Manufacturing method of support substrate for bonded wafer, and support substrate for bonded wafer

Abstract

To prevent a void defect in a lamination step.SOLUTION: There is provided a method for manufacturing a support substrate for a laminated wafer obtained by laminating a substrate for an active layer and a support substrate with an insulating film interposed therebetween, and the method for manufacturing a support substrate for a laminated wafer includes: a support substrate main body preparation step S21 of preparing a support substrate main body composed of a silicon single crystal wafer; an oxide film forming step S22 of forming an oxide film on the support substrate main body; a polycrystalline silicon layer deposition step S23 of depositing a polycrystalline silicon layer on the oxide film; a protective oxide film forming step S24 of forming a protective oxide film on a surface of the polycrystalline silicon layer; and a polishing step S25 of polishing to remove the protective oxide film and polishing the polycrystalline silicon layer.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for manufacturing a support substrate for a bonded wafer, and to a support substrate for a bonded wafer. [Background technology]

[0002] Conventionally, SOI (Silicon On Insulator) wafers have been used as substrates for radio frequency (RF) devices. SOI wafers have a structure in which an insulating layer such as silicon oxide (SiO2) and an active layer (e.g., silicon single crystal) are sequentially formed on a supporting substrate (e.g., silicon single crystal wafer).

[0003] One of the most common methods for manufacturing SOI wafers is the bonding method, which involves forming an insulating film on at least one of the support substrate and the active layer substrate, then bonding these substrates together with the insulating film in between, and then carrying out a heat treatment at a high temperature of about 1200°C to manufacture the SOI wafer (hereinafter, the SOI wafer manufactured by the bonding method will be referred to as a "bonded wafer").

[0004] The above bonded wafers have been able to handle RF by increasing the resistance of the supporting substrate (for example, resistivity of 3000 Ω cm or more). However, there is a demand for higher frequencies to support even faster device speeds, and it is becoming increasingly difficult to do so by simply increasing the resistance of the supporting substrate.

[0005] Therefore, a method has been proposed in which a polycrystalline silicon layer is formed as a carrier trap layer on the surface of a support substrate to trap and eliminate carriers generated during high-frequency operation (see, for example, Patent Document 1). In this method, in order to prevent epitaxial growth of silicon on the silicon single crystal of the support substrate, an extremely thin oxide film is formed on the support substrate, and polycrystalline silicon is then formed on top of the oxide film. The surface on which the polycrystalline silicon is formed is then polished, and is then bonded to an insulating film formed on the active layer side. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2000-200741 A Summary of the Invention [Problem to be solved by the invention]

[0007] However, in the case of bonded wafers, if void defects occur during the bonding process, film peeling occurs, resulting in a decrease in bonding yield. Patent Document 1 describes a technology for suppressing the occurrence of void defects during bonding heating and obtaining the required strength by making the surface roughness of the polycrystalline silicon layer 1 nm or less in terms of center line average roughness Ra.

[0008] However, even when bonded wafers are produced by the above-mentioned techniques, void defects may occur, and further measures are desired to improve the quality of bonded wafers.

[0009] An object of the present invention is to provide a method for producing a support substrate for a bonded wafer, which is capable of suppressing void defects in a bonding process, and a support substrate for a bonded wafer. [Means for solving the problem]

[0010] The method for manufacturing a support substrate for a bonded wafer of the present invention is a method for manufacturing a support substrate for a bonded wafer formed by bonding an active layer substrate and a support substrate with an insulating film interposed therebetween, and is characterized by comprising a support substrate body preparation step of preparing a support substrate body made of a silicon single crystal wafer, an oxide film formation step of forming an oxide film on the support substrate body, a polycrystalline silicon layer deposition step of depositing a polycrystalline silicon layer on the oxide film, a protective oxide film formation step of forming a protective oxide film on a surface of the polycrystalline silicon layer, and a polishing step of polishing and removing the protective oxide film and polishing the polycrystalline silicon layer.

