Method for manufacturing epitaxial wafer

Abstract

The present invention is a method for manufacturing an epitaxial wafer in which a single crystal silicon layer is formed on a single crystal silicon wafer with an oxygen atom layer interposed therebetween, the method being characterized by comprising: a step for removing a natural oxide film from the surface of the single crystal silicon wafer; a step for forming a thermal oxide film on the surface of the single crystal silicon wafer from which the natural oxide film has been removed; a step for thinning the thermal oxide film; and a step for epitaxially growing the single crystal silicon after the thinning of the thermal oxide film to form an epitaxial wafer in which the single crystal silicon layer is formed on the single crystal silicon wafer with the oxygen atom layer interposed therebetween. Provided, through this feature, is a method for manufacturing an epitaxial wafer in which an oxygen atom layer can be stably and easily introduced into an epitaxial layer in the manufacture of a silicon epitaxial wafer.

Description

Epitaxial wafer manufacturing method

[0001] The present invention relates to a method for manufacturing an epitaxial wafer.

[0002] Silicon substrates, which 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. A variety of gettering techniques have been proposed and put into practical use, including 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. Gettering by oxygen precipitation involves the capture of metals with a high ionization tendency (low electronegativity) against oxygen, which has a high electronegativity.

[0003] Another approach proposed is proximity gettering, which involves forming a gettering layer near the active region of a device. For example, a substrate can be formed by epitaxially growing silicon on a carbon-ion-implanted substrate. Gettering requires elements to diffuse to the gettering site (where the energy of the entire system is reduced by bonding or clustering at the site, rather than by the metal existing as a single element). The diffusion coefficients of metal elements in silicon vary depending on the element, and recent trends toward lower process temperatures have made it difficult for metals to diffuse to the gettering site. Taking this into account, proximity gettering 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 with 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 a native oxide film on the surface of a silicon wafer at 700° C. or less, and then applying nitrogen monoxide to the surface of the single crystal silicon wafer to a surface concentration of 1×10 １５ atoms / cm ２ The method described below involves forming an oxygen atomic layer and forming a single-crystal silicon layer thereon by epitaxial growth, and performing the oxygen atomic layer and single-crystal silicon layer forming steps 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 oxidized to form an oxygen atomic layer, and a single-crystal silicon layer is 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, followed by rinsing with pure water or leaving the wafer in an oxygen-containing atmosphere to form an oxygen atomic layer, and then epitaxially growing a single crystal silicon layer on top of 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 depositing SiH on an atomic layer of oxygen or the like having a thickness of 5 nm or less. ４ This shows a method for forming an epitaxial layer using a gas, and also shows a method for forming an oxygen atomic layer using oxygen gas.

[0011] Patent Document 6 describes a method in which an oxygen-containing precursor is supplied to a CVD epitaxy furnace to form an oxygen-inserted partial monolayer, and then a silicon epitaxial layer is formed.

[0012] Japanese Patent Application Laid-Open No. 2022-146664 Japanese Patent Application Laid-Open No. 2021-111696 International Publication No. 2022 / 158148 Japanese Patent Application Laid-Open No. 2009-016637 Japanese Patent Application Laid-Open No. 2019-004050 Japanese Patent Application Laid-Open No. 2022-22194

[0013] As mentioned above, the method of gettering metal impurities by forming an oxygen layer within the wafer has been used for some time. However, while this conventional technique can accurately obtain a thin oxygen layer, it has problems such as requiring the use of special gases and lengthy processes.

[0014] The technique described in Patent Document 1 has a problem in that it requires a special gas called nitrogen monoxide.

[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 across the wafer surface.

[0016] In the techniques described in Patent Documents 5 and 6, SiH ４ There was a problem that special equipment, such as a separate exhaust system and a robust interlock, was required to prevent the reaction of benzene with oxygen and cause an explosion.

[0017] Furthermore, Patent Document 4 has the problem 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 precision, 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 an object of the present invention is to provide a method for manufacturing an epitaxial wafer that can stably and easily introduce an oxygen atomic layer into an epitaxial layer in the manufacture of a silicon epitaxial wafer.

[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 employing such an epitaxial wafer manufacturing method, 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 or stacking faults. That is, the epitaxial wafer manufacturing method of the present invention makes it possible to stably and easily introduce the oxygen atomic layer into the epitaxial layer, and to manufacture an epitaxial wafer having a high-quality single crystal silicon epitaxial layer.

