JP3452629B2 - Method and apparatus for evaluating silicon oxide film, and method and apparatus for manufacturing semiconductor device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a silicon oxide film evaluation method and apparatus for evaluating a silicon oxide film formed on a silicon substrate, and a semiconductor device manufacturing method and apparatus using the evaluation method.

[0002]

2. Description of the Related Art Bipolar transistors, MOSFE
In silicon semiconductor devices such as T and memory devices, a silicon oxide film formed by thermally oxidizing a silicon substrate is used as its insulating film. Among the silicon oxide films formed by thermal oxidation, the field insulating film for element isolation is thick, but the silicon oxide film used as the gate insulating film and the dielectric film of the trench capacitor is very thin. But,
As the density of semiconductor devices increases, further thinning of these thin insulating films is required.

In the case of a thin oxide film of about 10 nm or less formed by the thermal oxidation method, this film thickness is several tens when converted into an atomic layer.
It corresponds to the atomic layer. Therefore, it is desired to evaluate the film quality of the silicon oxide film by physicochemical structural analysis performed at the atomic and molecular level. However, in the conventional evaluation method, there is no means for nondestructively evaluating the silicon oxide film, and the evaluation has to be made from the electrical characteristics of the formed semiconductor element. The electrical characteristics of the semiconductor element are greatly affected not only by the thermal oxidation step, but also by the subsequent electrode forming step and manufacturing steps such as a heat treatment step. Therefore, the thermal oxidation conditions cannot be clearly determined from the electrical characteristics of the semiconductor element, and trial and error must be repeated in order to determine the appropriate thermal oxidation conditions, which is inefficient. It was

As an example, the method of directly observing the surface or interface of a semiconductor device includes atomic absorption analysis, Auger electron spectroscopy, infrared reflection absorption spectroscopy, cross-section transmission electron, and the like. Methods using a microscope, a scanning tunneling electron microscope, a scanning atomic force microscope, etc. are known.

[0005]

However, in the methods such as atomic absorption spectrometry, Auger electron spectroscopy, cross-section transmission electron microscope, scanning tunneling electron microscope, and scanning atomic force microscope, the sample is destroyed during observation. With
The sample needs to be placed in a vacuum. Therefore, the semiconductor substrate being manufactured cannot be directly observed. Therefore,
It is necessary to prepare a dummy sample for observation separately from the semiconductor sample for observation.

However, the surface condition of the dummy sample does not always match the surface condition of the semiconductor substrate on which the semiconductor circuit is actually manufactured, and as a result, an error occurs. Further, since it is necessary to secure a space for the dummy sample in the semiconductor manufacturing apparatus, there is a problem that manufacturing efficiency is lowered and time and labor are required. On the other hand, since the infrared absorption analysis method is a non-contact, non-destructive observation method and can be observed under normal atmospheric pressure, the semiconductor substrate can be directly observed during the manufacturing process of the semiconductor device.

An object of the present invention is to provide a silicon oxide film evaluation method and apparatus capable of observing a silicon oxide film formed on a silicon substrate in a non-contact and non-destructive manner and evaluating the film quality. It is in. Another object of the present invention is to
An object of the present invention is to provide a method and an apparatus for manufacturing a semiconductor device capable of in-line evaluation of a silicon oxide film formed on a silicon substrate.

[0008]

The above object is to provide a silicon oxide film evaluation method for evaluating the film quality of a silicon oxide film formed on a silicon substrate, wherein the silicon oxide film has a predetermined wavelength range. Then , irradiate a plurality of incident light incident at different angles, respectively measure the reflected light at the silicon oxide film for the plurality of incident light, reflected from the plurality of incident light and the plurality of reflected light at different angles The silicon oxide film is characterized in that the respective dielectric constants are calculated, the dielectric function of the silicon oxide film is calculated based on the reflectance for the different angles, and the film quality of the silicon oxide film is evaluated based on the dielectric function. It is achieved by the evaluation method of.

In the above-described method for evaluating a silicon oxide film, the plurality of incident lights are incident light incident at an angle larger than Brewster's angle and incident light incident at an angle smaller than Brewster's angle. desirable. In the method for evaluating a silicon oxide film described above, the dielectric function of a reference silicon oxide film of a film quality that serves as a reference of a silicon oxide film formed on a silicon substrate is obtained, and the dielectric function of an evaluated silicon oxide film to be evaluated is obtained. It is desirable to evaluate the film quality of the silicon oxide film to be evaluated by comparing the dielectric function of the reference silicon oxide film and the dielectric function of the silicon oxide film to be evaluated.

In the above-described method for evaluating a silicon oxide film, the dielectric function of a reference silicon oxide film having a predetermined thickness, which serves as a reference for a silicon oxide film formed on a silicon substrate, is obtained, and the silicon oxide to be evaluated to be evaluated is obtained. The reflectance of the film is measured, and based on the dielectric function of the reference silicon oxide film and the film thickness of the silicon oxide film to be evaluated, the reflectance of the evaluation silicon oxide film is predicted to calculate the predicted reflectance. It is desirable to evaluate the film quality of the silicon oxide film to be evaluated by comparing the measured reflectance of the silicon oxide film to be evaluated with the predicted reflectance.

[0011]

In the above-mentioned method for evaluating a silicon oxide film, it is desirable to provide an infrared light absorbing region for absorbing infrared light in the silicon substrate. Further, it is desirable that the infrared absorption region has an absorbance of 2 or more. Further, it is desirable to form the infrared light absorbing region by introducing impurities into the silicon substrate. In the method for evaluating a silicon oxide film described above, the silicon substrate has a predetermined thickness or more so that the influence of the reflected light on the surface opposite to the surface on which the silicon oxide film to be evaluated is almost eliminated. Is desirable.

In the above-described method for evaluating a silicon oxide film, the interface between the silicon substrate and the silicon oxide film is
There is a mixed layer in which silicon particles and silicon oxide particles are mixed, and a model for determining the dielectric function of the mixed layer is set by the effective medium theory, and the dielectric function of the silicon oxide film calculated from the reflectance is used as the model. It is desirable to adapt. Further, it is desirable to evaluate the interface between the silicon substrate and the silicon oxide film based on the thickness of the mixed layer. Further, it is desirable to evaluate the interface between the silicon substrate and the silicon oxide film based on the size of the silicon particles or the silicon oxide particles forming the mixed layer.

[0014] The above object is achieved in the evaluation device of the silicon oxide film to evaluate the film quality of the silicon oxide film formed on a silicon substrate, with respect to the silicon oxide film, predetermined wave
Irradiating means having a long range and irradiating a plurality of incident lights incident at different angles, measuring means for respectively measuring reflected light on the silicon oxide film with respect to the plurality of incident lights, and the plurality of incident lights. And calculating means for calculating the dielectric function of the silicon oxide film based on the reflectances for the different angles from the plurality of reflected lights. Achieved by the evaluation device.

The above and other objects are achieved by a method of manufacturing a semiconductor device, which includes the step of evaluating using the above-described method of evaluating a silicon oxide film. Another purpose is to form a silicon oxide film on a silicon substrate by thermal oxidation, and to evaluate the silicon oxide film formed on the silicon substrate by using the above-described method for evaluating a silicon oxide film. And a step of depositing a polycrystalline silicon layer on the silicon oxide film.

[0016] The above other objects are arranged and a heat treatment apparatus for forming a silicon oxide film by thermal oxidation on the silicon substrate, as with the heat treatment apparatus capable of continuous processing, the
Has a certain wavelength range with respect to the silicon oxide film, and is different
An irradiation means for irradiating a plurality of incident lights incident at an angle;
Note: Reflected light from the silicon oxide film for a plurality of incident lights
Measuring means for respectively measuring the
The reflectance for different angles from multiple reflected lights
Based on the reflectance for the different angles,
And a calculation means for calculating the dielectric function of the silicon oxide film.
An evaluation device for evaluating the silicon oxide film based on the dielectric function, and a deposition for arranging a polycrystalline silicon layer on the silicon oxide film, the deposition being arranged so that continuous processing with the evaluation device is possible. and having a device
This is achieved by a semiconductor device manufacturing apparatus .

