JP2785790B2 - Aperture mask for charged particle beam exposure apparatus and method of manufacturing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aperture mask of a charged particle beam exposure apparatus used for manufacturing a semiconductor integrated circuit or a mask for forming an integrated circuit, and more particularly to a variable shaped electron beam for controlling a beam shape by a plurality of aperture masks. The present invention relates to an aperture mask of an electron beam lithography system of a partial batch exposure type having an lithography system and an aperture mask corresponding to a plurality of pattern shapes.

[0002]

2. Description of the Related Art In recent years, in order to improve the density and speed of a semiconductor integrated circuit, the size of each element of the semiconductor integrated circuit has been reduced. In order to miniaturize the element size, in an optical exposure apparatus utilizing ultraviolet light, a light wavelength used, a high NA (numerical aperture), an optical improvement of an exposure apparatus such as a deformed light source, a phase shift mask, and the like are required. New types of exposure methods are being studied. In parallel with this, development of a new exposure method such as electron beam or X-ray exposure is being promoted. In particular, various attempts using electron beam exposure have been proposed for forming an integrated circuit having a fine pattern such as a 256 Mbit DRAM.

[0003] These electron beam exposure apparatuses are classified into a point beam type and a variable rectangular beam type. In each case, the pattern is divided into unit small areas or rectangular areas, and the point beam is deflected and scanned, or according to the pattern. Since a pattern is exposed by one-stroke drawing by deflecting an electron beam having a beam spot having a large size, a long time is required for the exposure. For example, the 256 Mbit DRAM
In such a case, the exposure time per chip takes about 10 minutes, and the exposure time is required to be about 100 times longer than the optical exposure method. Another problem is that the exposure apparatus itself is more expensive than the optical exposure apparatus.

[0004] MBHeritage: Electron-projection micro
fabrication system, J.Vac.Technol., Vol.12, No.6, Nov.
/ Dec. (1975) 1133 discloses that in order to shorten the above-mentioned exposure time, a mask including a pattern corresponding to the entire memory chip is prepared and the entire chip is exposed by one electron beam irradiation. This is a study of a method for doing so.
However, since it is difficult to realize an electron optical system that guarantees sufficient accuracy over the entire surface of a chip having a size of several mm square or more, it has not been put to practical use.

Further, Japanese Patent Laid-Open No. 52-119185,
Or "Study of electron beam batch figure irradiation method-Part 1;
Electron Optics-Takashi Matsuzaka and others "" Study of electron beam batch figure irradiation method-Part 2; Aperture creation-", Yoshinori Nakayama and others, all 50th Proceedings of the 50th JSAP, 27a-K -6 (1989) 452, is a method of transferring a part of a repetitive pattern instead of the entire chip, and making the current density uniform among the periodic patterns in the chip. A partial area large enough to correspond to a beam spot large enough to be kept is prepared as a transmission aperture mask to shorten the exposure time, and the configurations of the electron optical system and the mask are realistic. Therefore, development as a mass production device is being advanced.

FIG. 3 is a schematic view showing a partial batch exposure method, in which an electron beam emitted from an electron gun 31 as an electron source is applied to a first aperture mask 32 to form a rectangular shape. A beam formed by irradiating an opening of an arbitrary shape on the second aperture mask 34 is reduced on a sample wafer 37 by a reduction lens 35 and a projection lens 36 to draw a pattern. However, in such a partial batch exposure type exposure apparatus, the mask pattern of the aperture mask is deformed and deteriorated by long-term use, and if used as it is, the pattern shape dimension on the wafer changes,
There is a problem that high-precision pattern drawing cannot be performed. Such deterioration is caused by the fact that the temperature of the metal used as the mask constituent material rises due to the irradiation of the electron beam, and the metal electrons move.

As a technique for preventing the temperature of the transmission aperture mask from increasing due to beam irradiation, which causes such mask pattern deformation, there is a technique in which the aperture mask is provided with means for heat shielding or heat radiation. For example, Japanese Unexamined Patent Publication
FIG. 4 shows the one described in Japanese Patent No. 5499.
In this technique, the first and second aperture masks are:
Each of them is constituted by two apertures of a beam limiting shielding aperture stop 41 and a transmission aperture mask 42 which are separately manufactured. 2 apertures 4
The distance between the reference numerals 1 and 42 is fixed to about 1 cm, and each is fixed to the fixing frame 43 using a conductive adhesive. The transmission aperture mask 42 is formed of a silicon single crystal substrate, and the shielding aperture stop 41 is formed of molybdenum in the first aperture mask and is formed of a silicon single crystal substrate in the second aperture mask. In this technique, the transmission aperture max.
Since the incident electrons that do not pass through the second aperture 2 are previously blocked by the upper beam-shielding aperture stop 41, the temperature of the transmission aperture mask 42 can be prevented from rising.

