JPS5928982B2 - Printing device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a 1.C pattern printing apparatus using a proximity method.

The 1.C pattern printing method, called the proximity method, is a method in which 1.C pattern printing is performed with a distance of several microns to several tens of microns between the mask and the wafer.

In recent years, in order to improve the resolution of the proximity method, a method of forming a secondary light source using a prism or a multi-lens has been shown in Japanese Patent Laid-Open No. 47-37657 and No. 47-4817. However, although an improvement in resolution was observed in conventional devices using a secondary light source, the reproducibility of patterns having sharp corners was unsatisfactory. That is, when a pattern having sharp corners as shown in FIG. 1a was printed on a wafer, the apexes were rounded, as shown in FIG. 1A, and the pattern could not be accurately reproduced. This phenomenon is due to Fresnel diffraction occurring between the mask and the wafer, and was a phenomenon that occurred along with the principle of proximity method. Conventionally, in order to eliminate this phenomenon, in the projection printing method using a lens, a method is known in which a hole is grown on the outside of the corner of the negative pattern, or the inside is shaved off, as shown in FIG. However, according to this method, it is difficult to put it into practical use because the shape of the part where the bumps are to be formed or the part to be cut depends on the magnification, aperture ratio, etc. of the lens. The purpose of the present invention is to focus on the above-mentioned patterns having sharp corners, particularly 1. Focusing on the fact that many rectangular patterns or orthogonal lines on the C mask have the same directionality, The purpose is to accurately print the pattern onto the wafer.

In the present invention, the above-mentioned drawbacks are improved by theoretically elucidating the Fresnel diffraction that occurs between the mask and the wafer, and by appropriately selecting the shape of the secondary light source.

The present invention will be explained in detail below using the drawings. Figure 3 shows I using the proximity method.

1 is a schematic diagram showing an embodiment of a C pattern printing apparatus.
1 is a light source, 2 is a reflecting mirror, and 3 is a first condenser lens having one focal point on the light source, which collimates the light beam from the light source.

Reference numeral 4 denotes an optical element for generating multiple light beams, such as a diffuser plate, a fly's eye lens, or a lenticular plate, which forms a secondary light source on or near its own surface, and which serves as one focal point of the second condenser lens 5. The position is provided to coincide with the secondary light source.

6 is a mask having a C pattern, and 7 is a wafer. The mask 6 and the wafer 7 are kept parallel to each other with a distance of several microns to several tens of microns.

A light beam from a light source 1 is collimated by a first condenser lens 3 and enters an optical element 4 for generating multiple light beams.

Each light beam generated from each point on the optical element for generating multiple light beams is collimated by the second condenser lens 5, passes through the pattern of the mask 6, and reaches the wafer 7. The phenomenon in which a pattern with sharp corners is rounded as described above due to Fresnel diffraction that occurs in the gap between the mask and the wafer is explained using the optical element 4 for generating multiple light fluxes, a fly's eye lens, and the mask 6.
Figure 4 uses a square opening with side 2a in the above pattern.
This will be explained using FIG. 5, FIG. 6, and FIG. 7 together.

In FIG. 4, reference numeral 4' denotes a circular convex lens constituting a fly's eye lens, and is provided so that its center is on the optical axis 8.

A square opening 9 with one side 2a is provided on the mask 6. The center of the aperture 9 is located on the optical axis 8;
is the Z axis, and coordinate axes XI and YI are taken on the mask 6 along each side of the opening 9. Furthermore, this Xl,
When both coordinate axes of yI are moved in parallel along the z-axis and the origin is moved on the wafer 7, it is defined as the X■ axis and y■ axis, and when the origin is similarly moved 4/above the secondary light source, it is defined as the X ■Axis,
Let the y-axis be the axis. FIG. 5 shows an example of a Fresnel diffraction image in the XIlY■ plane of FIG. 4. solid line 1
0 is the Fresnel diffraction pattern, and the dotted line s is the aperture width 2a
This is the slit. It can be seen that at the position where the diffraction pattern 10 accurately reproduces the slit width on the mask, the intensity of the diffraction pattern is considerably lower than the center intensity. Next, FIG. 6 shows a two-dimensional example of a case where this Fresnel diffraction pattern occurs in a square aperture with side 2a.

Variables in the x and y directions can be separated in the pattern function representation of Fresnel diffraction that generally occurs in a rectangular aperture. Therefore, the intensity distribution 1(XI[,y■) of the amount of light on the wafer due to Fresnel diffraction generated by a square aperture with side 2a is 47? It is shown in the form of 赫上12bゝVii′.

Here, (2) is a function representing the intensity distribution of a diffraction pattern created by a slit having a width corresponding to one side 2a of a square as shown in FIG. Assuming that the light intensity at the origin of the x and y coordinates on the wafer (on the z axis) is 1.0, and the light intensity at all edges of the square to be reproduced is 0.5, then 12 ( 0,0)=1.0.

Therefore, there are four points that reproduce the corners of the square opening provided on the mask on the wafer, that is, (x■, y■) =
The light intensity at the point (±A, ±a) is number ≦~7'. jri'v
-Nv, and it can be seen that the depression at the corner is larger than at other parts.

