Etching a substrate: processes – Gas phase etching of substrate – Application of energy to the gaseous etchant or to the...
Reexamination Certificate
1999-08-26
2002-03-12
Gulakowski, Randy (Department: 1746)
Etching a substrate: processes
Gas phase etching of substrate
Application of energy to the gaseous etchant or to the...
C216S068000, C438S725000
Reexamination Certificate
active
06355183
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an apparatus and method for plasma etching. More particularly, it relates to an apparatus and method for plasma etching wherein a target film is etched by a plasma generated with a high-frequency induction field produced by a spiral coil.
With the increasing miniaturization of a semiconductor integrated circuit element in recent years, exposing light with a shorter wavelength has been used in a lithographic step. At present, a KrF excimer laser (with a wavelength of 248 nm) or an ArF excimer laser (with a wavelength of 193 nm) is used.
As the wavelength of exposing light becomes shorter, the reflectivity of light reflected from a substrate after exposing a resist film becomes higher so that the reflected light from the substrate is more likely to cause variations in the size of a resist pattern.
To prevent the reflected light from being incident on the resist film, there has recently been used a process wherein an organic bottom anti-reflective coating (hereinafter referred to as ARC) is formed under the resist film. The ARC process is a technique used primarily in the process of manufacturing a semiconductor element in a high-performance device with design rules whereby a gate width is 0.25 &mgr;m or less.
In the ARC process, it is necessary to etch the ARC after a resist pattern is formed by a conventional lithographic technique. Of a variety of plasma etching apparatus used to etch the ARC, an inductively coupled plasma (ICP) etching apparatus having a spiral coil is used frequently.
As examples of the inductively coupled plasma etching apparatus having a spiral coil, an inductively coupled plasma etching apparatus having a planar coil (see U.S. Pat. No.4,948,458), an inductively coupled plasma etching apparatus having a domed coil (see U.S. Pat. No. 5,614,055), and the like are known.
Referring to FIGS.
5
(
a
) and
5
(
b
), a conventional inductively coupled plasma etching apparatus having a planar single spiral coil will be described.
As shown in FIGS.
5
(
a
) and
5
(
b
), a sample stage
102
as a lower electrode to which high-frequency power is applied is disposed in the lower portion of a grounded chamber
101
having an inner wall covered with an insulator such as ceramic, alumina, or quartz. A semiconductor substrate
103
as a sample to be etched is placed on the sample stage
102
. A gas inlet port
108
for introducing etching gas into the chamber
101
via a mass flow controller is provided around the sample stage
102
, while a gas outlet port
105
connected to a turbo pump for adjusting pressure in the chamber
1
to the order of 0.1 to 10 Pa is provided in the bottom portion of the chamber
101
.
A slide valve
109
having a valve seat and a valve element which rotates relative to the valve seat is provided between the sample stage
102
and the gas outlet port
105
to adjust the amount of gas exhausted from the gas outlet port
105
with the rotation of the valve element. As the slide valve
109
, there can be used, e.g., a known slide valve commercially available from VAT Holding AG, Switzerland under the trade name of VAT: Series65 (see Japanese Unexamined Patent Publication Nos. 9-178000 and 9-210222).
An inductively-coupled single spiral coil
104
is provided over a quartz plate
101
a
as the ceiling of the chamber
101
, i.e., over the chamber
101
in opposing relation to the sample stage
102
. A coil portion
104
a
of the single spiral coil
104
has an outermost end A connected to a high-frequency power supply source
106
via a power-supply-side withdrawn portion
104
b
including a matching circuit (not shown) and an innermost end B connected to a ground source
107
composed of a wall portion of the chamber
101
via a ground-side withdrawn portion
104
c.
