U.S. patent application number 10/725050 was filed with the patent office on 2004-06-10 for floating gate and method of fabricating the same.
Invention is credited to Chuang, Ying-Cheng, Huang, Chung-Lin, Lin, Chi-Hui.
Application Number | 20040108541 10/725050 |
Document ID | / |
Family ID | 31713629 |
Filed Date | 2004-06-10 |
United States Patent
Application |
20040108541 |
Kind Code |
A1 |
Chuang, Ying-Cheng ; et
al. |
June 10, 2004 |
Floating gate and method of fabricating the same
Abstract
A floating gate and fabrication method thereof. A semiconductor
substrate is provided, on which a gate dielectric layer, a
conducting layer, and a patterned hard mask layer are sequentially
formed. The surface of the conducting layer is covered by the
patterned hard mask layer to form a gate. The conducting layer is
etched to a predetermined depth to form an indentation using the
patterned hard mask layer as a mask. The conducting layer is
oxidized to form an oxide layer on the surface of the conducting
layer. The oxide layer and the conducting layer are etched to form
multiple tips using the patterned hard mask layer as a mask.
Inventors: |
Chuang, Ying-Cheng; (Taoyuan
Hsien, TW) ; Huang, Chung-Lin; (Taichung, TW)
; Lin, Chi-Hui; (Taipei, TW) |
Correspondence
Address: |
QUINTERO LAW OFFICE
1617 BROADWAY, 3RD FLOOR
SANTA MONICA
CA
90404
US
|
Family ID: |
31713629 |
Appl. No.: |
10/725050 |
Filed: |
December 1, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10725050 |
Dec 1, 2003 |
|
|
|
10436800 |
May 13, 2003 |
|
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|
Current U.S.
Class: |
257/315 ;
257/316; 257/E21.209; 257/E21.422; 257/E29.129; 438/257;
438/593 |
Current CPC
Class: |
H01L 29/66825 20130101;
H01L 29/40114 20190801; H01L 29/42324 20130101 |
Class at
Publication: |
257/315 ;
438/593; 438/257; 257/316 |
International
Class: |
H01L 029/788; H01L
021/3205; H01L 021/336; H01L 021/4763 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 15, 2002 |
TW |
91118388 |
Claims
What is claimed is:
1. A floating gate formed on the surface of a semiconductor
substrate, comprising: a conductive base having a first top portion
and a first bottom portion, wherein an edge of the first top is a
first tip, and the first bottom portion contacts to the
semiconductor substrate; a conductive protruding layer protruding
from the conductive base, and the conductive protruding layer has a
flat top, wherein the conductive protruding layer has a second top
portion and a second bottom portion, a edge of the second top
portion is a second tip, the second bottom portion is connected to
the first top portion, the conductive protruding layer has two
concave sidewalls; and wherein a multiple tip floating gate is
composed of the conductive base and the conductive protruding
layer.
2. The floating gate of claim 1, wherein the conductive base is a
poly layer.
3. The floating gate of claim 1, wherein the conductive protruding
layer is a poly layer.
4. A floating gate formed on the surface of a semiconductor
substrate, with a gate dielectric layer formed between the floating
gate and the semiconductor substrate, comprising: a base poly layer
having a first top portion and a first bottom portion, wherein an
edge of the first top portion is a first tip, and the first bottom
portion contacts to the gate dielectric layer; and a protruding
poly layer protruding from the base poly layer, and the protruding
poly layer has a flat top, wherein the protruding poly layer has a
second top portion and a second bottom portion, a edge of the
second top portion is a second tip, the second bottom portion
contacts the first top portion, the protruding poly layer has two
concave sidewalls, wherein a multiple tip floating gate is composed
of the base poly layer and the protruding poly layer.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional of co-pending U.S.
application Ser. No. 10/436,800, filed on May 13, 2003.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The invention is related to a floating gate, and more
particularly to a floating gate with multiple tips and a method for
fabricating the same.
[0004] 2. Description of the Related Art
[0005] Memory devices for non-volatile storage of information are
currently in widespread use, in a myriad of applications. A few
examples of non-volatile semiconductor memory include read only
memory (ROM), programmable read only memory (PROM), erasable
programmable read only memory (EPROM), electrically erasable
programmable read only memory (EEPROM) and flash EEPROM.
[0006] An advantage of EPROM is that it is electrically programmed,
but for erasing, still requires exposure to ultraviolet (UV)
light.
[0007] In many circuit designs it is desirable to have a
non-volatile memory device that can be erased and reprogrammed
in-circuit, without the need to remove the device for erasing and
reprogramming.
[0008] EEPROM devices have the advantage of electrical programming
and erasing, achieved by charging and discharging actions
controlled by the control gate. The actions also affect the
conductivity of the channel between source and drain.