[0017]

According to the present invention, in a silicon oxide film evaluation method for evaluating the film quality of a silicon oxide film formed on a silicon substrate, the silicon oxide film has a predetermined wavelength range.
The a, irradiating a plurality of light incident at different angles,
The reflected light from the silicon oxide film for each of the multiple incident lights is measured, the reflectances for different angles are calculated from the multiple incident light and the multiple reflected lights, and the reflectance of the silicon oxide film is calculated based on the reflectances for different angles. Since the dielectric function is calculated and the film quality of the silicon oxide film is evaluated based on the dielectric function, the silicon oxide film formed on the silicon substrate is observed without contact and non-destruction, and the film quality is evaluated. be able to.

Further, according to the present invention, the dielectric function of the reference silicon oxide film of the film quality which becomes the reference of the silicon oxide film formed on the silicon substrate is obtained, and the dielectric function of the silicon oxide film to be evaluated is calculated. Since the film quality of the silicon oxide film to be evaluated is evaluated by comparing the dielectric function of the reference silicon oxide film with the dielectric function of the silicon oxide film to be evaluated, the silicon oxide film formed on the silicon substrate is evaluated. The film quality can be evaluated by observing the film in a non-contact and non-destructive manner.

Further, according to the present invention, since the infrared light absorbing region for absorbing infrared light is provided in the silicon substrate, the influence of the reflection from the back surface of the silicon substrate can be eliminated.

Further, according to the present invention, a mixed layer in which silicon particles and silicon oxide particles are mixed is present at the interface between the silicon substrate and the silicon oxide film, and a model for obtaining the dielectric function of the mixed layer is set by the effective medium theory. Since the dielectric function of the silicon oxide film calculated from the reflectance is adapted to the model, the interface of the silicon oxide film can be accurately evaluated.

[0021] According to the present invention, in the evaluation device of the silicon oxide film to evaluate the film quality of the silicon oxide film formed on a silicon substrate, the silicon oxide film, where
Irradiation means for irradiating a plurality of incident lights having a constant wavelength range and incident at different angles, measuring means for measuring reflected light on the silicon oxide film with respect to the plurality of incident lights respectively, and a plurality of incident light and Since the reflectance for different angles is calculated from the reflected light and the calculating means for calculating the dielectric function of the silicon oxide film based on the reflectance for different angles is provided, the silicon oxide film formed on the silicon substrate Can be observed in a non-contact and non-destructive manner to evaluate the film quality.

[0022]

【Example】

[First Embodiment] A method for evaluating a silicon oxide film according to a first embodiment of the present invention will be described with reference to FIGS. The evaluation apparatus of the silicon oxide film by the evaluation device embodiment of the silicon oxide film shown in FIG. 1 (Tasumi Sansei Author: "Basic and Practice of FT = IR" see section 109 pages). The evaluation apparatus shown in FIG. 1 is based on Fourier transform infrared spectroscopy (FTIR).
It is an infrared reflection spectrum measuring apparatus of the external reflection type by Infrared Spectroscopy.

As a sample 8 to be evaluated, a silicon substrate having a silicon oxide film formed thereon is placed at the center. The infrared light incident from the illumination system on the right side of the sample 8 is reflected on the surface of the sample 8, and the reflected light is measured and analyzed by the measurement system on the left side. The illumination system on the right side of the sample 8 is provided with a light source 1 that emits infrared light, and an interferometer 2 and a polarizer 3 are provided on the emission side of the light source 1. Infrared light from the light source 1 is emitted as a bundle of parallel rays through the interferometer 2 and the polarizer 3. By providing the polarizer 3, P-wave infrared light whose electric field is parallel to the incident surface (optical path surface) is emitted.

The emitted infrared light is reflected by the mirror 4a, condensed by the concave mirror 4b and obliquely incident on the surface of the sample 8. By rotating the concave mirrors 4b and 4c to bring the height of the sample 8 to a predetermined position, the incident angle to the sample 8 can be changed. The reflected light from the sample 8 is a concave mirror 4c.
Becomes a bundle of parallel rays by and is reflected by the mirror 4d,
MCT (Mercury Cadmium Tellu
Ride) It is incident on the detector 5. The MCT detector 5 detects the reflected light from the sample 8. The detection signal from the MCT detector 5 is amplified by the preamplifier 6 and output to the arithmetic unit 7. The calculation unit 7 calculates the reflectance of the surface of the sample 8 based on the detection signal from the preamplifier 6 to obtain the dielectric function of the silicon oxide film as described later.

In the present embodiment, by rotating the concave mirrors 4b and 4c, a plurality of incident lights that are incident on the sample 8 at different angles are irradiated, and the reflected light from the sample 8 with respect to the plurality of incident lights is irradiated. Measure each. The reflectances for different angles are calculated from a plurality of incident lights and a plurality of reflected lights, and the dielectric function of the silicon oxide film is obtained based on the reflectances for different angles. The film quality of the silicon oxide film is evaluated based on the thus obtained dielectric function.

In the evaluation method of the silicon oxide film of this embodiment, regarding the light reflected on the dielectric surface, from the Brewster angle which is the incident angle at which the reflectance of the light in the incident plane of the electric vector becomes zero. Incident light that is incident at a large angle,
The reflectance of incident light incident at an angle smaller than the Brewster's angle largely changes the reflectance of silicon oxide with respect to the reflectance of silicon, and the dielectric function of the silicon oxide film can be obtained more accurately.

Principle of Evaluation Method of Silicon Oxide Film Next, the principle of the evaluation method of the silicon oxide film of this embodiment will be described. Generally, the spectrum obtained by infrared spectroscopy is dominated by the response of a substance, here a silicon oxide film, to electromagnetic waves, that is, the dielectric constant.
Since the dielectric constant reflects the structure at the atomic / molecular level of the substance, the substance structure can be evaluated by focusing on the absorption / reflection peak of the infrared spectrum. However, in the case of a substrate, an optical system, and a film, the actually measured spectrum is detected as a mixture of information on its thickness.

Therefore, in the conventional evaluation method, when analyzing the difference in the structure of the silicon oxide film, it is necessary to prepare a reference sample having the same film thickness in order to subtract the information of the film thickness. That is, it is necessary that the same optical system is used, the information on the silicon substrate is subtracted after the measurement, and the film thickness of the silicon oxide film is approximately the same (within 5%).

Therefore, in the conventional evaluation method by infrared spectroscopy, the structures of the silicon oxide films can be compared only with films having similar film thicknesses. The silicon oxide film evaluation method according to the present embodiment eliminates such a conventional inconvenience, and makes it possible to compare the film qualities of silicon oxide films of different film thicknesses.

Generally, the dielectric constant of a silicon oxide film is complexly expressed as ε = ε ′ + iε ″. An electromagnetic field such as infrared light is accompanied by a phase change when it enters a substance such as a silicon oxide film. Moreover, since the permittivity differs depending on the wavelength (wave number), it must be expressed as a function of wave number (dielectric function).

In this specification, the permittivity and the refractive index are treated as complex numbers, and they are represented as ε and n, respectively. Thus, the dielectric function is expressed in complex as a function of wave number. Therefore, as the dielectric function, there are two unknowns, the real part and the imaginary part, and the dielectric function cannot be obtained only by measuring the reflectance of the silicon oxide film by infrared light.

The inventors of the present application measure the reflected light of two or more infrared rays with different incident angles, and if two or more reflectances of the silicon oxide film are used, they are called a real part and an imaginary part. The idea is that a dielectric function with two unknowns can be obtained. That is, attention is paid to the fact that a dielectric function having two unknowns, a real part and an imaginary part, can be solved by numerical calculation based on two or more reflectances of a silicon oxide film by infrared light of different incident angles. It was decided to apply it to the evaluation method of the silicon oxide film.