[0011] In the above-mentioned method for manufacturing a supporting substrate for a bonded wafer, in the protective oxide film forming step, the protective oxide film may be formed by SC-1 cleaning.

[0012] In the above-described method for manufacturing a support substrate for a bonded wafer, in the protective oxide film forming step, the protective oxide film may be formed by ozone passivation.

[0013] In the above-described method for manufacturing a support substrate for a bonded wafer, the protective oxide film formed in the protective oxide film forming step may have a thickness of 0.5 nm or more and 10 nm or less.

[0014] The support substrate for a bonded wafer of the present invention is a support substrate for a bonded wafer formed by bonding an active layer substrate and a support substrate with an insulating film interposed therebetween, and comprises a support substrate body and a polycrystalline silicon layer deposited on the support substrate body, the root mean square roughness Rq of the polished surface of the polycrystalline silicon layer measured in an area of ​​10 μm×10 μm is 0.5 nm or less, the thickness of the polycrystalline silicon layer is 1.5 μm or more and 2.0 μm or less, and the number of pits of 2 nm or more detected on the surface of the polycrystalline silicon layer in DIC mode with a KLA-Tencor SP-1 is 1 / cm. 2 The present invention is characterized in that: Effect of the Invention

[0015] According to the present invention, in a support substrate for a bonded wafer formed by bonding an active layer substrate and a support substrate with an insulating film interposed therebetween, it is possible to suppress void defects during the bonding process. [Brief description of the drawings]

[0016] [Figure 1] 4 is a flowchart for explaining a process for manufacturing a bonded wafer according to an embodiment of the present invention. [Diagram 2] 1A to 1C are cross-sectional views showing steps of a method for manufacturing a bonded wafer according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will now be described in detail with reference to the accompanying drawings, in which: A support substrate for a bonded wafer according to the present invention is a support substrate used for a bonded wafer such as an SOI wafer formed by bonding an insulating film formed on an active layer substrate, for example.

[0018] The inventors of the present invention have conducted extensive research into a support substrate for a bonded wafer that can suppress the occurrence of void defects, and have found that when the polycrystalline silicon layer of the support substrate is polished, impurities such as slurry residues from a polishing device adhere to the polycrystalline silicon layer, and these impurities are detected as defects. Specifically, it was found that polishing with a small amount of slurry residue adhering to the polycrystalline silicon layer locally etches the surface of the polycrystalline silicon layer, forming pits (pit-like defects), and these pits become the cause of defects after bonding. The manufacturing method of the support substrate of the present invention is characterized by forming a protective oxide film that protects the polycrystalline silicon layer in order to eliminate the influence of impurities.

[0019] Fig. 1 is a flow chart for explaining steps of manufacturing a bonded wafer according to the present embodiment, and Fig. 2 is a cross-sectional view showing steps of the manufacturing method of a bonded wafer. As shown in FIG. 1, the method for manufacturing a bonded wafer includes an active layer substrate manufacturing process S1 for manufacturing an active layer substrate, a support substrate manufacturing process S2 (a method for manufacturing a support substrate) for manufacturing a support substrate separate from the active layer substrate manufacturing process S1, and a bonded wafer manufacturing process S3 for manufacturing a bonded wafer by bonding the active layer substrate and the support substrate together.

[0020] The active layer substrate manufacturing process S1 includes an active layer substrate main body preparation step S11, an insulating film growth step S12, an ion-implanted layer formation step S13, and a pre-bonding cleaning step S14.

[0021] In the active layer substrate main body preparation step S11, as shown in FIG. 2(a), an active layer substrate main body 10 which is a silicon single crystal wafer is prepared. In the insulating film growing step S12, as shown in FIG. 2(b), an insulating film 11 (oxide film) is grown around the active layer substrate body 10 by, for example, thermal oxidation or CVD.

[0022] In the ion-implanted layer forming step S13, hydrogen ions or rare gas ions are implanted from above the insulating film 11 by an ion implanter to form an ion-implanted layer 12 in the active layer substrate body 10.

