Method for determining cleaning conditions for semiconductor wafers and method for cleaning semiconductor wafers

Abstract

Provided is a method for determining a semiconductor wafer-cleaning condition that allows the thickness of a thermal oxide film to be well controlled. This method for determining a semiconductor wafer-cleaning condition comprises: a step for determining a cleaning correlation between the thicknesses and surface morphologies of chemical oxide films formed on the respective surfaces of a plurality of semiconductor wafers after cleaning processes and cleaning conditions; a step for determining a heat treatment correlation between increases in thickness of thermal oxide films formed on the respective surfaces of the plurality of semiconductor wafers after heat treatment processes under one or more different heat treatment conditions and the thicknesses and surface morphologies of the chemical oxide films; a step for determining a heat treatment condition for a heat treatment process and determining a target thickness of a thermal oxide film to be formed on the surface of a semiconductor wafer in a heat treatment process under the determined heat treatment condition; and a step for determining a cleaning condition under which the thickness of a thermal oxide film to be formed on the surface of a semiconductor wafer in a heat treatment process under the determined heat treatment condition becomes the target thickness.

Description

Technical Field

[0001] The present invention relates to a method for determining cleaning conditions of a semiconductor wafer and a method for cleaning a semiconductor wafer.

Background Art

[0002] In a device formation process, a semiconductor wafer, which is a substrate of a semiconductor device, is heat-treated to form a thermal oxide film on the surface of the semiconductor wafer. The thickness of the formed thermal oxide film affects the characteristics of the semiconductor device formed on the semiconductor wafer, and the variation in the thickness of the thermal oxide film affects the yield. Therefore, it is required to form the thermal oxide film with a target thickness without variation.

[0003] In Patent Document 1, based on the finding that the composition of the chemical oxide film formed on the surface of the semiconductor substrate by cleaning has a great influence on the thermal oxidation treatment, the correlation between the composition of the chemical oxide film and the thickness of the thermal oxide film is obtained, the composition of the chemical oxide film is determined such that the thickness of the formed thermal oxide film becomes a predetermined thickness, and the cleaning conditions for obtaining the composition of the chemical oxide film are determined to clean the semiconductor wafer, whereby a technique for forming the thermal oxide film with the predetermined thickness with good reproducibility is described.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, in order to clean the device in a way that yields the chemical oxide film structure determined by the technology described in Patent Document 1, significant changes to the cleaning conditions are necessary. Furthermore, other surface quality issues besides the thickness of the chemical oxide film (e.g., particle adhesion) after cleaning may deteriorate, potentially reducing the yield of the device. Therefore, there has been a need for a method that can effectively control the thickness of the thermal oxide film without changing the structure of the chemical oxide film.

[0006] This invention has been made in view of the above problems, and its objective is to propose a method for determining the cleaning conditions of a semiconductor wafer that can effectively control the thickness of the thermal oxide film. [Means for solving the problem]

[0007] The present invention, which solves the above problems, is as follows. [1] A method for determining the cleaning conditions of a semiconductor wafer, A cleaning correlation acquisition step is performed to obtain a cleaning correlation, which is the correlation between the thickness and surface state of the chemical oxide film formed on the surface of each of the semiconductor wafers and the cleaning conditions, and to prepare multiple semiconductor wafers that have undergone cleaning processes under multiple cleaning conditions. For each of the one or more different heat treatment conditions in the heat treatment process, a plurality of semiconductor wafers are prepared that have undergone the heat treatment process following the cleaning process, and a heat treatment correlation acquisition process is performed to determine the heat treatment correlation relationship, which is the correlation between the amount of increase in the thickness of the oxide film after the heat treatment process, the thickness of the chemical oxide film, and the surface state of the thermal oxide film formed on the surface of each of the plurality of semiconductor wafers. A heat treatment condition determination step, which determines the heat treatment conditions in the heat treatment step and the target thickness of the thermal oxide film formed on the surface of the semiconductor wafer in the heat treatment step under the determined heat treatment conditions, A cleaning condition determination step, based on the heat treatment correlation and the cleaning correlation, determines cleaning conditions such that the thickness of the thermal oxide film formed on the surface of the semiconductor wafer in the heat treatment step under the determined heat treatment conditions becomes the target thickness. A method for determining the cleaning conditions of a semiconductor wafer, including [the specified element].

[0008] [2] The method for determining the cleaning conditions of a semiconductor wafer according to [1], wherein the surface condition is indicated by the power spectral density of the surface roughness measured by an atomic force microscope.

[0009] [3] The heat treatment correlation is expressed by the following formula (1), where Y is the increase in the thickness of the oxide film after the heat treatment process, X1 is the thickness of the chemical oxide film, X2 is the surface state, and A, B and C are constants, in the method for determining the cleaning conditions of a semiconductor wafer as described in [1] or [2] above. Y = AX₁ + BX₂ + C (1)

[0010] [4] For each of the one or more heat treatment conditions, the constants A, B and C are determined, A method for determining the cleaning conditions of a semiconductor wafer according to [3], wherein the constants A, B, and C are determined according to the heat treatment conditions determined in the heat treatment condition determination step.

[0011] [5] The cleaning step includes at least an ozone treatment step as the final step of the cleaning step, in which only ozone-dissolved water is supplied to the semiconductor wafer as a chemical solution. A method for determining the cleaning conditions for a semiconductor wafer according to any one of the above [1] to [4], wherein the time of the final step differs in the above plurality of cleaning conditions.

