JP4086796B2 - Substrate cutting method - Google Patents

Description

  The present invention relates to a substrate cleaving method for separating a semiconductor substrate or the like in which a plurality of semiconductor element portions are arranged on a silicon wafer into individual element chips by laser processing.

  When a semiconductor substrate such as a silicon wafer is precisely cut into chips, conventionally, a circumferential blade having a width of several tens to several hundreds of μm is rotated at a high speed, and the blade surface abrasive is cut by grinding the semiconductor substrate. A blade dicing method is known. At this time, in order to reduce heat generation and wear due to cutting, cooling water is sprayed on the cut surface, but the semiconductor substrate and abrasive particles generated by cutting, an adhesive tape that fixes the semiconductor substrate and the processing table The pressure-sensitive adhesive particles and the like are mixed in the cooling water and scattered widely. In particular, in a semiconductor substrate on which ejection means such as inkjet nozzles are formed, if the fine particles are mixed as dust inside the nozzles or the like, there is a possibility that the ejection of liquid such as ink may be seriously affected.

  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 surface of the semiconductor substrate and the substrate is cut. However, in this method, since the periphery of the cut portion is also melted on the substrate surface, there is a problem of damaging a logic circuit or the like provided on the semiconductor substrate, and laser processing is performed from the laser incident side to the emission side. Since the substrate is melted and proceeds, the re-solidified product of the melt adheres to the substrate surface and becomes dust. Therefore, a dust problem occurs as in the case of blade dicing.

  Further, as a processing method for cutting a substrate by condensing a highly absorbing laser beam inside the substrate, for example, the methods disclosed in Patent Document 1 and Patent Document 2 are transmitted through a substrate that is a material to be processed. A denatured layer formed by condensing a highly specific laser beam with a specific wavelength inside the substrate is used as the starting point for cutting, and because it does not form a molten region on the substrate surface, it enables cutting with less dust It is.

  However, in the above method, since the starting point of cutting is limited to the deteriorated layer inside the substrate, it is difficult to precisely control the direction and position of the crack reaching the substrate surface from the starting point of cutting.

  In particular, in the case of a silicon substrate, since the growth of cracks is affected by the crystal orientation, if there is a small deviation between the planned cutting line and the crystal orientation due to industrial errors in the formation of the silicon substrate and elements, the above laser In the processing method, there is a high possibility of deviating from the planned cutting line in the process of the crack progressing to the surface of the substrate and destroying the logic circuit or the like of the element portion.

  More specifically, as shown in FIG. 24A, a laser beam L having a specific wavelength is condensed at a predetermined depth inside a silicon substrate 101 made of single crystal silicon having a crystal orientation (100) on the surface. The altered layer 102 is formed, and as shown in FIG. 5B, an external force F is applied to the planned cutting line C to generate a crack 103 from the altered layer 102 toward the substrate surface, thereby dividing the silicon substrate 101. In this case, since a high-order crystal orientation plane is formed at the tip 102a of the altered layer 102 by the laser processing, the actual crack 103a due to the external force F is inclined in the cleavage direction (110) of the single crystal silicon. End up. 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.

  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.

  The above problem becomes more conspicuous when cleaving a portion where two-way cleaving lines intersect.

  In addition, in the crossing portion, since internal processing is performed in a superimposed manner along two planned cutting lines orthogonal to each other at the same depth of the silicon substrate, a new problem arises.

As a countermeasure against this, Patent Document 3 discloses that the two-direction modified layers have a twisted positional relationship at the intersection.
JP 2002-192370 A (Patent No. 3408805) JP 2002-25180 A JP 2002-192371 A JP 2000-15467 A

  However, the method disclosed in Patent Document 3 forms a modified layer that is relatively far from the surface for one of the split lines. As described above, particularly in the case of a silicon substrate or the like that is affected by the crystal orientation, as the distance between the modified layer and the substrate surface increases, the risk of damage to the substrate surface increases, and proper cleaving is difficult. If this far modified layer is provided close to the substrate surface, the modified layer closer to the surface must be closer to the substrate surface, and the modified layer reaches the substrate surface during internal processing with laser light. There is a problem of contaminating the substrate surface.

  In addition, if a shielding object that blocks the optical path of the laser beam, such as a dummy inspection pattern used in manufacturing the substrate, is arranged on the planned cutting line on the substrate surface, the laser beam may be incident on the substrate surface from a substantially vertical direction. In the method disclosed in Patent Document 1 or the like, the modified layer directly under the shielding is incomplete or not formed at all, and an undesired crack is generated at the portion when cleaving by an external force. .

