U.S. patent application number 09/953189 was filed with the patent office on 2002-06-27 for near-room temperature thermal chemical vapor deposition of oxide films.
This patent application is currently assigned to Virginia Tech Intellectual Properties, Inc.. Invention is credited to Desu, Seshu B., Senkevich, John J..
Application Number | 20020081441 09/953189 |
Document ID | / |
Family ID | 26769857 |
Filed Date | 2002-06-27 |
United States Patent
Application |
20020081441 |
Kind Code |
A1 |
Desu, Seshu B. ; et
al. |
June 27, 2002 |
Near-room temperature thermal chemical vapor deposition of oxide
films
Abstract
This invention discloses methods for the deposition of SiO.sub.2
and other oxide dielectric materials using a near room temperature
thermal chemical vapor deposition process. The films have chemical,
physical, optical, and electrical properties similar to or better
than those of oxide films deposited using conventional, high
temperature thermal CVD methods. The films of the invention are
useful in the manufacture of semiconductor devices of sub-micron
feature size and for food packaging.
Inventors: |
Desu, Seshu B.; (Amherst,
MA) ; Senkevich, John J.; (Blacksburg, VA) |
Correspondence
Address: |
FLIESLER DUBB MEYER & LOVEJOY, LLP
FOUR EMBARCADERO CENTER
SUITE 400
SAN FRANCISCO
CA
94111
US
|
Assignee: |
Virginia Tech Intellectual
Properties, Inc.
|
Family ID: |
26769857 |
Appl. No.: |
09/953189 |
Filed: |
September 14, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09953189 |
Sep 14, 2001 |
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09302938 |
Apr 30, 1999 |
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60083891 |
May 1, 1998 |
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Current U.S.
Class: |
428/451 ;
427/255.27; 427/255.28; 427/255.29; 427/255.37; 427/447; 428/446;
428/702 |
Current CPC
Class: |
C23C 16/402 20130101;
C23C 16/407 20130101; C23C 16/405 20130101; C23C 16/452 20130101;
Y10T 428/31667 20150401; C23C 16/403 20130101 |
Class at
Publication: |
428/451 ;
427/255.28; 427/255.27; 427/255.29; 427/255.37; 428/702; 428/446;
427/447 |
International
Class: |
C23C 016/00; C23C
016/40; B32B 009/04 |
Claims
We claim:
1. A method for forming an oxide film on a substrate comprising the
steps of: (a) vaporizing an oxide precursor; (b) dissociating the
vaporized precursor at a temperature in the range of about
400.degree. C. to about 800.degree. C; and (c) polymerizing the
dissociated, vaporized precursors on the substrate at a temperature
below about 300.degree. C.
2. The method of claim 1, wherein the deposition temperature is in
the range of about 40.degree. C. to about 170.degree. C.
3. The method of claim 1, wherein said oxide precursor has a
structure selected from the group consisting of: C--O--M--O--C',
C--M--O--C' and C--M--C', wherein M is a metal atom, O is an oxygen
atom, and C. and C' are organic moieties.
4. The method of claim 1, wherein said oxide precursor comprises a
silicon atom.
5. The method of claim 3, wherein said oxide precursor has a metal
atom selected from the group consisting of silicon, aluminum,
yttrium, titanium, zirconium, tantalum, niobium, and zinc.
6. The method of claim 1, wherein said oxide precursor is an
alkoxysilane.
7. The method of claim 6, wherein said oxide precursor is selected
from the group consisting of DADBS and TEOS.
8. The method of claim 6, wherein said oxide precursor is selected
from the group consisting of tetraacetoxysilane, tetramethoxysilane
(TMOS), tetraallyloxysilane, tetra-n-butoxysilane,
tetrakis(ethoxyethoxy)silane, tetrakis(2-ethylhexoxy)silane,
tetrakis(2-methoxycryloxyethoxy)silane,
tetrakis(methoxyethoxyethoxy)silane, tetrakis(methoxyethoxy)silane,
tetrakis (methoxypropoxy)silane, and tetra-n-propoxysilane.
9. The method of claim 3, wherein said oxide precursor is selected
from the group consisting of aluminum (III) n-butoxide, yttrium
isopropoxide, titanium-di-n-butoxide (bis-2, 4-pentanedionate),
zirconium isopropoxide, tantalum (V) n-butoxide, niobium (V)
n-butoxide and zinc n-butoxide.
10. The method of claim 1, wherein said step of dissociating said
precursor is carried out using a resistive heater.
11. The method of claim 1, wherein the step of dissociating said
oxide precursor is carried out at a temperature in the range of
about 550.degree. C. to about 750.degree. C.
12. The method of claim 1, wherein the step of dissociating said
oxide precursor is carried out at a temperature in the range of
about 630.degree. C. and about 650.degree. C.
13. The method of claim 1, wherein the step of polymerizing is
carried out at a pressure in the range of about 0.01 Torr to about
1.0 Torr.
14. The method of claim 1, wherein the step of polymerizing is
carried out at a pressure in the range of about 0.03 Torr to about
0.2 Torr.
15. The method of claim 1, wherein the step of polymerizing is
carried out at a pressure in the range of about 0.05 Torr to about
0.1 Torr.
16. The method of claim 1, wherein the precursor is transported to
a dissociation chamber using a carrier gas.
17. The method of claim 16, wherein said carrier gas is selected
from the group consisting of nitrogen, argon and oxygen.
