JPS63299329A - Aligner - Google Patents

Abstract

PURPOSE:To realize the exact alignment, by providing light to detect only noise component in a position detection signal, in the close vicinity of different light which is detecting a position, and detecting the noise component in the position detection signal. CONSTITUTION:A signal output (a) contains Moire light intensity variation (b) of + or - first order diffraction light corresponding with relative positions between interference fringes and a grating, and noise component (c). Therefore, a reflection region 9 is arranged in the vicinity of the grating-forming region 8 of a substrate 7. A reflected light 16 from the reflection region and a diffraction light 17 from a reference grating 3 are overlapped and made to interfere with each other. The light intensity is detected by a photodetector 13. This output can detect a noise component only. By taking the difference signal between the output (a) and the output (c), an excellent position detection signal (d) free from the noise component can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an exposure apparatus equipped with high-precision alignment used for manufacturing semiconductor devices having fine patterns, particularly semiconductor devices having submicron rules of 1 micron or less. It is related to.

Conventional technology The position detection used for alignment of conventional projection exposure equipment is T.
The through-the-leus method is the mainstream, but the position detection sensitivity depends on the resolution of the projection lens, so in the current method, the position detection sensitivity is about 0.05 μm, and the high accuracy of the alignment accuracy of 0.1 μm is insufficient. Have difficulty. In addition, the double grating method for constructing an interferometer on Ueno has been studied [: W, R.

Trutna, Jr et xx PII (!3
PIE), 470 (1984) 82. S;Witt
ekoek SPIE 221 (
1980)2], but in this method the position detection sensitivity is 10n
0 m or less, but the detection accuracy was greatly affected by air vibrations, stage vibrations, etc.0 Problems that the invention seeks to solve.

In view of such conventional problems, the present invention has been made to
During the manufacturing process, the reticle and wafer are accurately aligned.In order to measure using particularly coherent light with an optical system, air vibrations and stage vibrations are directly added to the signal as noise. The object of the present invention is to provide an exposure apparatus having an optical system having the following characteristics.

Means to Solve the Problems The present invention eliminates noise components caused by air vibrations and stage vibrations between the mask and the sea urchin in gloximity exposure using X-rays, etc., and achieves highly accurate positioning in an exposure apparatus. In order to realize this, three coherent and conjugate beams are made incident on a grating provided on a substrate, and the first output of the interference light intensity of the light beams that are overlapped and diffracted from the grating and the grating are formed. The interference fringes and the grating are determined using the difference signal between the second output obtained by injecting other light into the part of the substrate that is not covered, and making the light reflected from the substrate interfere with the coherent light. This is to perform positioning between the two.

Furthermore, as an application of this method to a reduction projection exposure machine, among the light beams diffracted by the grating formed on the reticle surface,
Only the two pairs of diffracted lights are passed through a spatial filter in the spectral plane of the first lens system, and these two light beams are guided to the second lens system, and the interference generated in the imaging plane of the second lens system is A stripe is projected onto the wafer, the relative position between the reticle and the wafer is determined by measuring the intensity of the diffracted light diffracted from the grating on the wafer, and then the intensity of the diffracted light diffracted from the grating on the wafer is measured. A portion of the diffracted light from the reticle is incident, and the light reflected from the substrate is caused to interfere with the light diffracted from the reticle on the spectral plane of the first lens system, and the difference between the intensity of this interference light and the intensity of the diffracted light is determined at the position. As a matching signal,
This eliminates noise generated between the grating on the reticle and the grating on the wafer, and obtains an alignment signal with a high signal-to-noise ratio.

Function: By using the positioning signal according to the present invention, it is possible to obtain a positioning signal with a high signal-to-noise ratio, thereby realizing position detection and positioning with higher accuracy.

