Method for forming thermal oxide film on semiconductor substrate

Abstract

The present invention relates to a method for forming a thermal oxide film on a semiconductor substrate, comprising the following steps: a correlation acquisition step, in which a plurality of semiconductor substrates having chemical oxide films formed by cleaning having different compositions are prepared in advance, thermally oxidized under the same thermal oxidation treatment conditions to form thermal oxide films, and a correlation between the composition of the chemical oxide films and the thickness of the thermal oxide films is determined; a cleaning condition determination step, in which the composition of the chemical oxide films is determined based on the correlation obtained in the correlation acquisition step so that the thickness of the thermal oxide films formed on the semiconductor substrates is a predetermined thickness, and cleaning conditions for forming the chemical oxide films having the determined composition are determined; a substrate cleaning step, in which the semiconductor substrates are cleaned under the determined cleaning conditions; and a thermal oxide film forming step, in which the cleaned semiconductor substrates are thermally oxidized under the same thermal oxidation treatment conditions as those in the correlation acquisition step to form thermal oxide films on the surfaces of the semiconductor substrates. Thus, the thermal oxide films can be formed with a desired film thickness with good reproducibility.

Description

Technical Field

[0001] The present invention relates to a method for forming a thermal oxidation film on a semiconductor substrate. Background Art

[0002] As semiconductor integrated circuit elements become more multilayered and thinner, the various films that constitute the elements are required to be further thinned. For example, Patent Document 1 records that in the bonding of silicon wafers, the silicon wafers used need to have OH groups on the surface. If they are cleaned with a conventional SC1 cleaning solution, a natural oxide film will be formed on the surface. In addition, for example, Patent Document 2 has just disclosed a method for improving the gate characteristics of a MOS transistor. This method cleans the silicon surface before forming a gate oxide film, thereby forming a gate insulating film on the basis of hydrogen termination. Therefore, in order to form an extremely thin silicon oxide film uniformly and reproducibly within a surface or between substrates, it is impossible to ignore the influence of a natural oxide film or a chemical oxide film (an oxide film formed by a cleaning solution used in the cleaning process of the semiconductor substrate) formed in advance on the semiconductor substrate.

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Application Laid-Open No. 09-063910

[0006] Patent Document 2: Japanese Patent Application Laid-Open No. 2000-216156

[0007] Patent Document 3: Japanese Patent Application Laid-Open No. 2003-115516

[0008] Patent Document 4: Japanese Patent Application Laid-Open No. 2002-270596

[0009] Non-patent literature

[0010] Non-patent literature 1: Takahagi, Vacuum, 33(11), 854(1990) Summary of the Invention

[0011] Technical Problems to be Solved by the Invention

[0012] In fact, the present inventors conducted research and studies that revealed that, for example, different methods for cleaning semiconductor substrates can lead to differences in the thickness of the subsequent thermally oxidized film. They also discovered that this difference in thermally oxidized film thickness is not determined by the thickness of the natural oxide film or the chemical oxide film before thermal oxidation. Therefore, until actual thermal oxidation is performed on semiconductor substrates and the film thickness is evaluated, it is impossible to determine the actual differences in thermally oxidized film thickness, making it difficult to manage the thermal oxidation process.

[0013] Patent Document 3 proposes using heat to desorb OH groups contained in a CVD oxide film (evaluation of OH groups in the CVD oxide film using infrared spectroscopy) as water, thereby using this to calibrate and manage moisture meters. In Patent Document 3, a low-temperature heat treatment is performed to desorb OH groups contained in the CVD oxide film as water, but the relationship between this and the growth of the thermal oxide film is not discussed. This suggests that OH groups are contained in the oxide film and are a source of water, but CVD oxide films are relatively thick, and the OH groups contained in oxide films as thin as natural oxide films and the subsequent growth of the thermal oxide film are not discussed.

[0014] Patent Document 4 states that the Si2p spectrum directly above the silicon substrate can be determined by measuring the Si2p spectrum using X-ray photoelectron spectroscopy (XPS). 1+ 、Si 2+ 、Si 3+ However, the purpose is to determine the surface roughness between silicon and the oxide film, which is not related to the technology of the present invention for controlling the thickness of the thermal oxide film during the oxidation heat treatment.

[0015] The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a method for forming a thermal oxide film on a semiconductor substrate, which method can form the thermal oxide film to a desired thin thickness with good reproducibility.

[0016] Technical means to solve technical problems

[0017] The present invention is proposed to achieve the above-mentioned purpose. It is a method for forming a thermal oxide film on a semiconductor substrate. The method comprises the following steps: a correlation acquisition step, wherein a plurality of semiconductor substrates are prepared in advance, wherein the plurality of semiconductor substrates have chemical oxide films formed by cleaning and the compositions of the chemical oxide films are different, the plurality of semiconductor substrates are thermally oxidized under the same thermal oxidation treatment conditions to form thermal oxide films, and the correlation between the composition of the chemical oxide films and the thickness of the thermal oxide films is obtained; a cleaning condition determination step, wherein the correlation obtained in the correlation acquisition step is used to determine the correlation between the composition of the chemical oxide films and the thickness of the thermal oxide films. The composition of the chemical oxidation film is determined in such a manner that the thickness of the thermal oxidation film of the semiconductor substrate, which is the object of forming the thermal oxidation film, is a specified thickness, and the cleaning conditions for forming the chemical oxidation film having the determined composition of the chemical oxidation film are determined at the same time; a substrate cleaning process, wherein the semiconductor substrate is cleaned under the cleaning conditions determined in the cleaning condition determination process; and a thermal oxidation film forming process, wherein, for the semiconductor substrate cleaned in the substrate cleaning process, the semiconductor substrate is thermally oxidized under the same conditions as the thermal oxidation treatment conditions in the correlation acquisition process, thereby forming a thermal oxidation film on the surface of the semiconductor substrate.

[0018] According to such a method for forming a thermal oxide film on a semiconductor substrate, the thermal oxide film can be formed to a desired thin thickness with good reproducibility, thereby simplifying the management of the thermal oxidation process.

[0019] The present invention is proposed to achieve the above-mentioned purpose. It is a method for forming a thermal oxide film on a semiconductor substrate. The method is a method for forming a thermal oxide film on a semiconductor substrate. The method comprises the following steps: a correlation acquisition step, wherein a plurality of semiconductor substrates are prepared in advance, wherein the plurality of semiconductor substrates have chemical oxide films formed by cleaning and the amounts of OH groups contained in the chemical oxide films are different, the plurality of semiconductor substrates are thermally oxidized under the same thermal oxidation treatment conditions to form thermal oxide films, and the correlation between the amount of OH groups in the chemical oxide films and the thickness of the thermal oxide films is obtained; a cleaning condition determination step, wherein the correlation obtained in the correlation acquisition step is used to determine the relationship between the amount of OH groups in the chemical oxide films and the thickness of the thermal oxide films. The invention relates to a method for forming a thermal oxidation film comprising determining the amount of OH groups in the chemical oxidation film so that the thickness of the thermal oxidation film formed on the semiconductor substrate serving as the object for forming the thermal oxidation film is a specified thickness, and simultaneously determining the cleaning conditions for forming the chemical oxidation film having the determined amount of OH groups; a substrate cleaning process, wherein the semiconductor substrate is cleaned under the cleaning conditions determined in the cleaning condition determination process; and a thermal oxidation film forming process, wherein the semiconductor substrate cleaned in the substrate cleaning process is thermally oxidized under the same conditions as the thermal oxidation treatment conditions in the correlation acquisition process, thereby forming a thermal oxidation film on the surface of the semiconductor substrate.

[0020] According to this method for forming a thermal oxide film on a semiconductor substrate, a thin thermal oxide film having a predetermined thickness can be formed with good reproducibility, thereby simplifying the management of the thermal oxidation process.

[0021] At this time, the amount of the OH group is preferably determined by ATR-FT-IR measurement of the chemical oxidation film using a prism for ATR measurement and the amount of the OH group is preferably determined by ATR-FT-IR measurement at 3300 cm -1 It is calculated based on the absorbance of the nearby OH groups.

[0022] ATR-FT-IR has a higher sensitivity to OH groups present on the surface than conventional transmission FT-IR, and thus can evaluate the amount of OH groups with higher accuracy.

[0023] Preferably, after the substrate cleaning step and before the thermal oxidation film forming step, there is further a step of measuring the amount of OH groups, wherein the amount of OH groups contained in the chemical oxidation film formed on the semiconductor substrate by cleaning performed in the substrate cleaning step is measured.

[0024] By measuring the amount of OH groups contained in the chemical oxidation film between the substrate cleaning step and the thermal oxidation film forming step, the thermal oxidation film can be formed with further good reproducibility.

[0025] The present invention is proposed to achieve the above-mentioned purpose. It is a method for forming a thermal oxide film on a semiconductor substrate. The method is a method for forming a thermal oxide film on a semiconductor substrate. The method comprises the following steps: a correlation acquisition step, wherein a plurality of semiconductor substrates are prepared in advance, wherein the plurality of semiconductor substrates have chemical oxide films formed by cleaning and the stoichiometric ratios of the constituent elements of the chemical oxide films are different, the plurality of semiconductor substrates are thermally oxidized under the same thermal oxidation treatment conditions to form thermal oxide films, and the correlation between the stoichiometric ratios of the constituent elements of the chemical oxide films and the thickness of the thermal oxide films is obtained; a cleaning condition determination step, wherein the correlation obtained in the correlation acquisition step is used to determine the correlation between the stoichiometric ratios of the constituent elements of the chemical oxide films and the thickness of the thermal oxide films. relationship, so as to determine the stoichiometric ratio of the constituent elements of the chemical oxidation film in such a manner that the thickness of the thermal oxidation film formed on the semiconductor substrate as the object of forming the thermal oxidation film is a specified thickness, and at the same time determine the cleaning conditions for forming the chemical oxidation film with the determined stoichiometric ratio; a substrate cleaning process, wherein the semiconductor substrate is cleaned under the cleaning conditions determined in the cleaning condition determination process; and a thermal oxidation film forming process, wherein, for the semiconductor substrate cleaned in the substrate cleaning process, the semiconductor substrate is thermally oxidized under the same conditions as the thermal oxidation treatment conditions in the correlation acquisition process, thereby forming a thermal oxidation film on the surface of the semiconductor substrate.

[0026] According to such a method for forming a thermal oxide film on a semiconductor substrate, the thermal oxide film can be formed to a desired thin thickness with good reproducibility, thereby simplifying the management of the thermal oxidation process.

[0027] At this time, XPS is used to measure the peak intensities of the bond energy of the constituent elements of the chemical oxidation film in the state where the substrate atoms of the semiconductor substrate are not bonded to oxygen atoms and in the state where the substrate atoms are bonded to oxygen atoms to form a low-value oxide, as well as the peak intensities of the bond energy in the state where the substrate atoms are completely bonded to oxygen atoms. The stoichiometric ratio of the constituent elements of the chemical oxidation film is the ratio of the measured peak intensities.

