JPH065662B2 - Exposure equipment - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reflection type exposure apparatus having a highly accurate alignment used for manufacturing an apparatus having a fine pattern.

2. Description of the Related Art In the conventional reflection mirror type exposure apparatus, the alignment between the mask and the substrate is performed through the mirror system, and the alignment signal is deteriorated according to the resolution of the mirror system, which makes it impossible to perform highly accurate alignment. It was Further, for alignment, the image on the reticle is once formed on the substrate, the reflected light flux of this image is formed again after passing through the reflection optical system, and the light intensity of this image is read to perform alignment. .

However, this imaging performance, for example, astigmatism, directly affects the alignment signal, and the Offner type and its improved type reflection mirror system projection aligners (Japanese Patent Laid-Open No. 48-12039). The image formation is good only on the upper surface of the circular arc where the astigmatism of the sagittal image surface and the meridional image surface on the circular arc are almost the same. However, there was a problem with the alignment accuracy in the rotational direction.

In view of such conventional problems, the present invention provides an exposure apparatus having an accurate and easy alignment optical system for a mask and a substrate in a process such as LSI manufacturing.

Means for Solving the Problems The present invention, in order to perform highly accurate alignment in an exposure apparatus having a reflection type optical system, does not use a conjugate beam among coherent light beams diffracted by a diffraction grating formed on a mask. Only two light fluxes are passed by the spatial filter, the two light fluxes are projected on the substrate to cause the two light fluxes to interfere with each other in the vicinity of the substrate, and when this interference pattern and the grating provided on the substrate are aligned, The relative alignment between the interference pattern and the grating on the substrate is performed by using the moire interference of the diffracted lights of the two diffracted lights. Further, in order to further improve the positioning accuracy, in order to measure the rotation amount, three above-mentioned positioning systems are provided so that the positions can be measured at three locations at the same time, and highly accurate positioning is performed.

Operation With the configuration of the optical system according to the present invention, highly accurate alignment can be performed without directly participating in the resolution performance of the optical system used for alignment. Further, since not only the arc-shaped part of the Offner type and its modification type reflective exposure optical system (only two places) but also the three-position alignment optical system can be provided, the alignment error due to the rotational deviation is highly accurate. Can be corrected to a higher level and higher alignment can be performed.

EXAMPLE FIG. 1 shows an example of the present invention. First, the features of the exposure apparatus will be described. This optical system basically combines two concave-convex reflecting mirrors and exposes the pattern on the mask 2 onto the wafer 7 by using the arc-shaped light flux shown in FIG. The light emitted from the pattern on the mask 2 illuminated by the light flux 1 passes through the plane mirror 3, the concave mirror 4, the convex mirror, and the plane mirror 3, and is imaged on the wafer 7. The arc-shaped illumination slit image 6 is also projected on the wafer, and the pattern on the mask is transferred one-on-one onto the wafer. The mask 2 and the wafer 7 are simultaneously moved and scanned, and the image of the entire mask 2 is transferred onto the wafer.

At least 3 places on the mask (in the figure, 9, 10, 1
The alignment mark of 1) is formed, and the coherent beam 8 is incident on each mark. In the present invention, the marks 9, 10 and 11 on the mask side and the marks 12 and 12 on the wafer side
Since alignment is performed using the marks 13 and 14, alignment in the xy axis direction and alignment in the rotation direction can be performed.

FIG. 2 shows a principle diagram of the alignment of the present invention. Although only one alignment mark is shown in the principle diagram, the same applies to three alignment marks.

First, the alignment grating 9 which is a mark on the mask 2
The laser beam 8 is made incident on. Incident light is diffracted by the grating and is diffracted for each of the 01th order, ± 1st order, ± 2nd order. The diffracted light is reflected by the plane mirror, the concave mirror 4, the convex mirror 5, and the plane mirror 3 in this order, and is imaged on the wafer 7. A spatial filter 15 is provided on the alignment optical path, and in this example, it is considered that only ± first-order light passes. The ± first-order lights cross on the wafer and generate an interference pattern on the wafer surface. A mark, that is, an alignment grating 12 is formed on the wafer 7, and the alignment deviation amount X between the interference pattern 18 and the grating 12 generated as shown in FIG. Measured at. That is, the re-diffracted light of the 1st-order light indicated by + in the figure and the re-diffracted light of the -1st-order light indicated by and correspond to the light intensity of the moiré light that interferes with each other and the misalignment amount, It can measure with high position accuracy. As shown in FIG. 4, the pitch of the moire light intensity corresponds to the pitch of the interference draft, and if the S / N ratio is 40 dB, the alignment detection accuracy of 0.04 μm can be obtained by the peak adjustment of the moire light intensity. Is obtained. Further, in the center alignment, the alignment detection accuracy of 0.01 μm can be obtained.

