JP2004354372A - Optical thin film forming apparatus mounted with film thickness measuring apparatus and optical thin film forming method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem that a conventional method of controlling a film thickness at the time of NBPF production in an NBPF manufacturing process is different from an evaluation method after NBPF production.
SOLUTION: Based on a film design for obtaining desired optical characteristics, spectral characteristics at various thicknesses of each layer are calculated in advance as theoretical values, and the theoretical values and the actually measured spectral characteristics at the time of film formation are sequentially calculated. In order to compare and control the film thickness, the wavelength of the measurement light projected onto the film formation substrate is swept, and the spectral characteristics of the film formation substrate are actually measured. Specifically, a wavelength-tunable laser that sweeps the wavelength of the measurement light projected on the film-forming substrate receives light transmitted or reflected by the film-forming substrate, and synchronizes the light received in synchronization with the wavelength sweep of the wavelength-tunable laser. A photodetector for measuring spectral characteristics that performs photoelectric conversion and output, an optical power meter that measures and outputs the transmittance or reflectance of the film-forming substrate in synchronization with the output of the photodetector for measuring spectral characteristics, and an output of the optical power meter The spectral characteristics of the film-forming substrate are read from the transmittance or the reflectance, and are compared with the theoretical values. In addition, a method for alternatively selecting a monochromatic measurement method and a spectral characteristic method is also provided.
[Selection diagram] FIG.

Description

The present invention relates to an optical film thickness measuring device to be mounted on an optical thin film forming apparatus, and introduces a spectral characteristic measuring method used for optical characteristic evaluation after forming an optical thin film into a film thickness controlling method, thereby achieving high precision. 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 is used inside the optical multiplexer / demultiplexer. Optical specifications such as transmission bandwidth, flatness, transmission loss, and suppression ratio with adjacent wavelengths required for a narrow band pass filter (hereinafter referred to as NBPF) having a dielectric multilayer structure are described in It is a strict value in order to realize high speed and large capacity. FIG. 1 and Table 1 show an example of optical specifications required for the NBPF for 50 GHz (international telecommunications union: wavelength interval specified by ITU). The transmission loss in the transmission band is required to be 1.0 dB or less, the flatness in the transmission band is required to be 0.4 dB or less, and the rectangular characteristic of the waveform is required to be 0.5 dB bandwidth: 0.25 nm or more and 25 dB bandwidth: 0.6 nm or less. Have been.

The NBPF is one of the applied products of optical thin film utilizing light interference, and its structure is to alternately deposit high and low refractive index dielectric materials and use multiple reflection from the layer interface to achieve desired filtering characteristics. Is what you get. FIG. 2 shows the basic structure of the NBPF. The optical film thickness of each layer is λ / 4 with respect to the transmission wavelength: λ, ie, λ / 2 for a pair of a high refractive index substance (29) and a low refractive index substance (30). By forming a multilayer such that the reflection band layer (31) is added, the reflected light from the layer interface is added in phase. There are two reflection band layers (31), and a spacer layer (32) having an optical thickness of an integral multiple of λ / 2 is disposed between the two reflection band layers (31) to form a filter having a Fabry-Perot structure and face each other to form a cavity (33). . In order to satisfy the above optical specifications, the NBPF has a multi-cavity structure in which a filter having a Fabry-Perot structure is connected in a plurality of stages via a coupling layer (34), and has a multilayer structure of 100 or more layers. Furthermore, unless the optical film thickness of each layer is controlled with an accuracy of 0.01% or less, the above optical specifications cannot be satisfied.

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, a method for controlling the optical film thickness of 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

Is represented by Figure 3 is an optical film thickness when a refractive index of the transparent substrate is 1.52: n m _· d and reflectance: shows the relationship of R. _N g with the interference of light <For _{n m} energy reflectivity: R is _increased, n g> but when _{n m} decreases _Conversely, both the extreme value _{n m · d = λ / 4} . Thus, the optical film thickness: Energy reflectance for each n m _· d is an integer multiple of lambda / 4 (transmittance): R is an extreme value. The thickness control of each layer in the manufacture of the NBPF is performed at this extreme value.

FIG. 4 shows a configuration diagram of an NBPF vacuum film forming apparatus equipped with a conventional optical film thickness measuring apparatus. The vacuum vessel (1) is evacuated to a level of 1 × 10 ⁻⁵ Pa by a vacuum pump such as an oil diffusion pump or a cryopump (not shown). The film-forming 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 uniform the film thickness distribution in the substrate. Heated by a heating sheath heater (7) and a halogen heater (21). The temperature of the film-forming substrate (6) is measured using a radiation thermometer (17), and the measured data is input to a temperature controller (18), and the temperature controller (18) receives a preset temperature. And the measured temperature are compared and calculated, and based on the result, the power for the halogen heater is adjusted so that the substrate temperature is always kept constant even when the deposition substrate (6) receives the radiation heat from the electron beam or the heat generated during the plasma generation. Control the vessel (19) (JP 2002-229025).

