Method and system for high-speed, precise micromachining an array of devices

Information

  • Patent Grant
  • 7871903
  • Patent Number
    7,871,903
  • Date Filed
    Tuesday, December 22, 2009
    14 years ago
  • Date Issued
    Tuesday, January 18, 2011
    13 years ago
Abstract
A method and system for high-speed, precise micromachining an array of devices are disclosed wherein improved process throughput and accuracy, such as resistor trimming accuracy, are provided. Beam scanning and deflection are both used to distribute beam spots to elements of an array of elements for selective processing. The deflection can be performed with a solid state deflector.
Description
BACKGROUND OF THE INVENTION

1. Field of the Invention


This invention relates to methods and systems for high-speed, precise micromachining of an array of devices. This invention also relates to the field of resistor trimming, particularly trimming of serpentine resistors on thin film block structures. Laser resistor trimming involves laser-processing cuts in an area of resistive material between conductors.


2. Description of the Related Art


Resistor trimming (as well as trimming and micro-machining of other electronic components and circuits) has evolved over the laser 20 years and is now used for adjusting circuits for thick film, thin film, and other electronic technologies. The publication “Trimming”, LIA HANDBOOK OF LASER MATERIALS PROCESSING, Chapter 17, pages 583-588, 2001 contains contributions describing several aspects of laser trimming. FIGS. 1a-1c of the present application are incorporated from the publication. FIG. 1a illustrates current flow lines of an untrimmed resistor, whereas FIG. 1b illustrates an effect of laser trimming on the current flow lines. FIG. 1c summarizes several results (stability, speed, and tolerances) with various resistor geometries and cut types.


The following exemplary U.S. patents are related to laser trimming methods and systems: U.S. Pat. Nos. 6,510,605; 6,322,711; 5,796,392; 4,901,052; 4,853,671; 4,647,899; 4,511,607; and 4,429,298.


U.S. Pat. No. 4,429,298 relates to many aspects of serpentine trimming. Basically, a serpentine resistor is formed with sequential plunge cuts and a final trim cut is made parallel to the resistor edge from the last plunge. It describes “progressively” making plunge cuts on a resistor alternately from one end, considers maximum and minimum plunge cut lengths, a resistance threshold of the plunge cuts for the trim cut, a faster cutting speed for plunge cuts, and a structured process flow with various resistance and cut length tests.


There is a continuing need for improved high-speed, micromachining such as precise trimming at all scales of operation, ranging from thick film circuits to wafer trimming.


SUMMARY OF THE INVENTION

An object of the present invention is to provide an improved method and system for high-speed, precise micromachining an array of devices.


In carrying out the above object and other objects of the present invention, a method is provided for high-speed, precise micromachining an array of devices. Each of the devices has at least one measurable property. The method includes the steps of: a) selectively micromachining a device in the array to vary a value of a measurable property; b) suspending the step of selectively micromachining; c) while the step of selectively micromachining is suspended, selectively micromachining at least one other device in the array to vary a value of a measurable property; and d) resuming the suspended step of selectively micromachining to vary a measurable property of the device until its value is within a desired range.


The devices may be resistors.


The resistors may be film resistors.


The steps of selectively micromachining may be performed with at least one laser beam which cuts the devices.


The method may further include measuring one measurable property of at least one of the devices to obtain a measured value.


The method may further include comparing the measured value with a predetermined threshold to obtain a comparison and micromachining at least one of the other devices based on the comparison.


The method may further include selectively micromachining at least one of the other devices based on the measured value.


The method may further include determining not to measure a measurable property of at least one of the other devices based on the measured value.


The method may be for high-speed, precise laser trimming an array of resistors, and one of the measurable properties may be resistance.


Each of the steps of selectively micromachining may include the step of selectively removing material.


The array may include at least one of one or more rows and one or more columns.


At least one of the steps of selectively micromachining may be performed with a plurality of focused laser pulses to irradiate a plurality of devices substantially simultaneously.


At least one of the steps of selectively micromachining may be performed with a plurality of focused laser pulses. The method may further include distributing the focused laser pulses.


The step of distributing may include the steps of producing a distribution pattern with a plurality of laser beams and focusing the laser beams.


The laser trimming may produce a series of interdigited cuts in an area of resistive material between conductors of the resistors.


At least one of the steps of selectively micromachining may include the steps of positioning a laser beam at a location of each of the devices to be micromachined and selectively irradiating at least a portion of each of the devices to be micromachined with at least one laser pulse.


At least one of the steps of selectively micromachining may include the steps of generating and relatively positioning a laser beam to travel in a first direction within a field of the array and selectively irradiating at least a portion of at least one device within the field with at least one laser pulse.


The method may further include generating and relatively positioning a laser beam to travel in a second direction substantially opposite the first direction within the field and selectively irradiating at least a second portion of at least one device within the field with at least one laser pulse.


At least one of the steps of selectively micromachining may include the steps of generating and relatively positioning a laser beam to travel in a first scanning pattern across the devices, superimposing a second scanning pattern with the first scanning pattern and irradiating at least one device with at least one laser pulse.


The second scanning pattern may be a retrograde scan, and scan speed of the at least one laser pulse irradiating the at least one device is lower than a corresponding scan speed of the first scanning pattern. Laser energy may be concentrated at the at least one device for a period of time longer than a period of time associated with only the first scanning pattern whereby throughput is improved.


The second scanning pattern may include a jump from a first device to a second device.


The steps of selectively micromachining may be performed with a plurality of laser pulses, and at least one of the pulses may have an energy in the range of 0.1 microjoules to 25 millijoules.


The measured value may be a measured temperature value.


The devices may be substantially identical.


Further in carrying out the above objects and other objects of the present invention, a system is provided for high-speed, laser-based, precise micromachining an array of devices. Each of the devices has at least one measurable property. The system includes a pulsed laser subsystem. An optical subsystem is coupled to the pulsed laser system to selectively irradiate a portion of a device with a laser pulse. A controller is coupled to the subsystems to control the subsystems to: a) selectively micromachine a device in the array to vary a value of a measurable property; b) suspend the selective micromachining; c) while the selective micromachining is suspended, selectively micromachine at least one other device in the array to vary a value of a measurable property; and d) resume the selective micromachining to vary a measurable property of the device until its value is within a desired range.


