JP2606138C - - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aperture for an electron beam writing apparatus, and more particularly, to an aperture for an electron beam writing apparatus.
The present invention relates to an aperture stop for batch writing of an electron beam writing apparatus used in a semiconductor device manufacturing process. 2. Description of the Related Art A drawing method using an electron beam has been widely adopted in a manufacturing process of a ULSI having a fine pattern because a higher resolution can be obtained as compared with an optical lithography method. Is coming. Above all, the batch writing method has attracted attention because it can realize a higher throughput than other electron beam writing methods. This kind of electron beam lithography and the aperture used in it are described in Yoshinori NAKAYAMA, Hidetoshi SATOH et al, "Thermal Characteristics of Si Mask for EB Cell
Projection Lithography ", Jpn.J.Appl.PHYS.Vol.31 (1992) pp.4268-4272Par
tl, No.12B, December 1992 and Yoshinori NAKAYAMA, S.OKAZAKI, and N.SAT
OH, "Electron-Beam cell projection lithography: A new high-throughput ele
ctronbeam direct-writing technology using a specially tailored Siapature
, J. Vac. Sci. Technol. B8 (6), Nov / Dec 1990, etc. [0003] FIG. 5 is a conceptual diagram showing a schematic configuration of this type of electron beam writing apparatus. As shown in the figure, an electron beam emitted from an electron gun 51 is shaped by a first aperture 52, then deflected by a deflector 53 and incident on a second aperture 54, where it is formed into a desired pattern. Thereafter, the electron beam is irradiated onto a wafer 57 via a reduction lens 55 and a projection lens 56 to pattern an electron beam resist on the wafer. As described in the literature, silicon capable of ensuring high processing accuracy is employed, and Fig. 6 is a cross-sectional view in the order of steps showing a method for manufacturing the conventional aperture described above.
An opening 62a having a desired pattern is formed in the pattern portion 62 of the silicon substrate 61 by applying photolithography and dry etching. Here, the opening 62a
Is 20 μm (FIG. 6A). Next, the entire surface is covered with a silicon nitride film 63, and a photoresist 64 having a desired opening pattern is formed on the back surface of the substrate [
FIG. 6 (b)]. When the silicon nitride film 63 is selectively removed using the photoresist 64 as a mask, and then the substrate is etched from the back side using an isotropic wet etching method, the pattern portion 62 is formed to have a thickness of 20 μm. [FIG. 6 (c)]. Finally, the silicon nitride film 63 is removed, and an Au layer 65 for preventing charge-up is formed on the substrate surface.
Is formed (FIG. 6D). The thickness of the silicon substrate 61 is 500 μm, and although the above document does not describe the thickness of the Au layer 65, it is currently about 0.5 μm. [0005] It is extremely important to form a through-hole pattern of an aperture with high precision because it is directly related to the precision of a pattern drawn on a sample (a wafer or the like). In the conventional aperture for an electron beam lithography apparatus described above, an opening pattern (a later through-hole pattern) is formed by a resist process and a dry etching method in consideration of processing workability and accuracy. It is difficult to form an opening with a depth of about 20 μm while keeping the angle at 90 degrees. In particular, in an old model etching apparatus having a low degree of vacuum and low temperature control accuracy, if the etching depth exceeds 15 μm, it becomes extremely difficult. The reason why the opening is formed in a shape that does not match the mask pattern (photoresist pattern) is as follows. In the etching process, etching and deposition are performed simultaneously in parallel.
With an opening as deep as 0 μm, the deposition becomes uneven at the top and bottom, making it difficult to form the side walls vertically. Since the selectivity of silicon to resist etching is about 20 and not very high, as the etching proceeds, the mask itself is also etched and the mask shape becomes trapezoidal. This shape reflects the opening of the silicon and is tapered. For this reason, even if processing is performed using the present best technology, a taper of about 88 to 89 degrees is formed. Such a decrease in the precision of the opening can reduce the depth of the opening (the substrate thickness of the pattern portion) by 20.
