Manufacturing method for epitaxial wafer

Abstract

To provide a manufacturing method for an epitaxial wafer, by which the planar concentration of oxygen in an oxygen atomic layer can be controlled and the defect or roughness of the surface can also be improved.SOLUTION: A manufacturing method for an epitaxial wafer 10A includes: a hydrofluoric acid cleaning step of removing a natural oxide film on a surface of a silicon single-crystal wafer 1 with hydrofluoric acid; a pure water cleaning step of cleaning the surface of the silicon single-crystal wafer 1, from which the natural oxide film has been removed, with pure water so as to form an oxygen atomic layer 2 on the surface; an epitaxial growth step of epitaxially growing a single-crystal silicon layer 3 by a vapor growth method on the surface of the silicon single-crystal wafer 1 on which the oxygen atomic layer 2 has been formed; and a CMP step of performing a CMP process on the surface of the single-crystal silicon layer 3 that has been grown in the epitaxial growth step. In the pure water cleaning step, the planar concentration of oxygen in the oxygen atomic layer 2 is set to 1×1015 atoms / cm2 or less and pure water containing the dissolution oxygen is used.SELECTED DRAWING: Figure 3

Description

[Technical field]

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

[0002] Silicon substrates on which semiconductor elements such as solid-state image sensors and other transistors are formed are required to have the function of gettering elements that disrupt the characteristics of the elements, such as heavy metals.

[0003] Various methods have been proposed and put into practical use for gettering, including providing a polycrystalline silicon (Poly-Si) layer on the back surface of the silicon substrate, forming a damaged layer by blasting, using a silicon substrate with a high concentration of boron, and forming precipitates.

[0004] Gettering by oxygen precipitation involves the capture of a metal, which has a high ionization tendency (low electronegativity), in comparison with oxygen, which has a high electronegativity.

[0005] Proximity gettering has also been proposed, in which a gettering layer is formed near the active region of the device, for example, a substrate in which silicon is epitaxially grown on a substrate in which carbon is ion-implanted.

[0006] Gettering requires that elements diffuse to a gettering site (where the energy of the entire system is reduced by bonding or clustering at a site rather than by the metal existing as a single element).

[0007] The diffusion coefficient of metal elements contained in silicon varies depending on the element, and in addition, due to the recent trend towards lower process temperatures, metals are no longer able to diffuse to the gettering site. Considering this, a proximity gettering technique has been proposed.

[0008] 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, an epitaxial wafer having an oxygen atomic layer in the middle of the epitaxial layer can reliably getter metal impurities even in recent low-temperature processes.

[0009] In addition to gettering, the effect of suppressing the diffusion of dopants such as boron and phosphorus can also be expected. As described above, epitaxial wafers having an oxygen atomic layer in the middle of the epitaxial layer can improve device performance more than normal epitaxial wafers that do not have an oxygen atomic layer.

[0010] Moreover, such 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 epitaxial wafer δ doped with oxygen. Hereinafter, in the present invention, the oxygen atomic layer and the oxygen δ doped layer have the same meaning.

[0011] Next, a description will be given of the prior art regarding a method for manufacturing an epitaxial wafer in which oxygen is delta-doped. Patent Document 1 discloses a method for removing a native oxide film on the surface of a silicon single crystal wafer at 700° C. or less, and then, using nitric oxide, doping the surface of the silicon single crystal wafer with nitrogen monoxide to a planar concentration of 1×10 15 atoms / cm 2 A method for manufacturing an epitaxial wafer delta-doped with oxygen is described, in which a single crystal silicon layer formation step is performed one or more times, in which an oxygen atomic layer is formed and a single crystal silicon layer is formed thereon by epitaxial growth.

[0012] 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.

[0013] Patent Document 3 describes a method for producing an oxygen-delta-doped epitaxial wafer by removing a native oxide film on the surface of a silicon single crystal wafer with hydrofluoric acid, followed by rinsing with pure water or leaving the wafer in an oxygen-containing atmosphere to form an oxygen atomic layer, and then epitaxially growing a single crystal silicon layer on the oxygen atomic layer.

[0014] In addition, in Patent Document 3, the planar concentration of oxygen in the oxygen atomic layer is 1×10 15 atoms / cm 2 It is disclosed that a single crystal silicon layer can be grown without forming dislocations and stacking faults on the oxygen atomic layer by setting the density of the oxygen atoms to 1×10 15 If the oxygen concentration is higher than atoms, the quality of the single crystal silicon layer deteriorates, and if the oxygen concentration is even higher, lattice mismatch occurs and a polycrystalline silicon layer is formed.

[0015] Patent Document 4 describes a method of forming an SOI structure by forming an epitaxial film after forming an oxide film on a silicon substrate 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. Although the formed layer is single crystal, no evaluation results are disclosed regarding dislocations and stacking faults. Considering Patent Documents 1 to 3, it is presumed that the quality of the layer is degraded due to dislocations, stacking faults, etc.

[0016] Patent Document 3 discloses a method for forming multiple oxygen atomic layers by repeating oxide layer formation and epitaxial growth. Forming multiple oxygen atomic layers in this way is useful because it can further improve device performance compared to a single layer. [Prior art documents] [Patent documents]

[0017] [Patent Document 1] JP 2022-146664 A [Patent Document 2] Patent Publication No. 2021-111696 [Patent Document 3] International Publication No. 2022 / 158148 [Patent Document 4] JP 2009-016637 A Summary of the Invention [Problem to be solved by the invention]

[0018] Thus, there is a demand for a method of manufacturing an epitaxial wafer in which oxygen is delta-doped. In particular, in order to prevent deterioration of the quality of the silicon layer after epitaxial growth, the planar concentration of oxygen in the oxygen atomic layer is increased to 10 15 atoms / cm 2 There is a need for a method for manufacturing epitaxial wafers that can control the surface roughness and defects as well as the surface roughness.