  In addition, when a linear surface processing trace is formed on the substrate surface to concentrate stress so that an accurate crack is generated along the planned cutting line when cleaved by external force, light is scattered at that part. End up. Further, at a portion where the surface processing traces intersect at the intersection of the two splitting lines, the light flux is blocked by the two surface processing marks at the same time. Thus, if the energy which reaches | attains an internal condensing point reduces significantly by the influence of the obstruction | occlusion on a planned cutting line and a deformed part, it will become difficult to generate an internal crack stably.

  The present invention has been made in view of the above-mentioned unsolved problems of the prior art, and includes a shielding object that scatters light on a substrate surface, a linear processed part for concentrating stress on a planned cutting line, and the like. In addition, it is possible to allow sufficient laser energy to reach the condensing point inside the substrate even at a position where it intersects with a group of cracks previously formed by internal processing, and to stably perform internal processing with laser light. An object of the present invention is to provide a substrate cleaving method that can be used.

In order to achieve the above object, a substrate cleaving method of the present invention is a substrate cleaving method for separating a substrate into a plurality of element chips, and a plurality of linear shapes are formed on the substrate surface along the planned cutting line of the substrate. the processing unit, the steps of the linear processing unit is formed to have an intersection which intersect each other, the laser light emitted from the light source, the light flux splitting system, the four laser beams of laser energy respectively are equal Divide and split into two on both sides of the linear processed portion so that one laser beam is distributed to each of the four quadrants formed on the substrate surface by the two linear processed portions at the intersection. The laser beam is incident on different positions on the surface of the substrate and each laser beam is individually focused on a focusing point inside the substrate to generate an internal crack, and the focusing point is relatively moved along the linear processed portion. To let A step of relatively moving the laser beam, and a step of connecting the internal crack of the substrate and the linear processed portion of the substrate surface by applying an external force to the substrate, and the condensing point When the laser beam approaches the intersection, the laser light incident on the light beam splitting system is shifted by a beam shift system, so that the beam diameters of the two laser beams behind the traveling direction are increased, and the two lasers ahead of the traveling direction are When the beam diameter of the beam is reduced and the condensing point moves away from the intersection, the laser light incident on the light beam splitting system is shifted by a beam shift system, so that The present invention is characterized in that the beam diameter is increased and the beam diameters of the two laser beams behind the traveling direction are decreased.

  At least four laser beams are individually focused inside the substrate to efficiently form a crack group of internal cracks, and the substrate is cleaved by extending the crack group in the depth direction, which is the thickness direction of the substrate, by an external force. Therefore, there is no possibility of contaminating the substrate surface like blade dicing or conventional laser processing for cutting from the substrate surface.

  In addition, by forming a linear processed portion along the planned cutting line on the surface of the substrate, it is possible to induce cracks due to external forces to the linear processed portion, and to control the progress direction of the internal cracks very precisely. Therefore, in the cleaving process by external force, it prevents the cracks from deviating from the planned cutting line and damages the element part of the board, or the board itself is destroyed due to the influence of the opening formed in the board, etc. Highly cleaving can be performed.

  Since the internal cracks are formed by a group of at least four laser beams incident on different positions on the substrate surface, each laser beam is incident so as to avoid a linearly processed portion or a shield on the substrate surface. By selecting the position, energy loss can be avoided.

  In addition, energy loss can be reduced by adjusting the energy distribution of each laser beam when intersecting with a crack group previously formed by internal processing or at a position where two linear processed portions intersect.

  As shown in FIG. 1, a cleaving method for cleaving a silicon substrate 10 on which a logic element portion 10a, which is a plurality of semiconductor element portions, is formed along a cleaving line C on a substrate surface 11 and separating it into individual element chips. 2, when performing internal processing for generating internal cracks 12 (12 a, 12 b, 12 c) that are cracks that do not reach the substrate surface 11 in the silicon substrate 10, the same light concentration at a predetermined depth is obtained. As shown in FIGS. 7 to 13, at least four, preferably a beam Le, which is an integer multiple of 4, is individually condensed to form an internal crack 12, and the condensing point is formed. Is scanned (relatively moved) along the planned cutting line C to form a band-shaped crack group along the planned cutting line C.

