JP2010230623A - Optical film thickness measuring device and vacuum film forming apparatus including the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To effectively suppress influence of stray light resulting from cover glass and improve the measurement accuracy in an optical film thickness measuring device of a constitution where a light projecting section is close to a light receiving section and the cover glass is disposed on the front side of these. <P>SOLUTION: The interval between a light projection surface 122a of the light projecting section 121a and a light receiving surface 122b of the light receiving section 121b is defined as d, the interval between the cover glass 14 and the light projection surface 122a and light receiving surface 122b is defined as L, the numerical aperture of the light projecting section 121a is defined as NA<SB>1</SB>, and the numerical aperture of the light projecting section 121b is defined as NA<SB>2</SB>. The cover glass 14 is disposed at a position establishing 0<L<d/(tanθ<SB>1</SB>+tanθ<SB>2</SB>). Here, θ<SB>1</SB>=sin<SP>-1</SP>(NA<SB>1</SB>), θ<SB>2</SB>=sin<SP>-1</SP>(NA<SB>2</SB>), and both of θ<SB>1</SB>and θ<SB>2</SB>are less than 90°. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an optical film thickness measuring apparatus that measures a film thickness from a change in reflectance due to interference of light irradiated on a thin film, and a vacuum film forming apparatus including the optical film thickness measuring apparatus. The present invention relates to an optical film thickness measuring apparatus in which parts that receive light are close to each other and a protective member is provided on the front surface of these parts, and a vacuum film forming apparatus including the same.

  In an apparatus for forming various thin films on a substrate, the film thickness of the thin film is measured by various film thickness measurement techniques. As a typical film thickness measurement technique, there is an optical method for determining a film thickness from a change in reflectance due to interference of light irradiated on a measurement object (sample).

  In recent years, with the advancement of thin film formation technology, it has become possible to form a thin film with a smaller thickness. Therefore, in the film thickness measurement technique, it is required to accurately measure a thin film with a smaller thickness. It has been. Therefore, in the film thickness measurement technique using an optical method, conventionally, various reference values regarding reflected light are set in advance, and correction processing is performed using this reference value and an actually measured value (actually measured value). A technique for improving the measurement accuracy by performing it is known.

  For example, in Patent Document 1, in measurement of a thin film of a micrometer or less, an ideal spectral reflectance is calculated in advance from a sample, and a curve connecting the maximum point sequence of the ideal spectral reflectance and a curve connecting the minimum point sequence are: The maximum and minimum intermediate level curves are calculated, and from the spectral reflectance of the actual sample, the curve connecting the maximum point sequence of the reflectance, the curve connecting the minimum point sequence, and the maximum and minimum intermediate level curves are calculated. A technique for calculating a curve and calculating a true spectral reflectance from a function of each curve is disclosed.

  Further, although it is not a technique for measuring the thickness of a thin film on a substrate, Patent Document 2 discloses a technique for measuring the thickness of a silicon wafer by measuring a spectrum after transmission of light transmitted through a reference wafer and a measurement wafer. A plurality of provisional difference absorbance spectra are obtained from the spectrum before transmission, the spectrum after transmission of the reference wafer, the spectrum after transmission of the measurement wafer, and the thickness of the reference wafer. In this provisional difference absorbance spectrum, a peak based on phonon absorption is obtained. A technique for measuring the thickness when the light disappears as the thickness of the measurement wafer is disclosed.

  By the way, in the film thickness measurement technique based on the optical method, there is an optical film thickness measurement apparatus configured to bring a part that projects light onto a sample (light projecting part) and a part that receives reflected light (light receiving part) close to each other. Are known. With such a configuration, since the installation area of the light projecting unit and the light receiving unit is reduced, it is easy to install a measuring device for the equipment for forming a thin film, and it is preferably used for, for example, in-line film thickness measurement Can do.

  In the optical film thickness measuring apparatus having the above configuration, a protective member such as a cover glass is often provided on the front side of the light projecting unit and the light receiving unit. This is because if the light projecting unit and the light receiving unit are exposed in the processing space where the thin film is formed, the light projecting unit and the light receiving unit may be contaminated or corroded by the processing atmosphere.

  For example, in Patent Document 3, the emission end of the light projecting side optical fiber and the light receiving end of the light receiving side optical fiber are disposed adjacent to each other, and a window material is projected in front of the front ends of both optical fibers. A measuring device having a configuration arranged to be inclined with respect to the optical axis is disclosed. The inclination angle α of the window material is set to be larger than the smaller one of the spread angle Θ of the irradiated light determined by the numerical aperture specific to the optical fiber used or the allowable incident angle of the spectrometer. Has been.

Japanese Patent Laid-Open No. 62-127605 JP-A-8-105716 JP 2008-268093 A

  Here, in the optical film thickness measuring apparatus having the above-described configuration, when a protective member is provided on the front side of the light projecting unit and the light receiving unit, there arises a problem that measurement accuracy decreases due to stray light caused by the protective member. That is, when the protective member is provided in front of the light projecting unit and the light receiving unit, the light projected from the light projecting unit is reflected by the surface of the protective member and enters the light receiving unit as stray light. When such stray light is received by the light receiving unit, an error occurs in the detected reflectance, and the measurement accuracy decreases.

  In Patent Document 3, as described above, a configuration is disclosed in which the window material is inclined with respect to the optical axis of the white light to be projected, and the reflected light from the window material is not incident on the light receiving side optical fiber. However, since the window material that should originally be arranged horizontally is intentionally inclined, a special member or configuration for inclining and fixing the window material is required. Therefore, the configuration itself of the optical film thickness measuring device is complicated, and the degree of freedom in installing the window material (protective member) is also reduced.

