U.S. patent application number 13/615312 was filed with the patent office on 2013-06-27 for semiconductor devices having polysilicon gate patterns and methods of fabricating the same.
This patent application is currently assigned to SK HYNIX INC.. The applicant listed for this patent is Yong Seok EUN, Kyong Bong ROUH, Young Jin SON. Invention is credited to Yong Seok EUN, Kyong Bong ROUH, Young Jin SON.
Application Number | 20130161767 13/615312 |
Document ID | / |
Family ID | 48653700 |
Filed Date | 2013-06-27 |
United States Patent
Application |
20130161767 |
Kind Code |
A1 |
ROUH; Kyong Bong ; et
al. |
June 27, 2013 |
SEMICONDUCTOR DEVICES HAVING POLYSILICON GATE PATTERNS AND METHODS
OF FABRICATING THE SAME
Abstract
A semiconductor device including a gate insulation pattern on a
substrate, and a semiconductor gate pattern including an amorphous
silicon pattern and a polycrystalline silicon pattern stacked on a
side of the gate insulation pattern opposite to the substrate. The
amorphous silicon pattern includes anti-diffusion impurities that
suppress diffusion of impurity ions in the semiconductor gate
pattern.
Inventors: |
ROUH; Kyong Bong;
(Icheon-si, KR) ; EUN; Yong Seok; (Seongnam-si,
KR) ; SON; Young Jin; (Seoul, KR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
ROUH; Kyong Bong
EUN; Yong Seok
SON; Young Jin |
Icheon-si
Seongnam-si
Seoul |
|
KR
KR
KR |
|
|
Assignee: |
SK HYNIX INC.
Icheon-si
KR
|
Family ID: |
48653700 |
Appl. No.: |
13/615312 |
Filed: |
September 13, 2012 |
Current U.S.
Class: |
257/412 ;
257/E21.473; 257/E29.255; 438/514 |
Current CPC
Class: |
H01L 29/4941 20130101;
H01L 29/4925 20130101; H01L 21/28035 20130101 |
Class at
Publication: |
257/412 ;
438/514; 257/E29.255; 257/E21.473 |
International
Class: |
H01L 29/78 20060101
H01L029/78; H01L 21/425 20060101 H01L021/425 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 23, 2011 |
KR |
10-2011-0141640 |
Claims
1. A semiconductor device comprising: a semiconductor gate pattern
including a polycrystalline silicon pattern formed over an
amorphous silicon pattern, wherein the amorphous silicon pattern
includes anti-diffusion impurities and is configured to suppress
diffusion of impurity ions.
2. The semiconductor device of claim 1, further comprising: a gate
insulation pattern formed beneath the semiconductor gate pattern in
a substrate, and wherein the semiconductor gate pattern is stacked
on an opposite side of the gate insulation pattern as the
substrate, and a bottom surface of the amorphous silicon pattern
directly contacts a top surface of the gate insulation pattern, and
a top surface of the amorphous silicon pattern directly contacts a
bottom surface of the polycrystalline silicon pattern.
3. The semiconductor device of claim 1, wherein a thickness of the
amorphous silicon pattern is equal to or less than one third a
thickness of the semiconductor gate pattern.
4. The semiconductor device of claim 1, wherein the anti-diffusion
impurities include nitrogen atoms, carbon atoms, or oxygen
atoms.
5. The semiconductor device of claim 1, wherein the semiconductor
gate pattern has a thickness that is less than or equal to about
1000 angstroms (.PI.), and the amorphous silicon pattern has a
thickness that is less than or equal to about 200 angstroms
(.PI.).
6. The semiconductor device of claim 1, wherein a maximum impurity
ion concentration of the amorphous silicon pattern is at least
fifty times greater than an impurity ion concentration in a lower
portion of the polycrystalline silicon pattern adjacent to the
amorphous silicon pattern.
7. The semiconductor device of claim 1, wherein the polycrystalline
silicon pattern is formed not including anti-diffusion
impurities.
8. A method of fabricating a semiconductor device, the method
comprising: forming an amorphous silicon pattern; forming a
polycrystalline pattern over the amorphous silicon pattern to form
a semiconductor gate pattern, wherein the amorphous silicon pattern
includes anti-diffusion impurities and is configured to suppress
diffusion of impurity ions.
9. The method of claim 8, further comprising forming a gate
insulation pattern beneath the semiconductor gate pattern on a
substrate wherein the semiconductor gate pattern is stacked on an
opposite side of the gate insulation pattern as the substrate, and
a bottom surface of the amorphous silicon pattern directly contacts
a top surface of the gate insulation pattern, and a top surface of
the amorphous silicon pattern directly contacts a bottom surface of
the polycrystalline silicon pattern.
10. The method of claim 8, further comprising: forming a gate
insulation layer on a substrate; forming a first amorphous silicon
layer doped with anti-diffusion impurities on a side of the gate
insulation layer opposite to the substrate; forming a second
amorphous silicon layer on a side of the first amorphous silicon
layer opposite to the gate insulation layer; and selectively
crystallizing the second amorphous silicon layer to form a
polycrystalline silicon layer, wherein the first amorphous silicon
layer is doped with the anti-diffusion impurities and the
polycrystalline silicon layer constitutes a semiconductor gate
layer, and wherein the semiconductor gate layer and the gate
insulation layer are patterned to form the gate insulation pattern,
an amorphous silicon pattern and a polycrystalline silicon pattern
sequentially stacked on the substrate after the impurity ions in
the semiconductor gate layer are activated.
11. The method of claim 10, further comprising: forming the
polycrystalline silicon pattern using a first etching process and
forming the amorphous silicon pattern using a second etching
process, and wherein the second etching process is performed using
an etch recipe that exhibits less etch damage than the first
etching process.
12. The method of claim 10, wherein the anti-diffusion impurities
suppress crystallization of the first amorphous silicon layer and
the second amorphous silicon layer is selectively crystallized.
