Wafer division method, wafer processing method, and wafer division device

Abstract

To provide a wafer division method, a wafer processing method, and a wafer division device that can increase the utilization efficiency of a semiconductor material, mainly in power semiconductor applications.SOLUTION: A wafer division method obtains two thin wafers adhered to fixing plates by attaching the fixing plates to both sides of a wafer consisting of at least semiconductor crystals, and cutting the wafer near the middle of a thickness direction while holding the fixing plates on both sides.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a wafer dividing method, a processing method, and a wafer dividing device for obtaining thin wafers, and more particularly to a wafer dividing method, a processing method, and a wafer dividing device suitable for obtaining thin wafers suitable for manufacturing power semiconductors. [Background technology]

[0002] Various semiconductor devices are formed on a disk-shaped wafer and then diced into individual devices. Wafers are obtained by slicing a cylindrical or other shaped ingot (made of semiconductor) (see, for example, Patent Document 1).

[0003] This is shown in FIG. 9, where FIG. 9(a) shows the shape of a cylindrical ingot 1 obtained by crystal growth of a semiconductor. FIG. 9(b) shows the state where slicing of the ingot 1 is started, and shows the state where wires 170 are arranged at equal intervals in a direction almost perpendicular to the longitudinal direction of the ingot. Here, the wires 170 constitute a wire saw, and are made of piano wire or the like with a diameter of 120 μm to 300 μm to which hard particles (diamond, etc.) with an abrasive size of 10 μm to 30 μm are attached, and the wires 170 are run in a certain direction or in both directions to slice the ingot 1. FIG. 9(c) shows the state where slicing is completed, and each wafer 10 can be separated as shown in FIG. 9(d).

[0004] In addition, the semiconductor crystals forming the wafer 10 have crystal orientations suitable for subsequent device formation, and in the example of the wafer 10 shown in FIG. 9(d), the wafer surface 10S is a surface suitable for device formation.

[0005] 10 and 11 are diagrams for explaining a semiconductor process using the wafer 10 shown in FIG. 9(d), showing an example of a process for obtaining a power semiconductor device.

[0006] FIG. 10(a) shows a state where a backside fixing plate 2 is disposed on the opposite side (backside) of the wafer 10 from the wafer front side 10S. Here, the backside fixing plate 2 is a substrate 20 on which an adhesive film 21 is laminated, and the wafer 10 is fixed to the backside fixing plate 2 by adhering the backside of the wafer 10 to the adhesive film 21 as shown in FIG. 10(b). Incidentally, the wafer front side 10S is a surface generated by slicing with a wire 170, but is not necessarily a flat surface, so that devices cannot be formed on the wafer as is. Therefore, as a flattening process, the wafer front side 10S is polished, ground, etc., and then chemical mechanical polishing (CMP) is performed to obtain a wafer 101 having an atomically flat wafer front side 101S (FIG. 10(c)).

[0007] After that, a device process such as photolithography is performed on the wafer surface 101S to form the surfaces of a large number of devices 6 (FIG. 10(d)). After that, the opposite side of the wafer surface 101S is processed.

[0008] The preparation steps for this are shown in Figures 10(e) to 11(c). Here, the device protection fixing plate 4 is formed by laminating an adhesive film 41 on a substrate 40. The adhesive film 41 is placed facing the wafer front surface 101S (Figure 10(e)), and then adhered to the wafer front surface 101S (Figure 11(a)). After that, the rear surface fixing plate 2 is peeled off (Figures 11(b) to 11(c)).

[0009] At this stage, the wafer back surface 101B, which is the surface opposite to the wafer front surface 101S, of the wafer 101 is exposed (FIG. 11(d)). However, the wafer back surface 101B is not flat because it has been sliced ​​by the wires 170. Therefore, a flattening process is performed on the wafer back surface 101B to obtain a wafer 102 having a flat wafer back surface 102B as shown in FIG. 11(e). Thereafter, a metal film is formed on the wafer back surface 102B to form an electrode surface 102M (FIG. 11(f)). Thereafter, the device protection fixing plate 4 is peeled off, and a dicing process is performed to separate the devices 6.

[0010] Fig. 12 is a cross-section showing an example of the structure of an individual device 6, in which a p region 60, an n+ region 61, a gate oxide film 62, a gate electrode 63, and a source electrode 64 are formed in the device process leading to Fig. 10(d). Also, the electrode surface 102M on which the metal film is formed in Fig. 11(f) becomes a drain electrode 6102M in each device 6.

