The Study of Hafnium Silicate by Various Nitrogen Gas Annealing Treatment
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The Study of Hafnium Silicate by Various Nitrogen Gas Annealing Treatment Dong Chan Suh1, Kwun Bum Chung2, Mann-Ho Cho3, Young Dae Cho1, and Dae-Hong Ko1 1 Department of Ceramic Engineering, Yonsei University, Seoul, 120749, Korea, Republic of 2 Department of Physics, North Carolina State University, Raleigh, NC, 8202 3 Department of Physics, Yonsei University, Seoul, 120749, Korea, Republic of ABSTRACT Post annealing of Hf-silicate thin film grown by ALD was done with different kind of nitrogen gas and order of annealing. Annealing conditions are as follows: (1) NO gas only, (2) NH3 gas only, (3) NO gas + NH3 gas, and (4) NH3 + NO gas. With these conditions, the physical and electrical properties of nitrided Hf-silicate films were analyzed. Content of nitrogen is decreased with post NO gas annealing. In case of NH3, content of nitrogen is much higher than NO case. Most nitrogen atoms were distributed between Si substrate and Hf-silicate film for NO gas annealing. However, with NH3 gas annealing, nitrogen atoms were distributed in the whole Hfsilicate film evenly. Leakage current was decreased with post NO gas annealing and flat band voltage was also decreased. INTRODUCTION High-k gate dielectrics such as HfO2, ZrO2, rare earth oxides and their silicates have been considered as candidate of alternative gate dielectric materials for future ULSI to replace to the conventional gate insulator SiO2/SiON, because they can reduce leakage current and improve reliability.1,2 Among high-k materials, hafnium silicate (Hf-silicate) is one of the best promising materials for CMOS applications due to its relatively high dielectric constant, a large band gap, and good thermal stability on silicon.3,4,5 However, it was reported that Hf-silicate systems show the phase separation to SiO2 and HfO2 after annealing above 800 OC due to the positive enthalpy of mixed state of SiO2 and HfO2.6 The phase separation leads to the degradation of thermal stability, dielectric and electrical properties. Several researchers investigated that incorporated nitrogen could improve thermal stability.7,8 However, the reasons and mechanisms of the improvement in thermal stability were not fully understood. Moreover, research on nitridation through NO and NH3 has not progressed much, and it is the first time research has been carried out on two annealing processes of NO gas and NH3 gas simultaneously. In this paper, research was done on what physical, chemical, and electrical influences post-thermal annealing has on films by carrying out post-thermal annealing individually or continuously in NO and NH3 gas ambient. EXPERIMENTAL A p-type Si(100) substrate was cleaned chemically by the Radio Corporation of America (RCA) method and the native oxide was removed with a dilute HF solution. The Hf-silicate films are grown by Atomic Layer Deposition (ALD) systems, which have a vertical warm wall reactor with a showerhead and a heat susceptor. The Hf-silicate films with a thickness of ~4nm were deposited at a temperature of 320 OC using tetrakis (ethy
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