U.S. patent application number 12/345540 was filed with the patent office on 2010-05-13 for transistor for preventing or reducing short channel effect and method for manufacturing the same.
This patent application is currently assigned to HYNIX SEMICONDUCTOR INC.. Invention is credited to Young Hwan Joo, Kyoung Bong Rouh.
Application Number | 20100117131 12/345540 |
Document ID | / |
Family ID | 42164388 |
Filed Date | 2010-05-13 |
United States Patent
Application |
20100117131 |
Kind Code |
A1 |
Rouh; Kyoung Bong ; et
al. |
May 13, 2010 |
Transistor for Preventing or Reducing Short Channel Effect and
Method for Manufacturing the Same
Abstract
A transistor for preventing or reducing short channel effect
includes a substrate; a gate stack disposed over the substrate; a
first junction region disposed on the substrate at a first side
surface of the gate stack, said first junction layer being formed
of an epitaxial layer; a trench formed within the substrate at a
second side surface of the gate stack; and a second junction region
disposed below the trench, said second junction layer being lower
than the first junction region.
Inventors: |
Rouh; Kyoung Bong;
(Icheon-si, KR) ; Joo; Young Hwan; (Cheongju-si,
KR) |
Correspondence
Address: |
MARSHALL, GERSTEIN & BORUN LLP
233 SOUTH WACKER DRIVE, 6300 SEARS TOWER
CHICAGO
IL
60606-6357
US
|
Assignee: |
HYNIX SEMICONDUCTOR INC.
Icheon-si
KR
|
Family ID: |
42164388 |
Appl. No.: |
12/345540 |
Filed: |
December 29, 2008 |
Current U.S.
Class: |
257/300 ;
257/E21.615; 257/E29.255; 438/239 |
Current CPC
Class: |
H01L 29/78 20130101;
H01L 29/66666 20130101; H01L 29/1037 20130101; H01L 29/66659
20130101; H01L 29/66636 20130101; H01L 29/66575 20130101; H01L
29/66621 20130101; H01L 29/41766 20130101 |
Class at
Publication: |
257/300 ;
438/239; 257/E29.255; 257/E21.615 |
International
Class: |
H01L 29/78 20060101
H01L029/78; H01L 21/8232 20060101 H01L021/8232 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 12, 2008 |
KR |
10-2008-0111990 |
Claims
1. A transistor for preventing or reducing short channel effect,
comprising: a substrate; a gate stack disposed over the substrate;
a first junction region disposed on the substrate at a first side
surface of the gate stack, said junction layer formed of an
epitaxial layer; a trench formed within the substrate at a second
side surface of the gate stack; and a second junction region
disposed below the trench, said junction being lower than the first
junction region.
2. The transistor for preventing or reducing short channel effect
of claim 1, further comprising a first contact plug in contact with
the first junction region; and a second contact plug filling the
trench and in contact with the second junction region.
3. The transistor for preventing or reducing short channel effect
of claim 1, wherein the substrate comprises a trench formed within
the substrate at the first side surface of the gate stack, and the
first junction region is formed of an epitaxial layer filling the
trench.
4. The transistor for preventing or reducing short channel effect
of claim 1, wherein in a cell region, the first junction region
comprises a drain region to be connected to a capacitor.
5. The transistor for preventing or reducing short channel effect
of claim 1, wherein in a peripheral circuit region, the first
junction region comprises a drain region to which a drain-source
voltage V.sub.ds is to be applied.
6. The transistor for preventing or reducing short channel effect
of claim 1, wherein the epitaxial layer is formed of a doped
epitaxial layer.
7. The transistor for preventing or reducing short channel effect
of claim 6, wherein the doped epitaxial layer comprises an impurity
region into which N-type or P-type impurities are implanted.
8. The transistor for preventing or reducing short channel effect
of claim 1, wherein the gate stack fills a recess trench comprising
a first side wall formed within the semiconductor substrate in a
vertical direction and a second side wall having a predetermined
angle with respect to the surface of the semiconductor substrate
and a vertical end, which is in contact with a vertical end of the
first side wall.
