Radiant energy – Inspection of solids or liquids by charged particles – Electron probe type
Reexamination Certificate
1998-07-20
2001-01-09
Anderson, Bruce C. (Department: 2881)
Radiant energy
Inspection of solids or liquids by charged particles
Electron probe type
C250S398000, C250S505100, C250S515100
Reexamination Certificate
active
06172364
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a charged particle beam irradiation apparatus for use in the writing and measurement of a micropattern on a semiconductor device and, in particular, a charged particle beam irradiation apparatus having an improved reflection prevention board over a sample surface.
In the lithography process of the-state-of-the-art semiconductor manufacturing process, it is expected that an electronic beam writing type will become a future main-stream technique. The reason is that the electron beam writing method is outstandingly higher in image resolution than the light beam writing method.
The electronic beam writing apparatus is used for forming an etching mask on a sample for example. As shown in
FIG. 1
, an electron beam narrowly stopped down by an objective lens
61
is directed onto a resist
62
coated on a sample
63
, such as a mask, a wafer, etc., and the resist
62
is scanned with the electron beam. A pattern is formed on the resist
62
. And an etching mask is completed by doing so.
A portion of the electron beam thus directed for irradiation is reflected on the surface of the sample
63
. Secondary electrons are produced from the sample
63
. Some of the reflected electrons and secondary electrons
73
are reflected on the lower surface of the objective lens
61
and back onto the resist
62
, resulting in an error occurring on the resist
62
. Those reflected and secondary electrons
74
returned back onto the resist
62
are light-sensitized at other than a target location, resulting in a lowering in writing precision. In order to reduce such an error, a reflection prevention board is attached to the lower surface of the objective lens
61
, the sheet being made of a material of a lower atomic number, such as a carbon.
As a demand for a write precision becomes higher and higher, no adequate reflection preventing effect is obtained from the reflection prevention board made of the lower atomic number material. In order to improve the reflection prevention effect, proposals are made to provide a reflection prevention board with microholes opened perpendicular to the sheet. Further, as shown in
FIG. 2
, a proposal is also made to provide a honeycomb type reflection prevention board with a dense array of hexagonally prismatic microholes.
However, the proposed reflection prevention board has the following problems (1) and (2):
(1) The deeper the microholes in the reflection prevention board, that is, the thicker the reflection prevention board, the higher the reflection prevention effect. In general, with the microhole diameter set to 0.8 mm, at least 4 mm-thick sheet is preferable as the reflection prevention board. It is difficult, however, to form a regular honeycomb array of microholes in such a thick metal sheet by the mechanical working technique. And more working time is taken and, in spite of this, a poor yield and a very high manufacturing cost result. A proposal is also made to use the technique for metal-plating those holes in a thick-film resist patterned by an LIGA process, that is, the X-ray lithography. The LIGA process involves the problem of the reflection prevention board involving an upper size limitation and very high manufacturing cost.
(2) The conventional reflection prevention board can effectively prevent those vertically incident reflection electrons and secondary electrons. As shown, for example, in
FIG. 3
, it is not possible to effectively prevent those obliquely incident reflection electrons and secondary electrons. The reason is that the obliquely incident reflection electrons are reflected on the sidewall of the microhole and bounced out of the microhole.
As seen from the above, the existing reflection prevention board used in the electron beam writing apparatus presents the problems of being high in manufacturing cost, being unable to provide deeper microholes and being unable to effectively preventing the obliquely incident reflection electrons and secondary electrons.
BRIEF SUMMARY OF THE INVENTION
It is accordingly the object of the present invention to provide a charged particle beam irradiation apparatus which can prevent re-reflection of reflected particles/secondary particles at a lower manufacturing cost.
Another object of the present invention is to provide a charged particle beam irradiation apparatus which can effectively prevent re-reflection of reflected particles/secondary particles obliquely incident to a reflection prevention board.
A reflection prevention board of a charged particle beam irradiation apparatus of the present invention is comprised of a laminate sheet of thin films and a plurality of microholes formed therein. According to the present invention, the reflection prevention board can be manufactured at a lower cost. The reason is that it is very easier to form microholes in the thin films and then laminate these thin films in an aligned sheet than to form microholes in a thick board. By doing so, it is possible to improve a yield. Further, much deeper microholes, which might not otherwise be achieved on a thick board, can be formed by using more thin films.
In the charged particle beam irradiation apparatus of the present invention, a reflection prevention board is so formed as to have a plurality of inclined microholes therein. In this case, reflected particles and/or secondary particles obliquely incident to the reflection prevention board goes more deeply into the microholes so that a reflection prevention effect is improved.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.
REFERENCES:
patent: 4288697 (1981-09-01), Albert
patent: 4493097 (1985-01-01), Clayton
patent: 4845402 (1989-07-01), Smith
patent: 5012080 (1991-04-01), Griscom
patent: 5266802 (1993-11-01), Kasai
patent: 5362964 (1994-11-01), Knowles et al.
patent: 5569920 (1996-10-01), Phang et al.
K.K. Christenson, et al. “X-ray Mask Fogging by Electrons Backscattered Beneath the Membrane”, J. Vac. Sci. Technol. B 8(6), Nov./Dec. 1990, pp. 1618-1623.
Abe Takayuki
Itoh Masamitsu
Ogasawara Munehiro
Shimomura Naoharu
Takamatsu Jun
Anderson Bruce C.
Kabushiki Kaisha Toshiba
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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