JP4800710B2 - Optical filter and optical filter manufacturing method - Google Patents

Description

  The present invention relates to an optical filter and a method for manufacturing the optical filter.

The dielectric multilayer film constituting the optical filter that separates the wavelength of transmitted light is manufactured by a vapor deposition process using a vacuum apparatus. And in order to utilize a vacuum apparatus, it is striving to reduce manufacturing cost by processing as many wafers as possible at the same time. In-plane distribution becomes a problem when many wafers are processed simultaneously. The film thickness of the dielectric multilayer film is a very important factor that determines the optical characteristics, and is a factor that determines the yield. For this reason, it is required to perform film formation as much as possible and as uniformly as possible.
However, the current process has a limit in controlling uniformity by simply forming a dielectric multilayer film. Therefore, various studies have been made to improve the uniformity. For example, Non-Patent Documents 1 to 3 are known as research results that achieve high in-plane uniformity using an ECR sputtering apparatus. In these technologies, in the dielectric multilayer film of SiO ₂ / Ta ₂ O ₅ , the accuracy of the film thickness is ± 0.65% (8 inch wafer) and the refractive index distribution is ± 0.16% (8 inch wafer). is there.
The Japan Society of Applied Physics 2003 Fall 1p-YK-2 K. Saito, Y. Jin, and M. Shimada, Appl. Phys. Lett. 81, 3582 (2002) Kunio Saito, Kamiyoshi, Toshiro Ono, Takao Amazawa, Semiconductor FPD World, October 2001, pp.57-61.

However, in the sputtering apparatus used in Non-Patent Documents 1 to 3, the process that can be performed simultaneously is only one wafer. The vapor deposition that is normally available can process several wafers at a time and is much less expensive to manufacture. For this reason, there is a need for a technique that can process a number of wafers at a time using a vapor deposition apparatus and can control the film thickness with high accuracy.
SUMMARY OF THE INVENTION An object of the present invention is to make it possible to manufacture several wafers at a time using a vapor deposition apparatus, and to prevent the transmission spectrum from being different depending on the transmission position of the optical filter.

According to the first aspect of the present invention, in the optical filter having a dielectric multilayer film formed by periodically laminating a plurality of dielectrics having different refractive indexes, the spectrum correction layer for correcting that the transmission spectrum varies depending on the transmission position. The spectrum correction layer corrects that the transmission spectrum differs depending on the transmission position because the film thickness has an in-plane distribution .
The invention according to claim 2, in the optical filter according to claim 1, a plurality of the dielectric multilayer film includes a spacer layer between the plurality of the dielectric multilayer film, the spectrum correction layer, said spacer It is characterized by comprising the same material as the material constituting the layer or one of the plurality of materials constituting the dielectric multilayer film .
According to a third aspect of the present invention, in the optical filter according to the first or second aspect, the spectrum correction layer is made of a resin .
According to a fourth aspect of the present invention, in the optical filter according to any one of the first to third aspects, the spectral correction layer has a film thickness Dm of Dm = λ / 4n × N (where N: An even number, n: refractive index, and λ: incident light wavelength) are satisfied .
According to a fifth aspect of the present invention, in the optical filter according to the fourth aspect, the spectrum correction layer is formed adjacent to the spacer layer.
A sixth aspect of the present invention is the optical filter according to the fourth or fifth aspect, wherein the spacer layer is formed of an electro-optic material or a photorefractive material.
According to a seventh aspect of the present invention, in the method of manufacturing an optical filter according to any one of the first to sixth aspects, the film thickness of the spectrum correction layer is controlled by dry etching. It is a manufacturing method of an optical filter.
According to an eighth aspect of the present invention, in the optical filter manufacturing method for manufacturing the optical filter according to any one of the first to sixth aspects, the film thickness of the spectrum correction layer is controlled by photolithography. It is a manufacturing method of an optical filter.

