High-Temperature-Stable Polycrystalline ALD-InGaO Channels Enabled by Buffer-Layer Engineering

Oxide semiconductors show promise as DRAM channel materials owing to their low leakage, good mobility, and the possibility of deposition. However, high thermal stability up to 700 °C is essential for DRAM processing, which is challenging for many oxide semiconductors. In this study, crystalline indium gallium oxide (IGO) thin films were deposited on different buffer layers (amorphous SiO2, crystalline ZrO2, and HfO2). When IGO was deposited on the SiO2 buffer layer at a ratio of 5:1, the crystallinity changed rapidly after the post-treatment, and the mobility increased from 61.9 to 96.7 cm2/(V s). This suggests that the SiO2 buffer layer made the sensitivity greater to the annealing temperature. By contrast, the IGO on the HfO2 buffer layer maintained a stable polycrystalline structure even after high-temperature annealing. It exhibited minimal mobility variation from 18.4 to 22.5 cm2/(V s) and demonstrated excellent reliability, with a threshold voltage (VTH) shift of only 0.04 V under positive bias temperature stress at +3 MV/cm and 95 °C. These findings highlight that the surface condition of the buffer layer is crucial for maintaining the thermal stability of crystalline oxide semiconductors. Especially, the polycrystalline IGO remains highly stable even on the HfO2 buffer layer, which is commonly used in DRAM.