  In order to avoid the influence of stray light, it is conceivable to provide a protective member separately for each of the light projecting unit and the light receiving unit. That is, the light projecting unit is provided with a protective member dedicated to the light projecting unit, the light receiving unit is provided with a protective member dedicated to the light receiving unit, and stray light generated by the protective member dedicated to the light projecting unit is prevented from entering the light receiving unit. What is necessary is just to comprise. However, in this configuration, two protective members are required, and a configuration for preventing the incidence of stray light is also required, which increases the number of members and complicates the configuration. In addition, if the light projecting unit and the light receiving unit are too close to each other, a sufficient installation space for the two protection members cannot be secured, so that it is difficult to obtain the advantage that the installation area of the light projecting unit and the light receiving unit can be reduced.

  Furthermore, since the influence of the stray light generated by the protective member is not uniform, the correction process for setting the reference value related to the reflected light as disclosed in Patent Document 1 or 2 can sufficiently suppress the influence of the stray light. I can't.

  The present invention has been made to solve such problems, and in the optical film thickness measurement apparatus, the light projecting unit and the light receiving unit are close to each other, and a protective member is provided on the front side thereof. An object of the present invention is to effectively suppress the influence of stray light caused by a protective member and improve the measurement accuracy when having a configuration.

In order to solve the above problems, an optical film thickness measuring apparatus according to the present invention is arranged in parallel with a light projecting unit that projects light from a front end surface, and receives light at the front end surface. A light receiving portion; and a light-transmitting portion and a light-transmitting portion disposed in front of the front end surfaces of the light projecting portion and the light receiving portion so as to be parallel to the front end surfaces and transmitting light. D and the distance between the tip surfaces of the light projecting part and the protective member L, the numerical aperture of the light projecting part NA ₁ , and the numerical aperture of the light receiving part Is defined as NA ₂ , the protective member is represented by the following formula: 0 <L <d / (tan θ ₁ + tan θ ₂ )
(However, θ ₁ = sin ⁻¹ (NA ₁ ), θ ₂ = sin ⁻¹ (NA ₂ ), and θ ₁ and θ ₂ are both less than 90 °.)
The distance between the tip surface of the light receiving unit and the protection member is set to be equal to or less than the distance L.

  According to the said structure, the influence of the stray light resulting from a protection member can be effectively suppressed by setting the position of the protection member with respect to a light projection part and a light-receiving part by the positional relationship which satisfy | fills the said Formula. Therefore, the accuracy of film thickness measurement using the change in reflectance due to light interference is improved.

  In the optical film thickness measuring apparatus, in addition to the above configuration, a sample on which a thin film is formed is fixed at a position where light from the light projecting unit is projected, and received by the light receiving unit. A photoelectric converter that generates light intensity information of the received light by converting the received light into an electrical signal, and the thin film formed on the sample from the light intensity information generated by the photoelectric converter A film thickness calculator that calculates a thickness; and a storage device, wherein the film thickness calculator is configured to receive light from the light projecting unit in a state where the sample is not fixed by the sample fixing member. The light intensity information generated by the photoelectric converter is stored in the storage as background light intensity information, and the sample is fixed by the sample fixing member, and the light projecting unit is attached to the sample. When light is emitted from Generates corrected light intensity information obtained by subtracting the background light intensity information stored in the storage device from the light intensity information generated by the photoelectric converter, and the film of the thin film is generated from the corrected light intensity information. It is preferably configured to calculate the thickness.

  According to the said structure, in addition to the structure which sets the position of the said protection member, the structure which performs the data correction which reduces the influence of background light will be combined. Thereby, the influence of the stray light resulting from a protection member can be suppressed further.

  In the optical film thickness measurement apparatus, in addition to the above configuration, the light projecting unit and the light receiving unit are preferably optical fibers, and the protective member is a cover glass.

  The vacuum film forming apparatus according to the present invention includes the optical film thickness measuring apparatus having the above-described configuration.

  As described above, according to the present invention, when the configuration of the optical film thickness measuring device is a configuration in which the light projecting unit and the light receiving unit are close to each other and a protective member is provided on the front side thereof, It is possible to effectively suppress the influence of stray light caused by the protective member and improve the measurement accuracy.

It is a schematic diagram which shows an example of schematic structure of the optical film thickness measuring apparatus which concerns on Embodiment 1 of this invention. It is a schematic diagram which shows the positional relationship of the light projection part of the optical film thickness measuring apparatus shown in FIG. 1, a light-receiving part, and a cover member. It is a schematic diagram which shows an example of schematic structure of the optical film thickness measuring apparatus which concerns on Embodiment 2 of this invention. It is a schematic diagram which shows an example of schematic structure of the vacuum film-forming apparatus which concerns on Embodiment 3 of this invention. It is an optical spectrum chart which shows the result of Example 1 which measured the light reflection spectrum of the silicon nitride thin film using the optical film thickness measuring apparatus which concerns on Embodiment 1 of this invention. It is an optical spectrum chart which shows the result of the comparative example 1 with respect to Example 1 shown in FIG. 7 is an optical spectrum chart showing the results of Reference Example 1 with respect to Example 1 shown in FIG. 5 and Comparative Example 1 shown in FIG. 6. It is an optical spectrum chart which shows the result of Example 2 which measured the light reflection spectrum of the titanium dioxide thin film using the optical film thickness measuring apparatus which concerns on Embodiment 1 of this invention. It is an optical spectrum chart which shows the result of the comparative example 2 with respect to Example 2 shown in FIG. 10 is an optical spectrum chart showing the results of Reference Example 2 with respect to Example 2 shown in FIG. 8 and Comparative Example 2 shown in FIG. 9.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. In the following description, the same or corresponding elements are denoted by the same reference symbols throughout the drawings, and redundant description thereof is omitted.

(Embodiment 1)
[Configuration of optical film thickness measuring device]
First, the configuration of the optical film thickness measuring apparatus according to the present embodiment will be described with reference to FIG. 1 and FIG. FIG. 1 is a schematic diagram illustrating an example of a schematic configuration of a measurement apparatus according to Embodiment 1 of the present invention, and FIG. 2 is a positional relationship between a light projecting unit and a light receiving unit, and a cover member of the measurement apparatus illustrated in FIG. It is a schematic diagram which shows.

