JPH06186403A - Multilayer film optical member - Google Patents

Abstract

PURPOSE:To prevent the deformation due to internal stress of a thin film. CONSTITUTION:Stresses of materials having compression stress among each material constituting of a multilayer film are defined as S11, S12, S13,..., the total physical film thicknesses in the multilayer film of each material are defined as d11, d12, d13,..., and S11Xd11+S12Xd12+S13Xd13+... is defined as S1. On the other hand, the stressed of materials having tensile stress are definned as S21, S22, S23,... and the total physical film thicknesses in the multilayer film of each material are defined as d21, d22, d23,... and S21Xd21+S22Xd22+ S23Xd23+... is defined as S2. An adjusting layer not affecting to the optical performance and also enabling to satisfy the function of 2/3<S1/S2<3/2, is provided on at least one layer of the multilayer film.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multi-layer optical member formed by forming a multi-layer film as a reflective film on the surface of a substrate, and particularly to preventing distortion of the substrate due to internal stress of the formed thin film. The present invention relates to a multi-layer optical member capable of

[0002]

2. Description of the Related Art It has been conventionally known that a thin film formed on a substrate by a vacuum vapor deposition method, a sputtering method or the like has a constant internal stress and has a force to deform the substrate. When this stress is large, or especially when the thickness of the substrate is small, it may cause deformation that affects the optical performance. Especially 1 mm
With an extremely thin substrate having a thickness of not more than the thickness, even if highly accurate polishing of the order of λ / 100 (λ is the wavelength) is performed, the substrate is deformed to the order of λ after the multilayer film is formed.

When the substrate thus formed with the multilayer film is used as a movable mirror in the pickup portion of an optical disk, roughly, a laser beam from a laser light source is made into a parallel light flux, and then a condenser lens is passed through the movable mirror. To about 2 μm
When the spot diameter is set to and the signal is used to read the signal by irradiating the spot on the optical disc, the movable mirror is required to have high flatness so as not to impair the parallelism of the parallel light flux of the laser light.

Therefore, conventionally, as a method for suppressing the deformation of the substrate due to the internal stress of the multilayer film, the amount of deformation of the substrate due to the internal stress of the film is measured in advance, and the substrate surface is polished and processed in advance based on the result. There is a method of providing a curvature in the direction, or a method of canceling the force applied to the substrate by providing a film having the same stress on the back surface of the substrate as described in JP-B-62-18881. Are known.

[0005]

However, in the conventional method for polishing the substrate, a considerable accuracy is required for the curvature-polishing of the substrate surface, which is performed as a pre-process. In addition, the method of forming a film on the back surface has a drawback that the process is complicated because the film formation is required twice and cannot be used unless the film is formed on the back surface. Therefore, in the present invention, a multilayer optical member in which a multilayer film is formed so as to prevent distortion of the substrate surface by only one film formation on one surface without the need for pre-processing the substrate or multiple film formations. The purpose is to provide.

[0006]

In order to achieve the above object, the present invention provides a multilayer optical member comprising a substrate and a multilayer film formed on the surface of the substrate, wherein each substance constituting the multilayer film is formed. , The stress of the material with compressive stress is s ₁₁ ,
s _12, s ₁₃ , ..., The total physical film thicknesses of the respective materials in the multilayer film are d ₁₁ , d ₁₂ , d ₁₃ ,.
.., where S ₁ is s ₁₁ × d ₁₁ + s ₁₂ × d ₁₂ + s ₁₃ × d
And ₁₃ + ......, likewise, s ₂₁ stresses the material having a tensile _stress, s _22, s _23, ......, the sum of the physical thickness of the multilayer film of the respective materials To d ₂₁ , d ₂₂ , d
₂₃ , ..., S ₂ is s ₂₁ × d ₂₁ + s ₂₂ × d
₂₂ + s ₂₃ × when the d ₂₃ + · · · · · ·, without affecting optical performance, and, 2/3 <adjusting layer to be able to satisfy S ₁ / S ₂ <3/2 the relationship Was provided in at least one layer of the multilayer film.

