JP2011164384A - Concentration distribution mask and designing device of the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a concentration distribution mask that performs exposure to correct distortion of an optical imaging pattern due to an optical interference effect when a microlens array having a lens pitch of 1 μm or less is formed on a substrate of an imaging device using the concentration distribution mask. <P>SOLUTION: The concentration distribution mask for exposing, developing and forming the microlens array in which convex unit lenses are arranged, has isoconcentration in which a super ellipsoidal shape in a VW coordinate system using a super ellipsoidal parameter k whose isoconcentration of a light blocking pattern of the concentration distribution mask is 1 or less, and a VW axis intercept parameter r, is rotated 45 degrees, and expanded in an X direction and a Y direction, and a length in the X direction of a rectangle surrounding four corners projecting in a diagonal direction of the isoconcentration of the bottom face of the convex shaped unit lens is made equal to a pitch of the X direction of the microlens array, and a length of the Y direction of the rectangle is made equal to a pitch of the Y direction of the microlens array. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a density distribution mask used for manufacturing a microlens array used for an imaging device.

  Imaging devices used for video cameras, digital cameras, camera-equipped mobile phones, and the like are required to have high pixels. When a pixel is miniaturized, a light receiving element composed of a CCD (Charge Coupled Device), a CMOS (Complementary Metal Oxide Semiconductor), or the like constituting the pixel is also miniaturized. In order to increase the light collection efficiency to a fine light receiving element, a method of forming a microlens on the side of the light receiving element on which light enters is widely used. This is because the incident light to the pixel is efficiently condensed by the microlens and incident on the light receiving element to improve the light receiving sensitivity.

  In Patent Document 1 and Patent Document 2, this microlens is three-dimensionally formed by exposing and developing the pattern of the density distribution mask on the photosensitive material layer in order to form a curved surface in which adjacent microlenses overlap each other. A method of manufacturing an article having a surface shape of 2 has been proposed. According to the method using the density distribution mask, adjacent microlenses can be formed in contact with each other, so that the ratio of covering the pixel region with the microlenses can be increased, and the light collecting property can be improved.

JP 2002-244273 A JP 2004-145319 A

  In Patent Document 1, a microlens array in which unit lenses are arranged at equal pitches in the X direction and the Y direction is manufactured using a density distribution mask, and the pitch of the unit lenses of the microlens array is arranged at 1 μm or less. In this case, it has been found that a significant defect occurs. When the photosensitive material layer on the imaging device is exposed using a density distribution mask having circular isodensity lines, the light exposed to the positive photosensitive material layer on the imaging device is caused by the light interference effect. It was found that the contour line of the light amount of the light is not circular but becomes a contour line close to a rhombus. When a microlens array is manufactured by exposure at such a light density, the unit lens of the microlens array has a distortion that is not a spherical surface, and there is a problem in that the condensing ability of the unit lens is lowered and the performance is deteriorated. .

  This phenomenon occurs when, for example, a microlens array is formed in which convex lens-shaped unit lenses are arranged at equal pitches in the X and Y directions, and the density distribution mask is formed on the positive photosensitive material layer. The following phenomenon occurs when a pattern is exposed. That is, the imaging pattern in the case of forming a convex lens by exposing a positive photosensitive material layer is a unit lens in order to increase the exposure intensity for digging the photosensitive material layer to the bottom surface of the unit lens of the convex lens. There is a portion with a high amount of light at the four corner positions, and the light concentrated on the portion spreads outside the portion due to the interference effect of the light, so that the exposure image pattern projected by the density distribution mask is distorted.

Therefore, according to the present invention, when a microlens array having a lens pitch of 1 μm or less is formed on a substrate of an imaging device using a density distribution mask, the distortion of the light image formation pattern due to the light interference effect is corrected. An object is to obtain a density distribution mask to be exposed.

The invention according to claim 1 of the present invention is a density distribution mask for exposing and developing a microlens array in which convex lens-shaped unit lenses are arranged, in order to solve the above-mentioned problem, equidensity line of the light-shielding pattern of distribution mask, super elliptic equation using parameters k and VW-intercept parameter r of less than one super ^ellipse, in ^{(V / r) k + (} W / r) k = 1 of the VW coordinates Rotate the shape shown by 45 degrees, expand in the X direction and Y direction, and the length in the X direction of the rectangle surrounding the four corners that protrude in the diagonal direction of the isodensity line on the bottom of the convex lens unit lens Is a pitch in the X direction of the microlens array, and has a density distribution mask having equal density lines in which the length of the rectangle in the Y direction is equal to the pitch in the Y direction of the microlens array It is.

