WO2006092919A1

WO2006092919A1 - Optical element and method for manufacturing optical element

Info

Publication number: WO2006092919A1
Application number: PCT/JP2006/301435
Authority: WO
Inventors: Kunihiko Yoshino
Original assignee: Nikon Corporation
Priority date: 2005-02-28
Filing date: 2006-01-30
Publication date: 2006-09-08
Also published as: TW200641388A; TWI405999B; JP5098640B2; JPWO2006092919A1

Abstract

A multilayer optical thin film (4) is formed by alternately forming SiO2 thin films (2) and Nb2O5 thin films (3) approximately for 100 layers in total on a surface of a quartz substrate (1) having a thickness of 0.8mm or less. Since a linear expansion coefficient of the substrate (1) is small and a difference between a linear expansion coefficient of the multilayer optical thin film (4) is large, when the temperature of the substrate (1) is reduced to a normal temperature from a normal film forming state at approximately 200°C, compression stress of the multilayer optical thin film (4) and heat stress generated by temperature reduction cancel each other and deformation (warping) of the substrate (1) is reduced. Thus, a process of cutting the substrate (1) with a dicing saw and the like can be easily performed with less breakage, and surface accuracy of a cut out optical element is improved.

Description

Optical element and optical element manufacturing method

Technical field

The present invention relates to an optical element formed by forming a thin film such as a dielectric film on a substrate, and a method for manufacturing such an optical element.

Background art

[0002] In optical elements such as interference filters and antireflection films used for optical communications, etc., a thin film is formed in multiple layers on a glass with a thickness of lmm or less, and light interference in the multilayer thin film is prevented. Some of them have desired optical characteristics.

[0003] Such an optical element has, for example, a glass substrate (BK7) having a 50 mm square and a thickness of about 0.3 mm on a low refractive material SiO and high refractive materials Nb 2 O 3, Ta 2 O 3, TiO, ZrO, Hf

Layers of thin films such as 2 2 5 2 5 2 2 o are stacked alternately (the thickness of each thin film is typically

2

~ A few hundred). In addition, a thin film of the low refractive index material such as Al 2 O and a high refractive index

twenty three

A thin film having a refractive index in the middle of the thin film of the refractive index material may be a multilayer thin film having a film structure appropriately interposed between the low refractive index material and the high refractive index material.

[0004] For film formation, a sputtering method or an ion beam assist method is often used. After the film formation is completed, the substrate having the multilayer thin film on the surface is cooled to room temperature, cut into a predetermined size by a dicing saw or the like, and used as an optical element.

[0005] When manufacturing such an optical element, there is a problem that the substrate is warped due to the compressive stress of the multilayer thin film. In this case, the compressive stress is a stress that works to stretch the surface of the substrate on which the multilayer thin film is formed. For this reason, a multilayer thin film is formed on the substrate after film formation. Deforms so that the side is convex. Such compressive stress is NbO

In the case of 2 5, it is estimated that 50 to: L50 MPa, and in the case of SiO, 150 to 350 MPa.

2

[0006] If the deformation of the substrate exceeds the allowable limit, there is a problem that it becomes difficult to cut with a dicing saw or the like, or is damaged during handling. Further, there may be a problem that the surface of the cut out optical element does not become flat. If the surface of the cut optical element does not become flat, the optical characteristics change depending on the position of the light incident on the optical element. In addition, when these micro optical elements are arranged and sandwiched between other optical elements such as glass, the surface becomes uneven, causing problems such as poor adhesion.

Disclosure of the invention

[0007] The present invention has been made in view of such circumstances, and there are few deformations after the film formation is completed. Therefore, an optical element having good optical characteristics, which is easy to handle, such as cutting, and such It is an object to provide a method for manufacturing an optical element.

[0008] A first means for solving the above problem is an optical element formed by forming a thin film having a compressive stress on a substrate, and the substrate has a coefficient of linear expansion higher than that of the thin film. An optical element characterized by using a material with a small coefficient of linear expansion and a thickness of 0.8 mm or less.

In general, the thin film is formed by a sputtering method, an ion beam assist method, or the like, and these are performed at a high temperature. Therefore, if a material having a linear expansion coefficient smaller than that of the thin film is used as the substrate, the amount of contraction of the thin film becomes larger than the amount of contraction of the substrate at room temperature after completion of film formation. Therefore, the compressive stress of the thin film and the thermal stress generated between the substrate and the thin film cancel each other out, and the amount of deformation of the substrate generated by the compressive stress of the thin film is reduced when the substrate is at room temperature after film formation is completed. can do. When the thickness of the substrate is 0.8 mm or more, deformation due to film stress is reduced and the effectiveness of this means is reduced. Therefore, the thickness of the substrate is limited to 0.8 mm or less.

