JP2019201067A - Processing method of wafer - Google Patents

Abstract

To provide a processing method of wafer capable of restraining occurrence of processing failure when splitting a wafer.SOLUTION: A processing method of wafer comprises a calculation step of determining the size of regions that must be secured on both sides of a scheduled line to be irradiated with a laser beam, on the basis of impact of the deviation of heat conduction occurring the wafer by laser beam irradiation, and calculating the minimum 2satisfying N<2where N is the number of rows of devices included in the region, a 2processing step of forming the processing mark in the wafer by irradiating the scheduled line with the laser beam at intervals of minimum 2of the scheduled line, and a bisection processing step of repeating the step of forming the processing mark in the wafer by irradiating the scheduled line, bisecting the number of rows of device included, respectively, in a plurality of regions sectioned by the processing marks, with the laser beam, until the number of rows of device included in the regions sectioned by the processing marks becomes 1.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a wafer processing method for processing a wafer by irradiating a laser beam.

  By dividing a wafer on which a plurality of devices are formed along a division planned line (street), a plurality of device chips each including the device can be obtained. The wafer is divided using, for example, a cutting device having a spindle as a rotation axis. The wafer is cut along the planned division line by rotating the cutting blade mounted on the spindle tip of the cutting apparatus and cutting the cutting blade into the wafer along the planned division line.

  In the division of a wafer using a cutting device, various devices have been proposed in order to prevent device chip processing defects and cutting blade damage. For example, Patent Document 1 discloses that a wafer is first divided into two wafer pieces having substantially the same area, and then the wafer piece is further divided into two wafer pieces having substantially the same area. A method of dividing a wafer into a plurality of device chips is disclosed.

  According to said method, the area of the wafer of the both sides separated by the division | segmentation scheduled line which a cutting blade cuts becomes substantially the same, and the load which acts on a cutting blade at the time of cutting becomes equal by the surface side and a back surface side. Thereby, generation | occurrence | production of processing defects, such as a chip | tip of a device chip | tip, a crack, and the failure | damage of a cutting blade are suppressed.

  On the other hand, a technique using a laser processing apparatus for dividing a wafer instead of the cutting apparatus has been proposed. In this method, the wafer is divided by irradiating the wafer with a laser beam having a wavelength having an absorptivity along the division line. Patent Document 2 discloses a wafer processing method in which a processing trace (groove) is formed by irradiating a pulsed laser beam to a division line of a wafer, and the wafer is divided along the processing trace.

JP-A-4-245663 JP-A-10-305420

  When a wafer is processed using a laser processing apparatus as described above, processing defects such as chipping or cracks called chipping may occur in the wafer for some reason, leading to a decrease in device chip yield.

  The present invention has been made in view of such problems, and an object of the present invention is to provide a wafer processing method capable of suppressing the occurrence of processing defects when the wafer is divided by laser beam irradiation.

According to the present invention, there is provided a wafer processing method for processing a wafer in which devices are respectively formed in a plurality of regions partitioned by a plurality of division lines, by irradiating a laser beam along the division lines. And determining the size of the area to be secured on both sides of the division line to be irradiated with the laser beam based on the influence of the bias of the heat conduction generated in the wafer by the irradiation of the laser beam. And calculating the minimum 2 ⁿ satisfying N <2 ⁿ (n is a natural number), where N is the number of columns of the device (N is a natural number), and and 2 ⁿ processing step of forming the processing marks on the wafer by irradiating the laser beam at intervals of 2 ⁿ duty of outermost small, a plurality of territories that are partitioned by the processed traces A step of forming a processing mark on the wafer by irradiating a laser beam to the division line that bisects the number of columns of the device included in each of the devices, and the device included in a region defined by the processing mark And a bisection processing step that repeats until the number of rows becomes 1 is provided.

In the ²ⁿ processing step of the present invention, after forming the processing trace having a depth for cutting the wafer by irradiating the laser beam along the division planned line closest to the edge of the wafer, The laser beam may be irradiated to the other division planned lines at intervals of the minimum ^{2n of the} planned division lines.

  In the present invention, the wafer may be a GaAs wafer.

