In situ TEM study of the transitions between crystalline Si and nonstoichiometric amorphous oxide under bipolar voltage bias

Abstract

The electrical responses, either structurally or chemically, at the interface between a SiO2 thin film and a single crystalline Si substrate are an important research subject in Si-based devices. Dielectric breakdowninduced epitaxial migration of Si into SiO2 has been reported as a degradation mechanism in field effect transistors. Here, we show a direct observation of electric field induced conversion of single crystalline Si to nonstoichiometric amorphous oxide starting from the Si/native oxide interface using in situ transmission electron microscopy. We further show that nanocrystalline Si can form in the amorphous oxide under a voltage bias of reversed polarity. Electron energy loss spectroscopy and energy dispersive X-ray spectroscopy analyses indicate that the observed amorphization process was caused by the oxidation of Si and the recrystallization process was caused by the reduction of nonstoichiometric amorphous silicon oxide. Both transitions are a result of field-driven directional migration of oxygen which originally comes from its native oxide layer. Disciplines Engineering Physics | Materials Science and Engineering Comments This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in Tian, Xinchun, Tao Ma, Lin Zhou, Geoff Brennecka, and Xiaoli Tan. "In situ TEM study of the transitions between crystalline Si and nonstoichiometric amorphous oxide under bipolar voltage bias."

In Situ TEM Study of the Amorphous-to-Crystalline Transition during Dielectric Breakdown in TiO2 Film

“…The above experimental observations agree with the polarity-dependent oxygen migration in oxides under electric fields. − Under normal bias, significant lattice shearing took place in the Si substrate, while the W probe was unaffected. Combined with supporting evidence from the EELS spectra, it is plausible that Si was incorporating oxygen from a-TiO 2 , consistent with our previous work on the Si/SiO 2 system . Under reverse bias, the opposite scenario arose: Si remained intact, while the W probe was oxidized and melted.…”

“…Our group has recently developed an in situ TEM technique to apply an extremely high electric field to a desired region of the dielectric for breakdown study . To minimize the possible effects of flashover and surface tracking, we coat the dielectrics of interest on a conductive Si wedge substrate (Figure a) that is attached to one terminal of the voltage source.…”

“…Our group has recently developed an in situ TEM technique to apply an extremely high electric field to a desired region of the dielectric for breakdown study. 25 To minimize the possible effects of flashover and surface tracking, we coat the dielectrics of interest on a conductive Si wedge substrate (Figure 1a) that is attached to one terminal of the voltage source. When a fine W probe that is connected to the other terminal of the voltage source is placed into contact with the dielectric at the apex of the wedge, the region of dielectric at the contact point experiences the highest electric field, thereby localizing the highest probability of breakdown within the observable volume and enabling detailed examination and analysis of the sample during the breakdown process.…”

In Situ Transmission Electron Microscopy Study of Conductive Filament Formation in Copper Oxides

“…In situ TEM techniques using a specimen holder equipped with various capabilities enable the direct characterization of structure and physical properties of materials simultaneously. To study the dielectric breakdown in copper oxides, we coated copper oxides on a wedge shape Si substrate and loaded the substrate on a Hysitron PI95 STEM specimen holder which we have successfully used to study the effects of applied voltages on different oxides [10], [11]. Different parts of the copper oxide coating were selectively studied by placing a W probe in contact with the region of interest.…”

Direct Observations of Field-Intensity-Dependent Dielectric Breakdown Mechanisms in TiO2 Single Nanocrystals

“…11,13,[16][17][18] Studying dielectric breakdown micromechanisms with in-situ TEM must avoid surface tracking in the vacuum, which poses special requirements on specimen geometry and electrode configuration. 19,20 The common approach of specimen preparation from a bulk piece via focused ion beam inevitably leads to contaminated specimens and makes them unsuitable for such studies. 21 Nanocrystals synthesized with wet chemistry would be good specimens for in-situ TEM breakdown studies due to their small dimensions, high purity, 22 and absence of grain boundaries, if they can be individually placed between two electrodes without mechanical damage and chemical contamination.…”