Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Electron beam imaging
Reexamination Certificate
1999-06-07
2001-05-22
Young, Christopher G. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Electron beam imaging
C430S312000, C430S328000, C430S942000
Reexamination Certificate
active
06235450
ABSTRACT:
FIELD
The present invention is related to lithography methods that combine electron-beam exposure for high resolution and light exposure for high throughput. More particularly, the present invention relates to improved pattern-formation methods that allow the formation of reliable connections or junctions between a light-exposed portion and an electron-beam exposed portion of an individual resist layer.
BACKGROUND
Electron-beam lithography has been used to form a contact hole layer of a semiconductor device in which other layers are formed by light lithography. It has also been proposed (e.g., in IEEE ELECTRON DEVICE LETTERS, VOL. EDL-2, NO. 11, NOVEMBER 1981) to use light exposure and electron-beam exposure to expose respective portions of the same resist layer in the fabrication of a semiconductor device.
Using electron-beam lithography and light lithography for separate layers of a semiconductor device presents no particular difficulties. Problems can arise, however, when a light exposure and an electron-beam exposure are used within a single resist layer to form respective portions of a pattern in that layer. In particular, where a connection is required between a pattern element to be defined by light exposure and pattern element to be defined by electron-beam exposure, breaks in the pattern can occur at the connection region.
The present invention allows the use of both the high resolution of electron-beam exposure and the high throughput of light exposure in the same resist layer, while providing pattern-formation methods that minimize the occurrence of pattern breaks.
SUMMARY
The problem addressed by the present invention may arise as illustrated in FIG.
3
. FIG.
3
(A) is a top view of a pattern having an electron-beam exposure region and a light exposure region. FIG.
3
(B) is a graph showing the typical dosage distribution of the electron-beam exposure region and the light exposure region.
In FIG.
3
(A), a narrow line width (for example, 0.1 &mgr;m) electron-beam exposure pattern
81
and a wide line width (for example, 1.0 &mgr;m) light exposure pattern
83
are shown. The patterns
81
,
83
abut each other at a connection region
85
.
FIG.
3
(B) shows a dosage distribution along a line B—B (shown in FIG.
3
(A)) passing through both patterns
81
,
83
. The electron-beam dosage distribution
91
is shown on the left side of the figure, and the light dosage distribution
93
is shown on the right side of the figure. The relative scale of the dosages as shown corresponds to the sensitivity of the resist relative to each respective radiation type.
Broken line
95
represents the total dosage, i.e., the sum of the light dosage and the electron-beam dosage, in the vicinity of the connection region
85
. As shown in the figure, the total dosage
95
is not flat in the vicinity of the connection region
85
, but exhibits considerable variation including a valley
95
a
and a peak
95
b
. This variation depends on the characteristics of the curves at the edges of the respective dosage distributions. In the example shown in the figure, an edge curve
91
a
of the electron-beam dosage distribution
91
falls comparatively fast. In contrast, an edge curve
93
a
of the light dosage distribution
93
has a comparatively gentle slope. The dosage of an end portion
93
b
of the light dosage distribution edge curve is thus added to 100% of the dosage of the electron-beam dosage distribution
91
, resulting in a total dosage represented by the peak
95
b
. In contrast, an end portion
91
b
of the electron-beam dosage distribution
91
does not completely offset a portion
93
c
of the more sharply-sloped light dosage distribution
93
, resulting in a total dosage represented by the valley
95
a.
The significant variation of the total dosage shown in FIG.
3
(B), particularly the valley
95
a
, can tend to cause a break in the exposed and developed pattern, with a resulting break or short in the semiconductor structures to be formed. With a total dosage having a valley such as valley
95
a
at or near the connection portion
85
, pattern breaks can occur, even if the relative positioning of both patterns
81
and
83
is perfectly accurate. In practice, some degree of relative positioning error between an electron-beam exposure pattern and a light exposure pattern typically occurs, thereby increasing the danger of pattern breaks in the exposed and developed pattern.
According to one example embodiment of the present invention, a light exposure and an electron-beam exposure are used to expose respective portions of the same resist layer. The respective portions overlap to form a double-exposure region in which the resist is exposed by both light radiation and electron-beam radiation. The dosage of the light exposure and of the electron-beam exposure in the double-exposure region is desirably a gradually sloped dosage. The sum of the light exposure dosage and the electron-beam exposure dosage in the double-exposure region is chosen to be at least equal to or, desirably, somewhat larger than the dosage in the non-overlapping portions of the light exposure region and the electron-beam exposure region. This method of “gray splicing” prevents valleys in the total dosage distribution and facilitates smooth linking of the two differing exposure regions.
According to another example embodiment of the present invention, a light exposure and an electron-beam exposure are used to expose the same resist layer, with a narrow electron-beam exposure region extending into a wider light exposure region, with or without overlapping between the regions. By extending the electron-beam exposure region into the light exposure region, the continuity of the resulting circuit can be sufficiently ensured.
Other advantages and features of the invention will be apparent from the detailed description below.
REFERENCES:
patent: 5958626 (1999-09-01), Nakasuji
patent: 6020107 (2000-02-01), Niiyama et al.
patent: 9-314595 (1997-10-01), None
patent: 9-347319 (1997-12-01), None
Matsuda et al., “Electron Beam/Optical Intralevel Mix-and-Match Lithography for Deep Submicron Device Fabrication,”J. Vac. Sci. Technol.8:1914-1918 (1990).
Klarquist Sparkman Campbell & Leigh & Whinston, LLP
Nikon Corporation
Young Christopher G.
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