JPH0949784A - Inspecting method for projection optical system and illumination optical system used for the inspection - Google Patents

Abstract

PROBLEM TO BE SOLVED: To inspect and regulate a projection lens remaining mounted with a pupil filter. SOLUTION: An inspecting pattern 110 on a test reticle 109 is projected on a wafer 114 by a projection lens mounted with a pupil filter 112, and the aberration of the lens is inspected. In this case, the shape of an aperture stop 105 provided in an illumination optical system is varied in response to the directivity of the pattern, and the illumination light passed through the shield or phase inverter of the central area of the filter 112 is removed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used for an inspection method and an inspection method for inspecting a projection optical system of a projection exposure apparatus used in a lithography process in manufacturing semiconductor elements, liquid crystal display elements, thin film magnetic heads and the like. Illumination optics.

[0002]

2. Description of the Related Art In a lithography process for manufacturing a semiconductor device, a liquid crystal display device or the like, a pattern formed on a reticle or a mask is formed on a photosensitive substrate such as a semiconductor wafer or a glass plate coated with a photoresist by a projection exposure apparatus (hereinafter ,
Patterning is performed by projection exposure onto a wafer). Therefore, if there is an aberration in the projection lens of the projection exposure apparatus, the pattern formed on the reticle or mask cannot be accurately imaged on the wafer, and an element having desired performance cannot be manufactured.

Therefore, the inspection of the image forming characteristics of the projection exposure apparatus is an important check item in the management of the manufacturing process of semiconductor elements and the like, and conventionally, the aberration amount of the projection lens is obtained to inspect the projection optical system. Adjusts the image forming characteristics of the projection optical system based on the inspection result. For coma, for example, a test reticle with a so-called line-and-space pattern formed by arranging a plurality of line-shaped patterns is used. The line width difference and the pseudo peak intensity difference appearing on both sides are measured. Further, the spherical aberration is measured by determining the degree of symmetry of the collapse of the line and space image at the time of defocus with respect to the focus position.

[0004]

Recently, in order to form an image of a fine pattern, the shape of the secondary light source of the illumination system is changed from the conventional circular shape to an annular shape, or in accordance with the directionality of the pattern. So-called 4-aperture illumination has also been proposed in which four apertures are provided at positions symmetrical with respect to the optical axis. In these modified illuminations, of the diffracted light from the periodic pattern, 0
The effect of increasing the depth of focus is obtained by forming an image by two-beam interference of only the primary light and the secondary light.

On the other hand, in an isolated pattern such as a contact hole, diffracted light is generated not only in a specific direction but over a wide range. Therefore, it is difficult to form an image by two-beam interference between the 0th-order light and one of the 1st-order lights. Therefore, for the isolated pattern, the effect of increasing the depth of focus by the above-described modified illumination has almost no effect.

The modified illumination can be understood as a method in which a part of the Fourier transform surface inside the illumination optical system with respect to the reticle pattern surface is shielded by a spatial filter. On the other hand, there is a method of increasing the depth of focus of an isolated pattern by providing a light blocking member, a light attenuating member, a phase inversion member, etc. on a part of the Fourier transform surface inside the projection lens with respect to the reticle pattern surface. Proposed. This method is called a pupil filter method because a filter is provided on the Fourier transform plane (pupil plane) of the projection optical system. The pupil filter method reduces the wavefront aberration caused by defocusing by limiting the incident angle of the diffracted light that passes through the projection lens and interferes with each other at the image plane, or forms two defocused images. And the principle of maintaining the image intensity by combining them (coherent sum) are effective in increasing the depth of focus in isolated patterns, especially in hole patterns.

By the way, in the pupil filter method as described above, the main purpose is to improve the image forming characteristic of an isolated pattern such as a hole pattern, and the image forming characteristic of the projection optical system when the filter is attached forms an image for a periodic pattern. Properties are rarely considered. Therefore, if you try to inspect and adjust the projection lens by projecting the line and space pattern with the pupil filter attached, the imaging characteristics of the line pattern will change due to the pupil filter. However, there is a problem that the aberration cannot be measured due to.

