Wafer manufacturing method and wafer manufacturing system

Abstract

The present invention provides a wafer manufacturing method that facilitates the proper separation of wafers from ingots. [Solution] A wafer manufacturing method for manufacturing wafers from a crystalline ingot, comprising: a preparation step of preparing an ingot having a wafer formation region corresponding to a wafer and an outer peripheral excess region that includes the outer peripheral surface of the ingot and surrounds the wafer formation region; a separation layer formation step of forming a separation layer inside the ingot that does not reach the outer peripheral surface of the ingot by irradiating the inside of the outer peripheral surface of the ingot with a laser beam focusing point that is transparent to the ingot positioned inside the ingot and moving the ingot and the focusing point relatively; an exposure step of processing the outer peripheral excess region of the ingot to expose the side surface of the wafer formation region; and a separation step of obtaining a wafer by dividing the ingot starting from the separation layer after the separation layer formation step and the exposure step.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a wafer and a wafer manufacturing system for manufacturing a wafer from an ingot.

Background Art

[0002] In the manufacturing process of device chips, wafers in which devices are formed in a plurality of regions partitioned by a plurality of streets (division planned lines) arranged in a grid pattern are used. By dividing this wafer along the streets and fragmenting it, device chips equipped with devices are manufactured. The device chips are incorporated into various electronic devices such as mobile phones and personal computers.

[0003] Generally, wafers are manufactured by slicing a cylindrical ingot with a wire saw. However, the wire provided in the wire saw may have a diameter equal to or greater than the thickness of the wafer, making it difficult to precisely process the ingot. Therefore, when slicing the ingot with a wire saw, it is necessary to ensure a certain amount of cutting allowance, and a considerable amount of the ingot is removed without being used as a wafer. As a result, the number of wafers obtained from one ingot is limited, increasing the cost.

[0004] Therefore, a method has been proposed in which a modified region and a separation layer composed of cracks are formed inside the ingot by irradiating the ingot with a laser beam (see, for example, Patent Document 1). Since the region where the separation layer of the ingot is formed becomes more brittle than other regions, when an external force is applied to the ingot in which the separation layer is formed, the ingot is divided starting from the separation layer, and the wafer is separated from the ingot. By using such a technique, the removal amount of the ingot in the process of separating the wafer from the ingot is reduced, and the productivity of the wafer is improved.

Prior Art Documents

Patent Documents

[0005] [Patent Document 1] Japanese Patent Publication No. 2016-111143 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] To properly separate wafers from ingots, it is desirable for a high-quality separation layer to form inside the ingot. However, it has been confirmed that crystal defects are prone to forming in ingots, particularly on and near the outer surface. When a laser beam is irradiated onto an ingot in such a state to form a separation layer, the laser beam may irradiate crystal defects on and near the outer surface of the ingot, causing partial changes in the properties of the separation layer or causing cracks generated by the laser beam irradiation to propagate in unexpected directions. This degrades the quality of the separation layer, making it difficult for the separation layer to function as a separation starting point. As a result, proper separation of wafers from ingots may be hindered.

[0007] This invention has been made in view of the above problems and aims to provide a wafer manufacturing method and a wafer manufacturing system that can facilitate the proper separation of wafers from ingots. [Means for solving the problem]

[0008] According to one aspect of the present invention, a wafer manufacturing method is provided for manufacturing a wafer from a crystalline ingot, comprising: a preparation step of preparing an ingot having a wafer forming region corresponding to the wafer and an outer peripheral excess region that includes the outer peripheral surface of the ingot and surrounds the wafer forming region; a separation layer formation step of irradiating the inside of the outer peripheral surface of the ingot with a laser beam that is transparent to the ingot, while relatively moving the ingot and the focal point inside the ingot, thereby forming a separation layer that does not reach the outer peripheral surface of the ingot, at least inside the wafer forming region of the ingot; and an exposure step of processing the outer peripheral excess region of the ingot to expose the side surface of the wafer forming region.

[0009] Preferably, the exposure step is performed after the separation layer formation step, in which the separation layer is exposed on the side surface of the wafer formation region. Preferably, the wafer manufacturing method further comprises a separation step, after the separation layer formation step and the exposure step, in which the ingot is divided starting from the separation layer to obtain the wafer.

[0010] Preferably, the preparation step includes an inspection step of inspecting the ingot and determining whether there are any abnormal areas including at least one of the following: a crystal defect region in which crystal defects exist; a heteromorphic region in which the crystal shape differs from other regions; and an abnormal concentration region in which the concentration of impurities contained in the ingot is outside the permissible range; and an outer perimeter surplus region setting step of setting the outer perimeter surplus region so that the abnormal area is included in the outer perimeter surplus region when it is determined in the inspection step that the abnormal area exists within a predetermined range from the outer perimeter surface of the ingot.

[0011] Furthermore, preferably, the exposure step removes the region from the outer circumferential surface of the ingot to the wafer formation region. Alternatively, preferably, the exposure step forms a groove along the outer circumferential edge of the wafer formation region to a depth from the surface of the ingot to the separation layer.

[0012] Furthermore, according to another aspect of the present invention, a wafer manufacturing system for manufacturing wafers from a crystalline ingot is provided, comprising: a laser processing apparatus that positions a focal point of a laser beam that is transparent to the ingot, which has a wafer forming region corresponding to the wafer and an outer peripheral excess region that includes the outer peripheral surface of the ingot and surrounds the wafer forming region, and irradiates the inside of the outer peripheral surface of the ingot with the laser beam while relatively moving the ingot and the focal point, thereby forming a separation layer that does not reach the outer peripheral surface of the ingot, at least inside the wafer forming region of the ingot; and an exposure processing apparatus that processes the outer peripheral excess region of the ingot to expose the side surface of the wafer forming region.

[0013] Preferably, the wafer manufacturing system further includes a separation device that divides the ingot starting from the separation layer. [Effects of the Invention]

[0014] In a wafer manufacturing method and wafer manufacturing system according to one aspect of the present invention, the separation layer, which functions as the starting point for separating the wafer from the ingot, is formed so as not to reach the outer surface of the ingot. As a result, the laser beam used to form the separation layer is less likely to irradiate crystal defects that may exist on or near the outer surface of the ingot, and a high-quality separation layer is formed. Consequently, wafers are more easily separated from the ingot. [Brief explanation of the drawing]

[0015] [Figure 1] Figure 1(A) is a perspective view showing the ingot, and Figure 1(B) is a plan view showing the ingot. [Figure 2] This is a flowchart showing the wafer manufacturing method. [Figure 3] Figure 3(A) is a plan view showing the ingot during the inspection process, and Figure 3(B) is a plan view showing the ingot during the outer perimeter excess area setting process. [Figure 4]FIG. 4(A) is a perspective view showing an ingot in the separation layer forming step, and FIG. 4(B) is a cross-sectional view showing the ingot after the separation layer forming step. [Figure 5] FIG. 5(A) is a partial cross-sectional front view showing an ingot being machined by cutting in the exposure step, and FIG. 5(B) is a partial cross-sectional front view showing an ingot being machined by other cutting in the exposure step. [Figure 6] It is a partial cross-sectional front view showing an ingot being ground in the exposure step. [Figure 7] FIG. 7(A) is a partial cross-sectional front view showing a separation device holding an ingot, and FIG. 7(B) is a partial cross-sectional front view showing a separation device separating a wafer from an ingot. [Figure 8] It is a partial cross-sectional front view showing an ingot in the planarization step. [Figure 9] It is a partial cross-sectional front view showing an ingot in the exposure step according to a modified example. [Figure 10] FIG. 10(A) is a partial cross-sectional front view showing an ingot in which a groove is formed by cutting, and FIG. 10(B) is a partial cross-sectional front view showing an ingot in which a groove is formed by laser processing.

Embodiments for Carrying Out the Invention

[0016] Hereinafter, embodiments according to an aspect of the present invention will be described with reference to the accompanying drawings. First, a configuration example of an ingot that can be used in the method for manufacturing a wafer according to the present embodiment will be described. FIG. 1(A) is a perspective view showing an ingot 11, and FIG. 1(B) is a plan view showing the ingot 11.

[0017] The ingot 11 is a base material used for forming a wafer (substrate), and is typically a columnar ingot having crystallinity. By separating a part of the ingot 11 from the main body of the ingot 11, a wafer with a predetermined thickness can be obtained. For example, the ingot 11 is a single crystal ingot made of a semiconductor material such as silicon, silicon carbide, gallium nitride, or gallium oxide. In this case, a single crystal semiconductor wafer can be obtained by separating the wafer from the ingot 11.

[0018] The ingot 11 has a first surface (front surface) 11a, a second surface (back surface) 11b located on the opposite side of the first surface 11a, and an outer peripheral surface (side surface) 11c connected to the outer peripheral edges of the first surface 11a and the second surface 11b. The first surface 11a and the second surface 11b are arranged substantially parallel to each other, and the outer peripheral surface 11c is arranged substantially perpendicular to the first surface 11a and the second surface 11b. The diameter of the ingot 11 is appropriately selected according to the diameter of the wafer (6 inches, 8 inches, etc.) to be manufactured. Note that a notch such as an orientation flat indicating the crystal orientation of the ingot 11 may be provided on the outer peripheral portion of the ingot 11.

