Trimethyl-Aluminum and Ozone interactions with Graphite in Atomic Layer
Deposition of Al
2
O
3
Supplementary Information
Stephen McDonnell,
1
Adam Pirkle,
1
Jiyoung Kim,
1
Luigi Colombo
2
and Robert M.
Wallace
1,a)
1
Department of Materials Science and Engineering, The University of Texas at Dallas,
Richardson, Texas 75080, USA
2
Texas Instruments Incorporated, Dallas, Texas 75265, USA
I. Film composition on HF-last silicon
Low temperature ALD is not traditionally utilized for high-k dielectric deposition because it results in films with high leakage currents.
1
This reduction in film quality can be attributed to incomplete reaction products that are present in films grown at low temperatures. The presence of these incomplete reaction products can be monitored in the
C 1 s core-level feature. Characterization of these low temperature Al
2
O
3
ALD films is difficult for films grown on graphite, because the C 1 s spectrum is dominated by photoelectrons from the substrate. HF-last Si(100) contains a much smaller initial C 1 s feature which can be attributed to physisorbed species from atmospheric exposure.
Utilizing HF-last Si(100) spectator samples that received deposition simultaneously with the HOPG samples in this study, we can more easily identify the carbon species that are contained within the Al
2
O
3
films and characterize the effect of both the nitrogen purge time and the precursor pulse sequence on general film composition.
A. Purge Time dependence on HF-last silicon a) Corresponding author: rmwallace@utdallas.edu

To determine the effect of the nitrogen purge time on the Al
2
O
3
film composition, films were deposited using 18 ALD cycles at room temperature on HF-last silicon wafers.
The nitrogen purge time was varied from 30 s to 300 s and Figure S1 shows the a) O 1 s , b) C 1 s , c) Al 2 p and d) Si 2 p core-level features for these samples. The intensities of these core-levels have been normalized to the substrate (Si 2 p ) intensity for ease of comparison. The O 1 s spectra can be deconvolved into 3 separate features at 531.8 eV,
533.1 eV and 533.9 eV. These three features are assigned to alumina, methoxy and carbonate groups, respectively. The methoxy and carbonate groups are expected to result from the ozone/TMA reaction process and are consistent with the features observed in the
C 1 s spectra.
2
It is clear from these spectra that the total amount of Al
2
O
3
is independent
(to within 6%) of the purge time, which is expected for an ideal ALD process. The concentration of the partial reaction products however is strongly dependent on the purge time with the lowest concentrations being seen for the highest purge times.
The C 1 s spectrum for the 30 s purge time can be deconvolved into four separate features at 284.5 eV, 285.8 eV, 287.5 eV and 290.5 eV. Goldstein et al.
previously detected formate, methoxy and carbonate during TMA/O
3
reactions studies utilizing Fourier transform infrared spectroscopy (FTIR) and quadrople mass spectrometry (QMS).
2
Using the C 1 s core-level features deconvolved by Beamson and Briggs for many polymers, assignment of the feature at 287.5 eV to methoxy groups, the feature at 285.8 eV to methyl groups, and the feature at 290 eV to carbonate groups is possible.
3,4
The feature at
284.5 eV is most likely due to hydrocarbons since its presence is detected in the C 1 s spectra of the HF-last Si surface prior to ALD. The intensities of the features assigned to

partial reaction products are seen to decrease with increasing purge time, which is consistent with the trend observed in the O 1 s spectra. This observation from both the C
1 s and O 1 s core-level features suggests that the partial reaction products are only physisorbed to the surface and desorb with time.
In the Al 2 p spectra the Al-O bond concentration appears to depend on purge time, which would be inconsistent with the constant O-Al bond concentration monitored with the O 1 s core-level. Careful analysis of the Al 2 p feature reveals that the FWHM of the feature increases as purge time increases. This suggests that a second feature is present with an intensity that varies with the purge time. When the FWHM and intensity of the Al
2
O
3
assigned core-level feature at 75.3 eV are fixed, a second component at 75.1 eV is required to obtain a good fit. This feature can be assigned to aluminum bonded with the aforementioned partial reaction products in particular Al-CH
2
from Goldstein et al
2 assuming that oxygen insertion into the CH
3
is a possible initial reaction between Al-CH
3 and O
3
to form Al-CH
2
-OH + O
2
. Given the small separation of 0.2 eV between these features it is difficult to draw strong conclusions from the peak fit. However, when the
Al-O feature is fixed to follow the trend of the O-Al feature in the O 1s spectra, the Al-
CH
2
feature can be seen to match the trend of the features assigned to incomplete reaction products in the O 1 s and C 1 s core-level spectra (i.e. it reduces with increased purge time). Finally from the Si 2 p core-level feature it is clear that interfacial SiO x
forms even during room temperature ALD using TMA and O
3
precursors.

