KR20240095229A - Oxide film thickness evaluation method and oxide film-attached silicon substrate manufacturing method - Google Patents

Abstract

The present invention is a method for evaluating an oxide film on a silicon substrate whose surface roughness Sa value measured by AFM is 0.5 nm or less, comprising a substrate to be evaluated on which an oxide film is formed, and a power spectral density at a spatial frequency of 60 to 90/μm on the surface of the substrate. A process of preparing a reference substrate with an average value of 0.1 nm ³ or less, a first film thickness measurement process of measuring the film thickness of the oxide film on the substrate to be evaluated, a process of removing the oxide film on the substrate to be evaluated and the reference substrate, and an oxide film A process of forming an oxide film under the same conditions on the removed substrate to be evaluated and the reference substrate, a second film thickness measurement process of measuring the film thickness of the oxide film on the substrate to be evaluated and the reference substrate, and the film thickness obtained in the second film thickness measurement process. This is an evaluation method for an oxide film comprising a step of evaluating the film thickness due to a film thickness influencing factor in the oxide film on the substrate to be evaluated obtained in the first film thickness measurement process from the film thickness of the oxide film on the substrate to be evaluated and the reference substrate. . Accordingly, an oxide film thickness evaluation method is provided that evaluates the film thickness of the oxide film due to film thickness influencing factors with high precision.

Description

Oxide film thickness evaluation method and oxide film-attached silicon substrate manufacturing method

The present invention relates to a method for evaluating the film thickness of an oxide film and a method for manufacturing a silicon substrate with an oxide film.

In the manufacturing process of a single crystal silicon wafer for semiconductor devices, its main surface is finished by a polishing process. Furthermore, there is a cleaning process to remove abrasives and metal impurities attached to the surface of the silicon wafer during the polishing process. In this cleaning process, a cleaning method called RCA cleaning is used.

This RCA cleaning is a cleaning method that combines SC1 (Standard Cleaning 1) cleaning, SC2 (Standard Cleaning 2) cleaning, and DHF (Diluted Hydrofluoric Acid) cleaning according to the purpose. SC1 cleaning is a cleaning method using an alkaline cleaning solution mixed with ammonia water and hydrogen peroxide in a random ratio. It lifts off attached particles by etching the surface of the silicon wafer, and further uses the electrostatic repulsion between the silicon wafer and particles. , It is a cleaning method that removes particles while suppressing re-adhesion to the silicon wafer. Additionally, SC2 cleaning is a cleaning method that dissolves and removes metal impurities on the surface of a silicon wafer using a cleaning solution that mixes hydrochloric acid and hydrogen peroxide in an arbitrary ratio. Additionally, DHF cleaning is a cleaning method that removes the natural oxide film on the surface of a silicon wafer using dilute hydrofluoric acid. Furthermore, ozone water cleaning, which has strong oxidizing power, is also sometimes used to remove organic matter adhering to the surface of a silicon wafer or to form a natural oxide film on the surface of the silicon wafer after DHF cleaning. The surface quality of the silicon wafer after cleaning, such as particles and surface roughness, is important, and these cleaning methods are combined depending on the purpose.

Semiconductor elements such as MOS (Metal Oxide Semiconductor) capacitors and transistors are formed on the surface of a semiconductor silicon wafer. Insulating films such as gate oxide films formed in these semiconductor devices are used under high electric field strengths, and silicon oxide films, which are easy to form, are often used as these insulating films.

A method for evaluating the film thickness of the oxide film on a silicon substrate includes measurement using an ellipsometer. An ellipsometer is a device that determines the phase difference (Δdelta) and amplitude ratio (Ψpsi) by injecting polarized light into a substrate sample and measuring changes in the polarization state of the incident light and reflected light. Taking a silicon oxide film on a silicon substrate as an example, the polarization state changes as incident light is reflected by the silicon oxide film on the outermost surface and the interface between the silicon oxide film and the silicon substrate. On the other hand, in ellipsometers, there are a short-wavelength type that uses a laser as a light source and a spectral type that contains a large number of wavelength components and uses a white light source, and the short-wavelength type has delta and psi for a specific wavelength (for example, 633 nm). In contrast to measuring , the spectral type can measure delta and psi for each wavelength, and it is known that using the spectral type with a large amount of information can evaluate film thickness with greater accuracy.

As described above, the information obtained by measurement with an ellipsometer is the phase difference and amplitude ratio, and the film thickness cannot be directly obtained. To determine the film thickness, a model based on the substrate sample is created, and the delta and psi theoretically obtained from this model are compared with the delta and psi obtained by measurement with an ellipsometer. On the other hand, creation of the model is done by setting conditions according to the physical properties of the sample, and the items of the conditions to be set include the materials of the substrate and film, the film thickness of each film layer, and the optical constants of the substrate and film. In addition, for setting each item, a known reference according to the sample, a required dispersion equation that shows the wavelength dependence of the dielectric constant and has a plurality of parameters, etc. are usually used.

Furthermore, a process of changing the parameters of the dispersion equation and the film thickness of each film layer of the model is performed so that the degree of difference between the two is minimized for the above comparison (also called fitting). The difference between the two is usually obtained by calculation using the least squares method. When the result obtained by the least squares method is judged to be somewhat small through fitting, the refractive index and extinction coefficient of the film are calculated from the values of the parameters of the dispersion equation at that time. The film thickness can be obtained by specifying the film thickness at that time as the film thickness of the film of the sample. On the other hand, model creation, fitting, etc. are generally performed manually or automatically using a computer based on the required program.

When irregularities (also referred to as roughness or roughness) exist on the surface of a sample, a method called effective medium approximation may be used (for example, Patent Document 1, etc.). This method improves the calculation results of the least squares method by defining the roughness and voids as one plane layer. In addition, the effective medium approximation may be applied not only to the case where roughness exists on the film surface of the sample, but also to the interface layer when roughness exists at the interface between the substrate and the film or the interface between film layers. Furthermore, the effective medium approximation is sometimes used to lower the value of the refractive index as a technique in performing analysis, regardless of the presence of roughness. Naturally, by using the effective medium approximation, the calculation results of the least squares method also change, and as a result, the value of the film thickness also changes, so the operator can determine whether to use the effective medium approximation, for example, from the calculation results of the least squares method. There is a need to judge.

Patent Document 2 describes that the film thickness of a native oxide film on a silicon wafer obtained with an ellipsometer changes depending on the surface roughness. Specifically, the rougher the surface, the thicker the film thickness, and a method for quantitatively evaluating surface roughness based on the correlation between roughness and the film thickness of the natural oxide film has been disclosed. Additionally, atomic force microscopy (AFM) is known as a method for evaluating surface roughness on a silicon substrate. As an indicator of roughness, arithmetic mean height such as Ra value or Sa value is often used. Ra is the arithmetic mean height at the standard length and is a two-dimensional roughness index, and Sa is a parameter that extends Ra to a surface and is a three-dimensional roughness index.

As a method of evaluating roughness in more detail, conversion to the spatial frequency domain by spectral analysis can also be performed. This method can extract components at specific wavelengths from the measured surface profile, for example parameters relating to specific spatial wavelengths and amplitude intensity at those wavelengths, such as PSD (Power Spectrum Density). It is expressed as By performing PSD analysis in this way, it is possible to specify the spatial frequency of the dominantly formed roughness. Additionally, the Haze value obtained by the particle counter can be used as an index of roughness. Haze is expressed as so-called cloudiness and is widely used as an indicator of the roughness of the silicon surface. A high Haze level indicates that the surface of the wafer is rough.

A dense silicon oxide film with high insulating properties is produced by thermal oxidation of a silicon wafer. Since a natural oxide film formed by cleaning exists on a silicon wafer upon shipment from the viewpoint of particle adhesion, etc., thermal oxidation is performed on a silicon wafer with a natural oxide film formed on it. In many cases, it is processed. At this time, it is known that the thermal oxidation film thickness is influenced by the film quality (film thickness or structure) of the natural oxide film before thermal oxidation (Patent Document 3).

Recently, with the miniaturization and multilayering of semiconductor integrated circuits, further thinning of various films, including insulating films constituting devices, has been required. By this thinning, it is necessary to form an ultra-thin insulating film, that is, a silicon oxide film, uniformly and with good reproducibility within the plane or between substrates. For this purpose, it is required to control the film quality, especially the film thickness, of the natural oxide film at the time of shipment of the silicon wafer, which affects the quality of the silicon oxide film. In general, the thicker the natural oxidation film, the thicker the thermal oxidation film. If you want to make the thermal oxidation film thin, it is better for the natural oxide film to be thinner, and if you want to make the thermal oxidation film thick, it is better for the natural oxide film to be thicker. Therefore, controlling the natural oxide film thickness within a certain range with good reproducibility has recently been particularly demanded.

