U.S. patent application number 12/368265 was filed with the patent office on 2009-06-11 for floating gate of flash memory device and method of forming the same.
Invention is credited to Chang Hun HAN.
Application Number | 20090146205 12/368265 |
Document ID | / |
Family ID | 38192599 |
Filed Date | 2009-06-11 |
United States Patent
Application |
20090146205 |
Kind Code |
A1 |
HAN; Chang Hun |
June 11, 2009 |
Floating Gate of Flash Memory Device and Method of Forming the
Same
Abstract
Disclosed is a floating gate of a flash memory device, wherein a
tunneling oxide layer is formed on a semiconductor substrate, and a
floating gate is formed in the shape of a lens having a convex top
surface.
Inventors: |
HAN; Chang Hun; (Icheon-si,
KR) |
Correspondence
Address: |
THE LAW OFFICES OF ANDREW D. FORTNEY, PH.D., P.C.
401 W FALLBROOK AVE STE 204
FRESNO
CA
93711-5835
US
|
Family ID: |
38192599 |
Appl. No.: |
12/368265 |
Filed: |
February 9, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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11647021 |
Dec 27, 2006 |
7507626 |
|
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12368265 |
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Current U.S.
Class: |
257/316 ;
257/E29.3 |
Current CPC
Class: |
H01L 29/42324 20130101;
H01L 29/40114 20190801 |
Class at
Publication: |
257/316 ;
257/E29.3 |
International
Class: |
H01L 29/788 20060101
H01L029/788 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 28, 2005 |
KR |
10-2005-0132652 |
Claims
1. A floating gate of a flash memory device, comprising: a
tunneling oxide layer on a semiconductor substrate; a floating gate
having a lens shape and a convex top surface; a gate oxide on the
floating gate; and a concave control gate on the gate oxide.
2. The nonvolatile memory device of claim 1, wherein the gate oxide
and the control gate have a shape complementary to that of the
floating gate.
3. The nonvolatile memory device of claim 1, wherein the gate oxide
and the control gate also have a shape effective to increase the
capacitance or coupling ratio between the floating gate and the
control gate, relative to an otherwise identical nonvolatile memory
having a planar floating gate.
4. The nonvolatile memory device of claim 1, wherein the floating
gate has a width of from 45 nm to 150 nm.
5. The nonvolatile memory device of claim 4, wherein the floating
gate width is less than or equal to 100 nm.
6. The nonvolatile memory device of claim 2, wherein the control
gate has a width greater than that of the floating gate, and
portions of the floating gate extend along sidewalls of the
floating gate.
7. A nonvolatile memory device, comprising: a tunnel oxide layer on
a semiconductor substrate; a floating gate on the tunnel oxide
layer having a convex top surface; a gate oxide on the floating
gate; and a control gate on the gate oxide.
8. The nonvolatile memory device of claim 8, wherein the floating
gate has a shape effective to increase a capacitance or a coupling
ratio between the floating gate and the control gate.
9. The nonvolatile memory device of claim 9, wherein the gate oxide
and the control gate have a shape complementary to that of the
floating gate.
10. The nonvolatile memory device of claim 8, wherein the gate
oxide and the control gate also have a shape effective to increase
the capacitance or coupling ratio between the floating gate and the
control gate, relative to an otherwise identical nonvolatile memory
having a planar floating gate.
11. The nonvolatile memory device of claim 8, wherein the floating
gate has a width of from 45 nm to 150 nm.
12. The nonvolatile memory device of claim 12, wherein the floating
gate width is less than or equal to 100 nm.
13. The nonvolatile memory device of claim 9, wherein the control
gate has a width greater than that of the floating gate, and
portions of the floating gate extend along sidewalls of the
floating gate.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is a divisional of U.S. patent application
Ser. No. 11/647,021, filed Dec. 27, 2006, pending, which is
incorporated herein by reference in its entirety.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a floating gate and a
method of forming the same.
[0004] 2. Description of the Related Art
[0005] A flash memory is a kind of nonvolatile memory. Applications
of the flash memory have been extended, and a chip integration
density of the flash memory has also been improved.
[0006] Products in which a flash memory is embedded in a general
logic have been applied in various fields. Accordingly, it is a
problem to reduce manufacturing costs and power consumption.
[0007] To reduce manufacturing costs, a chip size must be reduced
and a process must be simplified. However, the chip size has been
currently reduced down to 0.10 .mu.m with the rapid development of
a photo process in accordance with a design rule.
[0008] Further, production costs can be reduced not only by
simplifying a process but also by eliminating a process in which
failure may occur in view of a yield.
[0009] Meanwhile, in a design of a flash memory device, a floating
gate requires high capacitance for the purpose of coupling a higher
floating gate voltage from a control gate.
[0010] As a method for obtaining high capacitance as described
above, there are methods of increasing an overlap between floating
and control gates, utilizing a material with an interlayer
dielectric constant, reducing the thickness of an interlayer
dielectric layer, and the like.
[0011] The method of utilizing a material with an interlayer
dielectric constant or reducing the thickness of an interlayer
dielectric layer has a disadvantage in that a leakage current is
large.
[0012] Therefore, the method of increasing an overlap between
floating and control gates is mainly used to obtain high
capacitance. However, the method of increasing an overlapping area
has a disadvantage in that a cell area is increased.
[0013] As a method for solving these disadvantages, there is a
method of increasing an overlapping area of a sidewall rather than
that of a plan, which causes many problems in view of
planarization.
[0014] One of such area increasing methods is a method of allowing
the shape of a floating gate to be uneven.