Based on the thus obtained dielectric function, the predicted reflectance is calculated by calculating from the film thickness of the silicon oxide film to be compared, and is compared with the actually measured reflectance of the silicon oxide film to be compared. The film quality of the silicon oxide film is evaluated by. The light reflected by the silicon oxide film is P-polarized light that is perpendicular to the surface (parallel to the incident surface). In the case of a silicon oxide film, the structure is expected to transition in the film thickness direction. Therefore, rather than using transmitted light or S-polarized light (polarized light perpendicular to the incident surface), P-polarized light is used as incident light as in this embodiment. Is preferred.

As a conventional method for obtaining the dielectric function, there is a method using the Kramers-Kronig relational expression. If the reflectance can be measured in the whole wave number region, the dielectric function can be obtained by the following Kramers-Kronig relational expression.

[0035]

[Equation 1] However, when there is reflected light due to complicated multiple reflections such as in the substrate, the method based on the Kramers-Kronig relational expression cannot be used. For this reason, it cannot be used for an evaluation target such as a silicon oxide film formed on a silicon substrate that undergoes multiple reflections.

In the method for evaluating a silicon oxide film according to the present embodiment, the reflectance r when the silicon oxide film is a single layer is expressed as follows.

[0037]

[Equation 2] Classically solving the incident electromagnetic field, the reflected electromagnetic field, and the refraction electromagnetic field is represented by the following formula known as Fresnel's formula. Y _j = (cos θ _j ) / n _j r = (Y ₁ −Y ₂ ) / (Y ₁ + Y ₂ ) When there are a plurality of interfaces such as a film on the substrate, the intensity ratio of the emitted light to the incident light Is the energy flowing through the membrane
Considering the interference with

[0038]

[Equation 3] Since this equation is the amplitude reflectance, the external reflection and internal reflection on the outer surface are calculated based on the equation representing the actually measured energy reflectance. Assuming that the multiple reflections in the silicon substrate do not interfere, but are simply added, when expressed in series,
The following equation is obtained. _{R = R 1 + (T 1} T 2 A 2 R 0) / (1-A 2 R
₀ R ₂ ) However, R ₀ , R ₁ , R ₂ : reflectance A: absorptance T ₁ , T ₂ : transmittance The detected reflectance R can be obtained by the above formula.

The term A ² R ₀ in the above equation is
The reflectance by the silicon substrate and the reflectance by the back surface of the silicon substrate are shown. This section indicates that in the case of a silicon substrate that actually forms a semiconductor device, the reflectance of the silicon substrate is different due to the addition of impurities, and scattering occurs because the back surface of the silicon substrate is not mirror-polished. Is a value considering.

This value is determined by fitting it to the actual measurement value. The absolute reflectance of only the silicon substrate on which the silicon oxide film is not formed is calibrated using a gold mirror. The gold mirror is a mirror used as a reflectance standard, and it can be assumed that the reflectance is 1 over the entire wavelength range. The reflectance of this gold mirror is set to 1, and the absolute reflectance of only the silicon substrate is obtained. The value of the A ² R ₀ term is calculated based on the measured values thus measured.

After that, if the dielectric function is given, a simulation of the actually measured spectrum can be performed. Evaluation Method of Silicon Oxide Film FIG. 2 shows the procedure of the method for obtaining the dielectric function from the reflectance at incident angles of two or more angles.

First, as initial values, the incident angle θ and the film thickness t
And the refractive index n are set (step S1). Incident angle θ
Can be known from the measurement conditions, and the film thickness t can be measured by another measurement method.
To measure. The refractive index n is the same as that of the silicon oxide film.
Dielectric constant ε (= n ²) Multiple
Set the value. Next, from the above equation,
The reflectance R with respect to the refractive index n of
S2). As a result, the calculated values of the refractive index n and the reflectance R
A graph showing the relationship is obtained.

Next, using the graph showing the relationship between the refractive index n and the calculated value of the reflectance R, the refractive index n of the silicon oxide film is obtained from the actually measured value of the reflectance R (step S3). The dielectric constant ε (= n ² ) can be calculated from the calculated refractive index n. Dielectric constant ε according to steps S1 to S3 described above
The dielectric function can be obtained by performing the calculation of (= n ² ) over the required wave number region.

Using the dielectric function thus obtained,
In this embodiment, the film quality of the silicon oxide film is evaluated. The general method will be described. First, a silicon oxide film is formed on a silicon substrate under manufacturing conditions that are strictly controlled so as to serve as a reference for evaluation. With respect to the reference silicon oxide film thus formed, the dielectric function is obtained by the method described above.

Subsequently, with respect to the silicon substrate on which the silicon oxide film to be evaluated is formed, it is assumed that the silicon oxide film has the same film quality as the reference silicon oxide film, and the same dielectric function is assumed, and a pseudo evaluation is performed. The reflectance spectrum of the target silicon oxide film is calculated. Then, the measured value of the reflectance spectrum of the silicon oxide film to be evaluated is compared with the pseudo-obtained reflectance spectrum. As a result of the comparison,
If there is a difference between the actually measured spectrum and the pseudo-obtained spectrum, it means that the difference reflects the difference in film structure between the silicon oxide film to be evaluated and the reference silicon oxide film. The film quality with respect to the oxide film can be evaluated.

Next, as a concrete method for evaluating the film quality of the silicon oxide film, the procedure of the method for evaluating the silicon oxide films having different film thicknesses will be described. First, as a reference silicon oxide film, a 100 nm-thick silicon oxide film is formed on a silicon substrate by thermal oxidation. With respect to the reference silicon oxide film thus formed, the dielectric function is obtained by the method described above. The reason why the silicon oxide film having a thickness of 100 nm is used as the evaluation standard is that the region where the change in the film thickness in the film thickness direction is considered to be dominant is dominant in the silicon oxide film having such a thickness. is there.

Then, the estimated film thickness of the silicon oxide film to be evaluated is measured by another means. Assuming that the silicon oxide film to be evaluated has the same film quality as the reference silicon oxide film and is different only in film thickness, the reflectance spectrum of the silicon oxide film to be evaluated is pseudo-calculated. Then, the reflectance spectrum of the silicon oxide film to be evaluated is measured, and the measured value is compared with the simulated reflectance spectrum. If there is a difference between the actually measured spectrum and the pseudo-obtained spectrum as a result of the comparison, the difference reflects the difference in film structure between the silicon oxide film to be evaluated and the reference silicon oxide film. Therefore, the film quality with respect to the reference silicon oxide film can be evaluated.

Next, as another specific method for evaluating the film quality of the silicon oxide film, the procedure of the method for evaluating the silicon oxide film having different oxidation temperatures will be described. First, as a reference silicon oxide film, a silicon oxide film is formed on a silicon substrate while accurately measuring the temperature. With respect to the reference silicon oxide film thus formed, the dielectric function is obtained by the method described above.

Then, the dielectric function is obtained by the above-mentioned method for the silicon oxide film manufactured under the same conditions except for the oxidation temperature. Comparing the dielectric function of the reference silicon oxide film thus obtained with the dielectric function of the silicon oxide film to be evaluated shows that the difference reflects the difference in film quality. The film quality can be evaluated.

Example 1-1 A silicon oxide film having a thickness of about 9 nm formed on a silicon substrate by thermal oxidation was evaluated, and the incident light incident at two or more different angles (40 °, 80 °) was evaluated. Measure reflectance. The measurement result is shown in FIG. The angle of incident light is set to 40 ° and 80 ° by selecting the angle before and after the Brewster angle (about 74 °) of the silicon oxide film.
This is to cause a large difference in reflectance with respect to incident light of different angles, as shown in FIG. The dielectric function is calculated by using the two measured values of reflectance shown in FIG.

The silicon oxide film was removed with hydrofluoric acid and the surface was removed.
Prepare a silicon substrate on which virtually nothing is formed,
Reflection of the evaluation target based on the reflectance of the silicon substrate
The rate is defined as a relative value. Nothing is formed on the surface
Measured reflectance of silicon substrate is assumed to be 1
It is set based on the reflectance of the gold mirror. This measurement
From the value of the absorption of the silicon substrate itself and the back of the silicon substrate
A by reflection²R₀Find the value of the term. Back depending on incident angle
Since the surface reflectance and the optical path length of transmitted light are different, the angle to be measured
Every A²R ₀Find the value of the term.

