JP2020101460A - Film thickness measuring apparatus and film thickness measuring method of silicon epitaxial layer in epitaxial silicon wafer with embedded diffusion layer, and manufacturing method of epitaxial silicon wafer with embedded diffusion layer using film thickness measuring apparatus or film thickness measuring method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a film thickness measuring device capable of measuring the film thickness of a silicon epitaxial layer with high accuracy even in an epitaxial silicon wafer with an embedded diffusion layer having a low dopant concentration of a silicon substrate. A film thickness measuring device 1 of the present invention mounts an infrared light source 2, an interferometer 3 that generates interference light L from infrared light, and an epitaxial silicon wafer W with an embedded diffusion layer. The reflected light R1 generated by the interference light L reflected on the surface of the silicon epitaxial layer 18 and the reflected light R2 generated by the interference light L reflected at the interface between the silicon epitaxial layer 18 and the embedded diffusion layer 16 are detected. A detector 5 and a control unit for calculating the thickness of the silicon epitaxial layer 18 from the output of the detector 5 are provided, and the measurement stage 6 has a reflectance of 15% or less at the peak wavelength of the infrared light spectrum. It is made of a certain material. [Selection diagram] Fig. 1

Description

The present invention relates to a film thickness measuring device and a film thickness measuring method for a silicon epitaxial layer in an epitaxial silicon wafer with a buried diffusion layer, and a method for manufacturing an epitaxial silicon wafer using the film thickness measuring device or the film thickness measuring method.

There is a silicon wafer in which a buried diffusion layer for an integrated circuit is formed on the surface layer of a silicon substrate, and a single crystal thin film such as a silicon epitaxial layer is formed on the buried diffusion layer. Patent Document 1 proposes a method of measuring the film thickness of a single crystal thin film on a silicon wafer on which a buried diffusion layer is formed by a Fourier transform infrared spectrometer (FTIR).

That is, the interference light is generated from the infrared light emitted from the light source, and the silicon wafer is irradiated with the interference light. Then, the detector detects the first reflected light generated by reflecting the interference light on the surface of the single crystal thin film. At the same time, the interference light is transmitted through the single crystal thin film and is reflected by the interface between the single crystal thin film and the buried diffusion layer, whereby the second reflected light is detected by the detector. Then, a cosine Fourier transform and an inverse transform are applied to the interferogram of the first reflected light and the second reflected light detected by the detector to obtain the first curve. Also, the same interferogram is subjected to sine Fourier transform and inverse transform to obtain a second curve. Then, the film thickness of the single crystal thin film is calculated from the peak having the minimum absolute value of the optical path difference of the reflected light among the plurality of peaks in the combined curve obtained by combining the first curve and the second curve.

JP-A-5-306910

When an epitaxial silicon wafer with a buried diffusion layer having a buried diffusion layer and a silicon epitaxial layer as a single crystal thin film is used as a wafer for a high-voltage power device, the dopant concentration of the silicon substrate is generally 2.8×10 ^17. It is set as high as over atoms/cm ³ (for p-type). On the other hand, when an epitaxial silicon wafer with a buried diffusion layer is used as a wafer for Bi-CMOS, for example, the dopant concentration of the silicon substrate is generally as low as 2.8×10 ¹⁷ atoms/cm ³ (in the case of p type). Is set. The film thickness of the silicon epitaxial layer in the former epitaxial silicon wafer with a buried diffusion layer can be accurately measured by the measuring method described in Patent Document 1. However, the inventors of the present invention have a new problem that even if the film thickness of the silicon epitaxial layer in the latter epitaxial silicon wafer with a buried diffusion layer is measured by the method described in Patent Document 1, it cannot be accurately measured. I recognized.

In view of the above problems, the present invention provides a film thickness measuring device and a film capable of measuring the film thickness of a silicon epitaxial layer with high accuracy even in an epitaxial silicon wafer with a buried diffusion layer having a low dopant concentration in a silicon substrate. It is intended to provide a thickness measuring method. Another object of the present invention is to provide a method for manufacturing an epitaxial silicon wafer with a buried diffusion layer, which can be obtained by the film thickness measuring device or the film thickness measuring method.

