U.S. patent application number 09/329894 was filed with the patent office on 2001-11-08 for hydrogen peroxide and acid etchant for a wet etch process.
Invention is credited to AKATSU, HIROYUKI, KOTECKI, DAVID E., LIAN, JINGYU JENNY, SHEN, HUA.
Application Number | 20010037995 09/329894 |
Document ID | / |
Family ID | 23287476 |
Filed Date | 2001-11-08 |
United States Patent
Application |
20010037995 |
Kind Code |
A1 |
AKATSU, HIROYUKI ; et
al. |
November 8, 2001 |
HYDROGEN PEROXIDE AND ACID ETCHANT FOR A WET ETCH PROCESS
Abstract
A process and solution for selectively wet etching a titanium
based perovskite material disposed on a silicon oxide or silicon
nitride substrate is disclosed herein. The solution is composed of
hydrogen peroxide, an acid and deionized water. The solution is
heated to a temperature between 25 and 90 degrees Celsius. The
titanium based perovskite material may be barium strontium
titanate, barium titanate, strontium titanate or a lead titanate.
The solution selectively etches the perovskite material while the
substrate is only minimally etched, if at all. The process and
solution allows for an etching rate up to thirty times greater than
conventional etching rates for similar perovskite materials
selective to various substrate, barrier and mask layers, including
SiO.sub.2.
Inventors: |
AKATSU, HIROYUKI; (YORKTOWN
HEIGHTS, NY) ; KOTECKI, DAVID E.; (HOPEWELL JUNCTION,
NY) ; LIAN, JINGYU JENNY; (WALLKILL, NY) ;
SHEN, HUA; (BEACON, NY) |
Correspondence
Address: |
WOOD PHILLIPS VANSANTEN CLARK & MORTIMER
500 W MADISON STREET
SUITE 3800
CHICAGO
IL
606612511
|
Family ID: |
23287476 |
Appl. No.: |
09/329894 |
Filed: |
June 10, 1999 |
Current U.S.
Class: |
216/100 ; 216/41;
257/E21.251; 438/754 |
Current CPC
Class: |
C04B 41/009 20130101;
C04B 41/5353 20130101; C04B 35/472 20130101; C04B 35/465 20130101;
H01L 21/31111 20130101; C04B 41/009 20130101; C04B 41/009 20130101;
C04B 41/91 20130101; C04B 2111/00853 20130101 |
Class at
Publication: |
216/100 ; 216/41;
438/754 |
International
Class: |
H01L 021/302; C23F
001/00 |
Claims
We claim:
1. A process for etching a perovskite ferroelectric material, the
process comprising: providing a substrate having a ferroelectric
film, the ferroelectric film composed of a perovskite material;
subjecting the ferroelectric film to a mixture of hydrogen peroxide
and an acid; and heating the mixture to a temperature between 30
and 90 degrees Celsius.
2. The process according to claim 1 wherein the perovskite material
is selected from the group consisting of barium strontium titanate,
barium titanate, strontium titanate, calcium titanate, lead
titanate, lead lanthanum zirconium titanate and lead zirconium
titanate.
3. The process according to claim 1 wherein the acid is selected
from the group consisting of sulfuric acid, hydrochloric acid ,
phosphoric acid and acetic acid.
4. The process according to claim 1 wherein the mixture is composed
of between approximately 20% to approximately 95% of hydrogen
peroxide, 5% to 80% acid, and 0% to 75% deionized water.
5. The process according to claim 1 wherein the mixture is composed
of approximately 45 percent hydrogen peroxide, approximately 10
percent acid and approximately 45 percent deionized water.
6. The process according to claim 1 wherein the step of subjecting
the ferroelectric film to the mixture comprises placing the
substrate with the ferroelectric film disposed thereon into a
solution of the mixture for a predetermined time period to effect
the necessary etching of the ferroelectric film.
7. The process according to claim 6 wherein the predetermined time
period is between 30 and 1000 seconds or longer.
8. A process for etching a perovskite ferroelectric material, the
process comprising: providing a substrate having a ferroelectric
film composed of a perovskite material selected from the group
consisting of barium strontium titanate, barium titanate, strontium
titanate and lead titanate, the substrate also having a silicon
oxide or silicon nitride component and an electrode; subjecting the
substrate having the ferroelectric film to a solution comprising
hydrogen peroxide and an acid; heating the solution to a
temperature between 25 and 90 degrees Celsius.