[0023] In the pre-bonding cleaning step S14, pre-bonding cleaning is performed in order to remove particles on the bonding surface of the active layer substrate body 10. Through the above steps, an active layer substrate 13 for a bonded wafer is manufactured.

[0024] The support substrate manufacturing process S2 includes a support substrate main body preparation process S21, an oxide film formation process S22, a polycrystalline silicon layer deposition process S23, a protective oxide film formation process S24, a polishing process S25, and a pre-bonding cleaning process S26.

[0025] In the support substrate body preparation step S21, a support substrate body 20 made of a silicon single crystal wafer is prepared as shown in Fig. 2(d). The silicon single crystal wafer can be one obtained by slicing a single crystal silicon ingot grown by the Czochralski method (CZ method) or the floating zone melting method (FZ method) with a wire saw or the like.

[0026] 2(e), in the oxide film forming step S22, an oxide film 21 is formed on the bonding surface side of the support substrate body 20. The thickness of the oxide film 21 is preferably, for example, 0.3 nm or more and 10 nm or less. By making the thickness of the oxide film 21 thin, it is possible to reduce the influence on the characteristics of the RF device caused by the oxide film 21 being interposed between the support substrate body 20 and a polycrystalline silicon layer 22 described later.

[0027] The oxide film 21 can be formed by wet cleaning such as alkaline cleaning (SC-1 cleaning) or acid cleaning (SC-2 cleaning). The method of forming the oxide film 21 is not limited thereto, and the oxide film 21 can be formed by thermal oxidation in an oxidizing atmosphere, oxidation heat treatment using a rapid heating and rapid cooling device, or the like.

[0028] In the polycrystalline silicon layer depositing step S23, as shown in Fig. 2(f), a polycrystalline silicon layer 22 is deposited on the oxide film 21 on the bonding surface side of the support substrate body 20. The polycrystalline silicon layer 22 can be deposited by, for example, a CVD method. The thickness of the polycrystalline silicon layer 22 is preferably 2 µm or more and 4 µm or less.

[0029] 2(g), the protective oxide film forming step S24 is a step of forming a protective oxide film 23 that functions as a protective film on the surface of the polycrystalline silicon layer 22. The thickness of the protective oxide film 23 is preferably, for example, 0.5 nm or more and 10 nm or less. If the thickness of the protective oxide film 23 is less than 0.5 nm, it cannot exert its protective film effect. Also, if the thickness of the protective oxide film 23 is more than 10 nm, the time required for polishing in the polishing step S25 increases, leading to an increase in manufacturing costs. From the viewpoint of the balance between the effect as a protective film and the manufacturing cost, it is more preferable that the thickness of the protective oxide film 23 be 0.7 nm or more and 2 nm or less.

[0030] The protective oxide film 23 is formed by alkaline cleaning (SC-1 cleaning). Specifically, in the protective oxide film forming step S24, the surface of the polycrystalline silicon layer 22 is cleaned with an aqueous solution of NH4OH (ammonium hydroxide) and H2O2 (hydrogen peroxide) to form an oxide film on the surface of the polycrystalline silicon layer 22.

[0031] 2(h), in the polishing step S25, the protective oxide film 23 is polished and removed, and the surface of the polycrystalline silicon layer 22 is polished and flattened. As a polishing method, a known chemical mechanical polishing (CMP) method or the like can be suitably used. In the polishing step S25, the polycrystalline silicon layer 22 is polished so that its thickness is 1.5 μm or more and 2.0 μm or less. Furthermore, in the polishing step S25, the polycrystalline silicon layer 22 is polished so that the root-mean-square roughness Rq measured in an area of ​​10 μm×10 μm of the polished polycrystalline silicon layer 22 is 0.5 nm or less. The thickness of the polycrystalline silicon layer 22 is measured at nine points on the surface of the substrate. The nine measurement points are the center point of the substrate, each vertex of a regular rectangle inscribed in a concentric circle whose radius is half the radius of the substrate, and each vertex of a regular rectangle inscribed in a concentric circle 6 mm inward from the outer peripheral edge of the substrate.

