Composite wafer and method for manufacturing composite wafer

Abstract

This composite wafer comprises: a functional substrate including a functional material; and a support substrate made of a semiconductor material and bonded to the functional substrate to support the functional substrate. A step is formed at the outer edge of the composite wafer, and a marking portion on which a specific character or symbol is printed is provided below the step.

Description

Composite Wafer and Method for Manufacturing Composite Wafer

[0001] The present invention relates to a composite wafer and a method for manufacturing the same.

[0002] Conventionally, LN (LiNbO ３ : lithium niobate) and LT (LiTaO ３ : lithium tantalate) and other piezoelectric materials. A composite wafer formed by bonding a functional substrate made of such a piezoelectric material and a supporting substrate made of a semiconductor material such as Si, and used for applications such as surface acoustic wave devices is known. For example, Patent Document 1 discloses, as an example of the above-mentioned composite substrate for a surface acoustic wave device, a POI (Piezoelectric On Insulator) substrate in which a charge trap layer for absorbing charges is provided between a piezoelectric layer and a supporting substrate. In the POI substrate, for example, polycrystalline silicon, amorphous silicon, porous silicon, or the like is used as the trap-rich layer.

[0003] In addition, when manufacturing semiconductor devices using semiconductor wafers as materials, laser marking, in which specific characters and symbols are engraved on each wafer surface using laser light, is sometimes performed for purposes such as traceability management. For example, Patent Document 2 describes a nitride semiconductor wafer with a laser mark marked on the front surface, back surface, or end face, wherein the laser mark is formed by arranging numbers, English letters, or symbols formed by double dots conforming to the SEMI standard, the maximum height per character of the numbers, English letters, or symbols is 0.7 mm or more and 1.3 mm or less, the maximum depth of the dots constituting the laser mark is 10 μm or more and 100 μm or less, and is 27% or less of the wafer thickness.

[0004] Japanese Patent Publication No. 2023-544271; Japanese Unexamined Patent Publication No. 2014-154661

[0005] A semiconductor wafer made of a composite substrate, such as that described in Patent Document 1, is used as a composite wafer for materials such as surface acoustic wave devices. However, if laser marking, as described in Patent Document 2, is performed on the surface of the functional substrate of such a composite wafer, it becomes impossible to form a circuit pattern in that area, making it unusable as a device. Thus, when laser marking is performed on a composite wafer, the effective area is reduced by the amount of the marked area.

[0006] The present invention has been made in view of the above, and its main objective is to perform marking on a composite wafer formed by joining a functional substrate and a support substrate without reducing the effective area.

[0007] The composite wafer according to the present invention comprises a functional substrate composed of a functional material and a support substrate made of a semiconductor material, which is bonded to the functional substrate and supports the functional substrate, wherein a step is formed on the outer edge of the composite wafer, and a marking area on the lower side of the step has a specific character or symbol printed on it. The method for manufacturing a composite wafer according to the present invention is a method for manufacturing a composite wafer comprising a functional substrate composed of a functional material and a support substrate made of a semiconductor material that supports the functional substrate, and includes a planarization step for reducing the surface roughness of the functional substrate and the support substrate, respectively; an activation step for activating at least one surface of the functional substrate and the support substrate using a rare gas after the planarization step; a bonding step for joining the surfaces of the functional substrate and the support substrate to form a bonded body after the activation step; a step formation step for removing the outer edge of the functional substrate of the bonded body formed in the bonding step to form a step; and a laser printing step for printing a character or symbol in the area on the lower side of the step formed in the step formation step by laser engraving.

[0008] According to the present invention, marking can be performed on a composite wafer formed by joining a functional substrate and a support substrate without reducing the effective area.

[0009] This is a diagram showing an overview of a composite wafer according to the first embodiment of the present invention. This is an enlarged view of the area near the marking. This is a cross-sectional view of the area near the marking. This is a flowchart showing the manufacturing process of a composite wafer according to the first embodiment of the present invention. This is a diagram showing an overview of a composite wafer according to the second embodiment of the present invention.

