Method for manufacturing a wafer

Abstract

A manufacturing method for a wafer, comprising: radiating a laser beam to a planned cut surface at which the ingot is to be cut off; and forming a plurality of modification portions (31) at the planned cut surface using the radiation of the laser beam to extend a crack from the modification portions, thereby cutting the wafer, wherein an energy density of the laser beam exceeds a modification threshold value (Eth). The energy density satisfies at least one of the following conditions: a peak value (Ep) of the energy density is less than or equal to 44 J / cm 2 ; a rising rate (a) of the energy density at a portion corresponding to a shallowest position at which the energy density reaches the modification threshold value Eth is greater than or equal to 1000 J / cm 3 ; and a depth range (W) in which the energy density exceeds the modification threshold value is less than or equal to 30 pm.

Description

[0001] Cross-references to related applications

[0002] This application is based on and claims the priority interests of prior Japanese Patent Application No. 2021-165323, filed on October 7, 2021, and prior Japanese Patent Application No. 2021-199290, filed on December 8, 2021, the descriptions of which are incorporated herein by reference. Technical Field

[0003] This disclosure relates to methods for manufacturing wafers. Background Technology

[0004] A method for manufacturing wafers from a semiconductor ingot includes a technique in which a laser beam can be radiated onto the semiconductor ingot for cutting the wafer from the ingot. Specifically, the laser beam is radiated onto the ingot to form reformed sections at a number of locations along a planned cutting surface within the ingot. The reformed sections are then broken, separating the wafer from the ingot.

[0005] However, when multiple modified sections are formed, they may be formed at a shallower location than the target depth. In other words, a modified section may be formed at the target depth, but some modified sections may be formed at other depths. This multi-stage modification can increase material loss in the semiconductor ingot, leading to low yield.

[0006] As a conventional technique, for example, Japanese Patent Application Publication No. 2014-147946 discloses a technique in which the annular portion of a laser beam is focused on a predetermined portion of the object to be processed, thereby precisely forming a fine modified part.

[0007] Using this technology, it is difficult to avoid multi-stage modification by simply radiating a ring-shaped portion of the laser beam. Therefore, the problem of reduced wafer dicing yield still exists. Summary of the Invention

[0008] This disclosure was made in view of the above circumstances, and a method for manufacturing wafers is provided.

[0009] The first aspect of this disclosure is a method for manufacturing a wafer, wherein a transparent or translucent ingot 2 is cut using a laser beam L to obtain the wafer. The method includes the steps of: radiating the laser beam onto the ingot at multiple locations from a direction intersecting with a planned cutting surface 21 from which the ingot is to be cut; and using the radiation of the laser beam, forming multiple modified portions 31 in the ingot at locations corresponding to depths of the planned cutting surface, to extend cracks 32 from these modified portions, thereby cutting the wafer.

[0010] in,

[0011] When the laser beam is irradiated onto the ingot, the energy density of the laser beam per unit area in the ingot exceeds the modification threshold Et, which is sufficient to modify a portion of the ingot on the surface to be cut in this plan.

[0012] The energy density satisfies at least one or more of the following conditions: Condition 1, Condition 2, and Condition 3:

[0013] Condition 1: The peak energy density Ep is less than or equal to 44 J / cm². 2

[0014] Condition 2: The rate of increase α of the energy density at the shallowest point corresponding to the energy density reaching the modification threshold Eth is greater than or equal to 1000 J / cm². 3

[0015] Condition 3: The depth range W where the energy density exceeds the modification threshold is less than or equal to 30 μm.

[0016] The effects and advantages of this invention are as follows. In the wafer manufacturing method, the energy density of the laser beam is controlled in the manner described above. Therefore, the modified portion can be formed at the desired depth location while suppressing multi-stage modification. Thus, material loss in the ingot is suppressed and manufacturing yield is improved.

[0017] As described above, manufacturing yield can be improved according to the aforementioned aspects. Note that the reference numerals in parentheses described in the claims and summary section indicate the relationship to the specific apparatus described in the embodiments described later, and do not limit the technical scope of this disclosure. Attached Figure Description

[0018] Figure 1 This is a perspective illustration showing the wafer manufacturing method according to the first embodiment;

[0019] Figure 2 This is an explanatory diagram showing the state of the laser beam radiating onto the planned cutting surface when viewed from a direction parallel to the planned cutting surface according to the first embodiment;

[0020] Figure 3A This is an explanatory diagram showing a planned cut surface with a virtual line and multiple modified parts, according to the first embodiment, where the virtual line intersects with the direction forming the off angle.

[0021] Figure 3B Is along Figure 3A The explanatory diagram corresponding to the cross-sectional view taken by line IIIb-IIIb in the first embodiment shows the relationship between the deviation angle and the virtual line.

[0022] Figure 4A This is an explanatory diagram showing a planned cut surface having a virtual line and multiple modified parts, according to the first embodiment, in the case where the virtual line is positioned along the direction forming the deviation angle.

[0023] Figure 4B Is along Figure 4A The explanatory diagram corresponding to the cross-sectional view taken by line IVb-IVb in the first embodiment shows the relationship between the deviation angle and the virtual line;

[0024] Figure 5 This is an explanatory cross-sectional view showing an ingot with a modified portion and cracks formed when viewed from a direction parallel to the planned cut surface, according to the first embodiment;

[0025] Figure 6 This is an explanatory diagram showing a cross-section of an ingot with a modified portion and cracks when viewed from a direction parallel to the planned cutting surface, in the case where the virtual line is positioned along the direction in which the deviation angle is formed, according to the first embodiment.

