CMOS-compatible fabrication of uniform, nm-scale insulating thin films for integrated circuits

Researchers in Stanford's Nanoscale Prototyping Laboratory have developed a low-temperature process for fabricating etch-resistant, pinhole-free spacer dielectrics a few nanometers thick. This technology uses plasma enhanced atomic layer deposition (PEALD) to create a silicon nitride (SiN)-aluminum nitride (AlN) composite layer that has insulating properties comparable to pure SiN. Previously, similar levels of etch rate and leakage current could only be achieved in films deposited at temperatures close to 800^oC. This new PEALD process can be performed at 350^oC, enabling continued scaling of next generation transistors and memory in advanced integrated circuit manufacturing nodes.

Measured wet etch rates for composite films of AlN and SiN as a function of Al content measured by XPS. The x-axis on the top of the graph indicates the AlN:SiN cycle ratio corresponding to the XPS-measured Al content displayed at the bottom. The error bars represent the standard deviation from nine measurements on the same sample.

Stage of Research
The inventors have used this process to fabricate films at 350^oC and demonstrated controlled AlN doping of the composite film. They produced films with wet etch rates in hydrofluoric acid too small to measure and electrical insulating properties essentially the same as pure SiN (50nA/cm2 @ 2MV/cm). Additionally, the AlN-SiN composite film is still easily etched by reactive ion etching in Cl₂ or BCl₃ chemistries similar to processing for SiN etching.