JP4856931B2 - Laser cleaving method and laser cleaving apparatus - Google Patents

Description

  The present invention relates to a laser cleaving method and a laser cleaving apparatus for concentrating a laser beam inside a cleaved member and cleaving the cleaved member so that the surface of the cleaved member is separated into a plurality of regions.

  Conventionally, there is a technique for separating the surface of a member to be cut into a plurality of regions by condensing the laser beam inside the member to be cut. For example, when a semiconductor substrate such as a silicon wafer is precisely cut into chips, conventionally, a circumferential blade with a width of several tens to several hundreds of μm is rotated at high speed, and the abrasive on the blade surface grinds the substrate. There is known a blade dicing method that cuts by cutting. In this method, cooling water is sprayed onto the cut surface in order to reduce heat generation and wear associated with cutting. At this time, debris such as chips of the substrate itself, fine particles of the abrasive, and adhesive particles of the adhesive tape that fixes the substrate and the processing table are mixed with the cooling water and scattered over a wide range. In particular, when the substrate is a semiconductor substrate, a large number of fine functional elements are formed on the surface of the substrate, which may seriously affect the reliability of the functional elements themselves.

  In order to solve this problem, it is desirable that the cutting can be performed in a dry environment without using cooling water. Therefore, a processing method is used in which a laser beam having a high absorption wavelength is focused on the substrate surface and the substrate is cut. However, this method has a problem that the periphery of the cut portion is also melted on the substrate surface. In particular, when the substrate is a semiconductor substrate, there is a problem of damaging a logic circuit or the like provided on the substrate. Further, since laser processing proceeds by melting the substrate from the laser incident side to the emission side, a re-solidified product of the melt adheres to the substrate surface and becomes dust. Therefore, similarly to blade dicing, a problem caused by dust occurs.

Further, as a processing method for cutting a substrate by condensing a highly absorbing laser beam inside the substrate, for example, there are methods disclosed in Patent Document 1 and Patent Document 2. This is because the internal processing area formed by condensing a laser beam with a specific wavelength that is highly transmissive to the substrate, which is the material to be processed, inside the substrate is the starting point of the cutting. Therefore, cutting with less dust is possible.
JP 2002-192370 A JP 2002-205180 A

  However, in the above method, since the starting point of cutting is limited only to the internal processing region inside the member to be cut, it is difficult to precisely control the direction and position of the crack reaching the surface of the member to be cut from the starting point of cutting. It is.

  In addition, if the internal processing region formed inside the member to be cut has a length in the depth direction that is too long and cracks have reached the surface, the cracks appearing on the surface may cause dust to be ejected or When a functional element is formed, the functional element is damaged.

  In particular, when the member to be cut is a silicon wafer, the progress of cracks is easily influenced by the crystal orientation. Therefore, due to industrial errors in the formation of the silicon substrate and elements, etc., if there is a gap between the planned cutting line and the crystal orientation, the laser processing method described above will cause the cutting planned line in the process of proceeding to the surface. The deviated crack may destroy the logic circuit or the like of the element portion.

  This will be described with reference to FIG. When the modified layer 102 is formed by condensing a laser beam having a specific wavelength at a predetermined depth inside the silicon substrate 101 made of single crystal silicon having a (100) surface, the tip of the modified layer 102 in the vicinity of the surface The crack 103a starting from 102a may reach the surface. In this case, since the higher-order crystal orientation plane is formed at the tip 102a of the modified layer 102 by laser processing, the actual crack 103a does not become the ideal crack 103 but is a cleavage plane of single crystal silicon. It is inclined in the direction along the (110) plane and (111) plane. FIG. 15 schematically shows a case where the surface is the (100) plane and the cleavage plane is the (111) plane. As a result, the substrate surface is divided at a position greatly deviated from the planned cutting line C on the surface of the silicon substrate 101. Further, when the modified layer 102 is formed deep inside the substrate, the distance between the tip 102a and the substrate surface may be too long, and the substrate may not be cleaved or separated.

  In particular, in an element substrate of a liquid discharge head in which an ejection port such as an ink jet nozzle is formed, an opening structure for supplying liquid such as ink exists under the ejection port, so that a crack develops in them and destroys the substrate. There is a problem of doing. This tendency becomes more conspicuous when the thickness of the substrate is larger than the internal modified layer.

  The present invention has been made in view of the above-mentioned unsolved problems of the prior art. While forming the internal processing region by condensing the laser beam inside the substrate, the internal processing region (particularly the internal processing region) An object of the present invention is to provide a laser cleaving method and a laser cleaving apparatus in which a crack or a processing mark) does not reach the substrate surface as a region.

In order to achieve the above object, the laser cleaving method according to the present invention condenses laser light from a surface of a member to be cut to a condensing point at a predetermined depth inside the member to be cut to form an internal processing region, and A laser cleaving method for cleaving the cleaved member so that the cleaving member is separated into a plurality of regions,
Dividing the laser light emitted from the light source with a beam splitter, irradiating the split member with one of the divided laser lights,
The other divided laser beam is guided to a loop optical system including an afocal optical system that is provided in a part of the optical path and has an optical element whose relative position is variable, and further guided to the beam splitter. A part of the guided laser beam is irradiated onto the member to be cut, and a part of the laser beam is re-guided to the loop optical system, thereby forming the internal processing region of a desired size on the member to be cut. It is characterized by.

