Selective area atomic layer deposition of rhodium and effective work function characterization in capacitor structures

Article abstract of DOI:10.1063/1.2234846

Atomic layer deposition (ALD) of rhodium was investigated using rhodium(III) acetylacetonate and oxygen, and capacitance versus voltage is used to extract the effective work function in metal/insulator/semiconductor structures. Self-limiting growth was observed, and the resistivity of Rh deposited at 300°C is ～ 10 μΩcm, approximately a factor of 2 larger than the Rh bulk resistivity (4.3 μΩ cm). Selective area deposition is achieved using patterned resist layers, enabling capacitor fabrication without Rh etching. In the as-deposited state, the effective work function was measured to be 5.43 and 5.25 eV on SiO₂ and HfO ₂ dielectrics, respectively. The ALD Rh films formed under conditions used likely contain residual oxygen which can affect oxygen vacancy creation and the effective work function at the metal/dielectric interface.

Full text of DOI:10.1063/1.2234846

Selective area atomic layer deposition of rhodium and effective work function
characterization in capacitor structures
K. J. Park and G. N. Parsons
Citation: Applied Physics Letters 89, 043111 (2006); doi: 10.1063/1.2234846
View online: http://dx.doi.org/10.1063/1.2234846
View Table of Contents: http://scitation.aip.org/content/aip/journal/apl/89/4?ver=pdfcov
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APPLIED PHYSICS LETTERS 89, 043111 ͑2006͒
Selective area atomic layer deposition of rhodium and effective work
function characterization in capacitor structures
a͒
K. J. Park and G. N. Parsons
Department of Chemical and Biomolecular Engineering, North Carolina State University,
Raleigh, North Carolina 27695
͑
Received 23 January 2006; accepted 4 June 2006; published online 26 July 2006͒
Atomic layer deposition ͑ALD͒ of rhodium was investigated using rhodium͑III͒ acetylacetonate and
oxygen, and capacitance versus voltage is used to extract the effective work function in metal/
insulator/semiconductor structures. Self-limiting growth was observed, and the resistivity of Rh
deposited at 300 °C is ϳ10 ␮⍀ cm, approximately a factor of 2 larger than the Rh bulk resistivity
͑
4.3 ␮⍀ cm͒. Selective area deposition is achieved using patterned resist layers, enabling capacitor
fabrication without Rh etching. In the as-deposited state, the effective work function was measured
to be 5.43 and 5.25 eV on SiO and HfO dielectrics, respectively. The ALD Rh films formed under
2
2
conditions used likely contain residual oxygen which can affect oxygen vacancy creation and the
effective work function at the metal/dielectric interface. © 2006 American Institute of Physics.
͓
DOI: 10.1063/1.2234846͔
Metals are of interest for advanced metal/oxide/
thickness, and x-ray photoelectron spectroscopy ͑XPS͒ and
Auger electron spectroscopy ͑AES͒ were used to determine
the film composition and nucleation selectivity. The film re-
sistivity was measured with a four-point probe, and capaci-
tance versus voltage ͑CV͒ was measured using an HP 4284A
LCR meter at 1 MHz using p-type silicon substrates with
semiconductor ͑MOS͒ devices to replace polycrystalline sili-
1
con gate electrodes to avoid effects of charge depletion and
to serve as nucleation and barrier layers for copper
2
interconnects. Noble metals, in particular, Ru, Rh, Pd, Re,
Ir, and Pt, are of interest for positive channel MOS ͑PMOS͒
gate electrodes because their vacuum work function is near
the conduction band edge of silicon. The effective work
function ͑⌽m,eff͒ of Ru in a MOS structure has been
1
7
15
−3
doping levels of 7ϫ10 and 3ϫ10 cm for SiO and
2
HfO , respectively. For some samples, post-metallization-
2
annealing ͑PMA͒ was done under a forming gas ͑10:1
N2:H2͒ at 400 °C for 30 min.
3
–5
measured
to be 4.7–5.2 eV, but materials with higher
⌽m,eff are desired. In addition, the value of ⌽m,eff on high-k
dielectrics is generally somewhat lower than that on SiO2,
and the effective work function of PMOS gates can be sen-
The Rh film thickness per deposition cycle is plotted
versus deposition temperature ͑on HfO2 substrates͒ in Fig. 1.
