U.S. patent application number 10/043218 was filed with the patent office on 2002-05-16 for flash eeprom cell and method of manufacturing the same.
This patent application is currently assigned to HYUNDAI ELECTRONICS INDUSTRIES CO., LTD.. Invention is credited to Chang, Hee Hyun, Lee, Dong Kee, Lee, Hee Youl, Lee, Min Kyu.
Application Number | 20020056870 10/043218 |
Document ID | / |
Family ID | 19597693 |
Filed Date | 2002-05-16 |
United States Patent
Application |
20020056870 |
Kind Code |
A1 |
Lee, Min Kyu ; et
al. |
May 16, 2002 |
Flash EEPROM cell and method of manufacturing the same
Abstract
The invention relates to a flash EEPROM cell and method of
manufacturing the same. The method of manufacturing a flash EEPROM
cell includes sequentially forming a tunnel oxide film, a
polysilicon layer for a floating gate and a hard mask layer on a
semiconductor substrate; patterning the hard mask layer and then
forming a hard mask layer spacer at the etching side of the
patterned hard mask layer; removing the exposed portion of the
ploysilicon layer for the floating gate by etching process using
the patterned hard mask layer and the hard mask layer spacer as
etching masks thus to form first and second patterns that are
separated in two; removing the patterned hard mask layer and the
hard mask layer spacer and then depositing a dielectric film and a
polysilicon layer for a floating gate on the entire structure, thus
forming a first floating gate, a second floating gate and a control
gate by self-aligned etching process; and forming a drain junction
and a source junction by cell source/drain ion implantation
process. Thus, the present invention can prevent lower of the
quality of the tunnel oxide film and thus increase the coupling
ratio.
Inventors: |
Lee, Min Kyu; (Ichon-Shi,
KR) ; Chang, Hee Hyun; (Sungnam-Shi, KR) ;
Lee, Hee Youl; (Ichon-Shi, KR) ; Lee, Dong Kee;
(Ichon-Shi, KR) |
Correspondence
Address: |
PENNIE & EDMONDS LLP
1667 K STREET NW
SUITE 1000
WASHINGTON
DC
20006
|
Assignee: |
HYUNDAI ELECTRONICS INDUSTRIES CO.,
LTD.
Ichon-Shi
KR
|
Family ID: |
19597693 |
Appl. No.: |
10/043218 |
Filed: |
January 14, 2002 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
10043218 |
Jan 14, 2002 |
|
|
|
09609337 |
Jun 30, 2000 |
|
|
|
Current U.S.
Class: |
257/314 ;
257/315; 257/317; 257/E21.209; 257/E29.308 |
Current CPC
Class: |
H01L 29/7887 20130101;
H01L 29/40114 20190801; G11C 11/5621 20130101; G11C 2211/5612
20130101; G11C 16/0458 20130101 |
Class at
Publication: |
257/314 ;
257/315; 257/317 |
International
Class: |
H01L 029/76; H01L
029/788 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 30, 1999 |
KR |
99-25769 |
Claims
What is claimed is:
1. A flash EEPROM cell, comprising: first and second floating
gates, that are different in size and separated in two, formed to
be electrically separated from a semiconductor substrate by a
tunnel oxide film; control gate formed to be electrically separated
from said first and second floating gates by a dielectric film;
drain junction formed on said semiconductor substrate at the side
of said first floating gate; and source junction formed on said
semiconductor substrate at the side of said second floating
gate.
2. The flash EEPROM cell according to claim 1, wherein the ratio of
the size of the first floating gate to the second floating gate is
{fraction (1/3)} to less than 1.
3. A flash EEPROM cell comprising: a semiconductor substrate;
spaced apart drain and source junctions formed in the semiconductor
substrate; spaced apart first and second portions of a first film
formed above the semiconductor substrate, the first portion of the
first film at least partially overlapping one of the drain and
source junctions and the second portion of the first film at least
partially overlapping the other of the drain and source junctions;
a first floating gate formed above the first portion of the first
film and a second floating gate formed above the second portion of
the first film, the first and second floating gates being spaced
apart from one another by a gap and having opposing sidewalls; a
dielectic film formed above the first and second floating gates and
also covering the opposing sidewalls of the first and second
floating gates; a control gate formed on the dielectric film, the
control gate extending over both the first and second floating
gates and also extending at least partially into said gap so as to
be interposed between the opposing sidewalls of the first and
second floating gates; wherein the first and second floating gates
are different in size.
4. The flash EEPROM cell according to claim 3, wherein a ratio of
the size of the first floating gate to the second floating gate is
{fraction (1/3)} to less than 1.
5. The flash EEPROM cell according to claim 3, wherein said first
film has a thickness of 50 through 150 Angstroms.
6. The flash EEPROM cell according to claim 3, wherein said
dielectric film is made of a combination of oxide and nitride and
has the thickness of 100 through 300 Angstroms.
7. The flash EEPROM cell according to claim 3, wherein the first
and second floating gates are formed from polysilicon having a
thickness of 300 through 2000 Angstroms.
8. The flash EEPROM cell according to claim 3, wherein the first
and second floating gates are formed from polysilicon having a
thickness of 300 through 2000 Angstroms.
