JPH10239037A - Observation device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately measure the dimensions of a pattern on a sample, especially, the dimensions or the like of a pattern of difference in level by adjusting the optical axis of an objective optical system in accordance with the inclination of a detected sample surface. SOLUTION: A lighting optical system 13 illuminates the surface of a sample. An objective optical system 14 converges the luminous flux from the sample surface for forming the image of the sample surface. An image pickup means 16 photoelectrically detects the image of the sample surface. A focus detecting system 19 photoelectrically detects the luminous flux from the sample surface through at least a part of the objective optical system 14, so that the focusing surface of the objective optical system 14 on the side of the sample surface and the sample surface are detected in a conformable condition. Then, inclination detecting means 33, 34, and 35 detect the inclinations of the sample surface. Further, an adjusting means 39 adjusts the optical axis of the objective optical system 14 in accordance with the inclinations of the sample surface detected by the inclination detecting means 33, 34, and 35. In this manner, since the main light rays on the observing side are inclined in accordance with the inclinations of the sample, accurate dimension measurement can be always carried out. Further, the reduction in the measurement and the measuring time can be possible.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an observation apparatus, and more particularly to an observation apparatus for measuring and observing dimensions of a stepped pattern such as a pattern formed on a liquid crystal substrate.

[0002]

2. Description of the Related Art FIG. 4 is a view schematically showing a configuration of an observation apparatus conventionally used for dimension measurement and the like. FIG.
The observation apparatus shown in FIG. 1 combines an illumination optical system 3 for irradiating a sample 2 held on a sample holder 1 with light, an objective lens 4 for condensing light reflected from the sample surface, and a light beam transmitted through the objective lens 4. An imaging optical system 5 for forming an image and an imaging unit 6 for photoelectrically converting the sample image formed by the imaging optical system 5 are provided. In such an optical system, the illumination optical system 3 and the imaging optical system 5 are configured to have a common optical axis with respect to the objective lens 4 by the optical path splitting means 7 and 8.

The auto-focusing means 9 detects a deviation between the sample surface and the focal plane of the objective lens 4 and moves the objective lens 4 or the sample holder 1 via a driving means (not shown), thereby obtaining the sample 2. The focus of the objective lens 4 can be automatically focused on the measurement surface of (1). In actual dimension measurement, the sample 2 is sequentially held in the sample holder 1 and set at the focal position of the objective lens 4. And
The pattern applied to the sample 2 is observed by the imaging means 6, and the actual size of the pattern on the sample is determined based on the size of the pattern on the image sensor, the imaging magnification, and the like.

[0004]

However, in the conventional observation apparatus, when the sample is mounted on the sample stage or on the sample holder at an angle, the pattern formed on the substrate is observed from an oblique direction. Dimension measurement cannot be performed.

In an observation device used for dimension measurement, etc.,
The length on the sample must be accurately measured on the observation surface. In other words, when measuring the equally-spaced pattern on the sample surface, it is impossible to measure the dimension accurately even on the observation surface unless the equally-spaced pattern is imaged. Further, it is necessary that the dimensions can be accurately measured even if the position of the sample is slightly before or after the optical axis. For this reason, a so-called telecentric optical system in which the pupil is located at an infinite position (the principal ray intersects the optical axis at the infinite position, that is, does not intersect in parallel) is employed in an observation device used for dimension measurement or the like.

Further, in the observation optical system of the conventional observation apparatus, when the objective lens 4 is set to a high magnification, the number of lenses constituting the objective lens increases, so that the pupil is formed in the lens group. I will. Such a phenomenon becomes more remarkable as the magnification of the objective lens becomes higher. As a result, since the pupil is formed in the lens system, the aperture stop for determining the size of the light beam that reaches the imaging means through the objective lens 4 is arranged at a position different from the actual pupil position. There must be.

If the pupil position and the stop position are different, the chief ray is not parallel to the optical axis but tilts, so that the so-called telecentricity deteriorates. If the chief ray is inclined, the center of the luminous flux to be captured with respect to the sample surface will be inclined due to the image height when measuring a pattern with a step, and the measured value will be measured as a value different from the actual value, and accurate This is a problem because dimension measurement cannot be performed.

