Epitaxial wafer manufacturing method

Abstract

To provide a method for manufacturing epitaxial wafers, capable of efficiently forming and controlling an oxygen atomic layer without worsening the surface roughness of a wafer.SOLUTION: There is provided a method for manufacturing epitaxial wafers with which a single-crystal silicon layer is formed on a silicon single-crystal wafer. The method includes: a hydrofluoric acid cleaning step of removing a natural oxide film on a surface of the silicon single-crystal wafer by using a cleaning solution containing hydrofluoric acid; an oxygen atomic layer formation step of forming, on the surface of the silicon single-crystal wafer where the natural oxide film has been removed, an oxygen atomic layer by cleaning; and an epitaxial growth step of epitaxially growing, on the surface of the silicon single-crystal wafer where the oxygen atomic layer has been formed, the single-crystal silicon layer by a vapor growth method. In the oxygen atomic layer formation step, a cleaning solution containing at least a hydrogen peroxide solution is used for the cleaning.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] Silicon substrates, which form semiconductor elements such as solid-state image sensors and other transistors, are required to have the ability to getter away elements that disrupt element characteristics, such as 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 incorporating metals with a high ionization tendency (low electronegativity) into oxygen, which has a high electronegativity.

[0003] Another method proposed is proximity gettering, which involves forming a gettering layer near the active region of a device. For example, there is a substrate in which silicon is epitaxially grown on a substrate into which carbon has been ion-implanted. 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 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 difficult for metals to diffuse to the gettering site, so the proximity gettering method has been proposed. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2022-146664 [Patent Document 2] Patent Publication No. 2021-111696 [Patent Document 3] International Publication No. 2022 / 158148 [Patent Document 4] Japanese Patent Application Laid-Open No. 2024-007890 [Patent Document 5] Japanese Patent Application Laid-Open No. 2009-016637 Summary of the Invention [Problem to be solved by the invention]

[0005] 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.

[0006] As described above, epitaxial wafers having an oxygen atomic layer in the middle of the epitaxial layer can improve device performance compared to ordinary epitaxial wafers that do not have an oxygen atomic layer. Furthermore, this high-concentration doping with a thickness of several atomic layers is called delta doping (also called "δ doping"). For example, when the doping element is oxygen, it is called oxygen δ doping. In other words, an epitaxial wafer having an oxygen atomic layer in the middle of the epitaxial layer is an oxygen δ-doped epitaxial wafer. Hereinafter, in this invention, the terms oxygen atomic layer and oxygen δ-doped layer have the same meaning.

[0007] Next, we will discuss the prior art regarding a method for manufacturing an epitaxial wafer in which oxygen is delta-doped. Patent Document 1 describes a method in which a native oxide film on the surface of a silicon wafer is removed at 700°C or less, and then a single crystal silicon wafer surface is doped with nitrogen monoxide to a planar concentration of 1×10 15 atoms / cm 2The present invention describes a method for producing an epitaxial wafer delta-doped with oxygen by performing the steps of forming an oxygen atomic layer and a single-crystal silicon layer one or more times, in which an oxygen atomic layer is formed and a single-crystal silicon layer is formed thereon by epitaxial growth.

[0008] Patent Document 2 describes a method for producing an oxygen delta-doped epitaxial wafer by removing a native oxide film on the surface of a wafer made of Group IV elements including silicon in a hydrogen-containing atmosphere, forming an oxygen atomic layer by oxidation treatment, and then epitaxially growing a single-crystal silicon layer on top of that.

[0009] Patent Document 3 describes a method for producing an epitaxial wafer in which oxygen is delta-doped by removing a native oxide film from the surface of a single crystal silicon wafer with hydrofluoric acid, rinsing the wafer 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. 15 atoms / cm 2 It is disclosed that by using the following method, a single-crystal silicon layer can be grown without forming dislocations and stacking faults on the oxygen atomic layer. On the other hand, if the oxygen concentration is too low, for example, the gettering function is not exhibited.

[0010] Patent Document 4 describes a method for producing an epitaxial wafer delta-doped with oxygen, in which an oxide film is formed on the surface of a silicon wafer using an oxidizing solution, the oxide film is thinned to form an oxygen atomic layer, and then a single-crystal silicon layer is epitaxially grown on the oxide film.

[0011] Patent Document 5 describes a method for forming an SOI structure by forming an epitaxial film on a silicon substrate after forming an oxide film using an oxidizing aqueous solution. However, this method does not form an oxygen atomic layer, but forms a silicon layer on a chemical oxide film of at least 1 nm.