Patent Document 3 describes the relationship between silicon wafers cleaned under various conditions and the oxide film thickness after thermal oxidation. Specifically, if the NH ₄ OH concentration of the SC1 cleaning solution is made high, the amount of OH groups contained in the natural oxidation film increases, and the film thickness after thermal oxidation becomes thicker. The composition (film quality) of the natural oxide film and the film thickness after thermal oxidation increase. A method of controlling film thickness after thermal oxidation by using correlation is disclosed.

Japanese Patent Publication No. 2005-283502 Japanese Patent Publication No. H6-163662 Japanese Patent No. 6791453 Publication

As described above, it is required to control the film thickness of the natural oxide film and the thermal oxide film on the silicon substrate. Generally, in the manufacturing process of a silicon substrate, the surface roughness of the substrate is formed through polishing and subsequent cleaning. SC1 cleaning, hydrofluoric acid cleaning, or ozone water cleaning are used to clean the substrate after polishing, and it is known that the cleaning process mainly uses SC1 cleaning, which has an etching effect, to roughen the surface.

Patent Document 3 describes the surface roughness Ra after SC1 cleaning or ozone water cleaning, and the value is about 0.06 to 0.12. This Ra value is the roughness value of recently used silicon substrates.

Patent Document 2 discloses that the surface roughness of the substrate affects the natural oxide film thickness measured with an ellipsometer, and the surface roughness value at this time is 0.22 to 2.05 nm as the Ra value of AFM measurement, as described above. It is very high compared to the surface roughness Ra value of 0.06~0.12nm.

In addition, it is generally known that the film thickness of the natural oxide film is about 1 nm. In Patent Document 2, when the Ra value is 0.22 nm, the film thickness of the natural oxide film is 0.097 nm, and when the Ra value is 1.23 nm, the film thickness of the natural oxide film is 1.586 nm. At an Ra value of 2.05 nm, the film thickness of the natural oxide film is 3.313 nm, which is far from approximately 1 nm in film thickness. In this way, the surface roughness and the film thickness of the natural oxide film described in Patent Document 2 are significantly different from the surface roughness and film thickness of recently used silicon substrates. The reason for this is thought to be that, in the invention described in Patent Document 2, treatment to intentionally roughen the surface is performed using a mixed solution of hydrofluoric acid and nitric acid, which is not used in normal cleaning solutions for silicon substrates. In other words, using the correlation disclosed in Patent Document 2, it is difficult to discuss the thickness of the natural oxide film and the roughness where Ra is in the range of 0.06 to 0.12 nm, for example, and the Ra value exceeds 1 nm. It is assumed that it can be applied in very rough cases.

Here, focusing on the Ra value of AFM when assigning the NH ₄ OH concentration of SC1 cleaning described in Patent Document 3 and the thermal oxide film thickness obtained by the spectroscopic ellipso method, the higher the NH ₄ OH concentration, the higher the AFM. There is a tendency that the Ra value is high and the thermal oxidation film thickness is also becoming thicker (FIG. 9 of Patent Document 3). In Patent Document 3, the composition (film quality) of the natural oxide film (chemical oxide film) formed in the cleaning process, for example, the amount of OH groups measured by ATR (Attenuated Total Reflectance)-FT (Fourier Transform)-IR (Infrared Spectoroscopy) method. It is disclosed that this is related to the thermal oxidation film thickness, and that the higher the NH ₄ OH concentration, the thicker the thermal oxidation film is because the amount of OH groups increases.

However, as described above, it is also a result that can be interpreted as if there is a correlation between the Ra value obtained by AFM measurement and the film thickness after thermal oxidation obtained by an ellipsometer. In this way, there are factors that affect the film thickness of the oxide film (hereinafter simply referred to as “film thickness influencing factors”), such as the surface roughness of the substrate formed in the manufacturing process of the recently used silicon substrate, and the ellipsometer The present inventors have discovered that there is a possibility of influencing the thickness of the natural oxide film and the thermal oxidation film obtained by , but there is no known literature that describes factors affecting the film thickness. For example, if the surface roughness of the substrate formed in the manufacturing process of a silicon substrate, such as an Ra value of 0.06 to 0.12 nm, is one of the factors affecting the oxide film thickness, in controlling the film thickness of the natural oxide film and the thermal oxidation film, It can be considered an important quality, similar to the composition (film quality) of the natural oxide film described above.

The present invention has been made to solve the above problem, and the film thickness value of the silicon substrate to be evaluated measured with an ellipsometer is a previously unknown film such as the surface roughness of the silicon substrate formed in the manufacturing process of the silicon substrate. The purpose is to provide a film thickness evaluation method of an oxide film that determines whether the film thickness value includes the influence of the thickness influencing factor and evaluates the film thickness due to the film thickness influencing factor with high precision.

The present invention has been made to achieve the above object, and is a method for evaluating an oxide film on a silicon substrate whose surface roughness Sa value measured by an atomic force microscope is 0.5 nm or less, comprising: a silicon substrate to be evaluated on which an oxide film is formed; , a substrate preparation process of preparing a reference silicon substrate with an average value of power spectral density of 0.1 nm ³ or less at a spatial frequency of 60 to 90/μm on the substrate surface, and measuring the film thickness of the oxide film on the silicon substrate to be evaluated using an ellipsometer. A first film thickness measurement process of measuring, an oxide film removal process of completely removing the oxide film on the silicon substrate to be evaluated and the reference silicon substrate, and on the silicon substrate to be evaluated and the reference silicon substrate after removing the oxide film, An oxide film formation process of forming an oxide film under the same conditions, a second film thickness measurement process of measuring the film thickness of the oxide film on the silicon substrate to be evaluated and the oxide film on the reference silicon substrate after the oxide film formation process with an ellipsometer, Based on the film thickness of the oxide film on the silicon substrate to be evaluated and the film thickness of the oxide film on the reference silicon substrate obtained in the second film thickness measurement step, the oxide film on the silicon substrate to be evaluated acquired in the first film thickness measurement step. A method for evaluating the film thickness of an oxide film is provided, which includes a film thickness evaluation process for evaluating the film thickness due to the film thickness influencing factors in the entire film thickness.

This method of evaluating the film thickness of the oxide film on a silicon substrate determines whether the film thickness value of the silicon substrate being evaluated measured with an ellipsometer is a film thickness value that includes the influence of film thickness influencing factors such as the surface roughness of the silicon substrate. It is possible to determine and evaluate the film thickness due to the film thickness influencing factors with high precision.

At this time, in the oxide film removal process, an oxide film evaluation method may be used in which the oxide film is removed by hydrofluoric acid cleaning.

Since hydrofluoric acid can only etch the natural oxide film on a silicon substrate, it can stably and completely remove only the natural oxide film, and the surface roughness does not change significantly before and after hydrofluoric acid cleaning, so it is particularly effective for evaluating the effect of surface roughness.

At this time, in the oxide film forming process, the oxide film thickness evaluation method may be used to form the oxide film by ozone water cleaning or hydrogen peroxide water cleaning.

Ozone water and hydrogen peroxide water have a strong oxidizing effect and can stably form a natural oxide film of about 1 nm, so the film thickness due to film thickness influencing factors can be evaluated more stably.

At this time, an oxide film thickness evaluation method may be used in which the film thickness of the oxide film on the silicon substrate to be evaluated is 25 nm or less.

When the film thickness is 25 nm or less, the influence of the surface roughness of the silicon substrate becomes more significant, so in the present invention, in the case of such a thinner film thickness, evaluation can be performed with higher precision.

At this time, the film thickness influencing factor in the film thickness of the oxide film includes the surface roughness of the silicon substrate to be evaluated, and in the film thickness evaluation process, the silicon substrate to be evaluated acquired in the second film thickness measurement process. When the differential film thickness obtained by subtracting the film thickness of the oxide film on the reference silicon substrate obtained in the second film thickness measurement process from the film thickness of the oxide film on the above is 0.02 nm or more and 0.20 nm or less, the film thickness obtained in the first film thickness measurement process This can be an oxide film thickness evaluation method that determines that the film thickness of the oxide film on the silicon substrate to be evaluated includes the film thickness of the oxide film resulting from the surface roughness of the silicon substrate to be evaluated.

With this evaluation method, it is possible to determine with greater precision whether the film thickness value obtained with the ellipsometer is affected by surface roughness.