[0019] In the ingot 11, a wafer formation region 13 corresponding to the wafer separated from the ingot 11 and an outer peripheral surplus region 15 surrounding the wafer formation region 13 are set. In FIGS. 1(A) and 1(B), the virtual boundary between the wafer formation region 13 and the outer peripheral surplus region 15 is shown by a dashed line.

[0020] For example, the wafer formation region 13 is a cylindrical region containing the center of the ingot 11, and corresponds to the region that will be separated from the ingot 11 as a wafer in a later process. In other words, the wafer formation region 13 of the ingot 11 is substantially used for wafer formation. The diameter of the wafer formation region 13 corresponds to the diameter of the wafer separated from the ingot 11, but it may be larger than the diameter of the wafer that will ultimately be used as a product. Specifically, a wafer with the same diameter as the wafer formation region 13 may be manufactured by separating the wafer formation region 13 from the ingot 11, and then this wafer may be further processed in other processes to ultimately manufacture a wafer with a desired diameter (6 inches, 8 inches, etc.).

[0021] The outer peripheral excess region 15 is a hollow cylindrical region including the outer peripheral surface 11c of the ingot 11, and corresponds to the region within a predetermined range (for example, within 50 mm) from the outer peripheral surface 11c of the ingot 11. As described later, the outer peripheral excess region 15 is a region that is removed in the process of separating the wafer from the ingot 11, and is not used in the formation of the wafer in practice.

[0022] Next, a specific example of a wafer manufacturing method for producing wafers from the ingot 11 described above will be explained. Figure 2 is a flowchart of the wafer manufacturing method. The details of each step included in the wafer manufacturing method according to this embodiment will be explained below.

[0023] When manufacturing a wafer from an ingot 11, first, an ingot 11 including a wafer formation region 13 and an outer peripheral excess region 15 is prepared (preparation step S1). In preparation step S1, the ingot 11 shown in Figures 1(A) and 1(B) is prepared. Note that the implementer of the wafer manufacturing method according to this embodiment may form the ingot 11 themselves, or may obtain the ingot 11 from another manufacturer.

[0024] In preparation step S1, a wafer formation region 13 and an outer peripheral excess region 15 are defined on the ingot 11. Specifically, the wafer formation region 13 and the outer peripheral excess region 15 are specified so that the shape and size of the wafer formation region 13 and the shape and size of the wafer to be manufactured are roughly matched.

[0025] In addition, in preparation step S1, the wafer forming region 13 and the outer perimeter excess region 15 may be set such that a predetermined abnormal part contained in the ingot 11 is included in the outer perimeter excess region 15. Specifically, an inspection step S11 for checking whether or not an abnormal part exists in the ingot 11, and an outer perimeter excess region setting step S12 for setting the outer perimeter excess region 15 based on the location of the abnormal part detected in inspection step S11, may be optionally performed.

[0026] Figure 3(A) is a plan view showing the ingot 11 in inspection process S11. The ingot 11 may contain crystal defect regions 19A where crystal defects exist, heteromorphic regions 19B where the crystal form is different from other regions, and abnormal concentration regions 19C where the concentration of impurities contained in the ingot 11 is outside the acceptable range. Therefore, for example, in inspection process S11, one, two, or all of the crystal defect regions 19A, heteromorphic regions 19B, and abnormal concentration regions 19C are detected as abnormal parts 17.

[0027] The crystal defect region 19A is a region where crystal defects exist, and the crystallinity of the crystal defect region 19A differs from the crystallinity of other regions of the ingot 11 (regions where crystal defects do not exist). Furthermore, the heteromorph region 19B is a region whose crystal form differs from other regions, and the crystallinity of the heteromorph region 19B differs from the crystallinity of other regions of the ingot 11. Therefore, by measuring the crystallinity of the ingot 11, the presence or absence of the crystal defect region 19A and the heteromorph region 19B can be checked.

[0028] There are no restrictions on the method for inspecting the crystallinity of ingot 11. For example, the crystallinity of ingot 11 can be detected by observation using an electron microscope or optical microscope such as photoluminescence, SEM (Scanning Electron Microscope), or STEM (Scanning Transmission Electron Microscope), or by X-ray topography or Raman spectroscopy. If crystal defect regions 19A and heteromorphic regions 19B are detected during the inspection of ingot 11, the location and extent of the crystal defect regions 19A and heteromorphic regions 19B are recorded.

[0029] Furthermore, it has been confirmed that crystal defect regions 19A and heteromorphic regions 19B are particularly likely to occur on and near the outer surface 11c of the ingot 11. This phenomenon is presumed to be partly due to the fact that a temperature gradient is generated in the ingot 11 during the crystal growth process, and the temperature difference between the inside of the ingot 11 and the outer surface 11c makes it easier for crystalline disorder to occur.

[0030] Furthermore, ingot 11 may contain impurities that are different components from the materials that make up ingot 11. If there are regions with abnormally high concentrations of impurities in ingot 11, it may negatively affect the quality of wafers manufactured from ingot 11.

[0031] For example, ingot 11 may unintentionally contain impurities, and there may be regions where the concentration of these impurities is particularly high. In addition, impurities (dopants) may be intentionally added to ingot 11 to control its electrical properties. Ideally, dopants are uniformly dispersed throughout ingot 11, but in reality, ingot 11 may have uneven concentrations of dopants, and there may be regions where dopants are excessive and / or deficient.

[0032] Therefore, in inspection step S11, the concentration of impurities contained in the ingot 11 may be measured, and it may be checked for the presence or absence of an abnormal concentration region 19C in which the concentration of impurities is outside a predetermined permissible range. There are no restrictions on the method for measuring the concentration of impurities contained in the ingot 11. For example, the concentration of impurities may be determined based on the resistivity value of the ingot 11 measured using the eddy current method, or the concentration of impurities may be determined based on the fluorescence spectrum measured by a spectrofluorometer. Furthermore, X-ray fluorescence analysis (XRF), X-ray photoelectron spectroscopy (XPS), energy-dispersive X-ray spectroscopy (EDX), Auger electron spectroscopy (AES), etc., can also be used to determine the concentration of impurities.

[0033] After measuring the concentration of impurities contained in the ingot 11, it is checked whether or not there is an abnormal concentration region 19C within the ingot 11 where the concentration of impurities is outside the acceptable range. Specifically, upper and / or lower limits for the concentration of impurities are set in advance, and the ingot 11 is inspected to see if there is a region where the concentration of impurities exceeds the upper limit and / or falls below the lower limit. If an abnormal concentration region 19C is detected, its location and range are recorded.

[0034] The permissible range for impurity concentration is set appropriately depending on the material of the ingot 11, the intended use of the wafers separated from the ingot 11, etc. As an example, let's assume that the ingot 11 is a SiC ingot and the concentration of impurities (dopants) is determined based on the resistivity value of the ingot 11 measured by the eddy current method. In this case, the permissible range for the resistivity value of the ingot 11 is set to, for example, ±10 mΩ·cm from the reference value (ideal resistivity value), preferably ±5 mΩ·cm. If there is a region in the ingot 11 where the resistivity value is outside the permissible range, the dopant concentration in that region is also determined to be outside the permissible range, and that region is set as the abnormal concentration region 19C.

[0035] In the inspection of the ingot 11 described above, the crystal defect region 19A, the heteromorph region 19B, and the abnormal concentration region 19C are set as abnormal parts 17, and the location and extent of the abnormal parts 17 in the ingot 11 are recorded. However, in inspection step S11, one or two of the crystal defect region 19A, the heteromorph region 19B, and the abnormal concentration region 19C may be set as abnormal parts 17. Alternatively, a predetermined region other than the crystal defect region 19A, the heteromorph region 19B, and the abnormal concentration region 19C may be set as abnormal parts 17.

[0036] Figure 3(B) is a plan view showing the ingot 11 in the outer perimeter excess area setting step S12. In the outer perimeter excess area setting step S12, if it is determined in the inspection step S11 that an abnormal part 17 exists within a predetermined range from the outer perimeter surface 11c of the ingot 11, the outer perimeter excess area 15 is set so that the abnormal part 17 is included in the outer perimeter excess area 15.

[0037] Specifically, first, based on the location and range of the abnormal part 17 detected in inspection step S11, it is confirmed whether or not the abnormal part 17 exists in a target area within a predetermined range from the outer peripheral surface 11c of the ingot 11. If the abnormal part 17 exists in the target area, the outer peripheral excess area 15 is set so that the abnormal part 17 is included in the outer peripheral excess area 15. In this way, the wafer formation area 13 and the outer peripheral excess area 15 can be specified so that the abnormal part 17 present on the outer peripheral of the ingot 11 is included in the wafer formation area 13 as much as possible.

[0038] Furthermore, the wafer formation region 13 and the outer peripheral excess region 15 do not necessarily have to coincide at their centers. For example, if the abnormal portion 17 is concentrated in a part of the ingot 11 (the lower right region of the ingot 11 in Figure 3(B)), the center of the wafer formation region 13 may be shifted to the opposite side of the region where the abnormal portion 17 is concentrated (upper left in Figure 3(B)) from the center of the ingot 11. This makes it possible to include the abnormal portion 17 in the outer peripheral excess region 15 while maintaining the diameter of the wafer formation region 13 above a certain level.