[0010] The embodiments of the present invention will be described below with reference to the drawings, but the present invention is not limited to these embodiments. In addition, the drawings may be schematically represented in terms of the width, thickness, shape, etc. of each part compared to the embodiments in order to make the explanation clearer, but these are merely examples and do not limit the interpretation of the present invention.

[0011] (First Embodiment) Figure 1 is a diagram showing an overview of a composite wafer according to the first embodiment of the present invention. Figure 1(a) is a plan view of the composite wafer 100 of this embodiment, and Figure 1(b) is a partial cross-sectional view of the composite wafer 100 of this embodiment.

[0012] The composite wafer 100 of this embodiment is a type of semiconductor wafer used as a material for various devices, such as optical elements that constitute optical waveguides, piezoelectric elements that constitute surface acoustic wave (SAW) filters, and various semiconductor elements. It has a structure in which a functional substrate 10 made of functional materials such as piezoelectric materials and semiconductor materials is bonded to a support substrate 20.

[0013] The material of the functional substrate 10 is, for example, LN(LiNbO ３ : Lithium niobate or LT (LiTaO) ３ (Lithium tantalate), quartz, silica, AlN (aluminum nitride), PZT (Pb(Zr,Ti)O ３Piezoelectric materials such as lead zirconate titanate are used. The material of the functional substrate 10 can be arbitrarily selected according to the application of the device formed using the composite wafer 100 as the material. For example, in addition to piezoelectric materials, the functional substrate 10 may be constructed using semiconductor materials such as Si, SiC, InP, GaN, GaP, and diamond, materials having electro-optical effects such as lithium niobate-lithium tantalate and KTP (potassium titanate phosphate), glass, and sapphire. In addition to these, a functional substrate 10 made of various functional materials can be used depending on the application of the device manufactured using the composite wafer 100.

[0014] The support substrate 20 supports the functional substrate 10 by being bonded to it. Any suitable substrate can be used as the support substrate 20. The support substrate 20 may be made of a single crystal or a polycrystalline material.

[0015] The support substrate 20 can be made of semiconductor materials such as Si, Ge, SiC, InP, or GaN, or insulating materials such as quartz glass or sapphire. The thickness of the support substrate 20 is, for example, 0.2 to 1 mm, but any other appropriate thickness can be used.

[0016] As shown in Figure 1(a), the composite wafer 100 has a substantially disc shape surrounded by a circumferential outer edge. An orientation flat portion 50 is formed on the composite wafer 100 by cutting a straight line out of a part of the outer edge. This orientation flat portion 50 is used for positioning the composite wafer 100 in the device manufacturing process. Alternatively, instead of the orientation flat portion 50, the composite wafer 100 may be positioned using a notch formed by making a cut in a part of the outer edge. The size of the composite wafer 100 can be appropriately set according to the intended use, for example, a diameter of 50 mm to 150 mm.

[0017] As shown in Figures 1(a) and 1(b), the composite wafer 100 has a structure in which a functional substrate 10 is bonded to a support substrate 20. However, a step is formed along the circumferential outer edge, and a region 21 is partially formed below this step, where the support substrate 20 is exposed on the surface side. This region 21 is provided in the composite wafer 100 to suppress the occurrence of lifting and the progression of delamination at the bonding interface between the functional substrate 10 and the support substrate 20. In other words, if region 21 is not provided in the composite wafer 100, the bonding interface between the functional substrate 10 and the support substrate 20 will be exposed on the outer peripheral end surface of the composite wafer 100, making it easier for lateral forces to be applied to the bonding interface, which may cause lifting and delamination. Therefore, in the composite wafer 100 of this embodiment, a step is formed along the outer edge, and the area below this step is designated as region 21 to suppress the occurrence of lifting and the progression of delamination at the bonding interface. Note that the support substrate 20 does not necessarily have to be exposed in region 21. For example, even if the surface of the support substrate 20 in region 21 is covered with an oxide film or the like, it is possible to suppress the occurrence of lifting and the progression of delamination at the bonding interface.