[0019] 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 control the planar oxygen concentration in the oxygen atomic layer and also improve surface defects and roughness. [Means for solving the problem]

[0020] The present invention has been made to achieve the above object, and is a manufacturing method of an epitaxial wafer comprising a silicon single crystal wafer and a single crystal silicon layer epitaxially grown on the silicon single crystal wafer, the method comprising the steps of: a hydrofluoric acid cleaning step of removing a native oxide film on a surface of the silicon single crystal wafer with hydrofluoric acid; a pure water cleaning step of cleaning the surface of the silicon single crystal wafer from which the native oxide film has been removed with pure water to form an oxygen atomic layer on the surface; an epitaxial growth step of epitaxially growing the single crystal silicon layer by a vapor phase epitaxy on the surface of the silicon single crystal wafer on which the oxygen atomic layer has been formed; and a CMP step of performing CMP processing on the surface of the single crystal silicon layer grown in the epitaxial growth step, wherein in the pure water cleaning step, a planar oxygen concentration of the oxygen atomic layer is reduced to 1×10 15atoms / cm 2 The present invention provides a method for producing an epitaxial wafer, characterized in that the method uses pure water containing dissolved oxygen as described below.

[0021] According to this method for producing an epitaxial wafer, the surface of the silicon wafer is oxidized by the oxygen dissolved in the pure water, and the surface is delta-doped with oxygen. Then, CMP processing is performed, so that an epitaxial wafer with improved surface defects and roughness can be produced.

[0022] In this case, in the pure water washing step, the pure water temperature and washing time are adjusted to make the planar oxygen concentration of the oxygen atomic layer 1×10 14 ~1×10 15 atoms / cm 2 It can be controlled within the range.

[0023] By adjusting the temperature of the pure water and the cleaning time in this manner, an oxygen atomic layer having a desired oxygen concentration can be formed with good reproducibility.

[0024] At this time, in the epitaxial growth step, the epitaxial growth can be performed at a temperature of 450° C. or more and 800° C. or less.

[0025] By setting the epitaxial growth temperature within this temperature range, epitaxial growth can be achieved more stably without generating defects.

[0026] In this case, at least the pure water washing step and the epitaxial growth step can be alternately performed a plurality of times.

[0027] By providing a plurality of oxygen atomic layers in this manner, 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.

[0028] In this case, when the pure water cleaning step and the epitaxial growth step are alternately performed multiple times, the conditions of the pure water cleaning step and / or the epitaxial growth step can be adjusted so that the amount of silicon film formed in the epitaxial growth step is greater than the amount of silicon etched in the pure water cleaning step.

[0029] In this way, by maintaining the relationship in which the amount of silicon film formed is greater than the amount of silicon etched, a plurality of oxygen atomic layers can be reliably formed as desired. Effect of the Invention

[0030] As described above, according to the method for producing an epitaxial wafer of the present invention, the planar oxygen concentration of the oxygen atomic layer can be controlled, and surface defects and roughness can also be improved. [Brief description of the drawings]

[0031] [Figure 1] 1 shows an example of an epitaxial wafer obtained by a method for producing an epitaxial wafer according to an embodiment of the present invention. [Diagram 2] 1 shows another example of an epitaxial wafer obtained by the epitaxial wafer manufacturing method of the present invention, which is an epitaxial wafer in which oxygen atomic layers and single crystal silicon layers are alternately stacked in multiple layers. [Diagram 3] 1 shows a flowchart of an example of a method for manufacturing an epitaxial wafer having an oxygen atomic layer according to the present invention. [Figure 4] 1 shows a graph of the relationship between the pure water cleaning conditions and the planar oxygen concentration of the oxygen atomic layer. [Diagram 5] 1 shows a graph of the relationship between the pure water temperature during cleaning and the Si etching rate. [Figure 6] 1 is a graph showing the relationship between silicon film formation time and film formation amount, and the Si etching amount when washed with pure water at 80° C. for 10 minutes. [Figure 7] 1 shows a graph of oxygen concentration distribution by SIMS when the Si film formation time in the epitaxial growth step of the first cycle is set to 2 seconds and 10 seconds. [Figure 8] This shows a cross-sectional TEM image of an epitaxial wafer manufactured with the aim of achieving a three-layer structure of oxygen atomic layers. [Figure 9] This shows a cross-sectional TEM image of an epitaxial wafer manufactured with the aim of achieving a two-layer structure of oxygen atomic layers. [Figure 10] This shows a cross-sectional TEM image of an epitaxial wafer manufactured with the aim of achieving a three-layer structure of oxygen atomic layers. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0032] The present invention will be described in detail below, but the present invention is not limited thereto.

[0033] As described above, there has been a demand for a method for manufacturing an epitaxial wafer that can control the planar oxygen concentration in the oxygen atomic layer and also improve surface defects and roughness.

[0034] As a result of intensive research by the inventors of the present invention into the above-mentioned problems, they have discovered a method for manufacturing an epitaxial wafer comprising a silicon single crystal wafer and a single crystal silicon layer epitaxially grown on the silicon single crystal wafer, the method comprising the steps of: a hydrofluoric acid cleaning step of removing a native oxide film on a surface of the silicon single crystal wafer with hydrofluoric acid; a pure water cleaning step of cleaning the surface of the silicon single crystal wafer from which the native oxide film has been removed with pure water to form an oxygen atomic layer on the surface; an epitaxial growth step of epitaxially growing the single crystal silicon layer by a vapor phase epitaxy on the surface of the silicon single crystal wafer on which the oxygen atomic layer has been formed; and a CMP step of performing CMP processing on the surface of the single crystal silicon layer grown in the epitaxial growth step, wherein in the pure water cleaning step, a planar oxygen concentration of the oxygen atomic layer is reduced to 1×10 15 atoms / cm 2 The inventors have found that a method for producing an epitaxial wafer, which is characterized by using pure water containing dissolved oxygen, makes it possible to control the planar oxygen concentration in the oxygen atomic layer and improve surface defects and roughness, and have completed the present invention.