[0032] Here, when the polishing step S25 is performed, since the polycrystalline silicon layer 22 is covered with the protective oxide film 23, impurities such as slurry residues resulting from the polishing device do not adhere to the polycrystalline silicon layer 22. In other words, the polycrystalline silicon layer 22 is not eroded by impurities.

[0033] In the pre-bonding cleaning step S26, particles on the polished surface of the polycrystalline silicon layer 22 are removed. Through the above steps, the support substrate 24 for the bonded wafer is manufactured. Note that the active layer substrate manufacturing step S1 (S11 to S14) and the support substrate manufacturing step S2 (S21 to S26) can be carried out in parallel.

[0034] Next, a bonded wafer manufacturing step S3 in which the active layer substrate 13 and the support substrate 24 are bonded together to manufacture a bonded wafer will be described. The bonded wafer manufacturing process S3 includes a bonding step S31, a delamination heat treatment step S32, and a bonding heat treatment step S33.

[0035] 2(i), in the bonding step S31, the polished surface of the polycrystalline silicon layer 22 of the support substrate 24 is bonded to the active layer substrate 13 via the insulating film 11. At this time, the bonding is performed so that the implantation surface of the active layer substrate 13 faces the polycrystalline silicon layer 22. In the delamination heat treatment step S32, a heat treatment (delamination heat treatment) is performed to generate a microbubble layer in the ion-implanted layer 12, and delamination is performed at the generated microbubble layer. As a result, as shown in Fig. 2(j), a bonded wafer 30 in which an insulating film 11 and an active layer 31 are formed on a support substrate 24 is manufactured. At this time, a delamination wafer 40 having a delamination surface 41 is formed. In the bonding heat treatment step S33, the bonded wafer 30 is subjected to a bonding heat treatment to increase the bonding strength at the bonding interface.

[0036] In the manner described above, the bonded wafer 30 can be manufactured. The support substrate 24 used in the above-mentioned manufacturing method of the bonded wafer has a root mean square roughness Rq of 0.5 nm or less when the surface of the polished polycrystalline silicon layer 22 is measured in an area of ​​10 μm×10 μm. The number of pits of 2 nm or more on the surface of the polycrystalline silicon layer 22 of the support substrate 24 is 1 / cm. 2 The pits are detected using the KLA-Tencor SP-1 in DIC mode.

[0037] According to the support substrate manufacturing process S2 of the above embodiment, when the polishing process S25 is performed, the polycrystalline silicon layer 22 is not corroded by impurities. This prevents the formation of pits caused by impurities, and can prevent the occurrence of void defects caused by pits after bonding.

[0038] In the above embodiment, the protective oxide film 23 is formed by SC-1 cleaning in the protective oxide film forming step S24, but the present invention is not limited to this. For example, the protective oxide film 23 may be formed by ozone passivation. In the protective oxide film formation step S24 using ozone passivation, no heat treatment is performed, but the deposited polycrystalline silicon layer 22 is exposed to high concentration ozone at room temperature to form a protective oxide film 23 on the surface of the polycrystalline silicon layer 22. This allows a dense protective oxide film 23 to be formed on the polycrystalline silicon layer 22.

[0039] Furthermore, the method for forming the protective oxide film 23 in the protective oxide film forming step S24 does not matter as long as the thickness of the protective oxide film 23 can be set to 0.5 nm or more and 10 nm or less. That is, the protective oxide film 23 may be a natural oxide film, a thermal oxide film, a deposited oxide film, or the like. EXAMPLES

[0040] The present invention will now be described in more detail with reference to examples, but the present invention is not limited to these examples in any way. In order to verify the effect of the protective oxide film of the present invention, the number of pits after polishing was compared for a support substrate on which a polycrystalline silicon layer was deposited and then polished without forming a protective oxide film (Comparative Example) and a support substrate on which a protective oxide film was formed and then polished (Examples 1 and 2).

