Radiation imagery chemistry: process – composition – or product th – Radiation modifying product or process of making – Radiation mask
Reexamination Certificate
2002-02-04
2004-10-05
Mohamedulla, Saleha R. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Radiation modifying product or process of making
Radiation mask
Reexamination Certificate
active
06800402
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an exposure mask used for the photolithography process as one of the semiconductor device fabrication processes. More particularly, the invention relates to a Levenson-type phase-shifting mask that suppresses effectively the optical proximity effect to thereby improve the resolution, and a method of forming a pattern using the mask.
2. Description of the Related Art
In recent years, high-speed operation and large-scale integration of semiconductor devices have been progressing further. According to this tendency, it has been required to further miniaturize the patterns of layers that form the devices.
More recently, the design rule has been decreased to approximately half of the wavelength of exposure light (i.e., exposure wavelength). Thus, it is extremely difficult to form small patterns with the size of approximately half of the exposure wavelength by using ordinary exposure methods. To cope with this, various types of “super-resolving technique” have been developed and discussed.
One of the known “super-resolving techniques” is the “phase-shifting mask”. This mask is an exposure mask having a patterned phase-shifting layer selectively formed on the transparent parts (e.g., openings) of the transparent substrate. The patterned phase-shifting layer eliminates the effect of diffraction of exposure light passing through adjoining transparent parts, thereby raising the resolution of the mask.
The “Levenson-type” phase-shifting mask provides much enhancement of the resolution, which is disclosed, for example, in the Japanese Examined Patent Publication No. 62-50811 published in 1987. With the “Levenson-type phase-shifting mask”, a patterned phase shifting layer is alternately formed on adjoining transparent parts of the transparent substrate. This is to make the light beams passing through the transparent parts opposite in phase to each other, thereby suppressing the interference between these two beams. In this way, the mask enhances its resolution.
The “Levenson-type” phase-shifting mask is very effective to enhancement of the resolution and the depth of focus for periodically-arranged pattern elements. This mask can resolve extremely miniaturized patterns with the size of approximately half of the exposure wavelength or less. Therefore, it has been thought that this type of mask is most hopeful as the technique that realizes formation of patterns with the size of approximately half of the exposure wavelength or less.
FIG. 3
shows an example of circuit or element patterns (hereinafter, which are referred as circuit/element patterns) to be formed. In
FIG. 3
, the circuit/element pattern
110
is used to pattern a conductive film formed on a gate dielectric film, thereby forming the gate electrodes of Metal-oxide-Semiconductor Field-Effect Transistors (MOSFETs) and the wiring lines connected thereto. The pattern
110
is made of any photoresist film.
The circuit/element pattern
110
includes an isolated pattern section
113
with an isolated, L-shaped pattern element
113
a
and a periodic pattern section
114
with closely-arranged, linear pattern elements
114
a
. The isolated pattern section
113
includes the L-shaped pattern element
113
a
only, in which no other pattern elements are located near the element
113
a
. The periodic pattern section
114
includes the linear pattern elements
114
a
that are arranged in parallel at equal spaces or intervals, which is termed the Line and Space (L/S) pattern.
Actually, the circuit/element pattern
110
of
FIG. 3
includes various types of other pattern elements than the elements
113
a
and
114
a
. However they are omitted in
FIG. 3
for the sake of simplification of explanation.
FIG. 1
shows a prior-art Levenson-type phase-shifting mask used to foam the circuit/element pattern
110
of FIG.
3
.
FIG. 2
shows a prior-art ordinary (e.g., non-phase-shifting) mask (not the Levenson-type) used to form the same pattern
110
.
The prior-art phase-shifting mask
120
of
FIG. 1
is of the positive type. The mask
120
comprises an L-shaped blocking or light-shielding part
122
a
for forming the pattern element
113
a
of the pattern section
113
of the pattern
110
in FIG.
3
and six linear blocking parts
122
b
for Forming the pattern elements
114
a
of the pattern section
114
of the same pattern
110
. The mask
120
further comprises a rectangular phase-shifting part
123
a
formed closely to the blocking part
122
a
and three strip-shaped phase-shifting parts
123
b
arranged alternately in the spaces between the blocking parts
122
b
. The remaining area of the mask
120
is a transparent part
124
.
In
FIG. 1
, a character “0” is attached to the transparent part
124
, because no phase shift occurs in the exposure light passing through the part
124
. A character “&pgr;” is attached to the phase-shifting parts
123
a
and
123
b
, because phase shift of “&pgr;(180°)” occurs in the exposure light passing through the parts
123
a
and
123
b.
The blocking part
122
a
has the same shape as the pattern element
113
a
of the circuit/element pattern
110
. Each of the blocking parts
122
b
has the same shape as a corresponding one of the pattern elements
114
a
of the pattern
110
.
The prior-art non-phase-shifting mask
130
in of the positive type, like the phase-shifting mask
120
. The mask
130
comprises a rectangular blocking part
132
that covers the blocking parts
122
a
and
122
b
of the mask
120
and the phase-shifting parts
123
a
and
123
b
thereof. The remaining area of the mask
130
is a transparent part
134
. The blocking part
132
has a following relationship with the blocking parts
122
a
and
122
b
and the phase-shifting parts
123
a
and
123
b
of the phase-shifting mask
120
.
Specifically, if the non-phase-shifting mask
130
is entirely overlapped with the phase-shifting mask
120
, the upper edge
132
a
of the blocking part
132
of the mask
130
approximately accords with the upper edges
122
aa
and
122
ba
of the blocking parts
122
a
and
122
b
of the mask
120
. In this state, the upper edges
123
aa
and
123
ba
of the phase-shifting parts
123
a
and
123
b
of the mask
120
are shifted upward from the upper edge
132
a
of the blocking part
132
in
FIGS. 1 and 2
, and overlapped with the transparent part
134
.
Next, a method of forming the circuit-element pattern
110
of
FIG. 3
using the phase-shifting mask
120
and the non-phase-shifting mask
130
with the double exposure method is explained below.
In the first exposure step, a photoresist film (not shown), which has been formed on an object
112
for pattern formation (e.g., a polysilicon film formed on the gate dielectric film), is irradiated by specific exposure light using the phase-shifting mask
120
of FIG.
1
. At this time, a latent image having the same shape as the L-shaped blocking part
122
a
and the linear blocking parts
122
b
is formed in the photoresist film thus exposed.
In the first exposure step, an undesired latent image is formed in the photoresist film thus exposed, which is due to the “0-&pgr; phase edges” formed at the locations corresponding to the edges
123
aa
and
123
ba
of the phase-shifting parts
123
a
and
123
b.
In the second exposure step, to eliminate the “0-&pgr; phase edges”, the photoresist film is irradiated with the same exposure light as used in the first exposure step again using the non-phase-shifting mask
130
of FIG.
2
.
Thereafter, the photoresist film including the latent image is developed with a known developing solution, thereby removing the unnecessary, irradiated parts of the photoresist film. Thus, the latent image is elicited, in other words, the photoresist film is patterned as desired. As a result, the circuit/element pattern
110
of
FIG. 3
is formed on the object
112
for pattern formation.
With the pattern format ion method using the above-described phase-shifting mask
120
and the non-phase-shifting mask
130
, however, the following problem wil
Mohamedulla Saleha R.
NEC Electronics Corporation
Young & Thompson
LandOfFree
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