13. The method of claim 10, wherein the anti-diffusion impurities
are injected into the first amorphous silicon layer during
formation of the first amorphous silicon layer.
14. The method of claim 10, wherein the anti-diffusion impurities
are injected into the first amorphous silicon layer after
deposition of the first amorphous silicon layer.
15. The method of claim 10, wherein the first amorphous silicon
layer is formed to a thickness which is equal to or less than one
third a thickness of the semiconductor gate layer.
16. The method of claim 10, wherein the anti-diffusion impurities
include nitrogen atoms, carbon atoms or oxygen atoms.
17. The method of claim 10, wherein the second amorphous silicon
layer is selectively crystallized using a rapid thermal annealing
process performed at a temperature of about 800.degree. C. to about
1000.degree. C.
18. The method of claim 10, further comprising injecting the
impurity ions into the semiconductor gate layer after the second
amorphous silicon layer is selectively crystallized, and annealing
the semiconductor gate layer at a temperature of about 900.degree.
C. to about 1000.degree. C. to activate the impurity ions in the
semiconductor gate layer after the impurity ions are injected into
the semiconductor gate layer.
19. A semiconductor device comprising: a semiconductor gate pattern
comprising a plurality of polycrystalline silicon patterns
comprised of at least a first and second polycrystalline silicon
pattern, and a plurality of amorphous silicon patterns comprised of
at least a first and second amorphous silicon pattern, that are
stacked to form a semiconductor gate pattern, wherein the plurality
of amorphous silicon patterns each include anti-diffusion
impurities and are configured to suppress diffusion of impurity
ions
20. The semiconductor device of claim 19, wherein the plurality of
amorphous silicon patterns and the plurality of amorphous silicon
patterns are alternately stacked on a gate insulation pattern over
a substrate.
Description
CROSS-REFERENCES TO RELATED APPLICATIONS
[0001] The present application claims priority under 35 U.S.C
119(a) to Korean Application No. 10-2011-0141640, filed on Dec. 23,
2011, in the Korean intellectual property Office, which is
incorporated herein by reference in its entirety as set forth in
full.
BACKGROUND
[0002] 1. Field of the Invention
[0003] Embodiments of the present disclosure relate to
semiconductor devices and methods of fabricating the same and, more
particularly, to semiconductor devices having polysilicon gate
patterns and methods of fabricating the same.
[0004] 2. Description of the Related Art
[0005] In general, semiconductor devices employ
metal-oxide-semiconductor (MOS) transistors as active elements to
reduce power consumption. Further, semiconductor devices may employ
resistors and/or capacitors as passive elements together with the
MOS transistors. The MOS transistors can be typically categorized
as either N-channel MOS transistors or P-channel MOS transistors
according to a conductivity type of inversion channel regions
thereof. In some application fields of the MOS transistors, a metal
layer has been used as gate electrode materials of the MOS
transistors. However, in some other application fields of the MOS
transistors, a polysilicon layer has been widely used as the gate
electrode material of the MOS transistors.
SUMMARY
[0006] Embodiments are directed to semiconductor devices having
polysilicon gate patterns and methods of fabricating the same.
[0007] According to some embodiments, a semiconductor device
includes a gate insulation pattern on a substrate and a
semiconductor gate pattern on a side of the gate insulation pattern
opposite to the substrate. The semiconductor gate pattern includes
an amorphous silicon pattern and a polycrystalline silicon pattern.
The amorphous silicon pattern includes anti-diffusion impurities
that suppress diffusion of impurity ions in the semiconductor gate
pattern.
[0008] A thickness of the amorphous silicon pattern may be equal to
or less than one third a thickness of the semiconductor gate
pattern.
[0009] The amorphous silicon pattern may be disposed between the
gate insulation pattern and the polycrystalline silicon
pattern.
[0010] The anti-diffusion impurities may include nitrogen atoms,
carbon atoms or oxygen atoms.
[0011] The semiconductor gate pattern may have a thickness which is
equal to or less than about 1000 angstroms (.PI.). The amorphous
silicon pattern may have a thickness which is less than or equal to
200 angstroms (.PI.).
[0012] According to another embodiment, a semiconductor device
includes a gate insulation pattern on a substrate and a
semiconductor gate pattern on a side of the gate insulation pattern
opposite to the substrate. The semiconductor gate pattern includes
an amorphous silicon pattern and a polycrystalline silicon pattern
stacked on the gate insulation pattern. The amorphous silicon
pattern has a maximum impurity ion concentration which is higher
than an impurity ion concentration in a lower portion of the
polycrystalline silicon pattern adjacent to the amorphous silicon
pattern.
[0013] The maximum impurity ion concentration of the amorphous
silicon pattern may be at least fifty times greater than the
impurity ion concentration in the lower portion of the
polycrystalline silicon pattern adjacent to the amorphous silicon
pattern. According to another embodiment, a method of fabricating a
semiconductor device includes forming a gate insulation layer on a
substrate, forming a first amorphous silicon layer doped with
anti-diffusion impurities on a side of the gate insulation layer
opposite to the substrate, forming a second amorphous silicon layer
on a side of the first amorphous silicon layer opposite to the gate
insulation layer, and selectively crystallizing the second
amorphous silicon layer to form a polycrystalline silicon layer.
The first amorphous silicon layer is doped with the anti-diffusion
impurities and the polycrystalline silicon layer constitutes a
semiconductor gate layer.
[0014] The anti-diffusion impurities may suppress crystallization
of the first amorphous silicon layer and the second amorphous
silicon layer is selectively crystallized.
[0015] The anti-diffusion impurities may be injected into the first
amorphous silicon layer during formation of the first amorphous
silicon layer.
[0016] The anti-diffusion impurities may be injected into the first
amorphous silicon layer after deposition of the first amorphous
silicon layer.
[0017] The first amorphous silicon layer may be formed to a
thickness which is equal to or less than one third a thickness of
the semiconductor gate layer.