The optical subsystem may include a beam deflector and a beam deflector controller for controlling the beam deflector to scan a laser beam along a first scan pattern which includes each of the devices to be micromachined.


The system may further include a measurement subsystem to measure one of the measurable properties of at least one of the devices.


The micromachining may be laser trimming and the array is an array of resistors, and the measurement subsystem may be a probe array.


The optical subsystem may include a second beam deflector to superimpose a higher-speed, second scan pattern on the first scan pattern whereby throughput of the system is improved.


The controller may be coupled to the subsystems so that the subsystems are controlled to generate a trimming sequence for at least one of the devices that reduces device temperature during micromachining.


The above object and other objects, features, and advantages of the present invention are readily apparent from the following detailed description of the best mode for carrying out the invention when taken in connection with the accompanying drawings.





BRIEF DESCRIPTION OF THE DRAWINGS


FIGS. 1
a-1b are schematic views which illustrate current flow lines before and after laser trimming, respectively;



FIG. 1
c is a chart which illustrates the effect of various cut types on several trim parameters;



FIG. 2
a is a schematic view of an array of chip resistors arranged in rows and columns and which illustrates results using laser trimming steps in accordance with an embodiment of the present invention;



FIG. 2
b is a block diagram flow chart further defining trimming steps corresponding to FIG. 2a;



FIG. 3 is a block diagram flow chart further defining the trimming operations of FIGS. 2a and 2b in a system of the present invention;



FIG. 4
a is a schematic view of an array of chip resistors arranged in rows and columns and which illustrates results using laser trimming steps in accordance with another embodiment of the present invention;



FIG. 4
b is a block diagram flow chart further defining trimming steps corresponding to FIG. 4a;



FIG. 5 is a block diagram flow chart further defining the trimming operations of FIGS. 4a and 4b in a system of the present invention;



FIG. 6
a is a schematic view of a laser trimming system which may be used in at least one embodiment of the invention;



FIG. 6
b is a schematic view of a resistor which has geometric properties to be measured, specifically edges of the resistor, using data obtained with the system of FIG. 6a;



FIG. 7 is a graph which shows position of a laser beam versus time during scanning of a resistor array in one embodiment wherein a fast scan with a solid state deflector is superimposed with a electro-mechanical linear scan to selectively form the cuts of either FIG. 2 or FIG. 4 at increased speed;



FIG. 8 is a schematic view of a system delivering multiple focused beams to at least one resistor so as to increase trimming speed; and



FIG. 9 is a schematic view of a system which provides multiple beams to at least one resistor in a laser trimming system.





DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

High-Speed Serpentine Trimming Process


In resistor trimming, the cuts direct the current flowing through the resistive material along a resistance path. Fine control and adjustment of the cut size and shape change the resistance to a desired value, as illustrated in FIGS. 1a-1c. Typically, chip resistors are arranged in rows and columns on a substrate. FIG. 2a shows an arrangement wherein a row of resistors R1,R2, . . . RN is to be processed. A probe array, having a probe 200 and depicted by arrows in FIG. 2a, is brought into contact 202 with the conductors of a row of resistors. A matrix switch addresses the contacts for a first pair of conductors (e.g.: contacts across R1) and a series of cuts and measurements is performed to change the resistance between the conductor pair to a desired value. When the trimming of a resistor is complete, the matrix switches to a second set of contacts at the next row element (e.g.: R2) and the trimming process is repeated. When a complete row of resistors (R1 . . . RN) has been trimmed, contact is broken between the contacts and the probe array. The substrate is then relatively positioned to another row, the probe array is brought into contact, and a second row is processed in the manner as the preceding row.


The trimming of serpentine thin film resistors, for instance as illustrated in FIG. 1c, involves laser processing to create interdigitated cuts in an area of resistive material between conductors. The interdigitated cuts direct current flowing through the resistive material along a serpentine path that wraps around the cuts. This geometry allows a wide range of resistances to be created with a single areal film/conductor layout. The approach outlined above would process a sequence of serpentine cuts with measurement steps at a resistor site and then move to the next resistor.


Referring to FIG. 2a, an initial laser position for any cut is depicted as 205, and a beam positioner directs the beam along the linear path through the resistor material. In accordance with the present invention, a new paradigm trims a leg on a first resistor (e.g. trim cut 204 of R1) and measures the resistance. If the resistance is below a predetermined threshold, similar collinear trims across other resistors R2 . . . RN in the row are made. A completed collinear trim along the row is illustrated at 210 in FIG. 2a, and the corresponding block 220 is further defined in FIG. 2b. In at least one embodiment of the present invention, a subset of resistors may be measured to determine thin film consistency across the substrate, but if the thin film is of known consistency one measurement may be sufficient.


The next collinear group of cuts along resistors of the row is made in the same manner as shown at 211 of FIG. 2a and further defined at block 221 of FIG. 2b, the resistor RN being trimmed initially. The process is repeated as shown in 212-213 of FIG. 2a with corresponding further defined at blocks 222-223 of FIG. 2b. If a measurement shows that a threshold has been crossed, trimming of the row R1 . . . RN proceeds with measurement of each resistor so as to trim to value before switching to the next resistor (depicted as 214 at block 224).


Limiting the number of measurements and maintaining a collinear trim trajectory both increase trim speed.


The flowchart of FIG. 3 further defines steps, corresponding to FIGS. 2a-2b, and additional processing steps used in a trimming system (e.g.: indexing and loading).


In at least one embodiment, cutting steps may be carried out based upon pre-determined information. By way of example, for some resistor types, a first series of elements may be cut before resistance is measured, the sequence based on pre-determined parameters of the resistor (e.g.: geometry) and/or known film properties, (e.g: sheet resistance). Similarly, a number of non-measured cuts may be determined in a learn mode at the first resistor (e.g: including at least one measurement, or iterative measurements). In one learn mode, iterative measurements are made and the number of non-trim cuts is determined based on the measurements and material properties. In at least one embodiment a number of the non-measured cuts may be calculated.