[0009] One of the advantages of flash memory is its capacity for
block-by-block memory erasure. Furthermore, memory erasure is fast,
normally taking just 1 to 2 seconds for the complete removal of a
whole block of memory. Another advantage of flash memory is low
power consumption. The voltages of a control gate, a source, and a
drain are adjusted to program or erase in a split gate flash
memory.
[0010] FIGS. 1a to 1c are cross-sections of the conventional method
for fabricating a floating gate of a split gate flash memory.
[0011] In FIG. 1a, a silicon substrate 101 is provided. A gate
oxide layer 102, a doped polysilicon layer 103, and a nitride layer
104 having an opening 105 are sequentially formed on the silicon
substrate 101.
[0012] In FIG. 1b, the doped polysilicon layer 105 exposed by the
opening 105 is oxidized to form an oxide layer 106 with a Bird's
Beak shape edge.
[0013] In FIG. 1c, the nitride layer 104 is removed. The doped
polysilicon layer 103 is anisotropically etched to form a floating
gate 103a using the oxide layer 106 as an etching mask.
[0014] A split gate flash memory is completed after a control gate
is formed on the floating gate and the silicon substrate 101 is
implanted to form source/drain devices.
[0015] In the program step, high voltage is applied between the
source and drain. More high voltage is applied to the control gate
and goes to the floating gate by the electric capacity coupling,
and a high electric field is produced on the film gate oxide layer.
The voltage is injected into the floating gate through the film
gate oxide layer from the drain.
[0016] In the erase step, high voltage is applied between the drain
and the control gate. A high electric field is produced on the film
gate oxide layer by the electric capacity coupling. The voltage is
injected into the drain through the film gate oxide layer from the
floating gate. The gate oxide layer is damaged by the high
voltage.
[0017] When the edge of the floating gate is a tip, the electrical
field is easily concentrated, and the point is easily discharged.
If the point discharge is increased, erasing effect is
stronger.
[0018] In addition, the die size is larger due to the addition of
programming circuitry and there are more processing and testing
steps involved in the manufacture of these types of memory
devices.
SUMMARY OF THE INVENTION
[0019] The present invention is directed to a floating gate with
multiple tips and a method for fabricating the same.
[0020] Accordingly, the present invention provides a method for
forming a floating gate. A semiconductor substrate is provided. A
gate dielectric layer, a conducting layer, and a patterned hard
mask layer are sequentially formed on the surface of the
semiconductor substrate. The surface of the conducting layer is
covered by the patterned hard mask layer to form a gate. The
conducting layer is etched to a predetermined depth to form an
indentation using the patterned hard mask layer as a mask. The
conducting layer is oxidized to form an oxide layer on the surface
of the conducting layer. The oxide layer and the conducting layer
are sequentially etched to form a multiple tip conducting layer as
a floating gate using the patterned hard mask layer as a mask. The
patterned hard mask layer is removed.
[0021] Accordingly, the present invention also provides a method
for forming a floating gate. A semiconductor substrate is provided.
A gate dielectric layer, a conducting layer, a hard mask layer, and
a patterned resist layer are sequentially formed on the surface of
the semiconductor substrate. The surface of the hard mask layer is
covered by the patterned resist layer to form a gate. The patterned
resist layer is removed. The conducting layer is etched to form a
remaining conducting layer using the hard mask layer as a mask. The
remaining conducting layer is oxidized to form an oxide layer on
the surface of the exposed conducting layer and the exposed
remaining conducting layer. The oxide layer and the conducting
layer are sequentially etched to form a multiple tip conducting
layer as a floating gate using the hard mask layer as a mask. The
hard mask layer and the exposed oxide layer are removed.
[0022] Accordingly, the present invention also provides a floating
gate formed on the surface of the semiconductor substrate
comprising a conductive base and a conductive protruding layer. The
conductive base has a first top portion and a first bottom portion.
An edge of the first top portion is a first tip. The first bottom
portion contacts the semiconductor substrate. The conductive
protruding layer protrudes from the conductive base. The conductive
protruding layer has a flat top. The conductive protruding layer
has a second top portion and a second bottom portion. An edge of
the top portion is a second tip. The second bottom portion contacts
the first top portion. The conductive protruding layer has two
concave sidewalls. A multiple tip floating gate is composed of the
conductive base and the conductive protruding layer.
