Bonded silicon wafer and manufacturing method thereof

Abstract

To provide a joint silicon wafer with a small thickness and a high infrared reflectance, and a method for manufacturing the joint silicon wafer.SOLUTION: A joint silicon wafer includes: a supporting substrate silicon wafer; a monocrystalline silicon layer on the supporting substrate silicon wafer; and an infrared reflection silicon film and a silicon oxide film between the supporting substrate silicon wafer and the monocrystalline silicon layer. The infrared reflection silicon film includes amorphous silicon or polycrystalline silicon. The infrared reflection silicon film has a thickness of at least 15nm and the silicon oxide film has a thickness of 100nm or smaller.SELECTED DRAWING: Figure 1A

Description

[Technical Field]

[0001] The present invention relates to a bonded silicon wafer and a method for manufacturing the same. [Background technology]

[0002] A known example of a bonded silicon wafer is an SOI wafer, which is manufactured by subjecting superposed substrates to a bonding heat treatment (see, for example, Patent Document 1). Meanwhile, in recent years, there has been a need for highly sensitive infrared light receiving sensors in fields such as surveillance cameras and automobile collision prevention sensors, and efforts are being made to utilize silicon wafers, which have traditionally been used as sensors in the visible light region. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-216356 Summary of the Invention [Problem to be solved by the invention]

[0004] Both single crystal silicon and silicon oxide have low reflectivity to infrared light and are relatively transparent. Therefore, if single crystal silicon or silicon oxide is used as the infrared reflective layer of an infrared light receiving sensor, the infrared reflective layer must be approximately 100 μm thick. If the thickness of the infrared reflective layer can be reduced, the infrared light receiving sensor can be made smaller. Therefore, an object of the present invention is to provide a bonded silicon wafer that is thin and has high infrared reflectivity, and a method for manufacturing the same. [Means for solving the problem]

[0005] The present inventors conducted research to solve the above-mentioned problems and investigated the use of amorphous silicon or polycrystalline silicon instead of silicon oxide, which has been commonly used as an infrared-reflecting silicon film in silicon wafer-based devices. Because both amorphous silicon and polycrystalline silicon have higher infrared reflectivity than silicon oxide, extensive research was conducted in the hope of obtaining a bonded silicon wafer with excellent infrared reflection efficiency. The present inventors then discovered that by controlling the thickness of the amorphous silicon layer or polycrystalline silicon layer in the infrared-reflecting layer and, from the perspective of the manufacturing method, controlling the heat treatment conditions during bonding, a bonded silicon wafer with significantly improved infrared reflectivity can be obtained. The present invention was completed based on the above-mentioned findings, and its gist and configuration are as follows.

[0006] <1> A bonded silicon wafer comprising: a silicon wafer for a support substrate; a single-crystal silicon layer on the silicon wafer for a support substrate; and an infrared-reflecting silicon film and a silicon oxide film provided between the silicon wafer for a support substrate and the single-crystal silicon layer, wherein the infrared-reflecting silicon film contains amorphous silicon or polycrystalline silicon, and the thickness of the infrared-reflecting silicon film is 15 nm or more, and the thickness of the silicon oxide film is 100 nm or less.

[0007] <2> The thickness of the infrared reflective silicon film is 25 nm or more. <1> 2. The bonded silicon wafer according to claim 1.

[0008] <3> The thickness of the single crystal silicon layer is 3 μm or more and 30 μm or less. <1> or <2> 2. The bonded silicon wafer according to claim 1.

[0009] <4> the above <1> ~ <3> a silicon oxide film forming step of forming a silicon oxide film having a thickness of 100 nm or less on the surface of a silicon wafer for use as a single crystal silicon layer; a bonding step of bonding the silicon wafer for use as a support substrate and the silicon wafer for use as a single crystal silicon layer together by heat treating the silicon wafer for use as a support substrate and the silicon oxide film at a temperature of 700°C or less, with the infrared reflective silicon film and the silicon oxide film interposed therebetween; and a thickness reducing step of reducing the thickness of the silicon wafer for use as a single crystal silicon layer to obtain the single crystal silicon layer, after the bonding step.

[0010] <5> the above <1> ~ <3> a silicon oxide film forming step of forming a silicon oxide film having a thickness of 100 nm or less on the surface of a silicon wafer for use as a single crystal silicon layer; a bonding step of bonding the silicon wafer for use as a single crystal silicon layer and the silicon wafer for use as a support substrate together by heat treating the silicon wafer for use as a single crystal silicon layer and the oxide film at a temperature of 700°C or less to bond the two wafers together; and a thickness reducing step of reducing the thickness of the silicon wafer for use as a single crystal silicon layer to obtain the single crystal silicon layer after the bonding step. [Effects of the Invention]

[0011] According to the present invention, it is possible to provide a bonded silicon wafer that is thin and has high infrared reflectivity, and a method for producing the same. [Brief explanation of the drawings]

