JP4547489B2 - Optical thin film forming apparatus equipped with film thickness measuring device and optical thin film forming method - Google Patents

Description

TECHNICAL FIELD The present invention relates to an optical film thickness measuring device mounted on an optical thin film forming apparatus, and introduces a spectral characteristic measuring method used for optical characteristic evaluation after optical thin film creation into a film thickness control method to provide high accuracy. An optical film thickness measuring apparatus is realized.

In a high-density wavelength division multiplexing transmission system (hereinafter referred to as DWDM), an optical multiplexer / demultiplexer is used for wavelength multiplexing and demultiplexing of multiplexed optical signals, but it is used inside the optical multiplexer / demultiplexer. Optical specifications such as transmission bandwidth, flatness, transmission loss, and suppression ratio between adjacent wavelengths required for a narrow band pass filter (hereinafter referred to as NBPF) with a dielectric multilayer structure It is a strict value for realizing high speed and large capacity. FIG. 1 and Table 1 show an example of optical specifications required for a NBPF for 50 GHz (International Telecommunication Union: wavelength interval defined by ITU). Transmission loss within the transmission band is 1.0 dB or less, flatness within the transmission band is required to be 0.4 dB or less, and the rectangular characteristics of the waveform require 0.5 dB bandwidth: 0.25 nm or more and 25 dB bandwidth: 0.6 nm or less. Has been.

The NBPF is one of the applications of optical thin films using light interference, and its structure is made by alternately depositing high and low refractive index dielectric materials and using multiple reflections from the layer interface to obtain the desired filtering characteristics. Is what you get. FIG. 2 shows the basic structure of NBPF. The optical film thickness of each layer is λ / 4 with respect to the transmission wavelength: λ, that is, λ / 2 for a pair of high refractive index material (29) and low refractive index material (30). As a result, the reflected light from the layer interface is added in phase to form the reflective band layer (31). There are two reflection band layers (31), and a spacer layer (32) having an optical film thickness of an integral multiple of λ / 2 is disposed between them to serve as a Fabry-Perot structure filter to form a cavity (33). . In order to satisfy the above optical specifications, NBPF has a multi-cavity structure in which a plurality of Fabry-Perot filters are connected via a coupling layer (34), and has a multilayer structure with 100 or more layers. Further, the optical specifications described above cannot be satisfied unless the optical film thickness of each layer is controlled with an accuracy of 0.01% or less.

で表される。図３は透明基板の屈折率を１．５２とした時の光学膜厚：ｎ_ｍ・ｄと反射率：Ｒの関係を示したものである。光の干渉に伴いｎ_ｇ＜ｎ_ｍの場合エネルギー反射率：Ｒは増加し、ｎ_ｇ＞ｎ_ｍの時は反対に減少するが、ｎ_ｍ・ｄ＝λ／４で共に極値となる。このように、光学膜厚：ｎ_ｍ・ｄがλ／４の整数倍となる毎にエネルギー反射率（透過率）：Ｒは極値となる。NBPF製造に於ける各層の膜厚制御は、この極値で行われる。 Next, an optical film thickness control method for each layer will be described. Refractive index: n _g refractive index on a transparent substrate: n thin film thickness of _m: is d deposited, the wavelength in air or in a vacuum: when the incident light of lambda, the energy reflectance: R is

It is represented by FIG. 3 shows the relationship between the optical film thickness: _nm · d and the reflectance: R when the refractive index of the transparent substrate is 1.52. The energy reflectivity: R increases with light interference when n _g < _nm , and decreases when _ng > _nm , but both have extreme values when _nm · d = λ / 4. Thus, every time the optical film thickness: _nm · d becomes an integral multiple of λ / 4, the energy reflectance (transmittance): R becomes an extreme value. The film thickness control of each layer in NBPF manufacturing is performed at this extreme value.

FIG. 4 shows a configuration diagram of a vacuum film forming apparatus for NBPF provided with a conventional optical film thickness measuring apparatus. The vacuum container (1) is evacuated to a level of 1 × 10 ⁻⁵ Pa by a vacuum pump (not shown) such as an oil diffusion pump or a cryopump. The film formation substrate (6) attached to the center of the substrate dome (5) is rotated at 1000 rpm together with the substrate dome (5) by a high-speed rotation mechanism (not shown) in order to make the film thickness distribution in the substrate uniform. Heated by a heating sheath heater (7) and a halogen heater (21). Further, the temperature of the film formation substrate (6) is measured using a radiation type thermometer (17), the actual measurement data is input to the temperature controller (18), and the temperature controller (18) is set at a preset temperature. Compare and calculate the measured temperature and the measured temperature, and based on the results, adjust the power for the halogen heater so that the substrate temperature is always constant even if the deposition substrate (6) receives radiant heat from the electron beam or heat generated during plasma generation. Control (19) (special issue 2002-229025).

