Norman J. Taylor

A LEED study of the epitaxial growth of copper on the (110) surface of tungsten

Abstract Low-energy electron-diffraction (LEED) has been employed in a study of the epitaxial deposition of copper on a single crystal (110) face of tungsten under ultra-high vacuum conditions. Copper was evaporated at 10 −9 Torr from a Knudsen cell placed in the LEED chamber. The flux of copper at the sample could be determined to an accuracy of ± 10%. Using a fluorescent-display, LEED apparatus, the structure of the deposit was continuously monitored and recorded. Evaporation onto clean tungsten at room temperature resulted in partial alloying and then the formation of well oriented, uniformly thin copper (111) layers. Strong multiple scattering was observed at coverages of between one and two atomic layers. Moderate heating resulted in diffusion into the tungsten and alloy formation. When a half monolayer of oxygen was first chemisorbed on the tungsten, epitaxy was severely inhibited. Very little sign of any ordered copper was apparent after a total flux corresponding to 20 atomic layers. Contributing to this was the apparent very low condensation coefficient for the copper on such a surface. If some physisorbed oxygen was present, in addition to the chemisorbed, there was a marked improvement in epitaxy, though it was still considerably poorer than that on the clean tungsten surface, since a spread in orientation of about ± 2° was observed. New structures involving only the tungsten and oxygen were observed on heating at this stage. Oxygen, when introduced at less than a monolayer coverage of copper, or at any time when the alloy was observed, displaced the copper from the tungsten-copper matrix and left it in well oriented form as on the clean tungsten surface. When the oxygen was introduced into the system after depositing about six atomic layers of the copper onto clean tungsten, no change in the diffraction pattern was observed, indicating that the oxygen was not readily chemisorbed on the copper film at room temperature. On heating, however, it was observed to be bound to the tungsten, while the surface of the copper remained unaffected in structure.

A low energy electron diffraction study of the structural effect of oxygen on the (111) face of a tungsten crystal

A low-energy electron-diffraction study of the structural effect of oxygen adsorption on the (111) face of a clean tungsten monocrystal has been carried out under various conditions of exposure and subsequent heating. The clean tungsten (111) surface is found to be unchanged after heating to temperatures as high as 2650° K. After an oxygen exposure of 5 × 10−6 Torr · sec, heating to 800° K brings about the rapid development of (211) planes, with a well defined surface structure which is stable up to 1800° K. The clean (111) surface is restored by heating to 1900° K for several minutes or 2100° K for several seconds. Other structures all based on arrangements on (211) surfaces are observed at increased exposure. For exposures in the range 10−3 to 10−7 Torr · sec at 300° K and with subsequent heating, three types of patterns are observed separated by disordered transition regions. The inconsistently small quantity of gas measured by the ionization gauge at the high temperature transitions indicates that the strongly bound oxygen leaves as some oxide which condenses on the walls, or that diffusion into the tungsten takes place. Further measurements are required to determine the nature of these high temperature transitions.

Observation of phosphorus pile‐up at the SiO2‐Si interface

The Si oxidation rate at high temperatures is increased by heavy P doping. Sputter ion‐Auger techniques have been used to investigate the oxide thickness and P concentration after 900 °C oxidation with an initial P surface concentration of between 2×1018 and 3.2×1020/cm3. Phosphorus was found to pile up in the Si‐SiO2 interface region. The maximum P concentration near the interface was found to depend on doping and was (at certain P concentrations) an order of magnitude larger than that predicted by redistribution theory. A vacancy–P‐complex model is presented to explain the observed behavior. A correlation between the selective pile‐up of P at the interface and the current gain of planar bipolar transistors is reported.

Crater‐edge profiling in interface analysis employing ion‐beam etching and AES

The crater edge formed in Si‐SiO2 films by appropriate ion‐beam etching provides an angle‐lapped surface analogous to that produced by usual mechanical means; however, the angle can be usefully reduced by 3 orders of magnitude, allowing much greater spatial resolution. Furthermore, in contrast to conventional depth profiling, the separation of the etching and analysis permits repetitive measurements to be made conveniently; a fact of considerable utility in interface analysis.

Auger Electron Spectroscopy of Clean Gallium Arsenide

The electron‐excited Auger spectrum of vacuum‐cleaved GaAs is presented. Measurements were made for initial holes in the L, M, and N shells. The different peaks are identified by their energy and by using trend lines for similar peaks from the elements Z=22 to Z=33.