Active solid-state devices (e.g. – transistors – solid-state diode – Physical configuration of semiconductor – Mesa structure
Reexamination Certificate
1999-04-15
2002-09-10
Williams, Alexander O. (Department: 2876)
Active solid-state devices (e.g., transistors, solid-state diode
Physical configuration of semiconductor
Mesa structure
C257S506000, C257S510000, C257S502000, C257S649000, C257S618000, C257S619000, C257S405000, C257S620000, 47, 47, 47, 47
Reexamination Certificate
active
06448630
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention and a manufacturing method thereof relates to a semiconductor device having a polish preventing pattern. More particularly, the present invention relates to a semiconductor device having a polish preventing pattern for preventing an end of an element formation region to be shaved when an interlayer oxide film is planalized by the CMP method in a subsequent process because the element formation region formed by trench isolation at a surface of a semiconductor substrate is arranged so as to be isolated horizontally from other element formation regions.
2. Description of the Background Art
The LOCOS (LOCal Oxidation of Silicon) method for forming an isolation oxide film, which has a uniform film thickness, near a surface of a semiconductor substrate by thermally oxidizing a silicon substrate has been employed as a means of forming an element isolation region for isolating an element formation region of the semiconductor device. The LOCOS method has been an effective means of isolating an element formation regions in conventional semiconductor devices with a relatively lower degree of integration.
However, in the LOCOS method, a bird's beak is formed, which is thermal oxidation at an end of an element formation region along a main surface of a semiconductor substrate. When the LOCOS method is used for a semiconductor device in which small element formation regions are formed, the bird's beak may oxidize all of the element formation regions. Accordingly, the element formation regions may be lost, and therefore the LOCOS method cannot be applied to highly integrated semiconductor devices.
As a means of isolating an element formation region as an alternative to the LOCOS method, the trench isolation method in which an insulation film is filled in a trench that is provided in a silicon substrate has been used. In the trench isolation method, a silicon substrate is first shaved by anisotropic etching to form a trench to a prescribed depth from the main surface of the silicon substrate. An insulation film such as an oxide film is then filled in the trench to such an extent that the insulation film slightly rises from the main surface of the silicon substrate. Thereafter, the insulation film is polished to such an extent that the insulation film surface approaches the main surface of the silicon substrate. Thus, the main surface of the insulation film is planarized while the surface of the element formation region is exposed. An element isolation region is formed in this manner.
As a method of planalizing the insulation film surface, the CMP (Chemical Mechanical Polishing) method in which an isolation insulation film is filled and thereafter the entire surfaces of the silicon substrate and the isolation insulation film are chemically and mechanically polished is used. In the CMP method, the entire surfaces of a silicon substrate and an isolation insulation film are polished by introducing a polishing liquid on the surfaces of the silicon substrate and the isolation oxide film and rotating the silicon substrate while pressing a polishing cloth against the entire surfaces of the silicon substrate and the isolation insulation film.
The CMP method is characterized in that a protruding portion of a silicon substrate is polished first. When such a portion as an element formation region that is not to be polished protrudes, a protection film such as a nitride film is generally provided on its surface to prevent polishing of the protruded portion.
However, the polishing speed of an oxide film is considerably higher than that of a nitride film. Thus, the following problems occur in the CMP method polishing. Referring to
FIGS. 38-48
, typical problems with the CMP method polishing will be described in the following.
In the CMP method polishing, as can be seen from the states before and after polishing shown in
FIGS. 38 and 39
, the proportion of area in which nitride films
112
a
,
112
b
,
112
c
,
112
d
,
112
e
,
112
f
are distributed and the proportion of area in which oxide films
114
a
,
114
b
,
114
c
,
114
d
,
114
e
are distributed are greatly different between regions that have a high density of element formation regions, that is, a region between element formation regions
102
a
and
102
b
, a region between element formation regions
102
b
and
102
c
, a region between element formation regions
102
d
and
102
e
, a region between element formation regions
102
e
and
102
f
, and a region that has a low density of element formation regions, that is, a region between element formation regions
102
c
and
102
d
. Accordingly, a region having a large area proportion of nitride films is hardly shaved and keeps a planar surface while a region having a larger area proportion of oxide films is easily shaved and shaved to a greater extent toward its center. Thus, a dent d
1
is created as shown in FIG.
39
. Dent d
1
affects formation of an aluminum interconnection and the like that are provided on oxide film
114
c
in a subsequent process.
As shown in
FIG. 40
, in the process of forming oxide film
114
to cover element formation regions
102
a
,
102
b
, the oxide film is deposited to the shape of protruding element formation regions
102
a
,
102
b
. Accordingly, the surface is roughened and have considerably large rise and falls as a whole. In order to etch the entire particularly protruded portion of oxide film
114
, a slightly dented portion of oxide film
114
may slightly be excessively etched. When the oxide film is successively etched from the state of
FIG. 40
to the states of
FIGS. 41
,
42
,
43
and
44
, nitride film
112
on an end of element formation region
102
a
and nitride film
113
formed on small element formation region
102
b
, which are under slightly dented oxide film
114
, locally receive large pressure from a polishing cloth. Accordingly, the etching speed of nitride film
112
on the end of element formation region
102
a
and nitride film
113
formed on small element formation region
102
b
increases compared with the etching speed of nitride films at other portions. Thus, nitride film
112
on the end of element formation region
102
a
and nitride film
113
formed on small element formation region
102
b
are greatly shaved compared with nitride films at other portions and lose their function as a protection film. As a result, the end of element formation region
102
a
and small element formation region
102
b
are disadvantageously polished as shown in FIG.
45
.
In order to prevent lowering of the function of nitride films
112
,
113
as a protection film, a method using a polish preventing pattern is utilized. Referring to
FIGS. 46-48
, the method will be described in the following.
In the process of forming element formation region
102
as shown in
FIG. 46
on semiconductor substrate
101
, element formation region
102
is formed on silicon substrate
101
and, at the same time, a trench is formed in semiconductor substrate
101
by using the same mask. By leaving the main surface, island-type polish preventing patterns
111
as dummy patterns are formed in an element isolation region to have the same size and regular intervals regardless of the position of element formation region
102
as shown in FIG.
47
.
By using this method, the surface of silicon substrate
101
has nitride films almost uniformly distributed on the entire surface not only on element formation region
102
but on a portion to be an element isolation region. Since the entire surfaces of element formation region
102
and the element isolation region are polished at an almost uniform etching speed, nitride film
112
on the end of element formation region
102
a
and nitride film
113
formed on small element formation region
102
b
as shown in
FIGS. 44 and 45
are prevented from being shaved to a greater extent than other portions and losing the function as a protection film.
However, the above described island-type polish preventing patterns
111
are formed in the
McDermott & Will & Emery
Mitsubishi Denki & Kabushiki Kaisha
Williams Alexander O.
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