Method for determining cleaning condition of semiconductor wafer and method for cleaning semiconductor wafer

Abstract

Provided is a method for determining a cleaning condition for a semiconductor wafer, the method being capable of satisfactorily controlling the thickness of a thermal oxide film. A method for determining a cleaning condition of a semiconductor wafer according to the present invention comprises: a step for determining a cleaning correlation between a cleaning condition and the thickness and surface state of a chemical oxide film formed on each surface of a plurality of semiconductor wafers after a cleaning step; a step in which, for each of the one or more heat treatment conditions, the heat treatment correlation between the amount of increase in the thickness of the oxide film after the heat treatment step and the thickness and surface state of the chemical oxide film after the heat treatment step is determined for the thermal oxide film formed on the surface of each of the plurality of semiconductor wafers after the heat treatment step; a step for determining a heat treatment condition in the heat treatment step, and determining a target thickness of a thermal oxide film formed on the surface of the semiconductor wafer in the heat treatment step under the determined heat treatment condition; and a step for determining a cleaning condition under which the thickness of a thermal oxide film formed on the surface of the semiconductor wafer in the heat treatment step under the determined heat treatment condition becomes the target thickness.

Description

TECHNICAL FIELD

[0001] The present application relates to a method for determining a cleaning condition of a semiconductor wafer and a method for cleaning a semiconductor wafer. BACKGROUND

[0002] In a device forming process, a heat treatment is performed on a semiconductor wafer that is a substrate of a semiconductor device, and a thermal oxide film is formed on the surface of the semiconductor wafer. The thickness of the formed thermal oxide film has an influence on the characteristics of the semiconductor device formed on the semiconductor wafer, and a deviation in the thickness of the thermal oxide film has an influence on the yield. Therefore, it is required to form the thermal oxide film with no deviation in the thickness as a target.

[0003] In Patent Literature 1, a technology is described in which, based on the insight that the composition of a chemical oxide film formed on the surface of a semiconductor substrate has a large influence on a thermal oxidation process, the correlation between the composition of the chemical oxide film and the thickness of the thermal oxide film is calculated in advance, the composition of the chemical oxide film that makes the thickness of the formed thermal oxide film a prescribed thickness is determined, the cleaning condition that makes the above-described composition of the chemical oxide film is determined, and the semiconductor wafer is cleaned, thereby forming the thermal oxide film of the above-described prescribed thickness with good reproducibility.

[0004] PRIOR ART DOCUMENTS

[0005] PATENT LITERATURE

[0006] Patent Literature 1: Japanese Patent No. 6791454 SUMMARY

[0007] PROBLEMS TO BE SOLVED BY THE INVENTION

[0008] However, in the technology described in Patent Literature 1, in order to perform cleaning in a manner that the determined composition of the chemical oxide film is obtained, the cleaning condition needs to be greatly changed, and in addition, the surface quality after cleaning (for example, the attachment of particles) other than the thickness of the chemical oxide film is sometimes deteriorated, and the yield of the device is reduced. Therefore, a method that can control the thickness of the thermal oxide film with good reproducibility without changing the composition of the chemical oxide film is desired.

[0009] The present application has been made in view of the above-described problems, and an object thereof is to provide a method for determining a cleaning condition of a semiconductor wafer that can control the thickness of a thermal oxide film with good reproducibility.

[0010] MEANS FOR SOLVING THE PROBLEMS

[0011] The present application that solves the above-described problems is as described below.

[0012] [1] A method for determining a cleaning condition of a semiconductor wafer, which is a method for determining a cleaning condition of a semiconductor wafer, comprising the following steps:

[0013] a cleaning-related relationship obtaining step of obtaining a cleaning-related relationship of a chemical oxide film formed on a surface of a semiconductor wafer, the cleaning-related relationship being a relationship between a thickness and a surface state of the chemical oxide film and a cleaning condition under which the semiconductor wafer is subjected to a cleaning process;

[0014] a heat treatment-related relationship obtaining step of, for each of one or more different heat treatment conditions in a heat treatment process, obtaining a heat treatment-related relationship of a thermal oxide film formed on a surface of a semiconductor wafer, the heat treatment-related relationship being a relationship between an increase in thickness of the thermal oxide film after the heat treatment process and a thickness of the chemical oxide film and a surface state of the chemical oxide film;

[0015] a heat treatment condition determining step of determining a heat treatment condition in the heat treatment process, and determining a target thickness of the thermal oxide film formed on the surface of the semiconductor wafer in the heat treatment process under the determined heat treatment condition; and

[0016] a cleaning condition determining step of determining a cleaning condition under which the thickness of the thermal oxide film formed on the surface of the semiconductor wafer in the heat treatment process under the determined heat treatment condition becomes the target thickness, based on the heat treatment-related relationship and the cleaning-related relationship.

[0017] [2] The cleaning condition determining method of a semiconductor wafer according to the above-mentioned [1], wherein the surface state is indicated by a power spectral density of surface roughness measured by an atomic force microscope.

[0018] [3] The cleaning condition determining method of a semiconductor wafer according to the above-mentioned [1] or [2], wherein the heat treatment-related relationship is represented by the following formula (1) with an increase in thickness of the thermal oxide film after the heat treatment process being Y, the thickness of the chemical oxide film being XI, the surface state being X2, and A, B, and C being constants,

[0019] Y = AX1 + BX2 + C (1).