It can be improved by setting it to μm or less. In the case where a metal film having a thickness of about 0.5 μm is formed on a substrate having a thickness of 20 μm as in the conventional example, when the acceleration voltage of electrons is 50 kV, the electron beam It is the limit thickness that can be cut off. Therefore, the opening In this case, the limit of the electron shielding capability is exceeded, and a pattern with high resolution cannot be drawn. Therefore, when the thickness of the substrate is reduced, it is conceivable to increase the thickness of the metal film. However, if the metal film is simply made thicker with the conventional structure, stress concentration occurs due to the difference in thermal expansion coefficient between the metal and silicon, and the metal film is easily peeled off by electron beam irradiation. Further, in the conventional aperture, the metal film is provided only on the front surface side of the substrate, so that there is a problem that the back surface of the substrate is easily charged up. When the back surface of the substrate is charged up, the electron beam is bent by the charge, and accurate drawing cannot be performed. The present invention has been made in view of such a situation, and an object of the present invention is to firstly provide an aperture having a highly accurate pattern. Second, the ability to cut off the electron beam is enhanced, third, the separation of the metal film can be prevented, and fourth, charge-up can be prevented and accurate drawing can be performed. It is to be. According to the present invention, there is provided an aperture for an electron beam writing apparatus for shaping an electron beam emitted from an electric gun into a desired shape. It has a base material constituting the aperture body and a metal film formed on both front and back surfaces of the base material, the thickness of the base material, and the total film thickness of the metal films formed on both front and back surfaces Are selected so as to block the passage of electrons accelerated by an acceleration voltage in a writing apparatus in which the aperture is used, and an aperture for an electron beam writing apparatus. In the aperture of the present invention, based on the inventor's recognition that the metal film provided on the back surface of the substrate is equivalent to the metal film provided on the surface of the substrate with respect to the electron beam shielding ability, Metal films are provided on both sides. Accordingly, when the thickness of the substrate in the pattern portion is reduced, the thickness of the metal film does not need to be extremely large. Since the metal film is relatively thin and formed on both surfaces to relieve stress, the metal film is less likely to peel. Also, since the substrate can be made thinner,
The processing accuracy is increased, and the accuracy of the aperture pattern can be increased. In particular, when the film thickness of the substrate is 15 μm or less, necessary pattern accuracy can be ensured without using an expensive latest etching apparatus. Further, since the metal film is also formed on the back surface of the substrate, it is possible to prevent charge-up on the back surface of the substrate. Next, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a view for explaining an embodiment of the present invention, and shows the density of a metal film (Au) and the film thickness of a metal film when writing is performed under the condition of an acceleration voltage of 50 kV by incident electrons of a Gaussian beam. FIG. 11 is a diagram illustrating a simulation (Monte Carlo method) result of a relationship between a thickness and a required aperture thickness (silicon substrate thickness: shown as incident electron arrival depth in the drawing). The achievable density of Au is about 10.0 to 18.9 (g / cm3), which is usually about 70% or more of the bulk density (19.3 g / cm3).
g / cm 3), when the substrate thickness is 20 μm, the required metal film thickness is 0.55 μm, and when the substrate thickness is 15 μm, the required metal film thickness is 1.47 μm.
m. In addition, it can be seen from the figure that the higher the density of the metal film, the thinner the film. Even if the metal film is made of a material other than Au, the metal film may have the same thickness as long as it has the same density. FIG. 2 is a graph showing the results of a simulation (Monte Carlo method) of the relationship between the required rear metal film thickness, the silicon substrate thickness, and the metal film density when the Au film thickness on the front surface is fixed at 1.0 μm. According to FIG. 2, when a metal film having a film thickness t (depending on the density of the metal) is divided into a surface (film thickness t1) and a back surface (film thickness t2) of the aperture, the film thickness t = t1 + t2 may be obtained. confirmed. When an Au layer is used as a metal film, for example, a Ti layer, a W layer, or the like serving as a barrier is formed between the silicon substrate and the Au layer at a thickness of about 500 °, and the thickness of the Au itself is accordingly thin. it can. However, for the sake of simplicity, the description of the film thickness assumes that other metals are converted to Au, and that the whole is formed of Au. FIG. 3 is a sectional view showing a first embodiment of the present invention. As shown in the figure, on the surface of a silicon substrate 31, a base metal layer 32a made of Ti and Au
A metal film 33a made of Ti is formed, and a base metal layer 32b made of Ti and a metal film 33b made of Au are similarly formed on the back surface of the substrate. In this embodiment, the thickness of the substrate in the pattern portion 34 is 15 μm, and an opening 34 a having a desired shape is formed here. Referring to FIG. 1, if the density of the metal film is 13.5 g / cm 3,
The required film thickness of the metal film is required to be about 1.5 μm, which corresponds to the surface (33a).
For example, if the thickness of the front surface metal film 33a is 0.75 μm, the thickness of the rear surface metal film 33b is 0.75 μm. Also, if the density of the metal film is 18.9 g / cm 3 (it is actually difficult to form such a high-density Au film), the total thickness of the metal film is as shown in FIG. It is required that the thickness be about 1.0 μm.