At this time, in the film thickness evaluation process, the influence of the surface roughness of the silicon substrate to be evaluated is determined by subtracting the differential film thickness from the film thickness of the oxide film on the silicon substrate to be evaluated obtained in the first film thickness measurement process. This can be done using an oxide film thickness evaluation method that evaluates the film thickness of the removed oxide film.

With this evaluation method, it is possible to evaluate the film thickness of the oxide film with the influence of surface roughness removed.

At this time, the surface roughness can be determined by evaluating the film thickness of the oxide film, which is a roughness component with a spatial frequency of 60 to 90/μm.

Accordingly, the influence of surface roughness can be evaluated with greater precision. This is because the roughness component with a spatial frequency of 60 to 90/μm affects the oxide film thickness.

At this time, the surface roughness can be determined by evaluating the film thickness of the oxide film, which is a roughness component formed by SC1 cleaning.

In this way, in the film thickness evaluation method according to the present invention, the influence of surface roughness resulting from a specific cleaning process can be evaluated with greater precision. This is because the roughness at a spatial frequency of 60 to 90/μm is especially formed by SC1 cleaning.

At this time, the cleaning conditions and/or oxidation conditions before forming the oxide film on the silicon substrate are set based on the film thickness due to the film thickness influencing factor evaluated by the film thickness evaluation method of the oxide film, and the cleaning conditions and/or oxidation conditions are set. It can be used as a manufacturing method for a silicon substrate with an oxide film, in which a silicon substrate with an oxide film is manufactured by cleaning the silicon substrate and forming an oxide film on the silicon substrate.

Accordingly, it is possible to manufacture a silicon substrate with an oxide film by controlling the film thickness of the oxide film with higher precision.

The present invention also provides a method for evaluating the film thickness of an oxide film formed on a silicon substrate, including the surface roughness of the silicon substrate as a film thickness influencing factor in the film thickness of the oxide film, and the space of the surface of the silicon substrate. When the average value of the power spectral density at a frequency of 60 to 90/μm is 0.15 nm ³ or more, the thickness of the oxide film formed on the silicon substrate is caused by the surface roughness of the silicon substrate, which is a factor influencing the film thickness. A method for evaluating the film thickness of an oxide film that determines that the film thickness of one oxide film is included is provided.

According to the oxide film thickness evaluation method of the present invention, it is possible to quickly and very easily determine whether the oxide film thickness value measured with an ellipsometer is affected by the surface roughness of the substrate.

As described above, according to the method for evaluating the film thickness of the oxide film according to the present invention, the film thickness value of the silicon substrate to be evaluated measured with an ellipsometer is determined by determining the surface roughness of the silicon substrate formed in the manufacturing process of the silicon substrate, etc. It is possible to determine whether the film thickness value includes the influence of a previously unknown film thickness influencing factor, and to evaluate the film thickness due to the film thickness influencing factor with high precision. Additionally, by calculating the film thickness value resulting from the surface roughness, etc., the natural oxidation film and the film thickness after thermal oxidation can be analyzed in more detail. By utilizing this analysis result, the oxide film thickness on the silicon substrate can be controlled with high precision.

1 is a flow chart showing an example of a method for evaluating the film thickness of an oxide film on a silicon substrate according to the present invention.
Figure 2 shows a flow chart according to the investigation of the relationship between the surface roughness of the silicon substrate and the oxide film thickness.
FIG. 3 shows a graph showing the relationship between the surface roughness (Haze) of a silicon substrate subjected to the roughening process of FIG. 2 using CMP and SC1 cleaning and the thickness of a natural oxide film and a 5 nm oxide film.
FIG. 4 shows a graph showing the relationship between the surface roughness (Haze) of a silicon substrate subjected to the roughening treatment of FIG. 2 by single-wafer cleaning and the thickness of a natural oxide film and a 5 nm oxide film.
Figure 5 shows Haze after cleaning the roughening treatment of Figure 2 with a liquid composition of NH ₄ OH:H ₂ O ₂ :H ₂ O=1:1:10, cleaning temperature of 80°C, and cleaning time of 0, 3, 6, and 12 min. A graph showing the relationship between natural oxide films is shown.
Figure 6 shows the AFM measurement results and PSD curves of each sample.
Figure 7 shows an example of the evaluation and analysis method according to the present invention when the film thickness of the native oxide film is changed by changing the SC1 cleaning.

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

As described above, the film thickness value of the oxide film on the silicon substrate measured with an ellipsometer includes the influence of previously unknown film thickness influencing factors such as surface roughness formed during the manufacturing process of the silicon substrate. There has been a demand for a film thickness evaluation method for the oxide film that determines whether or not it is recognized and evaluates the film thickness due to film thickness influencing factors with high precision.

As a result of intensive study of the above problem, the present inventors have developed a method for evaluating an oxide film on a silicon substrate with a surface roughness Sa value of 0.5 nm or less as measured by an atomic force microscope. The silicon to be evaluated has an oxide film formed thereon. A substrate preparation step of preparing a substrate and a reference silicon substrate having an average value of power spectral density of 0.1 nm ³ or less at a spatial frequency of 60 to 90/μm on the substrate surface, and determining the film thickness of the oxide film on the silicon substrate to be evaluated. A first film thickness measurement process using a lipsomometer, an oxide film removal process to completely remove the oxide film on the silicon substrate to be evaluated and the reference silicon substrate, and a process for completely removing the oxide film on the silicon substrate to be evaluated and the reference silicon substrate after removing the oxide film. an oxide film formation process of forming an oxide film under the same conditions, and a second film thickness measurement process of measuring the film thickness of the oxide film on the silicon substrate to be evaluated and the oxide film on the reference silicon substrate after the oxide film formation process using an ellipsometer. and, based on the film thickness of the oxide film on the silicon substrate to be evaluated acquired in the second film thickness measurement step and the film thickness of the oxide film on the reference silicon substrate, on the silicon substrate to be evaluated acquired in the first film thickness measurement step. The film thickness of the silicon substrate to be evaluated measured with an ellipsometer by the oxide film film thickness evaluation method including a film thickness evaluation process for evaluating the film thickness due to the film thickness influencing factors in the entire film thickness of the oxide film. Regarding the value, it is determined whether the film thickness value includes the influence of film thickness influencing factors such as the surface roughness of the silicon substrate, and it was discovered that the film thickness due to the film thickness influencing factors can be evaluated with high precision, thereby completing the present invention. did.

The present inventors also provide a method for evaluating the film thickness of an oxide film formed on a silicon substrate, including the surface roughness of the silicon substrate as a film thickness influencing factor in the film thickness of the oxide film, and the space of the surface of the silicon substrate. When the average value of the power spectral density at a frequency of 60 to 90/μm is 0.15 nm ³ or more, the thickness of the oxide film formed on the silicon substrate is caused by the surface roughness of the silicon substrate, which is a factor influencing the film thickness. Using the oxide film thickness evaluation method that determines that the film thickness of one oxide film is included, it is quickly and very easily determined whether the oxide film thickness value measured with an ellipsometer is affected by the roughness of the substrate surface. By discovering what could be done, the present invention was completed.

Hereinafter, description will be made with reference to the drawings.

The present inventors conducted intensive studies on factors affecting film thickness in oxide film formation. As a result, it was found that the roughness formed in the wafer manufacturing process, specifically the roughness formed in the polishing process and cleaning process, and the film quality of the oxide film affect the film thickness of the natural oxide film and thermal oxidation film measured with an ellipsometer. Found it. In particular, with regard to the surface roughness of the substrate, it was found that when the average value of the power spectrum density (intensity) of a certain frequency band exceeds a predetermined value, the film thickness of the oxide film becomes thick.

First, the relationship between various surface roughnesses formed during the manufacturing process of a silicon substrate and the film thickness of the oxide film is described. Figure 2 is a flow chart of the investigation. For the prepared silicon substrate, the CMP processing conditions and SC1 cleaning conditions were changed, and roughening treatment was performed to form roughness, thereby preparing silicon substrates of multiple levels. Next, the oxide film was completely removed by hydrofluoric acid cleaning using a batch scrubber, and then a natural oxide film was formed by ozone water cleaning. At both levels, the oxide film formed in the roughening treatment is completely removed by hydrofluoric acid cleaning, and the oxide film is formed by subsequent ozone water cleaning, so it can be interpreted that the oxide film is formed under the same conditions on the silicon substrate at multiple levels. After performing Haze measurement using a particle counter, some of the silicon substrates were thermally oxidized with a film thickness of 5 nm, and the film thicknesses of the natural oxide film and the oxide film formed with a 5 nm target were evaluated using spectroscopic ellipsometry.