Under these conditions, a deposition rate between 0.9 and
1.2 Å/cycle is observed between ϳ275 and 310 °C. At
300 °C, saturation in growth/cycle is observed between
0.9 and 1.2 Å/cycle, which is somewhat larger than
6
,7
sitive to oxygen vacancy generation at the metal/high-k
8
,9
interface. Atomic layer deposition ͑ALD͒ has been used to
2
,3,10–13
deposit many noble metals,
but the effective work
1
2
3
,13
ϳ0.8 Å/cycle obtained by Aaltonen et al. Recent results in
function of ALD noble metals is not widely reported. This
letter presents results of thermal ALD of rhodium deposited
our laboratory suggest that for ALD of noble metals depos-
1
0,12
ited by the ligand oxidation process,
the amount of metal
using rhodium͑III͒ acetylacetonate ͓Rh͑acac͒ ͔ and oxygen,
3
deposition per cycle scales with the extent of oxygen
exposure/cycle, so differences in pressure or cycle time can
affect metal growth rate per cycle, even under self-limiting
and deposition results are generally consistent with the work
1
2
of Aaltonen et al. that shows ALD-type growth using these
precursors. Selective area deposition of Rh is demonstrated
using patterned photoresist, and the effective work function
of selectively deposited ALD Rh is characterized on HfO2
1
4
ALD conditions. Figure 1 also shows that Rh film resistiv-
ity decreases with increasing temperature and reaches a mini-
mum of 10 ␮⍀ cm at 300 °C, approximately a factor of 2
and SiO dielectrics using capacitance analysis.
2
Atomic layer deposition was carried out in a homebuilt
hot-wall quartz tube reactor with a base pressure of ϳ5
−
6
ϫ10 Torr. The Rh͑acac͒ precursor is a solid at room tem-
3
perature, but attains a vapor pressure of ϳ20 mTorr upon
heating to 150 °C. The reactor was purged with Ar at an
operating pressure of 0.9 Torr, and the precursor and oxidant
gases were introduced into the reactor in pulses of 15 and
10 s, respectively, with a 15 s Ar purge between each reac-
tant. The Rh͑acac͒ was carried into the reactor using Ar
3
flow, and the total gas flow rate was constant at 300 SCCM
͑
SCCM denotes cubic centimeter per minute at STP͒. Sub-
strates were chemical vapor deposited HfO and thermally
2
grown SiO . Surface profilometry was used to measure film
2
FIG. 1. ALD rhodium film growth rate and resistivity vs deposition tem-
a͒Electronic mail: kjpark@ncsu.edu
perature as deposited on chemical vapor deposited ͑CVD͒ HfO substrate.
2
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003-6951/2006/89͑4͒/043111/3/$23.00 89, 043111-1 © 2006 American Institute of Physics
32.206.205.6 On: Thu, 04 Dec 2014 11:44:32
0
1

043111-2
K. J. Park and G. N. Parsons
Appl. Phys. Lett. 89, 043111 ͑2006͒
FIG. 4. Capacitance vs voltage behavior of selectively deposited ALD Rh
MOS capacitors: ͑a͒ on CVD HfO and ͑b͒ on SiO . Results show typical
2
2
metal-oxide-semiconductor behavior, and for the sample shown, the flatband
voltages VFB=0.72 and 0.18 V and equivalent oxide thicknesses EOT=5.7
and 4.8 nm for HfO and SiO , respectively.
FIG. 2. Rhodium film thickness vs number of ALD cycles deposited on
HfO2.
2
2
larger than the Rh bulk resistivity of 4.3 ␮⍀ cm. At 300 °C
the thickness per cycle increases linearly as shown in Fig. 2,
consistent with a typical ALD process. The error bars repre-
sent ±1 standard deviation obtained from approximately four
to six measurements for each sample.
small O 1s peaks are observed. The oxygen sensitivity factor
is small in XPS, making oxygen content difficult to quantify,
but the peaks indicate an O atomic fraction of ϳ0.09. We
believe further process optimization could reduce the oxygen
content.
The XPS spectra of rhodium films deposited on silicon
oxide are shown in Fig. 3͑a͒, and the peak positions are
consistent with those of metallic Rh. Approximately 10 Å of
the top surface was sputtered in the XPS chamber prior to
analysis to remove adventitious surface oxygen and carbon.