18. The method of claim 16, wherein the oxide precursor is
transported at a flow rate in the range of about 1 SCCM to about
1000 SCCM.
19. The method of claim 16, wherein the oxide precursor is
transported at a flow rate in the range of about 10 SCCM to about
100 SCCM.
20. The method of claim 16, wherein the oxide precursor is
transported at a flow rate of about 20 SCCM.
21. The method of claim 1, wherein said step of polymerizing is
carried out at a deposition rate of about 1 nm/min to about 200
nm/min.
22. The method of claim 1, wherein DADBS is the oxide precursor and
wherein said step of polymerizing is carried out at a deposition
rate of about 5 nm/min to about 200 nm/min.
23. The method of claim 22, wherein DADBS is the oxide precursor
and wherein said step of polymerizing is carried out at a
deposition rate of about 7 nm/min to about 15 nm/min.
24. The method of claim 1, wherein TEOS is the oxide precursor and
wherein said step of polymerizing is carried out at a deposition
rate of about 5 nm/min to about 200 nm/min.
25. The method of claim 24, wherein TEOS is the oxide precursor and
wherein said step of polymerizing is carried out at a deposition
rate of about 5 nm/min to about 10 nm/min.
26. A method for forming a silicon dioxide film on a substrate
comprising the steps of: (a) vaporizing an oxide precursor selected
from the group consisting of DADBS and TEOS; (b) dissociating the
vaporized precursor at a temperature in the range of about
400.degree. C. to about 800.degree. C; and (c) polymerizing the
dissociated, vaporized precursors on the substrate at a temperature
in the range of about 40.degree. C. to about 170.degree. C.
27. A method for forming a silicon dioxide film on a substrate
comprising the steps of: (a) vaporizing DADBS; (b) dissociating
DADBS at a temperature in the range of about 630.degree. C. to
about 650.degree. C; and (c) polymerizing the dissociated,
vaporized DADBS on the substrate at a temperature in the range of
about 70.degree. C. to about 90.degree. C. wherein the step of
polymerizing is carried out at a pressure in the range of about
0.05 Torr to about 0.1 Torr, and wherein the rate of deposition of
the silicon dioxide film is in the range of about 7 nm/min to about
15 nm/min.
28. A method for forming a silicon dioxide film on a substrate
comprising the steps of: (a) vaporizing TEOS; (b) dissociating the
vaporized TEOS at a temperature in the range of about 680.degree.
C; and (c) polymerizing the dissociated, vaporized TEOS on the
substrate at a temperature in the range of about 70.degree. C. to
about 90.degree. C., wherein the step of polymerizing is carried
out at a pressure in the range of about 0.05 Torr to about 0.1
Torr, and wherein the rate of deposition of the silicon dioxide
film is in the range of about 5 nm/min to about 10 nm/min.
29. A thin oxide film manufactured according to a method comprising
the steps of: (a) vaporizing an oxide precursor; (b) dissociating
the vaporized precursor at a temperature in the range of about
400.degree. C. to about 800.degree. C; and (c) polymerizing the
dissociated, vaporized precursors on the substrate at a temperature
below about 300.degree. C.
30. The thin oxide film of claim 29 comprising an oxide selected
from the group consisting of SiO.sub.2, Al.sub.2O.sub.3,
Y.sub.2O.sub.3, TiO.sub.2, ZrO.sub.2, Ta.sub.2O.sub.5,
Nb.sub.2O.sub.5 and ZnO.
31. The thin oxide film of claim 29 comprising SiO.sub.2 wherein
said oxide film is made from a precursor selected from DADBS and
TEOS.
32. The thin oxide film of claim 29 comprising SiO.sub.2 made from
a precursor selected from the group consisting of
tetraacetoxysilane, tetramethoxysilane (TMOS), tetraallyloxysilane,
tetra-n-butoxysilane, tetrakis(ethoxyethoxy)silane,
tetrakis(2-ethylhexoxy)silane, tetrakis
(2-methoxycryloxyethoxy)silane,
tetrakis(methoxyethoxyethoxy)silane, tetrakis(methoxyethoxy)silane,
tetrakis (methoxypropoxy)silane, and tetra-n-propoxysilane.
33. The thin oxide film of claim 29 made from a precursor selected
from the group consisting of aluminum (III) n-butoxide, yttrium
isopropoxide, titanium-di-n-butoxide (bis-2, 4-pentanedionate),
zirconium isopropoxide, tantalum (V) n-butoxide, niobium (V)
n-butoxide and zinc n-butoxide.
34. The film of claim 29, wherein the leakage current measured at 1
MV/cm is below about 8.times.10.sup.-9 A/cm.sup.2.
35. The film of claim 29, further being substantially free of
water.
36. The film of claim 29, further being substantially free of
Si--OH groups.
37. The film of claim 29, further being substantially free of
contaminants.
38. The film of claim 29, further being substantially free of
carbon.
39. The film of claim 29, further having an average index of
refraction of greater than about 1.433.
40. The film of claim 29, further having an extinction coefficient
measured at a wavelength of 330 nm of greater than about
5.41.times.10.sup.-3 .