[0012] [6] The cleaning step is A hydrofluoric acid treatment process in which only hydrofluoric acid solution is supplied to the semiconductor substrate as a chemical, A mixing process in which hydrofluoric acid water and ozone-dissolved water are simultaneously supplied to a semiconductor wafer as chemical solutions, An ozone treatment process in which only ozone-dissolved water is supplied to the semiconductor wafer as a chemical solution, Includes, A method for determining the cleaning conditions of a semiconductor wafer according to any one of the above [1] to [4], wherein the time of the mixing process differs in the above plurality of cleaning conditions.

[0013] [7] The cleaning step is A hydrofluoric acid treatment step of supplying only hydrofluoric acid water as a chemical solution to a semiconductor substrate, An ozone treatment step of supplying only ozone-dissolved water as a chemical solution to a semiconductor wafer, including The method for determining the cleaning conditions of a semiconductor wafer according to any one of the above [1] to [4], wherein the concentration of the ozone-dissolved water is different under the plurality of cleaning conditions.

[0014] [8] The cleaning step is A hydrofluoric acid treatment step of supplying only hydrofluoric acid water as a chemical solution to a semiconductor substrate, An ozone treatment step of supplying only ozone-dissolved water as a chemical solution to a semiconductor wafer, including The method for determining the cleaning conditions of a semiconductor wafer according to any one of the above [1] to [4], wherein the time of the final hydrofluoric acid treatment step is different under the plurality of cleaning conditions.

[0015] [9] The cleaning step is A hydrofluoric acid treatment step of supplying only hydrofluoric acid water as a chemical solution to a semiconductor substrate, An ozone treatment step of supplying only ozone-dissolved water as a chemical solution to a semiconductor wafer, including The method for determining the cleaning conditions of a semiconductor wafer according to any one of the above [1] to [4], wherein the rotation speed of the semiconductor substrate in the final hydrofluoric acid treatment step is different under the plurality of cleaning conditions.

[0016]

[10] A method for cleaning a semiconductor wafer, wherein the semiconductor wafer is cleaned under the cleaning conditions determined by the method for determining the cleaning conditions of a semiconductor wafer according to any one of the above [1] to [9].

[0017]

[11] The method for cleaning a semiconductor wafer according to the above

[10] , wherein the semiconductor wafer is a silicon wafer. [Advantages of the Invention]

[0018] According to the present invention, the thickness of the thermal oxide film can be controlled effectively. This improves the yield of devices, and consequently, improves production efficiency and reduces waste. [Brief explanation of the drawing]

[0019] [Figure 1] This diagram illustrates the growth behavior of thermal oxide films. [Figure 2] This diagram illustrates the influence of the surface state of a chemical oxide film on the formation of a thermal oxide film. (a) shows the case where the surface roughness is small, and (b) shows the case where the surface roughness is large. [Figure 3] This is a flowchart of the method for determining the cleaning conditions of a semiconductor wafer according to the present invention. [Figure 4] (a) The measurement locations of the power spectral density by AFM, and (b) An example of the measured power spectral density. [Figure 5] (a) This figure shows the configuration of the cleaning process, and (b) this figure shows the relationship between the time of the final ozone treatment process and the thickness of the chemical oxide film. [Figure 6] This diagram shows the ratio of the mixing process time to the total washing process time, with (a) being 0%, (b) 25%, (c) 50%, and (d) 100%. [Figure 7] This figure shows the relationship between the proportion of the mixing process and the proportion of the power spectral density. [Figure 8] (a) This figure shows the composition of the washing process, and (b) this figure shows the relationship between the time of the final hydrofluoric acid treatment process and the power spectral density ratio. [Figure 9] (a) This figure shows the configuration of the cleaning process, and (b) this figure shows the relationship between the concentration of ozone-dissolved water and the power spectral density ratio. [Figure 10] This figure shows the relationship between the predicted and measured increase in the thickness of the oxide film after the heat treatment process. [Figure 11] (a) A figure showing the thickness of the thermal oxide film for each of the three devices compared to the conventional example, and (b) A figure showing the thickness of the thermal oxide film compared to the conventional example and Invention Example 2. [Modes for carrying out the invention]

[0020] (Method for determining semiconductor wafer cleaning conditions) Embodiments of the present invention will be described below with reference to the drawings. The method for determining the cleaning conditions of a semiconductor wafer according to the present invention includes: a cleaning correlation acquisition step of preparing multiple semiconductor wafers that have undergone cleaning steps under multiple cleaning conditions, and determining a cleaning correlation relationship, which is the correlation between the thickness and surface state of the chemical oxide film formed on the surface of each of the multiple semiconductor wafers and the cleaning conditions; a heat treatment correlation acquisition step of preparing multiple semiconductor wafers that have undergone a heat treatment step following the cleaning step for each of one or more different heat treatment conditions in the heat treatment step, and determining a heat treatment correlation relationship, which is the correlation between the increase in the thickness of the oxide film after the heat treatment step and the thickness and surface state of the chemical oxide film for the thermal oxide film formed on the surface of each of the multiple semiconductor wafers; a heat treatment condition determination step of determining the heat treatment conditions in the heat treatment step and determining the target thickness of the thermal oxide film formed on the surface of the semiconductor wafer in the heat treatment step under the determined heat treatment conditions; and a cleaning condition determination step of determining the cleaning conditions such that the thickness of the thermal oxide film formed on the surface of the semiconductor wafer in the heat treatment step under the determined heat treatment conditions becomes the target thickness, based on the heat treatment correlation relationship and the cleaning correlation relationship.