The present invention solves the above problems, and the conventional projection lens inspection method using the line-and-space pattern can be applied even when the pupil filter is mounted, and the projection lens can be easily and accurately inspected. It is also an object of the present invention to enable the adjustment of the projection lens with the pupil filter attached using the inspection result.

[0009]

In order to achieve the above object, in the present invention, the incident angle of the light illuminating the reticle pattern at the time of inspection is limited so that the diffracted light from the pattern used for the inspection is It does not pass through the pupil filter of the projection lens, and the influence of light intensity and phase change at the pupil filter is eliminated. This is because, for example, the shape of the aperture stop provided in the illumination optical system is changed according to the directionality of the inspection pattern, and the illumination light that passes through the light-shielding portion, the dimming portion, or the phase-inverting portion in the central region of the pupil filter is used. Can be realized by removing

That is, according to the present invention, in a method of inspecting a projection optical system by projecting an inspection pattern, when the projection optical system is equipped with a pupil filter, that is, an optical filter having regions having different optical characteristics, the optical filter is mounted. The image of the inspection pattern is formed by a light beam that has passed through the region having the same optical characteristic. The inspection pattern can be a line and space pattern. The image of the inspection pattern may be detected by a photoelectric detector or may be transferred to a photosensitive substrate.

Further, the present invention is used for inspection of a projection optical system equipped with optical filters having regions having different optical characteristics, and in an illumination optical system for irradiating an inspection pattern with illumination light, the optical characteristics of the optical filter are It is characterized by having an aperture stop that limits the illumination light so that an image of the inspection pattern is formed by light rays that have passed through the same region.

Here, the inspection pattern is arranged on the object plane of the projection optical system, and the aperture stop is arranged on the surface in the illumination optical system which has a substantially Fourier transform relationship with the inspection pattern. Further, the present invention provides a projection exposure apparatus, which comprises a projection optical system having an optical filter having regions having different optical characteristics, and exposes a photosensitive substrate with a pattern image on a mask through the projection optical system. Illumination optics that illuminates the pattern with illumination light and limits the illumination light so that the image of the inspection pattern is formed by light that has been generated from the inspection pattern and has passed through a region where the optical characteristics of the optical filter are almost the same. It is characterized by having a system.

In this projection exposure apparatus, the inspection pattern is arranged on the object plane of the projection optical system. The illumination optical system can also be used as an illumination system that illuminates the pattern on the mask. Further, the illumination optical system has a diaphragm member arranged on a surface having a substantially Fourier transform relationship with the inspection pattern, and the mask can be irradiated with the illumination light that has passed through the aperture of the diaphragm member.

The projection exposure apparatus preferably comprises means for adjusting the image forming characteristic of the projection optical system according to the image forming state of the image of the inspection pattern projected by the projection optical system.

[0015]

According to the present invention, the imaging characteristics of the inspection pattern by the projection optical system are not affected by the pupil filter. Therefore, it is possible to inspect or adjust the projection optical system in the same manner as the conventional method by using the line and base pattern or the like as the inspection pattern with the pupil filter attached.

[0016]

The present invention will be described in detail below with reference to examples. FIG. 1 is a conceptual diagram of a projection exposure apparatus used in an embodiment of the present invention. Light emitted from a high-pressure mercury lamp 101, which is a light source, passes through an elliptical mirror 102, a shutter (not shown), and an input lens 103 to enter a fly-eye lens 104, and an illumination system aperture stop 105 provided on the fly-eye lens exit surface side, The pattern 110 on the test reticle 109 is illuminated via the first relay lens 106, the projection blind 107, and the second relay lens 108. The exit side focal plane of the fly lens 104 and the test reticle 10
The pattern formation surface (110) of No. 9 is substantially in a Fourier transform relationship, and the aperture stop 105 is arranged on the exit side focal plane or in the vicinity thereof.

The reticle pattern 110 for inspection is a so-called line-and-space pattern in which linear light-shielding portions and light-passing portions are alternately arranged in a vertical and horizontal diagonal direction. In this embodiment, as shown in FIG. 2, the line and space pattern 20 extending in the vertical direction (Y direction).
1. Line and space pattern 202 extending in the lateral direction (X direction) and line and space patterns 203, 20 extending in a direction inclined by 45 ° with respect to the X and Y directions.
4 is provided on the reticle 109.