[0039] Next, wafers are manufactured from the ingot 11 by processing the ingot 11 prepared in the preparation step S1 described above. Specifically, the wafers are separated from the ingot 11 by sequentially performing the separation layer formation step S2, the exposure step S3, and the separation step S4. Specific examples of each step are described below.

[0040] Figure 4(A) is a perspective view showing the ingot 11 in the separation layer formation process S2. For example, in the separation layer formation process S2, the ingot 11 is laser-processed using a laser processing device 10 to form a separation layer inside the ingot 11 that functions as a separation starting point. In Figure 4(A) and subsequent figures, the X-axis direction (first horizontal direction, left-right direction) and the Y-axis direction (second horizontal direction, front-back direction) are perpendicular to each other. The Z-axis direction (up-down direction, height direction, vertical direction) is perpendicular to the X-axis and Y-axis directions.

[0041] The laser processing apparatus 10 includes a chuck table (holding table) 12 for holding an ingot 11. The upper surface of the chuck table 12 is a flat surface that is generally parallel to the horizontal plane (XY plane) and forms a circular holding surface 12a for holding the ingot 11. The holding surface 12a is connected to a suction source (not shown), such as an ejector, via a flow path (not shown), a valve (not shown), etc., formed inside the chuck table 12.

[0042] The chuck table 12 is connected to a moving unit (not shown) that moves the chuck table 12 and a rotational drive source (not shown) that rotates the chuck table 12. The moving unit is composed of, for example, a ball screw type moving mechanism and moves the chuck table 12 along the X-axis and Y-axis. The rotational drive source is composed of a motor or the like and rotates the chuck table 12 around a rotation axis that is roughly parallel to the Z-axis.

[0043] The laser processing apparatus 10 also includes a laser irradiation unit 14 that irradiates the ingot 11 with a laser beam 20. The laser irradiation unit 14 includes a laser oscillator (not shown) such as a YAG laser, YVO4 laser, or YLF laser that emits a pulsed laser beam 20, and a housing 16 and a laser processing head 18 located above the chuck table 12. The housing 16 is formed in a hollow cylindrical shape and is arranged along the Y-axis. The laser processing head 18 that irradiates the laser beam 20 toward the chuck table 12 is mounted on the tip of the housing 16.

[0044] The housing 16 and the laser processing head 18 house an attenuator that adjusts the output of the laser beam 20 emitted from the laser oscillator, and an optical system that guides the laser beam 20 emitted from the laser oscillator to the ingot 11 held by the chuck table 12. The optical system consists of optical elements such as lenses, mirrors, a polarizing beam splitter (PBS), a diffractive optical element (DOE), and an LCOS-SLM (Liquid Crystal On Silicon - Spatial Light Modulator), and controls the direction of travel, shape, and focusing position of the laser beam 20.

[0045] The laser processing head 18 houses a light condenser (not shown), which is a component of the optical system. The light condenser is equipped with a focusing lens such as an fθ lens, and focuses the laser beam 20 to irradiate the ingot 11. Laser processing is performed on the ingot 11 by irradiating the ingot 11 with the laser beam 20 from the laser processing head 18.

[0046] Furthermore, the laser irradiation unit 14 is equipped with an imaging unit 22 for imaging the subject. For example, the imaging unit 22 is fixed to the housing 16 and installed adjacent to the laser processing head 18. The imaging unit 22 is equipped with an image sensor such as a CCD (Charged-Coupled Devices) sensor or a CMOS (Complementary Metal-Oxide-Semiconductor) sensor and images the ingot 11 held by the chuck table 12. There are no restrictions on the type of imaging unit 22; for example, a visible light camera or an infrared camera can be used.

[0047] The imaging unit 22 captures an image of the ingot 11. Based on the image acquired by the imaging unit 22, the ingot 11 is aligned with the laser processing head 18, and the condition of the ingot 11 is checked.

[0048] The housing 16 may also be connected to a moving unit (not shown) for moving the housing 16. For example, the moving unit may be composed of a ball screw type moving mechanism and move (raise and lower) the housing 16 along the Z-axis direction together with the laser processing head 18 and the imaging unit 22. This allows for adjustment of the height position of the focal point of the laser beam 20 and focusing of the imaging unit 22.

[0049] In the separation layer formation step S2, the ingot 11 is first held by the chuck table 12. For example, the ingot 11 is placed on the chuck table 12 such that the first surface 11a is exposed upwards and the second surface 11b faces the holding surface 12a. In this state, when the suction force (negative pressure) of the suction source is applied to the holding surface 12a, the ingot 11 is held by the chuck table 12.

[0050] Next, the laser irradiation unit 14 is activated, and the laser beam 20 is irradiated onto the ingot 11 from the laser processing head 18. This performs laser processing on the ingot 11. The irradiation conditions for the laser beam 20 are set so that a separation layer, which functions as a separation starting point, is formed inside the ingot 11.

[0051] Specifically, the irradiation conditions of the laser beam 20 are set so that the area of ​​the ingot 11 irradiated with the laser beam 20 is modified (altered) to form a modified region (altered region) 21. More specifically, the wavelength of the laser beam 20 is set so that at least a portion of the laser beam 20 penetrates the ingot 11. That is, the laser beam 20 is a pulsed laser beam that is penetrating to the ingot 11. Other irradiation conditions of the laser beam 20 are also set as appropriate so that the modified region 21 is properly formed in the ingot 11. For example, if the ingot 11 is a SiC ingot, the irradiation conditions of the laser beam 20 can be set as follows. Wavelength: 1064nm Average output: 2~4.5W Repeat frequency: 80kHz Machining feed rate: 120~260 mm / s

[0052] When the laser beam 20 is irradiated onto the ingot 11, the ingot 11 is first imaged by the imaging unit 22, and an image of the first surface 11a of the ingot 11 is acquired. Then, based on the acquired image, the positional relationship between the ingot 11 and the laser processing head 18 is adjusted. Specifically, the position of the chuck table 12 in the X-axis and Y-axis directions is adjusted so that the focal point of the laser beam 20 coincides with the edge of the ingot 11 in a plan view. In addition, the height position of the focal point of the laser beam 20 is adjusted to coincide with the height position inside the ingot 11 (between the first surface 11a and the second surface 11b). The difference in height between the first surface 11a of the ingot 11 and the focal point of the laser beam 20 at this time corresponds to the depth of the modified region 21 formed inside the ingot 11.

[0053] Then, while irradiating the laser beam 20 from the laser processing head 18, the chuck table 12 is moved along the X-axis direction at a predetermined processing feed rate, causing the ingot 11 and the focal point of the laser beam 20 to move relative to each other along the X-axis direction (processing feed). As a result, with the focal point of the laser beam 20 positioned inside the ingot 11, the laser beam 20 is irradiated from the first surface 11a side of the ingot 11 and scanned along the X-axis direction.

[0054] Subsequently, the chuck table 12 is moved along the Y-axis by a predetermined index amount (for example, about 250 to 400 μm), and the ingot 11 and the laser processing head 18 are moved relative to each other along the Y-axis (indexing feed). Then, the processing feed is performed while irradiating the laser beam 20 from the laser processing head 18 using the same procedure as above. By repeating this process, multiple generally parallel modified regions 21 are formed at predetermined intervals at predetermined depths inside the ingot 11.

[0055] The laser beam 20 may be irradiated onto the ingot 11 only on the forward pass of the processing feed, or it may be irradiated on both the forward and return passes of the processing feed. Alternatively, instead of moving the chuck table 12, the laser beam 20 may be scanned by moving the laser processing head 18. Furthermore, instead of moving the chuck table 12 or the laser processing head 18, a scanning optical system for scanning the laser beam 20 may be mounted on the laser irradiation unit 14. For example, the scanning optical system may include optical elements such as a galvanometer scanner, an acousto-optic element (AOD), and a polygon mirror.

[0056] As described above, when the ingot 11 is irradiated with the laser beam 20, the region within the ingot 11 where the focal point of the laser beam 20 is located and its surrounding area expand, causing disorder (strain) in the crystal structure, and thus modifying the ingot 11. As a result, a linear modified region 21 is formed inside the ingot 11 along the X-axis. In addition, internal stress acts within the modified region 21, causing multiple microcracks to form, and these cracks extend from the modified region 21 in a direction intersecting the thickness direction of the ingot 11.

[0057] Then, by forming multiple modified regions 21 at predetermined intervals, the modified regions 21 and cracks are formed throughout the entire ingot 11. As a result, a separation layer (modified layer, altered layer) 23, composed of the multiple modified regions 21 and cracks, is formed at a predetermined depth inside the ingot 11. The depth of the separation layer 23 (the distance between the first surface 11a of the ingot 11 and the separation layer 23) corresponds to the thickness of the wafer (see Figure 7(B)) that will be separated from the ingot 11 in a later process.

[0058] In this embodiment, the laser beam 20 is irradiated to the inside of the outer peripheral surface 11c of the ingot 11. Specifically, the laser beam 20 is scanned in at least the wafer formation region 13 of the ingot 11 (see Figures 1(A) and 1(B)), but is not irradiated to the outer peripheral excess region 15 (see Figures 1(A) and 1(B)), or is irradiated only to a part of the outer peripheral excess region 15 adjacent to the wafer formation region 13. Therefore, the laser beam 20 is not irradiated within a predetermined range from the outer peripheral surface 11c of the ingot 11 (part or all of the outer peripheral excess region 15).

