Proton-Induced Mobility Degradation in FinFETs With Stressor Layers and Strained SOI Substrates

Proton irradiation effects on fin-type field effect transistors (FinFETs) are examined from the viewpoint of their electrical-performance parameter of mobility. They are fabricated with various types of combination of strain/stress techniques to control their mobilities. The base stress level is globally modified by means of nonstrained or strained silicon-on-insulator wafers. Some process splits, additionally, receive a local strain tuning with a contact-etch-stop layer (CESL). Both n- and p-type FinFETs are evaluated. A 60-MeV proton irradiation with a fluence of 10¹² p/cm² leads to mobility changes for wide-fin samples: degradation for n-type and enhancement for p-type. These mobility variations can be explained with a change in the number of charged interface traps at the Si and buried-oxide interface. Narrow-fin devices exhibit mobility changes unnoticeable statistically. A comparison with previous studies indicates an elevated source/drain structure plays a role in this mobility preservation. Although the mobility is kept intact in the narrow-fin samples, a close investigation based on a two channel-component model can reveal noticeable mobility variations at a component level. In this study, observed mobility changes are complex depending on the adopted stress techniques as well as process parameters and cannot be explained by the stress levels simply.