  As shown in FIG. 1, an optical film thickness measurement apparatus 10 according to the present embodiment includes a light source 11, a Y-type optical fiber 12, a measurement probe 13, a cover glass 14, a spectrometer 15, a photoelectric conversion unit 16, and a sample fixing member. 17 and an analysis unit 21. The sample fixing member 17 fixes a sample 40 that is an object to be measured, and the sample 40 has a thin film 42 formed on the surface of a substrate 41.

  The light source 11 emits light (measurement light) projected onto the sample 40 in order to measure the film thickness. The type of the light source 11 is not particularly limited, but white light is generally used as the measurement light. Therefore, a tungsten halogen lamp is used as the light source 11 in the present embodiment. Alternatively, an incandescent bulb or a xenon lamp is also preferably used.

  The Y-type optical fiber 12 is configured such that the light-projecting-side optical fiber 12a and the light-receiving-side optical fiber 12b are combined into one on one end side and branched in the middle to form a “Y” shape. . The light projecting side optical fiber 12 a is a light guiding member on the light projecting side that transmits the measurement light emitted from the light source 11 to the measurement probe 13. Measurement light is projected from the measurement probe 13 onto the sample 40, and the measurement light is reflected by the sample 40 and received by the measurement probe 13 as reflected light, but the light-receiving-side optical fiber 12 b splits the received reflected light. It is a light guide member on the light receiving side that is transmitted to the container 15.

  The measurement probe 13 projects the measurement light transmitted from the light projecting side optical fiber 12 a toward the sample 40 and receives the reflected light from the sample 40. More specifically, for example, as shown in FIG. 2, the tip of the light projecting side optical fiber 12 a becomes the light projecting unit 121 a, and the measurement light is transmitted to the sample 40 from the light projecting surface 122 a that is the tip surface of the light projecting unit 121 a. It is projected toward. Further, the tip of the light receiving side optical fiber 12b becomes the light receiving portion 121b, and the light reflected from the sample 40 is received by the light receiving surface 122b which is the tip surface of the light receiving portion 121b. As shown in FIG. 2, the light projecting unit 121a and the light receiving unit 121b are disposed adjacent to each other so that the light projecting surface 122a and the light receiving surface 122b form a predetermined distance d. The light projecting surface 122a and the light receiving surface 122 are arranged so as to be substantially located on one plane.

  Further, although not shown in FIG. 2, in the present embodiment, the light projecting unit 121 a and the light receiving unit 121 b have one measuring probe 13 while the distance d is maintained by various protective members and interval holding members. It is summarized as. In this configuration, as shown partially in FIG. 2, the light projecting unit 121a and the light receiving unit 121b are grouped so that the end faces 122a and 122b of the optical fibers constituting each are in the same plane. It does not have to be. That is, in the measurement probe 13, the light projecting surface 122 a and the light receiving surface 122 b may be combined so as to ensure the distance d, and the overall configuration of the measurement probe 13 is not particularly limited.

  The cover glass 14 is a plate-like protective member provided to protect the tip of the measurement probe 13, that is, the light projecting surface 122a of the light projecting side optical fiber 12a and the light receiving surface 122b of the light receiving side optical fiber 12b. In particular, when various thin films are formed on a semiconductor substrate during the manufacture of a semiconductor device, when the thickness of the thin film is measured in-line, the light projecting surface 122a and the light reception are accompanied with the process of forming the thin film. The surface 122b may be dirty or damaged. Since such dirt or the like lowers the measurement accuracy, the cover glass 14 is provided as a dirt prevention cover that prevents dirt or the like on the light projecting surface 122a and the light receiving surface 122b. The cover glass 14 only needs to be formed of a material that transmits at least white light as measurement light. When used for in-line film thickness measurement, the cover glass 14 has durability capable of withstanding various thin film forming processes. It only has to be. In this embodiment, a known optical glass is used. Further, the size of the cover glass 14 is not particularly limited, and in the present embodiment, it is sufficient that there is an area that can reliably cover the light projecting surface 122a and the light receiving surface 122b. In FIG. 2, for convenience of explanation, the cover glass 14 is shown in cross section.

  In the present embodiment, the spectroscope 15 is interposed in the light receiving side optical fiber 12b between the branch point with the light projecting side optical fiber 12a and the photoelectric conversion unit 16, and the received reflected light is input to the photoelectric conversion unit 16. Before being performed, the light is dispersed for each predetermined wavelength. In the present embodiment, for example, a diffraction grating is used as the spectroscope 15. However, the spectroscope 15 is not limited to this, and is appropriate according to conditions such as the type of the sample 40 and the wavelength range of light assumed as reflected light. A spectroscope can be selected and used.

  The photoelectric conversion unit 16 converts the reflected light dispersed by the spectroscope 15 into an electric signal. The converted electrical signal is input to the analysis unit 21 as the light intensity information of the reflected light. The specific configuration of the photoelectric conversion unit 16 is not particularly limited, but in this embodiment, a charge coupled device (CCD) array is used. It is done. In this embodiment, as shown in FIG. 1, the spectroscope 15 and the photoelectric conversion unit 16 are separated from each other via the light-receiving side optical fiber 12b. However, the present invention is not limited to this and is integrated. It may be configured as a photoelectric conversion unit.

  The analysis unit 21 analyzes the electrical signal from the photoelectric conversion unit 16 and calculates the film thickness of the thin film 42. In the present embodiment, the reflected light from the sample 40 received by the measurement probe 13 is split by the spectroscope 15 and input to the photoelectric conversion unit 16 as described above, so that light interference information for each wavelength is obtained. Is output to the analysis unit 21. The analysis unit 21 analyzes the film thickness of the thin film 42 of the sample 40 based on this interference information. The specific configuration of the analysis unit 21 is not particularly limited, and a personal computer is used in the present embodiment. The calculation method of the film thickness by the analysis part 21 is not specifically limited, A well-known method can be used. For example, the film thickness may be calculated by comparing with the theoretical distribution waveform from the intensity distribution waveform in the light intensity information of the reflected light generated by the photoelectric conversion unit 16. The analysis unit 21 may be configured to be integrated with a photoelectric conversion unit using a microcomputer instead of an independent analysis device such as the personal computer.