[0035] The following description will be given with reference to the drawings. Hereinafter, a method for producing an epitaxial wafer according to an embodiment of the present invention will be described with reference to FIGS.

[0036] [Epitaxial wafer] First, a schematic configuration of an epitaxial wafer manufactured by a manufacturing method for an epitaxial wafer according to an embodiment of the present invention will be described with reference to Figures 1 and 2. As shown in Figure 1, an epitaxial wafer 10A has a silicon single crystal wafer 1 and a single crystal silicon layer 3, and has an oxygen atomic layer 2 between the silicon single crystal wafer 1 and the single crystal silicon layer 3.

[0037] The silicon single crystal wafer 1 supports the other layers constituting the epitaxial wafer 10A and is a substrate that serves as a base for growing the single crystal silicon layer 3. The silicon single crystal 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.

[0038] The oxygen atomic layer 2 is a layer that getstering metal impurities and inhibits the diffusion of dopants such as boron and phosphorus, and is formed on the surface of the silicon single crystal wafer 1 . The planar concentration of oxygen in the oxygen atomic layer 2 is 1×10 15 atoms / cm 2 or less. Unless the epitaxial wafer has an oxygen atomic layer 2 having a planar oxygen concentration within this range, stacking faults and dislocations will increase in the epitaxially grown single crystal silicon layer 3, and the crystallinity will also deteriorate. There is no lower limit to the planar oxygen concentration, and it is sufficient that it is greater than 0. In order to stably obtain gettering ability, it is necessary to use an oxygen atomic layer having an oxygen concentration of 1×1013 atoms / cm 2 It is preferable that the concentration is 1×10 or more. 14 atoms / cm 2 More preferably, the above is true.

[0039] The single crystal silicon layer 3 is a layer in which semiconductor elements such as solid-state imaging elements and other transistors are mainly formed, and is a layer epitaxially grown on the silicon single crystal wafer 1. More specifically, it is formed on the oxygen atomic layer 2. The thickness of the single crystal silicon layer 3 may be appropriately selected depending on the dimensions of the semiconductor elements to be formed, etc.

[0040] Although only one oxygen atomic layer 2 is provided in FIG. 1, multiple oxygen atomic layers 2 and single crystal silicon layers 3 may be alternately laminated as in the epitaxial wafer 10B shown in FIG. 2. In this case, the uppermost surface is the single crystal silicon layer 3. By forming multiple oxygen atomic layers 2, it is possible to improve the gettering function and the dopant diffusion suppression function more than a single layer. There is no limit to the spacing between the oxygen atomic layers 2, and the layer spacing can be adjusted according to the application. The above is a description of the schematic configuration of the epitaxial wafers 10A and 10B.

[0041] [Epitaxial wafer manufacturing method] Next, a method for producing the oxygen δ-doped epitaxial wafers 10A and 10B according to the present invention will be described with reference to FIG.

[0042] First, as shown in S1 of Fig. 3, a silicon single crystal wafer 1 is prepared. Here, the method of manufacturing the silicon single crystal wafer 1 used as the substrate is not particularly limited. The silicon single crystal wafer 1 may be manufactured by the CZ method, or may be manufactured by the FZ method. Also, a wafer in which single crystal silicon is epitaxially grown on a silicon single crystal wafer 1 manufactured by the CZ method or FZ method may be used.

[0043] 3, the native oxide film on the surface of the silicon single crystal wafer 1 is removed by cleaning with hydrofluoric acid (hydrofluoric acid cleaning step). In the present invention, it is necessary to form an oxygen atomic layer 2 instead of a native oxide film. Since the native oxide film is too thick to be used as a gettering layer and also inhibits the formation of the single crystal silicon layer 3, the native oxide film is first completely removed, and then the oxygen atomic layer 2 is formed in the subsequent step S3 (pure water cleaning step).

[0044] In this case, the hydrofluoric acid cleaning step only needs to be able to remove the native oxide film, and the chemical used may be hydrofluoric acid alone or a chemical containing other components such as buffered hydrofluoric acid.

[0045] The concentration of hydrofluoric acid may be, for example, 0.001 wt% or more and 60 wt% or less as long as it can remove the natural oxide film. More preferably, it may be 0.1 wt% or more and 10 wt% or less. The temperature of hydrofluoric acid 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.

[0046] The time for the process of removing the native oxide film using hydrofluoric acid (hydrofluoric acid cleaning process) can be set until water repellency can be confirmed, and can be set, for example, from 10 seconds to 1 hour. If it is set to 10 seconds or more, the native oxide film can be removed more reliably. Furthermore, if it is set to 1 hour or less, productivity can be maintained. More preferably, it can be set to 30 seconds to 360 seconds.

[0047] The hydrofluoric acid treatment (hydrofluoric acid cleaning step) may be performed using a batch type cleaning device or a single wafer type cleaning device. Also, the oxide film may be removed using hydrofluoric acid vapor.

[0048] Next, as shown in S3 of Fig. 3, the silicon single crystal wafer 1 from which the native oxide film has been removed is washed with pure water to form an oxygen atomic layer 2 on the surface (pure water washing step). In single crystal silicon, oxygen atoms are stable at the bond center positions between 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 1×10 15 atoms / cm 2 In this case, it corresponds to 0.74 atomic layers.

