JP4386546B2 - Concentration distribution mask and three-dimensional structure manufacturing method using the same - Google Patents

Description

で表わされ、面高さ：ｈ(ｎ)は、
ｈ(ｎ)＝（Ｘ²＋Ｙ²）^1/2
であり、傾き角θは、
θ＝arctan（ｄｚ／ｄｈ）
であり、傾斜度ｄｚ／ｄｈは、

である。また、
設計波長λ＝９８０（ｎｍ）、
基板厚さｔ＝１±０.０５（ｍｍ）
（平行度：φ５ｍｍで０.１μｍ以下）、
基板の屈折率ｎ＝１.５１１１８、
バックフォーカスＢＦ＝５.５８８２６８
である。また、
球面式＝ｃｈ(ｎ)²／{１＋（１−ｃ²ｈ(ｎ)²）^1/2}
である。また、１〜８の輪帯のサグ量を計算した結果を図１１に示す。
以上に基づいて８輪帯のフレネルレンズの各輪帯の高さが２１.０μｍの同じ高さになるようにレンズ設計し、製作した。
【００７０】
（フレネルレンズ製作の具体例１）
上記のレンズ設計に基づいて、感度曲線と計算式から濃度分布マスクパターンＮｏ.の配列を決定し、図５のレーザー光照射装置を用いてＣＡＤデータのパターンを描画した。また、濃度分布マスクレチクル製作の具体例１と同様の方法によって、現像、リンスして濃度分布マスクを製作した。ここでは輪体ごとに濃度分布マスクレチクルを製作し、合計８枚の濃度分布マスクレチクルを製作した。
【００７１】
次に、その８枚の濃度分布マスクレチクルを使用して製作するフレネルレンズの例を述べる。
ＳＦ−６ガラス基板を用意し、この基板上に記述のＴＧＭＲ−９５０レジストを約８.５μｍの厚さに塗布する。次に、ホットプレートを用いて、１００℃にてベーク時間１８０秒でプリベークした。
【００７２】
この基板を８枚の濃度分布マスクレチクルを用いて１／２.５ステッパーで露光した。露光条件は、次のような露光条件▲１▼から▲３▼で行なった。
▲１▼第１輪体：
デフォーカス：＋１０μｍ、照射量：３９０ｍＷ×１.９２秒
▲２▼第２から第７輪体（６枚の濃度分布マスクレチクルのそれぞれについて）：
デフォーカス：＋ ５μｍ、照射量：３９０ｍＷ×１.９２秒
▲３▼第８輪体：
デフォーカス：＋ ５μｍ、照射量：３９０ｍＷ×１.３８秒
【００７３】
この条件で露光後、ＰＥＢを６０℃にて２５分実施した。次いで、感光性材料の現像、リンスを行なった。その後、紫外線硬化装置にて１８０秒間紫外線を照射しながら真空引きを実施して、レジストのハードニングを行なった。このときのレジスト高さは、７.５μｍであった。
【００７４】
上記基板をＴＣＰドライエッチング装置にセットし、真空度：１.５×１０^-3Ｔｏｒｒ、ＣＨＦ₃：２０.０ｓｃｃｍ、ＢＣｌ₃：１.０ｓｃｃｍ、ＣＦ₄：１５.０ｓｃｃｍ、Ｏ₂：０.９ｓｃｃｍ、基板バイアス電力：１.２ｋＷ、上部電極電力：１.２５ｋＷ、基板冷却温度：−２０℃の条件下でドライエッチングを行なった。またこの時、基板バイアス電力と上部電極電力を経時的に変化させ、時間変化と共に選択比が大きくなるように変更しながらエッチングを行なった。基板の平均エッチング速度は、１.１μｍ／分であった。また、選択比は、２.８２で、エッチング後のレンズ高さは、２１.１μｍであった。実際のエッチンング時間は、２１.５分を要した。
これにより、各輪体の曲率は設計値通りの形状を有し、かつ各輪体の立ち上がり角度も平均８８.６°の急勾配を得ることができた。また、輪体間の立ち上がり部隙間距離も最大で２μｍ程度と非常に小さくなり、設計通りの光学性能を得ることができた。
【００７５】
（フレネルレンズ製作の具体例２）
フレネルレンズ製作の具体例１の場合と同様に、輪体ごとに濃度分布マスクレチクルを製作し、合計８枚の濃度分布マスクレチクルを製作した。
ＳＦ−６ガラス基板を用意し、この基板上に記述のＴＧＭＲ−９５０レジストを約８.５μｍの厚さに塗布する。次に、ホットプレートを用いて、１００℃にてベーク時間１８０秒でプリベークした。
【００７６】
この基板を８枚の濃度分布マスクレチクルを用いて１／２.５ステッパーで露光した。露光条件は、次のような露光条件▲１▼から▲３▼で行なった。各露光条件でのデフォーカス量の変更は連続して行なった。
▲１▼第１輪体：
デフォーカス：＋１０μｍ、照射量：３９０ｍＷ×０.６２秒
デフォーカス：＋ ５μｍ、照射量：３９０ｍＷ×０.５０秒
デフォーカス：＋ １μｍ、照射量：３９０ｍＷ×０.１６秒
露光条件▲１▼での総合露光量は、照射量：３９０ｍＷ×１.２８秒（照度：４９９ｍＪ）である。
▲２▼第２から第７輪体（６枚の濃度分布マスクレチクルのそれぞれについて）：
デフォーカス：＋ ５μｍ、照射量：３９０ｍＷ×０.３０秒
デフォーカス：＋ ４μｍ、照射量：３９０ｍＷ×０.２８秒
デフォーカス：＋ ３μｍ、照射量：３９０ｍＷ×０.２８秒
デフォーカス：＋ ２μｍ、照射量：３９０ｍＷ×０.２８秒
デフォーカス：＋ １μｍ、照射量：３９０ｍＷ×０.１４秒
露光条件▲２▼での総合露光量は、照射量：３９０ｍＷ×１.２８秒（照度：４９９ｍＪ）である。
▲３▼第８輪体：
デフォーカス：＋ ５μｍ、照射量：３９０ｍＷ×０.２０秒
デフォーカス：＋ ４μｍ、照射量：３９０ｍＷ×０.２０秒
デフォーカス：＋ ３μｍ、照射量：３９０ｍＷ×０.２０秒
デフォーカス：＋ ２μｍ、照射量：３９０ｍＷ×０.２０秒
デフォーカス：＋ １μｍ、照射量：３９０ｍＷ×０.１４秒
露光条件▲３▼での総合露光量は、照射量：３９０ｍＷ×０.９４秒（照度：３６７ｍＪ）である。いずれの露光でも、デフォーカス量の大きいものから小さいものへと順に行なった。
【００７７】
この条件で露光後、ＰＥＢを６０℃にて１８０秒実施した。次いで、感光性材料の現像、リンスを行なった。その後、紫外線硬化装置にて１８０秒間紫外線を照射しながら真空引きを実施して、レジストのハードニングを行なった。このときのレジスト高さは、７.５μｍであった。
【００７８】
上記基板をＴＣＰドライエッチング装置にセットし、フレネルレンズ製作の具体例１と同じ条件でドライエッチングを行なった。基板の平均エッチング速度は、１.１μｍ／分であった。また、選択比は、２.８２で、エッチング後のレンズ高さは、２１.１μｍであった。実際のエッチンング時間は、２１.５分を要した。
この具体例２でも、フレネルレンズ製作の具体例１と同様に、各輪体の曲率は設計値通りの形状を有し、かつ各輪体の立ち上がり角度も平均８８.６°の急勾配を得ることができた。また、輪体間の立ち上がり部隙間距離も最大で２μｍ程度と非常に小さくなり、設計通りの光学性能を得ることができた。
【００７９】
【発明の効果】
本発明にかかる濃度分布マスクでは、この濃度分布マスクは異なる露光領域ごとに作成された複数枚のマスクにより構成され、各マスクの露光領域は透明基板上に２次元の光強度分布を有する遮光パターンが形成されたものであり、各露光領域は適当な形状及び大きさの単位セルにより隙間なく分割されており、各マスクの各単位セル内の遮光パターンは、その光透過量又は遮光量が感光性材料パターンの対応した位置の高さに応じた値となるように設定されているようにしたので、マスクごとに単位セルの大きさや形を変えて形成することができるようになり、得ようとする表面形状に対処しやすくし、単位セル間の光透過量の隣接効果にも対処しやすくし、しかも設計の自由度も高めることができる。
【図面の簡単な説明】
【図１】６種類の単位セル形状の例を示す図である。
【図２】ＭＬＡの濃度分布マスクに配置される単位セルの例を示す図である。
【図３】単位セル内の光透過領域又は遮光領域の増加又は減少の起点となる初期パターンと光透過量又は遮光量を変化させる方法を示す図である。
【図４】単位セル内の光透過領域又は遮光領域を増加又は減少させる方法を示す図で、（ア）は単位セルが長方形の場合、（イ）は単位セルが正六角形の場合の例である。
【図５】濃度分布マスクレチクルの製作に用いるレーザー光照射装置の一例を示す概略構成図である。
【図６】マイクロレンズ用濃度分布マスクの遮光パターンの一例を示す図である。
【図７】６つに分割した各領域のパターンを形成した濃度分布マスクレチクルを示す概略平面図である。
【図８】縮小投影露光装置の一例を示す概略構成図である。
【図９】各分割マスクレチクルを配置したときの単位セルパターンの位置及び合計の光強度分布を示す図である。
【図１０】フレネルレンズの一部を示す断面図である。
【図１１】フレネルレンズの設計データを示す図である。
【符号の説明】
１ レーザー光発振装置
２ ビームスプリッター
４ 光変調器
５ 光変調制御装置
６ 光偏向器
７ 対物レンズ
８ Ｘ−Ｙステージ[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method of manufacturing an article having a three-dimensional surface shape, a density distribution mask used for exposure to form a photosensitive material pattern used in the manufacturing method, and a method of manufacturing the density distribution mask. It is about.