The dielectric function is set, and the reflectance R is calculated using the following expression using the obtained value of the A ² R ₀ term.

[0053]

[Equation 4] _{R = R 1 + (T 1} T 2 A 2 R 0) / (1-A 2 R
₀ R _{2) However, R 0, R 1, R} 2: reflection factor A: absorption rate T _1, T _2: compared with measurements of actual measured transmittance calculated reflectance R,
The dielectric constant value closest to the measured value is obtained over the required wave number region. Based on the thus obtained dielectric function, for example, the film thickness is changed and calculation is performed, and the film quality of the silicon oxide film having a different film thickness is evaluated by comparing with the measured value.

The method for evaluating a silicon oxide film according to the present embodiment includes, in addition to the silicon oxide films having different thicknesses, the oxidation temperature, the oxidation pretreatment, the oxidizing atmosphere, the temperature for introducing into and oxidizing from the oxidizing furnace,
It is also effective for films having different oxidation conditions such as post-oxidation heat treatment. When the conditions for forming the silicon oxide film are changed, the film structure of the silicon oxide film differs depending on the oxidation conditions. Therefore, the dielectric function is obtained by the method of this embodiment and the film structures are compared.

By obtaining the correlation between the comparison result and the electrical characteristics after the semiconductor element is formed, the manufacturing conditions of the manufacturing process of the silicon oxide film can be optimized. [Second Embodiment] A method for evaluating a silicon oxide film according to a second embodiment of the present invention will be described with reference to FIGS.

In this example, reflection infrared spectroscopy (IR-R
AS: I nfra R ed R eflection A b
sorption S pectroscopy) is used to evaluate the interface of the silicon oxide film. Principle of Evaluation Method of Interface of Silicon Oxide Film The inventors of the present application used reflection infrared spectroscopy (IR-RAS) to evaluate the structure of the silicon oxide film, and the wave number in the infrared absorption spectrum was 1250 cm. Around ^-1 and 106
It is proposed that it is effective to measure the signal near 0 cm ^-1 .

However, the signals near the wave numbers of 1250 cm ^-1 and 1060 cm ^-1 indicate information about the film structure of the silicon oxide film, but it is said that the characteristics of the semiconductor element are determined and the silicon substrate and the silicon are determined. It does not represent the structure of the oxide film interface. Wave number is 106
The signal around 0 cm ⁻¹ is the transverse optical (TO: Trans) of stretching vibration of the bond (Si—O) between the silicon atom and the oxygen atom.
The signal near the wave number of 1250 cm ⁻¹ is the longitudinal optical (LO: Longitudinal Optical) of the stretching vibration of the bond between the silicon atom and the oxygen atom (Si—O).
Represents absorption by phonons. As described above, both of these signals show the properties as the bulk (entire) of the silicon oxide film, and do not show the structure of the interface between the silicon substrate and the silicon oxide film.

Therefore, it has been unclear in which wave number range of the infrared absorption spectrum the signal representing the structure of the interface between the silicon substrate and the silicon oxide film, which has a great influence on the characteristics of the actual semiconductor element, effectively appears. . The inventors of the present application have conducted extensive studies as to which wave number range of the reflectance or absorptance spectrum by reflection infrared spectroscopy (IR-RAS), and as a result, silicon measured by reflection infrared spectroscopy. It has been found that among the spectra of the reflectance or the absorptance of the oxide film, signals having a wave number in the range of about 1100 to 1230 cm ⁻¹ may be focused.

Considering the interface between the silicon substrate and the silicon oxide film, this interface is not always flat, and as shown schematically in FIG. 4, the silicon oxide film 12 seems to be mixed in some places in the silicon substrate 10. It is thought to have a different structure. At this time, as shown in FIG. 4, the silicon oxide film 12 can be considered separately as a film portion 12a of the silicon oxide film 12 and a pile portion 12b which is bite into the silicon substrate 10 like a pile.

Of these, the film portion 1 of the silicon oxide film 12
2a has a wave number near 1250 cm ^-1 and 1060 cm ^-1
It can be evaluated by measuring nearby signals. On the other hand, the pile portion 12b of the silicon oxide film 12 is considered to be in an environment similar to that of silicon oxide precipitated in the silicon crystal during the heat treatment process or the like, because the periphery and the lower portion are the bulk of silicon.

In the silicon oxide which forms a solid solution in the silicon crystal
Infrared absorption signal is 1100 cm ^-1From 1230 cm
^-1It is pointed out that it appears in the wave number range of S.M.
Hu, J. Appl. Phys. , Vol 51, pa
ge 5945, (1980)). Therefore, silico
The infrared absorption signal from the pile portion 12b of the oxide film 12 is also 1
100 cm^-1From 1230 cm^-1In the wave number range of
Seem.

FIG. 5 is a graph showing the infrared absorption spectrum of silicon oxide when the silicon substrate is left in pure water for a certain period of time. It is known that when a silicon substrate is left unattended, an island-shaped natural oxide film is formed on the surface of the silicon substrate. If the standing time becomes long, oxidation progresses and the island-shaped natural oxide film becomes large. If left unattended for a long time,
As shown in FIG. 5, 1100 cm ^-1 to 1230 cm ^-1
The absorption in the wave number range of increases and increases gradually.

Since the interface between the silicon substrate and the silicon oxide film has a structure in which the silicon oxide film penetrates into silicon like the natural oxide film, the structure of the interface between the silicon substrate and the silicon oxide film is known. For 1100c
It can be seen that it is sufficient to monitor the signal in the wave number range from m ⁻¹ to 1230 cm ⁻¹ . Example 2-1 FIG. 6 shows IR-RAS of a natural oxide film formed by immersing the (100) surface of a silicon substrate in a mixed solution of sulfuric acid and hydrogen peroxide.
It is a spectrum (a) and an IR-RAS spectrum (b) of a natural oxide film formed by immersing in a nitric acid solution. FIG. 7 is a difference spectrum between the spectrum (a) and the spectrum (b).

LO near wave number 1230-1250 cm ^-1
Since the absorption peak due to the phonon and the absorption peak due to the TO phonon near the wave number of 1060 cm ⁻¹ are different in size and position, the difference spectrum also shows the difference as shown in FIG. 7. However, as shown in FIG. 7, it can be seen that there is also a spectrum difference in the range of wave numbers 1100-1200 cm ⁻¹ indicated by a.

FIG. 8 shows that the silicon substrate shown in FIGS. 6 and 7 was heated to 800 ° C. in an oxygen atmosphere at 1 atm and was heated to 3 nm.
It is an IR-RAS spectrum after forming a thermal oxide film of a certain degree. The spectrum (a) shows a natural oxide film formed by a mixed solution of sulfuric acid and hydrogen peroxide and then thermally oxidized (film thickness 2.9 nm), and the spectrum (b) shows a natural oxide film formed by a nitric acid solution. And then thermally oxidized (thickness: 3.2 nm). FIG. 9 is a difference spectrum between the spectrum (a) and the spectrum (b).

As shown in FIG. 8, the absorption peaks due to LO phonons and TO phonons are almost the same due to the subsequent thermal oxidation, and only a slight difference in film thickness is observed between them. Absent. It can be seen that the film thickness obtained by the nitric acid solution treatment is slightly thicker. Actually, when both thermal oxide films were measured by ellipsometry, the film thickness of the natural oxide film (spectrum (a)) formed by the mixed solution of sulfuric acid and hydrogen peroxide was 2.9 nm. The thickness of (spectrum (b)) is 3.2 n
m, which is slightly thicker by the nitric acid solution treatment.

However, in the wave number region of 1100-1200 cm ^-1 , the spectrum (a) is larger, which is in agreement with the tendency shown in FIGS. 6 and 7. That is, even after thermal oxidation, the effect of the pretreatment is 1100-12.
It appears over the wave number region of 00 cm ^-1 , and IR-RA
By focusing on this wave number region of the S spectrum, the difference in the composition of the thermal oxide film can be understood.

