U.S. patent application number 11/670429 was filed with the patent office on 2008-06-12 for gate structure and method for fabricating the same, and method for fabricating memory and cmos transistor layout.
This patent application is currently assigned to PROMOS TECHNOLOGIES INC.. Invention is credited to Jung-Wu Chien.
Application Number | 20080135943 11/670429 |
Document ID | / |
Family ID | 39496965 |
Filed Date | 2008-06-12 |
United States Patent
Application |
20080135943 |
Kind Code |
A1 |
Chien; Jung-Wu |
June 12, 2008 |
GATE STRUCTURE AND METHOD FOR FABRICATING THE SAME, AND METHOD FOR
FABRICATING MEMORY AND CMOS TRANSISTOR LAYOUT
Abstract
A method for fabricating a gate structure is provided. A pad
oxide layer, a pad conductive layer and a dielectric layer are
sequentially formed over a substrate. A portion of the dielectric
layer is removed to form an opening exposing a portion of the pad
conductive layer. A liner conductive layer is formed to cover the
dielectric layer and the pad conductive layer. A portion of the
liner conductive layer and a portion of the pad conductive layer
are removed to expose a surface of the pad oxide layer to form a
conductive spacer. The pad oxide layer is removed and a gate oxide
layer is formed over the substrate. A first gate conductive layer
and a second gate conductive layer are sequentially formed over the
gate oxide layer. A portion of the gate oxide layer is removed and
a cap layer to fill the opening.
Inventors: |
Chien; Jung-Wu; (Hsinchu
City, TW) |
Correspondence
Address: |
JIANQ CHYUN INTELLECTUAL PROPERTY OFFICE
7 FLOOR-1, NO. 100, ROOSEVELT ROAD, SECTION 2
TAIPEI
100
omitted
|
Assignee: |
PROMOS TECHNOLOGIES INC.
Hsinchu
TW
|
Family ID: |
39496965 |
Appl. No.: |
11/670429 |
Filed: |
February 2, 2007 |
Current U.S.
Class: |
257/369 ;
257/413; 257/E21.655; 257/E21.66; 257/E27.062; 257/E27.097;
257/E29.255 |
Current CPC
Class: |
H01L 21/28061 20130101;
H01L 27/10876 20130101; H01L 29/66583 20130101; H01L 27/10897
20130101; H01L 27/10894 20130101; H01L 29/66621 20130101 |
Class at
Publication: |
257/369 ;
257/413; 257/E29.255; 257/E27.062 |
International
Class: |
H01L 27/092 20060101
H01L027/092; H01L 29/78 20060101 H01L029/78 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 6, 2006 |
TW |
95145340 |
Claims
1. A gate structure, comprising: a first gate conductive layer,
disposed over a substrate; a second gate conductive layer, disposed
on the first gate conductive layer; a gate oxide layer, disposed
between the first gate conductive layer and the substrate, and at a
sidewall of the first conductive layer and a portion of the second
gate conductive layer; and a cap layer, disposed on the gate oxide
layer, covering the second gate conductive layer.
2. The gate structure according to claim 1, wherein a material of
the cap layer comprises silicon nitride.
3. The gate structure according to claim 1, wherein a material of
the first gate conductive layer comprises poly-silicon or doped
poly-silicon.
4. The gate structure according to claim 1, wherein a material of
the second gate conductive layer comprises tungsten silicide,
tungsten, titanium silicide, titanium, tantalum silicide or
tantalum.
5. A gate structure, comprising: a first gate conductive layer,
disposed in a recess exposing an upper surface of a substrate,
wherein an upper surface of the first gate structure is higher than
the upper surface of the substrate; a second gate conductive layer,
disposed on the first gate conductive layer; a gate oxide layer,
disposed between the first gate conductive layer and the substrate,
and at a sidewall of the first gate conductive layer and a portion
of the second gate conductive layer; and a cap layer, disposed on
the gate oxide layer, covering the second gate conductive
layer.
6. The gate structure according to claim 5, wherein a material of
the cap layer comprises silicon nitride.
7. The gate structure according to claim 5, wherein a material of
the first gate conductive layer comprises poly-silicon or doped
poly-silicon.
8. The gate structure according to claim 5, wherein a material of
the second gate conductive layer comprises tungsten silicide,
tungsten, titanium silicide, titanium, tantalum silicide or
tantalum.
9. A CMOS transistor layout, comprising: a first conductive type
MOS transistor disposed on a substrate; a second conductive type
MOS transistor disposed on a substrate and isolated by a gap from
the first conductive type transistor; a first contact connected
electrically the first conductive type MOS transistor; a second
contact connected electrically the second conductive type MOS
transistor; and A conductive layer connected electrically the first
conductive type MOS transistor and the second conductive type MOS
transistor.
10. The CMOS transistor layout according to claim 9, wherein a gate
structure of each of the first conductive type MOS transistor and
the second conductive type MOS transistor, comprising: a first gate
conductive layer, disposed over a substrate; a second gate
conductive layer, disposed on the first gate conductive layer; a
gate oxide layer, disposed between the first gate conductive layer
and the substrate, and at a sidewall of the first conductive layer
and a portion of the second gate conductive layer; and a cap layer,
disposed on the gate oxide layer, covering the second gate
conductive layer.
11. The CMOS transistor layout according to claim 10, wherein a
material of the cap layer comprises silicon nitride.