9. A method for manufacturing a transistor for preventing or
reducing short channel effect, comprising: forming a gate stack
over a substrate; exposing a side surface of the gate stack and a
first portion of the substrate; forming a first trench by etching
the exposed first portion of the substrate; forming a first
junction region by filling the first trench with an epitaxial
layer; exposing the other side surface of the gate stack and a
second portion of the substrate while blocking the first junction
region; forming a second trench which is deeper than the first
trench by etching the exposed second portion of the substrate; and
forming a second junction region within the substrate below the
second trench by performing an ion implantation process on the
exposed second trench.
10. The method of claim 9, wherein forming the gate stack
comprises: forming a recess trench including a first side wall
formed within the semiconductor substrate in a vertical direction
and a second side wall having a predetermined angle with respect to
the surface of the semiconductor substrate; forming the gate stack
so as to be aligned with the recess trench; and forming a spacer on
the side wall of the gate stack.
11. The method of claim 9, comprising forming the epitaxial layer
by Selective Epitaxial Growth (SEG).
12. The method of claim 9, wherein in a cell region, the first
junction region comprises a drain region to be connected to a
capacitor.
13. The method of claim 9, wherein in a peripheral circuit region,
the first junction region comprises a drain region to which a
drain-source voltage V.sub.ds is to be applied.
14. The method of claim 9, wherein forming the first junction
region comprises: forming the epitaxial layer as an undoped
Selective Epitaxial Growth (SEG) layer; implanting N-type
conductive impurities into the epitaxial layer; and annealing the
epitaxial layer thereby forming the first junction region.
15. The method of claim 9, wherein forming the first junction
region comprises: forming the epitaxial layer as an undoped
Selective Epitaxial Growth (SEG) layer; implanting N-type or P-type
conductive impurities into the epitaxial layer; and annealing the
epitaxial layer thereby forming the first junction region.
16. The method of claim 9, wherein forming the first junction
region comprises: forming the epitaxial layer as an doped Selective
Epitaxial Growth (SEG) layer; and annealing the epitaxial layer
thereby forming the first junction region.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] Priority to Korean patent application number
10-2008-0111990, filed on Nov. 12, 2008, the disclosure of which is
incorporated by reference in its entirety, is claimed.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates generally to a semiconductor
device, and more particularly, to a transistor for preventing and
reducing short channel effect and a method for manufacturing the
same.
[0004] 2. Description of Related Technology
[0005] As a design rule is rapidly reduced with an increase in
integration of semiconductor devices, a channel length of a
transistor has also been shortened. As the channel length of the
transistor is shortened, problems caused by short channel effect
degrade operation properties of the device. The short channel
effect is generated as a width of a depletion region, generated
between a substrate and a source, or between the substrate and a
drain, is increased when a junction is formed on the substrate.
When the channel length is shortened, intensity of an electric
field is increased in the vicinity of a drain region. When the
intensity of the electric field is increased, leakage current is
generated in a capacitor unit in a cell region, and this leakage
current deteriorates refresh properties of the device. Also, when
the intensity of the electric field is increased, hot carriers and
punch-through are generated and the operation properties and
stability of the device are thus lowered.
[0006] Accordingly, to prevent or reduce a short channel effect,
methods capable of ensuring an effective channel length without an
increase in the design rule are desirable. In a method of ensuring
an effective channel length, a recess gate in which a recess trench
is formed within a substrate or a step gate in which a gate
electrode is formed in a stepped form are typically employed to
lengthen the channel. By employing gates with increased channel
length through structural modification, it is possible to increase
margins for the prevention of hot carrier generation and
punch-through.
[0007] However, it is difficult to achieve a device operating at
high speed because drain saturation current (ID.sub.sat) is
noticeably reduced with the increase in the channel length. For
example, in a peripheral region of a Dynamic Random Access Memory
(DRAM) device, the leakage current is increased due to Drain
Induced Barrier Lowering (DIBL) phenomenon when a drain-source
voltage (V.sub.ds) is increased to increase the saturation current.
