METHOD FOR PRODUCE A SILICON EPITAXIAL WAFER, SILICON EPITAXIAL WAFER AND METHOD FOR PRODUCE A SOLID BODY IMAGE CAPTURE ELEMENT

Abstract

Method for producing a silicon epitaxial wafer (100, 200) comprising the following: a first step in the formation of a first epitaxial silicon layer (12) which contains a surface layer part with an oxygen concentration of 2 × 10 16 atoms / cm² 3 or less, on a silicon wafer (10) which has an oxygen concentration of 2 × 10 17 atoms / cm² 3 or more; a second step of irradiating the surface layer portion of the first epitaxial silicon layer (12) with first ions (18) containing carbon to form a first modification layer (14) in which the carbon is implanted in the surface layer portion of the first epitaxial silicon layer (12); and a third step of forming a second epitaxial silicon layer (16) on the first modification layer (14), wherein after the third step a silicon epitaxial wafer (100, 200) is obtained, wherein a peak concentration of an oxygen concentration profile in the first modification layer (14) 2 × 10 17 atoms / cm² 3 or less and an oxygen concentration of the second epitaxial silicon layer (16) 2 × 10 16 atoms / cm² 3 or less.

Description

TECHNICAL AREA

[0001] The present disclosure relates to a method for producing a silicon epitaxial wafer, a silicon epitaxial wafer and a method for producing a solid-state image acquisition device, in particular a method for producing a silicon epitaxial wafer which exhibits a higher getter capability. BACKGROUND

[0002] Metal contamination is one of the factors that degrade the characteristics of a semiconductor device. For example, in a back-illuminated solid-state imaging device (SIDE), metals mixed into a semiconductor epiaxial wafer to serve as a substrate cause increased dark current in the SIDE, leading to the formation of defects known as white spot defects. In recent years, back-illuminated SIDEs have been widely used in digital video cameras and mobile phones, such as smartphones, because they incorporate a wiring layer and other layers positioned beneath a sensor unit. This allows them to directly receive light from the outside and capture sharper images or motion-capturing images, even in dark scenes.Therefore, it was a goal in engineering to reduce white point errors as much as possible.

[0003] Metal contamination of silicon wafers occurs primarily during the silicon epitaxial wafer fabrication process and the solid-state imaging device (SEM) manufacturing process. Metal contamination during the former process can originate from heavy metal particles in epitaxial growth furnace components or from metal corrosion of furnace piping materials caused by chlorine-based gas used in the epitaxial growth process. While such metal contamination has been reduced to some extent in recent years by replacing epitaxial growth furnace components with highly corrosion-resistant materials, this reduction has not been sufficient.On the other hand, in the latter process of manufacturing a solid-state image acquisition device, heavy metal contamination of silicon epitaxial wafers would occur in process steps such as ion implantation, diffusion and oxidation treatment during the manufacturing process.

[0004] Metal contamination of silicon epitaxial wafers is generally avoided by forming a getter layer in the silicon epitaxial wafer to trap metals.

[0005] One technique for forming a getter layer involves irradiating an epitaxial silicon layer with cluster ions. WO 2012 / 157 162 A1 discloses a technique for forming a silicon epitaxial wafer that includes: irradiating a silicon wafer, or a first epitaxial silicon layer formed on the wafer, with carbon-containing cluster ions to form a modification layer in which carbon is tightly dissolved in a surface layer portion of the silicon wafer or the first epitaxial silicon layer; and forming a second epitaxial silicon layer, which becomes a device layer, on top of the modification layer. In this technique, the modification layer acts as a getter layer. WO 2012 / 157 162 A1 also states that the getter capability improves with increasing concentration of carbon in the modification layer, with the peak carbon concentration preferably being 1 × 10⁻⁶. 15up to 1 × 10 22 atoms / cm² 3 is.

[0006] German patent DE 11 2012 002 072 T5 describes a process for producing a silicon epitaxial wafer, in which a first epitaxial silicon layer is formed on a silicon wafer. This layer is irradiated with carbon-containing ions to form a modification layer. Then, a second epitaxial silicon layer is formed on top of the modification layer.

[0007] US patent 7 803 228 B2 discloses further methods for the production of silicon epitaxial wafers. SUMMARY (Technical Problem)

[0008] WO 2012 / 157162A1 demonstrates that a modification layer formed by cluster ion irradiation exhibits higher getter capability than an ion-implanted region obtained by implanting monomer ions (single ions). However, to further improve the characteristics of semiconductor devices, there remains a need to provide a silicon epitaxial wafer with higher getter capability.

[0009] In view of the preceding problem, one objective of the present disclosure is to provide a silicon epitaxial wafer capable of reducing metal contamination by exerting a higher getter capability, and a method for producing the same. (Solution to the problem)

[0010] To increase getter capability, it is indeed effective to raise the peak concentration of the carbon concentration profile in a modification layer formed by implanting carbon-containing ions. At this point, the amount of carbon trapped in the modification layer also increases, as does the peak concentration of the oxygen concentration profile within the modification layer. It was unknown how the concentration profile of oxygen trapped in this modification layer affects getter capability.