[0011] Note that Figures 13 and 14 show how the cross section of the area corresponding to each device 6 changes, with Figures 13(a) to 13(e) corresponding to each process in Figures 10(a) to 10(e), and Figures 14(a) to 14(f) corresponding to each process in Figures 11(a) to 11(f). [Prior art documents] [Patent documents]

[0012] [Patent Document 1] Patent No. 7100864 Summary of the Invention [Problem to be solved by the invention]

[0013] 12 shows the basic structure of a vertical diffusion MOSFET (abbreviated as VD-MOSFET) used as a so-called power semiconductor, in which carrier electrons controlled by a voltage applied to a gate electrode 63 flow from a source electrode 64 to a drain electrode 6102M (current flows from the drain electrode 6102 to the source electrode 64). That is, in the device 6 of FIG. 12, current flows in the thickness direction (d direction).

[0014] However, compared to logic semiconductors, power semiconductors control a larger current when energized and a higher voltage when cutoff. For this reason, they are required to have low resistance when energized and high withstand voltage when cutoff.

[0015] Therefore, in the device 6 having the structure shown in Fig. 12, it is preferable to make the thickness d thin in order to reduce the resistance when electricity is applied, but a minimum thickness d is ensured in order to ensure the withstand voltage. For example, in a device using silicon carbide as a semiconductor, a thickness of about 300 µm was conventionally required.

[0016] However, in recent years, it has become possible to obtain high-quality crystals with few defects even in compound semiconductors such as silicon carbide, making it possible to ensure a practical withstand voltage even with a thickness of several tens of micrometers. As a result, the thickness of power semiconductors made of silicon carbide has been reduced from the previous thickness of 300 μm or more to 100 μm or less.

[0017] On the other hand, if the thickness of the wafer 10 sliced ​​from the ingot 1 as shown in Figure 9(d) is reduced, warping and distortion will occur, and it will be difficult to attach it to the back surface fixing plate 2 as shown in Figure 10(a) without any gaps, which will cause problems in subsequent processes and affect the yield.

[0018] For this reason, the wafer 10 must be 300 μm thick or more, and must be thinned by polishing more than just the planarization process, using at least one of the planarization processes shown in Figures 10(c) and 13(c) and the planarization processes shown in Figures 11(e) and 14(e). As a result, the utilization efficiency of the semiconductor crystal is extremely low.

[0019] The present invention has been made in consideration of the above problems, and provides a wafer dividing method, a processing method, and a wafer dividing device that can increase the utilization efficiency of semiconductor materials, mainly in power semiconductor applications. [Means for solving the problem]

[0020] In order to solve the above problem, the invention described in claim 1 comprises: 1. A method for dividing a wafer to obtain thin wafers, comprising the steps of: This is a wafer dividing method in which fixing plates are attached to both sides of a wafer made of at least a semiconductor crystal, and while holding the fixing plates on both sides, the wafer is cut near the middle in the thickness direction to obtain two thin wafers attached to the fixing plates.

[0021] The invention described in claim 2 is This is a wafer processing method in which, of the two thin wafers obtained by the wafer dividing method described in claim 1, the thin wafer having an exposed surface on a predetermined crystal orientation side is attached to a fixed plate and flattened on the surface on the predetermined crystal orientation side, and then a plurality of devices are formed on the flattened surface.

[0022] The invention described in claim 3 is This is a wafer processing method in which, for one of two thin wafers obtained by the wafer dividing method described in claim 1, the surface of the thin wafer facing a predetermined crystal orientation is attached to a fixing plate, the exposed surface side is attached to the fixing plate, the fixing plate is peeled off from the surface facing the predetermined crystal orientation side, a flattening process is performed on the surface facing the predetermined crystal orientation side, and then a plurality of devices are formed on the surface that has been flattened.

[0023] The invention described in claim 4 is Fixing plates are attached to both sides of the wafer, and while the fixing plates on both sides are held, A wafer dividing device for dividing the wafer into two thin wafers, The wafer dividing device is equipped with a wafer rotation means that clamps the wafer on both sides via the fixed plate and rotates the wafer in a plane parallel to the wafer surface, and a wire saw having a wire arranged perpendicular to the rotation axis of the wafer rotation means.

[0024] The invention described in claim 5 is the wafer dividing apparatus described in claim 4, The wafer dividing device further comprises a laser irradiation means for irradiating the wafer with a laser beam focused on the location where the wire contacts the wafer.