[0002]
[Prior art]
Special surface shapes typified by spherical surfaces and aspheric surfaces have been used for the refractive surfaces and reflective surfaces of optical elements. In recent years, special surface shapes have been required for microlenses and the like in connection with liquid crystal display elements, liquid crystal projectors, and the like.
Therefore, as a method of forming the refracting surface and the reflecting surface without using molding or polishing, a layer of photoresist (a representative example of a photosensitive material) is formed on the surface of the optical substrate, and the two-dimensional structure is applied to the photoresist layer. Exposure through an exposure mask having a typical transmittance distribution, and developing the photoresist to obtain a convex or concave shape as the photoresist surface shape, and then anisotropically etching the photoresist and the optical substrate Is performed, and the surface shape of the photoresist is engraved on the optical substrate and transferred to obtain a desired three-dimensional refracting surface or reflecting surface shape on the surface of the optical substrate (Japanese Patent Laid-Open No. Hei 7). No. -230159 and JP-A-8-504515).
[0003]
There, as an exposure mask used to obtain a special surface shape of a three-dimensional structure such as a refracting surface or a reflecting surface, a two-dimensional transmittance distribution in which the transmittance changes stepwise according to the special surface shape. A density distribution mask (gradation mask (GM)) having the above is used.
[0004]
In the density distribution mask described in JP-T-8-504515 (this description is taken as the prior art), the mask pattern is used as a light transmission aperture in order to form a two-dimensional transmittance distribution pattern. The unit cell is divided so that the opening size of each unit cell is set to the light transmission amount or the light shielding amount corresponding to the height of the corresponding position of the photoresist pattern to be formed.
[0005]
[Problems to be solved by the invention]
In the density distribution mask of the prior art, the unit cell has a uniform shape and size, and a method for controlling the light transmittance and the light shielding amount as a whole is not described. For this reason, for example, when the inclination angle of the target resist pattern, and thus the surface shape of the final article is large, that is, it cannot cope with a shape that changes suddenly within a short distance.
In the prior art, the adjacent effect (difference in the amount of light diffraction) of the light transmission amount or the light shielding amount between unit cells is not considered. When the light transmission amount changes monotonously between unit cells, the light leakage amount from the adjacent unit cell can be predicted and controlled, but the light transmission amount or the light shielding amount between unit cells is different as in a Fresnel lens. If it changes discontinuously, the amount of light leakage is unpredictable. For example, the unit cell corresponding to the top (vertex) of the Fresnel lens and the unit cell immediately adjacent to the unit cell have different curvatures of the Fresnel zone, so the amount of light leakage to the top portion is naturally different. In order to deal with the adjacent effect of the light transmission amount, it is necessary to take measures such as correcting the arrangement of the light shielding pattern in the unit cell. However, if the unit cell has a uniform shape and size as in the prior art, it can be dealt with. Hard to do. In particular, when the desired shape is small or the inclination of the desired shape is large, the influence of the adjacent effect is very large, and it is difficult to quantify this effect, and the use of the conventional density distribution mask is very difficult. there were.
[0006]
In the concentration distribution mask for manufacturing an article having a surface shape of a three-dimensional structure, the present invention makes it easy to deal with the surface shape to be obtained, and makes it easy to deal with the adjacent effect of the light transmission amount between unit cells. Moreover, the purpose is to increase the degree of freedom of design.
[0007]
[Means for Solving the Problems]
The present invention is a proposal of a method for solving the above problems by using a density distribution mask method. The concentration distribution mask method has the following advantages over the resist thermal deformation method.
(1) In a micro-pitch micro lens array (MLA) having an adjacent interval as close as possible to zero, the height of the adjacent portion is different in adjacent tangential sections. However, even if this shape is manufactured by the conventional resist thermal deformation method, the MLA structure as designed cannot be manufactured. In the conventional resist thermal deformation method, the interval can be reduced by applying the resist multiple times, or the height of the adjacent cross section can be brought close to the destination, but it is adjacent to form an independent (isolated) resist block. It is virtually impossible to make the MLA interval zero.
(2) Formation of a Fresnel lens was impossible with the conventional resist thermal deformation method.
(3) In the conventional resist thermal deformation method, a diameter of about 500 μm is the limit of a large aperture lens.
(4) An aspherical shape can be easily manufactured.
(5) An irregular lens such as a toroid can be easily manufactured.
(6) Monotonically increasing convex structures such as prisms and pyramids can be easily manufactured.
(7) Complex structures such as micromachining can be easily manufactured.
[0008]
The object of the present invention can be achieved by the concentration distribution mask described in claim 1.
That is, the density distribution mask according to the present invention forms an article having a three-dimensional surface shape by forming a photosensitive material pattern having a three-dimensional structure on a substrate and engraving the photosensitive material pattern on the substrate. In this case, a density distribution mask used for exposure for forming a photosensitive material pattern, the density distribution mask is composed of a plurality of masks created for different exposure areas, and the exposure area of each mask is a transparent substrate. A light-shielding pattern having a two-dimensional light intensity distribution is formed thereon, and each exposure region is divided by unit cells having an appropriate shape and size without gaps, and the light shielding within each unit cell of each mask. The pattern is set so that the light transmission amount or the light shielding amount is a value corresponding to the height of the corresponding position of the photosensitive material pattern.