  In the wafer processing method according to the present invention, first, processing marks are formed on the wafer at a predetermined interval by irradiation with a laser beam, and then the number of device rows included in a plurality of regions defined by the processing marks is equal to two. The wafer is processed by repeating the step of irradiating the laser beam and forming a processing mark as shown. Thereby, since the bias of heat conduction caused by the laser beam irradiation is suppressed, it is possible to suppress a processing defect due to the bias of heat conduction and improve the yield of device chips.

It is a perspective view which shows the structural example of a wafer. It is a perspective view which shows the wafer of the state supported by the flame | frame. It is a perspective view which shows typically the state by which the wafer was supported by the laser processing apparatus. It is a top view which shows a mode that the wafer was divided | segmented into the 1st area | region and the 2nd area | region. It is a top view which shows a mode that the 2nd area | region was divided into the 3rd area | region and the some 4th area | region. It is a top view which shows a mode that the 4th area | region was divided into two 5th area | regions. It is a top view which shows a mode that the 5th area | region was divided into two 6th area | regions.

  Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a perspective view illustrating a configuration example of a wafer according to the present embodiment. As shown in FIG. 1, the wafer 11 is formed in a disk shape having a front surface 11a and a back surface 11b. As the wafer 11, for example, a GaAs wafer can be used.

  The wafer 11 is divided into a plurality of regions by a plurality of division lines. For example, as shown in FIG. 1, the wafer 11 is arranged such that the length direction is along the first direction (the direction indicated by the arrow A), and the second direction (indicated by the arrow B) intersecting the first direction. A plurality of first division lines 13a arranged along the direction), and a plurality of second divisions arranged along the first direction, the length direction being arranged along the second direction It is divided into a plurality of areas by the planned line 13b. FIG. 1 shows a wafer 11 in which the first direction and the second direction are substantially perpendicular.

  A device 15 composed of an IC (Integrated Circuit) or the like is formed on the surface 11a side of the plurality of regions defined by the plurality of first division lines 13a and the plurality of second division lines 13b. Yes.

  The material, shape, structure, size, etc. of the wafer 11 are not limited. For example, a wafer formed of a material other than GaAs, such as a semiconductor other than GaAs (silicon, InP, GaN, SiC, etc.), ceramics, resin, metal, or the like can be used as the wafer 11. Further, the type, quantity, shape, structure, size, arrangement, etc. of the device 15 are not limited.

  When the laser beam is irradiated along the plurality of first division planned lines 13a and the plurality of second division planned lines 13b, a processing mark is formed by ablation in the region of the wafer 11 irradiated with the laser beams. And if the wafer 11 is cut | disconnected along this process trace, the wafer 11 will be divided | segmented into the several device chip | tip with which the device 15 was formed in the surface. Irradiation of the laser beam onto the wafer 11 is performed using a laser processing apparatus.

  When processing the wafer 11 by laser beam irradiation, first, the wafer 11 is supported by a frame in order to hold the wafer 11 by a chuck table of a laser processing apparatus. FIG. 2 is a perspective view showing the wafer 11 supported by the annular frame 19. An annular frame 19 is attached along the outer periphery of the dicing tape 17, and the back surface 11 b side of the wafer 11 is attached to the dicing tape 17, thereby exposing the front surface 11 a side of the wafer 11 upward. Thereby, the wafer 11 is supported by the frame 19.

  Next, the wafer 11 supported by the frame 19 is supported by a laser processing apparatus. FIG. 3 is a perspective view schematically showing a state in which the wafer 11 is supported by the laser processing apparatus 2. The laser processing apparatus 2 includes a chuck table 4 that holds a wafer 11, and a laser processing unit 6 that irradiates the wafer 11 held by the chuck table 4 with a laser beam having a wavelength that absorbs the wafer 11. .

  The chuck table 4 sucks and holds the wafer 11 via the dicing tape 17. Specifically, the upper surface of the chuck table 4 is a holding surface for holding the wafer 11, and this holding surface is connected to a suction source (not shown) through a suction path (not shown) formed in the chuck table 4. It is connected.

  The frame 19 is fixed by a clamp (not shown) provided in the laser processing apparatus 2, and the negative pressure of the suction source is applied to the holding surface while the wafer 11 is supported by the holding surface of the chuck table 4. Is sucked and held in contact with the holding surface. The chuck table 4 is moved in a machining feed direction (X-axis direction) and an index feed direction (Y-axis direction) by a moving mechanism (not shown).