An electron beam evaporation source (2) is used to form a dielectric film which is an optical thin film. At that time, when high frequency power (frequency: 13.56 MHz) output from the high frequency power source (22) is directly applied to the substrate dome (5), glow discharge is generated in the space between the substrate dome (5) and the evaporation source (2). Then, a plasma state occurs, and a self-induced negative DC electric field is generated on the surface of the film formation substrate (6) attached to the substrate dome (5), and a thin film with high energy and high packing density is formed (special feature). Kai 2001-73136).

The matching box (23) matches the output impedance of the high-frequency power source (22) and the impedance of the discharge mechanism including the substrate dome (5) as a load. The quartz film thickness sensor (4) detects the evaporation rate and feeds back a detection signal to the electron beam evaporation source controller (not shown) to control the film formation rate to be constant. The optical film thickness measuring device mainly includes a laser light source (11), an optical fiber (13), an emission tube (14), a monochromatic photometric light receiver (15), and a controller (10). The laser beam (monochromatic light) emitted from the laser light source (11) passes through the depolarizer (12), the optical fiber (13), the emission tube (14), and the lower viewing window (8) to form the film formation substrate (6). Then, the light passes through the upper viewing window (9) and enters the monochromatic photometric light receiver (15). The amount of transmitted light that changes depending on the film thickness of the optical thin film deposited on the film formation substrate (6) is photoelectrically converted into an electrical signal by the monochromatic photometric light receiver (15). The controller (10) performs arithmetic processing on the photoelectrically converted electrical signal, and when the transmittance reaches the extreme value of λ / 4, the shutter (3) is closed, the film formation is terminated, and the dielectric materials are sequentially stacked. I will do it.

FIG. 5 is a detailed view of the film formation substrate (6). An antireflection film (36) for reducing interference between incident light and reflected light is formed on the back surface of the film formation substrate (6), and laser light is incident on the surface of the film formation substrate (6). Is the reference point (37), the point where the laser beam reflected from the back surface of the film formation substrate (6) returns to the surface of the film formation substrate (6) is the reflection point (38), and the reference point (37) and the reflection point (38) The rear surface side of the film formation substrate (6) is inclined so that the distance is longer than the wavelength of the laser beam, and the reflected light from the rear surface of the film formation substrate (6) is prevented from returning to the incident optical path (Japanese Patent Application No. 2002-229025).

In the manufacturing process of NBPF, after all the film formation using the vacuum film forming apparatus for NBPF is completed, the film formation substrate is taken out into the atmosphere, and a spectral characteristic measurement method using an optical spectrum analyzer or the like is used as shown in FIG. Measure and evaluate whether the specified optical specifications are met. Even when high-precision film thickness control is performed using the above-described monochromatic photometry optical film thickness measurement apparatus, accumulation of various measurement errors, various conditions during film formation (degree of vacuum, film formation speed, substrate temperature, etc.) ), The spectral characteristics of NBPF deteriorate, and the optical specifications shown in FIG. 1 and Table 1 may not be obtained. In this case, the film forming process for 10 to 20 hours is all wasted. I have a big problem.

This problem will be described with reference to FIG. Conventional film thickness control by monochromatic photometry corresponds to monitoring the film thickness at the center wavelength of NBPF, which is 1550.0 nm in FIG. If the result of the spectral characteristics of the NBPF formed on the substrate is normal spectral characteristics as indicated by the solid line (47) shown in FIG. 6, there is no problem, but the spectral characteristics as indicated by the dotted line (48). If there is an abnormality, it is impossible to determine the abnormality by the conventional monochromatic photometry method in which the film thickness is monitored only at the wavelength of 1550.0 nm. Furthermore, film thickness control by monochromatic photometry utilizes the fact that the transmittance becomes an extreme value every time the film thickness: _nm · d becomes an integral multiple of λ / 4, and the change in transmittance is monitored. Therefore, in the layer where the change amount of the transmittance is small, an error is likely to occur in the extreme value detection, resulting in a problem that the optical characteristics of the NBPF deteriorate. In order to solve the problem, the applicant changed the output of the laser light source, and in the layer where the amount of change in the transmittance was small, the intensity of the laser light was increased to expand the change in the amount of transmitted light, and the accuracy of film thickness control by extreme value detection (Japanese Patent Application No. 2003-282837).

FIG. 19 shows the simulation result of the transmittance change of each layer in NBPF. In the figure, the horizontal axis indicates the layer number, and the vertical axis indicates the transmittance. The layer number indicates how many layers are counted from the glass substrate, the layer numbers 1 to 15, 17 to 31, 33 to 47, 49 to 63 are reflective band layers, and the layer numbers 16 and 48 are spacer layers. The layer number 32 indicates a bonding layer. The method shown in Japanese Patent Application No. 2003-282837 is effective when a layer having a low transmittance such as a spacer layer is formed, but a layer having a high transmittance and a large amount of transmitted light is formed originally such as a bonding layer. In the case of forming a film, there is a limit to the change and expansion of the amount of transmitted light due to an increase in the output of the laser light source, and it has been difficult to accurately detect extreme values.