[0020] [4] The cleaning condition determining method of a semiconductor wafer according to the above-mentioned [3], wherein the constants A, B, and C are obtained in advance for each of the one or more heat treatment conditions,

[0021] the constants A, B, and C are determined based on the heat treatment condition determined in the heat treatment condition determining step.

[0022] [5] The cleaning condition determination method for a semiconductor wafer according to any one of the above [1] to [4], wherein the cleaning process includes, as the final process of the cleaning process, at least an ozone treatment process of supplying only ozone-dissolved water as a chemical liquid to the semiconductor wafer,

[0023] The time of the final process is different among the plurality of cleaning conditions.

[0024] [6] The cleaning condition determination method for a semiconductor wafer according to any one of the above [1] to [4], wherein the cleaning process includes:

[0025] a hydrofluoric acid treatment process of supplying only a hydrofluoric acid aqueous solution as a chemical liquid to the semiconductor substrate,

[0026] a mixed treatment process of simultaneously supplying a hydrofluoric acid aqueous solution and ozone-dissolved water as chemical liquids to the semiconductor wafer, and

[0027] an ozone treatment process of supplying only ozone-dissolved water as a chemical liquid to the semiconductor wafer,

[0028] The time of the mixed treatment process is different among the plurality of cleaning conditions.

[0029] [7] The cleaning condition determination method for a semiconductor wafer according to any one of the above [1] to [4], wherein the cleaning process includes:

[0030] a hydrofluoric acid treatment process of supplying only a hydrofluoric acid aqueous solution as a chemical liquid to the semiconductor substrate, and

[0031] an ozone treatment process of supplying only ozone-dissolved water as a chemical liquid to the semiconductor wafer,

[0032] The concentration of the ozone-dissolved water is different among the plurality of cleaning conditions.

[0033] [8] The cleaning condition determination method for a semiconductor wafer according to any one of the above [1] to [4], wherein the cleaning process includes:

[0034] a hydrofluoric acid treatment process of supplying only a hydrofluoric acid aqueous solution as a chemical liquid to the semiconductor substrate, and

[0035] an ozone treatment process of supplying only ozone-dissolved water as a chemical liquid to the semiconductor wafer,

[0036] The time of the final hydrofluoric acid treatment process is different among the plurality of cleaning conditions.

[0037] [9] The cleaning condition determination method for a semiconductor wafer according to any one of the above [1] to [4], wherein the cleaning process includes:

[0038] hydrofluoric acid treatment process of supplying only an aqueous solution of hydrofluoric acid as a chemical liquid to a semiconductor substrate, and

[0039] ozone treatment process of supplying only ozone-dissolved water as a chemical liquid to a semiconductor wafer,

[0040] Among the plurality of cleaning conditions, the rotation speed of the semiconductor substrate in the final hydrofluoric acid treatment process is different.

[0041]

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

[0042]

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

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

[0043] Effects of the Invention

[0044] According to the present invention, the thickness of the thermal oxide film can be controlled well. Thus, the yield of the device can be improved, and further, the production efficiency can be improved and the waste can be reduced.

[0045] Brief Description of the Drawings

[0046] Figure 1 is a graph illustrating the growth behavior of the thermal oxide film.

[0047] Figure 2 is a graph illustrating the influence of the surface state of the chemical oxide film on the formation of the thermal oxide film, (a) is a graph for the case where the surface roughness is small, and (b) is a graph for the case where the surface roughness is large.

[0048] Figure 3 is a flowchart of the cleaning condition determination method of a semiconductor wafer according to the present invention.

[0049] Figure 4 is a graph showing (a) a measurement position of the power spectral density based on AFM, and (b) an example of the measured power spectral density.

[0050] Figure 5 is a graph showing (a) the configuration of the cleaning process, and (b) the relationship between the time of the final ozone treatment process and the thickness of the chemical oxide film.

[0051] Figure 6 is a graph showing the proportion of the time of the mixed treatment process with respect to the time of the entire cleaning process, (a) is an example for the case where the proportion is 0%, (b) is an example for the case where the proportion is 25%, (c) is an example for the case where the proportion is 50%, and (d) is an example for the case where the proportion is 100%.

[0052] Figure 7is a graph showing the relationship of the proportion of the mixing process to the proportion of the power spectral density.

[0053] Figure 8 is a graph showing the relationship of (a) the constitution of the cleaning process, (b) the time of the final hydrofluoric acid treatment process to the proportion of the power spectral density.

[0054] Figure 9 is a graph showing the relationship of (a) the constitution of the cleaning process, (b) the concentration of the ozone dissolved water to the proportion of the power spectral density.

[0055] Figure 10 is a graph showing the relationship of the predicted value of the increase amount of the thickness of the oxide film after the heat treatment process to the measured value.

