JP2007298659A

JP2007298659A - Neutral density filter

Info

Publication number: JP2007298659A
Application number: JP2006125444A
Authority: JP
Inventors: Kenji Kameda; 健二亀田; Koji Watanabe; 晃司渡邉; Kazuyuki Eto; 和幸江藤
Original assignee: Japan Aviation Electronics Industry Ltd
Current assignee: Japan Aviation Electronics Industry Ltd
Priority date: 2006-04-28
Filing date: 2006-04-28
Publication date: 2007-11-15

Abstract

<P>PROBLEM TO BE SOLVED: To avoid cracking by preventing progress of roughness of a film at a boundary surface between different metals. <P>SOLUTION: An oxide film layer 5 comprising a hafnium oxide film layer or an aluminum oxide film layer is formed at a boundary between a first metal film layer 3 comprising aluminum and a second metal film layer 2 adjacent to the first metal film layer and comprising hafnium. The first metal film layer comprises aluminum and the second metal film layer comprises chromium 6 or silver 7. The first metal film layer comprises chromium 6 and the second metal film layer comprises silver 7. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

本発明は、膜の荒れの進行を防止した耐久性を有する中性濃度フィルタに関する。 The present invention relates to a neutral density filter having durability that prevents progression of film roughness.

中性濃度フィルタ（以下ＮＤフィルタという）は、入射光を減光するために用いられる光学フィルタであり、例えば分光透過特性が偏るＨｆ（ハフニウム）膜及びＡｌ（アルミニウム）膜を合成石英の透明基板上にスパッタリングにより積層して形成される（特許文献１参照）。
図５（ａ）は、従来のＮＤフィルタの成膜構造の一例を示すもので、合成石英基板１上にＨｆ層２及びＡｌ層３を被着し、最外層に所望の光学特性を得ると共に酸化や傷付を防ぐためにＨｆＯ２（酸化ハフニウム）層４を被着した構造である。この場合、各層の膜厚形成はイオンビームスパッタリングにより行われ、一例として光学濃度ＯＤ値１．４８の例を示すと図５（ｂ）に示すように１７．５８ｎｍのＨｆ層２、１２．８４ｎｍのＡｌ層３、１４．３５ｎｍのＨｆＯ２層４という具合に成膜されて平坦な分光透過特性を得ている。 A neutral density filter (hereinafter referred to as an ND filter) is an optical filter used to attenuate incident light. For example, an Hf (hafnium) film and an Al (aluminum) film whose spectral transmission characteristics are biased are made of a synthetic quartz transparent substrate. It is formed by laminating by sputtering (see Patent Document 1).
FIG. 5 (a) shows an example of a conventional ND filter film formation structure, in which a Hf layer 2 and an Al layer 3 are deposited on a synthetic quartz substrate 1 to obtain desired optical characteristics in the outermost layer. In this structure, an HfO2 (hafnium oxide) layer 4 is deposited to prevent oxidation and scratching. In this case, the film thickness of each layer is formed by ion beam sputtering. As an example, when an optical density OD value of 1.48 is shown, a 17.58 nm Hf layer 2, 12.84 nm as shown in FIG. The Al layer 3 and the 14.35 nm HfO 2 layer 4 are formed to obtain flat spectral transmission characteristics.

ＮＤフィルタとしては、この成膜後、予め使用環境下以上の熱負荷を加える熱処理が行われる。この熱処理は、金属膜が熱エネルギに晒される使用環境下での耐久性を向上させるために必要であり、経年変化により光学特性が変化しあるいは劣化を最小限とするため、事前に使用環境下以上の熱エネルギを与えて特性を固める処理となっている。
そして、ＮＤフィルタとしては、この熱処理後の品質が所望の耐久性を有し、しかも例えば平坦な分光透過特性となるように製造に当たり各金属膜の材質や各膜厚が選択・調整されることになる。
特開２００５−３００９６３号公報 As the ND filter, after this film formation, a heat treatment is applied in advance to apply a heat load higher than the usage environment. This heat treatment is necessary in order to improve the durability in the usage environment where the metal film is exposed to thermal energy, and the optical characteristics change due to aging or minimize the deterioration. It is the process which gives the above thermal energy and solidifies the characteristic.
As the ND filter, the material of each metal film and each film thickness are selected and adjusted so that the quality after the heat treatment has a desired durability and, for example, flat spectral transmission characteristics. become.
JP-A-2005-300963