[0021] The inventors of the present invention have diligently studied ways to better control the thickness of the thermal oxide film formed on the surface of a semiconductor wafer during the heat treatment process. The thermal oxide film is formed when oxygen diffuses from the surface of a chemical oxide film (native oxide film) already formed in a preceding process such as a cleaning process into the interior of the semiconductor wafer, and a chemical reaction occurs between the oxygen and the constituent elements of the semiconductor wafer at the interface between the chemical oxide film and the semiconductor wafer.

[0022] As shown in Figure 1, it is known that the growth behavior of oxide films differs between regions with small thickness (region 1 in the figure) and regions with large thickness (region 2 in the figure). Conventionally, according to the Geel-Grove equation, it was thought that in region 1, where the oxide film thickness is small, the reaction between the constituent elements of the semiconductor wafer and oxygen limits the rate of oxide film formation, while in region 2, where the oxide film thickness is large, the diffusion of oxygen limits the rate of oxide film formation. However, in recent years, it has been reported that even in region 1, the diffusion of oxygen limits the rate of oxide film formation (see, for example, T. Watanabe, K. Tatsumura, I. Ohdomari, Phys. Rev. Lett., 96, 196102 (2006)). The thickness of the thermal oxide film formed in the device fabrication process is about 30-50 Å, which belongs to region 1. Therefore, in order to control the thickness of the thermal oxide film to the target thickness, it is necessary to control the diffusion of oxygen in the oxide film.

[0023] In the process of diligently investigating ways to control the thickness of the thermal oxide film formed in the heat treatment process by controlling the diffusion of oxygen in the oxide film, the inventors found a good correlation between the thickness and surface state of the chemical oxide film formed on the surface of the semiconductor wafer in the cleaning process and the amount of increase in the thickness of the thermal oxide film formed on the surface of the semiconductor wafer in the heat treatment process.

[0024] In other words, when the thickness of the chemical oxide film is large, it takes time for oxygen taken in from the surface of the chemical oxide film to reach the interface between the chemical oxide film and the semiconductor wafer. Therefore, when the thickness of the chemical oxide film is large, it is thought that it takes longer for oxygen to reach the interface between the chemical oxide film and the semiconductor wafer. On the other hand, regarding the surface state of the chemical oxide film, as shown in Figure 2(a), for example, when the surface roughness is small, the specific surface area of ​​the chemical oxide film is small, and it is thought that oxygen is not easily taken in from the surface of the chemical oxide film. In contrast, as shown in Figure 2(b), when the surface roughness of the chemical oxide film is large, the specific surface area of ​​the chemical oxide film is large, and it is thought that oxygen is easily taken in from the surface of the chemical oxide film.

[0025] Based on the above findings, the present inventors have determined the correlation between the thickness and surface state of the chemical oxide film formed on the surface of the semiconductor wafer during the cleaning process and the cleaning conditions (cleaning correlation), and the correlation between the thickness and surface state of the chemical oxide film and one or more heat treatment conditions for the thermal oxide film formed on the surface of the semiconductor wafer during the heat treatment process and the amount of increase in the thickness of the oxide film after the heat treatment process (heat treatment correlation). By determining the heat treatment conditions and the target thickness of the thermal oxide film formed during the heat treatment process under those heat treatment conditions, the inventors have found that they can determine cleaning conditions that can effectively control the thickness of the thermal oxide film formed during the heat treatment process, thus completing the present invention. The following describes each step.

[0026] <Process for obtaining washing correlation> Figure 3 shows a flowchart of the method for determining the cleaning conditions for semiconductor wafers according to the present invention. First, multiple semiconductor wafers are prepared that have undergone cleaning processes under multiple cleaning conditions, and the correlation (cleaning correlation) between the thickness and surface state of the chemical oxide film formed on the surface of each of the multiple semiconductor wafers and the above cleaning conditions is determined.

[0027] The semiconductor wafer used to determine the cleaning correlation is not particularly limited, and bulk single-crystal wafers made of silicon, germanium, or compound semiconductors (GaAs, GaN, SiC) can be used. Such semiconductor wafers can be obtained by slicing single-crystal ingots of silicon, etc., grown by the Czochralski (CZ) method or the Floating Zone (FZ) method, using a wire saw or the like. Furthermore, carbon and / or nitrogen may be added to the semiconductor wafer to obtain gettering ability for heavy metals. In addition, an arbitrary dopant may be added to the semiconductor wafer at a predetermined concentration to create a so-called n + type or p + type, or n - type or p - It may also be used as a semiconductor wafer of a certain type.

[0028] Furthermore, as the semiconductor wafer, a semiconductor epitaxial wafer may be used, in which a semiconductor epitaxial layer is formed on the surface of a bulk semiconductor wafer. As such a semiconductor epitaxial wafer, for example, an epitaxial silicon wafer can be used, in which a silicon epitaxial layer is formed on the surface of a bulk single-crystal silicon wafer. The silicon epitaxial layer can be formed under general conditions by the CVD method.

