JP7090002B2 - Exposure device - Google Patents

Description

The present invention relates to an exposure apparatus that projects a pattern onto a substrate such as a printed wiring board using an optical modulation element array, and more particularly to a configuration of an illumination optical system.

In the maskless exposure apparatus, the light emitted from the light source is guided to the light modulation element array through the illumination optical system. In an optical modulation element array such as a DMD (Digital Micro-mirror Device), a plurality of micromirrors (hereinafter referred to as micromirrors) are two-dimensionally arranged, and each micromirror is ON / OFF controlled according to pattern data (drawing data). Will be done. When the micromirror is in the ON state, the light from the illumination optical system is reflected toward the substrate, and when the micromirror is in the OFF state, it is reflected toward the outside of the substrate.

There is a small gap between adjacent micromirrors. The illumination light incident on this gap does not contribute to the pattern light, and the illumination light which is UV light deteriorates the substrate of the light modulation element array and the like. A microlens array is arranged in the illumination optical system in order to improve the efficiency of the illumination light and prevent the life from being shortened. In the microlens array, the microlenses are two-dimensionally arranged in accordance with the two-dimensional arrangement of the micromirror. As a result, the light focused by the microlens becomes spot light smaller than the mirror size and forms an image on the micromirror (see Patent Document 1).

Japanese Unexamined Patent Publication No. 2016-188923

A light modulation element such as a micromirror switches the tilt angle of the mirror between the ON state and the OFF state, but the angle of incidence of the illumination light on the light modulation element array is constant. Therefore, a part of the light reflected near the edge of the light modulation element may hit the edge portion of the adjacent micromirrors. This causes stray light and diffracted light, leading to a decrease in contrast. On the other hand, if the size of the spot light is made too small, the exposure amount is lowered and the pattern resolution is affected.

Therefore, it is required to project the illumination light onto the light modulation element array so as to suppress the generation of stray light and diffracted light while maintaining the illumination efficiency.

The exposure apparatus of the present invention has an illumination optical system that guides light from a light source to an optical modulation element array in which a plurality of optical modulation elements are arranged in two dimensions, and projection optics that projects the light reflected by the optical modulation element array onto a substrate. A split optical system that is arranged between the light source and the optical modulation element array and divides the light from the light source into a plurality of lights (hereinafter referred to as split light) according to the arrangement of a plurality of light modulation elements. Be prepared.

In the light modulation element array, the position (attitude) of the light modulation element such as a micromirror can be controlled. For example, it is possible to control the light modulation element between the posture in which the light modulation element guides light to the substrate side (ON state) and the posture in which the light is guided to the outside of the substrate (OFF state).

The shape of the projection area in the light modulation element of the divided light is arbitrary, and it is possible to form the divided light having a rectangular, circular, or elliptical projection area. For example, the split optical system can be composed of a light-shielding member having a plurality of apertures formed according to the arrangement of the plurality of light modulation elements, and the aperture may be formed according to the shape of a desired projection area. On the other hand, it may be composed of a microlens array in which a plurality of microlenses are formed according to the arrangement of a plurality of light modulation elements, or a micromirror array in which a plurality of micromirrors are formed according to an arrangement of a plurality of light modulation elements. It is possible.

In the present invention, the split optical system forms a plurality of split lights having a luminous flux smaller than the size of the light modulation element, and the center position of the projection area of each split light is set to be larger than the center position of the corresponding light modulation element. Offset the split light closer to the incident direction. While the divided light is incident on the optical modulation element array at a specific incident angle, it is divided based on the relationship between the attitude of the optical modulation element that guides the reflected light to the substrate side and the attitude of the optical modulation element that guides the reflected light to the outside of the substrate. By offsetting the projection area toward the incident direction of the light, the generation of diffracted light and stray light is suppressed.

For example, the light modulation element is composed of a rectangular element that rotates about its axis diagonally. In that case, the split optical system may offset the projection center position of each split light along a diagonal line that intersects the diagonal line along the rotation axis.

Considering keeping the light-shielding region as small as possible, the split optical system can be configured to form a plurality of split lights having a projection area having a reduced size of the light modulation element. For example, by molding a plurality of divided lights in which a projected area having a reduced (scaled) size of the light modulation element is formed, a divided light having a projection area size and a projection area center position where the light blocking range is as small as possible can be obtained. Can be molded.

