Chemical vapour deposition of praseodymium oxide films on silicon: influence of temperature and oxygen pressure A. Abrutis a, ⁎ , M. Lukosius a , Z. Saltyte a , R. Galvelis a , P.K. Baumann b , M. Schumacher b , J. Lindner b a Vilnius University, Department of General and Inorganic Chemistry, Naugarduko 24, LT-03225 Vilnius, Lithuania b AIXTRON AG, Kackertstr 15-17, 52072 Aachen, Germany Received 29 September 2006; received in revised form 9 July 2007; accepted 19 August 2007 Available online 24 August 2007 Abstract Metal-organic chemical vapour deposition (MOCVD) of various phases in PrO x system has been studied in relation with deposition temperature (450–750 °C) and oxygen partial pressure (0.027–100 Pa or 0.2–750 mTorr). Depositions were carried out by pulsed liquid injection MOCVD using Pr(thd) 3 (thd = 2,2,6,6-tetramethyl-3,5-heptanedionate) precursor dissolved in toluene or monoglyme. By varying deposition temperature and oxygen partial pressure amorphous films or various crystalline PrO x phases (Pr 2 O 3 , Pr 7 O 12 , Pr 6 O 11 ) and their mixtures can be grown. The pure crystalline Pr 2 O 3 phase grows only in a narrow range of partial oxygen pressure and temperature, while high oxygen pressure (40–100 Pa) always leads to the most stable Pr 6 O 11 phase. The influence of annealing under vacuum at 750 °C on film phase composition was also studied. Near 90% step coverage conformity was achieved for PrO x films on structured silicon substrates with aspect ratio 1:10. In air degradation of Pr 2 O 3 films with transformation to Pr(OH) 3 was observed in contrast to Pr 6 O 11 films. © 2007 Elsevier B.V. All rights reserved. Keywords: Chemical vapour deposition; Praseodymium oxides; X-ray diffraction 1. Introduction For the continuous development of devices, e.g. for CMOS (complementary metal oxide-semiconductor) technology or DRAM (dynamic random access memory) applications, alter- native high-k materials are becoming more and more necessary to possibly replace SiO 2 [1]. Requirements for these materials include high-k value, low leakage current, high breakdown strength, high thermal stability on silicon, etc. Currently various metal oxides are investigated as alternative dielectrics. Howev- er, it is difficult to find an oxide satisfying all requirements. Potential high-k materials include HfO 2 , ZrO 2 , Ta 2 O 5 [2] or mixtures of different oxides. Rare-earth oxide thin films have also been considered as potential alternative high-k materials for silicon CMOS or DRAM technology [3,4]. They exhibit high dielectric constant, large energy band gap, and high conduction band offset with respect to silicon [5]. Moreover, complex rare- earth oxides such as GdScO 3 , DyScO 3 and LaScO 3 were re- cently identified as interesting option for gate dielectrics appli- cations since they remain amorphous up to 1000 °C [6]. Among the rare-earth oxides, La 2 O 3 and Pr 2 O 3 have become the most frequently studied rare-earth oxide films. Pr 2 O 3 has attracted attention due to high dielectric constant (26–30) [7], middle band gap (3.9 eV) [8], symmetrical band offset larger than 1 eV in respect to Si [9], and large energy formation (- 12 900 kJ/ mol) [10]. Moreover, it has been reported that Pr 2 O 3 films are compatible with conventional CMOS process [11]. Despite the thermodynamical data indicating to high stability of Pr 2 O 3 in contact with Si, the formation of a thin Pr silicate interlayer, especially at high temperature, has been reported [12–18]. However, the stability of Pr 2 O 3 in contact with Si is better than HfO 2 and ZrO 2 . Concerning the leakage current, promising results were reported for Pr 2 O 3 grown by molecular beam epitaxy (MBE)-films of equivalent oxide thickness (EOT) of Available online at www.sciencedirect.com Thin Solid Films 516 (2008) 4758 – 4764 www.elsevier.com/locate/tsf ⁎ Corresponding author. Tel.: +370 5 2331004; fax: +370 5 2330987. E-mail address: adulfas.abrutis@chf.vu.lt (A. Abrutis). 0040-6090/$ - see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.tsf.2007.08.097