  After or before the formation of such a crack group, surface processing for forming a surface processing mark 11a, which is a linear processing portion, is performed on the substrate surface 11 along the planned cutting line C.

  In the internal processing for forming the internal crack 12, each beam Le selects the incident position with respect to the substrate surface 11 on both sides of the planned cutting line C, so that the laser beam is emitted by the surface processing mark 11 a and the internal crack 12 formed earlier. It is possible to prevent vignetting and avoid a reduction in processing efficiency.

  If an external force for cleaving is applied after the surface processing of the surface processing mark 11a and the formation of the crack group by the beam group, first, the surface processing mark 11a and the internal crack 12 are connected to each other. The breaking line does not deviate from the breaking planned line C.

  As shown in FIG. 1C, the silicon substrate 10 shown in FIGS. 1A and 1B has a silicon wafer 1 formed in the (100) orientation and having a thickness of 625 μm as a base. An oxide film 2 having a thickness of about 1 μm is formed on the surface of the substrate, and a structure for discharging liquid such as ink, a logic element for driving them, and a structure made of epoxy resin containing wiring and the like are formed thereon. A certain nozzle layer 3 is arranged to constitute each logic element portion 10a.

  In this manner, 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 liquid discharge mechanism 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 element chips at the final stage 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 the logic element portions 10a to be individual element chips. This process includes a tape mounting process in Step 1, a wafer correction process in Step 2, and a process in Step 3. The process consists of a surface linear processing process (surface processing process), an internal crack forming process in step 4, a cleaving process in step 5, a repair process in step 6, and a pick-up process in step 7. 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 processing cannot be performed 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, thereby flattening the silicon substrate 10 and correcting the deformation.

"Surface linear processing process"
Subsequently, in order to cleave each logic element portion 10a of the silicon substrate 10 with high accuracy, a surface processing mark 11a that induces propagation of a crack to 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, stress concentration occurs at the time of cutting by an external force, and a crack is induced to the surface processing mark 11a. 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 cemented carbide or diamond along the planned 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 make the internal crack 12 large enough not to obstruct the optical path of each beam Le for laser processing. As the processing depth, a depth that causes stress concentration between the surface processing mark 11a and the crack at the time of cleaving is suitable, and this is the depth of the oxide film 2 that is the surface layer of the silicon substrate 10 as shown in FIG. The thickness may be smaller than the thickness, and even if the depth is equal to or greater than the thickness of the oxide film 2 as shown in FIG.

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

  The surface processing mark 11a may be formed after an internal crack forming step using a beam group including four beams Le.

"Internal crack formation process"
Each internal crack 12 shown in FIG. 2 is formed using the processing apparatus 50 shown in FIG. This processing apparatus 50 includes an automatic stage having a light source 51, a light source optical system 51a, a condensing optical system 52 having a microscope objective lens 52a, a mirror 52b, and the like, an X stage 53a, a Y stage 53b, a fine adjustment stage 53c, and the like. 53, an AF optical system 54, and an alignment optical system (not shown) that performs alignment by the orientation flat 10b (see FIG. 1) of the silicon substrate 10 that is the workpiece W. The light source 51 has a fundamental wave of a pulsed YAG laser. (1064 nm) is used. The pulse width is around 40 ns and a frequency of 10 to 100 KHz.

  The selection of the laser light is determined by the spectral transmittance of the silicon substrate. Therefore, any light in a wavelength range in which a strong electric field can be formed at the condensing point and silicon transmission is possible may be used. For example, it is a 1.3 to 1.5 μm laser beam generated by combining an ultrashort pulse and a wavelength converting means.

  The laser light L emitted from the light source 51 is divided into four beams Le, which are four laser beams, in the light source optical system 51a as shown in FIG. The beams Le are separately incident on each of the two beams, and each beam Le is individually focused at a condensing point A at a predetermined depth (a) to generate an internal crack 12 having a crack length (b).

  As shown in FIG. 8, the light source optical system 51 a includes a beam expansion system 55, a beam shift system 56, a light beam splitting system 57, and a beam shaping system 58, and the beam shift system 56 emits from the light source 51. The laser beam L has a function of translating in the cleaving direction, and this is realized by tilting the parallel flat glass as described later.

  The beam splitting system 57 uses a pair of quadrangular pyramids 57a and 57b to divide the parallel incident laser light L into four beams Le by the first quadrangular pyramid 57a on the incident side, and each of them is a second quadrangular pyramid. The light is emitted parallel to the optical axis by 57b. It is assumed that the ridge line directions of the first and second square pyramids 57a and 57b are the same.

