic of the incident beam (e.g., increasing the spot size of the primary beam relative to the incident beam), other beam characteristics of the incident beam (e.g., spot positioning, beam astigmatism, etc.) may result in undesirable changes. The beam analysis system 130 is used to measure one or more of these beam characteristics and provide the measurement data to the controller 122 so that the controller 122 can drive the first AOD or the second AOD to correct, compensate, or minimize such changes to the beam characteristics. Additionally, the measurement data transmitted from the beam analysis system 130 to the controller 122 may be used to optimize or adjust certain beam characteristics of the primary beam to enable various workpiece processing functions. Below is a description of an exemplary embodiment of a system and method for implementing this closed loop of the first positioner 106 using the beam analysis system 130.

[0042] A. Embodiments of a Beam Analysis System Configured to Control an AOD System Figure 2 shows a control schematic illustrating one embodiment of the functional relationships between the controller 122, the laser source 104, the AOD system 140 of the first positioner 106, and the beam analysis system 130, as described above with respect to Figure 1. In this embodiment, the AOD system 140 includes an ultrasonic transducer 142, an AOD crystal 144, and an RF source 146.

[0043] The RF source 146 is configured to generate and transmit an RF signal 170 (e.g., in response to one or more control commands 164 output from the controller 122). The RF signal 170 is transmitted to the ultrasonic transducer 142, which is configured to generate one or more acoustic waves or waveforms 148 (i.e., acoustic signals 148) propagable through the AOD crystal 144 in response to the applied RF signal 170. The acoustic signals 148 diffract the incident beam 150 (e.g., output from the laser source 104 in response to a control or trigger command 168 output from the controller 122 via a communication link 166) to generate a first order beam 152 that is diffracted (e.g., by an angle θ) to a detector plane 132 of the beam analysis system 130. The beam analysis system 130 is operative to measure at least one beam characteristic of the first order beam 152 and generate and transmit corresponding measurement data 160 to the controller 122 via a communication link 162. The controller 122 may then control the operation of one or more positioners (e.g., the first positioner 106, the second positioner 108, and the third positioner 110 (shown in FIG. 1), or any combination thereof) based at least in part on this measurement data.

[0044] In the illustrated embodiment, the first positioner 106 includes only one AOD system 140 that can induce astigmatism or cylindrical lensing along a single axis to generate the chirped first order beam 152. However, in other embodiments, the first positioner 106 includes multiple AOD systems 140 that are arranged to diffract the incident beam 150 along different axes (e.g., mutually orthogonal), and thus can induce astigmatism or cylindrical lensing along multiple axes to generate the chirped first order beam 152.

[0045] Regardless of the configuration of the first positioner 106, the beam analysis system 130 can be used to characterize the astigmatism of the generated chirped primary beam 152. See, for example, the following discussion of Figures 3 and 4. Figures 3 and 4 show cross-sectional views in the X and Y directions, respectively, of the chirped primary beam 152 propagating along the beam axis 118 through the scan lens 112 and incident on the detector plane 132 of the beam analysis system 130. In the example shown in Figures 3 and 4, the primary beam 152 is chirped in the X direction but not in the Y direction. However, it will be appreciated that the primary beam 152 may be chirped in the Y direction and not chirped in the X direction, or may be chirped in any manner in the X and Y directions.

[0046] As a result, the beam waist 250 of the chirped primary beam 152 is shifted away from the detector plane 132 (e.g., above or below the detector plane 132) along the Z direction (e.g., by a distance ΔZ). The beam analyzing system 130 can be operated to measure spot sizes in the X and Y directions at the detector plane 132, and the measurement data generated by the beam analyzing system 130 can be used to determine the distance ΔZ. In one exemplary embodiment, to measure ΔZ of the beam waist 250, the beam analyzing system 130 can be mounted on a Z-axis stage (e.g., of the third positioner 110) so that the beam analyzing system 130 (and the detector plane 132) can be moved in the ±Z direction while the spot size measurements are being made by the beam analyzing system 130. In another exemplary embodiment, the scan head 120 (shown in FIG. 1 ) is mounted on a Z-axis stage (e.g., of the third positioner 110) so that the beam waist can be moved in the ±Z direction while the spot size readings are being made by the beam analyzing system 130. Data representing the spot size is sent by beam analysis system 130 to controller 122 which calculates ΔZ of beam waist 250 by any suitable technique in the art. By measuring the spot size along the X and Y directions and the distance ΔZ of beam waists 250 and 260, beam analysis system 130 can generate measurement data 160 (shown in FIG. 2) representing the beam astigmatism to controller 122.

[0047] As described above, the AOD system 140 diffracts the incident beam 150 based on the frequency of the acoustic signal 148 propagating through the AOD crystal 144. If the acoustic signal 148 has a chirped waveform as described above, the AOD system 140 may diffract the incident beam 150 to produce a chirped first order beam 152 that is incident on a detector plane 132 of the beam analysis system 130. The temporal relationship (hereinafter referred to as the "timing offset") between the output of the control commands 164 sent to the AOD system 140 and the control commands 168 sent to the laser source 104 may be important for various laser processing applications where precise synchronization between a laser pulse (or multiple laser pulses) and the acoustic signal in the AOD crystal 144 is required.