In summary, partial reaction products containing aluminum, oxygen and carbon are present within these Al
2
O
3
films grown by ALD using TMA and ozone precursors.
These reaction products should be expected on HOPG substrates as well and as such these extra carbon species observed in the C 1 s feature are not attributed to substrate interaction (sp
3
bonding) in the main text but rather to these contaminants within the film.
B. Pulse sequence on HF-last silicon
In a typical TMA/H
2
O ALD process for gate dielectric quality Al
2
O
3
, a hydroxylated surface is exposed to TMA, resulting in a self-terminating monolayer.
5,6,7
Since the interactions between ALD precursors and the chemically inert graphite and graphene surfaces are not well understood, the optimum pulse sequence in not known and requires study. In order to distinguish between process effects and substrate effects, we first examine the effect of alternating the pulse sequence on a silicon surface. In this experiment 6 consecutive ALD cycles of Al
2
O
3
using TMA and ozone precursors are deposited on HF-last samples followed by post deposition in-situ XPS. The effect of alternating the precursor sequence (i.e. TMA first or ozone first) is studied.
The O 1 s spectra in Figure SI 2 highlights that there is an increase in the concentration of partial reaction products in the film when the TMA first process is used.
Fixing the ratio of Al-O bonds to Al-R (Where R is any radical assigned to partial reaction products, e.g. Al-CH
2
-OH) bonds in the Al 2 p spectra (b) to match the ratio for
O-Al and O-R bonds in the O 1 s spectra, we see that consistent fits can be obtained using the same binding energy separation of 0.22 eV determined in section SI A. The C 1 s

spectrum in c) also shows a notable increase in the feature at 290 eV while the features at
284.5 eV and 285.8 eV were significant on the pre-deposition surface (Figure SI 1c).
Also consistent for the O 1 s , C 1 s and Al 2 p features is the indication that the ozone-first process results in a slightly thicker film. In d) Monitoring the O 1 s signal intensity normalized to the Si 2 p signal with sequential pulses also shows that the difference in the final film thickness is not due to differences in the initial pulse sequence since the concentration of O-Al bonds is seen to be independent of pulse sequence. This would suggest that there are sufficient physisorbed hydroxyl groups on the HF-last surface to nucleate growth without the need for an ozone pulse first. These results highlights that the reduction in Al
2
O thickness seen for the ozone first process on HOPG is most likely substrate dependent.
References:
1
S. K. Kim, S. W. Lee, C. S. Hwang, Y.-S. Min, J. Y. Won, and J. Jeong, Journal of The
Electrochemical Society 153 , F69-F76 (2006).
2 D. N. Goldstein, J. A. McCormick, and S. M. George, The Journal of Physical
Chemistry C 112 , 19530 (2008).
3 G. Beamson, D. Clark, D. Law, and others, Surface and interface analysis 27 , 76 (1999).
4
D. Briggs and G. Beamson, Analytical Chemistry 64 , 1729 (1992).
5
A. W. Ott, K. C. McCarley, J. W. Klaus, J. D. Way, and S. M. George, Applied Surface
Science 107 , 128 (1996).
6 M. D. Groner, J. W. Elam, F. H. Fabreguette, and S. M. George, Thin Solid Films 413 ,
186 (2002).
7 M. D. Groner, F. H. Fabreguette, J. W. Elam, and S. M. George, Chemistry of Materials
16 , 639 (2004).

Figure Captions
Figure SI 1: Photoelectron spectra of a) O 1 s , b) Al 2 p , c) C 1 s and d) Si 2 p for Al
2
O
3 deposited on HF-last Si(100) by ALD at room temperature with 0.2 s pulse of TMA and
Ozone precursors with i) 30 s and ii) 300 s N
2
purge times. For c) the C 1 s spectra before deposition is shown in iii)
Figure SI 2 Photoelectron spectra of a) O 1 s , b) Al 2 p , c) C 1 s of Al
2
O
3
deposited on HFlast silicon in 6 cycles using a i) TMA first process and ii) ozone first process. D shows the ratio of the O 1 s to the Si 2 p integrated intensity which is related to the thickness of the Al
2
O
3
.
Figure SI 1

Figure SI 2