JPH06204120A - Detecting equipment of focal point position and detecting method of focal point position - Google Patents

Abstract

PURPOSE:To prevent generation of detection error, by moving a stage mounting a photosensitive substrate, in the optical axis direction of a projection optical system. CONSTITUTION:The image of an aperture pattern 1a on a stage 12 is projected on the pattern surface of a mask via a projection optical system 2, and the reflected light of the image is detected via the aperture pattern. While the optical length of light flux forming an image is changed by changing the pressure between lenses constituting the projection optical system, the reflected light amount of the image of the aperture pattern is detected. The position of a focal point is obtained on the basis of the pressure value wherein the light amount becomes a maximum or a minimum.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for obtaining a focus position for a projection optical system of a mask in a projection exposure apparatus used for manufacturing a semiconductor device, a liquid crystal display substrate, etc., and particularly for automatically correcting the focus position. The present invention relates to a focus position detection device suitable for use in a focus adjustment mechanism that operates.

[0002]

2. Description of the Related Art In an exposure apparatus used for manufacturing semiconductor devices and the like, a mask and a photosensitive substrate are arranged through a projection optical system, and a mask pattern is transferred onto the photosensitive substrate using exposure light such as ultraviolet rays. . At this time, it is important to dispose the photosensitive substrate at the conjugate position of the mask pattern with respect to the projection optical system, that is, focusing. Therefore, in general, this type of exposure apparatus is equipped with a focus adjusting mechanism for automatically performing focusing.

As such a focus adjusting mechanism, for example,
An irradiation optical system and a light receiving optical system, which are obliquely fixed to the outside of the projection optical system, are provided, and a light beam from the irradiation optical system is irradiated onto a photosensitive substrate, and the light beam reflected from this photosensitive substrate is received and projected. The height of the exposed surface of the photosensitive substrate (the height of the projection optical system in the optical axis direction) is measured using a measuring device that detects the height of the stage under the optical system and has its origin adjusted in advance to the conjugate position (focus position). ) Is indirectly detected to guide the photosensitive substrate to the focal position.

By the way, the focus adjusting mechanism as described above is
It is necessary to measure the conjugate position of the mask pattern in order to adjust the origin to the focus position in advance. As this focus position detecting device, there is a device as disclosed in JP-A-4-348019. This illuminates a light-transmissive aperture pattern formed on the same plane as the exposure surface of the photosensitive substrate provided on the stage, and the image of this aperture pattern is projected on the pattern surface of the mask through the projection optical system. To project. Then, the reflected light of the image from the pattern surface is detected via the projection optical system and the aperture pattern, and the light amount of the image transmitted through the aperture pattern is detected. This light amount detection is performed while moving the stage in the optical axis direction of the projection optical system, the change in light amount with the position of the stage is detected, and the stage position at which the maximum or minimum of this light amount change is obtained is the focus position.

[0005]

However, since the conventional focus position detecting device as described above adopts the method of driving the stage, the movement accuracy due to the backlash of the stage and the heat generated by the movement of the stage, or the driving unit. Deterioration (durability) deteriorates the positioning accuracy of the stage, making it impossible to accurately detect the focus position.

In view of the above problems, it is an object of the present invention to obtain a focus detection device which is not affected by the driving accuracy of the stage or heat generation.

[0007]

In order to solve the above problems, the present invention provides a mask (3) and a projection optical system (2).
A reference plane (1) having a light-transmissive aperture pattern (1a) which is arranged at a position substantially conjugate with the mask through a projection optical system, and an illumination means (8, 13) for illuminating the aperture pattern. Detecting means for detecting an image of the opening pattern illuminated by the illuminating means and projected on the mask through the projection optical system through the projection optical system and the opening pattern, and detecting a change in the light amount of the image passing through the opening pattern. (7,1
3, 14) and a focus position detecting device for detecting the conjugate position of the mask with respect to the projection optical system based on the detection result by the detecting means, at least a part (2, 22, 23) of the projection optical system, or Optical path length changing means (17, 19,) for changing the optical path length of the light flux forming the image of the aperture pattern by moving the mask (3) in the optical axis direction of the projection optical system or inclining it with respect to the optical axis. 21,
25).

