Support substrate for bonded wafers

Abstract

To suppress void defects in a bonding process.SOLUTION: A support substrate for a bonded wafer is formed by bonding a substrate for an active layer and a support substrate through an insulating film, and includes: a support substrate body; an oxide film provided on the support substrate body; and a polycrystalline silicon layer provided on the oxide film. Root-mean-square roughness Rq measured in an area region of 10 μm×10 μm of a surface of the polycrystalline silicon layer is 0.5 nm or less. Thickness of the polycrystalline silicon layer is 1.5 μm or more and 2.0 μm or less. The number of pits of 2 nm or more detected in a DIC mode of SP-1 manufactured by KLA-Tencor Corporation on the surface of the polycrystalline silicon layer is 1 / cm2 or less.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a support substrate for bonded wafers.

Background Art

[0002] Conventionally, an SOI (Silicon On Insulator) wafer has been used as a substrate for radio frequency (RF) devices. The SOI wafer has a structure in which an insulating film such as silicon oxide (SiO 2 ) and an active layer (for example, a single crystal silicon) are sequentially formed on a support substrate (for example, a single crystal silicon wafer).

[0003] One of the typical methods for manufacturing an SOI wafer is a bonding method. In this bonding method, an insulating film is formed on at least one of the support substrate and the active layer substrate, and then these substrates are bonded via the insulating film, and then heat treatment is performed at a high temperature of about 1200° C. to manufacture an SOI wafer (hereinafter, the SOI wafer manufactured by the bonding method is referred to as a "bonded wafer").

[0004] In the above bonded wafer, the high resistivity of the support substrate (for example, the resistivity is 3000 Ω·cm or more) has been used to cope with RF. However, in order to cope with further high-speed operation of the device, it is required to cope with higher frequencies, and it is becoming impossible to cope only with the high resistivity of the support substrate.

[0005] Therefore, a method has been proposed in which a polycrystalline silicon layer for trapping and eliminating carriers generated during operation at a high frequency is formed as a carrier trap layer on the surface of the support substrate (see, for example, Patent Document 1). In this method, in order to prevent silicon from epitaxially growing on the single crystal silicon of the support substrate, an ultrathin oxide film is formed on the support substrate, and polycrystalline silicon is formed thereon. Then, the surface on which the polycrystalline silicon is formed is polished, and further bonded to the insulating film formed on the active layer side.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0007] By the way, in a bonded wafer, when void defects occur in the bonding process, film peeling occurs, resulting in a problem that the bonding yield decreases. Patent Document 1 describes a technique for suppressing the occurrence of void defects during bonding heating and obtaining the required strength by setting the surface roughness of the polycrystalline silicon layer to 1 nm or less in terms of the center line average roughness Ra.

[0008] However, even when a bonded wafer is manufactured by the above technique, void defects may occur, and further measures for improving the quality of the bonded wafer are desired.

[0009] An object of the present invention is to provide a support substrate for a bonded wafer that can suppress void defects in the bonding process.

Means for Solving the Problems

[0010] 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 includes a support substrate body, An oxide film provided on the support substrate body and a polycrystalline silicon layer provided on the oxide film, wherein the root mean square roughness Rq measured in an area of 10 μm × 10 μm on the surface of the polished polycrystalline silicon layer 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 in the DIC mode of SP-1 manufactured by KLA-Tencor on the surface of the polycrystalline silicon layer is 1 per cm 2 It is characterized by the following.

Effect of the Invention

[0011] 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, void defects in the bonding process can be suppressed.

Brief Description of the Drawings

[0012]

Figure 1

Figure 2

Embodiments for Carrying Out the Invention

[0013] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. The support substrate for a bonded wafer of the present invention is, for example, 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.

[0014] The inventors of the present invention have conducted earnest research on a support substrate for a bonded wafer capable of suppressing the generation of void defects. As a result, when polishing the polycrystalline silicon layer of the support substrate, it has been found that impurities such as slurry residues caused by, for example, the polishing apparatus adhere to the polycrystalline silicon layer, and these impurities are detected as defects. Specifically, it has been found that when polishing with a small amount of slurry residue adhering to the polycrystalline silicon layer, the surface of the polycrystalline silicon layer is locally etched to form pits (pit-like defects), and these pits become the cause of defects after bonding. In the method for manufacturing a support substrate of the present invention, in order to eliminate the influence of impurities, it is characterized by forming a protective oxide film for protecting the polycrystalline silicon layer.

[0015] FIG. 1 is a flowchart for explaining the steps of manufacturing a bonded wafer according to the present embodiment. FIG. 2 is a cross-sectional view of the steps showing the method for manufacturing a bonded wafer. As shown in FIG. 1, the method for manufacturing a bonded wafer includes an active layer substrate manufacturing step S1 for manufacturing an active layer substrate, a support substrate manufacturing step S2 (method for manufacturing a support substrate) for manufacturing a support substrate separately from the active layer substrate manufacturing step S1, and a bonded wafer manufacturing step S3 for bonding the active layer substrate and the support substrate to manufacture a bonded wafer.