Description
RELATED APPLICATION
[0001] U.S. Utility Patent Application titled: "Oxide/Organic
Polymer Multilayer Thin Films Deposited by Chemical Vapor
Deposition." Inventors: Seshu B. Desu and John J. Senkevich, filed
concurrently.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] This invention relates to products comprising oxide films
where low temperature deposition is need. The low-temperature oxide
films are used in the manufacture of semiconductor devices and in
the food packing industry. The invention relates to the deposition
of dielectric layers in the manufacturing of semiconductor thin
films. More specifically, this invention relates to the deposition
of oxide dielectric thin films at temperatures near or below room
temperature. Additionally, this invention relates to the
manufacture of diffusion barriers to prevent food oxidation, and
barriers to the transmission of ultraviolet radiation to increase
the shelf life of food products.
[0004] 2. Description of Related Art
[0005] Conventional methods for depositing dielectric materials
such as SiO.sub.2 in semiconductor manufacture involve high
temperature chemical vapor deposition (CVD), spin-on-glass (SOG)
methods, rf magnetron sputtering, (Kollakowski et al., Vac. Sci.
Technol. B. 14(3):1712-1718 (1996); Jones, U.S. Pat. No. 3,442,686,
evaporation (Lucovsky et al. Thin Film Processes II, Eds. J. L.
Vossen & W. Kern, Academic Press, NY, pp: 565 (1991), and
plasma processes (Wen-Fa et al. Appl. Surf. Sci. 99:237-243 (1996);
Lee et al., J. Electrochem. Soc. 143(4):1443-1451 )1996); Plais et
al. J. Electrochem. Soc. 139(5):14989-14995 (1992); Sano et al.,
Mat. Res. Soc. Symp. Proc. 396:539-543 (1996); Decrosta et al., J.
Electrochem. Soc. 143(3):1079-1084 (1996); Samit et al., Adv. Mat.
Optics Electron 6:73-82 (1996)).
[0006] Moreover, in the food packaging industry, oxide films have
been used to provide oxidant barriers and ultraviolet barriers to
retard spoilage. However, the plasma methods used to deposit
SiO.sub.2 or TiO.sub.2 have several disadvantages.
[0007] However, each of these processes has major drawbacks in the
manufacture of semiconductor devices of sub-micron dimensions.
Spin-on-glass processes result in relatively uneven films.
Moreover, spin-on glass has high impurity levels and poor gap
filling abilities. This results in inherent problems with device
reliability. The other methods described all suffer from problems
associated with exposing the substrate to high temperatures or high
powered plasmas. Subjecting the substrate to the temperatures
required for conventional CVD, plasma, or rf magnetron sputtering
can cause the breakdown of thermally labile components of the
semiconductor devices. Moreover, as newer low dielectric materials
with lower thermal stability are being used, the maximum
temperatures to which semiconductor devices can be subjected during
manufacture decreases. Because SiO.sub.2 and other oxide
dielectrics confer desirable properties of dielectric layers, such
as thermal stability, mechanical strength, low impurity, good
adherence to substrates and good barrier to impurities, there is a
need to develop methods for the low-temperature deposition of oxide
dielectric materials in semiconductor manufacture.
[0008] To be compatible with the low dielectric constant polymer
materials, the SiO.sub.2 must be deposited at low temperatures,
less than the glass transition temperature (Tg) of polymers. Also,
to minimize stress between films, which can cause delamination, and
introduce charges at the interface, the films should all be
deposited at the same temperatures. The interface charges introduce
electronic signal degradation which defeats the purpose of using
low dielectric constant materials to minimize cross-talk.
[0009] One type of method for the low temperature deposition of
SiO.sub.2 is via remote dissociation and deposition. In this
process, the precursor for the dielectric material is subjected to
dissociating conditions in which reactive intermediates are
generated. The intermediates are then transported to another site,
where the intermediates can react with each other to form a thin
film on the semiconductor substrate. One proposal for remote
formation of a relative long-lived reactive intermediate was for a
--Si--H and was called HOMOCVD (Scott et al., Semiconductors and
Semimetals, Vol. Ed. J. I. Pankove, Academic Press, Boston, Vol.
21A: 123-49 (1984). However, this method is not appropriate for the
deposition of oxides, possibly due to high hydrogen content in the
films leading to reduced reliability.
[0010] To overcome the deficiencies in the prior art, one object of
this invention is the manufacture of oxide dielectric materials
with high mechanical and thermal stability, high dielectric
strength, and high transparency to visible electromagnetic
radiation.
[0011] Another object of this invention is the manufacture of oxide
dielectric materials at temperatures near room temperature.
[0012] A farther object of the invention is the high efficiency
deposition of oxide dielectric films from organometallic
precursors.
[0013] Yet another object of this invention is the manufacture of
integrated circuit chips using oxide dielectric films deposited at
near or below room temperature.
[0014] A further object of this invention is the manufacture of
low-temperature oxide films to reduce the diffusion of oxidants and
reduce the transmission of ultraviolet light into food
products.
SUMMARY OF THE INVENTION
[0015] This invention involves the use of remote thermal
dissociation of organometallic .precursors to deposit oxide films
at a site remote from the site of dissociation. Organometallic
precursors can be thermally dissociated at high-temperatures into
long-lived reactive intermediates and can be transported to a
remote site for near-room temperature deposition and polymerization
on a substrate, thereby forming a thin film of the oxide polymer.
The substrate can be maintained at a temperature well below that
needed for efficient dissociation of precursors. The films
deposited using the methods of this invention have unexpectedly low
leakage currents, based on the prior art films made using
conventional, high-temperature deposition methods.