[0018] The anti-diffusion impurities may include nitrogen atoms,
carbon atoms or oxygen atoms.
[0019] The second amorphous silicon layer may be selectively
crystallized using a rapid thermal annealing process. The rapid
thermal annealing process may be performed at a temperature of
about 800.degree. C. to about 1000.degree. C.
[0020] The method may further include injecting impurity ions into
the semiconductor gate layer after the second amorphous silicon
layer is selectively crystallized. The method may further include
annealing the semiconductor gate layer at a temperature of about
800.degree. C. to about 1000.degree. C. to activate the impurity
ions in the semiconductor gate layer after the impurity ions are
injected into the semiconductor gate layer. The method may further
include patterning the semiconductor gate layer and the gate
insulation layer to form a gate insulation pattern, a first
amorphous silicon pattern and a polycrystalline silicon pattern
sequentially stacked on the substrate after the impurity ions in
the semiconductor gate layer are activated. The polycrystalline
silicon pattern may be formed using a first etching process, and
the first amorphous silicon pattern may be formed using a second
etching process. The second etching process may be performed using
an etch recipe that exhibits less etch damage than the first
etching process. The second etching process may be performed such
that etch damage applied to the substrate is minimized.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] Embodiments of the inventive concept will become more
apparent in view of the attached drawings and accompanying detailed
description.
[0022] FIG. 1 is a cross sectional view illustrating an example of
MOS transistors having polysilicon gate patterns;
[0023] FIG. 2 is a graph illustrating a concentration profile of
P-type impurity ions distributed in a polysilicon gate pattern, a
gate insulation pattern and a channel region of the MOS transistor
of FIG. 1;
[0024] FIG. 3 is a cross sectional view illustrating a MOS
transistor having a silicon gate pattern according to an
embodiment;
[0025] FIG. 4 is a graph illustrating concentration profiles of
impurity ions distributed in the MOS transistors of FIGS. 1 and
3;
[0026] FIGS. 5, 6, 7 and 8 are cross sectional views illustrating
MOS transistors having silicon gate patterns according to some
example embodiments;
[0027] FIGS. 9 to 17 are cross sectional views illustrating methods
of fabricating a MOS transistor of FIG. 3; and
[0028] FIG. 18 is a graph illustrating test results of impurity
depletion characteristics of silicon gate patterns of MOS
transistors according to some example embodiments.
DETAILED DESCRIPTION OF THE EMBODIMENTS
[0029] Example embodiments are described below with reference to
the accompanying drawings. Many different forms and embodiments are
possible without deviating from the spirit and teachings of this
disclosure and so the disclosure should not be construed as limited
to the example embodiments set forth herein. Rather, these
embodiments are provided so that this disclosure will be thorough,
and convey a scope of the disclosure to those skilled in the art.
In the drawings, the sizes and relative sizes of layers and regions
may be exaggerated for clarity. The same reference numerals or the
same reference designators denote the same elements throughout the
specification.
[0030] Example embodiments are described herein with reference to
cross-section illustrations that are schematic illustrations of
embodiments (and intermediate structures). As such, variations from
the shapes of the illustrations as a result, for example, of
manufacturing techniques and/or tolerances, are to be expected.
Thus, embodiments may not be construed as limited to the particular
shapes of regions illustrated herein but may be construed to
include deviations in shapes that result, for example, from
manufacturing.
[0031] The terminology used herein is for the purpose of describing
particular embodiments only and is not intended to be limiting of
the embodiments. As used herein, the singular forms "a," "an," and
"the" are intended to include the plural forms as well, unless the
context clearly indicates otherwise. It will be further understood
that the terms "has", "having", "comprises," "comprising,"
"includes," and/or "including," when used herein, specify the
presence of stated features, steps, operations, elements, and/or
components, but do not preclude the presence or addition of one or
more other features, steps, operations, elements, components,
and/or groups thereof.
[0032] It will be understood that when an element is referred to as
being "coupled," "connected," or "responsive" to, or "on," another
element, it can be directly coupled, connected, or responsive to,
or on, the other element, or intervening elements may also be
present. In contrast, when an element is referred to as being
"directly coupled," "directly connected," or "directly responsive"
to, or "directly on," another element, there are no intervening
elements present. As used herein the term "and/or" includes any and
all combinations of one or more of the associated listed items.
[0033] It will be understood that, although the terms first,
second, etc. may be used herein to describe various elements, these
elements should not be limited by these terms. These terms are only
used to distinguish one element from another. Thus, a first element
could be termed a second element without departing from the
teachings of the present embodiments.
[0034] Unless otherwise defined, all terms (including technical and
scientific terms) used herein have the same meaning as commonly
understood by one of ordinary skill in the art to which these
embodiments belong. It will be further understood that terms, such
as those defined in commonly used dictionaries, should be
interpreted as having a meaning that is consistent with their
meaning in the context of the relevant art and will not be
interpreted in an idealized or overly formal sense unless expressly
so defined herein.
[0035] FIG. 1 is a cross sectional view illustrating an example MOS
transistor having polysilicon gate patterns. Referring to FIG. 1, a
pair of source/drain regions 120 may be disposed in a substrate
110, for example, a silicon substrate. The pair of source/drain
regions 120 may be spaced apart from each other by a channel region
112 corresponding to a portion of the substrate 110. A gate
insulation pattern 130 such as a silicon oxide pattern may be
disposed on the channel region 112, and a polysilicon gate pattern
140 may be disposed on a side of the gate insulation pattern 130
opposite to the channel region 112. The polysilicon gate pattern
140 should have a sufficiently high conductivity in order that the
polysilicon gate pattern 140 is used as a gate electrode. Thus, the
polysilicon gate pattern 140 should be heavily doped with impurity
ions to have a relatively high impurity concentration. The
polysilicon gate pattern 140, the gate insulation pattern 130 and
the source/drain regions 120 may constitute a MOS transistor
100.
