U.S. patent application number 11/065171 was filed with the patent office on 2005-07-14 for hardened nano-imprinting stamp.
Invention is credited to Jung, Gun-Young, Lee, Heon.
Application Number | 20050150404 11/065171 |
Document ID | / |
Family ID | 32106705 |
Filed Date | 2005-07-14 |
United States Patent
Application |
20050150404 |
Kind Code |
A1 |
Lee, Heon ; et al. |
July 14, 2005 |
Hardened nano-imprinting stamp
Abstract
A hardened nano-imprinting stamp and a method of forming a
hardened nano-imprinting stamp are disclosed. The hardened
nano-imprinting stamp includes a plurality of silicon-based
nano-sized features that have an hardened shell of silicon carbide,
silicon nitride, or silicon carbide nitride. The hardened shell is
made harder than the underlying silicon by a plasma carburization
and/or a plasma nitridation process. During the plasma process
atoms of carbon and/or nitrogen bombard and penetrate a plurality
of exposed surfaces of the nano-sized features and chemically react
with the silicon to form the hardened shell of silicon carbide,
silicon nitride, or silicon carbide nitride. The lifetime,
durability, economy, and accuracy of the resulting hardened
nano-imprinting stamp are improved.
Inventors: |
Lee, Heon; (Sunnyvale,
CA) ; Jung, Gun-Young; (Palo Alto, CA) |
Correspondence
Address: |
HEWLETT-PACKARD COMPANY
Intellectual Property Administration
P. O. Box 272400
Fort Collins
CO
80527-2400
US
|
Family ID: |
32106705 |
Appl. No.: |
11/065171 |
Filed: |
February 23, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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11065171 |
Feb 23, 2005 |
|
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10279407 |
Oct 24, 2002 |
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Current U.S.
Class: |
101/333 |
Current CPC
Class: |
G03F 7/0002 20130101;
B82Y 40/00 20130101; Y10T 428/24355 20150115; B82Y 10/00 20130101;
B81C 99/009 20130101; G03F 7/0017 20130101 |
Class at
Publication: |
101/333 |
International
Class: |
B41K 001/42 |
Claims
1. A hardened nano-imprinting stamp, comprising: a substrate
including a base surface; a plurality of nano-sized features
connected with the substrate and extending outward of the base
surface, the nano-sized features including an outer surface
defining an imprint profile, and the nano-sized features are made
from a material selected from the group consisting of silicon and
polysilicon; and a hardened shell extending inward of the outer
surface by a predetermined depth, the hardened shell is made from a
material selected from the group consisting of silicon carbide,
silicon nitride, and silicon carbide nitride, and the hardened
shell is operative to maintain the imprint profile of the
nano-sized features over repeated engagements of the
nano-imprinting stamp with a media to be imprinted.
2. The hardened nano-imprinting stamp as set forth in claim 1,
wherein the substrate comprises silicon.
3. The hardened nano-imprinting stamp as set forth in claim 1,
wherein the predetermined depth is in a range from about 10.0
angstroms to about 300.0 angstroms.
4-20. (canceled)
Description
FIELD OF THE INVENTION
[0001] The present invention relates generally to a structure and
method of hardening a nano-imprinting stamp. More specifically, the
present invention relates to a structure and method of hardening a
nano-imprinting stamp using a plasma carburization and/or
nitridation process.
BACKGROUND OF THE ART
[0002] Nano-imprinting lithography is a promising technique for
obtaining nano-size (as small as a few tens of nanometers)
patterns. A key step in forming the nano-size patterns is to first
form an imprinting stamp that includes a pattern that complements
the nano-sized patterns that are to be imprinted by the stamp.
[0003] In FIG. 1a, a prior nano-imprint lithography process
includes an imprinting stamp 200 having a plurality of imprint
patterns 202 formed thereon. In FIG. 1b, the imprint patterns 202
consists of a simple line and space pattern having a plurality of
lines 204 separate by a plurality of spaces 206 between adjacent
lines 204. The imprint patterns 202 are carried by a substrate 211.
By pressing (see dashed arrow 201) the imprinting stamp 200 into a
specially designed mask layer 203, a thickness of the mask layer
203 is modulated with respect to the imprint patterns 202 (see FIG.
1a) such that the imprint patterns 202 are replicated in the mask
layer 203.