[0010] As the thickness of the substrate becomes as thin as 0.7 mm, 0.6 mm, 0.5 mm, 0.4 mm, 0.3 mm, 0.2 mm, and 0.1 mm, the effect of this means increases. This means is not necessarily limited to a thin film formed by the sputtering method or the ion beam assist method.

[0011] A second means for solving the problem is the first means, wherein a ratio of the thickness of the thin film to the thickness of the substrate is between 1:80 and 3: 1. It is characterized by.

In most cases, the thickness of the thin film of the optical element formed by forming a thin film such as a dielectric film on the substrate is 10 μm to 30 μm. The thickness of the substrate is 10 μm to 0.8 mm. Therefore, the effect of the first means is particularly large when the ratio of the thickness of the thin film to the thickness of the substrate is between 1:80 and 3: 1.

[0013] The third means for solving the problem is the first means or the second means, The thin film has a multilayer structure.

[0014] The first means and the second means may be of a multilayer film structure that forms an interference filter or the like, but if the number of stacked layers increases, it becomes easy to realize various spectral transmittance characteristics. On the other hand, since the stress of the thin film itself also increases, the effect obtained by applying the first means and the second means is particularly great when the thin film has a multilayer structure.

[0015] A fourth means for solving the above problem is any one of the first means to the third means, wherein the material is quartz. .

[0016] Generally, the linear expansion coefficient of a thin film is about 50 X 10 ^_7 ZK. On the other hand, ^Sekiei 's linear expansion coefficient is about 5 Χ 10 ^_7 ΖΚ, which is an order of magnitude smaller, so it is particularly effective when used as a material for the first means or the second means.

[0017] A fifth means for solving the above problem is a method of manufacturing an optical element including a step of forming a thin film having a compressive stress on a substrate, wherein the thin film line is formed on the substrate. When a material having a linear expansion coefficient smaller than the expansion coefficient and having a thickness of 0.8 mm or less is used, and the substrate having a thin film formed on the surface is returned to room temperature after the film formation is completed, the substrate is deformed. The method of manufacturing an optical element is characterized in that film formation is performed at a temperature such that is within an allowable range.

[0018] As described above, when a material having a linear expansion coefficient smaller than that of the thin film is used as the substrate, the compressive stress and thermal stress of the thin film cancel each other, and deformation of the substrate at room temperature is reduced. Can do. The magnitude of the thermal stress when the substrate is returned to room temperature increases as the temperature of the substrate during film formation increases, so if the substrate temperature during film formation is adjusted, the compressive stress and thermal stress of the thin film The amount of deformation when the substrate is returned to room temperature can be reduced. The reason for limiting the thickness of the substrate to 0.8 mm or less is the same as the first means.

[0019] As the thickness of the substrate becomes as thin as 0.7 mm, 0.6 mm, 0.5 mm, 0.4 mm, 0.3 mm, 0.2 mm, and 0.1 mm, the effect of this means increases.

[0020] A sixth means for solving the above-mentioned problem is the fifth means, wherein the ratio of the thickness of the thin film to the thickness of the substrate is between 1:80 and 3: 1. It is characterized by.

[0021] The seventh means for solving the above-mentioned problem is the fifth means or the sixth means, The thin film has a multilayer structure.

[0022] An eighth means for solving the above problem is any one of the fifth means to the seventh means, wherein the material is quartz. .

Brief Description of Drawings

FIG. 1 is a diagram for explaining a method of manufacturing an optical element which is an example of an embodiment of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, an example of an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a diagram for explaining a method of manufacturing an optical element which is an example of an embodiment of the present invention. Using a sputtering device on the surface of a quartz substrate 1 (approximately 50 mm square, approximately 0.3 mm thick), SiO thin film 2

A total of about 100 layers of 2 and NbO thin films 3 are alternately formed to form a multilayer optical thin film 4. multilayer

twenty five

The thickness of the optical thin film 4 is about 30 μm.

[0025] As the substrate 1, for example, in addition to quartz, for example, Tahara Serum® made by OHARA Inc., Zerodure made by Schott, Pyrex glass made by Coung, tempax glass made by Schott, etc. Small optical materials can be used.

[0026] The multilayer optical thin film 4 has a linear expansion coefficient of about 50 X 10 ^_7 ZK (the linear expansion coefficient of Nb 0 is 6.

twenty five

The linear expansion coefficient of 5 X 10 ^_5 ZK and SiO is 4 to 5 X 10 ^_5 ZK. ) ₀ Conventional glass (ΒΚ7)

2

The linear expansion coefficient of the film is approximately 75 X 10 ^_7 mm, which is larger than the linear expansion coefficient of the multilayer optical thin film 4, so that the compressive stress and thermal stress work in the same direction when the substrate 1 after film formation is at room temperature The deformation of the substrate 1 was further increased.