[0009]
The three-dimensional structure manufacturing method according to the present invention forms an article having a three-dimensional structure surface shape by forming a photosensitive material pattern having a three-dimensional structure on a substrate and engraving the photosensitive material pattern on the substrate. A photosensitive material layer is formed on a substrate, and a photosensitive material pattern is formed by a photolithography process in which a plurality of masks are sequentially aligned and exposed using the concentration distribution mask according to claim 1. To do.
[0010]
By dividing and forming the density distribution mask into a plurality of masks created for different exposure areas, it becomes possible to change the size and shape of the unit cell for each mask. It is easy to cope with the surface shape to be formed, it is easy to cope with the adjacent effect of the light transmission amount between the unit cells, and the degree of design freedom can be increased. In particular, when a density distribution mask composed of a plurality of masks is used, the adjacent effect of the light transmission amount can be easily controlled by the light shielding pattern of each mask, and an article having a surface shape as designed can be easily manufactured.
[0011]
Further, by selecting the shape and size of the unit cell, it becomes possible to select an optimal design method that matches the drawing beam shape.
The density distribution mask is a function obtained experimentally from the relationship between the “sensitivity curve” of the photosensitive material, the light transmission region (area) unique to each unit cell of the density distribution mask, and the “light energy amount” that passes through this area. Is given. Here, “obtained experimentally” means that the “sensitivity characteristics” and light diffusion amount of the photosensitive material differ depending on the process conditions. That is, when the process condition parameter is changed, the given function is different. The “sensitivity curve” of the photosensitive material is basically determined by the relationship between the light irradiation energy to the photosensitive material and the photosensitive component of the photosensitive material. However, it is a curve (that is, a function) that is also changed by photolithography conditions (exposure conditions, development conditions, baking conditions, etc.).
[0012]
In addition, the amount of light transmitted is an exponential function of light energy (light quantity) according to the depth when light travels through the photosensitive material because the light absorption coefficient varies depending on the molecular structure contained in the photosensitive material. Decrease. That is, the irradiation light energy amount has an exponential function with respect to the thickness (depth) of the photosensitive material. Therefore, when the “light transmission amount” and the “sensitivity” (light absorption rate) of the photosensitive material are combined from the experimental data, it is possible to form a light energy distribution having a distribution in the thickness direction of the photosensitive material. The thickness T of the photosensitive material removed here is expressed by the following equation.
[0013]
T = (1 / α) · Ln (P · S) − (1 / α) · Ln (Y)
T = Ln {a · (S + b)^f・ F (X)}
T: the thickness of the photosensitive material to be removed (μm)
α: coefficient (a function of various process conditions, α> 0)
P: Light intensity on the surface of the density distribution mask (mJ)
S: Unit cell aperture ratio of the density distribution mask pattern, and therefore S <1
Y: Light quantity at depth T, exposure amount necessary for photosensitive material to be exposed (mJ)
a, b, f: coefficients
F (X): function (where F (X) = F (X1, X2, X3,..., Xn)) X1, X2, X3,..., Xn: photosensitive material process, photosensitive material itself That change depending on the sensitivity and concentration distribution mask design method
[0014]
The present invention is not intended to form a two-dimensional line pattern of a photosensitive material at a certain height as in a semiconductor process, but “a structure having a three-dimensional shape, that is, a pattern property controlled also in the height direction”. It is aimed at forming things. In the three-dimensional shape forming method in which the thickness of the photosensitive material layer is changed by the above method, the “light transmission region” or the “light shielding region” of the unit cell constituting the density distribution mask is two-dimensionally according to a desired shape. As a result, the light transmitted through the density distribution mask can develop a characteristic having a two-dimensional light intensity distribution.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
The plurality of masks in the concentration distribution mask according to the present invention are preferably prepared in accordance with the inclination angle of the surface shape of the article.
When the surface shape of the article to be manufactured is an aspherical shape, it is preferable that the plurality of masks be created corresponding to the inflection points of the surface shape of the article.
In the case where the article to be manufactured is a Fresnel lens, it is preferable that a plurality of masks be provided for each ring body of the Fresnel lens.
In any case, since the characteristics of the unit cells of the light shielding pattern can be made close to each other in each mask, it is easy to predict the adjacent effect of the light transmission amount.
[0016]
Further, the exposure process performed using the density distribution mask of the prior art is performed in a just-focus state where the photoresist layer is just in focus, whether it is a projection exposure method or a contact exposure method. Therefore, in order to make the surface shape of the target article substantially smooth, the number of gradations must be very large, and the unit of the opening dimension in the unit cell is exposed as illustrated. It is necessary to make the wavelength shorter than the wavelength of the light used for. And as the pattern becomes finer, its manufacturing cost increases. The surface shape of the target article is a step-like one, although it approaches a smooth one as the number of gradations increases. That said in the prior art literature is “substantially” means that.
[0017]
Therefore, in the three-dimensional structure manufacturing method according to the present invention, it is preferable that the photolithography process is performed with a defocus amount set for each mask.
The photolithography process is preferably performed while changing the defocus amount under a preset condition within the exposure time for each mask.
In the photolithography process, it is preferable to change the defocus amount from the side where the focus is greatly shifted to the side where the focus is achieved.
Here, the defocus amount refers to the degree of defocus.
[0018]
The defocus amount can be controlled by shifting the focus from the photosensitive material layer when the exposure is a projection exposure, and within the exposure time when the exposure is a proximity exposure in which the mask is brought close to the photosensitive material. One or both of the substrate and the mask on which the photosensitive material layer is formed may be moved in the plane.
By controlling the defocus amount, the change in the amount of light at the boundary between adjacent unit cells is reduced, and the three-dimensional pattern formed on the photoresist and thus the surface shape of the target article is made smoother. Can do.
Further, it is preferable to control the exposure amount according to the defocus amount within the exposure time.
[0019]
When a three-dimensional structure is manufactured using the concentration distribution mask of the present invention, an optical element composed of a continuous surface such as a spherical surface, an aspherical surface, or a conical shape can be manufactured. It is also possible to produce an optical element composed of: Furthermore, it is possible to form a reflective optical surface by forming a reflective optical surface on such an optical element.
[0020]
In manufacturing the concentration distribution mask reticle, first, a sensitivity curve of the resist material is obtained, and the relationship between the light irradiation amount and the resist removal amount is grasped.
When exposure is performed using the density distribution mask reticle, the removal amount of the resist material varies depending on the exposure amount, the light transmission amount or the light shielding amount of the unit cell. Thereby, “unit cell No.” (that is, the relationship characterized by the light transmission amount or the light shielding amount and the resist removal amount is expressed as one No.) is determined. “Unit cell No.” can be converted into a mathematical expression by graphing the above relationship and converting it into a function. Based on the above formula, the relationship between the desired “shaped lens height” and “resist remaining amount (“ resist film thickness ”−“ removed amount ”)” is formulated into a formula. Next, the relationship between “lens arrangement position” and “lens height (resist residual amount)” is clarified on CAD (Computer Aided Design). Furthermore, this is developed and replaced with the relationship between “lens arrangement position” and “unit cell number”. That is, based on the basic concept described above, a cell number is arranged by adding a lens height and a density distribution mask pattern cell number on the CAD design screen from a calculation formula and a program supported by detailed data.
[0021]
Next, the CAD data is converted into data and set in the laser beam irradiation apparatus.
As an example, the density distribution mask reticle is composed of unit cells divided into squares, and the light transmission amount or the light shielding amount in each unit cell is controlled. Of course, an optimal unit cell may be determined according to a desired shape and manufactured with an optimal dot. Here, in order to simplify the explanation, a square is used for explanation. There are (1) control of the Cr opening area, (2) control of the Cr film thickness, and combinations of (3), (1) and (2). Here, the method (3) was adopted.