[0048] In embodiments in which the first positioner 106 is provided as a multi-axis AOD system as described above, the controller 122 may independently control the chirp of the RF signal for each AOD in the pair of AODs. In this case, the spot size or shape in a first direction (e.g., X direction) may be different from the spot size or shape in a second direction (e.g., Y direction). Based on measurement data 160 characteristic of the spot size from the beam analysis system 130, the controller 122 may control the operation of the first AOD and second AOD systems 140 to change the degree of astigmatism at the workpiece 102 in one or both of the X and Y directions, thereby changing the beam circularity and spot size, as required by the process being performed by the laser processing apparatus 100.

[0049] i. Embodiments relating to modification of beam characteristics by a system operator or by automatic control As discussed above, the incorporation of the beam analysis system 130 into the laser processing apparatus 100 may enable various methods for controlling the beam characteristics. In one embodiment, if an operator of the laser processing apparatus 100 desires to irradiate the workpiece 102 with a laser energy beam having a particular beam diameter or spot size (e.g., to form a via in a printed circuit board), the beam analysis system 130 is used to measure the beam diameter and transmit measurement data representing the beam diameter to the controller 122. The system operator may review (e.g., on a software graphical user interface) the measurement data 160 received by the controller 122 and determine whether a change should be made. If the system operator desires to change the spot size based on the measurement data 160, the system operator may program the controller 122 to output an updated control command 164 for the RF source 146 to apply a chirped RF signal 170 to the ultrasonic transducer 142 to generate a chirped acoustic signal 148 in the AOD crystal 144 to generate a primary beam 152 having a particular spot size incident on the workpiece 102.

[0050] In other embodiments, when the laser processing apparatus 100 is operating in an automatic mode (e.g., based on an automatic routine or subroutine programmed by a system operator), the controller 122 can receive measurement data 160 from the beam analysis system 130 and, based on such programming, output updated control commands 164 for the RF source 146 to apply a chirp RF signal 170 to the ultrasonic transducer 142, thereby generating a chirp acoustic signal 148 in the AOD crystal 144 to generate a primary beam 152 having a particular spot size incident on the workpiece 102.

[0051] ii. Embodiments relating to methods for compensating for changes in beam characteristics In one embodiment, the beam analysis system 130 is used as part of the laser processing apparatus 100 to compensate for changes in various beam characteristics or to minimize the effect of a change in one beam characteristic (e.g., a "first" beam characteristic) on another beam characteristic (e.g., a "second" beam characteristic). For example, when the AOD system 140 operates to change a first beam characteristic (e.g., spot size) of an incident beam relative to a primary beam, this change may cause a change in a second beam characteristic (e.g., spot positioning, beam astigmatism, etc.) of the primary beam. To correct or reduce the effect of the change in the second beam characteristic, the beam analysis system 130 may measure the second beam characteristic and generate measurement data 160 representative of the second beam characteristic. The beam analysis system 130 may then transmit the measurement data 160 to the controller 122. The controller 122 may calculate and output update control commands 164 to the AOD system 140 based at least in part on the measurement data 160 such that the AOD system 140 may reduce the magnitude of the change in the second beam characteristic.

[0052] In one embodiment, the AOD system 140 operates to generate a chirp primary beam 152 based on a first chirp acoustic signal 148 to achieve a desired spot size at a workpiece. The center frequency of the first chirp acoustic signal 148 can cause a spot position error (a difference between a desired spot position and an actual spot position). The beam analysis system 130 can measure the spot position of the chirp primary beam 152 and send measurement data 160 representing the measured spot position to the controller 122. Upon receiving the measurement data 160, the controller 122 can calculate the spot position error and send an update control command 164 to the AOD system 140 to correct the spot position error by generating a second chirp acoustic signal 148 having the same chirp rate as the first acoustic signal but a different center frequency to reduce or eliminate the spot position error.

[0053] In another embodiment, the control commands 164 may operate to correct beam astigmatism of the primary beam 152. As described above, the chirp acoustic signal has the effect of applying a single-axis focusing term to the primary beam 152. This may cause beam astigmatism (defined as a beam having different foci in orthogonal axes). The beam analysis system 130 measures the beam astigmatism by measuring the height difference ΔZ between the focal point (or beam waist) and the detector plane 132 in the X direction and between the focal point (or beam waist) and the detector plane 132 in the Y direction (as described above). If the AOD system 140 is provided as a multi-axis AOD system, the controller 122 may operate one AOD (e.g., the second AOD) to generate a chirp acoustic signal that applies a single-axis defocusing term to the beam to correct the astigmatism caused by chirping the first AOD.