In the conventional manufacturing process of NBPF, the film thickness control method at the time of NBPF creation and the evaluation method after NBPF creation are different, so the above-mentioned problems have occurred. The present invention introduces a spectral characteristic measurement method, which is an evaluation method after NBPF creation, into the film thickness control method at the time of NBPF creation, thereby constantly measuring the spectral characteristics of NBPF that could not be distinguished by monochromatic photometry during film formation. It is an object of the present invention to provide a new type optical film thickness measuring device that controls the film thickness from the change in the spectral characteristics of NBPF.

The first means for achieving the above object stores the theoretical value of the spectral characteristic in the film thickness including at least the target film thickness value of the optical thin film having the desired spectral characteristic. In order to control the film thickness by sequentially comparing the measured values of the spectral characteristics, the measured light projected on the thin film sample is swept in wavelength, and the spectral characteristics of the thin film sample are measured. Specifically, a wavelength tunable laser that sweeps the wavelength of the actually measured light projected on the thin film sample, and the light transmitted or reflected through the thin film sample are received, and the received light is photoelectrically converted to measure the spectral characteristics of the thin film sample. An optical power meter, a computer that reads the spectral characteristic of the thin film sample output from the optical power meter and compares the spectral value with the theoretical value, and a control unit that controls film formation according to the comparison result of the computer may be provided. . Film formation is terminated when the measured value falls within the target range of the theoretical value. The calculation formula of the theoretical value of the spectral characteristics is shown below.

で表される。Ｎは複素屈折率、ｄは薄膜の厚さ、θは薄膜への光の入射角を表す。 The theoretical value of the spectral characteristics of NBPF can be obtained from the product of the four-terminal matrix,
Each layer of NBPF is a four-terminal matrix

It is represented by N represents the complex refractive index, d represents the thickness of the thin film, and θ represents the incident angle of light on the thin film.

となり、多層膜の振幅透過率：τ及びエネルギー透過率：Ｔは四端子行列の要素と媒質の屈折率：Ｎ_０及び基板の屈折率Ｎ_Ｓから

と表され、波長に対する透過率をプロットすると分光特性が得られる。 In addition, the multilayer film is expressed as the product of the four-terminal matrix for each layer.

The amplitude transmittance of the multilayer film: τ and the energy transmittance: T are obtained from the elements of the four-terminal matrix, the refractive index of the medium: N ₀ and the refractive index N _{S of the} substrate.

When the transmittance with respect to wavelength is plotted, spectral characteristics are obtained.

The second means for achieving the object stores the theoretical value of the spectral characteristic at the film thickness including at least the target film thickness value of the optical thin film having the desired spectral characteristic, In order to control the film thickness by sequentially comparing the measured spectral characteristics of the film, the broadband thin-wavelength light is projected onto the thin film sample, and the light that has been transmitted or reflected through the thin film sample is swept in wavelength. It is characterized by actually measuring. Specifically, a broadband light source that projects broadband multi-wavelength light onto a thin film sample, an optical spectrum analyzer that receives light transmitted through or reflected from the thin film sample, and measures the spectral characteristics of the thin film sample, and an optical spectrum analyzer A computer that reads the spectral characteristics of the thin film sample to be output and compares it with the theoretical value, and a control means for controlling the film formation according to the comparison result of the computer may be provided. Film formation is terminated when the measured value falls within the target range of the theoretical value.

Further, the first and second means include a film thickness control means by monochromatic photometry for projecting monochromatic light onto the film forming substrate and controlling the film thickness of the optical thin film from a change in transmittance or reflectance of the film forming substrate. A means for switching between film thickness control by spectral characteristic measurement and film thickness control by monochromatic photometry is provided, and film thickness control is performed by appropriately selecting the spectral characteristic measurement method and monochromatic photometry during film formation.

In the present invention, by introducing the spectral characteristic measurement method into the film thickness control method of the optical thin film, the spectral characteristics of the optical thin film that could not be discriminated by the film thickness control method of only monochromatic photometry are constantly measured during the film formation. It became possible to perform highly accurate film formation.

Description of Configuration of Example FIGS. 9 to 12 show the two-cavity NBPF composed of the first and second cavities as the subject, and the spectral characteristics of the optical film thickness in the coupling layer, spacer layer, and reflective band layer of the second cavity. The simulation result is shown. In the figure, a to e show how the optical film thickness changes to 0, λ / 16, λ / 12, λ / 8, and λ / 4, assuming that the optical film thickness is 0 at the start of film formation of each layer. In the simulation, Ta ₂ O ₅ is used as the high refractive index material, SiO ₂ is used as the low refractive material, the center wavelength is λ = 1550.00 nm, and the optical film thicknesses λ / 4 of Ta ₂ O ₅ and SiO ₂ are H, Assuming L, an NBPF having a film structure represented by a substrate / {[HL] ⁷ H8LH [LH] ⁷ } L {[HL] ⁷ H8LH [LH] ⁷ } is assumed. The refractive index was calculated from the results of single-layer deposition of Ta ₂ O ₅ and SiO _2, which are optical thin film materials, using the NBPF vacuum film deposition apparatus shown in FIG.