9. The flash EEPROM cell according to claim 3, wherein the control
gate is formed from polysilicon having a thickness of 300 through
2000 Angstroms
10. The flash EEPROM cell according to claim 3, wherein: the first
film has a thickness of 50 through 150 Angstroms; the dielectric
film is made of a combination of oxide and nitride and has a
thickness of 100 through 300 Angstroms; the first and second
floating gates are formed from polysilicon having a thickness of
300 through 2000 Angstroms; and the control gate is formed from
polysilicon having a thickness of 300 through 2000 Angstroms.
11. The flash EEPROM cell according to claim 10, wherein the ratio
of the size of the first floating gate to the second floating gate
is {fraction (1/3)} to less than 1.
12. The flash EEPROM cell according to claim 3, wherein the drain
junction is formed near the first floating gate and the source
junction is formed near the second floating gate.
13. The flash EEPROM cell according to claim 12, wherein the ratio
of the size of the first floating gate to the second floating gate
is {fraction (1/3)} to less than 1.
Description
RELATED APPLICATIONS
[0001] This is a Divisional of application Ser. No. 09/609,337,
filed Jun. 30, 2000, now U.S. Pat. No. 6,339,006.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The invention relates generally to a flash EEPROM cell and
method of manufacturing the same. More particularly, the present
invention relates to a flash EEPROM cell in which two floating
gates having different sizes can be simply formed at a single cell
using a hard mask layer in a multi-level cell, capable of
preventing lower of the quality of a tunnel oxide film and
increasing the coupling ratio, and method of manufacturing the
same.
[0004] 2. Description of the Prior Art
[0005] The greatest bottleneck to prevent customization of the
current flash EEPROM is that the cost per unit information is high.
For this, the higher integration of a cell is required and thus
various manufacturers have made an effort to develop it. However,
as the structure of the EEPROM is complicated compared to that of
the DRAM, there is a problem that the integration level of the
EEPROM is difficult to increase.
[0006] The conventional flash EEPROM cell has only two states
(storing only binary information) depending on whether the
electrons is charged at the floating gate or not. Thus, it has a
drawback that the chip size is increased due to one bit per one
cell in the large-scale configuration of the cell array depending
on it.
[0007] On the other hand, as the multi-level cell has four states,
it can store information at one cell instead of storing it at two
cells. Thus, it can store much information at the same area.
However, in the multi-level cell, as two floating gates have to be
formed at one cell, many processes has to be experienced to
manufacture it. Also, as forming the tunnel oxide film has to be
performed in two steps, it is difficult to assure the quality of
the tunnel oxide film and to assure the quality of the tunnel oxide
film below a poly spacer in case of using the poly spacer.
SUMMARY OF THE INVENTION
[0008] It is therefore an object of the present invention to
provide a flash EEPROM cell in which two floating gates having
different size can be simply formed at a single cell using a hard
mask layer in a multi-level cell, capable of preventing lower of
the quality of a tunnel oxide film and increasing the coupling
ratio, and method of manufacturing the same.
[0009] In order to accomplish the above object, a flash EEPROM cell
according to the present invention is characterized in that it
comprises first and second floating gates, that are different in
size and separated in two, formed to be electrically separated from
a semiconductor substrate by a tunnel oxide film; control gate
formed to be electrically separated from said first and second
floating gates by a dielectric film; drain junction formed on said
semiconductor substrate at the side of said first floating gate;
and source junction formed on said semiconductor substrate at the
side of said second floating gate.
[0010] Also, in order to accomplish the above object, the method of
manufacturing a flash EEPROM cell according to the present
invention is characterized in that it comprises the steps of
sequentially forming a tunnel oxide film, a polysilicon layer for a
floating gate and a hard mask layer on a semiconductor substrate;
patterning said hard mask layer and then forming a hard mask layer
spacer at the etching side of the patterned hard mask layer;
removing the exposed portion of the ploysilicon layer for the
floating gate by etching process using said patterned hard mask
layer and said hard mask layer spacer as etching masks thus to form
first and second patterns that are separated in two; removing said
patterned hard mask layer and said hard mask layer spacer and then
depositing a dielectric film and a polysilicon layer for a floating
gate on the entire structure, thus forming a first floating gate, a
second floating gate and a control gate by self-aligned etching
process; and forming a drain junction and a source junction by cell
source/drain ion implantation process.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] The aforementioned aspects and other features of the present
invention will be explained in the following description, taken in
conjunction with the accompanying drawings, wherein:
[0012] FIGS. 1A through 1D are sectional views for explaining a
flash EEPROM cell and method of manufacturing the same according to
the present invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0013] The present invention will be described in detail by way of
a preferred embodiment with reference to accompanying drawings, in
which like reference numerals are used to identify the same or
similar parts.
[0014] FIGS. 1A through 1D are sectional views for explaining a
flash EEPROM cell and method of manufacturing the same according to
the present invention.
[0015] Referring now to FIG. 1A, a field oxide film (not shown) is
formed and a tunnel oxide film 12 is formed on a semiconductor
substrate 11 in which an active region and a field region are
defined. Then, a polysilicon layer for the floating gate 13 is
formed on the tunnel oxide film 12. Next, a hard mask layer 14 is
formed on the polysilicon layer for the floating gate 13.