[0025] The invention described in claim 6 is the wafer dividing apparatus described in claim 5, A wafer dividing device that irradiates the wafer with laser light before the wire comes into contact with the wafer.

[0026] The invention described in claim 7 is the wafer dividing apparatus described in claim 6, Further comprising a fluid ejection means for ejecting a gas or a liquid, The wafer dividing device ejects gas or liquid toward the portion of the wafer that has come into contact with the wire saw.

[0027] The invention described in claim 8 is a wafer dividing apparatus according to any one of claims 4 to 7, In the wafer dividing device, the wire has a thickness of 30 μm or more and 100 μm or less.

[0028] The invention described in claim 9 is the wafer dividing apparatus described in claim 8, The wire has abrasive grains attached to its surface, and the maximum size of the abrasive grains is 5 μm or more and 10 μm or less.

[0029] The invention described in claim 10 is a wafer dividing apparatus according to any one of claims 4 to 7, The wafer dividing apparatus is a silicon carbide wafer.

[0030] The invention described in claim 11 is a wafer dividing apparatus according to any one of claims 5 to 7, In the wafer dividing apparatus, the wafer is a silicon carbide wafer, and the wavelength of the laser light is 430 nm or more and 470 nm or less.

[0031] The invention described in claim 12 is a wafer dividing apparatus according to any one of claims 4 to 7, The wafer dividing apparatus is configured so that the thickness of the wafer is not less than 250 μm and not more than 800 μm. Effect of the Invention

[0032] The present invention can improve the utilization efficiency of semiconductor crystals in the process of fabricating wafers from semiconductor crystal ingots into devices, and is particularly effective in the manufacture of power semiconductor devices in which current flows in the thickness direction of the device. [Brief description of the drawings]

[0033] [Figure 1] This explains an embodiment of the wafer dividing method of the present invention, and shows (a) a state in which fixed plates are placed opposite both sides of a wafer sliced ​​from a semiconductor ingot, (b) a state in which fixed plates are attached to both sides of the wafer, (c) a state in which the wafer in the same state is sliced ​​with a wire, and (d) a state in which the wafer has been divided into two thin wafers. [Diagram 2] FIG. 1 is an embodiment of a method for dividing a wafer according to the present invention, which illustrates the process of changing a thin wafer divided into two pieces from an exposed back surface to an exposed front surface, and shows (a) a state in which a fixed plate is placed opposite the back surface, (b) a state in which a fixed plate is attached to the back surface, (c) a state in which the fixed plate on the front surface side is peeled off, and (d) a state in which the front surface side is exposed. [Diagram 3] 1A and 1B are diagrams illustrating an embodiment of a wafer dividing device according to the present invention, in which FIG. 1A is an external view of components, and FIG. 1B is an external view showing a state in which a wafer is being divided. [Figure 4] 1A to 1C are cross-sectional views of the process in which an embodiment of the wafer dividing device of the present invention cuts and divides a wafer by grinding, in which (a) shows the state before grinding begins, (b) shows the state after grinding has started, and (c) shows the state after grinding has ended and the wafer has been divided. [Diagram 5] 1A and 1B show modified examples of an embodiment of a wafer dividing device of the present invention, in which (a) Modification 1 shows the state before grinding begins, (b) Modification 1 shows the state after grinding has ended, (c) Modification 2 shows the state before grinding begins, and (d) Modification 2 shows the state after grinding has ended. [Figure 6] FIG. 13 is a diagram illustrating a modified example 2A of the embodiment of the wafer dividing device of the present invention. [Figure 7]FIG. 13 is a diagram illustrating a modified example 2B of the embodiment of the wafer dividing device of the present invention. [Figure 8] 1A and 1B show modified examples of an embodiment of a wafer dividing device of the present invention, in which (a) Modified Example 3 shows the state before grinding starts, (b) Modified Example 4 shows the state before grinding starts, (c) Modified Example 5 shows the state before grinding starts, and (d) Modified Example 6 shows the state before grinding starts. [Figure 9] This explains the current method of obtaining wafers from an ingot, and shows (a) an example of the shape of an ingot made of a semiconductor, (b) a state in which the ingot is sliced ​​with a wire, (c) a state in which the ingot has been sliced, and (d) a state in which the ingot has been separated into multiple wafers by slicing. [Figure 10] This explains a semiconductor manufacturing process using wafers sliced ​​from an ingot, and shows (a) a fixed plate facing the back surface of the wafer, (b) the back surface being held by the fixed plate, (c) the front surface after planarization, (d) a number of semiconductor devices formed on the planarized surface, and (e) a fixed plate facing the surface on which the number of semiconductor devices are formed. [Figure 11] This explains the semiconductor manufacturing process using a wafer, and shows (a) the state in which a fixing plate is attached to a surface on which a large number of semiconductor devices are formed, (b) the state in which the entire wafer is inverted from the same state, (c) the state in which the fixing plate on the back side of the wafer is peeled off, (d) the state in which the fixing plate on the back side of the wafer has been peeled off, (e) the state in which the back side of the wafer has been thinned by grinding it and then flattened, and (f) the state in which an electrode film has been formed on the flattened back side of the wafer. [Figure 12] FIG. 1 is a cross-sectional view showing an example of the structure of a power semiconductor device. [Figure 13]The semiconductor manufacturing process using a wafer is explained using a cross section of one device region, and shows (a) a fixed plate facing the back surface of the wafer, (b) the back surface being held by the fixed plate, (c) the front surface after planarization, (d) semiconductor devices formed on the planarized surface, and (e) a fixed plate facing the surface on which the semiconductor devices are formed. [Figure 14] The semiconductor manufacturing process using a wafer is explained with a cross section of one device region, and (a) shows the state in which a fixing plate is attached to the surface on which the semiconductor device is formed, (b) shows the state after the entire process is inverted from the same state, (c) shows the state in which the fixing plate on the back side of the wafer is peeled off, (d) shows the state after the fixing plate on the back side of the wafer has been peeled off, (e) shows the state after the back side of the wafer has been thinned by grinding and then planarized, and (f) shows the state after an electrode film has been formed on the back side of the planarized wafer. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0034] An embodiment of the present invention will be described with reference to the drawings. Fig. 1 is a diagram for explaining an embodiment of a wafer dividing method of the present invention. In Fig. 1(a), a wafer 10 is sliced ​​from an ingot and has a disk shape with a thickness that is free of warping or distortion. Here, although it depends on the wafer size, for a 6-inch size, a thickness of less than 350 μm tends to cause warping, and for a 4-inch size, a thickness of less than 250 μm tends to cause warping, so the thickness of wafer 10 is preferably 250 μm or more. On the other hand, if the thickness after splitting into two is greater than or equal to a thickness that does not (single-handedly) cause warping or distortion, there is no point in implementing the present invention, so the thickness of wafer 10 in FIG. 1(a) is preferably 800 μm or less.