Further, in the focus position detecting device for detecting the conjugate position of the mask pattern surface on the stage side with respect to the projection optical system (2), the light transmissive aperture pattern (1a) formed on the stage (12) is illuminated. Illuminating means (8, 13) for illuminating; illuminating means, and detecting reflected light of the image of the aperture pattern projected on the mask pattern surface through the projection optical system through the projection optical system and the aperture pattern to open the aperture. Detection means (7, 13, 14) for detecting a change in the light amount of the image that has passed through the pattern; and at least a part (2, (22, 23) or by moving the mask pattern surface to change the optical path length of the light flux forming the image of the aperture pattern and the optical path length of the reflected light (1). , It was decided to have a 19,21,25) and.

Further, in a projection exposure apparatus that exposes the pattern of the mask (3) onto the object (11) via the projection optical system (2), the conjugate position of the pattern surface of the mask on the object side with respect to the projection optical system. In the focus position detecting method for detecting the object, a reference plane (1) arranged in the same plane as the object.
Positioning the aperture pattern (1a) formed in the inside at a plurality of predetermined positions with respect to the optical axis of the projection optical system; illuminating the aperture pattern at each of the plurality of positions, and masking through the projection optical system. Detecting reflected light of the image of the aperture pattern projected on the pattern surface via the projection optical system and the aperture pattern; at least a part of the projection optical system (2,
22 and 23) or a step of detecting the light amount of the image passing through the aperture pattern while changing the optical path length of the light flux forming the image of the aperture pattern and the optical path length of the reflected light by moving the mask; The step of obtaining the position of at least a part of the projection optical system or the mask that obtains the maximum or the minimum of the light amount; and the step of calculating the conjugate position based on the position obtained at each of the plurality of positions. And

[0010]

In the present invention, since the conjugate position is obtained by moving at least part of the pattern surface of the mask or the projection optical system in the optical axis direction of the projection optical system, the stage is set in the optical axis direction of the projection optical system. There is no need to move to and find the conjugate position.

[0011]

1 is a diagram showing a schematic configuration of a projection exposure apparatus having a focus detection device according to an embodiment of the present invention.
Prior to projection exposure, the focus position detection device detects the position of the in-focus point at any location on the stage (the height in the optical axis direction of the projection optical system), and the focus adjustment mechanism detects XY.
The height and inclination of the exposure surface of the wafer placed on the stage are adjusted so that the exposure surface coincides with the conjugate surface.

In FIG. 1, a mask 3 having a circuit pattern on its lower surface faces the stage 12 via a projection lens 2 and is illuminated by an illumination optical system 4 during projection exposure. The stage 12 on which the wafer 11 is placed can be positioned at an arbitrary position on the stage 12 with respect to the optical axis of the projection optical system by an XY drive system 15, and the entire stage 12 can be tilted at an arbitrary height and inclination by a Zθ drive system 9. Can be adjusted to A fiducial plate 1 having a predetermined opening pattern 1a formed on the surface thereof is provided on the stage 12, and the opening pattern 1a is illuminated by an illumination optical system including a light source 8, a glass fiber cable 13 and the like. , The reflected light transmitted through the opening pattern 1a is reflected by the glass fiber 1
3, a light quantity detector 7, a half mirror 14 and the like are used for detection. The projection optical system 2 is provided with oblique incidence focus sensors 5 and 6 for wafer surface detection.
The control system 10 inputs the outputs of the sensor 6 and the detector 7, and controls the drive system 9 based on these information. Further, the control system 10 is configured to change the pressure in the space between the lens elements in the projection optical system 2 by controlling the pressure adjusting mechanism 16 as the optical path length changing means.

In the focus adjusting mechanism constructed as described above, the illumination light output from the light source 8 is guided to the opening pattern 1a through the cable 13 and emitted upward, and the mask pattern is transmitted through the projection optical system 2. Opening pattern 1a on the surface
Form a projected image of. This projection image is generated by using the drive system 15 within the field of view of the projection optical system 2 by the fiducial plate 1.
Can be moved to any position on the mask pattern by scanning, and the focus position can be individually determined at each position.

