JP2007063574A - Multilayer film forming method and film forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the adhesion of a film in the formation of a multilayer film, suppress the generation of cracks, and manufacture an optical element having a small wavelength shift after the film formation.
A method for forming a multilayer film comprising: a step of forming a vapor deposition film that exhibits compressive stress by normal vapor deposition; and a step of forming a vapor deposition film that exhibits tensile stress by vapor deposition using plasma. In the film forming method, a vapor deposition film showing compressive stress and a vapor deposition film showing tensile stress were alternately laminated.
[Selection] Figure 1

Description

  The present invention relates to a film forming method for stacking a multilayer film on a substrate surface and a film forming apparatus for stacking the multilayer film.

  A vacuum vapor deposition method in which a thin film material is heated and evaporated in a vacuum and deposited on a substrate is one of the representative methods of thin film formation technology and is used in a wide range of fields. As the evaporation source for vaporizing the thin film material, resistance heating, electron beam heating, high frequency induction heating, laser beam heating, or the like is used. Among them, the electron beam accelerated to several kV to several tens kV is irradiated and heated. Electron beam heating is most utilized.

  In addition, ion beam assisted deposition that irradiates the substrate with gas ions during film formation, ion plating that causes ions of evaporated particles to collide with the substrate by some ionization means, etc. Since it is possible to form a simple film, it can be used for various purposes. Hereinafter, deposition using plasma including ion energy is referred to as “deposition using plasma”, and deposition not using plasma is referred to as “normal deposition”.

  Usually, vapor deposition has an advantage that the film forming speed is high, but there is a problem that the adhesion of the film is low and cracks are likely to occur in the film in an environmental test after film formation. Vapor deposition using plasma has the advantage of high film adhesion, but there is a problem that cracks are likely to occur after film formation because the internal stress of the film increases.

Thus, for example, Patent Document 1 and Patent Document 2 disclose film forming means that combines normal vapor deposition and vapor deposition using plasma in order to improve the adhesion of the film and reduce internal stress.
In Patent Document 1, by changing at least one of the film forming method and the film forming conditions during the process of forming at least one thin film, the internal stress of each thin film is changed from compressive stress to tensile stress or On the contrary, the internal stress of the optical thin film is canceled and reduced in each thin film to prevent the substrate from bending or peeling off.

  Patent Document 2 states that in a film forming method in which a plurality of films are stacked on a substrate and a lens, there are at least one film stacked by a vacuum deposition method and a film stacked by a method using plasma. Thus, a film forming method with high film adhesion, no film cracking, and high film forming speed is provided.

In addition, as another means of reducing internal stress, a deposition film showing compressive stress and a deposition film showing tensile stress are alternately laminated on the substrate many times and offset by balancing the internal stress of a pair of adjacent films. techniques Ru abolished the effect of stress on the substrate is, for example disclosed in Patent Document 3.

Patent Document 3 discloses that in a conventional optical laminate obtained by alternately laminating high refractive index ZrO ₂ and low refractive index SiO ₂ , both the internal stresses of ZrO ₂ and SiO ₂ are compressive stresses. This problem is solved by substituting TiO ₂ having a refractive index substantially equal to that of ZrO ₂ and exhibiting sufficient tensile stress to offset the compressive stress of SiO ₂ .
JP-A-9-85874 JP 2003-221663 A JP 59-10901

Optical thin films using light interference are applied to various products such as antireflection films and various filters and mirrors. There are various factors that determine the optical characteristics required for the optical thin film, such as wavelength, transmittance or reflectance, and deflection characteristics. However, since the optical interference effect is used, the optical film thickness n · d (n : Control of refractive index, d: physical film thickness) is the most important.
However, as disclosed in Patent Document 1, when an optical thin film is formed by intentionally changing the film forming method and film forming conditions, there is a problem that it becomes difficult to control the optical film thickness. This is because even after the same film forming material is used, the refractive index after film formation differs depending on the film forming method and film forming conditions. When the refractive index changes, the film thickness of each layer, the total number of films, etc. This is because the membrane design must be changed. Since the optical thin film manufacturing method disclosed in Patent Document 1 changes at least one of the film forming method and the film forming conditions during the step of forming a single thin film, the film thickness in each film forming method or film forming condition is somewhat different. The refractive index of the layer changes only with this error. That is, there arises a problem that the film thickness control accuracy must be improved as compared with the prior art in order to obtain the same optical specifications as in the prior art. Since the characteristics of the optical thin film depend on the refractive index of each layer to be laminated, it is very difficult to manufacture an element that satisfies a desired optical specification unless reproducibility of the refractive index is secured.

