A Study on P-Type Transition Metal Oxide and 3D Chalcogenide Semiconductor for Monolithic 3D Integration

The semiconductor industry has gained significant achievements in computing performance over the past few decades. However, the difficulties in physically scaling transistors and the memory bottleneck hindered progress. To address the issues, monolithic 3D integration has emerged as a promising solution. One of the key challenges is achieving high hole mobility in p-type semiconductors in the back-end-of-line (BEOL) to enable complementary metal oxide semiconductor transistors in logic and memory. In a BEOL-compatible process, a thermal restriction of below 450 °C is required. Oxide semiconductors are one of the candidate material groups, offering significant advantages in maintaining good electrical properties at low deposition temperatures. Many n-type oxide semiconductors have been discovered, but the lack of p-type oxide semiconductors with high hole mobility has limited applications to unipolar applications. The limitation of low mobility originates from the highly localized O 2p orbitals in the valence band maximum (VBM), resulting in a small curvature of the VBM and a large effective mass. Therefore, a transition metal with orbitals having similar energy to O 2p orbitals is introduced to hybridize and enable a larger band curvature to improve hole mobility. Palladium oxide (PdO) is chosen for investigation, and it is reported that, based on the density of state calculations, its amorphous phase is predicted to have higher hole mobility than the crystalline phase. Furthermore, 3D chalcogenide, zinc selenide (ZnSe), is another strategy for finding high hole mobility semiconductors. The cubic and orthorhombic 3D structures and bonding of chalcogenide-based materials show that the p orbitals of the chalcogens are more spatially extended compared to the O 2p orbitals. Additionally, the energy levels of the chalcogens' p orbitals, which are comparable to the metallic orbitals, are more favorable for covalent bonding and result in a smaller hole effective mass, leading to higher hole mobility.<p></p>