Method for manufacturing epitaxial wafer

Abstract

To provide a method for manufacturing an epitaxial wafer capable of stably and easily introducing an oxygen atom layer into an epitaxial layer in manufacturing a silicon epitaxial wafer.SOLUTION: A method for manufacturing an epitaxial wafer for forming a single crystal silicon layer on a single crystal silicon wafer via an oxygen atom layer includes the steps of: removing a natural oxide film from a surface of the single crystal silicon wafer; forming a thermal oxide film on the surface of the single crystal silicon wafer from which the natural oxide film has been removed; thinning the thermal oxide film; and after thinning the thermal oxide film, epitaxially growing a single crystal silicon to form an epitaxial wafer in which the single crystal silicon layer is formed on the single crystal silicon wafer via the oxygen atom layer.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for producing an epitaxial wafer. [Background technology]

[0002] Silicon substrates that form semiconductor elements such as solid-state imaging devices and other transistors are required to have the ability to getter away elements that disrupt device characteristics, including heavy metals. For gettering, various methods have been proposed and put into practical use, such as providing a polycrystalline silicon (Poly-Si) layer on the backside of the silicon substrate, forming a damaged layer by blasting, using a silicon substrate with a high concentration of boron, and forming precipitates. In gettering by oxygen precipitation, gettering is performed by taking in metals that have a high ionization tendency (low electronegativity) against oxygen, which has a high electronegativity.

[0003] Also, so-called proximity gettering has been proposed, in which a gettering layer is formed near the active region of the element. For example, there is a substrate in which silicon is epitaxially grown on a substrate in which carbon has been ion-implanted. In gettering, elements must diffuse to the gettering site (where the energy of the entire system is reduced by bonding or clustering at the site, rather than the metal existing as a single element). The diffusion coefficient of metal elements contained in silicon varies depending on the element, and in addition, the recent trend toward lower process temperatures has made it impossible for metals to diffuse to the gettering site, so the proximity gettering method has been proposed.

[0004] If oxygen can be used for proximity gettering, it is believed that a silicon substrate with a very effective gettering layer will be obtained. In particular, epitaxial wafers with an oxygen atomic layer in the middle of the epitaxial layer can reliably getter metal impurities even in recent low-temperature processes. In addition to gettering, it is also expected to have the effect of suppressing the diffusion of dopants such as boron and phosphorus.

[0005] As described above, an epitaxial wafer having an oxygen atomic layer in the middle of the epitaxial layer can improve device performance more than a normal epitaxial wafer not having an oxygen atomic layer.

[0006] Next, the prior art will be described. Patent Document 1 discloses a process of removing the native oxide film on the surface of a silicon wafer at 700° C. or less, and then oxidizing the surface of the single crystal silicon wafer with nitrogen monoxide to a plane concentration of 1×10 15 atoms / cm 2 The method described herein includes forming an oxygen atomic layer and forming a single crystal silicon layer thereon by epitaxial growth, the steps of which are carried out one or more times.

[0007] Patent Document 2 describes a method in which a native oxide film on the surface of a wafer made of Group IV elements including silicon is removed in a hydrogen-containing atmosphere, the wafer surface is then oxidized to form an oxygen atomic layer, and a single-crystal silicon layer is then epitaxially grown on the oxygen atomic layer.

[0008] Patent Document 3 describes a method in which a native oxide film on the surface of a single crystal silicon wafer is removed with hydrofluoric acid, and then the wafer is rinsed with pure water or left in an atmosphere containing oxygen to form an oxygen atomic layer, and then a single crystal silicon layer is epitaxially grown on the oxygen atomic layer.

[0009] Patent Document 4 describes a method in which an oxide film is formed on a silicon substrate using an oxidizing aqueous solution, and then a semiconductor single crystal layer is epitaxially grown on the oxide film.

[0010] Patent Document 5 discloses a method for forming an epitaxial layer on an atomic layer of oxygen or the like having a thickness of 5 nm or less by using SiH4 gas, and also discloses a method for forming an oxygen atomic layer by using oxygen gas.

[0011] Patent Document 6 describes a method in which an oxygen-containing precursor is fed into a CVD epitaxy reactor to form an oxygen-inserted monolayer, and then a silicon epitaxial layer is formed. [Prior art documents] [Patent documents]

[0012] [Patent Document 1] JP 2022-146664 A [Patent Document 2] Patent Publication No. 2021-111696 [Patent Document 3] International Publication No. 2022 / 158148 [Patent Document 4] JP 2009-016637 A [Patent Document 5] JP 2019-004050 A [Patent Document 6] Patent Publication No. 2022-22194 Summary of the Invention [Problem to be solved by the invention]

[0013] As described above, the method of gettering metal impurities by forming an oxygen layer within the wafer has been used for some time. However, while the conventional technology can accurately obtain a thin oxygen layer, it has problems such as the need to use special gases and the length of the process.

[0014] The technology described in Patent Document 1 has a problem in that it requires a special gas called nitric oxide.

[0015] The techniques described in Patent Documents 2 and 3 have the problem that a long period of oxidation is required to form an oxygen atomic layer. Also, the technique described in Patent Document 2 has the problem that it is difficult to make the oxygen concentration uniform within the wafer surface.

[0016] The techniques described in Patent Documents 5 and 6 have the problem that they require special equipment, such as a separate exhaust system or a robust interlock, to prevent an explosion caused by the reaction of SiH4 with oxygen.

