Radiant energy – Irradiation of objects or material – Irradiation of semiconductor devices
Reexamination Certificate
2002-05-22
2003-09-23
Berman, Jack (Department: 2881)
Radiant energy
Irradiation of objects or material
Irradiation of semiconductor devices
C430S005000, C250S491100
Reexamination Certificate
active
06624430
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to methods of measuring and calibrating inclination of an electron beam in an electron beam proximity exposure apparatus, as well as an electron beam proximity exposure apparatus.
2. Description of the Related Art
An electron beam proximity exposure apparatus of this kind has conventionally been disclosed in U.S. Pat. No. 5,831,272 (corresponding to Japanese Patent No. 2951947).
FIG. 11
shows a basic configuration of this electron beam proximity exposure apparatus. This electron beam proximity exposure apparatus
10
is composed of an electron gun
12
mainly including an electron beam source
14
which generates electron beams
15
, a lens
16
which makes the electron beams
15
parallel with each other, and a shaping aperture
18
; a scanning device
20
which includes main deflectors
22
and
24
and sub-deflectors
26
and
28
to cause the electron beams to scan a mask while remaining parallel with an optical axis; a mask
30
; an electrostatic chuck
50
; and an XY stage.
The mask
30
is arranged in proximity to a wafer
40
attracted to the electrostatic chuck
60
so that the gap between the mask
30
and the wafer
40
is, for example, 50 &mgr;m. In this state, when emitted perpendicularly to the mask
30
, electron beams pass through the mask pattern on the mask
30
and then fall on a resist layer
42
on the wafer.
The main deflectors
22
and
24
of the scanning device
20
controls deflection of the electron beams
15
so that the electron beams scan the entire surface of the mask
30
as shown in FIG.
12
. This causes the mask pattern of the mask
30
to be transferred to the resist layer
42
on the wafer
40
on an equal scale.
Further, the sub-deflectors
26
and
28
of the scanning device
20
controls an angle at which the electron beams are incident on the mask pattern so as to correct distortion of the mask (inclination correction). Now, when the angle at which the electron beams
15
are incident on the mask
30
is defined as &agr; and the gap between the mask
30
and the wafer
40
is defined as G as shown in
FIG. 13
, the amount &dgr; of deviation of a mask pattern transferred position resulting from the incident angle &agr; is expressed by the following equation:
&dgr;=
G
·tan &agr;.
In
FIG. 13
, the mask pattern is transferred to a position deviating from the regular one by the amount &dgr;. Accordingly, if the mask
30
is distorted, for example, as shown in FIG.
14
(A), the mask pattern is transferred without any distortion as shown in FIG.
14
(B) by controlling the inclination of the electron beams according to the distortion of the mask observed at a position scanned by the electron beams.
The XY stage
60
moves the wafer
40
attracted to the electrostatic chuck
50
, in two horizontally orthogonal axial directions. Each time the equal-scale transfer of the mask pattern is completed, the XY stage
60
moves the wafer
40
a predetermined distance to enable a plurality of mask patterns to be transferred to the single wafer
40
.
If the main deflectors
22
and
24
control deflection of the electron beams
15
so that the electron beams scan the entire surface of the mask
30
, then the electron beams must scan the mask while remaining parallel with the optical axis as shown in FIG.
11
. Thus, the inclination of the electron beams
15
must be accurately measured according to the position scanned by the electron beams
15
.
Further, if the sub-deflectors
26
and
28
control the angle at which the electron beams
15
are incident on the mask pattern, the relationship between a voltage applied to the sub-deflectors
26
and
28
and the angle at which the electron beams
15
are incident on the mask pattern must be previously determined.
SUMMARY OF THE INVENTION
The present invention is achieved in view of these points, and it is an object thereof to provide a method of measuring inclination of an electron beam in an electron beam proximity exposure apparatus, the method enabling the inclination of the electron beam to be accurately measured and enabling determination of the relationship between a voltage applied to sub-deflectors and the angle at which the electron beam is incident on a mask pattern.
It is another object of the present invention to provide a method of calibrating inclination of an electron beam in an electron beam proximity exposure apparatus as well as an electron beam proximity exposure apparatus wherein the electron beam can scan a mask while remaining parallel with an optical axis when the electron beam scans the entire surface of the mask.
To attain the above objects, the present invention is directed to a method of measuring inclination of an electron beam in an electron beam proximity exposure apparatus which transfers a mask pattern formed on a mask to a resist layer on a wafer, wherein the electron beam proximity exposure apparatus comprises: an electron gun that emits the electron beam with a predetermined sectional shape; the mask arranged in proximity to the wafer; a deflector that controls deflection of the electron beam emitted by the electron gun so that the electron beam scans an entire surface of the mask; a calibration mask having a plurality of marks previously formed thereon; a first electron beam detecting device which has a first mark and which converts the electron beam passing through the first mark into an electrical quantity; a second electron beam detecting device which has a second mark located above the first mark and below the calibration mask and which converts the electron beam passing through the second mark into an electrical quantity; and a moving device which moves the first and second electron beam detecting devices on an xy plane which is orthogonal to an optical axis of the electron beam, the method comprising the steps of: (a) loading the calibration mask and using the deflector to control deflection of the electron beam so that the electron beam impinges on an arbitrary mark of the calibration mask; (b) detecting a position of the first electron beam detecting device after movement when the electron beam, having passed through the mark of the calibration mask, passes through a first mark of the first electron beam detecting device to make the electrical quantity detected by the first electron beam detecting device largest; (c) detecting a position of the second electron beam detecting device after movement when the electron beam, having passed through the mark of the calibration mask, passes through a second mark of the second electron beam detecting device to make the electrical quantity detected by the second electron beam detecting device largest; (d) calculating the inclination of the electron beam observed when the electron beam is deflected so as to impinge on the arbitrary mark of the calibration mask according to positions of the first electron beam detecting device in x and y directions after movement, the positions being detected in the step (b), positions of the second electron beam detecting device in the x and y directions after movement, the positions being detected in the step (c), the amounts of positional difference between the first and second marks in the x and y directions, and a difference in height between the first and second marks; and (e) repeating the steps (a) to (d) for each mark of the calibration mask to determine the inclination of the incident electron beam for each mark.
According to the present invention, at the step (b), the position of the first electron beam detecting device after movement is detected when the mark of the calibration mask and the first mark are on the electron beam axis. Similarly, at the step (c), the position of the second electron beam detecting device after movement is detected when the mark of the calibration mask and the second mark are on the electron beam axis. Accordingly, when the amounts of positional difference between the first and second marks in the x and y directions are already known or detected, the inclination
Berman Jack
Leepl Corporation
Nixon & Peabody LLP
Safran David S.
Smith, II Johnnie
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