Semiconductor device manufacturing: process – Making field effect device having pair of active regions... – Having insulated gate
Reexamination Certificate
2001-06-07
2002-09-10
Chaudhuri, Olik (Department: 2813)
Semiconductor device manufacturing: process
Making field effect device having pair of active regions...
Having insulated gate
Reexamination Certificate
active
06448139
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATION
This application is based upon Japanese Patent Application No. 2000-173796 filed on Jun. 9, 2000, the contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a manufacturing method of a semiconductor device having a trench, and more particularly of a semiconductor device having a buried gate.
2. Related Arts
Recently, a semiconductor device with an electrical isolation (trench isolation) structure or a semiconductor device with an embedded gate (trench type gate) has been proposed in accordance with improved integration degrees of various semiconductor devices.
A semiconductor device with a trench is formed by a method shown in
FIGS. 13A
to
13
E as one method of prior art.
First, an opening portion
2
a
is formed in a mask member
2
for forming a trench by patterning the mask member
2
formed on a silicon substrate
1
as shown in FIG.
13
A. Then, a concavity portion
3
having a bowl shape is formed at a portion where a trench opening portion is to be formed by isotropic etching as shown in FIG.
13
B. After that, a trench
4
is formed in the silicon substrate
1
by anisotropic etching as shown in FIG.
13
C.
Subsequently, formation of a sacrificial oxide film, removal of the sacrificial oxide film, and removal of the mask member
2
(see
FIG. 13D
) are performed successively. After that, an insulation film
5
is formed in the trench
6
as shown in FIG.
13
C. Then, the trench
4
is filled with polycrystalline silicon
6
, and a part of the polycrystalline silicon
4
disposed outside of the trench
4
is removed as shown in FIG.
13
E.
According to this method, an angle at an opening portion of the trench
4
is prevented from becoming about 90° because a shape of the opening portion of the trench
4
is improved by the isotropic etching. However, as shown in
FIG. 13C
, a portion A contacting a side face of the trench
4
becomes a sharp edge because of the shape of the concavity portion
3
, or a portion B disposed at a corner of the trench
4
becomes a sharp edge.
Shapes of these portions A and B are not easily improved after a thermal oxidation step is conducted. When the sharp edge of the portion A or B remains, insulation characteristics of the insulation film
5
formed in the trench
4
is deteriorated since the portion A or B becomes a concentrating point of electric field.
Moreover, thermal treatment is conducted while an etching damage layer
7
remains (see FIG.
13
C), whereby a defect layer is easily formed on an inner surface of the trench
4
. Therefore, the insulation characteristics of the insulation film
5
formed in the trench
4
may be deteriorated in a case that the insulation film
5
is formed by oxidizing the remaining damage layer
7
or the defect layer.
Another method is shown in
FIGS. 14A
to
14
E. An opening portion
2
a
is formed in a mask member
2
as shown in FIG.
14
A. Then, a trench
4
is formed in a silicon substrate
1
by anisotropic etching as shown in FIG.
14
B. Subsequently, a shape at an opening portion of the trench
4
and a shape at a bottom portion of the trench
4
are improved by CDE (Chemical Dry Etching) treatment simultaneously as shown in FIG.
14
C. After that, formation of a sacrificial oxide film, removal of the sacrificial oxide film, and removal of the mask member
2
(see
FIG. 14
D) are performed successively. Then, after an insulation film
5
is formed in the trench
4
, the trench
4
is filled with a polycrystalline silicon
6
as shown in FIG.
14
E.
According to this method, formation of the portions A and B each having a sharp edge due to the shape of the concavity portion
3
shown in FIG.
13
C and the concentration of electric field caused by the portions A and B are restrained.
However, since etching by the CDE treatment is isotropic dry etching, etching amount of the silicon in the trench
4
becomes large to round the opening portion and the bottom portion of the trench
4
sufficiently. As a result, a shape of the trench
4
fluctuates greatly. In addition, a polymer
8
composed of Teflon is formed and remains in the trench by the CDE treatment. The polymer
8
also deteriorates the insulation characteristics of the insulation film
5
.
On the other hand, when the etching amount of the silicon is small, the shape of the trench
4
is not improved sufficiently, and the damage layer
7
remains in the trench
4
, which deteriorates the insulation characteristics of the insulation film
5
as described above.
SUMMARY OF THE INVENTION
The present invention is devised to solve the above problems, and has an object to provide a manufacturing method of a semiconductor device having a trench in which an insulation layer with a high withstanding voltage characteristics and high quality can be formed.
According to a first aspect of the invention, after a trench is formed in a semiconductor substrate by anisotropic etching, a wet process is performed so that the semiconductor substrate is etched by a mixed solution containing hydrofluoric acid and nitric acid, whereby a shape of the trench is improved and a damage layer remaining in the trench is removed. Thus, an insulation layer, a semiconductor layer or the like is formed on a surface of the trench, which is suitable for forming the layer of the insulation film, the semiconductor film or the like. Therefore, quality of the layer of the insulation film, the semiconductor film or the like becomes fine, whereby a semiconductor device can have good electrical characteristics.
According to a second aspect of the invention, a high impurity concentration region is formed in a surface region of the semiconductor substrate. The wet process depends on a concentration of impurities in the semiconductor substrate.
Therefore, an etching rate at the surface region of the semiconductor substrate is higher than that at a deep portion of the semiconductor substrate in the trench deeper than the surface region. Thus, a shape at an opening portion of the trench is modified from a right-angled shape after the anisotropic etching is performed into a rounded shape.
According to a third aspect of the invention, after the trench is formed in the substrate by the anisotropic etching, short-time heat treatment is performed, whereby crystallinity of the trench is improved. That is, the crystallinnity of the trench is restored.
According to a fourth aspect of the invention, after the wet process is performed, short-time heat treatment is conducted successively, whereby crystallinity of an inner surface of the trench is improved.
According to a fifth aspect of the invention, a semiconductor device having good electrical characteristics is achieved by a manufacturing method described below.
Namely, a trench is formed in a semiconductor substrate in a depth direction thereof through a mask member, which is formed on the semiconductor substrate, having an opening portion. Then, a polymer, generated in forming the trench, remaining in the trench is removed. Next, a wet process is performed so that the semiconductor substrate is etched by a mixed solution containing hydrofluoric acid and nitric acid. Thus, taper portions are formed on an opening portion and a bottom portion of the trench simultaneously by one feature inhering in the mixed solution that an etching rate depends on a face orientation of the semiconductor substrate, i.e., by a face orientation dependency of the etching rate.
Moreover, a damaged layer formed in the trench by the anisotropic etching for forming the trench, which may deteriorate quality of an insulation layer to be formed in the trench, can be removed by the other feature inhering in the mixed solution that an etching rate of the damaged layer in a semiconductor is different from that of a non-damaged layer in the semiconductor, i.e., by etching selectivity in the semiconductor.
Then, after a thermal oxidation film is formed in the trench as a sacrificial oxide film by thermal oxidizing treatment, the sacrificial oxide
Arakawa Takafumi
Ito Hiroyasu
Kato Masatoshi
Blum David S
Chaudhuri Olik
Denso Corporation
Law Offices of David G. Posz
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