When forming such divided light, it is possible to apply a light-shielding member having a plurality of apertures formed according to the arrangement of the plurality of light modulation elements. In the light-shielding member, a plurality of apertures may be configured to be offset with respect to the center of the region partitioned according to the size of the micromirror.

According to the present invention, in the exposure apparatus, the illumination light can be projected onto the light modulation element array so as to suppress the generation of stray light and diffracted light while maintaining the illumination efficiency.

It is a block diagram which shows the whole structure of the exposure apparatus by 1st Embodiment. It is a block diagram of an exposure head. It is a figure which partially showed the aperture array. It is a figure which showed the projection position in the micromirror of the light divided by an aperture array. It is a block diagram of the exposure head in 2nd Embodiment. It is a figure which showed the projection position in the micromirror of the light divided by an aperture array. It is a block diagram of the exposure head in 3rd Embodiment.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing an overall configuration of an exposure apparatus according to the first embodiment. FIG. 2 is a block diagram of the exposure head.

The exposure apparatus 1 is a direct (maskless) exposure apparatus that exposes a pattern on a substrate W on which a photosensitive material such as a photoresist is formed on the surface. The exposure apparatus 1 includes a light source unit 21 and an exposure head 10 that projects pattern light onto the substrate W, respectively. The light source unit 20 is configured here by a laser diode. However, it is also possible to use an LED light source, a discharge lamp, or the like.

The exposure head 10 includes a DMD 22 (light modulation element array), an illumination optical system 11, and an imaging optical system 23. The illuminance of the light radiated from the light source unit 20 is made uniform by the illumination optical system 11 and guided to the DMD 22. The light reflected by the DMD 22 is imaged on the substrate W by the imaging optical system 23.

When CAD / CAM data composed of vector data or the like is input to the exposure apparatus 1, the vector data is sent to the raster conversion circuit 26 and converted into raster data. The generated raster data is sent to the DMD drive circuit 24.

The DMD 22 is an optical modulation element array (optical modulator) in which micromicromirrors are arranged in two dimensions, and each micromirror can switch its posture between an ON state and an OFF state, and changes its posture at a predetermined timing. By switching, the light reflection direction is selectively switched. Each mirror is attitude-controlled (ON / OFF-controlled) by the DMD drive circuit 24, and light corresponding to the pattern is projected onto the surface of the substrate W through the imaging optical system 23 and exposed.

The exposure operation of the exposure apparatus 1 is controlled by the controller (exposure operation control unit) 30. The exposure stage drive mechanism 19 moves the exposure stage 18 on which the substrate W is mounted relative to the exposure head 10 according to the control signal from the controller 30. The position measuring unit 27 calculates the exposure position on the surface of the substrate W based on the signal sent from the exposure stage drive mechanism 19. The direction along the moving path of the stage is defined as the main scanning direction X, and the direction orthogonal to the direction along the moving path is defined as the sub-scanning direction Y.

During the exposure operation, the exposure stage 18 moves at a constant speed along the scanning direction X. The projection area (hereinafter referred to as an exposure area) formed by the entire DMD 22 relatively moves on the surface of the substrate W as the substrate W moves. The exposure operation is performed according to a predetermined exposure pitch, and the micromirror is controlled to project the light of the pattern exposure according to the exposure pitch. By adjusting the control timing of each micromirror of the DMD 22 according to the relative position of the exposure area, the light of the pattern to be drawn at the exposure position is sequentially projected and the pattern is formed.

As shown in FIG. 2, the illumination optical system 11 includes an optical system 13 that equalizes the illuminance distribution of light (hereinafter referred to as an illuminance uniform optical system) 13, an aperture array 12 that divides a light beam whose illuminance is uniform. A relay optical system 14 for irradiating the DMD 22 with the divided light beam is provided.

The illuminance equalizing optical system 13 includes a rod lens and a relay lens, and the relay lens is a relay lens in which the ejection surface of the rod lens and the aperture array 12 are coupled to each other. A flyeye lens may be provided instead of the rod lens, and the aperture array may be arranged at the image formation position of the flyeye lens.