[0049] Here, by cleaning the silicon single crystal wafer 1 with pure water containing dissolved oxygen, an oxidation reaction progresses on the silicon surface, and an oxygen atomic layer 2 can be formed.

[0050] Here, we will explain dissolved oxygen. In the manufacturing process of electronic devices such as semiconductors, ultrapure water (hereafter also referred to as pure water), which is highly purified water from which impurities have been removed to the utmost extent, is used.

[0051] The quality of pure water is often controlled using resistivity as an index. In addition to metal impurities, gases such as oxygen and nitrogen are dissolved in pure water. It is known that dissolved oxygen and other gases act on semiconductors such as silicon in the semiconductor manufacturing process. To avoid such effects, it is known to remove dissolved oxygen by degassing pure water.

[0052] For example, the dissolved oxygen in pure water can be controlled according to the application. In the present invention, the oxidation reaction between the dissolved oxygen and the silicon surface is actively utilized to form the oxygen atomic layer 2. The saturated oxygen concentration in pure water under atmospheric pressure is about 8.3 ppm at 25°C, about 5.6 ppm at 50°C, and about 1.6 ppm at 90°C, and is known to be temperature dependent.

[0053] In the present invention, it is desirable to use pure water containing at least 0.1 ppm or more of dissolved oxygen. If the dissolved oxygen concentration is at least 0.1 ppm or more, the oxygen atomic layer 2 can be reliably formed on the surface. There is no upper limit to the dissolved oxygen concentration, and it can be, for example, 100 ppm or less. These can be produced by not degassing the pure water.

[0054] In the present invention, in S3 (pure water cleaning step), the planar concentration of oxygen in the oxygen atomic layer 2 is set to 1×10 15 atoms / cm 2 The planar concentration of oxygen in the oxygen atomic layer 2 must be 1×10 15 If the oxygen concentration is higher than atoms, the quality of the single crystal silicon layer 3 grown in a later step will deteriorate, and if the oxygen concentration is even higher, lattice mismatch will occur and a polycrystalline silicon layer will be formed.

[0055] The temperature of the pure water used in the pure water cleaning process can be set to 10°C or higher and 99°C or lower. Higher temperatures reduce the dissolved oxygen concentration, but promote the reaction between oxygen and silicon, so the higher the temperature, the higher the oxygen concentration in the oxygen atomic layer 2 can be. The cleaning time in the pure water cleaning process can be set to 10 seconds or higher and 1 hour or shorter. If it is 10 seconds or longer, the oxygen atomic layer 2 can be reliably formed. Also, if it is set to 1 hour or shorter, productivity can be maintained.

[0056] 4 shows the planar oxygen concentration of the oxygen atomic layer 2 after epitaxial growth in the subsequent step S4, which is performed after cleaning with varying pure water temperature and cleaning time in S3 (pure water cleaning step). Here, the planar oxygen concentration can be measured by, for example, SIMS (Secondary Ion Mass Spectrometry).

[0057] When silicon (Si) containing an oxide layer such as an oxygen atomic 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 in the vicinity of the peak.

[0058] As a result, it can be seen that the higher the pure water temperature and the longer the cleaning time, the higher the oxygen concentration in the oxygen atomic layer 2. That is, by adjusting the conditions of the cleaning step S3, specifically the pure water temperature and cleaning time, the planar oxygen concentration in the oxygen atomic layer 2 can be increased to 1×10 14 ~1×10 15 atoms / cm 2 In this way, by adjusting the temperature of the pure water and the time, it is possible to form the oxygen atomic layer 2 having a desired oxygen concentration with good reproducibility.

[0059] The pure water cleaning may be performed using a batch type cleaning device or a single wafer type cleaning device.

[0060] Next, as shown in S4 of Fig. 3, a single crystal silicon layer 3 is epitaxially grown by vapor phase epitaxy on the surface of the silicon single crystal wafer 1 on which the oxygen atomic layer 2 has been formed (epitaxial growth step). Monosilane or disilane can be used as the gas used for growth. Nitrogen or hydrogen can also be used as the carrier gas.

[0061] The pressure in the chamber in which the epitaxial growth is performed may be any pressure that does not generate fine silicon crystals in the gas phase, for example, a pressure of 133 Pa or more and 13,300 Pa or less. The epitaxial growth apparatus may be of a batch type or a single wafer type.

[0062] Moreover, the epitaxial growth of the single crystal silicon layer 3 can be performed at a temperature of 450° C. or more and 800° C. or less. By performing the growth at such a temperature, the formation of dislocations and stacking faults in the single crystal silicon layer 3 can be prevented.

[0063] Since the higher the temperature, the higher the epitaxial growth rate, a thick epitaxial layer can be formed in a short time by depositing at a high temperature. On the other hand, if a thin single crystal silicon layer 3 is to be formed, the deposition temperature can be lowered. In this way, the growth temperature can be changed according to the desired thickness of the single crystal silicon layer 3. Also, the deposition time can be adjusted to adjust the thickness of the single crystal silicon layer 3.

[0064] In epitaxial growth of the single crystal silicon layer 3, hydrogen baking is usually performed immediately before the epitaxial growth to remove and clean the native oxide film on the substrate surface, but in the epitaxial growth process according to the present invention, it is preferable not to perform hydrogen baking and to start epitaxial growth when a predetermined growth temperature is reached in order to prevent the oxygen atomic layer 2 from disappearing.

[0065] The hydrogen bake mentioned here means to hold the silicon single crystal wafer 1 in a hydrogen atmosphere at 800°C or higher for a certain period of time. Since the oxygen atomic layer 2 is not lost at temperatures below 800°C, there is no problem in flowing hydrogen as a carrier gas before epitaxial growth at temperatures below 800°C.