[0028] The XPS method is a method that can evaluate information of the outermost layer of a semiconductor substrate easily and with high precision, thereby making it possible to form a thermal oxide film to a desired thin thickness with better reproducibility.

[0029] The present invention is proposed to achieve the above-mentioned purpose. It is a method for forming a thermal oxide film on a semiconductor substrate, wherein the thermal oxide film is formed on the semiconductor substrate. The method comprises the following steps: a correlation acquisition step, wherein a plurality of semiconductor substrates are prepared in advance, wherein the plurality of semiconductor substrates have chemical oxide films formed by cleaning and the amounts of hydrogen atoms contained in the chemical oxide films are different, the plurality of semiconductor substrates are thermally oxidized under the same thermal oxidation treatment conditions to form thermal oxide films, and the correlation between the amount of hydrogen atoms in the chemical oxide films and the thickness of the thermal oxide films is obtained; a cleaning condition determination step, wherein, based on the correlation obtained in the correlation acquisition step, The amount of hydrogen atoms in the chemical oxidation film is determined in such a manner that the thickness of the thermal oxidation film formed on the semiconductor substrate, which is the object of forming the thermal oxidation film, is a specified thickness, and the cleaning conditions for forming the chemical oxidation film having the determined amount of hydrogen atoms are determined at the same time; a substrate cleaning process, wherein the semiconductor substrate is cleaned under the cleaning conditions determined in the cleaning condition determination process; and a thermal oxidation film forming process, wherein, for the semiconductor substrate cleaned in the substrate cleaning process, the semiconductor substrate is thermally oxidized under the same conditions as the thermal oxidation treatment conditions in the correlation acquisition process, thereby forming a thermal oxidation film on the surface of the semiconductor substrate.

[0030] According to such a method for forming a thermal oxide film on a semiconductor substrate, the thermal oxide film can be formed to a desired thin thickness with good reproducibility, thereby simplifying the management of the thermal oxidation process.

[0031] In this case, the semiconductor substrate is a silicon wafer, and the thermal oxide film is a silicon oxide film.

[0032] The method for forming a thermal oxide film on a semiconductor substrate of the present invention is particularly suitable for forming a silicon oxide film on a silicon substrate.

[0033] In this case, the amount of hydrogen atoms can be calculated by performing RBS measurement on the chemical oxide film and obtaining the ratio of hydrogen atoms in the chemical oxide film.

[0034] Such a measurement method enables evaluation of the amount of hydrogen atoms with higher accuracy.

[0035] At this time, the amount of hydrogen atoms can be measured by ATR-FT-IR on the chemical oxide film using an ATR measurement prism and the amount of hydrogen atoms can be measured based on the wavelength of 2130 cm -1 It is calculated based on the absorbance of the nearby SiH3 groups.

[0036] ATR-FT-IR has higher sensitivity to hydrogen atoms present in chemically oxidized films than conventional transmission FT-IR, and thus can evaluate the amount of hydrogen atoms with higher accuracy.

[0037] At this time, it is preferred that a step of measuring the amount of hydrogen atoms is further provided after the substrate cleaning step and before the thermal oxidation film forming step, wherein the amount of hydrogen atoms contained in the chemical oxidation film formed on the semiconductor substrate by cleaning performed in the substrate cleaning step is measured.

[0038] By measuring the amount of hydrogen atoms contained in the chemical oxide film between the substrate cleaning step and the thermal oxide film forming step, the thermal oxide film can be formed with further good reproducibility.

[0039] In this case, the predetermined thickness is 1 to 10 nm.

[0040] If the thickness of the thermal oxide film to be formed is within this range, a thin thermal oxide film having a constant thickness can be formed with better reproducibility.

[0041] Effects of the Invention

[0042] As described above, according to the method for forming a thermal oxide film on a semiconductor substrate of the present invention, a thermal oxide film can be formed to a desired thin thickness with good reproducibility. As a result, the management of the thermal oxidation process becomes simple. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 The amount of OH groups (3300 cm -1 A graph showing the relationship between the relative absorbance of the thermal oxide film and the thickness of the thermal oxide film.

[0044] Figure 2 The concentration of NH4OH and the amount of OH groups (3300 cm -1 The relationship between the relative absorbance and the

[0045] Figure 3 The concentration of O3 and the amount of OH groups (3300 cm -1 The relationship between the relative absorbance and the

[0046] Figure 4 Graph showing the relationship between the concentration of NH4OH and the thickness of the thermal oxide film.

[0047] Figure 5 Graph showing the relationship between the concentration of O 3 and the thickness of the thermal oxide film.

[0048] Figure 6 To show Si 0～3+ A graph showing the relationship between the peak intensity ratio and the thickness of the thermal oxide film.

[0049] Figure 7 To show Si 4+ A graph showing the relationship between the peak intensity ratio and the thickness of the thermal oxide film.

[0050] Figure 8 It is a figure which shows an example of X-ray photoelectron spectroscopy (XPS) measurement.

[0051] Figure 9 FIG1 is a diagram showing an example of an XPS spectrum of a sample having a silicon oxide film on a silicon substrate.

[0052] Figure 10 The concentration of NH4OH and Si 0～3+ A graph showing the relationship between the ratio of peak intensities.

[0053] Figure 11 The concentration of NH4OH and Si 4+ A graph showing the relationship between the ratio of peak intensities.

[0054] Figure 12 The concentration of O3 and Si 0～3+ A graph showing the relationship between the ratio of peak intensities.

[0055] Figure 13 The concentration of O3 and Si 4+ A graph showing the relationship between the ratio of peak intensities.

[0056] Figure 14 It is a graph showing the relationship between the amount of hydrogen atoms (the ratio of hydrogen atoms in the chemical oxide film) obtained by RBS measurement and the thickness of the thermal oxide film.

[0057] Figure 15 The figure shows the amount of hydrogen atoms determined by ATR-FT-IR measurement (2130 cm -1 Graph showing the relationship between the absorbance of the thermal oxide film and the thickness of the thermal oxide film.

[0058] Figure 16 Graph showing the relationship between the concentration of NH4OH and the amount of hydrogen atoms (ratio of hydrogen atoms in the chemical oxide film: RBS measurement).

[0059] Figure 17 The concentration of NH4OH and the amount of hydrogen atoms (2130 cm -1 : ATR-FT-IR measurement). DETAILED DESCRIPTION

[0060] Hereinafter, the present invention will be described in detail, but the present invention is not limited thereto.

[0061] As described above, a method for forming a thermal oxide film on a semiconductor substrate is required that can form a thermal oxide film to a desired thin thickness with good reproducibility.

[0062] The inventors of the present application have conducted in-depth research on the above-mentioned technical problems and found that the following method for forming a thermal oxide film on a semiconductor substrate can form a thermal oxide film to an expected thin thickness with good reproducibility. As a result, the management of the thermal oxidation process becomes simple, and the present invention has been completed. The method for forming a thermal oxide film on a semiconductor substrate is a method for forming a thermal oxide film on a semiconductor substrate, and the method has the following steps: a correlation acquisition step, wherein a plurality of semiconductor substrates are prepared in advance, the plurality of semiconductor substrates have chemical oxide films formed by cleaning and the composition of the chemical oxide films is different, the plurality of semiconductor substrates are thermally oxidized under the same thermal oxidation treatment conditions to form thermal oxide films, and the correlation between the composition of the chemical oxide film and the thickness of the thermal oxide film is obtained; cleaning A washing condition determination process, wherein, based on the correlation obtained in the correlation acquisition process, the composition of the chemical oxidation film is determined in such a manner that the thickness of the thermal oxidation film formed on the semiconductor substrate, which is the object of forming the thermal oxidation film, is a specified thickness, and at the same time, the cleaning conditions for forming the chemical oxidation film having the determined composition of the chemical oxidation film are determined; a substrate cleaning process, wherein the semiconductor substrate is cleaned under the cleaning conditions determined in the cleaning condition determination process; and a thermal oxidation film forming process, wherein, for the semiconductor substrate cleaned in the substrate cleaning process, the semiconductor substrate is thermally oxidized under the same conditions as the thermal oxidation treatment conditions in the correlation acquisition process, thereby forming a thermal oxidation film on the surface of the semiconductor substrate.

[0063] The inventors of the present application have conducted in-depth research on the above-mentioned technical problems and found that a thin thermal oxidation film of a certain thickness can be formed with good reproducibility by the following thermal oxidation film forming method for semiconductor substrates. As a result, the management of the thermal oxidation process becomes simple, and the present invention is completed. The thermal oxidation film forming method for semiconductor substrates is a method for forming a thermal oxidation film on a semiconductor substrate, and the method has the following steps: a correlation acquisition step, wherein a plurality of semiconductor substrates are prepared in advance, and the plurality of semiconductor substrates have chemical oxidation films formed by cleaning and the amounts of OH groups contained in the chemical oxidation films are different. The plurality of semiconductor substrates are thermally oxidized under the same thermal oxidation treatment conditions to form thermal oxidation films, and the correlation between the amount of OH groups in the chemical oxidation film and the thickness of the thermal oxidation film is obtained. a cleaning condition determining step, wherein, based on the correlation obtained in the correlation acquiring step, the amount of OH groups in the chemical oxidation film is determined in such a manner that the thickness of the thermal oxidation film formed on the semiconductor substrate, which is the object of forming the thermal oxidation film, is a specified thickness, and at the same time, the cleaning conditions for forming the chemical oxidation film having the determined amount of OH groups are determined; a substrate cleaning step, wherein the semiconductor substrate is cleaned under the cleaning conditions determined in the cleaning condition determining step; and a thermal oxidation film forming step, wherein, for the semiconductor substrate cleaned in the substrate cleaning step, the semiconductor substrate is thermally oxidized under the same conditions as the thermal oxidation treatment conditions in the correlation acquiring step, thereby forming a thermal oxidation film on the surface of the semiconductor substrate.

[0064] The inventors of the present application have conducted in-depth research on the above-mentioned technical problems and found that the following method for forming a thermal oxide film on a semiconductor substrate can form a thermal oxide film to an expected thin thickness with good reproducibility. As a result, the management of the thermal oxidation process becomes simple, and the present invention is completed. The method for forming a thermal oxide film on a semiconductor substrate is a method for forming a thermal oxide film on a semiconductor substrate. The method has the following steps: a correlation acquisition step, wherein a plurality of semiconductor substrates are prepared in advance, the plurality of semiconductor substrates have chemical oxide films formed by cleaning and the stoichiometric ratios of the constituent elements of the chemical oxide films are different, the plurality of semiconductor substrates are thermally oxidized under the same thermal oxidation treatment conditions to form thermal oxide films, and the correlation between the stoichiometric ratios of the constituent elements of the chemical oxide films and the thickness of the thermal oxide films is obtained. a cleaning condition determining process, wherein, based on the correlation obtained in the correlation acquiring process, the stoichiometric ratio of the constituent elements of the chemical oxidation film is determined in such a manner that the thickness of the thermal oxidation film formed on the semiconductor substrate, which is the object of forming the thermal oxidation film, is a specified thickness, and at the same time, the cleaning conditions for forming the chemical oxidation film having the determined stoichiometric ratio are determined; a substrate cleaning process, wherein the semiconductor substrate is cleaned under the cleaning conditions determined in the cleaning condition determining process; and a thermal oxidation film forming process, wherein, for the semiconductor substrate cleaned in the substrate cleaning process, the semiconductor substrate is thermally oxidized under the same conditions as the thermal oxidation treatment conditions in the correlation acquiring process, thereby forming a thermal oxidation film on the surface of the semiconductor substrate.

