JP3352161B2 - Exposure apparatus and method of manufacturing semiconductor chip using the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exposure apparatus and a method for manufacturing a semiconductor chip using the same, and more particularly, to a projection lens system for forming a fine electronic circuit pattern such as an IC or LSI formed on a reticle (mask) surface. An exposure apparatus having a function of projecting and exposing on a wafer surface by a (projection optical system) and observing a state on the wafer surface via a projection lens system with light having a wavelength different from light for the exposure, and the same. And a method of manufacturing a semiconductor chip using the same.

[0002]

2. Description of the Related Art In a micro-projection type exposure apparatus for manufacturing semiconductors, a circuit pattern of a reticle as a first object is projected and exposed on a wafer as a second object by a projection lens system. The alignment mark on the wafer is detected by observing the wafer surface using an observation device (detection means), and the alignment between the reticle and the wafer, so-called alignment, is performed based on the detection result.

The alignment accuracy at this time largely depends on the optical performance of the observation device. Therefore, the performance of the observation apparatus is an important factor in the exposure apparatus.

Conventionally, in an exposure apparatus, an alignment mark formed on a wafer surface is observed by an observation microscope system, and the position of the alignment mark is detected by using a projected image signal to obtain positional information of the wafer. Is being done.

In particular, in recent years, non-exposure light having a relatively wide wavelength width has been used as observation illumination light mainly for the following two reasons.

The first reason is that when observing alignment marks formed on a wafer surface, a photosensitive material (resist) to which an electronic circuit pattern is transferred is often applied on the wafer surface. Since the resist usually absorbs a lot at the exposure wavelength, it becomes difficult to detect the alignment mark on the wafer through the resist film at the exposure wavelength, and when the alignment mark is observed with the exposure light, There is a problem that the resist is exposed to light and the detection of the alignment mark becomes unstable or cannot be detected. Therefore, a detection method using non-exposure light is desired.

The second reason is that when illumination light for observing non-exposure light is used, for example, light having a relatively wide wavelength range by a halogen lamp, a monochromatic light source such as a He-Ne laser is used on the wafer. Interference fringes, which tend to occur when the AA mark is observed due to unevenness in the thickness of a resist film or various functional films used in a semiconductor process, can be reduced, and better alignment can be performed.

For these reasons, an alignment mark observation microscope system can correct various aberrations with respect to observation illumination light having a relatively wide wavelength width by using non-exposure light to detect a good alignment mark. I am trying to.

[0009]

However, when light having a wide wavelength width is used as illumination light for observation as described above,
In order to correct coma aberration occurring in the entire observation microscope, for example, using a lens for adjusting coma aberration and decentering the lens from the optical axis, a color shift occurs due to a so-called prism effect, and the color shift occurs on the detection surface. There is a problem that the position of the projected image signal is projected to a different position depending on the color.

[0010]

[0011]

According to the present invention, there is provided an improved mark detection apparatus capable of detecting the position of a mark image with high accuracy when detecting a mark through a projection lens system using detection light (alignment light) having a wavelength different from that of exposure light. An object of the present invention is to provide an exposure apparatus having a mark detection function and a method for manufacturing a semiconductor chip using the same.

[0013]

According to the present invention, there is provided an exposure apparatus, comprising: a projection optical system for projecting a pattern of a first object onto a second object with exposure light; Forming an image of a mark of the second object with detection light having a wavelength different from that of the exposure light, and detecting means for detecting the mark image. The detecting means is characterized in that coma is corrected by an optical element whose chromatic aberration has been corrected with its optical axis decentered with respect to the optical axis of the detecting means.

According to a second aspect of the present invention, there is provided an exposure apparatus for projecting a pattern of a first object onto a second object using exposure light, and performing relative positioning between the first object and the second object. Therefore, the exposure light is an exposure apparatus having a detection image having a wavelength different from the detection light to form an image of the mark of the second object, and detection means for detecting the mark image, wherein the detection means,
It is characterized in that coma aberration is corrected by a cemented lens in which lenses having different variances are bonded to each other and whose optical axis is decentered with respect to the optical axis of the detecting means.