In the invention according to claim 2 of the present invention, the contour line of the height Z of the three-dimensional shape is expressed by a super elliptical equation using a super ellipse parameter k and a VW axis intercept parameter r smaller than 1, (V / r) ^k + (W / r) After rotating the shape represented by the VW coordinate of ^k = 1 by 45 degrees, it expands in the X direction and the Y direction, and in the diagonal direction of the isodensity line on the bottom surface of the convex lens unit lens The X-direction length of the rectangle surrounding the projected four corners is the pitch in the X direction of the microlens array, and the Y-direction length of the rectangle is represented by contour lines equal to the Y-direction pitch of the microlens array. And a density distribution mask transmittance calculating means for designing the three-dimensional shape, a density calculation means for the light shielding pattern of the density distribution mask, and a drawing data calculation means for the density distribution mask. It is a design apparatus of a distribution mask.

  In order to form a microlens array in which unit lenses are arranged in a lattice shape with a pitch d of 1 μm or less in the XY direction, when a pattern of a density distribution mask is exposed to a positive photosensitive material layer with light having a wavelength λ of 365 nm, The image formation pattern is distorted by the interference effect of light. The density distribution mask of the present invention is rotated by 45 degrees on the shape represented by the super elliptical VW coordinate using the super elliptical parameter k smaller than 1, and then expanded in the X and Y directions to form a convex lens shape. The length in the X direction of the rectangle surrounding the four corners of the bottom surface of the unit lens protruding in the diagonal direction is set to the pitch in the X direction of the micro lens array, and the length in the Y direction of the rectangle is set in the micro direction. A pattern density distribution mask having an equal density line equal to the pitch in the Y direction of the lens array is manufactured and used. By projecting the pattern of the density distribution mask onto the photosensitive material layer, the microlens array arranged in a lattice pattern with a pitch d of 1 μm or less reduces distortion of the imaging pattern due to the interference effect of light of wavelength λ. There is an effect that can be manufactured.

(A) It is a top view of the isodensity line of the pattern of the density distribution mask per unit lens of the 1st Embodiment of this invention. (B) It is a graph which shows distribution of the light transmittance P along the X direction of the pattern of the density distribution mask per unit lens of the 1st Embodiment of this invention. (A) It is a top view of the density distribution mask of this invention. (B) It is side sectional drawing of the imaging device which has the micro lens array of this invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1A shows an isodensity line for each light transmittance P of the density distribution mask 2 in the region of the convex lens unit lens of the microlens array 1 of the present invention. Here, the pattern size of the density distribution mask 2 is formed to be n times the pitch d of the unit lens, and the pattern of the density distribution mask 2 is reduced and projected to 1 / n to form the microlens array 1. FIG. 1B shows the distribution of the light transmittance P in the X direction of the density distribution mask 2. 2A shows a plan view (XY plane) of the density distribution mask 2, and FIG. 2B is obtained by exposing the photosensitive material layer on the imaging device using the density distribution mask 2. The cross-sectional shape of the microlens array 1 to be manufactured is shown. As shown in FIG. 2A, the density distribution mask 2 has unit lens density distribution patterns arranged in the X direction at a pitch of d × n corresponding to the lens pitch d and d × b × n in the Y direction. It has a pattern arranged at a pitch. The pattern of the density distribution mask 2 is a set of light-shielding patterns 3 having a fine dimension whose projection size onto the photosensitive material layer on the semiconductor substrate 11 forming the microlens array 1 is smaller than the resolution of the wavelength λ of light used for exposure. Form.

Here, the feature of the present invention is that the shape of the isodensity line having the same light transmittance P of the density distribution mask 2 for creating the microlens is defined by the super elliptic formula (Formula 1) to (Formula 3). is there.
(Formula 1) (V / r) ^k + (W / r) ^k = 1
(Formula 2) V≡ (X + Y / b) / 2
(Formula 3) W≡ (XY / b) / 2
(Expression 4) X-direction radius (X _r ) = 2r / 2 ^{(1 / k) of} isoconcentration lines
Here, a coordinate system obtained by rotating the (V, W) coordinate system by 45 degrees around the origin is defined as an X′Y ′ coordinate system, and the X ′ coordinate value in the X ′ coordinate system is multiplied by √2 to obtain X The coordinate value is set, and the Y ′ coordinate value is multiplied by b√2 to obtain the Y coordinate value. The (X, Y) coordinates represent the position coordinates of the unit lens area in the density distribution mask 2 as XY coordinates with the center of the unit lens as the origin. Further, the value of the coordinate of the point where the isodensity line intersects the V coordinate axis (or W coordinate axis) is equal to the V axis intercept parameter r.

