CN109530939B - Method and system for processing wafer by laser - Google Patents
Method and system for processing wafer by laser Download PDFInfo
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- CN109530939B CN109530939B CN201811625821.9A CN201811625821A CN109530939B CN 109530939 B CN109530939 B CN 109530939B CN 201811625821 A CN201811625821 A CN 201811625821A CN 109530939 B CN109530939 B CN 109530939B
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- 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
- B23K26/50—Working by transmitting the laser beam through or within the workpiece
- B23K26/53—Working by transmitting the laser beam through or within the workpiece for modifying or reforming the material inside the workpiece, e.g. for producing break initiation cracks
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- 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
- B23K26/03—Observing, e.g. monitoring, the workpiece
- B23K26/032—Observing, e.g. monitoring, the workpiece using optical means
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- 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
- B23K26/06—Shaping the laser beam, e.g. by masks or multi-focusing
- B23K26/064—Shaping the laser beam, e.g. by masks or multi-focusing by means of optical elements, e.g. lenses, mirrors or prisms
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- 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
- B23K26/70—Auxiliary operations or equipment
- B23K26/702—Auxiliary equipment
Abstract
The invention provides a method and a system for processing a wafer by laser, wherein the method comprises the following steps: scanning a cutting channel to be processed, and acquiring height data of the cutting channel by a laser follow-up device; fitting the height data to form a height curve of the cutting street; and determining a height set value of the laser follow-up device within a preset cutting distance according to the height curve, and controlling the piezoelectric ceramics to carry out laser processing on the cutting path within the preset cutting distance according to the height set value of the laser follow-up device. The invention not only can ensure that the distance between the laser focusing plane and the surface of the cutting path is always in the micron order without influencing the requirement of process effect, but also can avoid the control error caused by the fact that the laser follow-up device is in a vibration state at any time.
Description
Technical Field
The invention relates to the technical field of laser processing, in particular to a method and a system for processing a wafer by laser.
Background
In the field of semiconductor wafer processing, the requirements of the industry on novel integrated circuit technology, product packaging capacity and chip performance are continuously improved, so that the wafer is made to be thinner and thinner, the sensitivity of a device is made to be higher and higher, and the structure of a chip is made to be more and more complex, so that the requirements on the chip scribing process are more and more diversified, for example, the structure of an MEMS device is very fragile, the scribing process of cleaning by using high-pressure water is not allowed, and any dust or particles are not allowed to exist on the surface; a chip covered with Low-K dielectric does not allow for peeling of the film layers during dicing and also does not allow for any dust or dicing debris to be present on the surface.
The first step of chip packaging is wafer dicing, and the effect of the wafer dicing process directly affects the performance and production cost of the chip. Laser scribing is becoming the mainstream of advanced manufacturing as a precision machining technique. The laser invisible scribing is a scribing technology that laser beams are focused in the brittle material and scan along a preset path to change the interior of the brittle material, a starting point for cutting is formed, a stress layer is formed, and then the brittle material is separated by external force. The invisible scribing technology can effectively avoid a series of problems of edge breakage of materials, film layer stripping, overlarge heat affected zone, scribing debris splashing and the like because the processing is carried out in the wafer, and is a next-generation advanced wafer scribing technology.
Because the thinned wafer can generate a certain curvature, and the flatness of the wafer platform is increased along with the increase of the size, the horizontal error of the whole width is increased. Therefore, the prior art mainly applies a laser follow-up device, which feeds back to devices capable of generating micro displacement, such as piezoelectric ceramics, micro displacement shafts, electric springs and the like, by detecting the fluctuation change of the surface of a sample, so that a laser head changes along with the change of the surface of the sample. The micro-displacement device used by the device generally has low response. When the system is in high-speed reciprocating operation, the displacement speed of the laser head can generate larger hysteresis reaction, and the problems of step loss, processing position dislocation and the like can easily occur in the return processing process, so that the laser processing at the edge of the processing channel to the surface and the overlapping of the cutting channels with different cutting depths in the invisible cutting can be caused finally.
Meanwhile, the existing wafer laser cutting has high requirement on the consistency of cutting depth, the precision is at least in micron level, but high-speed cutting and the unevenness of the surface of the wafer form a pair of contradiction factors, a focusing plane is easy to separate from the plane of the wafer under the condition of high-speed movement, the condition of a breakpoint of the surface cutting of the wafer occurs, and the oscillation error of the laser follower can be caused by frequently updating the set value of the laser follower.
Disclosure of Invention
The method and the system for processing the wafer by the laser not only can ensure that the distance between the laser focusing plane and the surface of the cutting channel is always in a micron order without influencing the requirement of process effect, but also can avoid the control error caused by the fact that the laser follow-up device is in a vibration state at any time.
In a first aspect, the present invention provides a method for laser processing a wafer, including:
scanning a cutting channel to be processed, and acquiring height data of the cutting channel by a laser follow-up device;
fitting the height data to form a height curve of the cutting street;
and determining a height set value of the laser follow-up device within a preset cutting distance according to the height curve, and controlling the piezoelectric ceramics to carry out laser processing on the cutting path within the preset cutting distance according to the height set value of the laser follow-up device.
Optionally, the scanning the cutting street to be processed, and acquiring the height data of the cutting street by using the laser follower device includes:
presetting a height zero point value of the laser follow-up device, moving the Z axis, and controlling the laser follow-up device to move within a preset range;
presetting a height measurement starting point P of a cutting pathaEnd point of height measurement Pb；
At the beginning of height finding PaHeight measurement end point PbThe height of the focusing plane from the surface of the material is measured by a laser follower device according to the position interval d, and the measured height data is stored in an array H [ k ]]，k＝(Pa-Pb) D; wherein k is an integer.
