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

3.4.3.4 The Summary of This SectionUp to this point, various annealing conditions for La2O3 thin filmswith platinum upper electrodes were investigated. As the summary ofthese investigations, the comparison of C-V characteristics between PDA andPMA are shown in Figure 3-64. The tendency that PDA increased thecapacitance value but also shifted VFB toward negative side is quite similarto the case of aluminum upper electrodes. However, there were severaldifferences between both behaviors such as a way of recovering the VFB,variation of EOT dependent on the condition of PMA, the range of variationsof EOT and VFB or influence of annealing ambience and so on. Thereforethe reason why PMA with platinum could recover the VFB shift might bedifferent from the ones of aluminum. In order to explain these phenomena,more investigation must be done by adopting other metal material as upperelectrodes.Finally, plots of EOT versus VFB shift is shown in Figure 3-65. Itshould be noted that major plots of VFB shift stayed within -0.4 V. Theseresults could be the evidence that the mechanism of variations of VFB shift inthe case of platinum upper electrodes is different from ones of aluminumupper electrodes because VFB shift varied drastically owing to the annealingconditions in the case of aluminum upper electrodes. And same as the caseof aluminum, trade-off relationship between EOT and VFB shift exists andthere are 3 plots on the line which means the best result, PMA for100minutes in nitrogen ambience, PMA for 10minutes in nitrogen ambienceand PDA for 10 minutes in forming gas ambience. Hence, combining theseannealing conditions could bring much better results such as recovering VFBshift without an increase of EOT.- 86 -