Carbon reactions in reactive ion etched silicon

Reactive ion etching (RIE) of silicon creates interstitial defects in the near surface region which diffuse into the bulk material and are trapped at substitutional carbon sites. Photoluminescence (PL), current-voltage (I–V), and Rutherford backscattering (RBS) measurements show that silicon etched in a CF₄ + 8%O₂ or SF₆ + 8%O₂ plasma consists of two distinct regions, adisplacement damage region extending 1000Å from the surface and apoint defect reaction region which can extend to depths > 1 μm. The size of the point defect reaction region is determined by diffusion limited trapping of the interstitial silicon generated during the RIE resulting in the formation ofC _i - O_i orC _s -C_i defect pairs. The long range diffusion rate of the interstitial defects is enhanced by the plasma during the RIE processing, and by a recombination enhanced reaction path.     

Auger electron spectroscopy study of reactive ion etched silicon carbide

Reactive ion etching (RIE) of bulk 4H-SiC based on CHF₃-O₂ plasma was studied by varying the rf power and process pressure. The elements on the etched surface and the surface roughness were characterized by Auger electron spectroscopy and atomic force microscopy, respectively. It was found that the surface roughening is mainly caused by Al contamination and C rich layer (C residues) induced micromasking effect. The micromasking effect is in turn determined by the dc self-bias developed at the substrates. A threshold dc self-bias exists at around −320 to −330 V, beyond which no micromasking effect was observed. This observation is explained in terms of physical ion bombardment and sputtering in the RIE process.     

Preparation,characterization and application of RF sputter deposited boron doped silicon dioxide thin films

We report the preparation of thin film boron doped silicon dioxide (also called borosilicate–glass or BSG) by RF magnetron and its use as a boron diffusion source, especially for shallow junctions. For this purpose, a sputtering target of BSG was prepared through conventional solid state reaction route. Deposition rates of sputter deposited BSG film at different sputtering parameters were studied. The presence of boron in the deposited film was confirmed by hot probe and sheet resistance techniques on silicon wafer following a diffusion step. The structural evaluation of BSG thin film was performed using Fourier Transform Infrared Spectroscopy (FTIR). Secondary Ion Mass Spectroscopy (SIMS) was used to measure the concentration profile of boron in the BSG film. The effect of sputtering parameters on boron concentration in the deposited BSG film was also studied. A p–n junction diode was fabricated using BSG thin film as diffusion source of boron. The junction depth was measured to be in the range of 0.06–1.0 µm for different sputtering and diffusion parameters.     

Fabrication of short channel MOSFETs with refractory metal gates using RF sputter etching

Fabrication of sub-μm p-channel MOSFETs with refractory metal gates using novel refinements of conventional photolithographic procedures is described. The method avoids the need for direct electron beam writing on the wafer and for ion implantation instead of diffusion. Autoregistration Mo gate structures down to 2 μm corresponding to an estimated channel length of 0 · 7 μm were made using RF sputter etching for the drain-source windows while masking with a positive photoresist. This was contact patterned using a chromium-on-glass mask made by electron beam writing and RF sputter etching. Sputter-deposited boron-doped SiO₂ was used as the diffusion source for the source-drain areas.The transistors were made on (100) phosphorus doped n-type silicon with an impurity concentration of 2 . 10¹⁶ cm^?3. Fabricated devices with channel lengths ≥ 1 · 7 μm had an apparent threshold voltage of 2·5 V (10 μA criterion) and for 1·7 μm channel length an apparent punch-through voltage of 18 V. A sputtered Mo layer ? 1 μm thick was used as gate material.A distinct advantage of using sputter etching with a single system capable of both deposition and etching is that it is possible to go directly to the next steps without exposure to air. These steps are mask removal in a partial H₂ and O₂ plasma, followed by further Argon sputter-etching and sputter deposition of a doped oxide diffusion source on the sputter-etched cleaned surface. This promises a better reproducibility of surface doping as there should be less oxide and less contamination than in conventional processes. The characteristics of the fabricated transistors did not indicate any un-annealable drift or gate oxide damage due to the presence of the plasma provided the Mo layer was sufficiently thick. Thus sputter etching which offers good resolution can be used in MOS fabrication.Due to its lower resistivity, Mo, which can be used an an additional interconnection layer (isolated from the A1 layer) offers better speed potential than Si, in certain types of circuits, e.g. high speed memories with long address lines.With a proper background doping of the wafer and diffusion time and temperature it was possible to obtain $\text{? 0 · 6 μm}$ lateral diffusion below the gate from both source and drain regions. It was thus possible to obtain sub-μm p-channel MOSFETs even while working close to the limits of normal optical contact production of micropatterns, which is 1–2 μm.     