[0066] Next, as shown in S5 of Fig. 3, CMP (Chemical Mechanical Polishing) is performed on the surface of the single crystal silicon layer 3 grown in S4 (epitaxial growth step) (CMP step). This makes it possible to improve surface defects and roughness. 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 10A having an oxygen atomic layer 2 while leaving the single crystal silicon layer 3.

[0067] By carrying out the above steps S1 to S5, it is possible to manufacture the epitaxial wafer 10A in which oxygen is delta-doped, as shown in Fig. 1. More specifically, it is possible to manufacture the epitaxial wafer 10A in which the oxygen concentration in the oxygen atomic layer 2 is controlled and surface defects and roughness are improved.

[0068] Next, a method for manufacturing an epitaxial wafer 10B having a plurality of oxygen atomic layers 2 as shown in Fig. 2 will be described. Specifically, at least S3 (pure water cleaning step) in Fig. 3 and S4 (epitaxial growth step) in Fig. 3 are alternately performed a plurality of times to form a plurality of oxygen atomic layers 2, thereby manufacturing an epitaxial wafer 10B having a plurality of oxygen atomic layers 2.

[0069] By forming a plurality of oxygen atomic layers 2 in this way, the gettering function and the function of suppressing the diffusion of dopants can be improved compared to a single layer. In this case, there is no limit to the interval between the oxygen atomic layers 2, and the oxygen concentration and the layer interval of the oxygen atomic layers 2 can be adjusted according to the application. In addition, S2 to S4 may be repeated.

[0070] On the other hand, when the present inventors performed the formation of the oxygen atomic layer 2 using pure water and the epitaxial growth of the single crystal silicon layer 3 alternately multiple times on a silicon wafer prepared with reference to Patent Document 3, it was newly discovered that when the formation conditions of the oxygen atomic layer 2 and the epitaxial growth conditions are changed, multiple oxygen atomic layers 2 are formed as intended in some cases, but only a single oxygen atomic layer 2 is formed in other cases. Therefore, when forming multiple oxygen atomic layers 2, it is preferable to use manufacturing conditions that ensure the formation of multiple oxygen atomic layers 2 as intended.

[0071] Here, in order to reliably form multiple layers, when S3 (pure water cleaning step) and S4 (epitaxial growth step) are alternately performed multiple times, it is preferable to adjust the conditions of S3 and / or S4 so that the amount of silicon film formed in S4 (also referred to as silicon film thickness) is greater than the amount of silicon etched in S3.

[0072] Silicon surfaces that are exposed bare after cleaning with hydrofluoric acid or after epitaxial growth are slightly etched in pure water. Figure 5 shows the etching rate of silicon at each cleaning temperature. It can be seen that the higher the temperature, the more the etching reaction is promoted and the higher the etching rate.

[0073] That is, if the single crystal silicon layer 3 formed in S4 is completely removed by the pure water washing in S3, the oxygen atomic layer 2 will have a single layer structure instead of multiple layers. In such a case, even if a cycle process of repeating S3 to S4 or S2 to S4 is performed with the aim of forming multiple layers, only a single layer structure is formed, and multiple oxygen atomic layers 2 cannot be formed.

[0074] More specifically, the case where the cleaning temperature in S3 is 80° C. will be described as an example. The etching rate of silicon in pure water at a cleaning temperature of 80° C. is about 5.31 Å / min. The film formation rate of silicon in S4 is 10.9 Å / sec at a processing temperature of 700° C.

[0075] Here, if the cleaning conditions for S3 are 10 minutes of cleaning with 80°C pure water, the etching amount will be 53.1 Å. In Figure 6, the relationship between the film formation time and the silicon film formation amount (thickness) is shown by a solid line, and the Si etching amount is shown by a dotted line. In other words, in S4, it is necessary to form a silicon layer thicker than the 53.1 Å shown by the dotted line.

[0076] For example, when the deposition time of S4 is 2 seconds, the thickness of the single crystal silicon layer 3 is 21.8 Å, which is smaller than the etching amount of S3 of 53.1 Å, and therefore the single crystal silicon layer 3 is completely removed. On the other hand, when the deposition time is 10 seconds, the silicon layer thickness is 109 Å, which is larger than the etching amount of S3 of 53.1 Å, and therefore the silicon layer can remain with a thickness of about 55.9 Å.

[0077] FIG. 7(a) shows the oxygen concentration profile of the SIMS under the following conditions: the S3 cleaning condition in the first cycle (hereinafter sometimes referred to as the S3 condition) is cleaning with pure water at 80° C. for 10 minutes, the S4 film deposition condition (hereinafter sometimes referred to as the S4 condition) is film deposition at 700° C. for 2 seconds, the S3 cleaning condition in the second cycle is cleaning with pure water at 80° C. for 10 minutes, and the S4 film deposition condition is film deposition at 700° C. for 80 seconds.

[0078] Figure 7(b) shows the SIMS oxygen concentration profile for the first cycle, S3 condition: 10 minutes of cleaning with pure water at 80° C., S4 deposition condition: 10 seconds of deposition at 700° C., S3 condition for the second cycle: 10 minutes of cleaning with pure water at 80° C., S4 deposition condition: 80 seconds of deposition at 700° C. The only difference between Figure 7(a) and Figure 7(b) is the deposition time for the first cycle, S4 condition. The first cycle here refers to a case where S3 and S4 are performed at least once each, and the second cycle refers to a case where S3 and S4 are performed at least once each after the first cycle.