The DIBL phenomenon means that a potential energy barrier is
lowered by interaction of the source and the drain as the channel
length is reduced. The potential energy barrier for electrons in
the channel is lowered. The aforementioned problems caused by short
channel effect and the DIBL phenomenon depend on the width of the
depletion region and the electric field generated upon formation of
a junction region using an ion implantation process. Accordingly, a
method capable of controlling the width of the depletion region and
the intensity of the electric field and preventing the degradation
of device properties is desirable.
SUMMARY OF THE INVENTION
[0008] In one embodiment, a transistor for preventing or reducing a
short channel effect includes a substrate; a gate stack disposed
over the substrate; a first junction region disposed on the
substrate at a first side surface of the gate stack and formed of
an epitaxial layer; a trench formed within the substrate at a
second side surface of the gate stack; and a second junction region
disposed below the trench lower than the first junction region.
[0009] Preferably, the transistor may further include a first
contact plug in contact with the first junction region; and a
second contact plug filling the trench and in contact with the
second junction region.
[0010] Preferably, the substrate includes a trench formed within
the substrate at the first side surface of the gate stack, and the
first junction region is formed by filling the trench with an
epitaxial layer.
[0011] Preferably, in a cell region, the first junction region
includes a drain region connected to a capacitor.
[0012] Preferably, in a peripheral circuit region, the first
junction region includes a drain region to which a drain-source
voltage V.sub.ds is applied.
[0013] Preferably, the epitaxial layer is formed of a doped
epitaxial layer.
[0014] Preferably, the doped epitaxial layer may further include an
impurity region into which N-type or P-type impurities are
implanted.
[0015] Preferably, the gate stack is formed by filling a recess
trench, said trench including a first side wall formed within the
semiconductor substrate in a vertical direction and a second side
wall having a predetermined angle with respect to the surface of
the semiconductor substrate and a vertical end, which is in contact
with a vertical end of the first side wall.
[0016] In another embodiment, a method for manufacturing a
transistor for preventing or reducing short channel effect includes
forming a gate stack over a substrate; exposing a side surface of
the gate stack and a first portion of the substrate; forming a
first trench by etching the exposed first portion of the substrate;
forming a first junction region by filling the first trench with an
epitaxial layer; exposing the other side surface of the gate stack
and a second portion of the substrate while blocking the first
junction region; forming a second trench which is deeper than the
first trench by etching the exposed second portion of the
substrate; and forming a second junction region within the
substrate below the second trench by performing an ion implantation
process on the exposed second trench.
[0017] Preferably, the step of forming the gate stack includes
forming a recess trench including a first side wall formed within
the semiconductor substrate in a vertical direction and a second
side wall having a predetermined angle with respect to the surface
of the semiconductor substrate and a vertical end, which is in
contact with a vertical end of the first side wall; forming the
gate stack so as to be aligned with the recess trench; and forming
a spacer on the side wall of the gate stack.
[0018] Preferably, forming the first junction region includes
forming the epitaxial layer by undoped Selective Epitaxial Growth
(SEG); implanting N-type conductive impurities onto the epitaxial
layer; and forming the first junction region by performing
annealing over the epitaxial layer.
[0019] Alternatively, forming the first junction region includes
forming the epitaxial layer by undoped Selective Epitaxial Growth
(SEG); implanting N-type or P-type conductive impurities onto the
epitaxial layer; and forming the first junction region by
performing annealing over the epitaxial layer.
[0020] Alternatively, forming the first junction region includes
forming the epitaxial layer by doped Selective Epitaxial Growth
(SEG); and forming the first junction region by performing
annealing over the epitaxial layer.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] FIG. 1 illustrates a transistor for preventing or reducing
short channel effect according to an embodiment of the present
invention.
[0022] FIGS. 2 to 10 illustrate a process of manufacturing the
transistor for preventing or reducing short channel effects
according to an embodiment of the present invention.