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

[0023] By removing the native oxide film using a solution containing hydrofluoric acid in this way, the native oxide film can be removed in a short 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] Furthermore, when the oxide film thickness obtained as a result of performing spectroscopic ellipsometry measurement on the single crystal silicon wafer from which the native oxide film has been removed is defined as α, the thickness of the thermal oxide film can be set to a thickness greater than α+0.5 (nm).

[0027] By setting the thickness of the thermal oxide film in this range, 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 portion of the oxide film can be stably reduced, so that the native oxide film can be removed and the thermal oxide film can be made thinner more stably.

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

[0031] By setting the temperature within this range, it is possible to reliably reduce a portion of the oxide film, and therefore it is possible to more stably remove the native oxide film and thin the thermal oxide film.

[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] Plasma using a gas containing hydrogen atoms can stably reduce a portion of the oxide film at a low temperature, allowing for more effective and stable removal of native oxide films and thinning of thermal oxide films. Plasma using an inert gas can also sputter the oxide film with high-energy particles generated by the plasma, allowing for more effective and stable removal of native oxide films and thinning of thermal oxide films.

[0034] Furthermore, 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 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] Within this range of film thickness, the epitaxial layer can be prevented from becoming polycrystalline 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 carrying out epitaxial growth within this temperature range, it is possible to prevent dislocations and stacking faults from being formed in the epitaxial layer, and to more stably form a high-quality epitaxial layer.

[0038] Furthermore, CMP processing can be carried out 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 repeated.

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

[0042] As described above, the epitaxial wafer manufacturing method of the present invention enables stable and easy introduction of an oxygen atomic layer into the epitaxial layer of silicon epitaxial wafers used in cutting-edge devices without using any special equipment, and makes it possible to manufacture epitaxial wafers having high-quality single-crystal silicon epitaxial layers. It also makes it possible to manufacture proximity gettering substrates that have a proximity gettering effect due to the oxygen atomic layer.

[0043] Fig. 1 is a diagram showing a flow of the epitaxial wafer manufacturing method of the present invention. Fig. 2 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. Fig. 3 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. 4 is a graph showing the relationship between heating time in a hydrogen atmosphere and oxide film thickness in Example 1 and Comparative Example 1. Fig. 5 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.

[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 layer structure in which oxygen atoms are introduced into the Si-Si bond. ２ In single crystal silicon, oxygen atoms are stable at the bond center positions between silicon atoms and the nearest silicon atoms, so when one atomic layer of oxygen exists, the planar concentration of oxygen is 1.36 × 10 １５ atoms / cm ２ The planar concentration of oxygen is 1 x 10 １５ atoms / cm ２ 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 any 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 the oxygen atomic layer, can stably and easily introduce an oxygen atomic layer into the epitaxial layer without using special equipment in silicon epitaxial wafers used in advanced devices, and can also produce epitaxial wafers having a high-quality single crystal silicon epitaxial layer, thereby completing the present invention.

[0048] [Epitaxial Wafer] An epitaxial wafer obtained by the epitaxial wafer manufacturing method of the present invention will now 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] Figure 3 shows an example of another epitaxial wafer according to the present invention. As shown in Figure 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 multiple oxygen atomic layers 2 in this way can enhance the gettering effect compared to an epitaxial wafer with a single oxygen atomic layer 2.

[0050] [Method for Manufacturing an Epitaxial Wafer] Next, a method for manufacturing 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 for 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"). Furthermore, 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 also 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 of formation, it is necessary to remove the native oxide film in order to stably perform the thinning in step S14.

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

[0056] In 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 obtained by mixing hydrofluoric acid and ammonium fluoride. The concentration of hydrofluoric acid in the hydrofluoric acid-containing solution may be any concentration that can remove the native oxide film, and may be, for example, 0.001% to 60%. The temperature of the hydrofluoric acid-containing solution may be, for example, 10°C to 50°C. A temperature of 10°C or higher can prevent condensation from forming on the wafer after treatment with the hydrofluoric acid-containing solution. Furthermore, a temperature of 50°C or lower can suppress the amount of hydrofluoric acid that volatilizes, thereby avoiding safety issues.