[0035] The wafer 10 is made of semiconductor crystals, and the material is preferably silicon carbide (SiC), which is suitable for power semiconductors, but may also be a compound semiconductor such as gallium nitride (GaN) or gallium oxide (Ga2O3). The present invention is also effective for silicon (Si). In addition, the wafer is not limited to pure semiconductor crystals, and may contain dopants to make it a P-type semiconductor or an N-type semiconductor. In other words, the wafer 10 can be said to be made of at least semiconductor crystals.

[0036] Generally, the mobility of electrons varies depending on the crystal orientation. For this reason, in the device structure shown in FIG. 12, it is necessary to align the surface on which the device is formed with a specific crystal orientation so that the electron mobility in the thickness direction (d direction) is high. For this reason, the wafer surface 10S is aligned with the specific crystal orientation.

[0037] In FIG. 1(a), the back fixing plate 2 is a substrate 20 on which an adhesive film 21 is laminated, and as shown in FIG. 1(b), the back surface of the wafer 10 (the surface opposite to the wafer surface 10S) is brought into close contact with the adhesive film 21, thereby fixing the wafer 10 to the back fixing plate 2. The front fixing plate 3 is a substrate 30 on which an adhesive film 31 is laminated, and the wafer 10 is fixed to the front fixing plate 3 by bringing the wafer surface 10S into close contact with the adhesive film 31. Here, the surface shapes of the back fixing plate 2 and the front fixing plate 3 are circular and of the same size as the wafer 10, but are not limited to this. However, it is preferable that the back fixing plate 2 fixes the entire back surface, and the front fixing plate 3 fixes the entire surface of the wafer surface 10S. It is also preferable that the adhesive film has a property of being easily peeled off by carrying out some kind of treatment, and for example, REVALPHA (registered trademark), which is a thermal peeling sheet, is preferably used.