[0054] iii. Embodiments relating to correcting timing errors between a laser source and an AOD system 2, in some laser processing applications (e.g., to form one or more features on the workpiece 102), an incident beam 150 (e.g., a laser pulse or group of laser pulses) may be intended to pass through the AOD system 140 that coincides with a particular chirp acoustic signal 148 at the AOD crystal 144 (e.g., having a particular chirp rate to achieve a particular spot size and / or having a particular center frequency to achieve a particular spot location on the workpiece 102). Because the diffraction angle θ provided by the AOD system 140 corresponds to the center frequency of the chirp acoustic signal across the lateral dimension of the laser pulse in the AOD crystal 144, if the laser pulse does not pass through the AOD crystal 144 overlapping the expected or desired chirp acoustic signal 148, the laser pulse will be delivered to a spot location on the workpiece 102 that differs from the desired spot location. A control loop may be used to adjust a timing offset between the control commands 168 sent to the laser source 104 and the control commands 164 sent to the RF source 146 to correct for timing errors to ensure timing fidelity and prevent such spot location errors.

[0055] In one embodiment, the first and second chirp signals are distinct and time-separated chirp signals, and a timing error causes the laser pulse to pass through the AOD crystal 144 that corresponds to the second chirp signal (having the second chirp rate) instead of passing through the AOD crystal 144 that corresponds to the first chirp signal (having the first chirp rate). In another embodiment, each frequency band has a different center frequency, and a timing error causes the laser pulse to pass through the AOD crystal 144 that corresponds to a different (than intended) frequency band of a relatively long (e.g., longer than the transit time of the pulse through the AOD crystal 144) continuous (having a constant chirp rate) chirp signal. In yet another embodiment, a timing error causes the laser pulse to pass through the AOD system 140 in an area that is devoid of an acoustic waveform.

[0056] In one embodiment, the first and second chirp signals are separated in time, and a timing error causes a laser pulse to pass through the AOD crystal 144 that is coincident with the second chirp signal (having a second chirp rate) instead of passing through the AOD crystal 144 that is coincident with the first chirp signal (having a first chirp rate). In this embodiment, an exemplary method for correcting spot position errors due to such timing errors includes a measurement step that operates to first establish a correlation between a reference beam characteristic (e.g., spot position) and a timing offset. This correlation is used in a subsequent workpiece processing step that utilizes the correlation, and the timing offset has a predetermined relationship with the reference beam characteristic (spot position), thereby enabling the laser processing apparatus 100 to avoid, correct, or reduce spot position errors. During the measurement step, the beam analysis system 130 measures the laser spot position and generates measurement data 160 that represents the measured spot position for each laser pulse. This measurement data 160 is sent to the controller 122, which (e.g., automatically or programmed to do so by a system operator) establishes a correlation between the measured spot position and the timing offset. For example, the controller 122 sends a control command 164 to the AOD system 140 to cause the RF source 146 to generate a first chirp RF signal that results in a first chirp acoustic signal (e.g., having a chirp rate of 5 MHz / μs and a center frequency of 30 MHz) in the AOD crystal 144. The controller 122 also sends a control command 168 to the laser source 104 to emit a first laser pulse that is intended to overlap the first chirp acoustic signal in the hope that the AOD system 140 will diffract the pulse to the beam analysis system 130 to the desired spot position. In general, the control commands 164 and 168 are offset from one another in time (e.g., by a timing offset T0) to ensure that the chirp laser pulse is diffracted to the desired spot position.However, for example, a first laser pulse may miss the first chirp acoustic signal and instead overlap with a second chirp acoustic signal that is separated in time from the first chirp signal (e.g., has the same 5 MHz / μs chirp rate but a center frequency of 26 MHz), resulting in a spot position error (e.g., 1 μm). The beam analysis system 130 measures the spot position of the first laser pulse and sends measurement data 160 representing the measured spot position to the controller 122. The controller 122 then calculates a spot position error (e.g., E0) that is correlated with the timing offset T0 for the first laser pulse. By repeating the spot position measurement while adjusting the timing offsets (e.g., T1, T2, T3, and T4, etc.) and calculating the resulting spot position errors (e.g., E1, E2, E3, and E4, etc.), the controller 122 builds a correlation between the timing offsets and the spot position errors that characterizes the relationship between the timing offsets and the spot position errors. The controller 122 then applies a correction to the timing offset during a subsequent workpiece processing step to reduce or eliminate the spot position error. During this workpiece processing step, the controller 122 sends control commands 164 to the AOD 140 to generate a chirp acoustic signal 148 in the AOD crystal 144, and sends control commands 168 to the laser source 104 to emit laser pulses toward the workpiece 102 that are diffracted by the intended chirp signal. Because the timing offset is correlated to the beam characteristic (spot position) measured during the measurement step, the timing offset has a predetermined relationship to the reference characteristic (spot position). The controller 122 uses this predetermined relationship to improve the timing fidelity between the AOD control commands 164 and the control commands 168 to reduce or eliminate the spot position error.

