JP2003202420A - Multi-layered film filter, and method and system for film formation control - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a multi-layered optical filter which improves the maximum permissible error of optical film thickness while suppressing the number of stacked layers. <P>SOLUTION: The multi-layered optical filter 1 is formed by stacking optical films 3a<SB>1</SB>to 3aN and for obtaining a specified wavelength characteristic in a target wavelength band. The optical film thickness of at least one layer among the optical films 3a<SB>1</SB>to 3aN is optimized and the optical film thicknesses of the optical films 3a<SB>1</SB>to 3aN are designed on the basis of a basic film thickness which is (2n+1)/4 times (n: a natural number larger than 1) as large as a center wavelength set to 1/2 to 3/2 time as large as the target wavelength band so that the specified wavelength characteristic is obtained. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multilayer optical filter used for optical communication, a film forming control method and system therefor.

[0002]

2. Description of the Related Art With the advent of the broadband era, it is required to further increase the amount of data transmission. At present, WDM (Wave) that multiplexes and transmits optical signals of different wavelengths is transmitted.
There are great expectations for lengthDivision Multiplexing (wavelength division multiplexing) communication systems.

One of the key devices in this WDM communication system is an optical filter that optically acts on incident light. For example, as an optical filter, an optical band-pass filter (Band Pass Filter; BPF) that passes only light of a desired wavelength band set in advance from incident light in which different wavelengths are multiplexed, and EDFA (Eribium Doped
Gain flattening filter (Gain Flattenin) that flattens the output of an optical fiber amplifier such as
g Filter; GFF) etc.

As this type of optical filter, a multi-layer film filter composed of a plurality of dielectric multi-layer films having different refractive indexes is known. According to this multilayer filter, desired wavelength transmission characteristics can be obtained by appropriately setting the film thickness and refractive index of each layer.

As a multilayer film filter, that is, a film forming method and apparatus for producing a multilayer film, optical films (filter films, hereinafter also referred to as thin films) are sequentially formed on a substrate by using, for example, a vacuum deposition method or a sputtering method. Lamination methods and devices are known.

As described above, the multilayer filter obtains a desired filter characteristic (target loss wavelength characteristic) depending on the film thickness of each optical film layer forming the multilayer film. Highly accurate design and film formation are required.

For this reason, it is necessary to constantly measure the optical film thickness in parallel with the film forming process, and perform control to accurately stop the film forming process when the measured optical film thickness reaches a desired value. An example of this film formation control method is a B / A control method.

For example, according to the B / A control method, the thin film being generated is irradiated with the monitor light, and the change in the transmittance of the monitor light transmitted / reflected from the thin film is measured. This change in transmittance is
It can be expressed as a function of only the physical film thickness of the thin film. Since this change in transmitted light rate is a periodic function with respect to time, the ratio (B / A) of the change B from the extreme value of the amount of stop light to the upper and lower widths of the periodic waveform can be theoretically expressed.

Therefore, the optical film thickness can be replaced with the above B / A, and the film formation is stopped when the B / A value based on the actual change in transmittance matches the B / A value corresponding to the desired film thickness. By doing so, the film thickness during film formation is set to a desired film thickness.

[0010]

However, in a multilayer optical filter, in general, more optical film layers are required to obtain wavelength loss characteristics having steeper loss variation with respect to wavelength. However, for the reasons described above, it is very difficult to design a multilayer optical filter as the number of layers increases. Therefore, it takes time to optimize the film thickness to obtain the desired optical characteristics.

Further, when the multilayer optical filter is manufactured, if the error between the design optical film thickness of each layer and the actually formed optical film thickness exceeds the maximum allowable error, the target loss wavelength characteristic is realized. become unable.

As the number of layers of the multilayer optical filter increases, the maximum permissible error of the optical film thickness that can obtain the characteristics close to the target loss wavelength characteristics becomes smaller, and the accuracy of film formation control is required. Therefore, it is difficult to produce a multilayer optical filter having the target loss wavelength characteristic.

On the other hand, FIG. 15 is a graph showing an example of the result of film formation using the conventional film formation control method.

The data shown in FIG. 15 was produced by alternately laminating thin films of _two film forming materials (Ta ₂ O ₅ , SiO ₂ ) having different refractive indexes on a glass substrate as a film forming object. GFF
Data. From this data, within the signal band (Fig.
In the above, there is a large deviation between the design value (design data) of 1529 nm to 1561 nm) and the actual characteristic data. The flatness (Flatness), which is a measure of this loss deviation, is a value obtained by subtracting the minimum deviation from the maximum deviation, and reaches 2.514 dB in FIG.

When a GFF is manufactured, the required flatness (loss deviation) value varies depending on the case, but in general, a product satisfying 1.0 dB or less can be used as a product. Therefore, the GFF shown in FIG. 15 had a loss deviation of 2.541 dB and could not be used as a product.

Factors that greatly differ from the waveform based on the design value data (optical loss characteristic waveform) and the waveform of the optical loss characteristic of the actually formed filter will be examined.

Here, the actually desired film thickness (desired film thickness)
The difference between the film thickness and the actually deposited film thickness is called an error.

By controlling by the conventional film formation control method,
Theoretically, it is possible to stack accurate film thickness,
Actually, it is considered that an error has occurred. It is considered that due to this error, the film thickness of each layer differs from the desired film thickness, and the waveform is distorted. Among these phenomena, there are random errors that occur randomly,
Under a certain condition, there are two phenomena of an error (steady-state error) which is fixed to some extent. Hereinafter, an example of factors that are expected to cause a steady error will be described.

The first possible factor is the time constant of the optical system for outputting monitor light. The time constant of this optical system is
It is possible to investigate by monitoring the response when the optical axis of the monitor light is blocked / released.

Generally, an optical system includes a photodetector (O / E converter) for receiving monitor light and converting it into an electric signal, a lock-in amplifier for removing noise, and the like, and its constituent elements themselves. The time constant that is possessed occurs. Therefore,
The change in the light amount of the monitor light during vapor deposition (film formation) is slightly delayed by the above time constant as compared with the change in the actual light amount. Since the film formation control is performed on the basis of the delayed change in the amount of light, the film formation control (stop control) itself is slightly delayed, and the film is formed thicker by the delay.