[0012] [Figure 1A] FIG. 1 is a schematic cross-sectional view illustrating a first embodiment of a bonded silicon wafer according to the present invention. [Figure 1B]FIG. 2 is a schematic cross-sectional view illustrating a second embodiment of a bonded silicon wafer according to the present invention. [Figure 2] 1A to 1C are schematic cross-sectional views illustrating a first embodiment of a method for producing a bonded silicon wafer according to the present invention. [Figure 3] 5A to 5C are schematic cross-sectional views illustrating a second embodiment of a method for producing a bonded silicon wafer according to the present invention. [Figure 4] 1 is a cross-sectional view of a bonded silicon wafer for explaining a method for measuring the infrared reflectance of a bonded silicon wafer according to one embodiment of the present invention. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0013] (1. Overview) Prior to describing embodiments according to the present invention, the correspondence between the drawings will be explained. FIGS. 1A and 1B are schematic cross-sectional views of bonded silicon wafers 1 and 2 according to the present invention, respectively. Bonded silicon wafers 1 and 2 are bonded silicon wafers including a support substrate silicon wafer, a single-crystal silicon layer on the support substrate silicon wafer, and an infrared-reflecting silicon film and a silicon oxide film provided between the support substrate silicon wafer and the single-crystal silicon layer. Bonded silicon wafer 1 shows an embodiment in which the silicon oxide film is provided on the infrared-reflecting silicon film, while bonded silicon wafer 2 shows an embodiment in which the infrared-reflecting silicon film is provided on the silicon oxide film. Infrared-reflecting silicon film 30 may be amorphous silicon, polycrystalline silicon, or a mixed layer of amorphous silicon and polycrystalline silicon.

[0014] 2 is a schematic cross-sectional view illustrating an embodiment (hereinafter referred to as the first embodiment) of a method for manufacturing a bonded silicon wafer 1 when a silicon oxide film is formed on an amorphous silicon layer. In the first embodiment shown in FIG. 2, an amorphous silicon layer 131 is formed on a silicon wafer 110 for a support substrate. However, instead of this, an amorphous silicon layer can be formed on a silicon wafer 120 for a single crystal silicon layer to produce a bonded silicon wafer 2.

[0015] 3 is a schematic cross-sectional view illustrating an embodiment (hereinafter, referred to as the second embodiment) of the method for manufacturing the bonded silicon wafer 1 when a silicon oxide film is formed on a polycrystalline silicon layer. As in the first embodiment, in the second embodiment shown in FIG. 3, the polycrystalline silicon layer 135 is formed on the support substrate silicon wafer 110. However, instead of this, a polycrystalline silicon layer can be formed on the single crystal silicon layer silicon wafer 120 to produce a bonded silicon wafer 2.

[0016] An embodiment of the present invention will be described in detail below with reference to the drawings. First, an overview of bonded silicon wafers 1 and 2 according to the present invention will be described with reference to FIGS. 1A and 1B. Here, the infrared-reflecting silicon film 30 in the bonded silicon wafer 1 of FIG. 1A may be amorphous silicon, polycrystalline silicon, or a combination of amorphous silicon and polycrystalline silicon. Next, methods for manufacturing bonded silicon wafers according to first and second embodiments for obtaining the bonded silicon wafer 1 will be described, along with details of each component. After that, specific aspects applicable to the present invention will be described. Note that, for ease of explanation, the thickness of each component is exaggerated in each drawing. Therefore, the thickness of each component differs from the actual thickness ratio.

[0017] (2. Bonded Silicon Wafers) 1A and 1B, bonded silicon wafers 1 and 2 according to the present invention comprise a support substrate silicon wafer 10, a single-crystal silicon layer 21 on the support substrate silicon wafer 10, and an infrared-reflecting silicon film 30 and a silicon oxide film provided between the support substrate silicon wafer 10 and the single-crystal silicon layer 21, with the infrared-reflecting silicon film 30 comprising amorphous silicon or polycrystalline silicon. The infrared-reflecting silicon film 30 and the silicon oxide film 40 may be stacked in any order; in the bonded silicon wafer 1 of FIG. 1A, the silicon oxide film 40 is provided on the infrared-reflecting silicon film 30, while in the bonded silicon wafer 2 of FIG. 1B, the infrared-reflecting silicon film 30 is provided on the silicon oxide film 40.

[0018] Here, the single crystal silicon used for the support substrate silicon wafer 10 and the single crystal silicon layer 21, and the silicon oxide used for the silicon oxide film 40, are transparent to infrared radiation, whereas the amorphous silicon and polycrystalline silicon used for the infrared-reflecting silicon film 30 are opaque to infrared radiation. By forming the infrared-reflecting silicon film 30 made of amorphous silicon or polycrystalline silicon to a thickness of 15 nm or more, a thin bonded silicon wafer with high infrared reflectivity can be obtained. The infrared-reflecting silicon film 30 may be amorphous silicon, polycrystalline silicon, or amorphous silicon and polycrystalline silicon, but a thickness less than 15 nm does not adequately reflect infrared radiation. The thickness of the infrared-reflecting silicon film 30 is preferably 20 nm or more, more preferably 25 nm or more, and even more preferably 30 nm or more. The thicker the infrared-reflecting silicon film 30, the closer its reflectance approaches 100%, but the reflectance saturates at approximately 25 nm. There is no particular upper limit to the thickness. However, from the perspective of miniaturizing the bonded silicon wafer, the upper limit can be set to 40 nm. Furthermore, since the silicon oxide film does not need to function as an insulating layer, it only needs to be thick enough to function as an adhesive layer for bonding. Considering the formation of the silicon oxide film by thermal oxidation, a thickness of 100 nm or less is required from the perspective of productivity, with a range of 5 nm to 50 nm being preferred, and a range of 10 nm to 20 nm being more preferred. The thickness of the single-crystal silicon layer 21 onto which infrared rays are incident is not particularly limited, but is preferably 3 μm to 30 μm. Depending on the application of the bonded silicon wafer, the thickness of the single-crystal silicon layer 21 may be 5 μm or more, 10 μm or more, 20 μm or less, or 15 μm or less.