[0038] The substrates 20 and 30 are made of a material and have a thickness that allows them to be flat and have rigidity. It is also preferable that the adhesive films 21 and 31 are flat. It is also preferable that the adhesive film 21 generates as little degassing as possible even under vacuum.

[0039] After fixing both sides of the wafer 10 with the back fixing plate 2 and the front fixing plate 3 as shown in FIG. 1(b), a wire 70 as shown in FIG. 1(c) is placed near the middle of the wafer 10 in the thickness direction, and the wafer 10 is cut by grinding and divided into two pieces. FIG. 1(d) shows the state after division, in which the wafer 10 is divided into two pieces, the thin wafer 11 and the thin wafer 12. Here, the thicknesses of the thin wafers 11 and 12 are less than half the thickness of the wafer 10 (because at least the thickness portion corresponding to the thickness of the wire 70 is removed during grinding). For this reason, both the thin wafer 11 and the thin wafer 12 would be warped or distorted when used alone, but as shown in FIG. 1(d), the thin wafer 11 is fixed to the flat back fixing plate 2 and the thin wafer 12 is fixed to the flat front fixing plate 3, so no warping or distortion occurs.

[0040] Incidentally, in this embodiment, the wire 70 constitutes the wire saw 7 (not shown), and is a high-strength steel wire such as a piano wire with abrasive grains attached to it. Here, diamond, which has excellent hardness, is preferably used as the material of the hard particles that become the abrasive grains, but when the wafer 11 is modified using a laser as described later, zirconia (ZrO2), silicon carbide, etc. can also be used. Note that, assuming that the maximum size of the abrasive grains is the abrasive grain size, and the maximum width in a state where the abrasive grains are attached to the base wire is the wire thickness, in order to maintain the strength of the wire while grinding without damaging even thin wafers, the abrasive grain size is preferably 5 μm or more and 10 μm or less, and the wire thickness is preferably 30 μm or more and 100 μm or less. That is, the wire 70 is thinner and has a smaller abrasive grain size than the wire 170 shown in FIG. 9(b). This reduces the amount of material removed during cutting, and minimizes the unevenness of the cut surface after division.

[0041] After being divided as shown in Fig. 1(d), the thin wafer surface 11S of the thin wafer 11 is suitable for device formation, and since it is fixed to the rear surface fixing plate 2 shown in Fig. 10(b), the same processes as those shown in Fig. 10(c) to Fig. 11(f) can be carried out. However, since the thin wafer 11 is thinner than the wafer 10, the polishing thickness can be reduced in Fig. 11(d) to Fig. 11(e), and loss of semiconductor material can be reduced.

[0042] On the other hand, in the thin wafer 12 of Fig. 1(d), the wafer surface 10S of the wafer 10 is covered by the surface fixing plate 3, and the exposed back surface is not suitable for device formation. For this reason, the thin wafer 12 also needs to be in the state shown in Fig. 10(b), that is, in a state in which the thin wafer surface 12S (=wafer surface 10S) is exposed while the back surface is fixed. Fig. 2 shows the process of fixing the thin wafer 12 fixed to the surface fixing plate 3 to the back surface fixing plate 5 to expose the thin wafer surface 12S.

[0043] 2(a) shows a state in which a back fixing plate 5 is disposed near the back surface of a thin wafer 12 fixed to a front fixing plate 3. The back fixing plate 5 is formed by laminating an adhesive film 51 on a substrate 50, and as shown in FIG. 2(b), the back surface of the thin wafer 12 is brought into close contact with the adhesive film 51. Here, when proceeding with device formation on the thin wafer 12, the back fixing plate 5 is required to have the same function as the back fixing plate 2. In other words, the characteristics required for the substrate 50 and the adhesive film 51 of the back fixing plate 5 are the same as the characteristics required for the substrate 20 and the adhesive film 21 of the back fixing plate 2.

[0044] As shown in Fig. 2(b), an adhesive film 51 is adhered to the back surface of the thin wafer 12 and fixed with a back surface fixing plate 5, and then the front surface fixing plate 3 is peeled off as shown in Fig. 2(C). As a result, the thin wafer 12 fixed to the back surface fixing plate 5 is in a state in which the thin wafer front surface 12S (= wafer front surface 10S) is exposed as shown in Fig. 2(d). Since the back surface fixing plate 5 has the same function as the back surface fixing plate 2, the thin wafer 12 can be processed in the same manner as the thin wafer 11, as shown in Fig. 10(c) to Fig. 11(f).

