Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L22/00—Testing or measuring during manufacture or treatment; Reliability measurements, i.e. testing of parts without further processing to modify the parts as such; Structural arrangements therefor
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B26/00—Optical devices or arrangements for the control of light using movable or deformable optical elements
  • G02B26/08—Optical devices or arrangements for the control of light using movable or deformable optical elements for controlling the direction of light
  • G02B26/0816—Optical devices or arrangements for the control of light using movable or deformable optical elements for controlling the direction of light by means of one or more reflecting elements
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K26/00—Working by laser beam, e.g. welding, cutting or boring
  • B23K26/02—Positioning or observing the workpiece, e.g. with respect to the point of impact; Aligning, aiming or focusing the laser beam
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K26/00—Working by laser beam, e.g. welding, cutting or boring
  • B23K26/08—Devices involving relative movement between laser beam and workpiece
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K26/00—Working by laser beam, e.g. welding, cutting or boring
  • B23K26/08—Devices involving relative movement between laser beam and workpiece
  • B23K26/082—Scanning systems, i.e. devices involving movement of the laser beam relative to the laser head
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B26/00—Optical devices or arrangements for the control of light using movable or deformable optical elements
  • G02B26/08—Optical devices or arrangements for the control of light using movable or deformable optical elements for controlling the direction of light
  • G02B26/10—Scanning systems
  • G02B26/101—Scanning systems with both horizontal and vertical deflecting means, e.g. raster or XY scanners
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L23/00—Details of semiconductor or other solid state devices
  • H01L23/52—Arrangements for conducting electric current within the device in operation from one component to another, i.e. interconnections, e.g. wires, lead frames
  • H01L23/522—Arrangements for conducting electric current within the device in operation from one component to another, i.e. interconnections, e.g. wires, lead frames including external interconnections consisting of a multilayer structure of conductive and insulating layers inseparably formed on the semiconductor body
  • H01L23/525—Arrangements for conducting electric current within the device in operation from one component to another, i.e. interconnections, e.g. wires, lead frames including external interconnections consisting of a multilayer structure of conductive and insulating layers inseparably formed on the semiconductor body with adaptable interconnections
  • H01L23/5256—Arrangements for conducting electric current within the device in operation from one component to another, i.e. interconnections, e.g. wires, lead frames including external interconnections consisting of a multilayer structure of conductive and insulating layers inseparably formed on the semiconductor body with adaptable interconnections comprising fuses, i.e. connections having their state changed from conductive to non-conductive
  • H01L23/5258—Arrangements for conducting electric current within the device in operation from one component to another, i.e. interconnections, e.g. wires, lead frames including external interconnections consisting of a multilayer structure of conductive and insulating layers inseparably formed on the semiconductor body with adaptable interconnections comprising fuses, i.e. connections having their state changed from conductive to non-conductive the change of state resulting from the use of an external beam, e.g. laser beam or ion beam
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L2924/00—Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
  • H01L2924/0001—Technical content checked by a classifier
  • H01L2924/0002—Not covered by any one of groups H01L24/00, H01L24/00 and H01L2224/00

Definitions

• This invention relates to laser processing of circuit links and, in particular, to a laser system and method employing a laser beam and substrate positioning system that incorporates a steering mirror to compensate for stage positioning errors and enhance link severing throughput.
• FIGS. 1 , 2A, and 2B show repetitive electronic circuits 10 of an IC device or workpiece 12 that are typically fabricated in rows or columns to include multiple iterations of redundant circuit elements 14, such as spare rows 16 and columns 18 of memory cells 20.
• circuits 10 are also designed to include particular laser severable circuit links 22 between electrical contacts 24 that can be removed to disconnect a defective memory cell 20, for example, and substitute a replacement redundant cell 26 in a memory device such as a DRAM, an SRAM, or an embedded memory. Similar techniques are also used to sever links to program a logic product, gate arrays, or ASICs.
• Links 22 are designed with conventional link widths 28 of about
• link materials have been polysilicon and like compositions
• memory manufacturers have more recently adopted a variety of more conductive metallic link materials that may include, but are not limited to, aluminum, copper, gold nickel, titanium, tungsten, platinum, as well as other metals, metal alloys such as nickel chromide, metal nitrides such as titanium or tantalum nitride, metal suicides such as tungsten suicide, or other metal-like materials.
