Atomic-Layer-Deposited Al₂O₃ Layer Inserted in SiO₂/HfO₂ Gate-Stack-Induced Positive Flat-Band Shift with Dual Interface Dipoles for Advanced Logic Device

Al2O3 has been widely studied as an interface dipole inducer, but a deeper understanding of the physical mechanisms behind is still needed. In our work, using optimized in situ thermal atomic layer deposition (ALD), metal-oxide semiconductor (MOS) capacitors with different Al2O3 thicknesses were prepared. Through X-ray photoelectron spectroscopy (XPS) analysis, interface band alignments can be extracted before and after the Al2O3 dipole layer (DL) was inserted. The shift of valence band offset (ΔVBO) is determined to be 0.41 and 0.48 eV with 10- and 30-cycle Al2O3 DL, respectively. More detailed XPS results indicate that the dipole formed at SiO2/Al2O3 plays a dominating role benefiting the desired positive flat-band voltage (VFB) shift, while conversely, the dipole at Al2O3/HfO2 has an opposite effect minorly. Tested capacitance–voltage (C–V) curves show that a 0.86 nm (10 cycles) Al2O3 DL can induce a 330 mV positive VFB shift which increases and eventually saturates with increasing Al2O3 DL thickness. Using the parallel conductance method, the interface trap density (Dit) of each device was all calculated within 3.5 × 1011 eV–1 cm–2 with a small hysteresis window. This work achieves a low Dit and a large stable positive VFB shift through in situ ALD Al2O3 dipole first process. The VBO characterization of DL interfaces reveals a clear physical mechanism to deeply understand the VFB shift in interface dipole engineering (IDE).