An electron beam evaporation source (2) is used for forming a dielectric film which is an optical thin film. At this time, when high-frequency power (frequency: 13.56 MHz) output from the high-frequency power supply (22) is directly applied to the substrate dome (5), glow discharge occurs in the space between the substrate dome (5) and the evaporation source (2). In the plasma state, a self-induced negative DC electric field is generated on the surface of the film-forming substrate (6) attached to the substrate dome (5), and a thin film having a high filling density is formed by the high energy (particularly). No. 2001-73136).

The matching box (23) matches the output impedance of the high-frequency power supply (22) with 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 an electron beam evaporation source controller (not shown) to keep the film formation rate constant. The optical film thickness measuring device mainly comprises a laser light source (11), an optical fiber (13), an emission tube (14), a monochromatic photometric light receiving device (15), and a controller (10). The laser light (monochromatic light) emitted from the laser light source (11) passes through a depolarizer (12), an optical fiber (13), an emission tube (14), and a lower viewing window (8) to form a film forming 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, which is changed according to the thickness of the optical thin film deposited on the film forming substrate (6), is photoelectrically converted into an electric signal by the monochromatic photometric light receiver (15). The controller (10) performs arithmetic processing on the photoelectrically converted electric signal, and when the transmittance reaches an extreme value of λ / 4, closes the shutter (3), terminates the film formation, and sequentially laminates the dielectric substance. I will do it.

FIG. 5 is a detailed view of the film forming substrate (6). An anti-reflection film (36) for reducing interference between incident light and reflected light is formed on the back surface of the film-forming substrate (6), and a point where laser light is incident on the surface of the film-forming substrate (6). Is defined as a reference point (37), and the point at which the laser beam reflected on the back surface of the film-forming substrate (6) returns to the surface of the film-forming substrate (6) is defined as a reflection point (38). The back surface of the film-forming substrate (6) is inclined so that the distance is longer than the wavelength of the laser light, thereby preventing the light reflected on the back surface of the film-forming substrate (6) from returning to the incident optical path (Japanese Patent Application No. 2006-110630). 2002-229025).

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

This problem will be described with reference to FIG. Conventional film thickness control by monochromatic photometry is equivalent to monitoring the film thickness at the center wavelength of the NBPF, 1550.0 nm in FIG. If the result of the spectral characteristics of the NBPF formed on the substrate is normal as shown by the solid line (47) in FIG. 6, there is no problem. However, as shown by the dotted line (48), the spectral characteristics are good. If there is an abnormality, it is impossible to determine the abnormality by the conventional monochromatic photometry in which the film thickness is monitored only at the wavelength of 1550.0 nm. Further, the film thickness control by the monochromatic photometric method, the film thickness: are those n m _· d transmittance for each an integral multiple of lambda / 4 is utilized to an extreme value, monitoring the change in transmittance Therefore, in a layer having a small change in transmittance, an error is likely to occur in extreme value detection, and as a result, there is a problem that the optical characteristics of the NBPF deteriorate. In order to solve the problem, the applicant has changed the output of the laser light source, and in a layer having a small change in transmittance, the intensity of the laser beam is increased to increase the change in the amount of transmitted light, and the accuracy of the film thickness control by the extreme value detection is increased. (Japanese Patent Application No. 2003-282837).

FIG. 19 shows a result of simulating the transmittance change of each layer in the NBPF. In the figure, the horizontal axis indicates the layer number, and the vertical axis indicates the transmittance. The layer number indicates the number of the layer counting from the glass substrate, and the layer numbers 1 to 15, 17 to 31, 33 to 47, and 49 to 63 indicate the reflection band layers, and the layer numbers 16 and 48 indicate the spacer layers. , Layer number 32 indicates a bonding layer. The method disclosed 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 an originally large amount of transmitted light such as a coupling layer is formed. When a film is formed, there is a limit to the change in 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 an extreme value.

In the conventional NBPF manufacturing process, the above problem occurs because the method of controlling the film thickness at the time of NBPF preparation and the method of evaluation after NBPF preparation are different. The present invention introduces a spectral characteristic measurement method, which is an evaluation method after the NBPF is created, into the film thickness control method at the time of the NBPF creation, so that the spectral characteristics of the NBPF that cannot be distinguished by the monochromatic photometry are constantly measured during film formation. It is another object of the present invention to provide a new type optical film thickness measuring device that controls the film thickness based on the change in the spectral characteristics of the NBPF.