12. The CMOS transistor layout according to claim 10, wherein a
material of the first gate conductive layer comprises poly-silicon
or doped poly-silicon.
13. The CMOS transistor layout according to claim 10, wherein a
material of the second gate conductive layer comprises tungsten
silicide, tungsten, titanium silicide, titanium, tantalum silicide
or tantalum.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims the priority benefit of Taiwan
application serial no. 95145340, filed Dec. 6, 2006. All disclosure
of the Taiwan application is incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention generally relates to a semiconductor
device and a method for fabricating the same, and more
particularly, to a gate structure and a method for fabricating the
same, and a method for fabricating a memory.
[0004] 2. Description of Related Art
[0005] Currently, memory cells are often fabricated together with
their peripheral circuits in order to shorten the processing time
and to simplify the processing process. Furthermore, transistors
having certain characteristic functions are often respectively
formed in the memory cell area and the peripheral circuit area,
according to the functions required in the device. Specifically,
transistors of a dynamic random access memory (DRAM) include
transistors in the memory cell area and transistors in the
peripheral circuit area.
[0006] Typical transistors in a conventional memory cell area have
a stack type gate structure. When circuits become more integrated
and dimension of the device become smaller and smaller, channels of
the transistors thereof are shortened accordingly. Such shortened
channels often cause short channel effect (SCE). In order to
resolve the SCE problem, a recess channel process is often
conducted to elongate the length of the channel, and thus reducing
the SCE and the leakage current thereof. Typically, a recess
channel process often includes steps of: forming a recess in a
substrate, forming a conformal gate oxide layer in the recess,
forming a conductive layer to cover the gate oxide layer and fill
the recess, and performing a patterning process to define a gate
structure. Typically, the foregoing patterning process include:
covering an area in which the gate structure is to be formed later
with a patterning photo-resistant layer; and removing the
conductive layer which is uncovered by the patterning
photo-resistant layer. However, in the foregoing conventional
recess channel process, an alignment error often exists between the
patterning photo-resistant layer and the conductive layer.
Therefore, it is hard to correctly define the gate structure.
[0007] Further, typical transistors in a conventional peripheral
circuit area are complementary metal oxide semiconductor (CMOS)
transistors, including N-type CMOS (NMOS) transistors, and P-type
CMOS (PMOS) transistors. In more concentrated integrated circuit
and smaller devices, PMOS transistors are more likely to cause SCE.
In order to resolve this problem, a metal gate process is often
performed to replace a poly-silicon gate with a metal gate.
However, the metal gate process brings problems of poor thermal
stability and undesired gate dopant diffusion.
[0008] Accordingly, it is an important concern to avoid the above
problems and produce high-quality devices.
SUMMARY OF THE INVENTION
[0009] Accordingly, the present invention is directed to a gate
structure and a method for fabricating the same, and a method for
fabricating a memory, in which alignment error in defining the gate
structure, poor thermo stability and dopant diffusion may be
effectively reduced, thus improving process yield.
[0010] The present invention provides a method for fabricating a
gate structure. First, a pad oxide layer, a pad conductive layer
and a dielectric layer are sequentially formed on a substrate.
Next, a portion of the dielectric layer is removed to form an
opening exposing a portion of the pad conductive layer. Next, a
liner conductive layer is formed to conformably cover the
dielectric layer and the pad conductive layer. Next, a portion of
the liner conductive layer and a portion of the pad conductive
layer are removed to expose a surface of the pad oxide layer to
form a conductive spacer at a sidewall of the opening. Next, the
pad oxide layer at a bottom of the opening is removed. Next, a gate
oxide layer is formed over the substrate. Next, a first gate
conductive layer and a second gate conductive layer are
sequentially formed on the gate oxide layer at the bottom of the
opening, wherein an upper surface of the second gate conductive
layer is substantially lower than an upper surface of the
dielectric layer. Next, a portion of the gate oxide layer is
removed, so that an upper surface of the gate oxide layer is lower
than the upper surface of the second gate conductive layer. Next, a
cap layer is formed to fill the opening.
[0011] According to an embodiment of the present invention, the
gate oxide layer is removed by, for example, an etching
process.
[0012] According to an embodiment of the present invention, a
material of the foregoing cap layer is, for example, silicon
nitride.
[0013] According to an embodiment of the present invention, a
material of the foregoing first gate conductive layer is, for
example, poly-silicon or doped poly-silicon.
[0014] According to an embodiment of the present invention, a
material of the foregoing second gate conductive layer is, for
example, tungsten silicide, tungsten, titanium silicide, titanium,
tantalum silicide or tantalum.
[0015] According to an embodiment of the present invention, the
method for fabricating a gate structure further includes the steps
of removing the dielectric layer after forming the cap layer, and
removing the conductive spacer and the pad conductive layer.
[0016] The present invention further provides another method for
fabricating a gate structure. First, a pad oxide layer, a pad
conductive layer and a dielectric layer are sequentially formed on
a substrate. Next, a portion of the dielectric layer is removed to
form an opening exposing a portion of the pad conductive layer.