[0011] The inventors focused on the peak concentration of the oxygen concentration profile in the modification layer after the formation of a device layer and conducted extensive investigations regarding this aspect. As a result, they found that the getter capability increases with decreasing peak concentration of the oxygen concentration profile in the modification layer. The inventors also discovered a significant increase in getter capability when the peak concentration of the oxygen concentration profile in the modification layer is reduced to 2 × 10⁻⁶. 17 atoms / cm² 3 or less is set and the oxygen concentration of the epitaxial silicon layer, which is intended to be a component layer, is set to 2 × 10 16 atoms / cm² 3 or less (hereinafter referred to as "lower SIMS detection limit or less") is set.

[0012] The present disclosure was made based on the results described above, and its core is as follows: (1) A method for producing a silicon epitaxial wafer comprising: a first step in the formation of a first epitaxial silicon layer, which contains a surface layer portion with an oxygen concentration of 2 × 10 16 atoms / cm² 3 or less, on a silicon wafer which has an oxygen concentration of 2 × 10 17 atoms / cm² 3 or more; a second step of irradiating the surface layer portion of the first epitaxial silicon layer with first ions containing carbon to form a first modification layer in which the carbon is implanted in the surface layer portion of the first epitaxial silicon layer; and a third step of forming a second epitaxial silicon layer on the first modification layer, wherein after the third step a silicon epitaxial wafer is obtained, wherein a peak concentration of an oxygen concentration profile in the first modification layer is 2 × 10 17 atoms / cm² 3 or less and an oxygen concentration of the second epitaxial silicon layer 2 × 10 16 atoms / cm² 3 or less. (2) The method according to (1) above, wherein the first ions are cluster ions containing carbon as a constituent element. (3) The method according to (1) or (2) above, wherein in the first step a thickness of the first epitaxial silicon layer is determined according to an oxygen concentration of the silicon wafer, such that the surface layer part of the first epitaxial silicon layer before the second step has an oxygen concentration of 2 × 10 16atoms / cm² 3 or less. (4) The method according to (1) or (2) above, further comprising, prior to the first step, irradiating the silicon wafer with second ions containing carbon to form a second modification layer in which carbon is implanted in a surface layer part of the silicon wafer, such that, prior to the second step, the surface layer part of the first epitaxial silicon layer has an oxygen concentration of 2 × 10 16 atoms / cm² 3 or less. (5) The method according to (4) above, wherein the second ions are cluster ions containing carbon as a constituent element. (6) The method according to any of (1) to (5) above, wherein the first epitaxial silicon layer has a dopant concentration that is equal to or less than the dopant concentration of the second epitaxial silicon layer. (7) The method according to (6) above, wherein the first epitaxial silicon layer is not doped with a dopant. (8) A silicon epitaxial wafer comprising the following: a silicon wafer that has an oxygen concentration of 2 × 10 17 atoms / cm² 3 or more; a first epitaxial silicon layer that is formed on the silicon wafer; a first modification layer in which carbon is implanted, wherein the first modification layer is formed in a surface layer portion of the first epitaxial silicon layer; and a second epitaxial silicon layer formed on top of the first modification layer, where a peak concentration of an oxygen concentration profile in the first modification layer is 2 × 10 17 atoms / cm² 3 or less and an oxygen concentration of the second epitaxial silicon layer 2 × 10 16atoms / cm² 3 or less. (9) The silicon epitaxial wafer according to (8) above, wherein the first epitaxial silicon layer has a dopant concentration equal to or less than the dopant concentration of the second epitaxial silicon layer. (10) The silicon epitaxial wafer according to (9) above, wherein the first epitaxial silicon layer is not doped with a dopant. (11) A method for manufacturing a solid-state image acquisition device comprising the following: Forming a solid-state image acquisition device in the second epitaxial silicon layer of the silicon epitaxial wafer produced by the method according to one of (1) to (7) above, or of the silicon epitaxial wafer according to one of (8) to (10) above. (Beneficial effect)

[0013] According to the present disclosure, it is possible to provide a silicon epitaxial wafer capable of reducing metal contamination by exerting a higher getter capability, and a method for producing the same. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The following applies to the accompanying drawings: Fig. Figures 1A to 1E are schematic cross-sectional views illustrating a method for producing a silicon epitaxial wafer 100 according to a first embodiment of the present invention; Fig. Figures 2A to 2G are schematic cross-sectional views illustrating a method for producing a silicon epitaxial wafer 200 according to a second embodiment of the present invention; Fig. Figure 3 is a graph showing the results of a theoretical calculation of oxygen concentration profiles after the growth of a first epitaxial silicon layer 12 for different oxygen concentration profiles of a silicon wafer; Fig. Figure 4A is a graph showing oxygen concentration profiles of silicon epitaxial wafers for the inventive example and comparative examples 1 to 3; and Fig. Figure 4B is a graph showing concentrations of Fe trapped in the first modification layer for the invention example and comparison examples 1 to 3. DETAILED DESCRIPTION

