F206
Journal of The Electrochemical Society, 151 ͑9͒ F206-F213 ͑2004͒
0
013-4651/2004/151͑9͒/F206/8/$7.00 © The Electrochemical Society, Inc.
Study of the Thermal Properties of Pr„III… Precursors
and Their Implementation in the MOCVD Growth
of Praseodymium Oxide Films
a
b
b
Raffaella Lo Nigro, Roberta G. Toro, Graziella Malandrino,
b,z
c
c
Ignazio L. Fragal a` , Patrizia Rossi, and Paolo Dapporto
a
IMM, sezione di Catania, CNR, I-95121 Catania, Italy
b
Dipartimento di Scienze Chimiche, Universit a` di Catania, and INSTM, UdR Catania, I-95125 Catania, Italy
Dipartimento Energetica, I-50139 Firenze, Italy
c
A
praseodymium
adduct,
Pr͑hfa) •diglyme
͓(H-hfa ϭ 1,1,1,5,5,5-hexafluoro-2,4-pentandione, diglyme
3
ϭ CH O͑CH CH O) CH )] has been synthesized. It has been applied as a Pr source for the metallorganic chemical vapor
3
2
2
2
3
deposition ͑MOCVD͒ of praseodymium containing films on silicon substrate and compared with Pr͑tmhd)3 ͓(H-tmhd
ϭ 2,2,6,6-tetramethyl-3,5-heptandione)͔ precursor. Physical and thermal properties of both Pr͑hfa) •diglyme and Pr͑tmhd)
3
3
precursors have been fully analyzed and their efficacy as MOCVD precursors for the growth of praseodymium oxide films have
been fully tested. Depending on the oxygen partial pressure (pO2), different praseodymium oxide phases have been obtained.
©
2004 The Electrochemical Society. ͓DOI: 10.1149/1.1779336͔ All rights reserved.
Manuscript submitted October 13, 2003; revised manuscript received December 22, 2003. Available electronically August 25,
004.
2
Complementary metal-oxide-semiconductor large-scale inte-
grated circuits ͑CMOS LSIs͒ are the most popular devices for elec-
tronics. High-performance devices, require, however, downsizing of
components such as metal-oxide-semiconductor field effect transis-
thermal properties have been investigated in terms of temperature
dependencies of the saturated vapor pressure and thermodynamic
parameters of the vaporization process. The growth of praseody-
mium oxide films on Si͑100͒ substrates has been carried out as an
initial step to evaluate the potentiality of the MOCVD technique to
fabricate this material for CMOS and/or MIM device structures.
tors ͑MOSFETs͒. Today, SiO is the major material for MOSFET
2
gate insulator applications. In the near future, equivalent oxide
thickness ͑ETO͒ should reach 1 nm and it will become hard to use
SiO because of the unacceptable leakage current due to the direct
2
1
tunneling and consequently higher power consumption. A possible
Experimental
solution to the problem is the replacement of the ultrathin SiO layer
2
Reagents.—The chemical reagents H-hfa, H-tmhd, and diglyme
were purchased from Aldrich and used without further purification.
Pr͑NO ͒ •6H O was purchased from STREM Chemicals.
with a thicker film of an alternative insulator having higher dielec-
2
,3
tric constant. Rare earth oxides are potential candidates to replace
4
,5
the SiO layer. Among the rare earth oxides, praseodymium oxide,
3 3
2
2
Pr O , has not been studied for microelectronic applications so far,
2
3
General procedures.—Infrared spectra were recorded on a Per-
kin Elmer FTIR 1720 spectrometer as nujol mulls between NaCl
plates. Elemental microanalyses were performed in the analytical
laboratories of the University of Catania. FAB mass spectra were
obtained with a Kratos MS 50 spectrometer.
6
despite its high dielectric constant ( ϭ 26-30) and middle band-
gap ͑3.9 eV͒. To date, few reports on molecular beam epitaxial
7
͑
MBE͒ growth and pulsed laser deposition of PrO2 and/or Pr O
2
3
8
-10
films on silicon substrates have appeared in the literature.