[0004] Typically, the mask layer 203 is made from a material such
as a polymer. For instance, a photoresist material can be used for
the mask layer 203. The mask layer 203 is deposited on a supporting
substrate 205. Using a step and repeat process, the imprinting
stamp 200 is pressed repeatedly onto the mask layer 203 to
replicate the imprint patterns 202 in the mask layer 203 and to
cover the whole area of the mask layer 203.
[0005] In FIG. 2, after the step and repeat process, the mask layer
203 includes a plurality of nano-size impressions 207 that
complement the shape of the imprint patterns 202. Next, in FIG. 3,
the mask layer 203 is anisotropically etched (i.e. a highly
directional etch) to form nano-sized patterns 209 in the mask layer
203. Typically, the supporting substrate 205 or another layer (not
shown) positioned between the mask layer 203 and the supporting
substrate 205 serves as an etch stop for the anisotropic etch.
[0006] In FIG. 4, each line 204 includes opposed side surfaces
204s, a top surface 204t, opposed face surfaces 204f, and edges
204e. A space 206 separates each line 204. Typically, the imprint
stamp 200 is made from a material such as silicon (Si). For
example, the substrate 211 can be a silicon wafer and the line and
space features (204, 206) can be made from silicon (Si) or
polysilicon (.alpha.-Si). Silicon is the material of choice for
nano-imprint stamps because there are well established
microelectronics processes for manufacturing silicon based
structures and circuits and silicon is readily available at a
reasonable cost.
[0007] However, one of the disadvantages of the prior imprint stamp
200 is that silicon is a soft material and is subject to breakage,
damage, and wear from repeated pressing steps into the mask layer
203. In FIG. 4, a section E-E of the line feature 204 is
particularly subject to wear, damage, and breakage due to repeated
pressing steps. In FIG. 5, an enlarged view of the section E-E of
FIG. 4 illustrates that the edges 204e, the top surface 204t, the
side surfaces 204s, and the face surfaces 204f are particularly
susceptible to wear W from only a few pressing with the mask layer
203.
[0008] In FIG. 6, the imprint stamp 200 is pressed 201 into the
mask layer 203 so that the line features 204 are disposed in the
mask layer 203. Repeated pressing steps cause wear, damage, and
breakage denoted as W at the edges 204e and the top surface 204t of
the line features 204. Only ten or fewer pressing steps can result
in the imprint stamp 200 wearing to the point where it can no
longer be used to form consistent, repeatable, and accurate imprint
patterns 209.
[0009] In FIGS. 7a and 7b, a more detailed view of the wear to the
line features 204 illustrates that the wear is most severe along
the edges 204e and top surface 204t as those portions of the line
features 204 contact the mask layer 203 first and have surface
features that are substantially normal to the direction of pressing
201. Accordingly, as illustrated in FIGS. 8a and 8b, the line
feature 204 quickly deteriorates from the ideal line feature 204 of
FIG. 8a to the wom out line features 204 of FIG. 8b after only a
few pressing cycles with the mask layer 203.
[0010] Fabrication of the imprint stamp 200 is one of the most
crucial and most expensive steps in the entire imprinting
lithography process. Another disadvantage of the prior imprint
stamp 200 is that a cost of manufacturing the imprint stamp 200 is
not recouped because the imprint stamp 200 is damaged and/or wears
out before an adequate number of pressing steps required to justify
the manufacturing cost of the imprint stamp 200 can occur.
Accordingly, the prior imprint stamp 200 is not economical to
manufacture.
[0011] Consequently, there exists a need for a nano-size imprinting
stamp that is resistant to wear, damage, and breakage. There is
also an unmet need for a nano-size imprinting stamp that can retain
consistent, repeatable, and accurate imprint patterns over multiple
pressing cycles so that the cost of manufacturing the nano-size
imprinting stamp is recovered.
SUMMARY OF THE INVENTION
[0012] The hardened nano-imprinting stamp of the present invention
solves the aforementioned disadvantages and limitations of the
prior nano-imprinting stamps. The silicon-based hardened
nano-imprinting stamp of the present invention is made stronger and
tougher by a plasma carburization and/or nitridation process that
forms a hardened shell of silicon carbide (SiC), silicon nitride
(SiN), or silicon carbide nitride (SiCN) along the outer surface of
the hardened nano-imprinting stamp. The plasma carburization and/or
nitridation process easily converts the reactive silicon (Si)
material of the hardened nano-imprinting stamp into silicon carbide
(SiC), silicon nitride (SiN), or silicon carbide nitride (SiCN)
resulting in a hardened nano-size imprinting stamp that is much
stronger than prior imprinting stamps made only of silicon.