The next possible factor is delay in signal processing. That is, due to the influence of the signal processing structure based on the program incorporated in the control device (computer) that executes the film formation control, the signal processing capacity of the control device itself, the interface, etc. The film formation stop time is always delayed. It is conceivable that the vapor deposition is thick due to this delay.

Further, as another factor, the influence of mechanical operation can be considered. That is, the conventional film forming process stop operation is
By closing the shutter provided above the film formation source, the film formation material evaporated from the film formation source is prevented from being attached to the film formation substrate.

At this time, it takes a certain amount of time from when a shutter closing command is received from the control device until the shutter actually starts the shutter operation and finishes closing the shutter. It is conceivable that the film-forming substance is attached to the film-forming substrate from the film-forming source and a thick film is formed until the shutter is completely closed.

As another factor, the influence of wraparound through the shutter can be considered. That is, when the value of B / A or the like reaches the value corresponding to the desired film thickness, the corresponding shutter is closed via the control device. At this time,
Even when the shutter is closed, it is possible that the film forming material partially adheres to the substrate while the film forming material is heated by the film forming source.

The present invention has been made in view of the above-mentioned circumstances, and it is possible to obtain a wavelength loss characteristic having a steep loss variation while suppressing the number of laminated layers as compared with the prior art, and to obtain the maximum permissible error of the optical film thickness. To provide a multilayer optical filter and its designing method that can improve the
The purpose of.

Further, the present invention has been made in view of the above-mentioned circumstances, and it is possible to significantly suppress the influence of a steady-state error, which may have various factors, and to improve the characteristics of the deposited filter. A second object of the invention is to provide a control method and system.

[0027]

According to a first aspect of the present invention, there is provided a multilayer optical filter for laminating a plurality of optical films to obtain a predetermined wavelength characteristic in a target wavelength band. Then, the optical film thickness of each of the optical films is set to (2n + 1) / 4 times (n is a natural number of 1 or more) of the center wavelength set to 1/2 to 3/2 times the target wavelength band as a basic film. Designed as thick.

In the first aspect, the optical film thickness of at least one of the plurality of optical films is optimized so that the predetermined wavelength characteristic can be obtained.

In the first aspect, the optical film thickness of each optical film is a theoretical value representing the wavelength characteristics of the target wavelength band with the basic film thickness as an initial value and the optical film thickness of each optical film as a parameter. Is designed by fitting to a target wavelength characteristic set in advance in the target wavelength band.

In a second aspect of the present invention, there is provided a device for designing a multilayer optical filter, comprising a plurality of optical films laminated, for obtaining predetermined wavelength characteristics in a target wavelength band, wherein Means for designing the optical film thickness of the film with a basic film thickness of (2n + 1) / 4 times (n is a natural number of 1 or more) of the center wavelength set to 1/2 to 3/2 times the target wavelength band. Is equipped with.

According to the third aspect of the present invention, it is used in a film forming apparatus for forming a multi-layer film composed of a plurality of optical films on a film-forming object by a film-forming material emitted from a film-forming source. Match the optical film thickness of each optical film to the film thickness design value for each optical film that was previously designed using the monitor light transmitted / reflected (at least one of transmission and reflection) from the optical film. A film formation control system for controlling the film thickness of the multilayer film formed by the film forming apparatus, the storage unit storing data representing light transmission loss characteristics in a predetermined wavelength band, and the storage unit. And a film thickness error estimating means for estimating a film thickness error that constantly occurs in the optical film formed by the film forming apparatus, based on the light transmission loss characteristic data of the multilayer film, and a film thickness of each optical film. Based on design value and estimated film thickness error And a thickness control means for the film thickness control are.

In the third aspect, the film thickness error estimating means estimates the film thickness error as a deviation from the designed film thickness, and adjusts the designed film thickness so as to cancel the estimated deviation. It has and.

In the third aspect, the film thickness error estimating means is a means for estimating the film thickness error by converting it into a delay time during film formation.

In the third aspect, the film thickness error estimating means includes means for setting a plurality of delay times, and storage means for storing function data representing a light quantity change of the monitor light obtained from the designed film thickness. In the case of performing a film formation simulation of the optical film of each layer on the film formation target, a means for calculating a light amount change of the monitor light from each layer in the film formation in the simulation and a calculated light amount change are used. And means for fitting the function data to obtain the parameters of the function data of each layer, and means for calculating the film thickness of the optical film of each layer formed in the film formation control based on the function data containing the obtained parameters, When the film thickness is changed from the calculated film thickness of each layer by each delay time, a means for calculating the film thickness of the optical film of each layer for each delay time, and for each calculated delay time Means for calculating, for each delay time, data representing a light transmission loss characteristic in the predetermined wavelength band of a multilayer film composed of a plurality of optical film layers having a film thickness, and light transmission of the actually formed multilayer film The loss characteristic data and the light transmission loss characteristic data calculated for each delay time are compared, and means for obtaining an error for each delay time is compared with the obtained error for each delay time, and based on the comparison result. And means for obtaining an optimum delay time.

In the third aspect, the film thickness control means monitors the change in the light amount of the monitor light from the optical film layer being formed on the object to be formed, and the monitored change in the light amount. Means for fitting the function data using the means for finding a parameter of the function data corresponding to the optical film layer, and based on the function data including the found parameter, the optical film layer matches the film thickness design value. A means for calculating the time at the time, and a means for preventing the film-forming material from adhering to the film formation object when the current time matches the time obtained by subtracting the delay time from the calculated time. ing.

According to the fourth aspect of the present invention, it is used in a film forming apparatus for forming a multi-layer film composed of a plurality of optical films on a film-forming object by a film-forming material emitted from a film-forming source. A computer for controlling the optical film thickness of each optical film to match the film thickness design value of each optical film designed in advance by using the monitor light transmitted / reflected from the optical film can be executed. A program, a means for causing a computer to store, in a memory, data representing a light transmission loss characteristic in a predetermined wavelength band of a multilayer film actually deposited by the film deposition apparatus; and the multilayer stored in the memory. Means for estimating a film thickness error that constantly occurs in the optical film formed by the film forming apparatus based on the wavelength characteristic data of the film, film thickness design value of each optical film, and the estimated film thickness The film thickness based on the error To function as a means for performing control.