  The configuration of the sample fixing member 17 is not particularly limited as long as the sample fixing member 17 fixes the sample 40 that is a measurement object at a position where the measurement light from the measurement probe 13 is projected. In the example shown in FIG. 1, the sample 40 has a configuration in which a thin film 42 is formed on the surface of a light-transmitting substrate 41, and the measurement light is projected from the back surface of the substrate 41. The frame is such that the sample 40 is fixed from the periphery. In FIG. 1, for convenience of explanation, the sample 40 and the sample fixing member 17 are shown in cross section.

  A method for measuring a film thickness in the optical film thickness measuring apparatus having the above configuration will be described. First, the sample 40 is fixed to the sample fixing member 17. Although the measurement probe 13 and the cover glass 14 are not shown in FIG. 1, both are fixed and arranged in a predetermined positional relationship, which will be described later, so that the light source 11 emits light and is measured via the light-projecting side optical fiber 12a. Measuring light is projected from the light projecting portion of the probe 13 onto the sample 40. At this time, most of the measurement light passes through the cover glass 14, but a part of the measurement light is reflected on the surface of the cover glass 14 on the measurement probe 13 side and becomes stray light. The stray light will be described together with the positional relationship between the light projecting unit, the light receiving unit, and the cover glass.

  The measurement light transmitted through the cover glass 14 is reflected by the sample 40 to become reflected light, passes through the cover glass 14, and is received by the light receiving portion of the measurement probe 13. The received reflected light reaches the spectroscope 15 via the light receiving side optical fiber 12b. Since the reflected light is a light reflection spectrum including light of various wavelengths, the spectroscope 15 separates the light for each predetermined wavelength and enters the photoelectric conversion unit 16. The photoelectric conversion unit 16 converts the light intensity for each wavelength into an electrical signal and generates light intensity information. The generated light intensity information is input to the analysis unit 21, and the analysis unit 21 calculates the film thickness of the thin film 41 from the input light intensity information as described above.

[Positional relationship between light emitter, light receiver, and cover glass]
Next, in the optical film thickness measuring apparatus according to the present embodiment, a configuration for optimizing the positional relationship between the light projecting unit 121a and the light receiving unit 121b and the cover glass 14 in order to improve measurement accuracy is shown in FIG. Based on

  As shown in FIG. 2, in the present embodiment, the light projecting unit 121a and the light receiving unit 121b are arranged close to each other. With such a configuration, when it is intended to protect the light projecting surface 122a and the light receiving surface 122b with a single cover glass 14, a part of the measurement light projected from the light projecting surface 122a is on the surface of the cover glass 14. Reflected and further scattered, it becomes stray light. When this stray light is incident on the light receiving surface 122b, miscellaneous light other than the reflected light from the sample 40 is received, resulting in a decrease in measurement accuracy. Therefore, in this embodiment, in order to reduce the influence of stray light, the distance from the front end surface of the measurement probe 13 to the surface of the cover glass 14 is optimized.

  Specifically, since the distal end surface of the measurement probe 13 is a light projecting surface 122a and a light receiving surface 122b, the cover glass 14 has a light projecting surface 122a and a light receiving surface 122b (in other words, as shown in FIG. 2). , A plane including the light projecting surface 122a and the light receiving surface 122b). The distance between the light projecting surface 122a and the surface of the cover glass 14 is defined as L, and the distance between the light projecting surface 122a and the light receiving surface 122b is defined as d. In addition, the distance L is set to the numerical aperture (NA value) of the light projecting side optical fiber 12a constituting the light projecting part 121a, the NA value of the light receiving side optical fiber 12b constituting the light receiving part 121b, and the distance d. The distance between the light receiving surface 122b and the cover glass 14 is also set to the distance L.

  First, looking at the optical path of stray light, the measurement light is emitted from the light projecting surface 122a of the light projecting unit 121a, and this measurement light ideally transmits all of the cover glass 14, but in reality, a part thereof Is reflected on the surface of the cover glass 14 and enters the light receiving surface 122b of the light receiving portion 121b as stray light. At this time, the reflection part of the measurement light on the surface of the cover glass 14 which is a generation source of stray light is a position corresponding to between the light projecting surface 122a and the light receiving surface 122b.

Here, if the numerical aperture of the light projecting side optical fiber 12a and NA _1, theta ₁ is obtained from the sine inverse of NA _1. That is, θ ₁ = sin ⁻¹ NA ₁ . As shown in FIG. 2, the angle θ ₁ corresponds to an angle at which the measurement light emitted from the light projecting surface 122a spreads toward the front side of the light projecting surface 122a (the cover glass 14 or the sample 40 side). If the numerical aperture of the light receiving side optical fiber 12b is NA ₂ and the angle obtained from the inverse sine function of NA ₂ is θ ₂ (θ ₂ = sin ⁻¹ NA ₂ ), the light receiving surface from the front side of the light receiving surface 122b Assuming stray light incident on 122b, the angle θ ₂ corresponds to a limit angle at which the assumed light enters the light receiving surface 122b from the front side (see FIG. 2).

Therefore, if the configuration in which the light projecting surface 122a and the light receiving surface 122b are included on the same plane, that is, the distance between the light projecting surface 122a and the cover glass 14, and the distance between the light receiving surface 122b and the cover glass are equal, stray light is assumed. cover state but the incident distance d between the light projecting surface 122a and the light-receiving surface 122b are the sum of the angle theta ₁ of tangent tan .theta ₁ and the angle theta ₂ of the tangent tan .theta _2, a light projecting surface 122a and the light receiving surface 122b It is equal to a value obtained by multiplying the distance L from the glass 14. Therefore, if stray light is not incident, the distance d can be expressed by an inequality as shown in the following equation (1).

d <L (tan θ ₁ + tan θ ₂ ) (1)
Here, in the present embodiment, since the light projecting unit 121a and the light receiving unit 121b are combined as the measurement probe 13, it can be considered that the interval d is practically fixed. Therefore, in order to avoid the incidence of stray light, the cover glass 14 may be installed on the front side of the distal end surface of the measurement probe 13 so that the interval L satisfies the following formula (2). Thereby, since the influence of the stray light from the cover glass 14 can be reduced significantly, measurement accuracy can be improved.

