Semiconductor device manufacturing: process – Chemical etching – Vapor phase etching
Reexamination Certificate
2001-03-26
2004-02-03
Chen, Kin-Chan (Department: 1765)
Semiconductor device manufacturing: process
Chemical etching
Vapor phase etching
C438S723000, C438S724000
Reexamination Certificate
active
06686294
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to etching methods and etching apparatuses as well as manufacturing methods of semiconductor devices. More particularly, the invention relates to a method of etching a silicon nitride film and an etching apparatus for performing the etching method, as well as a method of manufacturing a semiconductor device employing that etching method.
2. Description of the Background Art
Semiconductor devices such as a DRAM (Dynamic Random Access Memory) have been known. These semiconductor devices are becoming finer and integration thereof is progressing to a greater degree. Accordingly, there arises a need for finer processing dimensions in a manufacturing process of the semiconductor devices. Further, a mask alignment margin is being reduced that is provided in consideration of mask alignment errors in a photolithography process step of the manufacturing process of the semiconductor devices.
An approach employed for addressing such finer processing dimensions is to form a self-aligned contact as described below, in a step of forming a contact hole between gate electrodes of a plurality of field effect transistors.
Specifically, according to the approach to form the self-aligned contact, sidewalls of the gate electrodes are covered with an insulating film to form a sidewall film. As a material for the insulating film constituting the sidewall film, a silicon nitride film or the like is used having a higher selective etching ratio with respect to a silicon oxide film which is a material for an interlayer insulating film. After the sidewall film is formed, the interlayer insulating film formed of the silicon oxide film is deposited on the gate electrodes. In this interlayer insulating film, a contact hole is formed between the gate electrodes. In an etching step for producing the contact hole, assume that the position of the contact hole is shifted from a predetermined position to a certain extent. As the sidewall film made of the silicon nitride film is formed on the sidewalls of the gate electrodes, this etching step never causes the contact hole to reach the gate electrodes. Even if the contact hole is filled with a conductive film, it is possible to prevent the conductive film and the gate electrodes from being short-circuited.
As shown in
FIGS. 14-17
, in order to produce such a self-aligned contact, it is necessary to form the silicon nitride film to cover the gate electrodes and thereafter partially remove the silicon nitride film by anisotropic etching thereby form a sidewall film formed of the silicon nitride film.
FIGS. 14-17
are cross sections showing a conventional method of manufacturing a semiconductor device, illustrating an etching step for forming the sidewall film. The conventional method of manufacturing a semiconductor device is now described in conjunction with
FIGS. 14-17
.
Referring to
FIG. 14
, a silicon oxide film
111
constituting a gate insulating film is deposited on a substrate
110
such as a silicon substrate. Silicon oxide film
111
here is 3 nm in thickness. On silicon oxide film
111
, a two-layer film
112
made of a tungsten silicide film and a polysilicon film is formed to produce gate electrodes. The tungsten silicide film and the polysilicon film each have a thickness of 50 nm. A silicon nitride film
113
is formed on two-layer film
112
. Silicon nitride film
113
is 150 nm in thickness. A resist film (not shown) is formed on silicon nitride film
113
. This resist film is photolithographically processed to form a resist film
114
having a gate pattern.
Resist film
114
is used as a mask to partially remove, through etching, silicon nitride film
113
thereby produce upper silicon nitride films
120
a
and
120
b
. Resist film
114
is thereafter removed. Upper silicon nitride films
120
a
and
120
b
are used as masks to partially remove, through etching, two-layer film
112
thereby produce gate electrodes
115
a
and
115
b
. The structure as shown in
FIG. 15
is thus achieved.
Referring to
FIG. 16
, a silicon nitride film
116
is formed to cover gate electrodes
115
a
and
115
b
. Silicon nitride film
116
is 40 nm in thickness.
Silicon nitride film
116
is partially removed through anisotropic etching to form sidewall films
117
a
-
117
d
formed of the silicon nitride film on the sidewalls of gate electrodes
115
a
and
115
b
as shown in FIG.
17
.
In the etching process for forming sidewall films
117
a
-
117
d
, if silicon nitride film
116
does not have its selective ratio higher enough relative to silicon oxide film
111
, silicon oxide film
111
is partially eliminated by this etching as shown in FIG.
17
. Consequently, there are generated a portion of the substrate cut away through this etching (substrate cutaway portion)
144
and a damaged portion
145
having defects in substrate
110
. This damage of substrate
110
causes a deteriorated reliability of a semiconductor device including components such as field effect transistors formed on substrate
110
.
Various techniques have accordingly been proposed for preventing such substrate cutaway portion
144
and damaged portion
145
of substrate
110
.
According to a method disclosed in Japanese Patent Laying-Open No. 11 -145113 for example, a silicon nitride film is etched to form a sidewall film by using a parallel plane RIE (Reactive Ion Etching) apparatus and chlorine gas as a reactant gas. The frequency of a high-frequency power supply and the power supplied to upper and lower electrodes are optimized to increase the selective ratio of the silicon nitride film with respect to a silicon oxide film (i.e. etching rate of silicon nitride film/etching rate of silicon oxide film).
Nevertheless, the selective ratio of the silicon nitride film relative to the silicon oxide film disclosed in Japanese Patent Laying-Open No. 11-145113 is approximately 10, and this value of the selective ratio is insufficient. Therefore, damages to silicon oxide film
111
and substrate
110
as shown in
FIG. 17
cannot surely be avoided.
According to a technique proposed in Japanese Patent Laying-Open No. 10-50660, a silicon nitride film is etched to form a sidewall film by using as a reactant gas a mixed gas of chlorine gas and hydrogen bromide gas and consequently the selective ratio of the silicon nitride film relative to a silicon oxide film is approximately 20.
An inventor reviewed this technique and found that an increased ratio of the hydrogen bromide in the reactant gas as described above would result in a problem as shown in
FIG. 18
that deposition on sidewall films
117
a
-
117
d
occurs in the etching process, and the deposition parts have functions as a mask in etching to cause partially abnormal shapes of sidewall films
117
a
-
117
d
.
FIG. 18
is a cross section illustrating the abnormal shapes of sidewall films
117
a
-
117
d
. Such abnormality in the shape of sidewall films
117
a
-
117
d
(shape defect) is one factor of any step on the upper surface of an interlayer insulating layer for example formed on gate electrodes
115
a
and
115
b
. Such a step may cause failures like disconnection in an interconnection layer formed on the interlayer insulating layer. As a result, the reliability of devices formed on substrate
110
deteriorates.
SUMMARY OF THE INVENTION
One object of the present invention is to provide an etching method that enables the selective ratio of a silicon nitride film to be sufficiently higher relative to a silicon oxide film without causing shape defects of the etched silicon nitride film, and an etching apparatus for applying this etching method.
Another object of the invention is to provide a method of manufacturing a semiconductor device having a high reliability, the semiconductor device being formed by using an etching method enabling the selective ratio of a silicon nitride film to be sufficiently higher relative to a silicon oxide film without causing shape defects of the etched silicon nitride film.
According one aspect of the invention, an etching method
Chen Kin-Chan
McDermott & Will & Emery
Mitsubishi Denki & Kabushiki Kaisha
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