[0012] Here, the comparative example in Patent Document 4 states that when a Si epitaxial film was formed on an oxide film formed using an oxidizing solution without thinning treatment, the number of defects reached the upper limit of measurement (approximately 20,000) (paragraph

[0120] ). In contrast, the number of defects in Example 1, in which thinning treatment was performed in a hydrogen atmosphere, was 27 or less, indicating that a single-crystal silicon epitaxial layer was formed on the oxygen atomic layer without generating defects. Furthermore, paragraph

[0103] states that when the amount of oxidation (planar oxygen concentration in the oxygen atomic layer) is low, the crystallinity of the single-crystal silicon wafer is maintained, thereby preventing the formation of defects in the epitaxial layer due to the oxygen atomic layer. Therefore, it is likely that the reason the number of defects reached the upper limit of measurement without thinning treatment was because the amount of oxidation was too high. Furthermore, Patent Document 5 does not disclose evaluation results regarding dislocations and stacking faults in the Si film formation layer. Considering Patent Documents 1 to 4, it is inferred that quality, such as dislocations and stacking faults, was degraded. Therefore, in order to produce a high-quality epitaxial wafer in which oxygen is delta-doped, it is necessary to appropriately control the planar oxygen concentration in the oxygen atomic layer.

[0013] The inventors of the present invention investigated the formation of an oxygen atomic layer by rinsing with pure water, as in the technique described in Patent Document 3, but found that the reactivity was low at room temperature and the oxygen concentration of the formed oxygen atomic layer was low. They then discovered that rinsing with heated pure water (i.e., warm pure water) increased the reactivity and enabled efficient control of the oxygen concentration. However, they found that the silicon itself was also etched during the formation of the oxygen atomic layer, significantly worsening the surface roughness. Thus, if the surface roughness is already poor before epitaxial growth, the quality after epitaxial growth will be even worse.

[0014] From the above, it is considered that the quality after epitaxial growth deteriorates as the oxygen concentration in the oxygen atomic layer increases and as the surface roughness before epitaxial growth increases. In other words, if the oxygen concentration of the oxygen atomic layer is the same, the quality after epitaxial growth improves as the surface roughness before epitaxial growth improves. Therefore, it is desirable to have a good surface roughness before epitaxial growth.

[0015] Furthermore, the method of Patent Document 4 has a problem in that, compared to Patent Document 3, a thinning step for thinning the oxide film is required, which increases the number of steps.

[0016] Therefore, there has been a demand for a method that can efficiently form and control an oxygen atomic layer without worsening the surface roughness of the wafer.

[0017] The present invention has been made to solve the above problems, and has an object to provide a method for manufacturing an epitaxial wafer that can appropriately control the planar oxygen concentration of an oxygen atomic layer so as not to deteriorate the quality of a silicon layer after epitaxial growth, in particular, and more specifically, a method for manufacturing an epitaxial wafer that can efficiently form and control an oxygen atomic layer without worsening the surface roughness of the wafer. [Means for solving the problem]

[0018] In order to achieve the above object, the present inventors conducted extensive research into whether an oxygen atomic layer could be formed on the surface of a silicon wafer by cleaning the silicon wafer with an aqueous solution containing hydrogen peroxide. As a result, they discovered that by adjusting the cleaning conditions, it is possible to control the planar oxygen concentration of the oxygen atomic layer while suppressing deterioration of surface roughness, and thus completed the present invention.

[0019] That is, 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 silicon single crystal wafer, the method comprising: a hydrofluoric acid cleaning step of removing a native oxide film on the surface of the silicon single crystal wafer with a cleaning liquid containing hydrofluoric acid; an oxygen atomic layer formation step of forming an oxygen atomic layer by cleaning on the surface of the silicon single crystal wafer from which the native oxide film has been removed; and an epitaxial growth step of epitaxially growing the single crystal silicon layer by a vapor phase epitaxy method on the surface of the silicon single crystal wafer on which the oxygen atomic layer has been formed, wherein in the oxygen atomic layer formation step, a cleaning liquid containing at least hydrogen peroxide water is used for the cleaning.

[0020] According to this method for producing an epitaxial wafer, the surface of a silicon single crystal wafer can be oxidized by hydrogen peroxide in an aqueous solution while suppressing deterioration of the surface roughness, and an oxygen atomic layer with an appropriately controlled planar oxygen concentration can be efficiently formed. Then, by performing epitaxial growth on such a silicon single crystal wafer, a high-quality epitaxial wafer can be produced.

[0021] In this case, it is possible not to carry out a process for thinning the oxygen atomic layer after the oxygen atomic layer forming step.

[0022] This eliminates the need for an additional step of thinning the oxygen atomic layer, and the oxygen concentration of the oxygen atomic layer can be appropriately controlled by the cleaning step alone.

[0023] In this case, the pH value of the cleaning liquid containing the hydrogen peroxide solution can be set in the range of 4 to 7.