FIG. 3 is a graph showing the relationship between the surface roughness (Haze) of a silicon substrate subjected to the roughening process of FIG. 2 by CMP and SC1 cleaning and the film thickness of the native oxide film and the 5 nm target oxide film. At the CMP level (■), even when the Haze value exceeded 10 ppm, the film thicknesses of the natural oxide film and the 5 nm target oxide film were the same, but at the SC1 cleaning level (●), when the Haze increased, the film thicknesses of the natural oxide film and the 5 nm target oxide film were reduced. A tendency toward thickening was also obtained. Since the oxide film was formed under the same conditions, the film thickness was assumed to be equivalent to the CMP level, but this was not the case for the SC1 cleaning level.

Furthermore, Figure 4 shows the relationship between the surface roughness (Haze) of a silicon substrate subjected to the roughening treatment of Figure 2 by sheet wafer cleaning combining hydrofluoric acid and ozone water cleaning and the film thickness of the native oxide film and the 5 nm target oxide film. In addition, hydrofluoric acid cleaning and ozone water cleaning after roughening treatment were performed using a sheet method rather than a batch method. In this case, since the oxide film formation method is different from the batch-type ozone water cleaning, it is not possible to compare the film thickness of the SC1 and CMP levels described above with the sheet wafer cleaning level, but the effect of Haze within the single wafer cleaning level is not possible. We can discuss. As a result, the sheet wafer cleaning level was the same as the CMP level, and the film thicknesses of the natural oxide film and the 5 nm target oxide film were the same even when the Haze changed. Summarizing the above results, it was newly found that the roughness formed by CMP and sheet wafer cleaning does not affect the film thickness of the oxide film, but the surface roughness of the substrate formed by SC1 cleaning influences the film thickness of the oxide film to be thicker. .

Accordingly, the results of additional investigation into the SC1 cleaning level will be explained. The SC1 cleaning of the roughening treatment was performed as a batch cleaning with a liquid composition of NH ₄ OH:H ₂ O ₂ :H ₂ O=1:1:10, a cleaning temperature of 80°C, and a cleaning time of 3, 6, and 12 min, followed by hydrofluoric acid cleaning. Figure 5 shows the results showing the film thickness and Haze value of the natural oxide film after completely removing the oxide film and performing ozone water cleaning. With respect to the film thickness of 1.207 nm of the natural oxide film without cleaning time (0 min), which is Ref., it became 1.258 nm at 3 min, 1.258 nm at 6 min, and 1.261 nm at 12 min. Since the difference between the average value of the film thickness of 1.259 nm for cleaning times of 3, 6, and 12 min and the film thickness of 1.207 nm without cleaning (cleaning time of 0 min) is 0.052 nm, the amount of film thickening due to the SC1 cleaning of the roughening treatment is approximately 0.052 nm. It is thought that Haze tends to increase as the cleaning time is longer, whereas the amount of film thickening at cleaning times of 3, 6, and 12 min is the same. Based on this, the specific roughness component formed by SC1 cleaning affects the thickening behavior of the film thickness, and 3 The fact that the film thicknesses of , 6, and 12min are equal is thought to mean that the roughness component involved in film thickness (film thickening) is equal.

To verify these, the surface roughness of substrates at representative CMP, SC1 cleaning, and sheetfed cleaning levels was evaluated using AFM (atomic force microscopy). The observation field of view was 1 μm × 1 μm, and in addition to the three-dimensional calculated average height Sa, a PSD curve was obtained from spectral analysis of the surface profile data. Figure 6 shows the AFM measurement results and PSD curves of each sample.

First, focus on the CMP level. At the CMP level, the level with the smallest Haze value (CMP-1) and the level with the largest Haze value (CMP-2) were evaluated in Figure 3. In CMP-2, the power spectrum density (intensity) in the low frequency band (1 to 10/μm) was very high, and the roughness on the low frequency side was dominant. The AFM image also showed an image with large relief and was consistent. As described above, since the roughness formed by CMP does not affect the oxide film thickness, it can be said that this low-frequency component does not affect the oxide film thickness.

Next, focus on the SC1 cleaning level. At the SC1 cleaning level, the liquid composition is NH ₄ OH:H ₂ O ₂ :H ₂ O=1:1:10, and the cleaning temperature and cleaning time are set at 3 levels: 60℃/3min, 80℃/3min, and 80℃/12min. evaluated. When an oxide film is formed under the same conditions, the film thickness becomes thicker by the same amount. As shown in Figure 6, compared to CMP-2, the roughness of all three levels is dominant in the high frequency range (10 to 100/μm), which is consistent with the fact that fine grain-like roughness is obtained in the AFM image. Therefore, it can be said that the roughness component (spatial frequency band) formed in CMP and SC1 cleaning is significantly different.

Lastly, focus on the level of sheetfed cleaning. At the sheet-fed cleaning level, in Figure 4, the level with the smallest Haze value (sheet-fed cleaning-1) and the level with the highest (sheet-fed cleaning-2) were evaluated. The power spectrum density (intensity) of the sheet wafer cleaning level was intermediate between CMP and SC1 cleaning in the high frequency range (10~100/μm).

These roughness evaluation results and their influence on the film thickness of the oxide film are considered. In particular, while the Sa value of both SC1 cleaning - 80℃/3min and single-wafer cleaning-2 is 0.108nm, the oxide film thickness becomes thicker in SC1 cleaning-80℃/3min, and thicker in single-wafer cleaning-2. Focus on results that do not give up. Looking at both PSD curves, while the power spectral density (intensity) in the low frequency band (1 to 10/μm) is equal, the power spectral density (intensity) in the high frequency band (especially 50/μm or more) is SC1 cleaning. -80℃/3min is greater than sheet cleaning-2. Therefore, although there is no significant difference between the two on the AFM, it can be said that the roughness in the high frequency range is more dominant in the SC1 cleaning - 80°C/3min from the PSD curve. Furthermore, based on the three levels of SC1 cleaning shown (60℃/3min, 80℃/3min, 80℃/12min) all being thickened by the same thickness (approximately 0.05nm), the power in the spatial frequency range of 60~90/μm It can be seen that the spectral density (intensity) is the same for all three levels and is also higher than that of Sheetwafer Cleaning-2. Therefore, it became newly clear that the roughness component in the 60-90/μm range is a roughness component that affects the film thickness of the natural oxide film and the 5 nm oxide film.

Meanwhile, the power spectrum density (intensity) of the spatial frequency band of 50/μm or less is within the 3 levels of SC1 cleaning,

80℃/12min>80℃/3min>60℃/3min

It becomes a magnitude relationship of and is a magnitude relationship of Sa value,

80℃/12min>80℃/3min>60℃/3min

This also coincides with the Sa value in this case, which is dominated by the roughness information on the low-frequency side with high intensity. Despite the same Sa value of 0.108 nm for the sheet-fed cleaning-2 and SC1 cleaning-80°C/3min described above, the oxide film It is thought that this is the reason for the difference in film thickness.

To summarize the above results, it is believed that if the average value of the power spectrum density (intensity), which is the roughness component in the spatial frequency band of 60 to 90/μm, is above the threshold, the oxide film becomes thick. Here, if we calculate the average value of the power spectrum density (intensity) in the range of 60~90/μm of the three levels of SC1 cleaning, it is 0.16nm ³ at SC1 cleaning-60℃/3min, 0.18nm ³ at SC1 cleaning-80℃/3min, In SC1 cleaning-80℃/12min, it was 0.17nm ³ . On the other hand, the average value of sheet-fed cleaning-2, in which the oxide film did not thicken as described above, was 0.11 nm ³ . Therefore, the average value of the power spectral density (intensity) of 60 to 90/μm, 0.15 nm ³ , is considered to be the critical value, and the film thickness of the silicon oxide film on the silicon substrate where the average value of the power spectral density (intensity) of 0.15 nm ³ or more exists is , it can be determined that the surface roughness of the substrate has an influence and the film thickness caused by the surface roughness of the substrate is included.

From the above knowledge, it can be interpreted that specific surface roughness is one of the factors affecting the oxide film thickness (film thickness influencing factors). Here, the factors influencing the film thickness of the natural oxide film and the thermal oxidation film include, for example, the structure of the natural oxide film (chemical oxide film) described in Patent Document 3 and the surface roughness of the silicon substrate described so far. there is. Therefore, it is believed that the film thickness of the natural oxide film and the thermal oxidation film can be controlled by adjusting the structure of the natural oxide film (chemical oxide film) and the surface roughness of the substrate. Furthermore, when the cleaning conditions are changed to thicken or thin the natural oxide film and thermal oxidation film, the film thickness of the silicon substrate after cleaning is more strongly influenced by either the structure of the natural oxide film or the surface roughness of the substrate. If you can interpret whether it exists, it will be useful knowledge in determining cleaning conditions. The method for evaluating the film thickness of an oxide film according to the present invention is very effective in such cases, and an example showing its effectiveness will be described in detail below.