9 shows the spectral characteristics of the coupling layer, FIG. 10 shows the spectral characteristics of the spacer layer, FIG. 11 shows the spectral characteristics of the first reflective band layer immediately after the spacer layer, and FIG. 12 shows the spectral characteristics of the final layer of the reflective band layer. It is the result of having simulated. In FIG. 9, a bonding layer is formed on a first cavity (33) formed of a reflective band layer (31), a spacer layer (32), and a reflective band layer (31) formed on a glass substrate. When the coupling layer film grows, the transmission loss of the subassembly A composed of the first cavity (33) and the coupling layer is shown. When there is no coupling layer film (film thickness is 0), the transmission loss is curve a, and the transmission loss becomes b, as the coupling layer film thickness becomes λ / 16, λ / 12, λ / 8, λ / 4. c, d, and e. At that time, the peak of the transmission loss curve a when the film thickness is 0 and the peak of the transmission loss curve when the film thickness is λ / 4 (that is, the target film thickness) are both 1550.0 nm of the center wavelength. In the film thickness, the peak of the transmission loss curve is shifted from the center wavelength of 1550.0 nm.

FIG. 10 shows a case where a reflection band (31) is formed on the above-described subassembly A composed of the first cavity and the coupling layer, and then a spacer layer (that is, the second cavity is formed on the reflection band layer (31)). When the spacer layer is formed, the transmission loss of the subassembly A, the reflection band layer, and the subassembly B composed of the spacer layer changes as the spacer layer film grows. In this case, each of the transmission loss curves a, b, c, d, and e has a peak at a wavelength of 1550.0 nm.

FIG. 11 shows the sub-assembly B and the reflection band when the first layer of the reflection band layer (that is, the first layer of the reflection band layer on the spacer in the second cavity) is formed on the sub-assembly B described above. The transmission loss characteristic of the subassembly C composed of the first layer is shown. As in FIG. 10, the curves a, b, c, d, and e all have a peak at a wavelength of 1550.0 nm.

FIG. 12 shows the transmission loss characteristics of the NBPF assembly when the last layer of the reflection band (that is, the final layer of the two-cavity NBPF assembly) is formed after the reflection band layer is overlaid on the sub-assembly C described above. As in FIG. 9, the peak of the transmission loss curve changes as the film grows.

FIGS. 9 to 12 show only the spectral characteristics of a specific layer at a specific film thickness as an example, but the spectral characteristics of an arbitrary film thickness in an arbitrary layer can be simulated. For example, FIG. 13 shows the result of simulating the spectral characteristics of NBPF having a 172 layer structure.

The present invention is equipped with an optical thin film forming device equipped with a spectral characteristic measuring device to constantly measure changes in spectral characteristics during the film formation process, and control the film thickness while sequentially comparing the obtained measurement data and simulation results. To do. The film formation is terminated when the target range of the spectral characteristics is set in advance based on the simulation result and the actually measured data falls within the target range. In the case shown in FIGS. 9 to 12, the transmission loss curve e may be controlled. Referring to FIGS. 9 to 12, a layer in which the peak of the transmission loss curve is constant during the film growth process as shown in FIGS. 10 and 11, and a layer in which the peak changes as shown in FIGS. There is. Since it is easy to observe changes in spectral characteristics in a layer where the peak of the transmission loss curve changes during the film growth process, the spectral characteristic measurement method is particularly effective in a layer where the peak of the transmission loss curve changes.

7 and 8 are schematic views of the spectral characteristic measuring apparatus. FIG. 7 shows a wavelength sweeping method on the light source side using a tunable laser (39) as the light source and an optical power meter (40) on the light receiving side. FIG. 8 shows a wavelength sweep method on the light receiving side using a broadband light source (45) as the light source and an optical spectrum analyzer (46) on the light receiving side. Both types can measure the spectral characteristics of NBPF. In the figure, (43) indicates a measurement substrate, (42) indicates a light receiving side collimator, and (44) indicates a light emitting side collimator.

The first configuration form of the present invention will be described below. In the first configuration, the spectral characteristic of the substrate during film formation is measured by performing wavelength sweeping on the light source side. FIG. 14 is a schematic view when the spectral characteristic measuring apparatus shown in FIG. 7 is mounted on the NBPF vacuum film forming apparatus shown in FIG. Components similar to those of the conventional apparatus are denoted by the same reference numerals and description thereof is omitted. In the figure, (11) shows a wavelength tunable laser that performs wavelength sweeping, (49) is a disturbance light cut filter that removes optical noise, and (27) is a deposition substrate in synchronization with the wavelength sweeping of the wavelength tunable laser (6) The optical power meter which measures the transmittance | permeability of is shown. The ambient light cut filter (49) prevents light emitted during plasma generation, light generated during electron beam evaporation, and light emitted by the halogen heater (21) from entering the optical receiver (25) as spectral noise. Yes. For the ambient light cut filter (49), for example, a band pass filter in which a high refractive index substance and a low refractive index substance are alternately laminated is used to reduce light in the vicinity of the measurement wavelength incident on the light receiver. It becomes possible.