Optionally, the fitting of the height data to form the height curve line of the cutting street is according to an array H [ k ]]The height data in (1) is subjected to curve fitting to form a height curve H～(ii) a Wherein the content of the first and second substances,
H～＝f(P，H，C)，H～is the fitting height of any point.
Optionally, the determining a set height value of the laser follower within a preset cutting distance according to the height curve includes:
presetting the cutting speed V of the processproSetting interval time T with follow-up updatesetUpdating the height setting value of the laser follow-up device every interval distance D, wherein D is VproTsetAnd D > D;
obtaining the height value H of the starting point of each distance D lengthaEnd point height value HbMaximum height value HtopWith a minimum height value Hbot；
Comparing the height values H of the starting pointsaHeight from end point HbDetermining a height set value H of a laser followerset。
Optionally, the comparison starting point height value HaHeight from end point HbDetermining a height set value H of a laser followersetThe method comprises the following steps:
when H is presenta＞HbThen Hset＝Htop；
When H is presenta＜HbThen Hset＝Hbot。
Optionally, the range of the position interval d is: d is more than or equal to 1mm and less than or equal to 100 mm.
Optionally, the method further comprises:
when the cutting channel is subjected to forward or reverse laser processing, the piezoelectric ceramics are controlled according to the height set value of the laser follow-up device determined by the height curve.
In a second aspect, the present invention provides a system for laser processing a wafer, comprising:
the laser follow-up device is used for scanning a cutting channel to be processed and acquiring height data of the cutting channel;
the curve fitting unit is used for fitting the height data to form a height curve of the cutting channel;
the piezoelectric ceramic is used for driving laser to carry out laser processing on the cutting path;
and the controller is used for determining a height set value of the laser follow-up device within a preset cutting distance according to the height curve and controlling the piezoelectric ceramics to carry out laser processing on the cutting path within the preset cutting distance according to the height set value of the laser follow-up device.
Optionally, the system further comprises:
the setting unit is used for presetting a height zero point value of the laser follow-up device, moving the Z axis and controlling the laser follow-up device to move within a preset range; and presetting a height measurement starting point P of the cutting pathaEnd point of height measurement Pb。
Optionally, the controller comprises:
a parameter setting module for presetting the cutting speed V of the processproSetting interval time T with follow-up updatesetUpdating the height setting value of the laser follow-up device every interval distance D, wherein D is VproTsetAnd D > D;
an obtaining module for obtaining the height value H of the starting point of each distance D lengthaEnd point height value HbMaximum height value HtopWith a minimum height value Hbot；
A determination module for comparing the starting point height value HaHeight from end point HbDetermining a height set value H of a laser followerset。
The method and the system for processing the wafer by the laser mainly record the height data of each position by scanning the cutting street at the shortest distance, and fit to form a height curve according to the height data recorded on the whole cutting street.
Meanwhile, the actual moving process of the laser follow-up device from receiving the height set value signal to moving to the set value position is in a non-step type, the whole moving track is similar to a hysteresis curve, the cutting speed is higher, the process form is more obvious, therefore, the maximum value or the minimum value of the height in a section of cutting distance can be regarded as the target set value of the follow-up system during high-speed cutting movement, the requirement that the distance between a laser focusing plane and the surface of a cutting path is in a micron-scale all the time and the process effect is not influenced is ensured, and the laser follow-up device is prevented from being in an oscillation state at any time to cause control errors.
Therefore, the method can achieve the purpose that the laser focusing plane and the surface of the cutting channel are always at the same height in the wafer cutting process, the breakpoint phenomenon cannot occur along with the fluctuation of the surface height of the cutting channel, and the control precision of the laser follow-up device is within the range of +/-1 mu m; the second aspect can also greatly improve the cutting speed, shorten the process time and improve the equipment productivity on the premise of not influencing the process cutting effect; the third aspect can also reduce frequent oscillation of the laser follow-up device in a small range, reduce measurement errors and prolong the service life of equipment to a certain extent.
Drawings
FIG. 1 is a flow chart of a method for laser processing a wafer according to an embodiment of the invention;
FIG. 2 is a schematic diagram of height information formed by recording according to an embodiment of the present invention;
FIG. 3 is a schematic diagram of a system for laser processing a wafer according to one embodiment of the present invention;
FIG. 4 is a schematic diagram of a system for laser processing a wafer according to one embodiment of the present invention;
FIG. 5 is a flowchart of a method of laser processing a wafer according to a second embodiment of the present invention;
FIG. 6 is a schematic diagram illustrating data processing of two pairs of altitude data according to an embodiment of the present invention;
FIG. 7 is a schematic diagram of a system for laser processing a wafer according to a second embodiment of the present invention;
FIG. 8 is a flowchart of a method of laser processing a wafer according to an embodiment of the present invention;
fig. 9 is a schematic structural diagram of a system for processing a wafer by three lasers according to an embodiment of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Example one
An embodiment of the present invention provides a method for processing a wafer by using a laser, as shown in fig. 1, the method includes:
s11, obtaining the feedback time of the piezoelectric ceramics;
s12, determining the sampling interval of the laser follow-up device according to the feedback time of the piezoelectric ceramic, and then carrying out height measurement and recording on height data through the laser follow-up device according to the determined sampling interval to form height information;
and S13, performing real-time control on the piezoelectric ceramics by adopting a feedforward compensation mechanism according to the height information, and performing laser processing on the cutting path.