[0023] Accordingly, the present invention also provides a floating
gate formed on the semiconductor substrate, and a gate dielectric
layer is formed between the floating gate and the semiconductor
substrate. The floating gate comprises a base poly layer and a
protruding poly layer. The base poly layer has a first top portion
and a first bottom portion. An edge of the first top portion is a
first tip. The first bottom portion contacts the gate dielectric
layer. The protruding poly layer protrudes from the base poly
layer. The protruding poly layer is flat top. The protruding poly
layer has a second top portion and a second bottom portion. An edge
of the second portion is a second tip. The second bottom portion
contacts the first top portion. The protruding poly layer has two
concave sidewalls. A multiple tip floating gate is composed of the
base poly layer and the protruding poly layer.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] For a better understanding of the present invention,
reference is made to a detailed description to be read in
conjunction with the accompanying drawings, in which:
[0025] FIGS. 1a to 1c are cross-sections of the conventional method
for fabricating a floating gate of a split gate flash memory;
[0026] FIGS. 2a to 2f are cross-sections of the method for
fabricating a multiple tip floating gate of a split gate flash
memory of the present invention.
[0027] FIG. 2g is the cross-section of the multiple tip floating
gate of a split gate flash memory of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0028] FIGS. 2a to 2f are cross-sections of the method for
fabricating a multiple tip floating gate of a split gate flash
memory of the present invention.
[0029] In FIG. 2a, a semiconductor substrate 201, such as silicon,
is provided. A gate dielectric layer 202, such as gate oxide layer,
a conducting layer 203, such as poly layer, a hard mask layer 204,
such as nitride layer, and a patterned resist layer 205 are
sequentially formed on the surface of the semiconductor substrate
201.
[0030] In FIG. 2b, the hard mask layer 204 is etched to form a hard
mask layer 204a using the patterned resist 205 as an etching mask.
The patterned resist layer 205 is removed.
[0031] In FIG. 2c, the conducting layer 203 is etched to form a
protruding conducting layer 203a and a remaining conducting layer
203b using the hard mask layer 204a as an etching mask. The
protruding conducting layer 203a is formed under the hard mask
layer 204a, and the remaining conducting layer 203b is the
conducting layer not covered by the hard mask layer 204a. The
thickness of the remaining conducting layer 203b is less than the
protruding conducting layer 203a.
[0032] In FIG. 2d, the exposed protruding conducting layer 203a and
the exposed remaining conducting layer 203b are oxidized to form an
oxide layer 206, such as silicon oxide layer, thereon. The
oxidizing process is thermal oxidation.
[0033] In FIG. 2e, the oxide layer 206 and the remaining conducting
layer 203b are sequentially etched to form the oxide layer 206a and
the conducting layer 203c using the hard mask layer 204a as an
etching mask. The oxide layer 206a is formed on the sidewall of the
conducting layer 203c, wherein a top edge of the conducting layer
203c is a tip by the Bird's beak shape oxide layer, and a bottom
edge of the conducting layer 203c is also a tip.
[0034] The oxide layer 206 seals against oxygen, such that the
conducting layer 203c covered by the hard mask layer 204a is not
oxidized.
[0035] In FIG. 2f, the hard mask layer 204a and the exposed gate
dielectric layer 202 are removed, and the gate dielectric layer
202a under the conducting layer 203c remains.
[0036] In FIG. 2g, an inter-gate dielectric layer 207, such as
oxide layer, and a control gate 208 are sequentially formed on the
multiple tip floating gate, and a complete flash memory is
formed.
[0037] The multiple tip floating gate 203c of the present invention
is composed of a conductive base 203d and a conductive protruding
layer 203e. The conductive base 203d has a first top portion and a
first bottom portion, wherein an edge of the first top portion is a
tip, and the first bottom portion contacts the semiconductor
substrate 201. A gate dielectric layer 202a is formed between the
first bottom portion and the semiconductor substrate 201. The
conductive protruding layer 203e protrudes from the conductive base
203d, and the conductive protruding layer 203e has a flat top. The
conductive protruding layer 203e has a second top portion and a
second bottom portion, wherein the second top portion is a second
tip, and the second bottom contacts the first top portion. The
conductive protruding layer 203e has two concave sidewalls. A
multiple tip floating gate is composed of the conductive base 203d
and the conductive protruding layer 203e.
[0038] The floating gate of the present invention provides a
conducting layer 203c with a tip of the top edge by the Bird's beak
shape oxide layer and another tip of the bottom edge.
[0039] Concentration of the electric field easily occurs in the
tip, and the point is easily discharged. Point discharge is
increased because of the floating gate's multiple tips in the
present invention. Therefore, data erasing for the flash memory
having the floating gate with multiple tips is increased.
[0040] While the invention has been described by way of example and
in terms of the preferred embodiments, it is to be understood that
the invention is not limited to the disclosed embodiments. To the
contrary, it is intended to cover various modifications and similar
arrangements (as would be apparent to those skilled in the art).
Therefore, the scope of the appended claims should be accorded the
broadest interpretation so as to encompass all such modifications
and similar arrangements.
* * * * *