[0065] The inventors of the present application have conducted in-depth research on the above-mentioned technical problems and found that the following method for forming a thermal oxide film on a semiconductor substrate can form a thermal oxide film to an expected thin thickness with good reproducibility. As a result, the management of the thermal oxidation process becomes simple, and the present invention is completed. The method for forming a thermal oxide film on a semiconductor substrate is a method for forming a thermal oxide film on a semiconductor substrate. The method has the following steps: a correlation acquisition step, wherein a plurality of semiconductor substrates are prepared in advance, the plurality of semiconductor substrates have chemical oxide films formed by cleaning and the amounts of hydrogen atoms contained in the chemical oxide films are different, the plurality of semiconductor substrates are thermally oxidized under the same thermal oxidation treatment conditions to form thermal oxide films, and the correlation between the amount of hydrogen atoms in the chemical oxide film and the thickness of the thermal oxide film is obtained. relationship; a cleaning condition determination process, wherein, based on the correlation obtained in the correlation acquisition process, the amount of hydrogen atoms in the chemical oxidation film is determined in such a way that the thickness of the thermal oxidation film formed on the semiconductor substrate, which is the object of forming the thermal oxidation film, is a specified thickness, and at the same time, the cleaning conditions for forming the chemical oxidation film having the determined amount of hydrogen atoms are determined; a substrate cleaning process, wherein the semiconductor substrate is cleaned under the cleaning conditions determined in the cleaning condition determination process; and a thermal oxidation film forming process, wherein, for the semiconductor substrate cleaned in the substrate cleaning process, the semiconductor substrate is thermally oxidized under the same conditions as the thermal oxidation treatment conditions in the correlation acquisition process, thereby forming a thermal oxidation film on the surface of the semiconductor substrate.

[0066] Hereinafter, description will be given with reference to the accompanying drawings.

[0067] The inventors of this application conducted in-depth research on the fact that different semiconductor substrate cleaning methods can lead to differences in the thickness of the thermal oxide film formed. They discovered that the composition of the chemical oxide film formed by cleaning the semiconductor substrate significantly affects the thermal oxidation process. By exploiting this phenomenon, they developed a thermal oxidation method that can reproducibly form thin thermal oxide films of a specified thickness.

[0068] For example, when the semiconductor substrate is a silicon wafer, the chemical oxide film is a silicon oxide film, which can be expressed as SiO x (0<x≤2). Various analysis results show that the elements related to the composition of chemical oxide film are silicon, oxygen, and hydrogen. x The x in the equation is called the oxygen ratio. The oxidation characteristics of the formed thermal oxide film are affected by the oxygen ratio (x) at the interface between the chemical oxide film and the silicon, causing the formation rate of the thermal oxide film to change. Fluctuations in the oxygen ratio refer to the presence of elements other than oxygen at varying ratios.

[0069] Hydrogen exists in the form of Si-H or Si-OH. That is, as the number of H increases, the ratio of oxygen decreases. While the ratio of H is low compared to other constituent elements such as oxygen or silicon, it affects the bonding state of silicon by capping it in the form of Si-H or existing in the back bond of silicon. Furthermore, the presence of functional groups such as OH groups plays an important role in determining reactivity.

[0070] Furthermore, silicon and oxygen, the main constituent elements, are referred to as suboxides due to their different bonding ratios with SiO2. Suboxides act as precursors to silicon oxide films and are important components in determining the properties of the resulting thermal oxide film. Therefore, by focusing on the oxygen ratio of the chemical oxide film and determining the correlation between the chemical oxide film's composition and the thermal oxide film's thickness, the thickness of the thermal oxide film can be controlled.

[0071] In the present invention, the semiconductor substrates prepared to obtain the correlation only need to have different chemical oxide film compositions, and the compositions include the amount of OH groups, the stoichiometric ratio of constituent elements, and the amount of hydrogen atoms.

[0072] In this specification, an oxide film formed by cleaning a semiconductor substrate is defined as a chemical oxide film. The cleaning method and conditions are not particularly limited. This includes oxide films formed by cleaning with a chemical solution or pure water.

[0073] Specific embodiments of the present invention will be described.

[0074] [First embodiment]

[0075] In a method for forming a thermal oxide film on a semiconductor substrate according to a first embodiment of the present invention, before thermal oxidation treatment of the semiconductor substrate, the composition of the chemical oxide film formed on the surface of the semiconductor substrate after cleaning is measured in advance, and the correlation between the composition of the chemical oxide film and the thickness of the thermal oxide film when thermally oxidizing the semiconductor substrate is determined. The composition of the chemical oxide film on the surface of the semiconductor substrate to be thermally oxidized is determined so that the thickness of the thermal oxide film formed on the semiconductor substrate is a predetermined thickness, and the cleaning conditions are adjusted to form the chemical oxide film with the determined composition. This allows for the reproducible formation of a thin thermal oxide film of the predetermined thickness.

[0076] The inventors of this application conducted in-depth research on the fact that different semiconductor substrate cleaning methods can lead to differences in the thickness of the thermal oxide film formed. They discovered that the composition of the chemical oxide film formed by cleaning the semiconductor substrate significantly affects the thermal oxidation process. By exploiting this phenomenon, they developed a thermal oxidation method that can reproducibly form thin thermal oxide films of a specified thickness.

[0077] A method for forming a thermal oxide film on a semiconductor substrate according to a first embodiment of the present invention will be described.

[0078] (Correlation acquisition process)

[0079] First, prepare multiple semiconductor substrates. Silicon wafers are preferably used as the semiconductor substrates. The thermal oxide film formed in this case is a silicon oxide film. Silicon wafers are widely used as semiconductor substrates, and thermal oxide films can be formed particularly during device fabrication. Therefore, forming a thermal oxide film and evaluating the silicon wafer itself allows for more accurate evaluation.

[0080] First, in order to create a state in which there is no oxide film on the surface of the prepared semiconductor substrate, it is preferably cleaned with HF (hydrofluoric acid). After the oxide film is removed by cleaning with HF, further cleaning is performed. The cleaning method performed after HF cleaning is not particularly limited, but for example, cleaning using chemical solutions such as SC1 cleaning and O3 cleaning can be performed, or cleaning such as pure water rinsing can also be performed. Chemical oxide films can be formed on the prepared multiple semiconductor substrates by cleaning after HF cleaning. At this time, the composition of the chemical oxide films of the multiple semiconductor substrates is made different. When cleaning is performed by a method using a chemical solution, semiconductor substrates with different compositions of chemical oxide films can be easily prepared, so it is preferred. It is preferred to perform the cleaning process for obtaining the correlation with as many different cleaning types and / or cleaning conditions as possible. In order to obtain the correlation, it is preferred to perform cleaning with as many different cleaning types and / or cleaning conditions as possible, so as to obtain in advance the correlation between multiple cleaning conditions and the composition of the chemical oxide film.

[0081] Next, the composition of the chemical oxide film formed by cleaning is measured. In this case, the measurement method is not particularly limited as long as it can clearly identify the difference in the composition of the chemical oxide film.

[0082] Next, multiple semiconductor substrates with different chemical oxide film compositions are thermally oxidized under the same thermal oxidation treatment conditions to form thermal oxide films. The conditions for forming the thermal oxide films are not particularly limited and can be performed using conventional methods. The thickness of the formed thermal oxide films is then measured. For example, this can be measured using ellipsometry.

[0083] The correlation between the composition of the chemical oxidation film thus obtained and the thickness of the formed thermal oxidation film was determined.

[0084] In addition, the composition of the chemical oxidation film or the thickness of the thermal oxidation film can be measured by using a monitor wafer that has undergone the same cleaning treatment and thermal oxidation treatment as the semiconductor substrate on which the thermal oxidation film is formed, or by extracting a portion of the same processed semiconductor substrate.

[0085] (Cleaning Condition Determination Step)

[0086] Cleaning conditions are determined to achieve a predetermined thickness for a thermal oxide film formed on a surface of a semiconductor substrate. Based on the correlation obtained in the correlation acquisition step, the composition of the chemical oxide film is determined to form a thermal oxide film of the predetermined thickness. Cleaning conditions are also determined to form a chemical oxide film having the determined composition. For example, a correlation between the cleaning conditions and the composition of the chemical oxide film may be obtained in advance and utilized.

[0087] (Substrate Cleaning Process)

[0088] Next, a new semiconductor substrate on which a thermal oxide film is actually to be formed is prepared, and cleaning is performed under the cleaning conditions determined in the cleaning condition determination step.

[0089] (Thermal Oxide Film Formation Process)

[0090] The thermal oxidation process is performed under the same conditions as those performed in the correlation acquisition step, thereby forming a thermal oxide film on the surface of the semiconductor substrate cleaned in the substrate cleaning step.

[0091] By forming a thermal oxide film on a semiconductor substrate through the above-described steps of the present invention, a thin thermal oxide film having a predetermined thickness can be formed with good reproducibility.

[0092] In addition, in the present invention, when the thickness of the thermal oxide film formed on the surface of the semiconductor substrate is as thin as 1 to 10 nm, a more significant effect can be obtained, and therefore it is suitable for forming the thermal oxide film in this range.

[0093] [Second embodiment]

[0094] The second embodiment of the present invention focuses on the differences in the amount of OH groups contained in a chemical oxide film. Prior to thermal oxidation of the semiconductor substrate, the correlation between the amount of OH groups in the chemical oxide film formed on the surface of the cleaned semiconductor substrate and the thickness of the thermal oxide film when the semiconductor substrate is thermally oxidized is determined. The amount of OH groups in the chemical oxide film is determined so that the thickness of the thermal oxide film formed on the semiconductor substrate is a predetermined thickness, thereby forming a chemical oxide film having the determined amount of OH groups. This allows for the reproducible formation of an oxide film of a predetermined thickness.

[0095] The inventors of this application conducted an in-depth study on the fact that different cleaning methods of semiconductor substrates will cause differences in the thickness of the thermal oxidation film formed. As a result, it was found that the amount of OH groups in the chemical oxidation film formed by cleaning the semiconductor substrate will have a huge impact on the thermal oxidation treatment.

[0096] Figure 1 Figure 2 shows the amount of OH groups in the chemical oxide film on the surface of the silicon wafer (3300 cm -1 The relationship between the relative absorbance of 3300cm and the thickness of the silicon thermal oxide film is shown in the figure. -1 The relative absorbance increases, and the thermal oxide film becomes thicker. This phenomenon is similar to the phenomenon that the oxidation rate of wet oxidation is faster than that of dry oxidation during thermal oxidation using an oxidizing gas. It is believed that the thickness of the thermal oxide film after thermal oxidation treatment varies depending on the amount of OH groups contained in the chemical oxide film formed on the surface of the silicon wafer.