  The wafer 11 is sucked and held by the chuck table 4 so that the surface 11a is exposed upward. FIG. 3 shows a state in which the wafer 11 is held such that the first direction of the wafer 11 substantially coincides with the X-axis direction and the second direction of the wafer 11 substantially coincides with the Y-axis direction. In this state, a linear processing mark is formed on the wafer 11 by irradiating the laser beam from the laser processing unit 6 along the plurality of first scheduled division lines 13a.

The laser processing unit 6 has a cylindrical casing 8. A collector for condensing a pulse laser beam oscillated from a pulse laser beam oscillator (not shown) such as a YAG laser oscillator or a YVO ₄ laser oscillator provided in the laser processing apparatus 2 is provided at the tip of the casing 8. 10 is installed.

  Further, the casing 8 is equipped with an image pickup means 12 for picking up an image of a processing area (laser beam irradiation area) of the wafer 11. The image acquired by the imaging unit 12 is used for image processing such as pattern matching for performing alignment between the condenser 10 and the first scheduled division line 13a or the second scheduled division line 13b. Thereby, the irradiation position of the laser beam can be adjusted.

  When irradiating the wafer 11 with the laser beam, the chuck table 4 is moved below the condenser 10, and a laser beam having a wavelength that absorbs the wafer 11 is condensed by the condenser 10. The chuck table 4 is moved in the machining feed direction (X-axis direction) while irradiating toward the scheduled division line 13a. As a result, the laser beam is irradiated along the first scheduled dividing line 13 a, and a processing mark composed of a linear groove is formed on the wafer 11.

  When the wafer 11 is divided by laser beam irradiation, a processing mark having a depth for cutting the wafer 11 is formed along the first division line 13a. For example, a processing trace having a depth for cutting the wafer 11 can be formed by irradiating the laser beam a plurality of times along the same first division planned line 13a. In this case, the number of times of laser beam irradiation is appropriately set so that the wafer 11 can be cut.

  The irradiation of the laser beam to the second scheduled division line 13b is also performed in the same manner as the first scheduled division line 13a. Specifically, the chuck table 4 is moved in the horizontal direction (XY plane direction) so that the first direction of the wafer 11 substantially coincides with the Y-axis direction and the second direction of the wafer 11 substantially coincides with the X-axis direction. The same operation is performed after rotating 90 °. In this way, when all the first division planned lines 13 a and the second division planned lines 13 b are cut, the wafer 11 is divided into a plurality of device chips each including the device 15.

  Here, consider the order in which the laser beam is applied to the division lines. For example, a laser beam is sequentially applied from one end portion to the other end portion in the second direction of the wafer 11 with respect to the plurality of first division planned lines 13a arranged along the second direction. When irradiating, the volume of the area | region of the both sides separated by the 1st division | segmentation scheduled line 13a irradiated with a laser beam will arise.

  Specifically, first, the laser beam is irradiated along a first division planned line 13a closest to one end in the second direction of the wafer 11 (hereinafter, the outermost first division planned line 13a). Is done. At this time, of the two regions of the wafer 11 divided by the outermost first division planned line 13a, the volume of the region including the one end is smaller than the volume of the other region.

  The volume deviation as described above causes a heat conduction deviation caused by laser beam irradiation. In other words, heat is generated when the laser beam is irradiated onto the first scheduled dividing line 13 a, and this heat is conducted inside the wafer 11. Here, if there is a volume deviation in the two regions of the wafer 11 divided by the first division line 13a irradiated with the laser beam, the heat conduction path is more limited in the region where the volume is small. Heat does not diffuse sufficiently and temperature tends to rise.

  In addition, when the laser beam is irradiated to the wafer 11 on which the processing marks (grooves) are already formed along the plurality of first division lines 13a, the processing marks prevent heat conduction, Conduction bias can occur. Specifically, when the laser beam is irradiated along the first division planned line 13a located in the region between the two processing marks formed on the wafer 11, the region is further divided into two small regions. Here, if the volumes of the two small regions are different, the heat conduction path may be more limited in the small region having a small volume.