The deterioration of the telecentricity is caused not only by the observation / imaging optical system but also by the illumination optical system.
It is a phenomenon that occurs similarly. That is, in the illumination optical system, if the pupil position and the stop position are different, the light illuminating the sample is inclined with respect to the optical axis. As a result, even if the sample is correctly set, the sample will be illuminated obliquely, and in a pattern with a step, etc., a shadow due to oblique illumination will occur, and accurate dimensional measurement must be performed. A problem arises that it cannot be performed.

Therefore, the present invention has been made in view of such a problem, and accurately measures the size of a pattern on a sample, particularly, the size of a stepped pattern, even when a sequentially set sample is inclined. It is an object of the present invention to provide an observation device capable of performing such operations.

[0010]

In order to solve the above-mentioned problems, the present invention provides an illumination optical system for illuminating a sample surface, and a method for forming an image of the sample surface by condensing a light beam from the sample surface. An objective optical system, an imaging unit for photoelectrically detecting an image of the sample surface, and photoelectrically detecting a light beam from the sample surface via at least a part of the objective optical system, and a sample surface side of the objective optical system. A focus detection system for detecting a state of alignment between the focal plane of the sample and the sample surface; a tilt detection unit for detecting a tilt of the sample surface; and the sample surface detected by the tilt detection unit. Adjusting means for adjusting the optical axis of the objective optical system according to the inclination of the objective optical system.

According to the present invention, the tilt of the sample set in the sample holder can be detected and the optical axis of the objective optical system can be adjusted based on the data, that is, the chief ray can be tilted. In addition, even if the sample is inclined, dimensional measurement and the like can be performed satisfactorily. In addition, it is possible to quickly measure or observe samples that are set one after another.

[0012]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a diagram showing a configuration of an embodiment of the present invention. The observation apparatus of the present embodiment includes an illumination optical system 13 for illuminating a sample 12 such as a liquid crystal substrate held by a sample holder 11, an objective lens 14 for condensing light reflected from the sample surface, and an objective lens An image is formed by a relay optical system 15a for relaying the pupil 20, an image forming optical system 15b for forming an image of a light beam reflected by the sample 12 and transmitted through the objective lens 14 and the relay optical system 15a, and an image forming optical system 15b. And imaging means 16 such as a CCD for photoelectrically converting the sample image thus obtained.

An optical path splitting means 1 such as a half mirror
7 and 18, the illumination optical system 13 and the relay optical system 15 are used.
Since a and the imaging optical system 15b are configured to have a common optical axis, both the illumination light and the reflected light from the sample pass through the objective lens. Here, the objective lens 1
The fourth pupil 20 and the observation-side (imaging system) aperture stop 22 are in an optically conjugate relationship with the sample surface 12 and the observation-side field stop 21, respectively. Maintaining such a conjugate relationship means that
In other words, it means that the pupil 20 of the objective lens 14 can be relayed by the relay lens system 15a and the aperture stop 22 can be placed at the relayed position. That is,
Even when the objective lens 14 has a high magnification and the pupil position enters the optical system of the objective lens and the aperture stop cannot be arranged at the actual pupil position, the aperture stop is placed at the relayed pupil position. Therefore, it is possible to maintain the telecentricity of the optical system. As a result, accurate dimension measurement can be performed even with a high-magnification objective lens.

On the other hand, the auto-focusing device 19 adjusts the focal plane of the objective lens 14 so as to coincide with the sample plane 12.
The alignment state is detected via the half mirror 18 and the objective lens 14.

The autofocus device 19 moves the objective lens 14 or the sample holder 11 in the vertical direction (the optical axis direction of the objective lens 14) via a drive system (not shown) based on the information detected by the photoelectric detection. Focusing is performed so that the focal plane of the objective lens 14 and the sample plane 12 match. The illumination optical system provided in the reflection direction of the half mirror 17 includes a light source LS for supplying illumination light and a light source L.
A condensing lens L1 for condensing the illumination light from S, and an illumination-side aperture stop 24 disposed at a condensing position of the condensing lens L1.
And a condenser optical system (L2, L3) for forming an image of the aperture stop on the pupil of the objective lens 14. A field stop 23 is provided in the condenser optical system.

The illumination optical system 13 includes a pupil 2 of the objective lens 14.
0 and the illumination system aperture stop 24 constitute Koehler illumination in which the sample surface 12 and the illumination system field stop 23 are respectively conjugate. As with the observation side optical system, even when a high-magnification objective lens is used, telecentricity in the illumination optical system, that is, vertical illumination of the sample is possible.
Therefore, even when a pattern or the like having a step is measured, accurate dimension measurement can be performed without a shadow or the like due to oblique illumination.

