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200 g/Nm3 . HfO2 ?lms are grown on p-type Si (100) wafers by ALD for different oxidants (O3, H2O) and deposition temperatures (150 °C,

200 °C, and

300 °C). In order to decrease the interface traps and the ?xed charges, the as-deposited ?lms are annealed in nitro- gen atmosphere. 3. Results and discussion 3.1. Comparison of physical properties of HfO2 3.1.1. Thickness of HfO2 ?lms Table

1 shows the thickness of HfO2 ?lms (Tox) measured by Woollam M2000D Spectroscopic Ellipsometer. Tox and growth- per-cycle (GPC) of H2O-based HfO2 ?lms depend on the deposition temperature greatly. Tox of H2O-based HfO2 ?lms increases with increasing temperature. The same dependent relation is observed for the O3-based HfO2 deposited at

150 °C and

200 °C respectively. However, Tox and GPC suddenly decrease for O3-based HfO2 ?lms deposited at

300 °C. There is the strong decomposition of O3 in the direction of gas ?ow when the temperature is higher than

250 °C, and GPC does not increase by increasing O3 or TEMAH dose 0026-2714/$ - see front matter ?

2012 Elsevier Ltd. All rights reserved. doi:10.1016/j.microrel.2012.01.010 ? Corresponding author. Tel.: +86

29 88204085;

fax: +86

29 88201641. E-mail address: [email protected] (J. Fan). Microelectronics Reliability

52 (2012) 1043C1049 Contents lists available at SciVerse ScienceDirect Microelectronics Reliability journal homepage: www.elsevier.com/locate/microrel [8]. Furthermore, the GPC of H2O-based HfO2 is more than 0.1 nm per cycle, and it is higher than that of O3-based HfO2. In order to obtain the accurate values of permittivity and EOT of the HfO2, the interlayer (TSiOx ) is measured by Woollam M2000D Spectro- scopic Ellipsometer and subtracted in the calculation, as shown in Eq. (2). The EOT and permittivity are determined as follows: EOTtotal ? A e0eSiO2 COX ?1? EOTHfO2 ? EOTtotal ? TSiOx ?2? eHfO2 ? THfO2 EOTHfO2 eSiO2 ?3? where A is the area, COX is the accumulation capacitance of HfO2 ?lms, eHfO2 and eSiO2 are the permittivity of HfO2 and SiO2 respec- tively. Table

1 shows the thickness of H2O-based and O3-based HfO2 ?lms deposited at different temperatures. The equivalent oxide thickness (EOT) decreases greatly with increasing deposition temperature and the permittivity increases obviously for O3-based HfO2 ?lms. While the EOT and permittivity of H2O-based HfO2 ?lms almost do not depend on the deposition temperature. Mean- while, the permittivity of H2O-based and O3-based HfO2 deposited at the same temperature shows signi?cant difference. In order to investigate the impact of the thermal treatments on the physical properties and electrical characteristics of HfO2 ?lms, the samples are annealed in nitrogen. The annealing time is

10 min and annealing temperature is

500 °C and

700 °C respectively. The completely different behaviors are observed after different anneal- ing conditions. Fig.

1 shows the thickness of HfO2 after annealing process. After

500 °C thermal annealing, the thickness of H2O- based HfO2 ?lms deposited at

150 °C,

200 °C and

300 °C increase 0.2 nm, 0.1 nm and 0.1 nm, respectively. The increasing magnitude can be negligible because it is within the experimental error. How- ever, the thickness increases signi?cantly after

700 °C thermal annealing due to the growth of interface layer. As shown in Fig. 1a, the ?lms deposited at

150 °C,

200 °C and

300 °C increase 0.8 nm, 0.4 nm and 0.3 nm, respectively. For the O3-based HfO2 ?lms, the thickness of the ?lms deposited at

150 °C decreases about 0.5 nm after