[0019] Whether the silicon oxide film 40 is provided on the infrared-reflecting silicon film 30 or the infrared-reflecting silicon film 30 is provided on the silicon oxide film 40 depends on the embodiment of the manufacturing method. Hereinafter, embodiments for manufacturing bonded silicon wafers 1 and 2 in which the infrared-reflecting silicon film is made of amorphous silicon and in which the infrared-reflecting silicon film is made of polycrystalline silicon will be described in order.

[0020] (3. First Embodiment of Method for Manufacturing Bonded Silicon Wafers) A method for manufacturing a bonded silicon wafer 100 according to the first embodiment will be described with reference to Fig. 2. This embodiment is a method for manufacturing the bonded silicon wafer 1 of Fig. 1A, and is an embodiment in which the infrared-reflecting silicon film 30 in the bonded silicon wafer 1 of Fig. 1A is made of amorphous silicon.

[0021] The method for manufacturing the bonded silicon wafer 100 includes an infrared-reflecting silicon film forming step (see S110 and S120 in FIG. 2) of forming an amorphous silicon layer 131 having a thickness of 15 nm or more on the surface of the support substrate silicon wafer 110, a silicon oxide film forming step (see S110 and S120 in FIG. 2) of forming a silicon oxide film on the surface of the single-crystal silicon layer silicon wafer 120, a bonding step (see S130 in FIG. 2) of bonding the support substrate silicon wafer and the single-crystal silicon layer silicon wafer together by heat treatment at a temperature of 700°C or less following the infrared-reflecting silicon film forming step and the silicon oxide film forming step, and a thickness reducing step (see S140 in FIG. 2) of reducing the thickness of the single-crystal silicon layer silicon wafer 120 to obtain the single-crystal silicon layer 121 after the bonding step. Each step will be described in detail below.

[0022] <Infrared reflective silicon film formation process> In the infrared reflection silicon film forming step (refer to S110 and S120 in FIG. 3), an amorphous silicon layer 131 made of amorphous silicon is formed on the surface of the silicon wafer 110 for the support substrate. The amorphous silicon layer 131 can be formed by a general method. Here, the thickness of the amorphous silicon layer 131 formed is set to be 15 nm or more so that the amorphous silicon region functions as an infrared reflection silicon film when the silicon wafers are joined. In this step, the thickness of the amorphous silicon layer 131 formed is preferably 20 nm or more, more preferably 25 nm or more, and even more preferably 30 nm or more. The upper limit of the thickness of the amorphous silicon layer 131 is not particularly limited, but considering industrial productivity, the upper limit is about 40 nm.

[0023] <<Formation of Amorphous Silicon Layer by CVD Method>> Also, the amorphous silicon layer 131 made of amorphous silicon can be formed on the surface of the silicon wafer 110 for the support substrate by using a CVD method such as a plasma CVD method. If the film is formed while the temperature of the silicon wafer 110 for the support substrate is set to 500 °C or more and 600 °C or less, an amorphous silicon layer made of amorphous silicon can be grown.

[0024] <Silicon Oxide Film Forming Step> Next, in the silicon oxide film forming step (refer to S110 and S120 in FIG. 2), a silicon oxide film 140 made of silicon oxide is formed on the surface of the silicon wafer 120 for the single crystal silicon layer by using an oxidation method such as a thermal oxidation method. When assuming the use as an infrared light receiving sensor, the silicon oxide film 140 does not necessarily have to function as an insulating layer, and from the viewpoint of productivity, the thickness may be 100 nm or less. The thickness of the silicon oxide film is preferably 5 nm or more and 50 nm or less, and more preferably 10 nm or more and 20 nm or less. If it is 100 nm or more, it takes time during the thermal oxidation treatment, resulting in a significant decrease in productivity. If it is 5 nm or less, the silicon oxide film does not function sufficiently as an adhesive layer in the subsequent bonding step.

[0025] The method used to form the silicon oxide film is not particularly limited, and in addition to the thermal oxidation method, the silicon oxide film 140 may be formed using a film formation (deposition) method such as a plasma CVD method, and a silicon oxide film densification heat treatment step may be further provided in which heat treatment is added.

[0026] <Joining process> In the bonding step (see S130 in FIG. 2 ), following the infrared-reflecting silicon film forming step and the silicon oxide film forming step, the support substrate silicon wafer 110 and the single-crystal silicon layer silicon wafer 120 are bonded together by heat treatment at a temperature of 700°C or less. The support substrate silicon wafer 110 and the single-crystal silicon layer silicon wafer 120 are then bonded together with the amorphous silicon layer 131 and the silicon oxide film 140 interposed therebetween, respectively. The bonding heat treatment can be performed in an oxidizing gas or inert gas atmosphere. Substrate temperatures above 700°C are undesirable because the amorphous silicon in the amorphous silicon layer previously formed on the support substrate silicon wafer recrystallizes, and the recrystallized silicon transmits infrared light. The heat treatment is preferably performed at a substrate temperature of 400°C to 600°C for 10 minutes to 6 hours. By setting the substrate temperature to 400°C or higher, sufficient bonding strength can be obtained, and by setting the substrate temperature to 600°C or lower, the thermal effects on the formed amorphous silicon layer can be further reduced.