  When the wafer 11 is divided by the laser beam irradiation, processing defects such as chipping and cracks, which are called chipping, may occur in the wafer 11, which is caused by uneven heat conduction on both sides of the region irradiated with the laser beam. It is speculated that this is due to the temperature difference. For this reason, it is preferable to irradiate the wafer 11 with the laser beam under a condition in which the bias of heat conduction on both sides of the region irradiated with the laser beam is small.

  In the present embodiment, the order in which the laser beam is irradiated onto the planned division line is set so that there is no significant difference in the volume of the regions located on both sides of the planned division line irradiated with the laser beam. Thereby, the bias of the heat conduction resulting from the difference in volume can be suppressed, and processing defects when processing the wafer 11 with the laser beam can be suppressed.

  In the wafer processing method according to the present embodiment, first, the interval at which the laser beam is irradiated is set based on the influence of the bias of heat conduction caused by the laser beam irradiation. Then, a laser beam is irradiated along the first division planned line 13 a of the wafer 11 at this interval to form a linear processing mark on the wafer 11. Thereafter, by repeating the step of further forming a processing mark by irradiating a laser beam to the first division planned line 13a that bisects the number of columns of devices included in the plurality of regions partitioned by the processing mark, A processing mark is formed along all the first division lines 13a.

  By using the above wafer processing method, the volume difference between the two regions separated by the region irradiated with the laser beam can be reduced, and processing defects can be suppressed. In addition, the irradiation of the laser beam to the 2nd division | segmentation scheduled line 13b is implemented by the same method.

  Details of the wafer processing method according to the present embodiment will be described below. In the following, as an example, the laser beam is irradiated to the wafer 21 in which the devices 15 are respectively formed in a plurality of regions partitioned by the 25 first division lines 23a and the 25 second division lines 23b. Then, the case of forming a processing mark will be described (see FIGS. 4, 5, 6, and 7). On the wafer 21, 24 rows of devices 15 are formed in a first direction (direction indicated by an arrow A) and a second direction (direction indicated by an arrow B), respectively.

<Calculation process>
In the wafer processing method according to the present embodiment, first, a calculation step of calculating an interval for irradiating the laser beam onto the first division planned line 23a in a subsequent step ( ²ⁿ processing step described later) is performed.

  The interval at which the laser beam is irradiated is set based on the influence of the bias of heat conduction that occurs on the wafer 21 due to the laser beam irradiation. For example, processing defects (such as chipping and cracks) due to uneven thermal conduction that occur in two regions of the wafer 21 defined by the first division line 23a irradiated with the laser beam do not occur, or the frequency of occurrence The interval for irradiating the laser beam is set so that is less than a certain value.

  Even if there is a volume difference between the two areas located on both sides of the laser beam irradiation area, the heat conduction caused by the laser beam irradiation can be observed in both areas if the volume of these areas is maintained at a certain level or more. It becomes substantially uniform, and processing defects due to uneven heat conduction are less likely to occur. Therefore, in the calculation step, the laser beam irradiation interval is calculated so that a region having a certain volume or more is secured on both sides of the laser beam irradiation region.

  Specifically, first, based on the influence of the bias of heat conduction generated on the wafer 21 by the laser beam irradiation, the size of the area to be secured on both sides of the first division line 23a irradiated with the laser beam is determined. decide. For example, the size of the region is determined so that processing defects (such as chipping and cracks) due to uneven heat conduction do not occur, or the frequency of occurrence does not exceed a certain level. In addition, the size of the region may be determined so that the temperature difference between the two regions located on both sides of the first division line 23a irradiated with the laser beam becomes a certain value or less.

  The size of the region is selected from, for example, the material of the wafer 21 (particularly thermal conductivity), the thickness of the wafer 21, the size of the device 15, the spacing between the devices 15, the wavelength of the laser beam, the intensity of the laser beam, and the like. It can also be determined based on one or more factors. In this case, the relationship between each of the above elements and the influence of the bias of heat conduction (the frequency of processing defects, the degree of temperature difference, etc.) is determined in advance based on experiments, and the irradiation region of the laser beam from each of the above elements What is necessary is just to determine the magnitude | size of the area | region which should be ensured on both sides of.

Next, the number of columns of devices 15 (the number of devices 15 in the second direction) N (N is a natural number) included in the area to be secured on both sides of the first scheduled division line 23a is specified. Based on the value of N, the minimum value of ²ⁿ that satisfies N <2 ⁿ (n is a natural number) is calculated. This minimum 2 ⁿ is a value to be calculated in the calculation step.