  The number (number) of beams Le to be split by the light beam splitting system 57 is preferably an integer multiple of 4 because the substrate surface 11 is divided into four quadrants at the portion where the surface processing marks 11a intersect. Each divided beam Le enters the second quadrangular pyramid 57b and is emitted as a divided light beam parallel to the optical axis. Regarding the size and interval of each emitted beam Le, the beam diameter of each beam Le is determined by the magnification of the beam expanding system 55, and the beam interval is determined by the separation distance between the pair of square pyramids 57a and 57b. It will be. The size and interval of each beam Le are variably adjusted within a predetermined range so that energy loss due to interference with the surface processing mark 11a of the substrate surface 11 or the previously formed internal crack 12 is minimized.

  At this time, the requirements to be noted are as follows.

(1) The variable range of the size and interval of each beam Le should be within the conditions for generating internal cracks.
(2) The variable range of the size and interval of each beam Le is a range that does not damage the substrate surface 11.

As shown in FIG. 9A, when the parallel flat glass of the beam shift system 56 is perpendicular to the optical axis, the four beams Le have the same size, and are shown by broken lines as shown in FIG. 9B. Although the laser energy is uniform across the ridgelines of the quadrangular pyramids 57a and 57b, when the laser beam L is translated by tilting the beam shift system 56, the state of incidence on the beam splitting system 57 changes. For example, the laser beam L is moved as shown by an arrow in FIG. 9 (c), the beam diameter of the beam Le shown below side as shown in (d) becomes large, the beam diameter of the upper side is reduced. In this way, the beam diameter of each beam Le entering the condensing optical system 52 can be freely controlled.

As shown in FIG. 10, the beam shift system 56 operates when the internal machining position by the beam group reaches the vicinity of the intersection C ₁₂ between the cutting lines C ₁ and C ₂ , and the beam diameter is controlled as follows. To be done. As shown in (a) of FIG. 10, but are not affected by surface processing traces 11a for four beams Le scanned along the expected splitting line C ₁ is to be moved on both sides of the surface processing traces 11a In the vicinity of the intersection C ₁₂ , the two front beams Le are interrupted by the surface processing marks 11 a along the planned cutting line C ₂ , and as such, as shown in FIG. Internal cracks are formed by only one beam Le, and the processing energy is insufficient. Therefore, as the working point approaches the intersection C _12, as shown in FIG. 10 (b), by tilting a parallel plate glass beam shift system 56 so that the beam diameter of the two beams Le of the front side is reduced The laser beam L is shifted upward. Machining point as shown in (c) of FIG. 10 is the shift amount to return the parallel flat glass if immediately below the intersection C ₁₂ back to 0, away from the processing point is an intersection C ₁₂ as shown in (d) In the process, the beam shift system 56 is tilted in the opposite direction to reduce the beam diameter of the two rear beams Le.

Beam if the shift system 56 is not operated, as shown in (b) and (d) of FIG. 11, before and after passing through the intersection C _12, 2 two beams Le is occurred eclipsed phenomenon by surface processing traces 11a Sufficient internal crack formation cannot be performed, resulting in unprocessed areas.

  Note that the microscope objective lens 52a of the condensing optical system 52 in FIG. 7 is, for example, one having a magnification of 20NA0.42 or a magnification of 50NA0.55. 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.

  FIG. 12 uses a pair of fly-eye lenses 57 c and 57 d as the light beam splitting system 57. The beam shaping system 58 collects four beams Le parallel to the optical axis emitted from the pair of fly-eye lenses 57c and 57d shown in FIG. 12B as shown in FIG. Shaping to match the pupil diameter of the optical optical system 52. The laser light L enters a first fly-eye lens 57c composed of four lenses, is divided into four beams Le, and passes through a second fly-eye lens 57d composed of four lenses corresponding to each, Each beam Le is emitted so as to be parallel to the optical axis. This is because when the focal length of each lens constituting the first fly-eye lens 57c is f1 and the focal length of each lens constituting the second fly-eye lens 57d is f2, the first and second fly-eye lenses 57c, 57d. This can be realized by setting the main plane interval of f1 + f2. The size of each beam Le can be controlled by f2 / f1 of the light beam splitting system 57 or the like. The size of the circumscribed circle of the four beams Le is controlled by the beam shaping system 58 on the rear side of the light beam splitting system 57.