For example, four cuts may be made without measurement. Referring to FIG. 4a, an initial condition 410 is illustrated wherein probes are placed in contact 202 with the row as in FIG. 2a. Referring to FIG. 4b, the initial condition is further defined at block 420. By way of example, FIGS. 4a-4b illustrate an embodiment of the trimming process wherein initially four cuts 411 are made without any measurement. As shown in FIG. 4b, block 421 defines a predetermined number of cuts (e.g: four), without measurement, based on at least one pre-trim value or condition. The scan path for completing four cuts is depicted at 405. Then the first resistor R1 in the row is trimmed at 406 and measured to determine if the target value is reached. If not, the remaining resistors R2 . . . RN are cut (e.g.: without measurement) as depicted at 412, further defined by block 422.


Then the process is repeated, beginning with trimming 407 of RN, and then cutting of R[N−1] to R1 as shown at 413 and further defined by block 423. Hence, with each change in direction either R1 or RN is trimmed, and if the target value is not reached the remaining resistors R2 . . . RN or R[N−1] . . . R1, respectively, are cut. A final step results after R1 or RN reaches a target value. Each resistor is connected and trimmed sequentially, illustrated at 414 and further defined by block 424.


The flowchart of FIG. 5 further defines steps corresponding to FIGS. 4a-4b, and additional processing steps used in a trimming system (e.g.: which includes the steps of indexing and loading).


In one embodiment, wherein pre-determined information is obtained using iterative measurements, pre-trim values are provided. The values may be specified by an operator, process engineer, or otherwise obtained. The software provides capability for specifying or using the pre-trim target values so that the applied test voltage and/or current is controlled. This feature is useful for avoiding voltages that are high enough to damage the part over the wide range of resistance change associated with serpentine trimming. When using a fast resistor measurement system in an embodiment of the invention, the voltage applied to the resistor for measurement is decreased for the initial low resistance cut to limit current through and potential damage to the resistor. As subsequent cuts are made and the resistance increases, the measurement voltage is increased.


The exemplary trim and cut sequences of FIGS. 2a and 2b and 4a and 4b may be modified so as to allow for variations in material properties and other process parameters and tolerances.


For example, in at least one embodiment of the present invention, additional steps may be utilized when a measured trim cut reaches the target value and length is within a predetermined margin of the maximum allowed cut length. Within the margin, variation in the material properties may leave some trim cuts short of the target value and require additional cuts.


In a first mode, trim cuts are made sequentially in a row of elements and the location of elements not reaching the target value are saved. With subsequent trim cuts, the remaining elements at the saved locations are trimmed to the target value.


In a second mode, based on the length of the first element trimmed to value, the cut length is reduced to prevent the target value from being reached and non-measurement cuts are processed to complete the row. Subsequent trim cuts bring all elements in the row to the target value.


In a third mode, the length of at least one prior cut on an element is modified to prevent subsequent cuts from falling into the marginal condition.


In at least one embodiment, additional steps may be utilized when the value of a measured trim cut is within a predetermined margin of the target value. Within the margin, variation in the material properties may leave some elements beyond the target value using full non-measurement cuts.


In a first mode, trim cuts are made sequentially in a row of elements and the location of elements not reaching the target value are saved. With subsequent trim cuts, the remaining elements at the saved locations are trimmed to the target value.


In a second mode, based on the value measured in the first element, the cut length is reduced to prevent the target value from being reached and non-measurement cuts are processed to complete the row. Subsequent trim cuts bring all elements in the row to the target value.


In a third mode, the length of at least one prior cut on an element is modified to prevent subsequent cuts from falling into the marginal condition.


Experimental data indicates improvements in throughput by cutting all the resistors in a row as shown in FIGS. 2-4, as opposed to the conventional single resistor trim technique. By way of example, approximate results are shown in the table below:












32 RESISTOR ROW, 20 CUTS PER RESISTOR









Laser Q-Rate
Single Resistor Trim



(KHz)
(Sec)
Row Trim (Sec)












5
39
28


10
27
16


20
20
10









The overall trim speed increases with an increasing number of resistors in a row, fewer measurements, and with reduced time for final (i.e., fine) trimming.


Further, each resistor has additional time to recover from laser generated energy. The sequence of cuts may be determined to manage temperature change in an element (e.g. reduce maximum element temperature during cutting). For example, with reference to FIG. 4a, the sequence 405 may be reversed so that a set of cuts are made starting near the center of an element and progressing to an end of the element approaching the conductor and probe. Other sequences, suitable sequences may be used (e.g: any sequence of non-adjacent cuts having advantage for thermal management). Preferably, a second element may be cut prior to an additional step of measuring.


Range of resistance change for serpentine cuts varies from about 1 order of magnitude (e.g: 10×), two orders of magnitude typical (100×), and up to about 500× with current materials.


Laser Trimming Systems


In at least one embodiment of the invention a laser trimming system may be first calibrated using a method as described in “Calibrating Laser Trimming Apparatus”, U.S. Pat. No. 4,918,284. The '284 patent teaches calibrating a laser trimming apparatus by controlling a laser beam positioning mechanism to move a laser beam to a desired nominal laser position on a substrate region, imprinting a mark (e.g., cutting a line) on a medium to establish an actual laser position, scanning the imprinted mark to detect an actual laser position, and comparing the actual laser position with the desired nominal position. Preferably, the laser beam operates on one wavelength, and the mark is scanned with a detection device that operates on a different wavelength. The detection device views a field that covers a portion of the overall substrate region, and determines the position of a mark within the field. The '284 patent further teaches determining where a beam position is in relation to a camera field of view.


Other calibration techniques may be used alone or in combination with the '284 method. For instance, U.S. Pat. No. 6,501,061 “Laser Calibration Apparatus and Method,” discloses a method of determining scanner coordinates to accurately position a focused laser beam. The focused laser beam is scanned over a region of interest (e.g. an aperture) on a work-surface by a laser scanner. The position of the focused laser beam is detected by a photodetector either at predetermined intervals of time or space or as the focused laser beam appears through an aperture in the work surface. The detected position of the focused laser beam is used to generate scanner position versus beam position data based on the position of the laser scanner at the time the focused laser beam is detected. The scanner position versus beam position data can be used to determine the center of the aperture or the scanner position coordinates that correspond with a desired position of the focused laser beam.


Subsequent to system calibration, which preferably includes calibration of numerous other system components, at least one substrate having devices to be trimmed is loaded into the trimming station.