[0097] In addition, the amount of OH groups contained in the chemical oxide film can be obtained by, for example, examining the infrared absorption characteristics of the chemical oxide film. As a measurement of infrared absorption characteristics, for example, FT-IR measurement can be performed, based on 3300 cm -1 The amount of OH groups can be calculated by the relative absorbance near 3300cm -1 The relative absorbance value near 3300cm is used as an indicator of the amount of OH groups. -1 The relative absorbance near the OH group is expressed as the amount of OH groups.

[0098] A method for forming a thermal oxide film on a semiconductor substrate according to a second embodiment of the present invention will be described.

[0099] (Correlation acquisition process)

[0100] First, prepare multiple semiconductor substrates in the same manner as in the first embodiment. Silicon wafers are preferably used as the semiconductor substrates. The thermal oxide film formed at this time is a silicon oxide film. Silicon wafers are widely used as semiconductor substrates, particularly because they can form thermal oxide films during device fabrication. Therefore, forming a thermal oxide film and evaluating the silicon wafer itself allows for more accurate evaluation.

[0101] Next, in order to create a state in which there is no oxide film on the surface of the prepared semiconductor substrate, it is preferably cleaned with HF (hydrofluoric acid). After the oxide film is removed by cleaning with HF, further cleaning is performed. The cleaning method performed after HF cleaning is not particularly limited, but for example, cleaning using chemical solutions such as SC1 cleaning and O3 cleaning can be performed, or cleaning such as pure water rinsing can also be performed. Chemical oxide films can be formed on the prepared multiple semiconductor substrates by cleaning after HF cleaning. At this time, the amounts of OH groups contained in the chemical oxide films of the multiple semiconductor substrates are made different. When cleaning is performed using a chemical solution, semiconductor substrates with different amounts of OH groups in the chemical oxide film can be easily prepared by using chemical solutions with different OH group concentrations, so it is preferred. Furthermore, if SC1 cleaning is performed, the higher the NH4OH concentration and the stronger the alkalinity, the higher the 3300cm -1 The greater the absorbance (i.e., the greater the content of OH groups), the easier it is to manufacture semiconductor substrates with different amounts of OH groups in the chemical oxide film by changing the NH4OH concentration. The range of correlation between the chemical solution concentration and the amount of OH groups varies depending on the cleaning method. Therefore, to obtain a correlation, it is preferable to perform cleaning using as many different cleaning types and / or cleaning conditions as possible, thereby obtaining correlations between multiple cleaning conditions and the amount of OH groups.

[0102] Next, the amount of OH groups contained in each chemical oxide film formed by each cleaning method is measured. In this case, ATR-FT-IR measurement of the chemical oxide film is preferably performed using an ATR measurement prism. Compared to conventional transmission FT-IR, ATR-FT-IR measurement can evaluate the OH groups present on the semiconductor substrate surface with sufficient sensitivity.

[0103] Figure 2 The concentration of NH4OH and the amount of OH groups in the chemical oxidation film (3300 cm -1 The relationship between the relative absorbance of Figure 3 The concentration of O3 and the amount of OH groups in the chemical oxidation film (3300 cm -1 The concentration of NH4OH and the amount of OH groups (3300cm -1 On the other hand, no correlation was found between the concentration of O3 and the amount of OH groups (3300cm -1 Therefore, depending on the cleaning method, there is sometimes no correlation between the concentration of the chemical solution and the amount of OH groups.

[0104] Next, multiple semiconductor substrates, each containing a different amount of OH groups in the chemical oxide film, are subjected to thermal oxidation treatment under the same thermal oxidation treatment conditions to form a thermal oxide film. The conditions for forming the thermal oxide film are not particularly limited and can be performed using conventional methods. The thickness of the formed thermal oxide film is then measured. For example, this can be measured using ellipsometry.

[0105] The relationship between the amount of OH groups in the chemical oxidation film and the thickness of the thermal oxidation film was found. -1 The relative absorbance near Figure 1 The correlation between the chemical oxide film and the thermal oxide film is found to be greater as the amount of OH groups in the chemical oxide film increases. Using this result, the amount of OH groups in the chemical oxide film is determined so that the thickness of the thermal oxide film formed on the semiconductor substrate is a predetermined thickness. By forming a chemical oxide film with the determined amount of OH groups, a thermal oxide film of a predetermined thickness can be formed.

[0106] In addition, the amount of OH groups in the chemical oxidation film (3300cm -1 The measurement of the relative absorbance near the semiconductor substrate or the thickness of the thermal oxide film can be performed by using a wafer control that has undergone the same cleaning treatment and thermal oxidation treatment as the semiconductor substrate on which the thermal oxide film is formed, or by extracting a part of the same processed semiconductor substrate.

[0107] (Cleaning Condition Determination Step)

[0108] The cleaning conditions for making the thickness of the thermal oxidation film formed on the surface of the semiconductor substrate a specified thickness are determined in the same manner as in the first embodiment. Based on the correlation obtained in the correlation acquisition process, the amount of OH groups in the thermal oxidation film of the specified thickness is determined, and at the same time, the cleaning conditions for forming a chemical oxidation film having the determined amount of OH groups are determined. In determining the cleaning conditions, for example, the correlation between the cleaning conditions and the amount of OH groups can be obtained in advance and the correlation can be utilized. For example, in the above specific example, when the specified thickness of the thermal oxidation film to be formed is 5.1 nm, based on the correlation obtained in the correlation acquisition process, Figure 1 The correlation between the thermal oxidation film thickness and the amount of OH groups is shown in Figure 2. It can be seen that the amount of OH groups is 0.145. Figure 2 Based on the relationship shown in FIG. 1 , the cleaning condition in which the amount of OH groups is 0.145 is selected and determined. In this specific example, SC1 cleaning is performed in which the concentration of NH 4 OH is 0.001 to 0.03%.

[0109] (Substrate Cleaning Process)

[0110] Next, a semiconductor substrate on which a thermal oxide film is actually to be formed is newly prepared in the same manner as in the first embodiment, and is cleaned under the cleaning conditions determined in the cleaning condition determination step.

[0111] (Step of measuring the amount of OH groups)

[0112] If the amount of OH groups contained in the chemical oxide film formed on the semiconductor substrate by cleaning in the substrate cleaning process is measured, the actual amount of OH groups can be confirmed before thermal oxidation, thereby enabling the thermal oxide film to be formed with better reproducibility. For example, when the amount of OH groups deviates from the target, HF cleaning can be performed to remove the oxide film first, and then the cleaning conditions can be determined again and cleaning can be performed, thereby forming a chemical oxide film with an amount of OH groups closer to the target. In addition, at this time, the amount of OH groups in the chemical oxide film (3300cm -1 The measurement of the relative absorbance near the semiconductor substrate (relative absorbance near the semiconductor substrate) can also be performed by using a wafer control that has been subjected to the same cleaning process as the semiconductor substrate on which the thermal oxide film is formed, or by extracting a part of the same processed semiconductor substrate.

[0113] (Thermal Oxide Film Formation Process)

[0114] Finally, in the same manner as in the first embodiment, a thermal oxidation treatment is performed under the same conditions as those performed in the correlation acquisition step, thereby forming a thermal oxidation film on the surface of the semiconductor substrate.

[0115] By forming a thermal oxide film on a semiconductor substrate through the above-described steps of the present invention, a thin thermal oxide film having a predetermined thickness can be formed with good reproducibility.

[0116] In the present invention, more significant effects can be obtained when the thickness of the thermal oxide film formed on the surface of the semiconductor substrate is as thin as 1 to 10 nm, so it is preferable to form the thermal oxide film in this range.

[0117] [Third embodiment]

[0118] Furthermore, a third embodiment of the present invention relates to a method for forming a thermal oxide film on a semiconductor substrate. This method focuses on differences in the stoichiometric ratios of the constituent elements of a chemical oxide film. Prior to thermal oxidation of the semiconductor substrate, the correlation between the stoichiometric ratios of the constituent elements of the chemical oxide film formed on the surface of the semiconductor substrate after cleaning and the thickness of the thermal oxide film when the semiconductor substrate is thermally oxidized is determined. The stoichiometric ratios of the constituent elements of the chemical oxide film on the surface of the semiconductor substrate to be thermally oxidized are determined so that the thickness of the thermal oxide film formed on the semiconductor substrate is a predetermined thickness. The cleaning conditions are then adjusted to achieve the determined stoichiometric ratios, thereby forming the chemical oxide film. This allows for the reproducible formation of a thin thermal oxide film of a predetermined thickness.

[0119] The inventors of this application conducted in-depth research on the differences in thickness of thermally oxidized films formed when different semiconductor substrate cleaning methods are used. They discovered that the stoichiometric ratio of the constituent elements of the chemically oxidized film formed by cleaning the semiconductor substrate significantly affects the thermal oxidation process. By exploiting this phenomenon, they developed a thermal oxidation method that can reproducibly form thin thermally oxidized films of a specified thickness.

[0120] A method for forming a thermal oxide film on a semiconductor substrate according to a third embodiment of the present invention will be described.

[0121] (Correlation acquisition process)

[0122] First, multiple semiconductor substrates are prepared in the same manner as in the first embodiment. Silicon substrates are preferably used as the semiconductor substrates. The thermal oxide film formed in this process is a silicon oxide film. Silicon substrates are widely used as semiconductor substrates, and because thermal oxide films can be formed during the device manufacturing process, more accurate evaluation can be performed by forming a thermal oxide film and then evaluating the silicon substrate itself.

[0123] Next, in order to create a state in which the surface of the prepared semiconductor substrate does not have an oxide film, it is preferably cleaned using HF (hydrofluoric acid). After the oxide film is removed by cleaning using HF, further cleaning is performed. The cleaning method performed after HF cleaning is not particularly limited, but for example, cleaning using chemical solutions such as SC1 cleaning and O3 cleaning can be performed, or cleaning such as pure water rinsing can also be performed. Chemical oxide films can be formed on multiple prepared semiconductor substrates by cleaning after HF cleaning. At this time, the stoichiometric ratios of the constituent elements in the chemical oxide films of multiple semiconductor substrates are made different. When cleaning using a chemical solution, semiconductor substrates with different stoichiometric ratios of the constituent elements of the chemical oxide film can be easily prepared by using various chemical solutions of different concentrations, so it is preferred. It is preferred to perform the cleaning process for obtaining the correlation with as many different cleaning types and / or cleaning conditions as possible. In addition, the range of the correlation between the concentration of the chemical solution and the stoichiometric ratio varies depending on the cleaning method, so in order to obtain the correlation, it is preferably cleaned with as many different cleaning types and / or cleaning conditions as possible, thereby obtaining the correlation between multiple cleaning conditions and the stoichiometric ratio.

[0124] Next, the stoichiometric ratio of the constituent elements of the chemical oxide film formed by cleaning is determined.

