JPH02174111A - X-ray projection aligner - Google Patents

Abstract

PURPOSE:To align a pattern highly accurately by installing the following: a condensing mirror which condenses X-rays with which a mask is irradiated; a reflecting-mirror optical system which is constituted of one or two aspheraical mirrors or of one spherical mirror out of the two mirrors. CONSTITUTION:The following are provided: a condensing mirror 11 which condenses X-rays; a reflecting-mirror optical system 15 which is composed of one or two aspherical mirrors or of one spherical mirror out of the two mirrors. X-rays are condensed, by using the condensing mirror 11, toward one point on an optical axis of the reflecting-mirror optical system 15; a pattern on a mask is irradiated with the X-rays; the pattern is projected in such a way that a principal ray is incident nearly perpendicularly on a specimen face by using the reflecting-mirror optical system 15. Thereby, a dislocation of the pattern by an up-and-down fluctuation of the specimen face, i.e. a water face, is not caused; a positional accuracy of a highly accurate pattern can be obtained. In addition, since the number of mirrors for the reflecting-mirror optical system 15 is small at one or two, a drop in an optical intensity by a reflection factor of a multilayer mirror is small; the pattern can be transcribed at high speed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an X-ray projection exposure apparatus used for forming fine patterns in semiconductor integrated circuit manufacturing, and particularly to a soft XI# exposure apparatus.

[Conventional technology]

X# using XN mask! The exposure method is fine.

In terms of productivity, this method is also superior to electron beam exposure (e.g., electron beam exposure). A transmission type X-ray mask is used, which is formed on a film transparent to IsK and processed with a pattern that absorbs X-rays. The X-ray mask is placed at a minute interval of several tens of micrometers from the wafer coated with resist.
Xi is irradiated uniformly. As a result, the resist is exposed to X-rays transmitted through the X-ray mask, and a resist pattern is obtained by developing the resist. By the way, in this conventional method, since the transfer is performed at the same magnification, it is not possible to obtain a transfer precision higher than the pattern density of the electron beam exposure device used for drawing the pattern of the X-ray mask. Additionally, in order to ensure X-ray transmittance, the film that supports the X-ray absorbing pattern of the XN mask is extremely thin, about 2 μm, so it is often difficult to manufacture large-area X-ray masks. This is causing problems such as:

Therefore, in order to solve such problems, an X-ray reduction projection exposure method using synchrotron radiation (Kinoshita et al.: Proceedings of the 47th Japan Society of Applied Physics, October 1986,
p322.28p-ZF-15) is being investigated. FIG. 7 shows a schematic diagram of the optical system. Here, TO is a mask, T1 is a slit, T2 is a reflective mirror optical system, and 7
3 is a wafer, 74 is a sample stage, and 75 is a chief ray. In this method, exposure is performed by reducing and projecting the image of the mask TO onto a wafer 73 coated with resist using a reflection mirror optical system 72 made of a Schwarzschild optical system. There are two types of mask 70: a transmission type mask and a reflection type mask.
Class s is considered. Incidentally, the reflective mask and reflective mirror optical system used in Xaa small projection exposure are coated with a multilayer film that reflects X-rays of a specific wavelength on the surface to increase the X-ray reflectance. At this time, the multilayer film includes, for example, tungsten W/carbon C.
Pairs of heavy atoms, such as molybdenum Mo/silicon Si, are used. It is known that the formation interval of the multilayer film is determined by Bragg diffraction conditions based on the X-ray wavelength and incident angle.

In addition to the Schwarzschild optical system, conventional optical systems such as those shown in FIG. 8 (for example, Hoh and H.

Tan1no: Bulletin of Electr
otechnical Laboratory.

vol, 49 No. 12 (1985) p47-54)
is considered. Here, 80 is a reflective mirror optical system;
81 is a chief ray, 82 is a mask, and 83 is a sample surface.

This consists of three mirrors 801-80. Optical system 80 by
The optical characteristics of this lens are comprised of the following, and provide optical characteristics with very low aberrations.

[Problem to be solved by the invention]

However, in a reflective mirror optical system using a conventional Schwarzschild optical system, the direction of incidence of the principal ray onto the wafer T3, that is, the sample surface, is oblique as shown in FIG. If the chief ray 75 obliquely enters the sample surface, which is the image plane, the position of the projected pattern will shift, considering that the sample surface deviates from a predetermined position. For example, consider a case where the chief ray is incident on the sample surface at an incident angle of 20. If the sample surface is shifted up or down by 1 μm, the exposed pattern position will be shifted by 0.36 μm from the designed position. Exposure of fine patterns requires extremely high alignment accuracy, so pattern position errors due to vertical fluctuations of the sample surface cannot be ignored. It is actually extremely difficult to obtain a flatness of 1 μm or less for the wafer, considering the inclination of the sample stage, the inclination of the wafer itself, and the steps of the elements. Therefore, with conventional optical systems, there is a problem in that it is difficult to achieve highly accurate alignment.