[0007]

According to the above structure, after designing only the ordinary optical characteristics, an adjusting layer is added so that the stress can be relaxed without impairing the required optical characteristics, and the compressive stress and tensile stress By balancing, the stress of the entire multilayer film is reduced. Here, in order to sufficiently maintain the optical performance of the multilayer optical member, the amount of deformation of the substrate due to film formation,
That is, when the amount of warpage is kept at 1/20 or less of the wavelength used, the product of the stress of the material having the compressive stress and the total physical film thickness of the respective material films forming the multilayer film is calculated. to the sum S _1, and the stress of the material having a tensile stress, the ratio S ₁ / S ₂ of the sum S ₂ of the product of the sum of the physical thickness of the multilayer film of the respective materials, with 2/3 or more 3 / Two
The following values are required, with values closer to 1 being more desirable.
As a result, a large deformation of the substrate that affects the optical performance is eliminated, and a good optical surface can be obtained without going through a process such as special pre-processing of a special substrate or film formation on the back surface of the substrate. Further, when the multilayer optical member of the present invention is used as a reflecting mirror in the pickup portion of an optical disc, a large substrate deformation does not occur, so that the deviation of the parallelism in the parallel light flux of the laser light is reduced, and the focus position by the focusing lens is reduced. Changes and spot diameter changes are minimized, and malfunctions and reading errors are less likely to occur.

[0008]

Example 1 The multilayer optical member of this example has a thickness of 780 nm.
With a reflection film for laser light having a wavelength of, a stress relaxation layer is formed on a glass substrate having a diameter of 10 mm and a thickness of 1 mm, and a high reflectance layer and a low reflectance layer are alternately formed on the stress relaxation layer. It was formed by forming a film. As a material for the reflective film, Ti is used for the high reflectance layer.
O ₂ and SiO ₂ were used for the low reflectance layer.

The multilayer optical member has a vacuum chamber with an oil diffusion pump of 5 × 10 ^-5 Torr.
Evacuate to 300, and fix the glass substrate fixed in the vacuum chamber to 300
It was heated up to 0 ° C., and a reflective film made of the above material was provided on a glass substrate to form a structure. The reflective film is a T layer having an optical thickness of 3λ (λ = 850 nm) as a stress relaxation layer on the first layer on the glass substrate side.
iO ₂ layer, λ / 4 SiO ₂ layer and λ / 4 Ti on it
Nine sets of O ₂ layers were alternately formed, and finally each layer of a λ / 8 SiO ₂ layer was formed by electron beam evaporation. FIG. 1 shows the spectral reflectance of the multilayer optical member according to the present embodiment when the light is reflected at 45 degrees.

According to this embodiment, as shown in FIG. 1, the reflection characteristic was 99% or more at the used wavelength (780 nm). The film stress of the reflective film was measured and found to be 7.5.
A × 10 ⁷ dyn / cm ^2, were examined substrate deformation before and after the film formation, the warpage amount was 20 nm.

By the way, when the multilayer optical member of this embodiment is used as a movable mirror in the pickup portion of an optical disk, the amount of substrate deformation due to film formation, that is, the amount of warpage is 1/20 or less of the wavelength λ = 780 nm used, that is, about. 40
It must be kept within nm. Therefore, in order to maintain sufficient optical performance, the sum of the products of the stresses of the substances having a compressive stress and the total physical film thickness of each substance forming the multilayer film of each substance The ratio S ₁ / S ₂ of the sum S ₂ of the product of S ₁ and the stress of the substance having the tensile stress to the total physical film thickness of the multilayer film of each substance is 2/3.
A value of 3/2 or less is required, and a value closer to 1 is more desirable. Therefore, it can be seen that the amount of warpage is sufficiently within the practical range in the multilayer optical member of this example.

[0012]

Second Embodiment The multilayer optical member of the present embodiment uses a material having a high reflectance of TiO ₂ and a low reflectance of SiO ₂ as in the case of the first embodiment. A reflection film for laser light having a wavelength of is provided.

The multi-layered film optical member has a vacuum chamber of 5 × 10 ⁻⁵ Torr using an oil diffusion pump.
Evacuated to 10 mm in diameter and fixed in a vacuum chamber, thickness 1
A glass substrate of mm was heated to 300 ° C., and a reflective film made of the above material was provided on the glass substrate. The reflection film has an optical film thickness λ / 2 (λ = 57) on the first layer on the glass substrate side.
0 nm) TiO ₂ layer, 9 pairs of λ / 4 SiO ₂ layer and λ / 2 TiO ₂ layer are alternately formed on the TiO ₂ layer, and finally λ / 8 Si layer.
Each of the O ₂ layers was formed by an electron beam evaporation method. The stress relaxation layer is a λ / 2 TiO ₂ layer. FIG. 2 shows the spectral reflectance of the multilayer optical member according to the present embodiment when the light is reflected by 45 degrees.