The X coordinate axis where Y = 0 in the XY coordinate system is a straight line where V = W in the VW coordinate system. Equation 1 is a super ellipse equation based on the coordinate system VW in the oblique direction, and the parameter k of the super ellipse is smaller than 1. FIG. 1 (a) shows isoconcentration lines on the XY plane (substrate surface) for each light transmittance P of the density distribution mask 2 expressed by the super elliptic formula of the formula 1 where the value of the parameter k of the super ellipse is 0.925. Represents the shape. Since the parameter k of the super ellipse is smaller than 1, the shape of the isoconcentration line is a shape in which the four corners of the square protrude diagonally. When the parameter k of the super ellipse approaches 1 with a value of 1 or less, the isodensity line approaches a square. When k is further smaller than 1, the proportion of protrusions at the four corners in the diagonal direction of the square increases. Radius X _r in the X direction equal concentrations line is represented by formula 4. The density distribution mask 2 makes the lens array pitch d (for example, 0.7 μm to 1 μm) n times equal to twice the VW axis intercept parameter r _{0 on} the bottom surface of the convex lens unit lens, and 2 × r ₀ Unit lens patterns are arranged in the X direction at a pitch. Further, the unit lens patterns are arranged in the Y direction at a pitch of 2b × r ₀ in accordance with the scale parameter b in the Y direction in Equations 2 and 3 that give the dimensions of the isodensity lines. Thereby, the length in the X direction of the rectangle surrounding the four corners protruding in the diagonal direction of the isodensity line representing the bottom surface of the unit lens by the density distribution mask 2 is equal to the pitch in which the unit lenses are arranged in the X direction. The length of the rectangle in the Y direction is equal to the pitch at which the unit lenses are arranged in the Y direction.

In FIG. 1A, the unit of length of the VW axis intercept parameter r _{0 on} the bottom surface of the unit lens is set to 1, and an isodensity line is represented. Since the pattern of the density distribution mask 2 is reduced and projected onto the photosensitive material layer of the imaging device 10 to produce the microlens array 1, the scales of the microlens array 1 and the density distribution mask 2 are different. Therefore, hereinafter, in order to simplify the description, the dimension of the density distribution mask 2 will be described in terms of a dimension to be reduced and projected to form the microlens 1.

The light transmittance P related to the VW axis intercept parameter r of the isodensity line of the density distribution mask 2 is set to a value determined by the following equation 5.
(Formula 5)
P = P ₁ + (P ₀ −P ₁ ) {r ₁ − (r ₁ ² −r ² ) ^1/2 } / {r ₁ − (r ₁ ² −r ₀ ² ) ^1/2 }
Here, P ₀ is the light transmittance of the density distribution mask 2 that gives the height of the bottom surface of the convex lens-shaped unit lens, and P ₁ is the light transmittance of the density distribution mask 2 that gives the height of the vertex of the unit lens. Yes, r ₁ is a parameter related to the radius of curvature of the unit lens. The isodensity line that gives the height of the bottom surface of the unit lens where the light transmittance P is P ₀ is an isodensity line related to the VW axis intercept parameter r ₀ of the bottom surface of the unit lens, and the radius X in the X direction of the isodensity line _r becomes ^{_{2r 0/2 (1 / k}} ).

FIG. 1B is a graph of the transmittance P on the X axis where the light transmittance P of the density distribution mask 2 expressed by Equation 5 is the vertical axis and the horizontal axis is the X coordinate X. The distribution of the light transmittance P is a shape in which the height of the three-dimensional shape of the unit lens is inverted because the positive photosensitive material layer is exposed to form a lens. As shown in FIG. 1B, in the case of the light transmittance P ₀ that gives the height of the bottom surface of the unit lens, the radius X _{r in} the X direction of the isodensity line is 0.94, and the vertex of the unit lens is The X-direction radius _Xr of the isoconcentration line of the light transmittance P ₁ giving the height is zero. Further, the light transmittance P concentration profile mask second region outside of the unit lens than equal concentrations line of light transmittance P ₀ in FIG. 1 (a) to P _0. However, the light transmittance P in the region of the unit lens outside the isodensity line of the light transmittance P ₀ may be designed to use the value calculated by Equation 5.

