Method for manufacturing epitaxial wafer

Abstract

The present invention is a method for manufacturing an epitaxial wafer, for forming a single-crystal silicon layer on a silicon single-crystal wafer. The method is characterized by comprising a hydrofluoric acid cleaning step for removing a natural oxide film from the surface of the silicon single-crystal wafer with a cleaning liquid containing hydrofluoric acid, an oxygen atomic layer forming step for forming, by cleaning, an oxygen atomic layer on the surface of the silicon single-crystal wafer from which the natural oxide film has been removed, and an epitaxial growth step for epitaxially growing, by a vapor-phase growth method, the single-crystal silicon layer on the surface of the silicon single-crystal wafer on which the oxygen atomic layer has been formed, wherein a cleaning liquid containing at least hydrogen peroxide water is used for the cleaning in the oxygen atomic layer forming step. Thus, a method for manufacturing an epitaxial wafer is provided that makes it possible to efficiently form and control an oxygen atomic layer without causing a deterioration in the surface roughness of the 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 methods 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, which have a high ionization tendency (low electronegativity), in contrast to 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] 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. 2024-007890 Japanese Patent Application Laid-Open No. 2009-016637

[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 without 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, a prior art method for manufacturing an epitaxial wafer in which oxygen is delta-doped will be described. Patent Document 1 discloses a method for manufacturing an epitaxial wafer in which a native oxide film on the surface of a silicon wafer is removed at a temperature of 700° C. or less, and then a method for manufacturing an epitaxial wafer in which nitrogen monoxide is used to form a single crystal silicon wafer having a planar concentration of 1×10 １５ atoms / cm ２ The present invention describes a method for producing an epitaxial wafer δ-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 epitaxial wafer delta-doped with oxygen, 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, an oxygen atomic layer is formed by oxidation treatment, and a single-crystal silicon layer is epitaxially grown on the oxygen atomic layer.

[0009] Patent Document 3 describes a method for producing an epitaxial wafer in which oxygen is δ-doped by removing a native oxide film on the surface of a single crystal silicon wafer with hydrofluoric acid, 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 thereon. １５ atoms / cm ２It 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 thereon.

[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 in thickness.

[0012] Here, the comparative example of Patent Document 4 states that when an Si epitaxial film is formed on an oxide film formed using an oxidizing solution without thinning treatment, the number of defects reaches the measurement upper limit (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 presumed that the reason the number of defects reached the measurement upper limit without thinning treatment was because the amount of oxidation was too high. 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 presumed that the quality of the silicon film, such as dislocations and stacking faults, was deteriorated. 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 present inventors 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.

[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 ２ It can be as follows:

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

[0027] At this time, in the epitaxial growth step, epitaxial growth can be performed at a temperature of 450° C. or more and 800° C. or less.

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

[0029] In this case, 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.

[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.

[0034] 1 is a flowchart showing an example of a method for manufacturing an epitaxial wafer according to the present invention;

[0023] FIG. 1 is a diagram showing an epitaxial wafer obtained by the method for manufacturing an epitaxial wafer according to the present invention;

[0024] FIG. 1 is a diagram showing an epitaxial wafer obtained by the method for manufacturing an epitaxial wafer according to the present invention, in which oxygen atomic layers and single crystal silicon layers are alternately stacked in multiple layers;

[0025] FIG. 2 is a graph showing the relationship between the hydrogen peroxide concentration and the planar oxygen concentration of the oxygen atomic layer when cleaning is performed at a cleaning solution temperature of 80°C for a cleaning time of 3 minutes;

[0026] FIG. 3 is a graph showing the relationship between the hydrogen peroxide concentration and the planar oxygen concentration of the oxygen atomic layer when cleaning is performed at a cleaning solution temperature of 25°C for a cleaning time of 3 minutes;

[0027] FIG. 4 is a graph showing the relationship between the cleaning time and the planar oxygen concentration of the oxygen atomic layer when cleaning is performed at a cleaning solution temperature of 25°C with a hydrogen peroxide concentration of 10,000 ppm (1 mass%);

[0028] FIG. 5 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. 1 is a graph showing the relationship between hydrogen peroxide concentration and surface roughness (haze value) when cleaning was performed with a cleaning solution temperature of 25°C for a cleaning time of 3 minutes. FIG. 2 is a graph showing the relationship between hydrogen peroxide concentration and pH at a temperature of 25°C. FIG. 3 is a graph showing the transition of haze value before cleaning, after cleaning, and after film formation for Example 1 and Comparative Examples 1 to 4. FIG. 4 is a graph showing the transition of haze value before cleaning, after cleaning, and after film formation for Example 2 and Comparative Examples 5 to 8. FIG. 5 is a graph showing the oxygen concentration of the oxygen atomic layer for Example 3 and Comparative Examples 9 to 12. FIG. 6 is a diagram showing a cross-sectional TEM image of the epitaxial wafer of Example 3.