According to this embodiment, as shown in FIG. 2, a reflection characteristic of 99% or more was obtained at the wavelength used (780 nm). Moreover, when the film stress of the reflective film was measured, it was 6.3 ×
It was 10 ⁷ dyn / cm ² , and when the substrate deformation before and after film formation was examined, the amount of warpage was 11 nm.

Next, a comparative example 1 with the first and second embodiments
Indicates. In the multilayer optical member of Comparative Example 1, similar to Examples 1 and ₂ , TiO ₂ was used as the high reflectance layer and SiO ₂ was used as the low reflectance layer.
A reflective film for laser light having a wavelength of 780 nm was provided using the material Further, the inside of the vacuum chamber was evacuated to 5 × 10 ⁻⁵ Torr using an oil diffusion, and a glass substrate having a diameter of 10 mm and a thickness of 1 mm fixed in the vacuum chamber was heated to 300 ° C. It was configured by providing a reflective film made of.

The reflection film was formed by forming a TiO ₂ layer having an optical film thickness of λ / 4 (λ = 850 nm) on the first layer on the glass substrate side, and forming a λ ₂ layer on the TiO ₂ layer.
9 pairs of / 4 SiO ₂ layers and λ / 4 TiO ₂ layers alternately,
Finally, each of the λ / 8 SiO ₂ layers was formed by an electron beam evaporation method. FIG. 3 shows the spectral reflectance of the multilayer optical member of Comparative Example 1 when the reflective film is incident at 45 degrees.

When the film stress of the reflective film of Comparative Example 1 was measured, it was 8.0 × 10 ⁸ dyn / cm ² , and when the substrate deformation before and after film formation was examined, the amount of warpage was 151 nm. As a result, the multilayer optical members of Examples 1 and 2 and Comparative Example 1 have similar reflection characteristics (99% or more at a wavelength of 780 nm), but the multilayer optical members of Examples 1 and 2 are Comparative Example 1 It can be seen that the amount of deformation of the substrate is 1/10 or less, which is very small compared to.

[0018]

Example 3 The multilayer optical member of this example uses Ta ₂ O _{5 for} the high reflectance layer and MgF ₂ for the low reflectance layer, and uses 780
A reflection film for laser light having a wavelength of nm was provided. For the multilayer optical member, a vacuum chamber was evacuated to 5 × 10 ⁻⁵ Torr using an oil diffusion pump, and a glass substrate having a diameter of 10 mm and a thickness of 1 mm fixed in the vacuum chamber was heated to 300 ° C. Then, a reflective film made of the above material was provided on the glass substrate.

The reflection film is a Ta ₂ O having an optical film thickness of 2λ (λ = 870 nm) as a stress relaxation layer on the first layer on the glass substrate side.
_Five layers, and each of the λ / 4 MgF ₂ layers were formed by electron beam evaporation. FIG. 4 shows the spectral reflectance of the multilayer optical member according to the present embodiment when the light is reflected at 45 degrees.

According to the present embodiment, as shown in FIG. 4, the reflection characteristic was 99% or more at the used wavelength (780 nm). The film stress of the reflective film was measured and found to be 3.5.
A × 10 ⁷ dyn / cm ^2, were examined deformation of before and after the film formation of the substrate, the warpage amount was 11 nm.

[0021]

[Embodiment 4] The multilayer optical member of the present embodiment is similar to Embodiment 3 in that the high reflectance layer is a Ta ₂ O ₅ layer and the low reflectance layer is MgF.
Using a material consisting of _two layers, and changing the film structure,
A reflective film for laser light having a wavelength of 0 nm was provided.

The above-mentioned multilayer optical member has a vacuum chamber of 5 × 10 ^-5 Torr using an oil diffusion pump.
The glass substrate having a diameter of 10 mm and a thickness of 1 mm fixed in a vacuum chamber was heated to 300 ° C., and a reflection film made of the above material was provided on the glass substrate.

The reflection film is formed in order from the glass substrate side first layer.
2λ / 6 Ta ₂ O with optical film thickness λ = 870 nm
Nine sets of ₅ layers and λ / 6 MgF ₂ layers were alternately arranged, and finally each λ / 8 MgF ₂ layer was formed by electron beam evaporation. The stress relaxation layer has a Ta of 2λ / 6.
₂ O ₅ layer and λ / 6 MgF ₂ layer.

FIG. 5 shows the spectral reflectance of the multi-layered optical member of this embodiment when the light is reflected at 45 degrees.