On the other hand, as shown in Fig. 8, there is an optical system in which a principal ray 81 is perpendicularly incident on a sample surface 83 using a reflecting mirror optical system 80 made up of three mirrors, but this poses a problem in that the number of reflections of X-rays increases. In other words, since the X-ray reflectance of the multilayer reflective surface used in the X-ray reflective mirror cannot be made very large, the problem is that the xg intensity incident on the sample is small, the exposure time increases, and the throughput becomes small. be. In particular, when using a reflective mask, there is a problem that the throughput decrease cannot be ignored because there are four reflections. Means for Solving] In order to solve the above problems, the present invention provides an X-ray projection exposure apparatus that uses X-rays to project a pattern on a mask onto a sample surface for exposure. a condensing mirror for illuminating the mask; and one or two aspherical mirrors, or one of the two mirrors so that the chief ray from the condensing mirror is incident almost perpendicularly to the sample surface. One is equipped with a reflecting mirror optical system composed of a spherical mirror.

[Effect]

In the present invention, the condensing mirror condenses incident X-rays and illuminates the mask so as to condense the condensed X-rays to one point on the optical axis of the reflection mirror optical system. This reflective mirror optical system can project the pattern on the mask so that the chief ray is incident on the sample surface almost perpendicularly. At this time, the reflection mirror optical system projects the reflected or transmitted X-rays from the pattern on the mask onto the sample at a predetermined magnification.

〔Example〕

Hereinafter, the present invention will be described in detail based on embodiments shown in the drawings.

FIG. 1 is a schematic diagram showing an embodiment of an X-ray projection exposure apparatus according to the present invention. In the figure, 10 is synchrotron radiation emitted from a light source (not shown), and 11 is a condensing mirror. -12 is a slit, 13 is a mask, 14 is a mask stage, 15 is a reflective mirror optical system, 16 is a wafer, 1
7 is a sample stage. Here, when the synchrotron radiation light 10 is incident on the condensing mirror 11, the condensing mirror 11 condenses the incident light and illuminates the pattern on the mask 13. That is, the condensing mirror 11 is composed of a toroidal mirror, and condenses the light source image of the synchrotron radiation 10 toward a certain point Za on the optical axis 2 of the reflective mirror optical system 15. work to do. This situation is shown in FIG. In this figure, the same reference numerals as in FIG. 1 indicate the corresponding parts, 20 is the irradiation area on the mask 13, and 21 is the optical axis. Here, a reflective mask 13
An example using . The synchrotron radiation light 10 has a fan-shaped radiation distribution, and the width line in the vertical direction Y is narrow, but the width in the horizontal direction X can be widened. Therefore, the mask irradiation area 20 formed by the slit 12 is
As described later, create a horizontally long arc-shaped area0
In addition, the condensing mirror 2-11 directs the synchrotron radiation 10 onto the optical axis 21 in both the horizontal and vertical directions.
Focus the light towards. The mask irradiation area 20 is
As shown in the figure.

In FIG. 3, the same reference numerals as in FIGS. 1 and 2 indicate the same or corresponding parts, 30 is a pattern area formed on the mask 13 or the striped substrate 13, 31 is the slit 12
Based on the above synchrotron radiation beam shape, the pattern region 30 is formed with a pattern for one LSI chip. Here, the irradiation area 20 on the mask 13 is an elongated arc-shaped irradiation area obtained through the arc-shaped slit 12 centered on the optical axis. The irradiation area 20 is made to sufficiently cover the lateral force direction area of the pattern area 30 where the pattern to be transferred exists. At this time, the irradiation area in the vertical direction is set narrower than in the horizontal direction because it is necessary to satisfy the tolerance value of the aberration of the reflection mirror optical system 15. Since the light rays passing through this region are rotationally symmetrical with respect to the optical axis, the aberrations are uniform in the arc direction. Since the irradiation area in the vertical direction is narrow, a large area can be exposed by scanning the irradiation area 20 by scanning the mask 13 in the vertical direction of the arrow 18 using a method described later. The reflected X-ray image of the pattern on the mask 13 is then reduced and projected onto the wafer 16 by the reflection mirror optical system 15. This wafer 16
The position of the focal point of the condensing mirror 11 is determined so that the principal ray L1 incident on the wafer is almost perpendicular to the wafer, and the reflective mirror optical system 15 with low aberration is designed in advance.
At this time, a multilayer film is formed on the mirror surface of the reflective mirror optical system 15 to increase the reflectance for X-rays of a specific wavelength. For example, if the wavelength of the X-ray used for exposure is set to about 50 wavelengths, which is less absorbed by carbon (C) in the resist, W/C, Rh/C, Ru/C, Cr/C, Re/C
, Os/C, Ir/C, etc., can have a high reflectance and are therefore desirable for use in reflective mirrors. A resist sensitive to X-rays is coated on the wafer 16, and a mask stage 14. While scanning the sample stage 17 in synchronization, the area on the mask 13 is sequentially transferred to the resist. As a result, mask stage 14. The sample stage 17 is scanned synchronously at the same ratio as the reduction ratio of the optical system. Also,
The pattern alignment is performed using mask 13. This is performed by forming marks on the wafer 16 in advance and detecting the mark positions using means such as a laser. Note that 19 in FIG. 1 indicates the scanning direction of the wafer 16.

