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 (V_FB) 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 V_FB shift which increases and eventually saturates with increasing Al₂O₃ DL thickness. Using the parallel conductance method, the interface trap density (D_it) of each device was all calculated within 3.5 × 10¹¹ eV^–1 cm^–2 with a small hysteresis window. This work achieves a low D_it and a large stable positive V_FB shift through in situ ALD Al₂O₃ dipole first process. The VBO characterization of DL interfaces reveals a clear physical mechanism to deeply understand the V_FB shift in interface dipole engineering (IDE).