[0059] Figure 4(B) is a cross-sectional view showing the ingot 11 after the separation layer formation process S2. For example, if the laser beam 20 is irradiated only to the wafer formation region 13, a modified region 21 is formed in the wafer formation region 13, but the laser beam 20 is not irradiated to the outer peripheral excess region 15, and no modified region 21 is formed there. As a result, a separation layer 23 is formed inside the ingot 11 that does not reach the outer peripheral surface 11c, and the separation layer 23 is not exposed at the outer peripheral surface 11c.

[0060] As mentioned above, crystal defects are likely to occur on the outer surface 11c of the ingot 11 and its vicinity due to temperature gradients during crystal growth of the ingot 11. If the laser beam 20 is scanned from one end of the ingot 11 to the other, the laser beam 20 will irradiate the outer surface of the ingot 11 where crystal defects are likely to exist. This can cause the properties of the separation layer 23 to change partially, or cracks generated by the irradiation of the laser beam 20 to propagate in unexpected directions. As a result, the quality of the separation layer 23 deteriorates, and the separation layer 23 becomes less able to function properly as a separation starting point.

[0061] On the other hand, in this embodiment, as described above, the laser beam 20 is not irradiated within a predetermined range from the outer surface 11c of the ingot 11. As a result, the laser beam 20 is less likely to irradiate crystal defects, and the deterioration of the quality of the separation layer 23 is suppressed.

[0062] Next, the excess outer region 15 of the ingot 11 is processed to expose the side surface of the wafer formation region 13 (exposure process S3). Figure 5(A) is a partial cross-sectional front view showing the ingot 11 being cut in the exposure process S3. For example, in the exposure process S3, the side surface of the wafer formation region 13 is exposed by cutting the ingot 11 using a cutting device 30.

[0063] The cutting device 30 includes a chuck table (holding table) 32 for holding the ingot 11. The upper surface of the chuck table 32 is a flat surface that is generally parallel to the horizontal plane (XY plane) and forms a circular holding surface 32a for holding the ingot 11. The holding surface 32a is connected to a suction source (not shown), such as an ejector, via a flow path (not shown), a valve (not shown), etc., formed inside the chuck table 32.

[0064] The chuck table 32 is connected to a moving unit (not shown) that moves the chuck table 32 and a rotational drive source (not shown) that rotates the chuck table 32. The moving unit is composed of, for example, a ball screw type moving mechanism and moves the chuck table 32 along the X-axis. The rotational drive source is composed of a motor or the like and rotates the chuck table 32 around a rotation axis that is roughly parallel to the Z-axis.

[0065] Above the chuck table 32, a cutting unit 34 is provided for cutting the ingot 11. The cutting unit 34 is equipped with a columnar spindle 36 arranged along the Y-axis. An annular cutting blade 38 for cutting the ingot 11 is attached to the tip (one end) of the spindle 36 by a fixing device such as a fixing nut (not shown). A rotational drive source (not shown), such as a motor, is connected to the base (other end) of the spindle 36 to rotate the spindle 36 around a rotation axis that is roughly parallel to the Y-axis. When the spindle 36 is rotated by the rotational drive source, the cutting blade 38 rotates around the rotation axis that is roughly parallel to the Y-axis.

[0066] As the cutting blade 38, for example, a hub-type cutting blade (hub blade) can be used. The hub blade comprises an annular hub base made of a metal such as an aluminum alloy, and an annular cutting edge formed along the outer edge of the hub base. The cutting edge of the hub blade is made of an electroformed grinding wheel containing abrasive grains made of diamond, cubic boron nitride (cBN), etc., and a binder such as a nickel plating layer that fixes the abrasive grains. However, a washer-type cutting blade (washer blade) can also be used as the cutting blade 38. The washer blade consists only of an annular cutting edge containing abrasive grains and a binder made of metal, ceramics, resin, etc. that fixes the abrasive grains.

[0067] The cutting unit 34 is connected to a moving unit (not shown) that moves the cutting unit 34. The moving unit is configured, for example, by a ball screw type moving mechanism and moves the cutting unit 34 along the Y-axis and Z-axis directions.

[0068] In the exposure process S3, the ingot 11 is first held by the chuck table 32. Specifically, the ingot 11 is placed on the chuck table 32 such that the first surface 11a is exposed upwards and the second surface 11b faces the holding surface 32a. In this state, when the suction force (negative pressure) of the suction source is applied to the holding surface 32a, the ingot 11 is held by the chuck table 32.

[0069] Next, the positional relationship between the ingot 11 and the cutting blade 38 is adjusted by moving the chuck table 32 and / or the cutting unit 34. Specifically, the positions of the chuck table 32 and the cutting unit 34 are set so that the cutting blade 38 is positioned to the side of the ingot 11. At this time, the cutting unit 34 is positioned so that the lower end of the cutting blade 38 is at the same height as the separation layer 23 formed in the ingot 11, or below the separation layer 23.

[0070] Next, while rotating the chuck table 32 and the cutting blade 38, the chuck table 32 and the cutting unit 34 are moved relative to each other in a direction that brings the ingot 11 and the cutting blade 38 closer together. For example, the cutting unit 34 is moved toward the ingot 11 along the Y-axis. This causes the rotating cutting blade 38 to contact the outer circumferential surface 11c of the ingot 11. As a result, the outer circumferential surface 11c of the ingot 11 is cut in an annular shape along the circumferential direction of the ingot 11.

[0071] Subsequently, while maintaining the rotation of the chuck table 32 and the cutting blade 38, the chuck table 32 and the cutting unit 34 are moved relative to each other further so that the cutting blade 38 approaches the center of the ingot 11. As a result, the excess outer region 15 of the ingot 11 is gradually cut away from the outer surface 11c toward the center of the ingot 11. Cutting of the ingot 11 is then continued until the cutting blade 38 reaches the wafer formation region 13.

[0072] When the cutting blade 38 reaches the wafer formation region 13, an annular region extending from the outer peripheral surface 11c of the ingot 11 to the wafer formation region 13 is removed. As a result, an annular step is formed on the first surface 11a side of the outer peripheral portion of the ingot 11, and the side surface 13a of the wafer formation region 13 is exposed. Consequently, the edge of the separation layer 23 formed inside the ingot 11 is exposed on the side surface 13a of the wafer formation region 13.

[0073] As described above, in the exposure process S3, the excess outer peripheral region 15 of the ingot 11 is processed to expose the side surface 13a of the wafer formation region 13, and the separation layer 23 is exposed on the side surface 13a. The processing method of the excess outer peripheral region 15 can be changed as appropriate, as long as it is possible to expose the side surface 13a of the wafer formation region 13.

[0074] Figure 5(B) is a partial cross-sectional front view showing the ingot 11 which is subjected to other cutting processes in the exposure process S3. For example, in the exposure process S3, the outer peripheral excess region 15 may be cut with a cutting blade 38A that is thicker than the cutting blade 38 to expose the side surface 13a of the wafer formation region 13. Specifically, the cutting apparatus 30 shown in Figure 5(B) includes a cutting unit 34A instead of the cutting unit 34. The configuration and function of the cutting unit 34A are the same as those of the cutting unit 34, except that a cutting blade 38A that is thicker than the cutting blade 38 is mounted on the tip of the spindle 36A.

[0075] The thickness of the cutting blade 38A is greater than or equal to the width of the outer peripheral excess region 15 of the ingot 11 (the distance from the outer peripheral surface 11c to the boundary between the wafer formation region 13 and the outer peripheral excess region 15). Then, in the exposure process S3, after positioning the cutting blade 38A directly above the outer peripheral excess region 15 of the ingot 11, the cutting unit 34A is lowered along the Z-axis while rotating the chuck table 32 and the cutting blade 38A. As a result, the cutting blade 38A contacts the first surface 11a side of the outer peripheral excess region 15 of the ingot 11, and the outer peripheral excess region 15 is cut. The cutting of the ingot 11 is continued until the cutting blade 38A reaches the separation layer 23.

[0076] When the cutting blade 38 reaches the separation layer 23, an annular region extending from the outer peripheral surface 11c of the ingot 11 to the wafer formation region 13 is removed. As a result, the side surface 13a of the wafer formation region 13 is exposed, and the edge of the separation layer 23 is exposed on the side surface 13a of the wafer formation region 13. In this way, when processing the excess outer peripheral region 15 of the ingot 11, the cutting blade 38A may be made to cut from the first surface 11a side (top surface side) of the ingot 11.

[0077] Furthermore, in the exposure process S3, the side surface 13a of the wafer formation region 13 may be exposed by performing a process other than cutting on the excess outer peripheral region 15 of the ingot 11. Figure 6 is a partial cross-sectional front view showing the ingot 11 being ground in the exposure process S3. For example, in the exposure process S3, the side surface of the wafer formation region 13 can also be exposed by grinding the ingot 11 using a grinding device 40.

[0078] The grinding device 40 includes a chuck table (holding table) 42 for holding the ingot 11. The upper surface of the chuck table 42 forms a circular holding surface 42a for holding the ingot 11. The holding surface 42a is connected to a suction source (not shown), such as an ejector, via a flow path (not shown), a valve (not shown), etc., formed inside the chuck table 42.