[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 the time is 1 second or more, the native oxide film can be stably removed. Furthermore, if the time is 1 hour or less, it is possible to prevent the process 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, which allows the oxide film to be stably reduced and etched, thereby enabling the native oxide film to 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 a 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. Plasma using a gas containing hydrogen atoms can stably reduce or etch the oxide film at low temperatures, allowing for more effective and stable removal of the native oxide film. Plasma using an inert gas can also sputter the oxide film with high-energy particles generated by the plasma, allowing for more effective and stable removal of the native oxide film.

[0064] Examples of such gases that can be used include molecular hydrogen, ammonia, nitrogen, argon, helium, neon, krypton, and xenon. These gases may also be used in combination. In the case of molecular hydrogen 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 by heating at 500° C. or less. The time for which the wafer is exposed to plasma depends on the plasma density, ion energy, etc., but by exposing the wafer to 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 these 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 may be a gas in which oxygen is added to a rare gas such as helium, neon, argon, krypton, or xenon, or nitrogen.

[0069] The heating device may be a vertical furnace, a horizontal furnace, or an RTA (Rapid Thermal Annealing) device. ４This can reliably prevent the mixture of oxygen and argon from exploding, allowing for the safe manufacture of epitaxial wafers with oxygen atomic layers. In addition, because a thermal oxide film does not grow during the process of transporting the wafer from the thermal oxidation equipment to the film formation equipment, there is no problem even if the thermal oxidation equipment and the film formation equipment are separated.

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

[0071] Spectroscopic ellipsometry is a technique for measuring the thickness and refractive index of thin films by measuring changes in the polarization state of incident and reflected light on a sample. The dielectric function of the thin film is modeled and the dielectric function is used to calculate changes in the polarization state of light to determine the thickness and refractive index. Because this method determines the thickness and refractive index, the optical thickness determined by spectroscopic ellipsometry may not match the physical thickness measured by a transmission electron microscope (TEM) or a scanning electron microscope (SEM) due to insufficient modeling accuracy. In particular, when measuring the oxide film thickness using spectroscopic ellipsometry after completely removing the native oxide film, the theoretical thickness should be zero, but a value α greater than zero is output. α is affected by factors such as the surface roughness of the substrate, the method of removing the native oxide film, and the measurement environment. On the other hand, even when the oxygen concentration is less than one atomic layer, a strong positive correlation is observed between the film 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 to be removed to thin the oxide film down to the oxygen atomic layer from the oxide film thickness measured by spectroscopic ellipsometry.

[0072] The oxide film thickness obtained by performing spectroscopic ellipsometry on a single crystal silicon wafer from which a native oxide film has been removed is defined as α (nm) (α is sometimes referred to as the "offset"), and the thickness of the thermal oxide film is preferably set to a thickness 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. The upper limit of the thickness is not particularly limited, but can be set to α + 2 (nm) [10α + 20 (Å)].

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

[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 control. 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. Heating in a hydrogen atmosphere allows a portion of the oxide film to be stably reduced, thereby thinning the thermal oxide film.

[0077] At this time, it is preferable to heat the single crystal silicon wafer to a temperature of 800°C or higher and 1250°C or lower to thin the thermal oxide film. Within this temperature range, a portion 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 higher and 5 minutes or lower. The temperature and time can be adjusted depending on the thickness of the thermal oxide film.

[0078] Furthermore, the thermal oxide film can be thinned by plasma using a gas containing hydrogen atoms or an inert gas. Plasma using a gas containing hydrogen atoms can stably reduce a portion of the oxide film at a low temperature, allowing for more effective and stable thinning of the thermal oxide film. Plasma using an inert gas can sputter the oxide film with high-energy particles generated by the plasma, allowing for more effective and stable thinning of the thermal oxide film.

[0079] Examples of such gases that can be used include molecular hydrogen, ammonia, nitrogen, argon, helium, neon, krypton, and xenon. These gases may also be used in combination. In the case of molecular hydrogen 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 thinning the oxide film using plasma as described above, the thinning may be carried out at room temperature or by heating at a temperature of 500° C. or less. The time for which the wafer is exposed to plasma depends on the oxide film thickness, plasma density, ion energy, etc., but a time of 1 second to 30 minutes, for example, allows for stable thinning.