Referring to FIG. 6a, partially incorporated from the '284 patent, an improved laser trimming system may include an infrared laser 602, typically having a wavelength from about 1.047 microns-1.32 microns which outputs a laser beam 603 along an optical path 604 to and through a laser beam positioning mechanism 605 to a substrate region 606. For application to trimming of thin film arrays, a preferred wavelength of about 0.532 microns may be obtained by doubling the output frequency of the IR laser using various techniques known in the art and commercially available.


The laser beam positioning mechanism 605, preferably includes a pair of mirrors and attached respective galvanometers 607 and 608 (various available from the assignee of the present invention). The beam positioning mechanism 605 directs the laser beam 603 through a lens 609 (which may be telecentric or non-telecentric, and preferably achromatized at two wavelengths) to a substrate region 606, over a field. The X-Y galvanometer mirror system may provide angular coverage of the entire substrate if sufficient precision is maintained. Otherwise, various positioning mechanisms may be used to provide relative motion between the substrate and the laser beam. For instance, a two-axis precision step and repeat translator illustrated schematically as 617 may be used to position the substrate within the field of galvanometer based mirror system 607,608 (e.g.: in the X-Y plane). The laser beam positioning mechanism 605 moves the laser beam 603 along two perpendicular axes thereby providing two dimensional positioning of the laser beam 603, across the substrate region 606. Each mirror and associated galvanometer 607, 608 moves the beam along its respective x or y axis under control of a computer 610. Illumination devices 611 which may be halogen lights or light emitting diodes produce visible light to illuminate substrate region 606.


A beam splitter 612 (a partially reflective mirror) is located within the optical path 604 to direct light energy reflected back along the path 604 from the substrate region 606 to a detection device 614. The detection device 614 includes a camera 615, which may be a digital CCD camera (e.g.: color or black/white) and associated frame grabber 616 (or digital frame buffer provided with the camera), which digitizes the video input from the television camera 615 to obtain pixel data representing a two-dimensional image of a portion of the substrate region 606. The pixel data are stored in a memory of the frame grabber 616, or transmitted, for instance, by a high speed link, directly to the computer 610 for processing.


The beam positioning subsystem may include other optical components, such as a computer-controlled, optical subsystem for adjusting the laser spot size and/or automatic focusing of the laser spot at a location of the substrate.


In applying the invention to thin film trimming of resistor arrays, at least one thin film array is supported by the substrate. The calibration data obtained as above is preferably used in combination with an automated machine vision algorithm to locate an element (e.g. resistor R1) of the array and measure the location of at least one geometric feature of an element 620 of FIG. 6b. For instance, the feature may be one of the horizontal edges 621 (e.g.: an edge parallel to the X-direction), and one of the vertical edges 622 (e.g.: an edge parallel to the Y direction) found by analysis of pixel data in memory using one of numerous available edge detection algorithms. The edges may include multiple edge measurements along the entire perimeter of a resistor, a sample of the edges, or edges from numerous resistors of the array. The width of the resistor is then determined which may be used to define the cutting length, typically as a predetermined percentage of the width. Preferably, the edge information is obtained automatically and used with calibration data to control the length of each cut within the row R1 . . . RN, for example. Other measurement algorithms may also be used where suitable, for instance image correlation algorithms or blob detection methods.


Calibration may be applied at one or more points along the cut. In at least one embodiment the starting point of at least one cut will be corrected with calibration data.


Preferably, the length and the starting point of a plurality of cuts in FIGS. 2 and 4 will be corrected.


Most preferably, the length and starting point of all cuts in FIGS. 2a and 4a will be corrected.


In one embodiment, the first resistor (e.g.: R1 or RN) will be calibrated, and a corresponding correction applied to all resistors (e.g.: R1, . . . ,RN) of the row.


Complete automation is preferred. However, a semi-automatic algorithm with operator intervention may be used, for instance where a galvanometer is positioned so that the array element 620 is in the field, then the beam is sequentially positioned along the element interactively and the intensity profile (or derivative or intensity) observed on a display 630 by an operator.


The use of the calibration information to adjust coordinates within the array region is valuable for improving the precision of laser beam positioning without throughput degradation. Measurements of resistor width and the alignment data is useful for both controlling the length of a cut and for correcting deviations from linearity and non-orthogonality of the array relative to the scanner X,Y coordinate system. The use of the calibration data for geometric correction is particularly well suited for use in laser trimming systems having one or more linear translation stages.


Geometric correction does not necessarily replace other useful system design features including f-theta lens linearity, fan beam compensation etc. The system tolerance stack-up may generally be used to determine tradeoffs between the number of cut calibration locations based on expected position error. When fanning out the beam, especially with large spacing across many resistors, only one is calibrated and aligned. For instance, when the spacing between resistors is relatively large, a single cut may be calibrated and aligned. Resulting errors in position are anticipated at elements, to be mitigated in part with system design, f-theta linearity, fan spread compensation etc. Closely spaced cuts of a transverse fan are expected to have smaller errors compared with on axis fan.


Further Throughput Improvements—Optical Techniques


In at least one embodiment of the present invention the throughput may be further improved by increasing the effective scan rate using one or more of the techniques below.


Further increases in processing speed with collinear trims can be accomplished with faster jumps across trim gaps between the resistors of a row. One such gap 216 is shown in FIG. 2a. Referring to FIG. 7, in at least one embodiment of the invention, a single-axis Acousto-Optic Beam Deflector (AOBD) superimposes a saw tooth linear scan pattern 701 as the galvanometer scans across the row at a constant velocity 702. During trimming the AOBD scans in retrograde motion 703, and, between trims, provides a fast jump 704 to the next cut. This allows the galvanometer to scan at constant velocity and minimizes the contributions of jumps to the total process time.


The use of acousto-optic deflectors in combination with galvanometers for speed improvements is known in the art. For instance, U.S. Pat. No. 5,837,962 discloses an improved apparatus for heating, melting, vaporizing, or cutting a workpiece. A two-dimensional acousto-optic deflector provided about a factor of five improvement in marking speed.


U.S. Pat. No. 6,341,029, which is incorporated by reference in its entirety, shows in FIG. 5 thereof an embodiment having several components which may be used in a complete system when practicing the present invention in a retrograde mode for increased speed. In the '029 patent, acousto-optic deflectors and galvanometers, with an associated controller, are shown for dithering CW beams for laser patterning. Also see col. 3, line 47 and col. 4 of the '029 patent for additional details regarding system construction.


