Method for manufacturing silicon wafers and silicon wafers

Abstract

This invention provides a method for manufacturing silicon wafers in which the oxygen concentration of the surface layer on the wafer surface side is reduced. [Solution] The present invention relates to a method for manufacturing a silicon wafer, comprising: a first heat treatment step (RTO) in which a silicon wafer prepared by slicing a silicon single crystal ingot grown by the CZ method is heated in an oxidizing gas atmosphere to a first maximum temperature of 1250°C to 1400°C, held at the first maximum temperature for a predetermined time, and then cooled; a surface oxide film removal step in which an oxide film formed on the wafer surface (front surface) is removed; and a second heat treatment step (RTA) in which the silicon wafer after the surface oxide film removal step is heated in a non-oxidizing gas atmosphere to a second maximum temperature of 800°C to 1350°C, held at the second maximum temperature for a predetermined time, and then cooled.

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing a silicon wafer suitable for use as a substrate for semiconductor devices, and to a silicon wafer manufactured by this manufacturing method. [Background technology]

[0002] For example, in image sensor devices, it is desirable to use silicon wafers with extremely low oxygen concentrations in the surface layer, which is the device's active region, in order to prevent the generation of oxygen-related defects that result in poor afterimage characteristics. On the other hand, if the oxygen concentration is too low, crystal defects such as slips may occur during the device process, so it is desirable to manufacture the wafers with a target low oxygen concentration without variation.

[0003] Therefore, in recent years, research has been underway to develop techniques for reducing oxygen concentration as intended in crystal growth using the Czochralski method (CZ method).

[0004] Patent Document 1 discloses a "method for manufacturing a silicon wafer" that combines the following steps: a first step of heat treatment performed in an oxidizing gas atmosphere under predetermined conditions (maximum temperature of 1300°C to 1380°C) using a raw silicon wafer with a predetermined oxygen concentration sliced ​​from a silicon single crystal ingot grown by the CZ method; a second step of peeling off the oxide film from the front and back surfaces (including the edges) of the silicon wafer; and a third step of heat treatment performed in a non-oxidizing gas atmosphere under predetermined conditions (maximum temperature of 1200°C to 1380°C). This method makes it possible to obtain a silicon wafer with a sufficiently reduced oxygen concentration on the surface. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2016-195211 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] In the above-mentioned Patent Document 1, by performing a third step of heat treatment in a non-oxidizing atmosphere (RTA: Rapid Thermal Annealing), the oxygen concentration on the surface layer of the silicon wafer (front and back surfaces), which increased during the first step of heat treatment in an oxidizing atmosphere (RTO: Rapid Thermal Oxidation), can be reduced.

[0007] In other words, conventional silicon wafer manufacturing methods have achieved a certain degree of effectiveness in terms of oxygen concentration, as they have been able to reduce the oxygen concentration on the wafer surface as intended.

[0008] However, if the oxide film on the front and back surfaces (the entire surface of the silicon wafer) is removed after RTO, which is a heat treatment in an oxidizing atmosphere, and then RTA, which is a heat treatment in a non-oxidizing atmosphere, is performed on the silicon wafer after the oxide film has been removed, slippage is more likely to occur in the silicon wafer held in the susceptor.

[0009] The present invention has been made in view of the above problems, and aims to provide a method for manufacturing a silicon wafer and a silicon wafer that can suppress slippage during RTA while reducing the oxygen concentration of the surface layer on the surface side of the silicon wafer. [Means for solving the problem]

[0010] The present invention relates to a method for manufacturing a silicon wafer, comprising: a first heat treatment step of heating a silicon wafer, prepared by slicing a silicon single crystal ingot grown by the CZ method, to a first maximum temperature of 1250°C to 1400°C in an oxidizing gas atmosphere, holding it at the first maximum temperature for a predetermined time, and then cooling it down to form an oxide film on both the front and back surfaces of the wafer; a surface oxide film removal step of removing the oxide film formed on the wafer surface (front side) of the silicon wafer after the first heat treatment step, while leaving the oxide film formed on the back side of the wafer; and a second heat treatment step of heating the silicon wafer after the surface oxide film removal step to a second maximum temperature of 800°C to 1350°C in a non-oxidizing gas atmosphere, holding it at the second maximum temperature for a predetermined time, and then cooling it down to reduce the oxygen concentration on the surface layer of the wafer surface.

[0011] In this process, the first heat treatment step is performed using a single-wafer heat treatment apparatus, and the second heat treatment step is performed using either a single-wafer heat treatment apparatus or a batch-type heat treatment apparatus. The holding time at the first maximum temperature is preferably 1 second or more and 60 seconds or less. The holding time at the second maximum temperature is preferably 1 second or more and 60 seconds or less in the case of a single-wafer apparatus, and preferably 1 minute or more and 240 minutes or less in the case of a batch-type apparatus.

[0012] For example, in the silicon wafer manufacturing method according to the present invention described above, the oxygen concentration of the wafer surface layer is increased to 1 × 10 by the heat treatment in the second heat treatment step. 17 atoms / cm 3 It is preferable to reduce the concentration to the following level. Furthermore, in the first heat treatment step, it is preferable to form an oxide film of 10 to 50 nm on the front and back surfaces of the wafer.

[0013] Also, in the method for manufacturing a silicon wafer according to the present invention, in the surface oxide film removing step, hydrofluoric acid is supplied to the wafer surface (front side) using a spin cleaning apparatus, and pure water is supplied to the back side of the wafer. In the second heat treatment step, heat treatment is performed while leaving the oxide film formed in the first heat treatment step on the back side of the wafer. And in the method for manufacturing a silicon wafer according to the present invention, it is preferable to further include a back side oxide film removing step for removing the oxide film remaining on the back side of the silicon wafer after the second heat treatment step.

