DIVISION PROCEDURE FOR A WORKPIECE

Abstract

Division method for a workpiece for dividing a workpiece (W) along roads set on the workpiece (W), comprising: a laser processing step for applying a pulsed laser beam (LB) to the workpiece (W) along the road to form several small holes (3) along the road extending in an application direction of the pulsed laser beam (LB), wherein one surface side (Wb) of the workpiece (W) is held by means of a holding table (11) and the laser beam (LB) passes through a condenser (17); and a division step for pressing the roads through a pressure element (18) to divide the workpiece (W) along the roads after the laser processing step has been carried out, wherein in the laser processing step a position of a focal point (P1) of a pulsed laser beam (LB) passing through an innermost part of the condenser (17) is positioned on one surface side (Wb) of the workpiece (W), and a position of a focal point (Pn) of a pulsed laser beam (LB) passing through an outer part of the condenser (17) is positioned on the other surface side (Wa) of the workpiece (W), the other surface side (Wa) being opposite the one surface side (Wb), wherein the small hole (3) has an end (3a) with an opening (4) on one surface side (Wb) and has a reduced diameter from one surface side (Wb) to the other end (3b) on the other surface side (Wa), and In the division step, the pressure element (18) is pressed against the other surface side (Wa) of the workpiece (W), where one end (3b) of the small hole (3) is not open.

Description

BACKGROUND OF THE INVENTION Technical field

[0001] The present invention relates to a method for dividing a workpiece along roads (dividing lines) that are placed on the workpiece. Description of the state of the art

[0002] A workpiece such as a wafer contains components such as integrated circuits (ICs) and large-scale integrated circuits (LSs) formed on a front surface in a state where it is divided by roads. Examples of methods for dividing the workpiece into individual chips include a method in which a focal point of a laser beam of a wavelength transmitted through the workpiece is positioned inside the wafer in a position corresponding to the road, in which the laser beam and the workpiece are placed in relative scanning, thereby forming multiple shielding tunnels inside the wafer along each road, and in which an external force is subsequently applied along each road to divide the workpiece (see, for example, Japanese patent application JP 2014-221 483 A). PRESENTATION OF THE INVENTION

[0003] However, in the process disclosed in Japanese patent application JP 2014-221 483 A, there is a problem that, depending on the surface against which a pressure element is pressed, the workpiece may be damaged or destroyed at the time an external force is applied to it.

[0004] JP 2015 / 0159821 A1 discloses a parting method for dividing a workpiece along paths defined on the workpiece. In a laser processing step, a pulsed laser beam is applied to the workpiece along the paths to form several small holes along the paths, extending in the direction of application of the pulsed laser beam. A parting step is described for dividing the workpiece along the paths after the laser processing step has been performed. In the parting step, an external force is applied to the workpiece, the small hole having an end opening on at least one front surface and one rear surface of the workpiece, and a reduced diameter from one end to the other.

[0005] JP 2017-076713 A discloses in a division step a pressure element to press against a surface of a wafer, at which one end of a small hole extending transversely to the thickness direction of the wafer is not open.

[0006] Therefore, an objective of the present invention is to provide a division method for a workpiece by which a workpiece can be divided without being damaged or destroyed.

[0007] In accordance with one aspect of the present invention, a dividing method for a workpiece is provided for dividing a workpiece along roads set on the workpiece, wherein the dividing method for a workpiece comprises: a laser processing step for applying a pulsed laser beam to the workpiece along the roads to form several small holes along the road extending in an application direction of the pulsed laser beam;and a division step for pressing the roads by a pressure element to divide the workpiece along the roads after the laser processing step has been carried out, wherein the small hole has one end open on at least one front surface and one rear surface of the workpiece and has a reduced diameter from one end to the other end, and in the division step the pressure element is pressed against the surface of the front surface and the rear surface of the workpiece, on which one end of the small hole is not open.

[0008] Preferably, the division method for a workpiece further includes a test step to check on which of the front surface and the rear surface of the workpiece one end or the other end of the small hole is formed before the division step is carried out.

[0009] According to the dividing method for a workpiece of the present invention, in the dividing step the pressure element is pressed against the surface of the front surface and the rear surface of the workpiece, where one end of the small hole is not open; therefore, the small hole is more easily pressed towards the open side at the diametrically larger one end than at the other end, so that the divisibility of the wafer is improved and accordingly the wafer can be advantageously divided without being damaged or broken.