Further, the laser cleaving apparatus of the present invention forms an internal processing region by condensing a laser beam from a surface of the cleaved member to a condensing point having a predetermined depth, so that a plurality of cleaved members are formed by the laser beam. A laser cleaving device for separating the region
A stage on which the cleaved member is placed;
A light source that emits laser light;
A loop optical system having a beam splitter;
An afocal optical system having an optical element provided in the optical path of the loop optical system, the relative position of which is variable;
Have
The laser light emitted from the light source is divided by the beam splitter, one of the divided laser lights is applied to the member to be cut, and the other divided laser light is guided to the loop optical system and further In addition to being incident on the beam splitter, a part of the other split laser beam that has been incident is irradiated on the member to be cut, and a part thereof is re-guided to the loop optical system.

  According to the present invention, when forming an internal processing region (for example, a crack) by condensing a laser beam inside the member to be cut, the internal processing region is formed according to the position in the depth direction from the surface of the member to be cut. Since the size can be changed, it is possible to avoid forming an internal processing region that reaches the surface. Therefore, there is no possibility that the surface of the non-cleavable member is contaminated unlike blade dicing or conventional laser processing for cutting from the substrate surface.

  In addition, a small internal machining area can be formed in the vicinity of the surface, and by forming a large number of such small internal machining areas, the connection of cracks at the time of cleaving is ensured, and the formation of crack propagation deviating from the planned fracture line is formed. Can be avoided.

  As shown in FIG. 1 (a), as an example of a member to be cut, a silicon substrate 10 having a plurality of logic element portions 10a formed on the surface thereof is used as a member to be cut, and the logic elements 10a are divided into individual elements. A cleaving method for separating into chips will be described.

  As shown in FIG. 2, an internal processing region (for example, a laser beam is focused on a focusing point at a predetermined depth inside the silicon substrate 10 and does not reach the substrate surface 11 on which the logic circuit or the like of the silicon substrate 10 is formed) Melting, cracking, state of change in crystal structure, etc.). When the silicon substrate 10 is used, a typical phenomenon is a crack as it can be visually recognized as an internal processing region. Thus, the internal crack 12 (12a-12c) is formed in the inside of the silicon substrate 10, and each condensing point is scanned along the cleaving planned line C (relative movement), thereby along the cleaving planned line C. To form a band-shaped crack group.

  After or before the formation of such a crack group, a recess is formed on the substrate surface 11 along the planned cutting line C (C1, C2). Specifically, surface processing is performed to form a surface processing mark 11a that is a linear processing portion by marking or the like.

  When an external force for cleaving is applied after the formation of the surface processing mark 11a and the internal processing of the crack group by the laser beam, stress concentrates on the surface processing mark 11a and is connected to the internal crack 12c. The actual breaking line to be performed does not deviate from the planned breaking line C.

  The silicon substrate 10 having a thickness of 625 μm shown in FIGS. 1A and 1B has a thickness of 1 μm on the surface of the silicon wafer 1 whose surface is formed in the (100) plane, as shown in FIG. A certain degree of oxide film 2 is formed. On top of that, a nozzle layer 3 which is a structure made of epoxy resin with a built-in structure for discharging liquid such as ink, logic elements for driving them, wiring, etc. is arranged. It is composed.

  In this way, a liquid supply port (ink supply port) 4 as an opening is formed by anisotropic etching of the silicon wafer 1 immediately below the nozzle layer 3 incorporating a structure for discharging liquid and the like. The nozzle layer 3 is disposed with a cleaving line C between each other so that the silicon wafer 1 can be cleaved into each element chip at the end of the manufacturing process. The cleavage line C is formed along the crystal orientation of the silicon wafer 1, and the interval S between the adjacent nozzle layers 3 is about 400 μm at the minimum.

  FIG. 3 is a flowchart for explaining a cleaving process for separating the silicon substrate 10 into logic element portions 10a which are individual element chips. The process shown in this flowchart includes a tape mount process, a wafer correction process, a surface linear process process (surface process process), an internal crack formation process (internal process area formation process), a cleaving process, a repair process, and a pickup process. It consists of 7 steps.

  Each step will be described below in order.

[Tape mounting process]
As shown in FIG. 4, the silicon substrate 10 is first tape-mounted to prevent the elements from being separated in the process up to cleaving. The tape mount is formed by attaching an adhesive dicing tape T to which the dicing frame M is attached to the back surface of the silicon substrate 10.

  As the dicing tape, an adhesive tape coated with an ultraviolet curable or pressure sensitive adhesive or an adhesive tape having a self-adhesive layer is used.