[0027] <Thickness reduction process for silicon wafers for single crystal silicon layers> After the bonding step using the heat treatment described above, a thickness reduction step (see S140 in FIG. 2) of the silicon wafer 120 for the single crystal silicon layer is performed. In this step, the silicon wafer 120 for the single crystal silicon layer is reduced in thickness from the side opposite to the bonded surface to obtain a single crystal silicon layer 121 made of single crystal silicon. To reduce the thickness, for example, the silicon wafer 120 for the single crystal silicon layer may be ground and polished. This allows a bonded silicon wafer 100 having a single crystal silicon layer 121 of a desired thickness to be obtained. The thickness of the single crystal silicon layer 121 can be determined appropriately depending on the device to be formed thereon, and is preferably 3 μm to 30 μm, but may also be 5 μm or more, 10 μm or more, 20 μm or less, or 15 μm or less. For this grinding and polishing, known grinding and polishing methods can be suitably used. Specifically, a surface grinding method and a mirror polishing method can be used.

[0028] The bonded silicon wafer 100 thus obtained comprises a support substrate silicon wafer 110, a single crystal silicon layer 121 on the support substrate silicon wafer 110, an infrared reflective silicon film 130 made of an amorphous silicon layer 131 having a thickness of 15 nm or more provided between the support substrate silicon wafer 110 and the single crystal silicon layer 121, and a silicon oxide film 140 having a thickness of 100 nm or less on the amorphous silicon.

[0029] The first embodiment of the method for manufacturing a bonded silicon wafer has been described above with reference to Fig. 2. In this first embodiment, the amorphous silicon layer 131 is formed on the silicon wafer 110 for the support substrate, and the silicon oxide film 140 is formed on the silicon wafer 120 for the single crystal silicon layer. However, as an alternative modification of the first embodiment, the bonded silicon wafer 100 shown in Fig. 2 can also be manufactured by performing the same steps as in the first embodiment, except that the amorphous silicon layer 131 is formed on the silicon wafer 120 for the single crystal silicon layer, and the silicon oxide film 140 is formed on the silicon wafer for the support substrate. That is, the bonded silicon wafer 100 can be manufactured by the following steps: an infrared-reflecting silicon film forming step of forming an amorphous silicon layer 131 made of amorphous silicon on the surface of the silicon wafer 120 for the single crystal silicon layer; a silicon oxide film forming step of forming a silicon oxide film 140 made of silicon oxide on the surface of the silicon wafer 110 for the support substrate; a bonding step of bonding the silicon wafer 110 for the support substrate and the silicon wafer 120 for the single crystal silicon layer together by heat treatment at a temperature of 700°C or less following the amorphous silicon forming step and the silicon oxide film forming step; and a thickness reducing step of reducing the thickness of the silicon wafer for the single crystal silicon layer to obtain the single crystal silicon layer 121 after the bonding step. The same grinding and polishing techniques as those described above in the first embodiment can be used for forming, bonding, and reducing the thickness of the amorphous silicon layer 131 and the silicon oxide film 140, and therefore a duplicated description will be omitted.

[0030] (2. Second Embodiment of Method for Manufacturing Bonded Silicon Wafers) A method for manufacturing a bonded silicon wafer 200 according to the second embodiment will be described with reference to Fig. 3. This embodiment is a method for manufacturing the bonded silicon wafer 1 of Fig. 1A, in which the infrared-reflecting silicon film 30 in the bonded silicon wafer 1 of Fig. 1A is made of polycrystalline silicon, unlike the first embodiment.

[0031] The manufacturing method of the bonded silicon wafer 200 includes an infrared reflective silicon film forming step (refer to S210 and S220 in FIG. 3) of forming a polycrystalline silicon layer 235 with a thickness of 15 nm or more on the surface of the silicon wafer 210 for the support substrate, a silicon oxide film forming step (refer to S210 and S220 in FIG. 3) of forming a silicon oxide film on the surface of the silicon wafer 220 for the single crystal silicon layer, and subsequent to this infrared reflective silicon film forming step and the silicon oxide film forming step, a bonding step (refer to S230 in FIG. 2) of bonding the silicon wafer for the support substrate and the silicon wafer for the single crystal silicon layer by heat treatment at a temperature of 700 °C or lower to bond both wafers, and a thinning step (refer to S240 in FIG. 3) of thinning the silicon wafer 220 for the single crystal silicon layer after the bonding step to obtain a single crystal silicon layer 221.