[0016] Thus, one aspect of this invention is the use of
alkoxysilane precursors to generate reactive intermediates with a
sufficiently low activation energy to form high quality SiO.sub.2
thin films.
[0017] A further aspect of this invention is the manufacture of
oxide dielectric thin films deposited at near room temperature.
[0018] Yet another aspect of this invention is the regulation of
the physical properties of the oxide film by controlling the
conditions of deposition.
[0019] A further aspect of this invention is the regulation of the
chemical properties of the oxide film by controlling the conditions
of deposition.
[0020] Another aspect of this invention is the regulation of the
electrical properties of the oxide film by controlling the
conditions of deposition.
[0021] A yet other aspect of this invention is the regulation of
the optical properties of the oxide film by controlling the
conditions of deposition.
[0022] Another aspect of this invention is the manufacture of
semiconductor devices incorporating the oxide dielectric materials
deposited at near or below room temperature.
[0023] A further aspect of this invention is the manufacture of
low-temperature oxide films which inhibit the diffusion of oxidants
and the transmission of ultraviolet light for food packaging.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] The invention will be described with respect to the
particular embodiments thereof. Other objects, features, and
advantages of the invention will become apparent with reference to
the specification and drawings in which:
[0025] FIG. 1 is a schematic diagram of the apparatus used for low
temperature thermal chemical vapor deposition of SiO.sub.2 films of
the invention.
[0026] FIG. 2 shows the relationship between DADBS vaporization
temperature and deposition rate for SiO.sub.2 thin films.
[0027] FIG. 3 shows the infrared spectra of SiO.sub.2 films
deposited from DADBS and TEOS determined at wavenumbers from about
750 cm.sup.-1 to about 1300 cm.sup.-1.
[0028] FIG. 4 shows the infrared spectra of SiO.sub.2 films
deposited from DADBS and TEOS determined at wavenumbers from about
2400 cm.sup.-1 to about 4000 cm.sup.-1.
[0029] FIG. 5 shows the relationships between index of refraction
(solid graph) and extinction coefficient (broken graph) and
wavelength of incident light of wavelengths from 300 nm to 1000
nm.
DETAILED DESCRIPTION OF THE INVENTION
[0030] To overcome the deficiencies in the prior art, this
invention involves methods for the manufacture of oxide dielectric
films to provide electrical insulation of semiconductor devices.
The oxide films can exhibit low leakage currents and thereby
provide better long-term electrical properties than films made
using conventional methods. The oxide films also can act as
suitable interfaces between low dielectric constant materials,
underlying metal and SiO.sub.2 layers as a barrier to possible
impurities in the low dielectric constant materials. These oxide
materials are also used as barriers to the contamination of
polymers by external moisture absorption. The oxide layers can also
be used as cap layers over polymer layers and can be used in the
manufacture of multilayered films comprising oxide layers and
layers of organic polymers. Multilayered films are described in
co-pending United States Patent Application titled: "Oxide/Organic
Polymer Multilayer Thin Films Deposited by Chemical Vapor
Deposition." Inventors: S. Desu et al, filed concurrently (herein
incorporated fully by reference).
[0031] The methods presented here involve a thermal chemical vapor
deposition (CVD) process starting with common alkoxyprecursors,
byway of example only, diacetoxy-di-t-butoxysilane (DADBS) and
tetraethoxysilane (TEOS). The method is general and can be applied
to the formation of other oxides, such as by way of example only,
Al.sub.2O.sub.3, Y.sub.2O.sub.3, TiO.sub.2, ZrO.sub.2,
Ta.sub.2O.sub.5, Nb.sub.2O.sub.5, and ZnO.
[0032] I. Chemical Reactions
[0033] The method of this invention maybe explained by the
following two-step reaction sequence: 1
[0034] Here, A is the alkoxy precursor (for example, DADBS or
TEOS), and B* is the relatively long-lived intermediate species.
SiO.sub.2 can be deposited at near and below room temperatures for
at least two reasons. First, a relatively long-lived intermediate
species can be formed through reaction (1), which can then be
transported to another chamber at near-room temperature where
reaction (2) can take place. Second, the activation energy for
reaction (2) Ea2 can be small, in the range of about 1 eV, since a
large activation energy for reaction (2) can prohibit formation of
a near-room temperature product (Adamson, Physical Chemistry of
Surfaces, John Wiley & Sons, New York pp. 595 (1990)). This
invention relies on physically separating reactions (1) and (2) to
permit deposition of SiO.sub.2 at temperatures near room
temperature.
[0035] The mechanisms for reaction 1 are not known with certainty,
but one theory proposed by Hoffman, et al. (Thermochimica Acta.
215:329-335 (1993)), is that the pyrolytic decomposition of DADBS
can occur by the formation of a six-arranged cyclic intermediate
before the production of acetic anhydride at temperatures above
about 200.degree. C. A similar mechanism was proposed by Ashby et
al. for metal alkosides (Ashbv et al., J. Org. Chem.
44(8):1221-1232 (1979)). At a pyrolysis temperature
T>400.degree. C., 2-methylpropene has been proposed to form by a
.beta.-hydride elimination mechanism. Both reactions would be
inclusive in reaction (1). The net-intermediate was proposed as
silicon acid. According to this theory, silicon acid then undergoes
a polycondensation reaction (according to Hofman, et al.) thus
producing H.sub.2O as a by-product and forming an amorphous network
of SiO.sub.2. However, there are other possible theories to account
for the observations, and this invention is not limited by any
particular theory of operability.
