Synthesis, structural characterization, and thermal properties of the first germanium N,N,N′,N′-tetraalkylguanidinates

Article abstract of DOI:10.1021/om900801w

The first examples of germanium N,N,N′,N′- tetraalkylguanidinates have been prepared, and two of them have been structurally characterized. All of them exihibit high stability and volatility. Their potential as low-temperature precursors for MOCVD of Ge a

Full text of DOI:10.1021/om900801w

Organometallics 2010, 29, 501–504 501
DOI: 10.1021/om900801w
Synthesis, Structural Characterization, and Thermal Properties of the
0
0
First Germanium N,N,N ,N -Tetraalkylguanidinates
,
Tianniu Chen,* William Hunks, Philip S. Chen, Chongying Xu,
†
†
†
†
‡
Antonio G. DiPasquale, and Arnold L. Rheingold
‡
†
Advanced Technology Development Division, Advanced Technology Materials Inc. (ATMI), 7 Commerce
Drive, Danbury, Connecticut 06810 and Department of Chemistry and Biochemistry, University of
‡
California, San Diego, 9500 Gilman Drive, MC 0358, Urey Hall 5128, La Jolla, California 92093-0358
Received September 14, 2009
0
0
Summary: The first examples of germanium N,N,N ,N -tetra-
alkylguanidinates have been prepared, and two of them have
been structurally characterized. All of them exihibit high stabi-
lity and volatility. Their potential as low-temperature precursors
undergo a thermally induced crystalline-amorphous phase
transition for data storage, has been demonstrated in the
next-generation nonvolatile phase change random access
memory (PRAM) to replace conventional dynamic and flash
1
8-23
for MOCVD of Ge and Ge Te films has been explored.
x
y
random access memory technology.
However, there are
some limitations associated with Ge(IV) precursors for
MOCVD of Ge alloy films, such as high deposition tem-
peratures, resulting poor film conformality and morphology,
hazardous process conditions, and premature decomposi-
Volatile germanium complexes have attracted consider-
able attention because of their potential applications as
precursors for metal organic chemical vapor deposition
1
2-17
(MOCVD), metal organic vapor-phase epitaxy (MOVPE),
tion experienced when germane is present.
In an
or atomic layer deposition (ALD) of metallic germanium
and germanium alloy films for graded SiGe buffer layers,
strained silicon being implemented in the next generation of
complementary metal oxide semiconductor (CMOS) field
effect transistor (FET) technology, silicon-based photonics,
(18) Ovshinsky, S. R. Phys. Rev. Lett. 1968, 21, 1450.
(19) Meijer, G. I. Science 2008, 319, 1625.
(20) Hudgens, S.; Johnson, B. Mater. Res. Bull. 2004, 1.
(
21) Pore, V.; Hatanp €a €a , T.; Ritala, M.; Leskela, M. J. Am. Chem.
Soc. 2009, 131, 3478.
22) Raoux, S.; Shelby, R. M.; Jordan-Sweet, J.; Munoz, B.; Salinga,
1
-7
(
and more efficient solar cells.
8
Recently the use of both
12-17
-11
M.; Chen, Y.; Shih, Y.-H.; Lai, Shih, E.-K.; Lee, M.-H. Microelectron.
Eng. 2008, 85, 2330.
(23) Akola, J.; Jones, R. O. Phys. Rev. B 2007, 76, 235207.
germanium(II)
and germanium(IV)
precursors for
MOCVD/ALD of phase-change chalcogenide alloy films
with the prototype of GeTe or Ge Sb Te (GST), which
(24) Synthesis of (TMG)
HTMG) (93.2 mmol, 5.00 g) was dissolved in 100 mL of ether and then
added slowly to the mixture of GeCl (23.3 mmol, 5.00 g) in 10 mL of
ether and NEt
(93.2 mmol, 9.43 g) at 0 ꢀC, and the mciixture was stirred
2 2 2 2
GeCl (1). Method A: (Me N) CdNH
2
2
5
(
4
*To whom correspondence should be addressed: Tel: (203) 739-1405.