[0036] N-type impurity ions, for example, phosphorus (P) ions or
arsenic (As) ions have been widely used as impurity ions for doping
the polysilicon gate pattern 140. However, if the MOS transistor
100 is a P-channel MOS transistor and the polysilicon gate pattern
140 is doped with N-type impurity ions, the P-channel MOS
transistor may be formed to have a buried channel structure that
causes an increase of channel leakage current. Thus, various
technologies for doping the polysilicon gate patterns of the
P-channel MOS transistors with P-type impurity ions, for example,
boron ions have been proposed to obtain a surface channel structure
of the P-channel MOS transistors.
[0037] If the MOS transistor 100 is a P-channel MOS transistor and
the polysilicon gate pattern 140 is doped with P-type impurity ions
such as boron ions, a lower portion of the polysilicon gate pattern
140 adjacent to the gate insulation pattern 130 may be
insufficiently doped with the boron ions. In this case, an impurity
depletion phenomenon may occur in the lower portion of the
polysilicon gate pattern 140, thereby degrading electrical
characteristics of the MOS transistor 100.
[0038] If the impurity ions are depleted in the lower portion of
the polysilicon gate pattern 140, a portion of a gate voltage
applied to the polysilicon gate pattern 140 may be applied to the
impurity depletion region of the polysilicon gate pattern 140.
Thus, a threshold voltage of the MOS transistor 100 may be
increased. That is, the impurity depletion region of the
polysilicon gate pattern 140 may cause the same effect as if the
gate insulation pattern 130 were thicker. As a result, an
on-current of the MOS transistor may be reduced.
[0039] When boron ions are implanted into the polysilicon gate
pattern 140, an implantation energy of the boron ions may be
increased to heavily dope the lower portion of the polysilicon gate
pattern 140 with the boron ions. In this case, the boron ions in
the lower portion of the polysilicon gate pattern 140 may be
diffused into the channel region 112 through the gate insulation
pattern 130 during the ion implantation process and/or a subsequent
annealing process (also, referred to as a thermal treatment
process) for activating the boron ions. This phenomenon may be
referred to as a boron penetration phenomenon.
[0040] FIG. 2 is a graph illustrating a concentration profile of
P-type impurity ions distributed in a polysilicon gate pattern, a
gate insulation pattern and a channel region of the MOS transistor
of FIG. 1. In FIG. 2, a line indicated by the reference numeral 210
represents a boron concentration profile of the polysilicon gate
pattern 140, the gate insulation pattern 130 and the channel region
112 constituting the MOS transistor 100 illustrated in FIG. 1 when
a lower portion of the polysilicon gate pattern 140 has a
relatively low boron concentration. In contrast, a line indicated
by the reference numeral 220 represents a boron concentration
profile in the polysilicon gate pattern 140, the gate insulation
pattern 130 and the channel region 112 of the MOS transistor 100
illustrated in FIG. 1 when a lower portion of the polysilicon gate
pattern 140 has a relatively high boron concentration.
[0041] As illustrated in a portion `A` of FIG. 1, an impurity
depletion phenomenon in the polysilicon gate pattern 140 may be
suppressed when the lower portion of the polysilicon gate pattern
140 is heavily doped with boron ions (see the line 220), while an
impurity depletion phenomenon in the polysilicon gate pattern 140
may more readily occur when the lower portion of the polysilicon
gate pattern 140 is lightly doped with boron ions (see the line
210).
[0042] As illustrated in portion `B` of FIG. 1, when the lower
portion of the polysilicon gate pattern 140 is heavily doped with
boron ions (see the line 220), the impurity depletion phenomenon in
the polysilicon gate pattern 140 may be suppressed whereas a boron
penetration phenomenon may occur to increase a boron concentration
in the channel region 112. Thus, a threshold voltage of the MOS
transistor 100 may unstably vary. As such, the impurity depletion
phenomenon and the boron penetration phenomenon may have a
trade-off relationship. As a thickness of the polysilicon gate
pattern 140 is reduced, it may be more difficult to suppress both
the impurity depletion phenomenon and the boron penetration
phenomenon.
[0043] FIG. 3 is a cross sectional view illustrating a MOS
transistor having a silicon gate pattern according to an example
embodiment. Referring to FIG. 3, a gate insulation pattern 320 may
be disposed on a substrate 310. The substrate 310 may be a silicon
substrate but is not limited thereto. For example, the substrate
310 may be a silicon-on-insulator (SOI) substrate. A pair of
source/drain regions 314, for example, a pair of impurity regions,
may be disposed in the substrate 310 to be spaced apart from each
other. The substrate 310 between the pair of source/drain regions
314 may act as a channel region 312. The gate insulation pattern
320 may be disposed on the channel region 312. The gate insulation
pattern 320 may include a silicon oxide layer or a high-k
dielectric layer. A semiconductor gate pattern 330 may be disposed
on a side of the gate insulation pattern 320 opposite to the
channel region 312. If a gate voltage over a threshold voltage is
applied to the semiconductor gate pattern 330, the channel region
312 may be converted to have an opposite conductivity type to the
substrate 310. The substrate 310, the source/drain regions 314, the
gate insulation pattern 320 and the semiconductor gate pattern 330
may constitute a semiconductor device 300, for example, a MOS
transistor.
[0044] In an embodiment, the semiconductor gate pattern 330 may be
a silicon gate pattern. For example, the semiconductor gate pattern
330 may be configured to include an amorphous silicon pattern 331
and a polycrystalline silicon pattern 333 which are sequentially
stacked, such that the polycrystalline silicon pattern 333 is
formed over the amorphous silicon pattern 331. A bottom surface of
the amorphous silicon pattern 331 may directly contact a top
surface of the gate insulation pattern 320, and a top surface of
the amorphous silicon pattern 331 may directly contact a bottom
surface of the polycrystalline silicon pattern 333. The amorphous
silicon pattern 331 may be doped with anti-diffusion impurities.
