Radiation imagery chemistry: process – composition – or product th – Registration or layout process other than color proofing
Reexamination Certificate
2000-12-07
2002-08-20
Young, Christopher G. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Registration or layout process other than color proofing
C430S030000, C430S296000, C430S942000
Reexamination Certificate
active
06436594
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to an electron-beam exposure method and, more particularly to, such the electron-beam exposure method as to perform electron-beam exposure by correcting an exposure position when a pattern is directly drawn on a semiconductor wafer using an electron-beam exposure apparatus.
The present application claims priority of Japanese Patent Application No. Hei 11-351080 filed on Dec. 10,1999, which is hereby incorporated by reference.
2. Description of the Related Art
FIG. 6
shows an electron-beam exposure apparatus to which a conventional electron-beam exposure method is applied.
An electron-beam exposure apparatus
100
comprises an electron gun
101
for emitting an electron-beam, a first aperture
102
for restricting an amount of the electron-beam emitted from the electron gun
101
, the beam shaping deflector
103
for deflecting the electron-beam from the first aparture
102
, a second aperture
104
for further restricting an amount of the electron-beam from the beam shaping deflector
103
, a reducing lens
105
for reducing the electron-beam from the second aperture
104
, an objective lens
106
for focusing, for image formation, the electron-beam from the reducing lens
105
on a semiconductor wafer, (hereinafter simply to as wafer)
200
, an alignment deflector
107
(main deflector) disposed inside the objective lens
106
, for deflecting the electron-beam in a predetermined direction, a reflected electron detector
108
for detecting an electron reflected from the surface of the wafer
200
, an X/Y stage
109
for loading thereon the wafer
200
to position it in X-axis direction and Y-axis direction, a cabinet
110
for housing all of these components, a alignment deflector control unit
111
for controlling the alignment deflector
107
, and a stage control unit
112
for controlling the X/Y stage.
The reflected electron detector
108
uses a diode detector to trap a reflected electron (that is, secondary electron) from the reflective wafer surface when electrons are applied onto an alignment mark formed as a recess in the wafer
200
, thus detecting a position of the alignment mark based on a difference between an amount of reflection from the alignment mark and that from its surrounding.
A pattern of the electron-beam from the electron gun
101
is determined through the first and second apertures
102
and
104
having their respective predetermined shapes of openings and the beam shaping deflector
103
and is reduced by the reducing lens
105
to a 1
scale and then focused by the objective lens
106
onto the wafer
200
. In addition, the electron-beam is positioned by the alignment deflector
107
and applied onto the wafer
200
set on the X/Y stage
109
. This wafer
200
is positioned to a predetermined place by the X/Y stage
109
. The beam shaping deflector
103
, the objective lens
106
, the alignment deflector
107
, or like are adjusted using a reference pattern (not shown) provided on the X/Y stage
109
. Drawing pattern data or like are stored in a memory
113
or
114
or a dedicated memory (not shown) or like. The alignment deflector
107
uses the drawing pattern data read out, to thereby control the alignment deflector
107
, so that a scanning electron-beam (that is, electron-beam deflected corresponding to the drawing pattern data) may be deflected by the alignment deflector
107
, thus drawing a pattern. At this point in time, on the wafer
200
, the alignment mark formed thereon has been scanned by the scanning electron-beam prior to pattern drawing, and a resultant reflected electron is detected to thereby find the position of the alignment mark. The alignment mark is thus found and, based on this, the pattern is drawn, to provide drawing on a desired place on the wafer
200
, thus avoiding misalignment even in a case where a plurality of drawing patterns is superposed one on top of another.
FIG. 7
shows a plurality of alignment marks provided on the wafer
200
.
FIG. 8
, on the other hand, shows a waveform of a detection signal obtained by the reflected electron detector
108
. An alignment mark
201
is cross shaped. The alignment mark
201
is detected when it is scanned by a scanning electron-beam
202
in both X-axis and Y-axis directions in the FIG.
8
. When the alignment mark
201
is thus detected, then the wafer
200
is moved by the X/Y stage so that the alignment mark
201
may be positioned at a deflection center of the electron-beam. The alignment mark
200
is scanned actually, for example, by the electron-beam shaped into approximately a 1 &mgr;m×1 &mgr;m square (may be rectangular) through the first and second apertures
102
and
104
and also by the beam shaping deflector
103
. During the scanning, a reflected electron resulting from electron-beam scanning is detected by the reflected electron detector
108
. In this case, based on differences in step or material of the alignment mark
201
, various reflected electron signals are obtained, such as that having a detected waveform
203
(obtained by X-axis directional scanning) shown in FIG.
8
. Such reflected electron signal can be differentiated and then processed by an edge method or a symmetry method, to determine location of the alignment mark.
When a plurality of alignment marks such as shown in
FIG. 7
is detected, based on the results of detection a shift in chip layout, a gain (magnification), and a rotation (degree of rotation) are calculated. An error in a chip array is corrected based on these calculation results. This method is referred to as a global alignment method. At a same time, as necessary, a mark at four corners of a chip is also detected, to correct chip shape. Following this alignment, the pattern is projected onto the wafer
200
under exposure.
In a case of electron-beam exposure, however, during exposure a drift in position of the scanning electron-beam
202
may develop due to charge-up (charging of vaporized resist when it is stuck to an inner wall) of a column (lens-barrel), fluctuations in an external magnetic field, wafer charge-up (charging due to electron-beam irradiation), or like.
FIG. 9
shows an example of positional drift of the scanning electron-beam
202
. A dotted line indicates a case with no positional drift and a solid line, a case with positional drift. Misalignment in superposing occurs if an amount of positional drift of the scanning electron-beam
202
is not negligible during a time from termination of detection of the alignment mark
201
to termination of exposure.
One proposal to solve this problem is disclosed in Japanese Patent Application Laid-open No. Sho 61-142740. By this electron-beam exposure method, a position detecting mark is set on the chip beforehand and is used to perform first positional detection, which is followed by electron-beam exposure onto the chip to subsequently perform second positional detection, to obtain drift amount in position between first and second positional detection operations, based on which drift amount is calculated an exposure-position correction amount as a time-wise function of exposure processing so that it may be reflected on a next operation of electron-beam exposure.
Also, a method of correcting exposure position by detecting a plurality of standard marks provided on the X/Y stage is disclosed in Japanese Patent No. 2788139 (Japanese Patent Application Laid-open No. Hei 5-84246). This method is described as follows.
FIG. 10
shows an electron-beam exposure method by use of the above-mentioned standard marks.
First, a wafer is set on an X/Y stage in an electron-beam drawing apparatus (step
301
). Next, a plurality of standard marks (reference marks) formed on the X/Y stage is detected by electron-beam exposure, to store in a memory thus detected position of the standard marks (step
302
). Based on detected results of the standard marks (shift amount, magnification, rotation amount, and other conditions), a correction factor is calculated, based on which is performed alignment (step
303
).
NEC Corporation
Young Christopher G.
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