The film thickness of the silicon epitaxial layer in the epitaxial silicon wafer with the embedded diffusion layer can be measured using, for example, the film thickness measuring device 1 shown in FIG. That is, the infrared light emitted from the light source 2 becomes the interference lights L and L′ by the interferometer 3, and enters the epitaxial silicon wafer W mounted on the measurement stage 7. Then, the first reflected light R1 generated by the interference light L being reflected on the surface of the silicon epitaxial layer 18 enters the detector 5. At the same time, the interference light L also passes through the silicon epitaxial layer 18 and is reflected by the interface between the silicon epitaxial layer 18 and the buried diffusion layer 16, and the second reflected light R2 is also incident on the detector 5. These reflected lights are detected by the detector 5. Then, the control unit (not shown) analyzes the interferogram of the first reflected light R1 and the second reflected light R2 output from the detector 5 to calculate the film thickness of the silicon epitaxial layer 18.

The present inventors have examined the state of interference light in the epitaxial silicon wafer W with a buried diffusion layer in which the dopant concentration of the silicon substrate 10 is low. Then, it was found that the third reflected light R3 caused by the interference light L'exists. It was found that the third reflected light R3 adversely affects the measurement of the film thickness of the silicon epitaxial layer 18. That is, as shown in FIG. 3(A), the interference light L′ is transmitted through the silicon epitaxial layer 18 and then through a region of the surface layer of the silicon substrate 10 where the embedded diffusion layer 16 is not present, with the embedded diffusion layer. It is reflected at the interface between the epitaxial silicon wafer W and the measurement stage 6 to become the third reflected light R3. As shown in FIG. 3B, the third reflected light R3 causes noise in the interferogram of the first reflected light R1 and the second reflected light R2, which causes the silicon epitaxial layer 18 to generate noise. Film thickness is calculated incorrectly. On the other hand, it was found that when the dopant concentration of the silicon substrate 10 is high, the interference light L′ does not pass through the silicon substrate 10, so that the above problem does not occur. As a result of further study, the noise in the interferogram can be reduced by selecting the material of the measurement stage 6 in consideration of the reflectance of infrared light, and as a result, the silicon epitaxial layer 18 It was found that the film thickness can be measured with high accuracy.

The present invention has been completed based on the above findings, and its gist configuration is as follows.
(1) Of the silicon epitaxial layer in an epitaxial silicon wafer with a buried diffusion layer, which includes a silicon substrate, a buried diffusion layer formed on a surface layer of the silicon substrate, and a silicon epitaxial layer formed on the buried diffusion layer. A film thickness measuring device for measuring the film thickness,
A light source that emits infrared light,
Arranged on the optical path of the infrared light, and, from the infrared light, an interferometer for generating interference light for irradiating the epitaxial silicon wafer with the buried diffusion layer,
The measurement stage for mounting the epitaxial silicon wafer with the buried diffusion layer so that the buried diffusion layer with the epitaxial silicon wafer is located on the optical path of the interference light,
First reflected light generated by the interference light being reflected on the surface of the silicon epitaxial layer, and the interference light being transmitted through the silicon epitaxial layer and reflected at the interface between the silicon epitaxial layer and the buried diffusion layer. A detector that is disposed on the optical path of the second reflected light generated by the above, and that detects the first reflected light and the second reflected light;
A control unit for calculating the film thickness of the silicon epitaxial layer based on the output of the detector;
Equipped with
The film thickness measuring device, wherein the measuring stage is made of a material having a reflectance of 15% or less at a peak wavelength of the spectrum of the infrared light.

(2) The film thickness measuring device according to (1), wherein the measuring stage is made of one or more materials selected from quartz, fluororesin, and ceramics.

(3) The film thickness measuring device as described in (1) or (2) above, wherein the measurement stage is a wafer holding part in a wafer transfer end effector.