The anti-diffusion impurities may act as interstitial impurities
that occupy voids between silicon atoms in the amorphous silicon
pattern 331. Thus, the anti-diffusion impurities may have a
meta-stable status. In an embodiment, the anti-diffusion impurities
may include nitrogen atoms, carbon atoms or oxygen atoms. In
contrast, the polycrystalline silicon pattern 333 may be partially
crystallized. Thus, the polycrystalline silicon pattern 333 may be
formed not including anti-diffusion impurities.
[0045] The semiconductor gate pattern 330 including the amorphous
silicon pattern 331 and the polycrystalline silicon pattern 333 may
have a thickness which is equal to or less than about 1000
angstroms (.PI.). In an embodiment, the semiconductor gate pattern
330 may have a thickness of about 600 angstroms (.PI.). The
amorphous silicon pattern 331 may have a thickness that is less
than or equal to approximately one third the thickness of the
semiconductor gate pattern 330. For example, when the semiconductor
gate pattern 330 has a thickness of about 600 angstroms (.PI.), the
amorphous silicon pattern 331 may have a thickness of about 200
angstroms (.PI.) or less.
[0046] FIG. 4 is a graph illustrating a difference in concentration
profiles of impurity ions distributed in the MOS transistors of
FIGS. 1 and 3. In FIG. 4, a line indicated by the reference numeral
410 represents a concentration profile of impurity ions distributed
in the polysilicon gate pattern 140, the gate insulation pattern
130 and the channel region 112 of the MOS transistor 100
illustrated in FIG. 1. A line indicated by the reference numeral
420 represents a concentration profile of impurity ions distributed
in the semiconductor gate pattern 330, the gate insulation pattern
320 and the channel region 312 of the MOS transistor 300
illustrated in FIG. 3.
[0047] The concentration profiles 410 and 420 in a portion `C` of
FIG. 4 shows that when the gate pattern was formed of only the
polysilicon gate pattern 140 (see the line 410), the impurity
concentration (i.e., a boron concentration) of the polysilicon gate
pattern 140 was approximately 1.5.times.10.sup.20 atoms/cm.sup.3 at
a depth of approximately 500 angstroms (.PI.) from a top surface of
the polysilicon gate pattern 140 (i.e., at a lower portion of the
polysilicon gate pattern 140, spaced apart from the gate insulation
pattern 130 by about 100 .PI.). In contrast, when the gate pattern
was formed of the semiconductor gate pattern 330 including the
amorphous silicon pattern 331 and the polycrystalline silicon
pattern 333 (see the line 420), the impurity concentration (i.e., a
boron concentration) of the semiconductor gate pattern 330 was
approximately 3.49.times.10.sup.20 atoms/cm.sup.3 at a depth of
about 500 angstroms (.PI.) from a top surface of the semiconductor
gate pattern 330 (i.e., at approximately a mid portion of the
amorphous silicon pattern 331, spaced apart from the gate
insulation pattern 320 by approximately 100 .PI.). As such, if the
semiconductor gate pattern 330 was formed to include the amorphous
silicon pattern 331 containing anti-diffusion impurities, the
impurity concentration of the amorphous silicon pattern 331
adjacent to the gate insulation pattern 320 was at least twice as
high as compared with the MOS transistor illustrated in FIG. 1.
Thus, the amorphous silicon pattern 331 may be configured to
suppress diffusion of the impurity ions. As a result, according to
the embodiment illustrated in FIG. 3, the impurity depletion
phenomenon in the lower portion of the semiconductor gate pattern
330 can be suppressed.
[0048] In other embodiments, the semiconductor gate pattern 330 may
be formed such that a maximum impurity concentration (e.g., boron
concentration) of the amorphous silicon pattern 331 is at least
fifty times greater than the impurity concentration (e.g., boron
concentration) in the lower portion of the polycrystalline silicon
pattern 333 adjacent to the amorphous silicon pattern 331.
[0049] As portion `D` of FIG. 4 illustrates, even though the
amorphous silicon pattern 331 of the MOS transistor 300 had a
relatively high boron concentration of about 3.49.times.10.sup.20
atoms/cm.sup.3 at a mid portion of thereof, the boron concentration
profile in the substrate 310 (e.g., the channel region 312) of the
MOS transistor 300 was substantially equal to the boron
concentration profile in the substrate 110 (e.g., the channel
region 112) of the MOS transistor 100 when a lower portion of the
polysilicon gate pattern 140 of FIG. 1 had a relatively low boron
concentration. This shows that the embodiment illustrated in FIG. 3
can suppress the boron penetration phenomenon. That is, the
anti-diffusion impurities in the amorphous silicon pattern 331 may
gather the boron ions and, thus the boron ions are diffused only in
a bulk region of the amorphous silicon pattern 331 even though a
subsequent annealing process (also, referred to as a thermal
treatment process) is performed. Consequently, the anti-diffusion
impurities in the amorphous silicon pattern 331 may impede the
boron ions in the semiconductor gate pattern 330 from diffusing
into the gate insulation pattern 320 and the substrate 310.
[0050] FIGS. 5, 6, 7 and 8 are cross sectional views illustrating
MOS transistors having silicon gate patterns according to some
example embodiments. Referring to FIG. 5, a semiconductor device
500 according to another embodiment, for example, a MOS transistor
may be configured to include a substrate 510, a gate insulation
pattern 520 disposed on the substrate 510, and a semiconductor gate
pattern 530 disposed on a side of the gate insulation pattern 520
opposite to the substrate 510. The semiconductor gate pattern 530
may be a silicon gate pattern. For example, the semiconductor gate
pattern 530 may include a polycrystalline silicon pattern 531 and
an amorphous silicon pattern 533 which are sequentially stacked on
a side of the gate insulation pattern 520 opposite to the substrate
510.
