JPH07183216A - Method of aligning wafer in projection exposure - Google Patents

Abstract

PURPOSE:To provide the title wafer alignment method in projection exposure capable of achieving stable alignment and improving the alignment precision. CONSTITUTION:For the illuminating light, a light beam of different wavelength from that of exposure light is used to irradiate a wafer 12 therewith not through the intermediary of a mask 11 but through the intermediary of projection lenses 16 so that the reflected light thereof may be picked up by a mirror 19 to be detected for performing alignment with the wafer 12.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a projection exposure technique,
In particular, the present invention relates to a method for aligning a wafer in projection exposure, which is suitable for use in a projection exposure apparatus equipped with an aligner mechanism that accurately positions a projection pattern of a mask (including a reticle) and an object to be exposed such as a wafer. is there.

[0002]

2. Description of the Related Art In photolithography, which is one of the manufacturing processes of semiconductor devices, a mask pattern formed on a mask is magnified or reduced in size and projected and exposed on a semiconductor wafer to pattern a thin film on the wafer. Needed. Further, in this projection exposure, all the patterns of the mask sequentially projected on the same wafer must be projected and exposed at the same position on the wafer, so that the relative positioning of the mask and the wafer during the projection exposure of each mask is performed. Must be done.

Conventionally, this kind of positioning is performed by aligning an alignment mark formed on a part of a pattern of a previous process formed on a wafer with an alignment mark formed on a part of a pattern of a current process. It is done by. For example, FIG. 1 shows an example of a conventional projection exposure apparatus (published by the Industrial Research Institute, Electronic Materials 1981, Supplement, pages 103 to 109).
Page, issue date: November 10, 1981), and the wafer 1 placed on the moving stage 2 is placed, while the projection lens 5 is arranged on the moving stage 2 and the projection lens 5 is placed. The mask 3 is installed on the upper surface, and the mask is illuminated by the light of the light source 4 (g line) emitted from above the mask 3, while the projection lens 5 projects the mask pattern onto the wafer 1. On the other hand, on the upper side of the mask 3, an aligner portion including a g-ray light source 6, a half mirror 7, a lens 8, a mirror 9 and a pattern detection unit 10 is provided.
Light is projected onto the wafer 1 through the mask 3 and the reflected light is detected by the pattern detection unit 10. The g-line is projected on the alignment mark forming portion of the wafer 1 after passing through the corner of the mask 3, and this alignment mark is detected to detect the relative position, that is, the relative alignment between the mask 3 and the wafer 1. Can be done.

[0004]

However, in this conventional structure, since the g-line of monochromatic light is used for pattern detection, interference occurs in the thin film on the surface of the wafer 1, and this interference changes due to fluctuations in film thickness. As a result, fluctuations in the signal waveform occur in the pattern detection unit, and the alignment accuracy becomes unstable. Further, since the same g-line as the light for exposure is used to detect the alignment mark, it is necessary to perform alignment in the peripheral portion of the chip on the wafer that is not affected by the exposure of the wafer, and the detection light is used. There is also a problem that the alignment accuracy is lowered due to deviation from the center axis of the mask.

It is an object of the present invention to provide a wafer alignment method in projection exposure that enables stable alignment and improves alignment accuracy.

The above and other objects and novel features of the present invention will be apparent from the description of this specification and the accompanying drawings.

[0007]

Of the inventions disclosed in the present application, a representative one will be briefly described below.
It is as follows.

That is, the method of aligning a wafer in projection exposure according to the present invention irradiates the wafer with an illumination light having a wavelength different from that of the exposure light through a projection lens without passing through a mask, a reticle, or the like. The reflected light from is extracted by a mirror and detected to align the wafer.

[0009]

According to the above means, the illumination light having a wavelength different from the exposure light is irradiated onto the wafer via the projection lens without passing through the mask, reticle, etc., and the reflected light from the wafer is taken out by the mirror. By detecting and aligning the wafer, the interference of light can be prevented while the alignment in the central portion of the chip is possible, whereby the alignment can be stabilized and the accuracy can be improved.

[0010]

【Example】

(Embodiment 1) FIG. 2 is a block diagram of an embodiment of a projection exposure apparatus for carrying out the method of the present invention, in which reference numeral 11 is a projection pattern in which a light-impermeable film is formed in a desired pattern on a glass substrate. And 12 is a wafer as an exposed body on which the pattern of the mask 11 is projected and exposed. A predetermined pattern is formed on the surface of the wafer 12 in the previous step, and an alignment mark is formed on a part of the pattern, but in the present embodiment, the alignment mark may not necessarily be provided as described later. . The wafer 12 is placed on a moving stage 13 and moved in the X, Y, Z, and θ directions by a stage moving mechanism 14.