[0022]
In order to manufacture a concentration distribution mask reticle, a Cr film having a thickness of, for example, 200 nm is formed on a transparent glass substrate, and the resist material is applied thereon to form a concentration distribution mask reticle blank. Drawing is performed by irradiating a laser beam using the laser beam irradiation apparatus in which the CAD data is set on the resist material. In laser light irradiation, an optimal beam shape is determined according to a desired shape, and a polygonal shape, a circular shape, or the like is shaped with an aperture.
The resist material portion irradiated with laser light by this laser light irradiation apparatus is removed by the next development process, and a mask pattern is formed on the resist material layer.
[0023]
Next, by using this patterned resist material layer as an etching mask, the Cr film is patterned by dry etching or wet etching, preferably dry etching, whereby the Cr film is patterned, and the "unit cell No." A density distribution mask having a desired two-dimensional transmission amount distribution arranged in the “lens arrangement position” is obtained. In the unit cell, a portion where the Cr film is removed and a portion where the Cr film remains are formed. One unit cell can be characterized and configured as its light transmission amount or light shielding amount.
[0024]
Commercially available mask blanks may be used as blanks for the density distribution mask reticle mask. In other words, a commercially available mask blank is obtained by applying a photosensitive material to about 1 μm on a quartz substrate having a Cr film of about 200 nm deposited (a two-layer film of Cr and Cr oxide if necessary).
In the above-described concentration distribution mask reticle fabrication, if the Cr film is patterned by etching, the light transmittance is 0% in the portion with the Cr film and 100% in the portion without the Cr film. A pattern is obtained.
[0025]
In addition, the resist material pattern that remains in the unit cell is exposed by the laser light irradiation apparatus so that the resist film pattern is continuously thicker toward the periphery in the periphery of the pattern in the unit cell. After forming a pattern in the material layer, if the Cr film is etched by anisotropic dry etching using the resist material pattern as a mask, the thickness of the Cr film pattern in the unit cell is continuous toward the periphery at the periphery. The light transmittance can be changed continuously.
[0026]
This manufacturing method can also be manufactured by electron beam drawing (EB drawing). However, in terms of device control such as control of the filament current for electron beam emission, thinning of the filament during long exposure, and control of the amount of electron beam (dose). The reproducibility is extremely poor. Also, since only a single beam can be emitted during production, the production takes a long time, and the fluctuation over time is large. From the above, in the present invention, an inexpensive and highly reliable laser beam irradiation apparatus was manufactured, and a concentration distribution mask was manufactured.
[0027]
【Example】
(The shape and arrangement in the unit cell, and the shape and arrangement of the “light transmission” and “light blocking” dots) Next, the shape and arrangement in the unit cell, and the shape of the “light transmission” and “light blocking” dots The arrangement will be described.
The following examples are representative examples, and unit cell dimensions, dot dimensions, starting point dimensions, etc. should be designed according to the desired shape. It is not limited. That is, since the number of gradations is determined by the size of each unit cell and dot, these dimensions are determined by the target shape and target gradation.
[0028]
FIG. 1 shows examples of six types of polygonal shapes as representative examples when changing the unit cell shape. (A) is a square, (b) is a regular hexagon, (c) is a right isosceles triangle, (d) is a rectangle, (e) is a hexagon, and (f) is an isosceles triangle. These polygons are determined in an optimum shape by “a method of covering a polygonal net from above when a desired shape is viewed from above”. "The most effective polygon" that expresses the density distribution mask characteristics according to the desired shape, that is, for example, when a gentle curved surface continues or when it is composed of discontinuous surfaces, depending on the amount of change in gradation And by selecting “the combination”, the optimum shape can be determined.
Similarly, the size of the unit cell is determined by how fine the necessary gradation is for a desired shape. That is, when many gradations are required at a short distance, it is desirable to select a unit cell having a relatively small size and make the dot size as small as possible.
[0029]
FIG. 2 shows an example of unit cell arrangement of an MLA density distribution mask. (A) shows an example of a combination pattern of unit cells arranged in the central part, and (A) shows an example of a combination pattern of unit cells arranged in the peripheral part. In both cases, the unit cell is indicated by a solid line, and the broken-line arrow indicates that the unit cell is also disposed in that direction.
[0030]
Since (a) is arranged near the center of the MLA, the desired shape is a gentle curved shape. For this reason, the number of gradations is not so much required. Therefore, it is composed of unit cells having relatively large dimensions, and the unit cells are arranged radially.
[0031]
Since (a) is arranged in the peripheral portion, the desired shape is a curved surface shape that changes rapidly. For this reason, a large number of gradations are required. Therefore, it is necessary to configure the unit cell with a smaller size as the four corners of the MLA are approached, and to reduce the dot size. Further, the unit cell is not limited to a quadrilateral shape but also a triangular one, and the dot position in the unit cell is changed to easily cope with the adjacent effect of the light transmission amount.
[0032]
FIG. 3 shows the difference in the position of the initial pattern that is the starting point of the increase or decrease of the light transmission region or the light shielding region in a typical unit cell, and a method for changing the light transmission amount or the light shielding amount. In each case, the outermost square represents a unit cell, and the inner square represents a light transmission region or a light shielding region, respectively. (A) shows that the starting point is in the center of the unit cell, and (B) shows that the starting point is arranged at one of the four corners.
[0033]
FIG. 4 shows an example in which the number of openings (portions where there is no Cr) that transmits light is increased. Although not specifically described, the same applies to the case where the light transmission area is decreased. FIG. 4A shows an example in which the area is increased spirally from the center. This example shows a representative example of a method of increasing dots from a certain unit cell number. In addition, a typical one-dot increasing method or decreasing method is shown. Therefore, the dimensions and dot dimensions of the initial rectangular shape arranged at the center of the dots shown here are model-like, and in the present invention, they are not limited to squares, and may be polygons such as rectangles and triangles. . Of course, a circular shape including an elliptical shape may be used.
[0034]
FIG. 4A shows an example where the unit cell is a regular hexagon. In this case, the dot indicated by the hatched portion is a circle, and the amount of transmission or light shielding changes by changing the size of the dot.
The increase / decrease in dot area is input data at the time of input, and the shape may be lost due to laser beam thickening or isotropic etching such as dry etching depending on the mask manufacturing conditions.
[0035]
(Design of density distribution mask)
An example of a minute pitch MLA in which the interval between adjacent microlenses is as close to zero as possible is shown. In the MLA for liquid crystal projectors, the pixel size for 0.9 ″ -XGA is 18 μm × 18 μm.
In this MLA, when there is a lens non-formation part of 1 μm on both sides of the lens, it becomes a micro lens area of 16 μm × 16 μm, and the MLA area occupying the entire area is 16 × 16/18 × 18 = 256 / 324 = 0.79, and even if all the light can be collected effectively by the MLA, the light collection efficiency is only 79%. That is, it is important to reduce the area of the MLA non-formation part in order to improve the light utilization efficiency. In this embodiment, the lens non-formation part is brought close to zero.
[0036]
Specifically, when a 1/5 times (reduced) stepper is used, the actually manufactured density distribution mask reticle pattern dimension is 90 μm × 90 μm. This one MLA is divided into 3.0 μm unit cells and divided into vertical × horizontal = 30 × 30 (pieces) = 900 (pieces) unit cells.
[0037]
Next, cell No. 1 (all chromium remaining) is placed in the 2 × 2 unit cell in the center (6 μm × 6 μm on the density distribution mask reticle, 1.2 μm × 1.2 μm in the actual pattern). In addition, cell No. 80 (no chrome remaining portion) is arranged at the four corners of the lens. No. 1 to No. 80 cells in the meantime correspond to “opening areas” corresponding to the respective “gradations”. This relationship is obtained from the exposure process and the resist sensitivity curve. Of course, if the resist material or process is different, it is necessary to grasp the sensitivity curve each time. In this way, CAD data of the MLA density distribution mask reticle is created. In this example, a CAD program was produced using the method shown in FIGS.
