摘要:

Optical second‐harmonic generation (SHG) data are presented on the cleaning of Si(001) surfaces covered with thin (20–40 Å) oxide layers. The removal of an oxide layer by annealing, results in the formation of a 2×1 reconstructed surface and a concurrent increase in second‐harmonic intensity of nearly two orders of magnitude. A comparable signal increase is observed in the transition from an unreconstructed passivated Si(001) surface, produced by etching, to a clean 2×1 reconstructed surface. It is concluded that SHG is very sensitive to the presence of surface states on the 2×1 reconstructed Si(001) surface.

ISSN:0734-211X    

DOI:10.1116/1.585389

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

Controlled expansion of high purity carbon dioxide through a nozzle forms a high velocity ‘‘snow’’ stream that effectively removes both particulate and thin film contaminants from silicon wafer surfaces [W. Whitlock, Presented at the 20th Annual Meeting of the Fine Particle Society, Boston, MA, August 22, 1989 (unpublished); R. Sherman and W. Whitlock, J. Vac. Sci. Technol. B8, 563 (1990)]. This process will clean surfaces leaving no detectable film residue as well as reduce adventitious (native) hydrocarbon surface content. This article discusses the performance of CO2snow cleaning on a variety of materials typically encountered in a surface analysis laboratory. Cleaning tests were performed on metals (aluminum and copper sheets), semiconductors (Si and InP wafers), and insulators (ceramics, laser optics, glass plates, and polymers). Performance is judged primarily through x‐ray photoelectron spectroscopy measurements with primary consideration given to reduction of surface hydrocarbons. These measurements are compared with samples which were cleaned with a conventional solvent process. The results indicate that CO2snow cleaning is comparable to solvent cleaning in its effectiveness for removal of hydrocarbon films. Recommendations are made for the use of CO2snow cleaning in both industrial and laboratory applications.

ISSN:0734-211X    

DOI:10.1116/1.585390

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

Pseudomorphic AlGaAs/InGaAs modulation doped field effect transistors have been fabricated by using methane/hydrogen (CH4/H2) reactive ion etching for gate recessing. Source‐drain resistance and Hall measurements on as etched and annealed samples are presented. The electrical degradation introduced by the plasma can be recovered after annealing at 400 °C. A threshold voltage (Vth) standard deviation of 14 mV over a 5 cm (2 in.) wafer was obtained.

ISSN:0734-211X    

DOI:10.1116/1.585391

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

We have constructed a new scanning tunneling microscope (STM) that usesxandzinchworms for micropositioning in an ultrahigh vacuum environment. One (zinchworm) is for approaching the tip to the sample surface and the other (xinchworm) is for both cleaving the sample and moving the sample to positions of interest. We have demonstrated that this STM is very useful for observing the cross section of a thin epitaxial layer, such as the cleaved (110) surface of a Ga0.47In0.53As/InP multiquantum well (MQW) structure. The STM image of GaInAs well layers and InP barrier layers has been shown to reflect the feature of the MQW potential. Moreover, we have obtained images of the filled states on the group‐V anions in the GaInAs and InP layers.

ISSN:0734-211X    

DOI:10.1116/1.585392

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

Electrochemically polished Au(111) substrates have been investigated by scanning tunneling microscopy in 0.5M NaClO4in absence and presence of Pb underpotential adsorbates. The nm‐scale morphology of the electropolished electrodes features densely terraced dome‐shaped domains with heights up to more than 5 nm, whereas only small atomically flat surface regions of ∼5 nm width are observed. During polarization in the ideally polarizable potential range in absence of Pb adsorbates, considerable smoothening and lateral displacement of the dome‐shaped domains occurs within a time scale of minutes. Extended polarization in presence of a full Pb adsorbate coverage leads to a marked increase in substrate corrugation, up to the scale of several nm. At Pb‐free substrates, controlled variations of the tip‐sample separation in the transition regime from tunneling to point contact exhibit a similar distance dependence of the tip current as observed in previous vacuum studies, and allow for the first time an approximate assessment of the tunneling distance range in an electrolytic system. In the case of Au tips, the transition from tunneling to point contact is observed at tunneling resistances of ∼2⋅104Ω, in good agreement with previous vacuum results. A tunneling regime withRT<107Ω is assigned approximately to a substrate‐tip separation range<1 nm.