[0024] Within this pH range, the oxygen atomic layer can be formed more stably.

[0025] At this time, in the oxygen atomic layer forming step, the plane concentration of oxygen in the oxygen atomic layer is set to 1×10 15 atoms / cm 2It can be as follows:

[0026] This reduces stacking faults and dislocations in the epitaxially grown single crystal silicon layer, resulting in higher crystallinity.

[0027] In this case, the epitaxial growth step can be performed at a temperature of 450°C or higher and 800°C or lower.

[0028] By carrying out the growth at such a temperature, epitaxial growth can be achieved more stably without generating defects.

[0029] At this time, after the epitaxial growth step, the surface of the single crystal silicon layer can be subjected to CMP processing.

[0030] This can improve defects and roughness on the surface of the epitaxial layer.

[0031] In this case, at least the oxygen atomic layer forming step and the epitaxial growth step can be alternately performed multiple times.

[0032] By providing a plurality of oxygen atomic layers in this way, it is possible to manufacture an epitaxial wafer that has a higher gettering effect and a higher effect of suppressing dopant diffusion than when a single layer is used. [Effects of the Invention]

[0033] As described above, according to the epitaxial wafer manufacturing method of the present invention, the surface of a silicon single crystal wafer can be oxidized by hydrogen peroxide in an aqueous solution while suppressing deterioration of the surface roughness, and an oxygen atomic layer with an appropriately controlled planar oxygen concentration can be efficiently formed. Then, by performing epitaxial growth on such a silicon single crystal wafer, it becomes possible to manufacture a high-quality epitaxial wafer. [Brief explanation of the drawings]

[0034] [Figure 1]1 is a flowchart showing an example of a method for manufacturing an epitaxial wafer according to the present invention. [Figure 2] 1 is a diagram showing an epitaxial wafer obtained by the epitaxial wafer manufacturing method of the present invention. [Figure 3] 1 is a diagram showing an epitaxial wafer obtained by the epitaxial wafer manufacturing method of the present invention, in which oxygen atomic layers and single crystal silicon layers are alternately stacked in multiple layers. [Figure 4] 1 is a graph showing the relationship between the hydrogen peroxide concentration and the planar oxygen concentration of the oxygen atomic layer when cleaning was performed with a cleaning liquid temperature of 80° C. for a cleaning time of 3 minutes. [Figure 5] 1 is a graph showing the relationship between the hydrogen peroxide concentration and the planar concentration of oxygen in the oxygen atomic layer when cleaning was performed with a cleaning liquid temperature of 25° C. for a cleaning time of 3 minutes. [Figure 6] 1 is a graph showing the relationship between cleaning time and the planar oxygen concentration of the oxygen atomic layer when cleaning was performed with a cleaning liquid temperature of 25° C. and a hydrogen peroxide concentration of 10,000 ppm (1 mass %). [Figure 7] 1 is a graph showing the relationship between the hydrogen peroxide concentration and the surface roughness (haze value) and etching rate when cleaning is performed with different hydrogen peroxide concentrations. [Figure 8] 1 is a graph showing the relationship between hydrogen peroxide concentration and surface roughness (haze value) when cleaning was performed with a cleaning liquid temperature of 25° C. for a cleaning time of 3 minutes. [Figure 9] 1 is a graph showing the relationship between hydrogen peroxide concentration and pH at a temperature of 25°C. [Figure 10] 1 is a graph showing the transition of haze values ​​before and after cleaning and after film formation in Example 1 and Comparative Examples 1 to 4. [Figure 11] 1 is a graph showing the transition of haze values ​​before and after cleaning and after film formation in Example 2 and Comparative Examples 5 to 8. [Figure 12] 1 is a graph showing the oxygen concentrations in the oxygen atomic layers of Example 3 and Comparative Examples 9 to 12. [Figure 13] FIG. 10 is a cross-sectional TEM image of the epitaxial wafer of Example 3. DETAILED DESCRIPTION OF THE INVENTION

[0035] The present invention will be described in detail below, but the present invention is not limited thereto.

[0036] As described above, in the production of epitaxial wafers, there has been a demand for a method that can efficiently form and control an oxygen atomic layer without worsening the surface roughness of the wafer.