[0017] Furthermore, Patent Document 4 has a problem in that it does not provide any specific description of how to form an epitaxial layer of single crystal silicon without generating dislocations and stacking faults.

[0018] As described above, while conventional techniques can produce an oxygen atomic layer with high accuracy, they have problems such as a complex device configuration, instability in introducing the oxygen layer, and inability to produce a high-quality single crystal silicon epitaxial layer.

[0019] The present invention has been made to solve the above problems, and has an object to provide a method for producing an epitaxial wafer that can stably and easily introduce an oxygen atomic layer into an epitaxial layer in the production of a silicon epitaxial wafer. [Means for solving the problem]

[0020] The present invention has been made to achieve the above-mentioned object, and provides a method for manufacturing an epitaxial wafer in which a single crystal silicon layer is formed on a single crystal silicon wafer via an oxygen atomic layer, the method comprising the steps of: removing a native oxide film from a surface of the single crystal silicon wafer; forming a thermal oxide film on the surface of the single crystal silicon wafer from which the native oxide film has been removed; thinning the thermal oxide film; and, after thinning the thermal oxide film, epitaxially growing single crystal silicon to form an epitaxial wafer in which the single crystal silicon layer is formed on the single crystal silicon wafer via an oxygen atomic layer.

[0021] By using such a method for producing an epitaxial wafer, single crystal silicon can be grown on the surface of the single crystal silicon wafer having the oxygen atomic layer while leaving the oxygen atomic layer, without forming dislocations and stacking faults. That is, the method for producing an epitaxial wafer of the present invention can stably and easily introduce the oxygen atomic layer into the epitaxial layer, and can produce an epitaxial wafer having a high-quality single crystal silicon epitaxial layer.

[0022] At this time, the native oxide film can be removed by using a solution containing hydrofluoric acid.

[0023] By removing the native oxide film using a solution containing hydrofluoric acid in this manner, the native oxide film can be removed in a short period of time.

[0024] The thermal oxide film can be formed by heat treatment at a temperature of 600° C. or more and 1200° C. or less in an oxygen-containing atmosphere.

[0025] Under such conditions for forming a thermal oxide film, the thermal oxide film can be formed stably and reliably.

[0026] In addition, the thickness of the thermal oxide film can be set to be greater than α+0.5 (nm), where α is the oxide film thickness value obtained as a result of performing spectroscopic ellipsometry measurement on the single crystal silicon wafer from which the native oxide film has been removed.

[0027] By setting the thermal oxide film to such a thickness, the oxide film can be formed stably with good reproducibility.

[0028] Furthermore, the removal of the native oxide film and the thinning of the thermal oxide film can be carried out by heating the single crystal silicon wafer in a hydrogen atmosphere.

[0029] By heating in a hydrogen atmosphere, a part of the oxide film can be stably reduced, so that the native oxide film can be more stably removed and the thermal oxide film can be made thinner.

[0030] At this time, the heating temperature in the hydrogen atmosphere can be set to 800° C. or more and 1250° C. or less.

[0031] By setting the temperature within this range, a part of the oxide film can be reliably reduced, so that the native oxide film can be more stably removed and the thermal oxide film can be made thinner.

[0032] Furthermore, the removal of the native oxide film and the thinning of the thermal oxide film can be carried out by using plasma using a gas containing hydrogen atoms or plasma using an inert gas.

[0033] If the plasma uses a gas containing hydrogen atoms, it is possible to stably reduce a part of the oxide film at a low temperature, and therefore it is possible to more effectively and stably remove the native oxide film and thin the thermal oxide film. If the plasma uses an inert gas, it is possible to more effectively and stably remove the native oxide film and thin the thermal oxide film by sputtering the oxide film with high-energy particles generated by the plasma.

[0034] Furthermore, the oxide film thickness value obtained as a result of performing a spectroscopic ellipsometry measurement on the single crystal silicon wafer from which the native oxide film has been removed is defined as α, and in the step of thinning the thermal oxide film, the oxide film thickness value measured by spectroscopic ellipsometry after thinning can be set to a thickness greater than α and not greater than α+0.5 (nm).

[0035] If the thickness falls within this range, the epitaxial layer can be prevented from becoming poly or amorphous.

[0036] In the step of epitaxially growing the single crystal silicon, the single crystal silicon can be epitaxially grown at a temperature of 450° C. or higher and 800° C. or lower.

[0037] By performing epitaxial growth within this temperature range, it is possible to prevent dislocations and stacking faults from being formed in the epitaxial layer, and it is possible to form a more stable, high-quality epitaxial layer.

[0038] In addition, CMP processing can be performed after the epitaxial growth step.

[0039] This makes it possible to improve the surface quality of the epitaxial wafer after film formation.

[0040] Furthermore, after the step of epitaxially growing the single crystal silicon, the step of forming the thermal oxide film, the step of thinning the thermal oxide film, and the step of epitaxially growing the single crystal silicon can be repeatedly performed.