[0013] The hardened nano-imprinting stamp has an increased lifetime
and therefore the cost of manufacturing the hardened
nano-imprinting stamp of the present invention can be recovered
because the hardened nano-imprinting stamp can endure several more
additional pressing cycles without wearing out, breaking, or being
damaged, unlike the prior nano-imprinting stamps.
[0014] Other aspects and advantages of the present invention will
become apparent from the following detailed description, taken in
conjunction with the accompanying drawings, illustrating by way of
example the principles of the present invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] FIGS. 1a and 1b are profile and top plan views respectively
of a prior imprint stamp and prior imprint patterns.
[0016] FIG. 2 is a profile view of a prior mask layer with
nano-size impression formed therein by the prior imprint stamp of
FIG. 1a.
[0017] FIG. 3 is a profile view of the prior mask layer of FIG. 2
after an anisotropic etch step.
[0018] FIGS. 4 and 5 are a cross-sectional and profile views
respectively that depict portions of a prior imprint stamp that are
most susceptible to wear, breakage, or damage.
[0019] FIG. 6 is a cross-sectional view depicting a prior imprint
stamp pressed into a mask layer.
[0020] FIGS. 7a and 7b depict wear to the prior imprint stamp
resulting from the pressing step of FIG. 6.
[0021] FIGS. 8a and 8b depict the rapid progression of wear to the
prior imprint stamp after only a few pressing cycles.
[0022] FIG. 9 is a profile view of a nano-imprinting stamp
including a plurality of nano-sized features before a hardening
process according to the present invention.
[0023] FIG. 10a is a profile view depicting exposed edges and
surfaces of the nano-sized features of FIG. 9.
[0024] FIG. 10b is a cross-sectional view depicting a plasma
hardening process for hardening the exposed edges and surfaces of
FIG. 10a according to the present invention.
[0025] FIG. 11 is a cross-sectional view of a hardened shell of a
hardened nano-imprinting stamp according to the present
invention.
[0026] FIGS. 12a and 12b are schematic views depicting a plasma
carburization process for forming a hardened shell according to the
present invention.
[0027] FIGS. 13a and 13b are schematic views depicting a plasma
nitridation process for forming a hardened shell according to the
present invention.
[0028] FIG. 14 is a cross-sectional view depicting a hardened
nano-imprinting stamp pressed into contact with a mask layer
according to the present invention.
[0029] FIGS. 15a and 15b are schematic views depicting a plasma
carburization process and a plasma nitridation process for forming
a hardened shell according to the present invention.
[0030] FIG. 16 is a profile view of a hardened nano-imprinting
stamp including a plurality of hardened nano-sized features
according to the present invention.
DETAILED DESCRIPTION
[0031] In the following detailed description and in the several
figures of the drawings, like elements are identified with like
reference numerals.
[0032] As shown in the drawings for purpose of illustration, the
present invention is embodied in a hardened nano-imprinting stamp
and a method of making a hardened nano-imprinting stamp. The
hardened nano-imprinting stamp comprises a plurality of silicon
based nano-sized features that include a hardened shell formed by a
plasma carburization and/or a plasma nitridation process. A plasma
with a gas comprising carbon and/or nitrogen bombards exposed
surfaces of the nano-sized features and penetrates those surfaces
to react with the silicon to form a silicon carbide, a silicon
nitride, or a silicon carbide nitride material. The atoms of carbon
and/or nitrogen only penetrate the exposed surfaces to a finite
depth so that only a portion of the silicon along the exposed
surfaces is converted into an outer shell of the silicon carbide,
silicon nitride, or the silicon carbide nitride material. As a
result, the nano-sized features have a hardened outer shell (i.e. a
hardened crust) that makes the nano-sized features more resilient
to wear and damage due to repeated pressing cycles with a media to
be imprinted by the nano-imprinting stamp.
[0033] The hardened nano-imprinting stamp of the present invention
is cost effective because the hardened nano-sized features are
durable and therefore have a longer service life that allows for
the cost of manufacturing the hardened nano-imprinting stamp to be
recovered before the service life has ended.