[0029] The thickness of a chemical oxide film can be measured, for example, by ellipsometry in a region on the surface of a semiconductor wafer. When measuring the thickness of a chemical oxide film by ellipsometry, the thickness can be measured at five points on the surface of the semiconductor wafer, for example, at the center (5), outer periphery (1), (2), and 1 / 2 of the radius R (3), (4) as shown in Figure 4(a) (for example, a measurement area of ​​1 μm), and the average value of these measurements can be taken as the thickness of the chemical oxide film.

[0030] The surface condition of a chemical oxide film can be, for example, determined by its surface roughness. As illustrated in Figure 4(b), the surface condition of a chemical oxide film can be indicated by, for example, the power spectral density of the surface roughness measured by an atomic force microscope (AFM). As a result of our investigations, we have found that there is a good single-phase relationship between the integral value of the power spectral density in a relatively small spatial wavelength band, for example, in the region of 3.9 nm to 10 nm, and the thickness of the thermal oxide film formed in the heat treatment process. Therefore, when using the power spectral density of the surface roughness measured by AFM as an indicator of the surface condition of a chemical oxide film, it is preferable to use the integral value of the power spectral density in a relatively small spatial wavelength band.

[0031] The lower limit of the spatial wavelength band described above is preferably measured from a smaller wavelength, but is preferably set to, for example, 3.9 nm, more preferably to 1 nm, and even more preferably to a value greater than 0 nm and less than 1 nm. On the other hand, the upper limit of the spatial wavelength band is preferably set to 10 nm.

[0032] Furthermore, the surface condition of a chemical oxide film can also be indicated by the ratio of the integral value in a relatively small spatial wavelength band (e.g., 3.9 nm to 10 nm) to the integral value in the entire region (e.g., 3.9 nm to 100 nm) of the power spectral density of the surface roughness measured by AFM (power spectral density ratio).

[0033] Furthermore, the surface condition of a chemical oxide film can also be assessed using Rq (mean square roughness) measured by AFM, with the spatial wavelength range restricted. For example, an image can be output with only the components in a wavelength range such as 25-80 nm extracted, and Rq can be calculated for this image. The calculated Rq can then be used as an indicator.

[0034] The cleaning process performed on a semiconductor wafer can be a cleaning process in the semiconductor wafer manufacturing process. The cleaning process in the semiconductor wafer manufacturing process may include a hydrofluoric acid treatment process in which only hydrofluoric acid water is supplied to the semiconductor wafer as the chemical solution. The cleaning process may also include an ozone treatment process in which only ozone-dissolved water is supplied to the semiconductor wafer as the chemical solution. Furthermore, the cleaning process may include a hydrofluoric acid treatment process and an ozone treatment process, and these processes may be configured to be performed alternately. Moreover, the cleaning process may include a hydrofluoric acid treatment process, a mixing process in which hydrofluoric acid water and ozone-dissolved water are simultaneously supplied to the semiconductor wafer, and an ozone treatment process, and these processes may be configured to be performed sequentially.

[0035] Examples of cleaning conditions in the cleaning process include the time of the final step (when the ozone treatment step is the final step of the cleaning process), the concentration of hydrofluoric acid water, the processing time of the hydrofluoric acid treatment step, the rotation speed of the semiconductor wafer in the hydrofluoric acid treatment step, the concentration of ozone-dissolved water, and the time of the mixing process. As shown in the examples described later, when the cleaning process includes the ozone treatment step as the final step, the thickness of the chemical oxide film formed on the surface of the semiconductor wafer during the cleaning process can be adjusted by changing the time of the final step.

[0036] Furthermore, as shown in the embodiments described later, if the cleaning process includes a hydrofluoric acid treatment process, a mixing process, and an ozone treatment process, and these processes are performed sequentially, the surface state of the chemical oxide film formed on the surface of the semiconductor wafer after cleaning can be adjusted by changing the time of the mixing process (or the ratio of the time of the mixing process to the total cleaning process time).

[0037] Furthermore, as shown in the embodiments described later, if the cleaning process includes a hydrofluoric acid treatment process and an ozone treatment process, and these processes are repeated until the final step is the ozone treatment process, the surface state of the chemical oxide film formed on the surface of the semiconductor wafer after cleaning can be adjusted by changing the time of the final hydrofluoric acid treatment process.

[0038] Furthermore, as shown in the embodiments described later, if the cleaning process includes a hydrofluoric acid treatment process and an ozone treatment process, and these processes are repeated until the final step is an ozone treatment process, the surface state of the chemical oxide film formed on the surface of the semiconductor wafer after cleaning can be adjusted by changing the rotation speed of the semiconductor wafer in the final hydrofluoric acid treatment process.

[0039] Furthermore, as shown in the examples described later, if the cleaning process includes an ozone treatment process, the surface condition of the chemical oxide film can also be adjusted by changing the concentration of the ozone-dissolved water. Similarly, if the cleaning process includes a hydrofluoric acid treatment process, the surface condition can also be adjusted by changing the concentration of the hydrofluoric acid solution.

[0040] Furthermore, the surface state of the chemical oxide film can be changed by combining one or three of the following: changing the time of the mixing process, changing the time of the final hydrofluoric acid treatment process, changing the rotation speed of the semiconductor wafer in the final hydrofluoric acid treatment process, changing the concentration of hydrofluoric acid water, and changing the concentration of ozone-dissolved water.

