Bottom-up method for work function tuning in high-k/metal gate stacks in advanced CMOS technologies

In this paper we have studied the application of porphyrin self-assembled monolayers (SAMs) for metal-gate work function tuning in high-k/metal gate technologies. Varying the dipole moment in porphyrin macrocycles by changing its central metal ion has been used to modify the work function. For HFCV analysis, porphyrin SAM was prepared on MOCVD grown hafnium oxide (HfO₂) and on sputtered aluminum oxide (Al₂O₃) gate oxides followed by Al evaporation to form MOS capacitors. UV absorption and FTIR spectra show the formation of SAM on high-k while the thermal gravimetric analysis (TGA) on Zn-porphyrin shows that the molecule is stable upto 450°C and can be effectively implemented in high-k/metal gate technologies involving gate-last CMOS processes.