[0016] The active layer substrate manufacturing step S1 includes an active layer substrate body preparation step S11, an insulating film growth step S12, an ion implantation layer formation step S13, and a pre-bonding cleaning step S14.

[0017] In the active layer substrate body preparation step S11, as shown in FIG. 2(a), an active layer substrate body 10 that is a single-crystalline silicon wafer is prepared. In the insulating film growth step S12, as shown in FIG. 2(b), for example, by thermal oxidation or CVD, an insulating film 11 (oxide film) is grown around the active layer substrate body 10.

[0018] In the ion implantation layer formation step S13, hydrogen ions or rare gas ions are implanted from above the insulating film 11 by an ion implanter to form an ion implantation layer 12 in the active layer substrate body 10.

[0019] In the pre-bonding cleaning step S14, pre-bonding cleaning is performed to remove particles on the bonding surface of the active layer substrate body 10. Through the above processes, the substrate 13 for the active layer for the bonded wafer is manufactured.

[0020] The support substrate manufacturing process S2 includes a support substrate 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 cleaning process S26 before bonding.

[0021] In the support substrate body preparation process S21, as shown in FIG. 2(d), a support substrate body 20 made of a single crystal silicon wafer is prepared. The single crystal silicon wafer can be a single crystal silicon ingot grown by the Czochralski method (CZ method) or the floating zone melting method (FZ method) and sliced with a wire saw or the like.

[0022] In the oxide film formation process S22, as shown in FIG. 2(e), 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 reducing the thickness of the oxide film 21, the influence on the characteristics of the RF device due to the presence of the oxide film 21 between the support substrate body 20 and the polycrystalline silicon layer 22 described later can be reduced.

[0023] The oxide film 21 can be formed by wet cleaning such as alkali cleaning (SC-1 cleaning) and acid cleaning (SC-2 cleaning). The method for forming the oxide film 21 is not limited to this, and it can be formed by thermal oxidation in an oxidizing atmosphere, oxidation heat treatment using a rapid heating and rapid cooling device, or the like.

[0024] In the polycrystalline silicon layer deposition process 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, for example, by the CVD method. The thickness of the polycrystalline silicon layer 22 is preferably 2 μm or more and 4 μm or less.

[0025] The protective oxide film formation 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, as shown in FIG. 2(g). 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, the effect as a protective film cannot be exerted. Also, if the thickness of the protective oxide film 23 is greater than 10 nm, the time required for polishing in the polishing step S25 increases, leading to an increase in manufacturing cost. From the balance between the effect as a protective film and the manufacturing cost, the thickness of the protective oxide film 23 is more preferably 0.7 nm or more and 2 nm or less.

[0026] The protective oxide film 23 is formed by alkaline cleaning (SC-1 cleaning). Specifically, in the protective oxide film formation step S24, the surface of the polycrystalline silicon layer 22 is washed with an aqueous solution of NH 4 OH (ammonium hydroxide) and H 2 O 2 (hydrogen peroxide) to form an oxide film on the surface of the polycrystalline silicon layer 22.

[0027] In the polishing step S25, as shown in FIG. 2(h), the protective oxide film 23 is polished and removed, and the surface of the polycrystalline silicon layer 22 is polished and flattened. As the polishing method, a known chemical mechanical polishing (CMP) method or the like can be preferably used. In the polishing step S25, polishing is performed so that the thickness of the polycrystalline silicon layer 22 is 1.5 μm or more and 2.0 μm or less. Further, in the polishing step S25, polishing is performed so that the root mean square roughness Rq measured in a 10 μm × 10 μm area region 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 in the plane of the substrate. The nine measurement points are the center point of the substrate, the vertices of a square inscribed in a concentric circle with a radius of half the radius of the substrate, and the vertices of a square inscribed in a concentric circle 6 mm inside the outer peripheral edge of the substrate.

[0028] Here, when the polishing step S25 is executed, since the polycrystalline silicon layer 22 is covered by the protective oxide film 23, impurities such as slurry residues caused by the polishing apparatus do not adhere to the polycrystalline silicon layer 22. That is, the polycrystalline silicon layer 22 is not eroded by impurities.

[0029] In the pre-bonding cleaning step S26, particles on the surface of the polished 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 proceed in parallel.

[0030] Next, the bonded wafer manufacturing step S3 for manufacturing a bonded wafer by bonding the active layer substrate 13 and the support substrate 24 will be described. The bonded wafer manufacturing step S3 includes a bonding step S31, a peeling heat treatment step S32, and a bonding heat treatment step S33.