(4) Of the silicon epitaxial layer in an epitaxial silicon wafer with a buried diffusion layer, which comprises a silicon substrate, a buried diffusion layer formed on a surface layer of the silicon substrate, and a silicon epitaxial layer formed on the buried diffusion layer. A film thickness measuring method for measuring the film thickness,
Generates interference light from infrared light,
Irradiating the interference light to the epitaxial silicon wafer with the embedded diffusion layer placed on the measurement stage,
First reflected light generated by the interference light being reflected on the surface of the silicon epitaxial layer, and the interference light being transmitted through the silicon epitaxial layer and reflected at the interface between the silicon epitaxial layer and the buried diffusion layer. Detecting the second reflected light generated by
Calculate the film thickness of the silicon epitaxial layer,
The film thickness measuring method, wherein the measuring stage is made of a material having a reflectance of 15% or less at a peak wavelength of the spectrum of infrared light.

(5) The film thickness measuring method according to (4), wherein the measuring stage is made of one or more materials selected from quartz, fluororesin, and ceramics.

(6) The film thickness measuring method as described in (4) or (5) above, wherein the measurement stage is a wafer holding part in a wafer transfer end effector.

(7) After forming an oxide film on the surface of the silicon substrate, the oxide film is formed into a patterned oxide film by photolithography,
After that, an impurity is injected into the silicon substrate from the patterned oxide film side, and then a heat treatment is performed to form a buried diffusion layer in the surface layer of the silicon substrate,
Then, the patterned oxide film is removed,
Then, a silicon epitaxial layer is formed on the buried diffusion,
After that, the film thickness of the silicon epitaxial layer is measured using the apparatus described in any one of (1) to (3) or the method described in any one of (4) to (6). A method for manufacturing an epitaxial silicon wafer with a buried diffusion layer, comprising:

According to the present invention, the film thickness of a silicon epitaxial layer can be measured with high accuracy even in an epitaxial silicon wafer with a buried diffusion layer in which the dopant concentration of the silicon substrate is low.

It is a schematic diagram which shows the film thickness measuring apparatus by one Embodiment of this invention. (A)-(G) is a schematic cross section explaining the manufacturing method of the epitaxial silicon wafer with a buried diffusion layer by one Embodiment of this invention. (A) is a schematic diagram showing a conventional film thickness measuring device, and (B) is a graph showing an interferogram detected by a detector in the conventional film thickness measuring device. (A) is a graph showing an interferogram detected by a detector in the invention example, and (B) is a graph showing an interferogram detected by a detector in a comparative example.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

(Film thickness measuring device)
Referring to FIG. 1, a film thickness measuring device 1 according to one embodiment of the present invention includes a light source 2, an interferometer 3, an irradiation chamber 4, a detector 5, and a control unit (not shown). .. The light source 2 emits infrared light having a peak wavelength in the range of 2.5 to 25 μm. As the light source 2, for example, a high brightness ceramic light source can be used. The interferometer 3 is arranged on the optical path of the infrared light emitted from the light source 2 and generates interference light L, L′ from the infrared light emitted from the light source 2. A known Michelson interferometer can be used as the interferometer 3. A measurement stage 6 for mounting the epitaxial silicon wafer W with a buried diffusion layer is arranged in the irradiation chamber 4 so that the epitaxial silicon wafer W with a buried diffusion layer is located on the optical path of the interference light L, L′. It The detector 5 is arranged on the optical paths of the first and second reflected lights R1 and R2 from the epitaxial silicon wafer W with the embedded diffusion layer, and detects these reflected lights. As the detector 5, for example, a pyroelectric detector such as DTGS can be used. The control unit calculates the film thickness of the silicon epitaxial layer 18 based on the output of the detector 5. The control unit can be realized by a central processing unit (CPU) inside the computer.