[0057] In other embodiments, the exemplary method can correct two errors (e.g., spot size error and spot position error in one or more directions) that occur simultaneously due to timing errors. In the exemplary workpiece processing scenario described above, it may be necessary to change the fluence of the primary beam 152 between ablation (with an unchirped beam) of a metal layer of a printed circuit board and ablation (with a chirped beam) of an underlying laminate. To achieve this, for the same process spot, an unchirped acoustic signal in the AOD crystal 144 that diffracts the incident beam 150 as a focused primary beam 152 is followed by a chirped acoustic signal that diffracts the incident beam 150 as a defocused laser primary beam 152 (having a lower laser fluence). If a laser pulse intended to ablate the metal layer (e.g., requiring an unchirped acoustic signal) passes through the AOD crystal 144 superimposed on the chirped acoustic signal, two problems can occur. First, the laser pulse can be caused to defocus by the chirped acoustic signal to a point where it does not have the fluence required to ablate the metal layer. Second, if the center frequency of the chirped acoustic signal across the laser pulse is not equal to the frequency of the non-chirped acoustic signal across the laser pulse, spot position errors may result. By applying methods similar to those described above, including a measurement step used to relate the timing offset to a reference beam characteristic (e.g., spot size and spot position), followed by processing the workpiece using an updated timing offset based on a predetermined relationship between the timing offset and the beam characteristic, the spot position and spot size errors are minimized, corrected, or avoided.

[0058] In this example, the beam analysis system 130 can measure the spot position and spot size during the measurement step, generate measurement data 160 indicative of both measured characteristics for each laser pulse, and transmit the measurement data 160 to the controller 122, which then establishes a correlation between the measured spot position, the measured spot size, and the timing offset. For example, the controller 122 can transmit a control command 164 to the AOD system 140 to cause the RF source 146 to generate in the AOD crystal 144 a non-chirped acoustic signal (e.g., having a frequency of 30 MHz) followed by a chirped acoustic signal (e.g., having a chirp rate of 5 MHz / μs and a center frequency of 32 MHz). The controller 122 then sends a control command 168 (e.g., with a timing offset T0 relative to the control command 164 sent to the AOD system 140) to the laser source 104 to emit a first laser pulse intended to overlap the non-chirp acoustic signal in the hope that the AOD system 140 will diffract the pulse to the beam analysis system 130 at the desired spot location with the desired spot size. However, for example, the pulse may miss the non-chirp acoustic signal and instead overlap with a portion of the chirp acoustic signal having a center frequency of 32 MHz, resulting in an undesired spot location and an undesired spot size. The beam analysis system 130 measures the spot location and spot size and sends measurement data 160 representing the measured spot location and measured spot size of that laser pulse to the controller 122, which allows the controller 122 to calculate a spot location error (e.g., measured spot location ESP0 relative to predicted spot location) and a spot size error (e.g., measured spot size ESS0 relative to predicted spot size). Both errors are correlated to the timing offset T0 for that laser pulse.By repeating the spot position and spot size measurements while adjusting the timing offsets (e.g., T1, T2, T3, and T4, etc.) and calculating the resulting spot position errors and spot size errors (e.g., ESP1, ESS1, ESP2, ESS2, ESP3, and ESS3, etc.), the controller 122 determines a timing offset T that characterizes the relationship between the timing offsets, the spot position errors, and the spot size errors. x ,Spot position error ESP x , and spot size error ESS x The timing offsets between the laser pulse, the non-chirp acoustic signal, and the chirp acoustic signal are correlated to the beam characteristics (spot position and spot size) measured during the measurement step so that the timing offsets have a predetermined relationship to both reference characteristics (spot position and spot size). The controller 122 uses these relationships to improve the timing fidelity between the AOD control commands 164 and the laser control commands 168 to reduce or eliminate spot position and spot size errors during the workpiece processing step.

[0059] iii. Embodiments Related to Control of System Operating Parameters The methods described above with respect to other closed-loop control of system performance using measurement data from the beam analysis system 130 may be more broadly applicable to various system operating parameters (e.g., RF signal frequency, RF signal chirp rate, acoustic signal chirp rate, AOD temperature, laser pulse burst envelope, pulse repetition rate, pulse energy, etc., or any combination thereof) that may be controlled to compensate for changes in performance of various components of the laser processing apparatus 100. As the laser processing apparatus 100 ages, various optical elements (e.g., gain crystals, gain fibers, harmonic generation crystals, optical gratings, prisms, relay optics, diffractive elements, beam delivery optics, AODs, lenses, etc., or any combination thereof) may degrade and change the nominal spot size. Below, an embodiment is described that uses the beam analysis system 130 to compensate for the effect of such degradation on the nominal spot size.