[0079] The chuck table 42 is connected to a moving unit (not shown) that moves the chuck table 42 and a rotational drive source (not shown) that rotates the chuck table 42. The moving unit is composed of, for example, a ball screw type moving mechanism or a turntable, and moves the chuck table 42 along the horizontal direction (XY plane direction). The rotational drive source is composed of a motor or the like, and rotates the chuck table 42 around a rotation axis that is roughly parallel to the Z-axis direction.

[0080] The grinding unit 44 is located above the chuck table 42 and is used to grind the ingot 11. The grinding unit 44 is equipped with a cylindrical spindle 46 arranged along the Z-axis. A disc-shaped wheel mount 48 made of metal such as SUS (stainless steel) is fixed to the tip (lower end) of the spindle 46. A rotational drive source (not shown), such as a motor, is connected to the base (upper end) of the spindle 46 to rotate the spindle 46.

[0081] An annular grinding wheel 50 for grinding the ingot 11 is mounted on the underside of the wheel mount 48. For example, the grinding wheel 50 is detachably fixed to the wheel mount 48 by fasteners such as bolts.

[0082] The grinding wheel 50 comprises an annular wheel base 52 and a plurality of grinding wheels 54 fixed to the wheel base 52. The wheel base 52 is made of a metal such as aluminum or stainless steel and is formed to be approximately the same diameter as the wheel mount 48. The plurality of grinding wheels 54 are fixed to the lower side of the wheel base 52. The upper side of the wheel base 52 is mounted to the lower side of the wheel mount 48.

[0083] For example, the grinding wheel 54 is formed in a rectangular parallelepiped shape and arranged in a ring shape at roughly equal intervals along the outer edge of the wheel base 52. The lower surface of the grinding wheel 54 constitutes the grinding surface for grinding the ingot 11. The grinding wheel 54 can be formed by fixing abrasive grains made of diamond, cBN (cubic boron nitride), etc., with a binder (bonding material) such as metal bond, resin bond, or vitrified bond. However, there are no restrictions on the number, shape, material, structure, size, etc., of the grinding wheel 54.

[0084] When the rotational drive source connected to the spindle 46 is activated, the spindle 46, wheel mount 48, and grinding wheel 50 rotate around a rotation axis that is roughly parallel to the Z-axis direction. As a result, the multiple grinding wheels 54 each rotate along an annular pivot path centered on the rotation axis.

[0085] In the exposure process S3, the ingot 11 is first held by the chuck table 42. Specifically, the ingot 11 is placed on the chuck table 42 such that the first surface 11a is exposed upwards and the second surface 11b faces the holding surface 42a. In this state, when the suction force (negative pressure) of the suction source is applied to the holding surface 42a, the ingot 11 is held by the chuck table 42.

[0086] Next, the positional relationship between the ingot 11 and the grinding wheel 50 is adjusted. Specifically, the chuck table 42 is positioned below the grinding unit 44. At this time, the chuck table 42 and the grinding unit 44 are positioned such that the rotation path of the grinding wheel 54 does not overlap with the wafer formation region 13 in the Z-axis direction, but overlaps with the outer peripheral excess region 15.

[0087] Next, the grinding unit 44 is lowered along the Z-axis while the chuck table 42 and grinding wheel 50 are rotated at a predetermined speed. As a result, the multiple grinding wheels 54 approach the ingot 11 while rotating and make contact with the first surface 11a side of the excess outer region 15 of the ingot 11. Consequently, the excess outer region 15 of the ingot 11 is ground away by the multiple grinding wheels 54. Grinding of the ingot 11 continues until the grinding wheels 54 reach the separation layer 23.

[0088] When the grinding wheel 54 reaches the separation layer 23, an annular region extending from the outer peripheral surface 11c of the ingot 11 to the wafer formation region 13 is removed. As a result, an annular step is formed on the first surface 11a side of the outer peripheral portion of the ingot 11, and the side surface 13a of the wafer formation region 13 is exposed. Consequently, the edge of the separation layer 23 formed inside the ingot 11 is exposed on the side surface 13a of the wafer formation region 13.

[0089] As described above, in the exposure process S3, a portion of the excess outer peripheral region 15 of the ingot 11, where the separation layer 23 was not formed in the separation layer formation process S2, is removed to form the side surface 13a of the wafer formation region 13, and the separation layer 23 is exposed on the side surface 13a of the wafer formation region 13. This makes it possible to obtain an ingot 11 in which a disc-shaped wafer formation region 13 is formed on the separation layer 23.

[0090] The exposure process S3 can also be performed before the separation layer formation process S2. Specifically, before forming the separation layer 23 on the ingot 11, the excess outer peripheral region 15 of the ingot 11 is processed to expose the side surface 13a of the wafer formation region 13 (exposure process S3). This forms a cylindrical protrusion in the center of the ingot 11, which is composed of a part of the wafer formation region 13 (see Figures 5(A) to 6). Subsequently, the separation layer 23 is formed inside the wafer formation region 13 by irradiating the wafer formation region 13 from one end to the other with a laser beam 20 (separation layer formation process S2). In this case, the separation layer 23 does not reach the outer peripheral surface 11c of the ingot 11, but is formed to be exposed on the side surface 13a of the wafer formation region 13.

[0091] However, if the laser beam 20 is irradiated onto the corner of the ingot 11 (the connection between the first surface 11a and the side surface 13a), the irradiation conditions of the laser beam 20 incident on the ingot 11 will fluctuate, which may have some effect on the quality of the separation layer 23 at the edge of the wafer formation region 13. Therefore, if the quality of the separation layer 23 is the top priority, it is preferable to perform the separation layer formation step S2, which forms a separation layer 23 that does not reach the outer peripheral surface 11c of the ingot 11, before the exposure step S3 (see Figures 4(A) and 4(B), etc.). This makes it possible to avoid the situation in which the laser beam 20 is irradiated onto the corner of the ingot 11 (the connection between the first surface 11a and the outer peripheral surface 11c).

[0092] Furthermore, although the above describes an example in which the excess outer region 15 of the ingot 11 is processed into a ring shape, in the exposure process S3, the excess outer region 15 can also be processed so as to shape the side surface 13a of the wafer formation region 13 into an arbitrary shape. In other words, the exposure process S3 may also serve as a process for shaping the side surface 13a of the wafer formation region 13.

[0093] Specifically, in the exposure process S3, the excess outer peripheral region 15 is removed, and a notch (notch, orientation flat, mirror surface, etc.) indicating the crystal orientation of the ingot 11 may be formed on a part of the side surface 13a of the wafer formation region 13. For example, the notch is formed at a predetermined position such that the line connecting the center of the ingot 11 and the notch is parallel or perpendicular to a predetermined crystal orientation of the ingot 11.

[0094] For example, after removing the annular region from the outer peripheral surface 11c of the ingot 11 to the wafer formation region 13 as described above, a notch or orientation flat can be formed by cutting and removing a part of the side surface 13a of the wafer formation region 13 with cutting blades 38, 38A (see Figures 5(A) and 5(B)). However, the notch or orientation flat may also be formed by processing tools other than the cutting blades 38, 38A or by irradiation with a laser beam.

[0095] Furthermore, a mirror surface (flat surface) may be formed on the side surface 13a of the wafer formation region 13 by cutting, laser processing, or the like. The mirror surface is a plane that is generally perpendicular to the first surface of the ingot 11 and functions as a marker detectable by an optical sensor. For example, when light is shone from a reflective optical sensor along the side surface 13a of the wafer formation region 13, the direction of reflection of the light differs depending on whether the light is shone on the mirror surface or on other areas, and the amount of light received by the optical sensor changes. Therefore, the position of the mirror surface can be determined based on the amount of light received by the optical sensor, and the crystal orientation of the ingot 11 can be determined based on the position of the mirror surface.

[0096] Then, after the separation layer formation step S2 and the exposure step S3, wafers are obtained by dividing the ingot 11 starting from the separation layer 23 (separation step S4). The region of the ingot 11 where the separation layer 23 is formed has lower mechanical strength and is more brittle than other regions of the ingot 11. Therefore, the separation layer 23 functions as a separation starting point (trigger for separation) when separating wafers from the ingot 11. Specifically, when an external force is applied to the ingot 11, the ingot 11 breaks starting from the separation layer 23, and wafers of a predetermined thickness are separated from the ingot 11.

[0097] For example, a separation device is used to separate the wafer from the ingot 11. Figures 7(A) and 7(B) show an example of the configuration of the separation device 60. The separation device 60 separates the wafer (substrate) 25 from the ingot 11 by applying an external force to the ingot 11.

[0098] The separation device 60 includes a chuck table (holding table) 62 for holding the ingot 11. The upper surface of the chuck table 62 is a flat surface that is generally parallel to the horizontal plane (XY plane) and forms a circular holding surface 62a for holding the ingot 11. The holding surface 62a is connected to a suction source (not shown), such as an ejector, via a flow path (not shown), a valve (not shown), etc., formed inside the chuck table 62.

[0099] Furthermore, the separation device 60 includes a separation unit 64 provided above the chuck table 62. The separation unit 64 includes a holding unit 66 that holds the side of the ingot 11 opposite to the side (first side 11a) held by the chuck table 62 (second side 11b). The lower surface of the holding unit 66 is a flat surface that is generally parallel to the horizontal plane (XY plane) and constitutes a circular holding surface 66a for holding the ingot 11.