[0037] As a result of extensive research into the above-mentioned problems, the inventors have discovered a method for manufacturing an epitaxial wafer for forming a single crystal silicon layer on a silicon single crystal wafer, the method comprising: a hydrofluoric acid cleaning step of removing a native oxide film on the surface of the silicon single crystal wafer using a cleaning solution containing hydrofluoric acid; an oxygen atomic layer formation step of forming an oxygen atomic layer on the surface of the silicon single crystal wafer from which the native oxide film has been removed by cleaning; and an epitaxial growth step of epitaxially growing the single crystal silicon layer by a vapor phase epitaxy method on the surface of the silicon single crystal wafer from which the oxygen atomic layer has been formed, wherein the oxygen atomic layer formation step uses a cleaning solution containing at least hydrogen peroxide solution for cleaning. This method oxidizes the surface of the silicon single crystal wafer while suppressing deterioration of surface roughness, and efficiently forms an oxygen atomic layer with an appropriately controlled planar oxygen concentration. The present invention was thus completed based on the discovery that high-quality epitaxial wafers can be manufactured by performing epitaxial growth on such silicon single crystal wafers.

[0038] [Epitaxial wafer] 2 is a diagram showing an epitaxial wafer obtained by the epitaxial wafer manufacturing method of the present invention. The 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.

[0039] Here, the planar concentration of oxygen in the oxygen atomic layer 2 of the epitaxial wafer 10A according to the present invention is 1×10 15 atoms / cm 2 It is desirable that the oxygen concentration is 1×10 or less. If an epitaxial wafer has an oxygen atomic layer having a planar concentration of oxygen in this range, the epitaxially grown single crystal silicon layer will have fewer stacking faults and dislocations, and will have higher crystallinity. There is no lower limit to the planar concentration of oxygen, and it is sufficient as long as it is greater than 0. In order to obtain stable gettering ability, it is desirable that the oxygen concentration be 1×10 or less. 13 atoms / cm 2 It is preferable that the concentration is 1×10 or more. 14 atoms / cm 2 More preferably, it is equal to or greater than this.

[0040] The single crystal silicon wafer 1 may be manufactured in any manner. For example, a CZ wafer manufactured by the Czochralski method (hereinafter referred to as the "CZ method") may be used, or an FZ wafer manufactured by the floating zone method (hereinafter referred to as the "FZ method") may be used. 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.

[0041] 3 is a diagram showing an epitaxial wafer 10B in which oxygen atomic layers and single crystal silicon layers are alternately stacked on a single crystal silicon wafer by the epitaxial wafer manufacturing method of the present invention. As shown in FIG. 3, the epitaxial wafer manufacturing method of the present invention can obtain an epitaxial wafer 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 in this case is the single crystal silicon layer 3.

[0042] [Epitaxial wafer manufacturing method] Figure 1 shows a flow diagram of an example of a method for manufacturing an epitaxial wafer according to the present invention, in which a single crystal silicon layer is formed on a silicon single crystal wafer. Step S1 in Figure 1 is a step of preparing a single crystal silicon wafer. Here, 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 CZ method or a single crystal silicon wafer manufactured by the FZ method. It is also possible to use 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.

[0043] [Hydrofluoric acid cleaning process] The step S2 in FIG. 1 is a hydrofluoric acid cleaning step in which a native oxide film is removed using a cleaning solution containing hydrofluoric acid (hereinafter referred to as "hydrofluoric acid cleaning solution"). In the present invention, it is necessary to form an oxygen atomic layer instead of a native oxide film. Because the native oxide film is too thick, the native oxide film is first completely removed, and then an oxygen atomic layer is formed in the oxygen atomic layer formation step S3.

[0044] In this case, it is sufficient that the native oxide film can be removed by hydrofluoric acid, and the chemical solution used may be hydrofluoric acid alone, or a chemical solution containing other components such as buffered hydrofluoric acid. The concentration of hydrofluoric acid is sufficient as long as it can remove the native oxide film, and can be, for example, 0.001 mass % or more and 60 mass % or less. More preferably, it is 0.1 mass % or more and 10 mass % or less. below The temperature of the hydrofluoric acid cleaning solution can be set to 10°C or higher and 50°C or lower, and more preferably 20°C or higher and 30°C or lower.

[0045] The time for the treatment (cleaning) of removing the native oxide film with hydrofluoric acid can be set until water repellency is confirmed, but can be set, for example, from 10 seconds to 1 hour. If the time is 10 seconds or longer, the native oxide film can be removed more reliably. Furthermore, by setting the time to 1 hour or shorter, productivity can be effectively maintained. More preferably, the time can be set to 30 seconds to 360 seconds. The hydrofluoric acid treatment (cleaning) can be performed using a batch-type cleaning device or a single-wafer cleaning device. Furthermore, the oxide film can be removed using hydrofluoric acid vapor.

[0046] [Oxygen atomic layer formation process] The step S3 in Figure 1 is an oxygen atomic layer formation step in which a single-crystal silicon wafer, from which the native oxide film has been removed, is cleaned with an aqueous solution containing at least hydrogen peroxide (hereinafter referred to as "H2O2 cleaning solution") to form an oxygen atomic layer on the silicon surface. In single-crystal silicon, oxygen atoms are stable at the bond center position between the silicon atom and the nearest silicon atom, so if we assume that one atomic layer of oxygen exists, the planar concentration of oxygen is 1.36 x 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.