The method for processing the wafer by the laser mainly compensates the slow reaction problem of piezoelectric ceramics (PZT) through the quick response capability of the controller; the method comprises the following steps of matching an optimal sampling interval according to the feedback time of the piezoelectric ceramics, measuring the height according to the matched optimal sampling interval, and then performing quick real-time control on the piezoelectric ceramics by a controller through a position trigger mode; and the reciprocating motion is informed when the laser invisible cutting is carried out on the cutting track by using the formed height information. Therefore, the method of the embodiment can realize that the laser is completely cut into the sample and the different cutting channels are not overlapped; and the high-precision height information can be matched with the real-time feedback effect of the high-speed controller by adopting a feedforward compensation mechanism on the piezoelectric ceramic, so that the follow-up high-precision control effect on the laser focus is finally realized.
Alternatively, as shown in fig. 2 and 3, the determining the sampling interval of the laser follower device according to the feedback time of the piezoelectric ceramic, and then forming the height information by the laser follower device according to the determined sampling interval to perform height measurement and record height data includes:
when the feedback time of the piezoelectric ceramic is T milliseconds, determining the distance from the height measurement starting point to the cutting direction needing retracting and the distance from the height measurement ending point to the cutting direction needing retracting according to the feedback time;
and a height measuring point is taken every T milliseconds between the height measuring starting point and the height measuring ending point by the laser follow-up device to measure the height and record height data to form height information.
Optionally, the distance X to be retracted is the platform running speed T/2.
Specifically, in the method of this embodiment, a height measurement point is taken every T milliseconds between a height measurement start point and a height measurement end point along the forward direction of the cutting track by the laser follower device to perform a height measurement and height data recording process, so that the height measurement and height data can be used as forward height measurement feedback information, and the forward height measurement feedback information is located at the center position of each actual cutting action including the course and runs at an even speed, so as to ensure the accuracy of the forward height measurement feedback information, thereby ensuring the high-precision processing of the laser.
Optionally, the performing real-time control on the piezoelectric ceramic by using a feed-forward compensation mechanism according to the height information, and the performing laser processing on the cutting path includes:
feeding back the height information to the controller;
the controller controls the piezoelectric ceramics to take the height measurement starting point as an actual operation starting value;
and then, moving the piezoelectric ceramics at the corresponding position on the Z axis every T milliseconds according to the height information to carry out laser processing on the cutting path in the forward direction until the cutting end point.
Optionally, after the piezoelectric ceramic is moved to a corresponding position on the Z axis every T milliseconds according to the height information to perform laser processing on the cutting track in the forward direction until the cutting end point, the method further includes:
inverting the position of the height measurement point to form reverse height information and feeding the reverse height information back to the controller;
the controller controls the piezoelectric ceramic to take a height measurement starting point formed after the inversion as a reverse actual operation starting value;
and then moving the piezoelectric ceramics at the corresponding position of the Z axis every T milliseconds according to the reverse height information to reversely process the cutting channel by laser until the cutting end point, so that the piezoelectric ceramics are positioned at the determined height measuring point when the laser processing is carried out on the cutting channel reversely.
Specifically, in the method of this embodiment, the laser processing for the forward direction or the reverse direction of the scribe line is performed at an even speed, and an interval T milliseconds is provided between each of the laser cutting operations for the forward direction and the reverse direction of the scribe line, for example, T is 10. The position of the height measuring point is inverted to form reverse height information which is successfully fed back to the controller; and the controller is used for rapidly controlling the piezoelectric ceramics through the internal high-speed operation function at the time interval to use a height measurement starting point formed after the piezoelectric ceramics are inverted as a reverse actual operation starting value, so that the laser processing is set to be in uniform-speed operation to ensure that the position of a laser focus is close to an actual processing position as far as possible, and in addition, the operation position of the piezoelectric ceramics at each point is further ensured to be unchanged when the cutting path is reversely cut through setting a reaction time interval.
Optionally, the feedback time T milliseconds of the piezoelectric ceramic is in a range of 5 milliseconds to 15 milliseconds.
Optionally, the platform operating speed is greater than or equal to 600 mm/s.
In summary, the method of the present embodiment mainly sets a feed-forward operation (i.e., feeding back height information in a forward direction) and two cutting actions (performing laser processing on the cutting track in a forward direction or a reverse direction), so as to effectively improve the laser processing precision. For example, in the method of this embodiment, based on a low speed at which the actual high-precision operation feedback time T of the piezoelectric ceramic is 10 milliseconds, a feed-forward compensation mechanism is adopted, and a laser follower device is used to obtain height information of high position precision in a cutting track; and then directly feeding back to the controller, and realizing real-time control on the piezoelectric ceramics (PZT) by using the high-speed operation function in the controller. Further, the operating time of the piezoelectric ceramic is about 10 milliseconds because it is slow. Therefore, the laser follow-up device takes the middle position of the actual 10-millisecond running road section and feeds the middle position back to the controller, and therefore the position of the laser focus is guaranteed to be close to the actual machining position as much as possible. When the laser processing (cutting) is carried out on the cutting track reversely, the position signal of the forward height measuring point is inverted and fed back to the high-speed controller, so that the running position of the piezoelectric ceramic at each point is unchanged, the problem of dislocation of the reverse cutting processing position is solved, and the conditions that the cutting tracks with different cutting depths are overlapped in the invisible cutting process are improved.