[0056] Figure 11 is (a) a graph showing the thickness of the heat oxide film of the prior example for each of the three devices, and (b) a graph showing the thickness of the heat oxide film of the prior example and the inventive example 2. DETAILED DESCRIPTION

[0057] (Method for determining cleaning conditions of semiconductor wafer)

[0058] An embodiment of the present application will be described below with reference to the accompanying drawings. The method for determining cleaning conditions of a semiconductor wafer of the present application includes the following processes: a cleaning correlation acquisition process of preparing a plurality of semiconductor wafers which have undergone a cleaning process under a plurality of cleaning conditions, and acquiring a correlation between a thickness and a surface state of a chemical oxide film formed on a respective surface of the plurality of semiconductor wafers and the cleaning conditions, i.e., a cleaning correlation; a heat treatment correlation acquisition process of preparing a plurality of semiconductor wafers which have undergone a heat treatment process after the cleaning process for each of one or more different heat treatment conditions in the heat treatment process, and acquiring a correlation between an increase amount of the thickness of the oxide film after the heat treatment process and the thickness and the surface state of the chemical oxide film for a heat oxide film formed on a respective surface of the plurality of semiconductor wafers, i.e., a heat treatment correlation; a heat treatment condition determination process of determining a heat treatment condition in the heat treatment process, and simultaneously determining a target thickness of the heat oxide film formed on the surface of the semiconductor wafer in the heat treatment process under the determined heat treatment condition; and a cleaning condition determination process of determining a cleaning condition in which the thickness of the heat oxide film formed on the surface of the semiconductor wafer in the heat treatment process under the determined heat treatment condition becomes the target thickness, based on the heat treatment correlation and the cleaning correlation.

[0059] The inventors have conducted in-depth research on a method for more effectively controlling the thickness of the thermal oxide film formed on the surface of a semiconductor wafer during a heat treatment process. The thermal oxide film is formed by the diffusion of oxygen from the surface of a chemical oxide film (natural oxide film) already formed in a preceding process such as cleaning into the interior of the semiconductor wafer. At the interface between the chemical oxide film and the semiconductor wafer, oxygen reacts chemically with the constituent elements of the semiconductor wafer to form the thermal oxide film.

[0060] like Figure 1 As shown, for oxide films, it is known that the growth behavior differs in regions with small thickness (region 1 in the figure) and regions with large thickness (region 2 in the figure). Previously, based on Geel-Grove's formula, it was believed that in region 1, where the oxide film thickness is small, the reaction of the semiconductor wafer's constituent elements with oxygen limits the rate of oxide film formation; on the other hand, in region 2, where the oxide film thickness is large, oxygen diffusion limits the rate of oxide film formation. However, in recent years, there have also been reports that oxygen diffusion limits the rate of oxide film formation in region 1 (e.g., see 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... The area to the left and right 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.

[0061] In the course of their in-depth research on a method for controlling the thickness of a thermal oxide film formed during a heat treatment process by controlling the diffusion of oxygen in the oxide film, the inventors discovered a good correlation between the thickness and surface condition of the chemical oxide film formed on the surface of a semiconductor wafer during a cleaning process and the increase in the thickness of the oxide film. The increase in the thickness of the oxide film refers to the increase in the thickness of the thermal oxide film formed on the surface of a semiconductor wafer during a heat treatment process after the heat treatment process.

[0062] That is, when the chemical oxide film is thick, 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 chemical oxide film is thick, it is considered that the arrival time of oxygen at the interface between the chemical oxide film and the semiconductor wafer is slower. On the other hand, regarding the surface state of the chemical oxide film, such as... Figure 2 As shown in (a), for example, when the surface roughness is small, it is assumed that the specific surface area of ​​the chemical oxide film is small, making it difficult for oxygen to be absorbed from the surface of the chemical oxide film. In contrast, as... Figure 2 As shown in (b), when the surface roughness of the chemical oxide film is large, it is assumed that the specific surface area of ​​the chemical oxide film is large, and oxygen can be easily taken in from the surface of the chemical oxide film.

[0063] The present inventors, based on the above insight, found that by previously obtaining a correlation between a thickness and a surface state of a chemical oxide film formed on a surface of a semiconductor wafer in a cleaning process and a cleaning condition (cleaning correlation), and a correlation between the thickness and the surface state of the above chemical oxide film and an increase amount of a thickness of an oxide film after a heat treatment process for a thermal oxide film formed on a surface of a semiconductor wafer in the heat treatment process for each of one or more heat treatment conditions (heat treatment correlation), determining a heat treatment condition, and simultaneously determining a target thickness of a thermal oxide film formed in the heat treatment process under the heat treatment condition, it is possible to determine a cleaning condition that can well control a thickness of a thermal oxide film formed in the heat treatment process, thereby completing the present application. Hereinafter, each process will be described.

[0064] <cleaning correlation obtaining process>

[0065] Figure 3 A flowchart of a method of determining a cleaning condition of a semiconductor wafer according to the present application is shown. First, a plurality of semiconductor wafers subjected to a cleaning process under a plurality of cleaning conditions are prepared, and a correlation between a thickness and a surface state of a chemical oxide film formed on each surface of the plurality of semiconductor wafers and the above cleaning condition (cleaning correlation) is obtained.

[0066] The semiconductor wafer used to obtain the cleaning correlation is not particularly limited, and a bulk single crystal wafer formed of silicon or germanium, a compound semiconductor (GaAs, GaN, SiC) can be used. As such a semiconductor wafer, a wafer sliced from a single crystal ingot of silicon or the like grown by a Czochralski (CZ) method or a floating zone (FZ) method using a wire saw or the like can be used. In addition, in order to obtain gettering ability for heavy metals, carbon and / or nitrogen can be added to the semiconductor wafer. Furthermore, any dopant can be added to the semiconductor wafer at a prescribed concentration to make a so-called n + type or p + type, or an n - type or p - type semiconductor wafer.

[0067] In addition, as the semiconductor wafer, a semiconductor epitaxial wafer in which a semiconductor epitaxial layer is formed on a surface of a bulk semiconductor wafer can be used. As such a semiconductor epitaxial wafer, for example, an epitaxial silicon wafer in which a silicon epitaxial layer is formed on a surface of a bulk single crystal silicon wafer can be used. The silicon epitaxial layer can be formed by a CVD method under general conditions.