[0014] Thus, in the method for manufacturing a silicon wafer according to the present invention, by performing a series of processes including a first heat treatment step (RTO), a surface oxide film removing step (removing only the oxide film on the wafer surface (front side) and leaving the oxide film on the back side of the wafer), and a second heat treatment step (RTA), it is possible to reduce the oxygen concentration in the surface layer on the wafer surface side, which is the device active region, and further suppress the variation in oxygen concentration caused by the CZ method.

[0015] Also, in the method for manufacturing a silicon wafer according to the present invention, since heat treatment by the second heat treatment step (RTA) is performed while leaving the oxide film formed in the first heat treatment step (RTO) on the back side (contact region with the susceptor), that is, heat treatment is performed while maintaining the strength of the back side of the wafer, the occurrence of slip can be suppressed.

[0016] Also, the silicon wafer according to the present invention manufactured by the above manufacturing method has a low oxygen region in the surface layer on the wafer surface side where the oxygen concentration is reduced to 1×10 17 atoms / cm 3 or less, a high oxygen region in the surface layer on the back side of the wafer where the oxygen concentration is 7×10 17 atoms / cm 3 or more, and an oxygen concentration higher than 1×10 17 atoms / cm 3 and lower than 7×10 17 atoms / cm 3It is characterized by having a mid-oxygen region that is lower than and in which BMD (Bulk Microdefect) nuclei are formed.

[0017] By reducing the oxygen concentration in the surface layer on the wafer surface side, the image sensor device using the silicon wafer according to the present invention can suppress oxygen-related defects that result in poor afterimage characteristics. Furthermore, because the silicon wafer according to the present invention has a high oxygen concentration on the back side, that is, the strength of the back side is maintained, slippage during RTA (Real-Time Attention) is suppressed during the device manufacturing process. [Effects of the Invention]

[0018] According to the silicon wafer manufacturing method of the present invention, it is possible to reduce the oxygen concentration of the surface layer on the surface side of the silicon wafer while suppressing slippage during RTA (Real-Time Analysis). [Brief explanation of the drawing]

[0019] [Figure 1] Figure 1 is a cross-sectional conceptual diagram showing an example of a single-wafer RTP apparatus used for heat treatment in the silicon wafer manufacturing method according to the present invention. [Figure 2] Figure 2 is a flowchart showing an example of a silicon wafer manufacturing method according to the present invention. [Figure 3] Figure 3 is a schematic diagram showing the manufacturing process of a silicon wafer according to the present invention. [Figure 4] Figure 4 is an illustrative diagram showing an example of heat treatment. [Figure 5] Figure 5 is a schematic diagram showing the layer structure of a silicon wafer manufactured by the silicon wafer manufacturing method according to the present invention. [Figure 6] Figure 6 is a flowchart showing a modified example of the silicon wafer manufacturing method according to the present invention. [Modes for carrying out the invention]

[0020] Hereinafter, a silicon wafer manufacturing method and embodiments of the silicon wafer according to the present invention will be described in detail with reference to the drawings. However, the present invention is not limited to these embodiments. Furthermore, in the specification and drawings of this application, elements that can be similarly described are denoted by the same reference numerals, thereby omitting redundant explanations.

[0021] <Overview of Manufacturing Method> The silicon wafer manufacturing method according to the present invention comprises a first heat treatment step (RTO) in which a silicon wafer (hereinafter sometimes simply referred to as "wafer") obtained by slicing a silicon single crystal ingot grown by the CZ method is heated in an oxidizing gas atmosphere to a first maximum temperature of 1250°C to 1400°C, held at the first maximum temperature for a predetermined time, and then cooled at a cooling rate of 25°C / second to 250°C / second to form an oxide film on the front and back surfaces of the wafer, and silicon The process includes a surface oxide film removal step, in which the oxide film formed on the wafer surface (front side) of the wafer is removed (peeled), while the oxide film formed on the back side of the wafer is left intact; and a second heat treatment (RTA) step, in which the silicon wafer after the oxide film on the wafer surface (front side) has been removed is heated in a non-oxidizing gas atmosphere to a second maximum temperature of 800°C to 1350°C, held at the second maximum temperature for a predetermined time, and then cooled to reduce the oxygen concentration on the surface layer of the wafer surface.

[0022] In this embodiment, the oxygen concentration is 3.0 × 10⁻⁶ by the CZ method. 17 atoms / cm 3 The above 1.9 × 10 18 atoms / cm 3 The following silicon single crystal ingots will be grown. The oxygen concentration of the grown silicon single crystal ingots will be 7 × 10⁻⁶. 17 atoms / cm 3 If the following conditions are met, the oxygen concentration in the bulk portion will remain low even after RTO and RTA in this embodiment, making it more desirable as a wafer for CIS applications. For example, using the FZ method (Floating Zone method), 3.0 × 10 17 atoms / cm 3A silicon single crystal ingot of less than may be grown.

[0023] Also, in the present embodiment, an oxide film of 10 μm or more and 50 μm or less is formed on the front and back surfaces of the wafer by RTO, and the oxygen concentration in the surface layer on the front side of the wafer (depth of 1 to 3 μm from the wafer surface (front surface)) is reduced to 1×10 17 atoms / cm 3 or less by RTA.

[0024] That is, by performing a series of processes including RTO, a surface oxide film removal process (removing only the oxide film on the front surface (front side) of the wafer and leaving the oxide film on the back surface of the wafer), and RTA, the oxygen concentration in the surface layer on the front side of the wafer, which is the device active region, can be reduced to 1×10 17 atoms / cm 3 or less, and further, the oxygen concentration in the intermediate layer can be made higher than that in the surface layer on the front side of the wafer, and the back surface layer of the wafer can be made higher than the intermediate layer.