[Wafer correction (warp correction) process]
As described above, the nozzle layer 3, which is a resin layer formed on the surface of the silicon substrate 10, undergoes thermal shrinkage during curing, and thus the entire silicon substrate 10 is deformed as shown in FIG. When laser irradiation to be described later is performed in such a deformed state, the incident angle is locally different on the substrate surface 11 and it cannot be processed with high accuracy. Therefore, it is necessary to correct this deformation in advance. Therefore, as shown in FIG. 5B, the silicon substrate 10 is sucked by the suction stage D from the dicing tape T side to flatten the silicon substrate 10 and correct the deformation.

[Surface recess processing step]
Subsequently, in order to cleave each logic element portion 10a of the silicon substrate 10 with high accuracy, a surface processing mark 11a, which is a recess that induces propagation of cracks in the cleaving line C, is formed on the substrate surface 11. That is, by forming the surface processing mark 11a along the planned cutting line C, when cleaving by an external force in a later step, stress concentration occurs in the surface processing mark 11a, and cracks are induced to the surface processing mark 11a. The Or the surface processing trace 11a becomes a starting point, and a crack progresses inside. Therefore, unnecessary cracks that destroy logic circuits and the like do not occur.

  As shown in FIG. 6, the surface processing mark 11 a may be formed by marking with a scriber using a tool 40 such as a cemented carbide blade or a diamond blade along the cutting line C. The surface processing mark 11a preferably has a width of 2 μm or more and a depth of 1 μm or more. However, it is necessary to have a size that does not interfere with the optical path of the laser beam L for processing the internal crack 12. As the processing depth, a depth that causes stress concentration between the surface processing mark 11a and the crack 12 at the time of cleaving is suitable. The processing depth may be smaller than the thickness of the oxide film 2 which is the surface layer of the silicon substrate 10 as shown in FIG. 6, or the depth is equal to or greater than the thickness of the oxide film 2. There is no problem.

  Further, the surface processing mark 11a is indispensable for at least the substrate surface 11 having the logic element portion 10a, but may be formed on both the front surface and the back surface of the silicon substrate 10.

  Moreover, when forming the surface processing mark 11a by scribing using the tool 40, by forming the surface processing mark before forming an internal crack described later as in the present embodiment, unnecessary cracks due to the processing load are formed. It can be avoided. On the contrary, when the surface processing trace is formed first, the processing trace itself can be used as a reference (line) indicating the processing position at the time of laser irradiation in the subsequent process, and the work efficiency of laser irradiation is improved. Can do.

  In addition, you may form the surface processing trace 11a after the internal crack formation process by the laser beam L. FIG. In this case, there is no influence of laser beam vignetting during internal crack formation (a phenomenon in which the amount of laser light reaching the inside of the substrate is reduced by reflecting the laser beam irradiated on the concave slope of the surface where the surface processing marks are formed) Internal crack formation can be performed more efficiently.

[Internal crack formation process]
The internal crack 12 shown in FIG. 2 is formed using the processing apparatus 50 shown in FIG. The processing apparatus 50 includes a light source optical system, a condensing optical system 52, and an automatic stage mechanism 53. Here, the light source optical system includes a light source 51, a beam expansion system 51a, a mirror 51b, and the like. The condensing optical system 52 includes a microscope objective lens 52a, a mirror 52b, an automatic focusing mechanism 52c, and the like. The automatic stage mechanism 53 has an X stage 53a, a Y stage 53b, a fine adjustment stage 53c, and the like. In addition, an alignment optical system (not shown) that performs alignment by the orientation flat 10b (see FIG. 1A) of the silicon substrate 10 that is the workpiece W is also provided.

  As the light source 51, a fundamental wave (1064 nm) of a pulse YAG laser is used. The pulse width is around 15 ns to 1000 ns, and the frequency is 10 KHz to 100 KHz. The laser excitation source is a semiconductor laser, and the power of the laser can be changed by an injection current to the semiconductor laser. The pulse width can be changed by changing the amount and frequency of the injected current.

  The selection of the laser light is determined by the spectral transmittance of the silicon substrate. Therefore, any light can be used as long as it can form a strong electric field at the condensing point and has a wavelength in which the silicon is transmissive.

  The laser light L emitted from the light source 51 enters the condensing optical system 52 through the beam expanding system 51a and the like. The microscope objective lens 52a of the condensing optical system 52 is, for example, one having a magnification of 20 NA (numerical aperture) 0.42 or a magnification of 50 NA 0.55. In addition, in consideration of the refractive index of silicon, it is possible to use a condensing lens optimal for silicon internal processing that can be applied to microscopic observation. As shown in FIG. 7B, the laser beam L focused on the workpiece W by the focusing optical system 52 is a substrate surface 11 having the logic element portion 10a of the silicon substrate 10 which is the workpiece W on the automatic stage 53. Incident from.