For example, when regions of three columns or more of the device 15 should be secured on both sides of the first division line 23a irradiated with the laser beam, N = 3, and the value of ²ⁿ to be calculated in the calculation step is The minimum value of ²ⁿ satisfying 3 < ²ⁿ , that is, 4, is obtained. The minimum interval of 2 ^{n of} the first scheduled division lines 23a corresponds to the interval of laser beam irradiation in the 2 ⁿ processing step described later.

< ²ⁿ processing steps>
Then, based on the value of the minimum of 2 ⁿ calculated by the calculation step, carried out 2 ⁿ processing step of irradiating the wafer 21 at intervals of outermost small of 2 ⁿ duty of the first division line 23a of the laser beam To do. For example, when the minimum ²ⁿ value is 4, the plurality of first division planned lines 23a are irradiated with laser beams at intervals of four. In the following description, when simply ^{denoted as 2n} , the minimum ²ⁿ calculated in the calculation step is indicated.

An example of the ²ⁿ processing step will be described with reference to FIGS. In the ²ⁿ processing step, first, a laser beam is irradiated along the first division planned line 23a (the outermost first division planned line 23a) closest to one end portion in the second direction of the wafer 21.

  By irradiation with the laser beam, a linear processing mark L1 is formed on the outermost first division planned line 23a, and the wafer 21 is formed with a first region 21a including the one end and a plurality of devices 15. The second region 21b is divided. FIG. 4 is a plan view showing a state in which the wafer 21 is divided into a first region 21a and a second region 21b.

Next, a laser beam is irradiated to the other first division planned lines 23a at intervals of ²ⁿ from the outermost first division planned line 23a. For example, when the value of 2 ⁿ is 4, the plurality of first division lines 23a are irradiated with laser beams at intervals of four. As a result, linear processing marks L2 are formed at intervals of 2 ⁿ of the plurality of first division planned lines 23a.

Due to the formation of the processing mark L2, the second region 21b includes the third region 21c located on the opposite side of the first region 21a in the second direction, and 2 ⁿ columns of devices 15 arranged in the second direction. Divided into a plurality of fourth regions 21d. FIG. 5 is a plan view showing a state in which the second region 21b is divided into a third region 21c and a plurality of fourth regions 21d.

  For example, when the plurality of first division planned lines 23a are irradiated with laser beams at intervals of four, six processing marks L2 are formed in the second region 21b as shown in FIG. Thus, the second region 21b is divided into a third region 21c and six fourth regions 21d in which four rows of devices 15 are arranged in the second direction.

The wafer 21 is divided into a plurality of regions by the above ²ⁿ processing steps. The 2 ⁿ processing step, between the plurality of first division lines 23a where the laser beam is irradiated, the N columns minute or more regions of the device 15 respectively are secured. For this reason, even if the heat conduction is hindered by the processing marks L1 and L2, the heat generated when the first splitting line 23a is irradiated with the laser beam is sufficiently diffused, resulting in uneven heat conduction. The occurrence of processing defects can be suppressed.

In the ²ⁿ processing step, the same first scheduled division line 23a may be irradiated with a laser beam a plurality of times to form processing marks L1 and processing marks L2 having a depth for cutting the wafer 21. . In this case, the laser beam irradiation order can be set freely.

  For example, the outermost first division line 23a is irradiated with a laser beam a plurality of times to form a processing mark L1 having a depth to cut the wafer 21, and then the laser beam is applied to each of the other first division lines 23a. May be formed a plurality of times to form a processing mark L2 having a depth at which the wafer 21 is cut. Further, by repeating the step of irradiating the outermost first division line 23a and the other first division line 23a with the laser beam one by one, the processing mark L1 and the processing depth L1 that cut the wafer 21 are processed. The mark L2 may be formed.

<Dividing process>
Next, a bisection processing step is performed in which a step of irradiating a laser beam to a division-scheduled line that substantially bisects the plurality of fourth regions 21d obtained by the ²ⁿ processing step is performed.

  First, a first division line 23a that bisects the number of columns in the second direction of the devices 15 included in the fourth region 21d is selected, and a laser beam is emitted along the first division line 23a. Irradiate.