[0051] A bottom surface of the polycrystalline silicon pattern 531
may directly contact a top surface of the gate insulation pattern
520, and a top surface of the polycrystalline silicon pattern 531
may directly contact a bottom surface of the amorphous silicon
pattern 533. The amorphous silicon pattern 533 may be doped with
anti-diffusion impurities, and the anti-diffusion impurities may
act as interstitial impurities that occupy voids between silicon
atoms in the amorphous silicon pattern 331. Thus, the
anti-diffusion impurities may have a meta-stable status. In an
embodiment, the anti-diffusion impurities may include nitrogen
atoms, carbon atoms or oxygen atoms. In contrast, the
polycrystalline silicon pattern 333 may have a partially
crystallized structure. Thus, the polycrystalline silicon pattern
333 may be formed not including the anti-diffusion impurities.
[0052] Referring to FIG. 6, a semiconductor device 600 according to
another embodiment, for example, a MOS transistor may be configured
to include a substrate 610, a gate insulation pattern 620 disposed
on the substrate 610, and a semiconductor gate pattern 630 disposed
on a side of the gate insulation pattern 620 opposite to the
substrate 610. The semiconductor gate pattern 630 may be a silicon
gate pattern. For example, the semiconductor gate pattern 630 may
include a first amorphous silicon pattern 631, a polycrystalline
silicon pattern 633 and a second amorphous silicon pattern 635
which are sequentially stacked on a side of the gate insulation
pattern 620 opposite to the substrate 610.
[0053] A bottom surface of the first amorphous silicon pattern 631
may directly contact a top surface of the gate insulation pattern
620, and a top surface of the first amorphous silicon pattern 631
may directly contact a bottom surface of the polycrystalline
silicon pattern 633. A top surface of the polycrystalline silicon
pattern 633 may directly contact a bottom surface of the second
amorphous silicon pattern 635. At least one of the first and second
amorphous silicon patterns 631 and 635 may be doped with
anti-diffusion impurities. In an embodiment, the anti-diffusion
impurities may include nitrogen atoms, carbon atoms or oxygen
atoms.
[0054] Referring to FIG. 7, a semiconductor device 700 according to
another embodiment, for example, a MOS transistor may be configured
to include a substrate 710, a gate insulation pattern 720 disposed
on the substrate 710, and a semiconductor gate pattern 730 disposed
on a side of the gate insulation pattern 720 opposite to the
substrate 710. The semiconductor gate pattern 730 may be a silicon
gate pattern. For example, the semiconductor gate pattern 730 may
include a first polycrystalline silicon pattern 731, a first
amorphous silicon pattern 733, a second polycrystalline silicon
pattern 735 and a second amorphous silicon pattern 737 which are
sequentially stacked on a side of the gate insulation pattern 720
opposite to the substrate 710.
[0055] The first and second polycrystalline silicon pattern 731 and
735, and the first and second amorphous silicon patterns 733 and
737, may be alternately stacked on the gate insulation pattern over
a substrate, such that a bottom surface of the first
polycrystalline silicon pattern 731 may directly contact a top
surface of the gate insulation pattern 720, and a top surface of
the first polycrystalline silicon pattern 731 may directly contact
a bottom surface of the first amorphous silicon pattern 733. A top
surface of the first amorphous silicon pattern 733 may directly
contact a bottom surface of the second polycrystalline silicon
pattern 735, and a top surface of the second polycrystalline
silicon pattern 735 may directly contact a bottom surface of the
second amorphous silicon pattern 737. At least one of the first and
second amorphous silicon patterns 733 and 737 may be doped with
anti-diffusion impurities. In an embodiment, the anti-diffusion
impurities may include nitrogen atoms, carbon atoms or oxygen
atoms.
[0056] Referring to FIG. 8, a semiconductor device 800 according to
another embodiment, for example, a MOS transistor may be configured
to include a substrate 810, a gate insulation pattern 820 disposed
on the substrate 810, and a semiconductor gate pattern 830 disposed
on a side the gate insulation pattern 820 opposite to the substrate
810. The semiconductor gate pattern 830 may be a silicon gate
pattern. For example, the semiconductor gate pattern 830 may
include a first amorphous silicon pattern 831, a first
polycrystalline silicon pattern 833, a second amorphous silicon
pattern 835 and a second polycrystalline silicon pattern 837 which
are sequentially stacked on a side of the gate insulation pattern
820 opposite to the substrate 810.
[0057] A bottom surface of the first amorphous silicon pattern 831
may directly contact a top surface of the gate insulation pattern
820, and a top surface of the first amorphous silicon pattern 831
may directly contact a bottom surface of the first polycrystalline
silicon pattern 833. A top surface of the first polycrystalline
silicon pattern 833 may directly contact a bottom surface of the
second amorphous silicon pattern 835, and a top surface of the
second amorphous silicon pattern 835 may directly contact a bottom
surface of the second polycrystalline silicon pattern 837. At least
one of the first and second amorphous silicon patterns 831 and 835
may be doped with anti-diffusion impurities. In an embodiment, the
anti-diffusion impurities may include nitrogen atoms, carbon atoms
or oxygen atoms.
[0058] FIGS. 9 to 17 are cross sectional views illustrating methods
of fabricating a MOS transistor of FIG. 3. Referring to FIG. 9, a
gate insulation layer 322 may be formed on a substrate 310. The
substrate 310 may be a silicon substrate but is not limited
thereto. For example, the substrate 310 may be a
silicon-on-insulator (SOI) substrate. The gate insulation layer 322
may be formed to include a silicon oxide layer or a high-k
dielectric layer. After formation of the gate insulation layer 322,
a cleaning process such as a wet cleaning process may be applied to
a surface of the gate insulation layer 322. A first amorphous
silicon layer 332 may be formed on the cleaned gate insulation
layer 322. The first amorphous silicon layer 332 may be formed to
have a thickness of about 200 angstroms (.PI.) or less. The first
amorphous silicon layer 332 may be formed using a typical
deposition process, for example, a chemical vapor deposition (CVD)
process. During the CVD process for forming the first amorphous
silicon layer 332, a dopant gas for doping the first amorphous
silicon layer 332 with anti-diffusion impurities in addition to a
source gas for depositing the first amorphous silicon layer 332 may
be supplied into a process chamber. A nitrogen gas may be used as
the dopant gas for doping the first amorphous silicon layer 332
with the anti-diffusion impurities. In other embodiments, a carbon
gas or an oxygen gas may be used as the dopant gas for doping the
first amorphous silicon layer 332 with the anti-diffusion
impurities. When the first amorphous silicon layer 332 is formed to
a thickness of about 200 angstroms (.PI.), the dopant gas may be
introduced into the process chamber at a flow rate of about 1
standard cubic centimeter per minute (sccm) to 5 sccm. The
anti-diffusion impurities may suppress diffusion of carrier
impurities such as boron ions into the first amorphous silicon
layer 332 during a subsequent annealing process. Further, the
anti-diffusion impurities may suppress crystallization of the first
amorphous silicon layer 332 during a subsequent annealing process.
