Radiant energy – Irradiation of objects or material – Irradiation of semiconductor devices
Reexamination Certificate
2000-09-27
2004-03-09
Lee, John R. (Department: 2881)
Radiant energy
Irradiation of objects or material
Irradiation of semiconductor devices
C250S310000, C250S311000, C250S398000, C250S491100, C250S492220, C250S492300
Reexamination Certificate
active
06703623
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an exposure apparatus which is used to expose a fine pattern in a manufacturing process of a semiconductor integrated circuit, etc., and more particularly to an electron beam proximity exposure apparatus in which a mask having an aperture corresponding to a pattern to be exposed is disposed in proximity to a surface of an object such as a semiconductor wafer and the mask is irradiated with an electron beam, thereby performing exposure of the pattern to an electron beam having passed through the aperture.
2. Description of 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 which 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 a manufacturing cost. New types of exposure apparatus such as an electron beam direct lithography apparatus and X-ray exposure apparatus have therefore been developed, but there still remain many problems in terms of stability, productivity, cost and so on.
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 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 diagram showing a fundamental configuration to realize the electron beam proximity exposure apparatus disclosed by U.S. Pat. No. 5,831,272. In an electron optical column
10
are disposed an electron gun
14
which emits electron beam
15
, a condenser lens
18
which collimates the electron beam
15
, a main deflecting coil
20
and a subsidiary deflecting coil
50
as shown in FIG.
1
. Though the main deflecting coil
20
is shown as a single deflecting coil in
FIG. 1
, they actually are configured in two stages so as to obtain electron beams which are in parallel with an optical axis and have different irradiating locations by deflecting an electron beam with a deflecting coil in a first stage and then in a reverse amount with a deflecting coil in a second stage. Similarly, the subsidiary deflecting coil
50
is also configured actually in two stages so that fine adjustment of an irradiating angle is possible without changing the irradiating locations changed with the main deflecting coils by deflecting the electron beams with a deflecting coil in a first stage and then in a reverse amount twice as large with a deflecting coil in a second stage. In a vacuum object chamber
8
are disposed a mask stage
36
which holds and moves a mask
30
, a reflected electron detector
38
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 detector
46
which detects height of the wafer
40
. Furthermore, a laser length measuring device
38
for the mask stage which detects travel amount of the mask stage
36
and a laser length measuring device
48
for the wafer stage which detects travel amount of the wafer stage
44
are disposed so that the travel amounts of the stages can be detected with remarkably high accuracy. The wafer stage
44
is movable in directions of at least two axes. Though the reflected electron detector
38
is used in this configuration, a secondary electron detector can also be used in place of this detector which detects secondary electrons.
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
38
, a detector disposed on the standard mark and the height detector
46
are supplied to a signal processor 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
by way of a condenser lens power source
71
. 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 coil
20
and the subsidiary deflecting coil
50
. The electron beam is deflected as desired accordingly.
The exposure apparatus described above positions the wafer
40
to the mask and exposes a pattern over an entire surface of the mask by scanning the electron beam
15
.
In case of a photomask to be used in a optical light exposure apparatus such as a stepper, a chromium layer or the like is patterned on a glass substrate, the glass substrate is checked whether or not the pattern is formed as predetermined and a pellicle layer is formed as a protective film on the pattern immediately when the pattern is free from a defect or after correcting a defect with a correcting device if any. A surface of the pellicle layer is monitored for dust adhesion and is cleaned when dust adheres on a problematic level. The pattern is not injured by cleaning. The surface of the pellicle layer causes defocusing by its thickness and no particular problem occurs so far as the adhering dust consists of small particles.
In contrast, a mask
30
which is to be used in the above described electron beam proximity exposure apparatus needs to be a stencil mask having an aperture formed as a hole on which the above described pellicle layer cannot be formed. Accordingly, dust or the like adhering to a surface of the mask causes a serious problem in the above described electron beam proximity exposure apparatus. This mask for proximity exposure is set in the electron beam exposure apparatus after being manufactured with a separate apparatus and inspected, but it is impossible to completely prevent dust from adhering to the surface of the mask for proximity exposure while it is carried from an inspecting device to the electron beam exposure apparatus. Accordingly, there arises a problem that even a mask which is free from a defect at an inspection stage cannot be warranted to be free from a defect when it is set in the electron beam exposure apparatus.
When a defect is produced by dust which adheres during use in the electron beam proximity exposure apparatus in particular, the surface of the mask can hardly be cleaned directly and a defective portion will be corrected with an apparatus such as a correcting device. When the mask for proximity exposure is removed from the electron beam proximity exposure apparatus, carried to an inspecting device and the correcting device or a cleaning device and set once again in the electron beam proximity exposure apparatus after correction or cleaning
Shimazu Nobuo
Utsumi Takao
Hughes James P.
Lee John R.
LEEPL Corporation
Nixon & Peabody LLP
Safran David S.
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