[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] 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 planar concentration of oxygen 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 that it is greater than 0. In order to stably obtain gettering ability, it is desirable that the planar concentration of oxygen is 1×10 or less. １３ atoms / cm ２ It is preferable that the ratio is 1×10 or more. １４atoms / 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] [Method for Manufacturing Epitaxial Wafer] 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] 1 is a hydrofluoric acid cleaning step in which a native oxide film is removed using a cleaning solution containing hydrofluoric acid (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 of S3.

[0044] In this case, it is sufficient that the hydrofluoric acid can remove the native oxide film, 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 may be, for example, 0.001% by mass or more and 60% by mass or less as long as it can remove the native oxide film. More preferably, it may be 0.1% by mass or more and 10% by mass or less. The temperature of the hydrofluoric acid cleaning solution may be 10°C or more and 50°C or less. More preferably, it may be 20°C or more and 30°C or less.

[0045] The time for the treatment (cleaning) of removing the native oxide film using 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-type cleaning device. Furthermore, the oxide film can be removed using hydrofluoric acid vapor.

[0046] [Oxygen Atomic Layer Formation Step] In the step S3 of FIG. 1, the single crystal silicon wafer from which the native oxide film has been removed is immersed in an aqueous solution containing at least hydrogen peroxide (hereinafter, “H ２ O ２ This is an oxygen atomic layer formation process in which an oxygen atomic layer is formed on the silicon surface by cleaning with a cleaning solution (referred to as a "cleaning solution"). In single-crystal silicon, oxygen atoms are stable at the bond center position between the silicon atoms and the nearest silicon atoms. Assuming that 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 10１５ atoms / cm ２ In this case, it corresponds to 0.74 atomic layers.

[0047] Hydrogen peroxide acts as an oxidizing agent, causing an oxidation reaction 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 in a single sputtering operation near the peak.

[0048] At this time, H ２ O ２ The oxygen concentration in the oxygen atomic layer can be controlled by adjusting the temperature of the cleaning solution, the hydrogen peroxide concentration, and the cleaning time. ２ O ２ The cleaning solution temperature and cleaning time were set to 80°C / 3 min, and the hydrogen peroxide concentrations were set to 0, 100, 250, and 500 ppm. ２ O ２ The planar concentration of oxygen in the oxygen atomic layer after cleaning with a cleaning solution and epitaxial growth in S4 is shown in FIG. ２ O ２ The cleaning solution temperature and cleaning time were set to 25°C / 3 min, and the hydrogen peroxide concentrations were set to 0, 10,000, 30,000, and 50,000 ppm (0, 1, 3, and 5 mass%, respectively). ２ O ２ The planar concentration of oxygen in the oxygen atomic layer after cleaning with a cleaning solution and epitaxial growth in S4 is shown in FIG. ２ O ２ The cleaning solution temperature was 25°C, the hydrogen peroxide concentration was 10,000 ppm (1 mass%), and the cleaning time was 3, 10, and 20 minutes, and the planar oxygen concentration of the oxygen atomic layer after epitaxial growth was performed in S4 was shown. ２ O ２ By adjusting the cleaning solution temperature, hydrogen peroxide concentration, and cleaning time, the oxygen concentration in the oxygen atomic layer can be controlled, especially to 1 × 10 １４ ~1 x 10 １５ atoms / cm ２It 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, H ２ O ２ The surface roughness of the wafer after cleaning with the cleaning solution will be described. ２ O ２ The cleaning solution temperature and cleaning time were set at 80° C. / 3 min, and the hydrogen peroxide concentration was varied in the range of 0 to 300 ppm. The relationship between the hydrogen peroxide concentration, surface roughness (haze), and etching rate after cleaning was shown.

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

[0052] In FIG. ２ O ２ The surface roughness (haze) of wafers after cleaning was shown, with the cleaning solution temperature and cleaning time set to 25°C / 3 min and the hydrogen peroxide concentration varied from 0 to 30,000 ppm (0 to 3 mass%). As a result, the haze value was independent of the hydrogen peroxide concentration, and was equivalent across all concentration levels. Furthermore, this haze value was lower than that of the cleaning temperature and time set to 80°C / 3 min in Figure 7, 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, H ２ O ２ The cleaning solution will be described in more detail. In the present invention, the oxidizing action of hydrogen peroxide is utilized. More specifically, the decomposition reaction of hydrogen peroxide (2H ２ O ２ →2H ２ O+O ２ The oxidation reaction proceeds with the oxygen released from the

[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 results of H peroxide decomposition when the hydrogen peroxide concentration is varied in the range of 0 to 50,000 ppm (0 to 5 mass%) at a temperature of 25°C. ２ O ２ The pH value of the aqueous solution is shown in Figure 9. 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] When the pH is 7 or less, it is possible to effectively prevent the formation of a thick oxygen atomic layer, which is formed when the decomposition reaction of hydrogen peroxide proceeds and the oxidation reaction is promoted when the pH is higher than 7. Furthermore, when the pH is 4 or higher, the decomposition reaction becomes more stable, and an oxygen atomic layer can be formed more stably with good reproducibility. Therefore, in the present invention, it is desirable to set the pH value of the cleaning solution containing hydrogen peroxide water in the range of 4 to 7. Furthermore, when the pH is higher than 7, the decomposition reaction becomes more stable and the oxygen atomic layer can be formed more stably with good reproducibility. ２ O ２ The cleaning solution contains at least hydrogen peroxide, and other chemicals and additives may also be added.