The diffracted light generated from the pattern 110 enters the projection lens 111 and forms an image of the pattern 110 on the wafer 114 placed on the wafer stage 113. Here, the pupil filter 11 is formed on the Fourier transform plane (so-called pupil plane) of the reticle pattern 110 in the projection lens 111.
2 are provided. Therefore, the aperture stop 105 and the pupil filter 112 are substantially in a conjugate relationship (imaging relationship). Further, the projection lens 111 is provided with a drive mechanism 116 for driving the lens element 115, and the lens element 115 is moved in the optical axis AX direction or in the direction perpendicular to the optical axis AX, or the optical axis AX is rotated. It is possible to adjust various aberration amounts by rotating the lens. In addition, one lens element 1
It is also possible to allocate the adjustment function of each aberration to not only 15 but also a plurality of lens elements, and move and / or rotate each lens element based on each aberration amount to adjust the aberration amount.

The wafer stage 113 is two-dimensionally moved in a plane (XY plane) perpendicular to the optical axis AX of the projection lens 111 by a drive motor (not shown), and is finely movable along the optical axis AX. There is. Further, on the wafer stage 113, a photoelectric detector 11 that receives an image of the reticle pattern 110 projected by the projection lens 111.
7 are arranged. The photoelectric detector 117 is, for example, a one-dimensional or two-dimensional line sensor or an image pickup device (CCD or the like), and outputs the photoelectric signal to the control device (minicomputer) 118. The controller 118 controls the waveform of the photoelectric signal from the photoelectric detector 117 or the reticle pattern 1
The 10 images are displayed on a display device (CRT or the like) 119.
The photoelectric signal (or image signal) is A / D converted and stored in the memory (not shown) of the controller 118.

Further, the control device 118 centrally controls the entire device including the drive mechanism 116, and is connected to an input device (keyboard etc.) 120. Further, a wide band (for example, a wavelength of about 550 to 750 nm) light is applied to the wafer 114.
An off-axis type alignment sensor 121 that irradiates an upper alignment mark and forms an image of the mark on a light receiving surface of an image sensor (CCD) is provided, and an image signal from the alignment sensor 121 is a control device 1.
Enter 18

The methods for measuring the image forming characteristics of the projection lens 111 are roughly classified into the following two methods. The first method is
The image of the reticle pattern 110 is received by the photoelectric detector 117, and the imaging characteristic is obtained based on the photoelectric signal.
The second method is to transfer the image of the reticle pattern 110 onto a photosensitive substrate, detect the pattern image formed on the substrate, and obtain the imaging characteristics. In the second method, the latent image formed on the substrate may be detected, or the resist image formed on the substrate by the development process may be detected. Usually, a substrate (for example, a wafer) whose surface is coated with a photoresist is used, however, in latent image detection, a substrate on which a magneto-optical recording material (for example, DyFe) is formed by vapor deposition, sputtering, or the like can also be used.

In the first method described above, the operator observes the waveform or image displayed on the display device 119 to form the image forming characteristics of the projection lens 111 (for example, Seidel's 5 aberrations, projection magnification, focus position, image plane). Slope, telecentricity, etc.)
Is confirmed, and if necessary, the correction amount of the imaging characteristic is input to the control device 118 via the input device 120. Control device 1
18 is a drive mechanism 11 based on the input correction amount.
The lens element 115 is driven by 6 to adjust the image forming characteristic of the projection lens 111. Here, although the operator obtains the correction amount of the imaging characteristic and inputs it to the control device 118, the control device 118 follows the program input in advance and based on the photoelectric signal from the photoelectric detector 117, The correction amount may be calculated, and the drive mechanism 116 may be controlled according to this calculated value.

In the above-described second method, the projected image of the reticle pattern 110 is transferred onto the wafer 114, and the resist pattern on the developed wafer 114 is observed by an operator with, for example, a scanning electron microscope (SEM). To do. Then, the correction amount of the image forming characteristic is input to the control device 118 via the input device 120, and the control device 118 drives the lens element 115 by the drive mechanism 116 based on the input correction amount. Alternatively, the latent image of the reticle pattern or the resist image formed on the wafer 114 is detected by the alignment sensor 121 provided in the projection exposure apparatus, and the control device 118 reads the alignment image from the alignment sensor 121 according to a program input in advance. The correction amount of the imaging characteristic is calculated based on the image signal, and the drive mechanism 116 is controlled according to this calculated value.