In other embodiments, after formation of the first amorphous
silicon layer 332, the anti-diffusion impurities may be then
injected into the first amorphous silicon layer 332.
[0059] Referring to FIG. 10, a second amorphous silicon layer 334
may be formed on a side of the first amorphous silicon layer 332
opposite to the gate insulation layer 322. The second amorphous
silicon layer 334 may be formed to a thickness of about 200
angstroms (.PI.) to 600 angstroms (.PI.) without injection of the
anti-diffusion impurities. The second amorphous silicon layer 334
may be formed using a typical deposition process, for example, a
chemical vapor deposition (CVD) process. In an embodiment, the
first and second amorphous silicon layers 332 and 334 may be formed
using an in-situ process. That is, the first and second amorphous
silicon layers 332 and 334 may be successively formed in the same
process chamber without a vacuum break. In the event that the first
and second amorphous silicon layers 332 and 334 are formed using an
in-situ process, the anti-diffusion impurities may be supplied into
the process chamber only during formation of the first amorphous
silicon layer 332.
[0060] Referring to FIG. 11, the second amorphous silicon layer
(334 of FIG. 10) may be selectively crystallized to form a
polycrystalline silicon layer 336. As a result, a semiconductor
gate layer including the first amorphous silicon layer 332 and the
polycrystalline silicon layer 336 may be formed on the gate
insulation layer 322. The selective crystallization of the second
amorphous silicon layer (334 of FIG. 10) may be achieved by
applying a first annealing process to the substrate including the
first amorphous silicon layer 332 and the second amorphous silicon
layer (334 of FIG. 10). In an embodiment, the first annealing
process may be performed using a rapid thermal annealing process.
The rapid thermal annealing process may be performed at a
temperature of about 800.degree. C. to about 1000.degree. C. During
the first annealing process, the second amorphous silicon layer
(334 of FIG. 10) may be crystallized but the first amorphous
silicon layer 332 may be formed without being crystallized because
of the presence of the anti-diffusion impurities therein. The
anti-diffusion impurities may have a meta-stable status.
[0061] Referring to FIG. 12, impurity ions may be implanted into
the first amorphous silicon layer 332 and the polycrystalline
silicon layer 336. In an embodiment, the impurity ions may be boron
ions. Alternatively, the impurity ions may be N-type impurities,
for example, phosphorus ions. The impurity ions may be implanted
using an ion implantation process, a plasma doping process or a
combination thereof. The impurity ions in the polycrystalline
silicon layer 336 may be vigorously diffused therein.
[0062] In contrast, the impurity ions in the first amorphous
silicon layer 332 may be formed without being diffused therein
because of the presence of the anti-diffusion impurities. That is,
the anti-diffusion impurities in the first amorphous silicon layer
332 may suppress and/or prevent the impurity ions in the first
amorphous silicon layer 332 from being diffused into the
polycrystalline silicon layer 336 and the gate insulation layer 322
as well as the substrate 310. Thus, most of the impurity ions in
the first amorphous silicon layer 332 may still remain therein even
though a subsequent annealing process is performed. Accordingly,
although an ion implantation energy and/or an ion implantation dose
are increased when the impurity ions are implanted into the first
amorphous silicon layer 332 and polycrystalline silicon layer 336,
the anti-diffusion impurities may suppress and/or prevent the
impurity ions in the first amorphous silicon layer 332 and the
polycrystalline silicon layer 336 from penetrating the gate
insulation layer 322 during a subsequent annealing process.
[0063] Referring to FIG. 13, a second annealing process may be
applied to the substrate where the impurity ions are implanted into
the first amorphous silicon layer 332 and the polycrystalline
silicon layer 336. The second annealing process may be performed at
a temperature of about 900.degree. C. to about 1000.degree. C. As a
result of the second annealing process, the impurity ions in the
first amorphous silicon layer 332 and the polycrystalline silicon
layer 336 are activated. The second annealing process may be
performed by sequentially applying a rapid thermal annealing
process and a laser annealing process to the substrate where the
impurity ions are implanted. The rapid thermal annealing process
may sufficiently activate the impurity ions in the polycrystalline
silicon layer 336, and the laser annealing process may sufficiently
activate the impurity ions in the first amorphous silicon layer
332.
[0064] According to a typical method of fabricating a semiconductor
device, it may be difficult to inject sufficient amounts of
impurity ions into a lower portion of a silicon gate layer because
of a penetration phenomenon that may cause the impurity ions to be
diffused into a channel region through a gate insulation layer
between the silicon gate layer and the channel region. If the
impurity ions are not sufficiently injected into the lower portion
of a semiconductor gate pattern, an impurity depletion phenomenon
may occur in the lower portion of the silicon gate layer. Thus,
there may be a limitation in reducing a sheet resistance of the
silicon gate layer. However, according to the present embodiment, a
sufficient amount of impurity ions may be injected and accumulated
in the lower portion (e.g., the first amorphous silicon layer 332)
of the semiconductor gate layer, and the impurity ions in the first
amorphous silicon layer 332 may be sufficiently activated using the
laser annealing process without out-diffusion of the impurity ions.