Further, as a technique proposed by the present applicant, there is a technique described in Japanese Patent Application No. 6-142233. As shown in FIG. 5, a concave portion 54 is formed on the back surface of a silicon substrate 51 which is a base of a transmission aperture mask, the portion is formed thin, and a pattern opening 55 is formed in the thin portion. I have. Further, metal films 52 and 53 are formed on the front and back surfaces of the silicon substrate 51, respectively.
Is formed, and the temperature rise of the base body 51 can be suppressed by the beam reflection and the heat shielding effect by the metal films 52 and 53.

[0009]

In these prior arts, the latter technique using a metal film cannot completely suppress the heat generation of the silicon substrate itself constituting the transmission aperture. Further, in the technique disclosed in the latter publication, since the beam limiting shielding aperture stop is formed by processing a silicon substrate having a thickness of several tens of microns, the processing accuracy is about 1 μm. Since it is necessary to design the opening size of the shielding aperture stop larger than the opening size of the transmission aperture mask by the processing accuracy, a part of the electron beam transmitted through the shielding aperture stop for beam limitation is absorbed by the transmission aperture mask. This may cause a rise in the temperature of the transmission aperture mask.

According to the technique described in the latter publication, when positioning the transmission aperture mask and the beam-limiting shielding aperture stop above the transmission aperture mask, it is necessary to manually fix the positions while observing both with a microscope. Therefore, there is also a problem that it takes time to perform the alignment. Furthermore, since the transmission aperture mask and the beam-limiting shielding aperture stop are arranged at an interval of about 1 cm, there is also a problem that it is difficult to increase the positioning accuracy by visual alignment using a microscope as described above. is there. Also,
In this case, the adhesive bonding the two apertures to the fixed frame becomes a gas generation source, contaminates the inside of the electron optical column which requires a high degree of vacuum, and generates the electron beam and the efficiency of the electron optical system. Performance may be degraded.

SUMMARY OF THE INVENTION An object of the present invention is to provide an aperture mask for a charged beam exposure apparatus capable of performing high-accuracy alignment without requiring the trouble of alignment, and a method of manufacturing the same. is there.

[0012]

According to the present invention, there is provided an aperture mask having a transmission aperture mask having a pattern opening for forming a pattern shape for exposure, and a predetermined interval provided on the surface of the transmission aperture mask. And a shielding aperture stop formed integrally and formed of a metal film having an opening corresponding to the pattern opening. Here, it is preferable that a metal film is integrally formed on each of the front surface and the back surface of the aperture mask.
In addition, it has a metal aperture mask holder formed in a tubular shape, the transmission aperture mask and the shielding aperture stop are internally fixed inside the aperture mask holder, and the shielding aperture stop is brought into contact with the aperture mask holder. Preferably. Further, it is preferable that the shielding aperture stop and the aperture mask holder are connected by a connecting line for heat radiation.

According to the method of manufacturing an aperture mask of the present invention, a first film is formed in a required pattern on a surface of a substrate such as silicon, and the entire surface is etched by a second film having etching selectivity with respect to the first film. Covering the surface of the second film with a metal film for forming a shielding aperture stop, and etching the back surface of the substrate to form a concave portion. Reducing the thickness of the substrate on the bottom surface of the substrate, forming a pattern opening from the metal film to a thin portion of the substrate by photolithography, etching and removing the first film through the pattern opening, And connecting and supporting the substrate and the metal film with the remaining second film.

[0014]

Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing a sectional structure of an aperture mask of the present invention. The metal aperture mask holder 4 is formed in a rectangular tube shape, and the aperture mask 1 is provided inside the aperture mask holder 4, and the aperture mask 1 is fixedly supported by a brazing material (not shown).
The aperture mask 1 includes an upper shielding aperture stop 2 and a lower transmission aperture mask 3, which are integrally formed. That is, the transmission aperture mask 3 is formed mainly of the silicon substrate 11, and its central region is formed thin by the concave portion 14 provided on the back surface, and the pattern opening 15 is provided in this thin portion.