FIG. 15 shows a flowchart for measuring the spectral characteristics. When measuring spectral characteristics, the wavelength tunable laser (11) repeats wavelength sweeping, and therefore it is necessary to perform initial setting of the sweep wavelength range and sweep wavelength interval (S1). When the sweep wavelength range is λ ₁ to λ ₂ (λ ₁ <λ ₂ ) and the sweep wavelength interval is Δλ, the wavelength tunable laser (11) has λ ₁ , λ ₁ + Δλ, λ ₁ + 2Δλ, λ ₁ + 3Δλ, ... A wavelength of λ ₂ is repeatedly emitted.

At the beginning spectroscopic characteristic measurement, a tunable laser (11) emits light having a wavelength lambda ₁ (S2). The emitted light passes through the film formation substrate, is reflected by the semitransparent mirror (26), and enters the spectral characteristic measurement light receiver (25) via the disturbance light cut filter (49). The spectral characteristic measuring photoreceiver (25) photoelectrically converts the received light into an electrical signal and outputs it to the optical power meter (27). An optical power meter (27) measures the transmittance of the deposition substrate (6) at a wavelength lambda ₁ to record the difference in the brightness of light incident on the light receiver (S3), and outputs to the computer (28). The computer (28) reads the measurement data of the optical power meter (27) (S4). Then tunable laser (11) emits light having a wavelength lambda _{1 +} [Delta] [lambda] (S2) likewise wavelength lambda _{1 +} [Delta] [lambda] Measurement of the transmittance of the deposition substrate (6) in (S3) and data reading (S4 )I do. Likewise, the tunable laser (11) is continuously varied wavelength intervals Δλ to a wavelength lambda _2, the computer (28) reads the transmission data at each wavelength. When the wavelength sweep from λ ₁ to λ ₂ is completed, the wavelength tunable laser (11) again emits light of wavelength λ ₁ to the film formation substrate (6), and repeats (S2) to (S4). At the same time, the computer (28) compares the measured value of the spectral characteristics with the simulation result (S5), and feeds back the comparison result to the controller (10) that controls the shutter (3). When the measured value of the spectral characteristics falls within the target range of the simulation result, the controller (10) closes the shutter and finishes the film formation. Since the target range varies depending on the specifications, it may be set according to the purpose. The set values of the sweep wavelength range and the sweep wavelength interval are arbitrary, but in this embodiment, the wavelength sweep of the wavelength range: several nm and the wavelength interval: 0.01 nm is repeated at a speed of 1 second or less. In the above embodiment, the wavelength sweep is continuously performed from the short wavelength to the long wavelength. However, the wavelength sweep may be changed from the long wavelength to the short wavelength or may be changed randomly.

In the apparatus shown in the figure, in order to enable film thickness control by the conventional monochromatic photometry method, both a monochromatic photometric photoreceiver (15) and a spectral characteristic measuring photoreceiver (25) are provided, and a wavelength tunable laser (11 ) Was used as a dual purpose. Furthermore, a semi-transparent mirror (26) is arranged at an angle of 45 ° with respect to the optical axis, and one of the measurement light transmitted through the film-forming substrate (6) is incident on the monochromatic photometric light receiver (15). On the other hand, the light is incident on the spectral characteristic measuring light receiver (25) through the ambient light cut filter (49). During monochromatic photometry, the measurement light emitted from the wavelength tunable laser (11) is fixed at a single wavelength, and the controller (10) measures the transmittance of the monochromatic light incident on the monochromatic photometry light receiver (15). Take control. For film thickness control of each layer, a conventional monochromatic photometry method and spectral characteristic measurement method are appropriately selected by using a switching means.

In the first configuration, the monochromatic photometry light receiver (15) may be omitted, and the monochromatic photometry method and the spectral characteristic measurement method may be switched using only the spectral characteristic photometry light receiver (25). In this case, the operation at the time of spectral characteristic measurement is the same as described above. During monochromatic photometry, the tunable laser (11) fixes the measurement light to a single wavelength, and the optical power meter (27) measures the transmittance of the monochromatic light, and performs film thickness control by monochromatic photometry. The film thickness control may be performed by appropriately selecting both the monochromatic photometry method and the spectral characteristic measurement method, or may be performed only by the spectral characteristic photometry method. When spectral characteristics are measured, the computer (28) plots a change in transmittance at a specific wavelength, so that monochromatic photometry and spectral characteristics measurement can be performed simultaneously.