When high-frequency power is supplied from the high-frequency power-supply source
106
to the single spiral coil
104
, a high-frequency induction field is generated around the single spiral coil
104
, which changes the etching gas introduced into the chamber
101
into a plasma. The etching gas that has been changed into the plasma is guided by the high-frequency power applied to the sample stage
102
to a target film on the semiconductor substrate
103
held by the sample stage
102
, thereby etching the target film.
By using the conventional inductively-coupled plasma etching apparatus and etching gas composed of a mixture of N
2
gas and O
2
gas, the present inventors performed an etching process with respect to the ARC as the target film, while holding the pressure in the chamber
101
constant and varying the total flow rate of the gas (the sum of the flow rates of N
2
gas and O
2
gas, i.e., varying the amount of introduced gas and the opening rate of the slide valve
109
. The etching conditions are as shown in Tables 1 and 2. As shown in Tables 1 and 2, etching was performed by varying the amount of introduced gas (N
2
/O
2
) and the opening rate of the slide valve.
TABLE 1
N
2
/O
2
30/30 (sccm)
ICP/RF
350/50 (W)
PRESSURE
8 (mTorr)
TEMPERATURE OF
10 (° C.)
SAMPLE STAGE
OPENING RATE OF
15 (%)
SLIDE VALVE
TABLE 2
N
2
/O
2
120/120 (sccm)
ICP/RF
350/50 (W)
PRESSURE
8 (mTorr)
TEMPERATURE OF
10 (° C.)
SAMPLE STAGE
OPENING RATE OF
40 (%)
SLIDE VALVE
In Tables 1 and 2, ICP represents high-frequency power applied to the single spiral coil
104
and RF represents high-frequency power applied to the sample stage
102
. The target film is the ARC
111
formed on the semiconductor substrate
110
, as shown in FIG.
6
.
As a result of performing etching under the foregoing conditions, the present inventors have found that the inplane uniformity of the etching rate is degraded if the flow rate of the etching gas is increased. The inplane uniformity of the etching rate is defined as the extent of variation of the etching rate across the surface of the target film and expressed as 3&sgr;/&mgr;×100 (%), where &sgr; is the standard deviation of a data value and &mgr; is the mean value of the data value. When variations in data value exhibit a normal distribution, 3&sgr; represents a deviation including 99.74% of the data value, as shown in FIG.
7
. The following equation 1 shows 3 &sgr; and &mgr; specifically.
3
σ
=
3
∑
i
=
1
n
(
Xi
-
μ
)
2
n
Equation
1
where
&mgr;: mean value=
∑
i
=
1
n
Xi
n
n: number of samples
Xi: i-th data value.
FIG. 8
is a view showing the relationship between the inplane uniformity of the etching rate and the total flow rate of the gas. In
FIG. 8
, the horizontal axes represent the total flow rate (sccm) of the etching gas and the opening rate (%) of the slide valve and the vertical axis represents the inplane uniformity (%) of the etching rate.
As will be understood from
FIG. 8
, the inplane uniformity of the etching rate changes when the total flow rate of the etching gas changes and the opening rate of the slide valve changes. Specifically, the inplane uniformity is improved temporarily (variation of the etching rate is reduced) if the opening rate changes from 10% to 20% but the inplane uniformity is degraded again (variation of the etching rate is increased) if the opening rate exceeds 20%.
The degraded inplane uniformity of the etching rate causes variations in the actual amount of etching across the surface of the target film. If the actual amount of etching varies across the surface of the target film, adverse effects are produced such as variations in the characteristics of a FET in the case of forming the gate electrode of the FET by etching.
SUMMARY OF THE INVENTION
In view of the foregoing, it is therefore an object of the present invention to prevent the inplane uniformity of the etching rate from changing even if the total flow rate of the etching gas and the opening rate of the slide valve change.
The present inventors have made a through examination on the cause of a change in the inplane uniformity of the etching rate which occurs when the total flow rate of the etching gas and the opening rate of the slide valve chan
Ahmed Shamim
Gulakowski Randy
Nixon & Peabody LLP
Robinson Eric J.
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