JP2599899B2 - Wafer alignment method in projection exposure - Google Patents

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,
More particularly, the present invention relates to a method of aligning a wafer in projection exposure suitable for use in a projection exposure apparatus having an aligner mechanism for highly accurately positioning 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 a photolithography technique, which is one of the manufacturing processes of a semiconductor device, a process of patterning a thin film on a wafer by projecting and exposing a mask pattern formed on a mask to a same size or a reduced size on a semiconductor wafer. Needed. At the time of this projection exposure, all the mask patterns that are sequentially projected on the same wafer must be projected and exposed at the same position on the wafer. Therefore, during the projection exposure of each mask, the relative positioning between the mask and the wafer is required. It is always done.

Conventionally, this type 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, pp. 103-109, 1981
Page, issue date: November 10, 1981), and a wafer 1 placed on a moving stage 2 is placed. On the other hand, a projection lens 5 is arranged on the moving stage 2, and the projection lens 5 The mask 3 is placed on the wafer 3, and the mask is illuminated with light 4 (g-line) emitted from a light source 4 from above the mask 3, while the mask pattern is projected and imaged on the wafer 1 by the projection lens 5. On the other hand, an aligner unit 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 above the mask 3.
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 passes through the corners of the mask 3 and is projected onto the alignment mark forming portion of the wafer 1, whereby the alignment marks are detected to determine the relative position, that is, the relative alignment between the mask 3 and the wafer 1. Can do it.

[0004]

However, in this conventional configuration, since monochromatic g-rays are used for pattern detection, interference occurs in the thin film on the surface of the wafer 1, and this interference changes due to a change in the film thickness. Therefore, the signal waveform in the pattern detection unit fluctuates, and the alignment accuracy becomes unstable. Further, since the same g-line as the light for exposure is used for detecting the alignment mark, the alignment must be performed at a chip peripheral portion on the wafer which is not affected by the exposure to the wafer. Also, there is a problem that the alignment accuracy is lowered due to deviation from the center axis of the mask or the like.

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

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

[0007]

SUMMARY OF THE INVENTION Among the inventions disclosed in the present application, the outline of a representative one will be briefly described.
It is as follows.

That is, in the method of aligning a wafer in projection exposure according to the present invention, a pattern detection light source separate from the exposure light source is prepared, the position of the pattern detection system is fixed, and illumination of a different wavelength from the exposure light is performed. Light is irradiated onto a wafer via a projection lens without passing through a mask, a reticle, or the like, and light reflected from the wafer is extracted by a mirror and detected to perform wafer positioning.

[0009]

According to the above means, a pattern detection light source separate from the exposure light source is prepared, the position of the pattern detection system is fixed, and illumination light having a wavelength different from the exposure light is transmitted through a mask, a reticle, or the like. Without irradiating the wafer through the projection lens, taking out the reflected light from the wafer with the mirror and detecting it, and aligning the wafer, it is possible to prevent light interference and to adjust the alignment at the center of the chip. This makes it possible to achieve stable alignment and improved accuracy.

[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 FIG. Reference numeral 12 denotes a wafer as an exposure target 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 process, and an alignment mark is formed on a part of the pattern. However, in the present embodiment, the alignment mark is not necessarily provided as described later. . The wafer 12 is mounted on a moving stage 13 and is moved in X, Y, Z, and θ directions by a stage moving mechanism 14.

An exposure light source 15 for emitting monochromatic light (g-line or the like) is provided 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 comprising 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 a high NA (numerical aperture), low optical distortion, and a wide exposure area with respect to the exposure light source light. These exposure light sources 15
And the projection lens system 16 constitute a projection exposure optical system.

On the other hand, a beam splitter 17 such as a prism or a half mirror is interposed at the center of the optical axis of the projection exposure optical system to form an optical axis of a pattern detection system in a direction at 90 ° to the optical axis. ing. On the optical axis of the pattern detection system, a chromatic aberration correcting lens system 18, a half mirror 19, and a pattern detection light source 20 are provided. It constitutes a detection unit. The pattern detection light source 20 can emit 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 correcting lens system 18 is configured to correct and eliminate chromatic aberration generated in the projection lens system 16 by using white light. Further, the pattern detection unit 2
Reference numeral 1 denotes a light detected from the surface of the wafer 12 (reflected light from the light source 20 for pattern detection) to detect a pattern formed on the wafer 12 up to the previous process and a pattern detection signal of an alignment mark of a part thereof. The pattern can be output and subjected to electrical processing to recognize the pattern. The output of the pattern detection unit 21 is sent to the control unit 22, and controls the stage moving mechanism 14 and various mechanisms and circuits (not shown).

