Wiring forming method

Details Wiring forming method Wiring forming method

2002-09-19

2004-12-28

Zarneke, David A. (Department: 2829)

Semiconductor device manufacturing: process

Coating with electrically or thermally conductive material

To form ohmic contact to semiconductive material

Reexamination Certificate

active

06835651

ABSTRACT:

BACKGROUND OF THE INVENTION
a) Field of the Invention
The present invention relates to a wiring forming method which is suitable to form a fine wiring in an LSI or the like, and more particularly to a wiring forming method aimed at improving the precision of the size of wiring patterns by forming antireflection coating on a wiring film and under a resist layer.
b) Description of the Related Art
A process for forming a wiring is indispensable for the manufacturing of a semiconductor integrated circuit. The wiring becomes complicated along with an improvement in the integration density, and the formation of a fine wiring and a multilayered wiring is required. After isolation regions and a large number of elements are formed in a semiconductor substrate, wiring for connecting those elements to each other is patterned. Wiring patterns are formed by depositing a wiring layer, forming resist patterns on the wiring layer and etching the wiring layer through utilization of the resist patterns as masks. If the base on which the wiring layer is formed is uneven, however, the surface of the wiring layer may also become uneven and have convex and concave parts (projections and recesses). Generally speaking, the wiring layer has a high reflectance with respect to light, especially with respect to short-wavelength light. When coating a resist layer on the uneven surface of the wiring layer and exposing the resist layer to light, the reflection of the light from the wiring layer is a problem.
A concave part of the surface of the wiring layer may form a concave mirror and the light reflected from the concave mirror may be converged at a region which is not to be exposed to light (this is known as “halation”). The halation causes the thinning and thickening of the wiring patterns, the breaking of the wiring and the formation of isolated spots.
A convex part of the surface of the wiring layer may form a convex mirror and the light reflected from the convex mirror may illuminate even a region which is not exposed to light. This degrades the accuracy of the light exposure.
The above-described phenomena can be reduced by reducing the light reflection from the underlying surface at the time of subjecting the resist layer to the light exposure.
It is generally known that in the case of forming a resist layer with the required patterns on a wiring material layer having a high reflectance by photolithography, antireflection coating is provided under the resist layer (and on the wiring material layer) so that the light reflection from the wiring material layer is suppressed to improve the pattern transfer accuracy. An inorganic single layer which is made of TiON, TiN, SiON, SiN or the like is often employed as an antireflection coating film of this type. Sometimes an organic single layer which can be formed by a simple coating process is adopted (as seen from Published Unexamined Japanese Patent Applications Kokai Nos. 61-231182, 62-62523 and 62-63427, for example).
In the case of employing a TiON (or TiN) single layer film as the antireflection coating film, the effect of preventing the reflection of a KrF excimer laser beam (having a wavelength of 248 nm) used in the far ultraviolet ray exposure is not satisfactory.
FIG. 13
shows the dependence of the reflectance on the film thickness. This dependence was obtained by performing a computer simulation as regards a TiON film P provided on a WSi
2
(tungsten silicide) layer.
Reflectivity of a multi-layer structure was obtained by computer simulation under the following conditions.
On a substrate, m layers are stacked. The uppermost layer exposed to air (n
0
=1, k
0
=0) is called the first layer. The underlying layers are called the second, third, . . . , and m-th layers. The substrate is called the (m+1)-th layer. The real part and the imaginary part of the complex refractive index ñ
j
of the i-th layer are denoted n
j
and k
j
. Therefore, ñ
j
=n
j
−ik
j
. The complex reflectivity is denoted by r, and the complex transmissivity is denoted by t. Complex reflectivities at the uppermost surface, the first, second, third, . . . , interfaces are denoted by r
0
, r
1
, r
2
, r
3
, . . . . The complex reflectivity on the substrate surface is r
m
. Complex transmissivity at the first, second, third, . . . interfaces are denoted by t
1
, t
2
, t
3
, . . . . The complex transmissivity at the substrate surfaces is t
m
. These notations are shown in FIG.
14
.
The intensity reflection on the substrate surface R
m
is
R
m
=|r
m
|
2
=|(1−ñ
m+1
)/(1+ñ
m+1
)|
2
The complex reflectivity of the j-th layer r
j−1
is
r
j−1
=[{exp(−2
iØ
j
)}(
F
j
−r
j
)−
F
j
(1
−F
j
r
j
)]
/[
F
j
{exp(−2
iØ
j
)}(
F
j
−r
j
)−(1
−F
j
r
j
)],
where F
j
=(n
0
−ñ
j
)/(n
0
+ñ
j
),
n
0
=1,
Ø
j
=2&pgr;ñ
j
d/&ggr;,
&ggr;: wavelength, and
d: thickness of the layer.
The simulation adopted obtains r
m−1
by substituting r
m
, then r
m−2
by substituting r
m−1
, . . . and r
0
by substituting r
j
.
The intensity reflection becomes
R
i
=|r
i
|
2
.
The simulation conditions in that case were as follows:
Wavelength of light: 248 nm
Refractive index “n” and
extinction coefficient “k” of TiON film:
n=2.28
k=1.5
Refractive index “n” and
extinction coefficient “k” of WSi
2
layer:
n=2.5
k=3.15
Reflectance at TiON/WSi
2
interface: 54.9%
It can be understood from
FIG. 13
that even though the film thickness was set at the optimum value, the reflectance could only be reduced to approximately 30% and thus the effect of preventing the light reflection was not satisfactory.
In the case of employing an SiON (or SiN) single layer film as the antireflection coating film, a CVD (Chemical Vapor Deposition) apparatus is required for the film formation, which lacks simplicity. If a film having an ideal refractive index and extinction coefficient is intended, the realization of both the uniformity of the film thickness and throughput is difficult.
In the case of using an organic single layer film as the antireflection coating film, the precision of the size of the wiring patterns is low.
The organic antireflection coating film is made of an organic material of the same kind as a resist. An etching gas which contains oxygen as the main component is frequently used in the dry etching of the organic film. When the organic antireflection coating film is subjected to the anisotropic dry etching process using the resist patterns as masks after the formation of the resist layer, not only the antireflection coating film but also the resist layer is etched. In a film thickness range B shown in
FIG. 12
, the antireflection coating film is thick, and accordingly the time required for the etching is long. Due to this, the amount of shift in the size of the resist layer (the amount of thinning) is large, resulting in the degraded precision of the size of the wiring patterns.
FIG. 12
shows the dependence of the reflectance on the film thickness. This dependence was obtained by performing a computer simulation as regards an organic antireflection coating film Q provided on an WSi
2
layer. The organic antireflection coating film Q may be formed of acrylic acid resin having side chains which contain organic group effectively absorbing KrF excimer laser light of a main wavelength of 248 nm, for example:
where R is a portion absorbing light of a wavelength 248 nm, such as
x=10 mol % to 80 mol %, and
y=20 mol % to 90 mol %.
Computer simulation was done using the formulae as described above. The simulation conditions in that case were as follows:
Wavelength of light: 248 nm
Refractive index “n” and
extinction coefficient “k” of film Q:
n=1.654
k=0.23
Refractive index “n” and
extinction coefficient “k” of WSi
2
layer:
n=2.5
k=3.15
Reflectance at film Q/WSi
2
interface: 54.9%
It can be understood

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