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

Is represented by N is the complex refractive index, d is the thickness of the thin film, and θ is the angle of incidence 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。 Also, since the multilayer film is expressed as the product of a four terminal matrix for each layer

Next, the amplitude transmittance of the multilayer film: tau and energy transmission: T is the refractive index of the element and the medium of four-terminal matrix: N ₀ and the refractive index N _S of the substrate

Is plotted, and spectral characteristics are obtained by plotting transmittance against wavelength.

A second means for achieving the above object is to store a theoretical value of a spectral characteristic at a film thickness including at least a target film thickness value of an optical thin film having a desired spectral characteristic, In order to control the film thickness by successively comparing the measured values of the spectral characteristics of the thin film sample, light of a wide band and multiple wavelengths is projected onto the thin film sample, and the wavelength of light transmitted or reflected by the thin film sample is swept, and the spectral characteristics of the thin film sample are Is actually measured. More specifically, a broadband light source that projects broadband and multi-wavelength light onto a thin film sample, an optical spectrum analyzer that receives light transmitted or reflected by the thin film sample and measures the spectral characteristics of the thin film sample, and an optical spectrum analyzer What is necessary is just to include 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 unit that controls film formation according to the comparison result of the computer. The 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 to 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. Means for switching between film thickness control by spectral characteristic measurement and film thickness control by monochromatic photometry are provided, and film thickness control is performed by appropriately selecting a spectral characteristic measuring method or a monochromatic photometric method during film formation.

In the present invention, by introducing a spectral characteristic measuring method to the film thickness control method of the optical thin film, the spectral characteristics of the optical thin film which cannot be determined by the film thickness control method using only monochromatic photometry can be constantly measured during film formation. This makes it possible to perform highly accurate film formation.

FIGS. 9 to 12 show the spectral characteristics of the optical film thickness in the coupling layer, spacer layer and reflection band layer of the second cavity, using a two-cavity NBPF composed of first and second cavities as a subject. The result of the simulation is shown. In the figures, a to e show how the optical film thickness changes to 0, λ / 16, λ / 12, λ / 8, λ / 4, with the optical film thickness being 0 at the start of film formation of each layer. In the simulation, Ta ₂ O ₅ is used as a high-refractive-index substance and SiO ₂ is used as a low-refractive-index substance. The center wavelength is λ = 1550.00 nm, and the optical film thickness λ / 4 of Ta ₂ O ₅ and SiO ₂ is H, respectively. When L is assumed, an NBPF having a film configuration 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 film formation of Ta ₂ O ₅ and SiO ₂ as optical thin film materials using the vacuum film forming apparatus for NBPF 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 reflection band layer immediately after the spacer layer, and FIG. 12 shows the spectral characteristics of the final reflection band layer. Is the result of simulation. FIG. 9 shows that a coupling layer is formed on a first cavity (33) including a reflection band layer (31), a spacer layer (32), and a reflection band layer (31) formed on a glass substrate. At this time, a state where the transmission loss of the subassembly A including the first cavity (33) and the coupling layer changes as the coupling layer film grows. When there is no coupling layer film (the film thickness is 0), the transmission loss is curve a, and as the coupling layer film thickness becomes λ / 16, λ / 12, λ / 8, λ / 4, the transmission loss becomes b, It changes to c, d, and e. At this 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 at the center wavelength of 1550.0 nm. In the film thickness, the peak of the transmission loss curve is shifted from the center wavelength of 1550.0 nm.

FIG. 10 shows that after forming a reflection band (31) on the above-described sub-assembly A including the first cavity and the coupling layer, a further 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 sub-assembly A, the sub-assembly B including the reflection band layer and the spacer layer changes as the spacer layer film grows. In this case, the transmission loss curves a, b, c, d, and e all have a peak at a wavelength of 1550.0 nm.

FIG. 11 shows the subassembly 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 subassembly B. 7 shows transmission loss characteristics of a subassembly C including a first layer. As in FIG. 10, 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 last layer of the two-cavity NBPF assembly) is formed after the reflection band layer is superimposed on the above subassembly C. As in FIG. 9, the peak of the transmission loss curve changes as the film grows.

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 layer at an arbitrary film thickness can be simulated. For example, FIG. 13 shows a result of simulating the spectral characteristics of an NBPF having a 172 layer structure.