An embodiment of the present invention further provides a system for laser processing a wafer, as shown in fig. 3, the system includes:
the acquisition unit is used for acquiring the feedback time of the piezoelectric ceramics;
the controller is used for determining the sampling interval of the laser follow-up device according to the feedback time of the piezoelectric ceramic, and then carrying out height measurement and recording on height data through the laser follow-up device according to the determined sampling interval to form height information; and the piezoelectric ceramics are controlled in real time by adopting a feedforward compensation mechanism according to the height information;
the laser follow-up device 17 is used for measuring the height at the determined height measuring point position;
and the piezoelectric ceramic 14 is used for driving the laser emitted by the laser processing unit to carry out laser processing on the cutting path.
The system for processing the wafer by the laser mainly compensates the slow reaction problem of piezoelectric ceramics (PZT) through the quick response capability of the controller; the method comprises the following steps of matching an optimal sampling interval according to the feedback time of the piezoelectric ceramics, measuring the height according to the matched optimal sampling interval, and then performing quick real-time control on the piezoelectric ceramics by a controller through a position trigger mode; and the reciprocating motion is informed when the laser invisible cutting is carried out on the cutting track by using the formed height information. Therefore, the system of the embodiment can realize that the laser is completely cut into the sample and the different cutting channels are not overlapped; and the high-precision height information can be matched with the real-time feedback effect of the high-speed controller by adopting a feedforward compensation mechanism on the piezoelectric ceramic, so that the follow-up high-precision control effect on the laser focus is finally realized.
Optionally, the controller comprises:
the retracting distance determining unit is used for determining the retracting distance of the height measuring starting point to the cutting direction and the retracting distance of the height measuring ending point to the cutting direction according to the feedback time when the feedback time of the piezoelectric ceramic is T milliseconds;
and the height measurement control unit is used for controlling the laser follow-up device to take a height measurement point every T milliseconds between the height measurement starting point and the height measurement ending point to measure the height and record height data to form height information.
Optionally, the controller further comprises:
the first control unit is used for controlling the piezoelectric ceramics to take a height measurement starting point as an actual operation starting value;
the forward cutting control unit moves the piezoelectric ceramics at corresponding positions on the Z axis every T milliseconds according to the height information to carry out laser processing on the cutting path in the forward direction until the cutting end point;
the second control unit is used for controlling the piezoelectric ceramics to take a height measurement starting point formed after the inversion as a reverse actual operation starting value;
and the reverse cutting control unit is used for moving the piezoelectric ceramics at the corresponding position on the Z axis to reversely carry out laser processing on the cutting channel until the cutting end point every T milliseconds according to the reverse height information so as to enable the piezoelectric ceramics to be positioned at the determined height measuring point when the laser processing is carried out on the cutting channel reversely.
In summary, as shown in fig. 3 and fig. 4, in the system of the present embodiment, the laser processing beam 16 sequentially passes through the coaxial lens barrel 13, the PZT14, and the 50X processing objective lens 15 and is focused on the surface of the wafer 19 to be processed; the coaxial lens barrel 13 is also provided with a CCD11 and a detection light source 12 for detecting laser processing beams; the laser follow-up device 17 and the optical element are fixed through a fixing back plate 18; so that the height B of the laser servo device 17 and the height A of the laser processing beam passing through the PZT14 and 50X processing objective lens 15 are at a fixed height C, and the accuracy of feeding back the height data obtained by the height measurement of the laser servo device 17 to the controller to control the piezoelectric ceramics is improved.
The system of this embodiment may be configured to implement the technical solutions of the method embodiments, and the implementation principles and technical effects are similar, which are not described herein again.
Example two
Because when equipment runs at a high speed, the laser follower device can not follow the problem of surface change of a sample slowly, and the machining precision that the focal point of laser machining is changed by +/-1 um from the surface of the sample can not be realized. Accordingly, an embodiment of the present invention provides a method for laser processing a wafer, as shown in fig. 5, the method includes:
s21, acquiring height data of a cutting path to be processed by the laser follow-up device;
s22, processing the acquired height data according to the feedback time of the piezoelectric ceramics and forming a positive and negative piezoelectric ceramics motion compensation table;
and S23, controlling the piezoelectric ceramics to adopt a feedforward compensation mechanism to carry out real-time control according to the positive and negative piezoelectric ceramics motion compensation table when carrying out forward or reverse laser processing on the cutting path.
The method for processing the wafer by the laser mainly can automatically adjust the height of the laser cutting head according to the fluctuation of the surface of the wafer, keep the preset laser focal length, solve the problem that a laser follower device is slow in response and cannot follow the change of the surface of a sample when equipment runs at a high speed, and realize the processing precision that the focal point of the laser processing is changed by +/-1 um from the surface of the sample. Firstly, a laser follow-up device acquires a great amount of dense height data in the height data of a cutting path to be processed by measuring, and the measurement interval time rarely acquires a great amount of height data; then, according to the feedback time of the piezoelectric ceramics, performing data processing on the obtained height data and forming a positive and negative piezoelectric ceramics motion compensation table, for example, performing screening, average processing, curve fitting and the like on the obtained height data according to the feedback time of the piezoelectric ceramics to form a high-precision positive and negative piezoelectric ceramics motion compensation table; finally, the piezoelectric ceramics are rapidly controlled in real time through a position trigger mode; the method can effectively solve the adaptability problem of piezoelectric ceramic control programs with different delays, and simplifies the precision requirement of hardware assembly by adopting a feedforward compensation mechanism, so that the hardware design is more flexible.