[0125] In addition, the method for obtaining and evaluating the stoichiometric ratio of the constituent elements of the chemical oxide film is not particularly limited, and any method may be used as long as it is a method for obtaining the stoichiometric ratio of the constituent elements of the chemical oxide film. For example, the XPS method is a method for simply and accurately evaluating the information of the outermost layer of a semiconductor substrate, and is applicable to the evaluation of the stoichiometric ratio of the present invention. XPS is used to measure the peak intensity of the bond energy of the state in which the substrate atoms of the semiconductor substrate are not bonded to oxygen atoms and the state in which the substrate atoms are bonded to oxygen atoms to form a low-value oxide, and the peak intensity of the bond energy of the state in which the substrate atoms are completely bonded to oxygen atoms, among the constituent elements of the chemical oxide film. The stoichiometric ratio of the constituent elements of the chemical oxide film is the ratio of the measured peak intensities. In addition, for example, the surface of the semiconductor substrate can be irradiated with He ions by the RBS method, and the energy of the colliding atoms can be obtained based on the range, and the stoichiometric ratio of the constituent elements of the chemical oxide film formed on the surface of the semiconductor substrate can be obtained based on the energy.

[0126] Furthermore, when the semiconductor substrate is a silicon substrate and the oxide film formed is a silicon oxide film, the constituent elements of the chemical oxide film are Si and O. In this case, the stoichiometric ratio is the ratio of the atomic bonding states of Si atoms and O atoms in the chemical oxide film, that is, the ratio of the Si-Si bonds where silicon atoms are not bonded to oxygen atoms to the so-called suboxides of the Si-O bonds (silicon oxide) where silicon atoms are bonded to oxygen atoms, and the Si-O bonds where they are completely bonded to oxygen atoms to form SiO2. The ratio of each bond can be determined by measuring the peak intensity of the bond energy using XPS.

[0127] like Figure 8 As shown in one example, the XPS method is a method of using a detector 2 to detect photoelectrons (from the outermost electrons) released from the sample surface (the surface of the silicon oxide film 3 formed on the silicon 4) by irradiating the sample surface with X-rays through an X-ray source 1 and measuring the kinetic energy to analyze the composition of the elements constituting the sample surface or the chemical bonding state. At this time, the irradiated X-ray source is not particularly limited, and any energy device can be used as long as the stoichiometric ratio of the constituent elements of the target chemical oxide film can be measured. Furthermore, the kinetic energy of the released photoelectrons is affected by the electronic state of the atoms such as the valence electrons (valence number) of the atoms and the distance between atoms. By observing the change in energy (chemical shift), the chemical bonding state can be easily identified. For the mean free path of photoelectrons, silicon is 2.1nm and silicon oxide film is 3.3nm, so it can be considered as one of the methods suitable for evaluating the outermost surface of the silicon substrate.

[0128] Figure 9An example of an XPS spectrum of a sample with a thin silicon oxide film on a silicon substrate is shown. The energy range of the sp3 orbital where the outermost electrons of silicon exist is illustrated. The outermost electrons contribute to the reaction, while the inner electrons that do not contribute to the reaction are omitted. The horizontal axis is the bond energy, and the vertical axis is the photoelectron count. The bond energy varies depending on the bonding state of Si and O, so the bonding state or bonded atoms can be evaluated. In addition, the vertical axis is the photoelectron count, which varies according to the number of each bonding state.

[0129] When the chemical oxide film is a silicon oxide film, it can be divided into 99 to 100 eV from the bonding state of Si-Si bond (Si 0 ), and 101 to 105 eV corresponding to the bonding state of the silicon atom and the oxygen atom (Si 1+～4+ ). Among them, Si 0 The peak of Si-Si bond is separated into two, which is caused by spin-orbit interaction. In addition, if one oxygen atom is bonded to a silicon atom, it is Si 1+ , the state of SiO2 with four oxygen atoms bonded to silicon atoms is Si 4+ There are four types of bonding states between silicon atoms and oxygen atoms because the oxide film is thin and does not necessarily form a stoichiometric composition.

[0130] There is also spin-orbit interaction in Si-O bonds, but it cannot be observed in conventional XPS due to energy resolution issues. 1+ To Si 3+ The bond energy intensity is low and has not been clearly observed, but it is known from previous knowledge that it exists. The intensity of each peak can be separated by energy spectrum to obtain the intensity.

[0131] When determining the stoichiometric ratio of the constituent elements of the silicon oxide film on the silicon substrate, that is, the ratio of the peak intensity of the bond energy of Si and O, the SiO2 composition is 4+ The peak intensity is related to the Si 0 To Si 3+ The peak intensities of each peak are accumulated as much as possible. 1+～3+ That is, all the Si components that may be oxidized are added together to form Si 0～3+ , with stoichiometric Si 4+ Separate the components and find Figure 9 The area of ​​the obtained peak intensity was defined as the ratio of the peak intensity.

[0132] The Si obtained above can be 0～3+ The peak intensity of Si 4+The ratio of the peak intensities of Si is summed up and the peak intensity ratio is obtained. 0～3+ With Si 4+ The correlation between the ratio of the peak intensities and the thickness of the thermal oxide film was obtained.

[0133] Next, a thermal oxidation treatment is performed on multiple semiconductor substrates having different stoichiometric ratios of the constituent elements of the chemical oxide film under the same thermal oxidation treatment conditions to form a thermal oxide film. The conditions for forming the thermal oxide film are not particularly limited and can be performed using conventional methods. The thickness of the formed thermal oxide film is then measured. For example, this can be measured using ellipsometry.

[0134] The correlation between the stoichiometric ratio of the constituent elements of the chemical oxide film obtained above, that is, the ratio of the peak intensities, and the thickness of the formed thermal oxide film was determined. Figure 6 To show Si 0～3+ The relationship between the peak intensity ratio and the thickness of the thermal oxide film is shown in the figure. Figure 7 To show Si 4+ The relationship between the ratio of the peak intensity of the thermal oxide film and the thickness of the thermal oxide film is shown in the figure. It can be found that there is a relationship between the thickness of the thermal oxide film and the stoichiometric ratio of the constituent elements of the chemical oxide film. Figure 6 and Figure 7 As shown in the correlation, it can be seen that as Si 0～3+ The ratio of the peak intensity of increases, the thickness of the thermal oxide film becomes thicker. 4+ The ratio of the peak intensities decreases, and the thickness of the thermal oxide film increases. This result can be used to determine the stoichiometric ratio of the constituent elements of the chemical oxide film so that the thickness of the thermal oxide film formed on the semiconductor substrate is a predetermined thickness, and a chemical oxide film having the determined stoichiometric ratio is formed, thereby forming a thin thermal oxide film of a predetermined thickness.

[0135] In addition, the analysis of the stoichiometric ratio of the constituent elements of the chemical oxidation film or the measurement of the thickness of the thermal oxidation film can be carried out by using a control wafer that has undergone the same cleaning treatment or thermal oxidation treatment as the semiconductor substrate on which the thermal oxidation film is formed, or by extracting a portion of the same processed semiconductor substrate.

[0136] (Cleaning Condition Determination Step)

[0137] In the same manner as in the first embodiment, cleaning conditions are determined so that the thickness of the thermal oxide film formed on the surface of the semiconductor substrate becomes a predetermined thickness. Based on the correlation obtained in the correlation obtaining step, the Si substrate under which the thermal oxide film of the predetermined thickness is formed is determined. 0～3+ and / or Si 4+The ratio of the peak intensities of the bonding, that is, the stoichiometric ratio of the constituent elements of the chemical oxide film, is determined, and at the same time, the cleaning conditions for forming the chemical oxide film having the determined peak intensity ratio are determined. In determining the cleaning conditions, for example, the correlation between the cleaning conditions and the peak intensity ratio can be obtained in advance and the correlation can be used. For example, in the above specific example, when the thickness of the target thermal oxide film is 5.15nm, according to the correlation obtained in the correlation acquisition process, Figure 6 The thickness of the thermal oxide film is shown in Figure 2. 0～3+ The correlation between the ratio of the bonding peak intensity and the Si 0 ～3+ The ratio of the peak intensity of the bond is 84.5%. Figure 10 Based on the relationship shown in FIG. 1 , the cleaning conditions that make the peak intensity ratio 84.5% may be selected and determined. In this specific example, SC1 cleaning with an NH 4 OH concentration of 3% is determined.

[0138] (Substrate Cleaning Process)

[0139] Next, in the same manner as in the first embodiment, a new semiconductor substrate is prepared as a target for actually forming a thermal oxide film, and cleaning is performed under the cleaning conditions determined in the cleaning condition determination step.

[0140] (Thermal Oxide Film Formation Process)

[0141] Finally, in the same manner as in the first embodiment, thermal oxidation treatment is performed under the same conditions as the thermal oxidation treatment performed in the correlation acquisition step, thereby forming a thermal oxidation film on the surface of the semiconductor substrate cleaned in the substrate cleaning step.

[0142] By forming a thermal oxide film on a semiconductor substrate through the above-described steps of the present invention, a thin thermal oxide film having a predetermined thickness can be formed with good reproducibility.

[0143] In addition, in the present invention, when the thickness of the thermal oxide film formed on the surface of the semiconductor substrate is as thin as 1 to 10 nm, a more significant effect can be obtained, and therefore it is suitable for forming the thermal oxide film in this range.

[0144] [Fourth embodiment]

[0145] Furthermore, a fourth embodiment of the present invention relates to a method for forming a thermal oxide film on a semiconductor substrate. This method focuses on the amount of hydrogen atoms contained in a chemical oxide film. Prior to thermal oxidation of the semiconductor substrate, the amount of hydrogen atoms in the chemical oxide film formed on the surface of the semiconductor substrate after cleaning is measured. The correlation between the amount of hydrogen atoms and the thickness of the thermal oxide film when thermally oxidizing the semiconductor substrate is determined. The amount of hydrogen atoms in the chemical oxide film on the surface of the semiconductor substrate to be thermally oxidized is determined so that the thickness of the thermal oxide film formed on the semiconductor substrate is a predetermined thickness. The chemical oxide film is then formed by adjusting cleaning conditions to achieve the determined amount of hydrogen atoms. This allows for the reproducible formation of a thin thermal oxide film of a predetermined thickness.

[0146] The inventors of this application conducted in-depth research on the difference in thickness of thermally oxidized films formed when different semiconductor substrate cleaning methods are used. They discovered that the amount of hydrogen atoms in the chemical oxide film formed by cleaning the semiconductor substrate significantly affects the thermal oxidation process. By exploiting this phenomenon, they developed a thermal oxidation method that can reproducibly form thin thermally oxidized films of a specified thickness.

[0147] A method for forming a thermal oxide film on a semiconductor substrate according to a fourth embodiment of the present invention will be described.

[0148] (Correlation acquisition process)

[0149] First, multiple semiconductor substrates are prepared in the same manner as in the first embodiment. Silicon wafers are preferably used as the semiconductor substrates. In this case, the thermal oxide film formed is a silicon oxide film. Silicon wafers are widely used as semiconductor substrates, particularly because they can form thermal oxide films during device fabrication. Therefore, forming a thermal oxide film and evaluating the silicon wafer itself allows for more accurate evaluation.