FIG. 3 is a diagram partially showing the aperture array 12. The aperture array 12 is a light-shielding member in which the apertures (openings) are two-dimensionally arranged. Here, the aperture 12A is composed of a glass mask in which a light-shielding film 12B such as chromium is provided on an ultraviolet-transmitting member such as a quartz glass plate. Are arranged in a matrix between the light-shielding films 12B. It is also possible to apply a metal mask having an aperture formed on a thin metal plate or the like.

The aperture 12A is formed at predetermined vertical and horizontal pitch intervals, and is formed according to the arrangement position of the micromirrors in the DMD 22. That is, the micromirror of DMD22 and the aperture 12A have a one-to-one correspondence. However, the number of apertures 12A does not have to be the same as the number of all micromirrors of DMD22, and may be formed by, for example, the number of micromirrors used for exposure in DMD22.

The luminous flux divided by the aperture 12A of the aperture array 12 is imaged on the corresponding micromirrors. The aperture 12A is formed in a rectangular shape here. Further, the size of the aperture 12A is set so that the light flux passing through the aperture 12 becomes smaller than the micromirror size (reflection surface size) when the light flux passing through the aperture 12 is imaged on the micromirror of the DMD22. The arrangement position of the aperture 12A is configured so that the divided light flux is formed at a position offset from the micromirror center position (reflection surface center position), as will be described later.

The relay optical system 14 is an imaging optical system in which the aperture 12A and the DMD 22 are coupled to each other, and is configured here as a reduction optical system that reduces the image of light passing through the aperture array 12 (for example, 0.5 times). The optical system. Therefore, the pitch of the aperture 12A in the aperture array 12 is set to a value obtained by multiplying the pitch of the micromirror in the DMD 22 by the reduction magnification of the relay optical system 14. The NA of the relay optical system 14 is set to a relatively small value so that the light divided by the aperture array 12 does not interfere with the adjacent micromirrors. Although the relay optical system 14 is used as a reduced projection optical system here, it is also possible to use an optical system having the same magnification depending on the size of the micromirror of the DMD 22.

FIG. 4 is a diagram showing the projection positions of the light divided by the aperture array 12 in the micromirror. However, a part of DMD22 is shown.

As described above, the DMD 22 has a configuration in which micromirrors 22M are two-dimensionally arranged on a memory cell, and the micromirrors 22M as pixels have a rectangular size of several tens of μm, and the adjacent micromirrors 22M have a number. There is a gap of μm.

The micromirror 22M can rotate about its axis along the diagonal line SL, and is tilted by ± a predetermined angle (for example, 15 °) with respect to the surface (plane) of the DMD 22. When the micromirror 22M is in the ON state, the split light is tilted to the minus side so as to be reflected in the direction of the substrate W. When the micromirror 22M is in the OFF state, the split light is tilted to the plus side so as to be guided to the outside of the substrate.

The incident direction of the divided light is constant in both the ON state and the OFF state of the micromirror 22M. When the micromirror 22M is in the ON state, the light ray L1 shown in FIG. 4 is the light that becomes the limit (boundary) of the range in which vignetting does not occur. Light outside this hits the adjacent micromirror 22M. On the other hand, when the micromirror 22M is in the OFF state, the light ray L2 is the light that is the limit of the range in which vignetting does not occur. As for the light outside this, the reflected light hits the back surface of the adjacent micromirror.

The range in which light vignetting does not occur is biased due to the difference in the tilt angle of the micromirror 22M in the ON / OFF state with respect to the incident direction of the divided light. Specifically, on the side close to the incident direction of the divided light, that is, on the side where the micromirror 22M is lowered when the micromirror 22M is in the ON state, the range is secured up to the vicinity of the edge portion 22T1 of the micromirror 22M, and the incident direction of the divided light On the distant side, that is, on the side where the micromirror 22M is lowered when the micromirror 22M is in the OFF state, vignetting occurs near the edge portion 22T2 of the micromirror 22M.

The projection area AL of the divided light is located at a position where the maximum area area can be secured within the range where light eclipse does not occur, and the center position AC is on the rotation axis of the micromirror 22M from the center position MC of the micromirror 22M. It is offset toward the incident direction of the divided light along the diagonal line TL that intersects the diagonal line SL.