[0038]
(Production of concentration distribution mask reticle)
The CAD data created as described above was irradiated with laser light using a laser light irradiation apparatus developed in-house shown in FIG. In this laser light irradiation, an optimal beam shape can be determined according to a desired shape, and a polygonal shape, a circular shape, or the like can be shaped with an aperture.
[0039]
The laser beam irradiation apparatus shown in FIG. 5 is bent by a laser beam oscillation device 1, a beam splitter 2 that divides the laser beam from the laser beam oscillation device 1 into a plurality of laser beams, a mirror 3 that folds the optical path of the laser beam, and a mirror 3. An optical modulator 4 that modulates the laser beam, an optical modulation controller 5 that controls the optical modulator 4 according to a signal from the data bus to control ON / OFF of each laser beam, and a laser from the optical modulator 4 An optical deflector 6 for deflecting light, an objective lens 7 for condensing laser light on a resist material layer, an XY stage 8 for moving a mounted mask blank in X and Y directions, and an optical deflector 6 and main components such as a control device 9 for controlling the operation of the XY stage 8.
[0040]
This laser beam irradiation device draws a desired mask pattern on the resist material layer of the mask blank by controlling the operation of the XY stage 8 and the ON / OFF and deflection of each laser beam according to the design data. To do. That is, a laser beam is irradiated onto the resist material layer by this laser beam irradiation apparatus, and a pattern is formed two-dimensionally so that a light transmission region or a light shielding region has a desired transmittance distribution for each unit cell. At this time, the laser light irradiation is controlled according to the transmission amount distribution of each unit cell calculated according to the desired special surface shape, and the light transmission region or the light shielding region in each unit cell is increased or decreased. The arrangement of dots is controlled.
The unit cell shape and the dot shape may be selected appropriately depending on the target product.
[0041]
The CAD data created as described above is installed in the laser beam irradiation apparatus shown in FIG. 5, and the XY stage, the ON / OFF state of the laser beam, and the beam shape are controlled by the aperture, and the density is determined by a predetermined method. The distribution mask blanks were exposed. Then, development and rinsing were performed by a predetermined method to pattern the resist material layer. Thereafter, the Cr film was patterned by dry etching.
[0042]
By using the laser beam drawing method and making the drawing beam shape rectangular and increasing the drawing region in a spiral shape, higher reproducibility than the electron beam drawing method can be obtained. When the drawing area is circular, the laser beam drawing method can obtain very high reproducibility when the diameter of the drawing area is 0.2 μm or more. When the diameter of the drawing area is smaller than 0.2 μm, the reproducibility is deteriorated. However, in the electron beam drawing method, the reproducibility is markedly lower than that when the dimension of the drawing area is smaller than 0.5 μm. Is excellent.
[0043]
The prediction of “adjacent effect” depends on the shape of the unit cell. When the unit cell shape is a square or a rectangle, it can be accurately drawn with a rectangular dot, so the adjacency effect can be predicted by calculation.
[0044]
From these results, the masks (a) and (b) in FIG. 1 were the best and were used. In the arrangement of FIG. 1A, both the types (A) and (B) of FIG. 3 were able to obtain good results. In the arrangement of (a) in FIG. 1, the dot arrangement of the (A) type in FIG. 3 was used. However, each method has advantages and disadvantages and can be used according to the target shape. In the following specific example, the CAD program was created using a circular dot shape (a method of increasing the laser light irradiation portion concentrically from the center).
In this manner, a density distribution mask reticle having a desired opening size and a density distribution was manufactured.
[0045]
(Specific example of density distribution mask reticle production)
Production of sparse liquid crystal MLA:
In manufacturing the concentration distribution mask reticle, positive resist material TGMR-950 (product of Tokyo Ohka Kogyo Co., Ltd.) was used as a resist material which is a photosensitive material.
[0046]
The density distribution mask is composed of unit cells divided into squares, and the light transmission amount or the light shielding amount in each unit cell is controlled. Of course, an optimal unit cell may be determined according to a desired shape and manufactured with an optimal dot. Here, in order to simplify the explanation, a square is used for explanation. There are (1) control of the Cr opening area, (2) control of the Cr film thickness, and combinations of (3), (1) and (2). Here, the method (3) was adopted.
[0047]
In order to manufacture a concentration distribution mask reticle, a Cr film having a thickness of, for example, 200 nm is formed on a transparent glass substrate, and the above resist material is applied thereon. Drawing was performed by irradiating the resist material with laser light using the laser light irradiation apparatus of FIG.
Thereafter, a mask pattern was formed on the resist material layer through development and rinsing, and the Cr film was patterned by dry etching using the resist pattern as an etching mask, thereby producing a concentration distribution mask.
[0048]
FIG. 6 shows an example of a 20 μm × 20 μm microlens as a typical arrangement example of the density distribution mask. The unit cell has a grid-like square shape. The unit cell does not necessarily have to be a square, and it is desirable that the unit cell have another polygonal shape according to a desired shape. The hatched portion is the portion where the Cr film remains.
The pattern shown in FIG. 6 is the sum of the apex portion of the microlens, four regions corresponding to the inclination angle (differential value) of the lens surface, and four corner portions (portions that transmit 100% of light). Dividing into six regions, the pattern of each region was formed on a separate density distribution mask reticle.
Here, when the shape of the microlens is simplified to a semicircular shape,
X²+ Y²= R²
And when differentiated,
dY / dX = X / (R²-X²)^1/2
It is. In this embodiment, R = 9 μm.
[0049]
In the intermediate four-divided area, (1) 0 to 0.36, (2) 0.36 to 0.67, (3) 0.67 to 1.20, (4) 1 depending on the differential (dY / dX) value. Divided into .20 or more.
Based on the above conditions, the density distribution mask pattern shown in FIG. 6 was divided into six areas, and the pattern of each area was formed on a separate density distribution mask reticle.
FIG. 7 shows a schematic plan view of the density distribution mask reticle.
Divided mask reticles (A), (B), (C), (D) are sequentially applied to the vertex portion, differential values (1), (2), (3), (4), and density distribution mask reticles corresponding to the four corner portions. ), (E), (F). In each divided mask reticle, a hatched portion indicates a region where a unit cell is formed. A register mark pattern for alignment on the stepper was formed on each divided mask reticle. Further, it goes without saying that each divided mask reticle is composed of the entire light shielding film (the remaining Cr portion) except for the region where the unit cells are arranged.
[0050]
(Manufacture of micro dimension MLA for liquid crystal)
(Specific example 1 for the production of MLA for liquid crystal)
Using the density distribution mask reticle (FIG. 6) of Example 1 of density distribution mask reticle fabrication as a mask, exposure is performed using a reduced projection exposure apparatus (1/5 stepper) shown in FIG. An example of an MLA for a liquid crystal projector manufactured by forming a pattern and transferring it to an optical device material will be described.
[0051]
First, the reduction projection exposure apparatus will be described.
The light from the light source lamp 30 is condensed by the condenser lens 31 and irradiates the exposure mask 32. The light transmitted through the mask 32 enters the imaging lens 33 having a reduction magnification, and a reduced image of the mask 32, that is, a reduced image of the transmittance distribution is formed on the surface of the optical device material 37 placed on the stage 34. Is imaged. The stage 34 on which the optical device material 37 is placed can be displaced in two directions orthogonal to each other within the plane orthogonal to the optical axis of the imaging lens 33 by the action of the step motors 35 and 36. The position 37 can be aligned with the optical axis of the imaging lens 33.
[0052]
A reduced image of the mask 32 by the imaging lens 33 is formed on the surface of the photoresist layer of the optical device material 37. This exposure is performed densely over the entire surface of the optical device material 37.