Embodiment An embodiment of the optical system according to the present invention is shown in FIG. Below, explanations will be added in the order of the light beams used for alignment. In addition, in the following explanation, in order to briefly describe the principle of the present invention,
It is assumed that the reticle or mask is illuminated with parallel light 1. The main components of the alignment optical system of the present invention are (1) a reticle or mask 2 provided with an alignment reference grating 3;
(2) A set of mirrors 4.9 for generating reference interference fringes by intersecting and interfering with the two beams diffracted from the reference grating.
, (3) Mask S provided with first alignment grating 6 , (4) Substrate 7 provided with second alignment grating 8 and reflective surface 9 , (5) Diffracted light from alignment gratings 6 and 8 Photodetector for detecting intensity 11.12. and a photodetector 13 that detects the interference light intensity of the two lights using an optical system 1o that causes the reflected light from the reflective surface 9 and the diffracted light from the reference grating 3 to interfere with each other.

An amplitude grating is formed as the reference grating 3 of the mask 20, and the incident light beam 1 of wavelength λ is made incident on this reference grating 3. From the grating 3 on the mask 2 with pitch P1, P1 sin ψ, = n
λ n=0. ±1. ±2. ±3...(1) n-th order diffracted light is diffracted. However, ψ is the n-th order diffraction angle.

In Fig. 1, only the ±1st-order diffracted light of the n-order diffracted light is refocused on the alignment gratings 6 and 8, and the two beams intersect, forming an interference pattern with a pitch P2 of P2 = λ/2 sin ψ1. generate. Interference fringes are generated on the surfaces of the grating 6 of the mask 5 and the grating 8 of the substrate 7. When a grating having a pitch that is an integral multiple of the pitch P2 of the interference fringes is provided on the mask 6 and the substrate T, strong diffracted light can be obtained from the grating. This diffracted light has two re-diffracted lights corresponding to the ±1st-order diffracted light from the reference mask overlapping, and by measuring the light intensity of moiré fringes caused by the interference of the two diffracted lights, the light intensity is generated in space. The interference fringes obtained can be aligned with the first grating 6 on the mask 6. Similarly, alignment with the second grating 8 on the substrate T can be performed. Second
The figure shows the moire fringe light intensity of the diffracted light 14.15 obtained from the first and second alignment gratings. As shown in FIG. 2, the signal output a has a noise component C when the moiré light intensity of ±1st order diffracted light changes corresponding to the relative position between the interference fringes and the grating. The noise component is generated due to the influence of fluctuations in the air between the reference grating 3 and the alignment gratings 6 and 8, vibrations of the mask 6 and the substrate 7, and the like. In order to remove this noise component, in this embodiment, as shown in FIG. The diffracted light 17 from 3 is superimposed to interfere with each other, and the light intensity is detected by the photodetector 13. Noise is caused by fluctuations in the air in which the laser propagates,
In particular, changes in air density due to local temperature changes, low-frequency vibrations, vibrations due to stage movement, fluctuations in laser light intensity, etc. can be detected by the photodetector 13.

As shown in FIG. 2C, only the noise component can be detected from this output, and when the difference signal between output a and output C is taken, a good position detection signal d free of noise components can be obtained.

The third example is a second embodiment according to the present invention. The main components of the alignment optical system of this embodiment are: (1) reticle 2;
alignment grating 2o on o, (2) first and second lens systems 23, (2) coupled in the Fourier spectral plane;
3) A reflecting mirror serving as a spatial filter 24 placed on the 7-reticle spectral plane; (4) A conjugate positional relationship corresponding to the grating 21 on the reticle 2o and the grating image on the reticle formed by the second lens system. A conversion optical system (6
) reduction projection lens 28, (6) alignment grating 30 on wafer 28 (semiconductor substrate) and reflective surface s 9 on wafer without grating, (7) diffracted light 34 from grating 30 on wafer 29 a photodetector s 7 that extracts the light on the Fourier spectrum plane and measures the moiré light intensity;
(8) Consists of an optical system 40 that causes the reflected light 36 reflected from the reflective surface 39 on the wafer to interfere with the light diffracted from the alignment grating 21 on the reticle, and a photodetector 38 that measures the intensity of the light. .