[0018] In the region 21 described above, a marking area 51 is provided adjacent to the orientation flat portion 50. Characters or symbols are printed on this marking area 51 by laser engraving. For example, by printing different characters or symbols on the marking area 51 for each individual composite wafer 100, individual identification of the composite wafer 100 becomes possible, which can be used for traceability management, etc. In addition to this, the characters or symbols to be printed on the marking area 51 can be determined according to any other purpose.

[0019] Here, as shown in Figure 1(a), the composite wafer 100 has a shape that is line-symmetric in the plane direction with respect to the axis of symmetry 101. The marking location 51 is located away from the center of the orientation flat portion 50 indicated by this axis of symmetry 101. In other words, the marking location 51 is located asymmetrically with respect to the axis of symmetry 101. This makes it possible to easily determine the front and back of the composite wafer 100 even if the front and back sides of the composite wafer are reversed, by recognizing the position of the marking location 51 and determining whether that position is to the left or right of the axis of symmetry 101. Furthermore, by placing the marking location 51 on the outer edge side rather than the functional substrate side, below the step formed along the outer edge of the composite wafer 100, it is possible to suppress heat conduction to the functional substrate.

[0020] Figure 2 is an enlarged view of the area around the marking location 51 in region 21 of Figure 1. Figure 2(a) shows the entire marking location 51, and Figure 2(b) shows a further enlargement of a part of the marking location 51 (the part indicated by reference numeral 52 in Figure 2(a)). The marking location 51 has a combination of characters and symbols printed on it, for example, as shown in Figure 2. Note that the combination of characters and symbols shown in Figure 2 is just an example, and any combination of characters and symbols can be printed on the marking location 51.

[0021] In the composite wafer 100 of this embodiment, as shown in Figure 2(a), for example, the characters or symbols printed on the marking area 51 and the parts of the region 21 other than the marking area 51 have different appearances. Specifically, the characters or symbols printed on the marking area 51 have a darker appearance than the rest of the region 21. This makes it easy to identify the characters or symbols printed on the marking area 51 with the human eye or a camera. Furthermore, the characters or symbols printed on the marking area 51 are formed by combining a plurality of grooves 53 (three in the example of Figure 2(b)) that are arranged in the line width direction, as shown in Figure 2(b). These grooves 53 correspond to the scanning traces of a laser irradiated onto the region 21, and can be formed by scanning the laser along any character or symbol.

[0022] Figure 3 is a cross-sectional view of the composite wafer 100 near the marking location 51. In Figure 3, the upper view shows a cross-section of the support substrate 20 including the marking location 51 (cross-section A-A' in Figure 2(b)). The lower view shows a magnified view of the cross-section of the printed portion 60 corresponding to the characters and symbols printed on the marking location 51.

[0023] As shown in Figure 3, in the printed area 60, a plurality of grooves 53, each having a roughly semicircular cross-section, are formed in a row on the surface of the support substrate 20, and characters and symbols are represented using lines formed by combinations of these grooves 53. The direction in which these grooves 53 are arranged coincides with the width direction of the lines used for characters and symbols. That is, in the marking area 51, the parts of the grooves 53 formed by irradiating the surface of the support substrate 20 exposed in the region 21 with a laser become valleys, and the parts sandwiched between adjacent grooves 53 become peaks. Since these parts have a different appearance and color compared to other parts, they can be used as lines to represent characters and symbols. The depth of the grooves 53 (valleys) in the marking area 51 is, for example, 2 μm or more and 8 μm or less. These lower and upper limits can be determined at appropriate values ​​based on the visibility of characters and symbols in the marking area 51 and the printing efficiency by laser irradiation.