FIG. 7 shows an equal light quantity distribution curve on the wafer by Fresnel diffraction in the apparatus shown in FIG. This equal light quantity distribution curve is created by a convex lens, which is one element of the fly's eye lens, and the fly's eye lens is provided with a large number of such convex lenses. Therefore, an equal light quantity distribution curve as shown in FIG. 7 is generated for each convex lens. In Figure 4, the center of the convex lens 4'' is the optical axis 8 (x = 0,
Since the convex lens element 4' was placed on the secondary light source surface, the maximum amount of light due to Fresnel diffraction appeared on the optical axis 8 (x■ = 0, y■ = 0) on the wafer. For example,
(2) When the position is shifted in the positive direction on the axis, the position on the wafer showing the maximum amount of light is similarly shifted in the negative direction on the X-axis on the wafer. In this case, the entire isometric distribution curve only moves in parallel in the negative direction on the x-axis on the wafer, and its shape does not change. The actual light quantity distribution on the wafer is a superposition of equal light quantity distribution curves as shown in FIG. Therefore, in order to improve the reproducibility of corners, the superimposed light intensity distribution on the wafer should be
The shape of the secondary light source may be considered so as to have a substantially equal light amount distribution. First, let's consider a positive-type photoresist that dissolves where the photoresist is exposed to light.

A photoresist is generally a photosensitive material with a high gamma, and it can be considered that only the portion exposed to approximately a certain amount of light or more becomes selectively soluble if it is of positive type, and hardened if it is of negative type. Therefore, in order to appear as a resist image, it is best to pay attention to iso-intensity lines with a light amount distribution. In case 11, when a rectangular opening 11 provided on a mask is cut out on a photoresist as shown in FIG. The light amount distribution curve becomes as shown by 12, and the corners are rounded because the shaded portion 13 is etched and removed.

Therefore, in this case, the amount of light may be increased selectively in directions having an angle of ±45 degrees with respect to the direction of the XI axis or YI axis of the pattern 11. To do this, the secondary light source may be modified so that the pattern on the mask has a larger amount of light in the desired direction on the surface of the secondary light source.
For example, as shown at 14 in Figure 8b, on the secondary light source surface, the secondary light source is ±452 with respect to the x-axis or y-axis direction.
The light source can be spread out in the direction of the angle of , making it almost like a pincushion. Similarly, in the second case of a positive type photoresist, as shown in FIG. 9a, a rectangular portion 15 provided on the mask is a portion that does not allow light to pass through, and is left on the rectangular portion 15 and the photoresist. In this case, the isoluminous quantity distribution curve by Fresnel diffraction is as shown in 16.

The shaded portion 17 is exposed and etched away, leaving a central portion 18. In this case, the portion 18 to be left on the photoresist will be offset between the rectangular portions 15 and 45 on the mask. Therefore, in this case, it is necessary to increase the amount of light in the X-axis and YI-axis directions of the pattern 15. Therefore, the shape of the secondary light source can be enlarged in the x-axis and y-axis directions to form a substantially pincushion shape, as shown in FIG. 9B19. Also, when using a negative photoresist that leaves the exposed areas, the shapes of the secondary light sources that are cut out and left on the photoresist are reversed compared to when a positive photoresist is used. .

That is, the shape of the secondary light source in the case of omission is 19 in FIG. 9b, and in the case of remaining, the shape is 14 in FIG. 8b. In addition to a diffuser plate, a fly's eye lens wrench killer plate, a prism, etc., any secondary light source may be used as long as the shape of the secondary light source can be changed freely.

Further, specific means for changing the shape of the secondary light source include, for example, when using fly's eye lenses as the secondary light source, arranging the fly's eye lenses in a desired shape within the plane of the secondary light source, or A slit may be provided to obtain a desired shape at a position where the collimated light beam from the light source is imaged by the fly's eye lens, for example at point S in FIG. 4.

If a diffuser plate is used, it should be made so that the desired shape of the diffuser plate can be replaced within the plane of the secondary light source, or a slit should be provided in close proximity to the diffuser plate surface to obtain the desired shape. It's okay. As described above, 1. of the proximity method using the secondary light source of the present invention. In C-pattern printing equipment, patterns with sharp corners on a mask, which were difficult to reproduce using the conventional proximity method due to Fresnel diffraction that occurs between the mask and the wafer, can be reproduced using the directivity of the pattern. By focusing on this, and changing the shape of the secondary light source as appropriate to increase the amount of light in the desired direction, it is possible to effectively reproduce sharp corners by effectively utilizing the Fresnel diffraction that occurs between the mask and wafer. This is a simple method that produces great effects.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the phenomenon of corners being rounded by the conventional proximity method, Figure 2 is an example of a conventional mask pattern, and Figure 3 is a schematic diagram showing an example of the conventional proximity method. Figure, Figure 4, Figure 5, Figure 6, Figure 7
The figures are for detailed explanation of the present invention, Figures 8 and 9.
The figure shows one implementation of the present invention. 4...Secondary light source, 6...Mask, 7.
...Wafer, 8...Optical axis, 9...
...Aperture, 12, 16... Equal light amount distribution curve.

Claims (1)

[Claims] 1. In a proximity type printing apparatus in which a mask for manufacturing semiconductor circuit elements and a wafer are placed a small distance apart, and the mask is printed onto the wafer by illuminating the mask with a light beam from a light source, the light source is approximately A printing device characterized by a secondary light source having a pincushion shape.