3
Fax: (203) 830-2123. E-mail: tchen@atmi.com.
and warmed tomac_opb;its complementary NMR spectra are provided
in the Supporting Information room temperature (RT) overnight. After
filtration, the solvent was removed in vacuo, yielding off-white solid 1.
(
(
1) Baxter, D. V.; Chisholm, M. H. Chem. Vap. Deposition 1995, 1, 49.
2) Vep ꢀs ek, S.; Prokop, J.; Glatz, F.; Merica, R.; Klingan, F. R.;
Herrmann, W. A. Chem. Mater. 1996, 8, 825.
3) Shenai, D. V.; DiCarlo, R. L., Jr.; Power, M. B.; Amamchyan,
A. R.; Goyette; Woelk, J. E. J. Cryst. Growth 2007, 298, 172.
4) Fang, Y. Y.; D’Costa, V. R.; Tolle, J. C.; Poweleit, D.; Kouvetakis,
J.; Men ꢁe ndez, J. Thin Solid Films 2008, 516, 8327.
5) Jalali, B.; Paniccia, M.; Reed, G. IEEE Microwave Magn. 2006, 7,
440.
4
Yield: 4.01 g (10.8 mmol, 46.4% based on GeCl ). Method B: LiTMG
(15.5 mmol, 11.3 g) was added to GeCl (23.3 mmol, 5.00 g) in 100 mL of
ether slowly at 0 ꢀC, and the mciixture was stirred and warmed
tomac_opb;its complementary NMR spectra are provided in the Sup-
porting Information RT overnight. After filtration, the solvent was
removed in vacuo, yielding off-white solid 1. Yield: 7.02 g (19.1 mmol,
(
4
(
(
1
82.0% based on GeCl
6.51; N, 22.60; Cl, 19.07. Found: C, 32.32; H, 6.56; N, 22.48; Cl, 18.86.
4 6 10 2
). Anal. Calcd for GeN C H24Cl : C, 32.29; H,
(
(
6) Green, M. A. Prog. Photovoltaics 2001, 9, 123.
7) Fang, Y.-Y.; Tolle, J.; Tice, J.; Chizmeshya, A. V. G.; Kouvetakis,
1
13
1
H NMR (RT, 300 MHz, C
NMR (RT, 75 MHz, C ): δ 39.58 (C(N(CH
(25) Synthesis of TMG) Ge(NMe (2). LiNMe
2
6
D
6
): δ 2.61 (24H, s, C(N(CH
), 164.94 (CdN).
(6.08 mmol, 0.310
3 2 2
) ) ). C{ H}
J.; D’Costa, V. R.; Men ꢁe ndez, J. Chem. Mater. 2007, 19, 5910.
8) Chen, T.; Xu, C.; Hunks, W.; Stender, M.; Stauf, G.; Chen, P.;
Roeder, J. ECS Trans. 2007, 11, 269.
9) Hunks, W.; Chen, P. S.; Chen, T.; Stender, M.; Stauf, G. T.;
Maylott, L.; Xu, C.; Roeder, J. F. Mater. Res. Soc. Symp. Proc. 2008,
071, F09–11.
10) Chen, P. S.; Hunks, W.; Stender, M.; Chen, T.; Stauf, G. T.; Xu,
C.; Roeder, J. F. Mater. Res. Soc. Symp. Proc. 2008, 1071, F09–10.
11) Chen, T.; Hunks, W.; Chen, P.; Stauf, G.; Cameron, T.; Xu, C.;
DiPasquale, A.; Rheingold, A. Eur. J. Inorg. Chem. 2009, 14, 2047.
12) Lee, J.; Choi, S.; Lee, C.; Kang, Y.; Kim, D. Appl. Surf. Sci. 2007,
53, 3969.