[0010] Where the test step for checking on which of the front and rear surfaces of the workpiece one end or the other end of the small hole is formed is provided before the division step is carried out, it is ensured that a continuation to the division step can be carried out after the one end of the small hole, on which the external force is applied by the pressure element when carrying out the division step, is identified, and accordingly the workpiece can be divided in a reliable manner.

[0011] The above and other aims, features and advantages of the present invention and the manner of realizing them will be made clearer and the invention itself best understood by studying the following description and attached claims with reference to the attached figures which show the preferred embodiments of the invention. BRIEF DESCRIPTION OF THE FIGURES Fig. Figure 1 is a perspective view of a wafer that is supported on a ring-shaped frame by an adhesive band; Fig. Figure 2 is a sectional view showing a first embodiment of a laser processing step; Fig. Figure 3 is a partially enlarged sectional view to explain a focal point position of a pulsed laser beam in the first embodiment; Fig. Figure 4 is a partially enlarged sectional view showing the state of a wafer after the laser processing step of the first embodiment has been performed; Fig. Figure 5 is a sectional view showing a first embodiment of a division step; Fig. Figure 6 is a sectional view showing a second embodiment of the laser processing step; Fig. Figure 7 is a partially enlarged sectional view to explain a focal point position of a pulsed laser beam in the second embodiment; Fig. Figure 8 is a partially enlarged sectional view showing the state of a wafer after the laser processing step of the second embodiment has been performed; and Fig. Figure 9 is a sectional view showing a second embodiment of the division step. DETAILED DESCRIPTION OF THE PREFERRED EXECUTION 1. First embodiment of the division method

[0012] A wafer W, which is in Fig. Figure 1 shows an example of a workpiece having a circular, disk-shaped substrate, and lines (dividing lines) S are arranged in a grid pattern on its front surface Wa. Components D are formed in respective areas divided by the lines S. On the other hand, a surface on the side opposite the front surface Wa of the wafer W is a rear surface Wb, onto which a laser beam is to be directed. The material of the wafer W is, for example, glass, LT / LN (lithium tantalate / lithium niobate), SiC (silicon carbide), Si (silicon), crystal, sapphire, a ceramic, or the like.

[0013] To divide the wafer W into chips comprising individual components D, an expandable adhesion promoter band 2 is applied to a lower surface of an annular frame 1 that is open at its center. The front surface Wa of the wafer W is attached to the adhesion promoter band 2, which is exposed from the center of the frame 1, with the rear surface Wb exposed to the top. In this way, the frame 1 and the wafer W are integrally formed by the adhesion promoter band 2. The adhesion promoter band 2 is not particularly restricted; for example, an expandable film having a two-layer structure, in which an adhesion promoter layer is applied to a base material formed from a polyolefin or polyvinyl chloride or the like, can be used. A first embodiment of a division method for dividing a wafer W into individual chips is described below. (1) Laser processing step

[0014] As in Fig. As shown in Figure 2, the wafer W, which is integrated with the frame 1, is held by a holding unit 10 for holding the wafer W, and the wafer W is laser-processed along the path S by an application unit 16 for a laser beam, which is arranged on the upper side of the holding unit 10. The holding unit 10 includes a holding table 11, which has a holding surface 11a for holding the wafer W, and a frame holding unit 12, which is arranged on a surrounding edge of the holding table 11.

[0015] The frame holding unit 12 includes a mounting base for a frame 13, to which the frame 1 is attached, shaft sections 14 connected to the mounting base 13, and clamping sections 15 that rotate with the shaft sections 14 as a pivot point and press against an upper surface of the frame 1 attached to the mounting base 13. The laser beam application unit 16 includes at least one condenser 17 incorporating a focusing lens for focusing a pulsed laser beam LB of a wavelength that forms small holes along the road S, a laser oscillator that oscillates the pulsed laser beam LB, and a power adjustment unit that adjusts the power of the pulsed laser beam LB oscillated by the laser oscillator.The laser beam application unit 16 can be moved vertically to move the condenser 17 up and down, thereby adjusting the focus position of the pulsed laser beam LB. The focusing lens is preferably a focusing lens exhibiting spherical aberration, positioning the focal point of the pulsed laser beam LB such that it extends along the thickness direction of the wafer W.Note that for the pulsed laser beam LB it is only necessary to be applied to the wafer W in a state in which an aberration is generated in an optical axis direction of the focusing lens; consequently, aberration can be formed by arranging a lens on the side of the laser oscillator or on the side of the wafer W of the focusing lens, or the pulsed laser beam LB, which has a predetermined propagation angle, can be oscillated by the laser oscillator and focused by the focusing lens.