[0036] Many different dielectric materials can be used to make the
oxide layers of this invention. In general, it can be desirable
that the oxide polymer have high thermal and mechanical stability,
and that the precursor be dissociable into reactive intermediates
which can be transported in the gas phase, and which can polymerize
on semiconductor substrates at temperatures below the glass
transition temperatures of any organic phase polymers used in
semiconductor manufacturing. Generally, any oxide can be deposited
using the methods of this invention in which the oxide precursor
has one of the following general formulae:
[0037] C--O--M--O--C', C--M--O--C', C--M--C'
[0038] where M is a metal atom, O is an oxygen atom, and C and C'
are organic moieties. Typically, oxides suitable for forming films
of this invention include silicates such as SiO.sub.2, or other
oxides such as Al.sub.2O.sub.3, Y.sub.2O.sub.3, TiO.sub.2,
ZrO.sub.2, Ta.sub.2O.sub.5, Nb.sub.2O.sub.5, or ZnO. This list is
by way of example only and is not intended to be limiting.
[0039] Typical precursors for the deposition of SiO.sub.2 include
alkoxysilane precursors, DADBS (C.sub.12H.sub.24O.sub.6Si), TEOS
(C.sub.8H.sub.20O.sub.4Si), tetraacetoxysilane
(C.sub.8H.sub.12O.sub.8Si)- , tetramethoxysilane (TMOS),
tetraallyloxysilane (C.sub.12H.sub.2O.sub.4Si- ),
tetra-n-butoxysilane (C.sub.16H.sub.36O.sub.4Si),
tetrakis(ethoxyethoxy)silane (C.sub.8H.sub.36O.sub.8Si),
tetrakis(2-ethylhexoxy)silane (C.sub.32H.sub.68O.sub.4Si),
tetrakis(2-methoxycryloxyethoxy)silane
(C.sub.24H.sub.36O.sub.12Si), tetrakis(methoxyethoxyethoxy)silane
(C.sub.20H.sub.44O.sub.12Si), tetrakis(methoxyethoxy)silane
(C.sub.12H.sub.28O.sub.8Si), tetrakis (methoxypropoxy)silane
(C.sub.16H.sub.36O.sub.8Si), and tetra-n-propoxysilane
(C.sub.12H.sub.28O.sub.4Si).
[0040] Typical precursors for the deposition of other metal oxides
include, by way of example only, aluminum (III) n-butoxide, yttrium
isopropoxide, titanium-di-n-butoxide (bis-2, 4-pentanedionate),
zirconium isopropoxide, tantalum (V) n-butoxide, niobium (V)
n-butoxide, and zinc n-butoxide.
[0041] II. Methods for Deposition of Oxide Films at Low
Temperatures
[0042] The processes of this invention can be carried out using a
custom-built modified CVD reactor as exemplified by FIG. 1. The CVD
reactor 100 has separate vaporization, pyrolysis, and deposition
chambers. The precursor (by way of example only, DADBS or TEOS) 108
is placed in a vaporization chamber 104. The precursor is vaporized
and the vaporized precursor passes through a valve 112 and
thereafter into pyrolysis chamber 120, containing baffles 124. The
pyrolysis chamber 120 is heated using any convenient means,
including by way of example only, a resistive heater. The
dissociation of precursors into reactive intermediates can take
place in the pyrolysis chamber at temperatures in the range of from
about 400.degree. C. to about 800.degree. C., alternatively from
about 550.degree. C. to about 750.degree. C., and in other
embodiments at about 630.degree. C. to about 650.degree. C. for
DADBS and about 680.degree. C. for TEOS. The flow of precursors and
reactive intermediates can be regulated by the rate of vaporization
of the precursor, which is controlled by the temperature of the
vaporizer 108, or by the flow of a carrier gas through the inlet
port 116.
[0043] After dissociation of precursors, the reactive intermediates
pass into deposition chamber 132 which can contain a clamp to hold
a substrate for oxide deposition (not shown). Substrates that can
be used for deposition are, by way of example only, Si(111), which
is suitable for optical characterization of the deposited films, or
thermal oxide. These substrates can then be cleaned using any
convenient means, including, by way of example only, a modified RCA
cleaning procedure consisting of sequential cleaning in heated
solutions of NH.sub.4OH, H.sub.2SO.sub.4 and HCl combined with
H.sub.2O.sub.2, to remove surface contaminants and additionally
cleaned with 10% HF for 60 seconds.
[0044] The wafer can be introduced into the chamber 132 by way of a
door 128. The temperature of the deposition chamber 132 can be
maintained using any convenient means, including, by way of example
only, an ethylene glycol/water mixture flowing through copper
tubing 134. Deposition temperatures can range from about 40.degree.
C. to about 170.degree. C., alternatively from about 60.degree. C.
to about 100.degree. C., and in other embodiments from about
70.degree. C. to about 90.degree. C.