By the way, the projected image reflected on the mask pattern surface is imaged on the conjugate surface of the projection optical system 2 of the mask pattern, going up the optical path of the illumination light. At this time, if the height of the reference surface of the fiducial plate 1 has a conjugate positional relationship with the mask pattern surface and the projection optical system 2, the projected image formed on the mask pattern surface has a clear boundary in focus. Therefore, the second projected image formed on the reference surface by the projected image reflected on the mask pattern surface also has a clear boundary in focus. Where the second
Of course, since the projection image has the same shape, the same dimensions, and the same posture as the opening pattern 1a, the optical information from the projection image formed on the mask pattern surface is transmitted through the opening pattern 1a to the maximum, and the detection optical system. To reach the detector 7 and give a peak of the amount of received light. On the other hand, when the height of the reference plane is displaced from the conjugate plane of the mask pattern surface, the projected image formed on the mask pattern surface and the second projected image on the reference surface are out of focus and the boundary is blurred. Become. Therefore, the optical information is lost by the amount of the second projected image protruding from the aperture pattern 1a, and the second projected image is transmitted through the aperture pattern 1a.
Decrease the amount of light received.

Therefore, the stage 12 is moved and positioned sequentially by the drive system 15 so that the projected image is formed at a plurality of positions defined on the mask pattern surface. Control system 10
Changes the optical path length of the light flux forming each projection image by adjusting the internal pressure of the projection optical system 2 by the pressure adjusting mechanism 16 so that the detector 7 detects the maximum or minimum of the light amount at each position. Let Then, the pressure value when this maximum or minimum of the light quantity is obtained (this pressure value corresponds to the optical path length) is stored corresponding to each position. The position of the in-focus point is obtained based on the relationship between the position and the pressure value thus obtained. For example, the relationship between the pressure value and the focus position of the projection optical system is measured in advance, and the focus position is obtained by comparing this information with the pressure value when actually measured. From the obtained position, the tilt angle on the stage 12 for the entire exposure surface of the wafer to coincide with the focus position is calculated. Then, the Zθ drive system 9 adjusts the tilt amount of the stage 12 to the obtained angle.

On the other hand, the origin adjustment of the oblique incidence focus sensors 5 and 6 is executed with respect to the reference surface of the fiducial plate 1 whose inclination is adjusted to the focal position. That is, the height of the reflected beam spot on the fiducial plate 1 is stored as the origin, and when the visual field of the projection optical system 2 is projected to an arbitrary position on the stage 12 thereafter, the beam is detected by the oblique incidence focus sensors 5 and 6. The surface height at the spot irradiation position is measured, and the control system 10 adjusts the stage height by the drive system 9 so that this surface height matches the origin height.

Next, another example of the optical path length changing means in this embodiment will be described with reference to FIG. Figure 2 (a) shows
It is a figure which shows the example which adjusts the height (position of the optical axis direction of a projection optical system) and inclination of the whole projection optical system 2 by the lens drive system 17 instead of a pressure adjusting mechanism. A drive section 19 such as a piezo element is provided on a support section 18 supporting the projection optical system 2,
The optical path length is changed by finely moving the projection optical system 2 by the drive system 17. At this time, the information about the light amount obtained by the detector 7 is input to the control system 10, and the height or tilt amount of the projection optical system 2 at which the maximum or minimum of the light amount is obtained and the position on the mask forming the projected image are associated with each other. Let me remember. The drive unit 19 is provided with a position detector such as a micrometer, and the control system 10 can obtain the in-focus position with high accuracy via the drive system 17.

FIG. 2B is a diagram showing a mechanism for driving a part of lens elements in the projection optical system 2 by the lens driving system 17. A drive unit 21 such as a piezo element is provided in the lens supporting unit 20 of a part of the lens element 22 of the projection optical system 2, and the lens drive system 17 changes the position of the lens element 22 or inclines the optical path length. Change. The drive unit 21 may drive a plurality of lens elements in the projection optical system 2.

FIG. 2C shows the lens drive system 17
This is a mechanism for driving a pair of wedge-shaped lens elements 23 in the projection optical system 2. The lens element 23 is moved by the lens driving system 17, and the lens interval and thickness of the lens element 23 are changed to change the optical path length.
FIG. 2D is a diagram showing an example in which the position of the mask and the amount of tilt are changed. The mask holder drive system 25 allows the mask 3
By driving the mask holder 24 on which is mounted, the position and the inclination of the mask 3 in the optical axis direction are changed to change the optical path length.