As a result of the laser beam irradiation, linear processing marks L3 that bisect the number of columns in the second direction of the device 15 are formed in the fourth region 21d, respectively. The fourth region 21d is in the second direction. Are divided into two fifth regions 21e each having 2 ^n-1 columns of devices 15. FIG. 6 is a plan view showing a state where the fourth area 21d is divided into two fifth areas 21e.

  When the fourth region 21d is irradiated with the laser beam, the laser beam is irradiated so as to bisect the number of columns in the second direction of the devices included in the fourth region 21d. The volume of the fourth region 21d located on both sides of the region is substantially equal. For this reason, the deviation in heat conduction when the laser beam is irradiated is small, and processing defects due to the deviation in heat conduction are less likely to occur.

  In the bisection processing step, the same first division line 23a may be irradiated with a laser beam a plurality of times to form a processing mark L3 having a depth for cutting the fourth region 21d. . In this case, the laser beam irradiation order can be set freely.

  For example, after irradiating one first planned division line 23a with a laser beam a plurality of times to form one processing mark L3, the other first divided division line 23a is irradiated with a laser beam to generate another processing mark. L3 may be formed. Further, a plurality of processing marks L3 may be formed by repeating the step of irradiating the plurality of first division planned lines 23a that divide the fourth region 21d into substantially equal parts one by one.

  In addition, depending on the number of columns of the device 15, the device 15 may be included in the third region 21c. In this case, the first division line 23a that bisects the number of columns in the second direction of the devices 15 included in the third region 21c is selected and irradiated with the laser beam. When the number of columns of devices included in the third region 21c is an odd number, the first region is set so that the volume difference between the regions located on both sides of the first scheduled division line 23a irradiated with the laser beam is minimized. The division schedule line 23a may be selected.

Next, the fifth region 21e is similarly irradiated with a laser beam to further divide the fifth region 21e into substantially equal halves. That is, a linear processing mark L4 is formed that bisects the number of columns in the second direction of the device 15 in the fifth region 21e. Thus, the fifth region 21e is divided into two sixth regions 21f having 2 ⁿ⁻² columns of devices 15 in the ^second direction. FIG. 7 is a plan view showing a state in which the fifth area 21e is divided into two sixth areas 21f.

  When irradiating the fifth region 21e with the laser beam, as in the case of irradiating the fourth region 21d with the laser beam (see FIG. 6), the fifth region located on both sides of the region irradiated with the laser beam. The volume of 21e becomes substantially equal. For this reason, the deviation in heat conduction when the laser beam is irradiated is small, and processing defects due to the deviation in heat conduction are less likely to occur.

  In the bisection processing step, the same first division planned line 23a may be irradiated with a laser beam a plurality of times to form a processing mark L4 having a depth for cutting the fifth region 21e. . In this case, the laser beam irradiation order can be set freely.

  For example, one first planned division line 23a may be irradiated with a laser beam a plurality of times to form one processing mark L4, and then the other first divided division line 23a may be irradiated with a laser beam. Further, a plurality of processing marks L4 may be formed by repeating the step of irradiating the plurality of first division planned lines 23a that divide the fifth region 21e into approximately equal halves one by one.

  As described above, the step of further forming the machining trace by irradiating the first division planned line 23a that bisects the number of columns of the devices 15 respectively included in the plurality of regions partitioned by the machining trace. By repeating the above, the wafer 21 is divided into a plurality of regions including the devices 15 for one row.

In the 2 ⁿ processing step, the wafer 21 is partitioned into a plurality of fourth regions 21d including the 2 ⁿ rows of devices 15 by the processing marks L1 and L2 (see FIG. 5). Therefore, by repeating the process of dividing the number of columns of the device 15 into two equal parts, it is possible to irradiate the laser beam to all the first division planned lines 23a included in the fourth region 21d.

  After the irradiation of the laser beam to all the first scheduled division lines 23a is completed, the laser beam is irradiated to the second scheduled division line 23b by the same process. Specifically, first, the chuck table 4 shown in FIG. 3 is placed horizontally so that the first direction of the wafer 21 substantially coincides with the Y-axis direction and the second direction of the wafer 21 substantially coincides with the X-axis direction. Rotate 90 ° in the direction.

