Radiant energy – Irradiation of objects or material
Reexamination Certificate
2001-01-22
2004-04-27
Lee, John R. (Department: 2881)
Radiant energy
Irradiation of objects or material
C250S492200, C250S492210, C250S492220, C250S492300, C250S397000, C250S398000, C250S3960ML
Reexamination Certificate
active
06727507
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to exposure apparatus and method, which are used to expose fine patterns in a manufacturing process of semiconductor integrated circuits, etc., and more particularly to electron beam proximity exposure apparatus and method, in which a mask having apertures corresponding to a pattern to be exposed is disposed in proximity to a surface of an object such as a semiconductor wafer, an electron beam is applied to the mask, and exposure with the electron beam having passed through the apertures is thereby performed.
2. Description of the Related Art
Attempts are being made to enhance integration degrees of semiconductor integrated circuits and finer circuit patterns are desired. Presently, a limit of the finer circuit patterns is defined mainly by exposure apparatuses, and a stepper, which is an optical exposure apparatus, takes various measures such as a light source that emits rays having shorter wavelengths, a larger NA (numerical aperture) and a phase shift method. However, much finer circuit patterns involve various kinds of problems such as a rapid increase of manufacturing costs. New types of exposure apparatus such as an electron beam direct lithography apparatus and an X-ray exposure apparatus have been therefore developed, but there still remain many problems in terms of stability, productivity, cost, etc.
An electron beam proximity exposure system is conventionally under research and development, since the exposure principle thereof is simple, as “High Throughput Submicron Lithography with Electron Beam Proximity Printing” (H. Bohlen et al., Solid State Technology, September 1984, pp. 210-217) (hereinafter referred to as a literature 1) exemplifies. However, it was thought that it was of no practical use since it was difficult to eliminate the proximity effect peculiar to the electron beam.
U.S. Pat. No. 5,831,272 (corresponding to Japanese Patent No. 2951947) and “Low energy electron-beam proximity projection lithography: Discovery of missing link” (Takao Utsumi, J. Vac. Sci. Technol. B 17(6), November/December 1999, pp. 2897-2902) disclose an electron beam proximity exposure apparatus that overcomes the above-mentioned problems and is usable for processing with very fine resolution at a mass production level.
FIG. 1
is a view showing a fundamental configuration of the electron beam proximity exposure apparatus disclosed in U.S. Pat. No. 5,831,272. Referring to this drawing, the electron beam proximity exposure apparatus disclosed in U.S. Pat. No. 5,831,272 will be briefly described. As shown in
FIG. 1
, in a column
10
are disposed an electron gun
12
, which includes an electron beam source
14
emitting an electron beam
15
, a shaping aperture
16
, and a condenser lens
18
collimating the electron beam
15
; scanning means
20
, which includes a pair of main deflecting devices
22
and
24
and scans with the electron beam parallel to the optical axis; a mask
30
, which has apertures corresponding to an exposed pattern; and an object (a semiconductor wafer)
40
, of which surface is coated with a resist layer. The mask
30
has a thin film
32
with the apertures formed at the center within a thick rim
34
, and the object
40
is disposed so that the surface thereof is in proximity to the mask
30
. In this state, when the electron beam is vertically applied to the mask, the electron beam passing through the mask's apertures is applied to the resist layer
42
on the surface of the object
40
. The entire surface of the thin film
32
on the mask
30
is scanned by deflecting the electron beam
15
(A, B, and C in
FIG. 1
denote the deflected beam toward three points) with the scanning means
20
, so that all aperture patterns of the mask
30
are exposed. The scanning means
20
has subsidiary deflecting devices
51
and
52
, which slightly lean the electron beam, and is used to position the mask
30
and the object
40
and to correct a difference between the exposure positions due to distortion of the mask and distortion of the object.
FIG. 2
is a view showing an entire configuration to practically realize the electron beam proximity exposure apparatus according to the fundamental configuration of FIG.
1
. The same function parts with
FIG. 1
are denoted with the same reference numbers.
As shown in the drawing, in an electron optical column
10
are disposed an electron gun
14
, which emits an electron beam
15
, a condenser lens
18
, which collimates the electron beam
15
, a blanker electrode
66
, which controls the application of the electron beam
15
to be on or off, a blanking aperture
68
, a main deflecting device
20
and a subsidiary deflecting device
50
. In a vacuum object chamber
8
are disposed a mask stage
36
, which holds and moves a mask
30
, a reflected electron detector
39
, which detects reflected electrons, a wafer stage
44
, which holds and moves a wafer
40
, a standard mark
60
disposed on the wafer stage
44
, and a height measurer
46
, which measures a height of the surface of the wafer
40
. A laser length measuring device
38
for the mask stage, which measures a travel amount of the mask stage
36
, and a laser length measuring device
48
for the wafer stage, which measures a travel amount of the wafer stage
44
, are disposed so that the travel amounts of the stages can be measured with remarkably high accuracy. The wafer stage
44
is movable in directions of at least two axes. Although the reflected electron detector
39
is used in this configuration, a secondary electron detector, which detects secondary electrons, can also be provided in place of the reflected electron detector. Generally, the use of the reflected electron detector so as to detect the mark position is suitable for detecting a mark made with heavy metal or the like, and the use of the secondary electron detector so as to detect the mark position is suitable in a case where difference in density is small between the mark and the surrounding material.
The electron beam proximity exposure apparatus is controlled by a computer
70
. Signals detected by the laser length measuring device
38
for the mask stage and the laser length measuring device
48
for the wafer stage are supplied to a data bus of the computer
70
. Signals detected by the reflected electron detector
39
, a detector disposed on the standard mark and the height measurer
46
are supplied to a signal processing circuit
76
, converted into digital signals and then supplied to the data bus of the computer
70
. The condenser lens
18
is an electromagnetic lens or an electrostatic lens, which is controlled by the computer
70
through a condenser lens power source
71
. Similarly, the blanker electrode
66
is controlled through a blanker driver
72
. The computer
70
supplies deflection amount data to a digital arithmetic circuit
75
, which performs an operation to correct the deflection amount data according to previously stored correction data and supplies corrected data to a main DAC/AMP
73
and a subsidiary DAC/AMP
74
. The main DAC/AMP
73
and the subsidiary DAC/AMP
74
convert the corrected deflection amount data into analog signals, amplify the analog signals and supply the resulting signals to the main deflecting device
20
and the subsidiary deflecting device
50
, respectively. The electron beam is deflected as desired accordingly.
The electron gun
14
is always in an operating state so as to stably output the electron beam, and always outputs the electron beam. Hence, it is necessary to provide a blanker to control as need arises whether or not the electron beam is applied to the mask
30
and to the wafer
40
through the mask
30
. The blanker comprises the blanker electrode
66
, the blanking aperture
68
and the blanker driver
72
, and controls the application of the electron beam to be on or off. When the blanker driver
72
applies no voltage to the blanker electrode
66
, the electron beam
15
just goes straight on, passes through the blanking aperture
68
, a
Shimazu Nobuo
Utsumi Takao
Lee John R.
LEEPL Corporation
Nixon & Peabody LLP
Safran David S.
Vanore David A.
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