[0047] When hydrogen peroxide acts as an oxidizing agent, an oxidation reaction occurs on the silicon surface, forming an oxygen atomic layer. The planar oxygen concentration can be measured, for example, by SIMS (Secondary Ion Mass Spectrometry). When Si containing an oxide layer is measured by SIMS, an oxygen peak is formed at the depth where the oxide layer is formed. The planar concentration can be calculated by integrating the product of the volume concentration and depth from a single sputtering near the peak.

[0048] The oxygen concentration of the oxygen atomic layer can be controlled by adjusting the temperature, hydrogen peroxide concentration, and cleaning time of the H2O2 cleaning solution. Figure 4 shows the planar oxygen concentration of the oxygen atomic layer after epitaxial growth in S4, which was performed by cleaning with H2O2 cleaning solutions containing hydrogen peroxide concentrations of 0, 100, 250, and 500 ppm at a temperature and cleaning time of 80°C for 3 minutes. Figure 5 shows the planar oxygen concentration of the oxygen atomic layer after epitaxial growth in S4, which was performed by cleaning with H2O2 cleaning solutions containing hydrogen peroxide concentrations of 0, 10,000, 30,000, and 50,000 ppm (0, 1, 3, and 5 mass%) at a temperature and cleaning time of 25°C for 3 minutes. Figure 6 shows the planar oxygen concentration of the oxygen atomic layer after epitaxial growth in S4, where the H2O2 cleaning solution temperature was 25°C, the hydrogen peroxide concentration was 10,000 ppm (1 mass%), and cleaning times were 3, 10, and 20 minutes. These results indicate that the oxygen concentration of the oxygen atomic layer can be controlled, especially to 1×10, by adjusting the H2O2 cleaning solution temperature, hydrogen peroxide concentration, and cleaning time. 14 ~1×10 15 atoms / cm 2 It can be seen that it can be controlled within the range of

[0049] The planar concentration of oxygen in the oxygen atomic layer is 1×10 15 atoms / cm 2 If the thickness is less than this, stacking faults and dislocations in the epitaxially grown single crystal silicon layer can be reduced, and the layer can have higher crystallinity, which is preferable.

[0050] Next, we will discuss the surface roughness of wafers after cleaning with H2O2 cleaning solution. Figure 7 shows the relationship between the hydrogen peroxide concentration and surface roughness (haze) and etching rate after cleaning with the H2O2 cleaning solution temperature and cleaning time set at 80°C / 3 min, and the hydrogen peroxide concentration varied from 0 to 300 ppm.

[0051] The higher the haze value, the worse the surface roughness. Haze was measured using a KLA particle counter SP3. The etching rate was calculated from the wafer thickness before and after cleaning. Figure 7 shows that the higher the hydrogen peroxide concentration, the smaller the haze and the better the surface roughness. It can be seen that the addition of hydrogen peroxide reduces the etching rate, thereby reducing the amount of silicon etched and improving surface roughness. This is probably because the oxygen atomic layer plays a role in protecting the silicon.

[0052] Figure 8 shows the surface roughness (haze) of wafers after cleaning with the H2O2 cleaning solution temperature and cleaning time set at 25°C / 3 min and the hydrogen peroxide concentration varied from 0 to 30,000 ppm (0-3 mass%). The results show that the haze value is independent of the hydrogen peroxide concentration and is consistent across all concentration levels. Furthermore, this haze value is lower than that of Figure 7, where the cleaning temperature and time were set at 80°C / 3 min, indicating better surface roughness. This is thought to be because the low temperature of 25°C makes it difficult for the etching action of Si to proceed. Therefore, from the perspective of surface roughness, it is more desirable to perform the process at room temperature, for example, around 25°C.

[0053] From the above results, it can be seen that cleaning with an aqueous solution containing hydrogen peroxide can appropriately control the planar oxygen concentration of the oxygen atomic layer while suppressing deterioration of surface roughness compared to conventional warm pure water that does not contain hydrogen peroxide. Furthermore, the cleaning process can be performed using either a batch-type cleaning equipment or a single-wafer cleaning equipment.

[0054] Next, we will explain the H2O2 cleaning solution in more detail. In this invention, the oxidizing effect of hydrogen peroxide is utilized. More specifically, the oxidation reaction proceeds due to the oxygen released from the decomposition reaction of hydrogen peroxide (2H2O2 → 2H2O + O2).