According to a third aspect of the present invention, in the first or second aspect, the detection light having a wavelength different from that of the exposure light is light from a halogen lamp.

According to a fourth aspect of the present invention, in the method of manufacturing a semiconductor chip, a mask is prepared as the first object, and a wafer is prepared as the second object.
A method of manufacturing a semiconductor chip, comprising: projecting an image of the circuit pattern on the wafer via a projection optical system by illuminating the circuit pattern of the mask using the exposure apparatus according to claim 7.

[0017]

[0018]

[0019]

FIG. 1 is a schematic view of a main part of an optical system according to a first embodiment when the present invention is applied to an exposure apparatus for manufacturing a semiconductor device.

In FIG. 1, reference numeral 8 denotes a reticle as a first object, which is mounted on a reticle stage 10. 3 is the second
It is a wafer as an object, and an alignment mark (AA mark) 4 is provided on its surface. Reference numeral 5 denotes a projection optical system, which is composed of a projection lens system, and is a reticle (mask).
Circuit patterns and the like on eight surfaces are projected onto the three surfaces of the wafer. The projection lens system 5 is a telecentric system on both the reticle 8 side and the wafer 3 side.

An illumination system 9 illuminates the reticle 8 with exposure light. Reference numeral 2 denotes a θ, Z stage on which the wafer 3 is placed. The θ rotation and focus adjustment of the wafer 3, ie, Z
The direction is being adjusted. The θ and Z stages 2 are mounted on an XY stage 1 for performing a step operation with high accuracy. An optical square (bar mirror) 6 serving as a reference for stage position measurement is placed on the XY stage 1.
The optical square 6 is monitored by a laser interferometer 7.

In this embodiment, the alignment (alignment) between the reticle 8 and the wafer 3 is performed indirectly by performing alignment with respect to a reference mark 17 whose positional relationship is determined in advance. Alternatively, exposure is performed by actually aligning a resist image pattern or the like, an error (offset) thereof is measured, and offset processing is performed in consideration of the subsequent value.

Next, each element of the detecting means 101 for detecting the position of the mark 4 on the surface of the wafer 3 will be described.

An observation microscope 11 observes the AA mark 4 on the surface of the wafer 3 with non-exposure light.

In this embodiment, an off-axis system for performing alignment without using the projection lens 5 is used.

A light source 14 for detecting the AA mark 4 comprises a halogen lamp which emits a light beam (non-exposure light) having a wavelength different from that of the exposure light. 15 is a lens,
The light flux (detection light) from the light source 14 is condensed and made incident on a beam splitter 16 for illumination. Reference numeral 12 denotes an objective lens.

Reference numeral 13 denotes a lens group as an optical element.
In order to correct coma generated by the observation microscope 11, the optical system is configured to be decentered from the optical axis S.

In this embodiment, the lens group 13 is composed of two lenses, a positive lens and a negative lens, made of materials having different dispersions, so as to correct chromatic aberration.

The detection light from the lens 15 reflected by the beam splitter 16 is reflected by a mirror M ₁ ,
Light is guided to the AA mark 4 on the surface of the wafer 3 via the objective lens 3 and the objective lens 12 for illumination.

Reference numeral 19 denotes a light source for illuminating the reference mark 17 and L
It consists of ED etc. 18 is a lens. Light source 19
Is condensed by the lens 18 and is guided to the reference mark 17 for illumination. 20 is a beam splitter for the reference marks, by reflecting the light beam from the reference mark 17 is incident on erector lens 21 via a mirror M _2. The erector lens 21 images the reference mark 17 and the AA mark 4 on the surface of the wafer 3 on the imaging surface of the CCD camera 22, respectively. The detection means 101 in the present embodiment has the above-described components.

In this embodiment, the non-exposure light (detection light) emitted from the light source 14 passes through the lens 15, the beam splitter 16, the mirror M ₁ , the lens group 13, and the objective lens 12, and passes through the AA mark 4 on the wafer 3. Light up. Wafer 3
Observation image information of the upper AA mark 4 is, in order, the lens group 13,
Objective lens 12, the mirror M _1, the beam splitter 1
6, the beam splitter 20, mirror M _2, forms an image on the CCD camera 22 through the erector lens 21.

