Semiconductor device manufacturing: process – Coating with electrically or thermally conductive material – To form ohmic contact to semiconductive material
Reexamination Certificate
2000-02-23
2001-06-12
Nelms, David (Department: 2818)
Semiconductor device manufacturing: process
Coating with electrically or thermally conductive material
To form ohmic contact to semiconductive material
C438S770000
Reexamination Certificate
active
06245660
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a process for producing a semiconductor device having fine contact plugs.
2. Description of the Related Art
In recent years, as semiconductor devices have become fine, the diffused layers formed in the semiconductor substrate have become fine as well. In this connection, the contact plugs electrically connecting these fine diffused layers with electrodes are becoming increasingly fine.
Contact plugs have heretofore been formed by forming contact holes in the inter-layer insulating film formed on a semiconductor substrate so as to reach the diffused layers formed in the semiconductor substrate and then filling each contact hole with a conductive material. However, as the contact holes become fine, the patterning therefore becomes very difficult when the diameter of hole is 1 &mgr;m or less. Hence, it is generally conducted to once form each contact hole so as to have a diameter slightly larger than actually required and then form, on the inner surface of the contact hole, a side wall made of an insulating material (e.g. silicon oxide) by CVD (chemical vapor deposition) to form fine contact holes.
In such a memory device as a storage electrode is formed above each bit line, each capacitor contact plug is present between bit lines. In order to prevent the short-circuiting between capacitor contact plug and bit lines, it is generally conducted to (1) cover the circumference of each bit line with an insulating film having an etching rate different from that of inter-layer insulating film, or (2) form an insulating film on the inner surface of each opening (each contact hole) for formation of capacitor contact plug and then fill each contact hole with a conductive material.
A conventional method for formation of fine contact plugs is described below on a case of forming a stack type capacitor of the memory cell region of DRAM, referring to FIGS.
5
(
a
)-
5
(
g
) and FIGS.
6
(
a
)-
6
(
e
).
First, as shown in FIG.
5
(
a
), on a semiconductor substrate
1
having, at given positions, element-insulating regions
2
made of a silicon oxide film is formed a gate oxide film (not shown) by a thermal oxidation method or the like; then, on the whole surface of the resulting material is formed an impurity-containing polysilicon film; the polysilicon film is subjected to patterning; thereby, gate electrodes
3
are formed.
Successively, as shown in FIG.
5
(
b
), ion implantation is conducted to form diffused layers
4
; then, on the whole surface of the resulting material is formed a first inter-layer insulating film consisting of a BPSG film (a boron-phosphorus-silica glass film) or the like.
Next, as shown in FIG.
5
(
c
), bit contact holes
6
are formed so as to reach the diffused layers
4
; successively, as shown in FIG.
5
(
d
), an insulating film
7
is formed, by CVD, on the first inter-layer insulating film
5
including the inner surface of each bit contact hole
6
. The CVD insulating film
7
is etched back to form each side wall
8
, as shown in FIG.
5
(
e
).
A film made of a conductive material is formed so as to fill each bit contact hole
6
having a side wall
8
; patterning is conducted; thereby, bit contact plugs
9
and bit lines
10
are formed as shown in FIG.
5
(
f
). Then, on the whole surface of the resulting material is formed a second inter-layer insulating film
11
consisting of a BPSG film or the like, and thereon is formed an insulating film
12
[FIG.
5
(
g
)].
Next, as shown in FIG.
6
(
a
), capacitor contact holes
13
are formed so as to reach the diffused layers
4
; then, as shown in FIG.
6
(
b
), an insulating film
14
is formed, by CVD, on the insulating film
12
and the inner surface of each capacitor contact hole
13
. Successively, the CVD insulating film
14
is etched back to form each side wall
15
, as shown in FIG.
6
(
c
).
A film made of a conductive material is formed so as to fill each capacitor contact hole
13
having a side wall
15
; patterning is conducted; thereby, each capacitor contact plug
16
and each storage electrode
17
are formed as shown in FIG.
6
(
d
).
Then, a capacitor insulating film (not shown) is formed. Thereon is formed an impurity-containing polysilicon film
18
for formation of plate electrode, whereby a capacitor structure is formed. Thereon is formed a third inter-layer insulating film (not shown), after which other constituents such as upper wiring and the like (not shown) are formed.
In the above conventional constitution, however, each side wall consisting of a CVD insulating film makes direct contact with the surface of a semiconductor substrate, which caused formation of GR center (generation-recombination center) to generate leakage current. This generation of leakage current particularly in the capacitor contact plugs of memory circuit is a very serious problem because it makes difficult the securement of a sufficient capacity in the current situation in which semiconductor devices are becoming increasingly fine.
SUMMARY OF THE INVENTION
The object of the present invention is to provide a process for producing a semiconductor device in which the leakage current of contact plug portion is suppressed, particularly a semiconductor device having good holding property at the memory circuit region.
The first aspect of the present invention lies in a process for producing a semiconductor device comprising an inter-layer insulating film formed on a semiconductor substrate and contact plugs contacting with the surface of the semiconductor substrate, each formed in the inter-layer insulating film by filling a conductive material into each contact hole having a side wall made of a CVD insulating film, which process comprises:
a step of forming, in an inter-layer insulating film formed on a semiconductor substrate, holes by anisotropic etching so that the surface of the semiconductor substrate is exposed,
a step of forming a CVD insulating film on the surface of the resulting wafer including the inner surface of each hole,
a thermal oxidation step of conducting heating in an oxygen-containing atmosphere to form a thermal oxide film at the surface portion of the semiconductor substrate at the bottom of each hole,
a step of etching back the CVD insulating film of the bottom of each hole and simultaneously removing the thermal oxide film formed in the thermal oxidation step, to expose the surface of the semiconductor substrate, and
a step of filling each hole with a conductive material to form each contact plug.
The second aspect of the present invention lies in a process for producing a semiconductor device according to the above process, which process comprises after the thermal oxidation step,
a step of forming a silicon nitride film on the surface of the wafer including the inner surface of each hole, and then etching back the silicon nitride film and the CVD insulating film of the bottom of each hole and simultaneously removing the thermal oxide film formed in the thermal oxidation step, to expose the surface of the semiconductor substrate.
The third aspect of the present invention lies in a process for producing a semiconductor device having a structure comprising a plurality of insulating films different in heat-flowability, laminated on a semiconductor substrate, which process comprises:
a step of laminating a plurality of insulating films on a semiconductor substrate,
a step of forming contact holes so as to extend through the plurality of insulating films,
a step of forming a side wall in each contact hole, and
a step of conducting a heat treatment after the formation of the side wall.
The fourth aspect of the present invention lies in a process for producing a semiconductor device according to the third aspect of the present invention, wherein the contact holes are formed so that the surface of the semiconductor substrate is exposed, and the heat treatment is conducted in an oxygen-containing atmosphere so that a thermal oxide film is formed at the surface portion of the semiconductor substrate conta
McGinn & Gibb PLLC
NEC Corporation
Nelms David
Nhu David
LandOfFree
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