[0060] In one embodiment, for example, the system operating parameter may be the chirp rate C of the RF signal 170 applied by the RF source 146 to the ultrasonic transducer 142 (e.g., in response to a control command 164 from the controller 122). In this embodiment, as the scan lens 112 ages, debris buildup during laser processing may increase absorption of the laser energy beam, which may result in higher operating temperatures for the scan lens 112 and potentially thermal lensing effects that change the nominal spot size, perhaps unseen by the controller 122 and system operator. Measurement of beam characteristics by the beam analysis system 130 may be used to detect such errors and compensate for such errors. In this embodiment, an exemplary method of accomplishing this includes measurement steps performed at various times throughout system operation, where a beam characteristic (e.g., spot size) is selected as a reference characteristic. If a particular measurement of a reference beam characteristic (e.g., by the beam analysis system 130) as a function of an associated system operating parameter deviates from an expected value (e.g., falls outside an expected tolerance or control limit), the controller 122 adjusts the system operating parameter using the measurement data 160 from the beam analysis system 130 (e.g., as described above with respect to FIG. 2). In this embodiment, the reference beam characteristic measured is the spot size S, which corresponds to the chirp rate C of the RF signal 170 applied to the ultrasonic transducer 142 by the RF source 146, which is a system operating parameter. The RF signal chirp rate C1 (e.g., 5 MHz / μs) used during the system use period A1 (e.g., when the spot size S1 is 100 μm) becomes the RF signal chirp rate reference value. The beam analysis system 130 then generates measurement data of the spot size S as a function of the system use period A (time) and correlates S with the chirp rate C and the use period A in the controller 122. As the system ages, for example during usage period A2, the spot size S2 produced by a nominal value of the RF signal chirp rate C1 (eg, 5 MHz / μs applied during usage period A1) may change to S2=120 μm.Using the measurement data from the beam analysis system 130, and by comparing the spot size (S2) to a baseline value of the RF signal chirp rate (C1) and the system usage period (A2), the controller 122 uses the relationship between the system operating parameters and the baseline characteristics to calculate an updated RF signal chirp rate C2 (e.g., 6 MHz / μs) to drive the AOD system 140 to achieve the desired spot size S1=100 μm. This method can be utilized to measure the chirp spot size and modify the chirp rate to ensure that the spot size at the workpiece surface is maintained over the life of the system, thereby ensuring consistent laser processing quality over time.

[0061] B. Signal-to-Noise Ratio Embodiments of the Beam Analysis System In some embodiments, when the beam analysis system 130 is used with a high-power beam delivery system, especially when attenuation of the primary beam 152 is required to avoid damage to components of the beam analysis system 130 (e.g., when measuring spot sizes of 10-20 μm with very high laser fluence), the intensity of the scattered light produced by the optical elements in the beam path can be comparable to the intensity of the processing beam detected by the photodetector. This can make it difficult to distinguish the signal of the primary beam 152 from the noise produced by the scattered light, resulting in a low signal-to-noise ratio that deteriorates the fidelity of the beam analysis data. To accurately measure spot sizes in this range, it is important to improve the signal-to-noise ratio by reducing the amount of scattered light that reaches the photodetector. Below, we describe an exemplary embodiment of the beam analysis system 130 that improves the signal-to-noise ratio performance.

[0062] 5 and 6 show various views of an exemplary embodiment of the beam analysis system 130 shown in FIG. 1. Referring to FIG. 5 and FIG. 6, the beam analysis system 130 includes a token 310 mounted or disposed on a photodetector assembly. The token 310 includes a substrate 311 (e.g., formed from glass, quartz, or other optically transparent material) with a material layer 312 (e.g., formed from a metal, ceramic, optical coating, etc.) configured to block at least a portion of the incident primary beam 152 from reaching the photodetector assembly. In this embodiment, the material layer 312 is provided as highly reflective chrome (also referred to herein as "HR chrome") configured to reflect a portion of the primary beam 152 incident on its surface. In another embodiment, the material layer 312 is provided as anti-reflective chrome (also referred to herein as "AR chrome"). In contrast to HR chrome, which has a high laser-induced damage threshold (LIDT) because it reflects incident light, the AR chrome material layer 312 has a lower LIDT than HR chrome because it absorbs incident light. The high LIDT of HR chrome requires less attenuation of the primary beam 152, thereby improving the signal-to-noise ratio. One or more apertures (e.g., one or more apertures 314 and / or 316) may be formed in the material layer 312. The apertures 314 and 316 are configured to allow a portion of the primary beam 152 (i.e., the transmitted portion 154) to pass through the substrate 311. The beam analyzing system 130 may further include a cover (not shown) configured to be selectively positioned over the token 310 to prevent debris or other contaminants from adhering to the apertures 314 and 316 or the material layer 312 (e.g., when the beam analyzing system 130 is not in use). In this embodiment, the photodetector assembly includes an integrating sphere 320 and a photodetector 326. The photodetector assembly is configured to measure the optical power or optical energy of a portion of the incident primary beam 152 having a beam axis 118 and propagating along the beam path 114 through the scan lens 112 as the beam axis is scanned over the token (e.g., along the X-axis or Y-axis).

[0063] As known in the art, the integrating sphere 320 is an optical component that includes a hollow spherical (or at least substantially spherical) cavity, the inner surface of which is coated with a diffuse reflective coating. The integrating sphere 320 includes an illumination port 322 and a detection port 324, and is arranged such that light propagating along the beam path 114 can enter the cavity of the integrating sphere 320 through the illumination port 322. Light incident at any point on the inner surface of the cavity is scattered and ultimately exits the integrating sphere 320 at the detection port 324 and is incident on a photodetector 326. The token 310 is positioned on or adjacent to the illumination port 322 of the integrating sphere 320. The energy power of the transmitted portion 154 of the primary beam 152 is measured by a photodetector 326 located at the detection port 324. The photodetector 326 is configured to absorb the light incident on the detection port 324 and communicate corresponding measurement data to the controller 122 (e.g., as described above).