According to a fifth aspect of the present invention, there is provided a method for designing a multilayer optical filter, which comprises a plurality of optical films laminated to obtain a predetermined wavelength characteristic in a target wavelength band. The optical film thickness of each optical film is (2n + 1) / 4 times (n is a natural number of 1 or more) of the center wavelength set to approximately 1/2 to 3/2 times the target wavelength band.
Is provided as a basic film thickness.

In the fifth aspect, the designing step includes a step of optimizing an optical film thickness of at least one of the plurality of optical films so that the predetermined wavelength characteristic can be obtained.

According to the sixth aspect of the present invention, when a film forming apparatus forms a multi-layered film composed of a plurality of optical films on a film formation target by a film forming material emitted from a film formation source, A film forming control method for controlling an optical film thickness of each optical film to match a film thickness design value for each optical film designed in advance by using monitor light transmitted / reflected from the optical film. ,
Based on the wavelength characteristic data of the multilayer film stored by the step of storing data representing light transmission loss characteristics in a predetermined wavelength band of the multilayer film actually formed by the film forming apparatus, A step of estimating a film thickness error that constantly occurs in the optical film formed by the film forming apparatus, and the film thickness control based on the film thickness design value of each optical film and the estimated film thickness error. And the steps to take.

[0040]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

In the following description, simply "film thickness"
The term means an optical film thickness, and when it means a physical film thickness, it is described as “physical film thickness”.

FIG. 1 is a diagram showing a multilayer filter 1 according to the first embodiment of the present invention.

As shown in FIG. 1, the multilayer filter 1 has
The substrate 2 and a plurality of thin film layers 3 (first layer 3a1 to Nth layer 3aN) formed and laminated on the substrate 2 by a method such as vapor deposition or sputtering are provided. Of the plurality of thin film layers 3a1 to 3aN, odd layers (first layer 3a1, third layer 3a3, ..., 2N-1 layer, ...
The refractive index of the film material of the thin film layer of () and the even layers (the second layer 3a2, the fourth layer 3a4, ..., The second N layer, ...
The refractive index of the film material of the thin film layer of *) is different from each other.

The optical film thickness, which is the product of the physical film thicknesses d1 to dN and the refractive indices n1 to nN of the respective thin film layers constituting the plurality of thin film layers 3, that is, the first layer 3a1 to the Nth layer 3an, is: Each thin film layer is accurately designed based on the film thickness designing process described later.

FIG. 2 is a diagram (partially sectional view) showing a schematic structure of a film forming system 11 including a film thickness designing apparatus and a film forming apparatus according to the embodiment of the present invention.

As shown in FIG. 1, the film forming system 11 includes
A vacuum container (chamber) 12 and, for example, two film forming sources 13a1 and 1a1 arranged side by side in the vacuum container 12, for example.
3a2 and film forming sources 13a1 and 1 in the vacuum container 12
3a2 is provided on the opposite side (upper part), and is provided with the film formation substrate 16 held by the substrate holder 15.

Film forming materials are set in the film forming sources 13a1 and 13a2, and the film forming materials have different refractive indexes.

The film forming system 11 includes the vacuum container 1
Electron guns 20a1 and 20a2 for irradiating the film forming sources 13a1 and 13a2 with an electron beam to heat the film forming materials in the film forming sources 13a1 and 13a2.
And a light source 21 that outputs, for example, white light, which is a wide wavelength band light, as the measurement light ML.

Further, the film forming system 11 has a film forming source 13 in response to a shutter signal transmitted from a control device which will be described later.
Shutter devices 22a1 and 22a2 for stopping the film forming operation by covering the upper part of a1 and 13a2 and opening the upper part of the film forming sources 13a1 and 13a2 in response to the opening signal to start the film forming operation, and a light source 21. A condenser lens 23 that condenses the transmitted light when the measurement light emitted from the condensate passes through the thin film F being formed and the substrate 16, and the transmitted light condensed by the condenser lens 23 is received for each wavelength. The optical fiber bundle 24 is provided.

The optical fiber bundle 24 extends through the inside of a shield box 25, which is airtightly attached to the upper wall of the vacuum vessel 12, for example, outside the vacuum vessel.

Then, the film forming device 11 only transmits the transmitted light having the wavelength corresponding to the wavelength determining signal indicating the monitor light wavelength transmitted from the control device described later, from the transmitted light transmitted through the optical fiber bundle 24. 29 as a monitor light, a light receiver 30 for sequentially receiving the monitor light dispersed by the spectrometer 29 and outputting a light amount signal corresponding to the received light amount, and a light receiver 30 sent from the light receiver 30. Lock-in amplifier 31 that removes noise components from the light intensity signal
And spectroscope 29 and shutter devices 25a1 and 25a2
And a control device 32 that is connected for data communication.

The control device 32 receives the light amount signal output from the light receiver 30 and individually transmits the shutter signal / release signal to the shutter devices 25a1 and 25a2 in accordance with the received light amount signal to perform the control. It has a function of controlling the film thickness of the thin film layer F formed on the film substrate 16, and the like.

FIG. 3 is a diagram showing a hardware configuration of the controller 32 in the film forming system 11 shown in FIG.

As shown in FIG. 3, the control device 32 is a computer system, and converts the light amount signal output from the light receiver 30 into a digital type light amount signal (digital light amount data).
To an A / D converter 40 for converting to, an input unit 41 that a designer can operate to input information, a computer 42 connected to the input unit 41, and a communicably connected computer 42. , A memory 43 as a storage medium that stores in advance a film thickness design program P1 for executing a film thickness design process described below and a film formation control program P2 for executing a film formation control process described below, and an external connection. An external input / output interface 44 that performs interface processing relating to output is provided. As the storage medium, various storage media such as a semiconductor memory and a magnetic memory can be applied.

Further, in the memory 43, a theoretical formula data file 45 containing theoretical formula data representing the theoretical value of the light transmittance at continuous wavelengths of the N layer multilayer film filter 1, and a predetermined wavelength band, that is, GFF. The target transmission loss value data file 46 including the target transmission loss value (target value) for each predetermined wavelength step width (incremental width) in the wavelength band for transmission loss characteristics (for example, 1530 nm to 1560 nm) is stored in advance. .

The theoretical formula data stored in the theoretical formula data file 45 will be described below.