[0026] Figure 7 This is a perspective illustration showing the state of separation between the wafer and the ingot according to the first embodiment;

[0027] Figure 8 This is an explanatory cross-sectional view showing the upper surface of the ingot and the lower surface of the wafer immediately following wafer separation, according to the first embodiment.

[0028] Figure 9 This is an explanatory cross-sectional view showing the upper surface of the ingot and the lower surface of the wafer after polishing according to the first embodiment;

[0029] Figure 10 This is a graph showing the relationship between the depth from the crystal ingot surface and the energy density of the laser beam according to the first embodiment;

[0030] Figure 11 This is a cross-sectional illustration showing the state in which the annular laser beam, according to the first embodiment, is focused on the surface to be cut.

[0031] Figure 12 It shows along Figure 11 The diagram shows the cross-sectional view of line XII-XII.

[0032] Figure 13A This is a diagram showing the intensity distribution of a Gaussian beam.

[0033] Figure 13B This is an explanatory diagram illustrating the multi-level nature of the renovation department;

[0034] Figure 14 This is a graph showing the relationship between the depth in the ingot and the energy density of the laser beam when a multi-stage modification section is formed;

[0035] Figure 15A This is a diagram showing the intensity distribution of a ring laser beam;

[0036] Figure 15B This diagram illustrates the state of preventing the modified part from having a multi-level structure;

[0037] Figure 16 It is a graph showing the relationship between the depth in the ingot and the energy density of the laser beam when the multi-stage modification section is not formed;

[0038] Figure 17 This is a graph showing the relationship between the depth from the ingot surface and the energy density of the laser beam when manufacturing sample A, based on an experimental example.

[0039] Figure 18 These are photographs showing cross-sectional views of sample A at two locations according to the experimental example;

[0040] Figure 19 This is a graph showing the relationship between the depth from the ingot surface and the energy density of the laser beam when manufacturing sample B, according to an experimental example.

[0041] Figure 20 These are photographs showing cross-sectional views of sample B at two locations according to the experimental example;

[0042] Figure 21 This is a graph showing the relationship between the depth from the ingot surface and the energy density of the laser beam when manufacturing sample C, according to an experimental example;

[0043] Figure 22 These are photographs showing cross-sectional views of sample C at two locations according to the experimental example;

[0044] Figure 23 This is a graph showing the relationship between the depth from the ingot surface and the energy density of the laser beam when manufacturing sample D, based on an experimental example.

[0045] Figure 24 These are photographs showing cross-sectional views of sample D at two locations according to the experimental example;

[0046] Figure 25 This is a graph showing the relationship between the depth from the ingot surface and the energy density of the laser beam when manufacturing sample E, according to an experimental example.

[0047] Figure 26 These are photographs showing cross-sectional views of sample E at two locations according to the experimental example;

[0048] Figure 27This is an explanatory diagram showing the state of the laser beam radiating onto the planned cutting surface when viewed from a direction parallel to the planned cutting surface according to the second embodiment;

[0049] Figure 28 This is an explanatory diagram showing the planned cutting surface of the ingot and the shape of the laser beam on the upper surface according to the third embodiment;

[0050] Figure 29 This is an illustrative diagram showing the shape of the annular laser beam on the planned cutting surface and the upper surface of the ingot;

[0051] Figure 30 This is an explanatory diagram showing the irradiation position of the portion of the ingot near the edge of the laser beam according to the fourth embodiment.

[0052] Figure 31 This is an explanatory diagram showing the irradiation position of the portion of the ingot near the edge of the laser beam according to the fifth embodiment; and

[0053] Figure 32 This is an explanatory diagram showing the irradiation position of the portion of the ingot near the edge of the laser beam according to the sixth embodiment. Detailed Implementation

[0054] (First Implementation)

[0055] Reference Figures 1 to 11 This will describe an implementation method for wafer manufacturing. For example... Figures 1 to 9 As shown, the manufacturing method of this embodiment is a method of obtaining wafer 20 by cutting ingot 2 with laser beam L. Here, ingot 2 is transparent or translucent.

[0056] First, such as Figure 1 and Figure 2 As shown, the laser beam L radiates onto the ingot 2 at multiple locations from a direction intersecting with the planned cutting surface 21 of the ingot 2 to be cut. Therefore, as... Figure 2 and Figures 3A to 3B As shown, a plurality of modified portions 31 are formed at a depth corresponding to the planned cutting surface 21 in the ingot 2. Then, as... Figure 5 As shown, crack 32 extends from the modified part 31, which is the origin of the crack. Therefore, as... Figure 7 and Figure 8 As shown, wafer 20 is cut from ingot 2.

[0057] When a laser beam is irradiated onto ingot 2, the energy density of the laser beam L per unit area in ingot 2 satisfies the following condition: The energy density of the laser beam L exceeds the modification threshold Eth on the planned cut. Note that the modification threshold Eth refers to the threshold of energy density required to modify a portion of ingot 2.

[0058] The energy density also satisfies at least one of the following conditions 1, 2, and 3.

[0059] Condition 1: Peak energy density is less than or equal to 44 J / cm³ 2

[0060] Condition 2: The rate of increase in energy density at the shallowest point corresponding to the energy density reaching the modification threshold Eth is greater than or equal to 1000 J / cm². 3 Note that the rate of increase in energy density refers to the increase in energy density per unit depth.

[0061] Condition 3: The depth range where the energy density exceeds the modification threshold Eth is less than or equal to 30 μm.