The arrangement of the '029 patent may be readily adapted, using available techniques, so as to provide modifications of optical components and scan control profiles so as to practice the retrograde scanning technique of the present invention, preferably with additional hardware calibration procedures.


In another embodiment of the invention, the collinear trims on serpentine resistors may be accomplished in a parallel fashion with multiple spots along the row. A fan-out grating or other multi-beam generating device is used to create a spot array so that 2 or more spots are formed and aligned according to the resistor pitch along the row. For example, U.S. Pat. No. 5,521,628 discloses the use of diffractive optics to simultaneously mark multiple parts. The multiple beams may be lower power beams generated from a more powerful laser source, or combined beams from multiple sources. The scan system scans the multiple beams and forms spots through a common scan lens simultaneously across multiple resistors. The trim process is similar to the single spot method with two or more cuts in parallel during non-measurement cutting steps. When the threshold is reached, the system converts to a single spot mode to serially trim each resistor to value.


Similarly, the collinear trims on serpentine resistors may be accomplished in a parallel fashion with multiple spots formed on a target to make parallel cuts. A fan-out grating or other multi-beam generating device is used to create a spot array so that 2 or more spots are formed, the spots being aligned to an element with predetermined spacing between cuts. If a predetermined number of cuts are performed (e.g. four as shown in FIG. 4a) then, in one embodiment, the number of passes could be reduced by 50% (e.g.: a single pass in each direction). This embodiment may be most useful if resistor process variations and tolerances are well established. The grating may be in an optically switched path so as to selectively form multiple spots or a single spot.


Published U.S. patent application No. 2002/0162973 describes a method and system for generating multiple spots for processing semiconductor links for memory repair. Various modifications in the lens system and deflector system may be used to generate multiple spots for use in the present invention.


In one embodiment, a single laser pulse is used to trim up to two resistors at one time (e.g., no, one or two cuts). Referring to FIG. 8, two focused spots 801,802 are formed on two cuts by spatially splitting the single collimated laser beam 803 into two diverging collimated beams 804,805. Fine adjustment of the differential frequency controls spot separation. The use of acousto-optic devices for spatially splitting beams in material processing applications is known in the art. For example, Japanese patent abstract JP 53152662 shows one arrangement for drilling microscopic holes using a multi-frequency deflector having selectable frequencies f1 . . . fN.


A laser 806 of FIG. 8 is pulsed at a predetermined repetition rate. The laser beam goes through relay optics 807 that forms an intermediate image of the laser beam waist into the acoustic optic modulator (AOM) aperture. The AOM 808, which operates in the Bragg regime, preferably is used to controllably generate the two slightly diverging collimated first order diffraction laser beams and control the energy in each beam. The AOM is driven by two frequencies, f1 and f2 where f1=f0+df and f2=f0−df where df is a small percentage of the original RF signal frequency f0. The angle between the two beams is approximately equal to the Bragg angle for f0 multiplied by 2(df/f0)). The AOM controls the energy in each of the laser beams by modulating the signal amplitudes of two frequency components, f1 and f2, in the RF signal 812 and making adjustments for beam cross-coupling.


After exiting the AOM 808, the beams go through an optional beam rotation control module 809 to rotate the beam 90 degrees so as to orient the beam in either X or Y. In one embodiment, a prism is used for this rotation, though many rotation techniques are well known as described in related U.S. patent publication No. 2002/0170898.


Next, the beam goes through a set of optics to position the beam waist and set the beam size to be appropriate for the zoom optics and objective lens 810. The zoom optics also modify the angle between the two beams, therefore the angle between the two beams exiting the AOM 808 has to be adjusted depending on the zoom setting to result in the desired spot separation at the focal plane. Next, the laser beams enter the objective lens 810 which provides a pair of focused spots 801,802 on two resistors. The two spots are separated by a distance that is approximately equal to the focal length of the lens 810 times the angle between the two beams. The retrograde and parallel methods can be combined for collinear trimming on serpentine resistors. For example, a beam is scanned by an AOBD then split into a pair and scanned across the field. Two adjacent resistors are trimmed simultaneously and the jump is from resistor N to resistor N+2 to the next pair or resistors.


Alternatively, or with a two-dimensional deflector, a pair of spots may be produced in a direction orthogonal to the serpentine scan direction. For instance, with relatively simple control and programming of a one-dimensional AOBD, the deflector may be used (with appropriate output power control) to simultaneously produce at least two of the four beams used for making four cuts as shown in FIG. 4a. As such, the scan time for the cuts may be reduced by 50%. As a result of programmable deflection, the AOBD may be preferred over a fan out grating. The multiple spots may also be produced during coarse and fine trim as needed.



FIG. 9 illustrates schematically an exemplary embodiment of an improved laser trimming system having a module 901 from FIG. 8 added for either retrograde scanning, parallel processing, or a combination thereof. For example, a signal 902 from the computer 610 may be used to control the AOBD or other solid state deflector 808 in one or more axes, and the beam rotation module 809, if provided. The module 901 may include relay optics 807 and other beam shaping components. Preferably, at least one AOBD is used so as to provide considerable flexibility and ease of use, for example with a digital RF generator providing the control signal 812 from the computer 610.


Furthermore, techniques for forming elongated or elliptical spots can be employed with this invention to further increase processing speed or quality. Improvements in trimming speed associated with spot shaping are described in co-pending published U.S. patent application No. 2002/0170898.


Numerous other design alternatives may be used in at least one embodiment of the invention for enhancing system performance and ease of use. For example, alternatives include but are not limited to the following:


1. The system may provide for computer-controlled spot size and/or focus adjustments. U.S. Pat. No. 6,483,071, assigned to the assignee of the present invention, illustrates an optical subsystem providing for both spot size control and dynamic focus for laser based memory repair.


2. Another alternative is control of beam energy with a variable beam attenuator. The attenuator may be an acousto-optic deflector (or modulator). Neutral density filters or polarization-based attenuators may be used, whether manually or automatically adjusted. In U.S. Pat. No. 6,518,540 a suitable variable attenuator is shown, by way of example, having a rotating half waveplate and a polarization-sensitive beam splitter.


