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

1.1.2 Limits of Silicon Dioxide (SiO2) ) as Gate InsulatorTo downsize the size of MOSFET, however, brings various difficultiesat the same time. One of them, considered as the decisive factor in future LSItechnology, is limits of SiO2 as gate insulator. As mentioned in formersection, shrinking the devices has brought magnificent improvement in LSItechnology. At the mention of gate insulator, SiO2 had been used as gateinsulator since MOSFET was invented because SiO2 has good property suchas high stability with silicon substrate at high temperature process or lowdensity of fixed charge, defects in bulk and at the interface. Consequently,SiO2 had played a significant role of MOSFET and been downsized over along period of time.It is said recently, however, that Thinning down SiO2 has beenreaching limits because of direct tunneling current. Table 1-2 shows theelectrical properties for 1 nm thickness SiO2 gate insulator. This table saysthat leakage current density reaches 100 A/cm 2 and, to make matters worse,when SiO2 thickness become below 0.8 nm, leakage current density willincrease over 1 kA/cm 2 caused by direct tunneling effect. Figure 1-3 showsthe schematic band diagram explaining direct tunneling mechanism. Incase of the thick insulator, that works as a barrier for carriers. Therefore,leakage current remains low. In case of thin insulator, however, thequantum effect can not be negligible and carriers can get to pass through theinsulator directly. Consequently, leakage current becomes hugeexponentially. This undesirable effect will lead the increase of powerconsumption and degradation of LSI reliability and these unacceptablephenomena must be averted.Table 1-3 shows technology roadmap for various element of MOSFET.This roadmap indicates the value of EOT (Equivalent Oxide Thickness) willreach 0.9 nm in 2007 and 0.5 nm in 2016. However, it is said that practicalsolutions to realize EOT=0.9 nm are not known yet.From the foregoing, it is considered that revolutionary change to solvethese problems is strongly required and one of the answers is to replace SiO2to new material.-4 -