In order to manufacture an MLA for a liquid crystal projector, a neo-serum substrate was prepared, and the above-described TGMR-950 resist was applied on the substrate to a thickness of 8.56 μm. Next, it was pre-baked on a hot plate at 100 ° C. with a baking time of 180 seconds.
[0053]
This substrate was exposed with a 1/5 stepper of FIG. The following exposure conditions (1) to (8) were continuously performed.
(1) Defocus: +11 μm, irradiation amount: 390 mW × 0.13 seconds
(2) Defocus: +10 μm, irradiation amount: 390 mW × 0.13 seconds
(3) Defocus: + 9 μm, irradiation amount: 390 mW × 0.11 seconds
(4) Defocus: +8 μm, irradiation amount: 390 mW × 0.11 seconds
(5) Defocus: + 7 μm, irradiation amount: 390 mW × 0.11 seconds
(6) Defocus: +5 μm, irradiation amount: 390 mW × 0.11 seconds
(7) Defocus: + 3 μm, irradiation amount: 390 mW × 0.11 seconds
(8) Defocus: + 1 μm, irradiation amount: 390 mW × 0.11 seconds
Under this condition, the total exposure amount is an irradiation amount of 390 mW × 0.92 seconds (illuminance: 359 mJ). Here, the + sign in the defocus amount display means that the focal point is above the resist surface.
[0054]
After exposure under these conditions, PEB (post-exposure baking) was performed at 60 ° C. for 180 seconds. Next, the photosensitive material was developed and rinsed. Thereafter, the resist was hardened by evacuation while irradiating with ultraviolet rays for 180 seconds with an ultraviolet curing device. The ultraviolet curing device irradiates a wavelength capable of curing the resist at a wavelength shorter than that used for resist exposure. By this operation, the plasma resistance of the resist is improved, and the resist can withstand processing in the next process. The resist height at this time was 7.5 μm.
Due to the effect of defocusing, it was possible to produce a shape without any special steps.
[0055]
Thereafter, the substrate is set in a TCP (inductively coupled plasma) dry etching apparatus, and the degree of vacuum is 1.5 × 10.^-3Torr, CHF_Three: 5.0 sccm, CF_Four: 50.0 sccm, O₂: Dry etching was performed under the conditions of 15.0 sccm, substrate bias power: 600 W, upper electrode power: 1.25 kW, and substrate cooling temperature: −20 ° C. At this time, the substrate bias power and the upper electrode power were changed with time, and etching was performed while changing the selection ratio so as to decrease with time. The average etching rate of the substrate was 0.63 μm / min, but the actual etching time required 11.5 minutes. The lens height after etching was 5.33 μm.
[0056]
(Specific example 2 for the production of MLA for liquid crystal)
The same density distribution mask reticle as that in Example 1 for manufacturing the micro dimension MLA for liquid crystal was used, and the exposure conditions in the stepper apparatus were changed.
The following exposure conditions (1) to (3) were continuously performed.
(1) Defocus: +10 μm, irradiation amount: 390 mW × 0.44 seconds
(2) Defocus: + 5 μm, irradiation amount: 390 mW × 0.44 seconds
(3) Defocus: +0 μm, irradiation amount: 390 mW × 0.13 seconds
Under this condition, the total exposure amount is an irradiation amount of 390 mW × 1.02 seconds (illuminance: 394 mJ).
[0057]
After exposure under these conditions, PEB, development and rinsing of the photosensitive material were performed. Next, the resist was hardened under the same conditions as in the specific example 1 for manufacturing the micro dimension MLA for liquid crystal. The resist height at this time was 7.2 μm.
Due to the effect of defocusing, it was possible to produce a shape without any special steps.
Thereafter, the substrate was set in a TCP dry etching apparatus, and dry etching was performed under the same conditions as those in Example 1 for producing a liquid crystal microscopic MLA. The average etching rate of the substrate was 0.67 μm / min, but the actual etching time required 11.0 minutes. The lens height after etching was 5.3 μm.
[0058]
(Specific example 3 for the production of MLA for liquid crystal)
Here, an aspherical MLA was manufactured. Using the same density distribution mask reticle as in the first specific example of manufacturing the above-mentioned micro dimension MLA for liquid crystal, the exposure conditions in the stepper apparatus were changed.
The following exposure conditions (1) to (8) were continuously performed.
(1) Defocus: +11 μm, irradiation amount: 390 mW × 0.08 seconds
(2) Defocus: +10 μm, irradiation amount: 390 mW × 0.08 seconds
(3) Defocus: + 9 μm, irradiation amount: 390 mW × 0.10 seconds
(4) Defocus: +8 μm, irradiation amount: 390 mW × 0.13 seconds
(5) Defocus: + 7 μm, irradiation amount: 390 mW × 0.18 seconds
(6) Defocus: +5 μm, irradiation amount: 390 mW × 0.20 seconds
(7) Defocus: + 3 μm, irradiation amount: 390 mW × 0.10 seconds
(8) Defocus: + 1 μm, irradiation amount: 390 mW × 0.05 seconds
Under this condition, the total exposure amount is an irradiation amount of 390 mW × 0.92 seconds (illuminance: 359 mJ).
[0059]
After exposure under these conditions, PEB, development and rinsing of the photosensitive material were performed. Next, the resist was hardened under the same conditions as in the specific example 1 for manufacturing the micro dimension MLA for liquid crystal. The resist height at this time was 7.7 μm.
Due to the effect of defocusing, it was possible to produce a shape without any special steps.
Thereafter, the substrate is set in a TCP dry etching apparatus, and among the conditions in the specific example 1 for manufacturing the micro dimension MLA for liquid crystal, O₂Was changed from 15.0 sccm to 0.9 sccm, and dry etching was performed. The average etching rate of the substrate was 0.55 μm / min, but the actual etching time required 14.0 minutes. The lens height after etching was 7.4 μm.
The MLA manufactured according to the specific example 3 was able to realize an MLA having a shorter focal length than the MLA generated in the specific example 1.
[0060]
(Specific example 4 for the production of micro dimension MLA for liquid crystal)
An example using the six density distribution mask reticles shown in FIG. 7 is shown.
A neo-serum substrate was prepared, and the aforementioned TGMR-950 resist was applied to the substrate to a thickness of 8.56 μm. Next, it was pre-baked on a hot plate at 100 ° C. with a baking time of 180 seconds.
[0061]
This substrate was exposed using the 1/5 stepper apparatus of FIG. 8 and the density distribution mask reticle of FIG. Each density distribution mask reticle was subjected to the following exposure conditions (1) to (3). FIG. 9 shows the position of the unit cell pattern and the total light intensity distribution when each divided mask reticle is arranged.
(1) MLA center (A):
Defocus: +0 μm, irradiation amount: 390 mW × 1.92 seconds
(2) MLA intermediate four-divided area (for each of the four density distribution mask reticles (B) to (E)):
Defocus: +15 μm, irradiation amount: 390 mW × 1.92 seconds
(3) Four outer corners of the MLA (F):
Defocus: +0 μm, irradiation amount: 390 mW × 1.92 seconds
The exposure amount under each condition is an irradiation amount of 390 mW × 1.92 seconds (illuminance: 720 mJ).
[0062]
After exposure under these conditions, PEB was performed at 60 ° C. for 25 minutes. Next, the photosensitive material was developed and rinsed. Thereafter, the resist was hardened by evacuation while irradiating ultraviolet rays for 180 seconds with an ultraviolet curing device. The resist height at this time was 7.5 μm.
Separate density distribution mask reticles were used at the boundaries of the six areas corresponding to the six density distribution mask reticles. However, due to the effect of defocusing, the shape was produced without causing any special steps in the overlapping parts of the patterns. We were able to.