Next, a liner conductive layer is formed to cover the dielectric
layer and the pad conductive layer. Next, a portion of the liner
conductive layer and a portion of the pad conductive layer are
removed to expose a surface of the pad oxide layer to form a
conductive spacer at a sidewall of the opening. Next, the pad oxide
layer at a bottom of the opening and a portion of the substrate are
removed to form a recess in the substrate. Next, a gate oxide layer
is formed over the substrate. Next, a first gate conductive layer,
and a second gate conductive layer are sequentially formed in the
recess and on the gate oxide layer over the bottom of the opening,
wherein an upper surface of the second gate conductive layer is
substantially lower an upper surface of the dielectric layer. Next,
a portion of the gate oxide layer is removed until an upper surface
of the gate oxide layer is substantially lower than the upper
surface of the second gate conductive layer. Next, a cap layer is
formed to fill the opening.
[0017] According to an embodiment of the present invention, the
gate oxide layer is removed by, for example, an etching
process.
[0018] According to an embodiment of the present invention, a
material of the foregoing cap layer is, for example, silicon
nitride.
[0019] According to an embodiment of the present invention, a
material of the foregoing first gate conductive layer is, for
example, poly-silicon or doped poly-silicon.
[0020] According to an embodiment of the present invention, a
material of the foregoing second gate conductive layer is, for
example, tungsten silicide, tungsten, titanium silicide, titanium,
tantalum silicide, and tantalum.
[0021] According to an embodiment of the present invention, the
method for fabricating a gate structure further includes the steps
of removing the dielectric layer after forming the cap layer, and
removing the conductive spacer and the pad conductive layer.
[0022] The present invention further provides a method for
fabricating a memory. First, a substrate is provided, wherein the
substrate having a memory cell area and a peripheral circuit area.
Next, a pad oxide layer, a pad conductive layer and a dielectric
layer are sequentially formed on the substrate. Next, a portion of
the dielectric layer is removed to form a first opening in the
memory cell area and a second opening in the peripheral circuit
area, the first opening exposing portions of the pad conductive
layer respectively. Next, a liner conductive layer is formed to
cover the dielectric layer and the pad conductive layer. Next, a
portion of the liner conductive layer and a portion of the pad
conductive layer are removed to expose the pad oxide layer to form
conductive spacers at sidewalls of respectively the first opening,
and two second openings. Next, a portion of the pad oxide layer at
a bottom of the first opening and a portion of the substrate are
removed to form a recess in the substrate, and the pad oxide layer
at bottoms of the two second openings are also removed. Next, a
gate oxide layer is formed over the substrate. Next, a first gate
conductive layer is formed in the recess and on the gate oxide
layer over a bottom of the first opening, while a second gate
conductive layer and a third gate conductive layer are respectively
formed on bottoms of two second openings. Next, a fourth gate
conductive layer is formed over the first, the second, and the
third gate conductive layers, wherein an upper surface of the
fourth gate conductive layer is lower than an upper surface of the
dielectric layer. Next, a portion of the gate oxide layer is
removed until an upper surface of the gate oxide layer is lower
than the upper surface of the fourth gate conductive layer. Next, a
cap layer is formed to fill up the first opening and the two second
openings.
[0023] According to an embodiment of the present invention, the
gate oxide layer is removed by, for example, an etching
process.
[0024] According to an embodiment of the present invention, a
material of the foregoing cap layer is, for example, silicon
nitride.
[0025] According to an embodiment of the present invention, the
foregoing first gate conductive layer is an N-type doped
poly-silicon layer, the second gate conductive layer is one of an
N-type doped poly-silicon layer and a P-type doped poly-silicon
layer, and the third gate conductive layer is another one of the
N-type doped poly-silicon layer and the P-type doped poly-silicon
layer.
[0026] According to an embodiment of the present invention, a
material of the foregoing fourth gate conductive layer is, for
example, silicide, tungsten, titanium silicide, titanium, tantalum
silicide or tantalum.
[0027] According to an embodiment of the present invention, the
method for fabricating a memory further includes a step of
performing a nitridation process to the gate oxide layer of the
peripheral circuit area after forming the gate oxide layer over the
substrate.
[0028] According to an embodiment of the present invention, the
method for fabricating a memory further includes the steps of
removing the dielectric layer after forming the cap layer, and
removing the conductive spacers and the pad conductive layer.
[0029] The present invention further provides a gate structure. The
gate structure includes a substrate, a first gate conductive layer,
a second gate conductive layer, a gate oxide layer and a cap layer.
The first gate conductive layer is disposed over the substrate. The
second gate conductive layer is disposed over the first conductive
layer. The gate oxide layer is disposed between the first gate
conductive layer and the substrate, and at a sidewall of the first
conductive layer and a portion of the second gate conductive layer.
The cap layer is disposed on the gate oxide layer covering the
second gate conductive layer.
[0030] According to an embodiment of the present invention, a
material of the foregoing cap layer is, for example, made silicon
nitride.
[0031] According to an embodiment of the present invention, a
material of the foregoing first gate conductive layer is, for
example, poly-silicon or doped poly-silicon.
[0032] According to an embodiment of the present invention, a
material of the foregoing second gate conductive layer is, for
example, tungsten silicide, tungsten, titanium silicide, titanium,
tantalum silicide, or tantalum.
[0033] The present invention further provides another gate
structure. The gate structure includes a substrate, a first gate
conductive layer, a second gate conductive layer, a gate oxide
layer and a cap layer. The first gate conductive layer is disposed
in a recess exposing an upper surface of the substrate, wherein an
upper surface of the first gate structure is higher than the upper
surface of the substrate. The second gate conductive layer is
disposed on the first gate conductive layer. The gate oxide layer
is disposed between the first gate conductive layer and the
substrate, and at a sidewall of the first gate conductive layer and
a portion of the second gate conductive layer. The cap layer is
disposed on the gate oxide layer covering the second gate
conductive layer.
