Effect of Post Metallization Annealing for La 2 O 3 Thin Film

Figure 3-5 shows the plots of EOT dependent on annealingtemperature of PDA. It was observed that EOT decreased proportionally asthe increase of annealing temperature. Moreover, leakage current alsodecreased with decrease in EOT as shown in Figure 3-6. These magnificentresults demonstrate not only the improvement in quality of films by PDA,but also the latent faculties of La2O3 as high-k gate dielectrics.Figure 3-7 shows the plots of VFB shift dependent on the annealingtemperature of PDA. Unfortunately, the value of VFB shift increasedabruptly from 300 o C to 400 o C of PDA and it seems quite difficult to recoverthe flat band voltage shift toward negative side by PDA. Figure 3-8 showsEOT versus VFB shift plots. Although it is desirable to approach toward thelower right side in this graph, experimental plots were headed for the lowerleft side. This phenomenon indicates that there is trade-off relationshipbetween EOT and VFB shift, and that also means that it is so difficult tocombine lower EOT and VFB shift by only PDA process.The dependence on the rising ratio, 75 o C/minute and 400 o C/minute,of PDA was examined. It was confirmed that in the case of PDA, there isalmost no dependence on rising ratio as shown in Figure 3-9EOT [nm]2.221.81.61.4As-depo.300 o CAl/La O / n-Si(100)/Al2 3HF-last 250 o C depo.400 o CAs-depo. & PDA450 o C0 100 200 300 400 500Annealing Temperature [ o C]Figure 3-5: EOT plots dependent on annealing temperature.- 36 -