  The method disclosed in Patent Document 2 has no suggestion regarding the selection between the vacuum deposition method and the plasma-based method in each layer, so that a sufficient effect cannot be obtained depending on the combination of the film forming material and the film forming method. There is a problem. As shown in the examples, when the first half layer is formed by a method using plasma and the second half layer is formed by a vacuum evaporation method, some substrate materials cannot withstand the stress of the laminated film, resulting in cracks or film peeling. May end up. In order to widen the reflection bandwidth, which is one of the optical characteristics, it is necessary to increase the difference in refractive index between the high refractive index layer and the low refractive index layer or increase the number of layers. Depending on the method used, the difference in refractive index becomes small, and the total number of films must be increased to obtain a desired reflection bandwidth.

The method disclosed in Patent Document 3 has a problem that the effect of reducing internal stress cannot be obtained when this is performed by vapor deposition using plasma. For example, SiO ₂ used in the examples shows compressive stress when deposited by normal vapor deposition, but shows tensile stress when deposited by vapor deposition using plasma. TiO ₂ shows tensile stress both when it is normally formed by vapor deposition and when it is formed by vapor deposition using plasma. As a result, when both films are vapor-deposited using plasma, the vapor-deposited film showing the tensile stress is laminated, the internal stress increases, and the substrate warps or cracks occur. When the invention is carried out by normal vapor deposition, the effect of reducing internal stress can be obtained, but there is a problem that the adhesive property is low and the change in optical characteristics after film formation becomes large.

  A first aspect of the present invention is a method for forming a multilayer film, the step of forming a vapor deposition film showing compressive stress by normal vapor deposition, and the step of forming a vapor deposition film showing tensile stress by vapor deposition using plasma. A film forming method comprising: Here, a vapor deposition film showing compressive stress and a vapor deposition film showing tensile stress were alternately laminated.

  The second aspect of the present invention is a method for forming a multilayer film in which a high refractive index layer and a low refractive index layer are alternately laminated, and at least one low refractive index layer is formed by ordinary vapor deposition. The film forming method includes a step and a step of forming at least one high refractive index layer by vapor deposition using plasma. Here, a layer of 1/4 or more of the entire low refractive index layer of the optical thin film that requires optical characteristics is formed by ordinary vapor deposition, and plasma is used for a layer of 1/4 or more of the entire high refractive index layer. The film was formed by conventional evaporation. Alternatively, the entire low refractive index layer was formed by ordinary vapor deposition, and the entire high refractive index layer was formed by vapor deposition using plasma.

  In the first or second aspect, when a multilayer film of n (n ≧ 3) layers is stacked on the substrate, the first side layer located on the substrate side and at least in contact with the substrate is included by vapor deposition using plasma. At least one of the initial layer and the outer layer including the n-th layer that is at least the outermost layer located away from the substrate was formed.

A third aspect of the present invention is a multilayer film formed by using the film forming method according to either the first or second aspect.
According to a fourth aspect of the present invention, there is provided an optical component comprising a substrate and the multilayer film formed on the third side surface on the substrate.
According to a fifth aspect of the present invention, there is provided an optical product having a light receiving portion, wherein the multilayer film of the third side surface is formed on the light receiving portion.

  According to a sixth aspect of the present invention, there is provided a multilayer film forming apparatus, comprising: a first film forming means for performing normal vapor deposition; a second film forming means by vapor deposition using plasma; A control device that switches between film formation by normal vapor deposition and film formation by vapor deposition using plasma based on a film program is provided, and a vapor deposition film that shows compressive stress is formed by normal vapor deposition by the first film formation means, and second The film forming apparatus forms a vapor deposition film exhibiting tensile stress by vapor deposition using plasma.