Here, the pupil filter 1 of the projection lens
Reference numeral 12 denotes a central portion (circular area) 301 having a light-shielding or dimming function as shown in FIG. 3A, or a central portion (circular area) 303 as shown in FIG. 3B. It is known that the phase of the image-forming light flux is inverted between the peripheral portion (ring zone area) 302 and the peripheral portion. In FIG. 3A, the circular area 301 is a light-shielding portion, and in FIG. 3B, at least one of the ring area 302 and the circular area 303 is an area that shifts the phase of the image-forming light beam.

In the performance inspection of the projection lens, the image of the inspection line-and-space pattern is transferred onto the wafer while changing at least one of the focus position (position in the optical axis direction of the wafer) and the exposure amount by computer control. Then, it is a general method to measure the defects in the shape of the resist pattern with a measuring machine such as an SEM after the development processing. For example, by measuring the line width difference between both ends of the resist pattern, the amount of asymmetry of the image due to coma and the like can be obtained, and by measuring the difference in the best focus position due to the difference in the pattern pitch, the spherical aberration The quantity can be calculated. When a pattern different from the pattern shown in FIG. 2 is used as the inspection pattern, the distortion and the telecentricity of the image can be obtained from the difference in the relative position of the transferred pattern. Then, based on the inspection result, the element 11 of the projection optical system
5 is moved to correct the detected aberration. The present invention
These inspection methods that have been conventionally used can be applied to a projection optical system equipped with a pupil filter.

The pupil filter 112 shown in FIG.
A method of inspecting the projection optical system (111) equipped with the filter shown in FIG. 3A or FIG. 3B using the line and space patterns 201 to 204 shown in FIG. 2 will be described. In the conventional measurement method, when the inspection pattern is illuminated, the aperture shape of the aperture stop of the illumination system is circular as shown in FIG. On the other hand, in this embodiment, the inspection pattern 201 shown in FIG.
The shape of the aperture stop 105 of the illumination system is inspected such that the aperture stop having the shape shown in FIG. 5A is used and the stop having the shape shown in FIG. It changes according to each of the patterns 201-204 for use. Here, the shaded portion in FIG. 5 is a light shielding portion. That is, the aperture stop shown in FIG. 5A has a light-shielding band 50 extending laterally in the central region of a conventional circular aperture stop.
The aperture stop shown in FIG. 5 (B) corresponds to the one covered with the light shielding band 5 extending in the longitudinal direction in the central region of the circular aperture stop.
It corresponds to the one covered with 02. The widths of the light blocking bands 501 and 502 are the same as those of the light blocking bands 50 projected on the pupil plane of the projection lens 111.
It is desirable that the widths of the images 1 and 502 are equal to or slightly larger than the diameter of the light shielding portion (or the light reducing portion) 301 of the pupil filter 112 or the phase inversion portion 303 on the pupil plane. For the inspection patterns 203 and 204 extending in the diagonal direction in FIG. 2, the aperture stop shown in FIG. 5A is rotated by 45 ° counterclockwise and clockwise, respectively.

The aperture stops shown in FIGS. 5 (A) and 5 (B) may be provided with apertures of different shapes separately, but paying attention to the fact that the shapes will match when they are rotated.
A necessary aperture stop shape may be realized by providing a stop rotation mechanism and rotating a single stop by a predetermined angle according to the inspection pattern for exposure. Further, a movable member (slider or the like) that holds the aperture stop in a removable manner may be provided so that the aperture stop shown in FIG. 5 is disposed in the illumination optical path only when the projection lens 111 is inspected. Further, a plurality of aperture stops corresponding to various inspection patterns are attached to a holding member (turret, slider, etc.), and the holding members are driven to replace the plurality of aperture stops and arrange them in the illumination optical path. You may comprise. Also, instead of the test reticle 109, a reticle having a device pattern is arranged on the object plane of the projection lens 111, and the reticle is illuminated with illumination light from a light source to expose a wafer with an image of the device pattern. An aperture stop for annular illumination or modified illumination may be disposed on the exit-side focal plane of the eye lens 104 or a surface in the vicinity thereof. Therefore, it is desirable to provide the above-mentioned holding member with an aperture stop used for such exposure.

