Search

The energy distributions of electron emission from a Schottky emitter have been studied at tip temperatures from 1450 to 1800 K and angular current densities from 0.1 to 240 μA/sr. We have observed broadening of the energy distribution, with increase of angular current density and decrease of tip temperature, from 0.4 to 1.32 eV resulting from electron tunneling and electron–electron interaction. Good agreement between the experimental results and predictions from Monte Carlo simulation of the emission process is observed.

This paper addresses the kinetics and related mechanisms of non‐self‐limiting nature of Si reduction of WF6 in cold wall systems for the first time. The growth of such films in low‐pressure chemical‐vapor deposition (LPCVD) and ultrahigh vacuum (UHV) systems is compared. Both systems produce non‐self‐limiting, uniform, controllable, nonporous films. The growth is controlled by process parameters such as the wafer temperature and WF6 concentration at the wafer surface. The order of the Si reduction reaction is 0.5 in the concentration of WF6. The tungsten films deposited in the LPCVD system contaminated with water vapor are thicker than the films grown in the UHV system even when the temperature is below 450 °C. Such thicker films are produced as a result of the formation of an amorphous W‐O layer. From the thermodynamic considerations, the origin of W‐O layer is attributed to a parallel reaction between water vapor, WF6, and substrate Si. The beneficial role played by the W‐O layer is that it prevents any volume shrinkage of the converted layer and restricts lateral encroachment. In the absence of such a layer as in the case of the UHV system, severe volume shrinkage and encroachment are observed. A theoretical model together with physical mechanisms explaining the non‐self‐limiting phenomenon are proposed. The mechanism suggests that a fine‐grained W structure surrounded by a W‐O layer, formed in the LPCVD system, assists faster out‐diffusion of Si through the tungsten films compared to the UHV system. The higher values of the diffusion coefficient for Si out‐diffusion through films grown in the LPCVD system as compared with the UHV system support this mechanism. The out‐diffused Si is substituted to W by reduction reaction to complete the film growth.

In this communication, we present a study of tip artifacts in atomic force microscope images of nanometer-scale cellular structures created on germanium surfaces by ion bombardment. It is demonstrated that the appearance of a columnar/granular morphology is due to severe image distortion when the tip size is comparable with the mean cell/hole diameter. These tip artifacts can often be deconvoluted by inverting the image and the lateral extension of the cell/hole can be reproduced with reasonable accuracy.

Common ion sputtering techniques for depth profiles can cause buildup of charge in low‐conductivity regions such as p‐n junctions in semiconductors, leading to erroneous results. We analyzed Ga0.1Al0.9As liquid phase epitaxial (LPE) layers on GaAs with secondary ion mass spectrometry (SIMS) and observed that the profiles of 69Ga+ and 27Al+ in the low‐conductivity region of these Zn‐diffused LPE layers were a function of the sample bias. We noticed that this artifact was due to the shift and broadening of the secondary ion energy distributions caused by positive charging of the specimen surface. We also found that this could be effectively remedied by integrating the secondary ion yields over a wide energy range. The use of an electron flood gun reduced this charging effect, but complete charge compensation was not achieved even at electron current densities far exceeding the ion current density. This can be explained by the fact that the electron‐induced secondary electron coefficient of GaAlAs is larger ...

Normalized ionization probabilities α+ are reported for binary Fe‐Ni alloys under O+2 bombardment at a 45° incidence angle. It is shown that the dependence of α+ on the composition is much smaller than at normal incidence. Photoemission spectroscopy reveals that both nickel and iron remain essentially metallic under oblique‐incidence bombardment, whereas almost complete oxidation occurs at normal incidence. This is attributed to our observation that sputter yields under oxygen bombardment increase much faster than cos α−1.