Germanium Incorporation in HfO[sub 2] Dielectric on Germanium Substrate

Abstract

It is widely reported that a significant amount of germanium is incorporated in HfO 2 gate dielectric during the formation of highgate stack on germanium substrate. In this paper, the dependences of germanium incorporation in HfO 2 on dielectric deposition method, annealing temperature, and annealing ambient were extensively studied by physical methods such as time-of-flight secondary ion mass spectroscopy. The results indicate that the high thermal budget of processes, including deposition and annealing, is the most critical factor to the Ge incorporation. The Ge incorporation in HfO 2 is identified by two mechanisms: Ge atoms out-diffusion from substrate and gaseous GeO diffusion downward into HfO 2 via airborne transportation in the chamber.Germanium is a promising channel material for metal-oxide semiconductor field effect transistor ͑MOSFET͒ applications. It has much higher mobility over silicon ͑two times higher for electrons and four times higher for holes͒. However, germanium oxide has a poor electrical quality and is water soluble. It is not possible to form a high-quality gate dielectric on germanium substrate by conventional oxidation techniques. With the recent successful development of high-material deposition, germanium MOSFETs with highgate dielectrics have attracted much research interest. High-mobility long-channel bulk germanium, germanium-on-insulator, and strained germanium MOSFETs with various high-gate dielectrics have been reported. 1-4 Deep submicrometer: ͑0.15 m͒ Ge MOSFETs with HfO 2 were also demonstrated in a 200-mm Si prototyping line, 5 illustrating that Ge MOSFET fabrication is compatible with mainstream Si processing technology. Compared to many reports on HfO 2 deposition on silicon, there is little knowledge of HfO 2 deposition on germanium substrates. Recently, it was reported that a large amount of germanium was found inside HfO 2 film deposited by metallorganic chemical vapor deposition ͑MOCVD͒ on germanium substrate. 6 Similar germanium incorporation was also observed in physical vapor deposition ͑PVD͒ HfO 2 on Ge substrate after high-temperature annealing. 7 However, there is no detailed investigation on the dependence of germanium incorporation in HfO 2 on process conditions. In this paper, the germanium incorporation in HfO 2 is extensively evaluated on bulk germanium wafers with varied deposition techniques and postdeposition annealing conditions. ExperimentalHfO 2 films were deposited on germanium ͑100͒ substrates by either MOCVD or PVD. Before deposition, the wafers were cleaned by diluted HF. MOCVD deposition used Hf t-butoxide precursor and O 2 at 400°C in the MOCVD chamber of a Jusung gate cluster. To evaluate the dependence of Ge incorporation on the deposition method, reactive sputtering using a pure Hf target in O 2 ambient at room temperature was used to prepare HfO 2 films. To study the Ge incorporation in HfO 2 upon subsequent thermal processes, postdeposition annealing ͑PDA͒ was performed in a rapid thermal processing ͑RTP͒ machine in N 2 or O 2 ambient at tem...

Effects of postgate dielectric treatment on germanium-based metal-oxide-semiconductor device by supercritical fluid technology

“…Sequentially, poor interface properties and high gate leakage current will be exhibited in the Ge-MOS device. [3][4][5][6][7] Various pre-gate surface modification techniques, such as surface nitridation or Si passivation, have been developed to improve the quality of gate insulator/Ge interface. 13 It was also reported that high-performance Ge MOSFET could be realized by careful control of interfacial GeO 2 formation.…”

Germanium-related deep electron traps in ALD-grown HfO2 insulators studied through Exhaustive PhotoDepopulation Spectroscopy

“…Previous studies [15] on HfO 2 deposited on Ge substrates indicate Ge in-diffusion and incorporation into the oxide upon thermal treatment in N 2 at temperature T a > 600 ˚C. Therefore, we analyzed the electron trap distribution in samples annealed at 500, 700 or 1000 ˚C in N 2 .…”

Effect of Annealing Ambient on Structural and Electrical Properties of Ge Metal-Oxide-Semiconductor Capacitors with Pt Gate Electrode and HfO<SUB>2</SUB> Gate Dielectric

“…A thermallyevaporated HfO 2 layer, which was deposited directly on Ge substrates, showed low leakage current characteristics and poor interface quality with low accumulation capacitance values upon N 2 annealing. 10) Wu et al 11) and Zhang et al 12) observed severe Ge incorporation into HfO 2 occurring during thermal annealing due to a haphazard IL between the HfO 2 and Ge. Chen et al 13) described degraded electrical properties on Ge substrates with different high-k gate dielectrics such as HfO 2 and Al 2 O 3 without an intentional IL after annealing in a forming gas (FG) ambient at $500 C, due to direct contact between the high-k material and the Ge.…”