Technology
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.
Second Harmonic Generation Overview
Non-destructive surface + subsurface analysis
High in-line throughput
No sample preparation
No consumables or reagents
Non-contact optical technique
Patterned and blanket wafers
Second Harmonic Generation Uses
Charge trap density
Strain/Stress
Trace metal contamination
Structural defects
Critical dimension measurements
Thin film quality
Technical Papers
-
(Semicon Korea 2016, MI Forum)
-
(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.
-
(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.
-
(ASMC 2018)
Substrate resistivity stability has become the most critical control for radio frequency (RF) device manufacturing. In this paper, we demonstrate nonlinear optics based metrology to measure electrically active oxygen interstitial sites (Oi) in high resistive bulk Si wafers, which are vulnerable to electric and mechanical property drift during device fabrication. Time dependent second harmonic generation (TD-SHG) governed by electric-field induced second harmonic (EFISH) effect provides consistent detection of thermal donors originating from Oi distributed near Si interface. The successful concept proof can be extended to test pad design for in-line monitor of substrate resistivity variations from annealing processes.