[0068] The thickness of the chemical oxide film can be measured on a region on the surface of the semiconductor wafer, for example, by an ellipsometer. In the case where the thickness of the chemical oxide film is measured by the ellipsometer, a plurality of positions on the surface of the semiconductor wafer, for example, as shown in FIG. 1, can be measured.Figure 4 (a) The thickness is measured at five points, the center (5), the outer peripheral portion (1), (2), and the 1 / 2 position of the radius R (3), (4) on the semiconductor wafer as illustrated, and the average value thereof is set as the thickness of the chemical oxide film (for example, the measurement region is 1 μm).

[0069] The surface state of the chemical oxide film can be considered as the surface roughness, for example. As the surface roughness, the average roughness Ra, the maximum height of the roughness Rz, the ten-point average roughness RzJ, the maximum height of the roughness Rmax, and the like can be used. Figure 4 (b) As the surface state of the chemical oxide film, the power spectral density of the surface roughness measured by an atomic force microscope (AFM) can be used as an index, as illustrated. As a result of the research by the present inventors and the like, it has been found that there is a good single correlation between the integral value of the power spectral density in a smaller spatial wavelength band, for example, a region of 3.9 nm to 10 nm, and the thickness of the thermal oxide film formed in the heat treatment step. Therefore, in the case where the power spectral density of the surface roughness measured by the AFM is used as an index of the surface state of the chemical oxide film, it is preferable to use the integral value of the power spectral density in a smaller spatial wavelength band.

[0070] The lower limit value of the spatial wavelength band is preferably measured from a smaller wavelength, and is preferably set to 3.9 nm, more preferably to 1 nm, and further preferably to a value more 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.

[0071] In addition, the surface state of the chemical oxide film can also be indexed by the ratio (power spectral density ratio) of the integral value of the power spectral density of the surface roughness measured by the AFM in a smaller spatial wavelength band (for example, 3.9 nm to 10 nm) to the integral value in the entire region (for example, 3.9 nm to 100 nm).

[0072] Further, the surface state of the chemical oxide film can also be indexed by Rq (root mean square roughness) in which the spatial wavelength band is limited in the measurement based on the AFM. For example, an image in which only the components in the wavelength range of 25 to 80 nm are extracted can be output, Rq can be calculated for the above image, and the calculated Rq can be used as an index.

[0073] The cleaning process performed on the semiconductor wafer can be a cleaning process in a semiconductor wafer manufacturing process. The cleaning process in the semiconductor wafer manufacturing process can include a hydrofluoric acid treatment process in which only an aqueous hydrofluoric acid solution is supplied to the semiconductor wafer as a chemical solution. In addition, the cleaning process can include an ozone treatment process in which only ozone-dissolved water is supplied to the semiconductor wafer as a chemical solution. Furthermore, the cleaning process can be configured in such a manner that the hydrofluoric acid treatment process and the ozone treatment process are included and these processes are alternately performed. Furthermore, the cleaning process can also be configured in such a manner that the hydrofluoric acid treatment process, a mixed treatment process in which the aqueous hydrofluoric acid solution and the ozone-dissolved water are simultaneously supplied to the semiconductor wafer, and the ozone treatment process are included, and these processes are sequentially performed.

[0074] As the cleaning conditions of the cleaning process, there can be mentioned the time of the final process when the ozone treatment process is set as the final process of the cleaning process, the concentration of the aqueous hydrofluoric acid solution, the treatment time of the hydrofluoric acid treatment process, the rotation speed of the semiconductor wafer in the hydrofluoric acid treatment process, the concentration of the ozone-dissolved water, the time of the mixed treatment process, and the like. As shown in the examples described later, in the case where the cleaning process includes the ozone treatment process as the final process, by changing the time of the final process, the thickness of the chemical oxide film formed on the surface of the semiconductor wafer in the cleaning process can be adjusted.

[0075] In addition, as shown in the examples described later, in the case where the cleaning process is configured in such a manner that the hydrofluoric acid treatment process, the mixed treatment process, and the ozone treatment process are included and these processes are sequentially performed, by changing the time of the mixed treatment process (or the proportion of the time of the mixed treatment process with respect to the time of the entire cleaning process), the surface state of the chemical oxide film formed on the surface of the semiconductor wafer after cleaning can be adjusted.

[0076] In addition, as shown in the examples described later, in the case where the cleaning process includes the hydrofluoric acid treatment process and the ozone treatment process, these processes are repeated, and the final process is set as the ozone treatment process, by changing the time of the final hydrofluoric acid treatment process, the surface state of the chemical oxide film formed on the surface of the semiconductor wafer after cleaning can be adjusted.

[0077] In addition, as shown in the examples described later, in the case where the cleaning process includes the hydrofluoric acid treatment process and the ozone treatment process, these processes are repeated, and the final process is set as the ozone treatment process, by changing the rotation speed of the semiconductor wafer in the final hydrofluoric acid treatment process, the surface state of the chemical oxide film formed on the surface of the semiconductor wafer after cleaning can be adjusted.

[0078] In addition, as shown in the examples described later, in the case where the cleaning process includes an ozone treatment process, the surface state of the chemical oxide film can also be adjusted by changing the concentration of the ozone-dissolved water. Similarly, in the case where the cleaning process includes a hydrofluoric acid treatment process, it can also be adjusted by changing the concentration of the hydrofluoric acid aqueous solution.

