摘要:

We have performedabinitiopseudopotential calculations of three alternative structures of the GaAs(001) surface to examine the dependence of the reflectance anisotropy spectrum (RAS) upon the precise surface configuration. Spectra were calculated based upon a hypothetical (2×1) surface, a (2×4)‐β surface using experimentally measured atom positions, and a (2×4)‐β surface using atom positions given by total‐energy minimization. It was found that the RA spectra depended significantly upon the atom positions, and in particular, that proper surface relaxation, including the Ga layer below the surface, was necessary in order to account for the low‐energy (2.5 eV) feature in the experimentally observed spectrum.

ISSN:1071-1023    

DOI:10.1116/1.587231

出版商:American Vacuum Society    

年代:1994

数据来源: AIP

摘要:

Terrace width distributions have been calculated from scanning tunneling microscopy (STM) images of molecular‐beam epitaxy (MBE)‐grown GaAs(001) surfaces misoriented by both 1° and 2° towards the (111)A direction. This analysis reveals a peak in the terrace width distribution at approximately 40–50 Å, regardless of the original miscut, with larger terraces forming in order to preserve the angle of vicinality. Growth of a tilted superlattice (TSL) improves the periodicity of the surface. A statistical analysis of the STM image of a 1° TSL capped with three monolayers of GaAs reveals a bell‐shaped distribution of terrace widths with a peak at the average terrace width. These results suggest that MBE growth of vicinal GaAs(001) does not result in equalized steps but that the growth of a TSL does tend towards step equalization. The differences between these two growth regimes are discussed.

ISSN:1071-1023    

DOI:10.1116/1.587232

出版商:American Vacuum Society    

年代:1994

数据来源: AIP

摘要:

We present a coverage dependent structural study of Na adsorption on the Si(111)2×1 surface by photoemission extended x‐ray‐absorption fine‐structure, core‐level, and valence‐band photo‐ emission spectroscopies using synchrotron radiation. In the submonolayer coverages, our results indicate the existence of two Na adsorption sites having a large difference in ionicity. Furthermore, a clear ionic to covalent transition is observed when completing the sodium monolayer saturation coverage, which corresponds to the alkali atom adsorbed on a threefold hollow site. These results indicate a very different behavior for the Na adsorption on Si(111)2×1 when compared to the Si(100)2×1 surface, where the Na–Si bond remains covalent in nature, even at low coverages.

ISSN:1071-1023    

DOI:10.1116/1.587233

出版商:American Vacuum Society    

年代:1994

数据来源: AIP

摘要:

The thermal reactivity of NH3with Si(001), Ge(001), Si1−xGex(001), and thinly Ge‐covered Si(001) or Si‐covered Ge(001) surfaces has been studied by means ofinsitux‐ray photoelectron spectroscopy in a temperature domain (T∼600 °C) compatible with the usual growth of Ge‐Si based heterostructures. A very marked difference between Si(001) and Ge(001) initial sticking coefficients is found, the latter surface being totally inert against nitridation by NH3in contrast with the Si(001) surface. This nitridation selectivity provides easy access to information about surface termination in different situations where Si and Ge are potentially mixed, the reactivity depending on whether Si appears at the reactive interface or not. As a test, comparing the nitrogen uptake curves in the early stages of NH3exposure, for all the studied structures except Si(001), a Ge‐like initial sticking coefficient or a non‐nitriding behavior is found. This is fairly explained on the basis of the well‐known concepts of the Stranski–Krastanov growth mode for the Ge/Si system and by Ge surface segregation for the Si1−xGexand Si/Ge systems. Our result also implies the need of plasma‐assisted treatments in order to achieve simultaneous Si and Ge nitridation of SiGe alloys.

ISSN:1071-1023    

DOI:10.1116/1.587234

出版商:American Vacuum Society    

年代:1994

数据来源: AIP

摘要:

The growth and the (electronic) structure of a single layer of aluminum on the Si(100) surface are examined by means of first principles calculations. The calculated local density of states is used to interprete scanning tunneling microscopy data. We identify the adsorption sites that give rise to the polymerization‐like one‐dimensional growth of Al. The Al‐induced surface states of thep(2×2) covered Si(100) surface are calculated. The surface bandgap is increased, as compared to the clean Si(100) surface, which means that the first adsorbed Al layer passivates the surface electrically.

ISSN:1071-1023    

DOI:10.1116/1.587235

出版商:American Vacuum Society    

年代:1994

数据来源: AIP

摘要:

Upon room‐temperature deposition of minute amounts of Cs on InAs(110) surfaces, one induces probably the highest Fermi‐level pinning position (≊0.6 eV) for a semiconductor above the conduction‐band minimum. Synchrotron‐radiation core‐level photoemission spectroscopy was used to follow the Fermi‐level movement from the shift of the In 4dand As 3dcore levels as a function of Cs coverages at room temperature. Already at very low coverages the Fermi level reaches an extremely high maximum above the conduction‐band minimum. The maximum of the Fermi‐level position correlates fairly well with the ionization energy of the individual atoms, as expected in the framework of the theory of donor‐type surface states induced by metallic adatoms. We thus consider that individual Cs adatoms produce donor‐type surface states placed at ≊0.6 eV above the conduction‐band minimum. This induces a very strong downward band bending which suggests the existence of a two‐dimensional electron gas at the open, nearly clean InAs(110) surface.