Example 2-2 FIG. 10 is an IR-RAS spectrum of a silicon substrate thermally oxidized at about 950 ° C. and taken out from the furnace at about 900 ° C. FIG. 11 is an IR-RAS spectrum of a silicon substrate extracted after cooling in the furnace to near room temperature. FIG. 12 is a difference spectrum between the spectrum of FIG. 10 and the spectrum of FIG.

As shown in FIG. 12, in this embodiment as well, L
Absorption peaks due to O phonons and TO phonons appear according to the film thickness. By the way, it should be noted that FIG.
Then, a peak not seen in FIGS. 10 and 11 appears near the wave number of 1114 cm ⁻¹ . It is known that the fixed charge amount in the silicon oxide film varies depending on the difference in the extraction temperature, and the peak near the wave number of 1114 cm ⁻¹ is considered to correspond to the difference in the fixed charge amount. It is known that the amount of fixed charges in the silicon oxide film depends on the uneven shape of the interface.

Moreover, the silicon substrate shown in FIG.
Since the difference in the silicon substrate in FIG. 11 is due to the difference in the last oxidizing atmosphere, it is considered that the structure of the interface between the silicon substrate and the silicon oxide film is different. Therefore, the peak near the wave number of 1114 cm ⁻¹ is considered to represent the difference in the structure of the interface between the silicon substrate and the silicon oxide film.

Example 2-3 FIG. 13 shows IR-RAS of a film having different pretreatment before thermal oxidation.
It is a spectrum. The spectrum (a) shows that the (100) surface of the silicon substrate was pretreated with 5% hydrofluoric acid for 1 minute, then immersed in a 1: 1 mixed solution of hydrogen peroxide and water for 20 minutes, and then at 100 ° C. This is a spectrum of the silicon oxide film formed on the silicon substrate by heat treatment in. The thickness of this silicon oxide film was measured by ellipsometry and found to be 1.54 nm.

The spectrum (b) is (1) of the silicon substrate.
(00) surface is mixed solution of 7: 1 with hydrofluoric acid and ammonium fluoride (BHF: Buffered Hydrogen).
Fluoride) pretreatment for 5 minutes, then soak in a 1: 1 mixed solution of hydrogen peroxide and water for 20 minutes, and then heat-treat at 100 ° C. to obtain a spectrum of the silicon oxide film formed on the silicon substrate. Is. The thickness of this silicon oxide film was measured by ellipsometry and found to be 2.18 nm.

[0073] As shown in FIG. 13, both of the silicon oxide film, an absorption peak due to LO phonons around wave number 1230-1250cm ^-1, T near the wave number 1060 cm ^-1
The absorption peaks due to O-phonons are the same, and the film quality of both silicon oxide films is almost the same. However, as shown in FIG. 13, the spectrum (a) is larger than the spectrum (b) in the wave number region of 1100-1200 cm ⁻¹ . Therefore. Even after the thermal oxidation, the influence of the pretreatment appears in the wave number region of 1100-1200 cm ^-1 . From FIG. 13, the interface of the spectrum (a) is
It can be seen that the unevenness is smaller than at the interface of spectrum (b). [Third Embodiment] A method for evaluating a silicon oxide film according to a third embodiment of the present invention will be described with reference to FIGS.

In the first and second embodiments described above, the light reflected by the silicon oxide film on the silicon substrate is measured to evaluate the silicon oxide film. However,
As shown in FIG. 14, although it is originally desired to measure only the reflected light b reflected by the silicon oxide film 22 as the incident light a, the light c reflected by the back surface of the silicon substrate 20 and transmitted through the silicon oxide film 22. Will be measured at the same time. Therefore, the silicon oxide film 2 formed on the silicon substrate 20
2 structure analysis, silicon substrate 20 and silicon oxide film 2
There was a problem that observation of the vicinity of the interface of No. 2 became inaccurate and time and labor were required for analysis and evaluation.

The present embodiment solves such a problem and
It is possible to measure only the reflected light b reflected by the silicon oxide film. Principle of this Embodiment The principle of this embodiment is shown in FIG. According to the principle shown in FIG. 15, the infrared light absorption region 24 that absorbs infrared light is provided in the silicon substrate 20 so that the reflection component from the interface of the silicon substrate which is not the measured side can be ignored. There is.

The infrared light absorbing region 24 for absorbing infrared light may be formed in the entire region of the silicon substrate 20, or a predetermined evaluation region may be provided in the silicon substrate 20 and the silicon substrate 20 in the evaluation region may be formed. It may be provided inside. Also,
The infrared light absorption region 24 may be provided in the region below the semiconductor element formed on the silicon substrate 20. It is possible to directly evaluate the gate oxide film to be used in the semiconductor element, which is effective when compared with the electrical characteristics of the finally formed semiconductor element.

Even if the absorbance is large, if the silicon substrate 20 is thin, the refracted light is not completely absorbed and is emitted again from the substrate surface. Therefore, it is desirable to increase the optical path length by making the silicon substrate 20 thick so as to absorb the transmission component while transmitting through the silicon substrate. Example 3-1 1 × 10 ¹⁵ boron was added to a 0.5 mm thick silicon substrate.
Consider the case of addition at a concentration of atoms / cm ³ .
The absolute reflectance when irradiated with infrared light having an incident angle of 80 degrees is about 8 to 10%.

On the other hand, the theoretical reflectance from the surface of the silicon substrate can be obtained by the following Fresnel's equation.

[0079]

[Equation 5] Assuming that the dielectric constant of silicon is 11.7, the theoretical reflectance from the surface of the silicon substrate is 5.5% from the above Fresnel's equation, so that the reflection from the silicon substrate to which boron is added at the above concentration is obtained. It can be seen that the light considerably contains multiple reflection components from the inside of the silicon substrate.

Here, the internal absorption component when the thickness of the silicon substrate is normalized to 1 cm is Lambert's law shown below.

[0081]

[Equation 6] When the absorbance is determined to be in accordance with, the value is about 0.1 to 0.3, which is insufficient for the absorption of the refractive index. To absorb the light refracted into the silicon substrate almost inside the substrate, the absorbance is 2
The thickness of the silicon substrate is preferably 10 mm or more, because the above (absorption rate is 99% or more) is sufficient.

The absorption of infrared light in the silicon substrate is
There are three possible modes: absorption due to lattice vibration of silicon, absorption due to free carriers, and absorption due to interstitial oxygen at a wave number of 1100 cm ^-1 . The absorption due to lattice vibration of silicon is weak, and the absorption due to interstitial oxygen is changed by heat treatment to bring about the absorption only in a specific region. Therefore, it is considered effective to utilize absorption by free carriers. Therefore, the concentration of free carriers may be increased in the measurement region of the silicon substrate to attenuate the transmission component in the substrate.

FIG. 16 is a graph showing the relationship between the concentration of boron added to a 5 mm thick silicon substrate and the absorbance. As is clear from FIG. 16, in the case of a 5 mm-thick silicon substrate, the free carrier concentration (boron concentration) at which the absorbance is 2 or more is 1 × 10 ¹⁸ / cm ³ or more. 1c
In the case of an m-thick silicon substrate, the free carrier concentration (boron concentration) is 1 × 10 ¹⁶ / cm ³ or more.

When such a high-concentration impurity is added to the silicon substrate, the mechanism of oxidation of the silicon substrate may change, possibly affecting the characteristics of the semiconductor device. Therefore, when forming the infrared light absorption region,
It is desirable to devise the method of introducing impurities.

For example, impurities are added by ion implantation from the back surface of the silicon substrate. It is possible to prevent the surface of the silicon substrate from being deteriorated by ion implantation. Alternatively, a protective film may be formed on the front surface of the silicon substrate and impurities may be added from the back surface by thermal diffusion. Further, when the infrared light absorption region is formed in the silicon substrate by ion implantation of impurities, it is desirable that the profile of the impurity concentration is not made steep.
This is because if the profile of the impurity concentration is too steep, the infrared light may be significantly reflected by the infrared light absorption region.

In the above description, boron is introduced into the silicon substrate to increase the concentration of holes as free carriers, but arsenic may be introduced to increase the concentration of electrons as free carriers. . [Fourth Embodiment] A method for evaluating a silicon oxide film according to a fourth embodiment of the present invention will be described with reference to FIGS.