The measurement stage 6 is made of a material having a reflectance of 15% or less at the peak wavelength of the spectrum of infrared light. More preferably, it is made of a material having a reflectance of 10% or less at the peak wavelength of the spectrum of infrared light. Specifically, the measurement stage 6 is preferably made of one or more materials selected from quartz, fluororesins, and ceramics. The technical significance of this will be described later. Further, the measurement stage 6 may be made of a single material having the above-mentioned reflectance. Alternatively, the measurement stage 6 is composed of a first material having a reflectance of 15% or less, and a second material laminated on the first material and having a reflectance of 10% or less. May be. When the measurement stage 6 does not come into contact with the entire back surface of the wafer, it is possible to reduce the difference in reflectance between the portion of the measurement stage 6 that comes into contact with the back surface of the wafer and the portion that does not come into contact with the back surface of the wafer. More preferable. Specifically, it is more preferable that the difference in reflectance is 1% or less.

From the viewpoint of increasing the mechanical strength of the measuring stage 6, it is more preferable to select ceramics. Further, from the viewpoint of enhancing the cleanliness of the measuring stage 6, it is more preferable to select the fluororesin. From the viewpoint of enhancing mechanical strength and cleanliness, it is more preferable that the base material of the measurement stage 6 is ceramics and the surface of the base material is covered with a fluororesin. Examples of ceramics include silicon carbide and black alumina. As the fluororesin, polytetrafluoroethylene (PTFE), perfluoroalkoxyalkane (PFA), tetrafluoroethylene/hexafluoropropylene copolymer (FEP), ethylene/tetrafluoroethylene copolymer (ETFE), One or more resins selected from polyvinylidene fluoride (PVDF), polychlorotrifluoroethylene (PCTFE), and ethylene/chlorotrifluoroethylene copolymer (ECTFE).

The measurement stage 6 may be a wafer holder in a general wafer transfer end effector. However, it is important that the wafer holder is made of a material having a reflectance of 15% or less at the peak wavelength of the above-mentioned infrared light spectrum.

(Film thickness measurement method)
Hereinafter, an example of a method of measuring the film thickness of the silicon epitaxial layer 18 in the epitaxial silicon wafer W with a buried diffusion layer, which can be performed using the film thickness measuring device 1 described above, will be described.

First, the epitaxial silicon wafer W with a buried diffusion layer that can be used in the film thickness measurement method according to the present embodiment will be described. Referring to FIG. 1, an epitaxial silicon wafer W with a buried diffusion layer includes a silicon substrate 10, a buried diffusion layer 16 formed on a surface layer of the silicon substrate 10, and a silicon epitaxial layer 18 formed on the buried diffusion layer 16. And.

With reference to FIG. 3, in the epitaxial silicon wafer W with a buried diffusion layer in which the dopant concentration of the silicon substrate is low, the interference light L′ passes through the silicon epitaxial layer 18 and the silicon substrate 10 to form an epitaxial silicon wafer with a buried diffusion layer. The interface between W and the measurement stage 7 is reached. Then, this interference light becomes reflected light and adversely affects the film thickness measurement of the silicon epitaxial layer 18. However, as will be described in detail later, when the epitaxial silicon wafer W with a buried diffusion layer having such a dopant concentration is subjected to the film thickness measuring device or the film thickness measuring method according to the present embodiment, the intensity of the reflected light can be suppressed. it can. As a result, the film thickness of the silicon epitaxial layer 18 can be measured with high accuracy. When the dopant concentration of the silicon substrate 10 is high, the interference light L′ is completely reflected at the interface between the silicon substrate 10 and the silicon epitaxial layer 18 and the interface between the buried diffusion layer 16 and the silicon epitaxial layer 18, and therefore, FIG. The above-mentioned problem described above does not occur. The dopant concentration of the silicon substrate 10 is 1.3×10 ^{15 to} 2.8×10 ¹⁷ atoms/cm ^{3 in} the case of p-type, from the viewpoint of ensuring the insulation and the like by the buried diffusion layer in the device process. Is preferred. For the reason of the device structure, n-type is widely used as the dopant type of the silicon epitaxial layer 18. However, the conductivity types of the silicon substrate and the silicon epitaxial layer are not limited to this combination, and n/n+, n/p+, p/p+, n/p/p+, n/n+/p+ structure And so on.