The size (length and width) and position of the projection area AL of the divided light that does not cause vignetting of light can be calculated by the following formula. First, assuming that the light-shielding region in the ON state of the micromirror 22M is ShON, it is required to satisfy the following equation.

ShON ≧ (Dp × tan (DaON))
× (tan (Ilin) + tan (ILINA))
・ ・ ・ ・ (1)

However, Dp is the diagonal length of the micromirror 22M, DaON is the tilt angle when the micromirror 22M is in the ON state, Ilin is the incident angle of the split light from the illumination optical system 11 to the DMD22, and ILINA is. , Represents the incident NA of the illumination optical system 11.

As described above, the light incident on the DMD 22 has a predetermined incident angle. When the divided light is incident while the micromirror 22M is ON, the reflected light becomes diffracted light in the peripheral portion where the micromirror 22M is raised. Further, in the peripheral portion where the adjacent micromirror 22M is lowered, the light is reflected in the same direction as the incident light, resulting in stray light.

Further, since the light incident on the DMD 22 from the relay lens 14 via the illumination optical system 11 has a spread of NA, a light-shielding region is defined in consideration of the spread of NA for the light-shielding range. A light-shielding region based on the above equation (1) is determined in consideration of the incident NA of the illumination optical system 11 while preventing such diffracted light and stray light from occurring.

On the other hand, assuming that the light-shielding region in the OFF state of the micromirror 22M is ShOFF, it is required to satisfy the following equation.


ShOFF ≧ (Dp × tan (DaOFF))
× (tan (Dout) + tan (ILINA))
・ ・ ・ ・ ・ ・ (2)
However, DaOFF represents the tilt angle when the micromirror 22 is in the OFF state, and Dout represents the reflection angle from the DMD22.

When the divided light is incident when the micromirror 22M is in the OFF state, the light reflected by the lower peripheral portion of the micromirror 22 hits the back surface of the raised peripheral portion of the adjacent micromirror and generates diffracted light. Since the diffracted light incident on the imaging optical system 23 becomes stray light or the like, a light-shielding region based on the above equation (2) is defined.

The light-shielding region ShDMD in the micromirror 22M can be obtained by the following equation if the projection area of the divided light is defined as the projection area obtained by reducing (scaling) the rectangular size of the micromirror 22M. That is, the light-shielding area can be determined so as to be equal to or less than the value obtained by adding the minimum values of the light-shielding areas of the equations (1) and (2). The light-shielding region defined by the equation (3) changes depending on the incident NA of the illumination optical system 11 and the incident angle of the light with respect to the DMD 22.

ShDMD ≤ ShON + ShOFF
・ ・ ・ ・ ・ ・ (3)

The projection area AL of the divided light satisfying the equation (3) is symmetrical with respect to the diagonal line TL, and the projection center position AC is offset from the micromirror center position MC along the diagonal line TL. When the equation (3) is an equation, the size of the projection area AL of the divided light and the offset position AC are the positions where the shading range is minimized within the range where vignetting or the like does not occur.

The aperture 12A of the aperture array 12 is offset with respect to the center of the region partitioned by the aperture array 12 according to the size and arrangement of the micromirror 22M according to the size and projection center position AC of the projection area AL shown in FIG. ing. However, the aperture array 12 in which the aperture 12A is not offset may be configured to be offset with respect to the optical axis of the entire illumination light.

As described above, according to the present embodiment, in the exposure apparatus 1 provided with the DMD 22, the illumination optical system 11 includes the aperture array 12 in which the aperture 12A is two-dimensionally arranged, and the light passing through the aperture 12A is divided and divided. The generated light is imaged on the micromirror 22M as spot light. The projection area of the divided light is smaller than the size on the micromirror 22M, and its projection position is offset from the center of the micromirror 22M.

By offset-projecting the divided light in this way, it is possible to irradiate the maximum area within the range where vignetting of light does not occur, that is, diffracted light and stray light do not occur, and it is possible to prevent a decrease in exposure amount. A pattern with high contrast can be formed. Further, since the spot light is not concentrated near the center of the micromirror 22M, the life of the micromirror 22M, that is, the DMD 22 can be extended. Further, by arranging the aperture array 12 on which the aperture 12A is formed, it is possible to form the divided light at no cost.