[0034] According to an embodiment of the present invention, a
material of the foregoing cap layer is, for example, silicon
nitride.
[0035] According to an embodiment of the present invention, a
material of the foregoing first gate conductive layer is, for
example, poly-silicon or doped poly-silicon.
[0036] According to an embodiment of the present invention, a
material of the foregoing second gate conductive layer is, for
example, tungsten silicide, tungsten, titanium silicide, titanium,
tantalum silicide, or tantalum.
[0037] The present invention further provides a method for
fabricating a CMOS transistor layout. The CMOS transistor at least
includes an N-type transistor and a P-type transistor, wherein a
gate electrode of the N-type transistor is disposed adjacent to a
gate electrode of the P-type transistor. First, a pad oxide layer,
a pad conductive layer, and a dielectric layer are sequentially
formed over a substrate. Next, a portion of the dielectric layer is
removed. Next, two openings that expose a portion of an upper
surface of the pad conductive layer, and defining a first area
where an N-type transistor is to be formed, and a second area where
a P-type transistor is to be formed; then forming a liner conducive
layer, conformably covering the dielectric layer and the pad
conductive layer; then removing a portion of the liner conductive
layer and a portion of the pad conductive layer to expose a surface
of the pad oxide layer, and forming a conductive spacer at
sidewalls of the two openings; then, conformably forming a gate
oxide layer over the substrate; then, forming a first gate
conductive layer and a second gate conductive layer on the gate
oxide layer over bottoms of the two openings, respectively. Then,
simultaneously forming a third gate conductive layer over the first
and the second gate conductive layers, wherein upper surfaces of
the third gate conductive layers are lower than an upper surface of
the dielectric layer; then removing a portion of the gate oxide
layer, so that an upper surface of the gate oxide layer is lower
than the upper surfaces of the third gate conductive layers; then
filling up the two openings with a cap layer.
[0038] According to an embodiment of the present invention, the
gate oxide layer is removed by performing, for example, an etching
process.
[0039] According to an embodiment of the present invention, a
material of the cap layer is, for example, silicon nitride.
[0040] According to an embodiment of the present invention, the
first gate conductive layer is comprised of an N-type doped
poly-silicon layer or a P-type doped poly-silicon layer, and the
second gate conductive layer is comprised of a N-type doped
poly-silicon layer or a P-type doped poly-silicon layer.
[0041] According to an embodiment of the present invention, a
material of the third gate conductive layer is, for example,
tungsten silicide, tungsten, titanium silicide, titanium, tantalum
silicide or tantalum.
[0042] According to an embodiment of the present invention, a
nitridation process is performed on the gate oxide layer of the
peripheral circuit area after forming the gate oxide layer over the
substrate.
[0043] According to an embodiment of the present invention, the
dielectric layer is removed after forming the cap layer, and the
conductive spacers and the pad conductive layer are removed.
[0044] The method of the present invention is adapted for avoiding
alignment errors when defining gate structures during a
conventional recess channel process. Further, according to the gate
structure of the present invention, the cap layer covers top
surface of the gate conductive layer, thus protecting the gate
conductive layer from damages due to subsequent processes.
Particularly, the area where the transistor is to be formed is
defined prior to forming the gate structure, and therefore gate
dopant diffusion, which often occurs in subsequent thermal process
in conventional CMOS transistors adversely affecting reliability of
the device, can be effectively avoided.
BRIEF DESCRIPTION OF THE DRAWINGS
[0045] The accompanying drawings are included to provide a further
understanding of the invention, and are incorporated in and
constitute a part of this specification. The drawings illustrate
embodiments of the invention and, together with the description,
serve to explain the principles of the invention.
[0046] FIGS. 1A through 1I are cross-sectional views showing a flow
of a method for fabricating a gate structure according to an
embodiment of the present invention.
[0047] FIGS. 2A through 2E are cross-sectional views showing a flow
illustrating a method for fabricating a gate structure according to
another embodiment of the present invention.
[0048] FIGS. 3A through 3K are cross-sectional views showing a flow
of a method for fabricating a memory according to an embodiment of
the present invention.
[0049] FIG. 4 is a schematic diagram illustrating a CMOS transistor
layout according to an embodiment of the present invention.
[0050] FIG. 5 is a schematic diagram illustrating a conventional
CMOS transistor layout.
DESCRIPTION OF THE EMBODIMENTS
[0051] Reference will now be made in detail to the present
preferred embodiments of the invention, examples of which are
illustrated in the accompanying drawings. Wherever possible, the
same reference numbers are used in the drawings and the description
to refer to the same or like parts.
[0052] FIGS. 1A through 1I are cross-sectional views showing a flow
of a method for fabricating a gate structure according to an
embodiment of the present invention.
[0053] First, referring to FIG. 1A, a pad oxide layer 102 is formed
on a substrate 100. A material of the pad oxide layer 102 is, for
example, silicon oxide, and may be formed by performing, for
example, a thermal oxidizing process. Next, a pad conductive layer
104 is formed on the pad oxide layer 102. A material of the pad
conductive layer 104 is, for example, undoped poly-silicon, and may
be formed by performing, for example, a chemical vapour deposition
(CVD) process. Next, a dielectric layer 106 is formed on the pad
conductive layer 104. A material of the dielectric layer 106 is,
for example, phosphor silicon glass (PSG), boron phosphor silicon
glass (BPSG), or other suitable dielectric materials, and may be
formed by performing, for example, a CVD process.
