(Invited) Second Harmonic Generation: A Powerful Non-Destructive Characterization Technique for Dielectric-on-Semiconductor Interfaces

The quality of interfaces between dielectrics and semiconductors has a tremendous impact on the performances of semiconductor devices. High-k dielectrics are omnipresent in the gate stack of advanced MOSFETs. They are also used as passivation layers for silicon in fields such as solar cells [1] or image sensors [2]. When referring to passivation, two mechanisms can be identified: chemical passivation (quantified by the interface state density, Dit) and electric-field passivation (quantified by fixed oxide charge density, Qox). An ideal characterization method for passivated silicon should give access to both chemical and field-effect relevant quantities (ideally being able to distinguish them) in a non-destructive way. Among the commonly used techniques, we can cite electrical methods based on current or capacitance monitoring of simple test devices [3], Corona characterization of semiconductors [4], carrier lifetime extraction [5] conducted through photoconductance or photoluminescence decay measurements, etc. The choice among these several options is based on criteria such as sensitivity, non-destructiveness, possibility of direct on-wafer probing without any additional device fabrication steps, ability to discriminate Dit and Qox, capability to provide a high spatial resolution. A recent technique which could meet all these criteria is the second harmonic generation (SHG) [6], provided that an appropriate calibration method is developed for Dit and Qox extraction.