[0041] The correlation between the thickness and surface condition of the chemical oxide film and the cleaning conditions (cleaning correlation) is determined. This cleaning correlation is the relationship between the thickness and surface condition of the chemical oxide film and the cleaning conditions, and it is sufficient that the relationship is such that, once the thickness and surface condition of the chemical oxide film determined in the heat treatment condition determination process described later is determined, the cleaning conditions in the cleaning process that will result in these thicknesses and surface conditions of the chemical oxide film can be determined.

[0042] <Heat Treatment Correlation Acquisition Process> Next, for each of the one or more different heat treatment conditions in the heat treatment process, multiple semiconductor wafers are prepared that have undergone the heat treatment process following the cleaning process. For the thermal oxide film formed on the surface of each of these multiple semiconductor wafers, the heat treatment correlation is determined, which is the correlation between the increase in the thickness of the oxide film after the heat treatment process and the thickness and surface state of the chemical oxide film. Note that the "increase in the thickness of the oxide film after the heat treatment process" is the difference between the thickness of the oxide film formed in the heat treatment process (thermal oxide film) and the thickness of the oxide film formed in the cleaning process (chemical oxide film).

[0043] As described above, the inventors have found that there is a good correlation (heat treatment correlation) between the thickness and surface state of the chemical oxide film formed on the surface of the semiconductor wafer during the cleaning process and the amount of increase in the thickness of the thermal oxide film formed on the surface of the semiconductor wafer during the heat treatment process. The above heat treatment correlation can be expressed, for example, by the following equation (1), where Y is the amount of increase in the thickness of the oxide film after the heat treatment process, X1 is the thickness of the chemical oxide film, X2 is the surface state, and A, B, and C are constants. Y = AX₁ + BX₂ + C (1)

[0044] When expressing the heat treatment correlation using the above equation (1), for each of the one or more heat treatment conditions, a multiple regression analysis is performed with X1 and X2 as explanatory variables and Y as the dependent variable for various combinations of chemical oxide film thickness X1 and surface state X2 and the increase in oxide film thickness Y after the heat treatment process, and constants A, B, and C are determined. Thus, when the heat treatment conditions are determined in the heat treatment condition determination process described later, A, B, and C corresponding to the determined heat treatment conditions can be determined, and equation (1) for the above heat treatment conditions can be obtained.

[0045] Furthermore, when determining the heat treatment correlation, instead of the increase in oxide film thickness Y after the heat treatment process, the oxide film thickness Z after the heat treatment process may be used, and a correlation equation may be created between the oxide film thickness Z after the heat treatment process and the chemical oxide film thickness X1 and surface state X2. In this case, since Z = Y + X1, the oxide film thickness Z after the heat treatment process can be expressed by the following equation (2). Z = (A + 1)X 1 + BX 2 + C (2)

[0046] <Heat treatment condition determination process> Next, the heat treatment conditions for the heat treatment process are determined, and the target thickness of the thermal oxide film formed on the surface of the semiconductor wafer during the heat treatment process under the determined heat treatment conditions is also determined. The heat treatment conditions can be selected from one or more heat treatment conditions for which a heat treatment correlation was obtained in the heat treatment correlation acquisition process. By determining the heat treatment conditions for the heat treatment process, for example, the constants A, B, and C in equation (1) above can be determined, and a heat treatment correlation corresponding to the heat treatment conditions can be obtained. Furthermore, the target thickness can be selected from the thickness of the thermal oxide film used when obtaining the heat treatment correlation for the determined heat treatment conditions, or it can be determined arbitrarily.

[0047] <Process for determining cleaning conditions> Then, based on the heat treatment correlation and the cleaning correlation, cleaning conditions are determined such that the thickness of the thermal oxide film formed on the surface of the semiconductor wafer during the heat treatment process under the determined heat treatment conditions becomes the target thickness. In this cleaning condition determination process, first, the target thickness of the thermal oxide film determined in the previous step, the heat treatment condition determination step, is input into the heat treatment correlation corresponding to the heat treatment conditions determined in the previous step, the heat treatment condition determination step. This allows for the determination of multiple sets of thickness and surface state of the chemical oxide film formed in the cleaning process such that the thickness of the thermal oxide film formed in the heat treatment process becomes the target thickness. Next, one set that is easily achievable with cleaning conditions is selected from the multiple sets of thickness and surface state of the chemical oxide film. Then, by referring to the cleaning correlation, cleaning conditions are determined that allow the obtained thickness and surface state of the chemical oxide film to be achieved in the cleaning process. The cleaning conditions can be selected from multiple cleaning conditions used when determining the cleaning correlation in the cleaning correlation acquisition step. In this way, cleaning conditions can be determined such that the thickness of the thermal oxide film formed on the surface of the semiconductor wafer during the heat treatment process becomes the target thickness.

[0048] (Method for cleaning semiconductor wafers) The semiconductor wafer cleaning method according to the present invention is characterized by cleaning the semiconductor wafer under cleaning conditions determined by the semiconductor wafer cleaning condition determination method according to the present invention described above.

[0049] As described above, the semiconductor wafer cleaning method determination method according to the present invention makes it possible to determine cleaning conditions that can effectively control the thickness of the thermal oxide film formed on the surface of the semiconductor wafer during the heat treatment process. By cleaning the semiconductor wafer under the determined cleaning conditions and then heat-treating the semiconductor wafer under the heat treatment conditions determined in the heat treatment condition determination step, the thickness of the thermal oxide film formed on the surface of the semiconductor wafer can be effectively controlled, that is, the thermal oxide film can be formed with reduced variation from the target thickness.