9. The process according to claim 8 wherein the electrode is
composed of platinum.
10. The process according to claim 8 wherein the acid is sulfuric
acid.
11. The process according to claim 10 wherein the solution is
composed of between approximately 20% to approximately 95% of
hydrogen peroxide, 5% to 80% acid, and 0% to 75% deionized
water.
12. The process according to claim 8 wherein the solution is heated
to a temperature between 30 and 70 degrees Celsius.
13. The process according to claim 8 wherein the step of subjecting
the substrate having a ferroelectric film to the solution comprises
placing the substrate having the ferroelectric film a bath of the
solution for a predetermined time period to effect the necessary
etching of the ferroelectric film.
14. The process according to claim 13 wherein the predetermined
time period is between 30 and 1000 seconds or longer.
15. A solution for a wet etch process for selective removal of a
titanium based perovskite material, the solution consisting
essentially of hydrogen peroxide to form a complex with the
titanium of the titanium based perovskite material, an acid capable
of stabilizing the complex formed between the hydrogen peroxide and
the titanium, and optionally deionized water.
16. The solution according to claim 15 wherein the solution is
composed of between approximately 20% to approximately 95% of
hydrogen peroxide, 5% to 80% acid, and 0% to 75% deionized
water.
17. The solution according to claim 15 wherein the acid is sulfuric
acid.
18. The solution according to claim 15 wherein the solution is
heated to a temperature between 25 and 90 degrees Celsius.
19. The solution according to claim 15 wherein the titanium based
perovskite material is selected from the group consisting of barium
strontium titanate, barium titanate, strontium titanate and lead
titanate.
20. The solution according to claim 15 wherein the solution etches
silicon oxide at a rate of less than 10 Angstroms per minute at a
temperature between 30 and 70 degrees Celsius.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a process for etching a
ferroelectric film disposed on a substrate. More specifically, the
present invention relates to a process and solution for wet etching
a perovskite material disposed on a silicon substrate.
BACKGROUND OF THE INVENTION
[0002] Ferroelectric films have been actively utilized for
electronic and optoelectronic applications such as memory devices,
transistors and optical devices. Many perovskite ferroelectric
materials are notable as advanced dynamic random access memory
("DRAM") capacitors for the one gigabit and beyond range. These
perovskite materials include barium titanate, BaTiO.sub.3 ("BTO"),
strontium titanate, SrTiO.sub.3 ("STO"), and their solid solutions,
barium strontium titanate, (Ba,Sr)TiO.sub.3 ("BSTO"). BSTO is
especially useful in electrical and optoelectrical devices because
of its lower leakage current and better aging properties.
[0003] A common structure employed in DRAM devices is a stacked
cell structure, in which a BSTO capacitor is connected to a pass
transistor via a poly silicon contact plug. Platinum is generally
used as the bottom electrode for the capacitor. The platinum is
placed on a silicon oxide or silicon nitride substrate and a
contact plug. Platinum is utilized since the bottom electrode must
endure a high temperature oxygen environment during the deposition
of the perovskite material. Additionally, to avoid an undesirable
reaction between the platinum electrode and the silicon substrate,
one or more diffusion barrier layers may be juxtaposed between the
platinum electrode layer and the silicon oxide or silicon nitride
substrate and the contact plug. The bottom electrode is patterned
and a ferroelectric perovskite material such as BSTO is deposited
onto the bottom electrode and the field region that does not
contain bottom platinum. Then a top electrode is deposited onto the
ferroelectric perovskite material. A cover and mask layer may be
placed onto the top electrode layer. Such a stacked cell structure
may be fabricated using established patterning technologies. Such
patterning technologies involve the etching of various layers of
the stacked cell structure to expose other layers for proper
functioning of the electronic device. Dry or wet etching techniques
may be employed to fabricate the finished stacked cell
structure.
[0004] One known etchant for BSTO is hydrogen fluoride. Although
hydrogen fluoride is an adequate etchant for BSTO, it has the
detrimental effect of etching exposed silicon and oxide surfaces.
Thus, the use of hydrogen fluoride to etch a BSTO layer of a
stacked cell structure would result in other layers being etched
thereby possibly damaging the electronic device.
[0005] Another etchant that may attack the titanate bonds of a
perovskite lattice is hydrogen peroxide. The hydrogen peroxide
forms a strong complex with the titanium. However, the etch rate of
BSTO in hydrogen peroxide is extremely slow, well below even the
lowest possible commercial production rate. Thus, the use of
hydrogen peroxide would substantially increase the production costs
of the electronic device.