Next, a specific example of the reflection mirror optical system of the X-ray projection exposure apparatus of the above embodiment will be shown. This reflective mirror optical system 15 has a magnification of 115 and includes two convex mirrors 151. Consists of 15 □ concave mirrors, each with a radius of curvature RO of 500
It is composed of an aspherical mirror of m5+. Here, the radius of curvature Ro of each mirror 15+ and 152 is made the same in order to set the Petzval sum to zero and flatten the image plane. By changing the aspherical shape, mirror spacing, etc., the total aberrations are minimized while taking into consideration the balance with higher-order aberrations. In this case, since the influence of diffraction is small in the X-ray region, N
Since A (numerical aperture) can be made smaller than that of light, the spherical aberration can be reduced to the third power of NA. Therefore, in particular,
Optimum design is performed by selecting initial values for the aspherical shape so as to reduce coma and astigmatism. In particular, as shown in FIG. 4, two convex protrusions 15. ．． The mirror spacing of the 15-fold concave mirror is larger than Ro/2 (L/RO>0.5
) can reduce aberrations. In this example, characteristics 1. when NA=0.01, 0.005 and image height is 50cm. n is shown respectively. However, L/RO
When approaches 1, the aberration is small, but the image plane becomes inside the mirror optical system, which is not practical. L/R
O) When the condition is 0.5, point Za on the optical axis 2 is connected to the convex mirror 15. By setting the beam to the rear of the Ueno 116 tube, the condition of normal incidence to the sample surface can be obtained. Here, the image height was 50 m. To give a design example based on this idea, if the mirror spacing L = 400-, the aspherical coefficients include a convex mirror = 13.35, a concave mirror = o, and an ellipsoid of o 811. 0The second-order aspherical shape is z=h"/(1+ 1-(k+1)h"/Ro")/R
.

0, where h is the axis height and 2 is the coordinate in the optical axis direction. The optical length is 689w5. An example of this aberration characteristic is shown in FIG. Here, if the wavelength λ of the X-ray is chosen to be 5OA, the image blur d due to diffraction is d=o, 5λ/NA
From the relationship, if NA=0.0125, d==0.2
It becomes μm. It can be seen that when NA=0.0125, the aberration of the optical system is 0.1 μm or less in both the X and Y directions, and blurring due to diffraction becomes dominant.

Further, even if NA=0.025, the aberration is 0.2 μm or less. In this example, the lateral exposure area can be on the order of 15 m.

Further, as another example, a convex mirror 151. Concave mirror 15 If RO = 300 days and L = 250 days, then
If the aspheric coefficient is k=10.67 for a convex mirror and =o, o 94 for a concave mirror, the optical length can be reduced to 407.6 m. The aberrations at this time are shown in Figure 5 (B
), even if NA=0.06, it is 0.2
Although it is small, less than μm, the strain is 93 times larger than that of the above embodiment, and the slit width cannot be made large.

However, one of the mirrors can also be made spherical, although the aberration will be somewhat larger. Further, even if the curvatures of the two convex ζ mirrors and the concave mirror are not the same and are changed by a few percent, aberrations can be reduced to a certain extent. Here, 2
Although an example using a curved surface of a higher order is shown, a curved surface of a higher order can also be used.

For this reason, it is possible to design various optical systems using two mirrors based on the configuration of the present invention. In this way, according to the X-ray projection exposure apparatus of the above-described embodiment, synchrotron radiation A condensing lens 11 that condenses the light of 10 and illuminates the mask 13, and two convex and concave aspherical mirrors are used to make the radii of curvature of the mirrors almost the same and the interval between the mirrors is 1/2 or more of the radius of curvature. Reflection mirror optical system 15
Equipped with a condensing mini 7-11, a reflective mirror optical system 1
Synchrotron radiation 1 towards a point on 50 optical axis 2
0 is focused to illuminate the pattern on the i-screen 13. Then, the pattern is reduced and projected by the reflection optical system 15 so that the chief ray is almost perpendicularly incident on the wafer 16 surface (image surface), thereby eliminating the pattern 0 position shift due to the vertical fluctuation of the wafer surface. This does not occur, and high pattern position accuracy can be obtained.

