Organic compounds -- part of the class 532-570 series – Organic compounds – Heavy metal containing
Reexamination Certificate
2002-06-24
2003-04-22
O'Sullivan, Peter (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Heavy metal containing
C556S051000
Reexamination Certificate
active
06552209
ABSTRACT:
BACKGROUND OF THE INVENTION
Metal oxide and nitride films have a number of chemical and physical properties, which make their use desirable for a multitude of applications. For instance, the applications of tantalum nitride include its use as wear resistant coatings and as thin layers for diffusion barriers and gate electrodes in integrated circuits. On the other hand, tantalum oxide is considered a candidate material for high dielectric constant thin film applications in microelectronic devices either as a gate dielectric or as the dielectric used in dynamic random access memories (DRAMs) storage capacitors. With the shrinkage of feature sizes in computer chips, chemical vapor deposition (CVD) and atomic layer deposition (ALD) provide a unique advantage over physical vapor deposition in achieving perfectly even and conformal thin films. For the CVD or ALD process to produce tantalum oxide or nitride thin films, both solid and liquid precursors have been utilized so far, but liquid precursors are always preferable due to their ease and repeatability of precursor delivery by either bubbling or direct liquid injection.
The following patents and articles provide the state of the art for the production of metal oxide and metal nitride thin films including compounds of the general formula
R
1
N═M(NR
2
R
3
)
3
and (R
1
N═)
2
M′(NR
2
R
3
)
2
.
U.S. Pat. No. 6,268,288 discloses the production of high quality conformal tantalum nitride films from tantalum halide precursors. In this work, tantalum pentachloride or tantalum pentabromide vapors are contacted with a nitrogen-containing process gas to deposit tantalum nitride films by a thermal CVD process on a substrate heated in the temperature range of 300 to 500° C. Once a thin film of metal nitride is thus grown, a hydrogen plasma anneal is applied to enhance the film quality before the thermal CVD process is repeated. In this way the deposition chemistry is alternated between thermal and plasma cycles until a desired film thickness is achieved. One potential problem with metal halide precursors is that they can leave halide residues in the metal nitride film that can lead to corrosion and other long-term stability problems.
U.S. Pat. No. 5,900,498 discloses the investigation of metal halo-organo complexes in a variation to the above process which teaches the utility of employing metal halo-organo precursors of the formula:
[MCl
2
(NR)(NHR)(NH
2
R)]
n
wherein R is alkyl, cycloalkyl, aryl, alkenyl, cycloalkenyl or NR
a
R
b
wherein R
a
and R
b
are independently alkyl, cycloalkenyl or together to form a heterocycle with the nitrogen and M can be tantalum or other suitable metal. Tantalum nitride. films are deposited by the thermal CVD of such single source metal halo-organo precursors, which are prepared by the reaction of tantalum halides with a primary amine or hydrazine. Specifically, the metal halo-organic precursor [TaCl
2
(NBu
t
)(NHBu
t
) (NH
2
Bu
t
)]
2
is prepared by reacting tantalum pentachloride with t-butylamine (~1 mole TaCl
5
/10 moles Bu
t
NH
2
). The metal halo-organic precursor [TaCl
2
(NNMe
2
)(HNNMe
2
)(H
2
NNMe
2
)]
2
is prepared by reacting tantalum pentachloride with dimethylhydrazine (~1 mole TaCl
5
/6 moles dimethylhydrazine). Since these metal halo-organic precursors contain halogens there is always the chance of halogen becoming incorporated into the final film.
As disclosed in a review article by Winter et al. (Winter, C. H. “
The Chemical Vapor Deposition of Metal Nitride Films Using Modern Metalorganic Precursors.” Aldrichimica Acta
33: 3-12, 2000.), tantalum amides have also been chosen as potential precursors for chemical vapor deposition of either tantalum oxide or tantalum nitride. For example, pentakis(diethylamino)tantalum, Ta(NEt
2
)
5
, prepared by reaction of tantalum pentachloride with excess lithium diethylamide, is a liquid at room temperature and has been reported to deposit tantalum nitride thin film by Sugiyama et al. (Sugiyama, K.; Pac, S.; Takahashi, Y.; Motojima, S. “
Low Temperature Deposition of Metal Nitrides by Thermal Decomposition of Organometallic Compounds” J. Electrochemical Society,
Vol. 122 (1975), 1545.). However, it was found later that the precursor used was actually a mixture consisting of Ta(NEt
2
)
5
, EtN═Ta(NEt
2
)
3
, and (Et
2
N)
3
Ta(&eegr;
2
—EtN═CHMe), thereby preventing the steady vaporization of just one species to provide a controllable vapor pressure.