[0025] <RTP Apparatus> FIG. 1 is a cross-sectional conceptual diagram showing an example of a single-wafer RTP apparatus used for heat treatment (RTP: Rapid Thermal Process) in the method for manufacturing a silicon wafer according to the present invention.

[0026] The RTP apparatus 10 shown in FIG. 1 includes a reaction chamber 20 for accommodating the wafer W and performing heat treatment, a wafer holding unit 30 provided in the reaction chamber 20 for holding the wafer W, and a heating unit 40 for heating the wafer W. When the wafer W is held by the wafer holding unit 30, a first space 20a, which is a space surrounded by the inner wall of the reaction chamber 20 and the surface (front surface: device formation surface) W1 of the wafer W, and a second space is formed, which is a space surrounded by the inner wall of the reaction chamber 20 and the back surface W2 of the wafer W facing the surface W1.

[0027] The reaction chamber 20 has a supply port 22 for supplying an atmosphere gas F A (solid line arrow), and the supplied atmosphere gas FA It has an outlet 26 for discharging from the first space 20a and the second space 20b. The reaction chamber 20 is made of, for example, quartz.

[0028] The wafer holding section 30 includes a ring-shaped susceptor 32 that holds the outer periphery of the back surface W2 of the wafer W, and a rotating body 34 that holds the susceptor 32 and rotates the susceptor 32 around the center of the wafer W as an axis. The susceptor 32 is made of, for example, SiC, and its surface is coated with an oxide film.

[0029] The heating unit 40 heats the wafer W from both sides by lamp heating through light irradiation from a plurality of halogen lamps 50 located outside the reaction chamber 20, above the surface W1 and below the back surface W2 of the wafer W held by the wafer holding unit 30.

[0030] When performing heat treatment using the RTP apparatus 10 shown in Figure 1, the wafer W is introduced into the reaction chamber 20 through a wafer inlet (not shown) provided in the reaction chamber 20, and the outer periphery of the back surface W2 of the wafer W is held on the ring-shaped susceptor 32 in the wafer holding section 30. Then, the atmospheric gas F A The wafer W is heated by the heating unit 40 while the wafer W is rotated.

[0031] <Manufacturing Method> Next, embodiments of the silicon wafer manufacturing method according to the present invention will be specifically described with reference to the drawings. Figure 2 is a flowchart showing an example of the silicon wafer manufacturing method according to the present invention, and Figure 3 is a schematic diagram showing the silicon wafer manufacturing process according to the present invention.

[0032] As shown in Figure 2, the silicon wafer manufacturing method in this embodiment includes a growth step (step S1) of growing a silicon single crystal ingot by the CZ method, a slicing step (step S2) of slicing the grown silicon single crystal ingot to produce a disc-shaped wafer W, a grinding step (step S3) of performing a planarization treatment on the front and back surfaces of the disc-shaped wafer W, the first heat treatment step (RTO: step S4), the surface oxide film removal step (step S5), the second heat treatment step (RTA: step S6), a back surface oxide film removal step (step S7) of removing (peeling off) the oxide film formed on the back surface of the wafer, a final polishing step (step S8) of mirror polishing at least the wafer surface (front surface) which will be the semiconductor device formation surface, and a final cleaning step (step S9) of performing single-wafer spin cleaning on the wafer W after mirror polishing.

[0033] In other words, in this embodiment, the heat treatment by the first heat treatment process (RTO) is performed on the wafer W after the grinding process. In the growth process of this embodiment, as an example, the oxygen concentration is 3.0 × 10⁻¹⁶ by the CZ method. 17 atoms / cm 3 The above 1.9 × 10 18 atoms / cm 3 The following silicon single crystal ingots are grown. The grinding process also includes a lapping process, which involves rough polishing to a certain thickness while removing cutting damage formed during slicing, and an etching process, which involves chemical etching to remove minute distortions and scratches introduced during the lapping process.

[0034] In the silicon wafer manufacturing method of this embodiment shown in Figure 2, in the first heat treatment step (RTO: step S4), the wafer W after the grinding step (step S3) (see Figure 3(a)) is heated in an oxidizing gas atmosphere to a first maximum temperature of 1250°C to 1400°C, held at the first maximum temperature for a period of 1 second to 60 seconds, and then cooled at a cooling rate of 25°C / second to 250°C / second.

[0035] Figure 4 is an illustrative diagram showing an example of heat treatment, with the vertical axis representing temperature (°C) and the horizontal axis representing time (sec). In Figure 4, the first heat treatment process (RTO) is indicated by section X. In this first heat treatment process (RTO), for example, by maintaining a maximum temperature T1 (1250°C to 1400°C) for a predetermined time t1 (1 second to 60 seconds), an oxide film 61 of 10 to 50 μm is formed on both sides of the wafer (see Figure 3(b)). This makes it possible to obtain a wafer W with excellent strength. In the first heat treatment process (RTO), as an example, the RTP apparatus 10 shown in Figure 1 is used. In addition, any known gas can be used as the oxidizing gas without particular restriction, but oxygen is usually used. Furthermore, the atmospheric gas during heat treatment does not have to be 100% oxygen gas; for example, any gas with an oxygen partial pressure in the range of 0.5 to 100% is acceptable.

[0036] Furthermore, by performing RTO, void defects such as COP (Crystal Originated Particles) and oxygen precipitates present on the wafer surface after the grinding process can be eliminated, while BMD (Bulk Microdefect) nuclei can be formed in the bulk region.

[0037] Furthermore, RTOs with a first maximum temperature of less than 1250°C are undesirable because the oxide film on the inner wall of the COP is difficult to dissolve, and the COP elimination effect may not be sufficient, and the elimination effect of oxygen precipitates may also be insufficient. In addition, if the first maximum temperature exceeds 1400°C, slip is more likely to occur, which is also undesirable.

