KR19980047266A - TTL alignment device of wafer stepper by holography method - Google Patents

Abstract

The present invention relates to an optical system for directly aligning a reticle and a wafer containing a circuit pattern in a through the lens (TTL) method in a step and step type semiconductor exposure apparatus using an ArF excimer laser as a light source. A method of correcting chromatic aberration of an exposure light source and an alignment light source by generating a phase conjugate wave by holography method, and using a ArF excimer laser as an exposure light source, We present a TTL alignment method that directly aligns positions.

Description

TTL alignment device of wafer stepper by holography method

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a TiTL (TTL) alignment device for wafer steppers by holography, particularly in a step scan type semiconductor exposure apparatus using ArF laser laser as a light source, and a reticle containing a circuit pattern. An optical system for directly aligning a wafer in a through the lens (TTL) manner.

Conventionally, TTL alignment is possible only by externally correcting chromatic aberration due to chromatic aberration caused by the wavelength difference between the ArF excimer laser (193 nm), which is an exposure light source, and the Ar laser (488,514.5 nm), which is an alignment light, but in the present invention, holography is performed. By presenting a method for correcting chromatic aberration by generating a phase conjugate wave by the method), a TTL method for directly aligning the position of the reticle and the wafer in a wafer stepper using an ArF excimer laser as an exposure light source is presented.

Recently, as the degree of integration of semiconductor memory chips increases, the line width of the circuit becomes smaller, and high resolution lithography equipment is required to satisfy this. The resolution (R) and depth of focus (DOF) in projected optical lithography are given by

R = K1 (λ / NA)

DOF = K2 (λ (NA) ²

Here, K1 and K2 are process constants, λ is the wavelength of the exposure light source, and NA is the numerical aperture of the lens. As shown in the above equation, the method of increasing the resolution of the wafer stepper, which is a lithography equipment, is to shorten the exposure light source and increase the numerical aperture. However, if the numerical aperture is increased to obtain the high resolution of the wafer stepper, the depth of focus decreases rapidly in inverse proportion to the square of the numerical aperture as shown in the above equation, and there are considerable technical difficulties in manufacturing a lens having a large numerical aperture. Following this, the method of reducing the wavelength of an exposure light source is taken in order to raise the resolution of a wafer stepper. The exposure light source of the wafer stepper, which is a lithography equipment, has now reached the ArF excimer laser having a wavelength of 248 nm from the g-line and i-line through an ArF excimer laser having a wavelength of 248 nm. As the exposure light source is shortened as in the ArF excimer laser, chromatic aberration, which is not a problem in the conventional g-line and i-line wafer steppers, becomes a problem. DUV light at 193 nm, which is the wavelength of ArF excimer laser, has strong absorption in the glass used to make a normal lens. Therefore, the projection lens of the wafer stepper is made of fused silica that transmits well to the light in the DUV region. You have to make it. However, in order to remove chromatic aberration, it is possible to use materials having different refractive indices. However, when the ArF excimer laser is used as an exposure light source, the material for manufacturing the projection lens is molten quartz, and thus chromatic aberration cannot be fundamentally removed.

In the exposure apparatus using the ArF excimer laser as a light source as described above, in the TTL alignment in which the reticle and the wafer are directly aligned through the projection lens without chromatic aberration, the ArF excimer laser (193 nm), which is an exposure light source, and the alignment light The large wavelength difference with the Ar laser (488, 514.5 nm) results in greater chromatic aberration. Thus, TTL alignment is possible only by correcting chromatic aberration externally. In order to satisfy these conditions, the present invention devises a method for correcting chromatic aberration by generating a phase conjugate wave by holography, and based on this design, ArF excimer laser light is used as an exposure light source. It is an object of the present invention to provide a TTL alignment position of the wafer stepper by holography which enables the alignment of the position of the reticle and the wafer in the wafer stepper to be used.

The present invention for achieving the above object is characterized in that when the polarized beam splitter (PBS) is used as the light splitting of the alignment light, the object wave and the reference wave from the wafer and the reticle cause interference on the recording medium to make a hologram. .

In addition, when the polarized beam splitter PBS is used as a light split of the alignment light, the object wave is reproduced using a phase conjugate wave as a leading beam on the hologram in which the information of the object wave is recorded, so that the wafer and the reticle are aligned. .

In addition, when the non-polarized beam splitter (Non-PBS) is used as the light splitting of the alignment light, the object wave and the reference wave from the wafer and the reticle interfere with the recording medium to make a hologram.

In addition, when a non-polarization beam splitter (Non-PBS) is used as a light splitting of alignment light, the wafer and the reticle are aligned by regenerating the object wave using a phase conjugate wave as a leading beam on the hologram on which the object wave and information are recorded. do.