[0062] Reference Figure 10 The conditions for the energy density described above will be described. Figure 10 Curve M in the figure roughly illustrates an example of the relationship between the depth of the laser beam L from the surface of the ingot 2 and the energy density of the laser beam L when the laser beam L irradiates the ingot 2. Here, the surface of the ingot 2 refers to the surface that serves as the incident surface of the laser beam L. Figure 10 The vertical axis indicates the depth from the surface of the ingot, making it deeper towards the bottom. The horizontal axis indicates the energy density of the laser, making the energy density higher towards the right.

[0063] like Figure 10 As shown, the laser beam L radiates onto the ingot 2, causing the energy density to increase at a certain depth. Here, the energy density is set to be at least greater than or equal to the modification threshold Eth at the depth of the planned cutting surface 21. On the other hand, at least one of the above conditions 1 to 3 is satisfied. More preferably, all of the above conditions can be satisfied.

[0064] As condition 1, the peak energy density Ep is set to be less than or equal to 44 J / cm². 3 Note that the peak value of the energy density Ep is simply referred to as the peak value Ep.

[0065] As condition 2, the rate of increase in energy density at the shallowest depth where the energy density reaches the modification threshold Eth is set to be greater than or equal to 1000 J / cm². 3 In other words, in Figure 10 In the curve M, the slope of the tangent T at point P1 is set to be greater than or equal to 1000 J / cm. 3 At point P1, the increase in energy density per unit depth is 1000 J / cm³. 3 Or even higher. Specifically, the rate of increase in energy density at the shallowest depth where the energy density reaches the modification threshold Eth is greater than or equal to 1000 J / cm².3 In the following text, the rate of increase in energy density at the shallowest depth where the energy density reaches the modification threshold Eth is also referred to as the rate of increase in energy density α.

[0066] As condition 3, the depth range where the energy density exceeds the modification threshold Eth is set to be less than or equal to 30 μm. This means that, in Figure 10 In this context, the width of the range indicated by the symbol W is 30 μm or less. In the following text, the depth range where the energy density exceeds the modification threshold Eth is simply referred to as the depth range W.

[0067] According to this embodiment, ingot 2 contains SiC (i.e., silicon carbide). For example... Figure 1 As shown, ingot 2 has a generally cylindrical shape. A laser beam L is radiated from a surface corresponding to either of the pair of generally cylindrical base surfaces onto ingot 2, which has a corresponding material and shape. Note that, for convenience, the surface on which the laser beam L is incident is referred to as the upper surface 23. The upper surface 23 of ingot 2 is planar. According to this embodiment, the laser beam radiated onto ingot 2 is a pulsed laser with a pulse width of 250 fs to 10 ns.

[0068] like Figure 1 and Figure 2 As shown, the planned cutting surface 21 is parallel to the upper surface 23. The planned cutting surface 21 is positioned at a depth from the upper surface 23 corresponding to the thickness of the wafer 20 to be obtained. A laser beam L radiates from the upper surface of the ingot 2, causing a plurality of modified portions 31 to be formed on the planned cutting surface 21. The laser beam L passes through a converging lens 41, thereby radiating the ingot 21 such that the energy density is greater than or equal to the modification threshold Eth at the depth position of the planned cutting surface 21. With respect to the modified portions 31, due to the energy of the laser beam L, a portion of the ingot 2 composed of SiC single crystals becomes a separated state of amorphous Si (silicon) and amorphous C (carbon), thereby forming the modified portions 31.

[0069] like Figures 1 to 3B As shown, the laser beam L converges at multiple locations on the planned cutting surface 21 of the ingot 2. Figure 3A and Figure 3B As shown, multiple modified sections 31 are formed along multiple parallel virtual lines VL on the planned cutting surface 21. A laser beam L scans the ingot 2 along the virtual lines VL. The virtual lines VL can be perpendicular to the direction defined by the deviation angle θ of the ingot 2. Figures 3A to 3B In the diagram, only a portion of the modified section 31 is shown. In reality, the modified sections 31 on the virtual line VL are densely packed and overlap each other. Furthermore, in... Figure 3B In the figure, the dashed line indicated by reference numeral 2c indicates the c-surface, which is tilted at an angle θ relative to the upper surface 23 of the ingot 2. This also applies to... Figure 4B .

[0070] However, as Figure 4A and Figure 4B As shown, when viewed from the axial direction of ingot 2, the virtual line VL can be a line parallel to the direction in which the deviation angle θ is formed on ingot 2. In this case, the tilt of the deviation angle θ exists in both the axial direction parallel to ingot 2 and the cross-section of the virtual line VL. A pulsed laser beam L is used to scan ingot 2 along such a virtual line VL. Therefore, multiple modified portions 31 are formed on multiple virtual lines VL.

[0071] When the modified part 31 is formed in the ingot 2, such as Figure 5 As shown, crack 32 originates from the modified part 31. Crack 32 extends along the c-surface of ingot 2. The c-surface is inclined at a constant deviation angle θ relative to the upper surface 23. There are a large number of c-surfaces within ingot 2. According to this embodiment, for example, the deviation angle can be set to 4°.

[0072] Therefore, crack 32 is formed, for example, at an angle of 4° relative to the upper surface 23. As described above, since multiple modified portions 31 are formed on the planned cutting surface 21, the cracks remain connected when the modified portions 31 are properly arranged. Therefore, as Figure 7 and Figure 8 As shown, wafer 20 is separated from ingot on a surface substantially along the planned cut surface 21.