[0079] As shown in FIG. 7, at the deposition time level of 2 seconds (a), there is one steep oxygen peak indicating the presence of oxygen atomic layer 2, whereas at the deposition time level of 10 seconds (b), there are two steep oxygen peaks.

[0080] That is, as shown in Fig. 7(a), the single crystal silicon layer 3 formed in the first cycle S4 for 2 seconds is completely etched and removed by the pure water cleaning in the second cycle. If the single crystal silicon layer 3 formed in the first cycle S4 is completely removed by the pure water cleaning in the second cycle S3, a single layer structure will result instead of multiple layers. In such a case, even if a cycle process of repeating S3-S4 or S2-S4 is performed with the aim of forming multiple layers, only a single layer structure will be formed, and multiple oxygen atomic layers 2 cannot be formed.

[0081] Next, as an example, Figure 8 shows cross-sectional TEM images of epitaxial wafers processed under the following conditions: in the first cycle, S3 condition is cleaning with pure water at 80°C for 10 minutes, and S4 condition is film formation at 700°C for 10 seconds; in the second cycle, S3 condition is cleaning with pure water at 80°C for 10 minutes, and S4 condition is film formation at 700°C for 10 seconds; and in the third cycle, S3 condition is cleaning with pure water at 80°C for 10 minutes, and S4 condition is film formation at 700°C for 100 seconds.

[0082] Here, the etching amount when washed with pure water at 80° C. for 10 minutes under the S3 condition is 53.1 Å (5.31 nm), the film thickness of the single crystal silicon layer 3 when formed for 10 seconds at 700° C. under the S4 condition is 109 Å (10.9 nm), and the film thickness of the single crystal silicon layer 3 when formed for 100 seconds at 700° C. under the S4 condition is 1090 Å (109 nm).

[0083] From this, it was calculated that the distance between the first and second oxygen atomic layers 2 was 55.9 Å (5.59 nm), the distance between the second and third layers was 55.9 Å (5.59 nm), and the film thickness of the single crystal silicon layer 3 immediately above the third δ-doped layer was 1090 Å (109 nm).

[0084] The cross-sectional TEM image confirmed the contrast change caused by the three oxygen atomic layers 2 as expected. Furthermore, since the contrast of the silicon single crystal wafer 1 and the Si deposition layer is equivalent, it can also be seen that the silicon layer is a single crystal silicon layer 3.

[0085] In addition, the distance between the oxygen atomic layers 2 between the first and second layers, measured from the images, was 59 Å (5.9 nm), the distance between the second and third layers was 55 Å (5.5 nm), and the silicon layer directly above the third δ-doped layer was 1100 Å (110 nm), which roughly agreed with the calculated results.

[0086] In this way, by performing the process multiple times so that the amount of silicon film formed in the epitaxial growth step S4 is greater than the amount of silicon etched in the pure water cleaning step S3, it is possible to reliably form multiple oxygen atomic layers 2. EXAMPLES

[0087] The present invention will be specifically described below with reference to examples, but the present invention is not limited thereto.

[0088] (Reference example 1) First, we prepared a silicon single crystal wafer 1 with a diameter of 300 mm, crystal plane orientation (100), p-type conductivity, and resistivity of 10 Ωcm as S1 in Figure 3, and an SOI (Silicon on Insulator) wafer for evaluating the Si etching rate. When the film thickness of the SOI wafer was evaluated using a spectroscopic ellipsometer, the silicon layer was approximately 55 nm and the SiO2 layer was approximately 80 nm.

[0089] Next, the prepared silicon wafers and SOI wafers were cleaned using a batch type cleaning machine. First, they were cleaned for 3 minutes in a HF cleaning solution with a concentration of 5.0 wt% at 25°C (S2 in Fig. 3) to remove the native oxide film, and then they were cleaned in pure water containing dissolved oxygen (S3 in Fig. 3).

[0090] The dissolved oxygen concentration was 8.2 ppm at 25° C. In order to adjust the oxygen concentration of the oxygen atomic layer 2 to be formed, cleaning was performed at different cleaning temperatures of 25, 50, and 80° C. and cleaning times of 3, 10, and 20 minutes.

[0091] At this time, the SOI wafers were cleaned in the same way at cleaning temperatures of 25, 50, and 80°C for a cleaning time of 20 minutes. The cleaned SOI wafers were evaluated using a spectroscopic ellipsometer, and the Si etching rate at each temperature was calculated from the amount of silicon layer reduction before and after cleaning. The results were 0.25 Å / min at 25°C, 1.05 Å / min at 50°C, and 5.31 Å / min at 80°C.

[0092] Next, in S4 of FIG. 3, epitaxial growth of the single crystal silicon layer 3 was performed in a single-wafer epitaxial furnace without hydrogen baking. The growth temperature was 700° C. and the growth time was 80 seconds. After that, the planar concentration of oxygen in the oxygen atomic layer 2 was measured by SIMS, and the number of stacked oxygen atomic layers 2 was determined from the number of steep oxygen peaks. The results are shown in Table 1.

[0093] [Table 1]

[0094] One steep oxygen peak was observed in all nine levels, and it was determined that the epitaxial wafer had one oxygen atomic layer 2 formed, as shown in Table 1. The planar concentration of the oxygen atomic layer 2 increased the higher the temperature and the longer the pure water cleaning conditions. This shows that the oxygen concentration can be controlled by adjusting the pure water cleaning conditions. In addition, the growth rate was calculated to be 10.9 Å / sec from cross-sectional TEM (Transmission Electron Microscopy) observations.

[0095] (Reference example 2) The same silicon single crystal wafer 1 as in Reference Example 1 was prepared. Here, by performing two cycles of S3 and S4, an epitaxial wafer was manufactured aiming for a two-layer structure (single crystal silicon layer 3 / oxygen atomic layer 2 / single crystal silicon layer 3 / oxygen atomic layer 2 / silicon single crystal wafer 1). The pure water cleaning conditions in the first and second cycles were 10 minutes of cleaning with 80°C pure water.

