摘要:

We report an optical, interferometric technique for measuring the temperature of semiconductor substrates during heating or cooling, which is applicable in vacuum. The technique circumvents many of the problems associated with thermocouple or pyrometer measurements. A low‐power infrared (IR) laser (e.g., λ=1.15‐μm He–Ne laser) having an energy below the band gap is directed at a wafer that is polished on both sides, where either reflected or transmitted laser light is detected by a photodiode. Interference results between reflections off the front and back surfaces of the wafer. As the temperature of the wafer is either increased or decreased, the temperature dependence of the refractive index, along with a smaller contribution from thermal expansion, causes the optical path within the wafer to change by λ/2n(i.e., a full interference cycle) for every ∼3 K for a typical Si, GaAs, or InP wafer thickness of 500 μm. Consequently, temperature changes of ±0.2 K are easily detected. This technique, has been used between room temperature and 600 °C on GaAs substrates in a low‐pressure metal‐organic chemical vapor deposition (MOCVD) system, and in an ultrahigh vacuum thermal desorption experiment. This method can be used well below room temperature, as well as at temperatures above 650 °C with the optimum choice in laser wavelength. Application of this method to other processes such as molecular beam epitaxy (MBE), reactive ion etching, and rapid thermal processing should be straightforward. We also describe a refinement of the method for measuring the sign, as well as magnitude of temperature changes for typical, slightly tapered wafers during heating or cooling cycles. In this case the reflected laser beam contains a series of parallel lines that move toward the thinner end of the region probed by the laser beam as the temperature increases. Sensing the direction that these spatial interference fringes move can be used to determine whether the sample is heating or cooling.

ISSN:0734-2101    

DOI:10.1116/1.576993

出版商:American Vacuum Society    

年代:1990

数据来源: AIP

ISSN:0734-2101    

DOI:10.1116/1.576994

出版商:American Vacuum Society    

年代:1990

数据来源: AIP

摘要:

X‐ray photoelectron spectroscopy (XPS) spectra have been obtained for TiNx, withx=0.25, 0.50, and 1.0, as determined by Rutherford backscattering (RBS) analyses, and with no detectable oxygen content. We find the shape of the Ti 2ptransition to be strongly dependent upon the nitrogen content, and interpret the spectrum as a mixture of Ti and TiN. TiN1.0samples with varying oxygen content were also examined, and the oxygen content serves to increase the background step in the Ti 2ptransition. Angle resolved measurements indicate that the inelastic scattering due to oxygen is superimposed over an intrinsic satellite structure in the Ti 2ptransition. Atom ratios, N/Ti, cannot be accurately determined by XPS without standardization. The binding energy of the Ti 2p3/2transition occurs at 454.5 eV and the N 1stransition occurs at 396.7 eV. The oxygen that is present in TiN at concentrations up to 12 at. % is most likely bound to Ti as TiO rather than TiO2. Valence band measurements agree well with previous reports.

ISSN:0734-2101    

DOI:10.1116/1.576995

出版商:American Vacuum Society    

年代:1990

数据来源: AIP

摘要:

The overlayer method for determining the attenuation length was simulated by the Monte Carlo method. The theoretical model was based on the elastic scattering cross sections resulting from the partial wave expansion method. Multiple elastic electron collisions in the solid were considered. Calculations were made for MgKα excited silver 3d photoelectrons ejected in the silver overlayer. The overlayer was ‘‘deposited’’ on a number of substrates having a wide range of atomic numbers. It was found that the values of attenuation length cover a wide interval (9.14–13.44 Å). The inelastic mean free path for Ag 3d photoelectrons assumed in calculations was equal to 13 Å. This effect is due to elastic photoelectron collisions. It turned out that the attenuation length depends on the substrate material, the range of the considered overlayer thickness, and the geometry of measurements. Thus, the overlayer experiment can provide any value of the attenuation length for considered photoelectrons from the above interval by suitable selection of the experimental conditions. The results obtained here, together with experimental problems in producing well characterized thin films, explain the scatter in the published experimental values of the attenuation length. The reliability of the theoretical model is extensively discussed.

ISSN:0734-2101    

DOI:10.1116/1.577041

出版商:American Vacuum Society    

年代:1990

数据来源: AIP

摘要:

Microhardness measurements were carried out on silicon, boron, boron nitride, and nickel films deposited on polished stainless steel substrates. A titanium diboride film on a sapphire subsubstrate was also examined. It is shown that a log–log plot of indentation size versus applied load (the Meyer plot) reveals the point at which the substrate begins to influence the hardness measurements. The ratio of indentation depth to film thickness at the critical point varied from 0.06 to 0.4 depending on both film and substrate hardness. The microhardness numbers differ from those calculated from data in the composite (film plus substrate) region by proposed formulas.