[0054] Next, referring to FIG. 1B, a portion of the dielectric
layer 106 is removed to form an opening 108 exposing a portion of
the pad conductive layer 104. The opening 108 is formed by
performing the following steps. First, a patterned photo-resistant
layer (not shown) is formed over the dielectric layer 106. Next,
the dielectric layer 106 etched using the patterned photo-resistant
layer as a mask to form an opening 104 until the pad conductive
layer 104 is exposed.
[0055] Next, referring to FIG. 1C, a liner conductive layer 110 is
formed over the substrate 100 to covering the dielectric layer 106
and the pad conductive layer 104. A material of the liner
conductive layer 110 is, for example, undoped poly-silicon, and may
be formed by performing, for example, a CVD process.
[0056] Next, referring to FIG. 1D, an etching process may be
performed to remove a portion of the liner conductive layer 110 to
form a conductive spacer 110a at a sidewall of the opening 108.
Further, when removing the portion of liner conductive layer 110 to
form the conductive spacer 110a, a portion of the pad conductive
layer 104 is simultaneously removed to expose a surface of the pad
oxide layer 102.
[0057] Next, referring to FIG. 1E, an etching process is performed
to remove the pad oxide layer 102 at a bottom of the opening 108.
Next, a gate oxide layer 112 is formed over the substrate 100. A
material of the gate oxide layer 112 is, for example, silicon
oxide, and may be formed by, for example, a thermal oxidizing
process.
[0058] Next, referring to FIG. 1F, a gate conductive layer 114 is
formed on the gate oxide layer 112 on the bottom of the opening
108. A material of the gate conductive layer 114 is, for example,
poly-silicon or doped poly-silicon. The gate conductive layer 114
may be formed by, for example, the following process. A conductor
layer (not shown) is formed over the substrate 100 to fill the
opening 108. Next, a chemical mechanical polishing (CMP) process is
performed to planarize the conductor layer. Next, an etching-back
process is performed to remove a portion of the conductor layer
until an upper surface of the conductor layer is lower than an
upper surface of the dielectric layer 106.
[0059] Next, referring to FIG. 1F, a gate conductive layer 116 is
formed on the gate conductive layer 114. A material of the gate
conductive layer 116 is, for example, tungsten silicide (WSi),
tungsten (W), titanium silicide (TiSi), titanium (Ti), tantalum
silicide (TaSi), tantalum (Ta), or any other suitable metal or
metal alloy. The gate conductive layer 116 may be formed by, for
example, the following process. A conductor layer (not shown) is
formed to cover the gate oxide layer 112 and the gate conductive
layer 114. Next, a CMP process is performed to planarize the
surface of the conductor layer. Next, an etching-back process is
performed to remove a portion of the conductor layer until an upper
surface of the conductor layer is lower than an upper surface of
the dielectric layer 106.
[0060] Next, referring to FIG. 1G, a portion of the gate oxide
layer 112 is removed to form a gate oxide layer 112a. The gate
oxide layer 112a is formed by performing a etch-back process to
remove a portion of the gate oxide layer 112 such that an upper
surface of the gate oxide layer 112a is lower than an upper surface
of the gate conductive layer 116.
[0061] Next, referring to FIG. 1G, a cap layer 118 is formed to
fill the opening 108. A material of the cap layer 118 is, for
example, silicon nitride or other suitable materials. The cap layer
118 may be formed by, for example, the following process. A cap
material layer (not shown) is formed over the substrate 100. Next,
a CMP process and an etching-back process are sequentially carried
out to remove a portion of the cap material layer. The cap layer
118, gate conductive layer 114, gate conductive layer 116 and gate
oxide layer 112a constitute a gate structure.
[0062] It is to be noted that the cap layer 118 is formed over the
gate conductive layer 116 to cover top portion of the gate
conductive layers 116, and therefore the cap layer 118 can protect
the gate conductive layer 116 from damaged caused by subsequent
processes.
[0063] Next, referring to FIG. 1H, the dielectric layer 106 is
removed after forming the cap layer 118. The dielectric layer 106
is removed by performing, for example, a wet etching process.
During the process of removing the dielectric layer 106, the
conductive spacer 110a and the pad conductive layer 104 function to
protect the gate structure from being damaged.
[0064] Next, referring to FIG. 1I, the conductive spacer 110a and
the pad conductive layer 104 are removed by performing, for
example, an etching process after removing the dielectric layer
106. Thereafter, lightly doped region, a source region and a drain
region may be formed by carrying out well known process familiar to
those of ordinary skill in the art.
[0065] Referring to FIG. 1I again, the structure of the gate
structure fabricated by the foregoing method is described
hereinafter. The gate structure includes a gate conductive layer
114, a gate conductive structure 116, a gate oxide layer 112a and a
cap layer 118. The gate conductive layer 114 is disposed over a
substrate 100. A material of the gate conductive layer 114 is, for
example, poly-silicon or doped poly-silicon. The gate conductive
layer 116 is disposed on the gate conductive layer 114. A material
of the gate conductive layer 116 is, for example, tungsten silicide
(WSi), tungsten (W), titanium silicide (TiSi), titanium (Ti),
tantalum silicide (TaSi), tantalum (Ta), or any other suitable
metal or metal alloy. The gate oxide layer 112a is disposed between
the gate conductive layer 114 and the substrate 100, and at
sidewalls of the gate conductive layer 114 and a portion of the
gate conductive layer 116. A material of the gate oxide layer 112a
is, for example, silicon oxide. The cap layer 118 is disposed on
the gate oxide layer 112a covering the gate conductive layer 116. A
material of the cap layer 118 is, for example, silicon nitride, or
other suitable materials.
