Semiconductor device manufacturing: process – Coating of substrate containing semiconductor region or of... – Multiple layers
Reexamination Certificate
1999-06-08
2001-11-27
Nelms, David (Department: 2818)
Semiconductor device manufacturing: process
Coating of substrate containing semiconductor region or of...
Multiple layers
C438S703000, C438S757000, C438S761000, C438S775000, C438S791000, C438S800000
Reexamination Certificate
active
06323138
ABSTRACT:
TECHNICAL FIELD
This invention pertains to methods of forming silicon nitride layers on silicon-comprising substrate surfaces, to methods of densifying silicon nitride layers, to methods of forming capacitors, and to capacitor constructions.
BACKGROUND OF THE INVENTION
Capacitors are commonly-used electrical components of semiconductor circuitry. A typical capacitor construction comprises a first conductive plate and a second conductive plate, with a dielectric
11
material between and separating the conductive plates. A typical dielectric material used in capacitor constructions comprises three layers, with a first layer being a silicon dioxide layer, a second layer being a silicon nitride layer, and a third layer being another silicon dioxide layer, with the silicon nitride layer being between the silicon dioxide layers. As silicon nitride has a higher dielectric constant than silicon dioxide, it would be desirable to eliminate one or both of the silicon dioxide layers from capacitor dielectric material.
A prior art method of forming a capacitor is described with reference to
FIGS. 1 and 2
. Referring first to
FIG. 1
, a semiconductive wafer fragment
10
is shown at a preliminary step of a prior art processing sequence. Wafer fragment
10
comprises a semiconductive substrate
12
and a first capacitor plate layer
14
overlying substrate
12
. Substrate
12
comprises a lightly doped monocrystalline silicon material. First capacitor plate layer
14
typically comprises conductively doped polysilicon. As will be recognized by persons of ordinary skill in the art, first capacitor plate layer
14
need not be formed in direct physical contact with a semiconductive substrate
12
.
To aid in interpretation of the claims that follow, the term to “semiconductive substrate” is defined to mean any construction comprising semiconductive material, including, but not limited to, bulk semiconductive materials such as a semiconductive wafer (either alone or in assemblies comprising other materials thereon), and semiconductive material layers (either alone or in assemblies comprising other materials). The term “substrate” prefers to any supporting structure, including, but not limited to, the semiconductive substrates described above.
An oxide layer
16
is formed over first capacitor plate layer
14
. Oxide layer
16
is typically native oxide which naturally forms over a polysilicon layer
14
upon exposure to an oxygen-comprising atmosphere.
A silicon nitride layer
18
is formed over silicon oxide layer
16
. Silicon nitride layer
18
is commonly formed by chemical vapor deposition and may be formed, for example, utilizing dichlorosilane and ammonia at a pressure of 500 milliTorr and a temperature of 680° C. Silicon nitride layer
18
commonly has a number of pinholes, or pits,
20
extending partially into or through silicon nitride layer
18
. Such pits are undesirable as they, if left unfilled, would permit shorting between an outer conductive plate
24
(shown in FIG.
2
and discussed below) and inner conductive plate
14
. Accordingly, pits
20
are typically filled.
Referring to
FIG. 2
, a layer of silicon dioxide
22
is formed over silicon nitride layer
18
and within pits
20
to fill pits
20
. Silicon oxide layer
22
is commonly formed by exposing wafer fragment
10
to a wet oxidizing atmosphere at about 850° C.
After formation of silicon oxide layer
22
, a second, or outer, conductive plate layer
24
is formed over oxide layer
22
to complete formation of a capacitor structure
30
. At least one of capacitor plate layers
14
or
24
is electrically connected to a circuit external of capacitor
30
for charging and discharging capacitor
30
.
Another aspect of the prior art pertains to nitridation of silicon surfaces. Such nitridation is commonly utilized to form an insulative layer over silicon services for electrically isolating components of a semiconductor circuit from one another. A prior art nitridation method is described with reference to a wafer fragment
40
in FIG.
3
. Wafer fragment
40
comprises a substrate
42
, a silicon-comprising conductive layer
44
overlying substrate
42
, and a silicon nitride layer
48
overlying conductive layer
44
. Substrate
42
may comprise, for example, a lightly doped monocrystalline silicon wafer. Conductive layer
44
may comprise, for example, conductively doped polysilicon. Also, although not shown, an oxide layer may be formed between conductive layer
44
and nitride layer
48
if, for example, conductive layer
44
comprises polysilicon and is exposed to oxygen prior to formation of silicon nitride layer
48
.
Silicon nitride layer
48
is formed by exposing a surface of silicon-comprising layer
44
to ammonia at a pressure of less than or equal to one atmosphere and at a temperature of about 1000° C. Such process is self-limiting due to poor diffusion of the nitrogen species through the initially formed layer of silicon nitride (Si
3
N
4
). The maximum silicon nitride layer thickness that can be achieved with such process is 35 Angstroms.
SUMMARY OF THE INVENTION
The invention encompasses methods of forming capacitors, methods : of forming silicon nitride layers on silicon-comprising substrates, methods for densifying silicon nitride layers, methods for forming capacitors, and capacitors.
In one aspect, the invention encompasses a method of forming a silicon nitride layer on a silicon-comprising substrate surface wherein the substrate surface is exposed to a nitrogen-comprising ambient having at least about two atmospheres of pressure.
In another aspect, the invention encompasses a method of densifying a silicon nitride layer wherein the silicon nitride layer is subjected to a nitrogen-comprising ambient having at least about two atmospheres of pressure.
In another aspect, the invention encompasses a method of forming a silicon nitride layer on a silicon-comprising substrate surface. The silicon-comprising substrate surface is exposed to a nitrogen-comprising ambient atmosphere having at least about 2 atmospheres of pressure and comprising at least one of N
2
, NH
3
or NO
x
. A temperature of the substrate surface is maintained at less than about 10000° C. during exposure of the substrate surface to the nitrogen-comprising ambient atmosphere. The exposure of the substrate surface to the nitrogen-comprising atmosphere is continued for a time period sufficient to form the silicon nitride layer to a thickness of at least about 20 Angstroms, and preferably to at least about 40 Angstroms.
In another aspect, the invention encompasses a method of forming
10
lo a capacitor. A first capacitor plate is formed, and a dielectric layer , is formed proximate the first capacitor plate. The forming of the dielectric layer includes chemical vapor depositing silicon nitride over a surface of the first capacitor plate surface to form a silicon nitride layer. The silicon nitride layer is exposed to a nitrogen-comprising ambient atmosphere having at least about 2 atmospheres of pressure and comprising at least one of N
2
, NH
3
or NO
x
. A second capacitor plate is formed over the dielectric layer capacitor plate.
In another aspect, the invention encompasses a capacitor. The capacitor includes a first conductive capacitor plate, a second conductive capacitor plate; and capacitor dielectric material intermediate the first and second capacitor plates. All of the dielectric material intermediate the first and second capacitor plates consists essentially of a single oxide layer and a single nitride layer.
In another aspect, the invention encompasses a capacitor. The capacitor includes a first conductive capacitor plate, a second conductive capacitor plate; and a dielectric layer intermediate the first and second capacitor plates. All of the dielectric material intermediate the first and second capacitor plates consists essentially of silicon nitride and has a thickness of at least about 20 Angstroms.
REFERENCES:
patent: 4254161 (1981-03-01), Kemlage
patent: 4882649 (1989-11-01), Chen et al.
patent: 4891684 (1990-01-01),
Berry Renee′ R.
Micro)n Technology, Inc.
Nelms David
Wells St. John P.S.
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