摘要:

Reactive ion beam etching of polyimide thin films was investigated using x‐ray photoelectron spectroscopy (XPS) and etch rate measurements. The etching mechanism and the near surface damage produced in polyimide by exposure to argon and oxygen ion beams were compared. The etch rate of polyimide by oxygen ions was studied as a function of ion current density and neutral oxygen molecular flux, and the results were found to match a model for the contribution of neutral fluxes to the etch process. Ion beam etching with inert argon ions was found to produce a graphitelike layer on polyimide. Reactive ion beam etching with oxygen ions resulted in much faster etching than for argon ions, and did not produce a graphitized layer.

ISSN:0734-211X    

DOI:10.1116/1.584420

出版商:American Vacuum Society    

年代:1988

数据来源: AIP

摘要:

The spontaneous thermal etching of silicon by CF3free radicals has been studied in a very‐low‐pressure photolysis reactor. The radical is produced by infrared multiphoton dissociation of either hexafluoracetone or CF3I, and is allowed to react with a temperature‐controlled silicon sample (560–745 K). Mass spectrometry is used to measure the extent of dissociation of the precursor gas and the formation of product molecules, C2F6and SiF4. The etch rate of the silicon is determined from the SiF4production. Resonance‐enhanced multiphoton ionization of CF3is used to determine the density and time history of the radical in the reactor. The measurements of the etch rate and CF3density are combined to derive the reaction probability. CF3etches silicon much more slowly than F atoms and at a rate comparable to molecular F2. A carbon layer, that is deposited on the silicon by the radicals, inhibits, but does not stop, further etching. Experiments on the etching of silicon by F2were performed both to validate the reactor design and to prepare the silicon surface for the CF3studies.

ISSN:0734-211X    

DOI:10.1116/1.584421

出版商:American Vacuum Society    

年代:1988

数据来源: AIP

摘要:

Reactive ion etching of GaAs with high selectivity over Al0.29Ga0.71As in SF6/SiCl4mixtures was studied. Selectivity, surface morphology, and anisotropy were investigated over a wide range of pressures (15–100 mTorr), dc bias values (−20 to −300 V), and SF6‐to‐SiCl4ratios (0–0.5). Higher pressures, lower dc biases, and higher SF6/SiCl4ratios increase the GaAs‐to‐AlGaAs selectivity. Electron spectroscopy for chemical analysis indicates that the formation of nonvolatile aluminum fluoride on AlGaAs is responsible for the selective etch process.

ISSN:0734-211X    

DOI:10.1116/1.584422

出版商:American Vacuum Society    

年代:1988

数据来源: AIP

摘要:

We have studied the role of aluminum in the formation of an etch barrier at the GaAs/ AlxGa1−xAs interface during reactive ion etching in CCl2F2plasma. The minimum AlxGa1−xAs thickness needed to form the barrier is Al mole fraction dependent and was determined with etching experiments monitored by optical emission spectroscopy. Effective AlxGa1−xAs layers for forming an etch barrier are 275 Å forx=0.02, 22 Å forx=0.10, 15 Å forx=0.15, 12 Å forx=0.20, and 9 Å forx=0.30. For all Al mole fractions exceptx=0.02, these thicknesses correspond to a sheet dose equivalent to 3/4 of a monolayer of Al in the original AlxGa1−xAs layer. Barrier layers forx=0.02, 0.10, 0.25, and 0.30 were examined without air exposure by angle‐dependent x‐ray photoelectron spectroscopy. For samples that are not overetched, the surface is covered with ∼20 Å of AlF3intermixed with a gallium halide containing chlorine and fluorine and is depleted of arsenic. For substantially overetched barriers, a 30 Å layer is formed with gallium halide present at the surface, AlF3found farther in, and arsenic depletion throughout the barrier. During extreme overetch, barrier layers on the order of tens of Å in thickness were not etched away and yet did not completely prevent very slow etching of underlying GaAs. Barrier layers on the order of 60 Å in thickness did prevent etching of underlying GaAs. Collectively the data suggest that the role of Al is formation of AlF3exclusively and that only this compound is responsible for stopping the GaAs etch.

ISSN:0734-211X    

DOI:10.1116/1.584423

出版商:American Vacuum Society    

年代:1988

数据来源: AIP

摘要:

Photoemission spectra were obtained from Ge surfaces after reactive ion etching with CF4and CF4/H2mixtures. These measurements indicate a surface layer of fluorinated Ge species as well as adsorbed carbon and CFxspecies. The shifted intensity in the Ge(2p3/2) core level suggests a layer of about 1 to 2 layers of GeFx, withx∼2–3. The accumulation of CFxoverlayer increases with increasing H2to CF4, but comparisons with Si etched under identical conditions indicate that there is less steady‐state film deposition of Ge during reactive ion etching than on Si. Thus, an increased thickness of carbonaceous overlayer on Ge compared to Si is unlikely to be the explanation for the observed drop in the selectivity toward etching Ge over Si with increasing hydrogen addition. Reactive ion etching of a Si35Ge65alloy was also investigated. Here, photoemission indicated a surface layer of GeFxsimilar to that found on pure Ge, but little evidence of SiFxspecies. The composition of the surface is enriched in Ge for about 3–5 layers.