ISSN:0734-2101    

DOI:10.1116/1.577042

出版商:American Vacuum Society    

年代:1990

数据来源: AIP

摘要:

Abinitiolocal spin density method has been used to investigate chemical bonding of aluminum with polyimide surfaces. We focused in this work on the carbonyl group, which is, as demonstrated by x‐ray photoelectron spectroscopy (XPS) and high‐resolution electron energy loss spectroscopy (HREELS), the active site, at least at low metal coverage. We found that the formation of a linear complex C–O–Al is favored over other positions in the vicinity of carbonyl group. The vibrational frequency corresponding to oxygen–aluminum stretching is calculated and compared with HREELS data. We also calculated core level chemical shifts. The agreement with XPS results is satisfactory. Finally, we suggest a mechanism for the adsorption of Al on polyimide surfaces.

ISSN:0734-2101    

DOI:10.1116/1.577043

出版商:American Vacuum Society    

年代:1990

数据来源: AIP

摘要:

The permanent presence of clusters on their own solid surface is shown to modify particle emission. These modifications affect atom/molecule emission, electron emission, and photon emission from pure metallic surfaces at a vacuum interface. Data for refractory metals, particularly for tungsten, are scrutinized for effects from these bound clusters, or Maxwell–Boltzmann (MB) particle aggregates, which do not exhibit a crystalline structure but are nevertheless part of the surface. It is shown that the so‐called work function temperature dependence can be alternatively accounted for by the presence of MB emission sites, and that the descriptions of mass evaporation and radiant heat emission are refined. In the case of photon emission, a complementary gas‐like line radiation emerges when measurements and the classical free‐electron theory in the near‐infrared and visible range are examined in the context of our postulate. Actual observations of individual particle behavior on pure surfaces are enumerated, and a theoretical backup for the predicted area ratio of MB sites to total sites is given.

ISSN:0734-2101    

DOI:10.1116/1.577044

出版商:American Vacuum Society    

年代:1990

数据来源: AIP

摘要:

The growth of polycrystalline Ni–Al bilayers deposited in ultrahigh vacuum (P<10−9Torr), and their modification by annealing are studied by Auger and photoemission spectroscopy. At room temperature, Ni deposition on Al causes a chemical shift of the 68‐eV Al Auger line and photoemission shows that the Ni 3dvalence‐band states for thin Ni overlayers are narrower and shifted away fromEfwhen compared to Ni metal. For Al deposited on Ni, the 68‐eV Al Auger line also undergoes a chemical shift and photoemission shows the Ni 3dvalence band is modified by the appearance of a new state at higher binding energy. Based on comparisons with photoemission and Auger data presented by others for Ni–Al intermetallic compounds, and photoemission, ion channeling and ion scattering results published for the chemically similar Pd–Al system, we conclude that polycrystalline Al and Ni films partially intermix and form a NiAl3‐like intermetallic compound at room temperature. We believe this Ni–Al compound may be found at the thin‐film interface, at grain boundaries or on the surface of 3‐D Ni or Al islands. Heating Ni/Al bilayers at 600 K promotes Al out diffusion and heating at higher temperatures leads to the formation of other Ni–Al compounds.

ISSN:0734-2101    

DOI:10.1116/1.577045

出版商:American Vacuum Society    

年代:1990

数据来源: AIP

摘要:

A cryogenic diffusion pump has been developed and tested. It uses the main constituent of the fusion reactor exhaust gas, i.e., deuterium–tritium (D–T), as a working fluid in a diffusion pump operating at low temperature, to separate and compress the minor constituent4He. Since a suitable tritium‐handling facility was not available, a prototype was tested using mixtures of deuterium with 1%, 2%, and 4% helium. As the deuterium is pumped by cryocondensation at 4 K, the entrained helium is staying in the gas phase, is compressed, and leaves the pump outlet at pressures up to 80% of the total inlet pressure. Compression ratios of up to 80 (for 1% helium) and inlet pumping speeds ranging from 1 to 2 m3 s−1have been measured for operating pressures between 3 and 10 Pa. Deuterium carry‐over into the helium exhaust was below the detection limit of the equipment. A design is presented incorporating the cryogenic diffusion pump in a complete fusion reactor forevacuum system, including the separation of impurities from hydrogen isotope mixtures.

ISSN:0734-2101    

DOI:10.1116/1.577047

出版商:American Vacuum Society    

年代:1990

数据来源: AIP

摘要:

A compact UHV‐compatible sample manipulator with three rotational and three translational degrees of freedom is described. The manipulator head has less than 25 mm radius and is completely manufactured from nonmagnetic materials. With liquid nitrogen as a coolant temperatures of 100 K can be achieved.

ISSN:0734-2101    

DOI:10.1116/1.577048

出版商:American Vacuum Society    

年代:1990

数据来源: AIP