[0015] The embodiments of the present disclosure are described in detail below with reference to the accompanying drawings. In principle, identical elements are designated by the same reference numerals, and a redundant description thereof is not provided. Fig. 1A to 1E and Fig. In contrast to the actual thickness ratio, 2A to 2G are the first and second epitaxial silicon layers 12, 16 and the first and second modification layers 14, 22, shown with an exaggerated thickness with reference to a silicon wafer 10 for the sake of simplicity. (Method for producing a silicon epitaxial wafer)

[0016] Fig. Figures 1A to 1E show a first embodiment of a method for producing a silicon epitaxial wafer of the present disclosure and Fig. Figures 2A to 2G show a second embodiment thereof.

[0017] First, with reference to Fig. Sections 1A to 1E describe a method for producing a silicon epitaxial wafer 100 according to a first embodiment of the present disclosure. In the following embodiment, an epitaxial silicon layer 12 is first formed on a silicon wafer 10 ( Fig. 1A and Fig. 1B). Next, the first epitaxial silicon layer 12 is irradiated with cluster ions 18 (first ions) containing carbon as a constituent element to form a first modification layer 14, in which the carbon is tightly dissolved, in a surface layer part of the first epitaxial silicon layer 12 ( Fig. 1C and Fig. 1D). Next, a second epitaxial silicon layer 16 is deposited on the first modification layer 14 ( Fig. 1E) formed. Fig. Figure 1E is a schematic cross-sectional view of a silicon epitaxial wafer 100 obtained by this manufacturing process.

[0018] Examples of silicon wafer 10 include monocrystalline bulk silicon wafers without an epitaxial silicon layer on the surface. Monocrystalline bulk silicon wafers are generally suitable for the fabrication of back-illuminated solid-state imaging devices. From the perspective of reducing the diffusion of oxygen into the first and second epitaxial silicon layers 12, 16, the silicon wafer 10 preferably exhibits an oxygen concentration of 18 × 10⁻⁶. 17 atoms / cm² 3 or less, preferably 8 × 10 17 atoms / cm² 3 or less. However, from the point of view of reducing the occurrence of slip and dislocation during epitaxial growth, the silicon wafer 10 preferably exhibits an oxygen concentration of 2 × 10 17 atoms / cm² 3or more. A silicon wafer exhibiting an oxygen concentration profile falling within the range described above can be prepared by slice cutting, using a wire saw or other tool, of a monocrystalline silicon ingot obtained by the Czochralski (CZ) process, which is commonly used in the industry. Remarkably, in the present disclosure, it is possible to reduce the oxygen concentration of the device layer to the lower SIMS detection limit or less by the process described below, without requiring a low-oxygen silicon wafer with an oxygen concentration of 1 × 10 17 atoms / cm² 3 or less, to have to use.

[0019] Carbon and / or nitrogen can be doped into the silicon wafer 10 to achieve a higher getter capability. Furthermore, the silicon wafer 10 can be made into an n-type or p-type by doping with any dopant.

[0020] The first and second epitaxial silicon layers 12, 16 can be formed by chemical vapor deposition (CVD) under general conditions. For example, a source gas, such as dichlorosilane or trichlorosilane, can be introduced into a chamber for epitaxial growth by CVD at approximately 1000 °C to 1150 °C, using hydrogen as a carrier gas. The second epitaxial silicon layer 16 becomes a component layer for fabricating a back-illuminated solid-state imaging device.

[0021] The second epitaxial silicon layer 16 can be made n-type or p-type by doping with any dopant, wherein the dopant concentration is preferably 9 × 10 13 atoms / cm² 3 up to 1 × 10 15 atoms / cm² 3 It is preferred that the dopant concentration of the first epitaxial silicon layer 12 is equal to or less than the dopant concentration of the second epitaxial silicon layer 16. It is more preferred that the first epitaxial silicon layer 12 is an epitaxial silicon layer that is not doped with a dopant, because it is possible to prevent the getter sites formed in the first modification layer 14 from being occupied by the dopant, and therefore a higher getter capability can be achieved.

[0022] From the perspective of ensuring a suitable area for forming a back-illuminated solid-state detection device, it is preferred that the thickness of the second epitaxial silicon layer 16 be in the range of 2 µm to 10 µm. Details of the thickness of the first epitaxial silicon layer 12 are described later.

[0023] Next, the first modification layer, which functions as a getter layer in the present disclosure, is described. In the present embodiment, as in Fig. 1C and Fig. As shown in Figure 1D, the first modification layer 14 is formed by irradiating a surface 12A of the first epitaxial silicon layer with carbon-containing cluster ions (first ions), such that carbon is tightly dissolved in a surface layer portion of the first epitaxial silicon layer 12. Alternatively, the first ions to be used can be monomer ions (single ions). However, from the perspective of obtaining a higher getter capability, it is preferred to use cluster ions. Any known or known generator can be used as a generator for monomer ions or cluster ions.