  The optical conditions at this time are set so that the surface processing mark 11 a may exist on the substrate surface 11. That is, measures are taken such as increasing the power in consideration of energy loss due to the surface processing mark 11a or selecting the light flux so as to be incident while avoiding the surface processing mark 11a. The light beam incident from the substrate surface 11 is refracted in the silicon substrate 10 and is condensed at a condensing point A at a predetermined depth (a) inside to generate an internal crack 12. The internal crack 12 is a crack extending in a direction toward and away from the substrate surface from the condensing point of the laser beam, and includes modification (melting, change in crystal structure, cracking) of the material at the condensing point. ) Formed in the internally processed region.

  According to the experiment, the processing conditions according to the condensing position, the film configuration of the oxide film 2, the laser wavelength to be used, etc., so that the crack tip of the innermost crack 12c shown in FIG. It is desirable to set This is to prevent the internal crack 12c and the substrate surface 11 from being inadvertently connected during processing, or the substrate surface 11 to be damaged depending on the laser irradiation conditions.

  The depth (a) of the condensing point A can be controlled by moving either the workpiece W, which is the silicon substrate 10, or the condensing optical system 52 in the optical axis direction and shifting the condensing position. The refractive index of the silicon substrate 10 with respect to a wavelength of 1064 nm is n, and the mechanical movement amount (movement amount when either the silicon substrate 10 or the condensing optical system 52 is moved in the optical axis direction) is d. At this time, the optical movement amount of the condensing point A is nd. The refractive index of the silicon substrate 10 is near 3.5 at a wavelength of 1.1 μm to 1.5 μm, and n is close to 3.5 when compared with the refractive index value actually measured in the experiment. That is, when the mechanical movement amount is 100 μm, the condensing point of the laser light L is formed at a position of 350 μm from the surface.

In addition, the fact that the refractive index is in the vicinity of 3.5 indicates that the reflectance is large. In general, the reflection at normal incidence is ((n−1) / (n + 1)) ² , and is about 30% in the silicon substrate. Although the remaining energy reaches the inside, the final energy at the condensing point is further reduced because there is also light absorption of the silicon substrate. When measured on a 625 μm thick silicon substrate, the transmittance was about 20%.

  When the laser beam L is condensed at the condensing point A, the crystalline state of silicon partially changes, and as a result, the internal crack 12 runs. In the experimental results, the crack length (b) (FIG. 7B) was about 2 μm to 100 μm. Here, the size of the internal processing region inside the substrate by the laser beam, for example, the crack length (b) can be changed by changing the oscillation pulse width of the laser beam. In the semiconductor laser pumped YAG laser, the crack length (b) can be changed by changing the injection current and the oscillation frequency into the semiconductor laser. From the experimental results, when the pulse energy of the laser is changed in the range of 2 μJ to 100 μJ and the pulse width is changed in the range of 15 nsec to 1000 nsec, it is possible to form a crack whose length is changed in the range of 2 μm to 100 μm. .

  Here, the length of the crack is considered to be determined by the balance between the compressive stress accompanying the temperature rise near the condensing point of the laser beam and the tensile stress accompanying the volume expansion due to the amorphization of the part. Therefore, in order to increase the crack length, it is desirable to reduce the compressive stress and increase the volume expansion. This can also be realized by increasing the pulse width with constant energy. However, even if laser light having a long pulse width is simply irradiated, if the pulse width increases, the peak value of the peak pulse also decreases accordingly. In this case, an electrolytic strength exceeding a certain threshold necessary for the phase transition to amorphous cannot be obtained. For this reason, no phase transition to amorphous occurs at the condensing point of the laser beam, so that a crack cannot be formed. For example, the threshold value in the range of the pulse width of 17 nsec to 1100 nsec is 2 μJ to 5 μJ. On the other hand, if the peak value of the peak pulse necessary for the formation of the crack is secured, the pulse width becomes shorter, and a crack having a desired length cannot be obtained.

  Therefore, if the peak pulse peak value necessary for crack formation can be obtained and the length of the width of a single pulse can be selected, a crack having a length corresponding to the pulse length is formed. It becomes possible. As described above, the pseudo pulse method of the present embodiment continuously irradiates the pulse having the peak value of the peak pulse necessary for the formation of the crack so that a part thereof overlaps. As a result, a short pulse can be superimposed to obtain a single pulse having a pulse width substantially longer than the short pulse width, and the desired pulse length can be adjusted by adjusting the number of short pulses. It forms a crack of length.

  FIG. 8A shows an optical system that can generate different pulse widths and change the condensing position by using one laser beam incident on the condensing optical system 52 (FIG. 7A). System 56 is shown. In this optical system 56, it is also possible to form a pseudo synthetic pulse by dividing the amplitude of the laser beam of the same pulse and forming a plurality of pulses.

  An emitted light beam is incident on the beam splitting system 52e from the beam expander 51a. In the beam splitting system 52e, the laser beam L is amplitude-divided by the beam splitter BS and branched into two light beams. At this time, the beam splitter BS may be a polarization beam splitter. The transmitted light beam is collected by the objective lens 52a of the condensing optical system 52 as it is.