[0015] That is, there is a method in which a floating gate is
primarily formed, and a mask process is then performed such that
the interior of the floating gate is removed by a predetermined
thickness, thereby allowing the shape of the floating gate to be
uneven.
[0016] In this case, the capacitance of a floating gate is
increased in accordance with the increase of an area due to
unevenness, and thus the coupling ratio of a flash memory is
increased.
[0017] However, there is a problem in that a mask process must be
performed twice in such a method, i.e., a process is complicated
and manufacturing costs are increased.
SUMMARY OF THE INVENTION
[0018] The present invention has been made to solve the above
mentioned problem occurring in the prior art, and it is an object
of the present invention to provide a floating gate of a flash
memory device and a method of forming the same, wherein the area of
the floating gate is extended, and a coupling ratio is
increased.
[0019] According to one aspect of the present invention, there is
provided a floating gate of a flash memory device, wherein a
tunneling oxide layer is formed on a semiconductor substrate, and a
floating gate is formed in the shape of a lens having a convex top
surface.
[0020] According to another aspect of the present invention, there
is provided a method of forming a floating gate in a flash memory
device, which includes the steps of: forming a tunneling oxide
layer on a semiconductor substrate; forming a conductive layer on
the tunneling oxide layer; coating a photoresist layer on the
conductive layer and then selectively patterning the photoresist
layer, thereby defining a floating gate area; selectively removing
the conductive layer by a predetermined thickness from a top
surface of the conductive layer by using the patterned photoresist
layer as a mask; performing a thermal process with respect to the
photoresist layer, thereby, reflowing the photoresist layer with
the shape of a lens having a convex top surface; and simultaneously
etching the photoresist layer subjected to reflowing and the
conductive layer, thereby forming a floating gate with the shape of
a lens having a convex top surface.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] FIG. 1 is a sectional view showing a floating gate of a
flash memory device according to the present invention; and
[0022] FIGS. 2A to 2E are sectional views illustrating a process of
forming a floating gate in a flash memory device according to the
present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0023] Hereinafter, a floating gate of a flash memory device and a
method of forming the same according to the present invention will
be described in detail with reference to the accompanying
drawings.
[0024] FIG. 1 is a sectional view showing a floating gate of a
flash memory device according to the present invention.
[0025] As shown in FIG. 1, a tunneling oxide layer 102 is formed on
a semiconductor substrate 101, and a floating gate is formed in the
shape of a lens having a convex top surface.
[0026] FIGS. 2A to 2E are sectional views illustrating a process of
forming a floating gate in a flash memory device according to the
present invention.
[0027] As shown in FIG. 2A, a tunneling oxide layer 102 is formed
in a thickness of 80 to 120 .ANG. on a semiconductor substrate 101,
and a poly-silicon layer 103 is formed in a thickness of 900 to
1100 .ANG. on the tunneling oxide layer 102.
[0028] Here, the poly-silicon 103 may be formed by allowing the
thickness of the poly-silicon layer 103 to be adjusted depending on
etching selectivity with a photoresist layer to be coated
later.
[0029] As shown in FIG. 2B, a photoresist layer 104 is coated on an
entire surface of the semiconductor substrate 101 having the
poly-silicon layer 103, and the photoresist layer 104 is
selectively patterned through an exposure and development process,
thereby defining a floating gate area.
[0030] Here, after the photoresist layer 104 has been coated, an
antireflective coating (not shown) may be formed in a thickness of
about 600 .ANG..
[0031] Meanwhile, in a method of coating the photoresist layer 104,
there are methods of spin coat, spray coat, dip coat and the like.
However, the spin coat performed while chucking and rotating a
wafer at a high speed under a vacuum atmosphere is advantageous to
stability and uniformity.
[0032] Then, a photo mask (not shown) corresponding to a desired
pattern is positioned on the photoresist layer 104, and a
photoresist pattern is then formed to have a desired size through
exposure and development processes.
[0033] Here, the development process is performed through
deposition or spraying. In the former, it is difficult to manage a
temperature, a density, a change in time and the like, while, in
the latter, it is relatively easy to manage. Currently, an
apparatus subjected to in-line through a spraying scheme has been
widely used.
[0034] As shown in FIG. 2C, the poly-silicon layer 103 is
selectively removed by a predetermined thickness from a top surface
thereof by using the patterned photoresist layer 104 as a mask.
[0035] Here, the thickness of the poly-silicon layer 103 removed by
the predetermined thickness is about 1/2 of the original thickness
of the poly-silicon layer 103.
[0036] As shown in FIG. 2D, a thermal process is performed with
respect to the photoresist layer 104 such that the photoresist
layer 104 is subjected to reflowing, thereby forming a photoresist
layer 104a with the shape of a lens having a convex top
surface.
[0037] As shown in FIG. 2E, the photoresist layer 104 subjected to
reflowing and the residual poly-silicon layer 103 are
simultaneously etched at etching selectivity of 1:1, thereby
forming a floating gate 105 with the shape of a lens having a
convex top surface.
[0038] Subsequently, after the floating gate 105 has been formed,
the residual photoresist layer 104 and impurities are removed, and
a washing process is performed.
[0039] As described above, a floating gate of a flash memory device
and a method of forming the same according to the present invention
has advantages as follows.
[0040] That is, a floating gate is formed in the shape of a lens
having a convex top surface through a simple process, so that the
area of the floating gate can be extended, and a coupling ratio can
be increased.
[0041] It will be apparent to those skilled in the art that various
modifications and variations can be made in the present invention.
Thus, it is intended that the present invention covers the
modifications and variations thereof within the scope of the
appended claims.
* * * * *