[0032] <Infrared Reflective Silicon Film Forming Step> In the infrared reflective silicon film forming step (refer to S210 and S220 in FIG. 3), a polycrystalline silicon layer 235 made of polycrystalline silicon is formed on the surface of the silicon wafer 210 for the support substrate. The polycrystalline silicon layer 235 can be formed by a general method. Here, the thickness of the polycrystalline silicon layer 235 formed is set to 15 nm or more so that the polycrystalline silicon region functions as an infrared reflective silicon film when the bonded silicon wafer 200 is formed. The thickness of the polycrystalline silicon layer 235 formed in this step is preferably 20 nm or more, more preferably 25 nm or more, and even more preferably 30 nm or more. The upper limit of the thickness of the polycrystalline silicon layer 235 is not particularly limited, but considering industrial productivity, the upper limit is about 40 nm.

[0033] <<Formation of Polycrystalline Silicon Layer by CVD Method>> Further, the polycrystalline silicon layer 235 made of polycrystalline silicon can be formed on the surface of the silicon wafer 210 for the support substrate by using a CVD method such as a plasma CVD method. If the film is formed in a state where the temperature of the silicon wafer 210 for the support substrate is 700 °C or higher and 900 °C or lower, a polycrystalline silicon layer made of polycrystalline silicon can be grown.

[0034] <Silicon oxide film formation process> Next, in the silicon oxide film formation step (see S210 and S220 in FIG. 3), a silicon oxide film 240 made of silicon oxide is formed on the surface of the silicon wafer 220 for the single crystal silicon layer using an oxidation method such as thermal oxidation. When using the silicon oxide film 240 as an infrared light receiving sensor, it does not necessarily have to function as an insulating layer, and from the viewpoint of productivity, it is sufficient that the silicon oxide film 240 has a thickness of 100 nm or less. The thickness of the silicon oxide film is preferably 5 nm to 50 nm, and more preferably 10 nm to 20 nm. If the thickness is 100 nm or more, the thermal oxidation process takes time, significantly reducing productivity. If the thickness is 5 nm or less, the silicon oxide film will not function sufficiently as an adhesive layer in the subsequent bonding step.

[0035] The method used for forming the silicon oxide film is not particularly limited, and in addition to the thermal oxidation method, the silicon oxide film 240 may be formed using a film formation (deposition) method such as a plasma CVD method, and a silicon oxide film densification heat treatment step may be further provided in which heat treatment is added.

[0036] <Joining process> Then, in the bonding step (see S230 in FIG. 3 ), following the infrared-reflecting silicon film forming step and the silicon oxide film forming step, a heat treatment is performed at a temperature of 700°C or less to bond the support substrate silicon wafer 210 and the single-crystal silicon layer silicon wafer 220. At this time, the support substrate silicon wafer 110 and the single-crystal silicon layer silicon wafer 220 are superimposed and bonded together with the amorphous silicon layer 231 and the silicon oxide film 240 interposed therebetween, respectively. The bonding heat treatment can be performed in an oxidizing gas or inert gas atmosphere. Substrate temperatures exceeding 700°C are undesirable because dislocations occur during recrystallization of the polycrystalline silicon in the polycrystalline silicon layer previously formed on the support substrate silicon wafer. The heat treatment is preferably performed at a substrate temperature of 400°C to 600°C for 10 minutes to 6 hours. By setting the substrate temperature to 400°C or higher, sufficient bonding strength can be obtained, and by setting the substrate temperature to 600°C or lower, the thermal effects on the formed polycrystalline silicon layer can be further reduced.

[0037] <Thickness reduction process> The subsequent thickness reduction step can be carried out in the same manner as in the first embodiment.

[0038] The bonded silicon wafer 200 thus obtained includes a support substrate silicon wafer 210, a single crystal silicon layer 225 on the support substrate silicon wafer 210, an infrared reflective silicon film 230 made of a polycrystalline silicon layer 235 having a thickness of 15 nm or more provided between the support substrate silicon wafer 210 and the single crystal silicon layer 221, and a silicon oxide film 240 having a thickness of 100 nm or less on the amorphous silicon.

[0039] The second embodiment of the method for manufacturing a bonded silicon wafer has been described above with reference to Fig. 3. In this second embodiment, the polycrystalline silicon layer 235 is formed on the silicon wafer 210 for the support substrate, and the silicon oxide film 240 is formed on the silicon wafer 220 for the single crystal silicon layer. However, as an alternative modification of the second embodiment, a bonded silicon wafer 200 according to the second mode shown in Fig. 3 can also be manufactured by going through the same steps as in the second embodiment, except that the polycrystalline silicon layer 235 is formed on the silicon wafer 220 for the single crystal silicon layer, and the silicon oxide film 240 is formed on the silicon wafer for the support substrate. That is, the bonded silicon wafer 200 can be manufactured through an infrared-reflecting silicon film forming step of forming a polycrystalline silicon layer 235 made of polycrystalline silicon on the surface of the silicon wafer 220 for the single crystal silicon layer, a silicon oxide film forming step of forming a silicon oxide film 240 made of silicon oxide on the surface of the silicon wafer 210 for the support substrate, a bonding step of bonding the silicon wafer 210 for the support substrate and the silicon wafer 220 for the single crystal silicon layer by heat treatment at a temperature of 700°C or less following the polycrystalline silicon forming step and the silicon oxide film forming step, and a thickness reducing step of reducing the thickness of the silicon wafer for the single crystal silicon layer to obtain the single crystal silicon layer 221 after the bonding step. The grinding and polishing techniques for forming, bonding, and reducing the thickness of the polycrystalline silicon layer 235 and the silicon oxide film 240 can be the same as those described above in the first embodiment, and therefore redundant explanations will be omitted.