0 <L <d / (tan θ ₁ + tan θ ₂ ) (2)
In Expression (2), the upper limit of the distance L is clear from Expression (1). However, the lower limit of the distance L is not to contact the cover glass 14 with the light projecting surface 122a and the light receiving surface 122b. Based on what must be provided.

[Modification]
In the configuration shown in FIG. 2 described above, the intervals between the light projecting surface 122a and the light receiving surface 122b and the cover glass 14 are the same, but the present invention is not limited to this, and the light receiving surface 122b. The distance between the cover glass 14 and the cover glass 14 may be shorter than the distance between the light projecting surface 122 a and the cover glass 14. That is, if the distance between the light projecting surface 122a and the cover glass 14 is defined as C ₁ and the distance between the light receiving surface 122b and the cover glass 14 is defined as C ₂ , the following formula is established in the present invention. By adopting a simple positional relationship, the influence of stray light can be effectively avoided.

L = C ₁ > C ₂ (3)
Further, in the present embodiment, the cover glass 14 is used as the protective member, but the present invention is not limited to this, and a resin cover may be used, or the cover glass 14 may be formed from other translucent materials. A protective member may be used. That is, the protective member only needs to be formed of a material that transmits measurement light.

  In this embodiment, the light projecting side optical fiber 12a and the light receiving side optical fiber 12b are both configured as one optical fiber in this embodiment. However, for example, a plurality of optical fibers are bundled to provide a protective member. It may be configured as a coated optical cable. Alternatively, for example, only the light receiving side optical fiber 12b may be replaced with an optical cable. The specific configuration of the light guide member is not limited to the Y-type optical fiber 12 used in the present embodiment. For example, the light emitting side optical fiber 12a and the light receiving side optical fiber 12b may be independent from each other.

  Furthermore, the light projecting unit 121a of the light projecting side optical fiber 12a and the light receiving unit 121b of the light receiving side optical fiber 12b are integrated as a single measurement probe 13, but the light projecting unit 121a and the light receiving unit 121b are integrated. They are not summarized and may be separated from each other. In this case, instead of the Y-type optical fiber 12, independent light projecting side optical fibers 12 a and light receiving side optical fibers 12 b are used. Further, when the light projecting unit 121a and the light receiving unit 121b are not combined, the interval d can be adjusted instead of the interval L.

(Embodiment 2)
In the first embodiment, the positional relationship between the light projecting unit 121a, the light receiving unit 121b, and the cover glass 14 is optimized by adjusting the distance L formed between the tip of the measurement probe 13 and the cover glass 14. In this embodiment, in addition to this optimization, stray light is further combined by combining a structure in which the light spectrum in the absence of the sample 40 is subtracted from the light spectrum at the time of film thickness measurement. To reduce the impact. FIG. 3 is a schematic diagram illustrating an example of a schematic configuration of the optical film thickness measuring apparatus 10b according to the present embodiment.
As shown in FIG. 3, the optical film thickness measuring apparatus 10b according to the present embodiment has basically the same configuration as the optical film thickness measuring apparatus 10a according to the first embodiment, but the analysis unit 21 includes a calculation unit 22, an I / O circuit 23, and a storage unit 24.

  The calculation unit 22 is constituted by a CPU of a microcomputer, for example, and performs various calculations related to the operation of the analysis unit 21. This calculation includes calculation for calculating the film thickness of the thin film 42 formed on the sample 40 from the electrical signal generated by the photoelectric conversion unit 16. Therefore, in the optical film thickness measurement apparatus 10b, the calculation unit 22 functions as a film thickness calculator. The I / O circuit 23 is connected to the calculation unit 22 and inputs an electric signal (light intensity information) generated by the photoelectric conversion unit 16 to the calculation unit 22. In addition, according to the specific structure of the optical film thickness measuring apparatus 10b, you may be comprised so that a control signal may be output with respect to the photoelectric conversion part 16 from the calculating part 22. FIG. The I / O circuit 34 is constituted by, for example, an I / O input / output circuit of a microcomputer.

  The storage unit 24 stores various information related to the operation of the analysis unit 21. In the present embodiment, the storage unit 24 stores at least light intensity information generated by the photoelectric conversion unit 16. The specific configuration of the storage unit 24 may be configured as, for example, an internal memory of a microcomputer, or may be configured as an independent memory. The storage unit 24 does not have to be a single unit, and may be configured as a plurality of storage devices (for example, an internal memory and an external hard disk drive).

  In the optical film thickness measuring apparatus 10b according to the present embodiment, the light projection surface 122a is such that the positional relationship between the measurement probe 13 and the cover glass 14 satisfies the formula (2) as described in the first embodiment. The distance L between the light receiving surface 122b and the cover glass 14 is set. Further, the light intensity information in a state where no sample exists is acquired in advance as background light intensity information and stored in the storage unit 24, and then the sample The light intensity information in the presence of the light is acquired, and the background light intensity information is subtracted from the light intensity information, thereby reducing the influence of stray light. That is, in the present embodiment, the interval L is set to a suitable range, and data correction is performed by subtracting background light from the detected reflected light.

  Specifically, in the present embodiment, measurement is performed in two stages, a background light detection stage and a subsequent actual measurement stage. First, the background light detection stage will be described.

  In the background light detection stage, before the sample 40 is fixed to the sample fixing member 17, measurement light is projected from the light projecting unit 121 a of the measurement probe 13 to a position where the sample 40 is fixed. In this state, the light receiving unit 121b of the measurement probe 13 does not receive the reflected light from the sample 40. However, the measurement light is scattered by the cover glass and its surrounding members, so that scattered light is generated and received as stray light. Incident on the part 121b. In many cases, this scattered light can be ignored, but when the film thickness is thin or when it is desired to measure the film thickness with higher accuracy, it is not preferable that the scattered light is received as stray light. Therefore, the light intensity of the scattered light is detected in advance.