[0150] Next, in order to create a state in which there is no oxide film on the surface of the prepared semiconductor substrate, it is preferably cleaned with HF (hydrofluoric acid). After the oxide film is removed by cleaning with HF, further cleaning is performed. The cleaning method performed after HF cleaning is not particularly limited, but for example, cleaning using chemical solutions such as SC1 cleaning and O3 cleaning can be performed, or cleaning such as pure water rinsing can also be performed. Chemical oxide films can be formed on the prepared multiple semiconductor substrates by cleaning after HF cleaning. At this time, the amount of hydrogen atoms in the chemical oxide films of the multiple semiconductor substrates is made different. When cleaning is performed using a chemical solution, semiconductor substrates with different amounts of hydrogen atoms in the chemical oxide film can be easily prepared by using various chemical solutions of different concentrations, so it is preferred. Furthermore, if SC1 cleaning is performed, the higher the NH4OH concentration and the stronger the alkalinity, the higher the ratio of hydrogen atoms or 2130cm -1The smaller the absorbance (i.e., the smaller the amount of hydrogen atoms), the easier it is to produce semiconductor substrates with different amounts of hydrogen atoms by changing the NH4OH concentration. It is preferable to perform the cleaning process for obtaining the correlation using as many different cleaning types and / or cleaning conditions as possible. Furthermore, the range of correlation between the concentration of the chemical solution and the amount of hydrogen atoms varies depending on the cleaning method. Therefore, to obtain the correlation, it is preferable to perform the cleaning process using as many different cleaning types and / or cleaning conditions as possible, thereby obtaining correlations between multiple cleaning conditions and the amount of hydrogen atoms.

[0151] Next, the amount of hydrogen atoms in the chemical oxide film formed by cleaning was determined.

[0152] In addition, the method for determining the amount of hydrogen atoms in the chemical oxidation film and the evaluation method are not particularly limited. Any method may be used as long as it can determine the amount of hydrogen atoms in the chemical oxidation film. For example, the amount of hydrogen atoms in the chemical oxidation film can be determined by examining the infrared absorption characteristics of the chemical oxidation film. As a measurement of infrared absorption characteristics, for example, ATR-FT-IR measurement can be performed, based on the 2130 cm -1 The amount of hydrogen atoms can be calculated by the absorbance near 2130cm -1 The absorbance near is the value of the relative absorbance of the stretching vibration of Si-H of SiH3, which can be used as an indicator of the amount of hydrogen atoms. In addition, as another method for determining the amount of hydrogen atoms, for example, Rutherford backscattering analysis (RBS) can be performed to determine the ratio of hydrogen atoms in the chemical oxide film and calculate it. In this case, the ratio of hydrogen atoms can be used as an indicator of the amount of hydrogen atoms. In the following, "2130cm -1 The absorbance of the hydrogen atom is called the "amount of hydrogen atoms".

[0153] Next, multiple semiconductor substrates having different amounts of hydrogen atoms in the chemical oxide film are subjected to thermal oxidation treatment under the same thermal oxidation treatment conditions to form thermal oxide films. The conditions for forming the thermal oxide film are not particularly limited and can be performed using conventional methods. The thickness of the formed thermal oxide film is then measured. For example, this can be measured using ellipsometry.

[0154] The correlation between the amount of hydrogen atoms in the chemical oxidation film obtained above and the thickness of the formed thermal oxidation film was determined. Figure 14 This is a graph showing the relationship between the amount of hydrogen atoms (the ratio of hydrogen atoms in the chemical oxidation film) obtained by RBS measurement and the thickness of the thermal oxidation film. Figure 15 The figure shows the amount of hydrogen atoms determined by ATR-FT-IR measurement (2130 cm -1The relationship between the absorbance of the thermal oxidation film and the thickness of the thermal oxidation film is shown in the figure. It can be found that there is a relationship between the thickness of the thermal oxidation film and the amount of hydrogen atoms in the chemical oxidation film. Figure 14 and Figure 15 The correlation shown in FIG1 shows that the thermal oxidation film tends to be thinner as the amount of hydrogen atoms increases. As the main reason for this tendency, it is known that the surface of silicon terminated with hydrogen becomes stable and loses its activity, as shown in non-patent document 1. Therefore, it is believed that the difference in the amount of hydrogen atoms contained in the chemical oxidation film formed on the surface by cleaning causes the oxidation rate to be different, so that even if thermal oxidation is performed under the same conditions, the film thickness after thermal oxidation will be different. This can be used to Figure 14 、 Figure 15 As a result, the amount of hydrogen atoms in the chemical oxidation film is determined so that the thickness of the thermal oxidation film formed on the semiconductor substrate is a specified thickness, and a chemical oxidation film having the determined amount of hydrogen atoms is formed, thereby forming a thin thermal oxidation film of a certain thickness.

[0155] In addition, the analysis of the amount of hydrogen atoms in the chemical oxidation film or the measurement of the thickness of the thermal oxidation film can be carried out by using a wafer control that has undergone the same cleaning treatment or thermal oxidation treatment as the semiconductor substrate on which the thermal oxidation film is formed, or by extracting a portion of the same processed semiconductor substrate.

[0156] (Cleaning Condition Determination Step)

[0157] In a similar manner to the first embodiment, cleaning conditions are determined to achieve a predetermined thickness for the thermal oxide film formed on the surface of the semiconductor substrate. Based on the correlation obtained in the correlation acquisition step, the amount of hydrogen atoms required to form the thermal oxide film of the predetermined thickness is determined, and cleaning conditions are simultaneously determined to form a chemical oxide film having the determined amount of hydrogen atoms. To determine the cleaning conditions, for example, a correlation between the cleaning conditions and the amount of hydrogen atoms can be obtained in advance and utilized.

[0158] For example, in the above specific example, when the target thermal oxide film thickness is 5.10 nm, according to the correlation relationship acquisition step, Figure 14 The correlation between the thickness of the thermal oxide film and the ratio of hydrogen atoms is shown in FIG. 1 , and it is known that a ratio of hydrogen atoms of 20% is sufficient. Figure 16 The cleaning conditions in which the amount of hydrogen atoms is 20% can be selected and determined based on the relationship shown. In this specific example, SC1 cleaning is determined to be performed with an NH4OH concentration of 0.03%.

[0159] (Substrate Cleaning Process)

[0160] Next, in the same manner as in the first embodiment, a new semiconductor substrate is prepared as a target for actually forming a thermal oxide film, and cleaning is performed under the cleaning conditions determined in the cleaning condition determination step.

[0161] (Step of measuring the amount of hydrogen atoms)

[0162] If the amount of hydrogen atoms contained in the chemical oxide film formed on the semiconductor substrate by cleaning in the substrate cleaning process is measured, the actual amount of hydrogen atoms can be confirmed before thermal oxidation, so that the thermal oxide film can be formed with better reproducibility. For example, when the amount of hydrogen atoms deviates from the target, HF cleaning can be performed to remove the chemical oxide film first, and then the cleaning conditions can be determined again and cleaning can be performed, so that a chemical oxide film with an amount of hydrogen atoms closer to the target can be formed. In addition, at this time, the amount of hydrogen atoms in the chemical oxide film (based on 2130cm -1 The measurement of the absorbance near the surface of the semiconductor substrate or the ratio of hydrogen atoms measured by RBS) can be performed by using a wafer control that has undergone the same cleaning treatment as the semiconductor substrate on which the thermal oxide film is formed, or by extracting a portion of the same processed semiconductor substrate.

[0163] (Thermal Oxide Film Formation Process)

[0164] Finally, in the same manner as in the first embodiment, thermal oxidation treatment is performed under the same conditions as the thermal oxidation treatment performed in the correlation acquisition step, thereby forming a thermal oxidation film on the surface of the semiconductor substrate cleaned in the substrate cleaning step.

[0165] By forming a thermal oxide film on a semiconductor substrate through the above-described steps of the present invention, a thin thermal oxide film having a predetermined thickness can be formed with good reproducibility.

[0166] In addition, in the present invention, when the thickness of the thermal oxide film formed on the surface of the semiconductor substrate is as thin as 1 to 10 nm, a more significant effect can be obtained, and therefore it is suitable for forming the thermal oxide film in this range.

[0167] Example

[0168] Hereinafter, the present invention will be described in detail with reference to Examples, but these Examples do not limit the present invention.

[0169] (Example 1)

[0170] Several boron-doped, normal-resistivity silicon single crystal substrates with a diameter of 300 mm were prepared. The surfaces of the silicon single crystal substrates were cleaned with 0.5% HF to initialize the substrate surfaces. SC1 cleaning was then performed at 70°C. During this cleaning, the NH4OH concentration was varied to 3, 0.3, 0.03, and 0.001%. Furthermore, an O3 cleaning (24°C) was performed as another cleaning step, with the O3 concentration fluctuating between 3, 20, and 40 ppm.

[0171] Then, a test piece of several centimeters square was cut out from the silicon single crystal substrate that had been cleaned in advance under each cleaning condition and subjected to ATR-FT-IR measurement (total reflection Fourier transform infrared spectroscopy) to measure the 3300 cm -1 The relative absorbance of NH4OH concentration, O3 concentration and the amount of OH groups in the chemical oxidation film (3300cm -1 The results are shown in Figure 2 、 Figure 3 In. Figure 2 As shown in the figure, as the concentration of NH4OH increases, the amount of OH groups (3300cm -1 The relative absorbance near the Figure 3 As shown, in the case of O3, no effect of O3 concentration on the amount of OH groups (3300cm -1 The dependence of the relative absorbance near the

[0172] The amount of OH groups (3300cm -1 The relative absorbance near ) varies depending on the cleaning conditions. This is because in the case of SC1 cleaning, the higher the NH4OH concentration and the stronger the alkalinity, the more OH groups it contains. However, in the case of O3 cleaning, the chemical solution is almost neutral and the amount of OH groups is small.

[0173] Next, another wafer cleaned under the same cleaning conditions as the wafer from which the test piece for ATR-FT-IR evaluation was cut was thermally oxidized (900°C, 5% oxygen, 60 minutes) so that the thickness of the thermal oxide film would be 5.1 nm. The thickness of the thermal oxide film was then measured by ellipsometry. The results are shown in Figure 4 、 Figure 5 middle. Figure 4 Graph showing the relationship between the NH4OH concentration and the thickness of the thermal oxide film. Figure 5 Graph showing the relationship between O3 concentration and thermal oxide film thickness.

[0174] According to the above results, we have Figure 1 The thickness of the thermal oxide film shown is 3300cm -1 The correlation between the relative absorbance near Figure 1As shown, it can be found that the thickness of the thermal oxidation film is about 3300cm -1 The relative absorbance near the surface of the film is correlated, and it can be found that the more OH groups in the chemical oxidation film formed after cleaning, the thicker the thermal oxidation film. Figure 1 The thickness of the thermal oxide film is shown to be related to the amount of OH groups (3300 cm -1 By determining the cleaning conditions when actually forming the thermal oxide film based on the correlation between the relative absorbance near the thermal oxide film and the relative absorbance near the thermal oxide film, a thermal oxide film with a thickness close to the expected thermal oxide film can be formed.