[0040] In the first and second embodiments, it is also preferable to perform a planarization process on the surfaces of the amorphous silicon layer and the polycrystalline silicon layer prior to the activation process. That is, in the first and second embodiments, it is preferable to planarize the amorphous silicon layers 131 and 231 and the silicon oxide films 140 and 240, respectively.

[0041] Although the conditions for planarization are not particularly limited, it is preferable to planarize the amorphous silicon layer or polycrystalline silicon layer so that the surface roughness Ra is 3 nm or less, and it is more preferable to set the polishing stock removal to 30 nm or less. This is because planarization ensures more reliable bonding after activation. For planarization, known chemical mechanical polishing (CMP) methods can be suitably used. Furthermore, the surface roughness Ra in this specification follows the definition of the arithmetic mean roughness Ra specified in JIS B 0601 (2001).

[0042] The bonded silicon wafer according to the present invention can be manufactured by the manufacturing methods of the first and second embodiments described above.

[0043] (7. Specific Embodiments) Specific embodiments of silicon wafers applicable to the silicon wafer 10 for a support substrate and the silicon wafer 20 for a single crystal silicon layer (single crystal silicon layer 21) that can be used in the present invention will be described below.

[0044] The surface orientation of the silicon wafer is arbitrary, and a (100) wafer or a (110) wafer may be used.

[0045] The thickness of the silicon wafer can be appropriately determined depending on the application, and can be 300 μm to 1.5 mm. As already mentioned, the thickness of the single crystal silicon layer made of single crystal silicon obtained from the silicon wafer for single crystal silicon layer is appropriately determined in the range of 100 nm to 1 mm.

[0046] The silicon wafer may be doped with a dopant such as boron (B), phosphorus (P), arsenic (As), or antimony (Sb), or may be doped with carbon (C) or nitrogen (N) to obtain desired properties.

[0047] There is no limitation on the diameter of the silicon wafer. The present invention can be applied to silicon wafers with a general diameter of 300 mm or 200 mm. Of course, the present invention can also be applied to silicon wafers with a diameter larger than 300 mm or smaller than 300 mm.

[0048] In this specification, the term "silicon wafer" may refer to a so-called "bulk" silicon wafer having no other layer formed on its surface, such as an epitaxial layer or an infrared-reflecting silicon film made of silicon oxide, or may refer to an epitaxial silicon wafer having a separate layer such as an epitaxial layer formed thereon. A native oxide film having a thickness of about several angstroms may be formed on the surface of the silicon wafer, and such a native oxide film may be present, or may be removed as necessary using a known cleaning method or the like. [Example]

[0049] The present invention will be described in more detail below using examples, but the present invention is not limited to the following examples in any way.

[0050] [Experimental Example 1] (Example 1-1) As the silicon wafer for the support substrate and the silicon wafer for the single crystal silicon layer, an n-type CZ silicon wafer (dopant: phosphorus) having a diameter of 8 inches (203.2 mm) and a thickness of 500 μm was prepared. Next, the silicon wafer for the support substrate was introduced into a plasma CVD apparatus, and the degree of vacuum in the apparatus was reduced to 1×10 -5 The pressure was kept below 100 Pa. Then, with the stage temperature maintained at 500°C, silane gas (CHSiH) was flowed at 55 sccm as the source gas and H gas at 110 sccm as the carrier gas, and an amorphous silicon layer with a thickness of 15 nm was formed on the surface of the silicon wafer for the support substrate by plasma CVD.

[0051] The silicon wafer for the single crystal silicon layer was then held in a furnace under an oxygen atmosphere at 1000° C. for 1 hour to form a silicon oxide film of 50 nm on the surface of the silicon wafer for the single crystal silicon layer.

[0052] Next, both the silicon wafer for support substrate and the silicon wafer for single crystal silicon layer were introduced into a furnace, and at this time, the silicon wafer for support substrate 110 and the silicon wafer for single crystal silicon layer 120 were overlapped so as to be bonded together via the amorphous silicon layer 131 and the silicon oxide film 140, respectively. Then, the two wafers were bonded together by maintaining the bonding temperature at 600°C for one hour in an oxygen atmosphere.

[0053] Finally, the silicon wafer for the single crystal silicon layer was ground and polished from the side opposite to the bonding surface so as to leave a thickness of 10 μm, thereby obtaining a bonded silicon wafer according to Invention Example 1-1.

[0054] TEM observation of the bonded interface of the bonded silicon wafer thus obtained confirmed that amorphous silicon with a thickness of 15 nm had been formed.

[0055] (Example 1-2) In Example 1-1, an amorphous silicon layer having a thickness of 15 nm was formed on the surface of the silicon wafer for use as a support substrate by plasma CVD, whereas in Example 1-2, an amorphous silicon layer having a thickness of 20 nm was formed. The bonded silicon wafer according to Example 1-2 was produced under the same conditions as those of Example 1-1.

[0056] (Examples 1-3) In Example 1-1, an amorphous silicon layer having a thickness of 15 nm was formed on the surface of the silicon wafer for use as a support substrate by plasma CVD, whereas in Example 1-3, an amorphous silicon layer having a thickness of 25 nm was formed. The bonded silicon wafer according to Example 1-3 was produced under the same conditions as those of Example 1-1.