As is clear from their configurations, the first and second embodiments can be considered to have the same positional relationship between the grating on the wafer, the position detection light, and the noise detection light, but in the second embodiment, Noise detection light 36 passes through the stepper reduction projection optical system 28
The reflected light 36 is passed through a Fourier transform lens 23.25
The light diffracted from the diffraction grating 21 on the reticle and the reflected light 36 are caused to interfere with each other, and the light is guided to the photodetector 37 and the optical intensity variation of the interfered light is detected. By extracting only the noise component shown in C and subtracting the signals a and C, an ideal positioning signal d free of noise components is obtained.

Effects of the Invention As described above, according to the present invention, another light beam that detects only the noise component in the position detection signal is provided in the close vicinity of the light beam that is performing position detection, and the noise component in the position detection signal is detected. By subtracting.

It is possible to perform ideal position detection and achieve highly accurate alignment. By reducing this noise component, the signal-to-noise ratio can be increased to 4 odB or more, and an extremely stable signal can be obtained. Furthermore, when positioning is performed using this positioning signal, the S/N
Since a ratio of 40 dB or more can be obtained, highly accurate alignment can be performed with alignment detection accuracy at the peak of 40 nm or less (as shown in Figure 2) and alignment detection accuracy at the midpoint of 10 nm or less. .

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram of an exposure apparatus according to a first embodiment of the present invention, FIG. 2 is a signal waveform diagram showing noise component removal of a detection signal according to the present invention, and FIG. 3 is a diagram showing a second embodiment of the present invention. FIG. 1 is a schematic configuration diagram of an example exposure apparatus. 1...Parallel light, 2,5...Mask, 3
...Reference grid, 4,9...Mirror, 6,8
....Alignment grid, 7.....Substrate, 9.
...Reflecting surface, 10...Optical system, 11゜1
2.13...Photodetector, a...Detection signal, b...Ideal signal, C...Noise component, d... ...Detection signal - noise component. Name of agent: Patent attorney Toshio Nakao and 1 other person 1″
-Parallel light 2-Mask 3-Reference grating 4.9--Mirror 5-Mask 6.8-@Placement tower chia-...& Extraction 9--Reflecting surface Fig. 2ttm Fig. 3

Claims (2)

[Claims] (1) Two coherent and conjugate beams are incident on the first area on the substrate with a grating and a second area where no grating is formed, and the intersection of the two beams causes The pitch of interference fringes to be generated is an integral multiple of the grating, and the first output of the interference light intensity of the light beams overlapped and diffracted from the grating and the second region on the substrate where the grating is not formed. means for aligning the interference fringes and the grating using a difference signal between a second output obtained by inputting another light and interfering the light reflected from the substrate with the coherent light; Exposure equipment. (2) Light source for alignment, illumination optical system, reticle, first
a second lens system, a spatial filter, a second lens system, an exposure light source, a projection lens, a substrate, and a photodetector, and a light beam emitted from the alignment light source is formed on the reticle through the illumination optical system. The diffracted light flux is guided into the first lens system, and a predetermined spectrum is selectively detected by the spatial filter provided on the spectral plane of the first lens system. The spectrum is transmitted to the second lens system, and the light beam passing through the second lens system generates interference fringes on the imaging plane of the second lens system. projecting onto the substrate through a projection lens and measuring the light intensity of the diffracted light diffracted from the second grating with the photodetector;
Furthermore, a part of the diffracted light from the reticle is incident on the surface of the substrate on which no grating is formed, and the light reflected from the substrate is caused to interfere with the light diffracted from the reticle on the spectral plane of the first lens system. A difference signal between the interference light intensity and the diffracted light intensity is used as an alignment signal, and the grating on the substrate and the grating on the reticle have a pitch that is an integral multiple of the interference fringes diffracted from the grating on the reticle. An exposure device that performs positioning.