[0045] The pressure in the deposition chamber can range from about
0.01 Torr to about 51.0 Torr, alternatively from about 0.03 Torr to
about 0.2 Torr, and in other embodiments from about 0.05 Torr to
0.1 Torr. The flow rate of reactive intermediates into the
deposition chamber can be regulated by the temperature of
vaporization of the precursor and/or by the flow rate of the
carrier gas, which can be, by way of example only, nitrogen, argon
or oxygen. When precursors having a metal atom bonded directly to a
carbon atom are used, as in precursors having the structural
formulae: C--M--O--C' or C--M--C', it can be desirable to use
oxygen in the precursor stream. Oxygen can be a reactive molecule
to aid in the dissociation of precursors, and can become part of a
reactive intermediate moiety. Flow rates of gas and precursors can
be in the range of from about I standard cubic centimeter per
minute (SCCM) to about 1000 SCCM, alternatively from about 10 SCCM
to about 100 SCCM, and in other embodiments at about 20 SCCM.
[0046] Depositions can be carried out for a sufficient time to
deposit a film of desired thickness. The rate of deposition of
SiO.sub.2 can depend on the vaporization temperature and upon the
rate of flow of carrier gas from the vaporization chamber to the
deposition chamber. FIG. 2 shows the relationship between the
vaporization temperature of DADBS and the rate of deposition of a
thin film of SiO.sub.2. At a vaporization temperature of about
84.degree. C., the rate of deposition is about 10 nm/min, whereas
at a vaporization temperature of about 89.degree. C., the rate of
deposition is about 15 Min/min.
[0047] The rate of deposition of SiO.sub.2 from DADBS can be in the
range of from about 1 nm/min to about 200 nm/min, alternatively
from about 5 nm/min to 200 nm/min, and in other embodiments from
about 7 to 15 nm/min. Rate of deposition of SiO.sub.2 from TEOS can
be in the range of from about 1 nm/min to about 200 nm/min,
alternatively from about 5 nm/min to about 200 nm/min, and in other
embodiments from about 5 nm/min to about 10 nm/min.
[0048] III. Methods for Characterizing Oxide Films
[0049] The thickness and optical characterization of oxide films
can be accomplished by using any convenient means, including, by
way of example only, a variable angle spectroscopic ellipsometer
(VASE) from J. A. Woollam Company. The wavelength of light used can
be in the range of from about 300 nm to about 1000 nm, and
measurements can typically be performed at several angles normal to
the sample, for example, at 70.degree., 75.degree. and 80.degree..
A Cauchy model can be used to calculate film thickness, the
dispersion curves for the index of refraction and extinction
coefficient for the films.
[0050] Infrared spectra can be obtained using a Nicolet FTIR device
with reflection attachment used at an angle of about 10.degree.
normal to the surface.
[0051] Electrical properties of oxide films such as SiO.sub.2,
including the dielectric constant and dielectric loss can be
obtained using standard methods in the art. By way of example,
impedance measurements can be made using a Solarton SI 1260
Impedance Analyzer. An alternating voltage of about 50 mV can be
applied to the sample. A top electrode made out of platinum can be
deposited onto the shadow masked SiO.sub.2 deposited film by a DC
magnetron sputter coating device. The platinum electrodes can have
an area of between about 4.26.times.10.sup.-4 cm.sup.2 and about
9.62.times.10.sup.-4 cm.sup.2. The bottom electrode can be a highly
doped p-type polycrystalline silicon.
[0052] For measurement of leakage current, electrical resistivity
and dielectric breakdown, SiO.sub.2 films can be grown on thin
films of titanium, which can be sputter coated onto Si(100)
substrates using a DC magnetron sputtering device. The top
electrode can be made out of platinum, and can be deposited onto
the shadow masked SiO.sub.2 film by a DC magnetron sputtering
device. Results can be obtained using a Hewlett Packard model 4140B
pico amp/DC voltage source. A voltage of 1 Mv/cm can be used to
measure the leakage current for each SiO.sub.2 film and generally
the leakage current stabilizes in less than about five minutes.
[0053] Films deposited using these low temperature deposition
methods can have the desired characteristics of films deposited by
conventional CVD methods. The film thickness, purity, refractive
index, chemical composition, bonding structures, and electrical
properties of films deposited at near or below room temperature
compare favorably with those of SiO.sub.2 films made using DADBS or
TEOS and deposited at higher temperatures, for example at about
400.degree. C.
[0054] The films of this invention, made with, by way of example
only, TiO.sub.2, can inhibit the transmission of ultraviolet light.
By inhibiting the transmission of harmful ultraviolet light through
food packaging materials, the spoilage rates can be decreased and
the shelf life of food products can be increased. Furthermore,
oxide films made using SiO.sub.2, by way of example only, can act
as barriers to the diffusion of oxidants such as O.sub.2. By
decreasing the diffusion of oxidants through food packaging
products, the oxidation of food products can be decreased and the
shelf life can be increased.
[0055] The invention may be further understood by reference to the
following Examples.