13) Choi, B. J.; Choi, S.; Shin, Y. C.; Hwang, C. S.; Lee, J. W.; Jeong,
D
3 2 2
) )
6
6
(
2
2
)
2
g) was added to complex 1 (2.96 mmol, 1.10 g) in 50 mL of ether slowly at
0 ꢀC, and the mciixture was stirred and warmed tomac_opb;its com-
plementary NMR spectra are provided in the Supporting Information
RT overnight. After filtration, the solvent was removed in vacuo,
yielding off-white sticky solid 2. Yield: 0.801 g (2.06 mmol, 69.6% based
(
1
(
on 1). Anal. Calcd for GeN
8
C
14
H
36: C, 43.23; H, 9.33; N, 28.80. Found:
C, 43.22; H, 9.34; N, 28.52. H NMR (RT, 300 MHz, C ): δ 2.66 (24H,
), C{ H} NMR (RT, 75 MHz,
), 41.24 (N(CH ), 161.07 (CdN).
Ge(NEt (3). LiNEt (25.3 mmol, 2.00 g)
1
(
6 6
D
1
3
1
s, C(N(CH
): δ 40.14 (C(N(CH
(26) Synthesis of (TMG)
3 2 2 3 2
) ) ), 3.05 (12H, s, N(CH )
(
C
6
D
6
3
)
2
)
2
3 2
)
2
2
2
)
2
2
(
was added to complex 1 (12.0 mmol, 4.50 g) in 50 mL of ether slowly at
0 ꢀC, and the mciixture was stirred and warmed tomac_opb;its com-
plementary NMR spectra are provided in the Supporting Information
RT overnight. After filtration, the solvent was removed in vacuo,
yielding pale yellow liquid 3. Yield: 4.02 g (9.03 mmol, 75.3% based
J.; Kim, Y. J.; Hwang, S.; Hong, S. K. J. Electrochem. Soc. 2007, 154,
H318.
(14) Kim, R.; Kim, H. Appl. Phys. Lett. 2006, 89, 102107.
(15) Yim, R. Y.; Kim, H. G.; Yoon, S. G. J. Appl. Phys. 2007, 102,
0
83531.
16) Choi, B. J.; Choi, S.; Shin, Y. C.; Kim, K. M.; Hwang, C. S.;
Kim, Y. J.; Son, Y. J.; Hong, S. K. Chem. Mater. 2007, 19, 4387.
17) Privitera, S.; Lombarbo, S.; Bongiorno, C.; Rimini, E.; Pirovano,
on 1). Anal. Calcd for GeN
8
C
18
H
44: C, 48.56; H, 9.96; N, 25.17. Found:
C, 48.49; H, 9.96; N, 25.07. H NMR (RT, 300 MHz, C ): δ 1.29 (24H,
t, N(CH CH ), 2.67 (12H, s, C(N(CH , 3.41 (8H, q, N(CH CH ).
C{ H} NMR (RT, 75 MHz, C ): δ 16.7 (N(CH CH ), 40.0
(C(N(CH ), 40.7 (N(CH CH ), 160.2 (CdN).
1
(
6 6
D
2
3
)
2
3
)
2
)
2
2
3 2
)
1
3
1
(
6
D
6
2
3 2
)
A. J. Appl. Phys. 2007, 102, 013516.
3
)
2
)
2
2
3 2
)
r 2009 American Chemical Society
Published on Web 12/18/2009
pubs.acs.org/Organometallics

5
02 Organometallics, Vol. 29, No. 2, 2010
Scheme 1. Reactions toward Complexes 1 and 2
Chen et al.
ongoing effort to design and synthesize microelectronic
materials to enable increased transistor performance, the
N,N,N ,N -tetramethylguanidinate (TMG) ligand is intro-
duced for the first time for the development of volatile,
thermally robust Ge(IV) precursors as potential sources for
low-temperature MOCVD processes.
toward mixed-ligand group 14 complexes for precursor
development.