[0045] Incidentally, the thin wafer 11 and the thin wafer 12 obtained by dividing the wafer 10 are not warped or distorted because either of their surfaces is fixed by a flat fixing plate. Therefore, the thin wafer 11 and the thin wafer 12 can be further divided to obtain ultra-thin wafers. For example, the thin wafer 12 in the state shown in FIG. 2(b) may be cut by grinding with the wire 70 from the same state as the wafer 10 in FIG. 1(c) to obtain two ultra-thin wafers. The thin wafer 11 can also be cut by attaching a fixing plate to the thin wafer surface 11S side and then cutting to obtain two ultra-thin wafers. Here, if the thickness of the thin wafer 11 or the ultra-thin wafer 12, or even the thickness of the ultra-thin wafer, is 100 μm or more, it is not difficult to divide it into two in terms of the cutting margin of the wire 70 and positional accuracy. In addition, since the thickness of the wafer 10 is 800 μm or less, the upper limit of the thickness of a thin wafer having either of its surfaces fixed to a fixing plate is 400 μm. Therefore, when the present invention is applied to a thin wafer (or an extremely thin wafer) bonded to a flat fixing plate, a thickness of 100 μm or more and 400 μm or less can be preferably used.

[0046] 1(c) and 1(d) show that the wire 70 cuts and divides the wafer 10 by grinding, and FIG. 3 shows an embodiment of a wafer dividing device that performs the cutting.

[0047] In Fig. 3(a), wafer rotation jig 8S consisting of rotation shaft 80S and pressure plate 81S, and wafer rotation jig 8B consisting of rotation shaft 80B and pressure plate 81B are arranged to rotate about the same linear rotation axis, constituting wafer rotation means 8. In Fig. 3, pressure plate 81S and pressure plate 81B have a square shape, but are not limited to this and may be a circle or a polygon (other than a square).

[0048] The pressing plate 81S has a function of holding the substrate 30 of the front fixing plate 3. That is, the surface of the pressing plate 81S facing the front fixing plate 3 has a function of holding the substrate 30 by suction or the like. Similarly, the pressing plate 81B has a function of holding the substrate 20 of the back fixing plate 2 by suction or the like.

[0049] With the pressing plate 81S holding the substrate 30 on the front surface fixing plate 3 and the pressing plate 81B holding the substrate 20 on the back surface fixing plate 2, the rotating jig 8 is in a state in which the wafer 10 is sandwiched on both sides via the front surface fixing plate 3 and the back surface fixing plate 2, as shown in Figure 3(b).

[0050] At least one of the rotating shafts 80S and 80B is connected to a rotational power source (not shown) to rotate the wafer 10. When the rotating jig 8 clamps the wafer 10 from both sides via the front fixing plate 3 and the back fixing plate 2, it is desirable to align the central axes of the rotating shafts 80S and 80B with the center of the wafer 10 as much as possible.

[0051] 3(b), when the wire 70 of the wire saw 7 is brought into close contact with the outer periphery of the wafer 10 while the wafer 10 is rotating, the outer periphery of the wafer 10 is ground by abrasive grains attached to the surface of the wire 70. In the process of grinding the wafer 10, the abrasive grains may come off the wire 70 or the wire 70 may be damaged. Therefore, the wire 70 is run in sequence to collect the portion used to grind the wafer 70.

[0052] 3(b), if the positions and interval DX between presser plates 81S and 81B are not stable, it is not preferable because the cut surface will be inclined or uneven. For this reason, while grinding is being performed by wire 70, the positions of presser plates 81S and 81B (in the X direction) are controlled to be suppressed.

[0053] 4 is a cross-sectional view showing the process in which the wire 70 cuts the wafer 10 by grinding. In FIG. 4(a), the wire 70 has left the wafer 10 and grinding has not started, but the wafer 10 is sandwiched between the presser plates 8 (8S and 8B) and rotating. In FIG. 4(b), grinding by the wire 70 progresses from the surface of the wafer 10 to the inside, and in FIG. 4(c), grinding has reached the center, and the wafer 10 has been divided into thin wafer 11 and thin wafer 12.

[0054] By the way, the wafer dividing device as shown in Fig. 3 can divide one wafer into two thin wafers, and the efficiency of material utilization is improved, but the time required from the start to the end of grinding is the same as in the conventional device. Therefore, some modified examples that were considered as a method of increasing the grinding speed for the embodiment shown in Fig. 3 and Fig. 4 are shown below.