FIG. 1 shows diffracted light diffracted at an alignment mark on a reflected light card reflected from a wafer when a ploarizing beam splitter (PBS) is used as light splitting of the alignment light. Also a device that produces a hologram.

2 is an apparatus for aligning a wafer and a reticle by reproducing an object wave using a phase-conjugated wave as a reading beam on a hologram in which a PBS (ploarizing beam splitter) is used as the light splitter of the alignment light and the information of the object wave is recorded.

3 shows a device for making holograms when a non-ploarizing beam splitter (Non-PBS) is used as the light split of the alignment light.

4 is a device diagram of aligning a wafer and a reticle by reproducing an object wave using a phase-conjugated wave when a non-plosizing beam splitter (Non-PBS) is used as light splitting of alignment light.

5 shows the principle of edge scattering detection.

* Description of the symbols for the main parts of the drawings *

101: alignment light source system 102: fiber1

103: fiber2104: fiber3

105: ploarizer1106: quarter wave platel

107: reticle align mount108: reticle

109: lens 1110: object wave S wave

111: reflector 112: lens 2

113: cube beam splitter 114: projection lens

115: wafer 116: catadioptric lens

117: quarter wave plate

119: ploarizing beam splitter 120: S wave

121: ploarizer2122: lens 3

123: ploarizer3124: lens 4

125: P wave to be used as reference wave 126: object wave from wafer and reticle

127: recording medium 128: ploarization control loop 1

129: ploarization control loop 2130: ploarization loop 3

131: fiber-optic beam coupler

(Figure 2)

201: alignment light source system 202: fiber

203: ploarization control loop 204: ploarizer

205 lens 1206 P wave to be used as a phase conjugate wave

207: hologram 208: ploarizing beam splitter

209: diffracted light diffracted on a wafer to be used as signal light

210: spatial filter1211: detector1

212: quarter wave plate

214: quarter wave plate 2215: catadioptric lens

216: projection lens 217: wafer

218: Lens 2219: Reflector 1

220: lens 3221: reticle

222: reticle align mount 223: reflector 2

224 diffracted light diffracted in a reticle to be used as signal light

225: spatial filter2226: detector2

(Figure 3)

301: alignment light source system 302: fiber1

303: fiber2304: fiber3

305: ploarizer1306: S wave

307: reticle align mount308: reticle

309 lens 1310 reflector

311: lens 2312: cube beam splitter1

313: projection lens 314: wafer

315: quarter wave plate 316: catadioptric lens

317: cube beam splitter 318: S wave

319: polarizer 2320: lens 3

321: ploarizer3322: lens 4

323 S wave to be used as reference wave 324: Object wave from wafer and reticle

325: recording medium 326: polarization control loop 1

327 polarization control loop 2328 polarization control loop 3

329: fiber-optic beam coupler

(Figure 4)

401: alignment light source system 402: fiber

403: polarization control loop 404: Polarizer

405: Lens 1406: S wave to be used as phase conjugate wave

407: hologram 408: cube beam splitter 1

409 diffracted light diffracted on the wafer to be used as signal light

410: spatial filter 1411: detector1

412: cube beam splitter

414: catadioptric lens 415: projection lens

416: Wafer 417: Lens 2

418: reflector 1419: lens 3

420: reticle421: reticle align mount

422 reflector 2

423: diffracted light diffracted in a reticle to be used as signal light

424: spatial filter2425: detector2

(Figure 5)

501: alignment light 502: scattering at the edge, diffracted light

503: scattering to the right of dark field, distribution of diffracted light

504: scattering to the left of Imsaiah, distribution of diffracted light

505: total scattering in each corner and direction of the dark field, distribution of diffracted light

506: distribution of reflected light in the bright field 507: detector aperture

Hereinafter, with reference to the accompanying drawings will be described an embodiment of the present invention;

