Semiconductor device manufacturing: process – Chemical etching – Vapor phase etching
Reexamination Certificate
1998-06-26
2001-07-31
Bowers, Charles (Department: 2813)
Semiconductor device manufacturing: process
Chemical etching
Vapor phase etching
C438S199000, C438S303000, C438S636000, C438S744000, C438S757000, C438S791000
Reexamination Certificate
active
06268295
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of manufacturing a semiconductor device and, more particularly, a method of manufacturing a semiconductor device including a step employing a light antireflection film upon exposure.
2. Description of the Prior Art
In order to improve performance of a semiconductor integrated circuit device, a higher integration degree and a higher speed operation of a semiconductor device have been requested. Miniaturization of a MOS transistor which is as a representative semiconductor device has been requested, for instance.
In the MOS transistor, size reduction of respective constituent elements in both a width direction and a thickness direction has been advancing. There has been such tendencies that, for example, a thickness of a silicon dioxide film used as a gate insulating film is made thinner than 10 nm and depths of extension source/drain layers become less than 100 nm.
A lithography technique performs a critical role in miniaturization of the MOS transistor. In general, various patterns can be formed with the use of optical exposure technique. However, in recent, it has not been seldom that a KrF excimer laser light (248 nm) can be used to develop a miniaturized MOS transistor. It is optical reflection that becomes an issue upon utilizing such exposure technique. In patterning a light reflecting film such as metal, silicon, or the like, light reflection has been suppressed by forming a antireflection film on the light reflecting film and then coating resist thereon.
Normally there are used silicon nitride or silicon nitride oxide as material used for the antireflection film.
If such antireflection film is applied to execute patterning of a gate electrode of the MOS transistor, the antireflection film remains on the gate electrode. In many cases, the antireflection film is removed after the gate electrode has been formed.
For example, as shown in
FIG. 11A
, a gate insulating film
102
, an impurity containing polysilicon film
103
, and a antireflection film
104
are formed in sequence on a silicon substrate
101
, and resist
105
is then coated on the antireflection film
104
. The resist
105
is patterned via exposure and developing processes to have a planar shape of the gate electrode. Then, as shown in
FIG. 11B
, with the use of the patterned resist
105
as a mask, the antireflection film
104
to the gate insulating film
102
are etched. Thus, the polysilicon film
103
may serve as a date electrode
103
g
. In addition, impurity ions are implanted into the silicon substrate
101
for the first time with the use of The gate electrode
103
g
as a mask, then sidewalls are formed on both side surfaces of the gate electrode
103
g
, and then impurity ions are implanted into the silicon substrate
101
for the second time with the use of the gate electrode
103
g
and the sidewalls
106
as a mask. Shallow and low concentration impurity diffusion layers
107
a
,
107
b
are formed by the first impurity ion implantation and also deep and high concentration impurity diffusion layers are formed by the second impurity ion implantation, whereby a source layer
107
s
and a drain layer
107
d
both having an LDD structure can be constructed. Thereafter, as shown in
FIG. 11C
, a silicon oxide film
108
is formed by thermally oxidizing a surface of the silicon substrate
101
at about 800° C. In this state, as shown in
FIG. 11D
, the antireflection film
104
is removed by use of a phosphoric solution.
By the way, if silicon nitride which is grown by plasma CVD is employed as material for the antireflection film
104
, it is common to remove the antireflection film
104
with the use of the phosphoric solution.
However, if phosphoric acid is used to remove the antireflection film
104
made of silicon nitride, it is likely that a surface of the silicon substrate
101
is made uneven by the phosphoric acid. In addition, if the surface of the silicon substrate
101
is brought directly into contact with the phosphoric acid, such surface is susceptible to &agr; particles due to polonium contamination to thus cause soft errors.
Therefore, as shown in
FIG. 11C
, commonly such a method has been employed that, prior to removal of the antireflection film
104
made of silicon nitride, a protection film (
108
) made of SiO
2
is formed on the surface of the silicon substrate
101
by thermally oxidizing the surface of the silicon substrate
101
.
In addition, since the sidewalls of the gate electrode
103
g
are exposed when thermal oxidation is to be carried out, insulating sidewalls
106
are formed on the sidewalls of the gate electrode
103
g
, as shown in
FIG. 11C
, in order to prevent oxidation of the sidewalls.
However, if the sidewalls
106
is made up of silicon nitride, the sidewalls
106
are made thinner and moved back simultaneously with removal of the antireflection film
104
which is also made of silicon nitride.
In the event that the sidewalls
106
are formed by such thinner layer, low concentration impurity diffusion layers
107
a
,
107
b
of the source/drain layers
107
s
,
107
d
having the LDD structure are exposed by a width X, as shown in FIG.
12
. For this reason, if a silicide film
110
is formed on surfaces of the source/drain layers
107
s
,
107
d
, the silicide film
110
is superposed on the low concentration impurity diffusion layers
107
a
,
107
b
. As a result, junction breakdown is liable to cause in the low concentration impurity diffusion layers
107
a
,
107
b.
If thermal oxidization of the surface of the silicon substrate
101
is needed, such thermal oxidization is to be performed at high temperature in the range of 700° C. to 900° C. As shown in
FIG. 13
, according to the temperature to such extent, impurity contained in the gate electrode
103
g
is caused to punch through the gate insulating film
102
and to diffuse into the silicon substrate
101
, otherwise impurity contained in the impurity diffusion layers
107
a
,
107
b
in the silicon substrate
101
is caused to diffuse laterally. As a consequence, such a problem has been caused that a short channel effect becomes worse.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a method of manufacturing a semiconductor device which is capable of preventing expansion of impurity diffusion in a semiconductor substrate and also suppressing retreat of side walls, during a step of removing a antireflection film made of silicon nitride or silicon nitride oxide.
According to the present invention, the silicon nitride or the silicon nitride oxide constituting the antireflection film is grown by the plasma CVD (chemical vapor deposition) method using the reaction gas containing the dilution gas such as nitrogen, argon, or helium. In this case, it is preferable that the antireflection film is grown at the temperature of less than 350° C. and more than 200° C.
The silicon nitride or the silicon nitride oxide grown on or over the semiconductor substrate under such conditions has the high etching rate due to the hydrofluoric acid and in addition the hydrofluoric acid never causes unevenness of the surface of the semiconductor substrate. As a result, the step of growing the oxide film on the surface of the semiconductor substrate by thermal oxidation as pre-process to remove the antireflection film can be omitted and also impurity rediffusion by the thermal oxidation can be prevented.
Furthermore, even if the silicon oxide film is used as material for the sidewall, the etching rate of the silicon nitride or silicon nitride oxide due to the hydrofluoric acid can be increased more than ten times the silicon oxide film and also retreat of the sidewalls can be suppressed.
In the event that the silicon nitride is used as material for the sidewalls, the sidewalls are scarcely etched by the hydrofluoric acid if the silicon nitride for the sidewalls is grown by the thermal CVD method. For this reason, the antireflection film can be selectively etched and therefore retreat of the sidewa
Ohta Hiroyuki
Satoh Hidekazu
Armstrong Westerman Hattori McLeland & Naughton LLP
Bowers Charles
Fujitsu Limited
Pham Thanhha
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