As for the concentration of impurities in the buried diffusion layer 16, it is necessary to measure the thickness of the epitaxial layer using reflection of interference light in the buried diffusion layer. Therefore, when the impurity is P (phosphorus), the concentration is 1.0×10 ^18. It is preferably at least atoms/cm ² , and when the impurity is B (boron), it is preferably at least 3.0×10 ¹⁸ atoms/cm ² , and when the impurity is As or Sb, 1. It is preferably 0×10 ¹⁸ atoms/cm ² or more. The region where the buried diffusion layer 16 is formed can be appropriately set according to the circuit pattern of the integrated circuit manufactured in the device forming process. For example, when the epitaxial silicon wafer W with a buried diffusion layer is viewed in a plan view, the ratio of the area of the buried diffusion layer 16 to the entire surface of the silicon substrate 10 can be 20 to 99%. It is more preferably 20 to 60%, further preferably 20 to 40%. If it is 20% or more, the thickness of the epitaxial layer can be stably measured, and if it is 60% or less, the generation of noise can be suppressed. The thickness of the buried diffusion layer 16 can be set to 1.0 to 20.0 μm, preferably 2.0 to 5.0 μm.

In the present embodiment, the film thickness of the silicon epitaxial layer 18 in the epitaxial silicon wafer W with a buried diffusion layer can be measured through the first to third steps described below.

[First step: generation of interference light]
Referring to FIG. 1, in a first step, interferometer 3 is used to generate interference lights L and L′ from infrared light emitted from light source 2. Here, the peak wavelength of infrared light can be selected from the range of 2.5 to 25 μm. The method of generating the interference lights L and L′ is not particularly limited, and can be performed using, for example, a known Michelson interferometer.

[Second step: irradiation of interference light]
With reference to FIG. 1, in the second step, the interference light L, L′ is irradiated to the epitaxial silicon wafer W with the embedded diffusion layer mounted on the measurement stage 6 in the irradiation chamber 4. The irradiated interference light L becomes the first reflected light R1 and the second reflected light R2, and is emitted from the epitaxial silicon wafer W with the embedded diffusion layer. Here, the first reflected light R1 is reflected light generated by the interference light L being reflected on the surface of the silicon epitaxial layer 18. The second reflected light R2 is the reflected light generated by the interference light L passing through the silicon epitaxial layer 18 and being reflected at the interface between the silicon epitaxial layer 18 and the buried diffusion layer 16.

[Third step: calculation of film thickness]
Referring to FIG. 1, in the third step, the detector 5 detects the first reflected light R1 and the second reflected light R2 generated in the second step. Then, the control unit (not shown) causes the peak wavelengths of the interferograms of the first reflected light R1 and the second reflected light R2 output from the detector 5, and the first reflected light R1 and the second reflected light. The optical path difference of R2 is analyzed using a known FTIR method. As a result, the film thickness of the silicon epitaxial layer 18 is calculated.

Hereinafter, the technical significance of the present invention will be described with reference to FIGS. 1 and 3A and 3B as appropriate. Referring to FIG. 3A, in the second step, in addition to the first reflected light R1 and the second reflected light R2, there is the third reflected light R3 generated from the interference light L'. That is, the third reflected light R3 is transmitted through the silicon epitaxial layer 18 after the interference light L'is transmitted through a region of the surface layer of the silicon substrate 10 where the buried diffusion layer 16 is not formed, and the third reflection light R3 is epitaxial with the buried diffusion layer. The reflected light is generated by being reflected at the interface between the silicon wafer W and the measurement stage 7. Here, also referring to FIG. 3B, when the intensity of the third reflected light R3 is high, in the interferogram analyzed in the third step, the peak is equivalent to the peak corresponding to the film thickness of the silicon epitaxial layer 18. A large amount of noise is generated. This noise is usually attempted to be removed by calibration, but it may occur in the measurement position (for example, only one point in the center) or the structure of the measurement stage (for example, the structure in which the measurement stage does not contact the entire back surface of the wafer) when performing the calibration. Due to this, the calibration becomes insufficient. Therefore, the control unit may mistakenly recognize a plurality of peaks included in noise as peaks corresponding to the film thickness of the silicon epitaxial layer 18, and the film thickness of the silicon epitaxial layer 18 may be calculated incorrectly. On the other hand, in the present embodiment, since the measurement stage 7 is made of a material having a reflectance of 15% or less at the peak wavelength of the spectrum of infrared light, the intensity of the third reflected light generated from the interference light L′. Can be reduced. Thereby, noise in the interferogram of the first reflected light R1 and the second reflected light R2 can be reduced, and as a result, the film thickness of the silicon epitaxial layer 18 can be measured with high accuracy. Even if only the surface of the measurement stage is made of a first material having a reflectance of 15% or less, and the portion other than the surface of the measurement stage is made of a second material having a reflectance of more than 15%. The interference light incident on the measurement stage is reflected at the interface between the first material and the second material, so that noise is generated. Therefore, even if only the surface of the measuring stage is made of a material having a reflectance of 15% or less, the effect of the present invention cannot be obtained.

