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

As the summary of this sub-section, the dependence on thetemperature of PMA, the comparison between PDA and PMA at 300 o C wasshowed in the pages that follow. Figure 3-21 shows the comparison of C-Vcharacteristics between PDA and PMA at 300 o C. Each sample wasannealed in nitrogen ambience for 10minutes. It was observed that VFBshift was only -0.1 V from the theoretical VFB value without surface fixedcharge in the case of PMA, and increase of hysteresis was suppressed under0.03 V. On the other hand, the VFB shift was -0.80 V in the case of PDA.Furthermore, PMA suppressed the leakage current more than 3 orders ofmagnitude as compared with PDA as shown in Figure 3-22. From the above,it can be presumed that the fittest temperature of PMA is around 300 o Cunder the condition of nitrogen ambience and 10 minutes annealing.However, some faults of PMA were also confirmed from these results.One of them is the increase of EOT. Figure 3-23 shows leakage current as afunction of EOT. It was found that PMA had higher value of EOT ascompared with one of PDA. Moreover, PMA would increase the interfacestate density. Figure 3-24 shows the comparison of frequency dependenceon C-V characteristics between PDA and PMA. It was observed that therewas no frequency dependence in the case of PDA. On the other hand,however, it was observed that there was frequency dependence at weakinversion region in the case of PMA. Although the fixed charge densitydramatically decreased by the PMA at 300 o C, interface state density seemsto increase. Further study to reduce the interface state density will berequired.- 49 -