The monomeric solid-state structures of 1 and 2 were
determined by single-crystal X-ray diffraction studies and
IV
are illustrated in Figures 1 and 2, respectively. The Ge
centers in both complexes occupy a distorted-tetrahedral
coordination geometry that is composed of two nitrogen
atoms and two chlorine atoms in 1 while it is composed of
four nitrogen atoms in 2, two of which come from the TMG
ligands and the other two from dimethylamido groups. The
N-Ge-N angles between TMG ligands in 2 are larger due to
0
0
We report here the synthesis of the first series of germa-
0
0
nium N,N,N ,N -tetraalkylguanidinates: (TMG) GeCl
2
2
(
(
1), (TMG) Ge(NMe ) (2), and (TMG) Ge(NEt ) (3)
2 2 2 2 2 2
2
4-27
Scheme 1).
Complexes 1 and 2 are also the first
0
0
structurally determined monomeric group 14 N,N,N ,N -
tetraalkylguanidinate complexes. The only other group 14
N,N,N ,N -tetraalkylguanidinate complex with a deter-
mined structure is the dimeric mixed-ligand Sn(II) complex
the different ligand effects imposed by Cl and NMe , respectively
2
0
0
(
1
—N1-Ge1-N4 = 107.17(9)ꢀ in 1; —N3-Ge1-N4 =
20.12(6)ꢀ in 2). The germanium-nitrogen bond lengths of
3
{
(η -Cp)Sn[μ -NdC(NMe ) ]} reported by Wright and
˚
2
2 2 2
Ge-NdC units in 1 (Ge1-N1 = 1.777(2) A, Ge1-N4 =
1
1
the Ge diphenylketimine Ge(NdCPh ) (1.872(5) A),
2
8
his co-workers. Furthermore, complex 1 (its complemen-
tary NMR spectra are provided in the Supporting Infor-
mation) could potentially serve as a “synthon” for a variety
of mixed-ligand germanium(IV) complexes. In addition,
˚
˚
.768(2) A) and 2 (Ge1-N3 = 1.8268(14) A, Ge1-N4 =
˚
.8135(13) A) are shorter than the reported bond lengths in
IV
32
˚
2
4
while they are more comparable to those in the Ge-N-N
2 4
the formation of complex 1 using GeCl with either
4
IV
units in the Ge hydrazide Ge(NMeNMe ) (1.828(2) and
2
9-31
[
as an HCl scavenger provides multiple scalable routes
LiTMG]6
or HTMG in the presence of triethylamine
33
.834(2) A). The bond lengths of CdN in the terminal
˚
1
TMG ligands in 1 (N1-C1 = 1.303(3), N4-C6 = 1.302(3)
˚
˚
A) and 2 (N3-C5 = 1.277(2), N4-C10 = 1.284(2) A) lie
within the scope of few reported data on bridged-chelating
(27) Single-crystal X-ray diffraction: data collection was performed
on a Bruker diffractometer with CCD detectors, equipped with a
cryogenic nitrogen cold stream and using graphite-monochromated
1
2
TMG ligands in {Cp Gd[ μ- η: η-NdC(NMe ) ]} (1.247
(8) A) and {(η -Cp)Sn[μ -NdC(NMe ) ]} (1.294(5) A).
2 2 2 2
2
2 2 2
3
1
3
28
˚
˚
˚
Mo KR radiation (0.710 73 A). The structures were solved by direct
methods and refined anisotropically with the SHELXL-97 pro-
gram suite. Crystallographic data for 1 (CCDC 728312) (colorless,
The Ge-NdC angles in 1 (Ge1-N1-C1 = 128.54(17)ꢀ,
Ge1-N4-C6 = 129.67(18)ꢀ) and 2 (Ge1-N3-C5 =
133.04(12)ꢀ, Ge1-N4-C10 = 129.77(12)ꢀ) are readily
distorted, which are consistent with the corresponding ob-
0
.30 ꢀ 0.30 ꢀ 0.20 mm): GeN
6 10 2 r
C H24Cl , M = 371.84, monoclinic,
˚
˚
˚
a = 10.0347(9) A, b = 11.4752(10) A, c = 14.8505(14) A, β =
3
˚
9
7.796(2)ꢀ, U = 1694.2(3) A , T = 100(2) K, space group P2
1
/n, Z = 4,
6971 reflections collected, 3651 unique (Rint = 0.0201), which were used in
all calculations. The final R
32
2
served angles in Ge(NdCPh ) (123.8(6) and 130.1(6)ꢀ)
2
4
w
(F ) value was 0.0952 (all data). Crystal-
lographic data for 2 (CCDC 728313) (colorless, 0.12 ꢀ 0.08 ꢀ 0.08 mm):
and most likely dependent on the packing effects in the solid
state. Therefore, when the dichloride groups in 1 are replaced
by dimethylamide groups in 2 or diethylamide groups in 3,
the low melting point solid 1 (mp 52.9 ꢀC) turns into the
lower melting solid 2 (mp 46.7 ꢀC) and the pale yellow liquid
˚
8 14 r
C H36, M = 389.10, monoclinic, a = 8.6692(4) A, b =
GeN
5.7430(7) A, c = 14.9497(7) A, β = 100.3190(10)ꢀ, U = 2007.32(16)
˚
˚
1
3
A , T = 100(2) K, space group P2
˚
1
/n, Z = 4, 15 557 reflections collected,
645 unique (Rint = 0.0216), which were used in all calculations. The
final R (F ) value was 0.0637 (all data).
