Optical Second Harmonic Generation (SHG) is a non-destructive, contactless, optical characterization method for characterizing surfaces, interfaces, thin-films, as well as bulk properties of materials.
In the SHG process, two photons of one energy incident upon a sample material generate a single photon of twice that energy. This process integrated over the many photons emitted from a laser source create a substantial number of doubled-energy photons, which are detected as the SHG signal. The values and time dependence of the SHG signal contain information about the material system being tested.
The Second Harmonic generated by laser irradiation occurs in places where symmetry in the material is broken, such as at hetero-interfaces and various types of crystalline defects. In non-centrosymmetric materials, such as III-V, Second Harmonic will also be generated from the bulk material.
Rapid Non-Destructive Detection Of Sub-Surface Cu in Silicon-On-Insulator Wafers by Optical Second Harmonic Generation (ASMC 2015)
Abstract - Time dependent second harmonic optical signals were measured across silicon-on- insulator (SOI) wafer coupons contaminated by Cu-63 ion implanted into the buried oxide (BOX) and near the SOI/BOX and BOX/Bulk interfaces. Average signals after 1 second of exposure for all spatial points were compared between wafers and used to differentiate contamination levels post ion-implantation.Non-Destructive Contamination Detection in Thick and Extremely-Thin SOI (ISTFA 2015)
Non-destructive optical second harmonic generation (SHG) is shown to be an effective method for detecting surface and subsurface non-visual defects in commercial thick and extremely-thin(ET) SOI wafers. A method is demonstrated for removing contributions (noise) from layer thickness variations observed in thick SOI, increasing the sensitivity and enabling detection of trace surface metal contamination. Sub-surface contamination, otherwise missed by the standard flow of non-destructive characterization methods, is shown to be detected by SHG.