[0073] However, as described above, crack 32 is inclined relative to the upper surface 23 and also relative to the planned cutting surface 21. Therefore, as Figure 8 As shown, the cut surfaces 321 and 322 formed by the continuously connected cracks 32 are uneven surfaces, in which numerous concave and convex portions are formed. These uneven cut surfaces 321 and 322 are produced on the wafer 20 and ingot 2 by polishing with a grinding stone. Therefore, as Figure 9 As shown, a wafer 20 is obtained, and the upper surface 23 of the cut ingot 2 is also planarized.

[0074] As described above, when the virtual line VL is parallel to the direction forming the deviation angle θ (see...) Figure 4A and Figure 4B This can minimize the unevenness. In this case, such as... Figure 6 As shown, adjacent modified portions 31 are aligned on the virtual line VL. These modified portions 31 are partially aligned in the direction forming the deviation angle θ, but are located within the aforementioned depth range W. Therefore, the unevenness can be significantly reduced.

[0075] According to this embodiment, when the modified part 31 is formed, as follows: Figure 11As shown, laser beams simultaneously radiate onto the ingot 2 from multiple directions. The laser beams from these multiple directions overlap within a portion of a depth region, including the depth location of the planned cutting surface 21 of the ingot 2. The overlapping portion Lc has a length h of 5 to 50 μm in the depth direction. Here, the depth direction corresponds to the normal direction of the upper surface 23 of the ingot 2.

[0076] Note that the simultaneous radiation of laser beams towards ingot 2 from multiple directions includes both the case of radiating a single laser beam from multiple directions and the case of radiating multiple laser beams from multiple directions.

[0077] According to this embodiment, a ring laser beam is used as the laser beam. For a ring laser beam, such as... Figure 12 As shown, for example, the shape of the cross-section taken along a line orthogonal to the optical axis, excluding the overlapping portion Lc, has an annular shape. Specifically, the annular laser beam is formed to have an annular intensity distribution in the portion excluding the overlapping portion Lc. The annular laser beam can be a laser beam that simultaneously radiates onto the ingot 2 from multiple directions.

[0078] Specifically, according to this embodiment, the aforementioned cross-sectional shape (i.e., intensity distribution) is annular. The annular laser beam has an annular cross-sectional shape before being incident on the converging lens 41. Figure 11 As shown, the ring laser beam is refracted at the converging lens 41 to form an overlapping portion Lc in the ingot 2. The overlapping portion Lc has a length h in the depth direction of 5 to 50 μm. Furthermore, the overlapping portion Lc is configured to be formed in a depth region including the depth position of the planned surface 21.

[0079] The laser beam is radiated to provide the aforementioned overlapping portion Lc, thereby controlling the energy density of the laser beam radiated onto the ingot 2.

[0080] Next, the effects and advantages of this embodiment will be described. In the above-described wafer manufacturing method, the energy density of the laser beam L radiated onto the ingot 2 is controlled in the manner described above. More specifically, the energy density of the laser beam L is controlled to be at least greater than or equal to the modification threshold Eth at the depth position of the planned cutting surface 21, and then controlled to satisfy at least one of the above conditions 1, 2, and 3. Specifically, at least one of the peak value Ep of the energy density of the laser beam L, the rate of rise α of the energy density, and the depth range W is controlled within a predetermined range (see [link to documentation]). Figure 10 Therefore, the modified section 31 is formed at the desired depth while preventing it from becoming a multi-level section. This suppresses material loss in the ingot 2 and improves manufacturing yield.

[0081] By controlling the energy density of the laser beam L radiated onto the ingot 2 to satisfy at least one of conditions 1, 2, and 3, the modified section 31 can be prevented from becoming a multi-stage section. If the energy density of the laser beam L does not satisfy any of conditions 1, 2, and 3, the problem arises of multi-stage modified sections appearing at many locations (see description later). Figure 13B When the modified section 31 is multi-level at many locations, the thickness corresponding to the multi-level modified section leads to material loss. In this regard, according to this embodiment, by controlling the various parameters related to the energy density of the laser beam in the manner described above, material loss can be suppressed and the manufacturing yield of the wafer 20 can be improved.

[0082] The following describes the modification section as a multi-level mechanism and the suppression mechanism of the multi-level modification section.

[0083] For example, the inventors of this disclosure discovered a phenomenon, such as Figure 13B As shown, where Figure 13A When a Gaussian-distributed laser beam is focused and radiates onto ingot 2, modified portions 311 and 312 can be formed at multiple depth locations. This is because a portion of the laser beam around its optical axis focuses at a relatively shallow depth location, and the energy density exceeds the modification threshold Eth to form modified portion 311. Simultaneously, a portion of the laser beam departing from the optical axis diffracts from the outer periphery of modified portion 311 and focuses at a relatively deep location, and the energy density exceeds the modification threshold Eth to form modified portion 312. Therefore, as... Figure 14 As shown, at multiple depth locations in ingot 2, the energy density exceeds the modification threshold Eth. Therefore, as Figure 13B As shown, the modified parts 311 and 312 are formed in multiple stages.

[0084] In contrast, according to this embodiment, such as Figure 15A As shown, a ring-shaped laser beam with no energy density near the optical axis converges and radiates onto ingot 2, thus... Figure 15B As shown, an overlapping portion forms at the target depth location. In this case, as... Figure 16 As shown, the energy density exceeds the modification threshold Eth at the target depth location, i.e., as... Figure 15B The depth position at which the planned cut-off surface 21 and the modified part 31 are formed is shown. At this time, as... Figure 16 As shown, there are no laser beams with energy densities exceeding the threshold at depths other than the depth at which the surface 21 is to be cut. Therefore, it is possible to prevent the modified section from becoming a multi-stage modified section.