[0066] FIGS. 2A through 2E are cross-sectional views showing a flow
illustrating a method for fabricating a gate structure according to
another embodiment of the present invention. FIG. 2A is consecutive
from FIG. 1D. Legends used in FIGS. 2A through 2E are consistent
with FIGS. 1A through 1I, in that same legends are used for same
items, and descriptions thereof are skipped over hereby.
[0067] Referring to FIG. 2A, the pad oxide layer 102 at a bottom of
the opening 108, and a portion of the substrate 100 are removed to
form a recess 109 in the substrate 100, by performing, for example,
an etching process.
[0068] Next, referring to FIG. 2B, a gate oxide layer 112 is formed
over the substrate 100. According to an aspect of the embodiment, a
pre-cleaning process may be performed before the gate oxide layer
112 is formed to remove residues in the recess 109.
[0069] Next, referring to FIG. 2C, a gate conductive layer 114 is
formed in the recess 109 and on the gate oxide layer 112 at the
bottom of the opening 108. Next, a gate conductive layer 116 is
formed on the gate conductive layer 114 after the gate conductive
layer 114 is formed, wherein an upper surface of the gate
conductive layer 116 is lower than an upper surface of the
dielectric layer 106.
[0070] Next, Referring to FIG. 2D, a gate oxide layer 112a is
formed by removing a portion of the gate oxide layer 112, wherein
an upper surface of the gate oxide layer 112a is lower than the
upper surface of the gate conductive layer 116. Next, the opening
108 is filled by a cap layer 118. The cap layer 118 covers top
portions of the gate conductive layer 116 to protect the gate
conductive layer 116 from damage caused by subsequent
processes.
[0071] The foregoing cap layer 118, gate conductive layer 114, gate
conductive layer 116 and gate oxide layer 112a constitute the gate
structure having a recess channel structure, which is adapted to
reduce SCE and leakage current.
[0072] Next, referring to FIG. 2E, after the cap layer 118 is
formed, the dielectric layer 106 is removed, during which the
conductive spacer 110a and the pad conductive layer 104 protect the
gate structure from damage. Next, after the dielectric layer 106 is
removed, the conductive spacer 110a and the pad conductive layer
104 are further removed. Thereafter, subsequent processes are
carried to form, for example a lightly doped region, a source
region and a drain region, well known to those of ordinary skill in
the art.
[0073] In summary, according to an aspect of the present invention,
the fabrication method may employed to effectively increase the
channel length to reduce the SCE and leakage current. Furthermore,
the alignment errors in defining gate structures may be effectively
avoided.
[0074] Referring to FIG. 2E again, the structure of the gate
structure fabricated by the foregoing method of the present
invention is described hereinafter. The gate structure includes a
gate conductive layer 114, a gate conductive layer 116, a gate
oxide layer 112a and a cap layer 118. The gate conductive layer 114
is disposed in a recess 109, which bottom exposes an upper surface
of the substrate 100, wherein an upper surface of the gate
conductive layer 114 is higher than the upper surface of the
substrate 100. The gate conductive layer 116 is disposed on the
gate conductive layer 114. The gate oxide layer 112a is disposed
between the gate conductive layer 114 and the substrate 100, and at
sidewalls of the gate conductive layer 114 and a portion of the
gate conductive layer 116. The cap layer 118 is disposed on the
gate oxide layer 112a covering the gate conductive layer 116.
[0075] The fabrication method of the present invention may also be
integrated with the process for forming the peripheral circuit
area, for example, in a process for forming a memory, in which the
memory cell area and the peripheral circuit area are simultaneously
fabricated. FIGS. 3A through 3K are cross-sectional views showing a
flow of a method for fabricating a memory according to an
embodiment of the present invention.
[0076] First, referring to FIG. 3A, a substrate 300 is provided.
The substrate 300 has a memory cell area 301 and a peripheral
circuit area 303. According to an aspect of the embodiment of the
present invention, a transistor having a recess channel is formed
in the memory cell area 301, and a dual work function CMOS
transistor is formed in the peripheral circuit area 303.
[0077] Next, referring to FIG. 3A, a pad oxide layer 302 is formed
on the substrate 300. The pad oxide layer 302 is comprised of, for
example, silicon oxide, and may be formed by performing, for
example, a thermal oxidizing process. Next, a pad conductive layer
304 is formed on the pad oxide layer 302. The pad conductive layer
304 is comprised of, for example, undoped poly-silicon, and may be
formed by performing, for example, a CVD process. Next, a
dielectric layer 306 is formed on the pad conductive layer 304. The
dielectric layer 306 is comprised of, for example but not limited
to, phosphor silicon glass (PSG), boron phosphor silicon glass
(BPSG), or other suitable dielectric materials, and may be formed
by, for example, a CVD process.