  The light beam reflected by the beam splitter BS reaches the beam splitter BS by the loop optical system 56 that is returned to the beam splitter BS again via the mirrors M1 to M4. In the optical path of the loop optical system 56, lenses LE1 and LE2 are arranged. The lenses LE1 and LE2 constitute an afocal optical system 57. When a parallel light beam is incident on the lens LE1, the parallel light beam is emitted from the lens LE2. The relationship between the objective lens 52a and the lenses LE1 and LE2 corresponds to the object plane position of the optical system in which the condensing point of the lens LE1 is formed by the lens LE2 and the objective lens 52a. Therefore, the light beam emitted from the lens LE2 is arranged so that the aperture efficiency becomes 100% regardless of the spatial position of the condensing point of the lens LE1. If the beam splitter BS is a polarization beam splitter, it is necessary to put a wave plate in the optical path of the loop optical system 56 to make it circularly polarized.

  The light beam returned to the beam splitter BS is amplitude-divided in the same manner as before, and this time the reflected light follows the optical path toward the objective lens 52a, while the transmitted light again follows the optical path in the loop optical system 56, Again, come back to the beam splitter BS. Then, the number of times of circulation through the loop optical system 56 is determined from the loss during passing through the optical system.

As a result, the condensing position formed by the objective lens 52a is spatially coincident, for example, P1, but is temporally delayed according to the number of passes through the loop optical system 56, and the condensing position P1. To reach. This time-delayed pulse is schematically shown in FIG. Originally, a pulse train composed of a plurality of pulses that are shifted in time from one pulse laser beam L and reach the converging position P1 can be regarded as one synthetic pulse that has a pulse width corresponding to the delay time. Since the speed of light is 3 × 10 ⁸ m / sec, a delay of about 3 nsec occurs when the optical path of 1 m becomes longer. By forming an optical path having an appropriate length, a pseudo pulse having a desired pulse width can be obtained.

  Further, when the lens LE1 of the afocal optical system 57 is finely moved in the X direction that is the optical axis direction or the Y direction that is a direction crossing the optical axis, the state of the afocal optical system 57 in the optical path changes. The condensing position of each light beam by the objective lens 52a due to this change is P2 and P3 which are spatially shifted from P1. The magnitude of the spatial deviation increases according to the number of passes through the afocal optical system 57. Cracks C <b> 1 to C <b> 3 shown in FIG. 8C indicate those according to the number of times the laser beam has passed through the afocal optical system 57. A crack when C1 does not pass through the afocal system 57 and a crack formed by condensing the laser light beam that has passed through the afocal optical system 57 in order of C2 and C3 are shown.

  The upper two views of FIG. 8C show the cracks C1 to C3 when the lens LE1 is moved in the X direction, and the cracks C1 to C3 are also shown when the lens LE1 is moved in the Y direction. It is the lower two figures of 8 (c).

  FIG. 8D shows a state of the cracks C1 to C3 when the lens LE1 is moved in combination with the X direction and the Y direction at the same time. For example, X1, X2, Y1, and Y2 are written in order from the top to the bottom of FIG. Then, the combined displacement of the displacement of X1 and the displacement of Y2, the combined displacement of the displacement of X2 and the displacement of Y2, the combined displacement of the displacement of X2 and the displacement of Y1, and the displacement of X1 in order from the top to the bottom of FIG. The state of the combined displacement of the displacement of Y1 is shown.

  These condensing point sequences are used to confirm the length of cracks to be formed by experiment, and to create a spatial and temporal shift so as to form a crack of the optimum size and position for cleaving the substrate. It can be obtained by designing the optical system 56. Also, changing the state of cracks in one silicon substrate according to the cutting location, such as the edge of the substrate, will not deviate from the planned cutting line on the substrate surface, or will not generate dust, etc. It can be performed.

  In order to enlarge the pulse width, a laser beam having a pseudo long pulse width generated by using a plurality of laser light sources may be used. A plurality of lasers may be generated by dividing one laser with an optical element. Moreover, you may use the optical system which can shift a condensing point temporally and spatially.

  Next, the irradiation position on the substrate surface of the laser beam forming the internal processing region is relatively moved along the substrate surface, and the internal processing region is formed in a direction along the substrate surface. Specifically, an internal crack 12 is formed from one point inside the silicon substrate 10, and the internal processing immediately below the planned cutting line C is performed by relatively moving the condensing point A along the planned cutting line C. As shown in FIG. 1A, the planned cutting line C of the silicon substrate 10 includes two planned cutting lines C1 and C2 that are orthogonal to each other with respect to the orientation flat 10b.

  The workpiece W, which is the silicon substrate 10, is placed on an automatic stage 53 that can move in the XY directions, and can move in the optical axis direction (depth direction) toward the automatic stage side on which the workpiece W is placed or the condensing optical system side. A Z stage (automatic focus mechanism) 52c is provided, and the interval between the condensing optical system 52 and the workpiece W is variable.