[0055] This decomposition reaction varies depending on the pH (potential hydrogen) of the aqueous solution. pH indicates the hydrogen ion concentration in the aqueous solution, with 7 being neutral, less than 7 being acidic, and greater than 7 being alkaline. Figure 9 shows the pH values ​​of an H2O2 aqueous solution when the hydrogen peroxide concentration is varied from 0 to 50,000 ppm (0 to 5% by mass) at a temperature of 25°C. As shown in Figure 9, it can be seen that the addition of hydrogen peroxide makes the solution weakly acidic. In such a weakly acidic environment, the decomposition reaction of hydrogen peroxide proceeds relatively slowly, and can be controlled by the temperature, concentration, and cleaning time of the aqueous solution.

[0056] A pH of 7 or less can effectively prevent the formation of a thick oxygen atomic layer, which occurs when the decomposition reaction of hydrogen peroxide progresses and the oxidation reaction is accelerated at a pH higher than 7. Furthermore, a pH of 4 or higher stabilizes the decomposition reaction, allowing for the formation of an oxygen atomic layer with good reproducibility and stability. Therefore, in the present invention, it is desirable to set the pH value of the cleaning solution containing hydrogen peroxide water to a range of 4 to 7. Furthermore, the H2O2 cleaning solution contains at least hydrogen peroxide, and other chemicals and additives may also be added.

[0057] Furthermore, in the present invention, the oxygen concentration of the oxygen atomic layer can be appropriately controlled in the oxygen atomic layer formation step, so there is no need to provide a step of thinning the oxygen atomic layer as described in Patent Document 4. In other words, it is possible to avoid performing a process of thinning the oxygen atomic layer after the oxygen atomic layer formation step. This eliminates the need for an additional step of thinning the oxygen atomic layer, thereby improving productivity.

[0058] [Epitaxial growth process] S4 in Figure 1 is the epitaxial growth process, in which a single-crystal silicon layer is epitaxially grown by vapor phase epitaxy on the surface of a silicon single-crystal wafer on which an oxygen atomic layer has been formed. Monosilane or disilane can be used as the gas used for growth. Nitrogen or hydrogen can also be used as the carrier gas. The pressure in the chamber in which epitaxial growth is performed need only be a pressure that does not produce minute silicon crystals in the vapor phase. For example, the pressure can be set to 133 Pa or more and 13,300 Pa or less. The epitaxial growth apparatus can be either a batch type or a single-wafer type.

[0059] Furthermore, the epitaxial growth of single crystal silicon can be carried out at a temperature of 450°C or higher and 800°C or lower. Growth at such a temperature effectively prevents the formation of dislocations and stacking faults in the epitaxial layer.

[0060] 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. Furthermore, the film formation time can be adjusted to adjust the thickness of the epitaxial layer.

[0061] In epitaxial growth of single-crystal silicon, hydrogen baking is usually performed immediately before epitaxial growth to remove and clean the native oxide film on the substrate surface. However, in the epitaxial growth process according to the present invention, it is preferable to not perform hydrogen baking and instead start epitaxial growth when the predetermined growth temperature is reached. This is to prevent the loss of the oxygen atomic layer. Here, hydrogen baking refers to holding the single-crystal silicon wafer in a hydrogen atmosphere at 800°C or higher for a certain period of time. Because the oxygen atomic layer is not lost at temperatures below 800°C, there is no problem with flowing hydrogen as a carrier gas before epitaxial growth at temperatures below 800°C.

[0062] By performing the above steps S1 to S4, an epitaxial wafer with oxygen δ-doped as shown in FIG. 2 can be manufactured, and the oxygen concentration of the oxygen atomic layer can be controlled.

[0063] Also, according to the purpose, the wafer surface after the S4 step can be subjected to CMP processing (S5). Thereby, the defects and roughness of the surface of the epitaxial layer can be improved.

[0064] In this case, by making the replacement by CMP processing smaller than the thickness of the silicon layer formed by epitaxial growth, a silicon layer can be left and an epitaxial wafer having an oxygen atomic layer can be manufactured.

[0065] The present invention can also manufacture an epitaxial wafer having a plurality of oxygen atomic layers as shown in FIG. 3 by alternately performing at least the oxygen atomic layer formation step and the epitaxial growth step a plurality of times. By forming a plurality of oxygen atomic layers in this way, the gettering function and the dopant suppression function can be improved compared to a single layer.

[0066] At this time, there is no limitation on the interval between the oxygen atomic layers, and the oxygen concentration and the layer interval of the oxygen atomic layer can be adjusted according to the application. However, as shown in FIG. 7, especially in a high temperature region where the temperature of the H2O2 cleaning solution is 80 ° C or the like, the outermost Si is etched. Therefore, in order to surely form a plurality of layers, it is preferable to adjust the conditions of the S3 and S4 steps so that the silicon etching amount in the oxygen atomic layer formation step of S3 < the silicon film formation amount in the epitaxial growth step of S4 (also referred to as the silicon film formation thickness). By performing a plurality of treatments so that the silicon etching amount in the oxygen atomic layer formation step of S3 < the silicon film formation amount in the epitaxial growth step of S4 in this way, a plurality of oxygen atomic layers can be surely formed.