Next, a second configuration form of the present invention will be described. In the second configuration, a spectral characteristic of the substrate at the time of film formation is measured by performing a wavelength sweep on the light receiving side using a broadband light source. Specifically, the spectral characteristic measuring apparatus shown in FIG. 8 is mounted on the NBPF vacuum film forming apparatus shown in FIG. In the second configuration, a broadband light source (45) is used as a light source, and an optical spectrum analyzer (46) is used on the light receiving side. The optical spectrum analyzer (46) sweeps the broadband multi-wavelength light transmitted through the film formation substrate (6) and measures the spectral characteristics of the film formation substrate (6). When monochromatic photometry is employed, the optical spectrum analyzer (46) measures only the transmittance of a single wavelength. The film thickness control may be performed by appropriately selecting both the monochromatic photometry method and the spectral characteristic measurement method, or may be performed only by the spectral characteristic measurement method, or the monochromatic photometry method and the spectral characteristic measurement method may be performed simultaneously.

In the above configuration, the spectral characteristic measuring device is mounted on the film forming apparatus shown in FIG. 4, but the film forming apparatus on which the spectral characteristic measuring apparatus is mounted is not limited to the apparatus shown in FIG. However, the invention of the present applicant's previous invention, means for projecting a laser beam having a reduced coherence by changing the phase characteristics and polarization characteristics, the incident light on the film formation substrate and the back surface of the substrate The spectral characteristic measuring device of the present invention is mounted on a film forming apparatus (Japanese Patent Application No. 2002-229025) equipped with a means for preventing interference with reflected light and a temperature control means for keeping the temperature of the film forming substrate constant. As a result, it is possible to suppress the fluctuation of the amount of light and perform film formation with higher accuracy.

By adopting a method of measuring the spectral characteristics of a thin film sample during the film formation process by sweeping the wavelength of the measured light according to the present invention, the monochromatic photometry method and the spectral characteristic measurement method can be arbitrarily selected during the film formation of the thin film sample. Thus, the accuracy of film thickness control can be remarkably improved. The monochromatic photometry method and the spectral characteristic measurement method can be freely combined according to various conditions, but the following combinations are conceivable as one proposal for forming a highly accurate NBPF.

The explanation is based on the two-cavity NBPF. Referring to the change in transmittance of each layer in the NBPF shown in FIG. 19, since the change in transmittance is large in the reflection band layer after the start of film formation on the glass substrate, extreme value detection can be performed with high accuracy. Employ monochromatic photometry. Although the amount of change in transmittance after reflection band layer deposition is small, the transmittance is low, so the method shown in Japanese Patent Application No. 2003-282837 is adopted, and the laser light output is increased to control the film thickness by monochromatic photometry. I do. Similarly, the monochromatic photometry method is used for film formation in the reflection band layer, spacer layer, and reflection band layer in the first cavity, and in the layer where the amount of change in transmittance is small, the output is increased by increasing the output of the laser light source. Thickness control is performed.

Next, in the bonding layer after the formation of one cavity, as shown in FIG. 19, it is difficult to improve the film thickness accuracy by controlling the output of the laser light source because the change in transmittance is small and the transmittance is high. As shown in FIG. 9, the peak wavelength of the transmission loss curve changes as the film thickness changes in the bonding layer, so that the film thickness control by the spectral characteristic method is easy, and the spectral characteristic measurement method is adopted in the formation of the bonding layer. As a result, the film thickness control using only the monochromatic photometry method has made it possible to control the film thickness of the bonding layer, whose accuracy has been limited. I understand that.

Since the amount of change in transmittance is again large in the second cavity reflection band layer, the monochromatic photometry method is adopted. After that, the amount of change in transmittance becomes small, but the monochromatic photometry method is also applied to the reflection band layer, spacer layer, and reflection band layer of the second cavity by controlling the film thickness while controlling the output of the laser light source in the same manner as described above. To do. However, the spectral characteristic measurement method is adopted for the final layer of the second cavity. This is because the characteristics of the final layer mean the final filter characteristics of NBPF.If only the center wavelength is monitored in the final layer, defects such as those shown in FIG. 6 cannot be found. This is because it is necessary to check the characteristics. In the final layer, the spectral characteristic measurement method is used, and the film formation is terminated when the spectral characteristic satisfies the standard of the NBPF filter characteristic which is a finished product. Alternatively, the final layer of the second cavity is completed by monochromatic photometry, and when adding a correction film that adjusts the two-cavity NBPF formed up to the final layer to the desired filter characteristics, the correction film is checked by spectral characteristics May be performed.

As described above, when forming a layer with a small transmittance change and a high transmittance, film thickness control is performed using a spectral characteristic measurement method, and a layer having a large transmittance change or a transmittance Even when the amount of change is small, a monochromatic photometry method may be used when forming a layer with low transmittance.

According to the present invention, the problem that the detection of the extreme value is likely to occur in the conventional film thickness control of the layer having a small transmittance change and a high transmittance, and the desired optical characteristics cannot be obtained. It is possible to control the film thickness with high accuracy by appropriately selecting the monochromatic photometry method and controlling the film thickness.