[0038] After the first heat treatment process (RTO), in the surface oxide film removal process (step S5), the oxide film formed on the wafer surface (front side) is removed (peeled). At this time, the oxide film is removed by performing hydrofluoric acid cleaning on the wafer surface (hydrofluoric acid cleaning is not performed on the back side of the wafer). Specifically, by single-wafer spin cleaning (cleaning using a spin cleaning device), a cleaning solution with a hydrofluoric acid concentration of 0.1 to 20 mass%, preferably 1 to 10 mass%, is supplied to the wafer surface to remove the oxide film, and at the same time, pure water is supplied to the back side of the wafer to perform pure water cleaning and leave the oxide film. That is, in this embodiment, considering the uniformity of oxygen concentration, the oxide film is removed from the entire wafer surface, including the bevel portion on the front side, and the oxide film 61a is left on the entire back side of the wafer, including the bevel portion on the back side, to suppress slippage (see Figure 3(c)). Here, the oxide film may be removed from the entire bevel portion, or the oxide film may be left on the entire bevel portion. It is sufficient for an oxide film to remain at least in the area that contacts the susceptor on the back side of the wafer. However, to suppress variations in oxygen concentration on the surface layer on the front side of the wafer, it is desirable that the oxide film on the bevel portion on the surface side be removed.

[0039] Furthermore, hydrofluoric acid cleaning with a hydrofluoric acid concentration of less than 0.1% by mass is undesirable because it results in a low etching rate of the oxide film and takes a long time. In addition, while hydrofluoric acid cleaning is preferable in the surface oxide film removal process considering productivity and quality, if it is acceptable to reduce productivity and / or quality, the oxide film on the wafer surface (front side) may be removed by polishing. However, the purpose is solely to remove the oxide film, and not to polish the wafer surface itself.

[0040] After the surface oxide film removal process, in the second heat treatment process (RTA: step S6), the wafer W (see Figure 3(c)) from which the oxide film on the wafer surface (front side) has been removed is heated in a non-oxidizing gas atmosphere to a second maximum temperature of 800°C to 1350°C, held at this second maximum temperature for 1 second to 60 seconds, and then cooled. The cooling rate is 25°C / second to 250°C / second, preferably 75°C / second to 150°C / second. In Figure 4, the second heat treatment process (RTA) is indicated by section Y. In this second heat treatment process (RTA), for example, the maximum temperature T2 (800°C to 1350°C) is held for a predetermined time t2 (1 second to 60 seconds). This makes it possible to reduce the oxygen concentration of the surface layer on the wafer surface side that was increased by the first heat treatment process (RTO). Specifically, the oxygen concentration in the surface layer (1-3 μm from the wafer surface (front side)) is set to 1 × 10⁻¹⁰ only on the wafer surface side. 17 atoms / cm 3 The oxygen concentration is reduced to the following levels (see Figure 3(d)). On the other hand, the oxygen concentration in the surface layer on the back side of the wafer (1-3 μm deep from the back side of the wafer) remains elevated due to RTO. Since an oxide film is formed on the back side of the wafer during RTA, oxygen does not diffuse outward, and therefore the oxygen concentration does not decrease. Consequently, in wafer W of this embodiment, the oxygen concentration on the surface side of the wafer becomes lower than before RTO, while the oxygen concentration on the back side of the wafer becomes higher than before RTO. Furthermore, by performing heat treatment in the second heat treatment process (RTA), residual COP on the surface layer of the wafer surface can also be eliminated.

[0041] In the second heat treatment (RTA) process, as an example, the RTP apparatus 10 shown in Figure 1 is used. Furthermore, while any known gas that does not oxidize the wafer W can be used as the non-oxidizing gas, argon is used, for example, because it does not form films such as nitride films or cause other chemical reactions.

[0042] The oxygen concentration in the wafer surface layer, which is reduced by the heat treatment in the second heat treatment process (RTA), is determined by the second highest temperature reached and its holding time (heat treatment conditions). Therefore, even if variations in oxygen concentration occur in the crystal length direction or in the crystal plane direction due to the CZ method, if the heat treatment conditions are constant, variations in oxygen concentration caused by the CZ method can be suppressed.

[0043] Furthermore, in the second heat treatment process (RTA), the oxide film 61 (oxide film 61a) formed in the first heat treatment process (RTO) is left on the back surface (the area in contact with the susceptor 32) while the heat treatment is performed (see Figures 3(c) and (d)). In other words, the heat treatment is performed while the strength of the back surface of the wafer is maintained, which suppresses the occurrence of slip from the back surface of the wafer.

[0044] Furthermore, a second heat treatment (RTA) process in which the second maximum temperature reached is less than 800°C is undesirable because the slow diffusion rate of oxygen makes it time-consuming to reduce the oxygen concentration on the surface layer of the wafer, thus reducing the production efficiency of the final silicon wafer W. Also, if the second maximum temperature reaches more than 1350°C, it is undesirable because a unique defect in which silicon is elevated may occur on the wafer surface (front side).

[0045] Furthermore, in this embodiment, the heat treatment in the first heat treatment process (RTO) and the second heat treatment process (RTA) are performed consecutively using a single-wafer RTP device 10 (see Figure 1), but this is not limited to this, and for example, different RTP devices 10 may be used for RTO and RTA. When heat treatment is performed using two RTP devices, heat treatment can be performed without reducing throughput.