[0078] Next, referring to FIG. 3B, a portion of the dielectric
layer 306 is removed to form an opening 308a exposing a portion of
the pad conductive layer 304 in the memory cell area 301, and
openings 308b and 308c exposing a portion of the pad conductive
layer 304 in the peripheral circuit area 303. The openings 308a,
308b and 308c may be formed by, for example, the following process.
First, a patterned photo-resistant layer (not shown) is formed on
the dielectric layer 306. Next, the dielectric layer 306 etched
using the patterned photo-resistant layer as a mask until the pad
conductive layer 304 is exposed to form the openings 308a, 308b,
and 308c. The opening 308a is adapted for defining an area of a
transistor of the memory cell area 301, and the openings 308b and
308c are adapted for respectively defining N-type, P-type CMOS
transistors in the peripheral circuit area 303.
[0079] Next, referring to FIG. 3C, a liner conductive layer 310 is
formed over the substrate 300 to cover the dielectric layer 306 and
the pad conductive layer 304. The liner conductive layer 310 is
comprised of, for example, undoped poly-silicon, and may be formed
by, for example, a CVD process.
[0080] Next, referring to FIG. 3D, a portion of the liner
conductive layer 310 is removed to form conductive spacers 310a on
sidewalls of the openings 308a, 308b and 308c. The portion of liner
conductive layer 310 is removed by performing, for example, an
etching process. Further, when removing the portion of liner
conductive layer 310 to form the conductive spacer 310a, a portion
of the pad conductive layer 304 is simultaneously removed to expose
a surface of the pad oxide layer 302.
[0081] Next, referring to FIG. 3E, the pad oxide layer 302 formed a
bottom of the opening 308a and a portion of the substrate 300 is
removed to form a recess 319 in the substrate 300. The recess 319
may be formed by, for example, the following process. A
photo-resistant layer (not shown) is formed to cover the dielectric
layer 306 in the peripheral circuit area 303, and the substrate
300. Next, the substrate 300 in the memory cell area 301 is etched
to form the recess 319. Next, the photo-resistant layer is
removed.
[0082] Next, further referring to FIG. 3E, a pre-cleaning process
is performed after the recess 319 is formed to clean the bottom of
the recess 319, and simultaneously remove the pad oxide layer 302
on bottoms of the openings 308b and 308c. The foregoing
pre-cleaning process is, for example, an etching process.
[0083] Next, referring to FIG. 3F, a gate oxide layer 312 is formed
over the substrate 300. The gate oxide layer 312 is comprised of,
for example, silicon oxide, and may be formed by performing, for
example, a thermal oxidizing process. According to an embodiment of
the present invention, after the gate oxide layer 312 is formed, a
nitridation process is performed to the gate oxide layer 312 in the
peripheral circuit area 303 to avoid dopant diffusion caused by
subsequent processes, which may otherwise adversely affects
functions of the device.
[0084] Next, referring to FIG. 3G, a gate conductive layer 314a is
formed in the recess 319 and on the gate oxide layer 312 at the
bottom of the opening 308a. Gate conductive layers 314b, 314c are
formed on the gate oxide layer 312 at respective bottoms of the
openings 308b and 308c. For example, the gate conductive layer 314a
of the memory cell area 301 is an N-type doped poly-silicon layer,
and the gate conductive layers 314b, 314c of the peripheral circuit
layer 303, are an N-type doped poly-silicon layer and a P-type
doped poly-silicon layer, respectively.
[0085] According to an embodiment of the present invention, the
gate conductive layers 314a, 314b and 314c are formed by, for
example, the following process. A N-type doped poly-silicon layer
(not shown) is formed over the substrate 300 to fill openings 308a,
308b and 308c, respectively. Next, a CMP process is performed to
planarize the N-typed doped poly-silicon layer. Next, an
etching-back process is performed to remove a portion of the N-type
doped poly-silicon layer until an upper surface of the N-type doped
poly-silicon layer is lower than an upper surface of the dielectric
layer 306. Next, using a photo-resistant layer as a mask to cover
areas of N-type devices, an ion implementation process is carried
out to transform one of the two N-type doped poly-silicon layers of
308b and 308c to a P-type doped poly-silicon layer.
[0086] According to another embodiment of the present invention,
the gate conductive layer 314a, 314b, 314c are formed by, for
example, the following process. An undoped poly-silicon layer (not
shown) is formed over the substrate 300 to fill the openings 308a,
308b and 308c. Next, a CMP process is performed to planarize the
updoped poly-silicon layer. Next, an etching process is performed
to remove a portion of the undoped poly-silicon until an upper
surface of the undoped poly-silicon layer is lower than an upper
surface of the dielectric layer 306. Next, using a photo-resistant
layer as a mask to cover areas of respectively N-type devices and
P-type devices, an ion implementation process is carried out to
transform the undoped poly-silicon layer in the opening 308a to an
N-type doped poly-silicon layer, and the undoped poly-silicon
layers in the openings 308b and 308c to an N-type doped
poly-silicon layer and a P-type doped poly-silicon layer,
respectively.
[0087] Next, referring to FIG. 3H, a gate conductive layer 316 is
formed on the gate conductive layers 314a, 314b and 314c. A
material of the gate conductive layer 316 is, for example, tungsten
silicide, tungsten, titanium silicide, titanium, tantalum silicide,
tantalum, or other suitable metal or metal alloy. A process of
forming the gate conductive layer 316, for example, is described as
follows. A conductive material layer (not shown) is formed to cover
the gate oxide layer 312 and the gate conductive layers 314a, 314b,
and 314c. Next, a CMP process is performed to planarize the
conductive material layer. Next, an etching process is performed to
remove a portion of the conductive material layer until an upper
surface of the conductive material layer is lower than the
dielectric layer 306.