EXAMPLES
Example 1
[0056] Chemical Characterization of SiO.sub.2 Films
[0057] Characterization of the chemical composition and bonding
structures were determined by Founrer Transformed Infrared spectral
analysis (FTIR). FIG. 3 shows the Reflection-FTIR spectra of
SiO.sub.2 deposited at 81.degree. C. from DADBS (bottom trace) and
from another film of SiO.sub.2 deposited at 66.degree. C. from TEOS
(top trace). Both spectra were obtained using a reflection angle of
10.degree.. The films produced by the methods of the invention are
highly pure and free of contamination by organic material. The two
spectra shown in FIG. 3 are nearly identical and only three
absorption peaks are present, at wavenumbers of 1078 cm.sup.-1, 943
cm.sup.-1 and 804 cm.sup.-1. The peaks observed at about 1078
cm.sup.31 1 are known in the art to be due to the broad
asymmetrical stretch of Si--O--Si and the peaks observed at 804
cm.sup.-1 are known in the art to be due to the symmetrical
Si--O--Si stretch. The peaks observed at 1078 cm.sup.31 1 are also
called the transverse optical (TO) mode and is known in the art to
result from the oxygen atom stretching parallel to Si--O--Si (Lee
et al., J. Electrochem. Soc. 143(4):1443-1451(1996)). The peak can
be deconvoluted into three separate peaks. In the case of TEOS,
peaks can be observed at about 1024 cm.sup.-1 to about 1052
cm.sup.-1, about 1071 cm.sup.-1 to about 1093 cm.sup.-1 and about
1123 cm.sup.-1 to about 1177 cm.sup.-1 (Goullet, et al., J. Appl.
Phys. 74:6876 (1987), where the highest wavenumber broad peak can
create the characteristic asymmetrical hump. This hump can result
from either non-stoichiometry (SiO.sub.x where X<2) or broken
Si--O bonds due to hydrolysis, which can shift the net peak to
lower wavenumbers (Lee et al., J. Electrochem. Soc. 143(4):
1443-1451 (1996); Pai et al., J. Vac. Sci. Technol. 4(3): 689-694
(1986); Almeida et al., J. Appl. Phys. 68: 4225 (1990)). In the
present study, the highest wavenumber peak is at about 1150
cm.sup.-1 and is can be due to anon-stoichiometry since the
composite peak is not shifted to lower wavenumbers. The rather
small peak observed at 943 cm.sup.-1 can be due to Si--OH bonding,
indicating the presence of only small amounts of hydroxylated
moieties on the surface.
[0058] Additionally, films can be made having little water present.
FIG. 4 shows the Reflection-FTIR spectra of SiO.sub.2 films
deposited from either TEOS (top trace) and DADBS (bottom trace) at
wavenumbers of about 2400 cm.sup.-1 to about 4000 cm.sup.-1. Water
present in films can generate a broad peak observed at about 3410
cm.sup.-1 due to the --OH stretch within the water molecule.
However, as can be seen in FIG. 4, there is no detectable peak at
near 3410 cm.sup.-1. We therefore conclude that little, if any,
water is present in the films.
[0059] Furthermore, little, if any Si--O--C or Si--C bonding was
observed in the films. This conclusion is based on the absence of
peaks that are characteristic of these types of bonds as observed
in the FTIR spectra. Ether linkages (--C--O--) can appear as peaks
at wavenumbers of about 1050 cm.sup.-1 to about 1180 cm.sup.-1.
Si--C bonds absorb IR radiation at wavenumbers of about 700
cm.sup.-1 to about 860 cm.sup.-1, and at about 1230 cm.sup.-1 to
about 1280 cm.sup.-1 (Wade, Organic Chemistry, Prentice Hall, N.J.
(1991)). Therefore, the absence of peaks at these wavenumbers can
mean that little carbon contaminants are present in the films.
[0060] Furthermore, results from x-ray photoelectron spectroscopy
(XPS) show an atomic ratio of 1 atom of silicon to 2.1 atoms of
oxygen. Thus, stoichiometrically pure SiO.sub.2 films were grown
without the incorporation of by-products or the precursors.
[0061] The above possible mechanisms accounting for the patterns of
peaks are presented only as theories to explain the observations.
Other theories may also explain the observations, and this
invention is not limited to any particular theory for
operability.
Example 2
[0062] Physical Characteristics of SiO.sub.2 Films
[0063] Film thickness can be a function of the deposition rate and
the time of deposition, However, there can be a dependence of film
thickness on precursor concentration at certain temperature ranges.
By way of example only, a film of SiO.sub.2 was deposited from
DADBS at vaporization temperatures of about 84.degree. C. to about
89.degree. C. FIG. 2 shows that at the lower vaporization
temperatures, the rate of deposition of SiO.sub.2 was about 10
nm/min, whereas at higher vaporization temperatures, the deposition
rate was about 15 nm/min.
[0064] A theory to possibly explain this observation is that at
these temperatures the deposition of SiO.sub.2 surface is under
mixed diffusion and surface reaction control. At lower temperatures
the surface effects can predominate, and at higher temperatures the
diffusion effects can predominate. By way of example only, for
DADBS deposited at a temperature of about 70.degree. C., the nature
of the substrate surface can affect the deposition rate and quality
of the SiO.sub.2 thin film. However, this is only a possible theory
to account for the observations, and other theories may account for
the observations.
[0065] The density of the SiO.sub.2 film can be determined from
measurements of the refractive index of the film. FIG. 5 shows that
the average index of refraction, as measured by VASE, was 1.433 (@
630 nm), which is only slightly lower than the other published
value for SiO.sub.2 (1.44) using DADBS as a precursor (Smolinsky,
Mat. Res. Soc. Symp. Proc. 390:490-496 (1986)). The index of
refraction varied from 1.425 to 1.439 and was not a function of the
vaporization temperature. Thus, the density of the SiO.sub.2 films
deposited at near room temperature is comparable to SiO.sub.2 films
deposited at higher temperatures.