[0175] Next, the cleaning conditions for SC1 cleaning were studied to achieve a thermal oxide film thickness of 5.1 nm. Figure 1 It can be seen that 3300cm is needed -1 The absorbance is 0.145. To obtain this absorbance, Figure 2 It is known that the concentration of NH4OH can be set to 0.001-0.03%. Therefore, after cleaning the silicon single crystal substrate with NH4OH adjusted to 0.03% during SC1 cleaning, the thermal oxidation treatment was performed. As a result, the thickness of the thermally oxidized film was 5.1 nm, which was the same as the target thickness.

[0176] Thus, by utilizing the previously determined correlation, the thermal oxidation treatment conditions are set to the same conditions as those used in the correlation acquisition step, and the cleaning conditions are adjusted so that the amount of OH groups is generated to achieve the target thermal oxidation film thickness. This allows for the reproducible formation of a thermal oxidation film of a constant thickness without deviation. As a result, it is clear that the management of the thermal oxidation step is simplified.

[0177] (Example 2)

[0178] A boron-doped, normal-resistivity silicon single crystal substrate with a diameter of 300 mm was prepared. The silicon substrate surface was initialized by cleaning with 0.5% HF, followed by SC1 cleaning at 70°C. During this cleaning, the NH4OH concentration was varied to 3, 0.3, 0.03, and 0.001%. Furthermore, an O3 cleaning (24°C) was performed as another cleaning step, with the O3 concentration fluctuating between 3, 20, and 40 ppm.

[0179] Then, a test piece was cut out from the silicon single crystal substrate and XPS measurement was performed to measure Si 0～3+ With Si 4+ The peak intensity of NH4OH concentration was correlated with Si 0～3+ and Si 4+ The results are shown in Figure 10 、 Figure 11 middle. Figure 10 The concentration of NH4OH and Si0～3+ A graph showing the relationship between the ratio of peak intensities. Figure 11 The concentration of NH4OH and Si 4+ In addition, the peak intensity was measured in the same way to analyze the relationship between O3 concentration and Si 0～3+ and Si 4+ The results are shown in Figure 12 、 Figure 13 middle. Figure 12 The concentration of O3 and Si 0～3+ A graph showing the relationship between the ratio of peak intensities. Figure 13 The concentration of O3 and Si 4+ The results show that as the NH4OH concentration increases, Si 0～3+ The ratio of the peak intensity of Si 4+ On the other hand, in the case of O3, no dependence of the peak intensity ratio on the O3 concentration was found. Therefore, depending on the cleaning method, there may be no correlation between the chemical solution concentration and the peak intensity ratio of the constituent elements of the chemical oxide film.

[0180] All of these substrates were thermally oxidized (900° C., 5% oxidation, 60 minutes) so that the thickness of the thermally oxidized film would be approximately 5.1 nm. The thickness of the thermally oxidized film was then measured by ellipsometry.

[0181] From the experimental results carried out in the above manner, we can obtain the following Figure 6 、 Figure 7 As shown in the correlation. Figure 6 、 Figure 7 As shown, it can be found that the thickness of the thermal oxide film is related to the Si 0～3+ 、Si 4+ The ratio of the peak intensity of Si 0～3+ The greater the ratio of the peak intensity, the thicker the thermal oxide film tends to be, and the Si 4+ The smaller the ratio of the peak intensity, the thicker the thermal oxide film. No dependence of the O3 concentration on the stoichiometric ratio was found, but a good correlation was found between the stoichiometric ratio and the thickness of the thermal oxide film formed after O3 cleaning. In addition, according to Figure 6 、 Figure 7 The correlation between the thickness of the thermal oxidation film and the peak intensity ratio of the constituent elements of the chemical oxidation film shown in FIG. Figure 6 、 Figure 7 When the detection line of the middle dotted line determines the conditions under which the thermal oxide film is actually formed, a thermal oxide film having a thickness close to the expected thermal oxide film can be formed. Figure 6 、 Figure 7The dashed lines in the figure are detection lines. The calculation formulas for each detection line are shown below.

[0182] (Oxide film thickness nm) = 0.0342 × (Si 0～3+ The ratio of the peak intensity of

[0183] (Oxide film thickness nm) = -0.0342 × (Si 4+ The ratio of the peak intensity of

[0184] Next, the cleaning conditions for SC1 cleaning were studied to achieve a thermal oxide film thickness of 5.15 nm. Figure 6 , need to make Si 0～3+ The peak intensity ratio is 84.5%, according to Figure 7 , need to make Si 4+ The ratio of the peak intensity is 15.5%. To obtain this value, according to Figure 10 The concentration of NH4OH and Si 0～3+ The ratio of the peak intensities or Figure 11 The concentration of NH4OH and Si 4+ The graph of the ratio of peak intensities indicates that a 3% NH4OH concentration is sufficient. Therefore, after cleaning the silicon single crystal substrate with the NH4OH concentration adjusted to 3% during SC1 cleaning, thermal oxidation was performed under the same conditions as when the correlation was obtained. The thermally oxidized film had a thickness of 5.16 nm, achieving the target thickness.

[0185] Thus, by utilizing the previously determined correlation, the thermal oxidation treatment conditions are set to the same conditions as those used in the correlation acquisition step, and the cleaning conditions are adjusted to achieve the stoichiometric ratio of the chemical oxide film's constituent elements that achieves the target thermal oxide film thickness. This allows for the reproducible formation of a thin thermal oxide film of a constant thickness without deviation. As a result, it is clear that the management of the thermal oxidation step is simplified.

[0186] (Experimental Example 1)

[0187] A method of adjusting the thermal oxidation treatment conditions by RBS measurement so that the thickness of the thermally oxidized film reaches a target thickness will be described.

[0188] First, a boron-doped constant-resistivity silicon wafer with a diameter of 300 mm was prepared, and the surface of the silicon wafer was initialized by cleaning with 0.5% HF, followed by SC1 cleaning at 70° C. During this cleaning, the NH 4 OH concentration was varied to 3, 0.3, 0.03, and 0.001%.

[0189] Then, a test piece was cut out from the silicon wafer in advance and subjected to RBS measurement to measure the ratio of hydrogen atoms and compare the NH4OH concentration with the ratio of hydrogen atoms. The results are shown in Figure 16 middle. Figure 16 The graph shows the relationship between the NH4OH concentration and the ratio of hydrogen atoms in the chemical oxide film obtained by RBS measurement. Figure 16 As shown in the figure, it can be seen that the ratio of hydrogen atoms decreases as the NH4OH concentration increases. It is believed that the difference in the ratio of hydrogen atoms depending on the cleaning conditions is because in the case of SC1 cleaning, the higher the NH4OH concentration and the stronger the alkalinity, the fewer hydrogen atoms there are.

[0190] All of these wafers were thermally oxidized (900° C., 5% oxygen, 60 minutes) so that the thickness of the thermal oxide film would be 5.10 nm, and the thickness of the thermal oxide film was measured by ellipsometry.

[0191] The results of the experiments described above can be used to obtain the following Figure 14 As shown in the correlation. Figure 14 As shown in Figure 2, it was found that the thickness of the thermal oxide film is correlated with the ratio of hydrogen atoms in the chemical oxide film after cleaning, and it was found that the greater the ratio of hydrogen atoms in the chemical oxide film after cleaning, the thinner the film thickness. Figure 14 The correlation between the thickness of the thermal oxidation film and the amount of hydrogen atoms (the ratio of hydrogen atoms in the chemical oxidation film obtained by RBS measurement) is shown. By determining the cleaning conditions when the thermal oxidation film is actually formed, a thermal oxidation film with a thickness close to the expected thermal oxidation film can be formed.

[0192] (Experimental Example 2)

[0193] Furthermore, as another method, a method of adjusting the thermal oxidation treatment conditions by ATR-FT-IR measurement so that the thickness of the thermal oxide film reaches a target thickness will be described.

[0194] First, a silicon wafer similar to that prepared in Experimental Example 1 was prepared. Then, a test piece was cut out from the silicon wafer and subjected to ATR-FT-IR measurement. The 2130 cm -1 The absorbance near 2130 cm -1 The results are shown in Figure 17 middle. Figure 17 The figure shows the relationship between the NH4OH concentration and the 2130 cm -1 The results show that as the concentration of NH4OH increases, the absorbance of 2130 cm -1 The absorbance in the vicinity decreases, and the amount of hydrogen atoms in the chemical oxide film after cleaning decreases.

[0195] All of these wafers were thermally oxidized in the same manner as in Experimental Example 1, and the following Figure 15 As shown in the correlation. Figure 15 As shown in the figure, it can be found that the thickness of the thermal oxidation film is 2130cm -1 The absorbance near the cleaned chemical oxidation film is correlated with 2130 cm -1 The greater the absorbance near the surface, the thinner the film thickness. Figure 15 The thickness of the thermal oxide film is shown to be related to the amount of hydrogen atoms (2130 cm -1 By determining the cleaning conditions when actually forming the thermal oxide film based on the correlation between the absorbance near the surface of the thermal oxide film and the expected thickness of the thermal oxide film, a thermal oxide film can be formed.

[0196] (Example 3)

[0197] In the same manner as in Experimental Example 1 above, the correlation between the ratio of hydrogen atoms obtained by RBS measurement and the thickness of the thermal oxide film is obtained. First, a plurality of boron-doped silicon wafers of normal resistivity with a diameter of 300 mm are prepared, and the surfaces of the silicon wafers are initialized by cleaning with 0.5% HF. Then, SC1 cleaning (70°C, NH4OH concentration: 3, 0.3, 0.03, 0.001%) is performed respectively to produce substrates with different ratios of hydrogen atoms. Next, a test piece is cut out from each silicon wafer and subjected to RBS measurement to pre-determine the ratio of hydrogen atoms. Then, each substrate under each cleaning condition is subjected to a prescribed thermal oxidation treatment (900°C, 5% oxygen, 60 minutes), the thickness of the thermal oxide film is measured, and the correlation between the ratio of hydrogen atoms and the thickness of the thermal oxide film is obtained. At this time, the thickness of the thermal oxide film for which the correlation is obtained is set to about 5.10 nm. Thus, the following is obtained: Figure 14 The correlation shown.

[0198] Based on the data obtained in the process of obtaining the correlation, the NH4OH concentration and the ratio of hydrogen atoms were compared. The results are shown in Figure 16 middle. Figure 16 : is a graph showing the relationship between the NH4OH concentration and the ratio of hydrogen atoms. As a result, it can be seen that the ratio of hydrogen atoms tends to decrease as the NH4OH concentration increases.