In this embodiment, a new model is set for the uneven structure of the interface of the silicon oxide film by infrared reflection absorption spectroscopy, and the dielectric function is determined so as to match the model, whereby the uneven structure of the interface is determined. It is what you want to quantify. The calculation of the reflectance of the silicon oxide film is performed by the following procedure (see "Optical Principles 1, 2, 3" by Born).

First, it is assumed that a plurality of layers 320, 321, ..., 32m are stacked on the silicon substrate 30 as shown in FIG. The reflectance R is calculated from the following equation using the characteristic matrix.

[0089]

[Equation 7]

[0090]

[Equation 8] The unknowns in the above equation are the incident angle θ and the incident light wave number ν
, And the dielectric function ε at each layer 320, 321, ..., 32 m
0, ε1, ..., εm, thickness of each layer d0, d1, ..., dm
Is. Principle of this Embodiment In this embodiment, as shown in FIG.
When the silicon oxide film 32 is formed on the silicon oxide film 32, the silicon oxide film 32 includes a layer 32a made of silicon oxide,
Mixed layer 3 in which silicon particles and silicon oxide particles are mixed at the interface
2b is set, and the dielectric function of the mixed layer 32b is obtained by the effective medium theory.

Responses such as reflection to an incident electric field in a system in which silicon oxide particles sufficiently small with respect to wavelength are present in a silicon substrate are explained by effective medium theory (see “Introduction to Solid State Physics”, upper and lower by Kittel). . The effective medium theory is that the medium responds to the sum of the external electric field and the polarized electric field due to the oxide, because the oxide in the substrate (medium) is polarized with respect to the external electric field.

According to the effective medium theory, the spectrum changes depending on the shape of silicon oxide, the arrangement with respect to the electric field, the size, and the density. As shown in FIG. 19, when the shape of the silicon oxide particles is an ellipsoid having principal axis lengths a1, a2, and a3, and the density thereof is f, the following equation is obtained.

[0093]

[Equation 9] Therefore, as shown by the mixed layer 32b in FIG. 17, the uneven structure of the interface is interpreted so that the effective medium theory can be approximately applied. As a result, the interface irregularities can be quantified from the shape, density and thickness of the interface irregularities. The procedure for quantitative evaluation of the interface structure of the silicon oxide film is as follows.

First, infrared light is incident on the silicon oxide film 32 on the silicon substrate 30 and the spectrum of the reflected light is measured. Next, the dielectric function of the silicon substrate 30 and the silicon oxide film 32 is obtained by the method of the first embodiment described above.
Next, by an optimization algorithm such as the least square method, the unknown number of the shape and size of the interface irregularities is determined from the actually measured infrared light spectrum.

Example 4-1 FIG. 20 shows measured values of infrared reflection spectrum. Spectrum a is an infrared reflection spectrum when a thick silicon oxide film having a thickness of about 5 nm is formed on the silicon substrate, and spectrum b is a red spectrum when a thin silicon oxide film having a thickness of about 2 nm is formed on the silicon substrate. It is an external reflection spectrum.
Both silicon oxide films were manufactured under the same thermal oxidation conditions except for the film thickness.

In the case of a thick silicon oxide film (spectrum a), the mixed layer 3 having unevenness in the interface is thicker than the entire film thickness.
Since the thickness ratio of 2b is low, the influence of the mixed layer 32b is small and it can be considered that there is no interface irregularity.
On the other hand, in the case of a thin silicon oxide film (spectrum b),
It is affected by the mixed layer 32b which is the interface irregularity.

Therefore, spectrum a and spectrum b
It is considered that the difference is mainly due to the concavo-convex structure of the interface when compared with. In FIG. 20,
When the spectrum a and the spectrum b are compared, the following differences are observed. First, L with a wave number of 1255 cm ^-1
The peak of O phonon is that the spectrum b is shifted to the lower wave number side than the spectrum a.

Secondly, in the wave number region of 1100-1200 cm ^-1 , the spectrum b is larger than the spectrum a. These characteristics change depending on the factors of the shape and size of the silicon oxide particles, which are the irregular shape of the interface. From the actual measurement values of FIG. 20, when the value of the factor of the unevenness of the interface is derived by the optimization method, the unevenness shape factor L = 0.
3 and the surface density f = 0.9.

The unevenness shape factor L of 0.3 means that the thickness direction and the surface direction of the silicon oxide grains are almost the same, and the surface density f of 0.9 means that the film has a surface density f of 0.9. It shows that 90% of the whole is a silicon oxide film. Therefore, in the case of a thin silicon oxide film, half of the film can be evaluated as an interface uneven region. A model is set on the basis of such an evaluation result, and an infrared reflection spectrum calculated from the model is shown in FIG. The spectrum a is an infrared reflection spectrum for a thick silicon oxide film, and the spectrum b is an infrared reflection spectrum for a thin silicon oxide film.

The spectrum of the actually measured value in FIG. 20 and the spectrum of the calculated value in FIG. 21 are almost in agreement, and it can be seen that the above-mentioned quantitative evaluation is appropriate. Example 4-2 FIG. 22 shows the mounted values of the infrared reflection spectrum. A spectrum a is an infrared reflection spectrum when a thick silicon oxide film having a thickness of about 5 nm is formed on the silicon substrate, and a spectrum b is a red spectrum when a thin silicon oxide film having a thickness of about 1 nm is formed on the silicon substrate. It is an external reflection spectrum.
Both silicon oxide films were manufactured under the same thermal oxidation conditions except for the film thickness.

The second embodiment is more than the first embodiment.
The LO phonon peak of spectrum b is large and shifted to the low wavenumber side. In the same manner as in Example 1, when the value of the factor of interface irregularity is derived, the irregularity shape factor L =
0.7 and surface density f = 0.9. The unevenness shape factor L of 0.7 indicates that the silicon oxide particles are flat and the surface direction is about 5 when the thickness direction is 1, and the surface density f is 0. A value of 9 indicates that 90% of the entire film is a silicon oxide film. Therefore, it can be evaluated that almost the entire silicon oxide film is an interface irregularity region.

The infrared absorption spectrum of the silicon oxide film changes under the influence of the oxidizing conditions such as the oxidizing temperature, the oxidizing atmosphere, the post-oxidation heat treatment and the pre-oxidation treatment. The factor of the uneven structure of the interface can be obtained for these spectra by the same method, and the uneven structure of the interface can be quantified. Further, when comparing infrared absorption spectra, as described above, pay attention to points such as the difference in the wave number of the peaks of the spectra, the difference in the relative height of the peaks, and the rise between the peaks and the valleys. Is desirable. [Fifth Embodiment] A semiconductor device manufacturing apparatus according to a fifth embodiment of the present invention will be described with reference to FIG.

In any of the cases, the silicon oxide film evaluation methods according to the above-described first to fourth embodiments are non-contact and non-destructive observation methods, and can be observed under normal atmospheric pressure. Therefore, as a manufacturing process of a semiconductor device, a process for executing the method for evaluating a silicon oxide film according to the above-described first to fourth embodiments is provided, and a semiconductor substrate being manufactured can be directly observed and evaluated.

FIG. 23 shows a semiconductor device manufacturing apparatus according to this embodiment. This semiconductor device manufacturing apparatus can implement a semiconductor device manufacturing method including an evaluation step. The heat treatment furnace 40 is provided on the most upstream side. Heat treatment furnace 4
At 0, heat treatment is performed to form a thermal oxide film on the silicon substrate. The heat treatment furnace 4 is provided downstream of the heat treatment furnace 40.
The IR-RAS measurement device 42 is arranged so that continuous processing with 0 can be performed. In the IR-RAS measuring device 42, the silicon oxide film evaluation method according to the first to third embodiments described above is executed.

On the downstream side of the IR-RAS measuring device 42,
A CVD device 44 is arranged so that continuous processing with the IR-RAS measuring device 42 is possible. In the CVD device 44, a polycrystalline silicon layer or the like is deposited on the silicon oxide film. Next, the operation of the semiconductor device manufacturing apparatus according to the present embodiment will be described by taking the case of forming a transistor on a silicon substrate as an example.