[0041] By forming a plurality of oxygen atomic layers in this manner, the gettering effect can be improved compared to the case of a single layer. Effect of the Invention

[0042] As described above, according to the epitaxial wafer manufacturing method of the present invention, in silicon epitaxial wafers used in advanced devices, an oxygen atomic layer can be stably and easily introduced into the epitaxial layer without using special equipment, and it is possible to manufacture epitaxial wafers having a high-quality single crystal silicon epitaxial layer. It is also possible to manufacture a proximity gettering substrate having a proximity gettering effect due to the oxygen atomic layer. [Brief description of the drawings]

[0043] [Figure 1] FIG. 2 is a diagram showing a flow of a method for manufacturing an epitaxial wafer according to the present invention. [Diagram 2] 1 is a schematic cross-sectional view of an example of an epitaxial wafer that can be manufactured by the epitaxial wafer manufacturing method of the present invention. [Diagram 3]4 is a schematic cross-sectional view of another example of an epitaxial wafer that can be manufactured by the epitaxial wafer manufacturing method of the present invention. FIG. [Figure 4] 1 is a graph showing the relationship between heating time in a hydrogen atmosphere and oxide film thickness in Example 1 and Comparative Example 1. [Diagram 5] 1 is a graph showing the distribution of oxide film thickness within the substrate surface of the epitaxial wafer after heating for 120 seconds in Example 1 and the epitaxial wafer in Comparative Example 2. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0044] The present invention will be described in detail below, but the present invention is not limited thereto.

[0045] In the present invention, the oxygen atomic layer means a layered structure in which oxygen atoms are introduced into the Si-Si bond. It may also be a structure in which SiO2 clusters are distributed discretely on a plane. In single crystal silicon, oxygen atoms are stable at the bond center position between a silicon atom and the nearest silicon atom, so when one atomic layer of oxygen exists, the plane concentration of oxygen is 1.36×10 15 atoms / cm 2 The planar concentration of oxygen is 1×10 15 atoms / cm 2 In this case, it corresponds to 0.74 atomic layers.

[0046] As described above, there has been a demand for a method for manufacturing an epitaxial wafer that does not require special equipment, can stably and easily introduce an oxygen atomic layer into an epitaxial layer, and can manufacture an epitaxial wafer having an epitaxial layer of high-quality single crystal silicon.

[0047] As a result of intensive research into the above-mentioned problems, the present inventors have found that a method for manufacturing an epitaxial wafer in which a single crystal silicon layer is formed on a single crystal silicon wafer via an oxygen atomic layer, the method comprising the steps of: removing a native oxide film from a surface of the single crystal silicon wafer; forming a thermal oxide film on the surface of the single crystal silicon wafer from which the native oxide film has been removed; thinning the thermal oxide film; and, after thinning the thermal oxide film, epitaxially growing single crystal silicon to form an epitaxial wafer in which the single crystal silicon layer is formed on the single crystal silicon wafer via an oxygen atomic layer, in silicon epitaxial wafers used in advanced devices, an oxygen atomic layer can be stably and easily introduced into the epitaxial layer without using a special device, and an epitaxial wafer having a high-quality single crystal silicon epitaxial layer can be manufactured, thereby completing the present invention.

[0048] [Epitaxial wafer] Hereinafter, an epitaxial wafer obtained by the epitaxial wafer manufacturing method of the present invention will be described with reference to Figures 2 and 3. As shown in Figure 2, an epitaxial wafer 10A according to the present invention has a single crystal silicon layer 3 on a single crystal silicon wafer 1, and has an oxygen atomic layer 2 between the single crystal silicon layer 3 and the single crystal silicon wafer 1.

[0049] An example of another epitaxial wafer according to the present invention is shown in Fig. 3. As shown in Fig. 3, an example 10B of another epitaxial wafer according to the present invention has multiple oxygen atomic layers 2 and single crystal silicon layers 3 alternately arranged on a single crystal silicon wafer 1. The uppermost layer is the single crystal silicon layer 3. The presence of a plurality of oxygen atomic layers 2 in this way can enhance the gettering effect as compared to an epitaxial wafer having a single oxygen atomic layer 2.

[0050] [Epitaxial wafer manufacturing method] Next, a method for producing an epitaxial wafer according to the present invention will be described with reference to Fig. 1. Fig. 1 shows a manufacturing flow of an epitaxial wafer having an oxygen atomic layer according to the present invention.

[0051] The step S11 in FIG. 1 is a step of preparing a single crystal silicon wafer.

[0052] The method of manufacturing the single crystal silicon wafer used as the substrate is not particularly limited. It may be a single crystal silicon wafer manufactured by the Czochralski method (hereinafter referred to as the "CZ method") or a single crystal silicon wafer manufactured by the floating zone method (hereinafter referred to as the "FZ method"). Also, an epitaxial wafer in which single crystal silicon is epitaxially grown on a single crystal silicon wafer manufactured by the CZ method or the FZ method may be used.

[0053] Step S12 in FIG. 1 is a step of removing a native oxide film from the surface of the single crystal silicon wafer prepared in step S11.

[0054] Since the quality of the native oxide film varies depending on the method for forming it, it is necessary to remove the native oxide film in order to stably perform the thinning in step S14.

[0055] For example, the native oxide film can be removed by a solution containing hydrofluoric acid (hydrofluoric acid). By using a solution containing hydrofluoric acid in this way, the native oxide film can be removed in a short time.