In this embodiment, the coma generated by the observation microscope 11 is corrected by a lens group 13 provided so as to be decentered from the optical axis S as described later. This gives a good A
The observation image of the A mark 4 is formed on the CCD camera 22.

On the other hand, the reference mark 17 transmits light emitted from a light source 19 comprising an LED for illuminating the reference mark to a lens 18.
The illuminated by focusing the beam splitter 20, and forms an image on the CCD camera 22 through the erector lens 21 via a mirror M _2.

The position of the observed image of the AA mark 4 on the wafer 3 formed on the CCD camera 22 on the CCD camera 22 is measured by a signal processing device (not shown), and the CCD camera 22 is also measured by the signal processing device. The accurate position information of the XY stage 1 is obtained by comparing the position of the projected image of the reference mark 17 which is imaged on the top and is always fixed, thereby performing highly accurate alignment.

Next, the optical function of the coma aberration adjusting lens group 13 of this embodiment will be described with reference to FIG.

The lens group 13 of this embodiment has two lenses having different dispersions.
A cemented color correction lens in which the two lenses are joined to correct the chromatic aberration generated in the lens group 13 is configured to be decentered from the optical axis, and the entire observation microscope 11 does not generate an image shift due to color on the detection surface 22. The generated coma can be corrected.

FIG. 2A shows a state in which an image is formed on a detection surface by a microscope imaging lens.
(B) shows a state in which a color shift due to a so-called prism effect occurs when one lens 13 is decentered from the optical axis.

FIG. 2C shows a state in which an image is formed on the detection surface by a cemented color correction lens 13 in which two lenses having different dispersions are cemented to correct chromatic aberration.

FIG. 2D shows that when the junction color correction lens 13 shown in FIG. 2C is decentered from the optical axis, no image shift due to color occurs on the detection surface.

In the present embodiment, coma aberration generated in the entire observation microscope 11 is corrected by configuring the lens group 13 as described above, and the detection surface (the imaging surface of the CCD camera 22)
A good image of the AA mark 4 is formed.

In this embodiment, a light source (eg, 633 ± 30 nm) having a center wavelength different from that of the exposure light from the halogen lamp and having a relatively wide wavelength width is used as the non-exposure light, and a light source such as a He—Ne laser is used. Interference fringes due to a resist film, which are likely to occur when observing an AA mark on a wafer using a monochromatic light source, are reduced, thereby achieving good alignment.

FIG. 3 is a schematic view of a main part of an optical system according to a second embodiment when the present invention is applied to an exposure apparatus for manufacturing a semiconductor device. 3, the same members as those shown in FIG. 1 are denoted by the same reference numerals.

This embodiment is different from the first embodiment shown in FIG. 1 in that the AA mark 4 on the wafer 3 is observed using light passing through the projection lens 5, that is, in the TTL system. The point that alignment is performed is different from the point that the optical system 24 is used, and other configurations are substantially the same.

In FIG. 3, the optical system 24 comprises a plane-parallel plate for correcting aberrations (eg, astigmatism) generated by the projection lens 5.

In this embodiment, the non-exposure light emitted from the halogen lamp 14 is sequentially transmitted to the lens 15, the beam splitter 16, the lens group 13, the objective lens 12, the optical system 24,
The AA mark 4 on the wafer 3 is illuminated via the mirror 23 and the projection lens system 5.

The observation image information of the AA mark 4 on the wafer 3 passes through the projection lens 5, the mirror 23, the optical system 24, the objective lens 12, the lens group 13, the beam splitter 16, the beam splitter 20, and the erector lens 21 in order.
An image is formed on the D camera 22. At this time, the projection lens system 5
Represents the electronic circuit pattern drawn on the reticle 8 on the wafer 3
The aberration is well corrected for the exposure light to project upward. Therefore, when the non-exposure light passes through the projection lens 5,
Aberration occurs.