3. The pulse width may be varied using methods known to those skilled in the art, with the understanding that the energy of a q-switched laser will vary with repetition rates, particularly at high repetition rates. For dynamic trimming, wherein a measurement is performed between pulses, it may be preferred to maintain substantially constant pulse energy. A method for pulse energy control is disclosed in the U.S. Pat. No. 6,339,604 patent which reduces the variation in energy at the target as the trimming speed is decreased (e.g.: larger pulse temporal spacing), corresponding to periods of precision measurement when the resistance value approaches the pre-determined target value.


4. In at least one embodiment, a diode-pumped, frequency-doubled, YAG laser is used to trim the resistor array. The output wavelength of 532 nm resulted in low drift, absence of microcracking, and negligible heat affected zone when compared to other wavelengths. A pulse width of about 25-45 ns may be preferred, with less than 30 ns typical. The preferred maximum laser repetition rate will be at least 10 KHz. The pulse width, much less than typical for thick film systems, provides for thin film material removal at a relatively high repetition rate. Preferably, the maximum available pulse energy at the reduced pulse widths and high repetition rates will allow for losses associated with the diffractive optics (e.g: grating or AOBD) so that multiple spots may be provided.


5. The laser may be focused to an approximate, diffraction-limited, spot size. The spot size will typically be less than about 30 microns or less, with a preferred spot size less than about 20 microns, and a most preferred spot size in the range of about 6-15 microns, for instance, 10-15 microns.


6. In the illustrated embodiments of the invention, serpentine cuts are illustrated as a series of parallel interdigitated cuts. However, it is to be understood that application of the present invention is not restricted to forming parallel cuts. Trimming or micromachining so as to produce a plurality of non-intersecting cuts with a reduced number of measurements is considered to be within the scope of the invention.


7. Further, embodiments of the invention are not restricted to thin film resistor measurements, but are applicable to other micromachining applications wherein a physical property is measurable. The measurement is not restricted to electrical measurements, but may be temperature monitoring (for instance, with an infrared sensor), stress, vibration, or other property.


While embodiments of the invention have been illustrated and described, it is not intended that these embodiments illustrate and describe all possible forms of the invention. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the invention.

Claims
  • 1. A method of precisely cutting selected substantially identical conductive circuit elements in an array of such elements arranged in at least one of one or more rows and one or more columns on a substrate, the cutting selectively removing material from the selected elements, the method comprising: generating at least one pulsed laser output beam; andirradiating the selected substantially identical conductive circuit elements with the pulsed laser output beam, the step of irradiating comprising: positioning and focusing the laser output beam to produce calibrated, aligned and focused beams to each of a plurality of selected elements of the array, wherein the step of positioning comprises: scanning the pulsed laser output beam in a scanning pattern over the array of elements; andsuperimposing a distribution pattern on the scanning pattern by deflecting the pulsed laser output beam with at least one programmable deflector; and,wherein the pulsed laser beam impinges each selected array element with controlled energy and wherein the pulsed laser beam selectively and accurately cuts each selected array element.
  • 2. The method of claim 1, comprising deflecting according to a programmed sequence of deflections.
  • 3. The method of claim 1, wherein the scanning pattern comprises a substantially continuous scan over the elements and wherein the deflecting provides fast jumps between elements within the substantially continuous scan.
  • 4. A method of reducing a number of passes across a substrate in a laser micro-machining sequence of precisely cutting selected substantially identical conductive circuit elements in an array of such elements arranged in at least one of one or more rows and one or more columns on the substrate, the cutting selectively removing material from the selected elements, the method comprising: forming a programmable distribution of multiple spots in a spot array, andmoving the spot array along a row or column to scan at least a portion of the substrate, andprocessing conductive elements of the array by selective irradiation with the programmable distribution;wherein forming a programmable distribution pattern comprises sequentially deflecting one or more beams to elements in multiple rows in first and second directions with a programmable acousto-optic deflector to jump across gaps between elements in a programmed sequence, whereby multiple rows are processed in a single pass and wherein a moving speed is increased by superimposing acousto-optic deflection and substrate scanning.
  • 5. A method of precisely processing selected substantially identical conductive circuit elements in an array of such elements arranged in multiple rows and one or more columns on a substrate, the processing selectively removing material from the selected circuit elements, the method comprising: moving the substrate along a row of conductive circuit elements;generating at least one pulsed laser output beam; andsubstantially irradiating sequentially with the pulsed laser output beam the selected substantially identical conductive circuit elements, the step of irradiating comprising:deflecting and focusing the pulsed laser output beam to each of a plurality of selected elements of the array in a sequence to produce a distribution pattern of multiple focused beams to each of a plurality of selected elements of the array, the plurality of selected elements distributed along the multiple rows of the array, the step of deflecting comprising deflecting in 2 axes, thereby providing fast jumps across gaps between elements relative to the moving substrate;wherein the steps of deflecting and focusing are carried out, at least in part, with at least one solid-state deflector and an objective lens and wherein at least one focused beam impinges each selected circuit element, and wherein the at least one laser pulse selectively and accurately cuts each selected circuit element.
  • 6. The method of claim 5, wherein the distribution pattern is a programmable spot distribution comprising a multiple spots in a spot array, the programmable distribution formed with a programmable acousto-optic deflector, the distribution pattern comprising a sequence of deflections, the sequence including jumps across gaps between elements in a programmed sequence, whereby multiple rows are processed in a single pass and wherein a moving speed is increased by superimposing acousto-optic deflection and substrate scanning.
  • 7. The method of claim 1, wherein the steps of deflecting and scanning are carried out with a multi-beam generator comprising the at least one solid-state deflector and an electromechanical scanner.
  • 8. The method of claim 7, wherein the solid-state deflector is a 2D solid-state deflector.
  • 9. The method of claim 7, wherein the electromechanical scanner is a 2D galvanometer based mirror scanner.
  • 10. The method as claimed in claim 1, wherein deflecting comprises generating control signals and controlling a signal generator in response to the control signals to generate one on more frequencies corresponding with locations in the distribution pattern.
  • 11. The method of claim 7, wherein the electromechanical scanner provides a linear scan with a stage driven apparatus.
  • 12. The method of claim 11, wherein the electromechanical scanner comprises a deflection mirror and stage driven apparatus, wherein the deflection mirror provides stage motion compensation.
  • 13. The method of claim 11, wherein the deflector provides fast jumps to thereby increase the effective linear scan rate.
  • 14. The method of claim 1, further comprising orienting the distribution pattern into a selected orientation.
  • 15. The method of claim 1, further comprising irradiating for a second time elements previously irradiated by a first laser beam.
  • 16. The method of claim 1, further comprising determining a sequence of non-adjacent cuts based on an advantageous thermal management.
  • 17. The method of claim 1, further comprising focusing multiple beams with a common scan lens.
  • 18. The method of claim 1, wherein the elements are resistors.
  • 19. The method of claim 1, wherein the elements are links.
CROSS-REFERENCE TO RELATED PATENTS AND APPLICATIONS