ISSN:0734-211X    

DOI:10.1116/1.584424

出版商:American Vacuum Society    

年代:1988

数据来源: AIP

摘要:

Germanium is experiencing a resurgence of interest due to superior intrinsic properties and recently overcome technological limitations. This paper addresses the problem of Schottky barrier height control. The Fermi level of metal/Ge contacts is pinned at between 0.54 and 0.61 eV below the conduction‐band edge, independent of the contacting metallization. We compare the modulation of effective barrier height by means of shallow ion implantation, epitaxial growth, and diffusion from a doped level to create a thin, highly doped interfacial region. Lowering ofn‐type contacts from 0.54 to 0.4 eV, at room temperature, and enhancement ofp‐type contacts from 0.09 to 0.23 eV, at 77 K, have been achieved. Experimental results are compared to computer model calculations.

ISSN:0734-211X    

DOI:10.1116/1.584426

出版商:American Vacuum Society    

年代:1988

数据来源: AIP

摘要:

A refractory, two‐zone, large‐capacity, baffle‐free arsenic cracking source for molecular‐beam epitaxy is presented. The new features of this design include the use of a molybdenum tube to provide efficient cracking, a horizontal sublimator at a right‐angle geometry to the cracking section, a baffle‐free design, and the use of expanded tantalum heating filaments. High‐efficiency cracking is obtained at cracking tube temperatures between 750 and 1050 °C. Bulk GaAs and GaAs/AlGaAs heterostructures grown using this source exhibit good electrical and optical properties, with clear improvements in electrical behavior when compared to an As4source. We believe this source design can be easily applied to other column V materials such as phosphorus and antimony.

ISSN:0734-211X    

DOI:10.1116/1.584427

出版商:American Vacuum Society    

年代:1988

数据来源: AIP

摘要:

Correct GaAs and InP substrate temperatures are monitored with an infrared optical pyrometer. The temperature calibration for the pyrometer is carried out with the help of an emissivity change, produced by an eutectic reaction, in the Al deposited Si substrate. It is found that large apparent temperature differences exist betweenn+‐ (orp+‐) and semi‐insulating GaAs and InP substrates when constant emissivity is assumed. The temperature difference is ∼60 °C at 500 °C for InP, and 10–30 °C for GaAs. The temperature differences are found to increase with increasing substrate temperature. A model calculation is given for substrate temperature monitoring with an infrared optical pyrometer. The apparent temperature difference is attributed to the presence of optical absorption mechanisms in ann+‐ (andp+‐) substrate and its absence in a semi‐insulating substrate. The limiting temperature of congruent evaporation and the native oxide evaporation temperature for GaAs are measured with an accurately calibrated infrared optical pyrometer. They are found to be 612±10 °C and ∼585 °C, respectively.

ISSN:0734-211X    

DOI:10.1116/1.584428

出版商:American Vacuum Society    

年代:1988

数据来源: AIP

摘要:

Low‐pressure chemical vapor deposited WSiXhas been characterized and optimized through the use of screening and modeling experimental designs. In the screening study, the effects of temperature, pressure, gas flow rates, and a predeposition treatment were determined for a list of properties which included deposition rate, resistivity, stress, stoichiometry, oxidation rate, particle generation, and resistance to chemical attack. Over the process domain covered, temperature, WF6flow rate, and SiH4flow rate were found to affect deposition rate, resistivity, film stress, and stoichiometry while stoichiometry was also affected by pressure. WSiXfilms produced in the screening study ranged in stoichiometry fromX=2.1 to 3.0. The oxidation rate of these samples was found to be insensitive to deposition conditions and unrelated to the as‐deposited stoichiometry. As‐deposited and annealed film stress were found to decrease linearly with increasing silicon content of the as‐deposited films. Similarly, the as‐deposited and postannealed resistivity of WSiXfilms were found to be a function of the initial stoichiometry. Manufacturability related properties such as particle generation, chemical resistance, and uniformity measures involving sheet resistance, resistivity, and film thickness were found to be largely insensitive to the process factors studied. Response surface models were developed for deposition rate, annealed resistivity, annealed stress, and stoichiometry and were used to guide the final process optimization. The optimized process window was relatively large and yielded WSiXfilms with an annealed (950 °C, 30 min) resistivity of ∼75 μΩ cm, an as‐deposited Si/W atom ratio of ∼2.5, annealed tensile stress of ∼1.2×1010dyne/cm2, and deposition rates of 9 to 10.5 Å/s.

ISSN:0734-211X    

DOI:10.1116/1.584429

出版商:American Vacuum Society    

年代:1988

数据来源: AIP

摘要:

A new approach to the study of semiconductor growth mechanisms is described which utilizes surface science and related photon‐based techniques. It is possible to study growth processes over the pressure range 5×10−11to 103mbar through the use of an isolatable atmospheric pressure reactor described briefly. As an illustration of the potential of the surface science approach, the effectiveness of the reducing hydrogen atmosphere employed in the pregrowth bake of a GaAs (100) metal‐organic vapor phase epitaxy (MOVPE) substrate in removing surface carbon and oxygen is determined using Auger electron spectroscopy. It is shown that at a pressure of 0.5 mbar of H2, temperatures as low as 600 K are sufficient to remove the surface carbon and oxygen contamination present on the substrate following wet chemical etching and heating in ultrahigh vacuum. This result implies that the conventional MOVPE sample bake at high temperatures (>850 K), in H2and AsH3is not necessary to produce clean substrates. Following the H2treatment the GaAs(100) surface gives rise to a (1×1) low‐energy electron diffraction pattern suggesting that it has been stabilized towards reconstruction via hydrogen chemisorption.

ISSN:0734-211X    

DOI:10.1116/1.584430

出版商:American Vacuum Society    

年代:1988

数据来源: AIP