An exposure light source 15 for emitting monochromatic light (g-line etc.) is installed above the mask 11 to irradiate the mask 11, while a plurality of sheets are provided below the mask 11. A projection lens system 16 including a lens is provided, and the pattern of the mask 11 is projected and imaged on the surface of the wafer 12 at a required magnification (1/10, 1/5, 1/1). The projection lens system 16 is preferably designed to have characteristics of high NA (numerical aperture), low optical distortion, and wide exposure area with respect to the exposure light source light. These exposure light source 15
The projection lens system 16 constitutes a projection exposure optical system.

On the other hand, a beam splitter 17 such as a prism or a half mirror is provided at the center position of the optical axis of the projection exposure optical system to form an optical axis of the pattern detection system in the direction of 90 ° with respect to the optical axis. ing. A chromatic aberration correction lens system 18, a half mirror 19, and a pattern detection light source 20 are arranged on the optical axis of the pattern detection system, and a pattern detection unit 21 is provided to face the half mirror 19 to form a pattern. It constitutes a detector. The pattern detecting light source 20 is capable of emitting continuous spectrum light such as white light, and this light does not expose a photoresist (not shown) provided on the wafer 12. On the other hand, the chromatic aberration correction lens system 18 is configured to correct and cancel the chromatic aberration generated in the projection lens system 16 by using white light. Furthermore, the pattern detection unit 2
Reference numeral 1 denotes a pattern detection signal of a pattern formed on the wafer 12 up to the previous step or a part of the alignment mark by detecting the reflected light from the surface of the wafer 12 (reflected light from the light source 20 for pattern detection). A pattern can be recognized by outputting and electrically processing this. The output of the pattern detection unit 21 is sent to the control unit 22 to control the stage moving mechanism 14 and various mechanisms and circuits not shown in the figure.

According to the above construction, the white light of the pattern detecting light source 20 is projected onto the alignment mark of the wafer 12 through the beam splitter 17 before the mask 11 is projected, and the reflected light is reflected by the beam splitter 17 and the half mirror. The light is reflected at 19 and input to the pattern detection unit 21. As a result, the pattern detection unit 21 detects the absolute position of the wafer 12 after pattern recognition of the alignment mark and other patterns by electric signal processing, and the controller 22 compares this with the mask position. As a result, a relative positional deviation between the mask 11 and the wafer 12 can be detected, and if the stage moving mechanism 14 is controlled based on this deviation, the wafer 12 can be moved to the moving stage 13
And the mask 11 can be aligned. At this time, since the continuous spectrum light is used for the pattern detection, optical interference does not occur in the photoresist thin film on the surface of the wafer 12, and therefore the reflected light accompanying the variation of the film thickness of the photoresist thin film is different from the conventional one. Does not occur, and a stable detection (electrical) signal can be obtained to perform stable pattern detection or alignment. The chromatic aberration generated in the projection lens system 16 by using the white light can be corrected by the chromatic aberration correction lens system 18, and the occurrence of a detection error is prevented. Also, by using white light, it is possible to prevent the photoresist from being exposed during alignment, so it is possible to detect the wafer position by performing pattern detection on the optical axis, in other words, in the center of the chip. It is possible to improve accuracy. As a result, alignment can be automated and throughput can be improved.

It is needless to say that the pattern of the mask 11 can be projected and imaged on the wafer 12 by the projection lens system 16 using the monochromatic light (g line) of the exposure light source 15 after the alignment.

(Embodiment 2) FIG. 3 is a constitutional view of another embodiment of the present invention, in which the constitutions of the projection exposure optical system and the pattern detecting portion are different from those of the above-mentioned embodiment. In the figure, the same or equivalent parts as in FIG. 2 are designated by the same reference numerals.

In this embodiment, a projection lens system 16 is arranged on a wafer 12 placed on a moving stage 13, and a dichroic mirror 17A as a beam splitter, a chromatic aberration correction lens system 18, and a half are arranged on the optical axis of the projection lens system 16. The mirror 19 and the pattern detection unit 21 are arranged. The pattern detection light source 20 is arranged facing the upper half mirror 19, while the mask 11 and the exposure light source 15 are arranged facing the dichroic mirror 17A. The pattern detection light source 20 uses white light that is continuous spectrum light, and the chromatic aberration correction lens 18 can correct and cancel chromatic aberration. The dichroic mirror 17A is configured to reflect only the g-line, and can reflect the g-line light of the exposure light source 15 that has passed through the mask 11 toward the wafer 12.