[0034] Additionally, the hardened nano-imprinting stamp of the
present invention is more accurate than the prior nano-imprinting
stamps because the hardened nano-sized features are more durable
and maintain their imprint profiles over repeated pressing cycles
with the media to be imprinted.
[0035] In FIG. 9, prior to a hardening process that will be
described below, a substrate 11 includes a base surface 13 and a
plurality of nano-sized features 12 that are in contact with the
substrate 11 and extend outward of the base surface 13. The
substrate 11 can be made from a material including but not limited
to silicon (Si), single crystal silicon, polysilicon (.alpha.-Si),
silicon oxide (SiO.sub.2), and silicon nitride (SiN.sub.x). For
example, the substrate 11 can be a wafer of single crystal silicon
such as the type commonly used for the fabrication of
microelectronic devices and structures.
[0036] The nano-sized features 12 have dimensions (i.e. a width W
and a height h) that are typically in a range of about 1.0 .mu.m or
less. A length L of the nano-sized features 12 may also be about
1.0 .mu.m or less. Dimensions of a few hundred nanometers or less
are desirable. The nano-sized features 12 can be made from a
silicon-based material including but not limited to silicon (Si)
and polysilicon (.alpha.-Si). For example, using well understood
microelectronics processing techniques, the nano-sized features 12
can be formed by depositing a layer of polysilicon (not shown) on
the base surface 13 of the substrate 11 followed by
lithographically patterning the layer of polysilicon with a mask
layer and then etching through the mask layer to form the
nano-sized features 12 of polysilicon.
[0037] The nano-sized features 12 include an outer surface that
defines an imprint profile. For instance, in FIG. 9, the nano-sized
features 12 have an outer surface that defines a rectangular
imprint profile. Accordingly, when the substrate 11 is pressed into
contact with a media to be imprinted (not shown) the imprint
profile of the nano-sized features 12 is transferred to the media.
The imprint profile of the nano-sized features 12 will be
application dependent and the present invention is not limited by
the imprint profiles of the nano-sized features 12 as illustrated
herein.
[0038] In FIG. 10a, the outer surfaces of the nano-sized features
12 includes opposed side surfaces 128, a top surface 12t, a front
surface 12f, a back surface 12b, edge surfaces 12e, and the base
surface 13. All of the aforementioned surfaces can be exposed
surfaces that are subject to wear, damage, or breakage resulting
from one or more pressing cycles in a nano-imprint lithography
process.
[0039] The edge surfaces 12e are particularly susceptible to wear
and damage. Moreover, the nano-sized features 12 are spaced apart
from one another by a spacing S that can vary among the nano-sized
features 12. That spacing S is also transferred to the media in
which the nano-sized features 12 are imprinted. Accordingly, wear
to the side surfaces 12s will cause the spacing S to increase
thereby reducing the accuracy of the imprint. Wear or damage to the
base surface 13 can also result in a reduction in accuracy of the
imprint. Essentially, the imprint profile and the accuracy of the
imprint made by the nano-sized features 12 depends on the
mechanical stability (i.e. toughness) of the exposed surfaces and
edges.
[0040] In FIG. 10b, the aforementioned outer surfaces (12s, 12e,
12t, 12', 12b) of the nano-sized features 12 and the base surface
13 are exposed to a plasma P. The plasma P bombards those surfaces
and atoms of a material in the plasma P penetrates those surfaces
to a predetermined depth d. The atoms of carbon (C) and/or nitrogen
(N.sub.2) can penetrate the exposed surfaces through a mechanism
such a diffusion, for example. The plasma P comprises a gas that
includes carbon (C) for a plasma carburization process, nitrogen
(N.sub.2) for a plasma nitridation process, and carbon (C) and
nitrogen (N.sub.2) for a plasma carburization and nitridation
process. Accordingly, either carbon atoms and/or nitrogen atoms
penetrate those surfaces to the predetermined depth d and
chemically react with the material of the nano-sized features 12.
The predetermined depth d can vary along the aforementioned
surfaces and need not be equal along all of the surfaces. For
example, the predetermined depth d may be greater (i.e deeper) on
the top surface 12t and base surface 13 than it is on the side
surfaces 12s.