1 is a hologram in which an object wave from a reticle and a wafer causes interference in a reference wave and a recording medium when a ploarizing beam splitter (PBS) is used as light splitting of alignment light. Is a device to make it. The Ar laser used as the alignment light source is divided into light for the reticle illumination 102, the wafer illumination 103, and the reference wave 104 by the fiver-optic beam coupler 31. The wave, which will act as an object wave with the information of the alignment marks in the reticle, illuminates the reticle through the optical fiber 102, wherein the light illuminating the reticle is linearly polarized by a polarizer 105 or otherwise a polarization-maintaining fiber. Or S wave by means of a polarization control loop (130). The S wave is again circularly polarized by the quarterwave plate 106. The circularly polarized light reflected by the cube beam splitter 113 via the lens systems 109 and 112 and the reflector 111 is polarized into P waves through another quarter wave plate 118 and is a polarizing beam splitting beam. Through the splitter 119, the recording medium 127 enters the recording medium 127 as an object wave having alignment mark information on the reticle. The light transmitted to the optical fiber 103 to obtain the object wave from the wafer is used as the illumination light of the wafer. Light from the optical fiber 103 passes through the lens 122 to obtain parallel light. The light passing through the lens 122 becomes the S wave by the polarizer 121, the PM fiber or the PCL 129, and the light reflected by the polarizing beam splitter 119 passes through the quarter wave plate 118. You get circularly polarized light. The circularly polarized light passing through the cube beam splitter 113 illuminates an aluminum coated scavenger mark on the wafer 115 after passing through the projection optical system 114. The illuminated light passes through the cube beam splitter 113 after reflection and then through the quarter wave plate 118, and then the circularly polarized light is converted into a P wave, passing through the ploarizing beam splitter 119 and the recording medium 127. Is incident on the object wave with the information of the hat mark on the wafer. As described above, the object wave 126 from the reticle and the wafer includes the reference wave 125 and the recording medium 127 in which light from the optical fiber 104 is polarized into a P wave by the polarizer 123, PM fiber or PCL 128. Interfere on) to produce a hologram.

FIG. 2 shows a method of regenerating an object wave using a phase conjugate wave as a reading beam on a hologram in which the object wave of the reticle and the wafer is recorded when the ploarizing beam splitter is used as a light split of the alignment light, and directly aligning the reticle and the wafer. It is an apparatus diagram. The light, which is the reading beam of the phase conjugate wave, comes through the optical fiber 202 and is then polarized into the P wave by the polarization control loop 203, the polarization-maintaining fiber or the polarizer 204, passes through the lens 205, and then parallel light 206 ) The reading beam is incident on the hologram to reproduce the object wave, and the light reproduced from the hologram has the information of each point of the object, and the alignment mark on the alignment track on the reticle and the wafer. ). The object wave with the wafer information reproduced first passes through the PBS 208 because it is a P-polarized pie. The circular shaped polarized light by the quarter wave plate 212 passes through the cube beam splitter 213 and passes through the projection lens system 216 to enter the alignment mark on the wafer. Alignment Mark The diffracted light from the alignment mark is polarized into the S wave after passing through the CBS 213 through the quarter wave plate 212 and the diffracted light reflected by the PBS 208 passes through the spatial filter 1 210 and then detector 1 Is detected by 211. The detector uses a photomultiplier tube (PMT) to detect scattering and diffracted light that occurs at the corners of the alignment mark in the + 45 ° and -45 ° directions, and the photodiode is used to detect the reflected light in the center part. The position of the wafer can be corrected from the detected signal. Next, the object wave with information of the reticle reproduced by the phase conjugate wave also passes through the PBS 208 because it is a P-polarized pie. The passing P wave becomes circularly polarized light by the quarter wave plate 212, and the reproduced object wave reflected by the CBS 213 passes through the lenses 218 and 220 and the reflector 219 and enters the alignment mark on the reticle. The light diffracted from the alignment mark passes through the reflector 223, passes through the spatial filter 2 225, and is detected by the detector 2 226. The detection principle is the same as that in the wafer. The position of the reticle can be aligned from the detected signal.

3 is a device for generating a hologram when a non-polarizing beam splitter (PBS) is used as a light splitter for an alignment light source and an object wave from a reticle and a wafer interferes with a reference wave and a recording medium. The ArF excimer laser used as the alignment light source 301 is divided into light for the reticle illumination 302, the wafer illumination 303, and the reference wave 304 by the fiber-optic beam coupler 329. The reticle illumination light is transmitted from the optical fiber 302 and linearly polarized by the polarizer 305 or S-wave by the polarization preservation optical fiber (PM fiber), the polarization controller 328. The S-polarized light is reflected by the CBS 312 through the lenses 309 and 311 and the reflector 310 and passes through another CBS 317 to enter the recording medium 325 as an object wave of the reticle. Wafer illumination light is transmitted from another optical fiber 303 and passes through the lens 320 to be parallel light, and S-wave by the polarizer 319, the polarization preservation optical fiber or the polarization controller 327. The S-waves reflected by the CBS 317 pass through another CBS 312, pass through the projection optical system 313, and enter / reflect to an aluminum coated scavenger mark on the wafer 314 to pass the two CBSs 312 and 317. Incident on the recording medium 325 as a passing object wave. A wave to be used as a reference wave is transmitted from the optical fiber 304 to become an S wave by the polarizer 321, the polarization preservation optical fiber, or the polarization controller 326, and then becomes parallel light by the lens 322. Thus, the object wave from the reticle and the wafer interferes with the reference wave, producing a hologram on the recording medium.