(Density distribution mask design device)
In FIG. 1A, the isoconcentration line has a shape in which four corners of a square protrude diagonally. The density distribution mask design apparatus uses the super elliptic equation (Equation 1 to Equation 3) for each (X _m , Y _p ) coordinate of the lattice point on the concentration distribution mask 2 by the transmittance calculation means of the concentration distribution mask. Thus, the VW axis intercept parameter r of the super ellipse of the unit lens is calculated. Next, the light transmittance value P = _Pmp is calculated by substituting the value of the VW axis intercept parameter r into Equation 5, and mxp array data giving the distribution of the light transmittance value _Pmp is stored. Store in the means. Next, the density distribution mask 2 uses the diameter-converted data of the light-shielding pattern for each transmittance, which is previously stored in the storage means for each light transmittance value P _{mp by the} light-shielding pattern diameter calculation means of the density distribution mask. The shading pattern diameter D _mp is calculated, and the dimensional data of the shading pattern composed of m × n array of data structure comprising the list of the X coordinate X _m , the Y coordinate Y _p and the shading pattern diameter D _mp is created. And store it in the storage means. Next, the density distribution mask drawing data calculation means instructs the density distribution mask pattern drawing apparatus to draw a shading pattern having a designated diameter D _mp for each grid point (X _m , Y _p ). Create mask drawing data. Based on the density distribution mask drawing data, a density distribution mask 2 on which a pattern as shown in FIG. 2A is drawn is manufactured using a density distribution mask pattern drawing apparatus.

  The microlens array 1 of the imaging device 10 as shown in FIG. 2B is manufactured by exposing and developing the photosensitive material layer by the following manufacturing method using the density distribution mask 2. That is, the microlens array 1 in which unit lenses are formed for each light receiving element 12 is formed on the color filter layer 14 on the planarizing layer 13 on the light receiving element 12 of the semiconductor substrate 11.

(Manufacturing method of microlens array)
The microlens array 1 is manufactured in the color imaging device 10 as shown in FIG. For example, the pixel size is composed of an array of light receiving elements 12 and each pixel corresponding to each light receiving element 12 has a square size ranging from approximately 0.5 μm to approximately 100 μm, and approximately 0.8 μm to approximately 1 μm. A semiconductor substrate 11 on which a plurality of CMOS imaging devices 10 are formed is used. A planarizing layer 13 having a thickness of approximately 0.1 μm is formed on the surface of the semiconductor substrate 11 with a thermosetting acrylic resin. Next, a color filter layer 14 composed of pixels of three colors of green, blue, and red having a thickness of about 1 μm is formed on the planarizing layer 13 with each pixel corresponding to each light receiving element 12. . Next, a positive photosensitive material layer mainly composed of an acrylic resin, a phenol resin, or a styrene resin is formed on the color filter layer 14 to a thickness of approximately 0.7 to 1 μm. Next, a 5 × reticle (n = 5) density distribution mask 2 pattern is reduced and projected on the photosensitive material layer with a stepper using light having a wavelength λ of 365 nm in the ultraviolet region. The microlens array 1 is formed by developing the photosensitive material layer thus exposed. Finally, the microlens array 1 shown in FIG. 2B is cured by baking with a heat treatment of about 200.degree. In this manner, in the semiconductor substrate 11, the height of the apex is formed on each pixel of the color filter layer 14 formed corresponding to each light receiving element 12 via the planarization layer 13 on the plurality of light receiving elements 12. Form a microlens array 1 having a thickness of 0.6 to 1 μm.