[0046] Furthermore, in the second heat treatment process (RTA), a batch-type heat treatment apparatus may be used to simultaneously heat-treat several tens to around 100 wafers W at once. In this case, multiple wafers W are heated in a non-oxidizing gas atmosphere to a second maximum temperature of 800°C to 1350°C, held at the second maximum temperature for a period of 1 minute to 240 minutes, and then cooled. The cooling rate is 2°C / second to 30°C / second, preferably 5°C / second to 15°C / second.

[0047] After RTA is performed, in the backside oxide film removal process (step S7), the oxide film 61a that remained formed on the backside of the wafer is removed (peeled) (see Figure 3(e)). At this time, the oxide film 61a is removed by performing hydrofluoric acid cleaning on the backside of the wafer (hydrofluoric acid cleaning is not performed on the frontside of the wafer). Specifically, hydrofluoric acid cleaning is performed on the backside of the wafer using a cleaning solution with a hydrofluoric acid concentration of 0.1 to 20% by mass, preferably 1 to 10% by mass, by single-wafer spin cleaning, and the frontside of the wafer is cleaned with pure water. However, gas may be blown instead of pure water to prevent the hydrofluoric acid cleaning from spreading to the front side of the wafer. Alternatively, hydrofluoric acid may be supplied only to the backside of the wafer for hydrofluoric acid cleaning, and nothing may be supplied to the frontside of the wafer.

[0048] In this embodiment, by carrying out the silicon wafer manufacturing method described above (steps S1 to S9), the oxygen concentration of the wafer surface layer (1 to 3 μm deep from the wafer surface (front side)) is increased to 1 × 10⁻¹⁶. 17 atoms / cm 3 A wafer W with a reduced concentration to the following level can be obtained.

[0049] <Silicon wafers> Figure 5 is a schematic diagram showing the layer structure of a silicon wafer manufactured by the silicon wafer manufacturing method according to the present invention. In the wafer W manufactured by the above-described manufacturing method, the oxygen concentration on the surface layer on the wafer side is reduced by the heat treatment in the second heat treatment process (RTA), but on the other hand, the oxygen concentration on the surface layer on the back side of the wafer is not reduced because the remaining oxide film 61a suppresses oxygen outward diffusion. On the contrary, oxygen is supplied from the oxide film 61a into the wafer interior, resulting in 7 × 10 17 atoms / cm 3 That concludes the explanation.

[0050] In other words, as shown in Figure 5, the wafer W manufactured by the manufacturing method of this embodiment has an oxygen concentration of 1 × 10⁻⁶ 17 atoms / cm 3 The low-oxygen region (DZ (Denuded Zone) layer: defect-free region) D1 on the surface layer of the wafer surface, with an oxygen concentration of 7 × 10⁻⁶ 17 atoms / cm 3 The above describes the high-oxygen region D2 on the surface layer of the back side of the wafer, and the oxygen concentration of 1 × 10⁻⁶ 17 atoms / cm 3 Higher than 7x10 17 atoms / cm 3 It has a three-layer structure consisting of a mid-oxygen region (bulk region) D3, which is lower and where BMD nuclei are formed.

[0051] Thus, the oxygen concentration on the surface layer of the wafer surface is 1 × 10⁻⁶ 17 atoms / cm 3 By manufacturing wafers W with reduced concentrations to the following levels, image sensor devices manufactured using these wafers W can suppress oxygen-related defects that result in poor afterimage characteristics.

[0052] Furthermore, as shown in Figure 5, the wafer W manufactured by the manufacturing method of this embodiment has an oxygen concentration of 7 × 10 on the surface layer of the back side of the wafer. 17 atoms / cm 3Because the concentration is increased to the above level, that is, the strength of the back side is maintained, slippage during RTA (Real-Time Analysis) can be suppressed even in the device process.

[0053] <Effects, etc.> As described above, the silicon wafer manufacturing method of this embodiment includes: a first heat treatment step (RTO) in which a silicon wafer W, prepared by slicing a silicon single crystal ingot grown by the CZ method, is heated in an oxidizing gas atmosphere to a first maximum temperature of 1250°C to 1400°C, held at the first maximum temperature for a predetermined time, and then cooled to form an oxide film 61 on both the front and back surfaces of the wafer; a surface oxide film removal step in which the oxide film formed on the wafer surface (front side) after the first heat treatment step is removed, while the oxide film formed on the back side of the wafer is left intact; and a second heat treatment step (RTA) in which the silicon wafer W after the oxide film removal step is heated in a non-oxidizing gas atmosphere to a second maximum temperature of 800°C to 1350°C, held at the second maximum temperature for a predetermined time, and then cooled to reduce the oxygen concentration on the surface layer of the wafer surface.

[0054] In this process, the first heat treatment process (RTO) is performed using a single-wafer RTP device 10, and the second heat treatment process (RTA) is performed using either a single-wafer RTP device or a batch-type heat treatment device. The holding time at the first highest temperature is preferably between 1 second and 60 seconds. The holding time at the second highest temperature is preferably between 1 second and 60 seconds in the case of a single-wafer device, and between 1 minute and 240 minutes in the case of a batch-type device.

[0055] For example, in the silicon wafer manufacturing method of this embodiment, the oxygen concentration of the wafer surface layer is increased to 1 × 10⁻¹⁶ by heat treatment in the second heat treatment step (RTA). 17 atoms / cm 3 It is preferable to reduce the concentration to the following levels. Furthermore, in the first heat treatment process (RTO), it is preferable to form an oxide film 61 of 10 to 50 nm on the front and back surfaces of the wafer.

[0056] Furthermore, in the silicon wafer manufacturing method of this embodiment, in the surface oxide film removal step, hydrofluoric acid cleaning is performed on the wafer surface (front side) and pure water cleaning is performed on the wafer back side, and in the second heat treatment step (RTA), heat treatment is performed with the oxide film 61 (oxide film 61a) formed in the first heat treatment step (RTO) remaining on the wafer back side. In addition, it is preferable that the silicon wafer manufacturing method of this embodiment further includes a back side oxide film removal step to remove the oxide film 61a remaining on the back side of the silicon wafer W after the second heat treatment step (RTA).

