Active solid-state devices (e.g. – transistors – solid-state diode – With means to control surface effects – Insulating coating
Reexamination Certificate
2001-11-26
2004-02-17
Eckert, George (Department: 2815)
Active solid-state devices (e.g., transistors, solid-state diode
With means to control surface effects
Insulating coating
C257S629000, C257S632000, C257S639000
Reexamination Certificate
active
06693345
ABSTRACT:
TECHNICAL FIELD
The invention pertains to methods of forming and patterning photoresist over silicon nitride materials, and to semiconductor wafer assemblies comprising photoresist over silicon nitride materials. The invention also relates generally to semiconductor processing methods of promoting adhesion of photoresist to an outer substrate layer predominantly comprising silicon nitride.
BACKGROUND OF THE INVENTION
Silicon nitride is frequently utilized in modern semiconductor fabrication methods. For instance, silicon nitride is an insulative material, and can be utilized to electrically isolate conductive components from one another. Also, silicon nitride is selectively etchable relative to other materials utilized in semiconductor fabrication processes, such as, for example, silicon dioxide, and is can thus be utilized as an etch stop material. Another example use of silicon nitride is for LOCOS (LOCal Oxidation of Silicon). LOCOS comprises growing oxide over field regions of a semiconductor substrate, while not growing the oxide over other regions of the substrate. The other regions of the substrate are typically protected by a thin layer of silicon nitride during the oxide growth.
In many applications of silicon nitride, a silicon nitride layer is patterned into a specific shape. An example prior art patterning process is described with reference to
FIGS. 1-2
. Referring to
FIG. 1
, a semiconductor wafer fragment
10
comprises a substrate
12
covered by a pad oxide layer
14
, a silicon nitride layer
16
, an antireflective coating
18
, and a photoresist layer
20
.
Substrate
12
can comprise, for example, monocrystalline silicon lightly doped with a p-type dopant. To aid in interpretation of the claims that follow, the term “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” refers to any supporting structure, including, but not limited to, the semiconductive substrates described above.
Pad oxide
14
is a thin layer (from about 40 to about 50 nanometers thick) of silicon dioxide, and is provided to alleviate stresses that can be caused by silicon nitride layer
16
. Pad oxide
14
can be formed by exposing a silicon-comprising substrate
12
to an oxidizing atmosphere.
Silicon nitride layer
16
can be formed over pad oxide
14
by, for example, chemical vapor deposition. A thickness of silicon nitride layer
16
will vary depending on the application of the silicon nitride layer. In LOCOS fabrication processes, silicon nitride layer
16
will typically be provided to a thickness of from about 100 nanometers to about 200 nanometers.
Antireflective coating
18
is a polymer film provided over silicon nitride layer
16
for two purposes. First, antireflective coating
18
absorbs light during photolithographic patterning of photoresist layer
20
. Such absorption can prevent light that has passed through photoresist layer
20
from reflecting back into the layer to constructively or destructively interfere with other light passing through layer
20
. Second, antireflective coating
18
functions as a barrier to prevent diffusion of nitrogen atoms from silicon nitride layer
16
into photoresist layer
20
. It is found that if nitrogen atoms diffuse into photoresist
20
, they can alter its sensitivity to light (so-called “poisoning” of the photoresist).
Photoresist layer
20
is provided to form a pattern over silicon nitride layer
16
. Photoresist layer
20
comprises a polymer composition which becomes selectively soluble in a solvent upon exposure to light. If photoresist
20
comprises a negative photoresist, it is rendered insoluble in a solvent upon exposure to light, and if it comprises a positive photoresist, it is rendered soluble in solvent upon exposure to light.
Referring to
FIG. 2
, photoresist layer
20
is exposed to a patterned beam of light to selectively render portions of the photoresist soluble in a solvent, while leaving other portions insoluble. After such exposure, the solvent is utilized to selectively remove portions of photoresist layer
20
and thereby convert photoresist layer
20
into the pattern shown.
Referring to
FIG. 3
, the pattern from layer
20
is transferred to underlying layers
18
,
16
and
14
by an appropriate etch. A suitable etch can comprise, for example, a plasma-enhanced etch utilizing NF
3
and HBr. In subsequent processing which is not shown, antireflective coating layer
18
and photoresist layer
20
can be removed to leave stacks comprising pad oxide
14
and silicon nitride
16
over substrate
12
. The stacks can then be utilized for subsequent fabrication processes. For instance, the stacks can be utilized for LOCOS by subsequently exposing wafer fragment
10
to oxidizing conditions to grow field oxide between the stacks. As another example, conductive metal layers may be provided between the stacks, and the stacks utilized for electrical isolation of such metal layers.
The above-described processing sequence requires formation of four distinct layers (
14
,
16
,
18
, and
20
), each of which is formed by processing conditions significantly different than those utilized for formation of the other three layers. For instance, antireflective coating
18
is commonly formed by a spin-on process, followed by a bake to remove solvent from the layer. In contrast, silicon nitride layer
16
is typically formed by a chemical vapor deposition process. The spin-on and baking of layer
18
will typically not occur in a common chamber as the chemical vapor deposition of layer
16
, as processing chambers are generally not suited for such diverse tasks. Accordingly, after formation of silicon nitride layer
16
, semiconductor wafer fragment
10
is transferred to a separate processing chamber for formation of antireflective coating
18
. The semiconductive wafer fragment
10
may then be transferred to yet another chamber for formation of photoresist layer
20
.
A continuing goal in semiconductive wafer fabrication processes is to minimize processing steps, and particularly to minimize transfers of semiconductive wafers between separate processing chambers. Accordingly, it would be desirable to develop alternative fabrication processes wherein fabrication steps could be eliminated.
It has been attempted to pattern silicon nitride layers without utilizing an antireflective coating over the layers. However, such creates complications, such as those illustrated in FIG.
4
. Identical numbering is utilized in
FIG. 4
as was utilized with reference to
FIGS. 1-3
, with differences indicated by the suffix “a”. A difference between the semiconductive wafer fragment
10
a
of FIG.
4
and the wafer fragment
10
of
FIGS. 1-3
is that antireflective coating
18
is eliminated from the wafer fragment
10
a
construction. Wafer fragment
10
a
of
FIG. 4
is shown at a processing step analogous to the processing step shown in FIG.
2
. Elimination of antireflective coating layer
18
has enabled nitrogen atoms to diffuse from silicon nitride layer
16
into a lower portion of photoresist layer
20
a
. The nitrogen atoms have altered the photoresist such that regions which should be removed by exposure to a solvent are no longer removable by the solvent. This can render semiconductive wafer fragment
10
a
unsuitable for the further processing described above with reference to FIG.
3
. It would be desirable to develop alternative methods of forming photoresist over silicon nitride which avoid the adverse effects illustrated in FIG.
4
.
Traditional silicon nitride layers have stoichiometries of about Si
3
N
4
. Silicon enriched silicon nitride layers (i.e., silicon nitride layers having a greater concentration of silicon than Si
3
N
4
, such as, for example, Si
4
N
4
) have occasionally been used in semico
DeBoer Scott Jeffrey
Fischer Mark
Martin Annette L.
Moore John T.
Niroomand Ardavan
Eckert George
Micro)n Technology, Inc.
Richards N. Drew
Wells St. John P.S.
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