Materials Science Forum Vols. 615-617 (2009) pp 545-548 online at http://www.scientific.net © (2009) Trans Tech Publications, Switzerland
Effect of Post Deposition Annealing on the Characteristics of Sol-gel Derived HfO2 on 4H-SiC Chee Chung Hoong and Kuan Yew Cheonga School of Materials & Mineral Resources Engineering, Engineering Campus, Universiti Sains Malaysia, 14300 Nibong Tebal, Penang, Malaysia a
[email protected]
Keywords: high-k dielectric, sol-gel, forming gas annealing, silicon carbide
Abstract. The effects of post deposition annealing in forming gas (5 % H2 in 95 % N2) ambient at different temperatures (850, 950, and 1050 oC) on metal-oxide-semiconductor characteristics of sol-gel derived HfO2 gate on n-type 4H-SiC have been investigated. After 30 min of the annealing, an accumulation of positive effective oxide charge (Qeff) has been observed in all samples. The total interface trap density and Qeff of the oxides annealed at 850 and 950 oC are comparable but an increment and reduction of the respective densities have been recorded when the oxide was annealed at 1050 oC. A reduction of near interface trap density has been revealed as the annealing temperature has been increased. These observation was closely related to the increment of leakage current density as the annealing temperature increased. Introduction Thermal nitrided silicon dioxide (SiO2) is considered as the best gate oxide to be employed in SiCbased metal-oxide-semiconductor (MOS) power device [1,2]. However, due to its relatively low dielectric constant (kSiO2=3.9) if compared with SiC (kSiC=10), it could contribute to oxide breakdown and reliability issues. The electric field strength in a dielectric is scaled by a factor of kSiC/k; assuming that a SiO2 gate is used, an approximately 2.5 times higher electric field is being imposed in the oxide rather than in the SiC. This leads to a severe oxide breakdown and deplete the purpose of using SiC as the substrate for power application. Therefore, numerous high k materials have been investigated in order to find a suitable candidate to replace the nitrided SiO2. Of these candidates, HfO2 is a preferable choice due to its relatively large band offset between the oxide and SiC. This oxide can be deposited via different techniques [3-6]. Sol-gel technique has been widely use because of its simplicity and economic of the deposition system and high homogeneous oxide thin film is able to be produced. In contrast, oxide-SiC interface density of the oxide deposited by this technique is relatively high compared with the other techniques. Hence, the annealing process is playing an important role to reduce the trap density and the reduction is mainly affected by the annealing ambient (air, argon and/or nitrogen) [7]. It has been reported that MOS characteristics of atomic-layer deposited HfO2 on 4H-SiC has been improved after the oxide underwent a forming gas (