[0024] Here, in order to confirm whether there is a difference in composition between the laser-irradiated and unirradiated parts of the printed portion 60 in Figure 3, EDX analysis was performed on the analysis positions indicated by reference numerals 61, 62, and 63 within the support substrate 20. Analysis position 61 corresponds to the unirradiated part inside the support substrate 20. On the other hand, analysis position 62 corresponds to the bottom of the groove 53 (valley) on the surface of the support substrate 20, and analysis position 63 corresponds to the peak of the mountain on the surface of the support substrate 20. These analysis positions 62 and 63 correspond to the laser-irradiated parts of the support substrate 20.

[0025] The EDX analysis results for the above analysis locations 61, 62, and 63 did not reveal any significant differences in composition at any of the analysis locations. This confirmed that laser marking does not cause any changes in composition when marking is performed on the support substrate 20.

[0026] Figure 4 is a flowchart showing the manufacturing process of a composite wafer according to the first embodiment of the present invention.

[0027] In step S101, the functional substrate 10 and the support substrate 20 are prepared. Here, for example, an X-cut LN substrate with a diameter of 4 inches and a thickness of 500 μm and a silicon substrate with a diameter of 4 inches and a thickness of 500 μm are prepared as the functional substrate 10 and the support substrate 20, respectively.

[0028] In step S102, the surfaces of the functional substrate 10 and the support substrate 20 prepared in step S101 are cleaned, and then a planarization process is performed to reduce the surface roughness of each. Here, for example, the surfaces of the functional substrate 10 and the support substrate 20 are polished and planarized so that the calculated average surface roughness of both surfaces is 0.2 nm or less.

[0029] In step S103, the surfaces of the functional substrate 10 and the support substrate 20, which were planarized in step S102, are activated. Here, for example, the activation treatment is performed by irradiating the surfaces of the functional substrate 10 and the support substrate 20 with a high-speed atomic beam (hereinafter referred to as FAB) using a noble gas such as Ar as the atomic species for a predetermined time. Alternatively, the activation treatment may be performed by irradiating only one of the surfaces of the functional substrate 10 or the support substrate 20 with the FAB.

[0030] In step S104, the surfaces of the functional substrate 10 and the support substrate 20, which were activated in step S103, are brought into contact with each other and pressurized to bond them together. As a result, the functional substrate 10 and the support substrate 20 are joined together, and a bonded body is obtained.

[0031] In step S105, the outer edge of the functional substrate 10 is removed from the bonded body obtained in step S104. Here, for example, an edge grinding device is used to remove the outer edge of the functional substrate 10 to a predetermined width and a predetermined thickness including the bonding interface with the support substrate 20. As a result, a step is formed at the outer edge of the bonded body, and the region 21 shown in Figure 1 is formed below this step. Note that at this time, not only the functional substrate 10 but also a part of the support substrate 20 is removed.

[0032] In step S106, laser printing is performed on predetermined positions in the region 21 formed on the joint in step S105. Here, for example, a YVO4 laser is periodically irradiated at a predetermined pulse frequency, and the irradiation position is moved in the planar direction to form a plurality of grooves 53 aligned along the shape of predetermined characters or symbols. By repeating this process, a specific combination of characters or symbols can be printed at predetermined positions in the region 21, forming the marking locations 51 shown in Figures 1 and 2.

[0033] In step S107, the bonded body, in which the marking location 51 was formed at a predetermined position in the region 21 in step S106, is polished until the thickness of the functional substrate 10 reaches a predetermined value (for example, 0.5 μm).

[0034] The composite wafer 100 shown in Figure 1 is manufactured through the steps S101 to S107 described above.

[0035] According to the first embodiment of the present invention described above, the following effects are achieved.

