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

3.4.1.5 The Combination Cof PDA and PMAThus far, the electrical characteristics by various conditions of PDAand PMA with aluminum upper electrodes were examined for theiroptimization. As a result, it was found that in the case of aluminum upperelectrodes, negative VFB shift was enlarged by PDA, while all the othercharacteristics such as EOT, leakage current or interface state density wereimproved. On the other hand, it was found that the VFB shift was almostcompletely recovered by PMA at 300 o C. However, PMA with Al upperelectrodes decreased the capacitance value. Also PMA was not sufficient todecrease the leakage current, and even increased the interface state density.From these results, it is natural to consider that combining PDA and PMAcould bring good characteristics owing to the counterbalance by each merit.Figure 3-35 shows the C-V characteristics in the case of thecombination of PDA and PMA compared to only PDA or PMA treatment, andtheir dependence on the time of PMA from 0 sec (spike) to 10 minutes. Thetemperature of PDA was 300 o C and the temperatures of PMA were 250 o Cand 300 o C respectively. All of samples were annealed in nitrogen ambience.In the case of spiked PMA at 250 o C, any effects of the suppression of the VFBshift did not appear as shown in Figure 3-35 (a). However, when the time ofPMA lengthened up to 10 minutes, the VFB shift was recovered on a levelwith PMA-only treatment without any degradation of electricalcharacteristics as shown in Figure 3-35 (c). On the other hand, in the caseof spiked PMA at 300 o C, the VFB shift was recovered on a level with PMA at250 o C for 10 minutes despite of spiked PMA as shown in Figure 3-35 (d).However, when the time of PMA lengthened up to 10 minutes, somedegradation of electrical characteristics such as a decrease of capacitancevalue or an increase of hysteresis width appeared, although the VFB shift wasrecovered on a level with PMA-only treatment as shown in Figure 3-35 (f).From these results, it was found that the combination of PDA andPMA was considerably effective in the suppression of VFB shift withmaintaining the capacitance value. However, it was also found that PMAfor aluminum upper electrodes were highly sensitive to the combination ofthe annealing temperature and time, therefore it is anticipated thatoptimizing the condition of the combination of PDA and PMA could make itpossible to suppress the VFB shift with remaining high capacitance value.- 60 -