上述のように従来ＮＤフィルタの製造にあたっては、Ｈｆ層２及びＡｌ層３等からなる異なる金属膜を熱処理するという工程を取ることになる。ところが、この熱処理によって図６に示す写真（合成石英基板／Ｈｆ／Ａｌ／ＨｆＯ２からなる積層構造の写真）のようにＨｆ層とＡｌ層との境界面において膜の荒れが進行し顕著になることが判明した。この荒れは、金属膜間の熱拡散によって極小径のピンホールの形成という現象に発展し、主にＮＤフィルタの外観の劣化をもたらしひいてはピンホール同士がその後の熱エネルギによる経年変化にて連結することによりクラックとなり、結果的に耐久性が得られないという問題を有する。 As described above, in manufacturing a conventional ND filter, a process of heat-treating different metal films including the Hf layer 2 and the Al layer 3 is taken. However, with this heat treatment, as shown in the photograph (synthetic quartz substrate / Hf / Al / HfO 2 laminated structure) shown in FIG. 6, the roughness of the film advances and becomes noticeable at the interface between the Hf layer and the Al layer. There was found. This roughness develops into the phenomenon of the formation of extremely small pinholes due to thermal diffusion between the metal films, which mainly causes the appearance of the ND filter to deteriorate, and the pinholes are connected by aging due to subsequent thermal energy. It becomes a crack by this, and has a problem that durability cannot be obtained as a result.

本発明は、上述の問題に鑑み、異なる金属間の境界面での膜の荒れの進行を防止してクラックが発生しないようにしたＮＤフィルタの提供を目的とする。 In view of the above-described problems, an object of the present invention is to provide an ND filter which prevents the occurrence of cracks by preventing the progress of film roughness at the interface between different metals.

上述の目的を達成する本発明は、基板に少なくとも２種類以上の金属膜を積層して形成されるＮＤフィルタにおいて、第１の金属膜層とこの第１の金属膜層に隣接する第２の金属膜層との境界に酸化膜層を形成したことを特徴とする。 The present invention that achieves the above-described object provides a first metal film layer and a second metal film adjacent to the first metal film layer in an ND filter formed by laminating at least two kinds of metal films on a substrate. An oxide film layer is formed at the boundary with the metal film layer.

本発明によれば、金属膜層間に酸化膜層を介在させることにより、金属膜層間の拡散による膜の荒れの進行を防止することができ、外観の劣化のみならずクラックの発生を防止してＮＤフィルタとして耐久性を得ることができる。 According to the present invention, by interposing the oxide film layer between the metal film layers, it is possible to prevent the roughening of the film due to diffusion between the metal film layers, and to prevent the occurrence of cracks as well as the deterioration of the appearance. Durability can be obtained as an ND filter.

以下、図１〜図４を参照して本発明の実施形態を説明する。なお、以下の図において図５と同一部分には同一符号を付す。
〔第1実施形態〕
図１は、合成石英基板１上には第１の金属膜層として短波長になるほど光透過率が低下するＨｆ層２が被着され、このＨｆ層２上に酸化膜層であるＨｆＯ２層５が被着され、更にこのＨｆＯ２層５上には第２の金属膜層として短波長になるほど光透過率が上昇するＡｌ層３が被着され、そして最外層に所望の光学特性を得ると共に酸化や傷付を防ぐために保護膜であるＨｆＯ２層４が被着されている構造である。各層の膜厚形成はイオンビームスパッタリングにより行われ、光学濃度ＯＤ値１．４８の具体例を示すと、図１（ｂ）に示すように４８．５５ｎｍのＨｆ層２、１４．６５ｎｍのＨｆＯ２層５、４．７０ｎｍのＡｌ層３、最外層に１４．６５ｎｍのＨｆＯ２層４という具合に成膜され、Ｈｆ層２とＡｌ層３とＨｆＯ２層４、５を積層することで、全体として平坦な分光透過特性を得るようにしている。 Hereinafter, an embodiment of the present invention will be described with reference to FIGS. In the following drawings, the same parts as those in FIG.
[First embodiment]
In FIG. 1, an Hf layer 2 whose light transmittance decreases as the wavelength of the first metal film layer is deposited on a synthetic quartz substrate 1, and an HfO 2 layer 5, which is an oxide film layer, is deposited on the Hf layer 2. Furthermore, an Al layer 3 whose light transmittance increases as the wavelength of the second metal film layer is deposited on the HfO 2 layer 5 as the second metal film layer, and desired optical characteristics are obtained and oxidized on the outermost layer. In order to prevent damage and scratches, an HfO 2 layer 4 as a protective film is deposited. The film thickness of each layer is formed by ion beam sputtering, and a specific example of an optical density OD value of 1.48 is shown as follows. As shown in FIG. 1B, a 48.55 nm Hf layer 2 and a 14.65 nm HfO 2 layer. 5 and 4.70 nm Al layer 3 and outermost layer 14.65 nm HfO 2 layer 4 are formed, and Hf layer 2, Al layer 3 and HfO 2 layers 4 and 5 are laminated to form a flat surface as a whole. Spectral transmission characteristics are obtained.