[0066] The dispersion of the index of refraction flattens around
630 nm but below that wavelength it varies from 1.433 @ 630 nm to
1.460 @ 300 nm. This rapid increase can be due to relative
closeness of the SiO.sub.2's absorption edge to its band gap of
about 9.0 eV. The observed dispersion is typical of a transparent
thin film or material with a relatively large band gap of greater
than about 3.0 eV.
[0067] The extinction coefficient was determined to be dependent on
the wavelength of electromagnetic radiation used to make the
measurements. At high wavelengths, characteristic of infrared light
(about 1000 nm), the extinction coefficient was about
7.05.times.10.sup.-5. The extinction coefficient measured at about
630 nm was observed to be about 2.10.times.10.sup.-4. When measured
at about 300 nm (corresponding to ultraviolet light), the
extinction coefficient was observed to be about
5.41.times.10.sup.-3. Thus, the films of this invention have low
ultraviolet transmittance, making them suitable for use as barriers
to the transmission of ultraviolet electromagnetic radiation. A low
extinction coefficient measured at wavelengths higher than
ultraviolet is typical for SiO.sub.2 thin films. It is known that
increased porosity can increase the extinction coefficient.
Typically however, no optical loss is associated with thermally
grown SiO.sub.2.
Example 3
[0068] Electrical Properties of SiO.sub.2 Films
[0069] To measure electrical properties of SiO.sub.2 films, we
carried out observations on films having a thickness of about 25 nm
deposited on titanium-coated substrates from DADBS. The films were
deposited according to the methods described above and were
deposited at temperatures in the range of from about 60.degree. C.
to about 90.degree. C. Measurements of the electrical properties of
the films were determined as described above and shown in Table
1.
1TABLE 1 Electrical Properties of SiO.sub.2 Films Deposited at Low
Temperature K @ 1 kHz 4.26 Dielectric loss at 1 kHz 0.0257
Dielectric breakdown 7.2 MV/cm Leakage current @ 1 MV/cm 1.8
.times. 10.sup.-10 A/cm.sup.2 Electrical resistivity @ 1 MV/cm 1.1
.times. 10.sup.13 .OMEGA. cm
[0070] The dielectric constant for SiO.sub.2 films of this
invention of 4.26 is close to other reported values for films of
SiO.sub.2 deposited from alkoxy precursors using CVD methods. The
SiO.sub.2 films showed a higher dielectric loss measured at 1 kHz
than SiO.sub.2 films deposited at higher temperatures. A theory to
possibly account for this observation is related to the nature of
the polycrystalline silicon substrate and the onrentational
polarization due to Si--OH bonding. However, other theories may
account for this observation.
[0071] The dielectric breakdown voltage was measured to be about 18
V, which normalized for the thickness of the film, was 7.2 MV/cm.
This value corresponds well with values reported previously for
SiO.sub.2 films deposited at higher temperatures (Lee, et al., J.
Electrochem. Soc. 143(4):1443-1451 (1996); Samit et al., Adv. Mat.
Optics Electron. 6:73-82 (1996)).
[0072] The leakage current was measured at 1.0 MV/cm, corresponding
to a thickness-normalized voltage of 2.5 V. The leakage current
observed under these conditions of 1.8.times.10.sup.-10 A/cm.sup.2
for the films of this invention was unexpectedly lower than the
published values of 8.times.10.sup.-9 A/cm.sup.2 to 10.sup.-7
A/cm.sup.2 observed for films made using conventional,
high-temperature methods (Smolinsky, Mat. Res. Soc. Symp.
390:490-496 (1986)). This result was completely unexpected based on
the publication of Smolinsky. A theory which may account for this
observation is that the presence of even small amounts of Si--OH
bonding as observed in the infrared spectra (FIG. 3) can increase
the leakage current slightly (Smolinsky, Mat. Res. Soc. Symp.
390:490-496 (1986)). Thus, by decreasing the amount of water in the
deposited film, there can be fewer Si--OH bonds in the film, and
therefore, the leakage current can be decreased. However, other
theories may account for the observations, and this invention is
not intended to be limited by any particular theory for
operability.
[0073] Additionally, the observed electrical resistivity of
1.1.times.10.sup.13 .OMEGA.cm was similar to that observed for
SiO.sub.2 films deposited at higher temperatures.
[0074] The films deposited using the methods of the present
invention have unexpectedly better electrical properties than films
made using conventional, high-temperature methods. Thus, the
chemical, physical, and electrical properties of the SiO.sub.2
films of this invention are comparable to or are better than those
observed for SiO.sub.2 films deposited from alkoxysilane precursors
at higher temperatures.
[0075] Unless otherwise incorporated by reference, all articles and
patents cited herein are incorporated herein fully by
reference.
[0076] The foregoing description and examples are intended to be
illustrative only, and are not intended to be limiting to the scope
of the invention.
[0077] INDUSTRIAL APPLICABILITY
[0078] Oxide films are deposited at low temperature and are useful
in the manufacture of semiconductor devices and in the food
packaging industry in which the advantages of conventional oxide
materials and conventional organic polymeric materials can be
attained in one thin film. In the semiconductor industry, low
temperature oxide films are useful for the manufacture of
dielectric thin films in which other components of the films cannot
be subjected to high temperatures. In the food packaging industry,
low-temperature oxide films are useful to inhibit the diffusion of
oxidants and the transmission of ultraviolet light into food
products. By decreasing the contamination and light-induced damage,
food products can have improved quality and shelf-life.
* * * * *