  FIG. 13 shows another light beam splitting system 57 in which a fly-eye lens 57e and a single lens 57f are combined as shown in FIG. 13B, and split condensing instead of the condensing optical system 52 of FIG. An optical system 59 is used. That is, in the split condensing optical system 59 composed of four lenses 59e, the respective beams Le are condensed inside the substrate by the respective lenses 59e, while avoiding the surface processing marks 11a and the previously formed cracks. As shown in FIG. 13C, each beam Le is condensed at a condensing point at a predetermined depth to form an internal crack 12.

Each of the condensing positions of the plurality of lenses 59e are as the same, as shown in FIG. 13 (d), except two beams Le forward according to surface processing traces 11a along the expected splitting line C ₂ at an intersection C ₁₂ It is also possible to provide a lens selection function that allows all laser energy to pass through the beam Le.

  According to the experiment, the crack tip of the uppermost internal crack 12c shown in FIG. 2 is processed according to the condensing position, the film configuration of the oxide film 2, the laser wavelength to be used, etc. so as to be at least 20 μm away from the substrate surface 11. It is desirable to set conditions. This is to prevent the internal crack 12c and the substrate surface 11 from being inadvertently connected during processing, or the substrate surface 11 may be damaged depending on the laser irradiation conditions.

  Further, the depth (a) of the condensing point A shown in FIG. 7B is obtained by moving either the work W, which is the silicon substrate 10, or the condensing optical system 52 in the optical axis direction, and shifting the condensing position. Can be controlled. When the refractive index with respect to the wavelength of 1064 nm of the silicon substrate 10 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, The optical movement amount of the condensing point A is nd. The refractive index of the silicon substrate 10 is in the vicinity of 3.5 at a wavelength of 1.1 to 1.5 μm, which is close to 3.5 when compared with the value actually predicted in the experiment.

That is, when the mechanical movement amount is 100 μm, the condensing point is formed at a position of 350 μm from the surface. The fact that the refractive index is in the vicinity of 3.5 indicates that the reflectance is large. In general, reflection at normal incidence is ((n−1) / (n + 1)) ² , and is about 30% for a 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 each beam Le is condensed at the condensing point A, the crystalline state of silicon partially changes, and as a result, the internal crack 12 runs. As a result of the experiment, it was confirmed that it travels below the condensing point A, that is, farther from the incident side of each beam Le, and the crack length (b) was about 50 to 100 μm.

In this way, the internal crack 12 is formed from one point inside the silicon substrate 10, and the condensing point A is relatively moved along the planned cutting line C to perform internal processing immediately below the planned cutting line C. As shown in FIG. 1, the planned cutting line C of the silicon substrate 10 includes two planned cutting lines C ₁ and C ₂ perpendicular 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 X and Y directions, and the optical axis direction (depth direction) is the Z stage 52c on the side of the automatic stage on which the workpiece W is placed or on the condensing optical system side. 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 frequency and crack shape, and the moving speed is generally 10 to 100 mm / sec at a normal frequency of 10 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 52d 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 54 is introduced to measure the distance from the workpiece W. The AF optical system 54 obtains the contrast of the image obtained by the observation camera 52d, 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.

  Internal machining is performed in this way, but attention should be paid to the following points when starting machining.

(1) As shown in FIG. 14, laser processing is started from the end point of the silicon substrate 10 as the workpiece W. However, since the vicinity of the end point is difficult to process from the central portion, each beam Le is processed when processing the vicinity of the end point. It is necessary to change the machining conditions such as raising the total energy of the beam group consisting of from the center of the workpiece W.
(2) As shown in FIG. 15, when processing an irregular shaped chip having a rectangular shape, first, the internal crack 12 is processed with the planned cutting line C ₁ on the long side as the first breaking direction, and then processing the internal crack 12 along a 20 percent cross direction expected splitting line C ₂ on the short side.

  As described above, the crack length formed at one condensing point is 50 to 100 μm, and the thickness of the target silicon substrate is 625 μm. It is necessary to perform processing. 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 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.

  However, the inside of the substrate is not limited thereto, and the internal cracks 12a to 12c may be divided in the depth direction as shown in FIG. Further, the crack group of the internal crack 12c closest to the substrate surface 11 is provided at a depth of 20 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. 16A, 16B, and 16C, the first method is a group of cracks having a height above 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. 16 (c), the crack groups of the internal cracks 12a, 12b, and 12c having different depths are formed immediately below one fracture line C, and then another fracture schedule is formed. A similar crack group of line 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 planarity of the silicon substrate 10 is necessary.

