Electron beam lithography system and method

Details Electron beam lithography system and method Electron beam lithography system and method

2001-11-09

2003-08-12

Lee, John R. (Department: 2881)

Radiant energy

With charged particle beam deflection or focussing

Magnetic lens

C250S39600R, C250S310000, C250S311000, C250S397000

Reexamination Certificate

active

06605811

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Technical Field of the Invention
The present invention relates to an electron beam lithography system and a method for applying a narrowly converged electron beam to a specimen substrate such as a semiconductor substrate to write a pattern thereon, and more particularly to an apparatus and a method for deflecting an electron beam in an electron beam lithography system.
2. Description of the Related Art
In an electron beam lithography system, a narrowly converged electron beam is scanned and applied sequentially to target positions on a specimen substrate to form a pattern thereon. As shown in
FIG. 1
of the accompanying drawings, an electron beam lithography system comprises an electron optical column
1
, a specimen chamber
6
, and a control system
9
. The electron optical column
1
has an electron gun
2
, at least one of electromagnetic lenses
3
and
4
, and at least two deflectors
5
. Each of the two deflectors
5
deflects an electron beam in the X and Y directions, and comprises deflection plates, a deflection amplifier, and a deflection power supply, and the like. The electron optical column
1
has a function for converging an electron beam emitted from the electron gun
2
to be smaller by the electromagnetic lenses
3
and
4
, deflecting the electron beam by the deflectors
5
which apply electromagnetic forces, and applying the electron beam to a substrate
8
at a desired position on its surface. Further, the electron optical column
1
has a blanking function for blocking the electron beam in response to an external signal. The electron beam lithography system is capable of writing graphic patterns on a substrate by the focusing, deflecting, and blanking functions of the electron beam in the electron optical column
1
. In the specimen chamber
6
, there are provided a specimen stage
7
for holding the substrate
8
and moving the substrate
8
, and a measuring mechanism (not shown) for measuring the position of the specimen stage
7
. The control system
9
has a function for controlling the overall apparatus including the electron optical column
1
, the specimen stage
7
, and the like by a computer, and controlling a deflection amount of the electron beam and the position of the substrate in a pattern writing process.
The electron beam lithography process is such a process that a desired graphic pattern is written by deflecting the electron beam
10
with the deflectors
5
to apply an appropriate amount of electric charges to only necessary portions of an electron beam resist which has been coated on the surface of the substrate
8
, as shown in FIG.
2
. Applying an electron beam to an electron beam resist and exposing the electron beam resist is referred to as electron beam exposure, and a rectangular region swept by an electron beam is referred to as a field.
Processes of deflecting an electron beam include a raster-scan process and a vector-scan process. According to the raster-scan process, one field is sequentially and fully scanned from one end to the other at the same speed, and the electron beam is applied to only an area where a graphic pattern is to be written and is blocked for an area where no graphic pattern is to be written by a blanking mechanism. This process is disadvantageous in that it wastes a long period of time because the electron beam is deflected in the area where no graphic pattern is to be written.
According to the vector-scan process, the electron beam is not applied to, but skips, an area where no graphic pattern is to be written, and the electron beam is deflected only in an area where a graphic pattern is to be written. While this process is advantageous in that the electron beam is not applied to, but skips, the area where no graphic pattern is to be written, it requires a period of time limited by the frequency band of the deflection amplifier to move the electron beam from a position where writing of one graphic pattern finishes to a position where writing of a next graphic pattern starts. Therefore, if one field contains many small graphic patterns, then a waiting time required for the electron beam to move from a graphic pattern to another graphic pattern increases.
Noise of an electronic circuit can be represented in the following:
N=K×V
max×
f
1/2  (1)
Where,
N . . . noise voltage,
Vmax . . . maximum value of the operating voltage of the electronic circuit,
f . . . frequency band, and
K . . . proportionality constant.
In the raster-scan process, the frequency band can be limited because the deflection direction, the deflection amount, and the deflection speed of the electron beam are constant. Therefore, the noise of the deflection amplifier can be reduced. In the vector-scan process, however, the deflection direction, the deflection amount, and the deflection speed of the electron beam are not constant depending on the graphic pattern to be written. After one graphic pattern has been written, it is necessary to move the electron beam quickly to a position where writing of a next graphic pattern starts. In order to lower the noise of the deflection amplifier to a certain value or less, the frequency band needs to be limited to a low frequency range, and there is a limit to acceleration of travel time of the electron beam.
In a conventional electron beam lithography system based on the vector-scan principle, when a solid graphic pattern is written, as shown in
FIG. 3
, the electron beam is scanned by a given width in the X direction, and thereafter deflected slightly in the Y direction and then scanned by the given width in the X direction. That is, the electron beam is deflected several times to fully scan a desired field in the X and Y directions.
FIGS. 4A and 4B
are graphs showing deflection signals in the X and Y directions for drawing the rectangular graphic pattern shown in FIG.
3
.
FIG. 4A
shows an X deflection signal and
FIG. 4B
shows a Y deflection signal. In
FIGS. 4A and 4B
, the horizontal axis represents time and the vertical axis represents the deflection signal (voltage signal). In this process, because the frequency band of the deflection signal (voltage signal) is limited to a low frequency range, the deflection speed of the electron beam is low, thereby requiring a long period of time to write the graphic pattern.
In order to solve the above problem, there has been proposed a method in which the deflection signal is divided into a main signal (voltage signal) having a low frequency and a large amplitude, and an auxiliary signal (voltage signal) having a high frequency and a small amplitude, whereby the electron beam is deflected in a large area by the main signal, and in a small area by the auxiliary signal. Because the noise of the signal is expressed by the equation (1), the overall noise can be reduced by dividing the deflection signal in this manner. According to a specific process, as shown in a conceptual view of
FIG. 5
, there has been proposed a method in which deflection plates dedicated for the main signal and the auxiliary signal are used. In the process shown in
FIG. 5
, main deflection plates
5
-
1
,
5
-
2
and auxiliary deflection plates
5
-
3
,
5
-
4
are provided. A main signal generator
11
and a main signal amplifier
13
are connected to the main deflection plates
5
-
1
,
5
-
2
, and an auxiliary signal generator
12
and an auxiliary signal amplifier
14
are connected to the auxiliary deflection plates
5
-
3
,
5
-
4
. In
FIG. 5
, only the main deflection plates
5
-
1
,
5
-
2
and the auxiliary deflection plates
5
-
3
,
5
-
4
for use in one direction, e.g., the X direction (or the Y direction) are illustrated. This method is disclosed in Japanese patent publication No. 1-52894, Japanese laid-open patent publications Nos. 57-90858, 11-224636, and 6-19639, for example. However, the method shown in
FIG. 5
is problematic in that because the number of deflection plates increases, the spatial efficiency of the electron optical system is lowered.
According to another method, as shown in a concept

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