[0100] For example, the holding unit 66 is composed of a disc-shaped holding member and has a plurality of suction ports (not shown) for sucking in the ingot 11. One end of the suction port is open at the holding surface 66a, and the other end of the suction port is connected to a suction source (not shown), such as an ejector, via a flow path (not shown) formed inside the holding unit 66. The number and arrangement of the suction ports are set appropriately so that the plurality of suction ports are closed by the ingot 11 when the ingot 11 comes into contact with the holding surface 66a.

[0101] A columnar support member 68 is connected to the upper surface of the holding unit 66 to support the holding unit 66. The lower end of the support member 68 is fixed to the center of the holding unit 66. A moving unit (not shown) for moving the support member 68 is connected to the upper end of the support member 68. For example, the moving unit is composed of a ball screw type moving mechanism and moves (raises and lowers) the support member 68 together with the holding unit 66 along the Z-axis.

[0102] Figure 7(A) is a partial cross-sectional front view showing the separation device 60 that holds the ingot 11. In separation step S4, the ingot 11 is first held by the chuck table 62 and the holding unit 66.

[0103] Specifically, the ingot 11 is placed on the chuck table 62 with a space wider than the thickness of the ingot 11 secured between the holding surface 62a of the chuck table 62 and the holding surface 66a of the holding unit 66. At this time, the ingot 11 is positioned so that the first surface 11a is exposed upwards and the second surface 11b faces the holding surface 62a. Then, the suction force (negative pressure) of the suction source is applied to the holding surface 62a. As a result, the ingot 11 is held in place by the chuck table 62.

[0104] Next, the holding unit 66 is lowered along the Z-axis direction by a moving unit (not shown), and the holding surface 66a is brought into contact with the first surface 11a side of the ingot 11. In this state, when the suction force (negative pressure) of the suction source is applied to the holding surface 66a, the ingot 11 is held in place by the holding unit 66. As a result, the ingot 11 is fixed to the holding surface 62a on the second surface 11b side and to the holding surface 66a on the first surface 11a side.

[0105] Figure 7(B) is a partial cross-sectional front view showing a separation apparatus 60 for separating a wafer 25 from an ingot 11. After the ingot 11 is fixed to the chuck table 62 and the holding unit 66, the holding unit 66 is raised along the Z-axis direction by a moving unit (not shown) while the position of the chuck table 62 is fixed. As a result, the holding surface 62a and the holding surface 66a are separated from each other, and an external force is applied to the ingot 11 that pulls the first surface 11a side of the ingot 11 apart from the second surface 11b side. As a result, the ingot 11 is divided starting from the separation layer 23, and the first surface 11a side of the ingot 11 (wafer formation region 13 on the separation layer 23) is separated from the rest of the ingot 11 as a wafer 25.

[0106] In this way, a plate-shaped wafer 25 is manufactured from the ingot 11. The depth to which the separation layer 23 is formed in the ingot 11 before the wafer 25 is separated (the distance between the first surface 11a of the ingot 11 and the separation layer 23) corresponds to the thickness of the wafer 25 separated from the ingot 11.

[0107] Furthermore, in the aforementioned separation layer formation step S2, the laser beam 20 irradiated onto the ingot 11 (see Figures 4(A) and 4(B)) generates internal forces (internal stress) in and around the separation layer 23, which may cause the wafer formation region 13 of the ingot 11 to be divided starting from the separation layer 23. Also, when processing the ingot 11 in the aforementioned exposure step S3 (see Figures 5(A) to 6), the cutting blades 38, 38A and grinding wheel 50 come into contact with the ingot 11, and the external forces applied to the ingot 11 may cause the wafer formation region 13 of the ingot 11 to be divided starting from the separation layer 23, resulting in the separation of the wafer 25 from the ingot 11. In these cases, since the wafer 25 is already manufactured by the time the exposure step S3 is completed, the above separation step S4 may be omitted.

[0108] However, if the wafer formation region 13 is divided in the separation layer formation step S2 or the exposure step S3, there is a risk that the wafer formation region 13 (wafer 25) separated from the ingot 11 may break off and be damaged during processing of the ingot 11 in the exposure step S3. Therefore, in the exposure step S3, it is preferable to process the outer peripheral excess region 15 while the first surface 11a side of the ingot 11 is fixed with a fixing member.

[0109] There are no restrictions on the configuration of the fixing member that secures the first surface 11a of the ingot 11. For example, a holding table that holds the ingot 11 can be used as the fixing member. The holding table is configured to rotate freely together with the ingot 11 and has a holding surface that holds the first surface 11a of the ingot 11. The holding surface of the holding table is connected to a suction source (not shown) via a flow path (not shown) formed inside the holding table.

[0110] In the exposure process S3, the first surface 11a of the ingot 11 is held in place by the holding table by applying suction force (negative pressure) from a suction source to the holding surface while the holding surface of the holding table is in contact with the first surface 11a of the ingot 11. This prevents the wafer 25 from flying off even if it separates from the ingot 11 during processing of the outer peripheral excess region 15.

[0111] The shape and size of the holding surface can be appropriately set within a range that allows the wafer 25 to be held. For example, the holding surface can be formed into a circular or polygonal shape. The holding surface may hold the entire first surface 11a of the ingot 11, or it may hold only a part of the first surface 11a of the ingot 11 (for example, the central part).

[0112] Furthermore, the fixing member may be a pressing member that presses against the first surface 11a of the ingot 11. For example, the pressing member may be formed in a columnar shape and positioned to overlap with the ingot 11. A moving mechanism that raises and lowers the tip of the pressing member is also connected to the pressing member. By operating the moving mechanism, the tip of the pressing member can be positioned in a position where it contacts the first surface 11a of the ingot 11 and presses the ingot 11 (pressing position), and in a state where it moves away from the first surface 11a of the ingot 11 and the pressure on the ingot 11 is released (release position).

[0113] In the exposure process S3, the tip of the pressing member is positioned at the pressing position to press the first surface 11a of the ingot 11. This prevents the wafer 25 from flying off even if it separates from the ingot 11 during processing of the outer peripheral excess region 15. In this case, two or more places on the first surface 11a of the ingot 11 may be pressed by multiple pressing members.

[0114] The wafer 25 separated from the ingot 11 can be used for manufacturing device chips, etc. Specifically, first, the side of the wafer 25 that was separated from the ingot 11 (separation surface) is subjected to grinding, polishing, etc. This removes or reduces the separation marks (irregularities) remaining on the separation surface side of the wafer 25.

[0115] Next, the wafer 25 is divided into multiple rectangular regions by multiple streets (division lines) arranged in a grid pattern that intersect each other. Then, devices such as ICs (Integrated Circuits), LSIs (Large Scale Integrations), LEDs (Light Emitting Diodes), and MEMS (Micro Electro Mechanical Systems) devices are formed in each of the regions divided by the streets. After that, the wafer 25 is divided into individual pieces along the streets using processing equipment such as a cutting machine or a laser processing machine. This produces multiple device chips, each containing a device.

[0116] On the other hand, when the wafer 25 is separated from the ingot 11, the side of the ingot 11 from which the wafer 25 was separated (separation surface) becomes a new first surface 11a of the ingot 11. The ingot 11 can then be reused in the manufacture of the next wafer 25. In this case, it is preferable to process the ingot 11 to flatten the first surface 11a (separation surface) side of the ingot 11 (flattening process). This removes or reduces the separation marks (irregularities) remaining on the first surface 11a side of the ingot 11, and the surface roughness of the first surface 11a of the ingot 11 is reduced.

[0117] Figure 8 is a partial cross-sectional front view showing the ingot 11 during the planarization process. For example, in the planarization process, the ingot 11 is ground using a grinding device 40 to remove or reduce the separation marks (irregularities) remaining on the first surface 11a (separation surface) of the ingot 11, thereby planarizing the first surface 11a of the ingot 11. The configuration and function of the grinding device 40 are as described in the exposure process S3 (see Figure 6).

[0118] In the planarization process, the ingot 11 is first held by the chuck table 42. Specifically, the ingot 11 is placed on the chuck table 42 such that the first surface 11a (separation surface, grinding surface) is exposed upwards and the second surface 11b faces the holding surface 42a. In this state, the ingot 11 is held by the chuck table 42 by applying the suction force (negative pressure) of the suction source to the holding surface 42a.

[0119] Next, the chuck table 42 is positioned below the grinding unit 44. At this time, the positional relationship between the ingot 11 and the grinding wheel 50 is adjusted so that the rotation axis of the chuck table 42 (the center of the ingot 11) and the rotation path of the grinding wheel 54 overlap in the Z-axis direction. Then, while rotating the chuck table 42 and the grinding wheel 50 at a predetermined speed, the grinding unit 44 is lowered along the Z-axis direction. As a result, the multiple grinding wheels 54 approach the ingot 11 while rotating and make contact with the first surface 11a of the ingot 11.

[0120] When multiple grinding wheels 54 come into contact with the first surface 11a of the ingot 11, the first surface 11a of the ingot 11 is ground away. This removes or reduces any remaining irregularities on the first surface 11a of the ingot 11. After the ingot 11 has been ground to a predetermined thickness, the grinding unit 44 rises and grinding stops.