Furthermore, when synchrotron radiation is used, if the exposure area is arc-shaped as in this example, the light distribution is horizontal and easy to illuminate, and there is no need to irradiate a wide two-dimensional area. Easy to obtain uniform light intensity. Furthermore, by using the reflective mirror optical system 15 made up of two aspherical mirrors, it is possible to obtain low aberrations while ensuring the conditions for perpendicular incidence to the wafer. Furthermore, since the number of mirrors is as small as two, the reduction in light intensity due to the reflectance of the multilayer mirror is smaller than in the past, and there is an advantage that pattern transfer can be performed at high speed. However, with an even number of sheets like 2 sheets Mi 2-, mask 1
3 and the wafer 16 are on opposite sides of the optical system, so the sample stage 1T of the wafer 16 does not block the reflected or transmitted X-rays from the mask 13.
It is advantageous in terms of structure, and has the advantage that patterns can be easily transferred to large-diameter wafers.

In addition, in the above embodiment, an example using synchrotron radiation light was shown, but a laser plasma X-ray source is used.

The same effect can be obtained by using an isotopic X-ray source such as an electron beam excited X-ray source.

In addition, it is also possible to use not only X-rays but also vacuum ultraviolet light as a light source.

Furthermore, if high resolution is not required, the apparatus can be constructed using a single aspherical mirror as shown in FIG. Here, 60 is a principal ray, 61 is a condensing mirror, 62 is a slit, 63 is a mask, 64 is a reflection mirror optical system consisting of one aspherical mirror, and 65 is a sample surface. At this time, if the light is condensed so that the condensing point Za of the condensing mirror 61 is near the focal point of the reflection mirror optical system 64, a condition of almost vertical incidence can be achieved.

Furthermore, although an example was shown in which a reflective mask was used as a mask, at a wavelength of about 50A, C (carbon) and a wavelength of 70A were used.
At grade A, a transmission type mask using a membrane mainly made of material such as BC (boron carbide) can be used similarly because it has high transmittance in a wavelength band slightly beyond the vicinity of the X-ray absorption edge of the constituent material. Even when a transmission type mask is used, the reflection mirror optical system itself may be exactly the same as when a reflection type mask is used, except that the condensing mirror is located on the opposite side of the mask.

〔Effect of the invention〕

As explained above, the X-ray projection exposure apparatus of the present invention
It is equipped with a reflection mirror optical system consisting of a condensing mirror that condenses the line, one or two aspherical mirrors, or one of the two mirrors is a spherical surface, and the condensing mirror , the pattern on the mask is focused by focusing X-rays toward a point on the optical axis of the reflecting mirror optical system, and the principal ray is almost perpendicular to the sample surface. By projecting the sample so that it is incident on the surface of the sea urchin, the position of the pattern does not shift due to vertical fluctuations of the surface of the sample, that is, the surface of the sea urchin, so that highly accurate positioning of the pattern can be achieved. In addition, since the number of mirrors in the reflective mirror optical system is small, 1 to 2, the decrease in light intensity due to the reflectance of the multilayer mirror is smaller than before, and high-speed patterning/transfer is possible. By using a spherical mirror, there are excellent effects such as being able to obtain low aberrations while ensuring the condition of perpendicular incidence to the wafer.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram of an embodiment of the X-ray projection exposure apparatus according to the present invention, FIG. 2 is a diagram for explaining the light focusing method of the embodiment, and FIG. 3 is a diagram of the mask of the above embodiment. An explanatory diagram of the irradiation area, FIGS. 4 and 5 are a characteristic diagram and an aberration characteristic diagram showing the relationship between aberration and mirror spacing of the reflective mirror optical system of the above embodiment, respectively, and FIG. 6 is another embodiment of the present invention. Schematic diagram of an optical system using one aspherical mirror according to Figures 7 and 8.
Each figure is a schematic diagram showing an example of a conventional X-ray projection exposure apparatus. 10...-synchrotron radiation, 11,61...
9 Condensing mirror 12, 62... Surin), 13, 6
3...Mask, 14@...Mask stage, 15
．． 64@...Reflecting mirror optical system, 15.・Rumor...Convex mirror 15. ...Concave mirror 16.e...Wafer,
1711...Sample stage. Figure 2 Figure 3 n O Figure 4 Figure 0.5 L/R. Figure 5

Claims (1)

[Claims] An X-ray projection exposure apparatus that projects and exposes a pattern on a mask onto a sample surface using X-rays includes a condensing mirror that condenses X-rays to illuminate the mask, and a chief ray from the condensing mirror. 1 or 2 sheets so that the incidence is almost perpendicular to the sample surface.
1. An X-ray projection exposure apparatus comprising a reflection mirror optical system in which one of two aspherical mirrors or one of the two mirrors is a spherical mirror.