Al/La2O3 Analysis of Post Metallization Annealed MISFET by XPS

Autor: Kuniyuki Kakushima, Jin Aun Ng, Kazuo Tsutsui, Nobuyuki Sugii, Yusuke Kuroki, Hideo Iwai
Rok vydání: 2006
Předmět:
Zdroj: ECS Transactions. 1:239-247
ISSN: 1938-6737
1938-5862
DOI: 10.1149/1.2209273
Popis: MISFETs with La2O3 gate insulator were fabricated and several heat treatments were performed. High effective mobility was obtained by Post Metallization Anneal (PMA). XPS analysis reveals the formation of Al2O3 between Al and La2O3 during the annealing, which may improve the mobility. INTRODUCTION La2O3 is expected as a new gate insulator for next generation thanks to its high dielectric constant and thermal stability. One of the common issues in high-k materials is the degradation in mobility. Several attempts to improve the mobility have been reported by inserting interfacial layer and so on. Here, we report the improvement of the mobility by annealing with Al gate. EXPERIMENTS Ultrathin La2O3 films were deposited on silicon substrate with isolation and source/drain structures by ebeam evaporation followed by H2SO4/H2O2 mixture (SPM) cleaning and HF-dip processes. Temperature during the deposition was set to 250C. Post Deposition Anneal (PDA) in N2 ambient was performed at 300C for 5min after La2O3 films were deposition. On the other hand, Post Metallization Anneal (PMA) in N2 and Forming Gas (N2:H2=97:3) ambient was performed at 300C for 5 min after Al gate formation. Source, drain and backside electrodes were formed afterwards. The complete structure of MISFET had gate length and gate width of 10 μm and 57 μm, respectively. RESULTS AND DISCUSSION Id-Vd characteristics of the fabricated MISFET is shown in figure 1, where the sample of PMA has high drain current compared to the sample of PDA. Relationship between effective mobility and effective electric field is shown in figure 2. Compared to the asdeposited sample, the PDA and PMA samples have higher effective mobility. The maximum effective mobility of the PDA and PMA samples were 183 cm/V-s (EOT=0.91nm) and 257 cm/V-s (EOT=2.37nm), respectively. The increase in EOT can be explained by the formation of interfacial layer between Al and La2O3. To investigate the effect of PMA, X-ray photoelectron spectroscopy (XPS) was performed to analyze the interface between La2O3 and Al gate electrode. Figure 3 shows the Al-2p spectra of the as-deposited and PMA samples. The peak of Al-Al reduced and Al-O increased, which suggests the formation of Al2O3. PMA of MISFET with Pt gate electrode should almost the same mobility as PDA Al-MISFET. Thus, we anticipate the Al2O3 has strong influence on higher mobility. CONCLUSION High effective mobility using La2O3 MISFET with Al gate electrode was obtained by Post Metallization Anneal (PMA). The formation of Al2O3 was detected by XPS analysis, which may have strong influence on higher mobility, whereas the EOT increased. Process optimization is required to overcome this problem. ACKNOWLEDGEMENT This work was partially supported by Semiconductor Technology Academic Research Center (STARC) and Special Coordination Funds for Promoting Science and Technology by Ministry of Education, Culture, Sports, Science, and Technology, Japan. REFERENCES [1] Jin-Aun Ng et al., ECS Proceeding (2004) [2] A. Kuriyama et al., ECS Proceeding, 285 (2003) Figure 1. Id-Vd characteristic of Al gate La2O3 nMISFET with PDA and PMA at 300°C in N2 ambient for 5 min Figure 2. Effective mobility of PDA, PMA and as- deposited (w/o anneal) Figure 3. Al-2p spectra of as-deposited and PMA samples with Al electrode 0 10 20 30 40 I d (μ A /μ m ) 50 60 Vd (V) 0 1.0 0.5 1.5 Open:PMA Solid:PDA Vg 0.25(V) 0.50(V) 0.75(V) 1.00(V) 0.8 0.4 0 Effective Electric Field (MV/cm) 1.0 0.6 0.2 0 100 200 300 400 E ff ec tiv e M ob ili ty (c m 2 /V s) AsDepo PDA-N2 PMA-FG PMA-N2 Universal 72 71 74 73 76 75 78 77 Binding energy (eV) In te ns ity (a .u .) AsDepo
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