Cross-sectional Scanning Transmission Electron Microscopy Research Articles

Structural defects in 3C–SiC grown on Si by supersonic jet epitaxy

3C–SiC thin films have been grown on Si(001) and Si(111) substrates by supersonic jet epitaxy. Cross-sectional high resolution scanning transmission electron microscopy (STEM) is used to study the SiC/Si interface structure and defects in the films. The occurrence of twins is evident in the selected area electron diffraction pattern taken from a SiC/Si(111) heterostructure. A 39° angle between twinned and untwinned {111} planes in the [11̄0] projection is confirmed by x-ray pole figure. Twinning is attributed to the growth on the {111} planes. Pure edge misfit dislocations are found at the interface to accommodate the extreme lattice mismatch in SiC/Si(001) heterostructures. A schematic model of the STEM image reveals that a pair of 60° dislocations intersect to form an edge misfit dislocation. A large number of stacking faults and microtwins are present in SiC thin films grown on both Si(001) and Si(111) substrates. The formation of planar defects is attributed to the coalescence of individual three-dimensional islands. Possible methods for the reduction of the planar defects are discussed.

Film properties of Ti/TiN bilayers deposited sequentially by ionized physical vapor deposition

Ionized physical vapor deposition (iPVD) has received much attention as a method for depositing material at the bottom and on the sidewalls of the high aspect ratio features proposed for sub-0.25 micron integrated circuits. In this article, we describe the film properties of Ti/TiN bilayers deposited sequentially using the iPVD technique. The experimental configuration consisted of a planar magnetron sputtering source in combination with an inductively coupled RF plasma. TiN was reactively sputtered from a titanium target which remained non-nitrided throughout the deposition, a process commonly referred to in non-ionized PVD as operating in the non-nitrided mode (NNM). These films were analyzed by cross-sectional scanning electron microscopy and transmission electron microscopy, automated four-point sheet resistance probe, x-ray diffraction, x-ray fluorescence, stress gauge, and Rutherford backscattering. Highly oriented 〈111〉 TiN was observed on 〈002〉 oriented Ti underlayers. At via aspect ratios of 4:1 with vertical sidewalls, bottom coverage approaching 100% was obtained. Varying process parameters did not change the bulk resistivity significantly, and values as low as 23 μΩ cm were measured for the NNM TiN films. Mechanical stress was strongly influenced by substrate temperature, as has been observed for both conventionally sputtered and collimated Ti/TiN. Below 200 °C, the films were highly compressive, but values below 2 GPa were obtained at 400 °C. RF plasma power and pressure were also found to affect stress. Deposition rates of 900 Å/min were measured, corresponding to a specific deposition rate of 1.8 Å/kW s.

A comparison of spectroscopic and microscopic observations of ion-induced intermixing in InGaAs/InP quantum wells

Using n-doped InGaAs/InP multi-quantum-well samples we compare measurements of ion-beam-induced quantum well broadening made by cross-sectional scanning tunneling microscopy and cross-sectional scanning transmission electron microscopy with the broadening calculated from the blueshift of the low temperature photoluminescence peak using different models of the intermixing process. Results are consistent with a simple square well model used to interpret photoluminescence shifts, but disagree with a model of separate Fick’s law diffusion on group III and V sublattices.

Comparison of Film Quality and Step Coverage for Silicon Dioxide Dielectrics Formed by RTCVD Using Tetraethoxysilane and Silane

ABSTRACTRapid thermal chemical vapor deposition (RTCVD) oxides formed using TEOS and oxygen (O2) are compared with RTCVD oxides formed using silane (SiH4) and nitrous oxide (N2O). These oxides were deposited under varying pressure and gas composition to investigate the film step coverage and electrical properties. Cross-sectional scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used in determining the oxide step coverage. Excellent oxide conformality, greater than 90 %, was achieved with SiH4 and N2O over a wide range of aspect ratios. The average breakdown field obtained for the SiH4/N2O oxides is approximately 13 MV/cm, which is greater than values measured for oxides formed by conventional dry thermal process. Oxides deposited using TEOS typically have an average breakdown field of about 8 MV/cm. We conclude that the SiH4/N2O oxide process for the deposition of SiO2 films in a RTCVD reactor is a very promising candidate for sidewall spacer formation in advanced device applications.

Characterization of vertical-cavity semiconductor structures

Several analytical tools are applied to characterize vertical-cavity surface-emitting laser structures grown on GaAs wafers. These epitaxial structures are amenable to x-ray, electron-beam, and optical metrologies. Cross-sectional scanning electron microscopy and transmission electron microscopy were used to measure layer thicknesses and uniformity. Photoluminescence wafer mapping was used to determine alloy composition uniformity across the wafer. Photoreflectance was also used to determine alloy composition. Cross-sectional microphotoluminescence was used to measure average alloy compositions in the top and bottom mirrors. Reflectance spectroscopy was used to characterize the cavity resonances and mirror layers. Double-crystal x-ray diffractometry (DCXRD) was used to characterize mirror layer dimensions, uniformity, and average alloy composition. Excellent agreement was found among these measurement techniques and between simulations and measurements. The results demonstrate the accuracy of the device simulation tools and the applicability of DCXRD in analyzing these structures.

Silicon-on-insulator device islands formed by oxygen implantation through patterned masking layers

Separation by implanted oxygen is recognized as a versatile technology to produce silicon-on-insulator substrates. The lateral isolation of device islands is achieved by subsequent local oxidation or mesa etching of the silicon top layer. In an alternative approach, implantation is performed through patterned masking layers leading to a continuous but nonplanar buried oxide. Thereby, total dielectric isolation (vertical and lateral) of the device island is achieved in a single implantation stage. The masking structures used in this investigation are thermal oxides and polycrystalline silicon layers with window openings as well as patterned wafers formed by local oxidation of the bulk silicon wafers. Oxygen was implanted with energies of 100 and 200 keV to doses up to 2.2 × 1018 O+ cm−2. The resulting structures are studied by cross-sectional scanning electron microscopy and transmission electron microscopy and the effects of mask material and implantation energy are discussed.

Microstructures of TiN films grown by various physical vapour deposition techniques

A study has been made of TiN coatings deposited on steel substrates by five commercially available physical vapour deposition (PVD) methods; low voltage electron beam evaporation, triode high voltage electron beam evaporation, random-arc evaporation, steered-arc evaporation and magnetron sputtering. The microstructure and substrate-film interfacial microchemistry of the films were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM) together with energy-dispersive X-ray spectroscopy (EDX), cross-sectional transmission electron microscopy (XTEM) and scanning transmission electron microscopy (STEM) combined with EDX analyses of XTEM samples. The XRD analyses showed that all the films were in a state of compressive stress with interplanar distances as much as 1.7% higher than reference bulk values. SEM examination revealed only minor variations in surface roughness among the samples except for the arc-evaporated films which contained large droplets and craters resulting from the detachment of droplets. The number density and average sizes of droplets and craters were lower in the steered-arc sample than in the random-arc sample. XTEM analyses showed that all the films had columnar structures with clearly defined substrate-film interfacial layers. The films appeared dense except for the magnetron-sputtered sample which exhibited intercolumnar porosity. STEM-EDX analyses showed large variations in the microchemistry of the substrate-film interfacial regions which consisted, depending on the sample, of renucleated near-surface substrate grains, intentionally (or, in at least one case, unintentionally) introduced foreign material or gas-bubble-like inclusions. However, the microchemistry of these interfacial regions was, in most cases, understandable on the basis of the substrate pretreatment and/or choice of film growth parameters.