JP2599899C - - Google Patents

Description

Description: BACKGROUND OF THE INVENTION [0001] 1. Field of the Invention [0002] The present invention relates to a projection exposure technique, and more particularly, to a highly accurate projection pattern of a mask (including a reticle) and a relative positioning with respect to an object to be exposed such as a wafer. 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 performing the above. 2. Description of the Related Art In a photolithography technique, which is one of the manufacturing processes of a semiconductor device, a mask pattern formed on a mask is projected or exposed on a semiconductor wafer at an equal size or a reduced size, and patterning of a thin film on the wafer is performed. Performing steps are required. 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 involves aligning an alignment mark formed on a part of a pattern in a previous process formed on a wafer with an alignment mark formed on a part of a pattern in 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, separate volume, pages 103 to 10).
9, the date of issue: November 10, 1981), the wafer 1 placed on the moving stage 2 is placed, while the projection lens 5 is placed on the moving stage 2,
The mask 3 is set on the projection lens 5, and four light sources 4 (
While the mask is illuminated with (g line), the mask pattern is projected and imaged on the wafer 1 by the projection lens 5. On the other hand, a g-line light source 6 and a half mirror 7
, A lens 8, a mirror 9, and a pattern detection unit 10. The aligner unit projects the light of the g-ray light source 6 onto the wafer 1 through the mask 3 and detects the reflected light 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. 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 is Since the signal changes in the pattern detection unit due to the change, 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. An object of the present invention is 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] The following is a brief description of an outline of typical inventions among the inventions disclosed in the present application. 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. removed photomask, without initiating a reticle or the like, is irradiated onto a wafer through a projection lens, the light reflected from the wafer at the mirror, front
The position of the wafer is adjusted by correcting and detecting chromatic aberration generated in the projection lens . According to the above-mentioned 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 used as a mask and a reticle. Irradiating the wafer through the projection lens without passing through the like, taking out the reflected light from the wafer with the mirror, correcting and detecting the chromatic aberration caused by the projection lens, and aligning the wafer to thereby adjust the position of the light. While preventing interference, alignment at the center of the chip is made possible, thereby stabilizing alignment and improving accuracy. (Embodiment 1) FIG. 2 is a block diagram of one embodiment of a projection exposure apparatus for carrying out the method of the present invention. In FIG. The reference numeral 12 denotes a wafer as an object to be exposed 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. The exposure light source 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 position 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 21 detects reflected light from the surface of the wafer 12 (reflected light from the light source 20 for pattern detection), and forms a pattern formed on the wafer 12 in the previous process and a part of the alignment mark. The pattern detection signal is output, and this is subjected to an electrical process 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 configuration, before projecting the mask 11, the white light of the pattern detection 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. Thereby, the pattern detection unit 21
After the alignment mark and other patterns are recognized by the electric signal processing, the absolute position of the wafer 12, that is, the absolute position of the wafer 12 with respect to the optical system is detected, and the detected position is compared with the mask position in the control unit 22. As a result,
The 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 by the moving stage 13 and the 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. After the alignment, the projection lens system 1 is used by using the monochromatic light (g-line) of the exposure light source 15.
It goes without saying that the pattern of the mask 11 can be projected and imaged on the wafer 12 at step 6. Embodiment 2 FIG. 3 is a configuration diagram of another embodiment of the present invention, in which the configurations of a projection exposure optical system and a pattern detection unit 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 the present embodiment, a projection lens system 16 is arranged on a wafer 12 mounted on a moving stage 13, and a dichroic mirror 17 A 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 configuration, the white light from the pattern detection light source 20 is
The light is projected onto the surface of the wafer 12 through the dichroic mirror 17A, the projection lens system 16 and the like, and the chromatic aberration is corrected by the chromatic aberration correcting lens system 18 while passing through the reverse process. Is recognized. By recognizing the pattern, the control unit 22 obtains a positional deviation from the mask 11, and
The stage moving mechanism 14 is actuated 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. Also in the present 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 stability is improved. it can. Also, because it uses white light,
It is possible to detect the 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. As described above, the invention made by the inventor has been specifically described based on the embodiments.
The present invention is not limited to the above embodiment, and it goes without saying that various changes can be made without departing from the scope of the invention. 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, the 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 a field of application as the background, has been described. Instead, the present invention can be applied to a reticle or photomask manufacturing technique. (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 reflected light from the wafer is mirrored. Take out with
Since the position of the wafer is adjusted by correcting and detecting the chromatic aberration generated by the projection lens ,
Highly accurate wafer positioning can be performed. 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, and a 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 correction 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 with the stabilization of the above-described pattern detection, thereby achieving automatic positioning and shortening the time to improve the throughput. (6) By using white light as the continuous spectrum light as the pattern detection light, for example, it is possible to prevent exposure to the photoresist at the time of alignment when performing projection exposure on a semiconductor wafer. In other words, it is also possible to detect the position of the semiconductor wafer by performing pattern detection 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.   It is a schematic structure figure of a conventional device.     FIG. 2   FIG. 2 is a configuration diagram of an example of an apparatus for performing the method of the present invention.     FIG. 3   FIG. 4 is a configuration diagram of another apparatus for performing the method of the present invention.     [Explanation of symbols] 11 Mask 12 wafers 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 unit

Claims (1)

Claims: 1. A pattern detecting light source separate from an exposure light source is prepared, and illumination light having a wavelength different from the exposure light is transmitted through a projection lens without passing through a mask, a reticle, or the like. irradiated on the wafer is taken out reflected light from the wafer at the mirror, the projection lens
A wafer alignment method in projection exposure, wherein the wafer alignment is performed by correcting and detecting the chromatic aberration caused by the laser beam. 2. The method according to claim 1, wherein the position of the pattern detection system is fixed.