  In the first method, as shown in FIGS. 16 (a) and 16 (b), the condensing point is moved in one direction along the planned cutting line, and as shown in FIG. 16 (c). The light spot may be reciprocated along the planned cutting line. The latter can shorten the machining time because the total operating 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).

In addition, as shown in FIG. 15, in the cutting planned lines C ₁ and C ₂ having two cutting directions, there is a point where they intersect (intersection C ₁₂ ). In the vicinity of the intersection C ₁₂ would beam Le for the inside machining of the same depth in the second percent cross direction it is blocked by the internal processing zone which is formed along the first percent cross direction. This does not occur in the entire internal machining zone in the second cleaving direction, but is a local phenomenon. Whether the machining conditions are changed near the intersection C ₁₂ in consideration of energy loss as described above. Alternatively, it is desirable to change the machining conditions when shifting to the second cleaving direction, and to machine the machining conditions different from the first cleaving direction over the entire second cleaving direction.

"Cleaving process"
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 is not connected to at least the surface processing mark 11a and the internal crack 12c immediately below the surface. 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 elements is performed as follows.

  As shown in FIG. 17, the silicon substrate 10 after the formation of the surface processing marks 11a and the internal cracks 12 (12a, 12b, 12c) is mounted on the dicing tape T so that the back surface of the silicon substrate 10 faces up. Then, it is placed on a rubber sheet 60 having elasticity 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 aforementioned 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 weakest point of the substrate surface 11, i.e. acts to widen the surface processing traces 11a on the planned cutting line C _1.

As a result, a crack is generated starting from the surface processing mark 11a, and the crack progresses to the back surface of the substrate by connecting the internal cracks 12a, 12b, and 12c due to laser irradiation inside the substrate, reaches the back surface of the substrate, and reaches the planned cutting line. The silicon substrate 10 is cleaved along C ₁ . 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 11 a, the crack does not deviate greatly from the planned cutting line C ₁ on the substrate surface 11. As the roller 61 advances, the silicon substrate 10 is sequentially cut along the cutting line C ₁ 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 C ₂ 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 FIG. 17 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 silicon substrate by the roller is not damaged so that the element and the nozzle material are not destroyed. It is necessary to select the compression load, the thickness of the rubber sheet, and the rubber hardness. In addition, the material and thickness of the dicing tape and the surface protection tape are selected so that unnecessary interference layers are not formed.

  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. 18, 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 part 10a to be cut is pushed upward by about 1 to 10 μm with the collet A 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 collet B62b so that the adjacent logic element portion 10a is not pushed upward. As a result, a stress that spreads the surface processing trace on the cleaving line C acts, a crack is generated starting from the surface processing trace, and is connected to the internal crack and reaches 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 made of ceramic or a ceramic and metal fired material (cermet material). By continuously hitting 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 laser-processed substrate by the method disclosed in Patent Document 4.

"Repair process"
In the cleaving step, the surface processing mark 11a and the crack due to the internal crack 12 are connected, and the crack reaches the back 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 FIG.

"Pickup process"
As shown in FIG. 20, the logic element unit 10a, which is an element chip separated in the cleaving process and the repair process, is carried out by the suction collet 65 and the pickup pin 66 and stored individually. At this time, the gap between the elements may be widened by an expander or the like. Further, fine dust generated during pick-up may be removed by suction.

  When the silicon oxide film 2, which is a film different from the substrate material, is present on the substrate surface 11, it is necessary to minimize the surface reflection of the laser beam that causes energy loss in order to stably form the internal crack. . Therefore, a part of the cleaving process of the first embodiment is changed.

  FIG. 21 shows the process flow of this embodiment. Step 1 tape mounting step, step 2 wafer correction step, step 3 irradiation window forming step, step 4 internal crack forming step, step 5 surface line. The process includes a cutting process, a cleaving process at step 6, a repair process at step 7, and a pickup process at step 8.

  In this embodiment, for the purpose of more efficiently condensing the laser energy for internal processing, as shown in FIG. 22, groove processing for optimizing the thickness of the oxide film 2 of the silicon substrate 20 is performed. . FIG. 23 is a graph showing the relationship between the thickness of the silicon oxide film and the reflectance. Based on this graph, the thickness of the oxide film 2 when the reflectance of the laser beam is lowest is selected.

