First Demonstration of BEOL Wafer-Scale All-ALD Channel CFETs Using IGZO and Te for Monolithic 3D Integration

In this work, we demonstrated for the first time Back-End-Of-Line (BEOL) compatible complementary field-effect transistors (CFETs) with wafer-scale all atomic-layer-deposited (ALD) channels for monolithic 3D integration. A p-type transistor based on Tellurium (Te)/Tellurium oxide (TeOx) heterostructure was fabricated on top of an InGaZnO (IGZO) n-type transistor using a common gate structure. An excellent IGZO device performance was achieved with an on-current (Ion) of $1\text{mA}/\mu\mathrm{m}$ at $\mathrm{V}_{\mathrm{d}\mathrm{s}}=1$ V in an enhancement-mode operation with a channel thickness $(\mathrm{T}_{\mathrm{c}\mathrm{h}}$) of 2 nm. The uniform wafer-scale growth of p-type semiconductor Te was achieved by introducing methanol in ALD process. Transistor arrays were measured on a four-inch wafer, demonstrating good uniformity and yield based on statistical electrical characterization. The ALD CFET-inverters were fabricated and confirmed by cross-sectional scanning transmission electron microscopy (STEM). They exhibit good electrical performance with a high gain of 116.5 V/V and a large noise margin of 2.2V (88%) at VDD = 5 V. The thermal budget of the entire ALD-CFET fabrication process is 225°C and BEOL compatible.