  According to a seventh aspect of the present invention, there is provided a multilayer film forming apparatus, a first film forming means for performing normal vapor deposition, a second film forming means for performing vapor deposition using plasma, and a pre-input A control device for switching between film formation by normal vapor deposition and film formation by vapor deposition using plasma based on a film formation program is provided, and at least one low refractive index layer is formed by normal vapor deposition by the first film formation means. The film forming apparatus forms at least one high refractive index layer by vapor deposition using plasma by the second film forming means.

  According to the present invention, the film formation by the normal vapor deposition and the film formation by the vapor deposition using the plasma are alternately repeated, and the vapor deposition film showing the compressive stress and the vapor deposition film showing the tensile stress are alternately laminated. It becomes possible to cancel internal stress. As a result, it becomes possible to improve the adhesion of the film, suppress the generation of cracks, and manufacture an optical element having a small wavelength shift after film formation. In addition, the difference in refractive index between the high refractive index layer and the low refractive index layer is obtained by depositing a low refractive index material by normal vapor deposition and laminating by depositing a high refractive index material by vapor deposition using plasma. Can be increased. Thereby, the reflection band can be widened, or an element having an equivalent reflection band can be designed with a small total number of films.

Embodiments of the present invention will be described below with reference to the drawings.
In FIG. 1, an optical thin film 3 formed by alternately laminating a high refractive index layer 1 formed of a high refractive index material and a low refractive index layer 2 formed of a low refractive index material is formed on a substrate 4. The optical element which obtains a desired filtering characteristic using the multiple reflection from a layer interface is shown. In the examples, an optical filter is manufactured, but the multilayer film that can be manufactured according to the present invention is not limited to an optical thin film.

The high refractive index layer 1 and the low refractive index layer 2 positioned in the outermost layer were formed by vapor deposition using plasma, and the other low refractive index layers 2 except the outermost layer were formed by ordinary vapor deposition. For the sake of explanation, a layer formed by vapor deposition using plasma is shown by shading. When the first layer in contact with the substrate is a low-refractive index material, all the high-refractive index layers 1 and the low-refractive index layers 2 positioned in the first layer are formed by vapor deposition using plasma. What is necessary is just to form the other low-refractive-index layer 2 except the 1st layer. In addition, a film forming material showing tensile stress was used as the high refractive index material, and a film forming material showing compressive stress was used as the low refractive index material. Here, the film-forming material exhibiting tensile stress is a film-forming material in which the vapor-deposited film exhibits tensile stress in normal vapor deposition, and examples thereof include TiO ₂ and ZrO ₂ . The film-forming material exhibiting compressive stress is a film-forming material whose vapor-deposited film exhibits compressive stress in normal vapor deposition, and examples thereof include SiO ₂ and ZnS.
The reason why the outermost layer is formed by vapor deposition using plasma is to prevent the occurrence of cracks after the environmental test due to moisture adsorption after the film formation.

  When forming a film-forming material exhibiting compressive stress by vapor deposition using plasma, a vapor-deposited film exhibiting tensile stress is formed. Features. A film of a film showing a compressive stress is normally formed by vapor deposition, and a film of a film showing a tensile stress is formed by vapor deposition using plasma, whereby a vapor deposited film showing a compressive stress and a vapor deposited film showing a tensile stress. Can be alternately laminated, the internal stress of the laminated multilayer film can be offset, and the occurrence of warping and cracking of the substrate can be suppressed. In addition, by repeating the normal vapor deposition and the vapor deposition using plasma, it is possible to improve the adhesion of the film and form a multilayer film in which no cracks or the like occur even after the environmental test. In the production of an optical element, it is possible to suppress changes with time in optical characteristics after film formation and contribute to improvement in accuracy. Further, since the stress applied to the substrate by the multilayer multilayer film is small, the effect can be obtained without limiting the substrate material. For example, even when a base material such as a plastic having a lower resistance than a glass material is used, warping, cracking, and film peeling of the substrate can be suppressed.