Nev-
ertheless the greater complexities of surface topographies and device
Thermogravimetric analyses were performed using a Mettler To-
structures, such as in 3D trench technology,1
1,12
require conforming
e
ledo TGA/SDTA 851 . Thermal investigation of Pr͑hfa) •diglyme
3
deposition methods, such as metallorganic chemical vapor deposi-
tion ͑MOCVD͒, to maintain a high uniform and conformal cover-
age. Large-scale film growth by MOCVD takes advantages of sim-
pler, less costly equipment, ready scalability, and higher throughput
and Pr͑tmhd) were carried out in purified nitrogen flow ͑30 sccm͒.
3
The weights of the sample were about 5-15 mg. Temperature was
measured with an accuracy of Ϯ0.1 K. The heating rate was 5 K/
min. Thermal investigation in vacuum was carried out at 20 Torr.
as compared to conventional physical vapor deposition ͑PVD͒
techniques.1
high quality Pr O films.
3-15
Synthesis of Pr(hfa) •diglyme.—Pr͑NO ͒ •6H O ͑1.67 g, 5.11
Recently, we reported on the MOCVD growth of
3
3 3
2
16,17
mmol͒ was first suspended in dichloromethane ͑100 mL͒. Diglyme
2
3
͑
0.63 g, 4.71 mmol͒ and NaOH pellets ͑0.56 g, 14.12 mmmol͒ were
The success of an MOCVD process depends critically on the
availability of volatile, thermally stable precursors that exhibit high
and constant vapor pressures, because poor performance affects the
film properties. Therefore, an accurate knowledge of the physical
properties and thermal behavior of precursors is of fundamental rel-
evance for the optimization of processes in the perspective of
achieving uniform and reproducible MOCVD film growth.
added to the suspension. H-hfa ͑2.94 g, 14.12 mmol͒ was added
under vigorous stirring after 10 min and the mixture was refluxed
for 2 h. The excess of praseodymium nitrate was filtered off from
the hot solution. The product was purified by crystallization from
pentane ͑or hexane͒ to yield green crystals. The reaction yield was
9
3%. The melting point of the crude product was 342-346 K.
PrC H F O ͑896.5͒: calcd. C 28.13, H 1.91; found C 28.32,
In the present work, we have synthesized and investigated
21 17 18
9
H 1.93.
the mass transport properties of
a
new praseodymium
IR ͑Nujol; , cmϪ1͒: 2923 ͑s͒, 1651 ͑vs͒, 1604 ͑w͒, 1556 ͑m͒,
531 ͑m͒, 1494 ͑s͒, 1463 ͑s͒, 1377 ͑m͒, 1253 ͑s͒, 1174 ͑s͒, 1149 ͑s͒,
050 ͑m͒, 1037 ͑w͒, 1018 ͑m͒, 962 ͑vw͒, 935 ͑w͒, 871 ͑m͒, 844 ͑w͒,
19 ͑w͒, 779 ͑vw͒, 754 ͑vw͒, 727 ͑w͒, 646 ͑s͒.
precursor, Pr͑hfa) •diglyme ͓(H-hfa ϭ 1,1,1,5,5,5-hexafluoro-2,4-
3
1
1
8
pentandione, diglyme ϭ CH O͑CH CH O) CH )], and of an alter-
3
2
2
2
3
native fluorine-free precursor, Pr͑tmhd)3 , ͓(H-tmhd ϭ 2,2,6,6-
tetramethyl-3,5-heptanedione͔͒. Both praseodymium -diketonate
precursors have been fully characterized and their mass transport
properties have been analyzed and compared. In particular, their
Synthesis of Pr(tmhd) .—Pr͑tmhd) was prepared using the
3
3
18
method proposed by Eisentraut and Sievers. Pr͑NO ͒ •6H O ͑1.67
3
3
2
g, 5.11 mmol͒ was dissolved in water ͑50 mL͒. H-tmhd ͑2.82 g,
1
5.33 mmol͒ was dissolved in ethanol ͑95%͒ and a stoichiometric
z
E-mail: lfragala@dipchi.unict.it
amount of NaOH ͑0.61 g, 15.33 mmol͒ was added to deprotonate
Lo Nigro, Raffaella