ここで、酸化膜層ＨｆＯ２層５は、Ｈｆ層２とＡｌ層３との間にあって、これら両者間の境界で発生する熱処理時の拡散を防止し、金属膜２及び３間の膜の荒れの進行を防止するために設けられる。このＨｆＯ２層５の膜厚がきわめて薄い場合には膜の荒れの進行防止効果は少ないことが判明しているので、ある程度の厚さが必要であるが、上述の例ではＨｆＯ２層５の厚さとして、１４．６５ｎｍの膜厚は十分な厚さである。酸化膜層の膜厚としてはＮＤフィルタ全体として所望の光学濃度での平坦な分光透過特性を得る膜厚であることを前提として、膜の荒れの進行防止効果が十分な膜厚が必要となる。また、酸化膜層としては、拡散を防止し膜の荒れの進行を防止することから種々の金属酸化物が適用可能であり、例えばＡｌ２Ｏ３（酸化アルミニウム）膜を被着させるようにしても良い。なお、このＡｌ２Ｏ３膜は、最外層の保護膜ともなり得る。 Here, the oxide film layer HfO 2 layer 5 is located between the Hf layer 2 and the Al layer 3 and prevents diffusion during the heat treatment that occurs at the boundary between the two, and the film roughness between the metal films 2 and 3 is prevented. Provided to prevent progression. When the film thickness of the HfO 2 layer 5 is extremely thin, it has been found that the effect of preventing the roughening of the film is small, so that a certain amount of thickness is necessary. As a result, the film thickness of 14.65 nm is sufficient. The film thickness of the oxide film layer is required to be sufficient to prevent the roughening of the film from progressing on the premise that the entire ND filter has a film thickness that can obtain flat spectral transmission characteristics at a desired optical density. . Further, as the oxide film layer, various metal oxides can be applied because it prevents diffusion and prevents the film from progressing. For example, an Al2O3 (aluminum oxide) film may be deposited. The Al2O3 film can also be an outermost protective film.

こうして、酸化膜層を金属膜間に介在することによって平坦な分光透過特性を得ると共に熱処理後でも膜の荒れのない図２に示すような写真（合成石英基板／Ｈｆ／ＨｆＯ２／Ａｌ／ＨｆＯ２からなる積層構造の写真）のＮＤフィルタを得ることができる。
ＮＤフィルタにおいてＡｌ膜は、図１の例では該当しないが、その厚さが一定以上厚くなった場合には、クラックが生じ易いという性質がある。このため、図３は、このＡｌ膜の性質に着目して所望の分光透過特性を得ようとしてＡｌ層を厚くしようとするとき、１層の厚さを薄くした多層のＡｌ層を形成した例を示す。図３（ａ）はＨｆ層２の上層及び下層にＡｌ層３１、３２を分割して積層した例を示し、このＨｆ層２とＡｌ層３１及び３２との間にＨｆＯ２層やＡｌ２Ｏ３層５１、５２を形成した例を示す。また、図３（ｂ）は６層のＨｆ層２１、２２、２３とＡｌ層３１、３２、３３との間にＨｆＯ２層やＡｌ２Ｏ３層５１、５２、５３、５４、５５を形成した例を示す。なお、図３にて４は例えばＡｌ２Ｏ３からなる保護膜である。 In this way, a flat spectral transmission characteristic is obtained by interposing the oxide film layer between the metal films, and a photograph (from a synthetic quartz substrate / Hf / HfO2 / Al / HfO2) as shown in FIG. An ND filter having a multilayer structure) can be obtained.
In the ND filter, the Al film does not correspond to the example of FIG. 1, but has a property that cracks are likely to occur when the thickness of the Al film exceeds a certain level. For this reason, FIG. 3 shows an example in which a multi-layered Al layer having a reduced thickness is formed when an attempt is made to increase the thickness of the Al layer in order to obtain a desired spectral transmission characteristic by paying attention to the properties of the Al film. Indicates. FIG. 3A shows an example in which the Al layers 31 and 32 are divided and stacked on the upper layer and the lower layer of the Hf layer 2, and an HfO 2 layer and an Al 2 O 3 layer 51 are interposed between the Hf layer 2 and the Al layers 31 and 32. The example which formed 52 is shown. FIG. 3B shows an example in which an HfO 2 layer or an Al 2 O 3 layer 51, 52, 53, 54, 55 is formed between the six Hf layers 21, 22, 23 and the Al layers 31, 32, 33. . In FIG. 3, reference numeral 4 denotes a protective film made of, for example, Al 2 O 3.