  If the scattered light is received by the light receiving unit 121b, as described above, the light is separated by the spectroscope 15 for each predetermined wavelength and is incident on the photoelectric conversion unit 16. The photoelectric conversion unit 16 converts the light intensity for each wavelength into an electrical signal and generates light intensity information. This light intensity information is input to the calculation unit 22 via the I / O circuit 23. Here, since the generated light intensity information is the light intensity information on the scattered light in the state where the sample 40 does not exist, the calculation unit 22 does not perform the calculation of calculating the film thickness from the light intensity information, The information is stored in the storage unit 24 as background light intensity information. This completes the background light detection stage.

  Next, the actual measurement stage will be described. If the sample 40 is fixed to the sample fixing member 17 after the background light detection stage is completed and the background light intensity information is stored in the storage unit 24, the light projecting unit 121a of the measurement probe 13 again applies to the sample 40. Measuring light is emitted. The measurement light is reflected by the sample 40 and received by the light receiving part 121b of the measurement probe 13 as a light reflection spectrum. At this time, since the scattered light is also received by the light receiving unit 121b as stray light, the light actually received by the light receiving unit 121b has a spectrum of reflected light and scattered light. For convenience of explanation, the optical spectrum actually received is referred to as actually measured light.

  The measured light is split by the spectroscope 15 as described above, is generated as light intensity information for each predetermined wavelength by the photoelectric conversion unit 16, and is input to the calculation unit 22. The input light intensity information of the actually measured light includes light intensity information of scattered light that is stray light in addition to the light intensity information of reflected light used for film thickness measurement. Therefore, the calculation unit 22 first generates corrected light intensity information by subtracting the background light intensity information stored in the storage unit 24 from the light intensity information of the actually measured light, and then generates the corrected light intensity information from the corrected light intensity information. The film thickness is calculated. By performing such data correction, the influence of not only the reflected light from the cover glass 14 but also the scattered light can be suppressed, so that the influence of stray light on the film thickness measurement is further reduced, and the measurement accuracy is improved.

  In the optical film thickness measuring apparatus 10b according to the present embodiment, the background light detection step may be configured to be performed manually by the user, or is the sample 40 fixed to the sample fixing member 17? By providing a sample sensor that detects whether or not, a control unit, a display unit, and the like, the background light detection step may be automatically performed.

(Embodiment 3)
In the first and second embodiments, only the configuration of the main part of the optical film thickness measuring apparatus 10a or 10b has been described. However, in the present embodiment, the film thickness measurement is performed in-line in the vacuum film forming apparatus. Next, a configuration in which the optical film thickness measuring apparatus is included in the vacuum film forming apparatus will be described. FIG. 4 is a schematic diagram showing an example of the configuration of the vacuum film forming apparatus according to the present embodiment.

  As shown in FIG. 4, the vacuum film forming apparatus 20 according to the present embodiment includes a film thickness measuring unit 10c and a vacuum chamber 18, and the tip of the measurement probe 13 included in the film thickness measuring unit 10c is vacuum. It is inserted above the chamber 18. Above the inside of the vacuum chamber 18, a cover glass 14 is disposed at the tip of the measurement probe 13, a sample fixing member 17 is provided at a position where measurement light can be projected from the tip of the measurement probe 13, and the sample 40 is fixed. ing. Further, an evaporation source 43 for evaporating a raw material (film forming material) of a thin film formed on the surface of the sample 40 is disposed below the vacuum chamber 18.

  The specific configuration of the vacuum film forming apparatus 20 is not particularly limited as long as the thin film is formed on the surface of the sample 40 in the vacuum chamber 18. Specifically, for example, a configuration using physical vapor deposition (PVD) or a configuration using chemical vapor deposition (CVD) may be used. In the present embodiment, although not shown in detail in FIG. 4, the vacuum film forming apparatus 20 has a configuration using an ion plating method which is a kind of PVD. Specifically, the evaporation source 43 disposed below the vacuum chamber 18 has a known configuration for evaporating the film forming material into the vacuum chamber 18 by resistance heating, for example. The film forming material evaporated from the evaporation source 43 is turned into plasma by a high frequency electric field formed in the vacuum chamber 18, and a film made of the plasma formed film forming material is formed on the sample 40.

  The specific configuration of the film thickness measuring unit 10c is the same as that of the optical film thickness measuring apparatus 10a (Embodiment 1) or the optical film thickness measuring apparatus 10b (Embodiment 2) described above. In the present embodiment, only the tip of the measurement probe 13 is inserted into the vacuum chamber 18, but the present invention is not limited to this, and the entire measurement probe 13 may be arranged in the vacuum chamber.

  In general, in a vacuum film forming apparatus, it is widely performed to measure the film thickness of a thin film formed on a product during the film forming process. For example, off-line measurement, that is, a product is extracted in each film forming process, transported to a place (for example, a measurement chamber) away from a place where a vacuum film forming apparatus is installed, and a film is measured by a film thickness measuring apparatus installed there. Measuring thickness is done.

  Here, when the measured film thickness is out of the allowable range, it is necessary to adjust the film forming conditions so that the film thickness falls within the allowable range. In the off-line measurement, it takes time to feed back the measured film thickness information to the operation of the vacuum film forming apparatus 20. Further, in the off-line measurement, since it is impossible to confirm whether or not the thin film formed on the product that has not been extracted is within the allowable range, the yield may be lowered. Therefore, in the vacuum film forming apparatus, in-line measurement, that is, without incorporating the optical film thickness measuring apparatus during or immediately after film formation in the product production line, without removing the product, Ideally, it has been widely attempted to measure the film thickness of all products.

  In the vacuum film forming apparatus, the raw material material of the film forming material is evaporated in the space in the vacuum chamber during the film forming process. Therefore, in an optical film thickness measurement apparatus that performs in-line measurement, it is essential to provide a protective member such as a cover glass on the front surface of the light receiving unit in order to prevent the film forming material from directly attaching to the light receiving surface. However, if the protective member is simply provided, the measurement light from the light projecting part is reflected on the surface of the protective member and enters the light receiving part as stray light, so that the measurement accuracy is lowered.