[0023] FIGS. 11 and 12 illustrate a gate stack structure according
to another embodiment of the present invention.
DESCRIPTION OF SPECIFIC EMBODIMENTS
[0024] Hereinafter, preferred embodiments will be described with
reference to the accompanying drawings. However, the embodiments
are for illustrative purpose only and are not intended to limit the
scope of the invention.
[0025] FIG. 1 illustrates a transistor for preventing or reducing
short channel effect according to an embodiment of the present
invention.
[0026] Referring to FIG. 1, in the transistor for preventing or
reducing short channel effect according to an embodiment of the
present invention, a gate stack 110 and a gate dielectric layer 105
are disposed over a semiconductor substrate 100. The gate stack 110
is preferably formed of, but not limited to, a polysilicon layer, a
tungsten layer and a nitride layer sequentially stacked.
[0027] Spacers 120 are typically formed at both sides of the gate
stack 110 and the gate dielectric layer 105. A first junction
region 125, made of an epitaxial layer, is disposed above the
semiconductor substrate 100 at a first side surface of the gate
stack 110. The first junction region 125 is a drain region
connected to a capacitor in a cell region and a drain region, to
which a drain-source voltage V.sub.ds is applied, in a peripheral
circuit region. The epitaxial layer may be formed of a doped
epitaxial layer. The doped epitaxial layer may include an impurity
region into which N-type or P-type impurities are implanted.
[0028] A trench 127 is formed within the semiconductor substrate at
a second side surface of the gate stack 110. A second junction
region 130 disposed below the trench 127, which is located lower
than the first junction region 125, is formed. A first contact plug
140 is formed in contact with the first junction region 125, and a
second contact plug 145 is formed to fill the trench 127 and be in
contact with the second junction region 130.
[0029] The first contact plug 140 connects a capacitor to be formed
later and the first junction region 125 in the cell region and
allows electrical operation in the second junction region to which
the drain-source voltage V.sub.ds is applied, in the peripheral
circuit region. The transistor for preventing or reducing short
channel effect can reduce an increase in the electric field because
the first junction region 125 is formed of an epitaxial layer. With
reduction in the electric field, the refresh properties can be
enhanced in the cell region and the DIBL properties, which have
been reduced upon increase in the drain-source voltage, can be
improved in the peripheral region. Also, it is possible to reduce
contact resistance by employing the epitaxial layer. Further, the
channel length is lengthened because the first junction region 125
formed of the epitaxial layer and the second junction region 130
are formed with asymmetric positions. Therefore, it is possible to
prevent the short channel effect caused by the reduction in the
device size.
[0030] A method for manufacturing the transistor for preventing or
reducing short channel effect according to an embodiment will be
described with reference to the accompanying drawings. FIGS. 2 to
10 illustrate a process of manufacturing the transistor for
preventing or reducing short channel effect according to an
embodiment.
[0031] Referring to FIG. 2, a gate stack 210 and a gate dielectric
layer 205 are formed over a semiconductor substrate 200. The gate
stack 210 is generally formed of, but not limited to, a
sequentially stacked structure comprising a polysilicon layer, a
tungsten layer and a nitride layer. A spacer 215 is formed on a
first and second side surfaces of the gate stack 210. The spacer
215 is preferably formed of a nitride layer.
[0032] Referring to FIG. 3, a hard mask layer pattern 220 is
formed, which exposes a side surface of the gate stack 210 and a
first portion of the semiconductor substrate 200. For example, a
hard mask layer is deposited over the front surface of the
semiconductor substrate 200. The hard mask layer typically includes
a nitride layer. A resist is coated over the hard mask layer and a
lithography process including exposure and development is performed
to form a resist layer pattern (not shown) that exposes some of the
hard mask layer. The exposed portion of the hard mask layer is
etched using the resist layer pattern as an etching mask to form
the hard mask layer pattern 220. The hard mask layer pattern 220
exposes the spacer 215 at a side surface of the gate stack 210 and
the first portion of the semiconductor substrate 200, but covers
the rest.