The theoretical formula of the light transmittance in the N-layer multilayer filter 1 with the optical film thickness of each of the layers 3a1 to 3aN as a parameter is that the incident angle is perpendicular (90 degrees) to the film surface of the multilayer filter 1. Assuming that there is, it is given by the equation of energy transmittance shown in the following equation (1) and the following equations (2) to (5).

[Formula 1]

[Formula 2]

[Formula 3]

[Formula 4]

[Formula 5] Here, τ in the equation (1) is represented by the equation (2), and the parameters m ₁₁ , m ₁₂ , m ₂₁ , m ₂₂ shown in the equation (2) are given.
Is each element of the characteristic matrix M in all N layers given by the equation (3), and M _j (j is an integer increasing from 1 by 1 in order such as 1, 2, ...) The characteristic matrix M _j of the j-th layer given by the total product is given by Expression (4).
G _j shown in Expression (4) is represented by Expression (5), n _j is the complex refractive index of the j-th layer, and d _j is the physical film thickness of the j-th layer.

Further, the wavelength for obtaining the transmittance is substituted for λ in the equation (5), and n ₀ and n _s are the complex refractive index of the medium and the complex refractive index of the filter substrate 2 at the wavelength λ, respectively. Further, in Expression (1), τ ^* is a conjugate complex number of τ, and i in Expressions (3) and (4) is an imaginary unit.

Therefore, by using these equations (1) to (5), the light transmission at the continuous wavelengths of the multilayer filter 1 having N consecutive layers is performed with the value of the optical film thickness of the j-th layer as a parameter. If the theoretical value of the rate is obtained and this light transmittance is converted into a light transmission loss value (insertion loss value), the light transmission loss value can be expressed using the optical film thickness and wavelength as variables (parameters).

When the entire layer on which film formation has been completed is represented by the characteristic matrix M, the change in transmittance of the layer during film formation can be represented by a function having the physical film thickness as a parameter.
When the vapor deposition rate (film forming rate) in the layer during film formation is constant, the physical film thickness is proportional to the film forming time, and thus the physical film thickness can be replaced with time.

Therefore, during film formation, the change in transmittance during film formation can be expressed as a periodic function of time.

That is, the change T in transmitted light amount during film formation (during vapor deposition) is expressed by the following equation (6) under the condition that the film formation rate in the thin film layer during film formation and the refractive index of the thin film are constant. That is, it can be expressed as a periodic function of the film formation time x.

[0063]

[Formula 6]

A ₀ and A ₁ in the equation (6) are coefficients (parameters) representing the amplitude and waveform of the periodic function, A ₂ is a parameter representing the film forming rate, and A ₃ is an initial value. It is a coefficient (parameter) representing each phase. Also,
The phase term of the periodic function is represented by (A ₂ x + A ₃ ). That is, (A ₂ x + A ₃ ) represents the phase at the current time x during the film formation described above.

That is, in the theoretical formula data file 45, the theoretical formula representing the light transmission loss value (insertion loss value) IL and the above formulas (1) to (6) are respectively stored in the theoretical formula data D.
It is stored as A.

The memory 42 stores the past wavelength characteristic data file 50 in which the data showing the wavelength characteristic (light transmission / reflection loss characteristic) of the multilayer filter actually deposited in the past by the film forming apparatus 11 is stored. Is remembered. In the configuration of the first embodiment, the past wavelength characteristic data file may be omitted. Next, the overall operation of this embodiment will be described.

In manufacturing the multilayer filter 1, first, the optical film thickness of each layer 3a1-3an of the multilayer filter 1 is designed.

In the present embodiment, the number of layers of the multilayer film is the minimum number of layers that can realize the target loss wavelength characteristic stored in the target transmission loss value data file 46. Further, in designing the multilayer film 3, in order to suppress the polarization dependence, the incident angle of the multilayer film filter 1 with respect to the film surface is set to 90 degrees, and one of the film forming materials of the multilayer film 3 is Ta ₂ O ₅ (for example, Film forming source 13
The film forming material of a1 is Ta ₂ O ₅ and the refractive index is 2.1654, and the other is SiO ₂ (for example, the film forming material of the film forming source 13a2 is
SiO ₂ ) and a refractive index of 1.4471. Further, the complex refractive index n _s of the filter substrate 2 was set to 1.5022, the refractive index of air as a medium was set to 1.0000, and there was no absorption by the substance.

That is, the designer uses the input unit 41 of the control device 31 as the characteristic calculation wavelength band, for example, GFF.
The target transmission loss value data required as is input to the computer 41 (step S1). The target transmission loss value data represents the target transmission loss characteristic,
For example, each wavelength λ _i (i is an integer increasing from 1 to N by 1 in order, which is discontinuous in the target transmission loss characteristic represented by S (a) in FIG. 6 below, i = 1, 2, 3,
, N−1, N).

Next, the designer sets the target characteristic wavelength band {1530 nm (λ _s ) as the initial value (basic film thickness) of the optical film thickness parameter (hereinafter referred to as film thickness parameter) a.
.About.1560 nm (λ _e )}, for example, a wavelength (1495 nm) that is about 0.95 times the central wavelength λ, and the central wavelength λ
7 times 1/4, that is, 7λ / 4 (1.75λ) is input (step S2).

The computer 41 operates according to the film thickness design program P1 and receives the input characteristic wavelength λi and the film thickness parameter a (initial value).

Next, the computer 41 sets the variable n to 0.
(Step S3), the variable n is incremented by 1 (step S4), and the wavelength parameter λ _n within the characteristic wavelength band is set to λ _i . Since n = 1 at this time, λ _n = λ ₁ (step S5).

Next, the computer 41 has a memory 42.
The theoretical formula data stored in the theoretical formula data file 45 is read, and the film thickness parameter a (basic film thickness = 7λ / 4)) is input to the read theoretical formula data DA. Then, the computer 41 obtains the insertion loss value IL (λ _n , a) of the multilayer film 3 of the entire N layers with the film thickness parameter a and the wavelength λ _n as variables. Then, the computer 21
Is the target transmission loss value IL (λ _n ) of the entire multilayer film 3 at the wavelength λ _n corresponding to the insertion loss value IL (λ _n , a) of the multilayer film 3.
Square error E _n (a) with:

[Formula 7] Look, the entire multilayer film 3 obtained E _n (a) memory 13
(Step S6).