In addition, according to the method, the problem of up-and-down fluctuation of the distance of the bidirectional invisible cutting path is solved by setting a feedforward work (namely a positive and negative piezoelectric ceramic motion compensation table formed by positive height measurement feedback height data of a laser follow-up device) and two cutting actions (for carrying out laser processing on the cutting path in a positive direction or a negative direction), so that the laser processing precision is effectively improved, the cutting speed can reach 2000mm/s, and the cutting precision can reach +/-1 mu m; and further can realize high-speed cutting of the wafer surface with little surface flatness change.
Optionally, as shown in fig. 5 and 6, the acquiring, by the laser follower device, the height data of the cutting street to be processed includes:
presetting the distance from the height measurement starting point to the cutting direction to be retracted and the distance from the height measurement ending point to the cutting direction to be retracted; for example, the unidirectional height measurement distance is preset to be positioned at the position of each actual cutting action (namely, a cutting path) including the starting point of the path, and the position is respectively retracted by 2mm to be used as a height measurement starting point and a height measurement ending point;
acquiring height data of a cutting path to be processed by a laser follow-up device according to height measurement sampling time between a height measurement starting point and a height measurement ending point;
optionally, the altimetry sampling time range is 0.5ms-5 ms; wherein, the sampling precision is the highest when the sampling time is 0.5 ms.
In addition, the operation section for acquiring the height data of the cutting path to be processed by the laser follow-up device through one-way height measurement can comprise whole-process constant-speed height measurement, whole-process variable-speed height measurement and partial-process constant-speed height measurement; and the maximum instantaneous speed does not exceed 2000mm/s during unidirectional height measurement operation.
Optionally, the performing data processing on the acquired height data according to the feedback time of the piezoelectric ceramic and forming the positive and negative piezoelectric ceramic motion compensation table includes:
acquiring the movement speed and the movement delay of the laser follow-up device, and calculating the actual X-axis position corresponding to the cutting track and the height data corresponding to the actual X-axis position according to the movement data and the movement delay of the laser follow-up device;
and obtaining the feedback time and the laser processing speed of the piezoelectric ceramics, and determining a positive and negative piezoelectric ceramics motion compensation table according to the feedback time and the laser processing speed of the piezoelectric ceramics.
Optionally, the obtaining the feedback time and the laser processing speed of the piezoelectric ceramic, and determining the positive and negative piezoelectric ceramic motion compensation table according to the feedback time and the laser processing speed of the piezoelectric ceramic includes:
obtaining feedback time and laser processing data of the piezoelectric ceramics, and calculating to obtain a compensation point coordinate according to the feedback time and the laser processing data of the piezoelectric ceramics;
screening out points to be compensated in the height measurement data according to the coordinates of the compensation points, and generating a positive and negative piezoelectric ceramic motion compensation table; wherein the content of the first and second substances,
the positive and negative piezoelectric ceramic motion compensation meter comprises a positive cutting piezoelectric ceramic motion compensation meter and a negative cutting piezoelectric ceramic motion compensation meter.
Optionally, when the cutting track is subjected to forward or reverse laser processing, the step of controlling the piezoelectric ceramics to perform real-time control by adopting a feed-forward compensation mechanism according to the forward and reverse piezoelectric ceramic motion compensation table comprises:
when the cutting channel is subjected to laser processing, judging the laser movement direction and the height measurement direction to determine the laser processing direction, and calling a piezoelectric ceramic movement compensation table in the corresponding direction according to the laser processing direction;
when the cutting channel is subjected to forward or reverse laser processing, the piezoelectric ceramics are controlled to be subjected to laser processing by adopting a feedforward compensation mechanism according to the calling of the piezoelectric ceramics motion compensation table in the corresponding direction.
Optionally, when the cutting track is subjected to forward or reverse laser processing, the step of controlling the piezoelectric ceramic to perform laser processing by using a feedforward compensation mechanism according to the piezoelectric ceramic motion compensation table in the calling corresponding direction includes:
taking the height measurement starting point as an actual operation starting point, triggering through the internal position of the controller, sending a triggering instruction at the piezoelectric ceramic triggering position, and controlling the piezoelectric ceramic to cut the cutting path in the forward direction in real time according to the called forward piezoelectric ceramic motion compensation table until the cutting end point;
and moving the Z axis for jumping, calling a reverse cutting piezoelectric ceramic motion compensation meter, and carrying out reverse follow-up cutting until the set number of cutting knives is finished.
In summary, the method of the present embodiment performs the measurement and the follow-up function in two steps; on one hand, the piezoelectric ceramic can be rapidly controlled in real time through a position trigger mode. On the other hand, the actual high-precision operation feedback time based on piezoelectric ceramics (PZT) is 6 milliseconds at a low speed, a feedforward compensation mechanism is adopted, and high-speed laser follow-up devices are utilized to obtain high-position precision height data in the cutting path. And then directly feeding back to the controller, and realizing real-time control on the PZT by using a high-speed operation function in the controller. The laser follow-up device takes height data and a corresponding X-axis position every 0.5 milliseconds; and calculating actual X-axis position and height data according to the delay time t of the laser follow-up device and the movement speed of the laser follow-up device. And calculating the X-axis position sent by the PZT fixed point when the PZT moves in the positive and negative directions according to the laser cutting speed and the 6 millisecond control delay of the PZT, and finally selecting the closest position from the height data as the corresponding height data of the point to be compensated. According to the difference of height measurement speed, the distance between the X-axis compensation position and the actual measurement position is less than 1mm, so that the laser focus position is ensured to be close to the actual processing position as far as possible. The processing method ensures that the operating position of the same point is unchanged when the piezoelectric ceramic moves in the positive direction and the negative direction, thereby solving the problem of vertical fluctuation of the distance of the bidirectional invisible cutting path and achieving the maximum control precision under the condition of ensuring PTZ delay.