According to the above arrangement, before projecting the mask 11, the white light of the pattern detecting light source 20 is projected through the beam splitter 17 onto the alignment mark of the wafer 12, 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. Thus, the pattern detection unit 21 recognizes the pattern of the alignment mark and other patterns by electric signal processing, and then detects the absolute position of the wafer 12, that is, the absolute position of the wafer 12 with respect to the optical system. Compare with the mask position. As a result, a relative position shift between the mask 11 and the wafer 12 can be detected, and if the stage moving mechanism 14 is controlled based on the shift, the wafer 12 can be moved to the moving stage 13.
, And alignment with the mask 11 can be performed. At this time, since continuous spectrum light is used for pattern detection, light interference does not occur in the photoresist thin film on the surface of the wafer 12, so that the reflected light due to the change in the thickness of the photoresist thin film is different from the conventional method. Therefore, a stable detection (electric) signal can be obtained and a stable pattern detection or alignment can be performed without causing a phenomenon such as fluctuation of the pattern. The chromatic aberration generated in the projection lens system 16 by using white light can be corrected by the chromatic aberration correction lens system 18 to prevent a detection error from occurring. Also, by using white light, it is possible to prevent exposure to the photoresist at the time of alignment, so that it is possible to detect the wafer position by detecting the pattern on the optical axis, in other words, at the center of the chip. The accuracy can be improved. As a result, the positioning can be automated, and the throughput can be improved.

It is needless to say that, after the alignment, 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.

(Embodiment 2) FIG. 3 is a block diagram of another embodiment of the present invention, in which the configurations of a projection exposure optical system and a pattern detecting section are different from those of the above-described embodiment. In the figure, the same or equivalent parts as those in FIG. 2 are denoted by the same reference numerals.

In this embodiment, a projection lens system 16 is arranged on a wafer 12 mounted on a moving stage 13, and a dichroic mirror 17A as a beam splitter, a chromatic aberration correction lens system 18, The mirror 19 and the pattern detection unit 21 are arranged. The pattern detection light source 20 is arranged to face the upper half mirror 19, while the mask 11 and the exposure light source 15 are arranged to face 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 eliminate 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 passing through the mask 11 toward the wafer 12.

According to the above arrangement, the white light of the pattern detecting light source 20 is projected on the surface of the wafer 12 through the half mirror 19, the dichroic mirror 17A, the projection lens system 16, etc. The chromatic aberration is corrected at 18 and the pattern detection unit 21
, Where the pattern on the wafer 12 is recognized. Based on the recognition of the pattern, the control unit 22 causes the mask 11
Then, the stage shift mechanism 14 is operated to move the moving stage 13 and the wafer 12, and the positioning with the mask 11 is performed. After the 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.

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

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

In the above description, a case where the invention made by the present inventor is mainly applied to a technique of projecting and exposing a mask pattern onto a semiconductor wafer, which is an application field of the background, has been described. Instead, the present invention can be applied to a reticle or photomask manufacturing technique.

[0021]

(1) Irradiation light having a wavelength different from that of the exposure light is irradiated onto the wafer through a projection lens without passing through a mask, a reticle, or the like, and the wafer is positioned. Wafer can be aligned. In particular, in the present invention, since the exposure light source and the pattern detection light source are separately prepared, an optimum pattern detection light source for alignment can be used, and the wavelength selectivity is increased. Significant advantages are obtained as compared to a common one. In addition, since the position of the pattern detection system is fixed, there is no mechanical displacement at the time of work, and the accuracy of alignment can be improved.

(2) Since continuous spectrum light is used for pattern detection when detecting the position of the object to be exposed, light interference by a thin film such as a photoresist on the surface of the object to be exposed can be prevented, and the thickness of the thin film varies. Thus, the fluctuation of the reflected light on the surface of the object to be exposed can be prevented, the stable pattern detection can be performed, and the stable alignment of the object and the mask can be performed.

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

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

(5) The signal processing method is simplified along with the above-mentioned stabilization of the pattern detection, so that the positioning is automated 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 at the time of alignment, for example, when performing projection exposure on a semiconductor wafer. In other words, it is also possible to detect the position of the semiconductor wafer by detecting the pattern at the center of the semiconductor chip, thereby improving the alignment accuracy, and further, automating the alignment and improving the throughput.

[Brief description of the drawings]

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

FIG. 2 is a configuration diagram of an example of an apparatus for performing the method of the present invention.

FIG. 3 is a configuration diagram of another apparatus for performing the method of the present invention.

[Explanation of symbols]

 DESCRIPTION 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 Light source for pattern detection 21 Pattern detection unit 22 Control part

 ──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-57-200029 (JP, A) JP-A-56-105635 (JP, A) Electronic materials VOL. 22 NO. 3 PP. 79-85 Electronic Materials VOL. 21 NO. 3 PP. 69-74

Claims (2)

(57) [Claims] 1. A pattern detecting light source separate from an exposure light source.
And irradiate the wafer with illumination light of a different wavelength from the exposure light via a projection lens without passing through a mask, reticle, etc., take out the reflected light from the wafer with a mirror, and detect the position of the wafer. A method of aligning a wafer in projection exposure, comprising performing alignment. 2. A method for fixing a position of a pattern detection system.
2. The method according to claim 1, wherein
Alignment method.