First, a wafer which is a silicon substrate is introduced into the heat treatment furnace 40, and a gate oxide film which is a thin silicon oxide film is formed on the surface of the silicon substrate. Next, the wafer on which the gate oxide film is formed is transferred to the IR-RAS measuring device 42, and the film structure of the gate oxide film is evaluated by the methods according to the first to third embodiments described above. Wafers judged to be defective as a result of the evaluation are rejected at this stage. Therefore, it is not necessary to perform a wasteful manufacturing process thereafter, and manufacturing efficiency is improved.

As a result of the evaluation, the wafer determined to be non-defective is transported to the CVD apparatus 44, and polycrystalline silicon to be a gate electrode is deposited on the gate oxide film. As described above, according to the present embodiment, the gate oxide film can be evaluated inline immediately after it is formed on the silicon substrate, and the heat treatment conditions and the like can be efficiently optimized based on the evaluation result. Can be done.

[0108]

As described above, according to the present invention, in a method for evaluating a film quality of a silicon oxide film formed on a silicon substrate, a predetermined wavelength range is set for the silicon oxide film. It has multiple incident lights that are incident at different angles, and the reflected light from the silicon oxide film for each of the multiple incident lights is measured, and the reflectance for different angles is calculated from the multiple incident lights and multiple reflected lights. By calculating the dielectric function of the silicon oxide film based on the reflectance for different angles and evaluating the film quality of the silicon oxide film based on the dielectric function, the silicon oxide film formed on the silicon substrate is calculated. Can be observed in a non-contact and non-destructive manner to evaluate the film quality.

Further, according to the present invention, the dielectric function of the reference silicon oxide film of the film quality which becomes the reference of the silicon oxide film formed on the silicon substrate is obtained, and the dielectric function of the silicon oxide film to be evaluated is calculated. Since the film quality of the silicon oxide film to be evaluated is evaluated by comparing the dielectric function of the reference silicon oxide film with the dielectric function of the silicon oxide film to be evaluated, the silicon oxide film formed on the silicon substrate is evaluated. The film quality can be evaluated by observing the film in a non-contact and non-destructive manner.

Further, according to the present invention, since the infrared light absorbing region for absorbing infrared light is provided in the silicon substrate, it is possible to eliminate the influence of reflection from the back surface of the silicon substrate.

Further, according to the present invention, a mixed layer in which silicon particles and silicon oxide particles are mixed is present at the interface between the silicon substrate and the silicon oxide film, and a model for determining the dielectric function of the mixed layer is set by the effective medium theory. Since the dielectric function of the silicon oxide film calculated from the reflectance is adapted to the model, the interface of the silicon oxide film can be accurately evaluated.

[0112] Further, according to the present invention, in the evaluation device of the silicon oxide film to evaluate the film quality of the silicon oxide film formed on a silicon substrate, the silicon oxide film, where
Irradiation means for irradiating a plurality of incident lights having a constant wavelength range and incident at different angles, measuring means for measuring reflected light on the silicon oxide film with respect to the plurality of incident lights respectively, and a plurality of incident light and Since the calculation means calculates the reflectances for different angles from the reflected light and calculates the dielectric function of the silicon oxide film based on the reflectances for different angles, the silicon oxide film formed on the silicon substrate Can be observed in a non-contact and non-destructive manner to evaluate the film quality.

[Brief description of drawings]

FIG. 1 is a diagram showing a silicon oxide film evaluation apparatus according to a first embodiment of the present invention.

FIG. 2 is a flowchart showing a procedure of a method for evaluating a silicon oxide film according to the first embodiment of the present invention.

FIG. 3 is a graph showing a measurement result by a method for evaluating a silicon oxide film according to the first embodiment of the present invention.

FIG. 4 is a diagram schematically showing an interface between a silicon substrate and a silicon oxide film.

FIG. 5 is a graph showing an infrared absorption spectrum when a silicon substrate is left in pure water.

FIG. 6 IR-RAS of a natural oxide film formed by dipping the (100) surface of a silicon substrate in a mixed solution of sulfuric acid and hydrogen peroxide.
It is a graph which shows the spectrum (a) and IR-RAS spectrum (b) of the natural oxide film formed by immersing in a nitric acid solution.

FIG. 7 is a graph showing a difference spectrum between the spectrum (a) and the spectrum (b) of FIG.

FIG. 8 is a graph showing an IR-RAS spectrum after a thermal oxide film is subsequently formed on the silicon substrate in FIGS. 6 and 7. The spectrum (a) shows a thermal oxidation after forming a natural oxide film with a mixed solution of sulfuric acid and hydrogen peroxide, and the spectrum (b) shows a thermal oxidation after forming a natural oxide film with a nitric acid solution. is there.

9 is a graph showing a difference spectrum between the spectrum (a) and the spectrum (b) of FIG.

FIG. 10 is a graph showing an IR-RAS spectrum of a silicon substrate taken out of a furnace at about 900 ° C. after being thermally oxidized at about 950 ° C.

FIG. 11: IR-RA of a silicon substrate taken out after being thermally oxidized at about 950 ° C. and then cooled in a furnace to near room temperature.
It is a graph which shows S spectrum.

12 is a graph showing a difference spectrum between the spectrum of FIG. 10 and the spectrum of FIG. 11.

FIG. 13: IR-RAS of films with different pretreatment before thermal oxidation
It is a graph which shows a spectrum. The spectrum (a) is
It is the spectrum of the silicon substrate when the (100) face of the silicon substrate is pretreated with 5% hydrofluoric acid, and the spectrum (b) shows the (100) face of the silicon substrate with 7: 1 of hydrofluoric acid and ammonium fluoride. 2 is a spectrum of a silicon substrate when pretreated with the mixed solution of FIG.

FIG. 14 is a diagram showing optical paths of incident light, refracted light, and reflected light on a silicon substrate on which a silicon oxide film is formed in IR-RAS measurement.

FIG. 15 is a diagram showing the principle of a method for evaluating a silicon oxide film according to a third embodiment of the present invention.

FIG. 16 is a graph showing the relationship between the concentration of boron added to a silicon substrate and the absorbance.

FIG. 17 is a diagram for explaining a model of a silicon oxide film in the fourth embodiment of the present invention.

FIG. 18 is a diagram for explaining a model of a silicon oxide film in the fourth embodiment of the present invention.

FIG. 19 is a diagram for explaining a model of a silicon oxide film in the fourth embodiment of the present invention.

FIG. 20 is a graph showing an actually measured value of an infrared reflection spectrum when a silicon oxide film is formed on a silicon substrate. The spectrum (a) is the case where a thick silicon oxide film is formed on the silicon substrate, and the spectrum (b) is the case
This is the case where a thin silicon oxide film is formed on a silicon substrate.

FIG. 21 is a graph showing calculated values of an infrared reflection spectrum when a silicon oxide film is formed on a silicon substrate. The spectrum (a) is the case where a thick silicon oxide film is formed on the silicon substrate, and the spectrum (b) is the case
This is the case where a thin silicon oxide film is formed on a silicon substrate.

FIG. 22 is a graph showing actually measured values of infrared reflection spectra when a silicon oxide film is formed on a silicon substrate. The spectrum (a) is the case where a thick silicon oxide film is formed on the silicon substrate, and the spectrum (b) is the case
This is the case where a thin silicon oxide film is formed on a silicon substrate.

FIG. 23 is a diagram showing a semiconductor device manufacturing apparatus according to a fifth embodiment of the present invention.