• Circuits 10, circuit elements 14, or cells 20 are tested for defects.
• FIGS. 2A and 2B show a laser spot 38 of spot size diameter 40 impinging a link structure 36 composed of a link 22 positioned above a silicon substrate 42 and between component layers of a passivation layer stack including an overlying passivation layer 44 (shown in FIG. 2A but not in FIG. 2B) and an underlying passivation layer 46 (shown in FIG. 2B but not in FIG. 2A).
• FIG. 2C is a fragmentary cross-sectional side view of the link structure of FIG. 2B after the link 22 is removed by the laser pulse.
• FIG. 3 is a plan view of a beam positioner travel path 50 performed by a traditional link processing positioning system. Because links 22 are typically arranged in rows 16 and columns 18 (representative ones shown in dashed lines), the beam position and hence the laser spots 38 are scanned over link positions along an axis in a first travel direction 52, moved to a different row 16 or column 18, and then scanned over link positions along an axis in a second travel direction 54. Skilled persons will appreciate that scanning may include moving the workpiece 12, moving the laser spot 38, or moving the workpiece 12 and the laser spot 38.
• Traditional positioning systems are characterized by X-Y translation tables in which the workpiece 12 is secured to an upper stage that moves along a first axis and is supported by a lower stage that moves along a second axis that is perpendicular to the first axis.
• Such systems typically move the workpiece relative to a fixed beam position or laser spot 38 and are commonly referred to as stacked stage positioning systems because the lower stage supports the inertial mass of the upper stage which supports workpiece 12.
• These positioning systems have excellent positioning accuracy because interferometers are typically used along each axis to determine the absolute position of each stage.
• split-axis positioning systems In split-axis positioning systems, the upper stage is not supported by, and moves independently from, the lower stage and the workpiece is carried on a first axis or stage while the tool, such as a fixed reflecting mirror and focusing lens, is carried on the second axis or stage.
• Split-axis positioning systems are becoming advantageous as the overall size and weight of workpieces 12 increase, utilizing longer and hence more massive stages.
• planar positioning systems More recently, planar positioning systems have been employed in which the workpiece is carried on a single stage that is movable by two or more actuators while the tool remains in a substantially fixed position. These systems translate the workpiece in two dimensions by coordinating the efforts of the actuators. Some planar positioning systems may also be capable of rotating the workpiece.
• SLP Semiconductor Link processing
• OTF on-the-fly link processing
• the laser beam is pulsed as a linear stage beam positioner passes designated links 12 under the beam position.
• the stage typically moves along a single axis at a time and does not stop at each link position.
• the on-axis position of beam spot 38 in the direction travel 52 does not have to be accurately controlled; rather, its position is accurately sensed to trigger laser spot 38 to hit link 22 accurately.
• An object of the invention is, therefore, to provide a system and/or method for achieving higher link-processing throughput while maintaining focused spot quality.
• Another object of the invention is to employ a two-axis steering mirror to correct for linear stage settling errors.
• Yet another object of the invention is to provide a positioner system employing coordinated motion for semiconductor link processing applications.
• This invention preferably employs a two-axis steering mirror, pivotally mounted at the entrance pupil of the focusing lens, to perform small- angle motions that deflect the laser beam enough to compensate for cross-axis settling errors on the order of tens of microns.
• a two-axis steering mirror is employed for these corrections because either axis of the linear stage may be used as the OTF axis.
• the beam steering mirror is preferably used for error correction only and does not require coordination with or modification of the linear stage position commands, although such coordination is possible.
• At least three technologies can be used to tilt a mirror in two axes about a single pivot point. These technologies include fast steering mirrors (“FSMs”) that employ a flexure mechanism and voice coil actuators to tilt the mirror, piezoelectric actuators that rely upon deformation of piezoelectric materials to tilt a mirror, and deformable mirrors that employ piezoelectric or electrostrictive actuators to deform the surface of the mirror. Piezoelectric actuators are preferred.