An upper metal film 12 is formed on the front surface of the silicon substrate 11, and a lower metal film 13 is formed on the back surface including the concave portion 14, and the pattern opening 15 including these metal films 12 and 13 is formed. Is provided. And
A columnar support 16 is provided on the surface of the silicon substrate 11, and the columnar support 16 allows the upper metal film 12 to be formed.
And the third metal film 17 is formed at a required interval. The third metal film 17 also has the pattern opening 1.
An opening 18 corresponding to the portion 5 is provided, so that the shielding aperture stop 2 is constituted by the third metal film 17. The shielding aperture stop 2 is connected to a heat radiating connection line 5 made of gold or the like, and is connected to the aperture mask holder 4.

FIG. 2 is a sectional view showing a method of manufacturing the aperture mask 1 of FIG. 1 in the order of steps. First, as shown in FIG. 2A, gold (Au) is formed as an upper metal film 12 on a silicon substrate 11 to a thickness of 1 μm, and a silicon oxide film 19 is further formed to a thickness of 1.5 μm on a silicon substrate 11. Formed. After that, the silicon oxide film 19 is partially removed by a normal photolithography technique and a dry etching technique to leave the silicon oxide film 19 only in a region corresponding to the pattern opening 15. Then, a polysilicon film 20 having a thickness of 2 microns is formed on the entire surface, and a silicon nitride film 21 is formed on the entire upper surface, lower surface, and side surfaces.

Next, as shown in FIG. 2B, after the surface of the silicon substrate 11 is flattened by a CMP (chemical mechanical polishing) technique, a silicon oxide film 19 is formed by a dry etching technique having uniform etching characteristics. Is etched until the surface of appears on the upper surface. Then, a third metal film 17 for shielding aperture stop is formed on the entire surface of the silicon substrate 11.
To form a molybdenum film with a thickness of 1 micron.

Next, as shown in FIG. 2C, the third metal film 17, the silicon oxide film 19, and the upper metal film 12 at the pattern positions of the pattern openings are formed by ordinary photolithography and dry etching. All the layers are removed by etching, and the silicon substrate 11 is further etched to a depth of 8 μm to form an opening 15. Thereafter, a silicon nitride film 22 is formed on the entire surface including the opening 15. Further, after removing a region of the back surface corresponding to the pattern opening 15 from the silicon nitride film 21 remaining on the back surface and the side surface of the silicon substrate 11, the silicon substrate 11 in this region is etched from the back surface side to form a pattern. The recess 14 is formed to a depth where the silicon nitride film 22 formed in the opening 15 is exposed on the back side.

Next, as shown in FIG. 2D, the entire silicon nitride films 21 and 22 are removed, and thereafter, the silicon oxide film 19 is selectively removed by performing wet etching through the pattern opening 15. The columnar support 16 is formed by the polysilicon film 20 left between the pattern openings. Further, a metal film 13 such as gold having a thickness of 1 micron is formed on the back surface of the silicon substrate 11. In this way,
After a desired pattern opening 18 is formed in the uppermost metal film 17 serving as a shielding aperture stop, this opening is used as it is as an opening pattern forming opening in the lower aperture mask main body portion, so that both openings are formed. An aperture mask having a structure with the pattern automatically aligned is formed.

The aperture mask 1 is housed in the holder 4 and is fixed to the holder 4 by the brazing material at the metal films 12 and 13. Also, the metal film 17 and the holder 4
Are connected by a heat-dissipating connection line 5.

Therefore, according to the aperture mask having this configuration, the pattern aperture 18 of the shielding aperture stop 2 is formed.
And the pattern opening 15 of the transmission aperture mask 3 are collectively formed by the photolithography technique, so that the openings 15 and 18 are automatically aligned, and a manufacturing process for alignment is performed. Is not required. Further, since the positioning accuracy is extremely high, the electron beam incident on the transmission aperture mask 3 through the opening 18 of the shielding aperture stop 2 is extremely small, and the temperature rise of the transmission aperture mask 3 is suppressed. In this case, even when the temperature of the transmission aperture mask 3 rises, the heat is transmitted to the peripheral portion by the metal films 12 and 13 provided on the upper and lower surfaces of the silicon substrate 11 and further radiated through the aperture holder 4. Effectively prevent ascent. Incidentally, according to the experiment of the present inventors, it was possible to suppress the temperature rise to 5 ° C. or less.

Further, between the third metal film 17 constituting the shielding aperture stop 2 and the lower transmission aperture mask 3, a pillar-shaped support region of the peripheral portion and a polysilicon film provided between blocks are provided. Since only the support portion 16 exists, the heat generated in the shielding aperture mask 2 is hardly transmitted to the transmission aperture mask 3. Therefore, the heat of the shielding aperture stop 2 is transmitted to the aperture mask holder 4 and is radiated therefrom. Further, since the heat dissipation connection line 5 is connected to the shielding aperture stop 2, heat dissipation by heat conduction to the aperture mask holder 4 is effectively performed.