Example

[0067] Hereinafter, the present invention will be specifically described with reference to examples, but this does not limit the present invention.

[0068] Example 1 A single crystal silicon wafer with a diameter of 300 mm, crystal plane orientation (100), conductivity type p-type, and resistivity of 10 Ωcm was prepared. The prepared wafer was inspected using a KLA SP5 to obtain the haze value, which indicates the surface roughness.

[0069] Next, the prepared single crystal silicon wafer was cleaned using a batch type cleaning machine. After cleaning for 3 minutes in a 5.0 mass% HF cleaning solution at 25°C to remove the native oxide film, the wafer was cleaned for 3 minutes in a 1 mass% hydrogen peroxide solution at 25°C. The pH of the hydrogen peroxide solution was 5.88.

[0070] The cleaned wafers were inspected using a KLA SP5 to obtain the haze value. Next, single-crystal silicon epitaxial growth was performed in a single-wafer epitaxial furnace without hydrogen baking. The growth temperature was 700°C and the growth time was 2 seconds. After film formation, the wafers were inspected using a KLA SP5 to obtain the haze value.

[0071] (Comparative Examples 1 to 4) Except for changing the cleaning solution after HF cleaning from hydrogen peroxide water to pure water, epitaxial wafers were manufactured and haze values ​​were obtained under the same conditions as in Example 1. The temperature of the pure water and cleaning time were 80°C / 10 min in Comparative Example 1, 80°C / 3 min in Comparative Example 2, 50°C / 3 min in Comparative Example 3, and 25°C / 3 min in Comparative Example 4.

[0072] Example 2 The epitaxial wafer was manufactured and the haze value was obtained under the same conditions as in Example 1, except that the film formation time during epitaxial growth was changed to 5 seconds.

[0073] (Comparative Examples 5 to 8) Epitaxial wafers were manufactured and haze values ​​were obtained under the same conditions as in Comparative Examples 1 to 4, except that the film formation time during epitaxial growth was changed to 5 seconds.

[0074] Example 3 An epitaxial wafer was manufactured under the same conditions as in Example 1, except that the deposition time during epitaxial growth was changed to 60 seconds. The oxygen atomic concentration of the oxygen atomic layer was evaluated by SIMS. The crystalline state of the deposition layer was also evaluated by cross-sectional transmission electron microscopy (TEM).

[0075] (Comparative Examples 9 to 12) Except for changing the film formation time during epitaxial growth to 60 seconds, epitaxial wafers were manufactured under the same conditions as in Comparative Examples 1 to 4. Here, the oxygen atom concentration in the oxygen atomic layer was evaluated by SIMS.

[0076] Figure 10 shows the transition of haze values ​​before, after, and after film formation for Example 1 and Comparative Examples 1 to 4. In Comparative Examples 1 to 4, the higher the temperature and longer the pure water cleaning conditions, the worse the haze after cleaning, and as a result, the haze also worsened after film formation. Compared to Comparative Examples 1 and 2, Example 1 had good haze in particular.

[0077] Figure 11 shows the transition of haze values ​​before, after, and after film formation for Example 2 and Comparative Examples 5 to 8. As in Figure 10, in Comparative Examples 5 to 8, the higher the temperature and the longer the pure water cleaning conditions, the worse the haze after cleaning, and as a result, the haze also worsened after film formation. In particular, compared to Comparative Examples 5 and 6, Example 2 had good haze. Comparative Examples 7 and 8 and Example 2 had similar haze after film formation, but it is thought that Example 2 obtained an oxygen atomic layer with a high oxygen concentration, as will be described later.

[0078] FIG. 12 shows the oxygen concentrations of the oxygen atomic layers of Example 3 and Comparative Examples 9 to 12. In Comparative Examples 9 to 12, the oxygen concentration increased with increasing temperature and duration of the pure water cleaning. In contrast, Example 3 had a higher oxygen concentration than Comparative Examples 9 to 12. In other words, the use of a hydrogen peroxide cleaning solution enabled efficient formation of an oxygen atomic layer while suppressing deterioration of surface roughness. As described above, the haze after film formation in Example 2 and Comparative Examples 7 and 8 in FIG. 11 was comparable. However, as shown in FIG. 12, the oxygen concentration of the oxygen atomic layer in Example 3 (where the cleaning conditions using hydrogen peroxide were the same as those in Example 2) was higher than that of Comparative Examples 11 and 12 (where the cleaning conditions using pure water were the same as those in Comparative Examples 7 and 8). This indicates that cleaning with hydrogen peroxide enabled the formation of an oxygen atomic layer with a high oxygen concentration, even when the haze of the epitaxial film was comparable. In other words, it can be said that the oxygen atomic layer was efficiently formed. The same can be seen in the comparison between Example 1 and Comparative Examples 3 and 4 in FIG. 10.