This application is a continuation of U.S. patent application Ser. No. 11/415,653, filed on May 2, 2006 and entitled Method and System for High-Speed, Precise Micromachining an Array of Devices, now U.S. Pat. No. 7,666,759, which is a continuation of U.S. application Ser. No. 11/131,668 filed on May 18, 2005, now U.S. Pat. No. 7,407,861, which is a divisional of U.S. application Ser. No. 10/397,541 filed on Mar. 26, 2003, now U.S. Pat. No. 6,951,995, and which is a continuation in part of U.S. application Ser. No. 10/108,101, filed on Mar. 27, 2002, now U.S. Pat. No. 6,972,268. This application further claims the benefit of U.S. provisional application Ser. No. 60/368,421, filed Mar. 28, 2002, entitled “Laser Based Micro-Machining Method And System, and an Application To High Speed Laser Trimming Of Chip Components And Similar Structures.” U.S. Pat. No. 6,341,029, entitled “Method and Apparatus for Shaping a Laser-Beam Intensity Profile by Dithering,” assigned to the assignee of the present invention with a common inventor, is hereby incorporated by reference in its entirety. This application is also related to U.S. Pat. No. 6,339,604, entitled “Pulse Control In Laser Systems,” also assigned to the assignee of the present invention. This application is also related to co-pending U.S. patent application Ser. No. 10/107,027, filed 27 Mar. 2002, now published U.S. patent application No. 2002/0170898, entitled “High Speed, Laser Based Method and System for Processing Material of One or More Targets Within a Field” also assigned to the assignee of the present invention.