[0016] At the time of laser processing of the wafer W, the front surface Wa of the wafer W, to which the adhesion-promoting strip 2 is attached, is fixed to the holding surface 11a of the holding table 11, and the frame 1 is positioned on the mounting base 13 for a frame. The clamping sections 15 are rotated around the shaft sections 14 to press and fix the upper surface of the frame 1. A laser processing step in the first embodiment is carried out, for example, with the following processing conditions 1. [Processing conditions 1] Wafer material: LT (lithium tantalate) Wavelength: 1030 nm Average power consumption: 3 watts Repetition frequency: 50 kHz Pulse width: 10 ps Spot diameter: 10 µm Processing feed speed: 500 mm / s (Numerical aperture of the focusing lens) / (Refractive index of the wafer): 0.05 to 0.20

[0017] The laser beam delivery unit 16 lowers the condenser 17 in the direction of approach to the wafer W and positions the focal points of the laser beam LB such that they extend in the thickness direction of the wafer W. For example, as in Fig. As shown in Figure 3, the position of a focal point P1 of a pulsed laser beam LB1, which travels along the optical axis O located at the innermost side of the condenser 17, is positioned at the rear surface Wb of the wafer W, whereas the position of a focal point Pn of a pulsed laser beam LBn, which travels along the outermost side of the condenser 17, is positioned at the side of the support stage 11 (the front surface Wa of the wafer W). As a result, the focal points of the pulsed laser beam LB, which travels through the focusing lens of the condenser 17, are positioned such that they extend over a region from the rear surface Wb to the front surface Wa of the wafer.

[0018] For example, in the case where the wafer thickness is 300 µm, it is preferred to position the focal points such that focal points P1 to Pn extend over a region spanning the thickness from the front surface Wa to the back surface Wb, namely over a thickness of 300 µm. While the length of focal points P1 to Pn need not necessarily be greater than the thickness of the wafer W, if the length is set over a region spanning the entire thickness from the front surface Wa to the back surface Wb of the wafer W, better shielding tunnels (small holes around modified regions formed by modifying the environments of the small holes in an amorphous state) can be formed in the wafer W.Note that while the pulsed laser beam LB is split into the pulsed laser beams LB1 to LBn and the focal point into the focal points P1 to Pn, to explain the focal point position of the pulsed laser beam LB in the example of . Fig. Since the laser beam is divided into three sections, the pulsed laser beams and the focus points are not observed in such a divided state in practice.

[0019] Next, during a processing feed of the wafer W, which is in Fig. As shown in Figure 2, the application unit 16, for example, applies a pulsed laser beam LB of a predetermined wavelength (1030 nm) along the road S, which is in a predetermined processing feed rate (500 mm / s) and in the direction of arrow X. Fig. As shown in Figure 1, from the rear surface Wb of the wafer W, several small holes 3 are formed along the road S, extending in the application direction of the pulsed laser beam LB and in Fig. Figure 4 shows each of the small holes 3. Each of the small holes 3 has an end 3a with an opening 4 formed at least on the rear surface Wb of the wafer W, and its diameter decreases from one end 3a to the other end 3b. The opening 4 is formed on the side of the surface where the pulsed laser beam LB strikes (on the side of the rear surface Wb). With the small holes 3 formed in the wafer W, it is ensured that, at the time the splitting step described later is performed, only a relatively small external force from the other end 3b will more easily expand the small holes 3 at the end 3a with the larger diameter than at the other end 3b, and that the wafer W can be split advantageously.

