Semiconductor device manufacturing: process – Formation of electrically isolated lateral semiconductive... – Recessed oxide by localized oxidation
Reexamination Certificate
2001-01-19
2001-09-18
Bowers, Charles (Department: 2813)
Semiconductor device manufacturing: process
Formation of electrically isolated lateral semiconductive...
Recessed oxide by localized oxidation
C438S225000, C438S297000, C438S424000, C438S435000
Reexamination Certificate
active
06291311
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a semiconductor device and a method for producing same. More particularly, it relates to a semiconductor device of high quality having a high element-to-element voltage withstanding properties, and a method for producing therefor.
BACKGROUND
Referring to the drawings, a conventional method for producing a semiconductor device is explained.
FIGS. 10
to
12
show cross-sectional views for illustrating the conventional method for producing a semiconductor device step-by-step.
FIGS. 10
to
12
are fractionated for convenience of the drawing.
Referring to
FIGS. 10
to
12
, a thermally oxidized film
12
is formed on a silicon substrate 1 to a thickness of 10 nm (
FIG. 10
b
), and a nitride film
13
is deposited thereon to a thickness of 120 nm (
FIG. 10
c
). This nitride film
13
is patterned to a field pattern, using a known lithographic technique (
FIG. 11
d
). The resulting assembly is thermally oxidized at 980° C. to form a field oxide film
3
to a thickness not less than 400 nm (
FIG. 11
e
).
The nitride film
13
then is removed and the oxide film
12
beneath the nitride film
13
also is removed. Then, boron 6 is implanted on the entire wafer surface at an acceleration energy of 100 kev at a doze of 1×10
12
to form a channel stop layer
14
(
FIG. 12
g
).
Here, the field oxide film is explained. For a semiconductor device formed on the semiconductor substrate, local oxidation of silicon (LOCOS) is routinely used for device isolation. However, as the device size becomes finer, the device region is reduced, such that bird's beak like defects (termed as “bird's beak” herein) at LOCOS ends tends to affect the device region to an increasing extent. Since the bird's beak at the LOCOS end can be reduced by reducing the LOCOS film thickness, the LOCOS is recently reduced in thickness and is formed to a thickness on the order of 300 nm.
SUMMARY OF THE DISCLOSURE
However, in the course of the investigations toward the present invention the following problems have been encountered. Namely, if, with the above-described conventional method for producing for the semiconductor device, crystal defects
2
(voids) are contained in a field oxide film
3
, the portion of the implanted crystal defect is exposed, due to subsequent etching of the oxide film
12
by general tens of nm, to produce a recess
4
in the field oxide film
3
due to the crystal defect. In this portion of the recess
4
, the film thickness of the field oxide film
3
is thinner than the other portions of the field oxide film
3
by an amount corresponding to the crystal defect
2
.
If, in this state, implanting for the channel stop layer
6
is performed at
6
by the field-through method, the channel stop layer is implanted below the field of the recess
4
in a deeper depth the case without recess, such that boron is not implanted sufficiently directly below the field. Thus, a low concentration region of channel stop layer
19
is produced.
If an impurity
7
then is implanted (doped) for forming a source/drain diffusion layer, the impurity is implanted into the bulk of the substrate below the field oxide film
3
into which the impurity inherently is not (to be) implanted, that is into the low concentration region of channel stop layer
19
, in the reduced film thickness portion of the field oxide film
3
produced due to the recess
4
ascribable to the crystal defect, thus yielding an inverted layer
20
. Since leakage of electrical charges occurs via this inverted layer
20
, element-to-element (generally termed as “inter-element”) voltage withstanding properties are lowered, thus producing reject products.
The reject products are liable to be produced as the film thickness of the field oxide film
3
is reduced with size refinement of the element and are produced most frequently in products having a minimum design rule of 0.35 &mgr;m (or less). It is noted that the larger the number of substrate pits ascribable to voids in the device isolation area per chip of the semiconductor device at the time of wafer delivery, that is the number of crystal originated particles (COP), the more likely is the inter-element leakage defect to be produced. Thus, for prohibiting the inter-element leakage defect from occurring, it becomes necessary to use crystals with a smaller number of the COP at the time of wafer delivery, or to develop a method for producing which possibly alleviate the effect of substrate pits.
In view of the above-described deficiency in the prior art, it is an object of the present invention to provide a semiconductor device whereby the inter-element leakage can be eliminated while the thin LOCOS oxide film thickness is maintained.
It is another object of the present invention to provide a method for producing such a semiconductor device.
For accomplishing the above object, the present invention provides semiconductor devices and methods according to various aspects. Particularly, according to a first aspect of the present invention there is provided a semiconductor device characterized in that an oxide film for device isolation, formed on a region of a substrate where the effective thickness in the vertical direction of the substrate is decreased due to the presence of a defect, is etched by a predetermined thickness until a recess ascribable to the presence of the defect is exposed, and that subsequently a new oxide film is formed on the first-stated oxide film in an amount corresponding to the predetermined thickness.
In the semiconductor device according to the present invention, an amorphousized portion is formed by implantation of pre-set ions in a portion of a substrate region destined for forming an oxide film for device isolation where the effective thickness in the vertical direction of the substrate is diminished by the presence of a defect.
According to another aspect of the present invention, there is provided a novel method for producing a semiconductor device. The method comprises: etching off the surface of an oxide film for device isolation, formed on a region of a substrate where the effective thickness in the vertical direction of the substrate is decreased due to the presence of a defect, by a predetermined thickness, until a recess ascribable to the presence of the defect is exposed ; and newly forming anoxide film on the first-stated oxide film in an amount corresponding to the predetermined thickness to diminish the depth of the recess ascribable to the presence of the defect.
Also, according to a third aspect, there is provided a method for producing a semiconductor device. In the method, ion implantation may be carried out divisionally a plural number of times when implanting ions for forming a channel stoplayer in a portion of the substrate including the substrate portion directly below the oxide film for device isolation. Thus, when implanting ions for forming the channel stop layer, the ions are caused to travel beyond the maximum film thickness portion of the oxide film for device isolation at the time of initial ion implantation to form a first channel stop and, for next and subsequent ion implantation, a second channel stop layer is formed to overlie the recess of the first channel stop layer in register with the recess of the oxide film for device isolation.
According to a fourth aspect, there is provided another method for producing a semiconductor device. In the method, the predetermined thickness of etching off the oxide film for device isolation is preferably set to a value which does not permit ion flight to a substrate portion directly below the oxide film for device isolation at the time of ion implantation for forming an impurity layer following the formation of the new oxide film on the first-stated oxide film in an amount corresponding to the predetermined thickness.
Also, in a method according to a further aspect of the present invention, inter-lattice oxygen in a substrate is captured in a defect in the substrate by heat-treating the substrate. The defect size can be decreased b
Kitano Tomohisa
Ohashi Takuo
Blum David S.
Bowers Charles
McGinn & Gibb PLLC
NEC Corporation
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