An embodiment of the present invention further provides a system for laser processing a wafer, as shown in fig. 7, the system includes:
the laser follow-up device 22 is used for acquiring height data of a cutting path to be processed;
the data processing unit is used for carrying out data processing on the acquired height data according to the feedback time of the piezoelectric ceramics and forming a positive and negative piezoelectric ceramics motion compensation table;
the piezoelectric ceramic 24 is used for driving laser to carry out forward or reverse laser processing on the cutting path;
and the controller is used for controlling the piezoelectric ceramics to adopt a feedforward compensation mechanism to carry out real-time control according to the positive and negative piezoelectric ceramic motion compensation table when carrying out forward or reverse laser processing on the cutting path.
The system for processing the wafer by the laser mainly can automatically adjust the height of the laser cutting head by the controller according to the fluctuation of the surface of the wafer, keep the preset laser focal length, solve the problem that the laser follower device is slow in response and cannot follow the change of the surface of a sample when equipment runs at a high speed, and realize the processing precision that the laser processing focal point is changed by +/-1 um from the surface of the sample. Firstly, a laser follow-up device acquires a great amount of dense height data in the height data of a cutting path to be processed by measuring, and the measurement interval time rarely acquires a great amount of height data; then, the data processing unit performs data processing on the acquired height data according to the feedback time of the piezoelectric ceramics and forms a positive and negative piezoelectric ceramics motion compensation table, for example, the acquired height data is subjected to screening, average processing, curve fitting and the like according to the feedback time of the piezoelectric ceramics to form a high-precision positive and negative piezoelectric ceramics motion compensation table; finally, the controller controls the piezoelectric ceramics in real time through a position trigger mode; the method can effectively solve the adaptability problem of piezoelectric ceramic control programs with different delays, and simplifies the precision requirement of hardware assembly by adopting a feedforward compensation mechanism, so that the hardware design is more flexible.
In addition, the system of the embodiment solves the problem of up-and-down fluctuation of the distance of the bidirectional invisible cutting path by setting a feedforward work (namely a positive and negative piezoelectric ceramic motion compensation table formed by positive height measurement feedback height data of the laser follow-up device) and two cutting actions (for carrying out laser processing on the cutting path in a positive direction or a negative direction), and effectively improves the laser processing precision, so that the cutting speed can reach 2000mm/s, and the cutting precision can reach +/-1 mu m; and further can realize high-speed cutting of the wafer surface with little surface flatness change.
Optionally, the system further comprises:
and the distance retraction setting unit is used for presetting the distance from the height measurement starting point to the cutting direction to be retracted and the distance from the height measurement ending point to the cutting direction to be retracted.
Optionally, the data processing unit includes:
the calculation module is used for acquiring the movement speed and the movement delay of the laser follow-up device and calculating the actual X-axis position corresponding to the cutting track and the height data corresponding to the cutting track according to the movement data and the movement delay of the laser follow-up device;
and the compensation meter determining module is used for obtaining the feedback time and the laser processing speed of the piezoelectric ceramics and determining the positive and negative piezoelectric ceramics motion compensation meter according to the feedback time and the laser processing speed of the piezoelectric ceramics.
In summary, as shown in fig. 7, in the system of the present embodiment, the laser processing beam 25 passes through the coaxial lens barrel 23, the PZT24, and the processing objective lens 26 in sequence along the Y-motion axis 27 and is focused on the wafer to be processed; a laser follower 22 and a coaxial lens cone 23 are arranged on the Z motion axis 21; the position of the laser follower 0-position focal point 29, and the laser focal point 210, are shown by the XY-processing plane 28 in fig. 7.
The system of this embodiment may be configured to implement the technical solutions of the method embodiments, and the implementation principles and technical effects are similar, which are not described herein again.
EXAMPLE III
Because the existing wafer laser cutting has higher requirement on the consistency of cutting depth and the precision is at least in a micron level, but high-speed cutting and the unevenness of the surface of the wafer form a pair of contradiction factors, a focusing plane is easy to separate from the plane of the wafer under the condition of high-speed movement, the condition of a breakpoint of the surface cutting of the wafer occurs, and the oscillation error of a laser follower can be caused by frequently updating the set value of the laser follower. Accordingly, an embodiment of the present invention provides a method for laser processing a wafer, as shown in fig. 8, the method includes:
s31, scanning the cutting road to be processed, and acquiring height data of the cutting road by a laser follow-up device;
s32, fitting the height data to form a height curve of the cutting channel;
and S33, determining the height set value of the laser follow-up device within the preset cutting distance according to the height curve, and controlling the piezoelectric ceramics to carry out laser processing on the cutting path within the preset cutting distance according to the height set value of the laser follow-up device.
The method for processing the wafer by the laser mainly comprises the steps of scanning the cutting lines, recording height data of each position at the shortest distance interval, and fitting a height curve according to the height data recorded on the whole cutting line.
