Method of producing a semiconductor device

Details Method of producing a semiconductor device Method of producing a semiconductor device

2001-10-09

2004-04-06

Zarabian, Amir (Department: 2822)

Semiconductor device manufacturing: process

Formation of electrically isolated lateral semiconductive...

Grooved and refilled with deposited dielectric material

C438S435000, C438S437000, C438S739000

Reexamination Certificate

active

06716718

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of producing a semiconductor device, and more particularly to a method of producing a semiconductor device for forming a trench isolation structure.
2. Description of the Background Art
Trench isolation is known as one of the isolation structures in semiconductor devices. In order to form a bird's beak in the trench isolation, an inner wall oxidation process for oxidizing an exposed inner wall of the trench is carried out after the trench is formed.
Hereafter, one example of such a method of producing a semiconductor device for forming a trench isolation structure according to a prior art will be described. First, referring to
FIG. 18
, a pad oxide film made of a silicon oxide film is formed on a silicon substrate
101
. A polysilicon film is formed on the pad oxide film. A silicon nitride film is formed on the polysilicon film. A photoresist pattern (not illustrated) is formed on the silicon nitride film.
With the use of the photoresist pattern as a mask, an anisotropic etching treatment is carried out on the silicon nitride film, the polysilicon film, and the pad oxide film to expose a surface of the silicon substrate
101
, thereby forming a mask pattern including a silicon nitride film
104
a
, a polysilicon film
103
a
, and a pad oxide film
102
a
for forming a trench. With the use of the mask pattern as a mask, an anisotropic etching treatment is carried out on the silicon substrate
101
to form a trench
106
.
Subsequently, referring to
FIG. 19
, a thermal treatment (inner wall oxidation process) is carried out to form an oxide film
107
on the exposed surface of the trench
106
, on the side surface of the pad oxide film, and on the side surface of the polysilicon film
103
a.
Next, referring to
FIG. 20
, a silicon oxide film
108
is formed to fill the trench
106
. Thereafter, a chemical mechanical polishing treatment is carried out to polish the surface of the silicon oxide film
108
. Next, referring to
FIG. 21
, a wet etching treatment is carried out on the silicon oxide film
108
to expose the silicon nitride film
104
a
almost completely.
Thereafter, the exposed silicon nitride film
104
a
is removed, and further the polysilicon film
103
a
and the pad oxide film
102
a
are successively removed. Thus, referring to
FIG. 22
, a bird's beak is formed in the trench isolation oxide film
109
.
Next, referring to
FIG. 23
, gate electrodes
113
are formed to cross over element forming regions
114
formed on the surface of the silicon substrate
101
by the trench isolation oxide film
109
. Thereafter, a semiconductor device such as a dynamic random access memory (DRAM) is formed, for example, by forming memory cells or the like in the element forming regions
114
.
However, the aforementioned conventional production method involves the following problem. As described above, the inner wall oxidation shown in
FIG. 19
is carried out in a state in which the side surface of the polysilicon film
103
a
is generally flush (coplanar) with the side surfaces of the pad oxide film
102
a
and the trench
106
, as shown in FIG.
18
.
In the inner wall oxidation, the oxidation rate of the polysilicon film
103
a
is substantially at the same level as the oxidation rate of the silicon substrate
101
(the surface of the trench
106
), while the oxidation rate of the pad oxide film
102
a
is smaller than the oxidation rate of the polysilicon film
103
a
. For this reason, an oxide film grows faster on the surface of the silicon substrate
101
and on the surface of the polysilicon film
103
a
than on the surface of the pad oxide film
102
a
, thereby forming an overhung configuration in which the part of the oxide film that has grown on the side surface of the polysilicon film
103
a
is hung over the oxide film that has grown on the side surface of the pad oxide film
102
a.
As a result of this, referring to
FIG. 19
, a recess
120
is formed between the part that has grown on the surface of the silicon substrate
101
and the part that has grown on the surface of the polysilicon film
103
a
in the oxide film
107
. When a buried oxide film
108
is buried in the trench
106
in the step shown in
FIG. 20
in a state in which the recess
120
has been formed, the part of the recess
120
is not filled with the buried oxide film
108
and remains as voids
121
.
Referring to
FIG. 22
, these voids
121
form recesses
122
in the trench isolation oxide film
109
after the silicon nitride film
104
a
, the polysilicon film
103
a
, and the pad oxide film
102
a
are successively removed. If an attempt is made to form gate electrodes
113
in a state in which such recesses
122
have been formed in the trench isolation oxide film
109
, an electrically conductive material
116
existing in the recesses
122
, which material is for forming the gate electrodes
113
, cannot be removed in patterning the gate electrodes
113
.
For this reason, referring to
FIG. 23
, adjacent gate electrodes may possibly be short-circuited with each other by the electrically conductive material
116
that is remaining in the recesses
122
. As a result of this, a desired operation may not be achieved in the semiconductor device.
SUMMARY OF THE INVENTION
The present invention has been made in order to solve the aforementioned problem of the prior art, and an object thereof is to provide a method of producing a semiconductor device that prevents voids from being formed in the trench isolation structure.
A method of producing a semiconductor device according to the present invention includes the following steps. A first film having a dielectric property, a second film having an oxidation property different from that of the first film, and a layer serving as a mask material are successively formed on a semiconductor substrate. A mask pattern for forming a trench in the semiconductor substrate is formed by performing an etching treatment on the first film, the second film, and the layer serving as a mask material. A trench is formed by performing an etching treatment on the semiconductor substrate using the mask pattern as a mask. An etching treatment is performed so that a position of a side surface of the second film exposed on a side surface of the mask pattern will be retreated from a position of a side surface of the first film. An oxide film is formed on a surface of the first film and the trench including the retreated side surface of the second film by performing a thermal treatment. A buried dielectric film is formed on the oxide film so as to fill the trench. In the retreating step of retreating the position of the side surface of the second film from the position of the side surface of the first film, the side surface of the second film is retreated in advance so that the oxide film that has grown on the side surface of the second film may not be hung over the oxide film that has grown on the side surface of the first film after the thermal treatment step of forming the oxide film by thermal treatment is performed.
According to this production method, the side surface of the second film is retreated in advance for a predetermined length so that the oxide film that has grown on the side surface of the second film may not be hung over the oxide film that has grown on the side surface of the first film. Therefore, voids can be prevented from being formed when the buried oxide film is buried in the trench. This can prevent generation of etching residues in a trench isolation structure, which may occur in a conventional semiconductor device, e.g. in forming two gate electrodes extending in parallel so as to cross the trench isolation structure, thereby preventing the two gate electrodes from being electrically short-circuited.
Preferably, the second film is retreated by dry etching in the retreating step.
This can facilitate control of the retreated amount of the second film (the amount of etching) and provides a better uniformity of the retreated amount in a surface of th

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