ISSN:1071-1023    

DOI:10.1116/1.587236

出版商:American Vacuum Society    

年代:1994

数据来源: AIP

摘要:

The macroscopic electronic behavior and atomic arrangements of the GaAs surfaces immersed in HCl solution were studied by surface current transport (SCT), band‐edge photoluminescence (PL), atomic force microscopy (AFM), and x‐ray photoelectron spectroscopy (XPS). SCT measurements indicated reduction of the surface band bending on immersion into HCl solution for bothn‐ andp‐type materials. A remarkable increase of the band‐edge PL intensity was also observed. In the AFM image taken in HCl solution, the (001) surface showed an array of atoms along [110] and [1̄10]direction with the spacing of 4.1 Å, indicating presence of a (1×1) structure. Similarly, (1×1) images with threefold symmetry were observed on the (111)Aand (111)Bsurfaces. The XPS analysis of the GaAs surfaces after immersion into HCl solution detected a monolayer level presence of gallium chloride. These results indicate that bond termination on the GaAs surface by adsorption of Cl atoms to surface Ga atoms realizes a nonstrained regular (1×1) passivation structure which removes surface states from the band‐gap region.

ISSN:1071-1023    

DOI:10.1116/1.587237

出版商:American Vacuum Society    

年代:1994

数据来源: AIP

摘要:

U.S. manufacturing capabilities are a key component of our global economic competitveness. Because the U.S. fell behind in several important manufacturing industries—especially in competition with the Japanese—federal attention to the health of these industries has grown. The Japanese cut into U.S. leadership through their attention to quality and continuous improvement. Current challenges in the field include reaping productivity benefits from computerization, developing environmentally friendly manufacturing methods, and shifting the federal research and development (R&D) emphasis from military defense to industrial R&D, including manufacturing technologies. Current federal proposals to increase federal support of manufacturing technologies may play an important role in future competitiveness of U.S. industry. The challenge is to grow these programs fast enough to meet the goals of defense conversion, yet not so fast that we do them poorly. Recommendations are offered on practical ways to target, adjust and apply these proposals.

ISSN:1071-1023    

DOI:10.1116/1.587238

出版商:American Vacuum Society    

年代:1994

数据来源: AIP

摘要:

While progress in the microelectronics industry is gated by the frontiers of high technology and its underlying science, competitiveness in this industry is determined at least as much by how effectively the relevant science and engineering are integrated to address those issues central to manufacturing. Competitive manufacturing places a premium on such factors as rapid learning in technology development and yield enhancement, process and factory control, minimization of capital costs, and equipment and product reliability, all factors which synthesize the individual science and engineering elements associated with microelectronics technology. This paper is a primer for research aimed at impacting microelectronics manufacturing science and technology. After presenting an overview of competitiveness requirements for manufacturing, it focuses on strategic elements: advanced process equipment, process/materials characterization and real time process control, defect identification/control and reliability, three‐dimensional processing and manufacturability, and process integration.

ISSN:1071-1023    

DOI:10.1116/1.587239

出版商:American Vacuum Society    

年代:1994

数据来源: AIP

摘要:

A number of system concepts in which the integrity of substrate surface and film interfaces are preserved are discussed. This includes stand‐alone tools with internal clean air or nitrogen facilities with wafer transfer between such tools in clean containers (‘‘minienvironments’’) and single‐wafer and batch‐type cluster systems in which the processing and wafer transfer modules are physically connected. Depending on the cleanliness requirements, wafer transfer and processing are done in pure atmospheric nitrogen, low‐pressure nitrogen, or vacuum. An analysis is given in which the ambient requirements are related to surface reactivity, wafer transfer time, and acceptable surface contamination level. Trade‐offs in terms of capital cost, throughput, flexibility, and film quality are analyzed. A number of different system concepts combining wafer preclean, thin oxide growth, and poly‐Si deposition processes are analyzed in terms of their economical performance. It appears that single‐wafer systems have a logistic advantage in terms of short cycle time and wafer inventory; however, the cost per wafer of batch‐type systems is considerably lower than single‐wafer ones. It is shown that the optimum choice between (fast, high‐temperature) single‐wafer and (slow, low‐temperature) batch‐type systems in terms of process performance depends on physical parameters such as activation energy and the occurrence of undesired, competing, processes.

ISSN:1071-1023    

DOI:10.1116/1.587240

出版商:American Vacuum Society    

年代:1994

数据来源: AIP