摘要:

Incident electrons, ions, and photons stimulate the desorption of surface oxygen from the (110) surface of SnO2. In the case of incident electrons, this oxygen desorption provides an extremely sensitiveinsitumeasure of electron beam effects, by means of the surface conductivity properties of the substrate. Energy relaxation processes other than stimulated desorption also follow the initial excitation, and raise the effective local temperature. Subsequent temperature‐dependent changes in the surface and subsurface composition and structure provide characteristic material‐dependent power dissipation thresholds, which can be detected with great sensitivity. At the (110) surface of the ionic semiconductor SnO2, the thermal threshold or activation energy for ion diffusion is apparently lowered by an electrostatic field, induced by the electron beam in the space‐charge region.

ISSN:1071-1023    

DOI:10.1116/1.584472

出版商:American Vacuum Society    

年代:1989

数据来源: AIP

摘要:

Excimer laser etching of copper using CCl4and CF2Br2vapors is described. These gases, unlike pure halogen gas, are inert toward copper in the absence of light. For pressures of 2–10 Torr, 248‐nm dissociation of CCl4or CF2Br2results in etching that is linear in pressure, and is approximately the same for both gases. At 351 nm, only CCl4causes etching. This wavelength variability, examined together with the gas‐phase absorption spectra, suggests that gas‐phase photolysis occurs prior to etching for CF2Br2at 248 nm, but that a surface mediated dissociation likely occurs for CCl4at 248 and 351 nm. A numerical solution of the one‐dimensional heat flow equation was used to obtain the laser‐induced surface temperature‐time profile for the case of a bare copper surface, and copper covered with differing thicknesses of CuCl. CuCl is the reaction layer assumed to form when CCl4dissociates on copper. Surface melting is not indicated, implying that etching occurs either by transient evaporation (solid→vapor) or by a quantum (nonthermal) process. Numerical solution of an etching model based upon transient evaporation of the CuCl reaction layer gives calculated etch rates that are many orders of magnitude smaller than the experimental rates. It is thus argued that nonthermal photophysical processes are responsible for material removal from the surface. The implications of these results for excimer laser etching of copper in Cl2or Br2gases are discussed.

ISSN:1071-1023    

DOI:10.1116/1.584473

出版商:American Vacuum Society    

年代:1989

数据来源: AIP

摘要:

The reaction of 〈100〉Si with Cl2and the excimer laser induced chemical etching process using 308 and 248 nm radiation have been investigated. Our results show that even at high Cl2pressures, only a thin passivating chlorinated surface layer is built up which impedes further reaction. Pulsed excimer laser etching at high energy fluences is dominated by thermal evaporation. At lower energy fluences the melt depth decreases and good etch profiles with excellent spatial resolution are observed. At the lowest laser fluences nonthermal, wavelength dependent etching occurs. The laser etching at 308 nm is based on locally enhanced surface chlorination due to effective photodissociation of Cl2in the gas phase. Photoinduced desorption, most likely due to nonradiative electron‐hole recombination, leads to etching. Conversely, at 248 nm, negligible gas phase photodissociation occurs and the surface reaction of Cl2molecules limits the etch rate. However, the higher photon energy (5.0 eV for 248 nm) leads to efficient photodesorption of surface atoms and molecules by direct bond breaking which can give rise to higher etch rates than at 308 nm. Depending on the actual conditions, etching at 308 or 248 nm is more efficient. High etch rates can be achieved by combining the effective photodesorption process at 248 nm with a high degree of surface chlorination due to generation of chlorine gas phase radicals in a microwave discharge. In addition, the spatial resolution capability for direct pattern transfer by excimer laser induced chemical etching has been analyzed as a function of energy fluence, gas pressure, and gas phase radical concentration.

ISSN:1071-1023    

DOI:10.1116/1.584474

出版商:American Vacuum Society    

年代:1989

数据来源: AIP

摘要:

The microscopic surfaces of small silicon clusters offer a model for studying chemistry at highly reactive silicon centers. Positively and negatively charged silicon clusters containing two to seven atoms are prepared by laser evaporation of a solid silicon target located outside of the ion cell of a Fourier transform mass spectrometer. The trapped clusters react with SiD4at room temperature primarily by addition of SiD2accompanied by loss of D2. Sequential reactions of bare silicon cluster cations and SiD+3to form still larger deuterated SixD+yspecies are also observed. All of the clustering sequences, however, encounter early bottlenecks which prevent further growth.Abinitioelectronic structure calculations are used together with phase space theoretical calculations to elucidate the potential surfaces for these reactions. Larger unreactive silicon clusters with six or seven atoms appear to lack the divalent silicon center required to activate Si–D bonds in SiD4under the mild conditions of these experiments. These findings indicate that ground‐state bare silicon clusters and SiH+3are not the important precursors leading to the formation of hydrogenated silicon dust in silane plasmas.

ISSN:1071-1023    

DOI:10.1116/1.584475

出版商:American Vacuum Society    

年代:1989

数据来源: AIP

摘要:

The decomposition of ammonia on Si(111) 7×7 was studied using laser‐induced thermal desorption (LITD), temperature‐programmed desorption (TPD), and Auger electron spectroscopy (AES). Product yields versus NH3exposure were determined using TPD and LITD measurements. Besides the NH3multilayer desorption, the only TPD products were H2and Si2N, which desorbed at ∼800 and 1350 K, respectively. H2was also observed in the LITD yield from NH3on Si(111) 7×7. In addition, NH3, SiNH2, and SiNH were detected in the LITD yield at temperatures above the NH3multilayer desorption. After saturation NH3exposures, the LITD desorption yield for NH3and SiNH2persisted until 700 K, and the SiNH LITD signals were observed up to 800 K. These SiNH2and SiNH LITD signals were assigned to reaction intermediates on the Si(111) 7×7 surface because neither SiNH2nor SiNH was observed in the TPD yield. The effect of preadsorbed deuterium on the reactive adsorption of NH3was also investigated. Deuterium was observed to decrease the product yield from NH3decomposition on Si(111) 7×7.

ISSN:1071-1023    

DOI:10.1116/1.584476

出版商:American Vacuum Society    

年代:1989

数据来源: AIP