Next, the computer 41 determines whether or not n> N (step S7). Since n = 1 now, the determination in step S7 is NO, the computer 41 returns to step S4, increments n by 1, and executes the processing from step S4.

That is, the computer 41 repeatedly executes the above-described processing of steps S4 to S7 until n> N, that is, until the processing of step S7 based on the wavelength parameter λ _n = λ _N is completed.

As a result, when the film thickness parameter a of each of the layers 3a1 to 3aN is set to the basic film thickness (7λ / 4), the theoretical light transmission loss value I for each step width in the entire characteristic wavelength band is obtained.
Target transmission loss value I at wavelength λ _n corresponding to L (λ _n , a)
The squared error E _n (a) with L (λ _n ) is obtained for each wavelength.

When the wavelength parameter λ _n coincides with the wavelength λ _e , the process in step S7 becomes YES, and the computer 41 adds the squared error E _n (a) of the entire multilayer film 3 in all the obtained characteristic wavelength bands. Mean value (root mean square error,
The mean square error) is calculated according to the following equation (8), and the mean square error of the calculated wavelength parameter a (basic value) is stored in the memory 42 (step S8).

[0078]

[Formula 8]

Thereafter, the computer 42 uses the film thickness parameter a (initial value = 7λ / 4) as a reference to form each layer 3a.
The fitting process is performed while changing the film thickness parameter a of 1 to 3 aN. That is, the computer 41
While individually changing the film thickness parameter a of each of the layers 3a1 to 3aN, the root mean square error of the entire corresponding multilayer film 3 is sequentially calculated to reduce the value of the root mean square error (step S9). ).

In this way, the fitting process of step S9 is sequentially repeated (steps S10 → N).
O), when the value of the root mean square error converges even if the film thickness parameter a of each of the layers 3a1 to 3aN is changed, or the transmission using the current optical film thickness values a (1) to a (N) Loss value IL (λ _{1 to} λ _N , a (1)) to transmission loss value IL (λ
_{1 to} λ _N , a (N)) and the corresponding target transmission loss value IL (λ
_{1 to} λ _N ) and the loss deviation (flatness) is a constant value (for example, 1
When it becomes less than or equal to dB), the fitting process ends (step S10 → YES).

As a result, the total number of layers is 26, and each layer 3a1
As for the optical film thickness of ˜3 aN, the design result shown in FIG. 5 was obtained based on the fundamental wavelength of 7λ / 4. In addition, in FIG.
The upper side is the medium and the lower side is the substrate.

FIG. 6 is a diagram showing the relationship between the target loss wavelength characteristic targeted by the multilayer filter 1 of the present embodiment and the loss wavelength characteristic designed by the above-described design method. In FIG. 6, the characteristic curve S (a) indicates that the wavelengths λ _i are discontinuous (i is 1, 2, 3, ..., N-1,
N) indicating the target loss wavelength characteristic, and S (b) is within the target wavelength band of the target loss wavelength characteristic (1530
nm to 1560 nm), a plurality of wavelengths λ arbitrarily selected
_Shows the loss wavelength characteristic of the multilayer filter 1 designed by the design method described in the present embodiment at _k (k is an integer that sequentially increases by 1 from 1 like 1, 2, 3, ..., N). ing.

As is clear from FIG. 6, the loss wavelength characteristic of the multilayer filter 1 designed in this embodiment has a loss wavelength characteristic very close to the above target wavelength loss characteristic.

Assuming that the center wavelength is 1327 nm and the optical film thickness of each layer of the multilayer film is 1/4 of the center wavelength, that is, 0.25 times the center wavelength, the film thickness is optimized. In this case (see FIG. 4), the number of layers of the multilayer film must be at least 76 layers, and when the basic film thickness is obviously designed as (2n + 1) / 4 times (n is a natural number of 1 or more) of the central wavelength. More layers are required.

That is, the fact that a larger number of layers is required means that the interference effect in the multilayer film becomes large, the calculation becomes complicated, and the design takes time. Therefore, by designing the basic film thickness as an optical film thickness of (2n + 1) / 4 times (3/4 times, 5/4 times, ...) Of the central wavelength, Compared with the case of designing as an optical film thickness of 4, it can be designed very easily.

Next, a method of manufacturing the multilayer optical filter 1 will be described by using 26 layers of optical film thicknesses each having a film thickness designed with the basic film thickness being 7/4 times the center wavelength.

For example, a film forming operation of a thin film layer L _j (1 ≦ j ≦ 26) in the 26-layered multilayer films L _{1 to} L ₂₆ (for example,
(It is assumed that the layer corresponds to the film forming material of the film forming source 13a2)
During the operation, the shutter device 22a2 of the film forming source 13a2 is opened and the shutter device 22a1 of the film forming source 13a1 is closed (shutter operation) under the control of the computer 41.

On the other hand, the electron guns 20a1 and 20a2 irradiate the film-forming sources 13a1 and 13a2 with an electron beam, and the film-forming materials heated and melted in the film-forming sources 13a1 and 13a2 are evaporated.

At this time, the film-forming material (evaporated particles) evaporated from the film-forming source 13a2 whose upper part is not covered by the shutter device rises in the vacuum container 12 and is evaporated on the film-forming substrate 16 to form a thin film layer. Part of L _j is formed.

In parallel with the above film forming operation, the light source 21 irradiates the thin film layer being formed with light in a wide wavelength band. Then, the transmitted light transmitted through the thin film layer being formed is incident on the spectroscope 29 via the substrate 16, the condenser lens 23, and the optical fiber bundle 24.

Then, only the monitor light having a predetermined monitor wavelength is split through the spectroscope 29 and received by the photodetector 30. The light amount signal corresponding to the amount of light received by the light receiver 30 is noise-removed via the lock-in amplifier 31 and then transmitted to the computer 41 of the control device 32.

Therefore, the current time x _i in the corresponding thin film layer L _j is sent to the computer 41 via the light receiver 30.
The light intensity change data {x _k , t _k (k = 1, 2, ..., i-1)} based on all the light intensity signals measured before is received and stored in the memory by the processing of the computer 41. It is stored in 42.

At this time, the computer 41 changes the light quantity based on all the light quantity signals stored in the memory 42 and measured before the current time x _i in the corresponding thin film layer L _j in accordance with the film formation control program P2. Data {x _k ,
The t _k}, by fitting the stored theory data file 45 in the memory 42 (6), to calculate the respective parameters A _0, A _1, A ₂ and A ₃ in the formula (6) (7; See step S11).