When the thickness is set to 50 μm, the thickness of the metal film 33b on the back surface becomes 0.50 μm. FIG. 4 is a sectional view showing a second embodiment of the present invention. In this figure, parts common to those of the first embodiment shown in FIG. In the example, the thickness of the substrate in the pattern section 44 is set to 12 μm. In this case, the total thickness of the metal films 43a and 43b needs to be about 2.0 μm from FIG.
5 g / cm 3), and the thickness of the surface-side metal film 43a is set to 1.0
If the thickness is set to μm, the thickness of the metal film 43b on the back surface may be 1.0 μm. Although the preferred embodiments have been described above, the present invention is not limited to the above-described embodiments, and various changes can be made without departing from the spirit of the present invention. For example, in the embodiment, Au is used as the metal film and the underlying layer is a Ti film.
Although a layer was used, it is not limited to this material. For example, Ti, Ta
, TiW, W, Cu, Ag, Al-Si-Cu, etc., can be used alone or together with the underlayer. . Further, in the embodiment, an example in which the metal film on the front surface side and the metal film on the back surface side have the same film thickness is described. However, it is not always necessary to make such a case. For example, the metal film on the front surface side is thicker. It can also be formed. The aperture for an electron beam writing apparatus according to the present invention can be applied to both the first aperture and the second aperture (see FIG. 5). As described above, the aperture for the electron beam lithography apparatus according to the present invention has the following effects because the metal film is formed on both the front and back surfaces of the substrate. By forming the metal film on both sides of the substrate, the same electron beam shielding ability can be secured as compared with the case where the metal film is formed on only one side, but the metal film on each side can be made thinner, and the stress can be reduced. Because of the relaxation, the peeling of the metal film can be prevented. Since the total thickness of the metal film can be increased, the thickness of the substrate in the pattern portion can be reduced. That is, since the etching depth when forming the opening as the pattern rod can be reduced, it is possible to provide a highly accurate aperture. In particular, when the substrate thickness of the pattern portion is set to 15 μm or less, a high-accuracy pattern can be formed even by using an inexpensive old model etching apparatus. it can. Since charge-up on the back surface of the substrate can be prevented, the beam is not bent by this charge, and a pattern can be drawn accurately.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram illustrating a density of a metal film, a thickness of a metal film,
9 is a graph showing a simulation result of a relationship between an electron beam and a depth reached in a substrate. FIG. 2 is a graph for explaining an embodiment of the present invention, showing a simulation result of a relationship between a substrate thickness and a required thickness of a back metal film when the thickness of a metal film on the front surface is fixed. . FIG. 3 is a sectional view showing a first embodiment of the present invention. FIG. 4 is a sectional view showing a second embodiment of the present invention. FIG. 5 is a conceptual diagram schematically showing an electron beam drawing apparatus. FIG. 6 is a sectional view in order of process for explaining a manufacturing method of a conventional example. DESCRIPTION OF SYMBOLS 31, 41, 61 Silicon substrates 32a, 32b, 42a, 42b Base metal layers 33a, 33b, 43a, 43b Metal films 34, 44, 62 Pattern portions 34a, 44a, 62a Opening 51 Electron gun 52 First Aperture 53 Deflector 54 Second aperture 55 Reduction lens 56 Projection lens 57 Wafer 63 Silicon nitride film 64 Photoresist 65 Au layer

Claims (1)

Claims 1. An aperture for an electron beam lithography apparatus for shaping an electron beam emitted from an electron gun into a desired shape, comprising: a base constituting an aperture main body; Having a metal film formed on both the front and back surfaces, the film thickness of the base material, and the total film thickness of the metal films formed on the front and back surfaces are accelerated by an acceleration voltage in a drawing apparatus using the aperture. An aperture for an electron beam writing apparatus, which is selected so as to be able to block the passage of electrons. 2. The aperture for an electron beam lithography apparatus according to claim 1, wherein said base material is formed of single crystal silicon. 3. The aperture for an electron beam lithography apparatus according to claim 1, wherein said metal film is formed by a base layer and an Au layer formed on said base layer. 4. The method according to claim 1, wherein the metal film is made of Ti, Ta, TiW, W, Cu, Ag or A.
The aperture for an electron beam lithography apparatus according to claim 1, wherein the aperture is formed of a metal layer mainly composed of l-Si-Cu.