[0121] By performing the planarization process described above, the first surface 11a of the ingot 11 is flattened. In addition to grinding, or in addition to grinding, polishing may be performed on the ingot 11 during the planarization process. For example, polishing fluid may be supplied to the first surface 11a of the ingot 11 while polishing the first surface 11a of the ingot 11 with a disc-shaped polishing pad. This further flattens and polishes the first surface 11a of the ingot 11 to a mirror finish.

[0122] Subsequently, the ingot 11 is reused to form the next wafer 25. Specifically, a new wafer 25 is formed by performing a separation layer formation process S2, an exposure process S3, and a separation process S4 on the ingot 11. Performing the planarization process described above makes it easier for the laser beam 20 (see Figure 4(A)) to be properly incident on the first surface 11a of the ingot 11.

[0123] As described above, the wafer manufacturing method according to this embodiment is realized by a wafer manufacturing system composed of multiple processing devices. Specifically, the wafer manufacturing system according to this embodiment includes a laser processing device 10 (see Figure 4(A)) that performs the separation layer formation step S2, an exposure processing device (cutting device 30 (see Figures 5(A), 5(B), 9, and 10(A)), a grinding device 40 (see Figure 6), a laser processing device 70 (see Figure 10(B)), etc.) that performs the exposure step S3, and a separation device 60 (see Figures 7(A) and 7(B)) that performs the separation step S4. By sequentially processing the ingot 11 with these processing devices, a wafer 25 is manufactured from the ingot 11.

[0124] There are no restrictions on the specific configuration of the wafer manufacturing system described above. For example, the wafer manufacturing system may be configured by installing the laser processing device 10, the exposure processing device, and the separation device 60 as independent processing devices within the same factory, and manufacturing wafers 25 from ingots 11 by having each processing device work together. Alternatively, the wafer manufacturing system may be configured by a single composite processing device that incorporates the grinding device 40, the exposure processing device, and the separation device 60. Furthermore, the wafer manufacturing system may also include a grinding device 40 (see Figure 8) that performs a planarization process.

[0125] As described above, in the wafer manufacturing method and wafer manufacturing system according to this embodiment, the separation layer 23, which functions as the starting point for separating the wafer 25 from the ingot 11, is formed so as not to reach the outer peripheral surface 11c of the ingot 11. As a result, the laser beam 20 for forming the separation layer 23 is less likely to irradiate crystal defects that may exist on or near the outer peripheral surface 11c of the ingot 11, thereby improving the quality of the separation layer 23. As a result, the wafer 25 is more easily separated from the ingot 11.

[0126] Furthermore, each step included in the wafer manufacturing method according to this embodiment can be appropriately modified within a range that can suppress the deterioration of the quality of the separation layer 23 caused by crystal defects that may exist on and near the outer peripheral surface 11c of the ingot 11. For example, the processing performed on the excess outer peripheral region 15 of the ingot 11 in the exposure step S3 is not limited to the cutting and grinding processes shown in Figures 5(A) to 6. A modified example of the exposure step S3 will be described below.

[0127] Figure 9 is a partial cross-sectional front view showing the ingot 11 in exposure step S3 according to the first modified example. In exposure step S3, the side surface of the wafer formation region 13 may be exposed by forming a groove 27 from the outer peripheral surface 11c of the ingot 11 to the wafer formation region 13.

[0128] For example, grooves 27 are formed in the ingot 11 by cutting the ingot 11 with a cutting device 30 equipped with a cutting unit 34B. The cutting device 30 shown in Figure 9 is equipped with a cutting unit 34B instead of a cutting unit 34 (see Figure 5(A)). Except for the matters described below, the configuration and function of the cutting unit 34B are the same as those of the cutting unit 34.

[0129] The cutting unit 34B includes a columnar spindle 36B arranged along the Z-axis. An annular cutting blade 38B for cutting the ingot 11 is mounted at the tip (one end) of the spindle 36. A hub blade or a washer blade can be used as the cutting blade 38B. The thickness of the cutting blade 38B is thinner than the depth of the separation layer 23 (the distance from the first surface 11a of the ingot 11 to the separation layer 23).

[0130] A rotational drive source (not shown), such as a motor, is connected to the base end (other end) of the spindle 36B to rotate the spindle 36B around a rotation axis that is approximately parallel to the Z-axis direction. When the rotational drive source rotates the spindle 36B, the cutting blade 38B rotates around a rotation axis that is approximately parallel to the Z-axis direction.

[0131] In the exposure process S3, first, the positional relationship between the ingot 11 held by the chuck table 32 and the cutting blade 38B is adjusted. Specifically, the position of the chuck table 32 and / or the cutting unit 34B is adjusted so that the cutting blade 38B is positioned to the side of the ingot 11. At this time, the cutting unit 34B is positioned so that the height position of the cutting blade 38B coincides with the height position of the separation layer 23 formed in the ingot 11.

[0132] Then, while rotating the chuck table 32 and the cutting blade 38B, the chuck table 32 and the cutting unit 34B are moved relative to each other in a direction that brings the ingot 11 and the cutting blade 38B closer together. For example, the cutting unit 34B is moved toward the ingot 11 along the Y-axis. As a result, the rotating cutting blade 38B comes into contact with the outer circumferential surface 11c of the ingot 11. Consequently, the outer circumferential surface 11c of the ingot 11 is cut in an annular shape along the circumferential direction of the ingot 11.

[0133] Subsequently, while maintaining the rotation of the chuck table 32 and the cutting blade 38B, the chuck table 32 and the cutting unit 34B are moved relative to each other further so that the cutting blade 38B moves closer to the center of the ingot 11. As a result, the excess outer region 15 of the ingot 11 is gradually cut away from the outer surface 11c toward the center of the ingot 11. Cutting of the ingot 11 is then continued until the cutting blade 38B reaches the wafer formation region 13.

[0134] When the cutting blade 38B reaches the wafer formation region 13, an annular groove 27 is formed along the circumferential direction of the ingot 11, extending from the outer peripheral surface 11c of the ingot 11 to the wafer formation region 13, and the region from the outer peripheral surface 11c of the ingot 11 to the wafer formation region 13 is removed. As a result, the side surface 13a of the wafer formation region 13 is exposed, and the edge of the separation layer 23 formed inside the ingot 11 is exposed on the side surface 13a of the wafer formation region 13.

[0135] Subsequently, in the separation process S4, the ingot 11 is divided to form a wafer 25 (see Figure 7(B)). In the configuration in which grooves 27 are formed in the ingot 11, the outer peripheral excess region 15 located above the grooves 27 (on the first surface 11a side) can also be used as part of the wafer 25 together with the wafer formation region 13. In this case, a wafer 25 having the same diameter as the ingot 11 is formed.

[0136] Furthermore, in the separation step S4, a groove with a depth from the first surface 11a of the ingot 11 to the separation layer 23 may be formed along the outer edge of the wafer formation region 13. The ingot 11 in the exposure step S3 according to the second modified example is shown in Figures 10(A) and 10(B).

[0137] Figure 10(A) is a partial cross-sectional front view showing an ingot 11 on which grooves 29 are formed by cutting. For example, in the exposure process S3, grooves 29 are formed in the ingot 11 by cutting the ingot 11 with a cutting device 30 equipped with a cutting unit 34C. The cutting device 30 shown in Figure 10(A) is equipped with a cutting unit 34C instead of a cutting unit 34 (see Figure 5(A)). Except for the matters described below, the configuration and function of the cutting unit 34C are the same as those of the cutting unit 34.

[0138] The cutting unit 34C includes a columnar spindle 36C arranged along the Y-axis. An annular cutting blade 38C for cutting the ingot 11 is mounted on the tip (one end) of the spindle 36C. A hub blade or a washer blade can be used as the cutting blade 38C. The thickness of the cutting blade 38C is thinner than the width of the outer peripheral excess region 15 (the distance from the outer peripheral surface 11c to the boundary between the wafer formation region 13 and the outer peripheral excess region 15).

[0139] A rotational drive source (not shown), such as a motor, is connected to the base end (other end) of the spindle 36C to rotate the spindle 36C around a rotation axis that is approximately parallel to the Y-axis direction. When the spindle 36C is rotated by the rotational drive source, the cutting blade 38C rotates around a rotation axis that is approximately parallel to the Y-axis direction.

[0140] In the exposure process S3, first, the positional relationship between the ingot 11 held by the chuck table 32 and the cutting blade 38C is adjusted. Specifically, the positions of the chuck table 32 and / or the cutting unit 34C are adjusted so that the cutting blade 38C overlaps with or is adjacent to the separation layer 23 formed on the ingot 11 in the Z-axis direction. For example, the cutting unit 34C is positioned so that the side surface of the cutting blade 38C is located directly above the boundary between the wafer formation region 13 and the outer peripheral excess region 15.

[0141] Then, by rotating the chuck table 32 and the cutting blade 38C while lowering the cutting unit 34C along the Z-axis, the ingot 11 and the cutting blade 38C are moved relative to each other along the Z-axis. As a result, the rotating cutting blade 38C cuts into the first surface 11a of the ingot 11, and the first surface 11a of the ingot 11 is cut in an annular shape. The cutting of the ingot 11 is continued until the cutting blade 38C reaches the separation layer 23.