The present invention mounts a spectral characteristic measuring device on an optical thin film forming apparatus, constantly measures changes in spectral characteristics during the film forming process, and controls the film thickness while sequentially comparing the obtained measurement data and simulation results. Is what you do. The film formation is completed when a target range of the spectral characteristics is set in advance based on the simulation result, and the measured data falls within the target range. In the case shown in FIGS. 9 to 12, it is sufficient to control the transmission loss curve e. Referring to FIGS. 9 to 12, a layer in which the peak of the transmission loss curve is constant during the film growth as shown in FIGS. 10 and 11, and a layer in which the peak changes as shown in FIGS. 9 and 12. There is. In a layer where the peak of the transmission loss curve changes during the process of film growth, a change in the spectral characteristic is easily observed. Therefore, the spectral characteristic measurement method is particularly effective for a layer where the peak of the transmission loss curve changes.

7 and 8 are schematic diagrams of the spectral characteristic measuring device. FIG. 7 shows a system in which the wavelength is swept on the light source side using a wavelength variable laser (39) as a light source and an optical power meter (40) on a light receiving side. FIG. 8 shows a method of sweeping the wavelength on the light receiving side using a broadband light source (45) as a light source and an optical spectrum analyzer (46) on the light receiving side. Both methods can measure the spectral characteristics of NBPF. In the drawing, (43) indicates a measurement substrate, (42) indicates a light receiving side collimator, and (44) indicates a light emitting side collimator.

Hereinafter, a first configuration mode of the present invention will be described. In the first configuration, the spectral characteristics of the substrate at the time of film formation are measured by performing a wavelength sweep on the light source side. FIG. 14 is a schematic diagram when the spectral characteristic measuring apparatus shown in FIG. 7 is mounted on the vacuum film forming apparatus for NBPF shown in FIG. The same components as those of the conventional device are denoted by the same reference numerals, and description thereof is omitted. In the figure, (11) indicates a tunable laser that performs a wavelength sweep, (49) indicates a disturbance light cut filter that removes optical noise, and (27) indicates a film-forming substrate in synchronization with the wavelength sweep of the tunable laser (6). 2 shows an optical power meter for measuring the transmittance of the optical power meter. The disturbance light cut filter (49) prevents light generated by plasma generation, light generated during electron beam evaporation, and light emitted by the halogen heater (21) from entering the spectral characteristic measuring receiver (25) as optical noise. I have. As the disturbance light cut filter (49), for example, a band-pass filter in which high-refractive-index substances and low-refractive-index substances are alternately laminated is used to reduce light incident on the photodetector near the measurement wavelength. It becomes possible.

FIG. 15 shows a flowchart at the time of measuring the spectral characteristics. At the time of measuring the spectral characteristics, since the wavelength tunable laser (11) repeats the wavelength sweep, it is necessary to perform initial setting of the sweep wavelength range and the sweep wavelength interval (S1). Assuming that 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) is λ ₁ , λ ₁ + Δλ, λ ₁ + 2Δλ, λ ₁ + 3Δλ, ... repeatedly emits a wavelength of λ _2.

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-forming substrate, is reflected by the translucent mirror (26), and is incident on the spectral characteristic measuring light receiver (25) via the disturbance light cut filter (49). The spectral characteristic measuring light receiver (25) photoelectrically converts the received light into an electric signal and outputs the electric signal 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). Next, the wavelength tunable laser (11) emits light of the wavelength λ ₁ + Δλ (S2). Similarly, measurement of the transmittance of the deposition substrate (6) at the wavelength λ ₁ + Δλ (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. Upon completion of the wavelength sweep from lambda ₁ to lambda _2, a tunable laser (11) emits a deposition substrate (6) with light of wavelength lambda ₁ again repeated (S4) from (S2). At the same time, the computer (28) compares the measured value of the spectral characteristic 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 characteristic falls within the target range of the simulation result, the controller (10) closes the shutter to terminate the film formation. Since the target range differs depending on the specification, it may be set according to the purpose. Although the set values of the sweep wavelength range and the sweep wavelength interval are free, 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, but the wavelength sweep may be changed from the long wavelength to the short wavelength or may be changed at random.

In the apparatus shown in the figure, both a monochromatic photometric photodetector (15) and a spectral characteristic measuring photodetector (25) are provided and a wavelength tunable laser (11 ) Is shared. Further, a translucent mirror (26) is arranged at a position of 45 ° with respect to the optical axis, and one of the measuring lights transmitted through the film forming substrate (6) is incident on the monochromatic photometric light receiving device (15). The other is configured to be incident on a spectral characteristic measuring light receiver (25) via a disturbance light cut filter (49). At the time of 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 photometric receiver (15). Perform control. For controlling the film thickness of each layer, the conventional monochromatic photometric method and spectral characteristic measuring method are appropriately selected by using a switching means.