[0085] Under this mechanism, controlling the energy density to satisfy at least one of conditions 1 to 3 prevents the modified part from becoming multi-stage. Furthermore, controlling the energy density to satisfy all conditions 1 to 3 further prevents the modified part from becoming multi-stage.

[0086] Furthermore, the laser beam L radiating onto ingot 2 is a pulsed laser beam with a pulse width ranging from 250 fs to 10 ns. Therefore, the modified section is formed at the desired depth position while preventing the modified section from becoming a multi-stage section.

[0087] The length h of the laser beam reaching the overlapping portion Lc of ingot 2 from multiple directions is 5 to 50 μm (see...). Figure 11 Using this configuration, the various parameters of energy density can be easily and reliably controlled within a predetermined range. Therefore, the manufacturing yield of wafer 20 can be improved.

[0088] As described above, according to this embodiment, a wafer manufacturing method that can improve manufacturing yield can be provided.

[0089] Assuming the virtual line VL is a straight line parallel to the deviation angle θ of ingot 2 when viewed from the axial direction of ingot 2, as described above, the height of the uneven portions of cut surfaces 321 and 322 can be significantly reduced. Therefore, material loss of ingot 2 can be suppressed.

[0090] (Experimental Example)

[0091] This example confirms the effect of preventing the modification section from being multi-staged by controlling the peak value Ep, the rate of increase in energy density α, and the depth range W within the ranges described in the first embodiment above.

[0092] As described above, the inventors of this invention have discovered that multi-stage modification can be suppressed by controlling the peak value Ep, the rate of increase in energy density α, and the depth range W within predetermined ranges. These predetermined ranges are summarized below.

[0093] Condition 1: Peak Ep is less than or equal to 44 J / cm 2

[0094] Condition 2: The rate of increase in energy density α is greater than or equal to 1000 J / cm³ 3

[0095] Condition 3: Depth range W is less than or equal to 30 μm

[0096] In this regard, according to this embodiment, samples are manufactured, namely, sample A in which a laser beam irradiates an ingot to satisfy all conditions 1 to 3, sample B, sample C, sample D in which a laser beam irradiates an ingot to satisfy at least one of conditions 1 to 3, and sample E in which a laser beam irradiates an ingot to satisfy none of conditions 1 to 3. The specific method of this example will be described below. Note that the method not specifically described in this example is the same as the method in the first embodiment. The scanning direction of the laser beam (i.e., the direction indicated by the virtual line VL) is set to a direction orthogonal to the direction forming the deviation angle (see...). Figure 3B ).

[0097] For each sample A through E, a pulsed laser beam irradiates the ingot at multiple locations. At this time, the pulsed laser beam follows the virtual line VL (see...). Figures 3A to 3B It radiates continuously and linearly multiple times. The radiation spacing is set to 0.5 μm. In addition, multiple virtual lines VL are provided, with the array spacing of the virtual lines set to 100 μm.

[0098] Furthermore, the wavelength of the pulsed laser beam to be irradiated was set to 1030 nm, the pulse width to 10 ps, ​​and the oscillation frequency to 10 kHz. The various conditions for different variations of samples A through E will be described below.

[0099] <Sample A>

[0100] As described above, the radiation conditions of the laser beam are set to satisfy conditions 1 to 3 below. A pair of axial prisms are used as a converging lens to converge the annular laser beam and radiate the converged laser beam onto the ingot. The radiated laser beam has an outer diameter of 2 mm and an inner diameter of 1 mm before being converged by the converging lens. The pulse energy is set to 3 μJ.

[0101] At this time, Figure 17 The diagram shows the state of the energy density of the laser beam radiated into the ingot (i.e., the relationship between the depth from the upper surface of the ingot and the energy density). Table 1 shows the measured data obtained under conditions 1 to 3.

[0102] [Table 1]

[0103] Sample:A

[0104]

[0105] In Table 1, the experimental values ​​can be found from... Figure 17The curves shown are read from the graphs and calculated based on the outer diameter of the laser beam incident on the converging lens, the NA value (numerical aperture value), the distance between the converging lens and the ingot, the depth from the top surface of the ingot, and the refractive index of the ingot. In the "Results" column, OK indicates that the result meets the target value under each condition, and NG indicates that the result does not meet the target value under each condition. This also applies to Tables 2 through 5 described later.

[0106] Then, for sample A, the ingot was cut open and the interior of the ingot was observed. Figure 18 The image shown is taken with a metallurgical microscope (magnification approximately 100). Figure 18 The accompanying image contains two different photographs, which are cross-sectional views of sample A at two different locations. The same applies to similar photographs described later. In each photograph, the portion indicated by arrow 31 refers to the modified section. As these photographs show, no multi-stage modified sections were observed in sample A.

[0107] <Sample B>

[0108] To manufacture sample B, the pulse energy of the laser beam irradiating the ingot was 6 μJ. Other irradiation conditions were the same as those for sample A.

[0109] At this time, Figure 19 The diagram illustrates the energy density of a laser beam radiating onto an ingot (i.e., the relationship between the depth from the top surface of the ingot and the energy density). Note that... Figure 19 The curve was obtained under the condition that the laser beam irradiated the ingot once. This also applies to the conditions described later. Figure 21 , Figure 23 , Figure 25 and Figure 27 Table 2 shows the measured data under conditions 1 to 3.