  The moving speed in the XY directions is determined in consideration of the laser oscillation frequency, crack shape, and the like, and the moving speed is generally 10 mm / sec to 100 mm / sec at a normal frequency of 10 KHz to 100 KHz. When the moving speed is 100 mm / sec or more, the internal processing is stepped in the moving direction, and the subsequent cleaving is affected, for example, the interval between adjacent cracks on the same cleaving line is significantly widened.

  Further, the condensing optical system 52 has an observation camera 52f so as to be conjugate with the workpiece irradiation point. On the other hand, the reflectance of the silicon substrate 10 is about 30%. Will be damaged. Therefore, a filter corresponding to the output of the laser is arranged. The illumination for observation uses a relay lens so that a light source can be formed at the position of the entrance pupil of the microscope objective lens 52a used for condensing so that Koehler illumination can be formed. In addition, illumination is also performed through a filter to eliminate damage to the illumination optical element as much as possible.

  In addition to the above observation optical system, an AF optical system (not shown) is introduced to measure the distance from the workpiece W. The AF optical system obtains the contrast of the image obtained by the observation camera 52f, and measures the focus and tilt from the obtained value. Actually, in order to measure this contrast, the distance to the workpiece W is measured while being finely fed to determine the best position. Note that it is determined whether or not the AF operation is performed in view of the parallelism of the workpiece W that is the silicon substrate 10. The information related to the AF operation is data used when the above-described laser oscillation conditions are changed.

  In addition, since the crack length formed at one condensing point is 2 μm to 100 μm and the thickness of the target silicon substrate is 625 μm, in order to cleave the silicon substrate, a plurality of internal processes are performed. It will be necessary. Also, the order of internal processing at one point starts from the far side (back side) from the substrate surface and approaches the surface. At this time, as shown in FIG. 9, it is preferable to set the laser oscillation condition using the processing position information, and to process the vicinity of the surface by shortening the crack length to be formed and increasing its density. Thereby, since cracks near the surface easily communicate with each other when cleaving the substrate, it becomes possible to perform more precise cleaving. Furthermore, the internal crack length excluding the vicinity of the substrate (the size of the internal processing region) is more efficient by forming a single crack that is long (large) in the thickness direction (depth direction). It is also possible to perform good cleaving.

  At the time of internal processing for forming internal cracks, processing is not performed in which internal cracks formed in the vicinity of the substrate surface reach the substrate surface having surface processing marks. In addition, it is assumed that a processing condition in which an existing internal crack near the condensing point grows due to the influence of heat or the like by laser irradiation and reaches the substrate surface is not selected. Therefore, in the crack formation near the surface, the pulse width is increased, and at the same time, the pulse energy is set to a value close to the crack formation threshold. As the optical system, processing near the surface preferably has a large NA, and the NA is increased to 0.55 or more up to 50 μm from the surface.

  However, this is not the case inside the substrate, and as shown in FIG. 2 (FIG. 9), the internal cracks 12a to 12c are divided in the depth direction (the thickness direction of the substrate or the direction crossing the surface of the substrate). Or may be linked.

  The internal crack 12c closest to the substrate surface 11 is provided at a depth of 10 μm to 100 μm from the substrate surface 11 of the silicon substrate and at a position not communicating with the surface processing mark 11a.

  Next, the processing order of each crack group will be described.

  As shown in FIGS. 10 (a), (b), and (c), the first method is a group of cracks having a height higher than the surface, for example, substantially the same for a plurality or all of the planned cutting lines C. After the formation of the crack group of the deep internal crack 12a is finished, the crack group of the internal crack 12b having a different depth is processed. Since the formation of the crack group for each depth is performed stepwise inside the silicon substrate 10, the influence of the adjacent planned cutting line C can be reduced.

  In the second method, as shown in FIG. 10 (d), the crack groups of the internal cracks 12a, 12b, and 12c having different depths are formed immediately below one planned fracture line C, and then another fracture planned line is formed. A similar crack group of C is processed. This method can reduce the number of AF operations at the processing start point when correction of the focal position with respect to the flatness of the silicon substrate 10 is necessary.

  Further, in the first method, as shown in FIG. 10 (a), the condensing point is moved in one direction along the planned cutting line, and the condensing point is shown in FIG. 10 (c). There is a case of reciprocating movement along the planned cutting line. The latter can shorten the processing time because the total length of the movement distance is shortened.

  In the present embodiment, the latter is selected, but the determination is made comprehensively based on the state of the object (parallelism or swell of the silicon substrate).

[Cleaving process]
In the silicon substrate 10 on which the surface processing mark 11a and the plurality of internal cracks 12a, 12b, 12c are formed for each planned cutting line C, at least the surface processing mark 11a and the internal crack 12c directly under the surface are not connected. Therefore, the individual logic element portions 10a of the silicon substrate 10 after laser processing are not cleaved. The procedure for cleaving the silicon substrate 10 in this state into element chips is performed as follows.