Meanwhile, the actual moving process of the laser follow-up device from receiving the height set value signal to moving to the set value position is in a non-step type, the whole moving track is similar to a hysteresis curve, the cutting speed is higher, the process form is more obvious, therefore, the maximum value or the minimum value of the height in a section of cutting distance can be regarded as the target set value of the follow-up system during high-speed cutting movement, the requirement that the distance between a laser focusing plane and the surface of a cutting path is in a micron-scale all the time and the process effect is not influenced is ensured, and the laser follow-up device is prevented from being in an oscillation state at any time to cause control errors.
Therefore, the method can achieve the purpose that the laser focusing plane and the surface of the cutting channel are always at the same height in the wafer cutting process, the breakpoint phenomenon cannot occur along with the fluctuation of the surface height of the cutting channel, and the control precision of the laser follow-up device is within the range of +/-1 mu m; the second aspect can also greatly improve the cutting speed, shorten the process time and improve the equipment productivity on the premise of not influencing the process cutting effect; the third aspect can also reduce frequent oscillation of the laser follow-up device in a small range, reduce measurement errors and prolong the service life of equipment to a certain extent.
Optionally, the scanning the cutting street to be processed, and acquiring the height data of the cutting street by using the laser follower device includes:
presetting a height zero point value of the laser follow-up device, moving the Z axis, and controlling the laser follow-up device to move within a preset range;
presetting a height measurement starting point P of a cutting pathaEnd point of height measurement Pb；
At the beginning of height finding PaHeight measurement end point PbThe height of the focusing plane from the surface of the material is measured by a laser follower device according to the position interval d, and the measured height data is stored in an array H [ k ]]，k＝(Pa-Pb) D; wherein k is an integer.
Optionally, the fitting of the height data to form the height curve line of the cutting street is according to an array H [ k ]]The height data in (1) is subjected to curve fitting to form a height curve H～(ii) a Wherein the content of the first and second substances,
H～＝f(P，H，C)，H～is the fitting height of any point.
Optionally, the determining a set height value of the laser follower within a preset cutting distance according to the height curve includes:
presetting the cutting speed V of the processproSetting interval time T with follow-up updatesetUpdating the height setting value of the laser follow-up device every interval distance D, wherein D is VproTsetAnd D > D;
obtaining the height value H of the starting point of each distance D lengthaEnd point height value HbMaximum height value HtopWith a minimum height value Hbot；
Comparing the height values H of the starting pointsaHeight from end point HbDetermining a height set value H of a laser followerset。
Optionally, the comparison starting point height value HaHeight from end point HbDetermining a height set value H of a laser followersetThe method comprises the following steps:
when H is presenta＞HbThen Hset＝Htop；
When H is presenta＜HbThen Hset＝Hbot。
Optionally, the range of the position interval d is: d is more than or equal to 1mm and less than or equal to 100 mm.
Optionally, the method further comprises:
when the cutting channel is subjected to forward or reverse laser processing, the piezoelectric ceramics are controlled according to the height set value of the laser follow-up device determined by the height curve.
For example, the specific scheme of the method according to this embodiment may be executed according to the following steps:
presetting a height zero point value of the laser follow-up device, and moving the Z axis to control the moving range of the laser follow-up device within a micron-sized adjustable range;
presetting a starting point of a cutting path as PaThe end point position is PbScanning the whole cutting path, measuring the height of the focusing plane from the surface of the wafer by the position interval d (d is more than or equal to 1mm and less than or equal to 100mm), sequentially recording all height data and storing the height data into an array H [ k ]]，k＝(Pa-Pb) K is an integer;
performing curve fitting according to height data in an array H [ k ], wherein H to f (P, H and C) is the fitting height of any point;
set the process cutting speed VproSetting interval time T with follow-up updatesetUpdating the set height value of the laser follow-up device every interval distance D, D being VproTsetSatisfying the condition D > D;
taking the height value H of the starting point of each length DaEnd point height value HbMaximum height value HtopWith a minimum height value HbotHigh speed set value Hset
When H is presenta＞HbThen Hset＝Htop；
When H is presenta＜HbThen Hset＝Hbot。
An embodiment of the present invention further provides a system for laser processing a wafer, as shown in fig. 9, the system includes:
the laser follow-up device 31 is used for scanning a cutting path to be processed and acquiring height data of the cutting path;
a curve fitting unit 32 for fitting the height data to form a height curve of the cutting street;
the piezoelectric ceramic 33 is used for driving laser to carry out laser processing on the cutting path;
and the controller 34 is used for determining a height set value of the laser follow-up device within a preset cutting distance according to the height curve, and controlling the piezoelectric ceramics to carry out laser processing on the cutting path within the preset cutting distance according to the height set value of the laser follow-up device.
The system for processing the wafer by the laser mainly scans the cutting streets, records the height data of each position at the shortest distance interval, and the curve fitting unit fits a height curve according to the height data recorded on the whole cutting street.
Meanwhile, the actual moving process of the laser follow-up device from receiving the height set value signal to moving to the set value position is in a non-step type, the whole moving track is similar to a hysteresis curve, the cutting speed is higher, the process form is more obvious, therefore, the maximum value or the minimum value of the height in a section of cutting distance can be regarded as the target set value of the follow-up system during high-speed cutting movement, the requirement that the distance between a laser focusing plane and the surface of a cutting path is in a micron-scale all the time and the process effect is not influenced is ensured, and the laser follow-up device is prevented from being in an oscillation state at any time to cause control errors.