• FIG. 1 is a schematic diagram of a portion of a DRAM showing the redundant layout of and programmable links in a spare row of generic circuit cells.
• FIG. 2A is a fragmentary cross-sectional side view of a conventional, large semiconductor link structure receiving a laser pulse characterized by a prior art pulse parameters.
• FIG. 4 is a simplified side view of a prior art fast positioner employing a pair of galvanometer-driven mirrors that deflect the laser beam along different respective single axes.
• FIG. 5 schematically illustrates a side sectional view of a preferred two-axis mirror employed in the practice of the invention.
• FIG. 6 schematically illustrate a partial front view of a preferred two-axis mirror employed in the practice of the invention.
• FIG. 7 illustrates the effect of the steering mirror during the OTF run.
• FIG. 10 is a simplified plan view of a representative two-axis steering mirror.
• the beam positioning system preferably employs a laser controller that controls a stacked, split-axis, or planar positioner system and coordinates with reflectors to target and focus laser system output to a desired laser link 22 on IC device or workpiece 12.
• the beam positioning system permits quick movement between links 22 on the same or different workpieces 12 to effect unique link-severing operations based on provided test or design data.
• the mechanism directing mirror system 100 preferably pivots the mirror 102 along at least two axes about pivot point 104, which is located at or near the entrance pupil of focusing optics or lens 108.
• settling errors in a cross-axis direction 110 are corrected by mirror 102, while motion in an on-axis direction 112 is not corrected.
• This single axis correction allows the linear stage interferometer feedback to be the sole source of laser pulse triggering.
• on-axis direction 112 steering mirror 102 motion is possible, although it complicates the design and introduces additional error sources that can degrade on-axis direction 112 accuracy if such errors are not addressed.
• Motion in each axis of mirror 102 exhibits scale factor and offset errors, noise, and cross-axis coupling. These error source can be well- controlled and calibrated out in the system, with noise and temperature stability effects controlled through conventional design techniques.
• Calibration of mirror system 100 through beam-to-work (“BTW”) alignments can correct for any non-linearity and alignment errors in steering mirror 102.
• beam-to-work is used as nomenclature for the process of scanning the linear stage back and forth, while directing the laser beam spot at low power at an alignment target on the wafer or workpiece 12 (FIG. 1 ).
• Optical measurements of the reflection off the target are used to precisely determine target and hence wafer location.
• By scanning several targets with BTW scans the offset and rotation of the wafer relative to the beam spot can be ascertained. It is also possible to map out other effects such as axis orthogonality and positional distortions.
• BTW type scans can be used to map out any inaccuracies/nonlinearities in steering mirror 102 response. This is accomplished by doing a BTW scan with mirror 102 in the nominal zero offset (in either axis) position. Then mirror 102 is tilted, and another BTW scan is performed to determine how much lateral offset of the laser beam spot is imparted by the tilt. By measuring the offset caused by numerous mirror tilts in the U and V axes, mirror system 100 can be fully characterized.
• mirror system 100 Once the response of mirror system 100 is determined to sufficiently fine precision, then instead of moving the linear stage back and forth, it is possible to use mirror system 100 for subsequent BTW type alignment scans.
• FIG. 7 illustrates the corrective effect of two-axis steering mirror system 100 during an OTF run.
• a linear stage ringing is represented by a ringing curve 120.
• Mirror 102 deflects the laser beam in cross-axis direction 110 as represented by a correction curve 122 that is the inverse of ringing curve 120.
• the resulting beam position is the sum of the linear stage motion and the deflected beam position and is represented by a resulting beam path curve 124, which is free, of cross-axis error.
• Link processing becomes far more efficient with MRCAD because the linear or stages do not have to be scanned or slewed down each row, so the total number of link row scans can be substantially reduced. As integration increases and link sizes, spot sizes, and pitch distance decrease, MRCAD scanning will become an even more valuable technique.
• supplemental on-axis dithering uses mirror 102 to deflect the beam in on-axis direction 112 (FIGS. 5-7).
• the beam can be quickly directed ahead in on-axis direction 112, severing links while the linear motion stage catches up.
• the SOAD scan ahead or scan behind the stage feature allows the positioning system to reduce stage velocity changes or to sever several links during a single slowed movement segment.