[0020] In the vicinity of the small hole 3, a modified region 5, which is modified in an amorphous state, is formed surrounding the small hole 3. The formation of the small hole 3 by applying the laser beam LB is carried out intermittently along the road S to form the multiple small holes 3. Cracks are partially formed between adjacent small holes 3. When the multiple small holes 3 and modified regions 5 are formed along all the roads S that are in Fig. The laser processing step is completed once the small holes 3, as shown in Figure 1, have been formed. For example, the small holes 3 have a diameter of 1 µm, and in the first embodiment, the processing feed speed of the wafer W is set to 500 mm / s and the repetition frequency of the pulsed laser beam LB is set to 50 kHz, resulting in the formation of small holes 3 at a distance of 10 µm along the paths S. (2) Verification step

[0021] At least before performing the division step, it is checked on which of the front surface Wa and the rear surface Wb of the wafer one end 3a (opening 4) or the other end 3b (the opening smaller than at one end 3a) of the small hole 3 is formed. As a method for checking, for example, the front surface Wa and the rear surface Wb of the wafer can be examined using a microscope, which is not shown. If the size of the small hole 3 on the front surface Wa of the wafer and the size of the small hole 3 on the rear surface Wb are compared in the first embodiment, it can be confirmed that one end 3a of the small hole 3 is formed on the rear surface Wb of the wafer W and the other end 3b of the small hole 3 is formed on the front surface Wa of the wafer W.In the event that one end 3a and the other end 3b of the small hole 3 cannot be confirmed even upon examination of the front and back surfaces Wa and Wb of the wafer, a process can be carried out in which, for example, before the splitting step, an unneeded area of ​​the wafer W or a test piece of the same material as a wafer W is cut by a cutting blade to completely cut the front and back surfaces Wa and Wb of the wafer W, and the cut of the wafer W is examined to verify on which of the front surfaces Wa and the back surfaces Wb of the wafer the one end 3a or the other end 3b of the small hole 3 is formed. Note that in the first embodiment, the small holes 3 and the modified areas 5 are clearly illustrated by schematically showing them in Figure 1. Fig. 4 and in Fig. Figures 5, which will be described later, are shown to simplify the explanation; however, the small holes 3 and modified areas 5, which are formed by actual machining, are not clearly visible but rather hidden. Even if they are so hidden, it is possible, at least by examining the front and back surfaces of the wafer W, to determine on which of the front surface Wa and back surface Wb of the wafer W one end 3a (opening 4) or the other end 3b (the opening smaller than at one end 3a) of the small hole 3 is formed. (3) Division step

[0022] As in Fig. As shown in Figure 5, the wafer is turned over from front to back. One end face 3a of the small hole 3 of the wafer W, or the side on which the opening 4 is formed, is supported, for example, by a support element 19. The wafer W is divided along the road by a pressure element 18, which is arranged on the upper side of the support elements 19. The support elements 19 have gaps 190 and can support the wafer W by means of the adhesion-promoting band 2. The pressure element is, for example, a fracture blade whose tip section 180 extends in a straight line along the straight line of a road S, which is in Fig. The pressure element 18, shown in Figure 1, is formed and can apply an external force to the interior of the wafer W. The pressure element 18 can be moved in the vertical direction by a lifting mechanism, which is not shown.

[0023] To align the wafer W's path S with the printing element 18, the path S is detected by an alignment camera (not shown). The wafer W is then attached to the support elements 19, with its rear surface Wb facing downwards. In this process, a single path S is moved to the interior of the gap 190 between the support elements 19, positioning the openings 4 of the small holes 3 formed along the single path S on the upper side of the gap 190.

[0024] Additionally, in the division step, the pressure element 18 is positioned relative to the surface of the front surface Wa and the rear surface Wb of the wafer W, where one end 3a of the small hole 3 does not open (the surface where the other end 3b is formed). In the first embodiment, the tip section 180 of the pressure element 18 is positioned above the front surface Wa of the wafer W and directly above the road S. Next, the pressure element 18 is lowered in the direction of approach to the wafer W, and the upper surface Wa of the wafer W is pressed downwards by a predetermined depth through the tip section 180 by the adhesion-promoting band 2, thereby applying an external force (bending stress). The predetermined depth is, for example, set to 20 µm from the height of the upper surface of the wafer W.As a result of such pressing of the wafer W, the small hole 3 is pressed wide open from the other end 3b, which has a smaller diameter, to the one end 3a with a larger diameter, the section which lies on the upper side of the gap 190 is pressed downwards and the wafer W, which cannot withstand the external force, is split.

[0025] After the wafer W has been divided along one road S, it is subjected to an index feed in the direction of arrow Y, for example, to move the adjacent road S to the inside of the gap 190 between the support elements 19. This aligns the tip section 180 of the pressure element 18 in a position where it can come into contact with road S. The wafer W can then be pressed downwards from its front surface Wa by the pressure element 18 along the adjacent road S, applying an external force in a manner similar to that described above. In this way, the wafer W is divided into individual component chips along all roads S by the pressure element 18, thus completing the division step.