[0063]
Thereafter, the substrate was set in a TCP dry etching apparatus, and the degree of vacuum was 1.5 × 10.^-3Torr, CHF_Three: 5.0 sccm, CF_Four: 50.0 sccm, O₂: Dry etching was performed under the conditions of 20.0 sccm, substrate bias power: 600 W, upper electrode power: 1.25 kW, and substrate cooling temperature: −20 ° C. At this time, the substrate bias power and the upper electrode power were changed with time, and etching was performed while changing the selection ratio so as to decrease with time. The average etching rate of the substrate was 0.63 μm / min, but the actual etching time required 11.5 minutes. The lens height after etching was 5.33 μm.
[0064]
(Specific example 5 for the production of MLA for liquid crystal)
An example of manufacturing an aspherical MLA is shown. Using the six density distribution mask reticles shown in FIG. 7, the exposure conditions were changed when each density distribution mask reticle was placed in a stepper apparatus.
The following exposure conditions (1) to (6) were performed.
(1) MLA center (A):
Defocus: +0 μm, irradiation amount: 390 mW × 1.92 seconds
{Circle around (2)} MLA middle quadrant (differential (dY / dX) value: 0 to 0.36) (B):
Defocus: + 5 μm, irradiation amount: 390 mW × 1.92 seconds
(3) MLA middle four-divided region (differential (dY / dX) value: 0.36 to 0.67) (C):
Defocus: +10 μm, irradiation amount: 390 mW × 1.92 seconds
(4) MLA intermediate four-divided region (differential (dY / dX) value: 0.67 to 1.20) (D):
Defocus: +10 μm, irradiation amount: 390 mW × 1.92 seconds
(5) MLA middle 4 divided region (differential (dY / dX) value: 1.20 or more) (E):
Defocus: + 5 μm, irradiation amount: 390 mW × 1.92 seconds
(6) Four corners of outer periphery of MLA (F):
Defocus: +0 μm, irradiation amount: 390 mW × 1.92 seconds
Under this condition, the total exposure is 390 mW × 1.92 seconds (illuminance: 720 mJ).
[0065]
After exposure under these conditions, PEB, development and rinsing of the photosensitive material were performed. Next, the resist was hardened under the same conditions as in the specific example 4 for the production of the minute dimension MLA for liquid crystal. The resist height at this time was 7.5 μm.
Separate density distribution mask reticles were used at the boundaries of the six areas corresponding to the six density distribution mask reticles. However, due to the effect of defocusing, the shape was produced without causing any special steps in the overlapping parts of the patterns. We were able to.
Thereafter, the substrate was set in a TCP dry etching apparatus, and among the conditions in Example 4, O₂Was changed from 20.0 sccm to 0.9 sccm, and dry etching was performed. The average etching rate of the substrate was 0.55 μm / min, but the actual etching time required 14.0 minutes. The lens height after etching was 7.4 μm.
[0066]
The MLA manufactured according to the specific example 5 was able to realize an MLA having a shorter focal length than the MLA prepared in the specific example 4 for manufacturing the micro dimension MLA for liquid crystal.
According to the specific examples 3 and 5, the aspherical shape of the MLA could be formed by controlling the amount of the adjacent effect of the light transmission amount in each mask. According to these specific examples 3 and 5, it was possible to form an aspheric surface with higher accuracy than the MLA created by the conventional concentration distribution mask method with good reproducibility.
[0067]
(Fresnel lens production)
The following products can be listed as products in which the concentration distribution mask method is most effective.
(1) With the resist thermal deformation method, it was impossible to form a Fresnel lens with a minute dimension. → The density distribution mask technology makes this possible.
(2) In the resist thermal deformation method, the lens dimensions that can be manufactured are limited, and a diameter of about 500 μm is the limit of a large-diameter lens. → The density distribution mask method can produce large-diameter lenses.
(3) A lot of data storage and know-how were required to produce an aspherical shape. → The concentration distribution mask method can produce various shapes.
[0068]
The density distribution mask method has the above-described features. An example of a Fresnel lens is given as one of the shapes that best represents these characteristics.
In this embodiment, an 8-band Fresnel lens having a focal length of F = 6.25 (mm) and a numerical aperture of NA = 0.4 (10λ gap) was manufactured as a Fresnel lens.
FIG. 10 shows a part of the right portion of the Fresnel lens 42 from the optical axis O, where t is the thickness of the substrate, h (n) (n = 1, 2, 3. The surface height from the axis O to each annular zone, ΔZ (n) is the sag amount representing the depth from the surface of each annular zone to the valley, and θ is the inclination angle.
[0069]
Here, the aspherical expression Z (n) representing the curved surface shape of each annular zone of the Fresnel lens is:

The surface height: h (n) is
h (n) = (X²+ Y²)^1/2
And the inclination angle θ is
θ = arctan (dz / dh)
And the slope dz / dh is

It is. Also,
Design wavelength λ = 980 (nm),
Substrate thickness t = 1 ± 0.05 (mm)
(Parallelity: 0.1 μm or less at φ5 mm),
The refractive index of the substrate n = 1.5118,
Back focus BF = 5.588268
It is. Also,
Spherical type = ch (n)²/ {1+ (1-c²h (n)²)^1/2}
It is. Moreover, the result of having calculated the sag amount of the 1-8 zone is shown in FIG.
Based on the above, the lens was designed and manufactured so that the height of each annular zone of the Fresnel lens of 8 annular zones would be the same height of 21.0 μm.
[0070]
(Frenel lens production example 1)
Based on the above lens design, the arrangement of the density distribution mask pattern No. was determined from the sensitivity curve and the calculation formula, and the CAD data pattern was drawn using the laser beam irradiation apparatus of FIG. In addition, a density distribution mask was manufactured by developing and rinsing in the same manner as in Example 1 of manufacturing the density distribution mask reticle. Here, a density distribution mask reticle was manufactured for each ring body, and a total of eight density distribution mask reticles were manufactured.
[0071]
Next, an example of a Fresnel lens manufactured using the eight density distribution mask reticles will be described.
An SF-6 glass substrate is prepared, and the described TGMR-950 resist is applied on the substrate to a thickness of about 8.5 μm. Next, using a hot plate, prebaking was performed at 100 ° C. with a baking time of 180 seconds.
[0072]
This substrate was exposed with a 1 / 2.5 stepper using eight density distribution mask reticles. The exposure conditions were the following exposure conditions (1) to (3).
(1) First wheel:
Defocus: +10 μm, irradiation amount: 390 mW × 1.92 seconds
(2) Second to seventh wheel bodies (each of six density distribution mask reticles):
Defocus: + 5 μm, irradiation amount: 390 mW × 1.92 seconds
(3) Eighth body:
Defocus: +5 μm, irradiation amount: 390 mW × 1.38 seconds
[0073]
After exposure under these conditions, PEB was performed at 60 ° C. for 25 minutes. Next, the photosensitive material was developed and rinsed. Thereafter, the resist was hardened by evacuation while irradiating with ultraviolet rays for 180 seconds with an ultraviolet curing device. The resist height at this time was 7.5 μm.
[0074]
The substrate is set in a TCP dry etching apparatus, and the degree of vacuum is 1.5 × 10.^-3Torr, CHF_Three: 20.0 sccm, BCl_Three: 1.0 sccm, CF_Four: 15.0 sccm, O₂: 0.9 sccm, substrate bias power: 1.2 kW, upper electrode power: 1.25 kW, substrate cooling temperature: −20 ° C. At this time, etching was performed while changing the substrate bias power and the upper electrode power over time and changing the selection ratio so as to increase with time. The average etching rate of the substrate was 1.1 μm / min. The selectivity was 2.82, and the lens height after etching was 21.1 μm. The actual etching time required 21.5 minutes.