[0079] Note that the surface state of the chemical oxide film can be changed by combining two or three of the changes in the time of the above-described mixed treatment process, the time of the final hydrofluoric acid treatment process, the rotation speed of the semiconductor wafer in the final hydrofluoric acid treatment process, the change in the concentration of the hydrofluoric acid aqueous solution, and the change in the concentration of the ozone-dissolved water.

[0080] The correlation between the thickness and surface state of the above-described chemical oxide film and the cleaning conditions (cleaning correlation) is obtained. The cleaning correlation is a correlation between the thickness and surface state of the chemical oxide film and the cleaning conditions, and is correlated in such a manner that the cleaning conditions in the cleaning process that can obtain the thickness and surface state of the chemical oxide film determined in the heat treatment condition determination process described later can be determined when the thickness and surface state of the chemical oxide film are determined.

[0081] <Heat treatment correlation obtaining process>

[0082] Next, for each of one or more different heat treatment conditions in the heat treatment process, a plurality of semiconductor wafers that have undergone the heat treatment process after the cleaning process are prepared, and for each of the thermal oxide films formed on the surface of each of the plurality of semiconductor wafers, the increase in the thickness of the oxide film after the heat treatment process, and the correlation between the thickness and surface state of the chemical oxide film, i.e., the heat treatment correlation, is obtained. 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 (thermal oxide film) formed in the heat treatment process and the thickness of the oxide film (chemical oxide film) formed in the cleaning process.

[0083] As described above, the present 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 in the cleaning process and the increase in the thickness of the oxide film, which is the increase in the thickness of the oxide film after the heat treatment process for the thermal oxide film formed on the surface of the semiconductor wafer in the heat treatment process. The above-described heat treatment correlation can be expressed by the following formula (1) by setting the increase in the thickness of the oxide film after the heat treatment process as Y, the thickness of the chemical oxide film as X1, the surface state as X2, and A, B, and C as constants, for example.

[0084] Y = AX1 + BX2 + C (1)

[0085] In the case where the heat treatment correlation relationship is expressed by the above-described formula (1), for each of one or more heat treatment conditions, a multiple regression analysis is performed with X1 and X2 as explanatory variables and Y as a target variable, for the combination of the thickness X1 and the surface state X2 of the chemical oxide film and the increase Y in the thickness of the oxide film after the heat treatment step, and the constants A, B, and C are calculated in advance. Thus, if the heat treatment condition is determined in the heat treatment condition determination step described later, A, B, and C corresponding to the determined heat treatment condition can be determined, and formula (1) for the above-described heat treatment condition can be obtained.

[0086] Note that, in calculating the heat treatment correlation relationship, the oxide film thickness Z after the heat treatment step can be used instead of the increase Y in the oxide film thickness after the heat treatment step, and a correlation formula of the oxide film thickness Z after the heat treatment step and the thickness X1 and the surface state X2 of the chemical oxide film can be created. In this case, since Z = Y + X1, the oxide film thickness Z after the heat treatment step can be expressed by the following formula (2).

[0087] Z = (A + 1) X1 + BX2 + C (2)

[0088] <Heat treatment condition determination step>

[0089] Subsequently, while the heat treatment condition in the heat treatment step is determined, 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 condition is determined. The heat treatment condition can be determined by selecting one or more heat treatment conditions from which the heat treatment correlation relationship is calculated in the heat treatment correlation relationship acquisition step. By determining the heat treatment condition in the heat treatment step, the constants A, B, and C of the above-described formula (1), for example, can be determined, and the heat treatment correlation relationship corresponding to the heat treatment condition can be calculated. In addition, the target thickness can be determined by selecting the thickness of the thermal oxide film used when the heat treatment correlation relationship for the determined heat treatment condition is calculated, or can be arbitrarily determined.

[0090] <Cleaning condition determination step>

[0091] Then, based on the heat treatment correlation and the cleaning correlation, a cleaning condition under which the thickness of the thermal oxide film formed on the surface of the semiconductor wafer in the heat treatment step determined under the determined heat treatment condition becomes the target thickness is determined. In the present cleaning condition determining step, first, a plurality of sets of the thickness and the surface state of the chemical oxide film formed in the cleaning step under which the thickness of the thermal oxide film formed in the heat treatment step becomes the target thickness are obtained by inputting the target thickness of the thermal oxide film determined in the heat treatment correlation corresponding to the heat treatment condition determined in the heat treatment condition determining step as a preceding step. Next, one set under which the cleaning condition is easily achieved is selected from the plurality of sets of the thickness and the surface state of the chemical oxide film. Then, by referring to the cleaning correlation, the cleaning condition under which the thickness and the surface state of the chemical oxide film obtained are obtained in the cleaning step is determined. The cleaning condition can be determined by selecting from a plurality of cleaning conditions used when the cleaning correlation is obtained in the cleaning correlation obtaining step. In this way, the cleaning condition under which the thickness of the thermal oxide film formed on the surface of the semiconductor wafer in the heat treatment step becomes the target thickness can be determined.

[0092] (Cleaning method of semiconductor wafer)

[0093] The cleaning method of the semiconductor wafer of the present application is characterized by cleaning the semiconductor wafer under the cleaning condition determined by the cleaning condition determining method of the semiconductor wafer of the present application described above.