Therefore, the system of the embodiment can achieve the purpose that the laser focusing plane is always at the same height with the surface of the cutting channel in the wafer cutting process, the breakpoint phenomenon cannot occur along with the fluctuation of the surface height of the cutting channel, and the control precision of the laser follow-up device is within the range of +/-1 μm; the second aspect can also greatly improve the cutting speed, shorten the process time and improve the system capacity on the premise of not influencing the process cutting effect; the third aspect can also reduce frequent oscillation of the laser follow-up device in a small range, reduce measurement errors and prolong the service life of the system to a certain extent.
Optionally, the system further comprises:
the setting unit is used for presetting a height zero point value of the laser follow-up device, moving the Z axis and controlling the laser follow-up device to move within a preset range; and presetting a height measurement starting point P of the cutting pathaEnd point of height measurement Pb。
Optionally, the controller comprises:
a parameter setting module for presetting the cutting speed V of the processproSetting interval time T with follow-up updatesetUpdating the height setting value of the laser follow-up device every interval distance D, wherein D is VproTsetAnd D > D;
an obtaining module for obtaining the height value H of the starting point of each distance D lengthaEnd point height value HbMaximum height value HtopWith a minimum height value Hbot；
A determination module for comparing the starting point height value HaHeight from end point HbDetermining a height set value H of a laser followerset。
The system of this embodiment may be configured to implement the technical solutions of the method embodiments, and the implementation principles and technical effects are similar, which are not described herein again.
It will be understood by those skilled in the art that all or part of the processes of the methods of the embodiments described above can be implemented by a computer program, which can be stored in a computer-readable storage medium, and when executed, can include the processes of the embodiments of the methods described above. The storage medium may be a magnetic disk, an optical disk, a Read-Only Memory (ROM), a Random Access Memory (RAM), or the like.
The above description is only for the specific embodiment of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are included in the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.
Claims (5)
1. A method of laser processing a wafer, comprising:
scanning a cutting channel to be processed, and acquiring height data of the cutting channel by a laser follow-up device;
fitting the height data to form a height curve of the cutting street;
determining a height set value of the laser follow-up device within a preset cutting distance according to the height curve, and controlling the piezoelectric ceramics to carry out laser processing on the cutting path within the preset cutting distance according to the height set value of the laser follow-up device;
wherein, the scanning is waited to process the cutting street, and obtain by laser servo device the height data of cutting street includes:
presetting a height zero point value of the laser follow-up device, moving the Z axis, and controlling the laser follow-up device to move within a preset range;
presetting a height measurement starting point P of a cutting pathaEnd point of height measurement Pb；
At the beginning of height finding PaHeight measurement end point PbThe height of the focusing plane from the surface of the material is measured by a laser follower device according to the position interval d, and the measured height data is stored in an array H [ k ]]，k＝(Pa-Pb) D; wherein k is an integer;
the height curve of the cutting path formed by fitting the height data is according to an array H [ k ]]The height data in (1) is subjected to curve fitting to form a height curve H～(ii) a Wherein the content of the first and second substances,
H～＝f(P，H，C)，H～fitting height for any point;
the determining the height set value of the laser follow-up device within the preset cutting distance according to the height curve comprises the following steps:
presetting the cutting speed V of the processproSetting interval time T with follow-up updatesetUpdating the height setting value of the laser follow-up device every interval distance D, wherein D is VproTsetAnd D > D;
obtaining the height value H of the starting point of each distance D lengthaEnd point height value HbMaximum height value HtopWith a minimum height value Hbot；
Comparing the height values H of the starting pointsaHeight from end point HbDetermining a height set value H of a laser followerset。
2. The method of claim 1, wherein the comparison start point height value HaHeight from end point HbDetermining a height set value H of a laser followersetThe method comprises the following steps:
when H is presenta＞HbThen Hset＝Htop；
When H is presenta＜HbThen Hset＝Hbot。
3. The method of claim 1, wherein the position interval d ranges from: d is more than or equal to 1mm and less than or equal to 100 mm.
4. The method of claim 1, further comprising:
when the cutting channel is subjected to forward or reverse laser processing, the piezoelectric ceramics are controlled according to the height set value of the laser follow-up device determined by the height curve.
5. A system for laser processing a wafer, comprising:
the laser follow-up device is used for scanning a cutting channel to be processed and acquiring height data of the cutting channel;
the curve fitting unit is used for fitting the height data to form a height curve of the cutting channel;
the piezoelectric ceramic is used for driving laser to carry out laser processing on the cutting path;
the controller is used for determining a height set value of the laser follow-up device within a preset cutting distance according to the height curve and controlling the piezoelectric ceramics to carry out laser processing on the cutting path within the preset cutting distance according to the height set value of the laser follow-up device;
wherein the system further comprises:
the setting unit is used for presetting a height zero point value of the laser follow-up device, moving the Z axis and controlling the laser follow-up device to move within a preset range; and presetting a height measurement starting point P of the cutting pathaEnd point of height measurement Pb；
The controller includes:
a parameter setting module for presetting the cutting speed V of the processproSetting interval time T with follow-up updatesetUpdating the height setting value of the laser follow-up device every interval distance D, wherein D is VproTsetAnd D > D;
an obtaining module for obtaining the height value H of the starting point of each distance D lengthaEnd point height value HbMaximum height value HtopWith a minimum height value Hbot；
A determination module for comparing the starting point height value HaHeight from end point HbDetermining a height set value H of a laser followerset。
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