(Method of manufacturing epitaxial silicon wafer with embedded diffusion layer)
Hereinafter, with reference to FIG. 2, an example of a method of manufacturing an epitaxial silicon wafer W with a buried diffusion layer, which can be performed using the above-described film thickness measuring device or film thickness measuring method, will be described.

[First step: formation of patterned oxide film]
In the first step, after forming the oxide film 12 on the surface of the silicon substrate 10 (FIGS. 2A and 2B), the oxide film 12 is formed into a patterned oxide film 14 by a photolithography method (FIG. B), (C)). The method for forming the oxide film 12 is not particularly limited, and a known thermal oxidation method, a chemical vapor deposition (CVD) method, or the like may be preferably used. The photolithography method is not particularly limited, and a known method may be preferably used. The pattern of the patterned oxide film 14 can be appropriately set according to the circuit pattern of the integrated circuit formed in the buried diffusion layer 16 in the device forming process. As the silicon substrate 10, a single crystal silicon substrate obtained from a single crystal silicon ingot grown by the Czochralski method (CZ method) or the floating zone melting method (FZ method) is added with a dopant such as B (boron). What was added in the density|concentration of 0.3*10< ¹⁵ >-2.8*10< ¹⁷ >atoms/cm< ³ > can be used.

[Second step: formation of buried diffusion layer]
In the second step, impurities are implanted into the silicon substrate 10 from the side of the patterned oxide film 14 (FIGS. 2C and 2D), and then heat treatment is performed, so that the silicon substrate 10 is buried and diffused in the surface layer. The layer 16 is formed (FIGS. 2D and 2E). When the impurity is P, the dose is preferably 1.0×10 ¹² atoms/cm ² or more, and when the impurity is B, the dose is 1.0×10 ¹³ atoms/cm ² or more. It is preferable to dope in a dose, and when As or Sb is used as the impurity, it is preferable to dope at a dose of 1.0×10 ¹⁴ atoms/cm ² or more. For these reasons, the above description is incorporated. Further, the ratio of the area of the embedded diffusion layer 16 to the entire surface of the silicon substrate 10 is set to 20 to 99%, and the thickness of the embedded diffusion layer 16 is set to 1.0 to 20.0 μm (preferably 2.0 to 5.0 μm). From the viewpoint, the heat treatment is preferably performed at 1000 to 1250° C. for 1 to 30 hours in an oxidizing atmosphere.

[Third step: removal of patterned oxide film]
In the third step, the patterned oxide film 14 is removed (FIGS. 2E and 2F). The method for removing the patterned oxide film 14 is not particularly limited, and an etching solution such as hydrofluoric acid can be preferably used.

[Fourth step: formation of silicon epitaxial layer]
In the fourth step, the silicon epitaxial layer 18 is formed on the buried diffusion layer 16 (FIGS. 2F and 2G). For example, the silicon epitaxial layer 18 can be grown by a CVD method with a carrier gas of hydrogen, a source gas of dichlorosilane, trichlorosilane, or the like and a substrate temperature of 1000° C. or higher and 1150° C. or lower. The thickness of the silicon epitaxial layer 18 may be appropriately selected from the range of 0.5 μm or more and 15 μm or less.