[0057] (Examples 1-4) In Example 1-1, an amorphous silicon layer having a thickness of 15 nm was formed on the surface of the silicon wafer for use as a support substrate by plasma CVD, whereas in Example 1-4, an amorphous silicon layer having a thickness of 30 nm was formed. The bonded silicon wafer according to Example 1-4 was produced under the same conditions as those of Example 1-1.

[0058] (Comparative Example 1-1) A silicon wafer for a support substrate and a silicon wafer for a single crystal silicon layer were prepared similarly to those in Invention Example 1-1. Then, while an amorphous silicon layer with a thickness of 15 nm was formed on the surface of the silicon wafer for a support substrate by plasma CVD in Invention Example 1-1, a bonded silicon wafer according to Comparative Example 1-1 was produced under the same conditions as Invention Example 1-1, except that an amorphous silicon layer with a thickness of 5 nm was formed in Comparative Example 1.

[0059] (Comparative Example 1-2) In Example 1-1, an amorphous silicon layer having a thickness of 15 nm was formed on the surface of the silicon wafer for support substrate by plasma CVD, whereas in Comparative Example 1, an amorphous silicon layer having a thickness of 10 nm was formed. A bonded silicon wafer according to Comparative Example 1-2 was produced under the same conditions as those of Example 1-1.

[0060] (Evaluation: Infrared reflectance evaluation) To evaluate the infrared reflectivity of the infrared-reflective silicon film, a film thickness measurement device (CHRocodile IT500, manufactured by Precitec) was used to irradiate infrared light onto the surface of the bonded silicon wafer and detect the signal intensity of the reflected light. The principle of infrared reflectivity measurement using the FTIR (Fourier Transform Infrared) method with this measurement device is briefly explained with reference to Figure 4. The laser light source used as the incident light for this measurement device is a superluminescence diode. Using this measurement device, near-infrared light L1 was irradiated onto the bonded silicon wafer, and the resulting reflected light L2 and reflected light L3 were detected to calculate the infrared reflectivity L2 / L3. Here, reflected light L2 is the light reflected from the surface 328A of the bonded silicon wafer 300, and reflected light L3 is the light reflected from the interface between the single-crystal silicon layer 321 and the amorphous silicon region 330. The unreflected infrared light continues on to the single-crystal silicon region 310 on the support substrate.

[0061] The results are shown in Table 1. From the evaluation results, it was confirmed that the amorphous silicon regions in Invention Examples 1-1 to 1-4 functioned sufficiently as an infrared reflective film, whereas the amorphous silicon regions formed in Conventional Example and Comparative Example 1 were insufficient to function as an infrared reflective film.

[0062] [Table 1]

[0063] [Experimental Example 2] (Example 2-1) As the silicon wafer for the support substrate and the silicon wafer for the single crystal silicon layer, an n-type CZ silicon wafer (dopant: phosphorus) having a diameter of 8 inches (203.2 mm) and a thickness of 500 μm was prepared. Next, the silicon wafer for the support substrate was introduced into a plasma CVD apparatus, and the degree of vacuum in the apparatus was reduced to 1×10 -5The pressure was kept below 800 Pa. Then, with the stage temperature maintained at 800°C, silane gas (CH3SiH3) was flown at 55 sccm as the source gas and H2 gas at 110 sccm as the carrier gas, and a polycrystalline silicon layer with a thickness of 15 nm was formed on the surface of the silicon wafer for the support substrate by plasma CVD.

[0064] The silicon wafer for the single crystal silicon layer was then held in a furnace under an oxygen atmosphere at 1000° C. for 1 hour to form a silicon oxide film of 50 nm on the surface of the silicon wafer for the single crystal silicon layer.

[0065] Next, both the silicon wafer for support substrate and the silicon wafer for single crystal silicon layer were introduced into a furnace, and at this time, the silicon wafer for support substrate 110 and the silicon wafer for single crystal silicon layer 120 were overlapped so as to be bonded together via the amorphous silicon layer 131 and the silicon oxide film 140, respectively. Then, the two wafers were bonded together by maintaining the bonding temperature at 600°C for one hour in an oxygen atmosphere.

[0066] Finally, the silicon wafer for the single crystal silicon layer was ground and polished from the side opposite to the bonding surface so as to leave a thickness of 10 μm, thereby obtaining a bonded silicon wafer.

[0067] When the bonded interface of the bonded silicon wafer thus obtained was observed using a TEM, it was confirmed that polycrystalline silicon with a thickness of 15 nm had been formed.

[0068] (Example 2-2) In Example 2-1, a polycrystalline silicon layer having a thickness of 15 nm was formed on the surface of the silicon wafer for use as a support substrate by plasma CVD, whereas in Example 2-2, a polycrystalline silicon layer having a thickness of 20 nm was formed. A bonded silicon wafer according to Example 2-2 was produced under the same conditions as those of Example 2-1.

[0069] (Example 2-3) In Example 2-1, a polycrystalline silicon layer having a thickness of 15 nm was formed on the surface of the silicon wafer for use as a support substrate by plasma CVD, whereas in Example 2-3, a polycrystalline silicon layer having a thickness of 25 nm was formed. A bonded silicon wafer according to Example 2-3 was produced under the same conditions as those of Example 2-1.