Next, the effect of changing the shape of the aperture stop of the illumination system according to the directionality of the inspection pattern will be described. FIG. 6 shows the distribution of the diffracted light from the inspection pattern on the pupil plane, and FIG. 6A shows the inspection pattern 201 extending in the vertical direction (FIG. 2) and the light shielding band 50 in the central region in the horizontal direction.
5 is a combination of the aperture stop shown in FIG. 5 (A) and the inspection pattern 2 extending in the lateral direction.
02 and the central region are shielded by a vertical shading band 502.
This is a case where the aperture stop of (B) is combined.

In FIG. 6A, the inspection is performed by the light from the illumination light source (the aperture of the aperture stop of FIG. 5A) which is effective for the light shielding portion (light reducing portion) of the pupil filter or the phase inversion portion 601. Pattern 2 when irradiating for-use pattern 201
Of the diffracted light generated from 01, the 0th-order light is distributed to the regions 602A and 602B outside the circular region 601 of the pupil filter, and the ± 1st-order diffracted lights are the regions 603A1 and 603, respectively.
3A2, 603B1, 603B2. The 0th order light on the pupil plane of the projection lens 111 and ± 1
The difference in the position of the next light depends on the pitch of the pattern 201 and the wavelength of the illumination light.

Similarly, also in FIG. 6B, the light from the illumination light source (the aperture of the aperture stop of FIG. 5B) effective for the light-shielding portion (light-reducing portion) of the filter or the phase inversion portion 604. Of the diffracted light generated from the inspection pattern 202 when the inspection pattern 202 is irradiated with, the 0th-order light is 605A,
605B, ± 1st order diffracted light is 606A
1, 606A2, 606B1, 606B2.

Therefore, in both cases shown in FIGS. 6A and 6B, the 0th order and ± 1 from the inspection pattern are obtained.
The next diffracted light does not pass through the light-shielding portion, the light-reducing portion, or the phase inverting portions 601 and 604 of the pupil filter. For this reason,
The image formation of the line and space patterns 201 and 202 is performed in the same manner as when the pupil filter is not provided, and there is no change in the image formation state due to a part of the diffracted light being blocked or the phase being inverted. Also, the inspection pattern 2
Even if the pitch of 01 and 202 is different, 0 from the pattern
The 1st and ± 1st order diffracted light does not pass through the light blocking portion or the phase inversion portion of the pupil filter. Therefore, regardless of the pitch of the inspection pattern, the projection lens 111 provided with the pupil filter 112 can be inspected by the same method as that for an ordinary projection lens not provided with the pupil filter. it can.

The present invention is not limited to the above embodiment. For example, in the above example, the inspection pattern was transferred onto the wafer and the pattern was observed with an SEM or the like. However, the relay lens system and the image sensor are mounted on the wafer stage, and the pattern is formed on the stage. The aerial image thus formed may be magnified by a relay lens and formed on an image sensor, and the image may be evaluated. Also,
A minute slit is provided on the wafer stage, and an optical sensor is provided below it, and the signal intensity from the optical sensor is obtained at each stage position while moving the stage in the direction orthogonal to the longitudinal direction of the inspection pattern image. The shape of the image may be obtained more.

Further, in the above-mentioned embodiment, the aperture stop having the band-shaped light shielding portions 501 and 502 as shown in FIG. 5 is used. However, for example, the optical characteristics of the central circular area and the outer ring area are different. When different pupil filters (Fig. 3) are used, if the ± 1st order diffracted light by the inspection pattern does not reach the circular area at the center of the pupil filter due to the relationship between the wavelength of the illumination light and the pitch of the inspection pattern, projection An aperture stop having a light-shielding portion that substantially covers an area on the pupil plane (Fourier transform surface) of the illumination optical system that has an image-forming relationship with the circular area on the pupil plane of the lens 111, in other words, an aperture having a ring-shaped aperture. A diaphragm may be used.