• At least three technologies can be employed to tilt mirror 102 in two axes about pivot point 104.
• These technologies include FSMs that employ a flexure mechanism and voice coil actuators, piezoelectric actuators that rely upon deformation of piezoelectric materials, and piezoelectric or electrostrictive actuators to deform the surface of a mirror.
• Suitable voice coil actuated FSMs are available from Ball Aerospace Corporation of Broomfield, Colorado and Newport Corporation of Irvine, California.
• the preferred actuator is a model S-330 Ultra-Fast Piezo Tip/Tilt Platform manufactured by Physik Instrumente (“PI”) GmbH & Co. of Düsseldorf, Germany.
• FIGS. 9 and 10 show an FSM two-axis mirror system 200 in which four electrical to mechanical vibration generators or transducers are supported by a transducer support platform 220 in a quadrature relationship, whereby a set of transducers 222, 224, 226, and 228 are positioned at 0, 90, 180, and 270 degrees with respect to a central axis 230 and are, therefore, at right angles with respect to each other.
• a movable mirror support member 232 has a central portion or hub 234 bearing a mirror or reflective surface 236 centered with respect to axis 230.
• Mirror 236 has a diameter of about 30 mm or less to reduce its weight and facilitate high frequency response for desired beam correction.
• Mirror 236 is coated with conventional laser optical coatings to account for laser wavelength or design parameters.
• Each lightweight rigid struts or elongated members 242, 244, 246, and 248 extend radially from hub 234 of mirror support member 232, and have respective peripheral terminal portions 252, 254, 256, and 258 affixed to respective transducers 222, 224, 226, and 228, which are electrically movable voice coils.
• transducers 222, 224, 226, and 228, which are electrically movable voice coils.
• the floating mirror support 232 can beneficially be made of a lightweight material, such as metal (e.g. aluminum or beryllium) or plastic, enabling rapid response to the electrical input signals to the voice coils to be described.
• a tip control generator 260 is connected to transducers 224 and
• a tilt control generator 262 is connected to transducers 222 and 226 to cause these coils to also move in a complementary push pull relationship with each other.
• a laser beam 270 is reflected off reflective surface 236 and a reflected beam 272 is positioned by the generators controlling the cross axis, which is perpendicular to OTF direction of travel, to compensate for cross axis errors.
• the pairs of signals produced by each generator assume a push-pull relationship, so that when transducer 222 is pulling upper terminal portion 252 of support member 232 to the right in FIG.
• lower transducer 226 is pushing terminal portion 256 to the left, to tilt reflective surface 236, thereby deflecting reflected beam 272.
• the actuation can be alternated at the beginning of an OTF run, for example, to move reflective surface 236 at a proper frequency and damped amplitude to compensate for linear stage ringing in cross-axis direction 110, thereby eliminating the negative effects of linear stage settling time and producing a relatively straight beam path.
• links that would otherwise be in the conventional buffer zone can be processed accurately.
• Mirror systems suitable for use with this invention can be implemented with a large enough field to do MRCAD scans by providing beam deflection in a range of about 50 to 100 microns; however, such mirror systems can also be implemented for cross-axis correction only by providing beam deflection in a range of about 10 to 50 microns or as little as about 10 to 20 microns.
• the mirror is preferably positioned within about plus or minus 1 mm of the entrance pupil of the focusing lens. These ranges are exemplary only and can be modified to suit the system design and particular link processing applications.
• the preferred model S-330 Tip/Tilt Platform manufactured by PI uses piezoelectric actuators for high speed, two-dimensional mirror tilting. Strain gage sensors accurately determine mirror position and provide feedback signals to the control electronics and drive circuitry. A more complete description of the model S-330 Tip/Tilt Platform is available at the PI web site, www.physikinstrumente.com.
• the main advantages of the PI Piezo Tip/Tilt Platform are that the device is commercially available and has a very compact size that readily mounts in an ESI model 9820 positioning system.
• FIG. 11 shows an embodiment of a positioner control system 300 of this invention for coordinating the positioning of X- and Y-axis motions stages 302 and 304, and also the positioning of a two-axis steering mirror 306 for positioning error correction.