[0033] Referring to FIG. 4, the exposed first portion of the
semiconductor substrate 200 is etched using the hard mask layer
pattern 220 as an etching mask to form a first trench 225 within
the semiconductor substrate 200. The first trench 225 is formed by
etching the semiconductor substrate 200 by a first depth D1 from
the surface of the semiconductor substrate 200.
[0034] Referring to FIG. 5, the first trench 225 is filled with an
epitaxial layer to form a first junction region 230. The first
junction region 230 is a drain region in which a capacitor is to be
inserted in the cell region and a drain region to which a
drain-source voltage V.sub.ds is to be applied in the peripheral
region. The epitaxial layer may be formed using Selective Epitaxial
Growth (SEG). For example, a source gas for the epitaxial growth is
supplied onto the semiconductor substrate 200 formed with the first
trench 225. The source gas preferably includes a silane (SiH.sub.4)
gas or a silicon source. A silicon layer is grown from the bottom
of the first trench 225 to form the epitaxial layer which fills the
first trench 225. The first junction region 230 may be formed in
such a manner that an epitaxial layer is formed as a doped SEG
layer and an annealing step may then be performed. The annealing
may be performed by Rapid Thermal Annealing (RTA). The first
junction region 230 may be formed by completely filling the first
trench 225 or by partially filling the first trench 225. The first
junction region 230 may also be formed in such a manner that an
epitaxial layer is formed as an undoped SEG layer, impurities are
implanted, and annealing is then performed. This will be further
described in FIG. 10.
[0035] The other side surface of the gate stack 210 blocked by the
hard mask layer pattern 220 is not affected by the SEG. Therefore,
it is possible to form the first junction region 230 by selectively
filling the first trench 225 alone with the epitaxial layer. As a
result, it is possible to decrease the intensity of the electric
field generated in the drain region because the first junction
region 230, formed of an epitaxial layer, is disposed above the
semiconductor substrate at a side surface of the gate stack 210.
Also, it is possible to form the more uniform intensity of the
electric field in the first junction region 230 than that in the
junction region formed by the implantation process. After that, the
hard mask layer pattern 220 is removed by a strip process.
[0036] Referring to FIG. 6, a resist layer pattern 235 is formed
which covers the first junction region 230 but exposes a second
portion of the semiconductor substrate 200. For example, a resist
layer is formed over a surface of the semiconductor substrate 200.
A lithography process including exposure and development is
performed on the resist layer to form the resist layer pattern 235.
The resist layer pattern 235 exposes the spacer 215 on the other
side surface of the gate stack 210 and the second portion of the
semiconductor substrate 200, but covers the first junction region
230.
[0037] Referring to FIG. 7, the exposed second portion of the
semiconductor substrate 200 is etched using the resist layer
pattern 235 as an etching mask to form a second trench 240. The
second trench 240 is formed by etching the semiconductor substrate
200 by a second depth D2 from the surface of the semiconductor
substrate 200. Preferably, the second depth D2 of the second trench
240 is greater than the first depth D1 of the first trench 225.
[0038] Referring to FIG. 8, as indicated by arrows, impurities are
implanted into the second trench 240 using the resist layer pattern
235 as an ion implantation barrier. The implanted impurities are
diffused and a second junction region 245 is formed within the
semiconductor substrate 200 below the second trench 240. The second
junction region may be disposed higher than the first junction
region 230 when the electric field is not large.
[0039] Referring to FIG. 9, a first contact plug 250 which fills
the second trench 240 and a second contact plug 255 in contact with
the first junction region are formed. For example, a conductive
layer is deposited over the semiconductor substrate 200. The
conductive layer may be formed of a polysilicon layer to a
thickness capable of fully filling the second trench 240. A
planarization process can be performed on the semiconductor
substrate 200 to separate the conductive layer. The planarization
may be performed by Chemical Mechanical Polishing (CMP). Then, the
first contact plug 250 which fills the second trench 240 and the
second contact plug 255 in contact with the first junction region
are formed over the semiconductor substrate 200. The first contact
plug 250 and the second contact plug 244 may be formed to a height
equal to the upper end of the gate stack 210.