[Fifth step: film thickness measurement]
Referring also to FIG. 1, in the fifth step, the film thickness of the silicon epitaxial layer 18 is measured using the film thickness measuring device or the film thickness measuring method described above. Thereby, the film thickness of the silicon epitaxial layer 18 can be measured with high accuracy. Note that, for details, the above description is incorporated.

As described above, by using this embodiment as an example, the film thickness measuring device and the film thickness measuring method of the silicon epitaxial layer in the epitaxial silicon wafer with the buried diffusion layer of the present invention, and the film thickness measuring device or the film thickness measuring method were used. The method of manufacturing an epitaxial silicon wafer with a buried diffusion layer has been described. However, the present invention is not limited to the above-mentioned embodiment, and appropriate modifications can be made within the scope of the claims.

(Invention example)
In order to confirm the effect of the present invention, as an example of the invention, an epitaxial silicon wafer with a buried diffusion layer and a film thickness measuring device described below were produced, and the film thickness of the silicon epitaxial layer was measured.

[Fabrication of epitaxial silicon wafer with embedded diffusion layer]
An oxide film was formed by a thermal oxidation method on the surface of a silicon substrate (dopant: boron, dopant concentration: 1.3×10 ¹⁵ atoms/cm ³ ) obtained by the CZ method (FIGS. 2A and 2B). .. Then, the oxide film was formed into a patterned oxide film by the photolithography method (FIGS. 2B and 2C). Next, Sb was implanted into the silicon substrate from the patterned oxide film side at a dose of 5×10 ¹⁴ atoms/cm ² (FIGS. 2C and 2D). Then, heat treatment was performed to form a buried diffusion layer (FIGS. 2D and 2E). In the plan view of the silicon substrate, the area ratio of the embedded diffusion layer to the entire surface of the silicon substrate was 30%, and the thickness of the embedded diffusion layer was 2.0 μm. Next, the patterned oxide film was removed using hydrofluoric acid (FIGS. 2E and 2F). Then, using a CVD method, hydrogen is used as a carrier gas, dichlorosilane is used as a source gas, the substrate temperature is 1080° C., and a silicon epitaxial layer (dopant: phosphorus; dopant concentration: 5×10 ¹⁵ atoms/ cm ³ ) was formed (FIGS. 2F and 2G). Thus, an epitaxial silicon wafer with a buried diffusion layer was obtained.

[Production of film thickness measuring device]
A film thickness measurement including a light source, an interferometer, an irradiation chamber in which a measurement stage (a wafer holding unit in a wafer transfer end effector) is arranged, a detector, and a control unit (not shown) shown in FIG. The device was made. A light source having a peak wavelength of 12.5 μm in the spectrum of emitted infrared light was used. As the measurement stage, a base material made of alumina ceramics and the surface of the base material coated with conductive black Teflon was used. At the peak wavelength (12.5 μm) of the spectrum of infrared light, the reflectance of the alumina ceramics was 8% and the reflectance of the conductive black Teflon was 7%.

[Measurement of film thickness]
Using this film thickness measuring device, the film thickness of the silicon epitaxial layer was measured by the film thickness measuring method described above. The interferogram detected by the detector is shown in FIG.

(Comparative example)
The film thickness of the silicon epitaxial layer was measured by the same method as in the inventive example except that a stainless steel base material was used as the measurement stage and the surface of the base material was coated with Teflon (registered trademark). .. The reflectance of stainless steel was 70% and the reflectance of Teflon (registered trademark) was 7% at the peak wavelength (12.5 μm) of the spectrum of infrared light. The interferogram detected by the detector is shown in FIG.

(Evaluation results and explanation of evaluation results)
In the comparative example shown in FIG. 4B, noise having a plurality of peaks having the same magnitude as the peak corresponding to the film thickness (13 μm) of the silicon epitaxial layer was generated. On the other hand, in the example of the invention shown in FIG. 4(A), the noise as shown in FIG. 4(B) can be reduced, and it is accurately understood that the film thickness of the silicon epitaxial layer is 13 μm. It was This is because in the invention example, the reflectance of the material of the measuring stage (that is, alumina ceramics and Teflon (registered trademark)) is set to 15% or less at the peak wavelength of the spectrum of infrared light, so that it enters the detector. This is because the intensity of the third reflected light could be weakened.