[0056] In the step S12 of removing the native oxide film, for example, hydrofluoric acid or buffered hydrofluoric acid may be used. Buffered hydrofluoric acid is a solution in which hydrofluoric acid and ammonium fluoride are mixed. The concentration of hydrofluoric acid in the solution containing hydrofluoric acid may be any concentration capable of removing the native oxide film, and may be, for example, 0.001% to 60%. The temperature of the solution containing hydrofluoric acid may be, for example, 10°C to 50°C. If the temperature is 10°C or higher, it is possible to prevent condensation from occurring on the wafer after processing with the solution containing hydrofluoric acid. Furthermore, if the temperature is 50°C or lower, it is possible to suppress the amount of hydrofluoric acid that volatilizes, and to avoid safety problems.

[0057] The time for cleaning (removal of native oxide film) with a solution containing hydrofluoric acid can be, for example, until water repellency is confirmed, and can be from 1 second to 1 hour. If it is 1 second or more, the native oxide film can be stably removed. Also, by setting it to 1 hour or less, it is possible to prevent it from taking too long.

[0058] Cleaning with a solution containing hydrofluoric acid (removal of native oxide film) may be performed using a batch type cleaning device or a single wafer type cleaning device.

[0059] In step S12, the native oxide film may be removed using vapor of a solution containing hydrofluoric acid.

[0060] Furthermore, the native oxide film can be removed by heating the single crystal silicon wafer in a hydrogen atmosphere. By heating in a hydrogen atmosphere, the oxide film can be stably reduced and etched, so that the native oxide film can be removed more stably.

[0061] At this time, it is preferable to heat the single crystal silicon wafer to a temperature of 800°C or more and 1250°C or less. Within this temperature range, the oxide film can be reliably reduced or etched, and the native oxide film can be removed more stably. It is more preferable to remove the native oxide film by maintaining the temperature within this range for 1 second or more and 5 minutes or less.

[0062] As the heating device, a vertical furnace or a horizontal furnace may be used, or an RTA (Rapid Thermal Annealing) device may be used.

[0063] Furthermore, the native oxide film can be removed by plasma using a gas containing hydrogen atoms or an inert gas. If the plasma uses a gas containing hydrogen atoms, the native oxide film can be more effectively and stably removed because the oxide film can be stably reduced or etched at a low temperature. If the plasma uses an inert gas, the native oxide film can be more effectively and stably removed by sputtering the oxide film with high-energy particles generated by the plasma.

[0064] Examples of such gases include hydrogen molecules, ammonia, nitrogen, argon, helium, neon, krypton, and xenon. These gases may be used in combination. In the case of hydrogen molecules and ammonia, which are gases containing hydrogen atoms, the native oxide film can be removed by hydrogen radicals generated by plasma. In the case of inert gases such as nitrogen, argon, helium, neon, krypton, and xenon, the native oxide film can be removed by sputtering with high-energy particles generated by plasma.

[0065] When the native oxide film is removed using plasma as described above, the native oxide film may be removed at room temperature, or may be removed by heating at 500° C. or less. The time for which the wafer is exposed to the plasma depends on the plasma density, ion energy, etc., but by exposing the wafer to the plasma for, for example, 1 second to 30 minutes, the native oxide film can be stably removed.

[0066] Step S13 in FIG. 1 is a step of forming a thermal oxide film on the surface of the single crystal silicon wafer from which the native oxide film has been removed in step S12.

[0067] The thermal oxide film is preferably formed by heat treating the single crystal silicon wafer in an oxygen-containing atmosphere at a temperature of 600° C. to 1200° C. Under such conditions, the thermal oxide film can be formed stably and reliably. It is more preferable to form the thermal oxide film by maintaining the temperature in this range for 1 second to 30 minutes.

[0068] The oxygen-containing atmosphere may be an atmosphere containing 100% oxygen, or a rare gas such as helium, neon, argon, krypton, or xenon, or a gas in which oxygen has been added to nitrogen.

[0069] The heating device may be a vertical furnace, a horizontal furnace, or an RTA (Rapid Thermal Annealing) device. By separating the thermal oxidation device from the film formation device, it is possible to reliably prevent SiH4 and oxygen from mixing and exploding, so that epitaxial wafers having an oxygen atomic layer can be safely manufactured. In addition, since the thermal oxide film does not grow during the process of transporting from the thermal oxidation device to the film formation device, there is no problem even if the thermal oxidation device and the film formation device are separated.

[0070] After the thermal oxide film is formed, the oxide film thickness can be measured by spectroscopic ellipsometry. The relationship between the oxidation heat treatment conditions and the thermal oxide film thickness may be obtained in advance.

[0071] Spectroscopic ellipsometry is a method for measuring the thickness and refractive index of thin films by measuring the change in the polarization state of incident light and reflected light on a sample. The dielectric function of the thin film is modeled, and the dielectric function is used to calculate the change in the polarization state of light to determine the thickness and refractive index. Therefore, due to insufficient modeling accuracy, the optical thickness determined by spectroscopic ellipsometry may not match the physical thickness measured by a transmission electron microscope (TEM) or scanning electron microscope (SEM). In particular, when the oxide thickness is measured by spectroscopic ellipsometry after the native oxide film is completely removed, the theoretical thickness should be 0, but a value α greater than 0 is output. α is affected by the surface roughness of the substrate, the method of removing the native oxide film, and the measurement environment. On the other hand, even if the oxygen concentration is less than one atomic layer, a strong positive correlation is observed between the thickness measured by spectroscopic ellipsometry and the planar oxygen concentration of the oxygen atomic layer measured by SIMS (Secondary Ion Mass Spectrometry) after forming silicon on the oxygen atomic layer. Therefore, it is possible to predict the amount of oxide film that needs to be removed to thin the oxide film down to an oxygen atomic layer from the oxide film thickness measured by spectroscopic ellipsometry.