US Referenced Citations (164)
Number Name Date Kind
3941973 Luck, Jr. et al. Mar 1976 A
4044222 Kestenbaum Aug 1977 A
4399345 Lapham et al. Aug 1983 A
4429298 Oberholzer Jan 1984 A
4511607 White Apr 1985 A
4532402 Overbeck Jul 1985 A
4551607 Moy Nov 1985 A
4647899 Moy Mar 1987 A
4761774 Ishibashi et al. Aug 1988 A
4826785 McClure et al. May 1989 A
4827325 Or-Bach et al. May 1989 A
4853671 Iversen et al. Aug 1989 A
4861964 Sinohara Aug 1989 A
4901052 Chapel et al. Feb 1990 A
4935801 McClure et al. Jun 1990 A
4962294 Beckham et al. Oct 1990 A
5059764 Baer Oct 1991 A
5087987 Simbal Feb 1992 A
5104480 Wojnarowski et al. Apr 1992 A
5111325 DeJager May 1992 A
5208437 Miyauchi et al. May 1993 A
5233327 Bartush et al. Aug 1993 A
5265114 Sun et al. Nov 1993 A
5294567 Dorfman et al. Mar 1994 A
5300756 Cordingley Apr 1994 A
5374590 Batdorf et al. Dec 1994 A
5404247 Cobb et al. Apr 1995 A
5473624 Sun Dec 1995 A
5498851 Hayashi et al. Mar 1996 A
5569398 Sun et al. Oct 1996 A
5633736 Griffith et al. May 1997 A
5656186 Mourou et al. Aug 1997 A
5662822 Tada et al. Sep 1997 A
5675310 Wojarowski et al. Oct 1997 A
5676866 in den Bäumen et al. Oct 1997 A
5685995 Sun et al. Nov 1997 A
5720894 Neev et al. Feb 1998 A
5742634 Rieger et al. Apr 1998 A
5744780 Chang et al. Apr 1998 A
5747869 Prall et al. May 1998 A
5751585 Cutler et al. May 1998 A
5753391 Stone et al. May 1998 A
5796392 Eglit Aug 1998 A
5808272 Sun et al. Sep 1998 A
5835280 Griffith Nov 1998 A
5837962 Overbeck Nov 1998 A
5838355 Narayan et al. Nov 1998 A
5841099 Owen et al. Nov 1998 A
5847960 Cutler et al. Dec 1998 A
5849623 Wojarowski et al. Dec 1998 A
5864430 Dickey et al. Jan 1999 A
5865832 Knopp et al. Feb 1999 A
5925271 Pollack et al. Jul 1999 A
5969877 Maeda Oct 1999 A
5976392 Chen Nov 1999 A
5998759 Smart Dec 1999 A
6031561 Narayan et al. Feb 2000 A
6037564 Tatah Mar 2000 A
6057180 Sun et al. May 2000 A
6103992 Noddin Aug 2000 A
6144118 Cahill et al. Nov 2000 A
6150630 Perry Nov 2000 A
6169014 McCulloch Jan 2001 B1
6172325 Baird et al. Jan 2001 B1
6181728 Cordingley et al. Jan 2001 B1
6184490 Schweizer Feb 2001 B1
6191486 Bernstein Feb 2001 B1
6225595 Wei et al. May 2001 B1
6239406 Onoma et al. May 2001 B1
6268586 Stuart et al. Jul 2001 B1
6281471 Smart Aug 2001 B1
6285002 Ngoi et al. Sep 2001 B1
6294778 Cappiello Sep 2001 B1
6297541 Ema et al. Oct 2001 B1
6300590 Lauer et al. Oct 2001 B1
6322711 Chen Nov 2001 B1
6339604 Smart Jan 2002 B1
6340806 Smart et al. Jan 2002 B1
6341029 Fillion et al. Jan 2002 B1
6441337 Isaji et al. Aug 2002 B1
6462306 Kitai Oct 2002 B1
6462307 Hennig et al. Oct 2002 B1
6472295 Morris et al. Oct 2002 B1
6483071 Hunter et al. Nov 2002 B1
6495791 Hunter et al. Dec 2002 B2
6501061 Kitai et al. Dec 2002 B1
6510605 Smejkal et al. Jan 2003 B1
6518543 Benz et al. Feb 2003 B1
6534743 Swenson et al. Mar 2003 B2
6541290 Bang et al. Apr 2003 B1
6541731 Mead et al. Apr 2003 B2
6573473 Hunter et al. Jun 2003 B2
6574250 Sun et al. Jun 2003 B2
6593542 Baird et al. Jul 2003 B2
6621040 Perry et al. Sep 2003 B1
6639177 Ehrmann et al. Oct 2003 B2
6662063 Hunter et al. Dec 2003 B2
6664498 Forsman et al. Dec 2003 B2
6664500 Wilbur et al. Dec 2003 B2
6689985 Lipman et al. Feb 2004 B2
6703582 Smart et al. Mar 2004 B2
6717101 Morris et al. Apr 2004 B2
6727458 Smart Apr 2004 B2
6738396 Filgas et al. May 2004 B2
6777645 Ehrmann et al. Aug 2004 B2
6816294 Unrath et al. Nov 2004 B2
6838639 Kreuter et al. Jan 2005 B2
6849824 Arai Feb 2005 B2
6875951 Sakamoto et al. Apr 2005 B2
6951995 Couch et al. Oct 2005 B2
6972268 Ehrmann et al. Dec 2005 B2
6989508 Ehrmann et al. Jan 2006 B2
7015418 Cahill et al. Mar 2006 B2
7027155 Cordingley et al. Apr 2006 B2
7050208 Overbeck May 2006 B2
7119351 Woelki Oct 2006 B2
7148447 Ehrmann et al. Dec 2006 B2
7176407 Hunter et al. Feb 2007 B2
7192846 Cordingley et al. Mar 2007 B2
7394476 Cordingley et al. Jul 2008 B2
7666759 Couch et al. Feb 2010 B2
20010045419 Dunsky et al. Nov 2001 A1
20020003130 Sun et al. Jan 2002 A1
20020005396 Baird et al. Jan 2002 A1
20020009843 Kyusho et al. Jan 2002 A1
20020050488 Nikitin et al. May 2002 A1
20020167581 Cordingley et al. Nov 2002 A1
20030042230 Gross et al. Mar 2003 A1
20030172527 Kitai et al. Sep 2003 A1
20030178396 Naumov et al. Sep 2003 A1
20040009618 Couch et al. Jan 2004 A1
20040134896 Gu et al. Jul 2004 A1
20040144760 Cahill et al. Jul 2004 A1
20040188399 Smart Sep 2004 A1
20050199598 Hunter et al. Sep 2005 A1
20050233537 Couch et al. Oct 2005 A1
20060000814 Gu et al. Jan 2006 A1
20060028655 Cordingley et al. Feb 2006 A1
20060086702 Smart Apr 2006 A1
20060108337 Gu et al. May 2006 A1
20060151704 Cordingley Jul 2006 A1
20060186096 Schramm Aug 2006 A1
20060189091 Gu Aug 2006 A1
20060191884 Johnson et al. Aug 2006 A1
20060192845 Cordingley et al. Aug 2006 A1
20060199354 Gu Sep 2006 A1
20060207975 Ehrmann et al. Sep 2006 A1
20060216927 Cordingley et al. Sep 2006 A1
20060256181 Ehrmann et al. Nov 2006 A1
20070031993 Nemets et al. Feb 2007 A1
20070052791 Cordingley et al. Mar 2007 A1
20070075058 Ehrmann et al. Apr 2007 A1
20070106416 Griffiths et al. May 2007 A1
20070117227 Gu May 2007 A1
20070173075 Lee et al. Jul 2007 A1
20070178714 Gu et al. Aug 2007 A1
20070199927 Gu et al. Aug 2007 A1
20070215575 Gu et al. Sep 2007 A1
20070215820 Cordingley et al. Sep 2007 A1
20080011852 Gu et al. Jan 2008 A1
20080035614 Smart Feb 2008 A1
20080067155 Gu Mar 2008 A1
20080073438 Gu et al. Mar 2008 A1
20080094640 Cordingley et al. Apr 2008 A1
Foreign Referenced Citations (36)
Number Date Country
0902 474 Mar 1999 EP
2 331 038 May 1999 GB
H2-137682 May 1980 JP
55-081095 Jun 1980 JP
56-143434 Nov 1981 JP
62-086839 Apr 1987 JP
62160726 Jul 1987 JP
63-136545 Jun 1988 JP
63-264286 Nov 1988 JP
63-302503 Dec 1988 JP
64-044295 Feb 1989 JP
02-089586 Nov 1989 JP
01-289586 Mar 1990 JP
02-063103 Mar 1990 JP
03-297588 Dec 1991 JP
04-098801 Mar 1992 JP
05-192779 Mar 1993 JP
04-006599 Aug 1993 JP
05-235169 Sep 1993 JP
07-124764 May 1995 JP
2531452 Jun 1996 JP
2531453 Jun 1996 JP
10-328873 Dec 1998 JP
11-104863 Apr 1999 JP
11-149317 Jun 1999 JP
11-245060 Sep 1999 JP
11-245073 Sep 1999 JP
2001-170788 Jun 2001 JP
2001-269790 Oct 2001 JP
2003-053575 Feb 2003 JP
2003-053576 Feb 2003 JP
2003334684 Nov 2003 JP
2005-104266 May 2005 JP
WO 9940591 Aug 1999 WO
WO 0073013 Dec 2000 WO
WO 0187534 Nov 2001 WO
Related Publications (1)
Number Date Country
20100140239 A1 Jun 2010 US
Provisional Applications (1)
Number Date Country
60368421 Mar 2002 US
Divisions (1)
Number Date Country
Parent 10397541 Mar 2003 US
Child 11131668 US
Continuations (2)
Number Date Country
Parent 11415653 May 2006 US
Child 12644832 US
Parent 11131668 May 2005 US
Child 11415653 US
Continuation in Parts (1)
Number Date Country
Parent 10108101 Mar 2002 US
Child 10397541 US