Ion Implantation and Synthesis of Materials - Studium

14.2 Issues During Device Scaling 197Fig. 14.3. Two-dimensional boron atomic distributions before and after annealing(calculated by Hong-Jyh Li at International SEMATECH)14.2.2 Hot-Electron EffectIn p-channel transistors, holes are accelerated from the source to the drain. Thevelocity of the hole during this acceleration process can sometimes be highenough to create electron-hole pairs in the channel by collision. The penetration ofholes into the oxide is difficult due to the high potential barrier at the silicon andgate oxide interface; such a barrier for electrons, however, is low. The electronscreated from electron-hole pair generation can be scattered into the gate oxide.Therefore, negative charge is built up in the oxide. This charge accumulation inthe oxide can cause holes to accumulate below the gate, as illustrated in Fig. 14.4.The hot-electron effect causes a reduction in channel length and makes the devicemore susceptible to short-channel effects. One effective way to reduce the hotelectroneffect is to reduce the high electric field in the channel region. Themaximum electric field usually takes place at the boundary between the channeland the highly doped source/drain region. The electric field can be reduced byforming lightly doped-drain (LDD) structures. The details of the LDD dopingmethod will be further discussed in Sect. 14.3.