4 is an apparatus diagram of reproducing an object wave and aligning a wafer and a reticle using a phase conjugate wave when non-PBS is used as light splitting of alignment light. As the reading beam, the phase conjugate wave is transmitted from the optical fiber 402 and becomes the S wave by the polarization controller 403 or the polarizer 404 or the polarization preserving optical fiber, and then passes through the lens 405 to become parallel light. Thus, the phase conjugate wave is incident on the hologram 407 having information about the object wave of the reticle and the wafer. The object wave of the reticle and the wafer reproduced from the hologram 407 enters the alignment mark on the alignment track with the object information of each point. The object wave of the first regenerated wafer passes through two CBSs 408 and 412 and then passes through the projection optical system 415 to the alignment mark on the wafer 416, and the diffracted light diffracted by the alignment mark passes through the on path again. While being reflected by CBS 408 and passed through spatial filter 1 410, it is detected by detector 1 411. The detection principle is the same as that in FIG. The position of the wafer can be aligned from the detected signal. Next, the reproduced object wave of the reticle passes through the CBS 408 and is reflected by the CBS 412. The alignment light passing through the lenses 417 and 419 and the reflector 418 is incident on the alignment mark on the reticle. Light diffracted from the alignment mark is reflected by the reflector 422 and then detected by detector2 425 via spatial filter2 424. The detection principle is the same as in the wafer. It is possible to align the position of the reticle from the detected signal.

Fig. 5 is a principle diagram showing the principle of edge scattering and diffraction in alignment marks by alignment light. As the alignment light 501 moves over the alignment mark 502, scattering 503 occurs at the right and left edge portions. In this case, scattering occurs more deeply at the edge and less scattering at the higher side. The light distribution plot 504 of the dark field scattered to the right at each corner is shown. Also shown is a light distribution 505 of dark field scattered to the left at each corner. The total scattered light distribution map 506 means the sum of scattered light at each corner. The bright field distribution diagram 507 is due to the reflected light. As described above, light detection of the bright field of the dark field is detected by the PMT 508 placed in the + 45 ° and -45 ° directions and the photodiode 509 located at the center.

According to the embodiment as described above, using the TTL alignment device of the wafer stepper using a phase conjugate wave by the holography method according to the present invention can obtain the following effects.

First, in order to remove the chromatic aberration existing in the lens, it is possible to design it in consideration of the lens design. However, in the present design, the chromatic aberration existing in the lens by the holography method is independent of the lens design. It became possible to remove.

Second, the method of eliminating chromatic aberration by holography method compensates not only the chromatic aberration present in the projection lens but also the image distortion caused by other defects that may be included in the design or manufacture of the lens. It has advantages.

According to the embodiment of the TTL alignment based on the above design, the alignment of the wafer has the following advantages.

First, in the case of the 193 nm ArF excimer laser wafer stepper whose wavelength of the exposure light source is the far-ultraviolet region, the TTL alignment method, which was possible in the case of g- and i-line wafer steppers, is impossible due to chromatic aberration problem. However, the proposed method has the advantage that TTL alignment can be performed regardless of the wavelength of the exposure light source because TTL alignment is performed without any change in the projection lens.

Second, in the case of TTL alignment using a holography method, there is almost no change in the alignment signal due to the change in the position of the hologram. Because reproducing the alignment light using a hologram, when the image is reproduced by the hologram, unlike the image formed by the lens, the image is formed by diffraction and interference. Does not affect.

Claims (4)

TTL alignment of the wafer stepper by holographic method characterized in that when the polarizing beam splitter is used as the light splitting of the alignment light, the object wave and the reference wave from the wafer and the reticle cause interference on the recording medium to produce a hologram. Device. Holographic type wafers, characterized in that when the polarization beam splitter is used as the light splitting of the alignment light, the object wave is reproduced using the phase conjugate wave as the leading beam on the hologram on which the information of the object wave is recorded so as to align the wafer and the reticle. TTL alignment device of stepper. TTL alignment device of the wafer stepper by holographic method characterized in that the object wave and the reference wave from the wafer and the reticle interfere with the recording medium when the non-polarized beam splitter is used as the light splitting of the alignment light to make the hologram . When the non-polarization beam splitter is used as the light splitting of the alignment light, the holographic method according to the holographic method characterized by aligning the wafer and the reticle by reproducing the object wave using the phase conjugate wave as a leading beam on the hologram on which the information of the object wave is recorded. TTL alignment device for wafer stepper.