[0050] The semiconductor wafers to be cleaned are not particularly limited and can be made of silicon, germanium, or compound semiconductors (GaAs, GaN, SiC). Among these, silicon wafers can be cleaned particularly well. [Examples]

[0051] The following describes examples of the present invention, but the present invention is not limited to these examples.

[0052] <<Relationship between the time of the final process (ozone treatment process) and the thickness of the chemical oxide film>> As shown in Figure 5(a), the cleaning process consisted of three alternating cycles: a hydrofluoric acid treatment cycle in which only hydrofluoric acid solution (concentration controlled between 1 and 3% by mass) was supplied to the silicon wafer, and an ozone treatment cycle in which only ozone-dissolved water (concentration of 25 ppm) was supplied to the silicon wafer. The final cycle was the ozone treatment cycle, and the cleaning process was performed while varying the duration of the final ozone treatment cycle. After the cleaning process was completed, the thickness of the chemical oxide film formed on the surface of the silicon wafer was measured by ellipsometry. Figure 5(b) shows the relationship between the duration of the final ozone treatment cycle and the thickness of the chemical oxide film.

[0053] As is clear from Figure 5(b), the longer the final ozone treatment process, the thicker the chemical oxide film formed on the surface of the silicon wafer. This shows that the thickness of the chemical oxide film can be adjusted by changing the duration of the final ozone treatment process.

[0054] <<Relationship between the proportion of time spent in the mixing process and the surface state of the chemical oxide film>> The cleaning process consisted of three steps: a hydrofluoric acid treatment step in which only hydrofluoric acid solution (controlled to a concentration between 1 and 3 mass%) was supplied to the silicon wafer; a mixing treatment step in which hydrofluoric acid solution and ozone-dissolved water (concentration of 25 ppm) were simultaneously supplied to the silicon wafer; and an ozone treatment step in which only ozone-dissolved water was supplied to the silicon wafer. The cleaning process was performed for cases where the ratio of the mixing treatment step time to the total cleaning time was set to 0% (Figure 6(a)), 25% (Figure 6(b)), 50% (Figure 6(c)), and 100% (Figure 6(d)). Five silicon wafers were cleaned in each of the above cases, and the power spectral density ratio was measured by AFM. Figure 7 shows the relationship between the ratio of the mixing treatment step time and the power spectral density ratio.

[0055] As is clear from Figure 7, the proportion of power spectral density increases as the proportion of time spent in the mixing process increases, indicating that the surface state of the chemical oxide film can be adjusted by changing the proportion of time spent in the mixing process.

[0056] <<Relationship between the time of the final hydrofluoric acid treatment process and the surface state of the chemical oxide film>> As shown in Figure 8(a), the cleaning process consisted of three alternating cycles of a hydrofluoric acid treatment, in which only hydrofluoric acid solution (concentration controlled between 0.5 and 3% by mass) was supplied to the silicon wafer, and an ozone treatment, in which only ozone-dissolved water (concentration of 25 ppm) was supplied to the silicon wafer. The final step was the ozone treatment, and the cleaning process was performed while varying the duration of the final hydrofluoric acid treatment. After the cleaning process was completed, the power spectral density ratio was measured by AFM. Figure 8(b) shows the relationship between the final hydrofluoric acid treatment time and the power spectral density ratio.

[0057] As is clear from Figure 8(b), the power spectral density ratio decreases as the final hydrofluoric acid treatment process time increases, indicating that the surface state of the chemical oxide film can be adjusted by changing the time of the final hydrofluoric acid treatment process. By adjusting the time of the final hydrofluoric acid treatment process, the surface state of the semiconductor wafer can be adjusted in a relatively short time.

[0058] Note that in Figure 8(b), the power spectral density ratio is used as the surface state of the chemical oxide film, but haze can also be used. Haze can be measured, for example, using a Surfscan SP2 from KLA-Tencor.

[0059] <<Relationship between semiconductor wafer rotation speed and chemical oxide film surface state during the final hydrofluoric acid treatment process>> The cleaning process consisted of alternating between a hydrofluoric acid treatment process, where only hydrofluoric acid solution (concentration controlled between 0.5 and 3% by mass) was supplied to the silicon wafer, and an ozone treatment process, where only ozone-dissolved water (concentration of 25 ppm) was supplied to the silicon wafer, repeated three times. The final step was the ozone treatment process, and the duration of the final hydrofluoric acid treatment process was set to 3 seconds. The semiconductor wafer rotation speed during the final hydrofluoric acid treatment process was varied between 100 rpm and 500 rpm during the cleaning process. After the cleaning process was completed, the haze was measured using an AFM with a KLA-Tencor Surfscan SP2. The results showed that the increase in haze value compared to the haze value of the silicon wafer before the cleaning process was 0.025 ppm at 100 rpm, 0.020 ppm at 300 rpm, and 0.016 ppm at 500 rpm.