[0096] From Reference Example 1, the Si etching rate at 80° C. was 5.31 Å / min, and the Si etching amount for a cleaning time of 10 minutes was estimated to be 53.1 Å. From Reference Example 1, the film formation rate was 10.9 Å / sec.

[0097] In order to make the amount of silicon film formed in the first cycle greater than the Si etching amount of 53.1 Å, the film formation times were set to 5, 10, 30, 60, and 80 seconds. The film formation times in the second cycle were all set to 80 seconds. The oxygen concentration was evaluated by SIMS in the same manner as in Reference Example 1, and the lamination was judged. The results are shown in Table 2.

[0098] [Table 2]

[0099] Two steep oxygen peaks were observed when the deposition time was 10, 30, 60, and 80 seconds, and it was determined that a two-layer structure had been formed, as shown in Table 2. On the other hand, when the deposition time was 5 seconds, only one peak was observed. Therefore, a cross-sectional TEM image of the epitaxial wafer with a deposition time of 5 seconds was obtained, and the image shown in Figure 9 was obtained.

[0100] Although the contrast is low in Figure 9, two oxygen atomic layers 2 were formed. It was thought that the SIMS depth resolution was insufficient due to the very narrow thickness interval, and the two peaks were observed as one. Therefore, it was determined that a two-layer structure was formed even when the film formation time was 5 seconds.

[0101] Since the amount of silicon film formed in the first cycle is greater than the amount of Si etched (53.1 Å) in the pure water cleaning in the second cycle, it is believed that an epitaxial wafer having an oxygen atomic layer 2 with a two-layer structure was manufactured as intended.

[0102] (Reference example 3) The same silicon single crystal wafer 1 as in Reference Example 1 was prepared. Here, three cycles of S3 and S4 were performed to manufacture an epitaxial wafer aiming for a three-layer structure (single crystal silicon layer 3 / oxygen atomic layer 2 / single crystal silicon layer 3 / oxygen atomic layer 2 / single crystal silicon layer 3 / oxygen atomic layer 2 / silicon single crystal wafer 1).

[0103] The pure water cleaning conditions for the first, second, and third cycles were 10 minutes of cleaning with pure water at 80° C. From Reference Example 1, the Si etching rate at 80° C. was 5.31 Å / min, and the Si etching amount for a cleaning time of 10 minutes was estimated to be 53.1 Å.

[0104] Here, in order to increase the amount of silicon film formed in the first and second cycles beyond the Si etching amount of 53.1 Å, the following two levels of conditions were selected. Specifically, the film formation time in the first and second cycles was set to 10 seconds, and the film formation time in the third cycle was set to 100 seconds, and the film formation time in the first and second cycles was set to 30 seconds, and the film formation time in the third cycle was set to 60 seconds. The oxygen concentration was evaluated by SIMS for these two levels, and the lamination was judged. The results are shown in Table 3.

[0105] [Table 3]

[0106] Three steep oxygen peaks were observed at both levels, and it was determined that a three-layer structure had been formed, as shown in Table 3. Furthermore, cross-sectional TEM observation revealed that three oxygen atomic layers 2 had been formed.

[0107] Figure 10 shows the results when the deposition time for the first and second cycles was 30 seconds, and the deposition time for the third cycle was 60 seconds. Here, we focused on the spacing between the oxygen atomic layers 2. From a deposition rate of 10.9 Å / sec, the thickness of the single crystal silicon layer 3 with a deposition time of 30 seconds was estimated to be 327 Å. From this, the Si etching amount of 53.1 Å in the second and third cycles was subtracted to estimate the spacing between the oxygen atomic layers 2 as 274 Å (27.4 nm).

[0108] Furthermore, when the spacing between the oxygen atomic layers 2 was measured from the cross-sectional TEM image, the spacing between the first and second layers was 260 Å (26 nm), and the spacing between the second and third layers was 250 Å (25 nm), which agreed well with the estimated calculated values. This is believed to be because the amount of silicon film formed in the first and second cycles was greater than the amount of Si etching (53.1 Å) in the pure water cleaning in the second and third cycles, making it possible to manufacture an epitaxial wafer with the targeted three-layer structure of oxygen atomic layers 2.

[0109] (Reference example 4) The same silicon single crystal wafer 1 as in Reference Example 1 was prepared. Here, epitaxial wafers were produced aiming for a two-layer structure (single crystal silicon layer 3 / oxygen atomic layer 2 / single crystal silicon layer 3 / oxygen atomic layer 2 / silicon single crystal wafer 1) when the pure water cleaning conditions (pure water temperature) were changed to 25, 50, and 80°C.

[0110] Since the cleaning temperature was different, the amount of silicon etched in the second cycle of pure water cleaning was calculated from the etching rate and cleaning time at each temperature. Next, the deposition time was determined so that the amount of silicon deposited in the first cycle would be greater than the calculated amount of etching. The conditions and results are shown in Table 4.

[0111] [Table 4]

[0112] In the SIMS evaluation, two steep oxygen peaks were observed at all levels, and the two-layer structure was also confirmed in the cross-sectional TEM images. From the above, it was found that in the present invention, even if the pure water cleaning conditions were changed, the silicon etching amount under each condition was calculated, and the film formation amount was increased beyond the calculated silicon etching amount, thereby enabling the formation of multiple oxygen atomic layers 2 as intended.

