(353j) Textured Growth and Electrical Characterization of Zinc Sulfide on Back-End-of-the-Line (BEOL) Compatible Substrates

Scaling of transistors has enabled continuous improvement in the performance of logic devices, especially with recent advances in materials engineering for transistors. However, there is a need to surpass the horizontal limitations in chip manufacturing and incorporate the vertical or third dimension. To enable monolithic three-dimensional (M3D) integration of high-performance logic, one needs to solve the fundamental challenge of low temperature (<400 °C) synthesis of high mobility n-type and p-type semiconductor thin films that can be utilized for fabrication of back-end-of-line (BEOL) compatible transistors.¹ Transition metal oxides are promising n-type materials; however there is a lack of p-type materials that can meet the stringent synthesis conditions of BEOL manufacturing. Zinc sulfide (ZnS), a transparent wide band-gap semiconductor, has shown room temperature p-type conductivity when doped with copper² and crystallizes below 400^oC when grown by pulsed laser deposition (PLD).³ Here, we report growth of crystalline thin films of ZnS by PLD on a variety of amorphous and polycrystalline surfaces such as silicon nitride, (Si_xN_y) thermal silicon dioxide, (SiO₂), hafnium dioxide, (HfO₂), yttrium oxide (Y₂O₃), platinum, sapphire (Al₂O₃), and titanium nitride (TiN). X-ray diffraction shows texturing of ZnS on all surfaces, including when ZnS is directly grown on HF buffered oxide etched silicon. Crystalline quality is investigated using grazing incidence wide angle X-ray scattering measurements. Surface and interface quality is measured using X-ray reflectivity and atomic force microscopy measurements. Electrical characterization of the ZnS films is done by J-V measurements of ZnS on platinum and metal-oxide-semiconductor capacitor (MOSCAP) measurements of ZnS on SiO₂ on heavily doped silicon. The J-V measurements indicate low leakage current on the order of 10^-5 A/cm^-2 with electric field of 0.40 MV/cm² and the MOSCAP characteristics show bilayer capacitor behavior, which points to ZnS being highly intrinsic with very low unintentional, electrically active point defects. Further work on doping ZnS with copper or other p-type candidate dopants are needed to demonstrate ZnS as a dopable wide band gap semiconductor for channels compatible with BEOL manufacturing. This work showcases the capability of novel thin film growth technique of a wide band-gap sulfide semiconductor in BEOL compatible conditions with potential for technological applications in transistor manufacturing.

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2. R. Woods-Robinson et al., Adv. Electron. Mater. 2, 1500396 (2016)
3. 3. M. Surendran et al., Adv. Mater. 36, 2312620 (2024)