[0110] [Table 2]

[0111] Sample: B

[0112]

[0113] As shown in Table 2, sample B does not satisfy condition 1, but it satisfies conditions 2 and 3. That is, the rate of increase in energy density α is sufficiently large, and the depth range is sufficiently small.

[0114] Then, for the manufactured sample B, the ingot was cut open and its interior was observed. Figure 20 The image shown is taken with a metallurgical microscope (magnification approximately 100). Figure 20As shown, multi-level modified sections were observed in sample B. In other words, modified sections 311 and 312 were observed to form at two locations in the depth direction. However, the scale of the multi-level portions in the modified sections is small, and the area of ​​the modified sections is small. Here, the area of ​​the modified section refers to the region in the ingot in the depth direction where the modified section is formed.

[0115] <Sample C>

[0116] To fabricate sample C, the laser beam radiating the ingot is a Gaussian beam. That is, a laser beam with a Gaussian intensity distribution is used, where the center of the laser beam is the optical axis. The radiated laser beam has an outer diameter of 2.2 mm before converging at the converging lens. The pulse energy is set to 3 μJ.

[0117] At this time, Figure 21 The figure shows the state of energy density of the laser beam radiating onto the ingot (i.e., the relationship between the depth from the upper surface of the ingot and the energy density). Table 3 shows the measured data under conditions 1 to 3.

[0118] [Table 3]

[0119] Sample: C

[0120]

[0121] As shown in Table 3, sample C does not satisfy conditions 2 and 3, but it does satisfy condition 1. That is, the peak Ep is sufficiently suppressed.

[0122] Then, for the manufactured sample C, the ingot is cut open and its interior is observed. Figure 22 The image shown is taken with a metallurgical microscope (magnification approximately 100). Figure 22 As shown in the photograph, multi-level modifications were observed in sample C. Furthermore, modifications 311, 312, and 313 were observed to form at three locations in the depth direction within sample C. However, compared to sample E, which will be described later, the multi-level portions in the modifications are smaller in scale and the area of ​​the modifications is also smaller.

[0123] <Sample D>

[0124] To manufacture sample D, the outer diameter of the laser beam irradiating the ingot was set to 1.8 mm and the inner diameter to 0.2 mm before it converged at the converging lens. Other irradiation conditions were the same as those for sample A.

[0125] At this time, Figure 23 The figure shows the state of the energy density of the laser beam radiated into the ingot (i.e., the relationship between the depth from the upper surface of the ingot and the energy density). Table 4 shows the measured data obtained under conditions 1 to 3.

[0126] [Table 4]

[0127] Sample: D

[0128]

[0129] As shown in Table 4, sample D does not satisfy condition 2, but it satisfies conditions 1 and 3. That is, the peak Ep is sufficiently suppressed and the depth range W is sufficiently small.

[0130] Then, for the manufactured sample D, the ingot is cut open and its interior is observed. Figure 24 The image shown is taken with a metallurgical microscope (magnification approximately 100). Figure 24 As shown in the photograph, multi-level modifications were observed in sample D. In other words, modifications 311 and 312 were observed to form at two locations in the depth direction. However, the multi-level portions within the modifications were small in scale, and the area of ​​the modifications was also small.

[0131] <Sample E>

[0132] To fabricate sample E, the laser beam radiating the ingot is a Gaussian beam. That is, a laser beam with a Gaussian intensity distribution is used, where the center of the laser beam is the optical axis. The radiated laser beam has an outer diameter of 2.2 mm before converging at the focusing lens. The pulse energy is set to 9 μJ.

[0133] at this time, Figure 25 The figure shows the state of energy density of the laser beam radiating onto the ingot (i.e., the relationship between the depth from the upper surface of the ingot and the energy density). Table 5 shows the measured data under conditions 1 to 3.

[0134] [Table 5]

[0135] Sample: E

[0136]

[0137] As shown in Table 5, sample E does not meet conditions 1, 2, and 3. That is, the peak value Ep is too large, the rate of increase in energy density α is too small, and the depth range W is too large.

[0138] Then, for the manufactured sample E, the ingot is cut open and its interior is observed. Figure 26 The image shown is taken with a metallurgical microscope (magnification approximately 100). Figure 26 As shown in the photograph, significant multi-level modifications were observed in sample E. In other words, modifications 311, 312, 313, and 314 were observed to form at three or more locations along the depth direction, and the area of ​​the modifications was small.

[0139] Table 6 below shows the conditions satisfied by the radiated laser beams and the observation results of the cross sections when manufacturing samples A, B, C, D and E.

[0140] [Table 6]

[0141] sample Condition 1 Condition 2 Condition 3 Multi-level parts Area of ​​the renovation department A OK OK OK none 20μm B NG OK OK Small 30-65μm C OK NG NG middle 50-100μm D OK NG OK Small 30-65μm E NG NG NG big 80-250μm

[0142] In Table 6, OK indicates that the conditions are met and NG indicates that the conditions are not met. As shown in Table 6, for sample E that does not meet any of conditions 1 to 3, a large multi-stage portion appears in the modified section. In contrast, for samples that meet at least one of conditions 1 to 3, the multi-stage portion of the modified section is suppressed. Among these samples, for samples that meet any two of conditions 1 to 3, the multi-stage portion of the modified section is further suppressed. Furthermore, for samples that meet all of conditions 1 to 3, no multi-stage modified section is generated. From these results, it can be recognized that multi-stage portions of the modified section can be effectively suppressed using samples that meet at least one of conditions 1 to 3. Furthermore, meeting all of conditions 1 to 3 effectively prevents the modified section from becoming multi-stage. Based on the experimental results of samples A, C, and D above, at least under the radiation conditions of this experimental example, the peak energy density Ep is less than or equal to 30 J / cm². 3 The conditions are considered valid.