• motion stages 302 and 304 may be combined into a single planar motion stage having positioning control in the X- and Y-axis directions.
• two-axis steering mirror 306 is used to correct positioning errors caused by X- and Y-axis motion stages 302 and 304.
• a position command generator 308 generates X- and Y-axis position command signals for delivery through summing junctions 310 and 312 to X- and Y-axis motion controllers 314 and 316 to respective X- and Y-axis motion stages 302 and 304.
• the actual positions of X- and Y-axis motion stages 302 and 304 are sensed by respective X- and Y-axis position sensors 318 and 320 and signals representing the actual positions are conveyed to adders or summing junctions 310 and 312 to generate X- and Y-axis position error signals.
• X- and Y-axis motion controllers 314 and 316 receive the error signals and act to minimize any errors between the commanded and actual positions.
• X- and Y-axis position sensors 318 and 320 are preferably interferometers.
• Residual error signals such as those generated by ringing, are conveyed through enabling gates 322 and 324 to a coordinate transformation generator 326, which may be optional depending on whether motion stages 302 and 304 share a common coordinate system with two-axis steering mirror 306. In either event, the residual error signals are passed through adders or summing junctions 328 and 330 to U- and V-axis steering mirror controllers 332 and 334, which act to tip and/or tilt steering mirror 306 by controlled amounts to deflect, for example, laser beam 270 (FIG. 9) to correct for positioning errors of X- and Y-axis motion stages 302 and 304.
• a coordinate transformation generator 326 which may be optional depending on whether motion stages 302 and 304 share a common coordinate system with two-axis steering mirror 306.
• the residual error signals are passed through adders or summing junctions 328 and 330 to U- and V-axis steering mirror controllers 332 and 334, which act to tip and/or tilt steering mirror 306 by
• the actual tip and/or tilt positions of two-axis steering mirror 306 are sensed by respective tip and tilt sensors 336 and 338 and signals representing the actual tip and tilt positions are conveyed to adders or summing junctions 328 and 330 to generate tip and tilt position error signals.
• U- and V-axis steering mirror controllers 332 and 334 receive the error signals and act to correct any errors between the commanded and actual positions.
• two-axis steering mirror 306 is preferably a piezoelectric tilt/tip platform, and position sensors 318 and 320 are preferably strain gages. Suitable alternative sensors may include optical, capacitive, and inductive sensing techniques.
• U- and V-axis steering mirror controllers 332 and 334 should be adapted to provide zero to 100 volt drive signals to the piezoelectric actuators deflecting two-axis steering mirror 306.
• a position command generator 342 In this mode of operation, a position command generator 342 generates X- and Y-axis positioning commands for X- and Y-axis motion stages 302 and 304 and also U- and V-axis tip and tilt commands for deflecting FSM 236. Summing junctions 328 and 330 generate the positioning command for FSM 236 as the sum of the error signals from X- and Y- axis motion stages 302 and 304 and, in this embodiment, also the U- and V-axis tip and tilt commands.
• the error signals are generated in the same manner as in the standard error correction mode.
• the additional U- and V-axis tip and tilt commands are produced by position command generator 342 to accomplish the desired beam-to-work scanning. Because beam-to-work and MRCAD applications typically require wider ranges of mirror deflection, this embodiment of the invention preferably employs voice coil actuated FSM two-axis mirror system 200.
• the position commands for MRCAD scanning are used to produce cross-axis motion of the laser beam without commanding cross-axis motion of the motion stages.
• other applications are envisioned that would benefit from on-axis supplemental dithering to boustrophedon scanning.
• control schemes depicted in these figures are intended to illustrate the basic implementation and operation of this invention. More advanced control schemes, such as those employing feedforward commands to the motion stages and steering mirror, will be obvious to those skilled in the art.
• two-axis steering mirror systems of this invention can be adapted for use in etched-circuit board via drilling, micro-machining, and laser trimming applications as well as for link severing.

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• Engineering & Computer Science (AREA)
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• Mechanical Engineering (AREA)
• General Physics & Mathematics (AREA)
• Manufacturing & Machinery (AREA)
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• Microelectronics & Electronic Packaging (AREA)
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