In the first configuration, the photodetector for monochromatic photometry (15) may be omitted, and switching between the monochromatic photometric method and the spectral property measuring method may be performed only by the photodetector for spectral characteristic photometry (25). In this case, the operation at the time of measuring the spectral characteristics is the same as described above. At the time of monochromatic photometry, the tunable laser (11) fixes the measurement light at a single wavelength, the optical power meter (27) measures the transmittance of monochromatic light, and controls the film thickness by monochromatic photometry. The film thickness control may be performed by appropriately selecting both the monochromatic photometric method and the spectral characteristic measuring method, or may be performed only by the spectral characteristic photometric method. Further, at the time of measuring the spectral characteristics, the computer (28) plots a change in transmittance at a specific wavelength, so that simultaneous photometry of the monochromatic photometric method and the spectral characteristic measuring method is possible.

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

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

According to the present invention, a method of measuring the spectral characteristics of a thin film sample by sweeping the wavelength of the actually measured light and measuring the spectral characteristics of the thin film sample during the film forming process can be arbitrarily selected between the monochromatic photometric method and the spectral characteristic measuring method during the film forming of the thin film sample And the precision of film thickness control can be significantly improved. The selection of the monochromatic photometric method and the spectral characteristic measuring method can be freely combined in accordance with various conditions, but the following combinations are considered as one proposal for forming a highly accurate NBPF film.

The description is based on a two-cavity NBPF. Referring to the change in the transmittance of each layer in the NBPF shown in FIG. 19, the change in the transmittance is large in the reflection band layer after the start of film formation on the glass substrate, and the extreme value can be detected with high accuracy. Adopt monochromatic photometry. Although the amount of change in transmittance after laminating the reflection band layer is small, the transmittance is low, so the method shown in Japanese Patent Application No. 2003-282837 is adopted, the output of the laser beam is increased, and the film thickness is controlled by monochromatic photometry. I do. Similarly, the film formation in the reflection band layer, the spacer layer, and the reflection band layer of the first cavity employs monochromatic photometry, and in the case of a layer with a small change in transmittance, the output is increased by increasing the output of the laser light source to expand the change. Perform thickness control.

Next, in the bonding layer after the formation of one cavity, as shown in FIG. 19, since the change in transmittance is small and the transmittance is high, it is difficult to improve the film thickness accuracy by controlling the output of the laser light source. According to FIG. 9, the peak wavelength of the transmission loss curve changes as the film thickness changes in the coupling layer, so that it is easy to control the film thickness by the spectral characteristic method. In forming the coupling layer, the spectral characteristic measuring method is adopted. As a result, the thickness control of the coupling layer, which had a limit in accuracy in the film thickness control using only the monochromatic photometric method, became possible by using the spectral characteristic measurement method, and the film thickness control with high accuracy was possible. You can see that.

In the reflection band layer of the second cavity, the change in the transmittance becomes large again, so that the monochromatic photometry is adopted. After that, the amount of change in transmittance becomes smaller, but by controlling the film thickness while controlling the output of the laser light source in the same manner as described above, the monochromatic photometry method is also used for the reflection band layer, the spacer layer, and the reflection band layer of the second cavity. I do. However, the spectral characteristics 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 the NBPF.If only the center wavelength is monitored in the final layer, the defect shown in FIG. This is because it is necessary to check the characteristics. In the final layer, the film formation is terminated when the spectral characteristics satisfy the standard of the NBPF filter characteristics of the finished product by using the spectral characteristics measuring method. Alternatively, when the final layer of the second cavity is completed by monochromatic photometry and a correction film that adjusts the two-cavity NBPF formed to the final layer to the desired filter characteristics is added, the formation of the correction film is checked by spectral characteristics. May be performed.

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

According to the present invention, the problem that the control of the film thickness of a layer having a small transmittance change and a high transmittance tends to cause an extreme value detection error and fail to obtain a desired optical property has been solved by the spectral property measurement method. By controlling the film thickness by appropriately selecting the monochromatic photometric method, the film thickness can be controlled with high precision.