Here, when the density distribution mask 2 having a microlens array pattern arranged with a lens pitch d of 1 μm or less on the substrate of the imaging device is projected onto the photosensitive material layer with light having a wavelength λ of 365 nm. A problem occurs in the light amount distribution to be projected due to light interference. The extent to which the defect can be corrected by a density distribution mask having an isodensity line represented by a super elliptical formula (Formula 1) was examined by simulation. The simulation conditions are as follows. The density distribution mask 2 having a pattern in which the microlens array 1 is enlarged by n = 5 times is used, and the pattern of the density distribution mask 2 having the distribution of the light transmittance P given by Expression 1 to Expression 5 is used. The photosensitive material layer is exposed to light having a wavelength λ of 365 nm using a stepper having a coherence lens factor σ of 0.6 of a normal reduction projection stepper and an NA of 0.63 of the projection lens. Then, a case where a pattern of the microlens array 1 having a lens array pitch d of 0.8 μm is projected was simulated. As a result, the results shown in Table 1 below were obtained.
(Table 1)
(Conditions) (Shape of exposure pattern)
(Condition 1) k <0.91 Strained into a diamond shape (Condition 2) 0.91 ≦ k ≦ 0.94 The exposure pattern was a good circular shape (Condition 3) k> 0.94 Strained into a square shape That is, a super ellipse When the parameter k is 0.91 or more and 0.94 or less, exposure using the density distribution mask 2 projects exposure light having a light amount distribution in which the light interference effect is well corrected on the photosensitive material layer. It was found that the surface of the unit lens of the microlens array 1 can be formed without distortion from the spherical surface. When k is larger than 0.94, the microlens array 1 is distorted in a rhombus shape, and when k is smaller than 0.91, the microlens array 1 is distorted in a square shape.

  As described above, in order to form a microlens array in which unit lenses are arranged in a lattice pattern with a pitch d of 1 μm or less in the XY direction, the pattern of the density distribution mask 2 is a positive type with light having a wavelength λ of 365 nm. When the photosensitive material layer is exposed, the imaging pattern is distorted due to the light interference effect. On the other hand, the density distribution mask of the present embodiment is represented by the VW coordinates of the super elliptical equation (Equation 1) of the super-elliptical parameter k smaller than 1 whose shape of the isodensity line is given by Equations 1 to 5. After the shape to be rotated is rotated 45 degrees, an isodensity line enlarged in the X direction and the Y direction is created. Then, the length in the X direction of the rectangle surrounding the four corners protruding in the diagonal direction of the isodensity line on the bottom surface of the convex lens-shaped unit lens is set to a pitch for arranging the unit lenses in the X direction, and the Y direction of the rectangle A density distribution mask 2 having an equal density line whose length is equal to the pitch at which unit lenses are arranged in the Y direction is manufactured. By reducing and projecting the density distribution mask 2 with a stepper, there is an effect that a unit lens having a pitch of 1 μm or less can be manufactured by reducing the distortion of the imaging pattern due to the interference effect of light of wavelength λ.

DESCRIPTION OF SYMBOLS 1 ... Micro lens array 2 ... Concentration distribution mask 3 ... Light-shielding pattern 10 ... Imaging device 11 ... Semiconductor substrate 12 ... Light receiving element 13 ... Flattening layer 14 ... Color Filter layer P: Light transmittance P of the density distribution mask _0: Light transmittance P that gives the height of the bottom surface of the unit lens ₁ ... Light transmittance b that gives the height of the vertex of the unit lens b Scale parameter d in Y direction: Lens pitch n: Magnification r, r _0: VW axis intercept parameter of density distribution mask pattern with respect to microlens array

Claims (2)

A density distribution mask for forming a microlens array in which convex lens-shaped unit lenses are arranged by exposure and development, wherein the isodensity line of the light shielding pattern of the density distribution mask is a super ellipse parameter k smaller than 1. And a super elliptical equation using the VW axis intercept parameter r,
(V / r) ^k + (W / r) ^k = 1
After rotating the shape represented by the VW coordinates of 45 degrees in the X direction and the Y direction, the rectangular X surrounding the four corners protruding in the diagonal direction of the isodensity line on the bottom surface of the convex lens unit lens A density having an isodensity line having a length in the direction equal to the pitch in the X direction of the microlens array and a length in the Y direction of the rectangle equal to the pitch in the Y direction of the microlens array. Distribution mask. A super-elliptic formula using a contour ellipse of height Z of the three-dimensional shape using a super-ellipse parameter k smaller than 1 and a VW-axis intercept parameter r;
(V / r) ^k + (W / r) ^k = 1
After rotating the shape represented by the VW coordinates of 45 degrees in the X direction and the Y direction, the rectangular X surrounding the four corners protruding in the diagonal direction of the isodensity line on the bottom surface of the convex lens unit lens The density for designing the three-dimensional shape is represented by contour lines in which the length in the direction is the pitch in the X direction of the microlens array, and the length in the Y direction of the rectangle is equal to the pitch in the Y direction of the microlens array. A density distribution mask design apparatus, comprising: a distribution mask transmittance calculation unit; a light shielding pattern diameter calculation unit of the density distribution mask; and a drawing data calculation unit of the density distribution mask.

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