Description of Action and Operation of Examples Based on the above-described examples, a NBPF having a 5-cavity configuration for 50 GHz was prepared using both monochromatic photometry and spectral characteristic measurement. The produced NBPF uses optical thin film materials of Ta ₂ O ₅ and SiO ₂ , and their optical film thickness is deposited and controlled at λ / 4 (λ: 1550 nm). When the optical film thicknesses of Ta ₂ O ₅ and SiO ₂ are λ / 4, and H and L respectively, the film configuration is substrate / {[HL] ⁷ H8LH [LH] ⁷ } L {[HL] ⁸ H8LH [LH ] ⁸ } L {[HL] ⁸ H8LH [LH] ⁸ } L {[HL] ⁸ H8LH [LH] ⁸ } L {[HL] ⁷ H8LH [LH] ⁶ } 1.1837L 0.88899H1.54721L / 172 layers in the atmosphere It was.

For the film thickness control, the spectral characteristic measurement method is used for the reflection band layer farthest from the spacer layer, and the monochromatic photometry method is used for the other layers. Was used. Specifically, film formation was performed using the monochromatic photometry method up to the 172nd layer, and a correction film was formed using the spectral characteristic measurement method after completion of the 172th layer. The film forming conditions are 400 ° C. at the set temperature of the temperature controller (18), and the degree of vacuum in the vacuum vessel (1) is 2.5 × 10 ⁻² Pa, SiO ₂ when Ta ₂ O ₅ is formed by introducing oxygen gas. During film formation, the film was held at 1.5 × 10 ⁻² Pa, and the film formation rates of Ta ₂ O ₅ and SiO ₂ were set to 0.4 nm / sec and 0.8 nm / sec, respectively.

FIG. 16 (51) shows the spectral characteristic measurement results after the 172nd layer. The transmission loss is -1.2 dB, and the flatness is 0.6 dB, which shows a large deviation from the design value (50), which does not satisfy the optical specifications. (52) in FIG. 17 shows the result of correction film formation using an H material using the spectral characteristic measurement method for improving the spectral characteristics. A change in spectral characteristics during film formation and a design value by simulation were sequentially compared, and the film formation was terminated when it was closest to the design value (50). Compared to FIG. 16, the transmission loss is improved by 25% to −0.9 dB, and the flatness is improved by 60% or more, and 0.2 dB, which is a good spectral characteristic satisfying optical specifications.

FIG. 18 shows the result of measuring the spectral characteristics using an optical spectrum analyzer after the film formation substrate (6) was taken out into the atmosphere after the film formation was completed. From the figure, -0.5 dB width: 0.297 nm, -25 dB width: 0.53 nm, flatness: 0.1 dB, and good results that satisfy optical specifications were obtained even in the atmosphere.

Conventionally, the film formation that fails because the optical specifications cannot be satisfied succeeded in satisfying the optical specifications according to the present invention. In the above example, the correction film was formed after the completion of the 172th layer by checking the spectral characteristics. However, the 172nd layer of the film can be obtained by checking the spectral characteristics when forming the 172th layer and obtaining the target filter characteristics. It was also possible to control the formation of.

Further, by controlling the film formation by spectral characteristics when forming the coupling layer between the cavities, NBPF with higher accuracy filter characteristics was obtained. In particular, in the case where the peak of the transmission loss curve deviates from the center wavelength (for example, 1550.0 nm) during film formation, a more accurate NBPF finished product was obtained by performing film formation by checking spectral characteristics.

Description of other examples, description of examples of diversion to other applications In the above examples, the creation of NBPF was described. However, the present invention is not limited to the formation of NBPF, and the film formation of other optical thin film elements Control is also possible. Moreover, in the said Example, although the transmittance | permeability was measured, you may measure a reflectance.