[0031] In the bonding step S31, as shown in FIG. 2(i), through the insulating film 11, the polished surface of the polycrystalline silicon layer 22 of the support substrate 24 and the active layer substrate 13 are bonded together. At this time, the implantation surface of the active layer substrate 13 is bonded so as to face the polycrystalline silicon layer 22. In the peeling heat treatment step S32, a heat treatment (peeling heat treatment) for generating a microbubble layer in the ion implantation layer 12 is performed, and peeling is performed at the generated microbubble layer. As a result, as shown in FIG. 2(j), a bonded wafer 30 having an insulating film 11 and an active layer 31 formed thereon is manufactured on the support substrate 24. Note that at this time, a peeling wafer 40 having a peeling 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 of the bonding interface.

[0032] As described above, the bonded wafer 30 can be manufactured. The support substrate 24 used in the method for manufacturing the bonded wafers described above has a root mean square roughness Rq measured in a 10 μm × 10 μm area region on the surface of the polished polycrystalline silicon layer 22 of 0.5 nm or less. Also, the number of pits of 2 nm or more on the surface of the polycrystalline silicon layer 22 of the support substrate 24 is 2 as follows. The pits are detected in the DIC mode of the SP-1 manufactured by KLA-Tencor Corporation.

[0033] According to the support substrate manufacturing step S2 of the above embodiment, when the polishing step S25 is executed, the polycrystalline silicon layer 22 is not eroded by impurities. As a result, the formation of pits due to impurities is suppressed, and the generation of void defects after bonding due to the pits can be suppressed.

[0034] In the above embodiment, in the protective oxide film forming step S24, the protective oxide film 23 is formed by SC-1 cleaning, but the present invention is not limited to this. For example, the protective oxide film 23 may be formed using ozone passivation. In the protective oxide film forming step S24 using ozone passivation, without performing heat treatment, the deposited polycrystalline silicon layer 22 is exposed to high-concentration ozone at room temperature, thereby forming the protective oxide film 23 on the surface of the polycrystalline silicon layer 22. As a result, a dense protective oxide film 23 can be formed on the polycrystalline silicon layer 22.

[0035] Also, as long as the thickness of the protective oxide film 23 formed in the protective oxide film forming step S24 can be set to 0.5 nm or more and 10 nm or less, the manufacturing method thereof is not limited. That is, the protective oxide film 23 may be a natural oxide film, a thermal oxide film, a deposited oxide film, or the like.

Example

[0036] Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited by these examples. To verify the effect of the protective oxide film of the present invention, after depositing a polycrystalline silicon layer, the number of pits after polishing was compared between a support substrate (comparative example) that was polished without forming a protective oxide film and support substrates (Example 1, Example 2) that were polished after forming a protective oxide film.

[0037] 〔Comparative Example〕 After depositing a polycrystalline silicon layer on the support substrate body, the support substrate was manufactured by polishing without forming a protective oxide film. 〔Example 1〕 After depositing a polycrystalline silicon layer on the support substrate body, a protective oxide film was formed by SC-1 cleaning, and then the support substrate was manufactured by polishing. 〔Example 2〕 After depositing a polycrystalline silicon layer on the support substrate body, a protective oxide film was formed by ozone passivation, and then the support substrate was manufactured by polishing. The presence or absence of the protective oxide film and the manufacturing method of the support substrate other than the method of forming the protective oxide film are the same.

[0038] Table 1 shows a table comparing the comparative example, Example 1, and Example 2 in terms of the average number of pits on the polycrystalline silicon layer. The number of pits is the number of pits of 2 nm or more detected in the DIC mode of SP-1 manufactured by KLA-Tencor. The measurement was performed on a plurality of support substrates, and the average is shown in Table 1.

[0039]

Table 1

[0040] As can be seen from Table 1, in the comparative example, the average number of pits is 1.14 pits / cm 2 On the other hand, in Example 1 where a protective oxide film was formed by SC-1 cleaning, the average number of pits is 0.39 pits / cm 2 , and in Example 2 where a protective oxide film was formed by ozone passivation, the number of pits is 0.49 pits / cm 2 , and both are less than 1 pit / cm 2It is as follows. That is, by forming a protective oxide film, the average number of pits on the support substrate for the bonded wafer can be made 1 piece / cm 2 or less, and thereby, void defects in the bonded wafer manufactured through the bonding process can be suppressed.

Explanation of Signs

[0041] S1... Active layer substrate manufacturing process, S2... Support substrate manufacturing process, S3... Bonded wafer manufacturing process, S21... Preparation process of support substrate body, S22... Oxide film formation process, S23... Polycrystalline silicon layer deposition process, S24... Protective oxide film formation process, S25... Polishing process, S26... Cleaning process before bonding, S31... Bonding process, 20... Support substrate body, 21... Oxide film, 22... Polycrystalline silicon layer, 23... Protective oxide film, 24... Support substrate, 30... Bonded wafer.

Claims

[Claim 1] 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; an oxide film provided on the support substrate body; a polycrystalline silicon layer provided on the oxide film; 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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