[0055] FIG. 5(a) shows a first modified example of the embodiment, showing a state before grinding is started. In the first modified example, a laser irradiation means 71 is provided. Here, the material constituting the wafer 10 is altered by irradiating the wafer with laser light L by the laser irradiation means 71, and the wire 70 can efficiently grind the wafer 10. When irradiating the wafer 10 with the laser light L, it is preferable that the irradiation spot diameter is 80% or more and 120% or less of the width (diameter) of the wire 70 in terms of grinding speed, accuracy, and grinding width. In addition, the optimum value of the wavelength of the laser light L differs depending on the material of the wafer 10, but in the case of silicon carbide, the absorption wavelength is preferably around 450 nm, and it is preferable that it is 430 nm or more and 470 nm or less.

[0056] In the first modification, the laser light emitted by the laser irradiation means 71 is focused on the location (depth) of contact with the wire 70. That is, in the process of the wafer 10 being ground by the wire 70, it is preferable to focus on a location of the wafer 10 just before the wire 70 comes into contact with the wafer 10. Fig. 5(b) shows the state after grinding is completed in the first modification of the embodiment.

[0057] As described above, it is preferable to focus the laser light emitted by the laser irradiation means 71 on a location (depth) just before contact with the wire 70, and such a location is the bottom of the groove formed by cutting with the wire 70. In such a groove, shavings may remain inside the groove, and the laser light may not reach the bottom of the groove.

[0058] In response to such a situation, the modified embodiment 2 shown in FIG. 5(c) and FIG. 5(d) is provided. The modified embodiment 2 is provided with a fluid ejection means 71 that uses a fluid to remove the shavings remaining in the groove. The fluid ejection means 71 ejects gas or liquid, and ejects the gas or liquid toward the groove of the wafer 10 (created by the cutting by the wire 70) to remove the shavings remaining in the groove. The fluid ejection means 71 is disposed along the rotation direction of the wafer 10 between the point where the wire 70 contacts and the point where the laser irradiation means 71 irradiates the laser light, so that the shavings created by the cutting by the wire 70 can be discharged from the groove before the laser light is irradiated into the groove, and the laser light can be irradiated to the bottom of the groove. This allows the wafer 10 to be efficiently ground and cut, and the time from the start of grinding shown in FIG. 5(c) to the completion of grinding shown in FIG. 5(d) can be shortened compared to the embodiment shown in FIG. 4. It is also possible to adopt a configuration in which the irradiation of the laser light L is performed to proceed partway with grinding by the wire 70, the shavings are removed, and then the irradiation of the laser light L and grinding by the wire 70 are repeated again.

[0059] Incidentally, in the figures described so far, an embodiment in which the wire 70 grinds the wafer 10 by descending the wafer 10 has been shown, but the wire 70 may not descend and the wafer 10 may rise. However, in the case of an apparatus configuration including the laser irradiation means 71 and the fluid jetting means 72, it is desirable that the location of the laser beam irradiated on the wafer 10 and the direction of jetting the fluid (gas or liquid) are constant, so it is preferable to have a configuration in which the positions of the laser irradiation means 71 and the fluid jetting means 72 relative to the wafer 10 are not changed and the whole is raised as in the modified example 2A of the embodiment in FIG. 6. In other words, it is preferable to have a configuration in which the wafer rotation means 8 for rotating the wafer 10, the laser irradiation means 71, and the fluid jetting means 72 are moved together, or the wire saw 7 is moved.

[0060] As a further modification of the modification 2 of the embodiment, modification 2B is shown in Fig. 7. Modification 2B is different from the configuration of modification 2 shown in Fig. 5(c) in that the inclination of the wire 70 is changed to slightly change the location where the wafer 10 is cut. By changing the inclination in this way, it is possible to prevent the shavings from clinging to the wire 70, and a decrease in cutting efficiency is prevented.

[0061] In addition, in the embodiment shown in Figures 4 to 6, the wire 70 is moved in a vertical direction, but this is not limited to this. For example, even if the wire 70 is moved in the -Y direction or -Z direction in the orientation of the wire 70 as shown in Figures 8(a) to 8(c), it is possible to grind and cut the wafer 10. Note that Figure 8(a) shows a third modified embodiment having the same components as Figure 4(a), Figure 8(b) shows a fourth modified embodiment having the same components as Figure 5(a), and Figure 8(c) shows a fifth modified embodiment having the same components as Figure 5(c).