  As shown in FIG. 11A, the back surface of the silicon substrate 10 remains on the dicing tape T while the silicon substrate 10 after the surface processing marks 11a and the internal cracks 12 (12a, 12b, 12c) are formed is mounted on the dicing tape T. It is placed on the rubber sheet 60 of the cleaving device so that it is on the top. The rubber sheet 60 is made of an elastic material such as silicone rubber or fluorine rubber. In addition, in order to avoid that the substrate surface 11 of the silicon substrate 10 is in contact with the rubber sheet 60 and the dirt is attached to the surface side, a commercially available product used for back grinding or the like on the surface side of the silicon substrate 10 after the formation of internal cracks. A protective tape R may be attached.

  The cleaving is performed by pressing the silicon substrate 10 through the dicing tape T with a stainless roller 61. First, the silicon substrate 10 is placed on the rubber sheet 60 so that one of the planned cutting lines C of the silicon substrate 10, preferably the first cutting direction, is substantially parallel to the roller axis. When the silicon substrate 10 is pressed while rolling the roller 61, the rubber sheet 60 immediately below the roller 61 is deformed so as to sink. In the silicon substrate 10, stress in the extending direction acts on the rubber sheet 60 side, that is, the surface side. This stress acts to widen the surface processing mark 11a on the weakest portion of the substrate surface 11, that is, the planned cutting line C1.

  As a result, as shown in FIG. 11B, a crack is generated starting from the surface processing mark 11a. This crack advances to the back surface of the substrate by connecting the internal cracks 12a, 12b, and 12c caused by laser irradiation inside the substrate, reaches the back surface of the substrate, and the silicon substrate 10 is cut along the planned cutting line C1. Although the progress of the crack occurs along the crystal orientation of the silicon substrate 10, since the cleaving is performed by the connection with the surface processing mark 11a, it does not deviate significantly from the planned cutting line C1 on the substrate surface 11. As the roller 61 advances, the silicon substrate 10 is sequentially cut along the cutting line C1 in the first cutting direction. The roller 61 is advanced from the end of the silicon substrate 10 toward the other end, or the vicinity of the center of the silicon substrate 10 is used as the starting point for pressing the roller 61 toward the end of the silicon substrate 10. Any may be sufficient.

  Next, the silicon substrate 10 is rotated by 90 ° so that the planned cutting line C2 in the second cutting direction and the axis of the roller 61 are substantially parallel. Similarly to the first cleaving direction, the silicon substrate 10 is pressed by the roller 61 to generate a crack starting from the surface processing mark 11a in the second cleaving direction and reach the back surface.

  Through the above steps, the silicon substrate 10 is separated into individual element chips.

  The cleaving process shown in FIGS. 11 (a) and 11 (b) is to apply the stress accompanying the deformation of the rubber sheet by the hard roller to the surface of the silicon substrate, but the logic element and the nozzle layer are not destroyed. should not. Therefore, it is necessary to select the pressing load of the silicon substrate by the roller, the thickness of the rubber sheet, and the rubber hardness. In addition, it is also necessary to select an appropriate dicing tape and surface protective tape material and thickness.

  Either of the following two methods may be used as a method of cleaving a silicon substrate having surface processing marks and internal cracks by an external force acting along the planned cutting line.

  In the first method, as shown in FIG. 12, bending stress is applied to the planned cutting line C between the logic element parts 10 a of the silicon substrate 10, and the elements are separated along the planned cutting line C. The logic element portion 10a to be cut is pushed upward by about 1 to 10 μm with the collet 62a sandwiching the front side and the pin 63 sandwiching the back side. At this time, a part of the adjacent logic element portion 10a is suppressed by the other collet 62b so that the adjacent logic element portion 10a is not pushed upward. As a result, a stress that spreads the surface processing mark 11a on the planned cutting line C acts, a crack is generated starting from the surface processing mark 11a, and is connected to the internal crack 12 to reach the back surface of the silicon substrate 10. .

  The second method is a method in which a mechanical impact is directly applied to the surface side of the silicon substrate 10 along the planned cutting line C as shown in FIG. The silicon substrate 10 after the formation of the surface processing mark 11a and the internal crack 12 is transferred to a single point bonder, and the substrate surface 11, preferably the vicinity of the surface processing mark 11a, is continuously hit with a fine and hard tool 64. A crack is formed starting from the surface processing mark 11a.

  Further, it is conceivable to cleave by applying a new thermal shock to the substrate after laser processing.

[Repair process]
In the cleaving step, the surface processing mark 11a and the crack caused by the internal crack 12 are connected by a new crack, and the crack also reaches the back surface side, so that the silicon substrate 10 is separated into each element chip.

  However, if there is no accidental complete separation, re-cleaving is necessary. As a re-cleaving method, for example, only the logic element part 10a that has not been cleaved is individually cleaved by using the mechanism shown in FIGS. 14A and 14B to completely cleave it.

[Pickup process]
The logic element portion, which is the element chip 10a separated in the cleaving process and the repair process, is carried out by the suction collet 65 and the pickup pin 66 as shown in FIGS. 14 (a) and 14 (b), and individually stored. At this time, picking up with the expander or the like widening the gap between the elements can make the picking work easier. In addition, it is effective for improving the reliability of the element chip 10a to suck and remove minute dust generated at the time of pickup.