[0024] When carbon-containing monomers are used as the first ions, the monomers are implanted at a depth within a predetermined distance from the surface of the first epitaxial silicon layer. The implantation depth depends on the type of monomer constituent and the monomer acceleration voltage. In this case, the first epitaxial silicon layer exhibits a relatively broad carbon concentration profile in the depth direction, and the carbon-implanted region (i.e., the first modification layer) has a thickness of approximately 0.5 µm to 1 µm. Here, "the surface layer portion of the first epitaxial silicon layer" that becomes the first modification layer is a region approximately 0.5 µm to 1 µm from the surface of the first epitaxial silicon layer when monomers are applied.

[0025] Monomerions can be implanted one or more times to introduce different types of elements. In particular, in addition to carbon, it is preferred to use one or more dopant elements selected from the group consisting of boron, phosphorus, arsenic, and antimony. Because different elements efficiently capture different impurity metals, the implantation of two or more different elements, including carbon, allows for the efficient capture of a broader range of impurity metals. For example, carbon can efficiently capture nickel, whereas boron can efficiently capture copper and iron.

[0026] The accelerating voltage of monomer ions is generally in the range of 150 to 2000 keV / atom and can be adjusted appropriately within this range. The dose of monomer ions is also not specifically limited and can, for example, be 1 × 1013 atoms / cm² 2 up to 1 × 10 16 atoms / cm² 2 carry.

[0027] With reference to Fig. 1C and Fig. When carbon-containing cluster ions 18 are applied as the first ions, the first modification layer 14, in which the constituent of the cluster ions 18 is tightly dissolved, is formed in a surface layer portion of the first epitaxial silicon layer 12. In this case, the first epitaxial silicon layer 12 exhibits a sharp carbon concentration profile in the depth direction compared to a case where monomer ions are applied, and the region where carbon exists (i.e., the first modification layer 14) has a thickness of approximately 500 nm or less (e.g., about 50 nm to 400 nm). The term "cluster ions" here means a cluster of atoms or molecules that are ionized by being given a positive or negative electrical charge. A cluster refers to a population of several (typically 2 to 2000) atoms or molecules that are bonded together.Here, "the surface layer portion of the first epitaxial silicon layer" that becomes the first modification layer is a region within approximately 500 nm of the surface of the first epitaxial silicon layer when cluster ions are applied.

[0028] The cluster ions 18 to be used contain carbon as a constituent element. Compared to silicon single crystals, carbon atoms at lattice sites have a small covalent bonding radius, thus generating a compression field in the silicon crystal lattice, which leads to a high getter ability to attract impurities between lattices.

[0029] It is preferred that the cluster ions 18 contain two or more different elements, including carbon, as constituent elements. In particular, in addition to carbon, it is preferred to use one or more dopant elements selected from the group consisting of boron, phosphorus, arsenic, and antimony. Because different elements to be deposited efficiently capture different impurity metals, the solid dissolution of two or more different elements, including carbon, allows a broader range of metal contaminations to be addressed. For example, carbon can efficiently capture nickel, whereas boron can efficiently capture copper and iron.

[0030] Compounds that can be ionized are not specifically limited. Examples of ionizable carbon-source compounds include ethane, methane, propane, benzyl (C7H7), and carbon dioxide (CO2), and examples of boron-source compounds include diborane and decaborone (B₂). 10 H 14 For example, if a mixed gas of benzyl and decaborone is used as a material gas, a hydrogen compound cluster can be produced in which carbon, boron, and hydrogen are accumulated together. Alternatively, if cyclohexane (C6H) is used... 12 When used as a material gas, cluster ions can be produced, which are formed from carbon and hydrogen. In particular, a cluster C is preferred as a carbon source compound. n H m (3 ≤ n ≤ 16, 3 ≤ m ≤ 10), which is made from pyrene (C 16 H 10 ), Dibenzyl (C 14 H 14) or similar is generated, because a small cluster ion beam can be easily controlled.

[0031] Next, by controlling the accelerating voltage and the cluster size of the cluster ions, the peak position of the concentration profile of the constituent element in the depth direction of the first modification layer 14 can be controlled. The term "cluster size" here refers to the number of atoms or molecules that constitute a cluster.

[0032] From the perspective of obtaining a higher getter capability, it is preferred that cluster ions are applied such that the peak of the carbon concentration profile in the first modification layer 14 lies at a depth within 150 nm of the surface 12A of the first epitaxial silicon layer. The peak concentration of the carbon concentration profile is preferably 3.8 × 10 18 atoms / cm² 3 up to 1.2 × 10 20atoms / cm² 3 .