[0064] Figure 6 shows a plan view of an embodiment of the token 310 shown in Figure 5. With reference to Figure 6, the size, shape, orientation, or other configuration of the apertures 314 and 316 (each collectively referred to as an "aperture") may be provided in any manner desired or advantageous. In this embodiment, one or more square-shaped apertures are provided having sides oriented in the X-axis and Y-axis (e.g., at 0 degrees and 90 degrees measured from the X-axis) (e.g., as identified at 314). One or more diamond-shaped apertures are also formed in the material layer 312 having sides offset from the X-axis and Y-axis (e.g., at 45 degrees and 135 degrees measured from the X-axis) (e.g., as identified at 316). The minimum distance between the edges of adjacent apertures (i.e., the "pitch" of the aperture array) is selected to minimize scattered light that occurs upstream in the optical train (e.g., at a turning mirror, lens, or other optical component) from passing through an adjacent aperture (i.e., an aperture toward which the primary beam 152 is not directed) into the integrating sphere 320 and reaching the photodetector 326. Additionally, the pitch of the aperture array can be selected to avoid or minimize scattered light from light that is reflected by the HR chrome of the material layer 312 toward other system components and reflected by these system components into adjacent apertures. For example, in one embodiment, the pitch of the aperture array is selected such that adjacent apertures are spaced far enough apart relative to their dimensions (e.g., apertures with dimensions of 250 μm and spaces between apertures of about 1-2 mm) and the material layer 312 (e.g., made of HR chrome) covers more than 95% of the area of ​​the token 310. Such a configuration minimizes or reduces the amount of scattered light incident on the photodetector 326. Another advantage of using the integrating sphere 320 is the reduced effect of aperture position on the photodetector measurements. If a photodetector is placed directly underneath the token 310, the amount of light from the primary beam that reaches the photodetector may be different for apertures placed at different positions on the token 310 (e.g., because the primary beam 152 is incident on the edge of the aperture at an angle to the face of the token).The use of an integrating sphere 320 can reduce this position sensitivity.

[0065] 5, during operation to measure a characteristic of the primary beam 152, the beam axis 118 is scanned across one or more edges of at least one aperture, and the optical power of the transmitted portion 154 of the primary beam 152 is sensed by the photodetector 326. The edge of the aperture acts similar to a knife edge used in various beam profilers (e.g., scanning slit profilometers). In one example, the beam characterization tool 130 can be used to measure one or more characteristics of the primary beam 152 and generate corresponding measurement data indicative of the beam power reaching the photodetector 326, which can be transmitted to and processed by the controller 122 (e.g., for any purpose as described above).

[0066] IV. BEAM STABILITY EMBODIMENTS In some cases, when the galvanometer mirrors are driven at or near their individual performance limits during operation of the laser processing apparatus 100, parasitic forces on the torque applied (e.g., by the galvanometer motor) can cause small imbalances in the galvanometer mirrors or axes. These effects combine to excite cross-axis angular motion (e.g., motion orthogonal to the primary rotation axis) in the mirrors (also referred to herein as "cross-axis wobble"), which causes errors in the angular position of the galvanometer mirrors. This cross-axis wobble is typically undetected by the galvanometer positioning system, and errors in the angular position of the galvanometer mirrors can result in laser spot position errors on the workpiece 102 surface (e.g., after the diffracted first order beam is focused by the scan lens). If the extent of the cross-axis wobble can be measured, adjustments to the operation of an AOD system located optically upstream from the galvanometers can proactively compensate for the cross-axis wobble, thereby reducing or avoiding positioning errors. In the following, embodiments are described that allow for detection and pre-compensation of cross-axis fluctuations.

[0067] A. Measuring cross-axis fluctuations using a beam analysis system In a laser processing apparatus 100 including a first positioner 106 (e.g., an AOD system) and a second positioner 108 (e.g., one or more galvanometers), the beam axis 118 is positioned such that half of the spot (or approximately half of the spot) is transmitted to the photodetector 326 (e.g., as shown in FIG. 5 ). One of the galvanometers is then driven not near its performance limit to scan the beam axis 118 in a direction parallel to the knife edge (e.g., an edge of one of the apertures 314 or 316). Measurement data obtained from this scan is sent to the controller 122, which stores this data (e.g., as a baseline measurement) for comparison to operation of the galvanometer at or near its performance limit.

[0068] If the galvanometers do not experience cross-axis fluctuations as a result of operating at or near their performance limits, the beam analyzing system 130 measurements will not change (e.g., when compared to the baseline measurements, as described above). If the galvanometers experience cross-axis fluctuations, the beam analyzing system 130 measurements will change compared to the baseline measurements. The measurement data is processed by the controller 122 into an error correction signal that is input to the AOD system 140 to correct for the cross-axis fluctuations. The controller 122 can process the measurement data by removing various frequencies, compensating for sensing delays (e.g., due to the sensor interface electronics), and compensating for processing delays (e.g., due to data transmission, scaling, filtering, and AOD command data transmission) and AOD delays (e.g., propagation delays in the AOD driver and AOD crystal). The controller 122 can geometrically map the measurement data to convert the fluctuation angles into displacements of the workpiece surface due to the shapes of the galvanometer mirrors and scan lens. In another example, measurements of the cross-axis fluctuations by the beam analysis system 130 can be used to detect increases in the magnitude of the cross-axis fluctuations that may indicate damage to one or more components of the galvanometer system.