[0072] The oxide film thickness value obtained by performing spectroscopic ellipsometry measurement on a single crystal silicon wafer from which the native oxide film has been removed is defined as α (nm) (α is sometimes called "offset"). It is preferable to set the thickness of the thermal oxide film to a value greater than α+0.5 (nm) [10α+5 (Å)]. By setting the thickness to such a value, the thermal oxide film can be formed more reproducibly and stably.

[0073] Note that α is the value of the oxide film thickness obtained by spectroscopic ellipsometry measurement when no oxide film exists, after removing the native oxide film from the single crystal silicon wafer. The actual oxide film thickness can be found by subtracting α from the value obtained by measuring the thickness of the actually formed oxide film by spectroscopic ellipsometry.

[0074] Step S14 in FIG. 1 is a step of thinning the thermal oxide film formed in step S13.

[0075] By forming an oxide film thicker than the target thickness of the oxygen atomic layer and then thinning it, the oxygen atomic layer can be formed more stably with better controllability. This is because the oxidation rate of the subsequent oxidation is slower and more controllable than that of the initial oxidation.

[0076] The thermal oxide film can be thinned by heating the single crystal silicon wafer in a hydrogen atmosphere. By heating in a hydrogen atmosphere, a part of the oxide film can be stably reduced, so that the thermal oxide film can be thinned.

[0077] At this time, it is preferable to heat the single crystal silicon wafer to a temperature of 800°C or more and 1250°C or less to thin the thermal oxide film. Within this temperature range, a part of the oxide film can be reliably reduced, and the thermal oxide film can be thinned. It is more preferable to thin the film by maintaining a temperature within this range for 1 second or more and 5 minutes or less. The temperature and time can be adjusted depending on the thickness of the thermal oxide film.

[0078] The thermal oxide film can be thinned by plasma using a gas containing hydrogen atoms or an inert gas. If the plasma uses a gas containing hydrogen atoms, a part of the oxide film can be stably reduced at a low temperature, so that the thermal oxide film can be thinned more effectively and stably. If the plasma uses an inert gas, the oxide film can be sputtered by high-energy particles generated by the plasma, so that the thermal oxide film can be thinned more effectively and stably.

[0079] Examples of such gases include hydrogen molecules, ammonia, nitrogen, argon, helium, neon, krypton, and xenon. These gases may be used in combination. In the case of hydrogen molecules and ammonia, which are gases containing hydrogen atoms, the oxide film can be etched by hydrogen radicals generated by plasma. In the case of inert gases such as nitrogen, argon, helium, neon, krypton, and xenon, the oxide film can be etched by sputtering with high-energy particles generated by plasma.

[0080] When the oxide film is thinned using plasma as described above, the thinning may be performed at room temperature or by heating at 500° C. or less. The time for which the wafer is exposed to the plasma depends on the oxide film thickness, plasma density, ion energy, etc., but a period of time of 1 second to 30 minutes, for example, ensures stable thinning.

[0081] Furthermore, in order to thin the thermal oxide film to a level that enables epitaxial growth in the epitaxial growth step of step S15, the oxide film thickness value measured by spectroscopic ellipsometry after thinning the thermal oxide film can be set to a thickness greater than α and less than α+0.5 (nm) [10α+5 (Å)], where α (nm) is the oxide film thickness value obtained by performing spectroscopic ellipsometry measurement on a single crystal silicon wafer from which a native oxide film has been removed.

[0082] Within this range of film thickness, the epitaxial layer can be reliably prevented from becoming polycrystalline or amorphous, and single-crystal silicon can be epitaxially grown on the oxygen atomic layer stably and reliably.

[0083] The planar concentration of oxygen in the oxygen atomic layer is 1×10 15 atoms / cm 2It is preferable that the oxygen atomic layer has a planar oxygen concentration in this range, and thus a single crystal silicon layer having fewer stacking faults and dislocations and higher crystallinity can be obtained by epitaxial growth. The lower limit of the planar oxygen concentration is not limited, and it is sufficient if it is greater than 0. In order to obtain a more stable gettering ability, it is preferable that the oxygen atomic layer has a planar oxygen concentration of 1×10 13 atoms / cm 2 More preferably, it is equal to or greater than this.

[0084] Step S15 in FIG. 1 is a step of epitaxially growing single crystal silicon after thinning the thermal oxide film in step S14, to form an epitaxial wafer in which a single crystal silicon layer is formed on the single crystal silicon wafer via an oxygen atomic layer.

[0085] For example, monosilane and disilane can be used as gases for epitaxial growth. Nitrogen and hydrogen can also be used as carrier gases. The pressure in the chamber can be any pressure that does not generate Si powder in the gas phase.

[0086] The epitaxial growth apparatus may be of a batch type or a single wafer type.

[0087] Moreover, the epitaxial growth of single crystal silicon can be performed at a temperature of, for example, 450° C. to 800° C. By performing the epitaxial growth in this temperature range, it is possible to prevent dislocations and stacking faults from being formed in the epitaxial layer, and it is possible to more stably form a high-quality epitaxial layer. Furthermore, in this temperature range, it is possible to more reliably prevent the oxygen from diffusing from the oxygen atomic layer and the oxygen atomic layer from disappearing.