[0081] Furthermore, in order to thin the thermal oxide film to a degree that enables epitaxial growth in the epitaxial growth step of step S15, the oxide film thickness measured by spectroscopic ellipsometry after thinning the thermal oxide film can be set to a thickness that is greater than α and not greater than α+0.5 (nm) [10α+5 (Å)], where α (nm) is the oxide film thickness obtained as a result of 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 ２ It is preferable that the oxygen atomic layer has a planar concentration of oxygen in this range, and thus a single-crystal silicon layer can be obtained by epitaxial growth more stably, with fewer stacking faults and dislocations and higher crystallinity. The lower limit of the planar concentration of oxygen 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 concentration of oxygen of 1×10 or less. １３ atoms / cm ２ It is preferable that this 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, thereby forming 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 chamber pressure can be set to a level 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] Furthermore, the epitaxial growth of single crystal silicon can be performed at a temperature of, for example, 450° C. or higher and 800° C. or lower. By performing the 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 more stably form a high-quality epitaxial layer. Furthermore, within this temperature range, it is possible to more reliably prevent oxygen from diffusing from the oxygen atomic layer and causing the oxygen atomic layer to disappear.

[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 desired, 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] The deposition time can be adjusted to adjust the thickness of the epitaxial layer. When deposition is performed at high temperatures, shortening the deposition time can prevent oxygen from diffusing outward from the single crystal silicon wafer, which can reduce the heat resistance of the oxygen atomic layer.

[0090] The epitaxial growth of single crystal silicon can also be performed, for example, by setting the partial pressure of the silicon source gas to 0.1 Pa or more and 2000 Pa or less. 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 performing the above steps S11 to S15, an epitaxial wafer 10A as shown in FIG. 2 can be obtained.

[0092] According to the studies of the present inventors, it is possible to form an oxygen atomic layer 2 with a uniform oxygen concentration within the wafer surface by forming an oxide film on the single crystal silicon wafer 1 as described above, thinning the oxide film, and then epitaxially growing single crystal silicon. This is thought to be because, since the oxidation rate of single crystal silicon slows as the oxide film grows, it is easier to control the film thickness by forming an oxide film to a thickness greater than the target thickness and then thinning it, rather than adjusting the formation of the oxide film so that it reaches the target thickness of the oxygen atomic layer 2. In addition, thinning of the oxide film is easier to control because it proceeds more slowly than oxidation.

[0093] Furthermore, depending on the purpose, defects and roughness of the surface can be improved by subjecting the wafer surface to CMP after the epitaxial growth step of 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, thereby forming a plurality of oxygen atomic layers 2, as shown in Fig. 3, for example. That is, according to the epitaxial wafer manufacturing method of 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 way, the gettering effect can be enhanced compared to when a single oxygen atomic layer 2 is formed.

[0096] When forming a plurality of oxygen atomic layers 2, 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] Furthermore, when forming multiple oxygen atomic layers 2, the maximum temperature in forming the thermal oxide film from the second time onwards or in thinning the thermal oxide film can be set to 1050°C or less, which more reliably prevents 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 any special equipment, and is capable of stably and easily forming an oxygen atomic layer for proximity gettering and forming a high-quality epitaxial layer, thereby producing a high-quality epitaxial wafer.

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

[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: 300 mm Crystal plane orientation: (100) Oxygen concentration: 14 ppma (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 was found to be 1 nm (10 Å). The single-crystal silicon wafer was previously transported to an RTA apparatus, heated in a hydrogen atmosphere at 1100°C for 30 seconds, and then the oxide film thickness was measured by spectroscopic ellipsometry. The oxide film thickness value α obtained by spectroscopic ellipsometry when no oxide film is present was found to be 0.2 nm (2 Å). From these results, the thermal oxide film thickness obtained by subtracting the oxide film thickness value α was found to be 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 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, i.e., 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 monosilane partial pressure was 60 Pa, and the film thickness was 100 nm. Hydrogen was used as the carrier gas. In this manner, 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 film formation revealed 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] 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 using a batch-type cleaning device, followed by rinsing with pure water, and then heated in a hydrogen atmosphere. The heating temperature was 1150°C for 1 minute.