Here, as an example, an example of controlling the thickness of the oxide film by assigning SC1 cleaning conditions is shown. As shown in Figure 7 (A), SC1 cleaning was performed on the silicon substrate. The cleaning conditions were that the liquid composition was NH ₄ OH:H ₂ O ₂ :H ₂ O=1:1:10, the cleaning time was 3 min, and the cleaning temperature was set at 3 levels of 45, 60, and 80°C. Meanwhile, a plurality of substrates were processed for each level. Next, half of the wafers at each level were cleaned with hydrofluoric acid to remove the natural oxide film, and then washed with ozone water to form an oxide film under the same conditions. Afterwards, the film thickness of the natural oxide film was evaluated by spectroscopic ellipsometry. As a result, as shown in Figure 7 (B), after SC1 cleaning (■), the higher the cleaning temperature, the thicker the film thickness was. Here, with respect to the film thickness after SC1 cleaning (■), the factor that the film thickness becomes thicker as the cleaning temperature increases is analyzed in more detail.

First, the influence of the surface roughness of the silicon substrate is described. The film thickness after HF→O ₃ cleaning (●) was 1.207 nm without SC1 cleaning, 1.206 nm at a cleaning temperature of 45°C, 1.258 nm at a cleaning temperature of 60°C, and 1.258 nm at a cleaning temperature of 80°C. 1.207 nm without SC1 cleaning and 1.206 nm with a cleaning temperature of 45°C can be interpreted as equivalent film thicknesses. On the other hand, at cleaning temperatures of 60 and 80°C, it can be interpreted that the film thickness is thicker due to surface roughness. When calculating the amount of film thickening due to surface roughness, at a cleaning temperature of 60℃, the difference between 1.258nm and 1.207nm without SC1 cleaning is 0.051nm, and at a cleaning temperature of 80℃, the difference between 1.258nm and 1.207nm without SC1 cleaning is 0.051nm. It became nm. This 0.051 nm is the amount of film thickening caused by roughness.

Next, the film thickness obtained by subtracting the amount of film thickening of 0.051 nm due to surface roughness from the film thickness at the cleaning temperature of 60°C and 80°C after SC1 cleaning (■) becomes the film thickness with the influence of surface roughness removed (▲). Since the cleaning temperature of 45°C has no effect on roughness, there is no need to consider it. Looking at the results, it was obtained as 1.058nm at a cleaning temperature of 60℃ and 1.072nm at a cleaning temperature of 80℃. Therefore, even after removing the influence of surface roughness, the higher cleaning temperature of 80°C has a thicker film thickness than 60°C, and this difference can be interpreted as resulting from the structure of the natural oxide film.

If the differential film thickness of the cleaning temperature of 60°C and 80°C with respect to the cleaning temperature of 45°C after removing the film thickness effect of the surface roughness is interpreted as the film thickness resulting from the structure of the natural oxide film, it is shown in Figure 7 (C). As shown, the amount of film thickening due to roughness and structure-related in the case of cleaning temperatures of 60°C and 80°C with respect to the SC1 cleaning temperature of 45°C can be distinguished. Since the amount of film thickening due to roughness at the cleaning temperature of 60℃ and 80℃ is the same, when the cleaning condition is set to 80℃, the film thickness due to the structure of the natural oxide film becomes thicker, and the total film thickness after cleaning becomes thicker. I was able to learn something new. This is an example in which the film thickness caused by roughness is saturated, but depending on the conditions, it is assumed that the roughness and the amount of thickened structure may not be saturated. In such cases, when it is required to manufacture the oxide film more stably and with high film thickness controllability by understanding the factors that cause film thickening using this evaluation method, such as the SC1 cleaning temperature of 60°C or 80°C as exemplified this time. By saturating the amount of film thickening due to roughness, the only factor influencing film thickness becomes the structure of the oxide film, and it is possible to manufacture with smaller fluctuations in film thickness. For the above reasons, a method for evaluating the film thickness of the oxide film on a silicon substrate considering the surface roughness of the substrate is very useful.

<First embodiment>

Based on the above-described content, the method for evaluating the film thickness of the oxide film according to the first embodiment of the present invention will be described in detail. 1 is a flow chart showing an example of a method for evaluating the film thickness of an oxide film on a silicon substrate according to the present invention.

[Method for evaluating the film thickness of oxide film]

The method for evaluating the film thickness of an oxide film according to the first embodiment of the present invention is a method for evaluating an oxide film on a silicon substrate whose surface roughness Sa value measured by an atomic force microscope is 0.5 nm or less, where the oxide film to be evaluated is formed. A substrate preparation process of preparing a silicon substrate to be evaluated and a reference silicon substrate with an average value of power spectral density of 0.1 nm ³ or less at a spatial frequency of 60 to 90/μm on the substrate surface, and the film thickness of the oxide film on the silicon substrate to be evaluated. A first film thickness measurement process of measuring with an ellipsometer, an oxide film removal process of completely removing the oxide film on the silicon substrate to be evaluated and the reference silicon substrate, and on the silicon substrate to be evaluated and the reference silicon substrate after removing the oxide film, An oxide film formation process of forming an oxide film under the same conditions, a second film thickness measurement process of measuring the film thickness of the oxide film on the silicon substrate to be evaluated and the oxide film on the reference silicon substrate after the oxide film formation process with an ellipsometer, and a second film thickness measurement process. Based on the film thickness of the oxide film on the silicon substrate to be evaluated and the film thickness of the oxide film on the reference silicon substrate obtained in the thickness measurement process, the film thickness of the entire film thickness of the oxide film on the silicon substrate to be evaluated acquired in the first film thickness measurement process. This is a film thickness evaluation method of an oxide film that includes a film thickness evaluation process for evaluating the film thickness due to influencing factors. Hereinafter, each process will be described in detail.

(Substrate preparation process)

First, as shown in Fig. 1 S1, a silicon substrate to be evaluated, which is an evaluation object, and a silicon substrate to be a reference (hereinafter referred to as a “reference silicon substrate”) are prepared. In either case, there are no restrictions on conductivity type, diameter, or sample shape. There is no limitation on the type of silicon oxide film on the silicon substrate being evaluated, and examples include natural oxide film, thermal oxide film, and CVD oxide film. On the other hand, the film thickness of the oxide film to be evaluated on the silicon substrate to be evaluated is not particularly limited, but is preferably 25 nm or less. When the film thickness is 25 nm or less, the influence of the surface roughness of the silicon substrate becomes more significant, so in the present invention, in the case of such a thinner film thickness, evaluation can be performed with higher precision. In addition, the lower limit of the film thickness of the oxide film to be evaluated on the silicon substrate to be evaluated is not particularly limited as long as it can be measured, but can be 0.5 nm or more.

However, there are limitations to surface roughness. First, the surface roughness of the silicon substrate being evaluated must be less than 0.5 nm in Sa value. The reason for this is that when the Sa value is greater than 0.5 nm, the film thickness value of the natural oxide film deviates greatly from 1 nm, as shown in Patent Document 2. Specifically, the composition of the SC1 cleaning solution was diluted to NH ₄ OH:H ₂ O ₂ :H ₂ O = 1:1:1000, and a two-level silicon substrate was produced with the surface intentionally roughened using a chemical solution with an etching advantage. As a result of evaluating the natural oxide film by AFM for roughness Sa and spectroscopic ellipsometry, the film thickness was 3.34 nm at an Sa value of 0.65 nm and a film thickness of 5.12 nm at an Sa value of 1.05 nm. In this way, if there is roughness with a Sa value exceeding 0.5 nm, the oxide film thickness calculated by spectroscopic ellipsometry greatly deviates from about 1 nm, so the Sa value needs to be set to 0.5 nm or less. On the other hand, in a typical polishing process for a silicon wafer, after DSP (double-side polishing), CMP (single-side polishing) is performed on the surface side, and cleaning is performed after each polishing process. Generally, the Sa value of the surface of a silicon wafer after CMP is 0.1 nm or less, and the Sa value of the back side (DSP surface) is about 0.2 to 0.4 nm. Therefore, in the normal silicon substrate manufacturing process, the Sa value is 0.5 nm. Excessive surface roughness is not formed. Any wafer that has undergone at least DSP processing and CMP processing can be used as a silicon substrate to be evaluated according to the present invention. In this way, the present invention can be applied to silicon substrates to be evaluated with a surface roughness of Sa value of 0.5 nm or less. Meanwhile, the lower limit of the surface roughness of the silicon substrate being evaluated is Sa value of 0.0 nm or more, but can also be 0.01 nm or more.