In this embodiment, the objective lens 12 corrects spherical aberration, axial chromatic aberration and the like generated by the projection lens system 5, and similarly corrects coma aberration by a lens group 13 which is provided so as to be decentered from the optical axis. With this configuration, a good observation image of the AA mark 4 is formed on the CCD camera 22.

On the other hand, the reference mark 17 is illuminated by condensing the light emitted from the LED light source 19 for illuminating the reference mark by the lens 18, and forms an image on the CCD camera 22 via the beam splitter 20 and the objective erector lens 21. .

The position on the CCD camera 22 of the observed image of the AA mark 4 on the wafer 3 formed on the CCD camera 22 is measured by a signal processing device (not shown), and the CCD camera 22 is also measured by the signal processing device. Accurate stage position information is obtained by comparing the position of the projection image of the reference mark 17 which is formed on the top and is always fixed, thereby performing high-precision alignment.

As described above, in the first and second embodiments, when the alignment is performed by observing the AA mark on the wafer with non-exposure light, the optical system element for correcting the coma aberration generated in the entire observation microscope. Is constituted by an optical system element in which the chromatic aberration is corrected, so that when the coma aberration generated in the entire observation microscope is corrected, an image shift due to color on the detection surface is prevented.

Thus, the thickness of the resist applied on the wafer surface, the thickness of various functional films used in the semiconductor process,
When the film thickness of the alignment mark formed on the wafer surface changes, the position of the image signal projected on the detection surface changes due to the change in the spectral characteristics of the alignment mark detection signal formed on the wafer surface The alignment error is reduced, and the alignment accuracy is improved.

FIG. 4 is a schematic view of a main part of an optical system of a first embodiment when the present invention is applied to an exposure apparatus for manufacturing a semiconductor device. 4, the same members as those shown in FIG. 1 are denoted by the same reference numerals.

This embodiment is different from the first embodiment in FIG.
An optical member 41 composed of at least two transparent wedge-shaped prisms is disposed in front of the D camera 22 as described later, and an AA mark image of a color generated by an error or the like of each optical element of the observation microscope 11 on the surface of the CCD camera 22. Correction of misalignment in lens and lens group 1 for coma aberration correction
3 is omitted, and other configurations are substantially the same.

Next, the configuration of the present embodiment will be described sequentially, although it partially overlaps the description of FIG.

In this embodiment , the non-exposure light emitted from the halogen lamp 14 illuminates the AA mark 4 on the wafer 3 through the lens 15, the beam splitter 16, the mirror M ₁ and the objective lens 12 in this order.

[0056] observation image information AA mark 4 on the wafer 3 in turn objective lens 12, the mirror M _1, the beam splitter 16, beam splitter 20, mirror M _2, erector lens 21, on the CCD camera 22 through the optical member 41 Form an image.

On the other hand, the reference mark 17 is illuminated by condensing the light emitted from the LED light source 19 for illuminating the reference mark by the lens 18, and illuminated by the beam splitter 20 and the mirror M.
_2. CCD camera 22 through objective erector lens 21
Image on top.

The position on the CCD camera 22 of the observed image of the AA mark 4 on the wafer 3 formed on the CCD camera 22 is measured by a signal processing device (not shown), and the CCD camera 22 is also measured by the signal processing device. Accurate stage position information is obtained by comparing the position of the projection image of the reference mark 17 which is formed on the top and is always fixed, thereby performing high-precision alignment.

In this embodiment, as in the first embodiment, a light source having a center wavelength different from that of the exposure light from the halogen lamp as the non-exposure light and having a relatively wide wavelength width (for example, 633 ±.
30 nm), interference fringes due to a resist film, which are likely to be generated when observing an AA mark on a wafer using a monochromatic light source such as a He-Ne laser, are reduced, thereby achieving good alignment.

[0060] Next, the optical action of the optical member 41 of the present embodiment will be described with reference to FIG.

In the present embodiment , the optical member 41 uses two wedge plates 41a and 41b to correct the displacement of the projected image due to the color generated by the error of the optical system element of the observation microscope system 11.