[0142] When the cutting blade 38C reaches the separation layer 23, an annular groove 29 is formed along the outer edge of the wafer formation region 13, extending from the first surface 11a of the ingot 11 to the separation layer 23. As a result, the side surface 13a of the wafer formation region 13, which corresponds to the side wall of the groove 29, is exposed, and the edge of the separation layer 23 is exposed on the side surface 13a of the wafer formation region 13.

[0143] Figure 10(B) is a partial cross-sectional front view showing an ingot 11 on which grooves 29 are formed by laser processing. The grooves 29 can also be formed by laser processing. For example, the grooves 29 can be formed by performing ablation processing on the ingot 11 using a laser processing device 70. The configuration and function of the laser processing device 70 are the same as those of the laser processing device 10 (see Figure 4(A)), except for the points described below.

[0144] The laser processing apparatus 70 comprises a chuck table (holding table) 72 having a holding surface 72a for holding the ingot 11, and a laser irradiation unit 74 having a laser processing head 76 for irradiating a laser beam 78. The details of the chuck table 72 and the laser irradiation unit 74 are the same as those of the chuck table 12 and laser irradiation unit 14 of the laser processing apparatus 10 (see Figure 4(A)).

[0145] In the exposure process S3, first, the positional relationship between the ingot 11 held by the chuck table 72 and the laser processing head 76 is adjusted. Specifically, the positions of the chuck table 72 and / or the laser processing head 76 are adjusted so that the laser processing head 76 overlaps with the ingot 11 in the Z-axis direction. In addition, the focal point of the laser beam 78 emitted from the laser processing head 76 is positioned at or near the boundary between the wafer formation region 13 and the outer peripheral excess region 15.

[0146] Then, while rotating the chuck table 72, the laser beam 78 is irradiated from the laser processing head 76 toward the ingot 11. As a result, the laser beam 78 is irradiated toward the first surface 11a side of the ingot 11 and scanned in a ring shape along the outer edge of the wafer formation region 13.

[0147] The irradiation conditions for the laser beam 78 are set so that ablation is performed on the area of ​​the ingot 11 irradiated by the laser beam 78 (irradiated area). Specifically, the wavelength of the laser beam 78 is set so that at least a portion of the laser beam 78 is absorbed by the ingot 11. In other words, the laser beam 78 is a pulsed laser beam that is absorbed by the ingot 11. Other irradiation conditions for the laser beam 78 are also set as appropriate so that the ingot 11 is subjected to proper ablation.

[0148] As described above, when the ingot 11 is irradiated with the laser beam 78, an annular groove 29 is formed on the first surface 11a side of the ingot 11 along the outer edge of the wafer formation region 13. Laser processing is then continued until the groove 29 reaches the separation layer 23. As a result, the groove 29 extending from the first surface 11a of the ingot 11 to the separation layer 23 is formed in an annular shape along the outer edge of the wafer formation region 13. In this way, a groove 29 can also be formed on the ingot 11 by laser processing.

[0149] As described above, after grooves 29 are formed in the ingot 11 in the exposure process S3, the separation process S4 is carried out. In the separation process S4, the disc-shaped region surrounded by the grooves 29 of the ingot 11 is separated from the ingot 11 starting from the separation layer 23. This yields a wafer 25 (see Figure 7(B)).

[0150] When the wafer 25 is separated from the ingot 11 in which the groove 29 is formed, the excess outer peripheral region 15 outside the groove 29 remains as an annular protrusion. Therefore, when the ingot 11 is to be reused in the manufacture of the next wafer 25, the outer peripheral portion of the ingot 11 is subjected to cutting, grinding, laser processing, etc., to remove the protrusion as appropriate.

[0151] Furthermore, when forming grooves 29 in the ingot 11 during the exposure process S3, external force is applied to the ingot 11 by contact with the cutting blade 38C (see Figure 10(A)) or irradiation with the laser beam 78 (see Figure 10(B)), and as described above, the wafer 25 may separate from the ingot 11. However, since the rotation speed of the chuck tables 32 and 72 during groove formation is relatively low, and the aforementioned protrusions remaining on the outer circumference of the ingot 11 function as walls, the phenomenon of the wafer 25 being ejected is unlikely to occur.

[0152] Furthermore, especially when forming grooves 29 by irradiation with a laser beam 78 (see Figure 10(B)), the grooves 29 may be formed by moving the focal point of the laser beam 78 without moving or rotating the chuck table 72. This makes it possible to form grooves 29 without moving the ingot 11, and the wafer 25 separated from the ingot 11 becomes less likely to shatter.

[0153] In the above embodiment, the case in which the ingot 11 is held by different chuck tables in the separation layer formation step S2, exposure step S3, separation step S4, and planarization step has been described (see Figures 4(A) to 10(B)). In this case, the ingot 11 is transported from one chuck table to another by a transport mechanism or operator between each step. However, the ingot 11 may be held by the same chuck table in two or more of the separation layer formation step S2, exposure step S3, separation step S4, and planarization step. In this case, the ingot 11 can be transported between each step by moving the chuck table holding the ingot 11 using a moving mechanism or the like.

[0154] Furthermore, the structure, method, etc., according to this embodiment can be modified as appropriate without departing from the scope of the object of the present invention. [Explanation of symbols]

[0155] 11 ingots 11a 1st side (front) 11b 2nd side (back side) 11c Outer surface (side) 13 Wafer Formation Area 13a side 15. Peripheral surplus area 17 Abnormal part 19A Crystal defect region 19B Heterogeneous polymorphic region 19C abnormal concentration area 21 Modification Region (Alteration Region) 23 Separation layer (modification layer, alteration layer) 25 Wafer (substrate) 27,29 Groove 10 Laser processing equipment 12. Chuck table (holding table) 12a Holding surface 14 Laser irradiation unit 16 Housing 18 Laser processing heads 20 laser beams 22 Imaging Unit 30 Cutting equipment 32 Chuck table (holding table) 32a Holding surface 34, 34A, 34B, 34C Cutting Unit 36, 36A, 36B, 36C spindles 38, 38A, 38B, 38C Cutting blades 40 Grinding equipment 42. Chuck table (holding table) 42a Holding surface 44 Grinding Unit 46 spindles 48 Wheel Mount 50 grinding wheels 52 Wheel base 54 Grinding Wheels 60 Separation device 62 Chuck Table (Holding Table) 62a Holding surface 64 Separation Units 66 Holding Unit 66a Holding surface 68 Support member 70 Laser processing equipment 72 Chuck Table (Holding Table) 72a Holding surface 74 Laser irradiation units 76 Laser processing heads 78 Laser beams

Claims

1. A method for manufacturing wafers from a crystalline ingot, A preparation step for preparing an ingot having a wafer forming region corresponding to the wafer and an outer peripheral excess region that includes the outer peripheral surface of the ingot and surrounds the wafer forming region, A separation layer formation step is performed by positioning the focal point of a laser beam that is transparent to the ingot inside the ingot, and irradiating the inside of the outer surface of the ingot with the laser beam while moving the ingot and the focal point relatively, thereby forming a separation layer that does not reach the outer surface of the ingot, at least inside the wafer formation region of the ingot. A method for manufacturing a wafer, comprising: an exposure step of processing the excess outer region of the ingot to expose the side surface of the wafer formation region.

2. The exposure step is performed after the separation layer formation step. The method for manufacturing a wafer according to claim 1, characterized in that the exposure step exposes the separation layer on the side surface of the wafer formation region.

3. The method for manufacturing a wafer according to claim 1, further comprising a separation step to obtain the wafer by dividing the ingot starting from the separation layer, after the separation layer formation step and the exposure step.

4. The preparation process is as follows: An inspection step of inspecting the ingot and determining whether there are any abnormal areas that include at least one of the following: a region with crystal defects, a region with a different crystal shape from other regions, and a region with an abnormal concentration where the concentration of impurities contained in the ingot is outside the acceptable range. A wafer manufacturing method according to any one of claims 1 to 3, characterized in that, if it is determined in the inspection step that the abnormal part exists within a predetermined range from the outer surface of the ingot, the outer periphery surplus region is set so that the abnormal part is included in the outer periphery surplus region.

5. The wafer manufacturing method according to any one of claims 1 to 3, characterized in that the exposure step removes the region from the outer surface of the ingot to the wafer formation region.

6. The method for manufacturing a wafer according to any one of claims 1 to 3, characterized in that, in the exposure step, a groove having a depth from the surface of the ingot to the separation layer is formed along the outer edge of the wafer forming region.

7. A wafer manufacturing system for manufacturing wafers from crystalline ingots, A laser processing apparatus that forms a separation layer within at least the wafer formation region of an ingot, which does not reach the outer surface of the ingot, by positioning the focal point of a laser beam that is transparent to the ingot inside the ingot, while relatively moving the ingot and the focal point, and irradiating the inside of the outer surface of the ingot with the laser beam while moving the ingot and the focal point relative to each other, the ingot having a wafer formation region corresponding to the wafer and an outer peripheral excess region that includes the outer peripheral surface of the ingot. A wafer manufacturing system characterized by comprising an exposure processing device for processing the excess outer region of the ingot to expose the side surface of the wafer formation region.

8. The wafer manufacturing system according to claim 7, further comprising a separation device for dividing the ingot starting from the separation layer.

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