w
3
2
(28) Stalke, D.; Paver, M. A.; Wright, D. S. Angew. Chem., Int. Ed.
3
, which can be distilled at 60 ꢀC under 60 mTorr of vacuum.
Engl. 1993, 32, 428.
(29) Pattison, I.; Wade, K.; Wyatt, B. K. J. Chem. Soc. A 1968, 837.
(
30) Clegg, W.; Snaith, R.; H. Shearer, M. M.; Wade, K.; Whitehead,
(32) Alcock, N. W.; Pierce-Butler, M.; Willey, G. R. J. Chem. Soc.,
Chem. Commun. 1975, 183.
(33) Mitzel, N. W.; Smart, B. A.; Blake, A. J.; Parsons, S.; Rankin,
G. J. Chem. Soc., Dalton Trans. 1983, 1309.
31) Zhang, J.; Zhou, X.; Cai, R.; Weng, L. Inorg. Chem. 2005, 44,
16.
(
7
D. W. H. J. Chem. Soc., Dalton Trans. 1996, 2095.

Note
Organometallics, Vol. 29, No. 2, 2010 503
Figure 1. Thermal ellipsoid plot of 1 showing 30% thermal ellip-
˚
2 4
Figure 3. TGA curves of precursors 1-3 and Ge(NMe ) .
soids. Selected bond lengths (A) and angles (deg): Ge1-N1 =
1
.777(2), Ge1-N4=1.768(2), Ge1-Cl1=2.1957(7), Ge1-Cl2=
2
.1954(7), N1-C1=1.303(3), N4-C6=1.302(3); N1-Ge1-N4=
07.17(9), N1-Ge1-Cl1=113.98(7), N4-Ge1-Cl1=113.43(7),
N1-Ge1-Cl2 108.39(7), Ge1-N1-C1 128.54(17),
Ge1-N4-C6=129.67(18).
1
=
=
Figure 4. Arrhenius plot showing Ge growth rate (log scale) in
GeTe films as a function of the inverse substrate temperature for
2 4 2
precursors Ge(NMe ) vs 2 in H .
volatility of the sample and are used to compare relative
3
4,35,36
volatilities.
The TGA plots (Figure 3) show the pre-
Figure 2. Thermal ellipsoid plot of 2 showing 30% thermal
˚
cursors are stable up to vaporization temperatures with
minimal mass residuals, indicating substantial vapor-phase
stability and exceptionally clean transport characteristics.
The combination of a lower T50 and lower onset temperature
strongly indicates their suitability for MOCVD/ALD appli-
cations.
Both germanium and binary GexTey films were deposited
using precursor 2, which shows the best combined volatility and
thermal stability among the three tetramethylguanidinates, in
ellipsoids. Selected bond lengths (A) and angles (deg): Ge1-N1=
1
.8312(14), Ge1-N2 = 1.8317(14), Ge1-N3 = 1.8268(14),
Ge1-N4 = 1.8135(13), N3-C5 = 1.277(2), N4-C10 =
.284(2); N1-Ge1-N2 = 100.91(6), N1-Ge1-N3 = 115.30(6),
N2-Ge1-N4 116.32(8), N3-Ge1-N4 120.12(6),
1
=
=
Ge1-N3-C5=133.04(12), Ge1-N4-C10=129.77(12).