[0041] In FIG. 11, a hardened nano-imprinting stamp 10 results from
the plasma carburization process, plasma nitridation process, or
plasma carburization and nitridation processes. As a result of
those plasma processes, the nano-sized features 12 include a
hardened shell 20 that extends inward of the outer surface to the
predetermined depth d. The hardened shell 20 comprises silicon
carbide (SiC) when the plasma process is the plasma carburization
process. Conversely, the hardened shell 20 comprises silicon
nitride (SiN) when the plasma process is the plasma nitridation
process. If both the plasma earburization process and the plasma
nitridation process are used, then the hardened shell 20 comprises
silicon carbide nitride (SiCN). The resulting silicon carbide
hardened shell 20, silicon nitride hardened shell 20, or silicon
carbide nitride hardened shell 20 is harder and more resilient to
wear, damage, and breakage than an underlying core of softer
silicon-based material that lies beneath the hardened shell 20 of
the nano-sized features 12. Essentially, the hardened shell 20
forms an outrer hardened crust of SiC, SiN, or SiCN that surrounds
an underlying core of the softer silicon (Si) based material.
Consequently, the imprint profile of the nano-sized features 12 is
maintained after repeated engagements of the hardened
nano-imprinting stamp 10 with a media that is to be imprinted by
the hardened nano-imprinting stamp 10.
[0042] The predetermined depth d will be application dependent and
can be determined by factors that include processing time and
temperature, just to name a few. The predetermined depth d is small
relative to the dimensions of the nano-sized features 12. For
example, a width dimension of the nano-sized features 12 (see
D.sub.1 and D.sub.2 in FIG. 11) can be on the order of a few
hundred nanometers. On the other hand, the predetermined depth d
can be on the order of a few hundred angstroms (.ANG.). The
predetermined depth d of the hardened shell 20 can be in a range
from about 10.0 .ANG. to about 300.0 .ANG.. However, for the
embodiments described herein, the predetermined depth d is not to
be construed as being limited to that range, and as was stated
above, the predetermined depth d is application specific.
[0043] In FIG. 14, the hardened nano-imprinting stamp 10 is pressed
into contact with an imprint target 50 that includes a support
substrate 51 and an imprint media 53. The imprint media 53 can be
made from a variety of materials. For example, the imprint media 53
can be a polymer such as a photoresist material used for
photolithography. The nano-sized features 12 of the hardened
nano-imprinting stamp 10 are pressed into the imprint media 53 to
form an imprint that complements the imprint profiles of the
nano-sized features 12. The aforementioned exposed surfaces are in
contact C.sub.P with the imprint media 53 and those points of
contact C.sub.P are resistant to wear and damage due to the
hardened shell 20.
[0044] Accordingly, the surfaces of the hardened nano-imprinting
stamp 10 that will come into contact with the imprint media 53 are
hardened against wear and damage, as is illustrated in FIG. 16,
where the exposed surfaces (12s, 12e, 12t, 12f, 12b shown in
cross-hatched line) of the nano-sized features 12 and the base
surface 13 include the hardened shell 20. Because wearing out of
the nano-sized features 12 is closely related with a hardness of
the material for the nano-sized features 12, a useful lifetime of
the hardened nano-imprinting stamp 10 of the present invention can
be increased by a factor of ten or more.
[0045] FIGS. 12a and 12b illustrate a method of hardening a
nano-imprinting stamp 10 using a plasm carburization process. In
FIG. 12a, the nano-imprinting stamp 10 includes a plurality of
silicon-based nano-sized features 12 that are carried by a
substrate 11. The nano-sized features 12 include a plurality of
exposed surfaces (see 12s, 12e, 12t, 12f, 12b, and 13 in FIGS. 10a
and 10b). The nano-sized features 12 can be made from a material
including but not limited to silicon (Si) and polysilicon
(.alpha.-Si).
[0046] The nano-sized features 12 are carburized in a plasma that
includes a carbon (C) containing gas (denoted as an encircled C in
FIG. 12a). In FIG. 12b, atoms of the carbon C bombard the exposed
surfaces and penetrate into those surfaces. The atoms of the carbon
C chemically react with the silicon of the nano-sized features 12
to form silicon carbide (SiC).
[0047] The carburizing continues until a hardened shell 20 of
silicon carbide (SiC) forms on the exposed surfaces and extends
inward of those surfaces to the predetermined depth d. Resulting is
the hardened nano-imprinting stamp 10 described above in reference
to FIGS. 11, 14, and 16.