[0088] Since the higher the temperature, the higher the epitaxial growth rate, a thick epitaxial layer can be formed in a short time by forming the film at a high temperature. On the other hand, if a thin epitaxial layer is to be formed, the film can be formed at a low temperature. In this way, the growth temperature can be changed depending on the desired thickness of the epitaxial layer.

[0089] In addition, the deposition time can be adjusted to adjust the thickness of the epitaxial layer. When depositing at high temperatures, the deposition time can be shortened to prevent oxygen from diffusing outward from the single crystal silicon wafer, which can reduce the heat resistance of the oxygen atomic layer.

[0090] Epitaxial growth of single crystal silicon can also be performed, for example, by setting the partial pressure of the silicon source gas to between 0.1 Pa and 2000 Pa. Within this pressure range, single crystal silicon can be more stably grown without generating dislocations or stacking faults on the oxygen atomic layer.

[0091] By carrying out the above steps S11 to S15, for example, an epitaxial wafer 10A as shown in FIG. 2 can be obtained.

[0092] According to the study by the present inventors, as described above, an oxide film is formed on the single crystal silicon wafer 1, the oxide film is thinned, and then single crystal silicon is epitaxially grown, whereby an oxygen atomic layer 2 having a uniform oxygen concentration within the wafer surface can be formed. This is thought to be because the oxidation rate in single crystal silicon slows down as the oxide film grows, so it is easier to control the film thickness by forming an oxide film to a thickness equal to or greater than the target thickness and then thinning it, rather than adjusting the formation of the oxide film so as to reach the target thickness of the oxygen atomic layer 2, and in addition, thinning of the oxide film is easier to control because it proceeds more slowly than oxidation.

[0093] Depending on the purpose, defects and roughness on the surface can be improved by subjecting the wafer surface to CMP after the epitaxial growth step in S15. In this case, by making the removal amount by CMP smaller than the thickness of the silicon layer formed by epitaxial growth, it is possible to manufacture an epitaxial wafer having an oxygen atomic layer while leaving the silicon layer.

[0094] After step S15 of epitaxially growing single crystal silicon, step S13 of forming a thermal oxide film, step S14 of thinning the thermal oxide film, and step S15 of epitaxially growing single crystal silicon are repeatedly performed, whereby a plurality of oxygen atomic layers 2 can be formed, for example, as shown in Fig. 3. That is, according to the method for producing an epitaxial wafer according to this embodiment, it is possible to obtain an epitaxial wafer 10B shown in Fig. 3 in which oxygen atomic layers 2 and single crystal silicon layers 3 are alternately and repeatedly stacked on a single crystal silicon wafer 1. The uppermost surface of the epitaxial wafer 10B in Fig. 3 is the single crystal silicon layer 3.

[0095] By providing a plurality of oxygen atomic layers 2 in this manner, the gettering effect can be enhanced compared to the case where a single oxygen atomic layer 2 is formed.

[0096] When a plurality of oxygen atomic layers 2 are formed, step S12 of removing a native oxide film may or may not be inserted before step S13 of forming a second or subsequent thermal oxide film.

[0097] In addition, when forming multiple oxygen atomic layers 2, the maximum temperature in forming the second or subsequent thermal oxide film or thinning the thermal oxide film can be set to 1050° C. or less to more reliably prevent oxygen from diffusing from the oxygen atomic layer and the oxygen atomic layer from disappearing.

[0098] The epitaxial wafer manufacturing method of the present invention as described above is a highly versatile method that does not require special equipment, and enables stable and easy formation of an oxygen atomic layer for proximity gettering and formation of a high-quality epitaxial layer, thereby producing a high-quality epitaxial wafer. EXAMPLES

[0099] The present invention will be specifically described below with reference to examples, but the present invention is not limited thereto.

[0100] [Example 1 and Comparative Example 1] The conductivity type, diameter, crystal plane orientation and oxygen concentration of the prepared single crystal silicon wafers are as follows. Wafer conductivity type: p-type Diameter: 300mm Crystal plane orientation: (100) Oxygen concentration: 14ppma (JEITA)

[0101] Next, in order to remove a native oxide film from the surface of the prepared single crystal silicon wafer, the single crystal silicon wafer was transferred to an RTA apparatus and heated in a hydrogen atmosphere at a temperature of 1100° C. for 30 seconds.

[0102] Thereafter, the atmosphere inside the chamber of the RTA apparatus was replaced with nitrogen, and the wafer was heated in an oxygen-containing atmosphere at a temperature of 900° C. for 16 seconds to form a thermal oxide film on the surface of the single crystal silicon wafer.

[0103] The thickness of the thermal oxide film was then measured by spectroscopic ellipsometry, and found to be 1 nm (10 Å). In advance, a single crystal silicon wafer was transported to an RTA device and heated in a hydrogen atmosphere at 1100°C for 30 seconds, after which the oxide film thickness was measured by spectroscopic ellipsometry. As a result, it was found that the oxide film thickness value α obtained by spectroscopic ellipsometry measurement when no oxide film exists is 0.2 nm (2 Å). From these results, the thermal oxide film thickness obtained by subtracting the oxide film thickness value α is 0.8 nm (8 Å), which is the actual thickness of the thermal oxide film.