According to this embodiment, as shown in FIG. 5, a reflection characteristic of 99% or more was obtained at the wavelength used (780 nm). Also, when the film stress of the reflective film was measured, it was 4.2 ×
It was 10 ⁶ dyn / cm ² , and when the deformation of the substrate before and after film formation was examined, the amount of warpage was 6 nm.

Next, a comparative example 2 with the third and fourth embodiments will be shown. The multilayer optical members of Comparative Example 2 are the same as those of Examples 3 and 4.
Similarly, the high reflectance layer has a Ta ₂ O ₅ layer and the low reflectance layer has M
A reflective film for laser light having a wavelength of 780 nm was provided using a material composed of a gF ₂ layer. In addition, the inside of the vacuum chamber is 5 × 10 ⁻⁵ Tor using an oil diffusion pump.
The glass substrate having a diameter of 10 mm and a thickness of 1 mm fixed in a vacuum chamber was heated to 300 ° C. after evacuation to r, and a reflection film made of the above material was provided on the glass substrate.

The reflective film was a Ta ₂ O ₅ layer having an optical film thickness of λ / 4 (λ = 850 nm) on the first layer on the glass substrate side, and a λ / 4 MgF ₂ layer and a λ / 4 Ta ₂ layer thereon. Alternating 9 layers of O ₅
Finally, each tank of λ / 8 MgF ₂ layer was formed by the electron beam evaporation method. FIG. 6 shows the spectral reflectance of the multilayer film optical member of Comparative Example 2 at the time of incidence of 45 degrees due to the reflection film.
Shown in.

When the film stress of the reflective film of Comparative Example 2 was measured, it was 6.5 × 10 ⁸ dyn / cm ² , and when the substrate deformation before and after film formation was examined, the amount of warpage was 135 nm. As a result, the multilayer optical members of Examples 3 and 4 and Comparative Example 2 have similar reflection characteristics (99% or more at a wavelength of 780 nm), but the multilayer optical members of Examples 3 and 4 are Comparative Example 2 It can be seen that the amount of deformation of the substrate is 1/10 or less, which is very small compared to.

The values of the reflectance, the film stress of the multilayer films and the film stress in the case of a single film material constituting each film in Examples 1 to 4 and each comparative example are summarized and shown in Table 1. .

[0030]

[Table 1]

[0031]

As described above, according to the present invention, the adjusting layer for adjusting the deformation of the substrate caused by the internal stress of the formed thin film is provided in at least one layer of the multilayer film to be formed. Since the deformation amount can be balanced in the multilayer film, it is possible to obtain the multilayer optical member in which the substrate is not deformed by only one film formation. In addition, since it is not necessary to perform a troublesome multiple times of film formation and highly accurate polishing, it is possible to inexpensively provide a multilayer optical member having a high yield and excellent optical properties.

[Brief description of drawings]

FIG. 1 is a graph showing the spectral reflectance of Example 1 of the present invention.

FIG. 2 is a graph showing the spectral reflectance of Example 2 of the present invention.

FIG. 3 is a graph showing the spectral reflectance of Comparative Example 1.

FIG. 4 is a graph showing the spectral reflectance of Example 3 of the present invention.

FIG. 5 is a graph showing the spectral reflectance of Example 4 of the present invention.

FIG. 6 is a graph showing the spectral reflectance of Comparative Example 2.

Claims (1)

[Claims] 1. A multilayer optical member comprising a substrate and a multilayer film formed on the surface of the substrate, wherein a stress of a substance having a compressive stress among the substances constituting the multilayer film is s ₁₁ ,
s _12, s ₁₃ , ..., The total physical film thicknesses of the respective materials in the multilayer film are d ₁₁ , d ₁₂ , d ₁₃ ,.
.., where S ₁ is s ₁₁ × d ₁₁ + s ₁₂ × d ₁₂ + s ₁₃ × d
And ₁₃ + ......, likewise, s ₂₁ stresses the material having a tensile _stress, s _22, s _23, ......, the sum of the physical thickness of the multilayer film of the respective materials To d ₂₁ , d ₂₂ , d
₂₃ , ..., S ₂ is s ₂₁ × d ₂₁ + s ₂₂ × d
₂₂ + s ₂₃ × when the d ₂₃ + · · · · · ·, without affecting optical performance, and, 2/3 <adjusting layer to be able to satisfy S ₁ / S ₂ <3/2 the relationship Is provided in at least one layer of the multilayer film.