[0006] Other etchants include hydrochloric acid, see U.S. Pat. Nos.
5,374,330 and 5,356,516, illuminated with radiation. Illumination
is required for etching titanates (such as BSTO) in the HCl acid
liquid ambient, which increases production costs.
[0007] The present invention is directed to solving one or more of
the problems discussed above in a novel manner.
SUMMARY OF THE INVENTION
[0008] The present invention provides a solution to the problems of
the prior art associated with the fabrication of DRAM devices and
other electronic devices. The present invention is able to
accomplish this by providing a process and solution for wet etching
of ferroelectric films at a commercially acceptable rate of
production.
[0009] One aspect of the present invention is a process for etching
a perovskite ferroelectric material. The process includes providing
a substrate having a ferroelectric film. The ferroelectric film is
composed of a perovskite material. The process also includes
subjecting the ferroelectric film to a mixture of hydrogen peroxide
and an acid. The process also includes heating the mixture to a
temperature between 30 and 90 degrees Celsius.
[0010] The perovskite material of the process may be barium
strontium titanate, barium titanate, strontium titanate, calcium
titanate, lead titanate, lead lanthanum zirconium titanate or lead
zirconium titanate. The acid of the process may be sulfuric acid,
hydrochloric acid, phosphoric acid, acetic acid or the like. The
mixture may be composed of between approximately 20% to
approximately 95% of hydrogen peroxide, 5% to 80% acid, and 0% to
75% deionized water.
[0011] More specifically, the mixture of the process may be
composed of approximately 45 percent hydrogen peroxide,
approximately 10 percent acid and approximately 45 percent
deionized water.
[0012] The step of subjecting the ferroelectric film to the mixture
may include placing the substrate with the ferroelectric film
disposed thereon into a solution of the mixture for a predetermined
time period to effect the necessary etching of the ferroelectric
film. The predetermined time period may be between 30 and 1000
seconds or longer.
[0013] Another aspect of the present invention is a process for
etching a perovskite ferroelectric material which includes
providing a substrate having a ferroelectric film composed of a
barium strontium titanate, barium titanate, strontium titanate or a
lead titanate. The substrate also has a silicon oxide or silicon
nitride component and an electrode. The process also includes
subjecting the substrate having the ferroelectric film to a
solution of hydrogen peroxide and an acid. The process also
includes heating the solution to a temperature between 25 and 90
degrees Celsius.
[0014] The electrode of the process may be composed of platinum.
The acid of the process may be sulfuric acid. The solution of the
process may be composed of between approximately 20% to
approximately 95% of hydrogen peroxide, 5% to 80% acid, and 0% to
75% deionized water. The solution of the process may be heated to a
temperature between 30 and 70 degrees Celsius. The step of
subjecting the substrate having a ferroelectric film to the
solution may include placing the substrate having the ferroelectric
film into a bath of the solution for a predetermined time period to
effect the necessary etching of the ferroelectric film. The
predetermined time period may be between 30 and 240 seconds.
[0015] Another aspect of the present invention is in a solution for
a wet etch process for selective removal of a titanium based
perovskite material. The solution consists essentially of hydrogen
peroxide which forms a complex with the titanium of the titanium
based perovskite material, an acid capable of stabilizing the
complex formed between the hydrogen peroxide and the titanium, and
optionally deionized water.
[0016] The solution may be composed of between approximately 20% to
approximately 95% of hydrogen peroxide, 5% to 80% acid, and 0% to
75% deionized water. The acid of the solution may be sulfuric acid.
The solution may be heated to a temperature of between 25 and 90
degrees Celsius. The titanium based perovskite material of the
solution may be barium strontium titanate, barium titanate,
strontium titanate or lead titanate. The solution may etch silicon
oxide at a rate of less than 10 Angstroms per minute at a
temperature of between 30 and 70 degrees Celsius.