The reference silicon substrate needs to have a Sa value of 0.5 nm or less and an average value of the power spectral density (intensity) in the spatial frequency range of 60 to 90/μm of 0.1 nm ³ or less. This is because if a silicon substrate with an average value of power spectrum density (intensity) in the spatial frequency range of 60 to 90/μm greater than 0.1 nm ³ is used as a reference silicon substrate, it becomes difficult to separate the thick oxide film due to surface roughness. As described above, since the roughness component of 60 to 90/μm is formed by SC1 cleaning rather than CMP or single-wafer cleaning, it is necessary to limit the cleaning conditions after polishing when preparing a reference silicon substrate. Usually, after polishing, a large amount of abrasive particles adhere, so a cleaning process is essential. At this time, by performing cleaning with a combination of hydrofluoric acid and ozonated water using a spin cleaner (sheet wafer cleaning) or cleaning with a combination of hydrofluoric acid and ozonated water using a batch method, the average value of the power spectrum density (intensity) in the range of 60 to 90/μm is 0.1nm ³ It can be done as below. Additionally, when performing SC1 cleaning, when the liquid composition is NH ₄ OH:H ₂ O ₂ :H ₂ O=1:1:10, the cleaning temperature is set to 45°C or lower to obtain the average value of the power spectrum density (intensity). It can be set to 0.1nm ³ or less. It is okay to perform a cleaning using a combination of hydrofluoric acid and ozone water cleaning and SC1. A reference silicon substrate can be prepared with this flow. At this time, it is more desirable to perform AFM measurement of the prepared silicon substrate and confirm that the average value of the power spectrum density (intensity) in the range of 60 to 90/μm is 0.1 nm ³ or less. Meanwhile, the lower limit of the average value of the power spectrum density (intensity) in the spatial frequency range of 60 to 90/μm is 0.0 nm ³ or more, but can also be 0.01 nm ³ or more.

(First film thickness measurement process)

Next, as shown in Fig. 1 S2, the oxide film thickness of the silicon substrate to be evaluated is measured with an ellipsometer. As described above, there are two types of ellipsometers: a short-wavelength type that uses a laser as a light source, and a spectroscopic type that includes multiple wavelength components and uses a white light source. There are no restrictions on the light source, but it is more preferable to use a spectroscopic type with a large amount of information that can accurately evaluate the film thickness. Additionally, the measurement method of the ellipsometer can be performed by a known method. To obtain the film thickness, it is necessary to create a model according to the substrate sample. This model is created by setting conditions according to the physical properties of the sample. The items of the conditions to be set include the materials of the substrate and film, the film thickness of each film layer, These include the optical constants of the substrate and film. In particular, it is necessary to cite known literature values for optical constants and the like, and at this time, there are multiple reported examples of literature values. Therefore, in the present invention, it is more preferable to make the model and quoted optical constants of the first film thickness measurement process and the second film thickness measurement process described later the same, and by making them the same, the film thickness can be evaluated with greater precision. At this time, the film thickness obtained in the first film thickness measurement may be affected by the surface roughness of the substrate described above. Accordingly, by a method described later, it is verified and determined whether the film thickness caused by this surface roughness is included.

(Oxidation film removal process)

We continue to investigate the influence of the surface roughness of the silicon substrate. As shown in Figure S3, the oxide film on the silicon substrate to be evaluated and the reference silicon substrate is completely removed. The removal method is not particularly limited, but hydrofluoric acid washing is more preferable. Because the action of hydrofluoric acid etches the oxide film but does not etch Si, only the natural oxide film can be completely removed easily and stably. Moreover, since the surface roughness does not change significantly before and after hydrofluoric acid cleaning, it is particularly useful to evaluate the effect of surface roughness. It is valid for At this time, there are no restrictions on the concentration of hydrofluoric acid or cleaning time, and the oxide film can be completely removed. For example, when the oxide film is completely removed, the bare surface is exposed and becomes a water-repellent surface. On the other hand, if an oxide film exists on the surface, it becomes a hydrophilic surface, so it can be determined whether the oxide film has been removed from the surface after cleaning. Examples of conditions include, for example, a hydrofluoric acid concentration of 0.3 to 5.0 wt%, a temperature of 10 to 30°C, and a cleaning time of 60 to 360 seconds.

(Oxide film formation process)

Next, as shown in S4 of FIG. 1, an oxide film is formed under the same conditions on the silicon substrate to be evaluated and the reference silicon substrate from which the oxide film has been completely removed. By forming the oxide film under the same conditions in this way, the influence of the surface roughness of the substrate can be discussed from the results of the second film thickness measurement described later. At this time, there is no particular limitation on the method of forming the oxide film, but it is more preferable to oxidize the substrate surface with ozone water or hydrogen peroxide water. Since ozone water and hydrogen peroxide have a strong oxidizing effect and can easily and stably form a natural oxide film of about 1 nm, the influence on film thickness due to film thickness influencing factors can be evaluated more stably. In particular, if it is a spin cleaning or batch cleaning machine, the hydrofluoric acid cleaning and the subsequent ozone water or hydrogen peroxide cleaning can be performed in one batch, requiring less effort. It is more preferable to clean with ozone water, which has a stronger oxidizing effect and is more stable than hydrogen peroxide. This is because it is desirable that the film thickness difference between the oxide film of the silicon substrate being evaluated and the reference silicon substrate in this process be as small as possible.

(Second film thickness measurement process)

Next, as shown in S5 in FIG. 1, the oxide film thickness of the silicon substrate to be evaluated and the reference silicon substrate on which the oxide film was formed under the same conditions are evaluated using an ellipsometer. The evaluation method may be the same as the first film thickness measurement.

(Film thickness evaluation process)

Next, as shown in Fig. 1 S6, the film thickness due to the film thickness influencing factor in the entire film thickness of the oxide film on the silicon substrate to be evaluated obtained in the first film thickness measurement process is evaluated.

First, the interpretation of the second film thickness measurement results will be described. In the second film thickness measurement, the film thickness of the oxide film formed under the same conditions is evaluated. Therefore, if there is no influence between the substrates (each level) due to film thickness influencing factors such as surface roughness, both will have the same film thickness. When the surface roughness of the substrate is influenced to thicken the film, the film thickness of the silicon substrate being evaluated becomes thicker than the film thickness of the reference silicon substrate. In this case, it can be determined that the film thickness of the oxide film on the silicon substrate to be evaluated, obtained in the first step, includes the film thickness of the oxide film resulting from the specific surface roughness on the silicon substrate to be evaluated.

At this time, specifically, the differential film thickness obtained by subtracting the film thickness of the oxide film on the reference silicon substrate obtained in the second film thickness measurement process from the film thickness of the oxide film on the silicon substrate to be evaluated obtained in the second film thickness measurement process is 0.02 nm or more. , if it is 0.2 nm or less, it is desirable to determine that the film thickness of the oxide film on the silicon substrate to be evaluated, obtained in the first film thickness measurement process, includes the film thickness of the oxide film resulting from the surface roughness of the silicon substrate to be evaluated. As a result of investigation by the present inventors, it is thought that if the differential film thickness is less than 0.02 nm, it may be due to deviation in the ellipsometer measurement. Therefore, if the lower limit threshold is set to 0.02 nm or more, the accuracy will be further increased. In addition, a plurality of silicon substrates to be evaluated to which cleaning conditions were assigned were prepared, and the differential film thickness obtained from the second film thickness measurement was calculated. As a result, the difference was 0.2 nm at the maximum, so the upper limit threshold was set to 0.2 nm. It is realistic. By performing evaluation in this way, it is possible to determine with high precision whether the film thickness value obtained with the ellipsometer is particularly affected by surface roughness.

Furthermore, the differential film thickness, that is, the film thickness resulting from surface roughness, is subtracted from the film thickness of the oxide film on the silicon substrate to be evaluated obtained in the first film thickness measurement process, so that the influence of the surface roughness of the silicon substrate to be evaluated is removed. The film thickness can be calculated and evaluated. In particular, when the silicon substrate to be evaluated has multiple levels, the film thickness variation factor between levels as shown in FIG. 7 can be relatively evaluated.

In addition, the surface roughness in the method for evaluating the film thickness of an oxide film according to the present invention can be a roughness component with a spatial frequency of 60 to 90/μm. Since the roughness component with a spatial frequency of 60 to 90/μm has a strong influence depending on the oxide film thickness, the influence of surface roughness can be evaluated with greater precision. Additionally, the surface roughness can be determined by the roughness component formed by SC1 cleaning. This is because the roughness component with a spatial frequency of 60 to 90/μm is especially formed by SC1 cleaning, and the influence of surface roughness resulting from a specific cleaning process can be evaluated with greater precision.