Description of the operation and operation of the embodiment Based on the above-described embodiment, an NBPF having a 5-cavity configuration for 50 GHz was produced by using both the monochromatic photometry method and the spectral characteristic measurement method. The prepared NBPF uses an optical thin film material of Ta ₂ O ₅ and SiO ₂ , and their optical film thickness is deposited and controlled at λ / 4 (λ: 1550 nm). Assuming that 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 of atmosphere And

The film thickness is controlled by using the spectral characteristic measurement method in the reflection band layer farthest from the spacer layer, where the rate of change of the center wavelength with respect to the film thickness change is large in the simulations shown in FIGS. 9 to 12, and by monochromatic photometry in the other layers. Was used. Specifically, film formation was performed using the monochromatic photometry method up to the 172th layer, and after the 172 layers were completed, a correction film was formed using the spectral characteristic measurement method. The film forming conditions are as follows: the temperature set at the temperature controller (18) is 400 ° C., 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 pressure was maintained at 1.5 × 10 ⁻² Pa, and the film formation rates of Ta ₂ O ₅ and SiO ₂ were 0.4 nm / sec and 0.8 nm / sec, respectively.

FIG. 16 (51) shows the result of measuring the spectral characteristics after the 172nd layer is completed. The transmission loss was -1.2 dB, and the flatness was 0.6 dB. It can be seen that a large deviation from the design value (50) occurred and did not satisfy the optical specifications. (52) of FIG. 17 shows the result of performing the correction film formation using the H material by using the spectral characteristic measuring method in order to improve the spectral characteristic. Changes in spectral characteristics during film formation were sequentially compared with design values obtained by simulation, and the film formation was terminated at a point closest to the design value (50). 16 that the transmission loss is improved by 25% to -0.9 dB, the flatness is improved by 60% or more, and a good spectral characteristic satisfying the optical specifications of 0.2 dB is obtained.

FIG. 18 shows the result of taking out the film-forming substrate (6) into the air after the film formation and measuring the spectral characteristics using an optical spectrum analyzer. As shown in the figure, -0.5 dB width: 0.297 nm, -25 dB width: 0.53 nm, and flatness: 0.1 dB, and good results satisfying the optical specifications were obtained even in the atmosphere.

Conventionally, the film formation that fails to satisfy the optical specifications and fails can be satisfied by the present invention. In the above example, the formation of the correction film after the completion of the 172 layer was performed by checking the spectral characteristics. However, the spectral characteristics were checked at the time of forming the 172 layer, and the 172 layer film that could obtain the target filter characteristics was obtained. It was also possible to control the formation of.

Further, by controlling the film formation based on the spectral characteristics at the time of forming the coupling layer between the cavities, an NBPF with more accurate 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 the film formation, the film formation was performed by checking the spectral characteristics, whereby a more accurate NBPF finished product was obtained.

Description of other examples, description of diversion examples to other applications In the above example, the creation of an NBPF was described, but the present invention is not limited to film formation of NBPF, and film formation of other optical thin film elements Control is also possible. In the above embodiment, the transmittance is measured, but the reflectance may be measured.

The figure which shows the spectral characteristic of NBPF. FIG. 3 illustrates a film configuration 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 the general structure of the film-forming apparatus mounted with the conventional optical film thickness measuring device. FIG. 4 illustrates details of a deposition substrate. FIG. 4 illustrates a monochromatic photometric method and a spectral characteristic measuring method. FIG. 3 illustrates a spectral characteristic measurement device. FIG. 3 illustrates a spectral characteristic measurement device. The figure which shows the spectral characteristic of the 2 cavity NBPF coupling layer by a 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 reflection band layer by a simulation. The figure which shows the spectral characteristic of the 2 cavity NBPF last layer by a simulation. The figure which shows the spectral characteristic of the 172 layer NBPF by simulation. FIG. 1 is a diagram showing a schematic configuration of a film forming apparatus equipped with an optical film thickness measuring apparatus of the present invention. FIG. 4 is a diagram illustrating a flowchart when measuring spectral characteristics according to the present invention. The figure which shows the data at the time of performing actual film-forming using the conventional optical film thickness measuring device. FIG. 4 is a view showing data when actual film formation is performed using the optical film thickness measuring apparatus of the present invention. FIG. 4 is a diagram showing data measured in the atmosphere after actual film formation is performed using the optical film thickness measurement device of the present invention. The figure which shows the simulation of the transmittance | permeability change of each layer in NBPF.