Table 1. STA Data of Complexes 1-3
complex
T
50 (ꢀC)
onset temp (ꢀC)
residual mass (%)
the presence of H and in a temperature range of 240-320 ꢀC
2
IV
a,b
(Figure 4). The commercially available Ge
precursor
Ge(NMe
2
)
4
115
230
207
222
104
210
190
203
7
3
0
0
b
1
Ge(NMe ) was also investigated under the same experimental
2 4
b
2
conditions for comparison. The growth rate of Ge was mon-
itored by wavelength dispersive X-ray fluorescence (XRF), and
the growth rates of Ge films using 2 are lower than those using
Ge(NMe ) in our process. However, the growth rates of 2 are
b
3
a
b
2 4
Included for comparison. Sample size (mg): 7.57, Ge(NMe ) ;
1
0.03, 1; 9.57, 2; 10.03, 3.
2
4
in line with the reported growth rates of Ge films using
12
Ge(NMe ) and higher than those using Ge(N(SiMe ) ) .
Our preliminary growth rates of Ge (0.3 A/min) during
The temperatures of 50% mass (T ) loss derived from
0
5
2
4
3 2 4
thermogravimetric analysis (TGA) in simultaneous thermal
analyses (STA) experiments for the novel germanium N,N,
˚
0
0
N ,N -tetraalkylguanidinates 1-3 are given in Table 1.
T50 values have been demonstrated to correlate with the
(
35) Li, Z.; Rahtu, A.; Gordon, R. G. J. Electrochem. Soc. 2006, 11,
C787.
(
36) Chen, T.; Xu, C., Baum, T. H.; Stauf, G. T.; Roeder, J. F.;
DiPasquale, A. G.; Rheingold, A. L. Chem. Mater. [Article ASAP].
DOI:10.1021/cm9009767. Published online: Nov. 25, 2009.
(34) Richardson, M. F.; Sievers, R. E. Inorg. Chem. 1971, 10, 498.

5
04 Organometallics, Vol. 29, No. 2, 2010
Chen et al.
MOCVD of GeTe films using complex 2 suggests it is an
alternative low-temperature Ge precursor as compared to
Ge(NMe ) , especially when the substrate temperature is
rates at low deposition temperatures versus the commer-
cially available precursor in the MOCVD of Ge Tey
x
films, for potential applications in MOS-FETs, selective
growth of Ge films directly on Si substrates, optoelec-
tronic devices, III/V integration on Si, and the integra-
tion of microelectronics with optical components
(photodiodes) into a single chip.
2
4
as low as 240 ꢀC. The lower temperature is of greater interest
for the growth of GeTe films because the tellurium precursors
21,37
usually are not thermally stable at 350 ꢀC and higher.
In summary, the first examples of monomeric group 14
0
0
N,N,N ,N -tetraalkylguanidinates have been prepared
and structurally characterized. Complex 1 was shown to
be a useful and versatile starting material for the design of
Acknowledgment. We gratefully thank Drs. G. T.
Stauf, J. F. Roeder, W. Li, M. Stender, and J. Zheng of
ATMI for helpful discussions.
IV
Ge MOCVD precursors 2 and 3. Complex 2 is highly
stable in the vapor phase, displays substantial vapor
pressure, and was explored as a potential Ge CVD
precursor. Complex 2 exhibited comparable Ge growth
1
Supporting Information Available: Figures giving H and
NMR spectra of the new compound 1 and CIF files giving X-ray
crystallographic data for 1 and 2. This material is available free
of charge via the Internet at http://pubs.acs.org.
13
C
(37) Boucham, J. E.; Maury, F. J. Anal. Appl. Pyrol. 1995, 44, 153.