In the present invention, the alignment marks are provided on the position marks 9, 10 and 11 shown in FIG. 1, and the position of the alignment marks 10 and 11 is within the slit width as shown in FIG. However, since the astigmatism of the sagittal image plane and the meridional image plane exceeds the allowable defocus at the position of the alignment mark 9, no resolution occurs.
When viewed as an alignment optical system, distortion of the wavefront occurs due to aberration, but this amount is 0.8
λ, but in the alignment optical system of the present invention, the wavefronts of the ± first-order lights are different from each other, so the aberration amount may be several λ, and even at the position of the alignment mark 9 shown in FIGS. The interference of wave fronts is obtained, and the moiré writing light intensity with a uniform illuminance is obtained, and good alignment can be performed.

Further, FIG. 5a shows an optical system using an Offner type concentric concave-convex surface mirror. In this optical system, the sagittal image surface is flat, so only the meridional image surface has astigmatism, but the absolute value of astigmatism is absolute. Since the amount is small at the alignment mark position 9,
There is a margin for alignment accuracy. Further, FIG. 5b shows an Offner-improved optical system. In this case, since the amount of astigmatism at the alignment mark position 9 is large, the alignment tolerance is small.

Further, when three alignment marks are aligned at the same time, alignment in the rotational direction can be measured as alignment of the grid.

Alignment in the rotation direction is performed using 10 and 11 in FIG. 1, and then alignment in the X direction and Y direction is performed using the gratings 9 and 10. When this alignment is completed, open the shutter and irradiate the mask with arcuate illumination from the exposure light source,
Further, the mask and the wafer are simultaneously scanned to expose the entire surface of the wafer.

EFFECTS OF THE INVENTION As described above, according to the present invention, it is possible to obtain the alignment accuracy corresponding to the interference draft corresponding to the half pitch of the pitch of the grating formed on the mask. For example, for an interference pattern with a pitch of 1 μm, a peak alignment of 40 nm can be obtained, and an alignment accuracy of 0.1 μm can be obtained, and high-precision alignment can be applied to a projection exposure machine using a reflecting mirror.

Further, since the mask and the wafer can be aligned at three points, alignment in the rotational direction can be realized with high accuracy.

[Brief description of drawings]

FIG. 1 is a perspective view of an essential part of an exposure apparatus having an alignment optical system according to an embodiment of the present invention, FIG. 2 is a principle diagram of the alignment optical system according to the present invention, and FIG. 3 is an interference with a grating on a wafer. FIG. 4 is a diagram showing the relationship with the draft, FIG. 4 is a waveform diagram of the alignment detection signal according to the present invention, and FIG. 5 is an Offner type used in the present invention.
It is explanatory drawing of the astigmatism of the improved concave-convex mirror. 1 ... Luminous flux, 2 ... Mask, 3 ... Planar mirror, 4 ...
Concave mirror, 5 ... Convex mirror, 6 ... Slit image, 7 ... Wafer, 8 ... Beam, 9, 10, 11, 12, 13, 14
……mark.

Claims (2)

[Claims] 1. A light source, an illumination optical system, an optical system having a set of a concave mirror and a convex mirror as a coaxial axis, an exposure optical system having a mask and a substrate at a conjugate position of this optical system, a coherent light source, Only the alignment grating provided on the mask, the alignment grating on the substrate having the same pitch as the alignment grating, and the two conjugate light beams diffracted from the alignment grating on the mask between the two alignment gratings. A spatial filter that allows the light to pass therethrough, a half mirror that reflects the light beam diffracted from the grating on the substrate, and a photodetector that measures the moire light intensity of the diffracted light from the substrate. And an exposure apparatus configured to read the relative position of the grid on the wafer. 2. The alignment grid on the mask has at least three.
There are 3 corresponding alignment grids on the wafer.
The exposure apparatus according to claim 1.