[0060] <<Relationship between ozone-dissolved water concentration and the surface state of chemical oxide films>> As shown in Figure 9(a), the cleaning process consisted of three alternating cycles: a hydrofluoric acid treatment cycle in which only hydrofluoric acid water (concentration controlled between 1 and 3% by mass) was supplied to the silicon wafer, and an ozone treatment cycle in which only ozone-dissolved water (concentration of 20 ppm) was supplied to the silicon wafer. The above cleaning process was also performed when the ozone concentration of the ozone-dissolved water was 25 ppm, 30 ppm, and 35 ppm. After the cleaning process was completed, the power spectral density ratio of the chemical oxide film formed on the surface of the silicon wafer was measured by AFM. The relationship between the concentration of ozone-dissolved water and the power spectral density ratio is shown in Figure 9(b).

[0061] As is clear from Figure 9(b), the power spectral density ratio increases as the concentration of ozone-dissolved water increases, indicating that the surface state of the chemical oxide film can be adjusted by changing the concentration of ozone-dissolved water.

[0062] (Example of Invention 1) The cleaning conditions for the silicon wafers were determined according to the flowchart shown in Figure 3. First, 194 silicon wafers were prepared that had undergone a cleaning process consisting of a hydrofluoric acid treatment process, a mixing process, and an ozone treatment process, with the final step being the ozone treatment process. The cleaning conditions for each of the 194 silicon wafers differed, specifically at least one of the following: the time of the final ozone treatment process, the time of the mixing process, and the ozone concentration of the ozone-dissolved water in the ozone treatment process.

[0063] For each of the 194 silicon wafers that underwent the above cleaning process, the thickness of the chemical oxide film formed on the wafer surface was measured by ellipsometry, and the power spectral density (wavelength range: 3.9 nm to 10 nm) was measured using AFM. The correlation between the chemical oxide film thickness X1 (Å) and the power spectral density ratio (X2 (%), ratio to the wavelength range: 3.9 nm to 100 nm) and the cleaning conditions was determined (cleaning correlation acquisition process). Next, each silicon wafer was introduced into a heat treatment furnace and subjected to a heat treatment process under the conditions of an oxidizing atmosphere (dry O2 (=100% dry oxygen)), 800°C, and 50 minutes. For each silicon wafer that underwent the heat treatment process, the thickness of the thermal oxide film formed on the wafer surface was measured by ellipsometry, and the increase in oxide film thickness Y (Å) was determined. Next, multiple regression analysis was performed using the obtained data on the thickness X1 (Å) and power spectral density percentage X2 (%) of the chemical oxide film, and the increase in oxide film thickness Y (Å), to determine the constants A, B, and C in equation (1). As a result, the following equation (3) was obtained as the heat treatment correlation (heat treatment correlation acquisition step). Y=-0.4254X1+0.0960X2+48.990 (3)

[0064] By inputting the thickness X1 (Å) of the chemical oxide film and the power spectral density ratio X2 (%) into equation (3) above, the increase in the thickness of the oxide film after the heat treatment process Y (Å) can be predicted.

[0065] Figure 10 shows the relationship between the predicted and measured increase in oxide film thickness after the heat treatment process. The correlation coefficient is 0.80, indicating a good correlation between the predicted and measured increase in oxide film thickness after the heat treatment process.

[0066] Subsequently, the heat treatment conditions for the heat treatment process were determined, and the target thickness of the thermal oxide film formed in the heat treatment process under these conditions was set to 45 Å (heat treatment condition determination step). Then, the thickness and power spectral density of the chemical oxide film corresponding to the above target thickness were determined, and the cleaning conditions corresponding to the determined thickness and power spectral density of the chemical oxide film were determined (cleaning condition determination step). In this way, the cleaning conditions for a silicon wafer that yields a thermal oxide film of the target thickness were determined.

[0067] (Conventional example) Thirty silicon wafers were prepared and divided into three groups. These wafers were then subjected to a cleaning process using three cleaning machines, consisting of a hydrofluoric acid treatment process, a mixing process, and an ozone treatment process, with the final step being ozone treatment. For all three cleaning machines, the cleaning conditions for the final ozone treatment were a process time of 30 seconds and an ozone concentration of 25 ppm. Next, each silicon wafer was introduced into a heat treatment furnace and subjected to a heat treatment process under the conditions of an oxidizing atmosphere (dry O2 (=100% dry oxygen)), 800°C, and 50 minutes. The target thickness of the thermal oxide film was set at 45 Å. For each silicon wafer after the heat treatment process, the thickness of the thermal oxide film formed on the wafer surface was measured by ellipsometry.

[0068] (Example of Invention 2) Using the same three cleaning devices as in the conventional example, the cleaning and heat treatment processes were performed in the same manner as in the conventional example. However, for each of the three devices, the cleaning conditions for the cleaning process were determined according to the flowchart shown in Figure 3. The determined cleaning conditions were: for device ID 1, a final ozone treatment process time of 75 seconds and an ozone concentration of 20 ppm; for device ID 2, a final ozone treatment process time of 15 seconds and an ozone concentration of 30 ppm; and for device ID 3, a final ozone treatment process time of 30 seconds and an ozone concentration of 25 ppm. Thirty silicon wafers were divided into three groups, and the cleaning process was performed using the three devices under the above determined cleaning conditions. All other conditions were the same as in the conventional example.

[0069] Figure 11(a) shows the thickness of the thermal oxide film formed in the heat treatment process for each of the three devices, compared to a conventional example. As is clear from Figure 11(a), the degree of variation in the thickness of the thermal oxide film differs depending on the cleaning device.