[0094] As described above, by the cleaning method determining method of the semiconductor wafer of the present application, the cleaning condition under which the thickness of the thermal oxide film formed on the surface of the semiconductor wafer in the heat treatment step can be well controlled can be determined. Therefore, by cleaning the semiconductor wafer under the determined cleaning condition and then heat treating the semiconductor wafer under the heat treatment condition determined in the heat treatment condition determining step, the thickness of the thermal oxide film formed on the surface of the semiconductor wafer can be well controlled, that is, the thermal oxide film can be formed while the deviation from the target thickness is suppressed.

[0095] The semiconductor wafer to be cleaned is not particularly limited and can be a semiconductor wafer formed of silicon, germanium, a compound semiconductor (GaAs, GaN, SiC). Among them, the silicon wafer can be well cleaned.

[0096] Example

[0097] Hereinafter, an example of the present application will be described, but the present application is not limited to the example.

[0098] Relationship between time of final step (ozone treatment step) and thickness of chemical oxide film

[0099] As Figure 5As shown in (a), as a cleaning process, a hydrofluoric acid treatment process in which only hydrofluoric acid aqueous solution (concentration controlled between 1 and 3% by mass) is supplied to the silicon wafer, and an ozone treatment process in which only ozone-dissolved water (concentration 25 ppm) is supplied to the silicon wafer, are performed alternately three times. At this time, the final process is set as the ozone treatment process, and the duration of the final ozone treatment process is varied. After the cleaning process, the thickness of the chemical oxide film formed on the surface of the silicon wafer is measured using an ellipsometry. The relationship between the duration of the final ozone treatment process and the thickness of the chemical oxide film is shown in [the figure]. Figure 5 (b)

[0100] Depend on Figure 5 (b) It is clear that the longer the final ozone treatment process takes, the thicker the chemical oxide film formed on the surface of the silicon wafer becomes. The thickness of the chemical oxide film can be adjusted by changing the time of the final ozone treatment process.

[0101] (Relationship between the time ratio of the mixing process and the surface state of the chemical oxide film)

[0102] As cleaning processes, a hydrofluoric acid treatment process was performed in which only an aqueous hydrofluoric acid solution (controlled at a concentration between 1% and 3% by mass) was supplied to the silicon wafer; a mixing treatment process was performed in which both an aqueous hydrofluoric acid solution and ozone-dissolved water (concentration 25 ppm) were supplied to the silicon wafer; and an ozone treatment process was performed in which only ozone-dissolved water was supplied to the silicon wafer. At this time, the ratio of the time for the mixing treatment process to the total time for the cleaning process was set to 0%. Figure 6 (a) 25% Figure 6 (b) 50% Figure 6 (c) 100% Figure 6 In case (d), a cleaning process is performed. For each of the above cases, five silicon wafers are cleaned, and the power spectral density ratio is measured using AFM. The relationship between the mixing process time ratio and the power spectral density ratio is shown in... Figure 7 .

[0103] Depend on Figure 7 It is clear that if the time ratio of the mixing process increases, the power spectral density ratio also increases. By changing the time ratio of the mixing process, the surface state of the chemical oxide film can be adjusted.

[0104] The Relationship Between the Time of the Final Hydrofluoric Acid Treatment Process and the Surface State of the Chemical Oxidation Film

[0105] like Figure 8(a) As shown, as the cleaning process, a hydrofluoric acid treatment process in which only an aqueous hydrofluoric acid solution (controlled to a concentration of between 0.5 and 3 mass%) is supplied to the silicon wafer and an ozone treatment process in which only ozone-dissolved water (concentration 25 ppm) is supplied to the silicon wafer are alternately repeated three times. At this time, the final process is set to the ozone treatment process, the amount of time of the final hydrofluoric acid treatment process is varied, and the cleaning process is performed. After the cleaning process is completed, the power spectral density ratio is measured by AFM. The relationship between the time of the final hydrofluoric acid treatment process and the power spectral density ratio is shown in FIG. 4. Figure 8 (b).

[0106] From Figure 8 (b), it is clear that if the time of the final hydrofluoric acid treatment process is increased, the power spectral density ratio becomes smaller, and by changing the time of the final hydrofluoric acid treatment process, the surface state of the chemical oxide film can be adjusted. By adjusting the time of the final hydrofluoric acid treatment process, the surface state of the semiconductor wafer can be adjusted in a short time.

[0107] Note that, in Figure 8 (b), as the surface state of the chemical oxide film, the power spectral density ratio can be used, but Haze can also be used. Haze can be measured, for example, using Surfscan SP2 manufactured by KLA-Tencor Corporation.

[0108] Relationship between the rotation speed of the semiconductor wafer in the final hydrofluoric acid treatment process and the surface state of the chemical oxide film

[0109] As the cleaning process, a hydrofluoric acid treatment process in which only an aqueous hydrofluoric acid solution (controlled to a concentration of between 0.5 and 3 mass%) is supplied to the silicon wafer and an ozone treatment process in which only ozone-dissolved water (concentration 25 ppm) is supplied to the silicon wafer are alternately repeated three times. At this time, the final process is set to the ozone treatment process, the time of the final hydrofluoric acid treatment process is set to 3 seconds. Then, the rotation speed of the semiconductor wafer in the final hydrofluoric acid treatment process is changed between 100 rpm and 500 rpm, and the cleaning process is performed. After the cleaning process is completed, Haze is measured by AFM and using Surfscan SP2 manufactured by KLA-Tencor Corporation. As a result thereof, for the increase in the Haze value with respect to the Haze value of the silicon wafer before being put into the cleaning process, it was 0.025 ppm at 100 rpm, 0.020 ppm at 300 rpm, and 0.016 ppm at 500 rpm.