As a result, the curvature of each ring body has a shape as designed, and the rising angle of each ring body has a steep slope with an average of 88.6 °. In addition, the gap distance between the rising portions between the rings was as small as about 2 μm at maximum, and the optical performance as designed could be obtained.
[0075]
(Specific example 2 of Fresnel lens production)
As in the case of the specific example 1 for manufacturing the Fresnel lens, a density distribution mask reticle was manufactured for each ring body, and a total of eight density distribution mask reticles were manufactured.
An SF-6 glass substrate is prepared, and the described TGMR-950 resist is applied on the substrate to a thickness of about 8.5 μm. Next, using a hot plate, prebaking was performed at 100 ° C. with a baking time of 180 seconds.
[0076]
This substrate was exposed with a 1 / 2.5 stepper using eight density distribution mask reticles. The exposure conditions were the following exposure conditions (1) to (3). The defocus amount was changed continuously under each exposure condition.
(1) First wheel:
Defocus: +10 μm, irradiation amount: 390 mW × 0.62 seconds
Defocus: + 5μm, irradiation amount: 390mW × 0.50sec
Defocus: + 1 μm, irradiation amount: 390 mW × 0.16 seconds
The total exposure amount under the exposure condition (1) is irradiation amount: 390 mW × 1.28 seconds (illuminance: 499 mJ).
(2) Second to seventh wheel bodies (each of six density distribution mask reticles):
Defocus: +5 μm, irradiation amount: 390 mW × 0.30 seconds
Defocus: + 4 μm, irradiation amount: 390 mW × 0.28 seconds
Defocus: + 3 μm, irradiation amount: 390 mW × 0.28 seconds
Defocus: +2 μm, irradiation amount: 390 mW × 0.28 seconds
Defocus: + 1 μm, irradiation amount: 390 mW × 0.14 seconds
The total exposure amount under the exposure condition (2) is irradiation amount: 390 mW × 1.28 seconds (illuminance: 499 mJ).
(3) Eighth body:
Defocus: +5 μm, irradiation amount: 390 mW × 0.20 seconds
Defocus: + 4 μm, irradiation amount: 390 mW × 0.20 seconds
Defocus: + 3 μm, irradiation amount: 390 mW × 0.20 seconds
Defocus: +2 μm, irradiation amount: 390 mW × 0.20 seconds
Defocus: + 1 μm, irradiation amount: 390 mW × 0.14 seconds
The total exposure amount under the exposure condition (3) is irradiation amount: 390 mW × 0.94 seconds (illuminance: 367 mJ). In both exposures, the exposure was performed in order from the largest defocus amount to the smallest.
[0077]
After exposure under these conditions, PEB was performed at 60 ° C. for 180 seconds. Next, the photosensitive material was developed and rinsed. Thereafter, the resist was hardened by evacuation while irradiating with ultraviolet rays for 180 seconds with an ultraviolet curing device. The resist height at this time was 7.5 μm.
[0078]
The substrate was set in a TCP dry etching apparatus, and dry etching was performed under the same conditions as in Example 1 for manufacturing the Fresnel lens. The average etching rate of the substrate was 1.1 μm / min. The selectivity was 2.82, and the lens height after etching was 21.1 μm. The actual etching time required 21.5 minutes.
In this specific example 2, as in the specific example 1 for producing the Fresnel lens, the curvature of each ring body has a shape as designed, and the rising angle of each ring body has a steep slope with an average of 88.6 °. I was able to. In addition, the gap distance between the rising portions between the rings was as small as about 2 μm at maximum, and the optical performance as designed could be obtained.
[0079]
【The invention's effect】
In the density distribution mask according to the present invention, the density distribution mask is composed of a plurality of masks created for different exposure areas, and the exposure area of each mask has a light shielding pattern having a two-dimensional light intensity distribution on a transparent substrate. Each exposure area is divided by unit cells of appropriate shape and size without gaps, and the light transmission pattern or the light shielding amount of the light shielding pattern in each unit cell of each mask is photosensitive. Since it is set to be a value corresponding to the height of the corresponding position of the conductive material pattern, it can be formed by changing the size and shape of the unit cell for each mask. It is easy to cope with the surface shape, and it is easy to cope with the adjacent effect of the light transmission amount between the unit cells, and the degree of design freedom can be increased.
[Brief description of the drawings]
FIG. 1 is a diagram showing examples of six types of unit cell shapes.
FIG. 2 is a diagram illustrating an example of a unit cell arranged in an MLA density distribution mask.
FIG. 3 is a diagram illustrating an initial pattern which is a starting point of increase or decrease of a light transmission region or a light shielding region in a unit cell and a method of changing a light transmission amount or a light shielding amount.
4A and 4B are diagrams illustrating a method of increasing or decreasing a light transmission region or a light shielding region in a unit cell. FIG. 4A is an example when the unit cell is a rectangle, and FIG. 4B is an example when the unit cell is a regular hexagon. is there.
FIG. 5 is a schematic configuration diagram showing an example of a laser beam irradiation apparatus used for manufacturing a density distribution mask reticle.
FIG. 6 is a diagram showing an example of a light shielding pattern of a microlens density distribution mask.
FIG. 7 is a schematic plan view showing a density distribution mask reticle in which a pattern of each region divided into six is formed.
FIG. 8 is a schematic block diagram showing an example of a reduced projection exposure apparatus.
FIG. 9 is a diagram showing a position of a unit cell pattern and a total light intensity distribution when each divided mask reticle is arranged.
FIG. 10 is a cross-sectional view showing a part of a Fresnel lens.
FIG. 11 is a diagram showing design data of a Fresnel lens.
[Explanation of symbols]
1 Laser oscillator
2 Beam splitter
4 Light modulator
5 Light modulation controller
6 Optical deflector
7 Objective lens
8 XY stage

Claims (8)

A photosensitive material pattern having a three-dimensional structure is formed by forming a photosensitive material pattern having a three-dimensional structure on a substrate and engraving the photosensitive material pattern on the substrate. In the density distribution mask used for exposure to
This density distribution mask is composed of a plurality of masks created for different exposure areas,
The exposure area of each mask is formed by forming a light-shielding pattern having a two-dimensional light intensity distribution on a transparent substrate, and each exposure area is divided without gaps by unit cells having an appropriate shape and size.
The light shielding pattern in each unit cell of each mask is set such that the light transmission amount or the light shielding amount is a value corresponding to the height of the corresponding position of the photosensitive material pattern. Density distribution mask. 2. The density distribution mask according to claim 1, wherein the plurality of masks are formed corresponding to an inclination angle of a surface shape of the article. 2. The density distribution mask according to claim 1, wherein the surface shape of the article is an aspherical shape, and the plurality of masks are created corresponding to inflection points of the surface shape of the article. The density distribution mask according to claim 1, wherein the article is a Fresnel lens, and the plurality of masks are provided for each ring of the Fresnel lens. In a method of manufacturing an article having a three-dimensional structure surface shape by forming a photosensitive material pattern having a three-dimensional structure on a substrate and engraving the photosensitive material pattern on the substrate.
A photosensitive material layer is formed on the substrate, and the photosensitive material pattern is formed by a photolithography process in which a plurality of masks are sequentially aligned and exposed using the concentration distribution mask according to claim 1. Forming a three-dimensional structure. The three-dimensional structure manufacturing method according to claim 5, wherein the photolithography step is performed by setting a defocus amount for each mask. The three-dimensional structure manufacturing method according to claim 5, wherein the photolithography process is performed while changing a defocus amount under a preset condition within an exposure time for each mask. The three-dimensional structure manufacturing method according to claim 7, wherein the photolithography step changes a defocus amount from a side where the focus is greatly shifted from a side where the focus is greatly shifted.

Images