Although the projection optical system described in the above embodiments is composed of a lens, the present invention is applicable not only to the refraction system but also to the reflection system or the projection optical system in which the refraction system and the reflection system are combined. Is also applicable. Furthermore, by using the aperture diaphragm in a state in which the aperture diaphragm is rotated even with respect to diagonal lines (patterns 203 and 204 in FIG. 2), measurement can be performed in the same manner as described above.

[0035]

As described above, according to the present invention, the conventional method of inspecting the aberration of the projection lens can be applied even when the pupil filter is attached, and the projection lens can be inspected easily and with high accuracy. Further, the aberration of the projection optical system can be adjusted with the pupil filter attached, based on the inspection result.

[Brief description of drawings]

FIG. 1 is a conceptual diagram showing an embodiment of the present invention.

FIG. 2 is a conceptual diagram of an inspection pattern used in an embodiment of the present invention.

FIG. 3 is a conceptual diagram of a pupil filter.

FIG. 4 is an explanatory diagram of a conventional illumination system aperture stop.

FIG. 5 is an explanatory diagram of an illumination system aperture stop used in an embodiment of the present invention.

FIG. 6 is a conceptual diagram showing the effect of the embodiment of the present invention.

[Explanation of symbols]

101: High-pressure mercury lamp 102: Elliptic mirror 103: Input lens 104: Fly-eye lens 105: Illumination system aperture stop 106: First relay lens 107: Projection blind 108: Second relay lens 109: Test reticle 110: Pattern 111: Projection Lens 112: Pupil filter 113: Wafer stage 114: Wafer 115: Lens element 201: Vertical line inspection pattern 202: Horizontal line inspection pattern 203, 204: Oblique line inspection pattern 301: Light shielding area 302, 303: Phases are mutually inverted Areas 601 and 604: Light-shielding parts or phase inversion parts of filters 602A, 602B, 605A, 605B: Zero-order light from illumination light sources 603A1, 603B1, 603A2, 603B2, 6
06A1, 606A2, 606B1, 606B2: ±
First-order diffracted light

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display location H01L 21/30 516C

Claims (9)

[Claims] 1. A method of inspecting a projection optical system by projecting an inspection pattern, wherein the projection optical system is equipped with an optical filter having regions having different optical characteristics, and the regions having the same optical characteristics of the optical filter. A method of inspecting a projection optical system, which comprises forming an image of the inspection pattern by a light ray that has passed through the. 2. The inspection pattern is a line-and-space pattern, and an image of the line-and-space pattern projected by the projection optical system is photoelectrically detected.
Alternatively, the method according to claim 1, wherein the method is formed on a photosensitive substrate. 3. An illumination optical system, which is used for inspection of a projection optical system equipped with optical filters having regions having different optical characteristics, and which irradiates an inspection pattern with illumination light, selects regions having the same optical characteristics of the optical filters. An illumination optical system having an aperture stop that limits the illumination light so that an image of the inspection pattern is formed by the passing light beam. 4. The inspection pattern is arranged on an object plane of the projection optical system, and the aperture stop is arranged on a surface in the illumination optical system which is substantially in a Fourier transform relationship with the inspection pattern. The illumination optical system according to claim 3, wherein: 5. A projection exposure apparatus, comprising: a projection optical system having an optical filter having regions having different optical characteristics, which exposes a photosensitive substrate with a pattern image on a mask through the projection optical system. While illuminating the pattern with illumination light, the illumination light is emitted so that an image of the inspection pattern is formed by light that has been generated from the inspection pattern and has passed through a region where the optical characteristics of the optical filter are substantially the same. A projection exposure apparatus comprising an illumination optical system for limiting. 6. The inspection pattern is arranged on an object plane of the projection optical system, and the illumination optical system is also used as an illumination system for illuminating a pattern on the mask. The described device. 7. The illumination optical system has a diaphragm member arranged on a surface having a substantially Fourier transform relationship with the inspection pattern, and the illumination light passing through the aperture of the diaphragm member covers the mask. Irradiation is carried out.
An apparatus according to claim 1. 8. The apparatus according to claim 5, further comprising a photoelectric detector that receives an image of the inspection pattern projected by the projection optical system. 9. The apparatus according to claim 5, further comprising means for adjusting an image forming characteristic of the projection optical system according to an image forming state of an image of the inspection pattern projected by the projection optical system. The apparatus according to any one of to 8.