In the present invention, a molybdenum film is used as a shielding aperture stop. However, the present invention is not limited to this material. For example, a metal film such as titanium, tantalum, tungsten, titanium tungsten, copper, silver, etc. Can be used alone or together with a base film for improving adhesion. It is needless to say that the aperture mask of the present invention can be applied to both the first aperture and the second aperture shown in FIG.

[0024]

As described above, according to the present invention, the shielding aperture stop is formed integrally with the transmission aperture mask by the metal film formed on the surface of the transmission aperture mask, and the shielding aperture stop and the transmission aperture mask are formed. Each pattern opening is integrally formed by photolithography technology, so the work of aligning the pattern apertures of the shielding aperture stop and the transmission aperture max becomes unnecessary, making manufacturing easy and high alignment accuracy. Can be manufactured. Further, the temperature increase in the transmission aperture mask can be suppressed by the high positioning accuracy, and a thermally stable aperture mask can be obtained.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of an aperture mask according to a first embodiment of the present invention.

FIG. 2 is a cross-sectional view showing a method of manufacturing the aperture mask of FIG. 1 in the order of steps.

FIG. 3 is a diagram showing a schematic configuration of an electron beam exposure apparatus to which the present invention is applied.

FIG. 4 is a cross-sectional view of an example of an aperture mask described in a conventional publication.

FIG. 5 is a sectional view of an aperture mask previously proposed by the present applicant.

DESCRIPTION OF SYMBOLS 1 aperture mask 2 shielding aperture stop 3 transmission aperture mask 4 holder 5 radiating connection line 11 silicon substrate 12, 13 metal film 14 recess 15 pattern opening 16 columnar support 17 third metal film 18 opening Part 19 silicon oxide film 20 polysilicon film 21 silicon nitride film

Claims (6)

(57) [Claims] 1. An aperture mask for shaping a charged particle beam into a desired pattern shape, comprising a transmission aperture mask having a pattern opening for forming the pattern shape, and a transmission aperture mask provided on a surface of the transmission aperture mask. An aperture mask for a charged particle beam exposure apparatus, comprising: a shielding aperture stop formed of a metal film having openings corresponding to the pattern openings. 2. The aperture mask for a charged particle beam exposure apparatus according to claim 1, wherein a metal film is integrally formed on each of a front surface and a rear surface of the aperture mask. 3. A metal aperture mask holder having a cylindrical shape, wherein a transmission aperture mask and a shielding aperture stop are internally fixed in the aperture mask holder, and the shielding aperture stop holds the aperture mask. 3. An aperture mask for a charged particle beam exposure apparatus according to claim 1, wherein said aperture mask is in contact with a tool. 4. The aperture mask for a charged particle beam exposure apparatus according to claim 1, wherein the shielding aperture stop and the aperture mask holder are connected by a heat radiating connection line. 5. A step of forming a first film on a surface of a substrate such as silicon in a required pattern, and covering the entire surface with a second film having an etching selectivity with respect to the first film; Forming a metal film for forming a shielding aperture stop on the surface of the film of No. 2 and forming a concave portion by etching the back surface of the substrate, and reducing the thickness of the substrate at the bottom surface of the concave portion. A step of forming a pattern opening from the metal film to a thin portion of the substrate by a photolithography technique; and etching the first film through the pattern opening to remove the remaining second film.
A step of connecting and supporting the substrate and the metal film by the film described in (1). 6. A first metal film is formed on the surface of a silicon substrate, a silicon oxide film is formed thereon in a required pattern, and the entire surface is a polysilicon film having etching selectivity. Covering, forming a second metal film on the entire front and back surfaces of the silicon substrate, flattening the surfaces of the second metal film and the polysilicon film on the surface of the silicon substrate, and shielding an aperture on the surface. Forming a third metal film for forming a silicon substrate, etching the second metal film on the back surface of the silicon substrate and the silicon substrate to form a concave portion, and reducing the thickness of the silicon substrate at the bottom surface of the concave portion. Forming a pattern opening from the third metal film to the first metal film or a thin portion of the silicon substrate by photolithography; A step of etching the silicon oxide film through a hole opening and connecting and supporting the silicon substrate and a third metal film with the remaining polysilicon film. Of manufacturing aperture mask for use.