[0113] Example 1 In order to improve the surface roughness after film formation, a wafer of level "1" in Reference Example 3 was prepared and subjected to CMP processing (CMP process) using a polishing pad made of urethane suede and polishing slurry of an ammonia-based alkaline aqueous solution (pH 10.5) containing water-soluble polymer and 0.05 wt% silica-based abrasive grains as S5 in Fig. 3. Since the film thickness of the outermost single crystal silicon layer 3 was about 100 nm, CMP processing was performed with a removal allowance of about 30 nm so that the outermost single crystal silicon layer 3 remained.

[0114] After CMP processing, the haze, an index of surface roughness, was evaluated using a KLA particle counter SP5. The higher the haze, the rougher the surface. Before CMP processing, the haze was 42 ppm, whereas after CMP processing, it was greatly improved to 0.045 ppm. Thus, it was found that CMP processing can improve surface quality.

[0115] (Reference example 5) The same silicon single crystal wafer 1 as in Reference Example 1 was prepared. Here, an epitaxial wafer was manufactured aiming for a two-layer structure (single crystal silicon layer 3 / oxygen atomic layer 2 / single crystal silicon layer 3 / oxygen atomic layer 2 / silicon single crystal wafer 1). Two cycles of processing were performed under the conditions in Table 5.

[0116] [Table 5]

[0117] Only one steep oxygen peak was observed in the SIMS evaluation. Also, only one oxygen atomic layer 2 was observed in the cross-sectional TEM observation. In other words, although the aim was to produce a two-layer structure, the epitaxial wafer in question was a single-layer structure.

[0118] Comparing the amount of silicon etched in the second cycle of pure water cleaning with the amount of silicon deposition in the first cycle shown in Table 5, it can be seen that the amount of silicon etched is greater for all levels. Therefore, it is believed that the silicon deposition layer was completely etched away, and the two-layer structure was not formed.

[0119] As described above, the epitaxial wafer manufacturing method according to the present invention makes it possible to control the oxygen concentration in the oxygen atomic layer 2 and improve surface defects and roughness. Moreover, by controlling the conditions of the pure water cleaning step and the epitaxial growth step, it is possible to reliably manufacture the epitaxial wafer 10B having multiple oxygen atomic layers 2.

[0120] The present specification includes the following aspects. [1]: A method for producing an epitaxial wafer comprising a silicon single crystal wafer and a single crystal silicon layer epitaxially grown on the 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 with hydrofluoric acid; a pure water cleaning step of cleaning the surface of the silicon single crystal wafer from which the native oxide film has been removed with pure water to form an oxygen atomic layer on the surface; 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; a CMP process for performing CMP processing on the surface of the single crystal silicon layer grown in the epitaxial growth process; Including, In the pure water washing step, the planar oxygen concentration of the oxygen atomic layer is set to 1×10 15 atoms / cm 21. A method for producing an epitaxial wafer, comprising the steps of: [2]: In the pure water cleaning process, the pure water temperature and cleaning time are adjusted to make the planar oxygen concentration of the oxygen atomic layer 1×10 14 ~1×10 15 atoms / cm 2 The method for producing an epitaxial wafer according to the above [1], characterized in that the thickness of the epitaxial wafer is controlled within the range of [3]: A method for producing an epitaxial wafer according to the above [1] or [2], characterized in that in the epitaxial growth step, epitaxial growth is carried out at a temperature of 450°C or higher and 800°C or lower. [4]: The method for producing an epitaxial wafer according to any one of [1] to [3] above, characterized in that at least the pure water cleaning step and the epitaxial growth step are alternately performed a plurality of times. [5]: The method for producing an epitaxial wafer according to claim 4, characterized in that, when the pure water cleaning step and the epitaxial growth step are alternately performed a plurality of times, conditions of the pure water cleaning step and / or the epitaxial growth step are adjusted so that an amount of silicon film formed in the epitaxial growth step is greater than an amount of silicon etched in the pure water cleaning step.

[0121] The present invention is not limited to the above-described embodiment. The above-described embodiment is merely an example, and anything that has substantially the same configuration as the technical idea described in the claims of the present invention and exhibits similar effects is included in the technical scope of the present invention. [Explanation of symbols]

[0122] 1...silicon single crystal wafer, 2...oxygen atomic layer, 3...single crystal silicon layer, 10A...epitaxial wafer, 10B...epitaxial wafer.

Claims

1. A method for producing an epitaxial wafer comprising a silicon single crystal wafer and a single crystal silicon layer epitaxially grown on the 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 with hydrofluoric acid; a pure water cleaning step of cleaning the surface of the silicon single crystal wafer from which the native oxide film has been removed with pure water to form an oxygen atomic layer on the surface; 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; a CMP process for performing CMP processing on the surface of the single crystal silicon layer grown in the epitaxial growth process; Including, In the pure water washing step, the planar concentration of oxygen in the oxygen atomic layer is set to 1×10 １５ atoms / cm ２ 1. A method for producing an epitaxial wafer, comprising the steps of:

2. In the pure water washing step, the pure water temperature and washing time are adjusted to make the planar oxygen concentration of the oxygen atomic layer 1×10 １４ ~1×10 １５ atoms / cm ２ 2. The method for producing an epitaxial wafer according to claim 1, wherein the temperature is controlled within a range of

3. 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 more and 800° C. or less.

4. 4. The method for producing an epitaxial wafer according to claim 1, wherein at least the pure water cleaning step and the epitaxial growth step are alternately performed a plurality of times.

5. 5. The method for producing an epitaxial wafer according to claim 4, wherein, when the pure water cleaning step and the epitaxial growth step are alternately performed a plurality of times, conditions of the pure water cleaning step and / or the epitaxial growth step are adjusted so that an amount of silicon film formed in the epitaxial growth step is greater than an amount of silicon etched in the pure water cleaning step.

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