Next, the computer 41 uses the calculated parameters A ₀ , A ₁ , A ₂ , A ₃ and the equation (6) so that the current phase corresponds to the target phase {designed target film thickness value. deposition time x _s at the time of reaching the stop index phase value}, i.e., it calculates the x _s to be _{(a 2 x s + a 3} ) = the stop index phase value (step S12).

The computer 41 repeats the processing from step S11 to step S12, and the current film formation time x
_{When i} reaches the film formation time x _s corresponding to the target phase (design film thickness) (see FIG. 8), a shutter signal is transmitted to the shutter device 12a2 corresponding to the film formation source 3a2 during vapor deposition. The evaporation of the film forming material evaporated from the film forming source 3a2 onto the substrate 6 is prevented (step S13).

As a result, the film thickness of the actually formed thin film layer L _j can be set as designed.

In the 26-layer multilayer optical filter 1 designed and manufactured as described above, the maximum allowable error in manufacturing the optical film thickness that can obtain the target loss wavelength characteristic is as follows: Compared with the maximum permissible error when manufacturing a multilayer optical filter using an optical film thickness of 76 layers designed to be 1/4 of the above, the required accuracy of the film formation film thickness should be relaxed. You can

Generally, when the number of layers of the multilayer film is reduced, the maximum allowable error in the production of the optical film thickness that can obtain the characteristics close to the target loss wavelength characteristics is increased, and the required accuracy of the film thickness is increased. It is alleviated, and it becomes easy to manufacture the multilayer optical filter having the target loss wavelength characteristic. (Second Embodiment) In the present embodiment, the structure of the film forming system 11 is substantially the same as that of the first embodiment.
The same reference numerals are used and the description thereof is omitted.

In this embodiment, after the film thickness design of each thin film layer 3a1-3aN of the multilayer film filter 1 is completed, the computer 41 constantly generates the multilayer film actually formed by the film forming system 11. In order to estimate the film thickness error and control the film formation,
The processing shown in FIG. 9 is performed.

That is, the computer 41 uses the delay time T corresponding to the time constant of the optical system of the film forming system 11, for example.
Setting d (FIG. 9; step S20), the light amount change when the film thickness is gradually increased is calculated with reference to theoretical formula data DA (simulation), assuming that the first layer is formed (deposited). (Step S21; refer to FIG. 10). Next, the computer 41 fits the calculation result of step S21 to the equation (6) to calculate the parameters A ₀ , A ₁ , A ₂ and A ₃ of the equation (6) (step S2).
2). Then, the computer 41 uses the calculated parameters A ₀ , A ₁ , A ₂ , A ₃ and the equation (6) to determine that the current phase is the target phase {stop index phase corresponding to the designed target film thickness value. Value h1 of the first layer when reaching
Is calculated (step S23).

Next, the computer 41 calculates the film thickness hd1 when the film thickness is longer than the calculated film thickness h1 by the delay time Td (step S24). In addition, in the process of this step S24, the vapor deposition rate is calculated using a fixed value on a performance basis.

The computer 41 sets the thickness of the first layer to hd
Assuming that the film is fixed at 1, and a second layer is vapor-deposited on the film, the change in the light amount when the film thickness is gradually increased is calculated with reference to the theoretical formula data DA (step S2).
5). Next, the computer 41 fits the calculation result of step S6 into the equation (6) and sets each parameter A
₀ , A ₁ , A ₂ and A ₃ are calculated (step S26).
Then, the computer 41 causes the calculated parameters A
₀ , A ₁ , A ₂ , A ₃ and the equation (6) are used, the second phase when the current phase reaches the target phase {stop index phase value corresponding to the designed target film thickness value} The film thickness h2 is calculated (step S27).

Next, the computer 41 calculates the film thickness hd2 when the film is formed with a delay time Td longer than the calculated film thickness h2 (step S28). continue,
The computer 41 sets the thicknesses of the first and second layers to hd1,
Assuming that the film is fixed at hd2 and the third layer is vapor-deposited on the film, the change in the light amount when the film thickness is gradually increased is calculated (step S29).

Thereafter, similarly, the computer 41 similarly performs calculations up to the final optical film layer (3aN), and outputs hd1 and hdd.
2, hd3, ..., Hdn are calculated (step S3
0), the obtained film thicknesses hd1, hd2, hd3, ..., H
The wavelength characteristic of the filter based on dn is calculated by theoretical formula data DA
And is calculated (step S31).

The computer 41 compares the past wavelength characteristic data obtained from the actual film-forming result stored in the past wavelength characteristic data file 50 of the memory 42 with the calculated wavelength characteristic data to obtain the error. (Step S
32).

The computer 41 then proceeds to step S
By executing the processing of 20 to S32 while changing Td, the delay time Td which is the minimum error is calculated from the errors of all the calculated delay times Td, and is set to the optimum delay time Td (OPT). (Step S33).

Here, FIG. 15 is a diagram showing a comparison between the wavelength characteristic data of the multilayer filter based on the designed film thickness and the wavelength characteristic data of the actually formed multilayer filter.
Further, FIG. 11 is a calculation result of the wavelength characteristic for each delay time obtained based on the delay time estimation processing of FIG. 9 above.

As can be seen from FIG. 11, the characteristic waveform changes as the delay time becomes longer. FIG. 12 shows the result of superposing the calculated waveform when Td = 1.7 sec in FIG. 11 and the actual characteristic data waveform shown in FIG.
As shown in FIG. 12, it can be seen that the waveforms of both are substantially the same.

That is, the coincidence of the waveforms and the minimum error have the same meaning, and the delay time Td with which the waveforms are approximated (the error is minimized) can be obtained as the optimum delay time Td (OPT).

The optimum delay time T thus obtained
The film formation is controlled using d (OPT). For example, it is assumed that the thin film layer L _j is formed as in the first embodiment.

That is, as shown in FIG. 13, the computer 41 according to the film formation control program P2 stores all the measured thin film layers L _j stored in the memory 42 before the current time x _i . The light quantity change data {x _k , t _k } based on the light quantity signal is fitted to the equation (6) stored in the theoretical data file 45 of the memory 42, and each parameter A ₀ , A ₁ , A of the equation (6) is fitted. ₂ and A ₃ are calculated (see FIG. 13; step S11).