  On the other hand, in the present embodiment, since the film thickness measuring unit 10c is included in the vacuum film forming apparatus 20, the film thickness of the thin film formed on the sample 40 during the film forming process is in-line. Can be measured. Moreover, as described in the first embodiment, the positional relationship between the light projecting part and the light receiving part of the cover glass 14 and the measurement probe 13 is set so as to satisfy the formula (2) (see FIG. 2). Therefore, it is possible to suppress the reflected light generated on the surface of the cover glass 14 from becoming stray light and affecting the measurement result. Furthermore, as described in the second embodiment, the background light intensity information is acquired in advance, and the corrected light intensity information is generated by subtracting from the light intensity information of the actually measured light. It is possible to suppress not only reflected light but also scattered light from becoming stray light and affecting measurement results.

(Example)
The present invention will be described more specifically based on examples, comparative examples, and reference examples, but the present invention is not limited thereto. Those skilled in the art can make various changes, modifications, and alterations without departing from the scope of the present invention. The “reference value” and “control value” of the thin films in the following examples, comparative examples and reference examples were measured as follows.

[Measurement of reference value]
For a sample to be measured in Examples, Comparative Examples or Reference Examples, a light reflection spectrum of a thin film formed on the sample is measured in advance using a spectrophotometer (manufactured by Hitachi, product number U-4100). did. This measurement is intended to measure the light reflection spectrum serving as a reference for the thin film using a commercially available spectrophotometer without using the optical film thickness measuring apparatus according to the present invention. Is referred to as a “reference value”.

[Measurement of control value]
First, an optical film thickness measuring apparatus used in Examples, Comparative Examples, or Reference Examples was prepared without a cover glass (referred to as a coverless measuring apparatus for convenience). Next, the light reflection spectrum of the thin film formed on the sample was measured in advance for the sample to be measured in the example, the comparative example, or the reference example, using a measurement apparatus without a cover. In this measurement, the light reflection spectrum of the thin film is measured in a state where the cover glass is not installed, that is, in the state where stray light is not generated, and is compared with the measurement result in the state where the cover glass is installed. Since the purpose is to confirm the influence on the measurement result, the measurement result is referred to as “control value”.

[Example 1]
In all the following examples, comparative examples and reference examples including this example, the optical film thickness measuring apparatus 10a having the configuration shown in FIG. 1 was used. First, as a sample, a test glass on which a silicon nitride (Si3N4) thin film having a thickness of 107 nm was formed was prepared, and the reference value of the silicon nitride thin film was measured as described above. Moreover, in the optical film thickness measuring apparatus 10a, a coverless measuring apparatus without the cover glass 14 was prepared, and the control value of the silicon nitride thin film was measured as described above.

Next, the light reflection spectrum of the silicon nitride thin film was measured using the optical film thickness measuring apparatus 10a having the configuration shown in FIG. In the optical film thickness measuring apparatus 10a used in this example, the distance d between the light projecting surface 122a and the light receiving surface 122b is 3 mm. Since the numerical aperture NA ₁ = 0.3 of the light projecting portion 121a and the numerical aperture NA ₂ = 0.3 of the light receiving portion 121b, θ ₁ = 17.5 ° and θ ₂ = 17.5 ° It becomes. Under this condition, the cover glass 14 installed on the front surface of the measurement probe 13, the light projecting surface 122a and the light receiving surface 122b, and the distance L were set to L = 3 mm so as to satisfy the above equation (2) (FIG. 2). reference). This measurement result is referred to as “measurement value”.

  The comparison results of the reference value, the control value, and the measured value are shown in FIG. In FIG. 5, the horizontal axis indicates the wavelength (nm) of the light reflection spectrum, and the vertical axis indicates the relative reflectance (%). The reference value is indicated by a solid line, the control value is indicated by a dotted line, and the measured value is indicated by a broken line. 6 to 10 showing the same results, the horizontal axis and the vertical axis, and the display of the reference value, the reference value, and the measured value are the same as those in FIG.

  As shown in FIG. 5, the measured value almost overlaps with the reference value, and the control value also overlaps with the reference value as well. Therefore, the interval L is preferably set so as to satisfy the expression (2). It can be seen that the influence of stray light caused by the cover glass 14 can be effectively reduced by setting to a small value.

[Comparative Example 1]
In Example 1, except that the disposed cover glass 14, the light projecting surface 122a, the light receiving surface 122b, and the distance L are set to L = 10 mm so as not to satisfy the formula (2). Similarly, the measured value of the silicon nitride thin film was measured and compared with the reference value and the control value. The comparison results are shown in FIG.

  As shown in FIG. 6, the measured value of this comparative example is entirely lower than the reference value and the control value. Therefore, it can be seen that if the distance L is not set to a suitable value, the light reflection spectrum is largely shifted due to stray light caused by the cover glass 14.

  As described in Example 1, the control value almost overlaps the reference value, and the measured value of this comparative example is deviated from the reference value and the control value. From the configuration, it can be seen that except for the cover glass 14, it does not adversely affect the measurement of the light reflection spectrum of the silicon nitride thin film.

[Reference Example 1]
In Comparative Example 1, the measured values of the silicon nitride thin film were measured and compared with the reference value and the reference value in the same manner as Comparative Example 1 except that the data correction described in the second embodiment was performed. The comparison results are shown in FIG.

  As shown in FIG. 7, the measurement value of this reference example is generally lower than the reference value and the control value, but if the measurement result of Comparative Example 1 is compared, the difference between the reference value and the measurement value is small. It has become a thing. Thus, although only a certain amount of stray light reduction effect can be obtained only by performing the data correction when measuring the film thickness, a remarkable stray light reduction effect as shown in the first embodiment cannot be obtained. Therefore, it can be seen that the influence of stray light cannot be sufficiently suppressed only by the correction processing for setting the reference value for the reflected light.

