Study of surface interactions for encapsulation of phase change memory materials

Switching of phase change memory (PCM) materials between crystalline and amorphous phase with electrical pulses and optical properties make it an important candidate for storage class memory and neuromorphic computing. However, PCM materials can be sensitive to air exposure during integration, therefore in-vacuo RIE and encapsulation is important to provide the required oxygen diffusion barrier. Low temperature SiN deposition can be used for low thermal budget integration schemes provided a good film conformality is achieved and damage or etching to the PCM elements is mitigated. In this work, ammonia- (NH3-) free, plasma enhanced chemical vapor deposition (PECVD) SiN films deposited at 40 degrees C (microwave plasma) and 200 degrees C (inductively coupled plasma), are compared and wet etch rates and optical properties are evaluated. NH3- free SiN films were deposited using SiH4, N-2, H-2, and Ar as source gases. Tuning the plasma parameters during encapsulation we observed simultaneous selective etching of GST and controlled SiN film deposition. Hydrogen and argon addition to the plasma mixture provided the main control knob for in-situ GST trimming during deposition, avoiding any type of elemental or structural damage to the GST films.