  In the above-described embodiment, in order to form spatially different crack lengths, a plurality of lasers having different pulse widths having wavelengths that are transmitted to the silicon substrate can be used. Alternatively, a laser system in which at least one of the pulse trains having a wavelength that is transparent to the silicon substrate is combined with a continuous wave laser having a wavelength that transmits the silicon substrate in the same manner can be used. In addition, since a plurality of light fluxes are generated using one laser, amplitude, wavefront, polarization, and the like can be used as the dividing means.

  According to the present embodiment as described above, when the laser beam is condensed inside the member to be cut to form an internal processing region (for example, a crack), the depth direction from the surface of the member to be cut depends on the position. Thus, the size of the internal machining area can be changed. Therefore, it is possible to avoid the formation of an internal processing region that reaches the surface, and there is no possibility that the surface of the non-cleaving member is contaminated as in the case of blade dicing or laser processing for cutting from the conventional substrate surface.

  In addition, a small internal machining area can be formed in the vicinity of the surface, and by forming a large number of such small internal machining areas, the connection of cracks at the time of cleaving is ensured, and the formation of crack propagation deviating from the planned fracture line is formed. Can be avoided.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 illustrates a silicon substrate according to an embodiment, in which (a) is a perspective view thereof, (b) is a partially enlarged perspective view showing an enlarged portion of (a), and (c) is a sectional view of (b). It is a fragmentary sectional view shown. It is a schematic diagram explaining an Example. It is a flowchart which shows the cleaving process by an Example. It is a figure explaining a tape mounting process. It is a figure explaining a wafer correction process. It is a figure explaining the surface recessed part process which forms a surface process trace. An internal crack formation process is demonstrated, (a) is a schematic diagram which shows the processing apparatus which irradiates a laser beam, (b) is a figure which shows the mechanism in which an internal crack generate | occur | produces. It is a figure explaining the condensing of a divided light beam by carrying out amplitude division of the same pulse. It is a figure explaining the crack in a substrate depth direction (thickness direction). It is a figure explaining the laser scanning method when forming the crack group of each depth. It is a figure explaining the cleaving process by a roller. It is a figure explaining the cleaving process by a collet. It is a figure explaining the case where it cleaves by giving the hit | damage with a tool. It is a figure explaining a repair process. It is a figure explaining the board | substrate cleaving method by one prior art example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Silicon wafer 2 Oxide film 2a Groove 3 Nozzle layer 4 Liquid supply port 10 Silicon substrate 10a Logic element part 11 Substrate surface 11a Surface processing trace 12, 12a, 12b, 12c Internal crack

Claims (7)

A laser beam is condensed from a surface of the member to be cut to a condensing point at a predetermined depth inside the member to be cut to form an internal processing region, and the member to be cut is separated so that the member to be cut is separated into a plurality of regions. A laser cleaving method for cleaving a member,
Dividing the laser light emitted from the light source with a beam splitter, irradiating the split member with one of the divided laser lights,
The other divided laser beam is guided to a loop optical system including an afocal optical system that is provided in a part of the optical path and has an optical element whose relative position is variable, and further guided to the beam splitter. A part of the guided laser beam is irradiated onto the member to be cut, and a part of the laser beam is re-guided to the loop optical system, thereby forming the internal processing region of a desired size on the member to be cut. A laser cleaving method characterized by the above.   The depth in the depth direction from the surface of the member to be cut in the internal processing region is larger in the internal processing region located farther than the internal processing region located near the surface of the member to be cut. The laser cleaving method according to claim 1.   3. The concave portion for concentrating stress when cleaving the cleaved member is formed on the surface of the cleaved member before forming the internal processing region inside the cleaved member. The method of cleaving laser.   3. A recess for concentrating stress when cleaving a substrate is formed on the surface of the cleaved member after forming an internal processing region inside the cleaved member. Laser cleaving method.   5. The laser cleaving method according to claim 3, wherein a crack reaching the internal processing region and the concave portion on the surface of the cleaved member is formed by applying an external force to the cleaved member.   The irradiation position of the laser beam to the member to be cut forming the internal processing region is relatively moved along the surface of the member to be cut, and the internal processing region is formed in a direction along the surface of the member to be cut. The laser cleaving method according to any one of claims 1 to 5. A laser cleaving device for separating the member to be cut into a plurality of regions by laser light by condensing laser light from a surface of the member to be cut to a condensing point having a predetermined depth to form an internal processing region. Because
A stage on which the cleaved member is placed;
A light source that emits laser light;
A loop optical system having a beam splitter;
An afocal optical system having an optical element provided in the optical path of the loop optical system, the relative position of which is variable;
Have
The laser light emitted from the light source is divided by the beam splitter, one of the divided laser lights is applied to the member to be cut, and the other divided laser light is guided to the loop optical system and further A laser cleaving apparatus characterized in that a part of the other divided laser beam incident on the beam splitter is irradiated onto the member to be cleaved and a part is re-guided to the loop optical system.

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