  However, from the result of this reference example, it can be seen that the influence of stray light can be reduced to some extent by the data correction alone. Therefore, it is expected that the influence of stray light is further reduced by combining the data correction with the setting of the interval L.

[Example 2]
A reference value, a reference value, and a measured value for the light reflection spectrum of the titanium dioxide thin film were obtained in the same manner as in Example 1 except that a test glass on which a titanium dioxide thin film having a thickness of 280 nm was used as a sample. Was measured. The comparison results are shown in FIG.

  As shown in FIG. 8, the measured value almost overlaps with the reference value, and the control value also overlaps with the reference value in the same manner. Therefore, by setting the interval L to a suitable value, the cover value can be obtained. It turns out that the influence of the stray light resulting from the glass 14 can be reduced effectively.

[Comparative Example 2]
In the second embodiment, the cover glass 14, the light projecting surface 122a and the light receiving surface 122b, and the distance L are set to values that do not satisfy the expression (2) as in the first comparative example. In the same manner as in 2, the measured value of the titanium dioxide thin film was measured and compared with the reference value and the control value. The comparison results are shown in FIG.

  As shown in FIG. 9, the measured value of this comparative example is a reference in the wavelength range near the two minimum values in the light reflection spectrum (the wavelength range of about 470 nm to about 490 nm and the wavelength range of about 660 nm to about 700 nm). Although it almost overlaps with the value and the reference value, it is lower than the reference value and the reference value in other wavelength regions. Therefore, it can be seen that if the interval L is not set to a suitable value, stray light caused by the cover glass 14 causes a large shift in the light reflection spectrum.

  As described in Example 2, the control value almost overlaps the reference value, and the measurement value of this comparative example is deviated from the reference value and the control value. From the configuration, it can be seen that except for the cover glass 14, it does not adversely affect the measurement of the light reflection spectrum of the titanium dioxide thin film.

[Reference Example 2]
In the comparative example 2, the measured value of the titanium dioxide thin film was measured and compared with the reference value and the reference value in the same manner as the comparative example 2 except that the data correction described in the second embodiment was performed. The comparison results are shown in FIG.

  As shown in FIG. 10, the measured value of this reference example is lower than the reference value and the reference value except for the wavelength range in the vicinity of the two minimum values, as in Comparative Example 2, but the maximum value (about In the wavelength region near 560 nm), the difference between the reference value and the measured value is smaller than in Comparative Example 2. Thus, although only a certain amount of stray light reduction effect can be obtained only by performing the data correction when measuring the film thickness, the remarkable stray light reduction effect as shown in the second embodiment cannot be obtained. Therefore, it can be seen that the influence of stray light cannot be sufficiently suppressed only by the correction processing for setting the reference value for the reflected light.

  However, from the result of this reference example, it can be seen that the influence of stray light can be reduced to some extent by the data correction alone. Therefore, it is expected that the influence of stray light is further reduced by combining the data correction with the setting of the interval L.

  The present invention is not limited to the description of each of the embodiments and examples, and various modifications are possible within the scope shown in the claims, and different embodiments or examples and Embodiments obtained by appropriately combining technical means disclosed in a plurality of modified examples are also included in the technical scope of the present invention.

  The present invention can be suitably used as the in-line film thickness measuring means in the field of the vacuum film forming apparatus, for example, in addition to being able to be suitably used in the entire field of the optical film thickness measuring apparatus.

10a Optical film thickness measuring device 10b Optical film thickness measuring device 10c Film thickness measuring unit (optical film thickness measuring device)
12 Y-type optical fiber 13 Measurement probe (probe)
14 Cover glass (protective member)
16 Photoelectric converter (photoelectric converter)
17 Sample fixing member 20 Vacuum film forming apparatus 21 Analysis unit 22 Calculation unit (film thickness calculator)
24 Memory unit (memory device)
121a Light emitting part 121b Light receiving part 122a Light emitting surface 122b Light receiving surface

Claims (4)

A light projecting unit that projects light from the tip surface;
A light receiving portion that is arranged in parallel to the light projecting portion and receives light at the tip surface;
A protective member that is disposed in front of the front end surfaces of the light projecting unit and the light receiving unit so as to be parallel to the front end surfaces, and transmits light;
The distance between the tip surfaces of the light projecting part and the light receiving part is d, the distance between the tip surface of the light projecting part and the protective member is L, the numerical aperture of the light projecting part is NA ₁ , and the light receiving part. If the numerical aperture of NA is defined as NA ₂ , the protective member has the following formula: 0 <L <d / (tan θ ₁ + tan θ ₂ )
(However, θ ₁ = sin ⁻¹ (NA ₁ ), θ ₂ = sin ⁻¹ (NA ₂ ), and θ ₁ and θ ₂ are both less than 90 °.)
Provided in a position that satisfies
The optical film thickness measuring apparatus, wherein an interval between the distal end surface of the light receiving unit and the protective member is set to be equal to or less than the interval L. A sample fixing member for fixing a sample on which a thin film is formed at a position where light from the light projecting unit is projected;
A photoelectric converter that generates light intensity information of the received light by converting the light received by the light receiving unit into an electrical signal;
A film thickness calculator that calculates the film thickness of the thin film formed on the sample from the light intensity information generated by the photoelectric converter;
A storage device,
The film thickness calculator, when light is projected from the light projecting unit in a state where the sample is not fixed by the sample fixing member, the light intensity information generated by the photoelectric converter, While storing in the storage as background light intensity information,
When the sample is fixed by the sample fixing member and light is projected from the light projecting unit to the sample, the light intensity information generated by the photoelectric converter is stored in the storage device. 2. The optical film thickness measuring device according to claim 1, configured to generate corrected light intensity information obtained by subtracting the background light intensity information, and to calculate the film thickness of the thin film from the corrected light intensity information. .   The optical film thickness measuring device according to claim 1 or 2, wherein the light projecting unit and the light receiving unit are optical fibers, and the protective member is a cover glass.   The vacuum film-forming apparatus provided with the optical film thickness measuring apparatus of any one of Claim 1 to 3.

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