Characterization of Bandgap Engineering on Operative Transistor Devices by Spectral Photon Emission

Abstract

In modern IC technologies, it is very common to use germanium enriched silicon in order to increase field effect transistor (FET) channel carrier mobility for high performance. The germanium content modifies the effective semiconductor band gap EG. Thus, the bandgap energy EG is an important technology performance parameter. EG can be obtained in an LED-like operation of electronic devices, requiring forward biased p-n junctions. P-n junctions in FETs are source or drain to body diodes, usually grounded or reversely biased. This investigation applies a bias to the body that can trigger parasitic forward operation of the source/drain to body p-n junction in any FET. Spectral photon emission (SPE) is taken here as non-destructive method to characterize engineered bandgaps in operative transistor devices, while the device remains fully functional. Proving this technique with the nominal silicon bandgap on an (unstrained) 120nm technology FET, the characterization capability for bandgap engineering is then successfully demonstrated using SiGe:C HBT. In IC technology, Ge enriched silicon is recently often used to increase channel carrier mobility. As a next step, 14/16nm p-type FinFET devices have been investigated by applying a bias voltage to the body and thereby activating one of the body/diffusion p-n junctions in forward bias. By measuring the spectral distribution of emission intensity through the backside of the operating device with an InGaAs detector, EG of the engineered bandgap can be determined in the FinFETs as well, in case of the investigated p-type FinFETs to 0.84 ev. This opens a new path for contactless fault isolation by quantitative local determination of bandgap engineering.