[0110] Relationship between the concentration of ozone-dissolved water and the surface state of the chemical oxide film

[0111] As Figure 9As shown in (a), as a cleaning process, a hydrofluoric acid treatment process in which only hydrofluoric acid aqueous solution (concentration controlled between 1 and 3% by mass) is supplied to the silicon wafer, and an ozone treatment process in which only ozone-dissolved water (concentration 20 ppm) is supplied to the silicon wafer, are performed alternately and repeatedly three times. The above cleaning process is also performed when the ozone concentration of the ozone-dissolved water is set to 25 ppm, 30 ppm, and 35 ppm. After the cleaning process, the power spectral density ratio of the chemical oxide film formed on the surface of the silicon wafer is measured by AFM. The relationship between the concentration of ozone-dissolved water and the power spectral density ratio is shown in... Figure 9 (b)

[0112] Depend on Figure 9 (b) It is clear that if the concentration of ozone dissolved water increases, the power spectral density ratio also increases. By changing the concentration of ozone dissolved water, the surface state of the chemical oxide film can be adjusted.

[0113] (Example 1 of the invention)

[0114] according to Figure 3 The flowchart shown illustrates the determination of cleaning conditions for silicon wafers. First, 194 silicon wafers were prepared that had undergone a cleaning process consisting of a hydrofluoric acid treatment step, a mixing treatment step, and an ozone treatment step, with the final step being an ozone treatment step. It should be noted that the cleaning conditions differed for each of the 194 silicon wafers; specifically, at least one of the following was different: the duration of the final ozone treatment step, the duration of the mixing treatment step, and the ozone concentration of the ozone-dissolved water in the ozone treatment step.

[0115] 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 using an ellipsometry, and the power spectral density (wavelength range: 3.9 nm to 10 nm) was measured using an AFM (Aspect-Measuring Fluid Dynamics) to determine the thickness of the chemical oxide film. The correlation between the power spectral density ratio (X2 (%), relative to the wavelength range: 3.9 nm to 100 nm) and cleaning conditions was determined (cleaning correlation acquisition process). Next, each silicon wafer was placed in a heat treatment furnace and subjected to heat treatment at 800°C for 50 minutes under an oxidizing atmosphere (dry O2 (= 100% dry oxygen)). For each silicon wafer after heat treatment, the thickness of the thermal oxide film formed on the wafer surface was measured using an ellipsometry, and the increase in oxide film thickness was calculated. Next, the thickness of the obtained chemical oxide film was used. The increase in power spectral density ratio X2 (%) and the increase in oxide film thickness. The data are subjected to multiple regression analysis to find the constants A, B, and C of equation (1). As a result, the following equation (3) is obtained as the heat treatment correlation (heat treatment correlation obtaining step).

[0116] Y = -0.4254X1+ 0.0960X2+ 48.990 (3)

[0117] By inputting the thickness of the chemical oxide film and the power spectral density ratio X2 (%) in the above equation (3), the increase in the thickness of the oxide film after the heat treatment step

[0118] The relationship between the predicted value and the measured value of the increase in the thickness of the oxide film after the heat treatment step is shown. The correlation coefficient is 0.80, and it is found that there is a good correlation between the predicted value and the measured value of the increase in the thickness of the oxide film after the heat treatment step. Figure 10 Then, the heat treatment condition in the heat treatment step is determined, and the target thickness of the thermal oxide film formed in the heat treatment step under the heat treatment condition is determined as

[0119] (heat treatment condition determining step). Further, the thickness of the chemical oxide film and the power spectral density corresponding to the above target thickness are determined, and the cleaning condition corresponding to the determined thickness of the chemical oxide film and the power spectral density is determined (cleaning condition determining step). In this way, the cleaning condition of the silicon wafer which can obtain the thermal oxide film of the target thickness is determined. (Conventional Example)

[0120] Thirty silicon wafers are prepared, and these silicon wafers are divided into three batches, and the cleaning step consisting of the hydrofluoric acid treatment step, the mixed treatment step, and the ozone treatment step, and the final step being the ozone treatment step is performed using three cleaning devices. The cleaning condition of the final ozone treatment step is set to a step time of 30 seconds and an ozone concentration of 25 ppm for all of the three cleaning devices. Next, each silicon wafer is introduced into a heat treatment furnace, and the heat treatment step is performed under the heat treatment condition of an oxidizing atmosphere (dry O2 (= dry oxygen 100%), 800°C, and 50 minutes. At this time, the target thickness of the thermal oxide film is set to

[0121] For each silicon wafer which has undergone the heat treatment step, the thickness of the thermal oxide film formed on the wafer surface is measured using an ellipsometer. (Invention Example 2)

[0122] The same three cleaning devices as in the conventional example are used, and the cleaning step and the heat treatment step are performed in the same manner as in the conventional example. However, for each of the three devices, the cleaning condition of the final ozone treatment step is set to a step time of 30 seconds and an ozone concentration of 25 ppm, and the thickness of the chemical oxide film and the power spectral density are set to 0.5 nm and 0.5%, respectively.