[0017] Having briefly described the present invention, the above
and further objects, features and advantages thereof will be
recognized by those skilled in the pertinent art from the following
detailed description of the invention when taken in conjunction
with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] FIG. 1 is a cross-sectional view of a precursor of a cell
stacked structure prior to etching of the top electrode;
[0019] FIG. 2 is a cross-sectional view of the precursor cell
stacked structure of FIG. 1 subsequent to etching of the top
electrode, however, prior to etching using the process and solution
of the present invention;
[0020] FIG. 3 is a cross-sectional view of the precursor cell
stacked structure of FIG. 1 subsequent to etching of the
ferroelectric perovskite material using the process and solution of
the present invention;
[0021] FIG. 4 is a graph of the etching rate versus temperature of
the present invention for BSTO, silicon oxide and titanium
nitride;
[0022] FIG. 5 is a table illustrating the selectivity of the wet
etching process and solution of the present invention;
[0023] FIG. 6 is a graph of the etching rate versus temperature for
a solution of only hydrogen peroxide for BSTO, silicon oxide and
titanium nitride;
[0024] FIG. 7 is a graph of the etching rate versus temperature for
a solution of only sulfuric acid at a first concentration for BSTO,
silicon oxide and titanium nitride; and
[0025] FIG. 8 is a graph of the etching rate versus temperature for
a solution of only sulfuric acid at a different concentration for
BSTO, silicon oxide and titanium nitride.
DETAILED DESCRIPTION OF THE INVENTION
[0026] The present invention is a process and solution for
selectively wet etching a ferroelectric perovskite material. The
process and solution is generally directed at the fabrication of
cell stacked structures for electronic and optoelectronic devices,
however, those skilled in the pertinent art will recognize the
ability to practice the present invention for the fabrication of
other devices without departing from the scope and spirit of the
claims of the present invention.
[0027] The ferroelectric perovskite material is titanium based, and
more specifically is composed of titanate. Such ferroelectric
perovskite materials include barium strontium titanate, barium
titanate, strontium titanate, calcium titanate, lead titanate, lead
lanthanum zirconium titanate and lead zirconium titanate. The
ferroelectric perovskite material is usually a single film layer of
a multiple layer integrated circuit such as a DRAM device. The
other layers will usually include silicon, a silicon oxide or a
silicon nitride substrate, polystalline silicon, a bottom and a top
electrode (generally platinum) and a cover and mask layer for the
top electrode layer which can be composed of titanium nitride.
Thus, in order to selectively etch the ferroelectric perovskite
material, the solution of the present invention is unreactive to,
or does not etch, the other components of the multiple layer
integrated circuit.
[0028] The solution of the wet etch process of the present
invention consists essentially of hydrogen peroxide, an acid and
optionally deionized water. The hydrogen peroxide is present in the
solution from between 20% to 95% concentration. The acid is present
from about 5% to 80% concentration. The deionized is present from
0% to 75%. The acid is preferably sulfuric acid (H.sub.2SO.sub.4).
However, the acid may range from hydrochloric acid (HCL) to
phosphoric acid (H.sub.3PO.sub.4). Another acid within the range is
acetic acid (CH.sub.3COOH).
[0029] As shown in FIG. 1, a typical precursor cell stacked
structure for a DRAM device is generally designated 10. The
structure 10 is separated, by a double line 12, into an array area
14 and a field area 16. The structure 10 has a silicon substrate
layer 18 and a silicon oxide or silicon nitride substrate layer 20,
with polysilicon contact plugs 22, on the layer 18. The other
layers are then deposited through conventional methods such as
vacuum deposition, PVD or CVD, epitaxial growth and the like. The
structure 10 has a patterned bottom electrode layer 24 which is
usually composed of platinum. Diffusion barrier layers 23 and 25
are disposed respectively between the contact plugs 22 and the
bottom electrode layer 24 and the layer 20 and a ferroelectric
perovskite material layer 26. The barrier layer 25 may be, for
example, a layer of SiNx or SiO.sub.2. The ferroelectric perovskite
material is deposited as the layer 26 onto the bottom electrode
layer 24. A preferred ferroelectric perovskite material is BSTO.
However, the ferroelectric perovskite material alternatively could
be barium titanate, strontium titanate, calcium titanate, lead
titanate, lead lanthanum zirconium titanate or lead zirconium
titanate. The ferroelectric perovskite material covers the entire
patterned bottom electrode layer 24 and areas in between. The top
electrode layer 28 is deposited onto the ferroelectric perovskite
material layer 26. The top electrode layer is preferably composed
of platinum. A mask and cover layer 30 is selectively deposited
onto the top electrode layer 28. The mask layer 30 is preferably
titanium nitride or silicon oxide, and its patterned deposition
dictates the etching of the top electrode layer 28. The top
electrode layer 28 is etched with an appropriate etchant for
platinum to produce the structure shown in FIG. 2. As can be seen,
because there is no mask layer 30 in the field area 16, the top
electrode layer 28 is removed in the field area 16.