According to the present invention, the film thickness of a silicon epitaxial layer can be measured with high accuracy even in an epitaxial silicon wafer with a buried diffusion layer in which the dopant concentration of the silicon substrate is low.

1 Film Thickness Measuring Device 2 Light Source 3 Interferometer 4 Irradiation Chamber 5 Detector 6,7 Measuring Stage 10 Silicon Substrate 12 Oxide Film 14 Patterned Oxide Film 16 Buried Diffusion Layer 18 Silicon Epitaxial Layer W Epitaxial Silicon Wafer with Buried Diffusion Layer L, L'Interference light R1 First reflected light R2 Second reflected light

Claims (7)

A silicon substrate, a buried diffusion layer formed on the surface layer of the silicon substrate, and a silicon epitaxial layer formed on the buried diffusion layer, a film thickness of the silicon epitaxial layer in the epitaxial silicon wafer with a buried diffusion layer A film thickness measuring device for measuring,
A light source that emits infrared light,
Arranged on the optical path of the infrared light, and, from the infrared light, an interferometer for generating interference light for irradiating the epitaxial silicon wafer with the buried diffusion layer,
The measurement stage for mounting the epitaxial silicon wafer with the buried diffusion layer so that the buried diffusion layer with the epitaxial silicon wafer is located on the optical path of the interference light,
First reflected light generated by the interference light being reflected on the surface of the silicon epitaxial layer, and the interference light being transmitted through the silicon epitaxial layer and reflected at the interface between the silicon epitaxial layer and the buried diffusion layer. A detector that is disposed on the optical path of the second reflected light generated by the above, and that detects the first reflected light and the second reflected light;
A control unit for calculating the film thickness of the silicon epitaxial layer based on the output of the detector;
Equipped with
The film thickness measuring device, wherein the measuring stage is made of a material having a reflectance of 15% or less at a peak wavelength of the spectrum of the infrared light. The film thickness measuring device according to claim 1, wherein the measuring stage is made of one or more materials selected from quartz, fluororesin, and ceramics. The film thickness measurement apparatus according to claim 1, wherein the measurement stage is a wafer holding unit in a wafer transfer end effector. A silicon substrate, a buried diffusion layer formed on the surface layer of the silicon substrate, and a silicon epitaxial layer formed on the buried diffusion layer, a film thickness of the silicon epitaxial layer in the epitaxial silicon wafer with a buried diffusion layer A film thickness measuring method for measuring,
Generates interference light from infrared light,
Irradiating the interference light to the epitaxial silicon wafer with the embedded diffusion layer placed on the measurement stage,
First reflected light generated by the interference light being reflected on the surface of the silicon epitaxial layer, and the interference light being transmitted through the silicon epitaxial layer and reflected at the interface between the silicon epitaxial layer and the buried diffusion layer. Detecting the second reflected light generated by
Calculate the film thickness of the silicon epitaxial layer,
The film thickness measuring method, wherein the measuring stage is made of a material having a reflectance of 15% or less at a peak wavelength of the spectrum of infrared light. The film thickness measuring method according to claim 4, wherein the measuring stage is made of one or more materials selected from quartz, fluororesin, and ceramics. The film thickness measuring method according to claim 4, wherein the measurement stage is a wafer holding unit in a wafer transport end effector. After forming an oxide film on the surface of the silicon substrate, the oxide film as a patterned oxide film by photolithography,
After that, an impurity is injected into the silicon substrate from the patterned oxide film side, and then a heat treatment is performed to form a buried diffusion layer in the surface layer of the silicon substrate,
Then, the patterned oxide film is removed,
Then, a silicon epitaxial layer is formed on the buried diffusion,
Thereafter, the film thickness of the silicon epitaxial layer is measured by using the apparatus according to any one of claims 1 to 3 or the method according to any one of claims 4 to 6. Manufacturing method of epitaxial silicon wafer with diffusion layer.

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