Then, the computer 41 uses the calculated parameters A ₀ , A ₁ , A ₂ , A ₃ and the equation (6) to form the film formation time x when the current phase reaches the stop index phase value. _s, i.e., to calculate the x _s as the _{(a 2 x s + a 3} ) = the stop index phase value (step S12). Note that film formation (x = 0 at the start of vapor deposition).

Then, the computer 41 proceeds to step S
By repeating the processing from 11 to step S12, the current film formation time x _i is a time (x _s ) before the film formation time x _s corresponding to the target phase (design film thickness) by the delay time Td (OPT).
When -Td (OPT)) is reached, a shutter signal is transmitted to the shutter device 12a2 corresponding to the film-forming source 3a2 being vapor-deposited to deposit the film-forming material evaporated from the film-forming source 3a2 onto the substrate 6. Is blocked (step S13a).

FIG. 14 is a diagram showing the relationship between the design characteristic data and the actual characteristic data of the multilayer filter actually formed by the film formation control process of FIG. As shown in FIG. 14, the two are very well approximated, and the loss deviation between them is also 0.32 dB.

Loss deviation (2.514 dB) shown in FIG. 15 above.
And the loss deviation (0.32 dB) shown in FIG. 14, the loss deviation can be significantly improved by using the film formation control method of the present embodiment.

As described above, according to this embodiment,
Multiple factors, such as optical system time constants, signal processing delays,
Even if a film thickness error occurs in each optical film layer that is actually formed due to the influence of mechanical operation and the influence of wraparound, etc., this film thickness error is estimated from the optical characteristic data of the actually formed multilayer filter, The film formation time can be adjusted by the estimated thickness error.

Therefore, even if a film thickness error occurs, the loss deviation of the obtained multilayer film filter can be maintained high without being affected by the film thickness error.

As a result, the reliability and practicality of the actually manufactured multilayer filter can be improved.

In the present embodiment, the film formation time is adjusted by using the estimated error amount, but the present invention is not limited to this. For example, each layer of the layers is adjusted so as to cancel the estimated error amount. It is also possible to adjust the design film thickness.

In the first and second embodiments, theoretical formula data corresponding to the phase control method is theoretical formula data that theoretically represents a change in the amount of transmitted light during film formation as a function formula of the film formation time. Although DT was used, the present invention is not limited to this.

That is, when the film formation control is performed using the ratio (B / A) of the change B from the extreme value of the stop light amount to the width A of the light amount change, the B / A is theoretically expressed. Theoretical formula data corresponding to the functional formula data file 3
5 and perform the processing shown in FIG. 7, FIG. 9, FIG.
The film thickness error (optimal delay time) corresponding to the control method can be estimated.

Further, in the present embodiment, the monitor light wavelength determination process and the film formation control process described above are executed by a single computer, but it is also possible to execute them by a plurality of computers.

Although the light transmitted through the thin film F and the substrate 16 is used as the monitor light in this embodiment, the present invention is not limited to this, and the light reflected from the thin film F is used as the monitor light. It is also possible.

[0124]

As described above, according to the multilayer optical filter and the apparatus for designing the same according to the present invention, as compared with the multilayer optical filter designed with the basic film thickness of λ / 4,
Even if the number of layers is the same, wavelength characteristics having a steeper loss variation with respect to wavelength can be obtained, so that it is possible to easily design a multilayer optical filter having target wavelength characteristics.

Further, according to the film formation control method and system of the present invention, the film formation is actually performed due to a plurality of factors such as the time constant of the optical system, the delay of signal processing, the influence of mechanical operation and the influence of wraparound. Even if a film thickness error occurs in each optical film layer, the film thickness error is estimated from the optical characteristic data of the multilayer film filter that was actually formed, and the film formation time and design film are estimated by the estimated film thickness error. The thickness can be adjusted.

Therefore, a small loss deviation can be maintained without being affected by the film thickness error, and the reliability and practicality of the manufactured multilayer optical filter can be improved.

[0127]

[Brief description of drawings]

FIG. 1 is a diagram showing a multilayer filter according to a first embodiment of the present invention.

FIG. 2 is a diagram (partial cross-sectional view) showing a schematic configuration of a film forming system 11 including a thin film monitor light wavelength determining device according to an embodiment of the present invention.

FIG. 3 is a diagram showing a hardware configuration of the control device shown in FIG.

FIG. 4 is a schematic flowchart showing an example of a film thickness designing process according to the first embodiment of the present invention.

FIG. 5 is a diagram showing a design result of film thickness of each layer of the multilayer filter according to the first embodiment.

FIG. 6 is a diagram showing a relationship between a target loss wavelength characteristic targeted by the multilayer filter of the first embodiment and a loss wavelength characteristic designed by the above-described design method.

FIG. 7 is a schematic flowchart showing an example of film formation control processing by the control device shown in FIG. 2 in the first embodiment.

FIG. 8 is a graph for explaining x _s that is a stop index phase value in the first embodiment.

FIG. 9 is a schematic flowchart showing an example of a film formation control process according to a second embodiment of the present invention.

FIG. 10 is a diagram illustrating a change in light amount according to the second embodiment.

FIG. 11 is a diagram showing a calculation result of wavelength characteristics for each delay time obtained based on the delay time estimation process of FIG. 9 in the second embodiment.

FIG. 12 is Td = 1.7s in the second embodiment.
16 is a graph showing the result of superimposing the calculated waveform for ec and the actual characteristic data waveform shown in FIG. 15.

FIG. 13 is a schematic flowchart showing an example of film formation control processing by a control device according to a second embodiment.

14 is a diagram showing a relationship between design characteristic data and actual characteristic data of a multilayer filter actually formed by the film formation control process of FIG.

FIG. 15 is a diagram showing a comparison between wavelength characteristic data of a multilayer filter based on a designed film thickness and wavelength characteristic data of an actually formed multilayer filter.