FIG. 5A shows a state in which a color shift has occurred due to the so-called prism effect of one wedge plate 51.

FIG. 5B shows a state of a positional shift of a projected image due to a color generated by an error of an optical system element of the observation microscope system 11 or the like.

FIG. 5C shows two wedge plates 41 a and 41.
The position shift of the projected image shown in FIG. 5B is corrected using b, and the set angle of the two wedge plates 41a and 41b is adjusted to generate in an arbitrary direction and size. The displacement of the projected image due to the color can be corrected.

FIGS. 6 and 7 are explanatory views of a part of the optical member 41 of Embodiments 2 and 3 of the present invention.

In the second and third embodiments , the structure of the optical member 41 is different from that of the first embodiment shown in FIG. 4, but the other structures are the same.

In the reference example 2 shown in FIG. 6, two wedge plates 41a1 and 41a2 (41b
1, 41b2) and two parallel flat plates 41a, 4
1b is used to correct the displacement of the projected image (AA mark image) due to the color generated due to an error in the optical system element of the observation microscope 11 shown in FIG.

In the present embodiment , the set angles of the two wedge plates are adjusted to correct the positional deviation of the projected image due to the color generated in an arbitrary direction and size. In particular, in this embodiment, two wedge plates 41a1 and 41 having different dispersions are used.
If the glass material constituting a2 (41b1, 41b2) has the same refractive index and a different dispersion at one wavelength (for example, center wavelength λ ₀ ) among the illumination wavelengths used for alignment, the two wedge plates have wavelengths of Since it has no refracting power to λ ₀ , when the wedge plate is inserted in the optical path to correct the positional shift of the projected image due to the color, the CCD camera 2
There is a feature that the optical axis of the observation image formed on the image 2 does not change.

In the third embodiment shown in FIG.
Two lenses 41c and 41d made of materials having different dispersions
Are used to form a parallel plane plate as a whole, thereby correcting the displacement of the projected image due to the color caused by the error of the optical system element of the observation microscope system 11 shown in FIG. I am trying to do it.

In this embodiment , the eccentric direction and the amount of eccentricity of the lens are adjusted to correct the positional deviation of the projected image due to the color generated in an arbitrary direction and size.

In particular, in the present embodiment , the glass materials forming the two lenses 41c and 41d made of materials having different dispersions have the same refractive index at one wavelength (for example, center wavelength λ ₀ ) of the illumination wavelength used for alignment. If the dispersion is different, there is no refracting power for the two lens wavelengths λ ₀ , so when the lens is inserted into the optical path to correct the positional shift of the projected image due to the color, the CCD
There is a feature that the optical axis of the observation image formed on the camera 22 does not change.

FIG. 8 is a schematic view of a main part of an optical system of Reference Example 4 when each Reference Example is applied to an exposure apparatus for manufacturing a semiconductor device. 8, the same members as those shown in FIG. 4 are denoted by the same reference numerals.

[0073] This reference example in comparison with the reference example 1 in FIG. 4, in that the AA mark 4 on the wafer 3 is observed with a light through the projection lens 5 are going, that is, the TTL system The difference is that alignment is performed, and the other configurations are substantially the same.

In this embodiment , the non-exposure light emitted from the halogen lamp 14 illuminates the AA mark 4 on the wafer 3 through the lens 15, the beam splitter 16, the objective lens 12, the mirror M ₁ and the projection lens system 5 in this order.

The observation image information of the AA mark 4 on the wafer 3 passes through the projection lens 5, the mirror M ₁ , the objective lens 12, the beam splitter 16, the beam splitter 20, the erector lens 21, the optical member 41, and the CCD camera 22 in this order.
Image on top.

On the other hand, the reference mark 17 is illuminated by condensing the light emitted from the LED light source 19 for illuminating the reference mark by the lens 18, passes through the beam splitter 20, the objective erector lens 21, and the optical member 41, and illuminates the CCD camera 22.
Image on top.