Although the maximum projection area can be secured in the above equation, the generation of diffracted light or the like can be suppressed only by the configuration in which the projection area of the divided light is offset toward the incident direction side of the light. Therefore, the aperture 12A is not limited to a rectangular shape (including a rhombus), but may be a circular shape, a polygonal shape, or the like. Such a shape can be realized by adopting the aperture array 12.

Next, the exposure apparatus according to the second embodiment will be described with reference to FIGS. 5 and 6. In the second embodiment, a microlens array is used. Other than that, the configuration is substantially the same as that of the first embodiment.

FIG. 5 is a block diagram of the exposure head according to the second embodiment. FIG. 6 is a diagram showing the projection positions of the light divided by the aperture array 12 in the micromirror.

The illumination optical system 110 includes an illuminance equalizing optical system 13, a relay optical system 14, and a microlens array 120. The microlens array 120 in which the microlenses are arranged in a two-dimensional manner divides the light from the light source 20, and the light collected by each microlens is imaged on the corresponding micromirror 22M of the DMD 22.

As shown in FIG. 6, the divided light flux has a circular cross section according to the lens shape, and the projection area AL also has a circular shape. Further, the projection area AL is offset along the diagonal line SL. By such offset projection of the divided light, the same effect as that of the first embodiment can be obtained.

A pinhole array may be provided adjacent to at least one of the front and rear surfaces of the microlens array 120. Further, the relay optical system 14 may be omitted. In this case, a defocused image is formed on the micromirror 22M.

Next, the exposure apparatus according to the third embodiment will be described with reference to FIG. 7. In the third embodiment, a micromirror array is used. Other than that, it is substantially the same as the second embodiment.

FIG. 7 is a block diagram of the exposure head according to the third embodiment. The illumination optical system 210 includes an illuminance equalizing optical system 13 and a micromirror array 220. The micromirror array 220 is an optical system in which concave lenses having positive power are two-dimensionally arranged, and forms split light as in the second embodiment.

1 Exposure device 10 Exposure head 11 Illumination optical system 12 Aperture array (divided optical system)
22 DMD (Light Modulation Element Array)
22M micromirror (light modulation element)
23 Projection optical system

Claims (8)

An illumination optical system that guides the light from the light source to a light modulation element array in which a plurality of light modulation elements are arranged two-dimensionally.
A projection optical system that projects the light reflected by the light modulation element array onto the substrate, and
A split optical system that is arranged between the light source and the light modulation element array and divides the light from the light source into a plurality of lights (hereinafter referred to as split light) according to the arrangement of the plurality of light modulation elements. Equipped with
The split optical system forms a plurality of split lights having a luminous flux smaller than the size of the light modulation element, and the center position of the projection area of each split light is set to be smaller than the center position of the corresponding light modulation element. An exposure device characterized by offsetting toward a direction closer to the incident direction. Each light modulation element is a rectangular element that rotates about its axis diagonally.
The exposure apparatus according to claim 1, wherein the split optical system offsets the projection center position of each split light along a diagonal line intersecting a diagonal line along a rotation axis. The exposure apparatus according to claim 1 or 2, wherein the split optical system forms a plurality of rectangular split lights. The exposure apparatus according to claim 3, wherein the split optical system forms a plurality of split lights in which a projection area having a reduced size of the light modulation element is formed. The exposure apparatus according to any one of claims 1 to 4, wherein the split optical system has a light-shielding member having a plurality of apertures formed according to the arrangement of the plurality of light modulation elements. The exposure apparatus according to claim 5, wherein in the light-shielding member, the plurality of apertures are offset with respect to the center of a region partitioned according to the size of the micromirror. The exposure apparatus according to claim 1 or 2, wherein the split optical system has a microlens array in which a plurality of microlenses are formed according to an arrangement of the plurality of light modulation elements. The exposure apparatus according to claim 1 or 2, wherein the split optical system has a micromirror array in which a plurality of micromirrors are formed according to an arrangement of the plurality of light modulation elements.

Images