[0143] (Second Implementation)

[0144] According to the second embodiment, such as Figure 27 As shown, multiple laser beams L1 and L2 with non-parallel optical axes are used. The multiple laser beams L1 and L2 simultaneously irradiate the ingot 2 to overlap on the planned cutting surface 21.

[0145] According to this embodiment, multiple laser beams L1 and L2, each having a non-parallel optical axis, converge at a converging lens 41 and overlap on the planned cutting surface 21. Each laser beam L1 and L2 is inclined relative to the normal direction of the planned cutting surface 21. The overlapping portion Lc of the multiple laser beams L1 and L2 has a large energy density. Therefore, a modified section 31 is formed in the planned cutting surface 21.

[0146] The laser beams L1 and L2 converged at the converging lens 41 can be Gaussian beams or ring beams. Furthermore, the multiple laser beams L1 and L2 can be configured such that laser beams oscillating at the same laser oscillator are branched through different optical paths.

[0147] Other configurations are the same as those in the first embodiment. In the reference numerals used in the second and subsequent embodiments, unless otherwise stated, configurations with the same reference numerals as those in the prior art indicate components that are the same as those in the prior art.

[0148] According to this embodiment, the optical axes of laser beams L1 and L2 are arranged on a plane orthogonal to the scanning direction of the laser beam toward the ingot 2, thereby allowing laser beams L1 and L2 to easily and completely incident on the upper surface 23 of the ingot 2, even at the edge of the planned cutting surface 21. Therefore, the reduction in the energy density of the laser beam on the planned cutting surface 21 can be suppressed. Furthermore, according to the second embodiment, the same effects and advantages as the first embodiment can be obtained. In this embodiment, three or more laser beams having mutually non-parallel optical axes can be used.

[0149] (Third Implementation)

[0150] According to the third embodiment, such as Figure 28 As shown, the intensity distribution of each laser beam is set to extend along a direction orthogonal to the virtual line VL, rather than along the direction of the virtual line VL. As described in the first embodiment, the ingot 2 has a generally cylindrical shape (see...). Figure 1 Then, multiple modified portions 31 are formed in the planned cut surface 21, each of which is formed along one of multiple parallel virtual lines VL orthogonal to the axial direction of the ingot 2 (see...). Figures 3A to 3B ).

[0151] According to this embodiment, such as Figure 28 As shown, when viewed from the axial direction, the intensity distribution of the laser beams used to form each modified part 31 is more extended in the direction orthogonal to the virtual line VL than in the direction along the virtual line VL. Figure 28 The elliptical profile Ld21 shown indicates the profile of the laser beam to be cut off on surface 21, and Figure 28 The elliptical profile Ld23 shown indicates the profile of the intensity distribution of the laser beam on the upper surface 23 of the ingot 2. Note that the profile of the intensity distribution is a closed curve surrounding a portion with a predetermined intensity or greater. Figure 28 As shown, when assuming the length of the direction orthogonal to the virtual line VL in the contour line Ld 23 is d1 and the length along the direction of the virtual line VL is d2, the lengths have a relationship of d1>d2. Other configurations are the same as those in the first embodiment.

[0152] According to this embodiment, compared with the energy density of the laser beam in other parts, it is easy to prevent the energy density of the laser beam radiating to the portion near the edge of the planned cutting surface 21 of the ingot 2 from being too small.

[0153] Here, as a comparative example of this embodiment, the following will be considered: Figure 29The situation shown, that is, the intensity distribution of the laser beam is a circular distribution with d1 = d2 or an elliptical distribution with d1 < d2. In this case, a part of the laser beam radiated to the vicinity of the edge portion of the ingot 2 may enter the side surface of the ingot 2. This is because, if the length d2 is large, as Figure 29 shown, a part of the contour Ld23 of the laser beam on the plane including the upper surface of the ingot 2 protrudes beyond the contour of the edge portion of the ingot 2. The protruding laser beam enters the side surface of the ingot 2.

[0154] Therefore, the energy density of the laser beam on the planned cutting surface 21 may decrease. In other words, the energy density of the laser beam radiated to the part near the edge portion may become smaller than the energy density of the laser beam radiated to the part inside the edge portion. This may result in insufficient modification state near the edge portion.

[0155] In this regard, according to the present embodiment, the intensity distribution of the laser beam is set to an elliptical shape with the length relationship d1 > d2, whereby it is also possible to prevent the laser beam radiated to the part near the planned cutting surface 21 from entering the side surface of the ingot 2. Specifically, compared with the case of the annular laser beam, even when the optical axis is set closer to the edge portion, the energy density does not necessarily decrease on the planned cutting surface 21. Therefore, the above problems can be avoided. In addition, according to the third embodiment, the same effects and advantages as those of the first embodiment can be obtained.

[0156] (Fourth Embodiment)

[0157] According to the fourth embodiment, as Figure 30 shown, in the edge portion of the ingot 2, the spacing between the radiation points Lp of the laser beams located adjacent to each other along the virtual line VL is set to be shorter than that of other parts.