U.S. Pat. No. 5,248,629 discloses a process for growing a tantalum oxynitride film by a chemical vapor deposition process using a tantalum amide precursor, pentakis(dimethylamino)tantalum (PDMAT), and ammonia. As with tantalum halides and other metal haloorgano complexes, PDMAT is a solid at room temperature and subsequently suffers from difficulties in providing a constant delivery rate to the reactor chamber. By contrast, tert-(butylimino)tris(diethylamino)tantalum (TBTDET) is a pure liquid at room temperature and has been reported as a precursor to deposit either tantalum oxide or nitride, depending on the CVD process gas used.
Further, Chiu et al. (Chiu, H. T.; Wang, C. N.; Chuang, S. H. “
Metal
-
Organic CVD of Tantalum Oxide from TBTDET and Oxygen” Chem. Vapor Deposition,
Vol. 6(2000), 223) disclose the CVD deposition of tantalum oxide thin film using TBTDET and oxygen. Park et al. (Park, J. S.; Park, H. S.; Kang, S. W. “Plasma-Enhanced Atomic Layer Deposition of Ta—N Thin Films” J. Electrochemical Society, Vol. 149(2002), C28-32) describe the plasma enhanced atomic layer deposition (PEALD) of tantalum nitride thin films at a temperature of 260° C. using (TBTDET) and hydrogen radicals. Thus, the tert-butyliminotris(diethylamino)tantalum (TBTDET) type compounds R
1
N═Ta(NR
1
R
2
)
3
where R
1
, R
2
and R
3
can independently be alkyl or trialkylsilyl are excellent precursors for both the preparation of tantalum oxide and nitride or other tantalum containing thin films by ALD or CVD via reacting vapors of the precursor with a suitable reactive gas at a substrate surface.
Bradley, D. C. and Thomas, I. M. “
Metallo
-
organic Compounds Containing Metal
-
Nitrogen Bonds,
Part III. Dialkylamino Compounds of Tantalum.”
Canadian Journal of Chemistry.
40: 1355-1360, 1962) disclose metallo-organic compounds containing metal-nitrogen bonds. In this publication, tantalum pentachloride is reacted with five-equivalents of a lithium dialkylamide, LiNR
2
, e.g., lithium di-n-propylamide or lithium di-n-butylamide to produce the corresponding tantalum pentakisdialkylamide. However, some of those pentakisdialkylamides are unstable at higher temperature and decompose to form RN═Ta(NR
2
)
3
type complexes with the concomitant release of RNH
2
.
Nugent, W. A. and Harlow, R. L. “
Structure and Reactivity in the Group
5
B t
-
butylimido Complexes Bu
t
N═
M
(
NMe
2
)
3
; X
-
ray Crystal and Molecular structure of t
-
butylimidotris
(
dimethylamido
)
tantalum.” Chem. Commun.:
579, 1978 similarly disclose the treatment of TaCl
5
with one equivalent of lithium tert-butylamide and four-equivalents of lithium dimethylamide to afford Bu
t
N═Ta(NMe
2
)
3
in a yield of 40%. However, the poor selectivity and low yield of this procedure prevents its implementation at a large production scale.
Chiu, H. T., Chuang, S. H., Tsai, C. E., Lee, G. H. Peng, S. M. “
Synthesis and Characterization of Organoimido Complexes of Tantalum; Potential Single
-
source Precursors to Tantalum Nitride.” Polyhedron
17: 2187, 1998 disclose the two-step synthesis of RN═Ta(NEt
2
)
3
(R=Bu
t
, Pr
i
, or Pr) by reacting TaCl
5
with two-equivalents of RNH(Me
3
Si) in the presence of pyridine (py) overnight to form the intermediate, RN═TaCl
3
(py)
2
, followed by reaction with excess of LiNEt
2
to replace the three remaining chloride ligands. In this process, RNH(Me
3
Si) is prepared in situ by the reaction of two equivalents of RNH
2
with one equivalent of Me
3
SiCl. As a result, a total four equivalents of primary amine are used in the process to produce on
Lei Xinjian
Norman John Anthony Thomas
Air Products and Chemicals Inc.
Chase Geoffrey L.
O'Sullivan Peter
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