The position on the CCD camera 22 of the observed image of the AA mark 4 on the wafer 3 formed on the CCD camera 22 is measured by a signal processing device (not shown), and the CCD camera 22 is also measured by the signal processing device. Accurate stage position information is obtained by comparing the position of the projection image of the reference mark 17 which is formed on the top and is always fixed, thereby performing high-precision alignment.

As described above, the reference examples 1 to 4 have an optical member for correcting an image shift due to a color generated on the detection surface when performing alignment by observing the AA mark on the wafer surface with non-exposure light. When the film thickness of the resist applied on the wafer surface, various functional films used in the semiconductor process, or the alignment mark formed on the wafer surface changes,
The alignment error when the position of the image signal projected on the detection surface changes with the change in the spectral characteristic of the alignment mark detection signal formed on the wafer surface is reduced, and the alignment accuracy is improved.

[0079]

According to the present invention, by setting each element as described above, when a mark is detected via a projection lens system with a detection light (alignment light) having a wavelength different from that of the exposure light, the mark is detected. It is possible to achieve an exposure apparatus having an improved mark detection function capable of detecting an image position with high accuracy, and a method of manufacturing a semiconductor chip using the same.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a main part of an optical system according to a first embodiment of an exposure apparatus of the present invention.

FIG. 2 is an explanatory view of an embodiment for correcting coma of the observation microscope of FIG. 1;

FIG. 3 is a schematic diagram of a main part of an optical system according to a second embodiment of the exposure apparatus of the present invention.

FIG. 4 is a schematic diagram of a main part of an optical system according to a first embodiment of the exposure apparatus of the present invention;

FIG. 5 is an explanatory diagram showing correction of a position shift of an AA mark image by a color shown in FIG. 4;

FIG. 6 is an explanatory diagram showing correction of a position shift of an AA mark image by a color shown in FIG. 4;

FIG. 7 is an explanatory diagram showing correction of a position shift of an AA mark image by a color shown in FIG. 4;

FIG. 8 is a schematic diagram of a main part of an optical system according to a fourth embodiment of the exposure apparatus of the present invention.

[Explanation of symbols]

Reference Signs List 1 XY stage 2 θ stage 3 Wafer 4 Alignment mark (AA mark) on wafer 5 Projection lens 6 Bar mirror 7 Laser interferometer for measuring XY stage position 8 Reticle 9 Exposure illumination system 10 Reticle stage 11 Projection by color Optical system for correcting image misalignment 12 Objective lens 13 Observation optical system for observing AA mark on wafer by non-exposure light 14 Halogen lamp light source for illumination 15 Illumination lens 16 Illumination beam splitter 17 Reference mark 18 Reference Mark illumination lens 19 LED light source for fiducial mark illumination 20 Beam splitter for fiducial mark 21 Electr lens 22 CCD camera

Claims (4)

(57) [Claims] 1. A projection optical system for projecting a pattern of a first object onto a second object using exposure light, and the exposure light for performing relative positioning between the first object and the second object. Forming an image of the mark of the second object with the detection light having a different wavelength, and a detection unit for detecting the mark image, wherein the detection unit is provided with respect to an optical axis of the detection unit. An exposure apparatus wherein coma aberration is corrected by an optical element whose optical axis is decentered and whose chromatic aberration is corrected. 2. A projection optical system for projecting a pattern of a first object onto a second object using exposure light, and the exposure light for performing relative positioning between the first object and the second object. An exposure apparatus having an image of a mark of the second object formed with detection lights having different wavelengths, and detection means for detecting the mark image, wherein the detection means has a light beam with respect to an optical axis of the detection means. An exposure apparatus, wherein coma aberration is corrected by a cemented lens in which lenses of different variances are bonded to each other with axes decentered. 3. The detection light having a wavelength different from that of the exposure light is light from a halogen lamp.
Or the exposure apparatus according to 2. 4. A mask as the first object, a wafer as the second object are prepared, and the circuit pattern of the mask is formed by using the exposure apparatus according to claim 1. A method of manufacturing a semiconductor chip, wherein an image of the circuit pattern is projected onto the wafer through a projection optical system by illuminating.