According to the above construction, the white light of the pattern detecting light source 20 is projected onto the surface of the wafer 12 through the half mirror 19, the dichroic mirror 17A, the projection lens system 16 and the like, and the chromatic aberration correcting lens system goes through the reverse process. The chromatic aberration is corrected at 18, and the pattern detection unit 21
The pattern on the wafer 12 is recognized. Upon recognition of the pattern, the control unit 22 causes the mask 11
Then, the stage moving mechanism 14 is operated to move the moving stage 13 and the wafer 12, and the position of the mask 11 is adjusted. After alignment, the mask 11 is illuminated with the light from the exposure light source 15, and the pattern of the mask 11 is projected and exposed on the wafer 12 by the projection lens system 16 using the reflection of the dichroic mirror 17A.

Also in this embodiment, since white light is used for detecting the alignment pattern of the wafer 12, the unstable detection due to the interference in the photoresist thin film on the wafer 12 is prevented and the stabilization is improved. it can. Further, since white light is used, it is possible to detect the pattern at the center of the optical axis, that is, the center of the chip, and improve the alignment accuracy. Further, in this embodiment, the projection lens system 16 and the chromatic aberration correction lens system 18 can be arranged on the linear optical axis, so that the pattern detection accuracy can be further improved.

Although the invention made by the present inventor has been specifically described based on the embodiments, the present invention is not limited to the embodiments and various modifications can be made without departing from the scope of the invention. Needless to say. For example,
A general half mirror may be used for the beam slitter, and the arrangement position thereof may be slightly different from the configuration of the projection lens system. Further, the light for pattern detection may be continuous spectrum light in a wavelength range capable of preventing interference.

In the above description, the invention mainly made by the present inventor is applied to the technique of projecting and exposing a mask pattern on a semiconductor wafer, which is the field of application which is the background of the invention, but the invention is not limited thereto. The present invention is also applicable to a reticle or photomask manufacturing technique instead of the above.

[0021]

【The invention's effect】

(1) .Illumination light having a different wavelength from the exposure light is irradiated onto the wafer through the projection lens without passing through a mask, reticle, etc., and the wafer is aligned, so that the wafer can be accurately aligned. Can be done.

(2) Since continuous spectrum light is used for pattern detection when detecting the position of the exposed object, light interference due to a thin film such as photoresist on the surface of the exposed object can be prevented and fluctuations in the thickness of the thin film can be prevented. It is possible to prevent the fluctuation of the reflected light on the surface of the exposed object due to the above, to perform stable pattern detection, and to perform stable alignment between the exposed object and the mask.

(3) A beam splitter is arranged in the projection exposure optical system, and a pattern detection system is provided so as to face the beam splitter. Pattern detection light having a continuous spectrum is used for pattern detection in this pattern detection system. Since it is configured to detect the pattern on the object to be exposed, it is possible to detect the pattern at the center of the semiconductor chip, which is the center of the optical axis, and improve the pattern detection accuracy to improve the alignment accuracy. Can be achieved.

(4) Since the chromatic aberration correction lens system is arranged in the pattern detection system, by using the pattern detection light composed of continuous spectrum light, the chromatic aberration generated in the projection lens system is eliminated, and the pattern The detection can be suitably performed.

(5) With the stabilization of the pattern detection described above, the signal processing system is simplified, the alignment is achieved automatically, and the time is shortened to improve the throughput.

(6) By using white light as the continuous spectrum light as the pattern detection light, it is possible to prevent exposure to the photoresist during alignment during projection exposure to a semiconductor wafer, so that on the optical axis In other words, it becomes possible to detect the position of the semiconductor wafer by detecting the pattern in the central portion of the semiconductor chip, and it is possible to improve the alignment accuracy and, in turn, to automate the alignment and improve the throughput.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a conventional device.

FIG. 2 is a block diagram of an example of an apparatus for carrying out the method of the present invention.

FIG. 3 is a block diagram of another apparatus for carrying out the method of the present invention.

[Explanation of symbols]

 11 Mask 12 Wafer 13 Moving Stage 15 Exposure Light Source 16 Projection Lens System 17 Beam Splitter 17A Dichroic Mirror 18 Chromatic Aberration Correction Lens System 20 Pattern Detection Light Source 21 Pattern Detection Unit 22 Control Section

Claims (1)

[Claims] 1. A mask for illumination light having a wavelength different from the exposure light,
A method of aligning a wafer in projection exposure, which comprises irradiating the wafer through a projection lens without using a reticle or the like, and extracting reflected light from the wafer with a mirror to detect the wafer to align the wafer.