[0036] (1) The composite wafer 100 comprises a functional substrate 10 made of a functional material and a support substrate 20 made of a semiconductor material, which is bonded to the functional substrate 10 and supports the functional substrate 10. A step is formed on the outer edge of the composite wafer 100, and below this step, a region 21 is formed in which the support substrate 20 is exposed on the surface side. The region 21 has a marking area 51 on which a specific character or symbol is printed. In this way, the marking area 51 is formed within the region 21 which is provided to suppress the occurrence of lifting and the progression of delamination at the bonding interface between the functional substrate 10 and the support substrate 20, so that marking can be performed on the composite wafer 100 formed by bonding the functional substrate 10 and the support substrate 20 without reducing the effective area.

[0037] (2) As shown in Figure 3, at the marking location 51, characters or symbols are printed by grooves 53 formed on the surface of the support substrate 20. These grooves 53 are formed to have a roughly semicircular cross-section with a depth of, for example, 2 μm or more and 8 μm or less, and the composite wafer 100 has a plurality of grooves 53 in the width direction of the line forming the character or symbol. In this way, any character or symbol can be printed at the marking location 51 in a form that is easy to read and will not disappear during the device manufacturing process.

[0038] (3) The composite wafer 100 has a substantially disc shape with an orientation flat portion 50 (or notched portion) formed on a part of its outer circumference. The marking location 51 is positioned adjacent to the orientation flat portion 50 (or notched portion). This makes it easy to position the marking location 51.

[0039] (4) In the composite wafer 100, the marking location 51 is positioned away from the center of the orientation flat portion 50. In other words, as shown in Figure 1, the composite wafer 100 has a shape that is symmetrical in the plane direction, and the marking location 51 is positioned asymmetrically with respect to the axis of symmetry 101 of the composite wafer 100. This makes the marking location 51 on the composite wafer 100 easily visible. Furthermore, when a transparent substrate or a substrate that can transmit infrared light is used as the composite wafer 100, it becomes possible to easily distinguish between the front and back sides of the composite wafer 100 from the position of the marking location 51.

[0040] (5) As shown in Figure 2, the characters or symbols printed on the marking area 51 and the parts of the area 21 other than the marking area 51 have different appearances. In this way, any character or symbol can be printed in a readable form at the marking area 51.

[0041] (6) A method for manufacturing a composite wafer 100 includes: a planarization step (step S102) to reduce the surface roughness of the functional substrate 10 and the support substrate 20, respectively; an activation step (step S103) to activate at least one surface of the functional substrate 10 and the support substrate 20 using a rare gas after the planarization step; a bonding step (step S104) to join the surfaces of the functional substrate 10 and the support substrate 20 to form a bonded body after the activation step; a step formation step (step S105) to remove the outer edge of the functional substrate 10 of the bonded body formed in the bonding step to form a step; and a laser printing step (step S106) to print characters or symbols in the region 21 below the step formed in the step formation step by laser engraving. In this manner, the functional substrate 10 and the support substrate 20 are joined together, and a region 21 is formed on the outer edge where the support substrate 20 is exposed on the surface side, making it possible to manufacture a composite wafer 100 having a marking area 51 with specific characters or symbols printed on it within the region 21.

[0042] (Second Embodiment) FIG. 5 is a diagram outlining a composite wafer according to a second embodiment of the present invention. FIG. 5(a) is a plan view of the composite wafer 100A of the present embodiment, and FIG. 1(b) is a partial cross-sectional view of the composite wafer 100A of the present embodiment.

[0043] Similarly to the composite wafer 100 described in the first embodiment, the composite wafer 100A of the present embodiment is a type of semiconductor wafer used as a material for various devices, such as optical elements constituting optical waveguides, piezoelectric elements constituting surface acoustic wave (SAW) filters, and various semiconductor elements. The difference between the composite wafer 100A of the present embodiment and the composite wafer 100 of the first embodiment lies in that the composite wafer 100A includes an intermediate layer 30 between the functional substrate 10 and the support substrate 20. In other respects, the composite wafer 100A of the present embodiment has the same structure as the composite wafer 100 of the first embodiment.