[0104] Next, in Example 1, the wafer on which the thermal oxide film was formed was transferred to a film forming apparatus and heated in a hydrogen atmosphere to thin the thermal oxide film. The heat treatment temperature was 900° C., and the time was 111, 116, 120, 124, 127, 130, and 133 seconds.

[0105] The oxide film thickness after thinning was measured by spectroscopic ellipsometry, and the results are shown in Figure 4. The oxide film thickness values ​​after subtracting α were 0.5 nm (5.0 Å), 0.44 nm (4.4 Å), 0.29 nm (2.9 Å), 0.18 nm (1.8 Å), 0.14 nm (1.4 Å), 0.06 nm (0.6 Å), and 0.05 nm (0.5 Å), respectively. In each case, the oxide film thickness was measured at nine points on the surface, and the change in the oxide film thickness was less than 0.02 nm (0.2 Å).

[0106] In Comparative Example 1, the oxide film was not thinned by heating in a hydrogen atmosphere, that is, the heating time in a hydrogen atmosphere in Comparative Example 1 was 0 seconds.

[0107] Thereafter, single crystal silicon was epitaxially grown on the surfaces of the single crystal silicon wafers of Example 1 and Comparative Example 1 using monosilane. The temperature was 700°C, the partial pressure of monosilane was 60 Pa, and the film thickness was 100 nm. Hydrogen was used as the carrier gas. In this way, epitaxial wafers were manufactured in each of Example 1 and Comparative Example 1.

[0108] In Example 1, the thinning of the thermal oxide film and the epitaxial growth of the single crystal silicon were carried out in the same chamber.

[0109] On the other hand, in Comparative Example 1, single crystal silicon was epitaxially grown without thinning the oxide film by heating in a hydrogen atmosphere as described above.

[0110] Cross-sectional TEM observation after the film formation showed that when the thinning process of Comparative Example 1 was not performed, the film layer was polycrystalline, whereas when the thinning process of Example 1 was performed by forming a thermal oxide film, the film layer was single crystal silicon in both cases.

[0111] [Comparative Example 2] In Comparative Example 2, first, the same single crystal silicon substrate as in Example 1 was prepared. Next, in order to remove a native oxide film from the surface of the prepared single crystal silicon wafer, the single crystal silicon wafer was subjected to hydrofluoric acid cleaning in a batch-type cleaning device, rinsed with pure water, and then heated in a hydrogen atmosphere. The heating temperature was 1150°C and the heating time was 1 minute.

[0112] The surface of the single crystal silicon wafer was then oxidized by leaving it in the air for five hours to form an oxygen atomic layer.

[0113] The oxide film thickness was measured at five points on the surface by spectroscopic ellipsometry after the oxygen atomic layer was formed, and the results are shown by (▲) in Figure 5. Also, in Example 1, the oxide film thickness was measured at five points on the surface by spectroscopic ellipsometry after the thinning time in a hydrogen atmosphere was set to 120 seconds, and the results are shown by (●) in Figure 5.

[0114] As shown in FIG. 5, in Comparative Example 2 in which an oxygen atomic layer was formed by leaving the wafer in the air, the oxide film thickness was non-uniform, i.e., the oxygen concentration was non-uniform within the wafer surface. This is because the oxidation rate of silicon was faster at the periphery of the wafer than at the center. The reason for the change in oxidation rate within the wafer surface is thought to be a change in air flow velocity. A higher air flow velocity provides a larger amount of oxygen, and therefore the oxidation rate of silicon is faster. From these facts, it is thought that the oxygen concentration changed within the wafer surface due to a flow velocity distribution in which the air flow velocity increases from the center to the periphery of the wafer.

[0115] As described above, in Example 1 which is an example of the present invention, an oxygen atomic layer could be stably and simply introduced into the epitaxial layer, as compared with Comparative Example 2 in which neither formation of a thermal oxide film by heating in a hydrogen atmosphere nor thinning of the oxide film was performed, and an epitaxial wafer having a high-quality single crystal silicon epitaxial layer could be manufactured, as compared with Comparative Example 2 and Comparative Example 1 in which thinning of the oxide film was not performed.