[Manufacturing method of silicon substrate with oxide film]

Based on the film thickness due to the film thickness influencing factors evaluated by the film thickness evaluation method of the oxide film according to the present invention, cleaning conditions and/or oxidation conditions before forming the oxide film on the silicon substrate are set, and these cleaning conditions and/or oxidation conditions are set. A method for manufacturing a silicon substrate with an oxide film is provided, in which a silicon substrate with an oxide film is manufactured by cleaning the silicon substrate and forming an oxide film on the silicon substrate using conditions. According to the method for evaluating the film thickness of the oxide film according to the present invention, it is possible to determine the thickness of the film due to the film thickness influencing factor. For example, the film thickness of the oxide film of a silicon substrate is determined by either the structure of the natural oxide film or the substrate surface roughness. It is possible to analyze whether the factors of can be manufactured.

<Second Embodiment>

Next, a method for evaluating the film thickness of an oxide film according to a second embodiment of the present invention will be described in detail.

[Method for evaluating the film thickness of oxide film]

When the average value of the power spectral density at a spatial frequency of 60 to 90/μm on the surface of the silicon substrate is 0.15 nm ³ or more, the surface of the silicon substrate, which is a film thickness influencing factor in the film thickness of the oxide film formed on the silicon substrate, A method for evaluating the film thickness of an oxide film is provided, which determines that the film thickness of the oxide film resulting from roughness is included. As described above, if the average value of the power spectrum density (intensity) in the spatial frequency range of 60 to 90/μm is more than 0.15 nm ³ , the film thickness of the natural oxide film measured with an ellipsometer is due to the surface roughness of the silicon substrate. Thickness is included. Therefore, by performing AFM measurement of the silicon substrate and obtaining a PSD curve from spectral analysis of the surface profile data, it can be easily determined whether the film thickness of the oxide film resulting from the surface roughness of the silicon substrate, which is a film thickness influencing factor, is included. .

Using the method for evaluating the oxide film on a silicon substrate described above, it is possible to evaluate the film thickness of the oxide film obtained with an ellipsometer, taking into account the influence of film thickness influencing factors such as surface roughness. Furthermore, it is possible to distinguish the factors causing variation in the film thickness of the oxide film from the surface roughness of the silicon substrate and the structure of the native oxide film, making it possible to evaluate the film thickness of the oxide film on the silicon substrate with greater precision than before.

Example

Hereinafter, the present invention will be described in detail through examples, which do not limit the present invention.

(Example 1)

As a silicon substrate to be evaluated, a silicon wafer cleaned by CMP polishing, sheet wafer cleaning, and SC1 cleaning was prepared. Specific conditions are listed in Table 1.

In advance, AFM measurement was performed on a level 0 substrate with an observation field of view of 1 μm x 1 μm, and a PSD curve was obtained from spectral analysis of the profile data. Sa is 0.0521 nm, which is 0.5 nm or less, and the average value of the power spectrum density (intensity) at a spatial frequency of 60 to 90/μm is 0.081 nm ³ and is 0.1 nm ³ or less, so this level of 0 was used as the reference silicon substrate. . And levels 1 to 6 were used as silicon substrates to be evaluated. Next, the first film thickness measurement of the silicon substrate to be evaluated was performed using a spectroscopic ellipsometer M-2000V manufactured by JAWoollam. As a result, level 1 was 1.033nm, level 2 was 1.109nm, level 3 was 1.121nm, level 4 was 1.169nm, level 5 was 1.114nm, and level 6 was 1.109nm.

Next, 0.5 wt% hydrofluoric acid cleaning was performed on a total of 7 levels (level 6 of the evaluated silicon substrate and level 1 of the reference silicon substrate) to remove the oxide film at a cleaning temperature of 25°C and a cleaning time of 3 minutes. Since the surface after washing was a water-repellent surface, it was confirmed that the oxide film had been completely removed. Next, the substrates of the above total 7 levels were cleaned with ozone water with a concentration of 20 ppm at a cleaning temperature of 25°C and a cleaning time of 3 minutes, and a natural oxide film was formed on the surface under the same conditions.

Subsequently, the second film thickness of a total of 7 levels of silicon substrate was measured using a spectroscopic ellipsometer M-2000V manufactured by J.A.Woollam. As a result, level 0 was 1.199nm, level 1 was 1.202nm, level 2 was 1.248nm, level 3 was 1.250nm, level 4 was 1.291nm, level 5 was 1.206nm, and level 6 was 1.202nm. As a result of calculating the differential film thickness of each level and level 0 in the second film thickness, level 1 was 0.003 nm, level 2 was 0.049 nm, level 3 was 0.051 nm, level 4 was 0.092 nm, and level 5 was 0.007 nm. , level 6 became 0.003nm. Since the differential film thickness of levels 1, 5, and 6 was 0.01 nm or less, it was determined that the first film thickness of levels 1, 5, and 6 did not include the film thickness due to surface roughness. In levels 2, 3, and 4, the differential film thickness was 0.02 nm or more and 0.20 nm or less, so it was judged that the first film thickness of levels 2, 3, and 4 included the film thickness caused by surface roughness.

Furthermore, the film thickness excluding the influence of surface roughness was calculated from the first film thickness. Levels 2, 3, and 4 were calculated by subtracting the difference film thickness from level 0 in the second film thickness from the first film thickness. For example, considering at level 2, 1.060 nm obtained by subtracting the differential film thickness of 0.049 nm of the second film thickness from the first film thickness of 1.109 nm becomes the film thickness with the influence of surface roughness removed from the first film thickness. On the other hand, since there is no influence of roughness in levels 1, 5, and 6, the first film thickness was adopted as is, and the film thickness after removing the influence of surface roughness from the first film thickness was set to the same value as the first film thickness. As a result of calculation in this way, the film thickness after removing the effect of surface roughness from the first film thickness is 1.033 nm for level 1, 1.060 nm for level 2, 1.070 nm for level 3, 1.077 nm for level 4, and 1.114 nm for level 5. nm, level 6 became 1.109nm.

Here, focusing on levels 1, 2, 3, and 4, both the magnitude relationship between the film thickness that removes the influence of surface roughness from the first film thickness and the magnitude relationship between the first film thickness are:

Level 4>Level 3>Level 2>Level 1

It became. Since levels 1, 2, 3, and 4 are levels where the SC1 cleaning conditions are changed, it was found that the value of the first film thickness changed due to both the surface roughness and structure of the natural oxide film acting depending on the cleaning conditions.

Furthermore, Table 2 shows the results of analysis of the factors that cause the film thicknesses of levels 2, 3, and 4 to become thicker with respect to level 1, where the first film thickness is the thinnest, in levels 1, 2, 3, and 4. Here, the differential film thickness for level 1 of the second film thickness is the film thickness (α) due to surface roughness, the film thickness with the effect of surface roughness removed from the first film thickness, and level 1 of levels 2-4. The differential film thickness was taken as the film thickness (β) due to the structure of the natural oxide film.

As a result, α became 0.046 nm at level 2, 0.048 nm at level 3, and 0.089 nm at level 4, and β became 0.027 nm at level 2, 0.037 nm at level 3, and 0.044 nm at level 4. Furthermore, calculating α/β, level 2 was 1.703, level 3 was 1.297, and level 4 was 2.022. Considering this result, since the values of α for levels 2 and 3 are almost equal, it is considered that the film thickness at levels 2 and 3 is saturated due to surface roughness. It was found that the film thickness of level 3 in the first measurement was thicker than that of level 2 because the film thickness of level 3 was thicker due to the structure of the natural oxide film. Level 4 has the highest α/β, and it is thought that this changes the liquid composition from 1:1:10 to 1:1:100, making it a more etching-dominant chemical liquid, and the film thickness caused by the surface roughness becomes dominant. In this way, it was possible to analyze in detail the factors causing variation in film thickness when cleaning conditions were changed.

(Example 2)

In Example 2, the film thickness of the thermal oxidation film was evaluated. As a silicon substrate to be evaluated, a silicon substrate cleaned by sheet wafer cleaning or SC1 cleaning after CMP polishing was prepared. Specific conditions are shown in Table 3.