[0057] Thus, in the silicon wafer manufacturing method of this embodiment, by performing a series of processes consisting of a first heat treatment step (RTO), a surface oxide film removal step (removing only the oxide film on the wafer surface (front side) and leaving the oxide film 61a on the back side of the wafer), and a second heat treatment step (RTA), the oxygen concentration of the surface layer on the wafer side, which is the device active region, can be reduced, and furthermore, variations in oxygen concentration caused by the CZ method can be suppressed.

[0058] Furthermore, in the silicon wafer manufacturing method of this embodiment, the heat treatment by the second heat treatment (RTA) is performed with the oxide film 61 formed in the first heat treatment (RTO) remaining on the back surface (the area in contact with the susceptor 32). In other words, the heat treatment is performed while the strength of the back surface of the wafer is maintained, thus suppressing the occurrence of slip.

[0059] Furthermore, the silicon wafer of this embodiment manufactured by the above manufacturing method has an oxygen concentration of 1 × 10⁻⁶ 17 atoms / cm 3 The low-oxygen region D1 on the surface layer of the wafer surface, where the oxygen concentration has been reduced to the following level, and the oxygen concentration of 7 × 10 17 atoms / cm 3 The above describes the high-oxygen region D2 on the surface layer of the back side of the wafer, and the oxygen concentration of 1 × 10⁻⁶ 17 atoms / cm 3 Higher than 7x10 17 atoms / cm 3It has a mid-oxygen region D3 that is lower than and in which a BMD nucleus is formed.

[0060] By reducing the oxygen concentration in the surface layer on the wafer surface side, the image sensor device using the silicon wafer W of this embodiment can suppress oxygen-related defects that result in poor afterimage characteristics. Furthermore, since the silicon wafer W of this embodiment has a high oxygen concentration on the back side, that is, the strength of the back side is maintained, slippage during RTA (Real-Time Analysis) can be suppressed during the device process.

[0061] It should be noted that the present invention is not limited to the embodiments described above. The embodiments described above are illustrative, and any configuration that has substantially the same technical idea as described in the claims and produces similar effects is included within the technical scope of the present invention.

[0062] <Examples of manufacturing methods> Next, a modified example of the silicon wafer manufacturing method according to the present invention will be specifically described with reference to the drawings. Figure 6 is a flowchart showing a modified example of the silicon wafer manufacturing method according to the present invention. Here, a process different from the silicon wafer manufacturing method shown in Figure 2 will be described.

[0063] In the silicon wafer manufacturing method shown in Figure 6, the wafer W after the grinding process (step S3) is mirror polished (final polishing process: step S8), and the wafer W, which has a highly flat mirror finish, is subjected to the heat treatment by the first heat treatment process (RTO: step S4) described above.

[0064] Subsequently, similar to the manufacturing method shown in Figure 2, the oxide film is removed by a surface oxide film removal step (step S5), and heat treatment is performed by a second heat treatment step (RTA: step S6). Finally, single-wafer spin cleaning is performed on the wafer W after RTA (final cleaning step: step S9). In the modified example shown in Figure 6, a silicon wafer W with the oxide film 61a remaining on the back surface of the wafer is obtained without removing the oxide film 61a (see Figure 3(d)).

[0065] In other words, according to this modification, the wafer has an oxide film 61a on the back surface, and the oxygen concentration of the surface layer on the wafer surface side is 1 × 10⁻¹⁶ 17 atoms / cm 3 A wafer W with a reduced concentration to the following level can be obtained. [Examples]

[0066] Next, the method for manufacturing a reconstituted wafer according to the present invention will be further described based on examples. However, the present invention is not limited to the following examples.

[0067] <Example 1> According to the CZ method, the oxygen concentration was 7 × 10 17 atoms / cm 3 A silicon single crystal ingot was grown, and then a well-known planarization process, including slicing and grinding, was performed to prepare five silicon wafers with a diameter of 300 mm.

[0068] Next, using a single-wafer RTP apparatus, RTO was performed on the prepared silicon wafer under the following first heat treatment conditions in an oxygen gas atmosphere to form an oxide film on both the front and back surfaces of the wafer. • First heat treatment conditions Maximum temperature reached →1300℃ Holding time at the highest temperature reached → 20 seconds Heating rate → 75°C / second Cooling rate → 75℃ / sec

[0069] Next, single-wafer spin cleaning was performed on the silicon wafers after RTO (Return to Oxide). Specifically, hydrofluoric acid cleaning was performed on the wafer surface (front side) using a cleaning solution with a hydrofluoric acid concentration of 10% by mass, and pure water cleaning was performed on the wafer back side to remove the oxide film formed on the wafer surface.

[0070] Next, using a single-wafer RTP apparatus, RTA (Recycled Tissue Analysis) was performed on a silicon wafer with an oxide film remaining on the back surface in an argon gas atmosphere under the second heat treatment conditions described below, and the oxygen concentration in the surface layer on the wafer surface side (3 μm deep from the wafer surface (front side)) was increased to 7 × 10⁻¹⁰ 16 atoms / cm 3 The oxygen concentration was reduced to this level. On the other hand, the oxygen concentration on the surface layer of the back side of the wafer (3 μm deep from the back of the wafer) was 1.2 × 10⁻¹⁰. 18 atoms / cm 3 Without reducing the oxygen concentration, the concentration was slightly increased from the concentration before heat treatment. • Second heat treatment conditions Maximum temperature reached →1250℃ Holding time at the highest temperature reached → 30 seconds Heating rate → 40°C / second Cooling rate → 70℃ / sec

[0071] Next, single-wafer spin cleaning was performed on the silicon wafers after RTA. Specifically, hydrofluoric acid cleaning was performed on the back surface of the wafer using a cleaning solution with a hydrofluoric acid concentration of 10% by mass, and pure water cleaning was performed on the front surface of the wafer to remove the oxide film remaining on the back surface.