The figure which shows the spectral characteristic of NBPF. The figure explaining the film | membrane structure of NPBF. The figure which shows the relationship between the optical film thickness of a dielectric thin film, and a reflectance. The figure which shows schematic structure of the film-forming apparatus carrying the conventional optical film thickness measuring device. The figure which shows the detail of a film-forming board | substrate. The figure explaining a monochromatic photometry method and a spectral characteristic measurement method. The figure explaining a spectral characteristic measuring apparatus. The figure explaining a spectral characteristic measuring apparatus. The figure which shows the spectral characteristic of the 2 cavity NBPF coupling layer by simulation. The figure which shows the spectral characteristic of the 2 cavity NBPF spacer layer by simulation. The figure which shows the spectral characteristic of the 2 cavity NBPF reflective belt layer by simulation. The figure which shows the spectral characteristics of the 2 cavity NBPF final layer by simulation. The figure which shows the spectral characteristic of 172 layer NBPF by simulation. The figure which shows schematic structure of the film-forming apparatus mounted with this invention optical film thickness measuring device. The figure which shows the flowchart at the time of the spectral characteristic measurement of this invention. The figure which shows the data at the time of performing actual film-forming using the conventional optical film thickness measuring apparatus. The figure which shows the data at the time of performing actual film-forming using the optical film thickness measuring apparatus of this invention. The figure which shows the data measured in air | atmosphere after performing actual film-forming using the optical film thickness measuring apparatus of this invention. The figure which shows the simulation of the transmittance | permeability change of each layer in NBPF.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Vacuum container 2 Electron beam evaporation source 3 Shutter 4 Quartz sensor 5 Substrate dome 6 Deposition substrate 7 Substrate heating sheath heater 8 Lower viewing window 9 Upper viewing window 10 Controller 11 Wavelength variable laser 12 Depolarizer 13 Optical fiber 14 Output tube 15 Monochromatic photometer 16 Viewing window 17 Radiation type thermometer 18 Temperature controller 19 Halogen heater power regulator 20 Low voltage introduction electrode 21 Halogen heater 22 High frequency power supply 23 Matching box 24 High voltage introduction electrode 25 Spectral characteristic measurement light receiver 26 Half Transparent mirror 27 Optical power meter 28 Computer 29 High refractive index material
DESCRIPTION OF SYMBOLS 30 Low-refractive-index substance 31 Reflection band layer 32 Spacer layer 33 Cavity 34 Coupling layer 35 Substrate 36 Antireflection film 37 Reference point 38 Reflection point 39 Wavelength variable laser 40 Optical power meter 41 Optical fiber
42 Light receiving side collimator 43 Measurement board 44 Light emitting side collimator 45 Broadband light source 46 Optical spectrum analyzer
47 Spectral characteristics at normal time 48 Spectral characteristics at abnormal time 49 Disturbance light cut filter 50 Design value of NBPF for 50 GHz 51 Spectral characteristics at the end of the 172nd layer using monochromatic photometry 52 Correction film formation using spectral characteristic measurement method Spectral characteristics after performing

Claims (2)

In a thin film forming apparatus, a predetermined bandwidth for wavelength division multiplexing optical transmission is formed by a multi-cavity structure in which a Fabry-Perot filter having a spacer layer disposed between two reflection band layers is connected in multiple stages through a coupling layer. An optical multilayer film structure which is a bandpass filter having an optical film thickness of each of the layers of the structure, the optical film thickness of the reflection band layer being λ when the bandwidth center wavelength of the bandpass filter is λ In the method of manufacturing an optical multilayer film structure in which the optical film thickness of the spacer layer is an integer multiple of λ / 2, which is an integral multiple of / 4,

(A) A simulation theoretical value of spectral characteristics of light transmittance at least in a predetermined light wavelength band is stored for the sub-assembly of the optical multilayer film structure consisting of n layers,

During the formation of the coupling layer as the nth layer of the subassembly, the optical transmittance value of the subassembly at a plurality of different wavelengths within the optical wavelength band is measured at a predetermined repetition period,

For each repetition period, the stored theoretical value of the spectral characteristic is compared with the measured light transmittance values at the plurality of different wavelengths to estimate the nth film thickness for each repetition period. And when the actually measured value becomes a simulation theoretical value of the target film thickness of the nth layer, outputting an instruction to stop the formation of the nth layer in the thin film forming apparatus,

The actual measurement of the light transmittance value is performed by a wavelength tunable laser and a device that photoelectrically converts received light,

During the formation of the nth layer of the subassembly, the wavelength tunable laser is formed by outputting a plurality of light of different wavelengths with a wavelength interval of 0.01 nm or less within the optical wavelength band at the repetition period. Irradiating the sub-assembly of

The photoelectric conversion device receives a transmission component of light from the wavelength tunable laser irradiated to the subassembly being formed, and obtains an actual measured value of light transmittance at the plurality of different wavelengths for each repetition period. And

(B) During the formation of the Fabry-Perot structure reflecting band layer and spacer layer as the m-th layer of the sub-assembly of the optical multilayer structure, which is composed of m layers, the predetermined wavelength is applied by the wavelength tunable laser. Illuminating the sub-assembly of the m layer being formed with a light output of a fixed wavelength, which is the central wavelength of the bandwidth,

The photoelectric conversion device obtains measured values of the light transmittance of the m-layer subassembly being formed at the fixed wavelength at predetermined time intervals,

When an amount of change of the actual measurement value is obtained for each time interval based on the actual measurement value of the light transmittance of the m-layer subassembly at each time interval, and an extreme value in the transition of the change in the actual measurement value is detected The formation of the mth layer in the thin film forming apparatus is stopped,

A method in which the wavelength tunable laser is set to a wavelength tunable mode when the nth layer is formed, and the wavelength tunable laser is switched to a fixed wavelength mode when the mth layer is formed.
2. The manufacturing method according to claim 1, wherein the optical multilayer structure is a bandpass filter.
A method for producing an optical multilayer film structure having a 5 dB bandwidth of 0.6 nm or less.

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