Evaluation of a Novel Cu(I) Precursor for Chemical Vapor
Deposition
D.-X. Ye,
a,z
B. Carrow,
a
S. Pimanpang,
a
H. Bakhru,
b
G. A. Ten Eyck,
c
G.-C. Wang,
a
and T.-M. Lu
a
a
Center for Integrated Electronics and Department of Physics, Applied Physics and Astronomy, Rensselaer
Polytechnic Institute, Troy, New York 12180-3590, USA
b
Department of Physics, State Univesity of New York-Albany, Albany, New York 12222, USA
c
Department of Electrical, Computer, and Systems Engineering, Rensselaer Polytechnic Institute, Troy,
New York 12180-3590, USA
We have synthesized and investigated a novel precursor, 2- Me
3
Si
2
C CuC
5
H
4
N
2
, 1, for chemical vapor deposition CVD of
Cu thin films using H
2
as a reducing agent. The alkyl compound 1 is thermally stable but sublimable when heated in a vacuum.
Cu was selectively deposited on Si100 substrate with Pd as a seed layer. X-ray photoelectron spectroscopy showed that a pure
Cu film was deposited on the Pd seed layer at 250°C, and the film is clean in terms of possible contaminants. Thus the CuI alkyl
compound is suitable for CVD.
© 2005 The Electrochemical Society. DOI: 10.1149/1.1922868 All rights reserved.
Manuscript submitted February 10, 2005; revised manuscript received March 11, 2005. Available electronically May 12, 2005.
The electronic and structural properties of the bulk and the sur-
face of metallic Cu have been vigorously studied both theoretically
and experimentally.
1-5
Recently, metallic quantum wells QWs con-
taining ultra thin Cu layers were fabricated and studied.
6
Moreover,
Cu has been introduced into photonic crystals PCs to operate at the
near infrared and optical frequencies.
7-9
In the microelectronics in-
dustry and related research laboratories, metallic Cu thin films have
been extensively evaluated and studied in the past decade. Cu inter-
connects, for example, have been chosen to replace Al at and be-
yond the 0.25 m node of very large scale integration VLSI.
10-14
As many researchers have pointed out, chemical vapor deposi-
tion CVD is an attractive technique to provide high quality and
conformal Cu thin films for the applications of interconnects and
dual damascene metallization.
10,13,15-17
Based on the oxidation state
of the Cu ions in the CVD precursors, two basic types of Cu-
containing coordination compounds are used in CVD: a volatile
Cu
II
-diketonate complexes, such as Cu acac
2
18
and
Cu hfac
2
,
19,20
and b Cu
I
-diketonateL complexes, where L is a
Lewis base ligand stabilizing the highly reactive Cu
I
-diketonate
complexes. The most important -diketonate ligand is 1,1,1,5,5,5-
hexafluoroacetylacetonate hfac, such as is found in hfacCu-
VTMS VTMS = vinyltrimethylsilane
17,21
and hfacCuMHY
MHY = 2-methyl-1-hexen-3-yne.
22
CuII complexes in a are
thermally and chemically stable but usually also possess a high sub-
limation temperature and low vapor pressure in vacuum.
23
Com-
paratively, CuI precursors in b are in a liquid state with high
vapor pressure and a high growth rate. However, the thermal stabil-
ity and precursor delivery are among the problems reported in the
literature.
23-25
Furthermore, the deposition of Cu thin films using b
is accomplished through the disproportionation of two CuI precur-
sors to obtain one Cu0 and one Cu
II
hfac
2
byproduct which can-
not be further reduced into Cu0 at substrate temperatures lower
than 250°C.
26
The most common substrate temperatures studied are
within the range of 150-250°C when b precursors are employed in
CVD. Thus, only 50% efficiency can be ideally obtained in CVD
processing. Because the -CF
3
containing hfac ligand is used in
both a and b precursors, the deposited Cu thin film might be
potentially contaminated by fluorine, carbon and oxygen.
27
Modifi-
cations of both a and b precursors have been carried out to pro-
vide more stable and viable Cu CVD precursors in the
literature.
22,25,28
To the best of the authors’ knowledge, only a mini-
mal effort has been applied to develop new chemicals without F and
O as potential CVD precursors.
In this paper, we introduce a novel precursor, 2- Me
3
Si
2
C CuC
5
H
4
N
2
1 in this report, for thermal CVD of Cu thin
films. The chemical structure of 1 is shown in Fig. 1. From the
proposed structure of 1, Cu-N is a pseudo bond and the bond
strength of Cu-C is weak. There is no O in 1. We expected a
compound similar to 1 to be a good CVD precursor owing to
the weak Cu-C bond and absence of O in the compound. We
prepared 1 following the method proposed by Papasergio et al.
29,30
The synthesis of 1 was conducted under an atmosphere of N
2
and
obtained by the chelation of 2-bistrimethylsilylmethylpyridine
2 with CuI chloride in anhydrous THF/n-BuLi solution at room
temperature from the procedure reported by Papasergio et al.
30
Compound 2 was prepared from 2-picoline as described by Pa-
pasergio et al.
31
Lime green crystals of 1 were twice recrystallized
from hexane with a melting point of 164-166°C literature reported
162-164°C, in Ref. 30. The efficiency of 1, which is a dimer, as a
Cu precursor was expected to be higher than both a and b pre-
cursors described above because one molecule of 1 can provide
two Cu ions. In addition, 1 has a remarkable thermal stability and
is sublimable in vacuum 10
-3
Torr at 160°C.
29
We used a
1
H
nuclear magnetic resonance spectrometer NMR, Unity INOVA 300,
Varian Inc., USA to verify the proposed structure of 1 as shown in
Fig. 1. N.M.R. CDCl
3
:
1
H, 0.26 s, 18 H, 6.82 m, 1 H, 7.00
m, 2 H, 7.91 m, 1 H. The
1
H NMR spectrum of 1 is in agree-
ment with the expected structure, based on the analysis of Papaser-
gio et al.
30
z
E-mail address: yed@rpi.edu
Figure 1. A schematic of the chemical structure of 2- Me
3
Si
2
C CuC
5
H
4
N
2
compound 1.
Electrochemical and Solid-State Letters, 8 7 C85-C88 2005
1099-0062/2005/87/C85/4/$7.00 © The Electrochemical Society, Inc.
C85
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