[0072] Subsequently, the silicon wafer, after oxide film removal, underwent final polishing and cleaning, resulting in an oxygen concentration of 7 × 10⁻¹⁰ on the surface layer of the wafer. 16 atoms / cm 3 Therefore, the oxygen concentration on the surface layer of the back side of the wafer is 1.2 × 10⁻⁶. 18 atoms / cm 3 And the oxygen concentration is 1 × 10 17 atoms / cm 3 Higher than 7x10 17 atoms / cm 3 A silicon wafer of Example 1 was obtained, having a bulk portion that was lower than the BMD nucleus and in which BMD nuclei were formed.

[0073] The silicon wafer from Example 1 was inspected using SIMS (Secondary Ion Mass Spectrometry), and it was confirmed that there was little variation in oxygen concentration and no problems. Furthermore, the occurrence of slip during RTA (Real-Time Analysis) was suppressed. In addition, it was confirmed that the image sensor device manufactured using the silicon wafer from Example 1 also showed suppressed slip and degradation of afterimage characteristics, and no problems were found.

[0074] <Example 2> According to the CZ method, the oxygen concentration was 10 × 10 17 atoms / cm 3 A silicon single crystal ingot was grown, and then a well-known planarization process including slicing and grinding was performed to prepare five silicon wafers with a diameter of 300 mm. Subsequently, the same process as in Example 1 was performed on the prepared silicon wafers, and as a result, the oxygen concentration of the surface layer on the wafer surface side was 1 × 10⁻⁶. 17 atoms / cm 3 Therefore, the oxygen concentration on the surface layer of the back side of the wafer is 1.5 × 10⁻⁶. 18 atoms / cm 3 And the oxygen concentration is 1 × 10 17 atoms / cm 3 Higher than 7x10 17 atoms / cm 3 A silicon wafer of Example 2 was obtained, having a bulk portion that was lower than the BMD nucleus and in which BMD nuclei were formed.

[0075] Inspection of the silicon wafer from Example 2 using SIMS confirmed that there was little variation in oxygen concentration and no problems. Furthermore, slippage during RTA was suppressed. Additionally, the image sensor device manufactured using the silicon wafer from Example 2 also showed suppressed slippage and degradation of afterimage characteristics, confirming that there were no problems.

[0076] <Example 3> According to the CZ method, the oxygen concentration was 7 × 10 17 atoms / cm 3A silicon single crystal ingot was grown, and then a well-known planarization process including a slicing process and a grinding process was performed to prepare five silicon wafers with a diameter of 300 mm. Thereafter, the same treatment as in Example 1 was performed on the prepared silicon wafers, except that the maximum temperature reached by RTO was 1350 °C and the maximum temperature reached by RTA was 800 °C. As a result, the oxygen concentration in the surface layer on the front side of the wafer was 6×10 16 atoms / cm 3 and the oxygen concentration in the surface layer on the back side of the wafer was 1.2×10 18 atoms / cm 3 Moreover, a silicon wafer of Example 3 having a bulk portion in which the oxygen concentration was higher than 1×10 17 atoms / cm 3 and lower than 7×10 17 atoms / cm 3 and in which BMD nuclei were formed was obtained. <�

[0077] As a result of inspecting the silicon wafer of Example <�

[0078] using SIMS, it was confirmed that the variation in oxygen concentration was small and there were no problems. Also, the occurrence of slips during RTA was suppressed. Moreover, it was confirmed that there were no problems with the imaging device device manufactured using the silicon wafer of Example 3, either, as slips and degradation of afterimage characteristics were suppressed. <Example 4> By the CZ method, a silicon single crystal ingot with an oxygen concentration of 7×10 17 atoms / cm 3 was grown, and then a well-known planarization process including a slicing process and a grinding process was performed to prepare five silicon wafers with a diameter of 300 mm. Thereafter, the same treatment as in Example 1 was performed on the prepared silicon wafers, except that a batch heat treatment with a maximum temperature reached of 1000 °C, a holding time at the maximum temperature of 120 minutes, a heating rate of 5 °C / second, and a cooling rate of 5 °C / second was performed. As a result, the oxygen concentration in the surface layer on the front side of the wafer was 5×10 16 atoms / cm 3 and the oxygen concentration in the surface layer on the back side of the wafer was 1.2×10 18 atoms / cm 3And the oxygen concentration is 1 × 10 17 atoms / cm 3 Higher than 7x10 17 atoms / cm 3 A silicon wafer of Example 4 was obtained, having a bulk portion that was lower than the BMD nucleus and in which BMD nuclei were formed.

[0079] Inspection of the silicon wafer from Example 4 using SIMS confirmed that there was little variation in oxygen concentration and no problems. Furthermore, slippage during RTA was suppressed. Additionally, the image sensor device manufactured using the silicon wafer from Example 4 also showed suppressed slippage and degradation of afterimage characteristics, confirming that there were no problems.

[0080] <Example 5> According to the CZ method, the oxygen concentration was 4 × 10 17 atoms / cm 3 A silicon single crystal ingot was grown, and then a well-known planarization process including slicing and grinding was performed to prepare five silicon wafers with a diameter of 300 mm. Subsequently, the same process as in Example 1 was performed on the prepared silicon wafers. As a result, the oxygen concentration of the surface layer on the wafer surface side was 4 × 10⁻¹⁶. 16 atoms / cm 3 Therefore, the oxygen concentration on the surface layer of the back side of the wafer is 9 × 10 17 atoms / cm 3 And the oxygen concentration is 1 × 10 17 atoms / cm 3 Higher than 7x10 17 atoms / cm 3 A silicon wafer of Example 5 was obtained, having a bulk portion that was lower than the BMD nucleus and in which BMD nuclei were formed.

