Characterisation of silicon nitride thin films used as stressor liners on CMOS FETs

Performance enhancement thanks to process induced strained technology is mandatory in recent CMOS technology (90 nm and beyond) to meet the device specifications [1]. In fact the strain induced in the Si channel results in band structure distortion and mobility increase [2]. Silicon Nitride (SiN) Contact Etch Stop Layers (CESL) are widely used for this purpose and bring for example up to 70 % saturation current increase in PMOS transistors. Typical physical and chemical characterisations are usually carried out but mechanical measurements are not common on such high stressed thin films. The purpose of this paper is the measurement of Young's modulus and hardness by nanoindentation and picosecond acoustic. In this paper, we demonstrate that contrary to what the nanoindentation theory expect, one can mechanically characterise our 200 nm thickness high stressed SiN thin film. Moreover, picosecond acoustic appears as the best method for thinner films mechanical characterisation.