According to the first aspect of the present invention, an optical filter that transmits an arbitrary wavelength can be produced by using a dielectric multilayer film. In this case, the transmission wavelength shifts from the design value due to the film thickness deviating from the design value can be corrected by a spectrum correction layer that corrects that the transmission spectrum differs depending on the transmission position of the optical filter.
The optical filter of the present invention can be manufactured by using a vapor deposition apparatus and can process many wafers at a time, thereby reducing the manufacturing cost. The spectrum correction layer can also correct the point that the film thickness deviates from the design value due to the in-plane distribution in the vapor deposition apparatus, causing the yield as a defective product and increasing the manufacturing cost.
Moreover, it can correct | amend with the film thickness of a spectrum correction layer that a transmission spectrum changes with the transmission positions of this optical filter.
According to the second aspect of the present invention, the manufacturing cost can be greatly reduced by manufacturing the same material.
In addition, a narrow bandpass filter can be realized by using a cavity type optical filter.
According to the third aspect of the present invention, unlike the vapor phase growth such as vapor deposition, the resin can be easily formed, so that the manufacturing cost can be reduced.
According to the invention described in claim 4 , the transmittance of the spectrum correction layer can be improved.

According to the invention described in claim 5 , since the adjacent of the spacer layer greatly affects the optical characteristics, if the adjacent layer is a spectrum correction layer, the spectrum can be corrected efficiently with a small film thickness control or refractive index control. The manufacturing cost can be reduced by performing the above-described correction efficiently.
According to the sixth aspect of the present invention, the refractive index can be controlled by an external voltage or light by using an electro-optic material or a photorefractive material for the spacer layer. Changing the refractive index of the spacer layer is equivalent to controlling the optical length, thereby changing the optical characteristics as an optical filter. The spacer layer is the part that most affects the optical characteristics, and the optical characteristics can be controlled efficiently by changing the refractive index of the spacer layer. Further, this refractive index change can be controlled with high accuracy, and can be controlled with higher accuracy than that controlled by photolithography or etching.
According to the seventh aspect of the present invention, the vapor deposition can be controlled only in the direction in which the in-plane thickness is simply increased. On the other hand, since etching is used, the thickness of the formed film is reduced. Can be processed. Etching can turn the etching gas into plasma at an arbitrary position, and the plasma controlled at an arbitrary position scrapes off the film at that position. The film can have a controlled film thickness in the plane.
According to the eighth aspect of the invention, since photolithography is used, it is possible to apply a mask at an arbitrary position and form a photosensitive resist in an arbitrary shape. Thus, a film having an arbitrary in-plane distribution can be formed by leaving a mask at a controlled position in the plane and etching from above. This film having an arbitrary thickness serves as a spectrum correction layer.

The best mode for carrying out the invention will be described below.
[Embodiment 1]
FIG. 1 is an enlarged longitudinal sectional view (a) of a conventional optical filter, an enlarged longitudinal sectional view (b) of the optical filter of the present embodiment, and a graph for explaining the relationship between the measurement position and the center wavelength of both optical filters. (C).
A conventional optical filter 101 shown in FIG. 1A is formed by laminating a substrate 2, a dielectric multilayer film 3, a spacer layer 4, and a dielectric multilayer film 5 in order from the bottom. The dielectric multilayer films 3 and 5 are formed by periodically laminating a plurality of dielectrics having different refractive indexes.
The optical filter 1 of this embodiment shown in FIG. 1B is different from the conventional optical filter 101 in that a spectrum correction layer 6 is interposed between the dielectric multilayer film 5 and the spacer layer 4. It is.
That is, as shown in FIG. 1C, the optical spectrum of the conventional optical filter 101 varies depending on the position in the range where light is used (FIG. 1C). This factor arises because each film thickness varies depending on the position.
Therefore, in this embodiment, in order to correct this film thickness variation, the spectrum correction layer 6 is introduced to correct the spectrum. Therefore, in this embodiment, it is suppressed that an optical spectrum changes with positions (FIG.1 (c) b). That is, the film thickness or refractive index of the spectrum correction layer has a distribution in the plane.
The dielectric multilayer films 3 and 5 are formed by periodically laminating a plurality of dielectrics having different refractive indexes. In this example, the SiO ₂ layer 11 and the TiO ₂ layer 12 are alternately laminated in order from the layer close to the substrate 2. In the dielectric multilayer films 3 and 5, the thicknesses of the SiO ₂ layer 11 and the TiO ₂ layer 12 were set to 70 nm and 45 nm, respectively, with the reference wavelength being 1/4 of the optical wavelength of 632.8 nm. Dielectric multilayer films 3 and 5 consisted of 6 pairs of SiO ₂ layer 11 and TiO ₂ layer 12 respectively.