  FIG. 2 shows a film forming apparatus as an example. For example, a film forming apparatus shown in FIG. 2 may be used for manufacturing the element shown in FIG. Two evaporation sources 12 are arranged inside the film forming chamber 10 including the exhaust unit 14 and the gas introduction unit 15, and a substrate dome 13 that is a holding unit for the substrate 11 is arranged at a position facing the evaporation source 12. The evaporation source 12 includes an electron gun 20 that irradiates and heats the film forming material 18 with an electron beam, and an openable / closable shutter 19 that shields the film forming material 18. One evaporation source is highly refracted as a film forming material. For the other evaporation source, a low refractive index material is used as a film forming material. Alternatively, a high refractive index material and a low refractive index material may be appropriately supplied to one evaporation source 12 disposed in the film forming chamber 10 using a film forming material supply mechanism or the like.

  The film forming apparatus shown in FIG. 1 includes an ion source 17, and in addition to normal vapor deposition (hereinafter referred to as EB method) using an electron gun, ion beam assisted vapor deposition (hereinafter referred to as IAD method) as vapor deposition using plasma. ) Can be implemented. A control device 16 connected to at least the evaporation source 12 and the ion source 17 is provided outside the film formation chamber 10. The film formation method and film formation conditions are controlled by the control device 16, and in accordance with the film formation program inputted in advance. Thus, the EB method and the IAD method may be switched.

  When film formation is performed by the EB method, the inside of the film formation chamber 10 is maintained in a predetermined vacuum atmosphere using the exhaust unit 14 and the gas introduction unit 15, and an electron beam is applied to the film formation material 18 with the shutter 19 closed. The film forming material 18 is heated and vaporized by irradiation. When various conditions such as melting and rate are satisfied, the shutter 19 is opened and film formation is started. The film forming material 18 scatters in the film forming chamber 10 and is deposited on the substrate 11 to form a thin film. When the film thickness reaches the target value, the shutter 19 is closed, the electron gun 20 and the like are stopped, and the film formation is terminated.

  When film formation is performed by the IAD method, a predetermined vacuum atmosphere is maintained as in normal vapor deposition, and the film forming material 18 is irradiated with an electron beam while the shutter 19 is closed. At the same time, the gas introduced into the ion source 17 is ionized to generate plasma, and gas ions in the plasma are extracted to irradiate the substrate. When various conditions are satisfied, the shutter 19 is opened and film formation is started. When the shutter 19 is opened, the film-forming material 18 scatters in the film-forming chamber 10, and gas ions are irradiated from the ion source 17 to the substrate 11. A strong and dense film is formed. When the film thickness reaches the target value, the shutter 19 is closed, the electron gun 20 and the ion source 17 are stopped, and the film formation is completed.

  The apparatus shown in the figure selects the IAD method as the deposition using plasma, but the present invention is not limited to this, and an ion plating method, a sputtering method, or the like may be selected. In addition, the EB method is selected as the normal vapor deposition, but not limited thereto, resistance heating, high frequency induction heating, laser beam heating, or the like may be selected. The film forming apparatus only needs to have both a film forming means for performing normal vapor deposition and a film forming means for performing vapor deposition using plasma, and switching of the film forming means can be automatically controlled based on a program inputted in advance. desirable.

Hereinafter, the results of actually producing the optical element shown in FIG. 1 using the film forming apparatus shown in FIG. 2 will be shown. The total number of optical thin films produced was 40 layers, and TiO ₂ was used as the high refractive index material and SiO ₂ was used as the low refractive index material. The conditions for film formation using the EB method and the IAD method are as shown in Table 1.

Table 2 shows the visual appearance immediately after the film formation, the visual appearance after the environmental test, and the wavelength shift amount after the environmental test of the optical element manufactured according to this example. In the environmental test, an optical element produced at a temperature of 60 ° C. and a humidity of 90% was left for 72 hours. A wavelength shift means the amount of change before and after an environmental test for a wavelength having a reflectance of 50% (wavelength of about 500 nm). For comparison, an element in which an optical element having a film design equal to that in FIG. 1 under the film formation conditions shown in Table 1 is produced only by the EB method, and a film design equivalent to that in FIG. An evaluation of an element produced by using only the IAD method is also shown.