[0070] (Examples 2-4) In Example 2-1, a polycrystalline silicon layer having a thickness of 15 nm was formed on the surface of the silicon wafer for use as a support substrate by plasma CVD, whereas in Example 2-4, a polycrystalline silicon layer having a thickness of 30 nm was formed. A bonded silicon wafer according to Example 2-4 was produced under the same conditions as those for Example 2-1.

[0071] (Comparative Example 2) In Example 2-1, a polycrystalline silicon layer having a thickness of 15 nm was formed on the surface of the silicon wafer for use as a support substrate by a plasma CVD method. In Comparative Example 1, a bonded silicon wafer according to Comparative Example 2 was produced under the same conditions as those of Example 2-1, except that a polycrystalline silicon layer having a thickness of 10 nm was formed.

[0072] (Evaluation: Infrared reflectance evaluation) The infrared reflectance in Experimental Example 2 was evaluated using the film thickness measuring device described above, as in Experimental Example 1. In Experimental Example 2, reflected light L2 is light reflected from surface 328A of bonded silicon wafer 300, and reflected light L3 is light reflected from the interface between single crystal silicon layer 321 and region 330 formed of amorphous silicon and polycrystalline silicon.

[0073] The results are shown in Table 2. From the evaluation results, it was confirmed that the regions formed from amorphous silicon and polycrystalline silicon in Inventive Examples 2-1 to 2-4 function as infrared reflective films, while the regions formed from amorphous silicon and polycrystalline silicon in Comparative Example 2 were insufficient to function as an infrared reflective film.

[0074] [Table 2] [Industrial Applicability]

[0075] According to the present invention, A bonded silicon wafer having a small thickness and high infrared reflectance can be obtained. [Explanation of symbols]

[0076] 1,2,100,200 bonded silicon wafers 10,110,210 Silicon wafer for support substrate 120,220 Silicon wafers for single crystal silicon layers 30,130,230 Infrared reflective silicon film 131,231 Amorphous silicon layer 35,235 Polycrystalline silicon layer

Claims

1. a silicon wafer for a support substrate; a single crystal silicon layer on the support substrate silicon wafer; a bonded silicon wafer having an infrared reflective silicon film and a silicon oxide film provided between the support substrate silicon wafer and the single crystal silicon layer, the infrared-reflective silicon film comprises amorphous silicon or polycrystalline silicon; The thickness of the infrared reflective silicon film is 15 nm or more and 40 nm or less, a bonded silicon wafer, wherein the silicon oxide film has a thickness of 5 nm or more and 100 nm or less.

2. 2. The bonded silicon wafer according to claim 1, wherein the infrared-reflecting silicon film has a thickness of 25 nm or more.

3. 2. The bonded silicon wafer according to claim 1, wherein the single crystal silicon layer has a thickness of 3 μm or more and 30 μm or less.

4. A method for manufacturing a bonded silicon wafer, comprising: an infrared reflective silicon film forming step of forming an infrared reflective silicon film having a thickness of 15 nm or more and 40 nm or less on a surface of the support substrate silicon wafer; a silicon oxide film forming step of forming a silicon oxide film having a thickness of 5 nm to 100 nm on a surface of a silicon wafer for a single crystal silicon layer; a bonding step of bonding the silicon wafer for the support substrate and the silicon wafer for the single crystal silicon layer together by performing heat treatment at a temperature of 400° C. or higher and 700° C. or lower via the infrared reflective silicon film and the silicon oxide film; a thickness reduction step of reducing the thickness of the silicon wafer for the single crystal silicon layer to obtain the single crystal silicon layer after the bonding step, The obtained bonded silicon wafer has: a silicon wafer for a support substrate; a single crystal silicon layer on the support substrate silicon wafer; an infrared reflective silicon film and a silicon oxide film provided between the support substrate silicon wafer and the single crystal silicon layer, the infrared-reflective silicon film comprises amorphous silicon or polycrystalline silicon; The thickness of the infrared reflective silicon film is 15 nm or more, a silicon oxide film having a thickness of 100 nm or less;

5. A method for manufacturing a bonded silicon wafer, comprising: an infrared reflective silicon film forming step of forming an infrared reflective silicon film having a thickness of 15 nm or more and 40 nm or less on a surface of a silicon wafer for a single crystal silicon layer; a silicon oxide film forming step of forming a silicon oxide film having a thickness of 5 nm to 100 nm on the surface of the support substrate silicon wafer; a bonding step of bonding the silicon wafer for single crystal silicon layer and the silicon wafer for support substrate together by heat treatment at a temperature of 400° C. or higher and 700° C. or lower via the infrared reflective silicon film and the silicon oxide film; a thickness reduction step of reducing the thickness of the silicon wafer for the single crystal silicon layer to obtain the single crystal silicon layer after the bonding step, The obtained bonded silicon wafer has: a silicon wafer for a support substrate; a single crystal silicon layer on the support substrate silicon wafer; an infrared reflective silicon film and a silicon oxide film provided between the support substrate silicon wafer and the single crystal silicon layer, the infrared-reflective silicon film comprises amorphous silicon or polycrystalline silicon; The thickness of the infrared reflective silicon film is 15 nm or more, a silicon oxide film having a thickness of 100 nm or less;

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