[0199] Next, the cleaning conditions for SC1 cleaning were studied to achieve a thermal oxide film thickness of 5.10 nm. Figure 14 , the ratio of hydrogen atoms needs to be 20%. To obtain this value, according to Figure 16The graph showing the relationship between NH4OH concentration and the ratio of hydrogen atoms shows that a NH4OH concentration of 0.03% is sufficient. Therefore, after cleaning the silicon substrate with the NH4OH concentration adjusted to 0.03% during SC1 cleaning, thermal oxidation was performed under the same conditions as when the correlation was obtained. The resulting thermally oxidized film had a thickness of 5.10 nm, achieving the target thickness.

[0200] (Example 4)

[0201] The 2130 cm-1 concentration obtained by ATR-FT-IR measurement was determined in the same manner as in Experimental Example 2. -1 First, prepare multiple pieces of 300mm diameter boron-doped silicon wafers with normal resistivity, clean them with 0.5% HF to initialize the silicon wafer surface, and then perform SC1 cleaning (70℃, NH4OH concentration: 3, 0.3, 0.03, 0.001%) to make 2130cm -1 Next, a test piece was cut out from each silicon wafer and subjected to ATR-FT-IR measurement. The 2130 cm -1 Then, each substrate under each cleaning condition was subjected to a predetermined thermal oxidation treatment (900°C, 5% oxygen, 60 min), and the thickness of the thermal oxidation film was measured to obtain the absorbance around 2130 cm -1 The correlation between the absorbance near the thermal oxide film and the thickness of the thermal oxide film. At this time, the thickness of the thermal oxide film for which the correlation is obtained is about 5.10nm. Figure 15 The correlation shown.

[0202] According to the data obtained in the process of obtaining the correlation, the NH4OH concentration and 2130cm -1 The results are shown in Figure 17 middle. Figure 17 The NH4OH concentration and 2130 cm -1 The results show that as the concentration of NH4OH increases, the absorbance at 2130 cm -1 The absorbance near the surface tends to decrease.

[0203] Next, the cleaning conditions for SC1 cleaning were studied to achieve a thermal oxide film thickness of 5.10 nm. Figure 15 , need to make 2130cm -1 The absorbance near is 1.0. To obtain this value, according to Figure 17 The NH4OH concentration shown is related to the 2130 cm -1The graph of the relationship between absorbance and the surrounding area shows that an NH₄OH concentration of 0.03% is sufficient. Therefore, the silicon substrate was cleaned with the NH₄OH concentration adjusted to 0.03% during SC1 cleaning. Thermal oxidation was then performed under the same conditions as when the correlation was obtained. The resulting thermally oxidized film had a thickness of 5.10 nm, achieving the target thickness.

[0204] As shown in Examples 3 and 4, by utilizing the previously determined correlation, the thermal oxidation treatment conditions are set to the same conditions as those used in the correlation acquisition step. By adjusting the cleaning conditions so that the amount of hydrogen atoms is sufficient to achieve the target thermal oxide film thickness, a thin thermal oxide film of a constant thickness can be formed with good reproducibility and without deviation. As a result, it can be seen that the management of the thermal oxidation step is simplified.

[0205] The present invention is not limited to the above-described embodiments, which are merely examples, and any embodiments having substantially the same configuration and exhibiting the same functions and effects as the technical concept described in the claims of the present invention are within the technical scope of the present invention.

Claims

1. A method for forming a thermal oxide film on a semiconductor substrate, wherein: The method has the following steps: a correlation obtaining step, wherein a plurality of semiconductor substrates are prepared in advance, each of the plurality of semiconductor substrates having a chemical oxide film formed by cleaning and having different compositions, the plurality of semiconductor substrates are thermally oxidized under the same thermal oxidation treatment conditions to form thermal oxide films, and a correlation between the composition of the chemical oxide film and the thickness of the thermal oxide film is obtained; a cleaning condition determining step of determining the composition of the chemical oxide film so that the thickness of the thermal oxide film formed on the semiconductor substrate on which the thermal oxide film is to be formed becomes a predetermined thickness based on the correlation obtained in the correlation acquiring step, and simultaneously determining cleaning conditions for forming the chemical oxide film having the determined composition of the chemical oxide film; a substrate cleaning step, wherein the semiconductor substrate is cleaned under the cleaning conditions determined in the cleaning condition determining step; and A thermal oxidation film forming process, wherein, for the semiconductor substrate cleaned in the substrate cleaning process, the semiconductor substrate is thermally oxidized under the same conditions as the thermal oxidation treatment conditions in the correlation acquisition process, thereby forming a thermal oxidation film on the surface of the semiconductor substrate.

2. A method for forming a thermal oxide film on a semiconductor substrate, wherein: The method has the following steps: a correlation obtaining step, wherein a plurality of semiconductor substrates are prepared in advance, each of the plurality of semiconductor substrates having a chemical oxide film formed by cleaning, wherein the amount of OH groups contained in the chemical oxide film varies, the plurality of semiconductor substrates are thermally oxidized under the same thermal oxidation treatment conditions to form thermal oxide films, and a correlation between the amount of OH groups in the chemical oxide film and the thickness of the thermal oxide film is obtained; a cleaning condition determining step of determining the amount of OH groups in the chemical oxide film so that the thickness of the thermal oxide film formed on the semiconductor substrate on which the thermal oxide film is to be formed becomes a predetermined thickness based on the correlation obtained in the correlation acquiring step, and simultaneously determining cleaning conditions for forming the chemical oxide film having the determined amount of OH groups; a substrate cleaning step, wherein the semiconductor substrate is cleaned under the cleaning conditions determined in the cleaning condition determining step; and A thermal oxidation film forming process, wherein, for the semiconductor substrate cleaned in the substrate cleaning process, the semiconductor substrate is thermally oxidized under the same conditions as the thermal oxidation treatment conditions in the correlation acquisition process, thereby forming a thermal oxidation film on the surface of the semiconductor substrate.

3. The method for forming a thermal oxide film on a semiconductor substrate according to claim 2, wherein: The amount of the OH group was measured by ATR-FT-IR on the chemical oxidation film using an ATR measurement prism and the amount of the OH group was measured according to 3300 cm -1 It is calculated based on the absorbance of the nearby OH groups.

4. The method for forming a thermal oxide film on a semiconductor substrate according to claim 2 or 3, wherein: After the substrate cleaning step and before the thermal oxide film forming step, there is further provided a step of measuring the amount of OH groups, wherein the amount of OH groups contained in the chemical oxide film formed on the semiconductor substrate by cleaning performed in the substrate cleaning step is measured.

5. A method for forming a thermal oxide film on a semiconductor substrate, wherein: The method has the following steps: a correlation obtaining step, wherein a plurality of semiconductor substrates are prepared in advance, each of the plurality of semiconductor substrates having a chemical oxide film formed by cleaning, wherein the stoichiometric ratios of constituent elements of the chemical oxide film are different, the plurality of semiconductor substrates are subjected to thermal oxidation treatment under the same thermal oxidation treatment conditions to form thermal oxide films, and a correlation between the stoichiometric ratios of constituent elements of the chemical oxide film and the thickness of the thermal oxide film is obtained; a cleaning condition determining step of determining a stoichiometric ratio of constituent elements of the chemical oxide film so that the thickness of the thermal oxide film formed on the semiconductor substrate on which the thermal oxide film is to be formed becomes a predetermined thickness based on the correlation obtained in the correlation acquiring step, and simultaneously determining cleaning conditions for forming the chemical oxide film having the determined stoichiometric ratio; a substrate cleaning step, wherein the semiconductor substrate is cleaned under the cleaning conditions determined in the cleaning condition determining step; and A thermal oxidation film forming process, wherein, for the semiconductor substrate cleaned in the substrate cleaning process, the semiconductor substrate is thermally oxidized under the same conditions as the thermal oxidation treatment conditions in the correlation acquisition process, thereby forming a thermal oxidation film on the surface of the semiconductor substrate.

6. The method for forming a thermal oxide film on a semiconductor substrate according to claim 5, wherein: XPS is used to measure the peak intensities of the bond energy of the constituent elements of the chemical oxidation film, namely, the state in which the substrate atoms of the semiconductor substrate are not bonded to oxygen atoms and the state in which the substrate atoms are bonded to oxygen atoms to form a low-value oxide, as well as the peak intensities of the bond energy of the state in which the substrate atoms are completely bonded to oxygen atoms. The stoichiometric ratio of the constituent elements of the chemical oxidation film is the ratio of the measured peak intensities.

7. The method for forming a thermal oxide film on a semiconductor substrate according to any one of claims 1, 2 or 5, wherein: The semiconductor substrate is a silicon wafer, and the thermal oxide film is a silicon oxide film.

8. A method for forming a thermal oxide film on a semiconductor substrate, wherein: The method has the following steps: a correlation obtaining step, wherein a plurality of semiconductor substrates are prepared in advance, each of the plurality of semiconductor substrates having a chemical oxide film formed by cleaning, wherein the amount of hydrogen atoms contained in the chemical oxide film varies, the plurality of semiconductor substrates are thermally oxidized under the same thermal oxidation treatment conditions to form thermal oxide films, and a correlation between the amount of hydrogen atoms in the chemical oxide film and the thickness of the thermal oxide film is obtained; a cleaning condition determining step of determining the amount of hydrogen atoms in the chemical oxide film so that the thickness of the thermal oxide film formed on the semiconductor substrate on which the thermal oxide film is to be formed becomes a predetermined thickness based on the correlation obtained in the correlation acquiring step, and simultaneously determining cleaning conditions for forming the chemical oxide film having the determined amount of hydrogen atoms; a substrate cleaning step, wherein the semiconductor substrate is cleaned under the cleaning conditions determined in the cleaning condition determining step; and A thermal oxidation film forming process, wherein, for the semiconductor substrate cleaned in the substrate cleaning process, the semiconductor substrate is thermally oxidized under the same conditions as the thermal oxidation treatment conditions in the correlation acquisition process, thereby forming a thermal oxidation film on the surface of the semiconductor substrate.

9. The method for forming a thermal oxide film on a semiconductor substrate according to claim 8, wherein: The semiconductor substrate is a silicon wafer, and the thermal oxide film is a silicon oxide film.

10. The method for forming a thermal oxide film on a semiconductor substrate according to claim 8 or 9, wherein: The amount of hydrogen atoms is calculated from the ratio of hydrogen atoms in the chemical oxide film obtained by performing RBS measurement on the chemical oxide film.

11. The method for forming a thermal oxide film on a semiconductor substrate according to claim 9, wherein: The amount of hydrogen atoms was measured by ATR-FT-IR of the chemical oxidation film using an ATR measurement prism and the results were obtained based on the results at 2130 cm -1 It is calculated based on the absorbance of the nearby SiH3 groups.

12. The method for forming a thermal oxide film on a semiconductor substrate according to claim 8, wherein: After the substrate cleaning step and before the thermal oxide film forming step, there is further provided a step of measuring the amount of hydrogen atoms, wherein the amount of hydrogen atoms contained in the chemical oxide film formed on the semiconductor substrate by cleaning performed in the substrate cleaning step is measured.

13. The method for forming a thermal oxide film on a semiconductor substrate according to any one of claims 1, 2, 5 or 8, wherein: The predetermined thickness is 1 to 10 nm.

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