[0033] As a condition necessary to adjust the tip position so that it falls within the depth range described above, the accelerating voltage of the cluster ions is set to more than 0 keV / cluster and less than 100 keV / cluster, preferably to 80 keV / cluster, more preferably to 60 keV / cluster. Furthermore, the cluster size is set to 2 to 100 atoms or molecules, preferably 60 atoms or molecules or less, more preferably 50 atoms or molecules or less.

[0034] The dose of cluster ions can be adjusted by controlling the irradiation time. In particular, the carbon dose is preferably 2 × 10 14 atoms / cm² 2 up to 1 × 10 15 atoms / cm² 2 A carbon dose of 2 × 10 14 atoms / cm² 2or more, enables sufficient capture of oxygen diffusing from the silicon wafer 10 to the first epitaxial silicon layer 12. A carbon dose of 1 × 10 15 atoms / cm² 2 or less can reduce damage to the surface 12A of the first epitaxial silicon layer.

[0035] A key aspect of the present revelation is, after the third step ( Fig. 1E) to obtain a silicon epitaxial wafer 100 wherein the peak concentration of the oxygen concentration profile in the first modification layer 14 2 × 10 17 atoms / cm² 3 or less and the oxygen concentration profile of the second epitaxial silicon layer 16 2 × 10 16 atoms / cm² 3or less. Their technical significance is discussed below. The term "concentration profile" here means a concentration distribution in the depth direction, as measured by secondary ion mass spectrometry (SIMS). The term "oxygen concentration of the second epitaxial silicon layer" here means an average value of the oxygen concentration profile over the second epitaxial silicon layer in the depth direction, when the oxygen concentration in the second epitaxial silicon layer is measured by SIMS.

[0036] The inventors focused on the peak concentration of the oxygen concentration profile in the first modification layer and conducted extensive investigations. As a result, they discovered a significant increase in getter capability when the peak concentration of the oxygen concentration profile in the first modification layer is reduced to 2 × 10⁻⁶ after the formation of the second epitaxial silicon layer. 17 atoms / cm² 3 or lower, and the oxygen concentration of the second epitaxial silicon layer is reduced to the lower SIMS detection limit or less. The following describes a possible reason for this.

[0037] The first modification layer contains getter sites formed by irradiation with first ions. If the first modification layer has a high oxygen concentration, most of the getter sites are undesirably occupied by oxygen atoms. If oxygen atoms occupy most of the getter sites, the getter capability decreases because the getter sites cannot completely capture metals. In contrast, according to the present disclosure, there is a significant increase in getter capability because the present disclosure makes it possible to reduce the number of oxygen atoms occupying the getter sites by limiting the peak concentration of the oxygen concentration profile in the first modification layer to 2 × 10⁻⁶. 17 atoms / cm² 3or less. This also sufficiently reduces the diffusion of oxygen from the silicon wafer 10, so that the oxygen concentration of the second epitaxial silicon layer can also be reduced to the lower SIMS detection limit or less.

[0038] As a result of further investigations carried out by the inventors, it was found that it is important to make the oxygen concentration in a surface layer portion of the first epitaxial silicon layer equal to or less than the lower SIMS detection limit when carbon-containing first ions are applied, in order to reduce the peak concentration of the oxygen concentration profile in the first modification layer to 2 × 10 17 atoms / cm² 3 or set it lower and to increase the oxygen concentration of the second epitaxial silicon layer (to be a component layer) to 2 × 10 16 atoms / cm² 3or less (the lower SIMS detection limit or less).

[0039] With reference to Fig. 1A to 1E and Fig. Section 3 describes the following method to make the oxygen concentration in the surface layer part of the first epitaxial silicon layer 12 equal to or less than the lower SIMS detection limit (2 × 10) before the second step. 16 atoms / cm² 3 ) close.

[0040] With reference to Fig. 1A and Fig. 1B In the first embodiment of the present disclosure, the thickness of the first epitaxial silicon layer 12 is determined in the first step according to the oxygen concentration of the silicon wafer 10, such that the oxygen concentration in the surface layer portion of the first epitaxial silicon layer 12 is equal to or less than the lower SIMS detection limit before the second step. With reference to Fig. Section 3 describes the following as an example of a method for determining the thickness of the first epitaxial silicon layer 12.

[0041] First, an appropriate oxygen diffusion coefficient can be set, taking into account the epitaxial growth condition. Next, based on this oxygen diffusion coefficient, as described in Fig. As shown in Figure 3, it is possible to obtain oxygen concentration profiles after the growth of the first epitaxial silicon layer 12 for different oxygen concentrations of the silicon wafer 10 by theoretical calculation. During epitaxial growth, the thickness of the epitaxial silicon layer 12 to be formed can vary by approximately 500 nm in the case of cluster ions or by approximately 0.5 µm to 1 µm in the case of monomer ions from the depth positions (a, b, c, d) in Figure 3. Fig. 3. The oxygen concentration profile curves intersect the straight line representing the lower SIMS detection limit. Accordingly, it can be learned that the higher the oxygen concentration in the silicon wafer 10, the greater the thickness of the first epitaxial silicon layer 12 required to keep the oxygen concentration in the surface layer portion of the first epitaxial silicon layer 12 equal to or less than the lower SIMS detection limit.

