JPH0719742B2 - Mask alignment method - Google Patents

Description

The present invention relates to a lithographic technique for manufacturing a semiconductor device, and particularly to improvement of a mask alignment technique.

(B) Conventional technology In the field of semiconductors, the problem when performing fine processing of about 1/4 μm is mask alignment. Previously, "High-precision alignment method for X-ray lithography" 1986 (Showa 61)
Proceedings of the 33rd Spring Joint Lecture Meeting on Applied Physics p.
As described in 326, the laser beam is applied to appropriate marks, zone plates and diffraction gratings provided on the mask to perform the alignment, but highly accurate alignment of about 0.01 μm is not easy.

C) Problems to be solved by the invention In order to perform submicron fine processing, it is necessary to transfer several types of patterns in an overlapping manner, and a mask alignment accuracy of about 0.01 μm is required. As the degree of freedom of position, there are a total of three degrees of freedom, namely rotation or azimuth in the plane of the mask and translation in two directions parallel to the plane. It is necessary to accurately control all three, but practical use of X-ray lithography is required. Therefore, the advent of alignment technology with higher accuracy than at present is awaited.

D) Means for Solving the Problems In the present invention, attention is paid to the fact that a high-quality single crystal can be used as a substrate for a mask, and among these problems, the degrees of freedom of orientation and translation are decomposed and considered. We propose a method to accurately determine only the orientation of the mask using the reflection phenomenon.

E) Action The orientation of the mask can be accurately and easily detected by using the Bragg reflection phenomenon of X-rays by the single crystal mask substrate.

F) Example FIG. 2 shows an example of a Bragg reflection curve (rocking curve) of X-ray by a perfect crystal surface having absorption. The horizontal axis is the angle and the vertical axis is the reflectance. The angular width at which total internal reflection occurs depends on the crystal plane used, but is usually several seconds. Using a silicon single crystal as the mask substrate, as shown in FIG.
The side surface is cut so that a specific crystal plane (for example, 110 plane) appears. Since the Bragg reflection by the crystal lattice is used, the smoothness of the surface and a slight deviation from the 110 plane do not matter, but it is necessary to chemically polish the surface so that lattice distortion does not enter.

FIG. 1 shows the configuration of an apparatus for carrying out the present invention. In the figure, (1) is an X-ray generator, (2) is a monochromator that allows passage of only X-rays of a desired wavelength, (3) is a mask substrate crystal, and (4) is an X-ray detector. The relative position of the incident X-ray and the cut surface made in advance on the side surface of the mask substrate is arranged so that Bragg reflection occurs, and the intensity of the reflected X-ray is detected in (4). The X-ray reflectance of the single crystal is very sensitive to the angle change of (3), so it is possible to detect a crystal shift of about 0.1 second. Accurate azimuth adjustment can be performed by feeding back the output of the detector to the azimuth adjusting mechanism of the mask aligner.

Next, specific examples of the present invention will be described with numerical values. X
Enclosed type X using, for example, a copper target as a line generator
A line tube (fine focus is better) is arranged as shown in FIG.
The wavelength of Cu-Kα rays is λ = 1.5405Å, and the monochromator uses a three-crystal asymmetrical arrangement of silicon single crystal (lattice constant 5.4301Å). The case where a 100 silicon wafer is used as a mask substrate is taken as an example. Since there are 110 lattice planes perpendicular to the substrate plane, we use 220 reflections on that plane. The Bragg angle is θ _B = 23.
It is 65 degrees. The angular spread of monochromatic X-rays is about 0.1 seconds. The intensity of the reflected X-ray is detected by a scintillation counter. The crystal orientation is controlled with the accuracy of 0.1 second order by measuring the reflectance curve. Disturbance of azimuth for 1 second is about 0 at the other end when one end of a 10 mm square mask is combined.
Since a position shift of 5 μm occurs, in the case of a mask having a line width of 1/4 μm, it is sufficient to have an orientation detection accuracy of the order of 0.1 seconds. If the mask size is smaller than this, the orientation detection accuracy may be lower.

G) As is apparent from the above description, the present invention uses the single crystal as the mask substrate and detects the intensity of the X-rays reflected from the crystal lattice plane, so the orientation of the mask is detected extremely accurately. Can be used together. If it is used for current aligners and steppers, the problem of orientation adjustment of aligners for microfabrication of 0.01 μm or less can be solved. If the azimuth is accurately determined by this method, only one mark used for translational alignment is sufficient, and a plurality of marks (for example, 4 marks) as in the conventional aligner can be used.
It is freed from the hassle of using (in the corner) to process the signals from them.

It is obvious that the method of the present invention can be applied to both the mask pattern formation on the mask substrate and the X-ray exposure using the mask.

[Brief description of drawings]

FIG. 1 is a plan view showing the structure of an apparatus for carrying out the present invention, FIG. 2 is a reflectance curve diagram of X-rays from a single crystal surface, and FIG. 3 is a mask substrate and a lattice plane for reflecting X-rays. It is a perspective view which shows the relationship of. (1) ... X-ray generator, (2) ... monochromator, (3) ... mask substrate, (4) ... X-ray detector.

Claims (1)

[Claims] 1. An X-ray generator, a monochromator which passes only X-rays of a desired wavelength, a single crystal mask substrate which reflects X-rays of a desired wavelength obtained from this monochromator, and an X which is reflected from this mask substrate. A mask alignment method comprising: a detector for detecting a line; and accurately controlling the orientation of the mask by detecting the X-ray intensity.