[0048] The carbon containing gas can be a hydrocarbon including but
not limited to methane (CH.sub.4) and ethane (C.sub.2H.sub.6). The
plasma carburization process can occur at a temperature in a range
from about 300.degree. C. to about 900.degree. C.
[0049] Similarly, FIGS. 13a and 13b illustrate a method of
hardening a nano-imprinting stamp 10 using a plasma nitridation
process. In FIG. 13a, the nano-imprinting stamp 10 includes a
plurality of silicon-based nano-sized features 12 that are carried
by a substrate 11. The nano-sized features 12 include a plurality
of exposed surfaces (see 12s, 12e, 12t, 12f, 12b, and 13 in FIGS.
10a and 10b). The nano-sized features 12 can be made from a
material including but not limited to silicon (Si) and polysilicon
(.alpha.-Si).
[0050] The nano-sized features 12 are nitridized in a plasma that
includes a nitrogen (N.sub.2) containing gas (denoted as an
encircled N in FIG. 13a). In FIG. 13b, atoms of the nitrogen N
bombard the exposed surfaces and penetrate into those surfaces. The
atoms of the nitrogen N chemically react with the silicon of the
nano-sized features 12 to form silicon nitride (SiN).
[0051] The nitridizing continues until a hardened shell 20 of
silicon nitride forms on the exposed surfaces and extends inward of
those surfaces to the predetermined depth d. Resulting is the
hardened nano-imprinting stamp 10 described above in reference to
FIGS. 11, 14, and 16.
[0052] The nitrogen containing gas can be a material including but
not limited to nitrogen (N.sub.2) or ammonia (NH.sub.3). The plasma
nitridation process can occur at a temperature including but not
limited to room temperature (i.e. 25.degree. C.) or a temperature
that is above room temperature.
[0053] FIGS. 15a and 15b illustrate a method of hardening a
nano-imprinting stamp 10 using a plasma carburization process and a
plasma nitridation process. In FIG. 15a, the nano-imprinting stamp
10 includes a plurality of silicon-based nano-sized features 12
that are carried by a substrate 11. The nano-sized features 12
include a plurality of exposed surfaces (see 12s, 12e, 12t, 12f,
12b, and 13 in FIGS. 10a and 10b). The nano-sized features 12 can
be made from a material including but not limited to silicon (Si)
and polysilicon (.alpha.-Si).
[0054] The nano-sized features 12 are carburized in a plasma that
includes a carbon (C) containing gas (denoted as an encircled C in
FIG. 15a) and nitridized in a plasma that includes a nitrogen
(N.sub.2) containing gas (denoted as an encircled N in FIG. 15a).
In FIG. 15b, atoms of the carbon C and the nitrogen N bombard the
exposed surfaces and penetrate into those surfaces. The atoms of
the carbon C and nitrogen N chemically react with the silicon of
the nano-sized features 12 to form silicon carbide nitride (SiCN).
The carburizing and nitridizing continues until a hardened shell 20
of silicon carbide nitride (SiCN) forms on the exposed surfaces and
extends inward of those surfaces to the predetermined depth d.
Resulting is the hardened nano-imprinting stamp 10 described above
in reference to FIGS. 11, 14, and 16.
[0055] The carbon containing gas can be a hydrocarbon including but
not limited to methane (CH.sub.4) and ethane (C.sub.2H.sub.6). The
plasma carburization process can occur at an elevated temperature
in a range from about 300.degree. C. to about 900.degree. C. The
nitrogen containing gas can be a material including but not limited
to nitrogen (N.sub.2) or ammonia (NH.sub.3). The plasma nitridation
process can occur at a temperature including but not limited to
room temperature (i.e. 25.degree. C.) or a temperature that is
above room temperature. The plasma carburization process can occur
first followed by the plasma nitridation process or vice-versa. The
plasma carburization process and the plasma nitridation process can
occur substantially at the same time in a plasma that includes a
carbon (C) containing gas and a nitrogen (N.sub.2) containing gas.
Those gasses (C, N.sub.2) can be mixed together (i.e. premixed)
before introduction into a chamber in which the plasma
carburization and plasma nitridation will occur.
[0056] Although several embodiments of the present invention have
been disclosed and illustrated, the invention is not limited to the
specific forms or arrangements of parts so described and
illustrated. The invention is only limited by the claims.
* * * * *