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

Abstract

Al 2 O 3 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 Al 2 O 3 thicknesses were prepared. Through X-ray photoelectron spectroscopy (XPS) analysis, interface band alignments can be extracted before and after the Al 2 O 3 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 Al 2 O 3 DL, respectively. More detailed XPS results indicate that the dipole formed at SiO 2 /Al 2 O 3 plays a dominating role benefiting the desired positive flat-band voltage (V FB ) shift, while conversely, the dipole at Al 2 O 3 /HfO 2 has an opposite effect minorly. Tested capacitance−voltage (C−V) curves show that a 0.86 nm (10 cycles) Al 2 O 3 DL can induce a 330 mV positive V FB shift which increases and eventually saturates with increasing Al 2 O 3 DL thickness. Using the parallel conductance method, the interface trap density (D it ) of each device was all calculated within 3.5 × 10 11 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 Al 2 O 3 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).