High-k / substrate interface reaction by plasma assisted ALD and PVD
プラズマ支援 ALD 及び PVD での high-k 膜/基板界面反応
Takeshi Kitajima and Toshiki Nakano
北嶋武, 中野俊樹
Department of Electronics and Electrical Engineering, National Defense Academy,
1-10-20, Hashirimizu, Yokosuka, Kanagawa 239-8686 Japan.
防衛大学校電気電子工学科 〒239-8686 横須賀市走水 1-10-20
Plasma assisted atomic layer deposition (PAALD) and Plasma enhanced physical vapor deposition (PEPVD) are thecandidates of plasma utilized growth method for high-k dielectrics in micro- and nano-electronic applications. In PAALD,the atomically smooth HfO2 film is grown on Si with TEMAH and O2 ICP exposure although the interfacial SiO2 thickness isincreased with the ALD cycle. In PEPVD, the interface reaction of Hf metal with SiO2 inhibits the increase although the film
thickness and flatness is limited with the surface diffusion or film strain. The non-uniformity is suppressed with the small(10%) coverage of Ti over Hf metal.
1. Introduction
For reliable high-k gate dielectric film formation of highperformance MOSFETs, Hafnium based oxides arecommonly used currently. There are several issues on thehigh-k film such as leak current, uniformity, stabilities overannealing etc. The interfacial layer of SiO 2 needs to becontrolled on its thickness due to the requirement of lower
EOT (Equivalent oxide thickness) value. For the applicationof plasma generated reactants for the high-k growth process,
PAALD and PEPVD are the candidates that can control thenano-thin film properties. The advantage of PAALD is thesuperior conformability and controllability of the thickness.
In high-k PVD, the use of metal source enables the lower
impurity of the film due to the absence of carbon atoms
induced by CVD/ALD processes that use metalorganic
precursors [1]. The merit is also applicable to the plasma
enhanced process as well. The detailed surface chemistry ofthe nano-thin interfacial SiO2 layer between the high-kmaterial and Si substrate within PAALD and PEPVD isstudied.
We clarify the kinetics using in-situ ultra high vacuum
scanning probe microscope (UHV-SPM), XPS and SEM
from the viewpoint of the nanoscale reactions of the high-kmaterial and interfacial layer induced by the plasma
exposure.

30 mTorr and the distance of the coil end and the sample is30 mm.
The PAALD chamber is equipped with the liquid MFC
and evaporator for TEMAH supply with nitrogen buffer. O 2
ICP source is equivalent to the PEPVD and the pressure is380 mTorr. The growth temperature is 150 ℃. The intervalof the nitrogen flow between the TEMAH supply and O 2
ICP is 1 min.

2. Experimental
The PEPVD growth chamber consists of the UHV-SPM(Omicron VT-AFM) with e-beam evaporator for Hf
deposition and the inductive coupled plasma (ICP) chamberpumped with TMP/RP. The 10 turn N 2 ICP with 50 MHz
excitation is separated from the UHV chamber by the gatevalve. The Si(100) sample with SiO2 (thick ~ 1.0 nm) isintroduced from the ICP chamber and degassed in the UHVat 750 K. The sample is exposed to the Hf and Ti beam atroom temperature. The total metal layer is equivalent to theHfO2 film of 2.5 nm thick. Hf(Ti)SiON film is formed bythe exposure of N2 ICP (50W) for 30 min. The N 2 pressure isFig.1. (a) AFM and (c,d) SEM image of HfSiONfilm by PEPVD with N2 ICP exposure to Hf metal(2.5nm) on SiO2/Si(100). (b) Hf0.9Ti0.1SiON filmgrown by PEPVD.

(a)

(b)

(c)

(d)

3. Results and discussion
Figure 1 (a) shows the AFM image of PEPVD grown
HfSiON film. The top surface has nano-scale roughness dueto the initial Hf nano-particles (shown in inset) of 3-7 nm indiameter. The grown film has dispersed holes around 0.8 nm
in depth. The cross-sectional SEM image of the film in
Fig.1(d) shows that the holes are generated due to the fewer

Atomic Concentration [%]NOSi100

1000

Hf100
101in Fig.3 (c) and (d) shows the film thickness is uniform from
10 nanometer to 1 micrometer range. Figure 3 (b) shows theHfO2 film grown by PAALD with O2(1%)/Ar(99%) ICP.
The Ar dilution leads to the twice increase of metastable
Interfacial SiO 2 thickness[nm]coverage of the Hf. Wider view in Fig.1(c) shows the film
thickness varies with several hundred nm lateral period.
Fig.1(b) shows the 10 % Ti coverage over Hf suppresses thehole generation. Film strain or surface diffusion can be theorigin of the holes.

1.8
1.6
1.4
1.2
10.8
0.6
0.4
0.2
000.1
11010000 100000

510152025

PAALD cycle

Hf thickness [nm]Fig.2. Atomic concentration change of HfSiON film grownby PEPVD for increased initial Hf thickness.

(a)

(b)

(c)

(d)

Fig.3. (a) AFM and (c,d) SEM image of HfO2 film by
PAALD on SiO2/Si(100) with pure O2 ICP. (b) Use ofO2(1%)/Ar(99%) ICP reduces surface roughness.
Figure 2 shows the atomic concentration change of thePEPVD grown HfSiON film for increased Hf thickness after
1 min. N2 ICP exposure. The N atom incorporation into thefilm is enhanced with the decrease of the initial Hf metal
thickness showing higher reactivity of Hf nano-particles
which have higher surface to volume ratio. Si fraction in thefilm is increased with the N 2 ICP exposure time (not shownhere) showing Si of SiO2 layer diffuses to the Hf layer due
to the plasma exposure. XPS spectrum shows the diffused Si
react with N atoms as the plasma exposure time increases.
Figure 3 (a) shows the AFM image of the 20 cycle
PAALD grown HfO2 film. The surface is free from holes
and the RMS roughness is 0.23nm. The cross-sectional SEM

Fig. 4. Interfacial SiO2 layer thickness with the PAALDcycle.
O(1D) atom density in the plasma [3] and three times
increase of the flux to the surface [4]. The improved RMS
roughness of 0.11 nm is due to the increased O(1D) flux
which enhances the oxidation of TEMAH on the growing
surface.
Figure 4 shows the the change of interfacial SiO 2 layer
thickness for increased PAALD cycle. The PAALD cycle
increase leads to the increase of the SiO 2 thickness due tothe increase of the plasma exposure time. However, thetrend of the increase shows that the SiO2 thickness in thefirst growth stage is thinner than the initial SiO2 thickness ofthe wafer. This implies the initial SiO 2 layer reacts with thechemisorbed TEMAH under O2 ICP exposure.
In conclusion, interfacial reaction of the initial SiO 2 layer
with the deposited high-k material under plasma exposure is
examined for PEPVD and PAALD. In PEPVD, theinterfacial reaction leads to the incorporation of Si into thehigh-k film layer. In PAALD, interfacial reaction leads to thedecrease of the SiO2 layer in first growth stage. Overall, thethickness uniformity of the PAALD grown film surpasses
that of PEPVD, while PAALD have more carbon
incorporation into the film.
Acknowledgements
T.K cordially express thanks to the support from JSPS Grantin-Aid for Young Scientists (B) No.21760033 for this work.
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