[0070] Figure 11(b) shows the thickness of the formed thermal oxide film for the conventional example and Invention Example 2. As is clear from Figure 11(b), Invention Example 2 shows less variation in the thickness of the thermal oxide film relative to the target thickness compared to the conventional example. Thus, it can be seen that the thickness of the thermal oxide film formed in the heat treatment process can be well controlled by the present invention. [Industrial applicability]

[0071] According to the present invention, the thickness of the thermal oxide film can be controlled effectively. This improves the yield of devices, thereby achieving increased production efficiency and reduced waste.

Claims

1. A method for determining the cleaning conditions for a semiconductor wafer, A cleaning correlation acquisition step is performed to obtain a cleaning correlation, which is the correlation between the thickness and surface state of the chemical oxide film formed on the surface of each of the semiconductor wafers and the cleaning conditions, and to prepare multiple semiconductor wafers that have undergone cleaning processes under multiple cleaning conditions. For each of the one or more different heat treatment conditions in the heat treatment process, a plurality of semiconductor wafers are prepared that have undergone the heat treatment process following the cleaning process, and a heat treatment correlation acquisition process is performed to determine the heat treatment correlation relationship, which is the correlation between the amount of increase in the thickness of the oxide film after the heat treatment process, the thickness of the chemical oxide film, and the surface state of the thermal oxide film formed on the surface of each of the plurality of semiconductor wafers. A heat treatment condition determination step, which determines the heat treatment conditions in the heat treatment step and the target thickness of the thermal oxide film formed on the surface of the semiconductor wafer in the heat treatment step under the determined heat treatment conditions, A cleaning condition determination step, based on the heat treatment correlation and the cleaning correlation, determines cleaning conditions such that the thickness of the thermal oxide film formed on the surface of the semiconductor wafer in the heat treatment step under the determined heat treatment conditions becomes the target thickness. A method for determining the cleaning conditions of a semiconductor wafer, including [the specified element].

2. The method for determining the cleaning conditions of a semiconductor wafer according to claim 1, wherein the surface condition is indicated by the power spectral density of the surface roughness measured by an atomic force microscope.

3. The method for determining the cleaning conditions of a semiconductor wafer according to claim 1 or 2, wherein the heat treatment correlation is expressed by the following formula (1), where Y is the increase in the thickness of the oxide film after the heat treatment process, X1 is the thickness of the chemical oxide film, X2 is the surface state, and A, B, and C are constants. Y=AX1+BX2+C (1)

4. For each of the one or more heat treatment conditions mentioned above, the constants A, B, and C are determined. A method for determining the cleaning conditions of a semiconductor wafer according to claim 3, wherein the constants A, B, and C are determined according to the heat treatment conditions determined in the heat treatment condition determination step.

5. The cleaning process includes, at least as the final step of the cleaning process, an ozone treatment step in which only ozone-dissolved water is supplied to the semiconductor wafer as a chemical solution. The method for determining the cleaning conditions for a semiconductor wafer according to claim 1 or 2, wherein the time of the final step differs in the plurality of cleaning conditions.

6. The aforementioned cleaning step, A hydrofluoric acid treatment process in which only hydrofluoric acid solution is supplied to the semiconductor substrate as a chemical, A mixing process in which hydrofluoric acid water and ozone-dissolved water are simultaneously supplied to a semiconductor wafer as chemical solutions, An ozone treatment process in which only ozone-dissolved water is supplied to the semiconductor wafer as a chemical solution, Includes, A method for determining the cleaning conditions of a semiconductor wafer according to claim 1 or 2, wherein the time of the mixing process differs in the plurality of cleaning conditions.

7. The aforementioned cleaning step, A hydrofluoric acid treatment process in which only hydrofluoric acid solution is supplied to the semiconductor substrate as a chemical, An ozone treatment process in which only ozone-dissolved water is supplied to the semiconductor wafer as a chemical solution, Includes, A method for determining the cleaning conditions of a semiconductor wafer according to claim 1 or 2, wherein the concentration of the ozone-dissolved water differs in the plurality of cleaning conditions.

8. The aforementioned cleaning step, A hydrofluoric acid treatment process in which only hydrofluoric acid solution is supplied to the semiconductor substrate as a chemical, An ozone treatment process in which only ozone-dissolved water is supplied to the semiconductor wafer as a chemical solution, Includes, A method for determining the cleaning conditions of a semiconductor wafer according to claim 1 or 2, wherein the time of the final hydrofluoric acid treatment step differs in the plurality of cleaning conditions.

9. The aforementioned cleaning step, A hydrofluoric acid treatment process in which only hydrofluoric acid solution is supplied to the semiconductor substrate as a chemical, An ozone treatment process in which only ozone-dissolved water is supplied to the semiconductor wafer as a chemical solution, Includes, A method for determining the cleaning conditions of a semiconductor wafer according to claim 1 or 2, wherein the rotation speed of the semiconductor substrate in the final hydrofluoric acid treatment step differs in the plurality of cleaning conditions.

10. A method for cleaning a semiconductor wafer, comprising cleaning the semiconductor wafer under cleaning conditions determined by the method for determining semiconductor wafer cleaning conditions described in claim 1 or 2.

11. The method for cleaning a semiconductor wafer according to claim 10, wherein the semiconductor wafer is a silicon wafer.

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