[0069] Configured as described above, the beam analysis system 130 can also be used to measure the effect of disturbances on the laser processing apparatus 100 that affect operating parameters (e.g., spot size, spot position, etc., or any combination thereof) or that prevent the beam analysis system 130 itself from providing correct measurements. By positioning the beam axis 118 of the primary beam 152 directly at the edge of one or more apertures 314 and monitoring the fluctuations in optical power measured by the photodetector 326, the beam analysis system 130 can detect and quantify such disturbances. For example, in one embodiment, measurement data acquired by the beam analysis system 130 while the debris ejection system is operating may exhibit an unacceptable signal-to-noise ratio. Measurements acquired by the beam analysis system 130 when debris ejection is occurring can be compared to measurements acquired when debris ejection is not occurring to determine the cause of the instability.

[0070] B. Pre-compensation using cross-axis wobble compensation system 7 shows a diagram of an embodiment of an apparatus (e.g., cross-axis wobble compensation system 520) operative to measure cross-axis wobble of the galvanometer mirrors during operation of the laser processing apparatus 100. The primary beam 152 is incident on a first galvanometer mirror (e.g., X-axis galvanometer mirror 502 driven by galvanometer motor 500) and a second galvanometer mirror (e.g., Y-axis galvanometer mirror 508 driven by galvanometer motor 506) which directs the primary beam 152 to the workpiece 102 via the scan lens 112. The wobble compensation system 520 includes a reference laser source 522 operative to direct an incident reference laser beam 524 to a reflective surface 504 formed on the back surface of the X-axis galvanometer mirror 502. The incident reference laser beam 524 is reflected off the surface 504 as a reflected beam 526 that is incident on a reference spot 528 on the auxiliary sensor 600. In other embodiments, an LED light source (not shown) may be used to project the incident reference beam onto the reflecting surface 504 .

[0071] FIG. 8 shows a diagram of an embodiment of the auxiliary sensor 600. In this embodiment, the auxiliary sensor 600 is provided as a four-cell segment photodiode formed on a substrate 602 and having four segments 604, 606, 608, and 610. When the reference spot 528 is incident on the photodiode, each illuminated segment generates a photocurrent proportional to the optical power incident on that segment. The difference between the photocurrents of the segments indicates the position of the reference spot 528. Therefore, the auxiliary sensor 600 is configured to sense the position of the reference spot 528 and send measurement data representative of the position of the reference spot 528 to the controller 122. The controller 122 then sends control commands to the first positioner 106 (i.e., the X AOD and the Y AOD) to ensure that the cross-axis fluctuation 510 does not cause a positioning error of the process spot on the workpiece 102, so that the measurement data can be used to calculate a correction or compensation factor to correct or compensate for the cross-axis fluctuation 510.

[0072] In this embodiment, during operation of the cross-axis wobble compensation system 520, the reference spot 528 moves in the ±X direction on the auxiliary sensor 600 as the X-axis galvanometer mirror scans the primary beam 152 in the ±X direction. For example, if a cross-axis wobble 510 occurs (e.g., in the Y direction), the reference spot 528 may move in the ±Y direction in addition to the ±X direction, causing a change in the amount of light absorbed by the upper segments 604 and 606 relative to the amount of light absorbed by the lower segments 608 and 610. Measurement data representing the difference in absorption of this reference spot 528 is transmitted from the auxiliary sensor 600 to the controller 122. The controller 122 then outputs a control command (e.g., to the Y-axis AOD of the first positioner 106) to compensate for (and thereby correct) the Y-direction wobble and calculate a compensation factor to prevent positioning errors of the process spot on the workpiece 102.

[0073] In other embodiments, the auxiliary sensor 600 is provided as a dual cell segmented photodiode (not shown) with two segments arranged on either side (e.g., in the Y direction) of a gap (e.g., oriented in the X direction). This dual cell arrangement may avoid errors due to non-linearity of the photodiode signal (e.g., from a four-cell auxiliary sensor 600 as the reference spot 528 crosses the Y-oriented gap between segments 606, 608 and segments 604, 610). In other embodiments, the auxiliary sensor 600 is provided as a continuous position-sensing photodiode (PSD). In other embodiments, the auxiliary sensor 600 may be provided as a capacitive displacement sensor, an eddy current sensor, or an inductive sensor.

[0074] In other embodiments, the beam analysis system 130 (as described above with respect to FIGS. 5 and 6) is used as the auxiliary sensor 600. For example, the reflected beam 526 may be directed at the token 310, and the axis of the reflected beam 526 may be scanned along the X-direction along one or more edges of the aperture 314. When cross-axis fluctuations 510 occur (e.g., in the Y-direction as shown in FIG. 7), the axis of the reflected beam 526 crosses back and forth across the edge of the aperture 314, causing a change in the amount of laser energy entering the integrating sphere 320. Measurement data representing the fluctuations in the amount of laser energy measured by the photodetector 326 is sent to the controller 122, which calculates a correction or compensation factor and outputs a control command (e.g., to the Y-axis AOD of the first positioner 106) to correct or pre-compensate (and thereby correct) the Y-direction fluctuations.