[0112] Thereafter, the surface of the single crystal silicon wafer was oxidized by leaving it in the air for 5 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 Figure 5, in Comparative Example 2, in which an oxygen atomic layer was formed by leaving the wafer in the atmosphere, the oxide film thickness was non-uniform, i.e., the oxygen concentration was non-uniform across the wafer surface. This was because the silicon oxidation rate was higher at the periphery of the wafer than at the center. The reason for the change in oxidation rate across the wafer surface is thought to be a change in air flow velocity. A higher air flow velocity results in a greater supply of oxygen, which increases the silicon oxidation rate. From these facts, it is thought that the change in oxygen concentration across the wafer surface was due to a flow velocity distribution in which the air flow velocity increased 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 to 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 to Comparative Example 2 and Comparative Example 1, in which thinning of the oxide film was not performed.

[0116] This 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 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. [2]: A method for manufacturing an epitaxial wafer according to [1] above, which includes removing the native oxide film using a solution containing hydrofluoric acid. [3]: A method for manufacturing an epitaxial wafer according to [1] above, which includes forming the thermal oxide film by heat treatment at a temperature of 600°C to 1200°C in an oxygen-containing atmosphere. [4]: The method for manufacturing an epitaxial wafer according to [1], [2], or [3], comprising: setting the thickness of the thermal oxide film to a thickness greater than α+0.5 (nm), where α is the oxide film thickness value obtained by performing spectroscopic ellipsometry measurement on the single crystal silicon wafer from which the native oxide film has been removed. [5]: The method for manufacturing an epitaxial wafer according to [1], [2], [3], or [4], 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 manufacturing an epitaxial wafer according to [5], comprising setting the heating temperature in the hydrogen atmosphere to 800°C or higher and 1250°C or lower. [7]: The method for manufacturing an epitaxial wafer according to [1], [2], [3], or [4], comprising removing the native oxide film and thinning the thermal oxide film by plasma using a gas containing hydrogen atoms or plasma using an inert gas.[8]: The method for manufacturing an epitaxial wafer according to [1], [2], [3], [4], [5], [6] or [7], comprising: 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 be greater than α and not greater than α + 0.5 (nm), where α is the value of the oxide film thickness obtained by spectroscopic ellipsometry measurement of the single crystal silicon wafer from which the native oxide film has been removed. [9]: The method for manufacturing an epitaxial wafer according to [1], [2], [3], [4], [5], [6], [7] or [8], comprising: in the step of epitaxially growing the single crystal silicon, performing epitaxial growth of the single crystal silicon at a temperature of 450°C or higher and 800°C or lower.

[10] : A method for manufacturing an epitaxial wafer according to [1], [2], [3], [4], [5], [6], [7], [8] or [9], which comprises performing CMP processing after the epitaxial growth step.

[11] : A method for manufacturing an epitaxial wafer according to [1], [2], [3], [4], [5], [6], [7], [8] or [9], which comprises, after the step of epitaxially growing single crystal silicon, repeatedly performing 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.

[0117] The present invention is not limited to the above-described embodiments. The above-described embodiments are merely examples, and anything that has substantially the same configuration as the technical idea described in the claims of the present invention and that exhibits similar effects is included within the technical scope of the present invention.

Claims

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, 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.

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

3. A method for producing an epitaxial wafer according to claim 1, characterized in that the thermal oxide film is formed by heat treating the substrate in an oxygen-containing atmosphere at a temperature of 600° C. or higher and 1200° C. or lower.

4. A method for producing an epitaxial wafer as described in claim 1, characterized in that the oxide film thickness obtained as a result of performing 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 made to be greater than α + 0.5 (nm).

5. A method for producing an epitaxial wafer according to claim 1, characterized in that 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. A method for producing an epitaxial wafer according to claim 5, characterized in that the heating temperature in the hydrogen atmosphere is 800° C. or higher and 1250° C. or lower.

7. A method for producing an epitaxial wafer according to claim 1, characterized in that the removal of the native oxide film and the thinning of the thermal oxide film are carried out 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 as described in claim 1, characterized in that 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 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 is set to a thickness greater than α and not greater than α + 0.5 (nm).

9. A method for producing an epitaxial wafer according to claim 1, characterized in that in the step of epitaxially growing the single crystal silicon, the single crystal silicon is epitaxially grown at a temperature of 450°C or higher and 800°C or lower.

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

11. A method for producing an epitaxial wafer according to any one of claims 1 to 9, characterized in that 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 are repeatedly carried out.

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