[0030] After the top electrode etching, the structure 20 will have
an etched top electrode layer 28 with portions of the ferroelectric
perovskite material layer 26 exposed for wet etching with the
process and solution of the present invention. The top electrode
layer 28 can act as a mask. The precursor structure 10 of FIG. 2
will be placed within a bath of the solution of the present
invention for a predetermined time period depending on the
thickness of the ferroelectric perovskite material layer 26 and its
composition. The time period may range from 30 to 1000 seconds or
longer. The hydrogen peroxide is present in the solution from
between 20% to 95% concentration, the acid is present from about 5%
to 80% concentration and the deionized water is present from 0% to
75%. In a preferred embodiment, the solution is 45% hydrogen
peroxide, 10% sulfuric acid and 45% deionized water. The solution
is heated to a temperature of between 25 and 90 degrees Celsius.
The temperature of the solution and the etch time will vary
depending on the thickness of the ferroelectric perovskite material
layer 26 and its composition.
[0031] FIG. 3 illustrates the structure 20 subsequent to the wet
etching process and solution of the present invention. The
ferroelectric perovskite material layer 26 has a predetermined
pattern, corresponding to that of the electrode layers 24 and 28,
wherein the exposed areas have been removed by the process and
solution of the present invention. Also, the wet etching process
and solution will not substantially effect the other layers, that
is the other layers will not be etched by the wet etching process
and solution of the present invention. After the ferroelectric
perovskite material layer 26 has been etched, a cover layer may be
deposited onto the ferroelectric perovskite material layer 26
during further processing of the structure 10. The cover layer, not
shown, may be oxide to act as a protective coating for the exposed
areas including the ferroelectric perovskite material layer 26.
[0032] The etching rate for BSTO, titanium nitride and silicon
oxide, when subjected to the wet etching process and solution of
the present invention, are illustrated in FIG. 4. As shown in FIG.
4, the wet etching process solution of the present invention
minimally etches titanium nitride and silicon oxide while providing
a tremendous etching rate for BSTO, an etching rate that is thirty
times greater than some conventional etching methods. Of note is
the fact that the etching rate for BSTO increases as the
temperature of the solution is increased toward 70 degrees Celsius.
Thus, at 50 degrees Celsius, the etching rate is approximately 100
Angstroms per minute while at 70 degrees Celsius the etching rate
increases to over 600 Angstroms per minute. The etching rate for
the silicon oxide remains low at any temperature indicating the
selectivity of the wet etching process and solution of the present
invention. However, the etching rate of the titanium nitrate also
increases with increases in the temperature of the solution.
[0033] FIG. 5 further illustrates the selectivity of the wet
etching process and solution of the present invention. The columns
correspond to temperature changes.
[0034] FIG. 6 is a graph of the etching rate of BSTO, titanium
nitride and silicon oxide, when subjected to only hydrogen peroxide
at various temperatures. As illustrated in FIG. 6, the etch rate is
substantially slower than the etch rate of the wet etching process
and solution of the present invention. Thus, even at 70 degrees
Celsius, the etch rate for a solution of only hydrogen peroxide is
only eighteen Angstroms per minute.
[0035] FIGS. 7 and 8 are graphs of the etching rate of BSTO,
titanium nitride and silicon oxide, when subjected to only acid and
deionized water at various temperatures. The solution of FIG. 7 has
a 10% concentration of sulfuric acid while the solution of FIG. 8
has a 20% concentration of sulfuric acid. As illustrated in FIGS. 7
and 8, the etch rate is substantially slower than the etch rate of
the wet etching process and solution of the present invention.
Thus, at 70 degrees Celsius, the etch rate for both sulfuric acid
solutions is only thirty-five Angstroms per minute.
[0036] From the foregoing it is believed that those skilled in the
pertinent art will recognize the meritorious advancement of this
invention and will readily understand that while the present
invention has been described in association with a preferred
embodiment thereof, and other embodiments illustrated in the
accompanying drawings, numerous changes, modifications and
substitutions of equivalents may be made therein without departing
from the spirit and scope of this invention which is intended to be
unlimited by the foregoing except as may appear in the following
appended claims.
* * * * *