Hence, the sheet resistance of the semiconductor gate layer may be
reduced. Accordingly, after the second annealing process is
performed, the semiconductor gate layer including the first
amorphous silicon layer 332 and the polycrystalline silicon layer
336 may exhibit the same or similar impurity concentration profile
to the line plotted by the reference numeral 420 of FIG. 4.
[0065] Referring to FIG. 14, a mask pattern 350 may be formed on
the polycrystalline silicon layer 336. The mask pattern 350 may be
formed of a photoresist layer or a hard mask layer. The hard mask
layer may be formed of a material layer having a sufficiently high
etch selectivity with respect to the first amorphous silicon layer
332 and the polycrystalline silicon layer 336. The mask pattern 350
may be formed to have an opening 352 that leaves exposed a portion
of the polycrystalline silicon layer 336. A first etching process
may be then applied to the exposed portion of the polycrystalline
silicon layer 336, as indicated by arrows in FIG. 14.
[0066] Referring to FIG. 15, as a result of the first etching
process, the exposed portion of the polycrystalline silicon layer
336 may be removed to form a polycrystalline silicon pattern 333
that remains under the mask pattern 350 and leaves a portion of the
first amorphous silicon layer 332 exposed. Subsequently, a second
etching process may be applied to the exposed portion of the first
amorphous silicon layer 332, as indicated by arrows in FIG. 15.
During the second etching process, the gate insulation layer 322
may also be etched. The second etching process may be performed
using an etch recipe that exhibits less etch damage than the first
etching process. This is for minimizing the etch damage applied to
the substrate 310 during second etching process.
[0067] Referring to FIG. 16, as a result of the second etching
process, an amorphous silicon pattern 331 and a gate insulation
pattern 320 may be formed under the polycrystalline silicon pattern
333. The amorphous silicon pattern 331 and the gate insulation
pattern 320 may be formed to have substantially the same width as
the polycrystalline silicon pattern 333. The amorphous silicon
pattern 331 and the polycrystalline silicon pattern 333 may
constitute a semiconductor gate pattern 330, for example, a silicon
gate pattern.
[0068] The second etching process may apply relatively less etch
damage to the substrate 310 as compared with the first etching
process, as described above. In this case, an etch rate of the
second etching process may be gradually reduced as the etching time
elapses, and the amorphous silicon pattern 331 may be formed to
have a sloped sidewall profile indicated by dotted lines F.
However, according to the present embodiment, the amorphous silicon
pattern 331 can be heavily doped with a sufficient amount of
impurity ions. Thus, the high impurity concentration of the
amorphous silicon pattern 331 may compensate for the low etch rate
of the second etching process. Further, an amorphous material may
exhibit a relatively high etch rate as compared with a
polycrystalline material and a single crystalline material.
Accordingly, the crystallographic structure of the amorphous
silicon pattern 331 may also compensate for the low etch rate of
the second etching process. Consequently, the amorphous silicon
pattern 331 may be formed to have substantially a vertical sidewall
profile S even though the second etching process is performed using
an etch recipe that exhibits less etch damage than the first
etching process.
[0069] Referring to FIG. 17, an ion implantation process and a
drive-in process (e.g., an annealing process) may be applied to the
substrate, as indicated by arrows in FIG. 17. As a result of the
ion implantation process and the drive-in process, a pair of
impurity junction regions such as source/drain regions 314 may be
formed in the substrate 310.
[0070] FIG. 18 is a graph illustrating test results of impurity
depletion characteristics of silicon gate patterns of MOS
transistors according to example embodiments. In FIG. 18, the
abscissa represents split groups of test wafers, and the ordinate
represents impurity depletion rates of silicon gate patterns. In
FIG. 18, the split group indicated by the symbol "#1" was
fabricated to include silicon gate patterns having only
polycrystalline silicon patterns, and the split groups indicated by
the symbols "#2" and "#3" were fabricated to include silicon gate
patterns according to the example embodiments described above. That
is, each of the silicon gate patterns of the test wafers #2 and #3
was formed to include an amorphous silicon pattern doped with
nitrogen atoms (acting as anti-diffusion impurities) and a
polycrystalline silicon pattern, as described with reference to
FIGS. 9 to 17. The test wafer #3 was doped with higher doping
energy than the test wafer #2. Further, impurity ions (acting as
carrier impurities) in the amorphous silicon pattern were activated
using a laser annealing process. As the test results of FIG. 18
shows, the impurity depletion rates (PDR) of the silicon gate
patterns of the test wafers #2 and #3 were higher than the impurity
depletion rates (PDR) of the silicon gate patterns of the test
wafers #1. Thus the impurity depletion phenomenon may be suppressed
more in the test wafer #2 and #3 than in the test wafer #1.
Further, the impurity depletion rates (PDR) of the silicon gate
patterns of the test wafers #3 were higher than the impurity
depletion rates (PDR) of the silicon gate patterns of the test
wafers #2.
[0071] According to the embodiments set forth above, at least a
lower portion of a semiconductor gate pattern adjacent to a gate
insulation pattern can be heavily doped with sufficient amounts of
impurity ions and anti-diffusion impurities. Thus, an impurity
depletion phenomenon that may occur in the semiconductor gate
pattern can be suppressed to improve electrical characteristics of
a semiconductor device including the semiconductor gate
pattern.
[0072] Further, the anti-diffusion impurities suppress and/or
prevent the impurity ions in the semiconductor gate pattern from
being diffused into a substrate through the gate insulation
pattern. Thus, the semiconductor device can stably operate.
[0073] The example embodiments of the inventive concept have been
disclosed above for illustrative purposes. Those skilled in the art
will appreciate that various modifications, additions and
substitutions are possible, without departing from the scope and
spirit of the inventive concept as disclosed in the accompanying
claims.
* * * * *