[0057] Furthermore, in the present invention, since the oxygen concentration of the oxygen atomic layer can be appropriately controlled in the oxygen atomic layer formation step, 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 to add a step of thinning the oxygen atomic layer, thereby improving productivity.

[0058] [Epitaxial Growth Step] S4 in FIG. 1 is the epitaxial growth step 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 at which minute silicon crystals do not form in the vapor phase. For example, the pressure can be 133 Pa or more and 13,300 Pa or less. The epitaxial growth apparatus can be 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. By carrying out growth at such a temperature, it is possible to effectively prevent dislocations and stacking faults from being formed 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 a 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 carrying out the above steps S1 to S4, an epitaxial wafer delta-doped with oxygen as shown in FIG. 2 can be manufactured, and the oxygen concentration in the oxygen atomic layer can be controlled.

[0063] Furthermore, depending on the purpose, the wafer surface after step S4 can be subjected to CMP (S5), which can improve defects and roughness on the surface of the epitaxial layer.

[0064] 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.

[0065] The present invention also makes it possible to manufacture an epitaxial wafer having a plurality of oxygen atomic layers as shown in Fig. 3 by alternately repeating 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 dopant suppression function can be improved compared to a single layer.

[0066] In this case, there is no limit to the spacing between oxygen atomic layers, and the oxygen concentration and spacing between oxygen atomic layers can be adjusted depending on the application. ２ O ２In a high temperature region of the cleaning solution such as 80° C., the Si on the outermost surface is etched, and therefore, in order to reliably form multiple layers, it is preferable to adjust the conditions of steps S3 and S4 so that the amount of silicon etched in the oxygen atomic layer formation step S3 is less than the amount of silicon film formed in the epitaxial growth step S4 (also referred to as silicon film thickness). In this way, by performing the treatment multiple times so that the amount of silicon etched in the oxygen atomic layer formation step S3 is less than the amount of silicon film formed in the epitaxial growth step S4, multiple oxygen atomic layers can be reliably formed.

[0067] The present invention will be specifically explained below with reference to examples, but the present invention is not limited to these examples.

[0068] Example 1 A single crystal silicon wafer having a diameter of 300 mm, a crystal plane orientation of (100), a p-type conductivity, and a resistivity of 10 Ωcm was prepared. The prepared wafer was inspected using an SP5 manufactured by KLA Corporation, and a haze value indicating surface roughness was obtained.

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

[0070] The wafer after cleaning was inspected using a KLA SP5 to obtain a haze value. Subsequently, 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. The wafer after film formation was inspected using a KLA SP5 to obtain a haze value.

[0071] (Comparative Examples 1 to 4) Epitaxial wafers were manufactured and haze values ​​were obtained under the same conditions as in Example 1, except that the cleaning solution after HF cleaning was changed from hydrogen peroxide water to pure water. In this case, the temperature of the pure water and the 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 An epitaxial wafer was manufactured and its 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 Example 1, except that the film formation time during epitaxial growth was changed to 60 seconds. Here, the oxygen atomic concentration of the oxygen atomic layer was evaluated by SIMS. In addition, the crystalline state of the film formation layer was evaluated by cross-sectional transmission electron microscopy (TEM).

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

[0076] 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 the 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 in particular, Example 1 had good haze.

[0077] Figure 11 shows the transition of haze values ​​before cleaning, after cleaning, 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 with hydrogen peroxide were the same as those in Example 2) was higher than that of Comparative Examples 11 and 12 (where the cleaning conditions with 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 obtained. The same can be said for 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] 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 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 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 includes using a cleaning solution containing at least a hydrogen peroxide solution for the cleaning. [2]: A method for manufacturing an epitaxial wafer according to [1] above, which includes not performing a process to thin the oxygen atomic layer after the oxygen atomic layer formation step. [3]: A method for manufacturing an epitaxial wafer according to [1] above, which includes adjusting the pH value of the cleaning solution containing a 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 manufacturing an epitaxial wafer according to [1], [2], or [3] above, which includes the following: [5]: A method for manufacturing an epitaxial wafer according to [1], [2], [3], or [4] above, which includes performing epitaxial growth at a temperature of 450°C or higher and 800°C or lower in the epitaxial growth step. [6]: A method for manufacturing an epitaxial wafer according to [1], [2], [3], [4], or [5] above, which includes 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] above, which includes alternately performing at least the oxygen atomic layer formation step and the epitaxial growth step a plurality of 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.

Claims

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

2. The method for producing an epitaxial wafer according to claim 1, wherein no treatment for thinning the oxygen atomic layer is performed after the oxygen atomic layer forming step.

3. 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.

4. 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:

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

6. The method for producing an epitaxial wafer according to claim 1, wherein the surface of the single crystal silicon layer is subjected to CMP processing after the epitaxial growth step.

7. A method for producing an epitaxial wafer according to any one of claims 1 to 6, characterized in that at least the oxygen atomic layer forming step and the epitaxial growth step are alternately performed multiple times.

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