[0041] Comparative Example After a polycrystalline silicon layer was deposited on the support substrate body, the support substrate was polished without forming a protective oxide film. Example 1 After a polycrystalline silicon layer was deposited on the support substrate body, a protective oxide film was formed by SC-1 cleaning, and then polishing was performed to produce the support substrate. Example 2 After a polycrystalline silicon layer was deposited on the support substrate body, a protective oxide film was formed by ozone passivation, and then polishing was performed to manufacture the support substrate. The manufacturing method of the support substrate is the same except for the presence or absence of a protective oxide film and the method of forming the protective oxide film.

[0042] Table 1 shows a comparison of the average number of pits on the polycrystalline silicon layer among Comparative Example, Example 1, and Example 2. The number of pits is the number of pits of 2 nm or more detected in DIC mode of KLA-Tencor SP-1. Measurements were performed on multiple support substrates, and the average is shown in Table 1.

[0043] [Table 1]

[0044] As can be seen from Table 1, in the comparative example, the average number of pits was 1.14 / cm 2 In contrast, in Example 1, in which the protective oxide film was formed by SC-1 cleaning, the average number of pits was 0.39 / cm 2 In Example 2, in which a protective oxide film was formed by ozone passivation, the number of pits was average Quantity: 0.49 pieces / cm 2 And, both are 1 piece / cm 2 That is, by forming a protective oxide film, the average number of pits on the support substrate for the bonded wafer is reduced to 1 pit / cm. 2 This can suppress void defects in a bonded wafer produced through a bonding process. [Explanation of symbols]

[0045] S1...active layer substrate manufacturing process, S2...support substrate manufacturing process, S3...bonded wafer manufacturing process, S21...support substrate main body preparation process, S22...oxide film formation process, S23...polycrystalline silicon layer deposition process, S24...protective oxide film formation process, S25...polishing process, S26...pre-bonding cleaning process, S31...bonding process, 20...support substrate main body, 21...oxide film, 22...polycrystalline silicon layer, 23...protective oxide film, 24...support substrate, 30...bonded wafer.

Claims

1. A method for manufacturing a support substrate for a bonded wafer, which is formed by bonding an active layer substrate and a support substrate with an insulating film interposed therebetween, comprising the steps of: a support substrate body preparation step of preparing a support substrate body made of a silicon single crystal wafer; an oxide film forming step of forming an oxide film on the support substrate body; a polycrystalline silicon layer depositing step of depositing a polycrystalline silicon layer having a thickness of 2 μm or more and 4 μm or less on the oxide film; a protective oxide film forming step of forming a protective oxide film having a thickness of 0.5 nm or more and 10 nm or less on a surface of the polycrystalline silicon layer; a polishing step of polishing and removing the entire protective oxide film, and polishing the polycrystalline silicon layer to a thickness of 1.5 μm or more and 2.0 μm or less.

2. 2. The method for manufacturing a supporting substrate for a bonded wafer according to claim 1, wherein in the protective oxide film forming step, the protective oxide film is formed by SC-1 cleaning.

3. 2. The method for producing a supporting substrate for a bonded wafer according to claim 1, wherein in the protective oxide film forming step, the protective oxide film is formed by ozone passivation.

4. A support substrate for a bonded wafer, which is formed by bonding an active layer substrate and a support substrate with an insulating film interposed therebetween, A support substrate body; a polycrystalline silicon layer deposited on the support substrate body; The root mean square roughness Rq of the polished surface of the polycrystalline silicon layer measured in an area of ​​10 μm×10 μm is 0.5 nm or less, the thickness of the polycrystalline silicon layer is 1.5 μm or more and 2.0 μm or less, and the number of pits of 2 nm or more detected on the surface of the polycrystalline silicon layer using a DIC mode of an SP-1 manufactured by KLA-Tencor Corporation is 1 / cm. ２ A support substrate for a bonded wafer, which is:

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