[0079] 13 shows a cross-sectional TEM image of the epitaxial wafer of Example 3. A contrast change due to the oxygen atomic layer was observed, and the contrast between the substrate and the deposited layer was equivalent, confirming that the deposited layer was a single crystal layer.

[0080] As described above, according to the examples of the present invention, it was possible to control the oxygen concentration in the oxygen atomic layer, and to manufacture epitaxial wafers having an oxygen atomic layer and a good haze value.

[0081] 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 silicon single crystal wafer, the method comprising: a hydrofluoric acid cleaning step of removing a native oxide film on the surface of the silicon single crystal wafer with a cleaning solution containing hydrofluoric acid; an oxygen atomic layer formation step of forming an oxygen atomic layer by cleaning on the surface of the silicon single crystal wafer from which the native oxide film has been removed; and an epitaxial growth step of epitaxially growing the single crystal silicon layer by a vapor phase epitaxy method on the surface of the silicon single crystal wafer on which the oxygen atomic layer has been formed, wherein the oxygen atomic layer formation step comprises using a cleaning solution containing at least hydrogen peroxide water for the cleaning. [2]: The method for producing an epitaxial wafer according to [1] above, wherein a process for thinning the oxygen atomic layer is not performed after the oxygen atomic layer forming step. [3]: The method for producing an epitaxial wafer according to [1] or [2] above, which comprises adjusting the pH value of the cleaning liquid containing the hydrogen peroxide solution to a range of 4 to 7. [4]: In the oxygen atomic layer forming step, the planar concentration of oxygen in the oxygen atomic layer is 1×10 15 atoms / cm 2 A method for producing an epitaxial wafer according to [1], [2] or [3] above, which comprises the following steps: [5]: The method for producing an epitaxial wafer according to [1], [2], [3] or [4], wherein the epitaxial growth step comprises performing epitaxial growth at a temperature of 450°C or higher and 800°C or lower. [6]: A method for producing an epitaxial wafer according to [1], [2], [3], [4] or [5], comprising performing CMP processing on the surface of the single crystal silicon layer after the epitaxial growth step. [7]: A method for manufacturing an epitaxial wafer according to [1], [2], [3], [4], [5] or [6], comprising alternately repeating at least the oxygen atomic layer formation step and the epitaxial growth step multiple times.

[0082] 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. [Explanation of symbols]

[0083] 1...single crystal silicon wafer, 2...oxygen atomic layer, 3...single crystal silicon layer, 10A, 10B...Epitaxial wafers according to the present invention.

Claims

1. A method for manufacturing an epitaxial wafer for forming a single crystal silicon layer on a silicon single crystal wafer, comprising: a hydrofluoric acid cleaning step of removing a native oxide film on the surface of the silicon single crystal wafer using a cleaning solution containing hydrofluoric acid; an oxygen atomic layer forming step of forming an oxygen atomic layer by cleaning on the surface of the silicon single crystal wafer from which the native oxide film has been removed; an epitaxial growth step of epitaxially growing the single crystal silicon layer by a vapor phase epitaxy method on the surface of the silicon single crystal wafer on which the oxygen atomic layer has been formed, In the oxygen atomic layer forming step, a cleaning solution containing at least hydrogen peroxide solution is used for the cleaning, a step of forming an oxygen atomic layer on the substrate; a step of forming an oxygen atomic layer on the substrate;

2. 2. The method for producing an epitaxial wafer according to claim 1, wherein the pH value of the cleaning solution containing the hydrogen peroxide solution is set in the range of 4 to 7.

3. In the oxygen atomic layer forming step, the plane concentration of oxygen in the oxygen atomic layer is set to 1×10 １５ atoms / cm ２ 2. The method for producing an epitaxial wafer according to claim 1, wherein the following steps are performed:

4. 2. The method for producing an epitaxial wafer according to claim 1, wherein the epitaxial growth step is performed at a temperature of 450° C. or higher and 800° C. or lower.

5. 2. The method for producing an epitaxial wafer according to claim 1, wherein a CMP process is performed on the surface of the single crystal silicon layer after the epitaxial growth step.

6. 6. The method for producing an epitaxial wafer according to claim 1, wherein at least the oxygen atomic layer forming step and the epitaxial growth step are alternately performed a plurality of times.

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