[0081] Inspection of the silicon wafer from Example 5 using SIMS confirmed that there was little variation in oxygen concentration and no problems. Furthermore, slippage during RTA was suppressed. Additionally, the image sensor device manufactured using the silicon wafer from Example 5 also showed suppressed slippage and degradation of afterimage characteristics, confirming that there were no problems.

[0082] <Comparative Example 1> According to the CZ method, the oxygen concentration was 7 × 10 17 atoms / cm 3 A silicon single crystal ingot was grown, and then a well-known planarization process including slicing and grinding was performed to prepare five silicon wafers with a diameter of 300 mm. Subsequently, the prepared silicon wafers were subjected to the same process as in Example 1, except that the oxide film on the entire wafer surface (front and back) was removed after RTO, and the oxygen concentration on the surface layer of the front and back sides of the wafer was reduced to 7 × 10⁻⁶. 16 atoms / cm 3 A silicon wafer for Comparative Example 1 was obtained.

[0083] Inspection of the silicon wafers in Comparative Example 1 using SIMS confirmed that there was little variation in oxygen concentration and no problems. However, slippage occurred on the back surface of 3 out of 5 wafers during RTA.

[0084] <Comparative Example 2> According to the CZ method, the oxygen concentration was 10 × 10 17 atoms / cm 3 A silicon single crystal ingot was grown, and then a well-known planarization process, including slicing and grinding, was performed to prepare five silicon wafers with a diameter of 300 mm.

[0085] Next, the prepared silicon wafer was subjected to the same treatment as in Comparative Example 1, and the oxygen concentration on the surface layers of both the front and back sides of the wafer was reduced to 1 × 10⁻⁶. 17 atoms / cm 3 A silicon wafer for Comparative Example 2 was obtained.

[0086] Inspection of the silicon wafers in Comparative Example 2 using SIMS confirmed that there was little variation in oxygen concentration and no problems. However, slippage occurred on the back surface of 2 out of 5 wafers during RTA. [Explanation of Symbols]

[0087] 10 RTP device 20 Reaction Chamber 20a 1st space 20b 2nd space 22 supply ports 26 Outlet 30 Wafer holding section 32 Susceptors 34. Solids of revolution 40 Heating section 50 Halogen Lamps 61 Oxide film 61a Oxide film

Claims

1. A first heat treatment step involves slicing a silicon single crystal ingot grown by the CZ method to prepare a silicon wafer, heating it in an oxidizing gas atmosphere to a first maximum temperature of 1250°C to 1400°C, holding it at the first maximum temperature for a predetermined time, and then cooling it to form an oxide film on both the front and back surfaces of the wafer. After the first heat treatment step, a surface oxide film removal step is performed in which the oxide film formed on the surface of the silicon wafer is removed, while the oxide film formed on the back surface of the wafer is left intact. A second heat treatment step is performed in which the silicon wafer after the surface oxide film removal step is heated in a non-oxidizing gas atmosphere to a second maximum temperature of 800°C to 1350°C, held at the second maximum temperature for a predetermined time, and then cooled to reduce the oxygen concentration on the surface layer of the wafer surface. A method for manufacturing silicon wafers, characterized by including the following:

2. In the first heat treatment step, heat treatment is carried out using a single-wafer type heat treatment apparatus. The method for manufacturing a silicon wafer according to claim 1, characterized in that the second heat treatment step is performed using a single-wafer type heat treatment apparatus or a batch type heat treatment apparatus.

3. The holding time at the first highest temperature reached is set to 1 second or more and 60 seconds or less. The method for manufacturing a silicon wafer according to claim 2, characterized in that the holding time at the second highest temperature reached is 1 second or more and 60 seconds or less in the case of a single-wafer type, and 1 minute or more and 240 minutes or less in the case of a batch type.

4. The heat treatment in the second heat treatment step increases the oxygen concentration of the wafer surface layer to 1 × 10⁻¹⁶. 17 atoms / cm 3 A method for manufacturing a silicon wafer according to claim 1, characterized by reducing the concentration to the following level.

5. The method for manufacturing a silicon wafer according to claim 1, characterized in that an oxide film of 10 to 50 nm is formed on the front and back surfaces of the wafer in the first heat treatment step.

6. In the aforementioned surface oxide film removal process, hydrofluoric acid is supplied to the wafer surface and pure water is supplied to the wafer back surface using a spin cleaning apparatus. The method for manufacturing a silicon wafer according to claim 1, characterized in that the second heat treatment step is performed while the oxide film formed in the first heat treatment step remains on the back surface of the wafer.

7. The method for manufacturing a silicon wafer according to claim 6, further comprising a backside oxide film removal step for removing the oxide film remaining on the back surface of the silicon wafer after the second heat treatment step.

8. A silicon wafer made by slicing a silicon single crystal ingot grown by the CZ method, The oxygen concentration is 1×10 17 atoms / cm 3 or less in the low-oxygen region of the surface layer on the front side of the wafer with the oxygen concentration reduced to a low level, the high-oxygen region of the surface layer on the back side of the wafer with the oxygen concentration of 7×10 17 atoms / cm 3 or more, and the middle-oxygen region with the oxygen concentration higher than 1×10 17 atoms / cm 3 and lower than 7×10 17 atoms / cm 3 and in which a BMD (Bulk Microdefect) nucleus is formed. A silicon wafer characterized by having these regions.

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