  In the IAD method, the temperature of the substrate is greatly increased due to the substrate heating by ion irradiation and the radiation heat of the ion source. There is a problem that cracks are likely to occur, and an element manufactured only by the IAD method has cracks immediately after film formation. In addition, the film formed by the EB method has a problem that the density is low and cracks are likely to occur due to moisture adsorption after the film formation, and the element manufactured only by the EB method has cracks after the environmental test. By combining the IAD method and the EB method in this example, the occurrence of cracks could not be confirmed immediately after film formation and after environmental testing, and the film stress of the entire multilayer film was reduced while keeping the film density high. It can be seen that was produced.

  In addition, Table 2 shows that the wavelength shift after the environmental test is very small in the element produced by this example as compared with the element produced only by the EB method or only the IAD method. By alternately performing normal vapor deposition and vapor deposition using plasma, it is possible to suppress changes over time in the optical characteristics after film formation and contribute to improving the accuracy of the optical element.

FIG. 3 shows the spectral characteristics of each optical element shown in Table 2. The refractive index (n _H ) of the high refractive index layer formed by the EB method was 2.0, and the refractive index (n _L ) of the low refractive index layer was 1.4. Further, the refractive index (n _H ) of the high refractive index layer formed by the IAD method was 2.4, and the refractive index (n _L ) of the low refractive index layer was 1.45. The refractive index (n _H ) of the high refractive index layer according to this example is 2.4, the refractive index (n _L ) of the low refractive index layer is 1.45 only for the outermost layer, and the others are 1.4. From the figure, it can be seen that the spectral characteristics of the present example have a high reflectance in the widest wavelength range.

  In general, even if the same material is used, the refractive index after film formation is higher when plasma deposition is performed than when vapor deposition is performed. Thus, the difference in refractive index between the high refractive index material and the low refractive index material can be increased. This makes it possible to widen the reflection bandwidth when designing a highly reflective mirror or the like in the optical thin film having the same total number of films. That is, it is possible to obtain a reflection bandwidth equal to the conventional one with a smaller total number of films than before, facilitating film design, and significantly improving the productivity of optical thin films having similar optical characteristics. The reduction of the total number of films contributes to the reduction of stress in the entire optical thin film at the same time and is effective in reducing the occurrence of cracks.

  In addition, if attention is paid only to the step of forming a single thin film, the film forming method and the film forming conditions are the same, so that the refractive index can be easily controlled and reproducibility can be ensured. By reducing the total number of films and improving the refractive index control accuracy, an optical element having desired optical characteristics can be easily manufactured.

In the above embodiment, TiO ₂ or SiO ₂ is used as a material for forming each thin film, but MgF ₂ , ZrO ₂ , Al ₂ O ₃ , Ta ₂ O ₅ or the like may be used instead.
Note that the low refractive index layer 2 using vapor deposition using plasma is only one layer close to the air side of the multilayer film, but by increasing the number of layers within the range where cracks due to film stress do not occur, cracks after the environmental test May be less likely to occur. Alternatively, the low refractive index layer 2 located on the substrate side may be formed by the IAD method to improve the adhesion between the substrate and the film and prevent film cracking. For example, an n-layer multilayer optical thin film includes an initial layer that includes the first layer and is positioned on the substrate side, an outer layer that includes the outermost layer and is positioned away from the substrate, and an intermediate layer positioned between the initial layer and the outer layer. It may be divided into layers, and one or both of the initial layer and the outer layer may be formed by vapor deposition using plasma, and the intermediate layer may be formed by vapor deposition using plasma and normal vapor deposition. What is necessary is just to select the number of layers of an initial stage layer and an outer layer suitably.

  In the embodiment, the outermost layer and the first layer are formed by vapor deposition using plasma, but the entire low refractive index layer is formed by normal vapor deposition, and the entire high refractive index layer is formed by vapor deposition using plasma. May be formed. Alternatively, a part of the low refractive index layer may be formed by ordinary vapor deposition, and a part of the high refractive index layer may be formed by vapor deposition using plasma. It is effective to form at least ¼ or more of the entire low refractive index layer by ordinary vapor deposition and to form at least ¼ or more of the entire high refractive index layer by vapor deposition using plasma. .

  In the embodiment, a film-forming material exhibiting compressive stress and a film-forming material exhibiting tensile stress are laminated, but two kinds of film-forming materials showing compressive stress may be selected and laminated (where one material is When the film is formed by vapor deposition using plasma, the vapor deposited film exhibits tensile stress). By alternately repeating the normal vapor deposition and the vapor deposition using plasma, the vapor deposition film showing the compressive stress and the vapor deposition film showing the tensile stress are alternately laminated, and the same effect can be obtained.