The prepared silicon substrate was thermally oxidized with a target film thickness of 5 nm. After that, AFM measurement was performed on the level A substrate with an observation field of view of 1 μm x 1 μm, and a PSD curve was obtained from spectral analysis of the profile data. As a result, Sa was 0.011 nm, which is 0.5 nm or less, and the average value of the power spectrum density (intensity) at the spatial frequency of 60 to 90/μm was 0.094 nm ³ , which was 0.1 nm ³ or less, so this level A substrate was considered the reference silicon substrate. , and four level substrates of levels B, C, D, and E were used as silicon substrates to be evaluated.

Next, the first film thickness measurement of the silicon substrate to be evaluated was performed using a spectroscopic ellipsometer M-2000V manufactured by J.A.Woollam. As a result, level B was 5.185 nm, level C was 5.269 nm, level D was 5.272 nm, and level E was 5.318 nm.

Next, a 5 wt% hydrofluoric acid cleaning was performed on a total of 5 levels of the silicon substrate to be evaluated (level 4 and standard silicon substrate level 1) at a cleaning temperature of 25°C and a cleaning time of 10 minutes. Because the film thickness was thick, the concentration and cleaning time were changed from Example 1. Since the surface after washing was a water-repellent surface, it was confirmed that the oxide film had been completely removed. Next, a total of 5 levels of substrate were cleaned using ozonated water with a concentration of 20 ppm at a cleaning temperature of 25°C and a cleaning time of 3 minutes, and a natural oxide film was formed on the surface under the same conditions.

Subsequently, the second film thickness of a total of 5 levels of silicon substrate was measured using a spectroscopic ellipsometer M-2000V manufactured by J.A.Woollam. As a result, level A was 1.201 nm, level B was 1.201 nm, level C was 1.249 nm, level D was 1.249 nm, and level E was 1.285 nm. As a result of calculating the differential film thickness of each level B, C, D, E and level A in the second film thickness, level B was 0.000 nm, level C was 0.048 nm, level D was 0.048 nm, and level E was 0.084 nm. It became nm. Since the differential film thickness of level B was 0.01 nm or less, it was determined that the first film thickness of level B did not include the film thickness due to surface roughness. Since the differential film thickness of levels C, D, and E was 0.02 nm or more and 0.20 nm or less, it was determined that the first film thickness of levels C, D, and E included the film thickness due to surface roughness.

Furthermore, the film thickness after removing the influence of surface roughness was calculated from the first film thickness. Levels C, D, and E were calculated by subtracting the difference film thickness from level A in the second film thickness from the first film thickness. Since level B has no influence of roughness, the first film thickness was adopted as is, and the film thickness after removing the influence of surface roughness from the first film thickness was set to the same value as the first film thickness. As a result of calculation in this way, the film thickness after removing the effect of surface roughness from the first film thickness was 5.185 nm for level B, 5.221 nm for level C, 5.224 nm for level D, and 5.234 nm for level E.

Here, focusing on levels B, C, D, and E, the magnitude relationship between the film thickness excluding the influence of surface roughness from the first film thickness and the magnitude relationship between the first film thickness are:

Level E>Level D>Level C>Level B

It has become. Since levels B, C, D, and E are levels where the SC1 cleaning conditions are changed, it was found that the value of the first film thickness changed due to the effect of both the surface roughness and structure of the natural oxide film depending on the cleaning conditions.

Furthermore, Table 4 shows the results of analysis of the factors that cause the film thicknesses of levels C, D, and E to become thicker with respect to level B, where the first film thickness is the thinnest, in levels B, C, D, and E. Here, the differential film thickness for level B of the second film thickness is the film thickness (α) caused by surface roughness, and the film thickness obtained by removing the influence of surface roughness from the first film thickness is level B of levels C, D, and E. The differential film thickness was taken as the film thickness (β) due to the structure of the natural oxide film.

As a result, α became 0.048 nm at level C, 0.048 nm at level D, and 0.084 nm at level E, and β became 0.036 nm at level C, 0.039 nm at level D, and 0.049 nm at level E. Furthermore, calculating α/β, level C was 1.333, level D was 1.230, and level E was 1.714. In this way, it was possible to analyze in detail the factors causing variation in film thickness when cleaning conditions were changed.

As described above, according to the embodiment of the present invention, it is determined whether the film thickness value includes the influence of film thickness influencing factors such as wafer surface roughness formed in the silicon wafer manufacturing process, and the film thickness due to the film thickness influencing factor is determined. could be evaluated with high precision.

Meanwhile, the present invention is not limited to the above embodiments. The above-mentioned embodiment is an example, and anything that has substantially the same structure as the technical idea described in the claims of the present invention and exhibits the same effects is included in the technical scope of the present invention.

Claims (10)

A method for evaluating an oxide film on a silicon substrate with a Sa value of surface roughness measured by an atomic force microscope of 0.5 nm or less,
A substrate preparation step of preparing a silicon substrate to be evaluated on which an oxide film is formed, and a reference silicon substrate having an average power spectral density of 0.1 nm ³ or less at a spatial frequency of 60 to 90/μm on the surface of the substrate;
A first film thickness measurement process of measuring the film thickness of the oxide film on the silicon substrate to be evaluated with an ellipsometer;
An oxide film removal process to completely remove the oxide film on the silicon substrate to be evaluated and the reference silicon substrate;
An oxide film forming step of forming an oxide film under the same conditions on the silicon substrate to be evaluated and the reference silicon substrate after removing the oxide film;
A second film thickness measurement process of measuring the film thickness of the oxide film on the silicon substrate to be evaluated and the oxide film on the reference silicon substrate after the oxide film formation process with an ellipsometer;
Based on the film thickness of the oxide film on the silicon substrate to be evaluated and the film thickness of the oxide film on the reference silicon substrate obtained in the second film thickness measurement step, the oxide film on the silicon substrate to be evaluated acquired in the first film thickness measurement step. A method for evaluating the film thickness of an oxide film, comprising a film thickness evaluation process for evaluating the film thickness due to the film thickness influencing factors in the entire film thickness. According to paragraph 1,
A method for evaluating the film thickness of an oxide film, characterized in that in the oxide film removal step, the oxide film is removed by hydrofluoric acid cleaning. According to claim 1 or 2,
In the oxide film forming process, a method for evaluating the film thickness of an oxide film, characterized in that the oxide film is formed by ozone water cleaning or hydrogen peroxide water cleaning. According to any one of claims 1 to 3,
A method for evaluating the film thickness of an oxide film, wherein the film thickness of the oxide film on which the evaluation is performed on the silicon substrate to be evaluated is set to 25 nm or less. According to any one of claims 1 to 4,
The film thickness influencing factor in the film thickness of the oxide film includes the surface roughness of the silicon substrate to be evaluated,
In the film thickness evaluation process, the difference obtained by subtracting the film thickness of the oxide film on the reference silicon substrate obtained in the second film thickness measurement process from the film thickness of the oxide film on the silicon substrate to be evaluated obtained in the second film thickness measurement process. When the film thickness is 0.02 nm or more and 0.20 nm or less, the film thickness of the oxide film on the silicon substrate to be evaluated obtained in the first film thickness measurement process includes the film thickness of the oxide film resulting from the surface roughness of the silicon substrate to be evaluated. A method for evaluating the film thickness of an oxide film, characterized in that it is determined that the film is thick. According to clause 5,
In the film thickness evaluation process, the influence of the surface roughness of the silicon substrate to be evaluated is removed by subtracting the differential film thickness from the film thickness of the oxide film on the silicon substrate to be evaluated obtained in the first film thickness measurement process. A method for evaluating the film thickness of an oxide film, characterized in that the film thickness is evaluated. According to claim 5 or 6,
A method for evaluating the film thickness of an oxide film, wherein the surface roughness is a roughness component with a spatial frequency of 60 to 90/μm. According to any one of claims 5 to 7,
A method for evaluating the film thickness of an oxide film, wherein the surface roughness is a roughness component formed by SC1 cleaning. Based on the film thickness due to the film thickness influencing factor evaluated by the oxide film thickness evaluation method according to any one of claims 1 to 8, the cleaning conditions and/or oxidation conditions before forming the oxide film on the silicon substrate are set. and cleaning the silicon substrate and forming an oxide film on the silicon substrate using the cleaning conditions and/or oxidation conditions to manufacture a silicon substrate with an oxide film. As a method for evaluating the film thickness of an oxide film formed on a silicon substrate,
When the film thickness influencing factor in the film thickness of the oxide film includes the surface roughness of the silicon substrate, and the average value of the power spectral density at the spatial frequency of the surface of the silicon substrate is 60 to 90/μm is 0.15 nm ³ or more. A method for evaluating the film thickness of an oxide film, characterized in that it is determined that the film thickness of the oxide film formed on the silicon substrate includes the film thickness of the oxide film resulting from the surface roughness of the silicon substrate, which is a factor influencing the film thickness.