[Explanation of symbols] 1 Multilayer filter 2 substrates 3a1-3aN optical film layer 11 Film forming system 21 vacuum container 13a1, 13a2 film forming source 15 Substrate holder 16 Deposition substrate 20a1, 20a2 electron gun 21 light source 22a1, 22a2 shutter device 30 light receiver 32 control device 40 A / D 41 Computer 42 memory 45 theoretical formula data file 46 Purpose transmission loss value data file 50 Past wavelength characteristics data file

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Kazunori Mizuno             2-6-1, Marunouchi, Chiyoda-ku, Tokyo             Kawa Electric Industry Co., Ltd. F term (reference) 2H048 GA04 GA18 GA33 GA57 GA60                       GA62                 4K029 BB02 BC07 BD00 EA00 EA01

Claims (13)

[Claims] 1. A multilayer optical filter for laminating a plurality of optical films to obtain predetermined wavelength characteristics in a target wavelength band, wherein the optical film thickness of each optical film is set to the target wavelength. (2n + of the center wavelength set to 1/2 to 3/2 times the band)
1) / 4 times (n is a natural number of 1 or more) is designed as a basic film thickness, and a multilayer optical filter is characterized. 2. The multilayer optical filter according to claim 1, wherein the optical film thickness of at least one of the plurality of optical films is optimized so that the predetermined wavelength characteristic can be obtained. 3. A theoretical value that represents the optical film thickness of each optical film with the basic film thickness as an initial value and the wavelength characteristics of the target wavelength band using the optical film thickness of each optical film as a parameter. The multilayer optical filter according to claim 1, wherein the multilayer optical filter is designed by fitting with respect to a target wavelength characteristic set in advance in a wavelength band. 4. A multilayer film optical filter designing apparatus for obtaining a predetermined wavelength characteristic in a target wavelength band, comprising a plurality of optical films laminated, wherein: (2n +) of the center wavelength set to 1/2 to 3/2 times the target wavelength band
1) A multilayer film optical filter designing device comprising means for designing a basic film thickness of 1/4 times (n is a natural number of 1 or more). 5. An optical film thickness of each optical film, which is used in a film forming apparatus for forming a multilayer film composed of a plurality of optical films on an object to be formed by a film forming material emitted from a film forming source, A film formation control system for controlling a film thickness design value for each optical film, which is designed in advance, by using monitor light transmitted / reflected from each of the optical films. A storage unit that stores data representing the light transmission loss characteristic of the multilayer film formed in a predetermined wavelength band, and based on the light transmission loss characteristic data of the multilayer film stored in the storage unit, the film forming apparatus A film thickness error estimating means for estimating a film thickness error that constantly occurs in the formed optical film, and the film thickness control based on the film thickness design value of each optical film and the estimated film thickness error. And a film thickness control means. Membrane control system. 6. The film thickness error estimating means includes means for estimating the film thickness error as a deviation from the design film thickness, and means for adjusting the design film thickness so as to cancel the estimated deviation. The film forming control system according to claim 5, wherein 7. The film forming control system according to claim 5, wherein the film thickness error estimating unit is a unit that estimates the film thickness error by converting it into a delay time during film formation. . 8. The film thickness error estimating means, means for setting a plurality of delay times, and storage means for storing function data representing a light quantity change of the monitor light obtained from the designed film thickness,
When performing a film formation simulation of the optical film of each layer on the film formation target, using a means for calculating a change in the light amount of the monitor light from each layer during film formation in the simulation, and the calculated light amount change Means for fitting the function data to obtain parameters of the function data of each layer, means for calculating the film thickness of the optical film of each layer formed in film formation control based on the function data containing the obtained parameters, and calculating When the film thickness is changed by each delay time from the film thickness of each layer formed, means for calculating the film thickness of the optical film of each layer for each delay time, and a plurality of means having the calculated film thickness for each delay time Means for calculating, for each delay time, data representing the light transmission loss characteristic of the multilayer film including the optical film layer in the predetermined wavelength band, and the light transmission loss of the actually formed multilayer film. Property data and the light transmission loss characteristic data calculated for each delay time are compared, and a means for obtaining an error for each delay time is compared with an error for each obtained delay time, and the optimum is obtained based on the comparison result. 6. The film forming control system according to claim 5, further comprising means for obtaining a large delay time. 9. The film thickness control means monitors a change in the amount of monitor light from the optical film layer being formed on the film formation target, and the function using the monitored change in the light amount. By fitting the data, a means for obtaining the parameter of the function data corresponding to the optical film layer, and the time when the optical film layer matches the film thickness design value based on the function data including the obtained parameter. A means for calculating, and a means for preventing the film-forming material from adhering to the film formation target when the current time matches the time obtained by subtracting the delay time from the calculated time. The film formation control system according to claim 8. 10. An optical film thickness of each optical film, which is used in a film forming apparatus for forming a multilayer film composed of a plurality of optical films on an object to be formed by a film forming material emitted from a film forming source, It is a computer-executable program for performing control so as to match a film thickness design value for each optical film designed in advance by using monitor light transmitted / reflected from each optical film. Based on the wavelength characteristic data of the multilayer film stored in the memory, means for storing data representing the light transmission loss characteristic in a predetermined wavelength band of the multilayer film actually formed by the film forming apparatus, A means for estimating a film thickness error that constantly occurs in the optical film formed by the film forming apparatus, and a film thickness control based on the film thickness design value of each optical film and the estimated film thickness error. Functions as a means to do Program for causing. 11. A method of designing a multilayer optical filter for obtaining a predetermined wavelength characteristic in a target wavelength band, comprising a plurality of optical films laminated, wherein: (2n of the center wavelength set to approximately 1/2 to 3/2 times the target wavelength band)
A method of designing a multilayer optical filter, comprising a step of designing +1) / 4 times (n is a natural number of 1 or more) as a basic film thickness. 12. The designing step includes the step of optimizing an optical film thickness of at least one layer of the plurality of optical films so that the predetermined wavelength characteristic is obtained. A method for designing the multilayer optical filter described. 13. An optical film thickness of each optical film when a multi-layer film including a plurality of optical films is formed on a film forming object by a film forming apparatus by a film forming material emitted from a film forming source, A method for controlling film formation, which uses monitor light transmitted / reflected from each optical film so as to match the film thickness design value for each optical film designed in advance. A step of storing data representing a light transmission loss characteristic in a predetermined wavelength band of the formed multilayer film, and a film forming apparatus for forming a film based on the wavelength characteristic data of the multilayer film stored in the storing step. And a step of performing the film thickness control based on the film thickness design value of each of the optical films and the estimated film thickness error. A characteristic film forming control method.