Etching a substrate: processes – Gas phase etching of substrate – With measuring – testing – or inspecting
Reexamination Certificate
2000-08-01
2004-06-15
Norton, Nadine G. (Department: 1765)
Etching a substrate: processes
Gas phase etching of substrate
With measuring, testing, or inspecting
C216S079000, C216S080000, C438S014000, C438S723000
Reexamination Certificate
active
06749763
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a plasma processing method for use in a fabrication process of semiconductor devices, and more particularly relates to a plasma processing method, by which an etching or deposition process is carried out using plasma created from fluorocarbon gas.
In recent years, downsizing of semiconductor devices has accelerated so much that the required pattern definition is on the verge of reaching the 0.1 &mgr;m order at last.
However, the fabrication process of semiconductor devices is basically no different from what it used to be. That is to say, first, a thin film is deposited on a semiconductor substrate. Next, a resist film (i.e., an organic film) is defined on the thin film by a photolithographic process. And then the thin film is etched using the resist film.
Nevertheless, the type of exposing radiation, typically adopted in a lithographic process, has lately changed from line into KrF or ArF excimer laser radiation to cope with the accelerating downsizing trend of semiconductor devices. In addition, organic resist films have also been developed responsive to the change of exposing radiation.
The application of the ArF excimer laser radiation as exposing radiation to the 0.1 &mgr;m-order patterning is now under research and development. However, it is known that an organic resist film would be poorly resistant to an etching process in that case.
Thus, to ensure a high selectivity with respect to the resist film, various techniques have been proposed. For example, a technique takes advantage of a property of a silicon material as a fluorine scavenger by making a member inside a reaction chamber out of the silicon material. That is to say, according to the technique, the selectivity against the resist film can be improved by decreasing the concentration of fluorine in an etching gas.
Hereinafter, a known plasma processing method will be described with reference to FIG.
1
.
FIG. 1
illustrates a schematic construction of an inductively coupled plasma processing system. As shown in
FIG. 1
, the inner walls of a reaction chamber
10
are covered with quartz plates
11
. An induction coil
12
is wound around the outside of the reaction chamber
10
. One end of the induction coil
12
is connected to a first RF power supply
13
, while the other end of the induction coil
12
is grounded.
A gas inlet port
14
of the reaction chamber
10
is connected to a gas supply source (i.e., gas cylinder)
16
via a mass flow controller
15
. A gas outlet port
17
of the reaction chamber
10
is connected to an exhaust pump
19
by way of a pressure control valve
18
. Accordingly, the gas pressure inside the reaction chamber
10
is controlled using the mass flow controller
15
and/or the pressure control valve
18
and exhaust pump
19
.
A sample stage
20
, which will be a lower electrode, is provided inside the reaction chamber
10
and connected to a second RF power supply
22
by way of a matching circuit
21
.
A control unit
23
provides control signals to the first and second RF power supplies
12
and
22
, mass flow controller
15
and pressure control valve
18
. In this manner, the unit
23
controls first RF power supplied from the first RF power supply
12
to the induction coil
12
, second RF power supplied from the second RF power supply
22
to the sample stage
22
, the flow rate of the gas supplied from the gas supply source.
16
to the reaction chamber
10
and that of the gas exhausted from the reaction chamber
10
.
The gas pressure inside the reaction chamber
10
is normally controlled to a predetermined value between 0.133 and 1.33 Pa by adjusting the pressure control valve
18
with the exhaust pump
19
operated continuously.
The first RF power is applied from the first RF power supply
13
to the induction coil
12
with a process gas supplied through the gas inlet port
14
into the reaction chamber
10
and with the gas pressure inside the reaction chamber
10
kept at the predetermined value. In this manner, plasma is created from the process gas. Thereafter, the second RF power is applied from the second RF power supply
22
to the sample stage
20
, thereby getting the created plasma attracted to a semiconductor substrate that has been placed on the sample stage
20
. As a result, a thin film, which has been formed on the surface of the semiconductor substrate, is etched or a thin film is deposited on the surface of the semiconductor substrate.
As described above, a silicon material functions as a fluorine scavenger. Accordingly, if an etching gas containing fluorine is introduced into the reaction chamber
10
, then silicon, which is the material of the sample stage
20
and a silicon ring (not shown), combines with that fluorine to produce SiF
x
(where x=3 or 4). In this manner, the concentration of fluorine in the etching gas is adjustable and therefore the etch rate is controllable. It is well known that the concentration of fluorine affects the etch rate of a resist film.
Thus, Japanese Laid-Open Publication No. 10-98024 suggests that a fluorocarbon gas, in which the ratio of carbon to fluorine (which will be herein called a “C/F ratio”) is relatively high (e.g., C
5
F
8
gas), is preferably used to increase the selectivity of a silicon dioxide film being dry-etched (or plasma-etched) to a resist film used as a mask.
However, when the present inventors dry-etched a silicon dioxide film using the C
5
F
8
gas with a high C/F ratio and masking the silicon dioxide film with a resist film, we didn't find that the resultant selectivity increased compared to the conventional C
2
F
6
gas with a low C/F ratio.
We carried out the experiment in the following manner.
An ICP plasma-enhanced dry etching system was used as an etching system. The power applied to create plasma was set at 1600 W. A mixture of C
5
F
8
and Ar gases was used as an etching gas. The flow rates of the C
5
F
8
and Ar gases were defined at 4.7 and 4.0 ml/min, respectively. And the gas pressure was set at 1.33 Pa. A silicon dioxide film was etched using a resist film as a mask under the process conditions such as these.
As a result, although a gas with a high C/F ratio (i.e., the C
5
F
8
gas) was used, the selectivity against the resist film was just 1.81, which is not so much different from that of the conventional gas with a low C/F ratio (e.g., C
2
F
6
gas).
SUMMARY OF THE INVENTION
In view of these, an object of the present invention is increasing the selectivity attained when dry etching is carried out using a fluorocarbon gas with a C/F ratio of 0.5 or more.
The present inventors believe that if a silicon dioxide film is dry-etched using a fluorocarbon gas with a high C/F ratio, the selectivity thereof to a resist film increases because of the following reason. Specifically, we believe that a polymer film would be deposited on the surfaces of the silicon dioxide and resist films and decrease the etch rates. Accordingly, if the decrease in etch rate of the silicon dioxide film is less than the decrease in etch rate of the resist film, then the selectivity to the resist film would increase. On the other hand, if the decrease in etch rate of the silicon dioxide film is equal to or greater than the decrease in etch rate of the resist film, then the selectivity to the resist film would not increase.
Thus, the selectivity to the resist film does not always increase by the use of a fluorocarbon gas with a high C/F ratio. More exactly, the selectivity to the resist film can be increased not only by using the fluorocarbon gas with the high C/F ratio but also by making the etch rate of the silicon dioxide film decrease less than the etch rate of the resist film.
Furthermore, we paid special attention to the residence time &tgr; of the fluorocarbon gas, which is given by P×V/Q, where P is the pressure (unit: Pa) of the fluorocarbon gas, V is the volume (unit: L) of the reaction chamber and Q is the flow rate (unit: Pa·L/sec) of the fluorocarbon gas. By applying numerous combinations of pressures and flow rates of
Ahmed Shamim
Matsushita Electric - Industrial Co., Ltd.
Nixon & Peabody LLP
Norton Nadine G.
Studebaker Donald R.
LandOfFree
Plasma processing method does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Plasma processing method, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Plasma processing method will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3365481