Next, the measurement procedure will be described. When the sample 12 held in the sample holder 11 is sequentially set at the focal position of the objective lens 14, the tilt of the sample 12 is detected by tilt detection means (not shown). Based on the obtained data on the tilt, the observation-side aperture stop 22 is moved in a plane perpendicular to the optical axis to adjust the optical axis of the objective optical system (20, 15a, 15b).

The adjustment of the optical axis will be described in more detail with reference to FIG. In order to maintain the telecentricity of the optical system and perform accurate dimension measurement and the like, when considering the optical system L on the observation side, as shown in FIG. And must be vertical.
The principal ray CR is a ray passing through the center of the aperture stop AS, and is parallel to the optical axis AX of the optical system L in a telecentric optical system.

The optical system L shown in FIG. 5 corresponds to a combined system of the objective lens 14 and the relay optical system 15a in FIG. When the optical system L shown in FIG. 5 is viewed as a part of an illumination optical system described later, it corresponds to a combined system of the objective lens 14 and the condenser optical systems (L2, L3) in FIG.

However, as shown in FIG. 5B, when the sample surface O is tilted, an angle shift θ occurs between the principal ray CR and the normal of the tilted sample surface O ′, and accurate dimension measurement and the like are performed. Can not be done. Then, when the aperture stop AS is moved to the position of AS ', the chief ray is a ray passing through the center of AS' and becomes CR '. At this time, according to the inclination θ of the sample O, the optical axis AX of the lens system L passing through the center of the aperture stop AS is as shown in FIG.
The aperture stop AS is tilted as shown by AX ′ in FIG.
Of the optical axis AX 'passing through the center of
Is parallel to the optical axis AX before the movement of the aperture stop AS.

Therefore, as shown in FIG. 5 (b), if the optical axis is adjusted by moving the aperture stop AS by .DELTA.m in the direction perpendicular to the optical axis AX in accordance with the inclination .theta. The principal ray CR 'is perpendicular to the sample surface O', and becomes a telecentric system, enabling accurate dimension measurement and the like.

The optical system on the observation side has been described above.
The same can be said for the optical system on the illumination side. That is, by moving the aperture stop 24 provided in the illumination optical system perpendicular to the optical axis of the illumination optical system and adjusting the optical axis, the angle between the principal ray on the illumination side and the sample surface can be arbitrarily adjusted. Is possible.

Accordingly, the movement of the aperture stop causes the sample surface 1
It is possible to eliminate the angular deviation between the optical axis of the objective lens 14 for observing and measuring the surface and the optical axis of the illumination optical system, and the inclined axis (tilted optical axis) perpendicular to the sample surface 12. I can do it.

Next, an example of the inclination detecting means is shown in FIG. In FIG. 2, a light source 31 such as a semiconductor laser is provided on a sample surface 32 separately from an illumination light source for measuring a pattern size of the sample.
Is provided, the light beam from the light source 31 is irradiated on the sample 32, and the reflected light is condensed, and the condensing position is detected by the position detecting means 33 such as a position detecting sensor. At this time, the inclination of the sample 32 can be detected from the movement of the position of the condensing point on the position detection sensor 33.

Another example of the observation apparatus of the present invention using such a tilt detecting means will be described with reference to FIG. In FIG. 3, apart from the tilt detecting means described with reference to FIG. 2, in addition to the tilt detecting optical system 34 and the position detecting sensor 35, the reflected light from the sample surface 12 of the light from the illumination light source is used.
, It is also possible to detect the inclination of the sample surface 12. These tilt detecting means may be incorporated in the apparatus singly, but when used in combination, the tilt of the sample can be detected more accurately.

Data relating to the tilt of the sample from the tilt detector is taken into a telecentricity controller 37 for controlling the telecentricity of the optical system, and a drive unit 38 controls the aperture stops 22 and 24 on the observation side and the illumination side. Drive. By moving the aperture stop 24 of the illumination optical system, the chief ray on the illumination side can be tilted, and by moving the aperture stop 22 on the observation side, the imaging light (light reflected from the sample on the observation side The principal ray of light that is taken into the optical system can be tilted. For this reason, even when the sample 12 is tilted, by tilting the chief ray,
The telecentricity of the optical system can be maintained, and accurate dimension measurement can be performed. The tilt of the principal ray is not limited to the movement of the aperture stop, but may be performed by moving other optical components.