ISSN:0734-211X    

DOI:10.1116/1.585393

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

A surface grid assisted charging technique for noncontacte‐beam testing of very large scale integrated package substrates has been developed. Successful charging of packages with a variety of combination of conductor/substrate materials (i.e., Au/alumina ceramic, Mo/alumina ceramic, Solder/polyimide, and chromium/polyimide) has been demonstrated using this technique. In this paper, both theoretical and experimental results concerning the role of a surface grid in addressing various testing issues such as package material parameters, charge localization, secondary electron redistribution, local field effect, and the electron detector response characteristic will be discussed.

ISSN:0734-211X    

DOI:10.1116/1.585394

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

Rapid thermal chemical vapor deposition has been applied towards the growth of Si and Si1−xGexstructures on a 100 Å scale. In this paper the relative merits of gas switching versus temperature switching for the growth of such structures are discussed. Active temperature control in the 600–700 °C range using infrared transmission for temperature measurement is demonstrated. The growth technique is applied to 45 Å period superlattices with individual layer temperature control, and to heterojunction bipolar transistors with near‐ideal electrical characteristics.

ISSN:0734-211X    

DOI:10.1116/1.585395

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

We report on the growth of germanium–silicon and silicon epitaxial layers by ultrahigh vacuum/chemical vapor deposition. When aninsituclean is used, films grown at 600 °C are defect‐free by planar section transmission electron microscopy and no oxygen is detectable by secondary ion mass spectroscopy at the growth interface.Insitudoping has been studied using B2H6/H2and PH3/H2as source gases. Ge0.13Si0.87films doped with boron up to 5×1019cm−3have been grown and sharp doping transitions have been obtained. Phosphorus doping concentrations in silicon are limited by a decrease in growth rate with increasing phosphorus flow rate which is attributed to phosphorus blocking of reaction sites. A model for the decrease in growth rate with PH3/H2flow is proposed which provides a good fit to the measurements.

ISSN:0734-211X    

DOI:10.1116/1.585769

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

Heteroepitaxial Ge films have been deposited on (100) Si substrates at low temperature (325 °C) by electron cyclotron resonance plasma enhanced chemical vapor deposition. The substrates were subjected to aninsituhydrogen/argon plasma etch prior to film growth to remove carbon and oxygen. The surface morphology has been observed with optical and scanning electron and scanning tunneling microscopy. Surface roughness due to three dimensional growth is strongly influenced by ion flux and arrival rate of reactive species on the growth surface. Surface roughness has a detrimental effect on the crystallinity of the deposited films as determined by reflection high‐energy electron diffraction and x‐ray diffraction measurements.

ISSN:0734-211X    

DOI:10.1116/1.585770

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

We are investigating the use of low energy ions (<1 keV) in low temperature thin film growth techniques, ion beam deposition (IBD) and combined ion and molecular deposition (CIMD). In IBD, a thin film is directly grown from a low energy ion beam as the only source of material, while in CIMD, low temperature growth of thin films is achieved by depositing materials simultaneously from a low energy ion beam and one or several molecular beams. A simple model of the IBD process has been developed and accounts for atomic collisions and thermal diffusion during thin film growth. Computer simulation of IBD of Si on Si have been conducted as a function of ion energy to support more quantitatively this physical description of IBD. The results show that the IBD growth mechanism is mediated by the fast diffusing interstitials and establish a low energy limit to achieve epitaxial growth by IBD that depends on the point defect diffusivities. The defect generation has to be confined in the subsurface region in order to favor interstitial recombination with the surface, leading to net thin film growth, and vacancy annihilation to prevent amorphization. The effect of point defect diffusivities on the IBD growth process is also investigated. It is found that a model including fast moving interstitials can account for various experimental observations specific to IBD.

ISSN:0734-211X    

DOI:10.1116/1.585771

出版商:American Vacuum Society    

年代:1991

数据来源: AIP