Next, SiO ₂ is adopted as the material of the spacer layer 4 so that the film thickness is an even multiple 2N of 1/4 of the reference wavelength. As a result, a band-pass filter having a narrow band in which the peak position of the transmittance spectrum comes to the reference wavelength. This time, the integer was set to N = 6.
When an optical filter, which is a bandpass filter designed in this way, is manufactured, as described above, a film thickness distribution is generated in a region where light is transmitted as shown in FIG. This film thickness distribution is due to the film forming apparatus, and it is difficult to increase this accuracy. In FIG. 1, only the spacer layer 4 is depicted as being distributed, but in reality, the dielectric multilayer films 3 and 5 are also distributed. However, the film thickness distribution of the dielectric multilayer films 3 and 5 does not have much influence on the optical characteristics, and is about 1/10 of the influence of the spacer 4 layers.
The material of the spectrum correction layer 6 can be selected in various ways such as an organic resin or an inorganic material. This time, since the film forming equipment can be used continuously, the same SiO ₂ as the spacer layer 4 is used. Thus, there is no problem even if the same material as the spacer layer 4 is used. The thickness of the spectrum correction layer 6 is about 500 nm. The spectrum correction layer 6 has its film thickness adjusted in the plane, and realizes that the transmission spectrum is almost the same in the plane.
The film thickness Dm of the spectrum correction layer 6 is
Dm = λ / 4n × N
(However, N: Even number, n: Refractive index, λ: Incident light wavelength)
Meet the requirements of
A dielectric multilayer film 5 is formed on the spectrum correction layer 6, and the optical filter 1 is a cavity type optical filter sandwiched between the dielectric multilayer films 3 and 5. The optical filter 1 functions as a narrow-band bandpass filter, and its in-plane distribution is very small.
Note that the spectrum correction layer 6 may correct that the transmission spectrum differs depending on the transmission position of the optical filter 1 of the present embodiment because the refractive index has an in-plane distribution. In this case, the refractive index of the spectrum correction layer 6 can be controlled by doping an arbitrary impurity, and the in-plane distribution can be controlled. The refractive index can control the optical characteristics of the filter as an optical length in the configuration of the optical filter.