[0026] Consequently, in the first embodiment of the division method according to the present invention, at the time of carrying out the division step, after the laser processing step has been performed to form the small holes 3 along the paths S extending in the application direction of the pulsed laser beam LB, the surface of the front and rear surfaces Wa and Wb of the wafer W, on which the other end 3b of the small hole 3 with a reduced diameter is formed (for example, the front side Wa), is pressed by the pressure element 18. Therefore, the side of one end 3a, whose diameter is larger compared to the other end 3b, is simply pressed open significantly, so that the divisibility of the wafer W is improved compared to the case in which one end side 3a is pressed, and accordingly, the wafer W can be advantageously divided without being damaged or destroyed.Additionally, in the present invention, a verification step is performed at least before the division step to check on which of the front surface Wa and the rear surface Wb of the wafer W the end 3a or the end 3b of the small hole 3 is formed. Therefore, the division step can be carried out after the end 3a of the small hole 3, on which the external force by the pressure element 18 is to be applied at the time of the division step 18, has been identified, and accordingly the wafer W can be reliably divided. 2. Second embodiment of the division method

[0027] A second embodiment of the division method for dividing wafer W1 into individual chips is described below with reference to Fig. 6, Fig. 7 to Fig. 8 described. (1) Laser processing step

[0028] As in Fig. As shown in Figure 6, the front surface Wa of wafer W1, with the adhesive strip 2 attached to it, is similarly attached to the holding surface 11a of the holding table 11, and the frame 1 is placed on the mounting base 13 for a frame. The clamping sections 15 are rotated around the shaft sections 14 to press and fix the upper surface of the frame 1. A laser processing step in the second embodiment is carried out, for example, under the following processing conditions 2. Wafer W1 is designed similarly to wafer W mentioned above, except for the material, and therefore the same reference numerals are used as above. [Processing conditions 2] Wafer material: SiC (silicon carbide) Wavelength: 530 nm Average power consumption: 3 W Repetition frequency: 50 kHz Pulse width: 10 ps Spot diameter: 10 µm Processing feed speed: 500 mm / s (Numerical aperture of the focusing lens) / (Refractive index of the wafer): 0.05 to 0.20

[0029] The laser beam delivery unit 16 lowers the condenser 17 in the direction of approach to the wafer W1 and positions the focal point of a laser beam LB' such that it extends in the thickness direction of the wafer W1. For example, as in Fig. Figure 7 shows the position of a focal point P1 of a pulsed laser beam LB1, which travels along an optical axis O located in the innermost side of the condenser 17, on the holding table side 11 (the front surface Wa of the wafer W1), which is in Fig. As shown in Figure 6, the focal point Pn of the pulsed laser beam LBn, which travels along the outermost side of the condenser 17, is positioned at the rear surface Wb of the wafer W1. As a result, the focal points of the pulsed laser beam LB', which passes through the focusing lens of the condenser 17, are positioned such that they extend from the rear surface Wb to the front surface Wa of the wafer W1. Next, while the wafer W1 is subjected to processing at a specific processing feed rate (500 mm / s) in the direction of arrow X, the laser beam application unit 16, for example, delivers the pulsed laser beam LB' of a predetermined wavelength (530 nm) along the path S, which is shown in Figure 6. Fig. 1 is shown, from the rear surface side Wb of the wafer W1 to create several small holes 6 extending in the application direction of the pulsed laser beam LB' and in Fig. 8 are shown, to be formed along road S.

[0030] Each of the small holes 6 is a small hole having an end 3a with an opening 7 formed on at least the front surface Wa of the wafer W1, and whose diameter decreases from one end 6a to the other end 6b and is formed in the opposite direction to the small hole 3 in the first embodiment. In particular, the opening 7 is formed on the side (the front surface Wa) opposite the surface on which the pulsed laser beam LB' strikes, and the other end 6b of the small hole 6 is formed in the interior of the wafer W on the rear surface Wb. Since the pulsed laser beam LB1, which is in Fig. As shown in Figure 1, the laser beam LBn, which travels along the central side of the focusing lens, has a higher power or processing power than the laser beam LBn. In the second embodiment, the opening 7 is formed on the side of the focal point P1 of the pulsed laser beam LB1. With the small holes 6 formed in the interior of the wafer W1, it is possible, at the time the division step described later is carried out, to more easily force the small hole 6 wider at one end 6a, whose diameter is increased, than at the other end 6b of the small hole 6, and thus the wafer W1 can be advantageously divided, by applying only a comparatively small force from the other end 6b. In the vicinity of the small hole 6, a modified region 8, which is modified in an amorphous state, is formed surrounding the small hole 6.Cracks are partially formed between adjacent small holes 6. Once the multiple small holes 6 and modified areas 8 have been formed along all the roads S, the laser processing step is complete. For example, the small hole 6 has a diameter of 1 µm, and in the second embodiment, the processing feed rate of the wafer W1 is also set to 500 mm / s, and the repetition frequency of the pulsed laser beam LB' is set to 50 kHz, resulting in the formation of small holes 6 spaced 10 µm apart along the road S. (2) Verification step