  The optical thin film (multilayer film) produced by using the film forming method of the present invention can be applied to various optical parts, optical products and the like. For example, in FIG. 1, an optical thin film 3 having a predetermined filter characteristic is formed on a substrate 4 such as plastic or glass, and the optical characteristic of the substrate 4 and the filter characteristic of the optical thin film 3 are taken into consideration. An optical component such as an optical low-pass filter can be formed by designing a film so that desired spectral characteristics can be obtained. Further, in an optical product having a light receiving unit and a device for processing incident light from the light receiving unit, such as a digital camera or a camera-equipped mobile phone, the optical thin film can be formed on the light receiving unit. Thereby, it is possible to obtain an optical component, an optical product, or the like having a wide reflection band and high reliability.

The figure which shows the optical element of this invention Schematic diagram of deposition system The figure which shows the spectral characteristic of the optical element produced by the Example

Explanation of symbols

1 High refractive index layer
2 Low refractive index layer
3 Optical thin film
4 Board
10 Deposition chamber
11 Board
12 Evaporation source
13 Substrate dome
14 Exhaust means
15 Gas introduction means
16 Control unit
17 Ion source
18 Film-forming materials
19 Shutter
20 electron gun

Claims (11)

A method for forming a multilayer film,
A film forming method comprising the steps of: forming a vapor deposition film showing compressive stress by normal vapor deposition without using plasma; and forming a vapor deposition film showing tensile stress by vapor deposition using plasma. In the film-forming method of Claim 1,
A film forming method comprising alternately laminating a vapor deposition film exhibiting compressive stress and a vapor deposition film exhibiting tensile stress. A method for forming a multilayer film in which a high refractive index layer and a low refractive index layer are alternately laminated,
Forming at least one low refractive index layer by normal vapor deposition without using plasma; and
A film forming method comprising the step of forming at least one high refractive index layer by vapor deposition using plasma. In the film-forming method according to claim 3, a layer of 1/4 or more of all the low-refractive index layers of the optical thin film that requires optical properties is formed by ordinary vapor deposition,
A film forming method characterized in that a layer having a quarter or more of all the high refractive index layers is formed by vapor deposition using plasma. In the film-forming method of Claim 3,
The entire low refractive index layer is formed by ordinary vapor deposition,
A film forming method comprising forming the entire high refractive index layer by vapor deposition using plasma. In the film-forming method of Claims 1 thru | or 4,
When laminating the multilayer film of n (n ≧ 3) layers on the substrate,
By vapor deposition using plasma,
Forming at least one of an initial layer including at least a first layer located on the substrate side and in contact with the substrate; and an outer layer including at least the nth layer that is positioned away from the substrate and is the outermost layer. A characteristic film forming method.   A multilayer film formed by using the film forming method according to claim 1.   An optical component comprising a substrate and the multilayer film according to claim 7 formed on the substrate.   An optical product having a light receiving portion, wherein the multilayer film according to claim 7 is formed on the light receiving portion. A film forming apparatus for a multilayer film,
First film forming means for performing normal vapor deposition without using plasma, second film forming means for performing vapor deposition using plasma, and film formation by normal vapor deposition and plasma based on a film input program inputted in advance. Equipped with a control device that switches between film deposition by conventional vapor deposition,
A vapor deposition film showing compressive stress by normal vapor deposition is formed by the first film forming means,
A film forming apparatus characterized in that a vapor deposition film showing tensile stress is formed by the second film forming means by vapor deposition using plasma. A film forming apparatus for a multilayer film,
First film forming means for performing normal vapor deposition without using plasma, second film forming means for performing vapor deposition using plasma, and film formation by normal vapor deposition and plasma based on a film input program inputted in advance. Equipped with a control device that switches between film deposition by conventional vapor deposition,
At least one low refractive index layer is usually formed by the first film forming means by vapor deposition,
A film forming apparatus, wherein at least one high refractive index layer is formed by the second film forming means by vapor deposition using plasma.

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