Thereafter, the above calculation step, ²ⁿ processing step, and bisection processing step are performed on the second scheduled division line 23b. It should be noted that the value of 2 ⁿ when irradiating the second scheduled division line 23b with the laser beam is the same as the value of 2 ⁿ when irradiating the first scheduled division line 23a with the laser beam. May be.

  Through the above steps, processing marks are formed on all the first planned division lines and the second planned division lines 23b. Further, when these processing traces are processing traces having a depth to cut the wafer 21, the wafer 21 is divided into a plurality of device chips each having the device 15.

  As described above, in the wafer processing method according to the present embodiment, the process of irradiating the laser beam to the division line that divides the fourth region 21d divided by the processing mark L1 and the processing mark L2 into approximately equal halves is repeated. . As a result, the volumes on both sides of the region irradiated with the laser beam are substantially the same, and the bias of heat conduction caused by the laser beam irradiation is suppressed. Therefore, it is possible to suppress processing defects due to uneven heat conduction and improve the yield of device chips.

In addition, when a laser beam is irradiated to the same 1st division | segmentation scheduled line 23a in multiple times and the processing trace of the depth which cut | disconnects the wafer 21 is formed, a laser is passed through a ²ⁿ processing process and a bisection processing process. The order of beam irradiation can be set as appropriate. For example, after the wafer 21 is irradiated with the laser beam a plurality of times in the ²ⁿ processing step to divide the wafer 21 into a plurality of fourth regions 21d, the fourth region 21d is irradiated with the laser beam in the bisection processing step. May be.

  Further, the wafer 21 may be divided by irradiating all the first scheduled division lines 23a with the laser beam once each in the order shown in FIGS. 4 to 7, and then repeating the same operation.

  Further, in the above-described embodiment, an example in which the laser beam is irradiated to the second scheduled division line 23b by the same method after the step of irradiating the laser beam to all the first division planned lines 23a has been described. However, the order of laser beam irradiation is not limited to this. For example, the irradiation of the laser beam onto the first scheduled division line 23a and the irradiation of the laser beam onto the second scheduled division line 23b may be performed alternately. In this case, every time the laser beam is irradiated onto the division line, the chuck table 4 shown in FIG. 3 is rotated 90 ° in the horizontal direction.

  In addition, the structure, method, and the like according to the above-described embodiment can be appropriately modified and implemented without departing from the scope of the object of the present invention.

DESCRIPTION OF SYMBOLS 11 Wafer 11a Front surface 11b Back surface 13a 1st scheduled division line 13b 2nd scheduled division line 15 Device 17 Dicing tape 19 Frame 21 Wafer 21a 1st area | region 21b 2nd area | region 21c 3rd area | region 21d 4th area | region 21e 5th area | region 21f 6th area | region 23a 1st division | segmentation planned line 23b 2nd division | segmentation planned line 2 Laser processing apparatus 4 Chuck table 6 Laser processing unit 8 Casing 10 Condenser 12 Imaging means

Claims (3)

A wafer processing method for processing a wafer in which devices are respectively formed in a plurality of regions partitioned by a plurality of division lines, by irradiating a laser beam along the division lines.
Based on the influence of the thermal conduction bias generated on the wafer by the irradiation of the laser beam, the size of the area to be secured on both sides of the division line to be irradiated with the laser beam is determined, and the area included in the area is determined. A calculation step of calculating the minimum 2 ⁿ satisfying N <2 ⁿ (n is a natural number) when the number of columns of the device is N (N is a natural number);
A 2 ⁿ processing step of forming a processing mark on the wafer by irradiating the laser beam at the minimum 2 ⁿ intervals of the planned dividing line to the planned dividing line;
A step of forming a processing mark on the wafer by irradiating a laser beam to the line to be divided that bisects the number of columns of the devices respectively included in a plurality of regions partitioned by the processing mark; And a bisection processing step that repeats until the number of rows of the devices included in the region partitioned by 1 is 1. In the ²ⁿ processing step, after the laser beam is irradiated along the planned division line closest to the edge of the wafer to form the processing trace having a depth for cutting the wafer, 2. The wafer processing method according to claim 1, wherein the laser beam is irradiated to the other divided lines at intervals of the minimum 2 ⁿ lines. 3.   3. The wafer processing method according to claim 1, wherein the wafer is a GaAs wafer.