Next, a method for manufacturing the optical filter 1 will be described.
The optical filter 1 can be manufactured by sequentially performing the following steps.
(1) Step 1 (see FIG. 2 (a))
First, the dielectric multilayer film 3 and the spacer layer 4 are sequentially formed on the substrate ₂ made of SiO ₂ . In this case, a film forming method employs an electron beam evaporation method in a vacuum chamber.
(2) Step 2 (see FIG. 2B)
Subsequently, the spectrum correction layer 6 is formed. In this state, the spectrum correction layer 5 and the spacer layer 4 are in-plane distribution, and the optical characteristics are different in the plane.
(3) Process 3
Next, the in-plane distribution of the film thickness of the spacer layer 4 and the spectrum correction layer 6 is measured. If a measurement method using a light interference phenomenon is used, the measurement method has high measurement accuracy and is suitable for this measurement.
(4) Step 4
Aggregate this data and design a grayscale mask based on that data. The gray scale mask is produced in the same manner as a photographic dry plate, and an arbitrary gray scale pattern can be transferred using a spatial modulation element such as a liquid crystal. This gray scale pattern is designed so as to reflect the previously measured film thickness distribution and to function as the spectrum correction layer 6. In this case, the design is performed in anticipation of deformation due to photolithography and etching, which are subsequent processes.
(5) Process 5
Next, a photoresist 21 is applied (see FIG. 2C), and exposure is performed through the gray scale mask 22 from above (see FIG. 3A).
(6) Step 6 (see FIG. 3B)
Then, by developing the exposed photoresist 21, a photoresist processed into an arbitrary shape is obtained.
(7) Step 7 (see FIG. 3C)
The shape of the photoresist 21 can be transferred to the spectrum correction layer 6 by dry etching from above.
(8) Step 8 (see FIG. 3 (d))
Finally, the dielectric multilayer film 5 is formed on the spectrum correction layer 6 processed into this arbitrary shape.

[Embodiment 2]
FIG. 4 is a partially enlarged vertical sectional view of the optical filter 1 of the present embodiment. In addition, about the member common to Embodiment 1, the same code | symbol is used and detailed description is abbreviate | omitted.
As shown in FIG. 4, the optical filter 1 according to the present embodiment uses an electro-optic material for the spacer layer 4, and between the spacer layer 4 and the dielectric multilayer film 3, as well as the spectrum correction layer 6 and the dielectric multilayer film. 5, the refractive index of the spectrum correction layer 6 can be arbitrarily controlled by applying a voltage by the transparent electrodes 31 and 32 interposed between them. Optical characteristics can be controlled by changing the refractive index.
In this embodiment, it is a cavity type narrow-band bandpass filter in which the spacer layer 4 is sandwiched between mirrors formed of dielectric multilayer films 3 and 5, and the center wavelength of the transmission spectrum is an important item as optical characteristics. The spectrum correction layer 6 is introduced in the same manner as in the first embodiment so that the center wavelength does not have a distribution in the plane. However, the portion that cannot be corrected by the spectrum correction layer 6 is finely adjusted by the electro-optic material (spacer layer 4).
The transparent electrodes 31 and 32 are in a matrix so that the in-plane distribution can be finely adjusted with the electro-optic material. That is, the transparent electrodes 31 and 32 arranged on the upper and lower sides have a strip shape, and the upper and lower strips are perpendicular to each other. Thereby, the refractive index of the spacer layer 4 which is an electro-optic material can be controlled in a matrix form.
The in-plane distribution to which the voltage is applied is limited by the configuration of the upper and lower electrodes 31 and 32, but it is easy to create a simple continuous distribution, such as receiving a large voltage at the center and a small voltage at the end. . In addition, the voltage applied to the electro-optic material (spacer layer 4) can be changed with time, and the characteristics of the optical filter 1 that varies depending on external factors can be stabilized. In particular, expansion of the spacer due to heat or the like is one of the most likely external factors.