[0123] Figure 3 ​The flowchart shown determines the cleaning conditions of the cleaning process. The determined cleaning conditions are: for the apparatus ID 1 apparatus, the process time of the final ozone treatment process is 75 seconds and the ozone concentration is 20 ppm, for the apparatus ID 2 apparatus, the process time of the final ozone treatment process is 15 seconds and the ozone concentration is 30 ppm, and for the apparatus ID 3 apparatus, the process time of the final ozone treatment process is 30 seconds and the ozone concentration is 25 ppm. Thirty silicon wafers are divided into three batches, and the three apparatuses are used to perform the cleaning process under the determined cleaning conditions described above. The other conditions are all the same as in the past example.

[0124] Figure 11 (a) indicates the thickness of the thermal oxide film formed in the heat treatment process for each of the three apparatuses in the past example. The thickness of the thermal oxide film is determined by Figure 11 (a) clearly shows that the deviation of the thickness of the thermal oxide film differs depending on the cleaning apparatus.

[0125] Figure 11 (b) indicates the thickness of the thermal oxide film formed in the past example and in the inventive example 2. The thickness of the thermal oxide film is determined by Figure 11 (b) clearly shows that the deviation of the thickness of the thermal oxide film in the inventive example 2 is smaller than that in the past example. Thus, according to the present application, it is known that the thickness of the thermal oxide film formed in the heat treatment process can be well controlled.

[0126] Industrial applicability

[0127] According to the present application, the thickness of the thermal oxide film can be well controlled. Thereby, the yield of the device can be improved, and the improvement of the production efficiency and the reduction of waste can be achieved.

Claims

1. A method for determining cleaning conditions for a semiconductor wafer, wherein, Includes the following processes: The cleaning correlation acquisition process involves preparing multiple semiconductor wafers that have undergone cleaning processes under various cleaning conditions, and determining the correlation between the thickness and surface condition of the chemical oxide film formed on the respective surfaces of the multiple semiconductor wafers and the cleaning conditions, i.e., the cleaning correlation. The heat treatment correlation acquisition process involves preparing multiple semiconductor wafers that have undergone heat treatment following the cleaning process, for each of the more than one different heat treatment conditions in the heat treatment process. For the thermal oxide film formed on the surface of each of the multiple semiconductor wafers, the correlation between the increase in the thickness of the oxide film after the heat treatment process and the thickness of the chemical oxide film and the surface state is determined, i.e., the heat treatment correlation. The heat treatment condition determination process determines the heat treatment conditions in the heat treatment process and simultaneously determines the target thickness of the thermal oxide film formed on the surface of the semiconductor wafer in the heat treatment process under the determined heat treatment conditions. and The cleaning condition determination process, based on the heat treatment correlation and the cleaning correlation, determines the cleaning condition for the thickness of the thermal oxide film formed on the surface of the semiconductor wafer in the heat treatment process under the determined heat treatment conditions to be the target thickness.

2. The method for determining cleaning conditions for semiconductor wafers according to claim 1, wherein, The surface state is indicated by the power spectral density of surface roughness as measured by atomic force microscopy.

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

4. The method for determining cleaning conditions for semiconductor wafers according to claim 3, wherein, For each of the more than one heat treatment conditions, the constants A, B, and C are determined in advance. The constants A, B, and C are determined based on the heat treatment conditions determined in the heat treatment condition determination process.

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

6. The method for determining cleaning conditions for a semiconductor wafer according to claim 1 or 2, wherein, The cleaning process includes: Hydrofluoric acid treatment process in which only an aqueous solution of hydrofluoric acid is supplied to the semiconductor substrate. A mixing process in which hydrofluoric acid aqueous solution and ozone dissolved water are simultaneously supplied as chemical solutions to semiconductor wafers, and The ozone treatment process that uses only ozone-dissolved water as a chemical solution to supply to semiconductor wafers. The duration of the mixing process varies among the multiple cleaning conditions.

7. The method for determining cleaning conditions for a semiconductor wafer according to claim 1 or 2, wherein, The cleaning process includes: Hydrofluoric acid treatment processes that only supply hydrofluoric acid aqueous solutions to semiconductor substrates, and The ozone treatment process that uses only ozone-dissolved water as a chemical solution to supply to semiconductor wafers. The concentration of ozone dissolved in the water varies in the multiple cleaning conditions.

8. The method for determining cleaning conditions for a semiconductor wafer according to claim 1 or 2, wherein, The cleaning process includes: Hydrofluoric acid treatment processes that only supply hydrofluoric acid aqueous solutions to semiconductor substrates, and The ozone treatment process that uses only ozone-dissolved water as a chemical solution to supply to semiconductor wafers. The time required for the final hydrofluoric acid treatment process varies among the various cleaning conditions.

9. The method for determining cleaning conditions for a semiconductor wafer according to claim 1 or 2, wherein, The cleaning process includes: Hydrofluoric acid treatment process in which only hydrofluoric acid aqueous solution is supplied to the semiconductor substrate, and The ozone treatment process that uses only ozone-dissolved water as a chemical solution to supply to semiconductor wafers. In the multiple cleaning conditions, the rotational speed of the semiconductor substrate in the final hydrofluoric acid treatment process is different.

10. A method for cleaning a semiconductor wafer, wherein, The semiconductor wafer is cleaned under the cleaning conditions determined by the method for determining cleaning conditions for semiconductor wafers according to claim 1 or 2.

11. The semiconductor wafer cleaning method according to claim 8, wherein, The semiconductor wafer is a silicon wafer.

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