[0042] Next, the following describes, with reference to Fig. Sections 2A to 2G describe a method for producing a silicon epitaxial wafer 200 according to a second embodiment of the present disclosure. The same elements as those in the first embodiments are not described.

[0043] In the present embodiment, the silicon wafer 10 is first irradiated with cluster ions 20 (second ions) containing carbon as a constituent element to form a second modification layer 22, in which carbon is tightly dissolved, in a surface layer part of the silicon wafer 10 ( Fig. 2A, Fig. 2B and Fig. 2C). Next, a first epitaxial silicon layer 12 is deposited on the second modification layer 22 ( Fig. 2D). Next, the first epitaxial silicon layer 12 is irradiated with cluster ions 18 (first ions) containing carbon as a constituent element to form a first modification layer 14, in which the carbon is tightly dissolved, in a surface layer part of the first epitaxial silicon layer 12 ( Fig. 2E and Fig. 2F). Next, a second epitaxial silicon layer 16 is deposited on the first modification layer 14 ( Fig. 2G) formed. Fig. Figure 2G is a schematic cross-sectional view of a silicon epitaxial wafer 200 obtained by this manufacturing process.

[0044] From the perspective of improving the getter capability of the second modification layer 22, it is preferred to use cluster ions containing carbon as a constituent element as the second ions. Remarkably, the irradiation conditions for the second ions can be the same as those for the first ions. In the second embodiment, the thickness of the first epitaxial silicon layer 12 is not specifically limited, but is preferably 1 µm to 10 µm.

[0045] Accordingly, in the second embodiment, the diffusion of oxygen present in the silicon wafer 10 into the first epitaxial silicon layer 12 can be reduced because the second modification layer 22, formed in the surface layer portion of the silicon wafer 10, acts as a getter layer to capture the oxygen diffusing from the silicon wafer 10. As a result, it is possible to make the oxygen concentration in the surface layer portion of the first epitaxial silicon layer 12 equal to or less than the lower SIMS detection limit before the second step.

[0046] A method for making the oxygen concentration in a surface layer portion of the first epitaxial silicon layer 12 equal to or less than the lower SIMS detection limit has been described above for the first and second embodiments. However, it is noted that any method can be used to make the oxygen concentration in the surface layer portion of the first epitaxial silicon layer 12 equal to or less than the lower SIMS detection limit. For example, prior to the first step of forming the first epitaxial silicon layer, the silicon wafer can be subjected to a heat treatment to diffuse out oxygen, forming a layer with diffused oxygen in a surface layer portion of the silicon wafer. The following describes a heat treatment for diffusing out oxygen.

[0047] By performing an oxygen diffusion heat treatment, oxygen present in the surface layer portion of the silicon wafer is diffused outwards (i.e., to the outside of the silicon wafer). This results in the formation of a layer of diffused oxygen that has a lower oxygen concentration than the central portion of the silicon layer in the surface layer portion of the silicon wafer. Any condition can be used for the oxygen diffusion heat treatment, as long as the oxygen concentration in the surface layer portion of the first epitaxial silicon layer can be reduced to or below the lower SIMS detection limit. Specifically, an oxygen diffusion heat treatment is performed in the temperature range of 1100 °C to 1250 °C for 1 to 5 hours.The heat treatment to diffuse out oxygen can be carried out in any known heat treatment furnace. (Silicon epiaxial wafer)

[0048] With reference to Fig. 1E and Fig. 2G describes the following silicon epitaxial wafers 100 and 200, which are obtained by the fabrication processes described above. The silicon epitaxial wafers 100 and 200 each comprise a silicon wafer 10, a first epitaxial silicon layer 12 formed on the silicon wafer 10, a first modification layer 14 in which carbon is implanted in a surface layer portion of the first epitaxial silicon layer 12, and a second epitaxial silicon layer 16 on the first modification layer 14. As shown in Fig. As shown in Figure 2G, the silicon epitaxial wafer 200 further includes a second modification layer 22 in which carbon is implanted in a surface layer portion of the silicon wafer 10. In each of the silicon epitaxial wafers 100, 200, the peak concentration of the oxygen concentration profile in the first modification layer 14 is 2 × 10 17 atoms / cm² 3 or less, and the oxygen concentration of the second epitaxial silicon layer is 16 2 × 10 16 atoms / cm² 3 or less.

[0049] The oxygen concentration of the silicon wafer 10 is preferably 2 × 10 17 atoms / cm² 3 up to 18 × 10 17 atoms / cm² 3 The peak concentration of the carbon concentration profile in the first modification layer 14 is preferably 3.8 × 10 18 atoms / cm² 3 up to 1.2 × 10 20 atoms / cm² 3The dopant concentration of the first epitaxial layer 12 is preferably equal to or less than the dopant concentration of the second epitaxial silicon layer 16, and the first epitaxial silicon layer 12 is preferably an epitaxial silicon layer that is not doped with a dopant. The reasons for this are as discussed above.