3,15
To achieve selective deposition,
photoresist
͑
ϳ1 ␮m͒ was first deposited on SiO and HfO and pat-
2 2
terned, and then baked in air at 100 °C for 5 min. Substrates
with patterned resist were then transferred into the deposition
chamber and heated at the deposition temperature for 15 min
before deposition was initiated. After 300 cycles, deposition
was visible on the oxide, with no visible deposition on the
photoresist, consistent with inhibited Rh nucleation on the
The measured Rh 3d3 and 3d peak positions at 312.5 and
/2
5/2
3
07.7 eV ͑referenced to carbon at 285 eV measured before
sputtering͒ have a peak ratio of 2:3, while no C 1s and very
3
,5
resist. Figure 3͑b͒ shows AES data from one sample ex-
posed to 300 cycles of the Rh ALD process at 300 °C. Data
were collected from a region of the sample ͑AES probe area
ϳ10− cm ͒ originally not covered by resist ͑top spectrum͒
and a region covered by resist ͑bottom spectrum͒. The AES
spectrum on the resist shows a distinct C KLL peak, with no
evidence of the Rh MNN peak at 320 eV or satellite peaks
between 200 and 280 eV. This demonstrates selectivity to Rh
nucleation on the resist within the sensitivity of the AES
4
2
͑
͑
ϳ0.5 at. %͒. We note that when hexamethydisilazane
HMDS͒ was used as a resist adhesion promoter, nucleation
was also inhibited on the oxide surface. Contact angle mea-
surements suggest that some HMDS remains on the oxide
surface after resist patterning, which likely impedes precur-
sor adsorption.
A key benefit to selective area deposition is that it elimi-
nated the need for Rh etching in device fabrication. Capaci-
tors were formed by direct selective area ALD, and the CV
behavior, shown in Figs. 4͑a͒ and 4͑b͒, was evaluated di-
rectly upon removal of the samples from the reactor system.
To extract the effective work function of the gate electrode in
1
6
the metal/oxide/semiconductor stack, the flatband voltage
1
7
͑
VFB͒ was estimated for several capacitors with various
equivalent oxide thicknesses ͑EOTs͒. Under conditions of
minimal bulk dielectric charge, a plot of V versus EOT is
FB
expected to follow the relation VFB=⌽ −͑Q EOT͒/␧ ,
where the slope ͑Qf͒ is the fixed charge at the
semiconductor/dielectric interface and the linear intercept
ms
f
ox
FIG. 3. ͑a͒ Rh 3d XPS spectrum of an ALD rhodium film on SiO . ͑b͒ AES
2
spectra showing selective area deposition of ALD Rh. The top spectrum is
for Rh deposited on SiO2 at 300 °C for 300 cycles using conditions de-
scribed in text. The lower Auger spectrum ͑labeled “resist”͒ is from the
same sample, after exposure to 300 ALD cycles, collected from a region of
sample covered with resist. The spectrum is consistent with carbon in the
resist, with no rhodium on the resist surface within the sensitivity of the
͑⌽ ͒ is the metal/semiconductor work function difference.
ms
The value for the effective work function ͑⌽m,eff͒ is found
from the semiconductor work function ͑⌽ ͒ using ⌽
s
ms
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AES ͑ϳ0.5 at. %͒.
=⌽
−⌽ . Plots of V versus EOT are shown in Fig. 5,
m,eff s FB
1
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043111-3
K. J. Park and G. N. Parsons
Appl. Phys. Lett. 89, 043111 ͑2006͒
excess oxygen diffusing from the Rh to oxidize the silicon
substrate. It is important to note that the values of effective
work function reported here for Rh in the as-deposited state
are higher by ϳ100–200 meV than the highest values ob-
served for other elemental PMOS gate metals such as Pt and
8
Re. Further studies related to controlling effective work
function of Rh or other PMOS metal gate materials will re-
quire further process optimization, including detailed analy-
sis of oxygen content, as well as vacancy creation and oxy-
gen stability at the high-k/metal interface.
The authors gratefully acknowledge support from
SEMATECH and the Semiconductor Research Corporation
͑SRC͒ under the Front End Processing Research Center.
FIG. 5. VFB vs EOT for ͑a͒ Rh/SiO /Si and Ru/SiO /Si and ͑b͒
2
2
1
7
Rh/HfO /Si and Ru/HfSiO /Si. p-type Si with doping levels of 7ϫ10
2
x
1
5
−3
and 3ϫ10 cm was used for SiO and HfO , respectively. All fits show a
2
2
quality ͑R͒ of ϳ0.9.