  That is, when the light source to be used is a YAG fundamental wave (wavelength 1064 nm), nd = 270 nm (about λ / 4) and the reflectance becomes the lowest value of about 4% (see FIG. 23). Therefore, the groove 2a is formed by groove processing such as etching so that the thickness of the oxide film 2 becomes this value. Needless to say, the groove 2a by etching is formed in a region irradiated with a beam group at the time of forming an internal crack.

  Alternatively, the oxide film 2 may be formed with an optimum film thickness when the oxide film 2 is formed on the silicon wafer.

  Laser irradiation is performed in the oxide film region optimized as described above to generate an internal crack. Further, as described above, the surface processing trace is formed by marking with a scriber such as cemented carbide along the planned cutting line.

  This surface processing mark may be formed before laser irradiation. According to this, unnecessary cracks due to processing loads can be avoided by forming surface processing marks before forming internal cracks by laser irradiation. In addition, by forming the surface processing mark first, the processing mark itself can be used as a reference (line) indicating a processing position at the time of laser irradiation in a subsequent process, so that the work efficiency of laser irradiation can be improved.

  According to this embodiment, when an oxide film is formed on the substrate surface, the loss of laser energy due to the surface reflection can be minimized, and the energy consumption in the internal crack formation process can be suppressed. In addition, it is possible to prevent the internal processing from becoming unstable due to uneven thickness of the oxide film, non-uniformity in film characteristics, or the like.

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. 1 is a schematic diagram illustrating Example 1. FIG. It is a flowchart which shows the cleaving process by Example 1. FIG. It is a figure explaining a tape mounting process. It is a figure explaining a wafer correction process. The surface linear processing for forming the surface processing trace is described. (A) is the case where the surface processing trace is within the thickness of the oxide film, and (b) is the same as the thickness of the oxide film. It is a figure which shows a case. 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 light source optical system of the apparatus of FIG. It is a figure explaining the function to adjust the beam diameter of the beam divided | segmented by the light source optical system of the apparatus of FIG. It is a figure explaining control of the beam diameter when a beam group passes an intersection. It is a figure explaining the case where a beam diameter is not changed when a beam group passes an intersection. It is a figure explaining another light source optical system. It is a figure explaining another light source optical system. It is a figure explaining the internal crack formation process in the edge part of a silicon substrate. It is a figure explaining the case where a deformed element chip is cut out. 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 flowchart which shows the cleaving process by Example 2. It is a figure which shows the groove | channel formed in the oxide film by the etching. It is a graph which shows the relationship between the thickness of an oxide film, and a reflectance. 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 40 Tool 50 Processing apparatus 51 Light source 51a Light source optical system 52 Condensing optical system 53 Automatic stage 54 AF optical system 55 Beam expansion system 56 Beam shift system 57 Beam splitting system 57a, 57b Square pyramid 57c, 57d, 57e Fly's eye lens 57f Single lens 58 Beam shaping system 59 Dividing condensing optical system

Claims (1)

A substrate cleaving method for separating a substrate into a plurality of element chips,
A step of forming a plurality of linear processed portions on the substrate surface along the planned cutting line of the substrate so as to have intersections where the linear processed portions intersect each other;
The laser light emitted from the light source, the beam splitting system, the laser energy each divided into four laser beams are equal, the four quadrants the linear processing unit of the two in the intersection is formed on the substrate surface The laser beam is divided into two on both sides of the linearly processed portion so that one laser beam is distributed to each of the laser beam, and is incident on different positions on the substrate surface, and each laser beam is individually applied to a condensing point inside the substrate. A step of generating an internal crack by condensing and relatively moving the laser beam so as to relatively move the condensing point along the linearly processed portion;
Connecting the internal crack of the substrate and the linear processed portion of the substrate surface by applying an external force to the substrate;
When the condensing point approaches the intersection, the laser light incident on the light beam splitting system is shifted by a beam shift system, so that the beam diameters of the two laser beams behind the traveling direction are increased. The laser beam incident on the beam splitting system is shifted by a beam shift system when the beam diameters of the two laser beams ahead in the traveling direction are reduced and the focusing point moves away from the intersection. A substrate cleaving method characterized by increasing the beam diameter of two laser beams in the front direction and decreasing the beam diameter of two laser beams in the rear direction of travel.

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