〔第２実施形態〕
平坦な分光透過特性を得る他の例のＮＤフィルタとして、図４に示すようにＡｌ膜３にＣｒ（クロム）膜６を積層した構造のものがある。このＮＤフィルタは、透過率が一定で、ある波長域（４００〜７００ｎｍ）にてきわめて平坦な分光透過特性を得るものである。そして、図４（ａ）に示すような構造においても、Ａｌ膜３とＣｒ膜６との間にたとえばＡｌ２Ｏ３層５のような酸化膜層を形成することにより、膜の荒れの進行を防止することができる。 [Second Embodiment]
As another example of an ND filter that obtains flat spectral transmission characteristics, there is a structure in which a Cr (chromium) film 6 is laminated on an Al film 3 as shown in FIG. This ND filter has a constant transmittance and obtains a very flat spectral transmission characteristic in a certain wavelength region (400 to 700 nm). Also in the structure as shown in FIG. 4A, an oxide film layer such as an Al 2 O 3 layer 5 is formed between the Al film 3 and the Cr film 6 to prevent the film from progressing. be able to.

また、前述のようにＡｌ膜にクラックが生じ易いことから、図４（ｂ）ではＡｌ膜３に似た特性を有するＡｇ（銀）膜７をＡｌ膜３とＣｒ膜６との間に介在させているが、この場合もＡｌ膜３とＡｇ膜７との間、Ａｇ膜７とＣｒ膜６との間にそれぞれ例えばＡｌ２Ｏ３膜５１、５２のような酸化膜層を被着形成することにより、膜の荒れの進行を防止することができる。 Further, as described above, since cracks are easily generated in the Al film, an Ag (silver) film 7 having characteristics similar to the Al film 3 is interposed between the Al film 3 and the Cr film 6 in FIG. In this case as well, an oxide film layer such as Al2O3 films 51 and 52 is deposited between the Al film 3 and the Ag film 7 and between the Ag film 7 and the Cr film 6, respectively. Further, the progress of film roughness can be prevented.

第１実施形態を例示する構成および説明図である。It is the structure and explanatory drawing which illustrate 1st Embodiment. 図１に示す第１実施形態にかかる部分拡大写真である。It is a partial enlarged photograph concerning 1st Embodiment shown in FIG. 第１実施形態の変形例の構成図である。It is a block diagram of the modification of 1st Embodiment. 第２実施形態を例示する構成図である。It is a block diagram which illustrates 2nd Embodiment. 従来例の構成および説明図である。It is a structure and explanatory drawing of a prior art example. 図５に示す従来例にかかる部分拡大写真である。6 is a partially enlarged photograph according to the conventional example shown in FIG.

Claims

In a neutral density filter formed by laminating at least two kinds of metal films on a substrate,
A neutral density filter comprising an oxide film layer formed at a boundary between a first metal film layer and a second metal film layer adjacent to the first metal film layer.

The neutral density filter according to claim 1,
The neutral density filter, wherein the first metal film layer is made of aluminum and the second metal film layer is made of hafnium.

The neutral density filter according to claim 2,
The neutral density filter, wherein the oxide film layer is a hafnium oxide film layer or an aluminum oxide film layer.

The neutral density filter according to claim 1,
The neutral density filter, wherein the first metal film layer is made of aluminum, and the second metal film layer is made of chromium or silver.

The neutral density filter according to claim 1,
The neutral density filter, wherein the first metal film layer is made of chromium and the second metal film layer is made of silver.