1
S.-H. Lo, D. A. Buchanan, and Y. Taur, IBM J. Res. Dev. 43, 327 ͑1999͒.
2
H. Kim, J. Vac. Sci. Technol. B 21, 2231 ͑2003͒.
and the effective work functions of as-deposited ALD Rh on
SiO and HfO were determined to be 5.43 and 5.25 eV,
3
K. J. Park, J. M. Doub, T. Gougousi, and G. N. Parsons, Appl. Phys. Lett.
2
2
8
6, 051903 ͑2005͒.
respectively. The slope of the fit gives a negative fixed
4
V. Misra, H. C. Zhong, and H. Lazar, IEEE Electron Device Lett. 23, 354
͑2002͒.
charge density of 1.5ϫ1012 cm at the Si/HfO interface
−2
2
1
1
−2
5
and a positive fixed charge density of 8.1ϫ10 cm at the
S. K. Dey, J. Goswami, D. F. Gu, H. de Waard, S. Marcus, and C.
Werkhoven, Appl. Phys. Lett. 84, 1606 ͑2004͒.
Si/SiO interface. Also included in Fig. 5 are results from
2
6
7
Y.-C. Yeo, T.-J. King, and C. Hu, J. Appl. Phys. 92, 7266 ͑2002͒.
V. V. Afanas’ev, M. Houssa, A. Stesmans, and M. M. Heyns, J. Appl.
Phys. 91, 3079 ͑2002͒.
CV analysis of ALD ruthenium films after reactive ion etch
patterning and post-metal-anneal, deposited in the same re-
3
8
9
0
actor system using similar dielectric materials. It is interest-
D. Lim, R. Haight, M. Copel, and E. Cartier, Appl. Phys. Lett. 87, 072902
͑2005͒.
ing to note that the as-deposited Rh capacitors have the same
fixed charge as the Ru capacitors measured after post-metal-
anneal. Thermal stability of Rh capacitors was also measured
after forming gas anneal, and results showed a significant
increase in EOT after anneal, consistent with oxidation of the
semiconductor substrate.
J. K. Schaeffer, L. R. C. Fonseca, S. B. Samavedam, Y. Liang, P. J. Tobin,
and B. E. White, Appl. Phys. Lett. 85, 1826 ͑2004͒.
T. Aaltonen, M. Ritala, Y. L. Tung, Y. Chi, K. Arstila, K. Meinander, and
M. Leskela, J. Mater. Res. 19, 3353 ͑2004͒.
1
11
O. K. Kwon, J. H. Kim, H. S. Park, and S. W. Kang, J. Electrochem. Soc.
151, G109 ͑2004͒.
1
1
2
Oxygen vacancies at the dielectric/metal interface cre-
ated by annealing in reducing ambient can lead to a change
in interface dipole and a net decrease in the apparent work
T. Aaltonen, M. Ritala, and M. Leskela, Electrochem. Solid-State Lett. 8,
C99 ͑2005͒.
3
J. C. Hooker, T. Aaltonen, A. Rahtu, M. Ritala, M. Leskela, F.
Roozeboom, E. Van den Heuvel, J. Van Zijl, M. Maas, and T. Raymakers,
Proceedings of the AVS Atomic Layer Deposition Conference 2004, Hels-
inki, Finland, 16–18 August 2004 ͑AVS, Chico, CA, 2004͒.
K. J. Park, S. M. Stwart, and G. N. Parsons ͑unpublished͒.
R. Chen, H. Kim, P. C. Mclntyre, and S. F. Bent, Appl. Phys. Lett. 84,
8
,9
function, and subsequent annealing in an oxidizing ambi-
ent can return the work function to the previous values. In
the ALD process reported here, some oxygen is present in
the as-deposited Rh, likely resulting from residual oxygen
used in the deposition process. This oxygen could be acting
to passivate or impede vacancy creation in the as-deposited
films, promoting the observed high work function values.
The increase of EOT observed upon anneal is consistent with
1
1
4
5
4
017 ͑2004͒.
1
1
6
D. K. Shroeder, Semiconductor Materials and Device Characterization
Wiley, New York, 1990͒.
7͑
J. R. Hauser and K. Ahmed, in Characterization and Metrology for ULSI
Technology edited by D. G. Seiler ͑AIP, New York, 1998͒, pp. 235–239.
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1