[0044] The intermediate layer 30 is disposed between the functional substrate 10 and the support substrate 20, and bonds the functional substrate 10 and the support substrate 20 to each other by being respectively coupled to these substrates. For the material of the intermediate layer 30, for example, an oxide of Si or Ge is used.

[0045] Similarly to the composite wafer 100 of the first embodiment, in the composite wafer 100A of the present embodiment, a step is formed along the circumferential outer edge, and a region 21 is formed on the lower side of this step. In this region 21, a marking portion 51 is provided at a position adjacent to the orientation flat portion 50, and the same characters and symbols as those described in the first embodiment are printed on the marking portion 51 by engraving using laser light.

[0046] The composite wafer 100A of the present embodiment is manufactured by adding a step of forming the intermediate layer 30 between, for example, step S101 and step S102 in the manufacturing process of FIG. 4 described in the first embodiment. In this film forming step, the intermediate layer 30 can be formed on the functional substrate 10 by, for example, sputtering or vapor deposition. Alternatively, the intermediate layer 30 may be formed on the support substrate 20, or an oxide film formed on the support substrate 20 may be used as the intermediate layer 30.

[0047] According to the second embodiment of the present invention described above, the same effects and advantages as those of the first embodiment are achieved.

[0048] It should be noted that the present invention is not limited to the embodiments described above, and can be implemented using any components without departing from the spirit of the invention.

[0049] The embodiments and modifications described above are merely examples, and the present invention is not limited to these, as long as the features of the invention are not impaired. Furthermore, although various embodiments and modifications have been described above, the present invention is not limited to these. Other embodiments conceivable within the scope of the technical idea of ​​the present invention are also included within the scope of the present invention.

[0050] 10: Functional substrate 20: Support substrate 21: Region 30: Intermediate layer 50: Orientation flat area 51: Marking area 100, 100A: Composite wafer 101: Axis of symmetry

Claims

1. A composite wafer comprising a functional substrate composed of a functional material and a support substrate made of a semiconductor material, which is bonded to the functional substrate and supports the functional substrate, wherein a step is formed on the outer edge of the composite wafer, and a marking area with a specific character or symbol printed on the lower side of the step is provided.

2. A composite wafer according to claim 1, wherein the letters or symbols are printed at the marking locations by grooves formed on the surface of the support substrate.

3. A composite wafer according to claim 2, wherein the groove has a depth of 2 μm or more and 8 μm or less and has a substantially semicircular cross-section.

4. A composite wafer according to claim 2, wherein the composite wafer has a plurality of grooves in the width direction of the lines forming the characters or symbols.

5. A composite wafer according to claim 1, wherein the composite wafer has a substantially disc shape with an orientation flat portion or a notched portion formed on a part of its outer circumference, and the marking portion is arranged adjacent to the orientation flat portion or the notched portion.

6. A composite wafer according to claim 5, wherein the marking location is located away from the center of the orientation flat portion.

7. A composite wafer according to claim 5, wherein the composite wafer has a shape that is symmetrical in the plane direction, and the marking location is arranged at a position asymmetrical to the left and right with respect to the axis of symmetry of the composite wafer.

8. A composite wafer according to claim 1, wherein the characters or symbols printed on the marking area and the parts other than the marking area have different appearances from each other.

9. A method for manufacturing a composite wafer comprising a functional substrate made of a functional material and a support substrate made of a semiconductor material that supports the functional substrate, the method comprising: a planarization step of reducing the surface roughness of the functional substrate and the support substrate; an activation step of activating at least one surface of the functional substrate and the support substrate using a rare gas after the planarization step; a bonding step of joining the surfaces of the functional substrate and the support substrate together to form a bonded body after the activation step; a step formation step of removing the outer edge of the functional substrate of the bonded body formed in the bonding step to form a step; and a laser printing step of printing characters or symbols in the region below the step formed in the step formation step by laser engraving.

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