The tilt of the sample 12 itself can be corrected by the stage tilt adjusting means 39 based on the data from the telecentricity control section 37.
That is, the correction of the tilt of the sample 12 itself and the correction of tilting the principal ray by moving the aperture stop can be performed simultaneously. In such a case, it is preferable to use the correction of the tilt of the sample 12 itself for coarse adjustment and the correction of tilting the light beam by moving the diaphragm for fine adjustment.

In the present invention, the inclination of the sample is detected,
If this can be corrected, the arrangement of the optical system, the inclination detecting means, the autofocus device, and the like are not limited to the embodiments. Further, the optical path splitting means of the present invention may include a half prism, a dichroic mirror,
The dichroic prism and the like can be appropriately selected according to the required wavelength, light amount, and the like. Further, it goes without saying that the present invention can be implemented with any device for measuring dimensions, such as a line width measuring device and an overlay measuring device, or an alignment device for a microscope or an exposure device.

As described above, according to the present invention, the inclination of the sample surface set one after another is detected, the optical axis of the objective optical system is adjusted, and the principal ray on the observation side is adjusted according to the inclination of the sample. Since it is inclined, accurate dimension measurement can always be performed.
In addition, measurement and measurement time can be reduced.

[Brief description of the drawings]

FIG. 1 is a view schematically showing an embodiment of an observation apparatus according to the present invention.

FIG. 2 is a diagram showing a tilt detection device according to the present invention.

FIG. 3 is a view showing another embodiment of the observation device according to the present invention.

FIG. 4 is a diagram showing a conventional observation device.

FIG. 5 is a diagram showing a relationship between a principal ray and an aperture stop.

[Explanation of symbols]

1,11 ... Sample holder 2,12 ...
Sample 3,13 ... Illumination optical system 4,14 ...
Objective lens 5 Image forming optical system 6 Image pickup device 7, 8, 17, 18, 36 Half mirror 9, 19 Auto focus unit 15a Relay optical system 15b Image forming optical system 16 ... Image pickup device 20... Objective lens pupil 21... Observation-side field stop 22... Observation-side aperture stop 23... Illumination-side aperture stop 31. Position detection sensor 34 Position detection optical system 37 Telecentricity control unit 38 Drive unit 39 Stage tilt adjustment unit O, O 'Sample AX, AX'
…… Optical axis CR, CR ′ …… Principal ray AS, AS ′
... Aperture stop L ... Lens LS ... Light source L1 ... Condenser lens L2, L3 ...
… Condenser optical system

Claims (4)

[Claims] An illumination optical system for illuminating a sample surface, an objective optical system for condensing a light beam from the sample surface to form an image of the sample surface, and an imaging unit for photoelectrically detecting the image of the sample surface A focus detection system that photoelectrically detects a light beam from the sample surface via at least a part of the objective optical system and detects a matching state between the sample surface-side focal surface of the objective optical system and the sample surface; A tilt detecting means for detecting the tilt of the sample surface; and adjusting the optical axis of the objective optical system according to the tilt of the sample surface detected by the tilt detecting means. And an observation device. 2. The apparatus according to claim 1, wherein said adjusting means further adjusts an optical axis of said illumination optical system in accordance with a tilt of said sample surface detected by said tilt detecting means. Observation device. 3. The illumination device is arranged in the illumination optical system at a position optically conjugate with a pupil of the objective optical system, and is movable in a direction orthogonal to an optical axis of the illumination optical system. A side aperture stop, and an observation side aperture that is disposed in the objective optical system at a pupil of the objective optical system or at a position optically conjugate with the pupil and is movable in a direction orthogonal to the optical axis of the objective optical system. 3. The apparatus according to claim 2, further comprising an aperture.
2. The observation device according to 1. 4. The objective optical system includes: an objective lens system for condensing light from the sample surface; and a relay optical system for receiving a light beam from the objective lens system and re-imaging a pupil of the objective lens. An imaging lens system for condensing light from a pupil re-imaged by the relay optical system to form an image of the sample surface, and being disposed between the objective lens system and the relay optical system. A light splitting member, wherein the light splitting member guides illumination light from the illumination optical system to the sample surface via the objective lens, and directs light from the sample surface through the objective lens system. The observation apparatus according to claim 3, wherein the observation apparatus has a function of leading to the relay optical system, and the observation-side aperture stop is arranged at an image position of an objective lens pupil formed by the relay optical system.