[0040] Therefore, a transistor is formed, which includes the first
junction region 230, which is formed of an epitaxial layer and
disposed above the semiconductor substrate 200 at a first side
surface of the gate stack 210 and a second junction region 245
formed below the trench formed within the semiconductor substrate
200 at a second side surface of the gate stack 210 over the
semiconductor substrate 200. In this transistor, a channel C1 is
formed between the first junction region 230 and the second
junction region 245. Accordingly, the channel length C1 of the
transistor according to an embodiment is increased because the
first junction region 230 and the second junction region 245 are
formed with asymmetric positions as compared to a conventional
transistor having a channel length equal to the line width of the
gate stack. Therefore, it is possible to prevent short channel
effect caused by reduction in the device size. Also, it is possible
to reduce the electric field because the epitaxial layer is formed
by SEG in the first junction region 230. With reduction in the
electric field, the refresh properties can be enhanced in the cell
region, and the DIBL properties, which have been weak upon increase
in the drain-source voltage, can be improved in the peripheral
circuit region. Also, it is possible to reduce contact resistance
by employing the epitaxial layer.
[0041] Alternatively, the first junction region 230 may be formed
in such a manner that an epitaxial layer is formed as an undoped
SEG layer, impurities are implanted, and annealing is then
performed. Referring to FIG. 10, a resist layer pattern 237 is
formed which covers some of the gate stack 210. The resist layer
pattern 237 covers only the gate stack 210 and exposes the first
junction region 230 and the second trench 240. Next, conductive
impurities are implanted into the exposed first junction region 230
and the semiconductor 200 corresponding to the second trench 240
using the resist layer pattern 237 as an ion implantation barrier
layer. N-type conductive impurities are implanted in the cell
region and N-type or P-type conductive impurities are implanted in
the peripheral circuit region. By performing annealing, the
implanted impurities are diffused and a second junction region 245
is formed within the semiconductor substrate 200 below the second
trench 240. Also, an impurity region 265 is formed within the first
junction region 230. In this case, even though the epitaxial layer
is formed as an undoped SEG layer and the ion implantation process
is subsequently performed thereon, the same effect as the ion
implantation into the silicon bulk can be obtained with
implantation of small amount of impurities because of the unique
mobility of the epitaxial layer.
[0042] In addition, it is possible to further increase the channel
length by modifying the structure of the gate stack 210. FIGS. 11
and 12 illustrate a gate stack structure according to another
embodiment of the present invention.
[0043] Referring to FIGS. 11 and 12, the gate stack 210 may be
formed to fill the recess trench 310 including a first side wall
300 formed within the semiconductor substrate 200 in a vertical
direction (90.degree. relative to the substrate surface) and a
second side wall 305 having a predetermined angle relative to the
surface of the semiconductor substrate 200 and a vertical end,
which is in contact with a vertical end of the first side wall 300.
Also, a first junction region 315 formed of an epitaxial layer and
a second junction region 320 are disposed above the semiconductor
substrate 200 at both side surfaces of the gate stack 210. The
first junction region 315 and the second junction region 320 may be
disposed at the same level over the semiconductor substrate 200
(refer to FIG. 11), or the first junction region 315 and the second
junction region 320 may be disposed in different vertical positions
(refer to FIG. 12).
[0044] Therefore, the channel C2 is formed along the lower portion
of the first side wall 300 and the second side wall 305. The
transistor with this structure can prevent or reduce the short
channel effect because its channel length is longer than
conventional flat transistors. Also, even though the gate length is
the same, the channel length can be adjusted by varying the lengths
of the first side wall 300 and the second side wall 305. Also, by
adjusting the length of the second side wall 305, it is possible to
control the threshold voltage without changing the gate length.
[0045] While the present invention has been described with respect
to the specific embodiments, it will be apparent to those skilled
in the art that various changes and modifications may be made
without departing from the spirit and scope of the invention as
defined in the following claims.
* * * * *