[0116] The present specification includes the following aspects. [1]: A method for manufacturing an epitaxial wafer in which a single crystal silicon layer is formed on a single crystal silicon wafer via an oxygen atomic layer, the method including the steps of: removing a native oxide film from a surface of the single crystal silicon wafer; forming a thermal oxide film on the surface of the single crystal silicon wafer from which the native oxide film has been removed; thinning the thermal oxide film; and, after thinning the thermal oxide film, epitaxially growing single crystal silicon to form an epitaxial wafer in which the single crystal silicon layer is formed on the single crystal silicon wafer via an oxygen atomic layer. [2]: The method for producing an epitaxial wafer according to [1] above, further comprising removing the native oxide film with a solution containing hydrofluoric acid. [3]: A method for producing an epitaxial wafer according to [1] or [2] above, comprising forming the thermal oxide film by heat treatment at a temperature of 600° C. or higher and 1200° C. or lower in an oxygen-containing atmosphere. [4]: A method for producing an epitaxial wafer according to [1], [2] or [3] above, comprising: setting a value of an oxide film thickness obtained as a result of performing a spectroscopic ellipsometry measurement on the single crystal silicon wafer from which the native oxide film has been removed, as α, and setting a thickness of the thermal oxide film to a thickness greater than α+0.5 (nm). [5]: A method for producing an epitaxial wafer according to [1], [2], [3] or [4] above, comprising removing the native oxide film and thinning the thermal oxide film by heating the single crystal silicon wafer in a hydrogen atmosphere. [6]: The method for producing an epitaxial wafer according to [5] above, further comprising setting the heating temperature in the hydrogen atmosphere to 800°C or higher and 1250°C or lower. [7]: A method for producing an epitaxial wafer according to [1], [2], [3] or [4], comprising removing the native oxide film and thinning the thermal oxide film by using a plasma using a gas containing hydrogen atoms or a plasma using an inert gas. [8]: A method for producing an epitaxial wafer according to [1], [2], [3], [4], [5], [6] or [7], comprising: a value of an oxide film thickness obtained by performing a spectroscopic ellipsometry measurement on the single crystal silicon wafer from which the native oxide film has been removed, and in a step of thinning the thermal oxide film, a value of an oxide film thickness measured by spectroscopic ellipsometry after thinning is set to be greater than α and not greater than α+0.5 (nm). [9]: The method for producing an epitaxial wafer according to [1], [2], [3], [4], [5], [6], [7] or [8], wherein the step of epitaxially growing the single crystal silicon comprises epitaxially growing the single crystal silicon at a temperature of 450°C or higher and 800°C or lower.

[10] : A method for producing an epitaxial wafer according to [1], [2], [3], [4], [5], [6], [7], [8] or [9], comprising carrying out a CMP process after the epitaxial growth step.

[11] : A method for producing an epitaxial wafer according to [1], [2], [3], [4], [5], [6], [7], [8] or [9], comprising, after the step of epitaxially growing the single crystal silicon, repeatedly carrying out the steps of forming a thermal oxide film, thinning the thermal oxide film and epitaxially growing the single crystal silicon.

[0117] The present invention is not limited to the above-described embodiment. The above-described embodiment is merely an example, and anything that has substantially the same configuration as the technical idea described in the claims of the present invention and exhibits similar effects is included in the technical scope of the present invention. [Explanation of symbols]

[0118] 1...single crystal silicon wafer; 2...oxygen atomic layer; 3...single crystal silicon layer; 10A...An example of the epitaxial wafer of the present invention, 10B...An example of another epitaxial wafer of the present invention.

Claims

1. A method for manufacturing an epitaxial wafer, comprising forming a single crystal silicon layer on a single crystal silicon wafer via an oxygen atomic layer, the method comprising the steps of: removing a native oxide film from a surface of the single crystal silicon wafer; forming a thermal oxide film on the surface of the single crystal silicon wafer from which the native oxide film has been removed; thinning the thermal oxide film; a step of epitaxially growing single crystal silicon after thinning the thermal oxide film to form an epitaxial wafer in which the single crystal silicon layer is formed on the single crystal silicon wafer via an oxygen atomic layer; A method for producing an epitaxial wafer, comprising:

2. 2. The method for producing an epitaxial wafer according to claim 1, wherein the native oxide film is removed by using a solution containing hydrofluoric acid.

3. 2. The method for producing an epitaxial wafer according to claim 1, wherein the thermal oxide film is formed by heat treatment at a temperature of 600° C. or more and 1200° C. or less in an oxygen-containing atmosphere.

4. 2. The method for producing an epitaxial wafer according to claim 1, wherein a value of an oxide film thickness obtained as a result of performing a spectroscopic ellipsometry measurement on the single crystal silicon wafer from which the native oxide film has been removed is defined as α, and the thickness of the thermal oxide film is set to a thickness greater than α+0.5 (nm).

5. 2. The method for producing an epitaxial wafer according to claim 1, wherein the removal of the native oxide film and the thinning of the thermal oxide film are carried out by heating the single crystal silicon wafer in a hydrogen atmosphere.

6. 6. The method for producing an epitaxial wafer according to claim 5, wherein the heating temperature in the hydrogen atmosphere is set to 800° C. or more and 1250° C. or less.

7. 2. The method for producing an epitaxial wafer according to claim 1, wherein the removal of the native oxide film and the thinning of the thermal oxide film are performed by using plasma using a gas containing hydrogen atoms or plasma using an inert gas.

8. 2. The method for producing an epitaxial wafer according to claim 1, wherein a value of an oxide film thickness obtained as a result of performing a spectroscopic ellipsometry measurement on the single crystal silicon wafer from which the native oxide film has been removed is defined as α, and in the step of thinning the thermal oxide film, a value of the oxide film thickness measured by spectroscopic ellipsometry after thinning is set to a thickness greater than α and not greater than α+0.5 (nm).

9. 2. The method for producing an epitaxial wafer according to claim 1, wherein in the step of epitaxially growing the single crystal silicon, the single crystal silicon is epitaxially grown at a temperature of 450° C. or more and 800° C. or less.

10. 2. The method for producing an epitaxial wafer according to claim 1, further comprising the step of performing CMP after the epitaxial growth step.

11. 10. The method for producing an epitaxial wafer according to claim 1 , further comprising the steps of: forming the thermal oxide film; thinning the thermal oxide film; and epitaxially growing the single crystal silicon, the steps being repeated after the step of epitaxially growing the single crystal silicon.

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