In addition, the wavelength of the illumination light from the light source 8 shown in FIG. 1 may be changed to detect the change of the light amount at that time. In each of the examples of the optical path length changing means shown in FIG. 2, the focus position may be obtained by using only one type, or a plurality of types may be used in combination to measure the focus position by each. May be. If the focus position is measured by statistically processing a plurality of detection results, it is possible to perform measurement independent of external factors.

[0021]

As described above, according to the present invention, when determining the conjugate position (focus point) of the pattern surface of the mask with respect to the projection optical system, the stage on which the photosensitive substrate is mounted is moved in the optical axis direction of the projection optical system. There is no need to move to. Therefore, the detection error of the focus position due to the movement accuracy of the stage is eliminated.

[Brief description of drawings]

FIG. 1 is a diagram showing a schematic configuration of a projection exposure apparatus including a focus position detection device according to an embodiment of the present invention.

FIG. 2 is a diagram showing another example of the optical path length changing means.

[Explanation of symbols]

 1 Fiducial plate 1a Opening pattern 16 Pressure adjustment mechanism 17 Lens drive system 19,21 Drive unit 23 Wedge type lens element 25 Mask holder drive system

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁵ Identification code Office reference number FI Technical display location G03F 7/207 H 7316-2H

Claims (4)

[Claims] 1. A mask, a projection optical system, a reference plane disposed at a position substantially conjugate with the mask through the projection optical system, and having a light-transmissive aperture pattern, and illuminating the aperture pattern. An illumination unit and an image of the aperture pattern illuminated by the illumination unit and projected onto the mask through the projection optical system is detected through the projection optical system and the aperture pattern, and passes through the aperture pattern. A detecting means for detecting a change in the light amount of the image, and a focus position detecting device for detecting a conjugate position of the mask with respect to the projection optical system, based on a detection result by the detecting means, at least the projection optical system. An image of the aperture pattern is formed by moving a part or the mask in the optical axis direction of the projection optical system or by inclining the mask with respect to the optical axis. Focal position detecting apparatus comprising the optical path length changing means for changing the optical path length of a light beam. 2. The focus position detecting device according to claim 1, wherein the optical path length changing unit is a pressure adjusting unit that adjusts a pressure in a space between optical elements forming the projection optical system. 3. A focus position detecting device for detecting a conjugate position of a mask pattern surface on a stage side with respect to a projection optical system, comprising: an illuminating means for illuminating an optically transparent aperture pattern formed on the stage; and the illuminating means. The reflected light of the image of the aperture pattern, which is illuminated by the projection optical system and projected onto the mask pattern surface, is detected via the projection optical system and the aperture pattern, and the image passed through the aperture pattern. At least a part of the projection optical system up to a position where the maximum or the minimum of the change in the light amount is obtained based on the output of the detection unit,
Alternatively, the focus position detecting device is provided with an optical path length changing means for changing the optical path length of the light flux forming the image of the aperture pattern and the optical path length of the reflected light by moving the mask pattern surface. 4. A focus position detection for detecting a conjugate position of a pattern surface of the mask on the object side with respect to the projection optical system in a projection exposure apparatus for exposing a pattern of the mask onto the object via the projection optical system. In the method, the step of positioning an aperture pattern formed in a reference plane arranged in the same plane as the object at a plurality of predetermined positions with respect to the optical axis of the projection optical system; Illuminating the aperture pattern in each, and detecting reflected light of the image of the aperture pattern projected on the mask pattern surface via the projection optical system via the projection optical system and the aperture pattern; By changing at least a part of the projection optical system or the mask, the optical path length of the light flux forming the image of the aperture pattern and the optical path length of the reflected light are changed. While detecting the amount of light of the image that has passed through the aperture pattern; and obtaining the maximum or minimum of the detected amount of light, at least a part of the projection optical system, or a position of the mask. A step of calculating the conjugate position based on the position obtained at each of the plurality of positions, the focus position detecting method.