Explanation of reference numerals

DESCRIPTION OF SYMBOLS 1 Vacuum container 2 Electron beam evaporation source 3 Shutter 4 Crystal 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 Exit tube 15 Monochromatic photometric receiver 16 Viewing window 17 Radiation thermometer 18 Temperature controller 19 Power supply for halogen heater 20 Low-voltage introduction electrode 21 Halogen heater 22 High-frequency power supply 23 Matching box 24 High-pressure introduction electrode 25 Spectral characteristic measurement receiver 26 Half Transparent mirror 27 Optical power meter 28 Computer 29 High refractive index substance
Reference Signs List 30 low refractive index material 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 tunable laser 40 optical power meter 41 optical fiber
42 Receiver collimator 43 Measurement substrate 44 Projector collimator 45 Broadband light source 46 Optical spectrum analyzer
47 Spectral characteristics at normal operation 48 Spectral characteristics at abnormal operation 49 Disturbance light cut filter 50 Design value of NBPF for 50 GHz 51 Spectral characteristics at the end of the 172th layer using monochromatic photometry 52 Correction film formation using spectral characteristics measurement Characteristics after performing

Claims (17)

  In an optical film thickness measuring device mounted on a thin film forming apparatus, a tunable laser on a light emitting side, an optical power meter on a light receiving side for measuring spectral characteristics during thin film formation, and actual measured values of spectral characteristics and at least a target. An optical film thickness measuring device comprising means for sequentially comparing theoretical values of spectral characteristics with respect to film thickness including film thickness value and outputting a signal for film thickness control.   In the optical film thickness measuring device mounted on the thin film forming apparatus, a broadband light source on the light projecting side, an optical spectrum analyzer on the light receiving side for measuring spectral characteristics during thin film formation, and actual measured values of spectral characteristics and at least a target film An optical film thickness measuring apparatus comprising means for sequentially comparing theoretical values of spectral characteristics with respect to film thickness including a thickness value and outputting a signal for controlling film thickness. A theoretical value of the spectral characteristic at a film thickness including at least a target film thickness value of the optical film having a desired spectral characteristic is stored, and the theoretical characteristic value is sequentially compared with an actual measured value of the spectral characteristic during film formation. An optical thin film forming apparatus for controlling a film thickness,
A wavelength tunable laser that sweeps the wavelength of the measured light projected on the thin film sample,
Optical power meter means for receiving light transmitted or reflected by the thin film sample, photoelectrically converting the received light, and actually measuring the spectral characteristics of the thin film sample;
A computer that reads the spectral characteristics of the thin film sample output from the optical power meter and compares the spectral characteristics with the theoretical value; and a control unit that controls film formation according to the comparison result of the computer. Equipment for forming optical thin films. The wavelength tunable laser includes means for fixing the wavelength of the actually measured light, and means for switching between wavelength sweeping and fixed wavelength of the actually measured light,
The optical thin film forming apparatus includes a monochromatic photometric light receiving device that receives monochromatic light transmitted or reflected by the thin film sample, and a controller that measures the transmittance or the reflectance of the thin film sample and measures the film thickness. ,
4. The apparatus for forming an optical thin film according to claim 3, wherein when the wavelength variable laser emits monochromatic light, film thickness control is performed using the monochromatic photometric light receiver and the controller.   The light receiving device for measuring spectral characteristics is provided with a disturbance light cut filter in which a high refractive index material and a low refractive index material are alternately laminated on a light incident surface. Equipment for forming optical thin films.   A translucent mirror is arranged on the optical path of the light transmitted or reflected by the thin film sample at a predetermined angle with respect to the optical axis, and a monochromatic photometric light is received on one of the optical axis straight line and the reflection optical path straight line by the translucent mirror. 5. The apparatus for forming an optical thin film according to claim 4, wherein the device is provided with a photodetector for measuring spectral characteristics on the other side.   The apparatus for forming an optical thin film is provided with a temperature control means for always keeping the temperature of the thin film sample constant, and the thin film sample is provided with an antireflection film on the back surface, and has a slope on the back surface side so that the surface of the thin film sample has 7. An apparatus for forming an optical thin film according to claim 3, further comprising means for preventing interference.   The optical thin film forming apparatus is configured to generate a phase difference by transmitting the depolarizer or the depolarizing plate to make the measured light in a non-polarized state further pass through a lens and condensing the light, and apply the light to the thin film sample. The apparatus for forming an optical thin film according to claim 7, which emits light. The theoretical value of the spectral characteristic of the optical thin film having a desired spectral characteristic at a film thickness including at least the target film thickness value is stored, and the theoretical spectral characteristic value is sequentially compared with the actually measured spectral characteristic value during film formation. An apparatus for forming an optical thin film that performs thickness control,
A broadband light source that projects broadband multi-wavelength light onto the thin film sample,
An optical spectrum analyzer that receives light transmitted or reflected by the thin film sample and measures spectral characteristics of the thin film sample;