[0075] In another embodiment, the beam analysis system 130 can be used to generate pre-compensation for the cross-axis fluctuations by generating a fluctuation frequency response, defined as the gain and phase between the on-axis position (due to the galvo axis rotation) and the cross-axis fluctuation motion (perpendicular to the on-axis motion) based on measurements obtained by the beam analysis system 130. A dynamic model of the fluctuation frequency response can be derived from this measured data, and this model can be used to predict and pre-compensate for the fluctuations in real time (using the modeled fluctuation data) during processing of the workpiece 102.

[0076] Although the above embodiment is directed to cross-axis wobble compensation system 520 being used to compensate for cross-axis wobble 510 of X-axis galvanometer mirror 502, a similar or identical wobble compensation system (not shown) can be used to measure and compensate for cross-axis wobble (e.g., along the X direction) of Y-axis galvanometer mirror 508. In other embodiments, cross-axis wobble compensation can also be achieved using a separate beam steering device, such as a fast steering mirror (FSM).

[0077] V. Conclusion The above is a description of the embodiments and examples of the present invention, and should not be construed as being limiting thereto. Although some specific embodiments and examples have been described with reference to the drawings, those skilled in the art will readily recognize that many modifications to the disclosed embodiments and examples and other embodiments are possible without significantly departing from the novel teachings and advantages of the present invention. Accordingly, all such modifications are intended to be included within the scope of the present invention as defined in the claims. For example, those skilled in the art will understand that the subject matter of any sentence, paragraph, example, or embodiment can be combined with any or all of the subject matter of any other sentence, paragraph, example, or embodiment, unless such combinations are mutually exclusive. Thus, the scope of the present invention should be determined by the following claims and the equivalents of such claims to be included therein.

Claims

1. a laser source operative to generate a beam of laser energy propagating along a beam path; an acousto-optic deflector (AOD) disposed in the beam path and operative to diffract the laser energy beam; a controller coupled to the AOD; a beam analysis system operative to measure one or more beam characteristics of the laser energy beam, generate measurement data representative of the measured one or more beam characteristics, and transmit the measurement data to the controller; Equipped with the controller is operative to control operation of the AOD based at least in part on the measurement data. Laser processing equipment.

2. 2. The laser processing apparatus of claim 1, wherein the one or more beam characteristics of the laser energy beam is at least one of a pulse repetition rate, a beam diameter, a spot size, a circularity, an astigmatism, a focal height, a beam waist, or a beam axis position.

3. The laser processing apparatus of claim 1 , wherein the AOD comprises a pair of AODs operative to diffract the beam path in a first direction and a second direction, respectively.

4. 10. The laser processing apparatus of claim 1, wherein the beam analysis system includes at least one of a camera-based beam profiler, a Rayleigh scattering beam profiler, and a rotating slit beam profiler.

5. 2. The laser processing apparatus of claim 1, wherein the controller is operative to control operation of the AOD to vary at least one of a beam diameter, spot size, circularity, astigmatism, focal height, beam waist, or beam axis position of the laser energy beam.

6. The AOD is operative to change a first beam characteristic of the laser energy beam, thereby changing a second beam characteristic of the laser energy beam; The beam analysis system includes: measuring the second beam characteristic; generating measurement data representative of the measured second beam characteristic; transmitting the measurement data from the beam analysis system to the controller; Outputting control commands from the controller to the AOD based at least in part on the measurement data. It works like this: the AOD is operative to reduce a magnitude of the change in the second beam characteristic.

2. The laser processing apparatus according to claim 1.

7. The laser processing apparatus of claim 6, wherein the AOD includes a pair of AODs.

8. 1. A method for controlling laser beam characteristics, comprising: generating a beam of laser energy; directing the beam of laser energy along a beam path to a beam analysis system using at least one AOD; measuring one or more beam characteristics of the beam of laser energy using the beam analysis system; generating measurement data representative of the measured one or more beam characteristics; transmitting the measurement data from the beam analysis system to a controller; outputting control commands from the controller to the at least one AOD based at least in part on the measurement data; method.

9. The method of claim 8, wherein the one or more beam characteristics of the laser energy beam are at least one of pulse repetition rate, beam diameter, spot size, circularity, astigmatism, focal height, beam waist, or beam axis position.

10. 10. The method of claim 8, wherein the at least one AOD is operative to vary at least one of a beam diameter, a spot size, a spot position, a circularity, an astigmatism, a focal height, a beam waist, and a beam axis position of the laser energy beam based on the measurement data.

11. the at least one AOD is operative to change a first beam characteristic of the laser energy beam, thereby changing a second beam characteristic of the laser energy beam; moreover, measuring the second beam characteristic using the beam analysis system; generating measurement data representative of the measured second beam characteristic; transmitting the measurement data from the beam analysis system to the controller; outputting control commands from the controller to the at least one AOD based at least in part on the measurement data; the at least one AOD is operative to reduce a magnitude of the change in the second beam characteristic. The method according to claim 8.

12. The method of claim 8 , wherein the at least one AOD comprises a pair of AODs.

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