Thereafter, a photoresist pattern 21 is formed on the hard mask 14
by exposure and developing process using the mask for the floating
gate.
[0016] In the above, the tunnel oxide film 12 is formed in
thickness of 50 through 150 Angstrom and the polysilicon layer 13
for the floating gate is formed in thickness of 300 through 2000
Angstrom. The hard mask layer 14 is formed of nitride, oxy-nitride,
oxide etc. having a high etch selectivity upon etching of the
polysilicon layer, in thickness of 200 through 2000 Angstrom. The
photoresist pattern 21 is formed at a minimum feature size that can
be formed by exposure process in order to reduce its chip size.
[0017] Referring to FIG. 1B, the mask layer 14 is patterned by
etching process using the photoresist pattern 21 as an etching
mask. After the photoresist pattern 21 is removed, a hard mask
layer spacer 15 is formed at the etching face of the patterned hard
mask layer 14.
[0018] In the above, the hard mask layer spacer 15 is formed of
nitride, oxy-nitride, oxide etc. having a high etch selectivity
upon etching of the polysilicon layer, in thickness of 200 through
2000 Angstrom, using blanket etching process. As the hard mask
layer spacer 15 is formed, still smaller size of spacer can be
obtained than the minimum size that can be formed by exposure
process, thus increasing the effect of reducing the chip size.
[0019] Referring now to FIG. 1C, by etching process using the
patterned hard mask layer 14 and the hard mask layer spacer 15 as
etching mask, the exposed portion of the polysilicon layer for the
floating gate 13 is removed to form a first pattern 13a and a
second pattern 13b which are separated in two section. Then,
annealing process for recovering the portion of the tunnel oxide
film 12 that is damaged by etching process is performed.
[0020] Referring to FIG. 1D, the patterned hard mask layer 14 and
the hard mask layer spacer 15 are removed and a dielectric film 16
and a polysilicon layer for the floating gate 17 are deposited on
the entire structure including the first pattern 13a and the second
pattern 13b which are separated in two section. Then, self-aligned
etching process using the control gate as a mask is used to allow
the polysilicon layer for the floating gate 17 and the polysilicon
layer for the floating gate 13 etching the first pattern 13a and
the second pattern 13b which are separated in two section, thus
forming a first floating gate 130a made of some of the first
pattern 13a, a second floating gate 130b made of some of the second
pattern 13b and a control gate 17 lying over the floating gates
130a and 130b. Then, a drain junction 18a and a source junction 18b
are formed by cell source/drain ion implantation process.
[0021] In the above, the dielectric film 16 is consisted of the
combination of oxide and nitride and has the thickness of 100
through 300 Angstrom. The polysilicon layer for the floating gate
17 is formed in thickness of 300 through 2000 Angstrom. A polycide
layer may be formed instead of the polysilicon layer for the
floating gate 17. The first floating gate 130a and the second
floating gate 130b are different in size, wherein the ratio of the
size of the first floating gate 130a to the second floating gate
130b is {fraction (1/3)} through 1. The drain junction 18a is
formed on the semiconductor substrate 11 at the side of the first
floating gate 130a and the source junction 18b is formed on the
semiconductor substrate 11 at the side of the second floating gate
130b.
[0022] Meanwhile, additional process may be added, by which the
patterned hard mask layer 14 and the hard mask layer spacer 15 are
removed and then dopants different in polarity with the
semiconductor substrate 11 are ion-implanted at the dose of 1E14
through 7E16 ions/cm.sup.2.
[0023] In the flash EEPROM cell of the present invention formed by
the above process, the separated first and second floating gates
130a and 130b having different sizes are formed to be electrically
separated from the semiconductor substrate 11 by the tunnel oxide
film 12, the control gate 17 is formed to be electrically separated
from the first and second floating gates 130a and 130b by the
dielectric film 12, the drain junction 18a is located at the side
of the first floating gate 130a and the source junction 18b is
located at the side of the second floating gate 130b.
[0024] In the flash EEPROM cell manufactured by an embodiment of
the present invention, the erase operation is performed to
discharge from the floating gates to the junction or the channel
region due to a tunneling method, and the program operation does
not have a significant hot carrier injection problem.
[0025] As described above, the flash EEPROM cell using the
multi-level cell of the present invention can increase the
productivity of the wafers due to the effect of chip size reduction
because it allows a data memory of two bits on one cell, can assure
the quality of the tunnel oxide film since it can simply form the
floating gate most important in the multi-level cell, and can
increase the throughput due to increased speed and uniformity upon
program and erase because the coupling ratio between the control
gate and the floating gate is increased as much as the hard mask
layer spacer.
[0026] The present invention has been described with reference to a
particular embodiment in connection with a particular application.
Those having ordinary skill in the art and access to the teachings
of the present invention will recognize additional modifications
and applications within the scope thereof.
[0027] It is therefore intended by the appended claims to cover any
and all such applications, modifications, and embodiments within
the scope of the present invention.
* * * * *