[0088] In the foregoing, the gate conductive layers 314a and 316 in
the memory cell area 301 serve as a gate of the transistor having a
recess channel, and the gate conductive layers 314b, 316, and gate
conductive layers 314c, 316 that are located in the peripheral
circuit area 303 serve as the gate of the dual work function CMOS
transistor.
[0089] Next, referring to FIG. 3I, a portion of the gate oxide
layer 312 is removed to form a gate oxide layer 312a. The gate
oxide layer 312a is formed by performing an etch-back process to
remove a portion of the gate oxide layer 312 until an upper surface
of the gate oxide layer 312a is lower than an upper surface of the
gate conductive layer 316.
[0090] Next, referring to FIG. 3J, a cap layer 318 is formed to
fill the openings 308a, 308b, and 308c. A material of the cap layer
318 is, for example, silicon nitride or other suitable materials.
The cap layer 318 is formed by, for example, the following process.
A cap material layer (not shown) is formed over the substrate 300.
Next, a CMP process and an etching process are sequentially
performed to remove a portion of the cap material layer. The cap
layer 318 covers top portions of the gate conductive layer 316 to
protect the gate, conductive layer 316 by from damage during the
subsequent processes.
[0091] Next, referring to FIG. 3K, the dielectric layer 306 is
removed after the cap layer 318 is formed. The dielectric layer 306
is removed by performing, for example, a wet etching process.
During the process of removing the dielectric layer 306, the
conductive spacer 310a and the pad conductive layer 304 protect the
gate from being damaged. After the dielectric layer 306 is removed,
the conductive spacer 310a and the pad conductive layer 304 are
removed by performing, for example, an etching process. Thereafter,
subsequent processes well known to those skilled in the art are
carried out to form for example, a lightly doped region, a source
region, and a drain region.
[0092] In general, the cap layer 318, the gate conductive layer
314a, the gate conductive layer 316 and the gate oxide layer 312a
constitute a gate structure 320. The gate structure 320 is a
transistor having a recess channel in the memory cell area 301.
Further, the cap layer 318, the gate conductive layer 314b, the
gate conductive layer 316 and the gate oxide layer 312a also
constitute a gate structure 330, and the cap layer 318, the gate
conductive layer 314c, the gate conductive layer 316, and the gate
oxide layer 312a constitute another gate structure 340. The gate
structures 330 and 340 are two gate structures of the dual work
function CMOS transistor in the peripheral circuit area 303, which
are an N-type gate structure and a P-type gate structure,
respectively.
[0093] In the fabricating method according to the present
invention, the gate of the transistor having a recess channel in a
memory cell area 301 are aligned in a self aligned manner so that
alignment errors that often occur in the conventional recess
channel process can be effectively avoided. Furthermore, problems
like poor thermal stability and gate dopant diffusion that often
occur in the conventional gate structures for dual work function
CMOS transistors in peripheral circuit areas can also be
effectively avoided.
[0094] The present invention is adapted for forming a CMOS
transistor layout. In such a CMOS transistor layout, CMOS
transistors thereof are dual work function CMOS transistors, and
they are also cut-off type CMOS transistors as can be illustrated
with reference to FIG. 4. The method for fabricating the CMOS
transistor layout is similar to the process flow of the above
illustrated memory in the peripheral circuit area 303. Therefore,
those of ordinary skill in the art can deduce the method described
with reference to FIGS. 3A through 3K.
[0095] Referring to FIG. 4, a CMOS transistor layout according to
an embodiment of the present invention is shown. The CMOS
transistor includes an N-type transistor and a P-type transistor,
wherein a gate electrode 404 of the N-type transistor and a gate
electrode 406 of the P-type transistor are isolated by a gap from
each other. A source/drain zone 408 of the N-type transistor and a
source/drain zone 410 of the P-type transistor are respectively
disposed at two sides of the gate electrodes 404 and 406. Two
contacts 412 and 414 formed on the gate electrodes 404 and 406,
respectively. A conductive layer 416 is formed on the contact
windows 412 and 414, so as to electrically connect the two gate
electrodes 404 and 406.
[0096] Compared a conventional CMOS transistor layout as shown in
FIG. 5, source/drain regions 504 and 506 of the N-type transistor
and the P-type transistor are distributed at two sides of the gate
electrode 502, and the contact window 508 is electrically connected
to the gate electrode 502. Therefore, the gate dopant diffusion in
subsequent thermal treatment process may be effectively
avoided.
[0097] In summary, the fabricating method according to the present
invention may be adapted for avoiding alignment errors in defining
gate structures. Further, the cap layer covering top portions of
the gate conductive layer may serve to protect the gate conductive
layer from damage during subsequent processes. Furthermore, the
area where the transistors are to be formed defined before forming
the gate structure, so that gate dopant diffusion in subsequent
thermal treatment process that would adversely affect reliability
of the device may be effectively avoided.
[0098] It will be apparent to those skilled in the art that various
modifications and variations can be made to the structure of the
present invention without departing from the scope or spirit of the
invention. In view of the foregoing, it is intended that the
present invention cover modifications and variations of this
invention provided they fall within the scope of the following
claims and their equivalents.
* * * * *