As shown in FIG. 4, the basic configuration of the optical filter 1 of the present embodiment is a substrate 2, dielectric multilayer films 3 and 5, a spacer layer 4 made of an electro-optic material, a spectrum correction layer 6, and a patterned transparent electrode. 31 and 32.
The dielectric multilayer films 3 and 5 are composed of a SiO ₂ layer 11 and a TiO ₂ layer 12 in order from a layer close to the substrate 2. For the dielectric multilayer films 3 and 5, the SiO ₂ layer 11 and the TiO ₂ layer 12 were set to 70 nm and 45 nm, respectively, with the reference wavelength being 1/4 of the optical wavelength of 632.8 nm. Each of the dielectric multilayer films 3 and 5 has six pairs of SiO ₂ layers 11 and TiO ₂ layers 12.
In this example, PLZT is used for the spacer layer 4 so that the film thickness is an even multiple 2N of 1/4 of the incident wavelength. The integer N was about 40 and the film thickness was about 10 nm. PLZT has a secondary electro-optic coefficient of “9E-16 [m2V-2]”, and its refractive index change is about 0.0001 when a voltage of 10 V is applied. With this change in refractive index, the amount of movement λm at the peak position of the transmittance is about 1.5 nm. This movement amount λm can also be controlled by the applied voltage and the film thickness integer N of the defect layer.
A spectrum correction layer 6 is formed on the spacer layer 4. In this example, resin is used as a material. Any resin can be used without any problem, and it is desirable to use an epoxy-based UV curable resin from the viewpoint of ease of production. The thickness of the spectrum correction layer 6 is about 500 nm. The spectrum correction layer 6 has its film thickness adjusted in the plane, and realizes that the transmission spectrum is almost the same in the plane.
Transparent electrodes are used as electrodes 31 and 32 at both ends of the spacer layer 4 and the spectrum correction layer 6. The transparent electrode can be formed by sputtering as ITO. ITO is patterned by a normal photolithography process. The ITO patterning is a strip with a pitch of 10 nm.
A dielectric multilayer film 5 is formed on the spectrum correction layer 6, which is a cavity type optical filter sandwiched between the dielectric multilayer films 3 and 5. This optical filter 1 functions as a narrow-band bandpass filter, and its in-plane distribution is very small.

(A) is an enlarged longitudinal sectional view of a conventional optical filter, (b) is an enlarged longitudinal sectional view of the optical filter of Embodiment 1, and (c) is a measurement position and a center wavelength of the optical filter of (a) and (b). It is a graph explaining the relationship. (A)-(c) is explanatory drawing of the manufacturing method of the optical filter which concerns on Embodiment 1. FIG. (A)-(d) is explanatory drawing of the manufacturing method of the optical filter which concerns on Embodiment 1. FIG. 6 is a partially enlarged longitudinal sectional view of an optical filter according to Embodiment 2. FIG.

Explanation of symbols

1 Optical filter 3, 5 Dielectric multilayer 4 Spacer layer (electro-optic material)
6 Spectral correction layer

Claims (8)

In an optical filter including a dielectric multilayer film formed by periodically laminating a plurality of dielectrics having different refractive indexes,
A spectrum correction layer for correcting that the transmission spectrum varies depending on the transmission position,
The optical filter according to claim 1, wherein the spectrum correction layer corrects that the transmission spectrum varies depending on the transmission position because the film thickness has an in-plane distribution.   A plurality of the dielectric multilayer films;
A spacer layer is provided between the plurality of dielectric multilayer films,
  2. The optical filter according to claim 1, wherein the spectrum correction layer is made of the same material as one of a material constituting the spacer layer or a plurality of materials constituting the dielectric multilayer film. .   The optical filter according to claim 1, wherein the spectrum correction layer is made of a resin.   The spectral correction layer has a film thickness Dm,
  Dm = λ / 4n × N
  (However, N: Even number, n: Refractive index, λ: Incident light wavelength)
The optical filter according to any one of claims 1 to 3, wherein the following condition is satisfied.   The optical filter according to claim 4, wherein the spectrum correction layer is formed adjacent to the spacer layer.   6. The optical filter according to claim 4, wherein the spacer layer is made of an electro-optic material or a photorefractive material.   In the manufacturing method of the optical filter which manufactures the optical filter as described in any one of Claims 1 thru | or 6,
  A method of manufacturing an optical filter, wherein the film thickness of the spectrum correction layer is controlled by dry etching.   In the manufacturing method of the optical filter which manufactures the optical filter as described in any one of Claims 1 thru | or 6,
  A method of manufacturing an optical filter, wherein the film thickness of the spectrum correction layer is controlled by photolithography.

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