[0158] As disclosed in the third embodiment, a part of the laser beam radiated to the edge portion of the ingot 2 may enter the side surface of the ingot 2. Therefore, the energy density on the planned cutting surface 21 may decrease compared with the energy density of other parts. In this regard, according to the present embodiment, in the edge portion of the ingot 2, the spacing between the radiation points Lp of the laser beams is set to be shorter than that of other parts. Therefore, an appropriate modification portion 31 with a sufficient modification state can be formed even at the edge portion of the planned cutting surface 21. In addition, according to the fourth embodiment, the configuration is the same as that of the first embodiment, and the same effects and advantages as those of the first embodiment can be obtained.

[0159] (Fifth Embodiment)

[0160] According to the fifth embodiment, as Figure 31As shown, the energy of the laser beam radiating to the edge of ingot 2 is set to be greater than the energy of other parts. Note that... Figure 31 The size of the point Lq shown indicates the amount of energy of each laser beam. According to this embodiment, as described above, a laser beam with higher energy is radiated onto the edge of the ingot 2 where the energy density may decrease on the planned cutting surface 21. Therefore, even at the edge of the planned cutting surface 21, a suitable modified portion 31 with a sufficiently modified state can be formed. Furthermore, according to the fifth embodiment, the configuration is the same as that of the first embodiment, and the same effects and advantages as those of the first embodiment can be obtained.

[0161] (Sixth Implementation Method)

[0162] According to the sixth embodiment, such as Figure 32 As shown, the spacing between virtual lines VL positioned away from the central axis 2C of the ingot 2 is set to be narrower than the spacing between virtual lines VL positioned closer to the central axis 2C. According to this embodiment, as described above, the virtual lines VL are concentrated at the edges of the ingot 2 where the energy density may decrease. Then, a laser beam is radiated along these virtual lines VL. Therefore, even at the edge of the planned cutting surface 21, a suitable modified portion 31 with a sufficiently modified state can be formed. Furthermore, according to the sixth embodiment, the configuration is the same as that of the first embodiment, and the same effects and advantages as those of the first embodiment can be obtained.

[0163] This disclosure is not limited to the various embodiments described above, but can be modified in various ways without departing from the spirit of this disclosure.

Claims

1. A method for manufacturing a wafer, wherein, The method of obtaining the wafer by cutting a transparent or translucent crystal ingot with a laser beam includes the following steps: The laser beam is radiated onto the ingot at multiple locations from a direction intersecting the planned cutting surface, the ingot to be cut at the planned cutting surface; and Using the radiation of the laser beam, multiple modified portions are formed in the ingot at depths corresponding to the planned cutting surface, so that cracks extend from these modified portions, thereby cutting the wafer. in, When the laser beam is irradiated onto the ingot, the energy density of the laser beam per unit area in the ingot exceeds the modification threshold that can modify a portion of the ingot on the planned cutting surface; The energy density satisfies all of the following conditions 1, 2, and 3: Condition 1: The peak energy density is less than or equal to 44 J / cm³. 2 ; Condition 2: The rate of increase of the energy density at the shallowest position corresponding to the energy density reaching the modification threshold is greater than or equal to 1000 J / cm². 3 ; Condition 3: The depth range in which the energy density exceeds the modification threshold is less than or equal to 30 μm.

2. The manufacturing method according to claim 1, wherein, The laser beam radiating onto the ingot is a pulsed laser with a pulse width of 250 fs to 10 ns.

3. The manufacturing method according to claim 1 or 2, wherein, The laser beam is simultaneously radiated onto the crystal ingot from multiple directions; The laser beams from the plurality of directions overlap each other in a portion of a depth region including the depth location of the intended cutting surface of the ingot, thereby forming an overlapping portion; and The overlapping portion has a length of 5 to 50 μm in the depth direction.

4. The manufacturing method according to claim 1 or 2, wherein, Multiple laser beams with non-parallel optical axes are simultaneously irradiated onto the ingot, causing the multiple laser beams to overlap on the surface to be cut.

5. The manufacturing method according to claim 1 or 2, wherein, The ingot has a cylindrical shape; Multiple modified portions are formed in the planned cutting surface, each of which is formed along one of multiple parallel virtual lines orthogonal to the axial direction of the ingot; as well as When viewed from the axial direction, the intensity distribution of the laser beams used to form the various modified parts extends in a direction orthogonal to the virtual line rather than along the virtual line.

6. The manufacturing method according to claim 1 or 2, wherein, The ingot has a cylindrical shape; Multiple modified portions are formed in the planned cutting surface, each of which is formed along one of multiple parallel virtual lines orthogonal to the axial direction of the ingot; as well as In the edge portion of the ingot, the spacing between the radiation points of the laser beam, which are positioned adjacent to each other along the virtual line, is set to be shorter than in other portions.

7. The manufacturing method according to claim 1 or 2, wherein, The ingot has a cylindrical shape; Multiple modified portions are formed in the planned cutting surface, each of which is formed along one of multiple parallel virtual lines orthogonal to the axial direction of the ingot; as well as The energy of the laser beam radiating to the edge of the ingot is set to be greater than the energy of the other parts.

8. The manufacturing method according to claim 1 or 2, wherein, The ingot has a cylindrical shape; Multiple modified portions are formed in the planned cutting surface, each of which is formed along one of multiple parallel virtual lines orthogonal to the axial direction of the ingot; and The spacing between virtual lines positioned away from the central axis of the ingot is set to be narrower than the spacing between virtual lines positioned closer to the central axis.

9. The manufacturing method according to claim 1 or 2, wherein, Multiple modified sections are formed along each of a plurality of mutually parallel virtual lines on the planned cut surface; and The virtual line is a line that is parallel to the direction in which an offset angle is formed on the ingot when viewed from the axial direction of the ingot.

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