A computer that reads the spectral characteristics of the thin film sample output from the optical spectrum analyzer and compares the spectral characteristics with the theoretical values; and a control unit that controls film formation according to the comparison result of the computer. For forming an optical thin film. The computer includes means for plotting a transmittance change at a specific wavelength,
10. The apparatus for forming an optical thin film according to claim 3, wherein switching to monochromatic photometry or simultaneous photometry is performed. The theoretical value of the spectral characteristic of the optical thin film having the desired spectral characteristic at the film thickness including at least the target film thickness value is stored, and the theoretical value and the actually measured value of the spectral characteristic during film formation are sequentially compared, and the film thickness control is performed. A method for forming an optical thin film,
The wavelength of the measured light projected on the thin film sample is swept,
The transmittance or reflectance of each wavelength is measured in synchronization with the wavelength sweep of the actually measured light, and the actually measured spectral characteristics of the thin film sample are read,
A method for forming an optical thin film, comprising: comparing the theoretical value and the measured value; and controlling the film forming conditions and terminating the film formation according to the comparison result. The method for forming the optical thin film, the measured light is projected on the thin film sample in a state where the coherence is weakened by changing phase characteristics and polarization characteristics,
Prevent interference between incident light and reflected light from the back surface in the thin film sample,
12. The method for forming an optical thin film according to claim 11, wherein the temperature of the thin film sample is kept constant. The theoretical value of the spectral characteristic of the optical thin film having the desired spectral characteristic at the film thickness including at least the target film thickness value is stored, and the theoretical value and the actually measured value of the spectral characteristic during film formation are sequentially compared, and the film thickness control is performed. A method for forming an optical thin film,
Broadband multi-wavelength light is projected on the thin film sample,
The wavelength of the light transmitted or reflected by the thin film sample is swept, and the spectral characteristics of the thin film sample are measured.
A method for forming an optical thin film, comprising: reading measured spectral characteristics of the thin film sample, comparing the theoretical value with the measured value, and controlling the film forming conditions and terminating the film formation according to the comparison result. In the method of controlling the film thickness when forming an optical thin film,
The spectral characteristics at a film thickness including at least the target film thickness of the optical thin film having the desired spectral characteristics are stored as theoretical values, and the measured light projected on the thin film sample is wavelength-swept to measure the spectral characteristics of the thin film sample. Film thickness control means by actual spectral characteristic measurement to control the thickness of the optical thin film by successively comparing the theoretical value and the actual measured value of the spectral characteristic during film formation,
Thickness control means for projecting monochromatic light on the thin film sample and controlling the thickness of the optical thin film from a change in transmittance or reflectance of the thin film sample by monochromatic photometry,
14. The film thickness control method according to claim 11, further comprising means for switching between film thickness control by actual measurement of the spectral characteristics and film thickness control by the monochromatic photometry during film formation. The spectral characteristics of the optical thin film having the desired spectral characteristics at the film thickness including at least the film thickness target value are stored as theoretical values, and the theoretical values and the actually measured values of the spectral characteristics during film formation are sequentially compared, and the optical thin film A system for controlling the film thickness,
Means for sweeping the wavelength of the actually measured light projected on the thin film sample,
Means for measuring the transmittance or reflectance of the thin film sample in synchronization with the wavelength sweep;
Means for reading the transmittance or reflectance of the thin film sample as an actual measurement value and comparing the theoretical value, and a control device for film formation,
The controller according to claim 1, wherein the controller stops the film formation when the measured value falls within a target range of a theoretical value. A monochromatic photometry method in which a monochromatic light is projected on a thin film sample, the change in transmittance or reflectance is monitored, and the film thickness is controlled by detecting an extreme value;
The spectral characteristics of the optical thin film having the desired spectral characteristics at a film thickness including at least the target film thickness value are stored as theoretical values, and the wavelength of the actually measured light projected on the thin film sample is swept to measure the spectral characteristics of the thin film sample. Then, by successively comparing the theoretical value and the actually measured value of the spectral characteristics during film formation, the NBPF film forming film thickness is controlled by selectively selecting the spectral characteristic method of controlling the film thickness of the optical thin film. The method,
When forming a layer having a large change in transmittance during film formation or a layer having a small change in transmittance during film formation and a low transmittance, the monochromatic photometry is performed while controlling the output of a laser light source. Control the film thickness using
A film forming method for an NBPF, wherein the film thickness is controlled using the above-described spectral characteristic measurement method when forming a layer having a small change in transmittance and a high transmittance. A reflection band layer, a spacer layer, a method for forming a NBPF formed from a bonding layer,
When forming the reflection band layer and the spacer layer, the film thickness is controlled using a monochromatic photometric method,
A film forming method for an NBPF, wherein the film thickness is controlled by using a spectral characteristic measuring method at the time of forming a bonding layer and at the final stage of NBPF production.

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