[0031] At least before the division step is carried out, it is checked on which of the front surfaces Wa and the rear surface Wb of wafer W1 one end 6a (opening 7) or the other end 6b (the opening smaller than that of one end 6a) of the small hole 6 is formed. In the second embodiment, it can be confirmed that the opening 7 or one end 6a of the small hole 6 is formed on the front surface Wa of wafer W and the other end 6b of the small hole 6 is formed on the rear surface Wb of wafer W1. The verification procedure is similar to the first embodiment. Note that in the second embodiment, the small holes 6 and the modified areas 8 are also clearly shown schematically in Fig. 8 and Fig. 9, which are described later, are shown to simplify the explanation, however the small holes 6 and modified areas 8 formed by the actual machining are not clear, but blurred. (3) Division step

[0032] As in Fig.As shown in Figure 9, one end face 6a of the small hole 6, or the side where the opening 7 is formed, of the wafer W1 is supported by the support elements 19, for example, and the wafer W1 is split along the path S by the pressure element 18, which is arranged on the upper side of the support elements 19. Similar to the first embodiment, the path S is detected by the alignment camera, which is not shown. Subsequently, the wafer W1 is attached to the support elements 19 with the side of the adhesive strip 2 facing downwards. In this case, the path S is moved to the inside of the gap 190 between the support elements 19, whereby the openings 7 of the small holes 6, which are formed along the path S, are positioned on the upper side of the gap 190.

[0033] Furthermore, in the second embodiment, the pressure element 18 is also positioned relative to the surface of the front surface Wa and the rear surface Wb of the wafer W1, where one end 6a of the small hole 6 is not open (the surface on the side where the other end 6b is formed). In the second embodiment, the tip section 180 of the pressure element 18 is positioned above the rear surface Wb of the wafer W1 and directly above the road S. The pressure element 18 is lowered in the direction of approach to the wafer W1, and the rear surface Wb of the wafer W1 is pressed downwards by a predetermined depth through the tip section 180, thereby applying an external force (bending stress). The predetermined depth is set to 20 µm from the height of the upper surface of the wafer W1.With the wafer W1 pressed in this manner, the small hole 6 is forced wide open from the other end 6b with the smaller diameter to the one end 6a with the larger diameter, the section located on the upper side of the gap 190 is forced downwards, and the wafer W1, which cannot withstand the external force, is split. Note that, while the rear surface Wb of the wafer W1 is pressed directly by pressing the pressure element 18 in the present embodiment, the rear surface Wb can be pressed by means of an adhesion-promoting strip or the like.

[0034] After splitting along a path S, the wafer is subjected to an index feed in the direction of arrow Y, for example, to move the adjacent path S to the inside of the gap 190 between the support elements 19. This aligns the tip section 180 of the pressure element 18 in a position where it can come into contact with the path S. The wafer W1 is then pressed from the rear surface Wb along the adjacent path S by the pressure element 18 in a similar manner to the above, thereby applying an external force. When the wafer W1 has been split into individual chips along all paths S by the pressure element 18, the splitting step is complete.Consequently, in the second embodiment of the division method according to the present invention, at the time of the division step, the surface of the front and rear surfaces Wa and Wb of the wafer W1, on which the other end 6b of the small hole 6 with a reduced diameter is formed (for example, the rear surface Wb), is pressed through the pressure element 18; therefore, the small hole 6 is more easily pressed wide open at one end 6a with an increased diameter than at the other end 6b, so that the divisibility of the wafer W1 is improved compared to the case of pressing only one end 6a, and accordingly, the wafer W1 can be advantageously divided without being damaged or destroyed.

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