[0050] Accordingly, according to the silicon epitaxial wafers 100, 200 of the present embodiments, it is possible to reduce metal contamination by exerting a high getter capability. (Method for manufacturing a solid-state image acquisition device)

[0051] A method for fabricating a solid-state image acquisition device according to an embodiment of the present disclosure includes the formation of a solid-state image acquisition device in the second epitaxial silicon layer 16 of the silicon epitaxial wafer 100, 200 fabricated by the method described above, or of the silicon epitaxial wafer 100 described above. Solid-state image acquisition devices obtained by this fabrication method are more sensitive and produce fewer white spot defects than conventional ones.

[0052] The present disclosure has been described based on representative embodiments. EXAMPLES (Invention example)

[0053] A silicon wafer (300 mm in diameter and 725 µm thick) with an oxygen concentration (ASTM F121-1979) of 14 × 10 17 atoms / cm² 3 was prepared from a monocrystalline CZ silicon ingot.

[0054] Next, the silicon wafer was transferred to a single-wafer processing epitaxial growth unit (Applied Materials, Inc.) and subjected to hydrogen annealing at 1120 °C for 30 seconds. A first epitaxial silicon layer, 8 µm thick, was then epitaxially grown onto the silicon wafer by CVD at 1150 °C using hydrogen as the carrier gas and trichlorosilane as the source gas. The oxygen concentration of the first epitaxial silicon layer in a region 500 nm from the surface was no greater than the lower SIMS detection limit (2.0 × 10⁻⁶). 16 atoms / cm² 3 ), as measured by SIMS. Remarkably, the first epitaxial silicon layer was not doped with a dopant.

[0055] Next, C3H5 cluster ions generated from cyclohexane using a cluster ion generator (Nissin Ion Equipment Co., Ltd., model: CLARIS) were deposited onto the surface of the first epitaxial silicon layer at a carbon dose of 1.0 × 10 15 atoms / cm² 2 Applied at an accelerating voltage of 80 keV / cluster to convert a surface layer portion of the first epitaxial silicon layer into a first modification layer.

[0056] Next, a second epitaxial silicon layer was deposited (thickness: 8 µm, dopant type: phosphorus, dopant concentration 9 × 10⁻⁶). 13 atoms / cm² 3 ) on the first modification layer by the same process as that used for the formation of the first epitaxial silicon layer.

[0057] A carbon concentration profile was measured by SIMS. The first modification layer was identified by confirming the presence of a steep peak at a distance of 80 nm from the surface of the first epitaxial silicon layer. The peak value of the carbon concentration profile in the first epitaxial silicon layer was 1 × 10⁻⁶. 20 atoms / cm² 3 . (Comparative example 1)

[0058] A silicon epitaxial wafer was obtained by the same manufacturing process as in the inventive example, except that the surface of the silicon wafer was irradiated with cluster ions without forming the first epitaxial silicon layer. (Comparative example 2)

[0059] A silicon epitaxial wafer was obtained by the same fabrication process as in the inventive example, except that the thickness of the first epitaxial silicon layer was set to 0.5 µm. The oxygen concentration of the first epitaxial silicon layer in a region 500 nm from the surface was 7 × 10⁻⁶ before irradiation with cluster ions. 17 atoms / cm² 3 ), as measured by SIMS. (Comparative example 3)

[0060] A silicon epitaxial wafer was obtained by the same fabrication process as in the inventive example, except that the thickness of the first epitaxial silicon layer was set to 6.0 µm. The oxygen concentration of the first epitaxial silicon layer in a region 500 nm from the surface was 3 × 10⁻⁶ before irradiation with cluster ions. 16 atoms / cm² 3 ), as measured by SIMS. (Evaluation procedure)

[0061] The following evaluation was carried out on the invention example and the comparative examples. <Sauerstoffkonzentrationsverteilung, gemessen durch SIMS>

[0062] In the inventive example and the comparative examples, the oxygen concentration after formation of the second epitaxial silicon layer was measured by secondary ion mass spectrometry (SIMS). The measurement results are presented in Fig. 4A shown. <Auswertung der Getter-Fähigkeit>

[0063] The surface of the silicon epitaxial wafer samples prepared in the inventive example and comparative examples 1 to 3 was intentionally treated with an Fe-contaminated liquid (1 × 10 13 atoms / cm² 2The material was contaminated by the spin-coat contamination method and subsequently heated to 1050 °C for 2 hours. The Fe concentration was then measured by SIMS. Peak concentrations of concentration profiles of Fe trapped in the first modification layer are shown for the inventive example and the comparative examples in Fig. 4B shown. (Explanation of evaluation results)