[Explanation of symbols]

1 ... Light source 2 ... Interferometer 3 ... Polarizer 4a, 4d ... Mirror 4b, 4c ... concave mirror 5 ... MCT detector 6 ... Preamplifier 7 ... Operation part 9 ... Sample 10 ... Silicon substrate 12 ... Silicon oxide film 12a ... Membrane part 12b ... Pile part 20 ... Silicon substrate 22 ... Silicon oxide film 24 ... Infrared light absorption region 30 ... Silicon substrate 32a ... Silicon oxide layer 32b ... mixed layer 40 ... Heat treatment furnace 42 ... IR-RAS measuring device 44 ... CVD apparatus

Front page continuation (72) Inventor Carlos Inomata Carlos Inagawa 1015, Kamiodanaka, Nakahara-ku, Kawasaki City, Kanagawa Prefecture (56) References JP 62-251636 (JP, A) JP 63-52004 (JP, JP, 5-52004) A) J. ELECTROCHEM. SOC. , 1991, Vol. 138, No. 6 (1991), p1770-1778 J. APPL. PHYS. , 1990, Vol. 68, No. 10 (1990), p5300-5308 (58) Fields investigated (Int.Cl. ⁷ , DB name) G01N 21/00-21/01 G01N 21/17-21/61 JOIS, PATOLIS

Claims (24)

(57) [Claims] 1. A method for evaluating a film quality of a silicon oxide film formed on a silicon substrate, comprising: a plurality of films having a predetermined wavelength range and incident at different angles with respect to the silicon oxide film. Of the incident light, the reflected light at the silicon oxide film for each of the plurality of incident light is measured, respectively, the reflectance for different angles is calculated from the plurality of incident light and the plurality of reflected light, respectively, the different A method for evaluating a silicon oxide film, comprising: calculating a dielectric function of the silicon oxide film based on a reflectance with respect to an angle, and evaluating a film quality of the silicon oxide film based on the dielectric function. 2. The method for evaluating a silicon oxide film according to claim 1, wherein the plurality of incident lights are incident light incident at an angle larger than Brewster's angle and incident light incident at an angle smaller than Brewster's angle. A method for evaluating a silicon oxide film, which is light. 3. The method for evaluating a silicon oxide film according to claim 1 or 2, wherein the dielectric function of a reference silicon oxide film having a film quality that serves as a reference for a silicon oxide film formed on a silicon substrate should be obtained and evaluated. Obtaining the dielectric function of the silicon oxide film to be evaluated, by comparing the dielectric function of the reference silicon oxide film, and the dielectric function of the silicon oxide film to be evaluated, to evaluate the film quality of the silicon oxide film to be evaluated A characteristic silicon oxide film evaluation method. 4. The method for evaluating a silicon oxide film according to claim 1 or 2, wherein a dielectric function of a reference silicon oxide film having a predetermined thickness, which serves as a reference for the silicon oxide film formed on a silicon substrate, is obtained and evaluated. The reflectance of the evaluated silicon oxide film to be measured is measured, and the reflectance of the evaluated silicon oxide film is predicted based on the dielectric function of the reference silicon oxide film and the film thickness of the evaluated silicon oxide film. And calculating the predicted reflectance, and comparing the measured reflectance of the silicon oxide film to be evaluated with the predicted reflectance to evaluate the film quality of the silicon oxide film to be evaluated. Evaluation method of oxide film. 5. The method for evaluating a silicon oxide film according to claim 4, wherein the reference silicon oxide film and the silicon oxide film to be evaluated are films having different oxidation temperatures. Method. 6. The method for evaluating a silicon oxide film according to claim 4, wherein the reference silicon oxide film and the silicon oxide film to be evaluated are films having different oxidizing atmospheres. Method. 7. The method for evaluating a silicon oxide film according to claim 4, wherein the reference silicon oxide film and the silicon oxide film to be evaluated are films having different heat treatment temperatures after oxidation. Evaluation method of silicon oxide film. 8. The method for evaluating a silicon oxide film according to claim 4, wherein the reference silicon oxide film and the silicon oxide film to be evaluated are films having different atmospheres before and after oxidation. Evaluation method. 9. A method of evaluating silicon oxide film according to any one of claims 1 to 8, the silicon to be in the silicon substrate, characterized by providing a infrared light absorbing region that absorbs infrared light Evaluation method of oxide film. 10. The method for evaluating a silicon oxide film according to claim 9 , wherein the infrared absorption region has an absorbance of 2 or more. 11. The evaluation method according to claim 9 or 10 silicon oxide film according, evaluation of silicon oxide film and forming the infrared light absorbing region by introducing an impurity into said silicon substrate Method. 12. The method for evaluating a silicon oxide film according to claim 11 , wherein impurities are introduced into the silicon substrate by ion implantation or thermal diffusion. 13. A method for evaluating a silicon oxide film according to claim 11 or 12, wherein the method of evaluating a silicon oxide film, which comprises introducing boron as the impurity in the silicon substrate. 14. The method for evaluating a silicon oxide film according to claim 13 , wherein the concentration of boron in the infrared absorption region is 1 c or less.
A method for evaluating a silicon oxide film, which is about 1 × 10 ¹⁶ atoms / cm ² or more per m. 15. A method of evaluating silicon oxide film according to any one of claims 9 to 14, substantially no influence of the reflected light on the surface opposite to the silicon oxide film formed surface to be evaluated Thus, the method for evaluating a silicon oxide film is characterized in that the silicon substrate has a predetermined thickness or more. 16. The method for evaluating a silicon oxide film according to claim 15 , wherein the silicon substrate has a thickness of 1 cm or more. 17. A method of evaluating silicon oxide film according to any one of claims 1 to 16, the interface between the silicon substrate and the silicon oxide film, there is a mixed layer silicon particles and silicon oxide particles are mixed A method for evaluating a silicon oxide film, characterized in that a model for obtaining a dielectric function of the mixed layer is set by an effective medium theory, and a dielectric function of the silicon oxide film calculated from the reflectance is adapted to the model. 18. The method for evaluating a silicon oxide film according to claim 17 , wherein the interface between the silicon substrate and the silicon oxide film is evaluated based on the thickness of the mixed layer. Method. 19. A method of evaluating silicon oxide film according to claim 17 or 18, wherein the interface of the silicon grains or on the basis of the size of the silicon oxide particle, the silicon substrate and the silicon oxide film constituting the mixed layer A method for evaluating a silicon oxide film, which comprises: 20. A silicon oxide film evaluation apparatus for evaluating the film quality of a silicon oxide film formed on a silicon substrate, comprising: a plurality of silicon wafers having a predetermined wavelength range and incident at different angles with respect to the silicon oxide film. Irradiating means for irradiating the incident light, measuring means for respectively measuring the reflected light on the silicon oxide film with respect to the plurality of incident light, and the reflectance for different angles from the plurality of incident light and the plurality of reflected light. An apparatus for evaluating a silicon oxide film, comprising: a calculating unit that calculates each value and calculates the dielectric function of the silicon oxide film based on the reflectance for the different angles. 21. The apparatus for evaluating a silicon oxide film according to claim 20 , wherein the irradiation unit has an angle larger than Brewster's angle,
An evaluation device for a silicon oxide film, characterized by irradiating incident light incident at an angle smaller than Brewster's angle. 22. A method of manufacturing a semiconductor device which comprises a step of evaluation by using evaluation method of a silicon oxide film according to any one of claims 1 to 19. Forming a silicon oxide film by thermal oxidation 23. silicon substrate, the formed by using the evaluation method of a silicon oxide film according to any one of claims 1 to 19 on the silicon substrate A method of manufacturing a semiconductor device, comprising: a step of evaluating a silicon oxide film; and a step of depositing a polycrystalline silicon layer on the silicon oxide film. 24. a heat treatment apparatus for forming a silicon oxide film by thermal oxidation on a silicon substrate, a continuous process and the heat treatment apparatus is arranged so as to be, with respect to the silicon oxide film, a predetermined wavelength range Have
Irradiation that irradiates multiple incident lights that are incident at different angles
Means and the silicon oxide film for the plurality of incident lights
Measuring means for respectively measuring the reflected light at
Reflected against the different angles from the incident light the plurality of reflected light
Calculate the respective reflectances to obtain the reflectance for the different angles.
Based on the dielectric function of the silicon oxide film.
An evaluation device that has a calculation means and evaluates the silicon oxide film based on the dielectric function, and is arranged so that continuous processing with the evaluation device is possible,
Compost depositing a polycrystalline silicon layer on the silicon oxide film
Apparatus for manufacturing a semiconductor device characterized by having a product device.