In the present embodiment, since the linear expansion coefficient of the substrate 1 is smaller than the linear expansion coefficient of the multilayer optical thin film 4, when the substrate 1 is brought from room temperature to a room temperature, which is usually about 200 ° C., the multilayer The compressive stress of the optical thin film 4 and the thermal stress generated by the temperature drop cancel each other, and the deformation (warp) of the substrate 1 is reduced. Therefore, when the substrate 1 is cut with a dicing saw or the like, it is easy to handle, and it is less likely to be damaged, and the surface accuracy of the cut out optical element is improved.

[0028] Further, when the multilayer optical thin film 4 is formed, the film forming temperature is adjusted within a range that does not affect the film forming conditions, thereby adjusting the thermal stress when the substrate 1 is at room temperature. The deformation of the substrate 1 at room temperature can be reduced. As the method, for example, the material of the substrate 1 After determining the film formation temperature, the film formation temperature is changed, and the film formation is performed. After that, the film formation temperature that minimizes the deformation when the substrate 1 is brought to the room temperature is found, and the film formation is performed at that temperature. What should I do?

[0029] When the film forming temperature is limited, for example, the amount of deformation when the material of the substrate 1 is changed and the film is formed at a predetermined film forming temperature, and then the substrate 1 is brought to a normal temperature state. It is only necessary to find the material of the substrate 1 with the smallest value and use the material as the material of the substrate 1.

[0030] Substances constituting the thin film used in the present invention include Ta O, Ti in addition to SiO and NbO.

2 2 5 2 5

In addition to materials such as O, ZrO, HfO, and Al O, materials that generate compressive stress during film formation

2 2 2 2 3

Can be used.

Example

[0031] As a substrate 1 as shown in FIG. 1, 50 mm square and 0.3 mm thick quartz was used, and 51 layers of SiO and 50 layers of Nb 0 were alternately formed on the surface of the substrate by a sputtering device. . Deposition temperature is about

2 2 5

200 ° C. The average thickness of one layer of SiO is about 150nm, and the average thickness of one layer of Nb0 is 250η.

2 2 5

m. The thickness of the multilayer optical thin film 4 thus formed was about 20 m.

[0032] The amount of warpage of the substrate 1 during the film formation was observed to be about 1.1 mm. When the substrate 1 was brought to room temperature after the film formation was completed, the amount of warpage of the substrate 1 was improved to 0.5 mm.

[0033] By cutting this substrate with a dicing saw, a large number of optical elements having a thickness of 0.3 mm and 8 mm x 0.3 mm square were cut out. When these elements were sandwiched between waveguides, they could be inserted into the grooves formed in the waveguides without any problems. In addition, desired optical characteristics could be obtained.

Comparative example

[0034] An optical element was manufactured in the same manner as in Example 1 except that glass (BK7) was used as the substrate 1.

[0035] The amount of warpage of the substrate 1 during the film formation was observed to be about 0.9 mm. After the film formation was completed, when the substrate 1 was brought to room temperature, the warping amount of the substrate 1 deteriorated to 1.4 mm. That is, the amount of warpage was about three times that of the example. By cutting this substrate with a dicing saw, a large number of optical elements having a thickness of 0.3 mm and 8 mm × 0.3 mm square were cut out. When these elements were sandwiched between waveguides, some of them could not be fitted into the grooves formed in the waveguide. In addition, there was a force that could not obtain the desired optical characteristics. This is presumed to be caused by the fluctuation of the incident angle due to the warp of the surface.

Claims

The scope of the claims

[1] An optical element formed by forming a thin film having a compressive stress on a substrate, the substrate having a linear expansion coefficient smaller than that of the thin film and having a thickness of 0.8 mm An optical element characterized in that the following materials are used.

2. The optical element according to claim 1, wherein the ratio of the thickness of the thin film to the thickness of the substrate is between 1:80 force 3: 1.

[3] The optical element according to [1], wherein the thin film has a multilayer structure.

4. The optical element according to claim 1, wherein the material is quartz.

[5] A method of manufacturing an optical element including a step of forming a thin film having compressive stress on a substrate, wherein the substrate has a linear expansion coefficient smaller than a linear expansion coefficient of the thin film. Using a material of 0.8 mm or less, after completion of film formation, when the substrate with the thin film formed on the surface is returned to room temperature, the film formation should be performed at such a temperature that the deformation of the substrate falls within an allowable range. A method for manufacturing an optical element.

6. The method of manufacturing an optical element according to claim 5, wherein the ratio of the thickness of the thin film to the thickness of the substrate is between 1:80 force 3: 1.

7. The optical cord manufacturing method according to claim 5, wherein the thin film has a multilayer film structure.

8. The method for manufacturing an optical element according to claim 5, wherein the material is quartz.