[0064] First, in comparative examples 1 to 3, as in Fig. Figure 4A shows that the peak concentration of the oxygen concentration profile in the first modification layer is greater than 2 × 10 17 atoms / cm² 3 Furthermore, the oxygen concentration in the second epitaxial silicon layer was greater than 2 × 10 16 atoms / cm² 3 Accordingly, they showed how in Fig. As shown in Figure 4B, comparison examples 1 to 3 all exhibit low getter capability. In contrast, the invention example, as shown in Figure 4B, had a low getter capability. Fig. Figure 4A shows that the peak concentration of the oxygen concentration profile in the first modification layer is not greater than 2 × 10 17 atoms / cm² 3 and the oxygen concentration in the second epitaxial silicon layer was consistently no greater than the lower SIMS detection limit in the depth direction. At this point, as shown in Fig. 4B showed that getter capability increased significantly. INDUSTRIAL APPLICABILITY

[0065] According to the present disclosure, it is possible to provide a silicon epitaxial wafer that can reduce metal contamination by exerting a higher getter capability, and a method for manufacturing the same. REFERENCE MARK LIST 100, 200 silicon epitaxial wafers 10 silicon wafers 10A Silicon wafer surface 12 First epitaxial silicon layer 12A First epitaxial silicon layer surface 14 First modification layer 16 Second epitaxial silicon layer 18 Carbon-containing cluster ions (first ions) 20 carbon-containing cluster ions (second ions) 22 Second modification layer

Claims

[1] Method for producing a silicon epitaxial wafer (100, 200) comprising the following: a first step in the formation of a first epitaxial silicon layer (12) which contains a surface layer part with an oxygen concentration of 2 × 10 16 atoms / cm² 3 or less, on a silicon wafer (10) which has an oxygen concentration of 2 × 10 17 atoms / cm² 3 or more; a second step of irradiating the surface layer portion of the first epitaxial silicon layer (12) with first ions (18) containing carbon to form a first modification layer (14) in which the carbon is implanted in the surface layer portion of the first epitaxial silicon layer (12); and a third step of forming a second epitaxial silicon layer (16) on the first modification layer (14), wherein after the third step a silicon epitaxial wafer (100, 200) is obtained, wherein a peak concentration of an oxygen concentration profile in the first modification layer (14) 2 × 10 17 atoms / cm² 3 or less and an oxygen concentration of the second epitaxial silicon layer (16) 2 × 10 16 atoms / cm² 3 or less. [2] Method according to claim 1, wherein the first ions are cluster ions (18) containing carbon as a constituent element. [3] Method according to claim 1 or 2, wherein in the first step a thickness of the first epitaxial silicon layer (12) is determined according to an oxygen concentration of the silicon wafer (10), such that the surface layer part of the first epitaxial silicon layer (12) has an oxygen concentration of 2 × 10 before the second step 16 atoms / cm² 3 or less. [4] A method according to claim 1 or 2, further comprising, prior to the first step, irradiating the silicon wafer (10) with second ions (20) containing carbon to form a second modification layer (22) in which carbon is implanted in a surface layer part of the silicon wafer (10), such that the surface layer part of the first epitaxial silicon layer (12) has an oxygen concentration of 2 × 10⁻⁵ before the second step. 16 atoms / cm² 3 or less. [5] Method according to claim 4, wherein the second ions (20) are cluster ions containing carbon as a constituent element. [6] Method according to any one of claims 1 to 5, wherein the first epitaxial silicon layer (12) has a dopant concentration that is equal to or less than a dopant concentration of the second epitaxial silicon layer (16). [7] Method according to claim 6, wherein the first epitaxial silicon layer (12) is not doped with a dopant. [8] Silicon epitaxial wafer (100, 200) comprising the following: a silicon wafer that has an oxygen concentration of 2 × 10 17 atoms / cm² 3 or more; a first epitaxial silicon layer (12) formed on the silicon wafer (10); a first modification layer (14) in which carbon is implanted, wherein the first modification layer (14) is formed in a surface layer part of the first epitaxial silicon layer (12); and a second epitaxial silicon layer (16) formed on the first modification layer (14), wherein a peak concentration of an oxygen concentration profile in the first modification layer (14) 2 × 10 17 atoms / cm² 3or less and an oxygen concentration of the second epitaxial silicon layer (16) 2 × 10 16 atoms / cm² 3 or less. [9] Silicon epitaxial wafer (100, 200) according to claim 8, wherein the first epitaxial silicon layer (12) has a dopant concentration that is equal to or less than a dopant concentration of the second epitaxial silicon layer (16). [10] Silicon epitaxial wafer (100, 200) according to claim 9, wherein the first epitaxial silicon layer (12) is not doped with a dopant. [11] Method for manufacturing a solid-state image acquisition device comprising: Forming a solid-state image acquisition device in the second epitaxial silicon layer (16) of the silicon epitaxial wafer (100, 200) produced by the method according to one of claims 1 to 7, or of the silicon epitaxial wafer (100, 200) according to one of claims 8 to 10.

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