[0062] Furthermore, the present invention is also effective in a configuration in which the wire 70 is attached in the vertical direction (Z direction) as in the sixth modified example of the embodiment shown in FIG. 8(d).

[0063] As described above, the semiconductor wafer dividing method of the present invention makes it possible to increase the number of wafers that can be obtained from a semiconductor crystal ingot compared to the conventional method, and the semiconductor wafer processing method of the present invention makes it possible to obtain many devices. Furthermore, the wafer separation device of the present invention makes it possible to increase the grinding speed compared to conventional wire grinding, making it possible to divide the wafers at high speed. [Explanation of symbols]

[0064] 1 ingot 2 Rear fixing plate 3 Surface fixing plate 4 Device protection fixing plate 5 Back fixing plate 6. Semiconductor Devices 7 Wire saw 8 Wafer Rotation Means 8S, 8B Wafer rotation fixture 10 Wafer (original thickness) 10S Wafer surface 11, 12 Thin wafer 11S, 12S thin wafer surface 20, 30, 40, 50 boards 21, 31, 41, 51 Adhesive film 60p area 61 n+ region 62 Gate oxide 63 Gate electrode 64 Source electrode 70, 170 Wire 71 Laser irradiation means 72 Fluid ejection means 80, 80S, 80B Rotating shaft 81, 81S, 81B Presser plate 6102M Drain electrode F Fluid (liquid flow or air flow) L Laser light RC Rotating Axis

Claims

1. 1. A method for dividing a wafer to obtain thin wafers, comprising the steps of: Fixing plates are attached to both sides of a wafer made of at least a semiconductor crystal; With both sides of the fixing plate held in place, A wafer dividing method in which the wafer is cut near the middle in the thickness direction to obtain two thin wafers attached to a fixing plate.

2. Of the two thin wafers obtained by the wafer dividing method according to claim 1, the thin wafer having the surface with the predetermined crystal orientation exposed is divided into two thin wafers, After the surface of the substrate on the specified crystal orientation side is flattened while the substrate is attached to the fixed plate, A wafer processing method in which a plurality of devices are formed on the surface that has been subjected to the planarization treatment.

3. Of the two thin wafers obtained by the wafer dividing method according to claim 1, the thin wafer having a surface with a predetermined crystal orientation attached to a fixing plate is divided into two thin wafers by the following steps: After the exposed surface is attached to a fixing plate, the fixing plate of the surface having the predetermined crystal orientation is peeled off, After flattening the surface on the specified crystal orientation side, A wafer processing method in which a plurality of devices are formed on the surface that has been subjected to the planarization treatment.

4. Fixing plates are attached to both sides of the wafer, and while the fixing plates on both sides are held, A wafer dividing device for dividing the wafer into two thin wafers, a wafer rotating means for holding the wafer on both sides via the fixing plates and rotating the wafer in a plane parallel to the wafer surface; a wafer dividing device comprising a wire saw having a wire provided perpendicular to the rotation axis of the wafer rotating means;

5. 5. The wafer dividing apparatus according to claim 4, Further comprising a laser irradiation means, A wafer dividing device that irradiates the wafer with laser light, focusing the light on the point where the wire contacts the wafer.

6. 6. The wafer dividing apparatus according to claim 5, A wafer dividing device that irradiates the wafer with laser light before the wire contacts the wafer.

7. 7. The wafer dividing apparatus according to claim 6, Further comprising a fluid ejection means for ejecting a gas or a liquid, A wafer dividing device that ejects gas or liquid toward the portion of the wafer that comes into contact with the wire saw.

8. A wafer dividing apparatus according to any one of claims 4 to 7, A wafer dividing device, wherein the wire has a thickness of 30 μm or more and 100 μm or less.

9. 9. The wafer dividing apparatus according to claim 8, The wire has abrasive grains attached to its surface, A wafer dividing device, wherein the maximum size of the abrasive grains is 5 μm or more and 10 μm or less.

10. A wafer dividing apparatus according to any one of claims 4 to 7, A wafer dividing apparatus, wherein the wafer is a silicon carbide wafer.

11. A wafer dividing apparatus according to any one of claims 5 to 7, A wafer dividing apparatus, wherein the wafer is a silicon carbide wafer and the wavelength of the laser light is 430 nm or more and 470 nm or less.

12. A wafer dividing apparatus according to any one of claims 4 to 7, A wafer dividing device, wherein the thickness of the wafer is 250 μm or more and 800 μm or less.

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