An ellipsometric study of the RF sputter oxidation of lead—indium alloys

A simple ellipsometer and an inexpensive 13-MHz sputteretch assembly have been used with a conventional evaporator to make in, situ measurements of the growth of thin oxide layers (≤ 10 nm) on pure lead and pure indium films, and also on a series of alloy films containing up to 46 at % In. Our lead results agree with results of earlier workers. For pure indium, we find that equilibrium oxide thicknesses are typically smaller than for lead, and that equilibrium time constants are longer; moreover, increased RF power leads to increased, rather than decreased, oxide thicknesses. Alloy films show an intermediate behavior in general, but in the range 26-36 at % In the oxide thickness rises to a maximum before falling to its equilibrium value. We agree with results obtained by other methods of oxidation and analysis which show the oxide to have a disproportionately large In2O3content, and, in particular, that there is 100 percent In2O3for all alloys containing more than 35 at % In. We show that the difference between PbO and In2O3as regards the dependence of oxide thickness on RF power can be accounted for by slightly modifying the oxide growth model of Greiner, to make the diffusion length of oxygen ions very slightly dependent on RF voltage. To account for the intermediate behavior, we introduce a simple coupled Greiner model involving separate columns of two oxides, in which oxygen ions can interdiffuse between columns as they find their way to the alloy surface. As the parameters of the model are changed, the growth behavior changes from a simple monotonic growth of thickness with time, through a behavior in which there is an intermediate maximum, and then back to a monotonic growth behavior again.     

A study of sputter deposited silicon films

Thermal annealing, oxidation, and impurity doping of room-temperature dc magnetron sputter deposited silicon films are examined. It was found that even with a fine grain structure, the films can be doped to the desired sheet resistances suitable for device applications, although the sheet resistances are higher (2 to 5 times) than those obtained from single crystal silicon. It was also found that pre-diffusion annealing decreases sheet resistance of boron-doped films, but increases the sheet resistance of phosphorus-doped films, this is correlated to the different behavior of boron and phosphorus at the grain boundaries. Oxidation rates are enhanced in both boron-doped and phosphorus doped films. Film thickness reductions of 11 to 31% after high temperature processes was observed. Effects of doping on the shrinkage in film thickness are presented.     

Characterization of GaN films etched using reactive ion etching technique by secondary ion mass spectrometry

We investigated GaN films etched by using reactive ion etching (RIE) technique to fabricate the GaN-based devices. The samples were grown on sapphire substrate by metal organic chemical vapor deposition (MOCVD), and Ti/Al contacts were formed on n-GaN surfaces after etching processes. The effects of the kinds of reactive gases were evaluated by secondary ion mass spectrometry (SIMS). The results showed that in the sample etched using BCl₃ gas, the signal from boron contaminations was strongly detected at the interface between the contact metal and n-GaN, and we found that additional etching in Cl₂ plasma after etching with BCl₃ gas was essential to make a good contact.     

Electron backscattering diffraction investigation of focused ion beam surfaces

A focused ion beam (FIB) instrument has been used to mill surfaces in single-crystal Si and single-crystal Cu for subsequent electron backscattering diffraction (EBSD) analysis. The FIB cuts were performed using a 30 keV and a 5 keV Ga⁺ ion beam at a stage tilt of 20° to provide a readily obtainable 70° surface for direct EBSD investigation in a scanning electron microscope (SEM). The quality of the patterns is related to the amount of FIB damage induced in the Cu and Si. These or similar methods should be directly transferable to a FIB/SEM dual beam instrument equipped with an EBSD detector.     

Spectral engineering of terahertz quantum cascade lasers using focused ion beam etched photonic lattices

Focused ion beam etching has been used to introduce one-dimensional photonic lattices, of periods 9.11, 9.24, 9.44 /spl mu/m, between the cleaved facets of three 4.44 THz Fabry-Perot quantum cascade lasers. Singlemode lasing has been achieved at precisely defined wavelengths of 67.59, 68.48, 70.00 /spl mu/m, respectively.     

碘过饱和KOH溶液对硅(110)晶面腐蚀的改善

将非金属元素碘作为硅的KOH腐蚀液的添加物,在对(100)和(110)单晶硅片的各向异性腐蚀中,获得了更为丰富的异向腐蚀特性和更为光滑的腐蚀表面。当温度在95℃,KOH腐蚀液中碘的摩尔比为0.5时,得到了粗糙度均小于10nm的Si-(100)和(110)光洁表面,两晶面的腐蚀速率均为1.4μm/min。这两晶面在相同的条件下同时达到最佳光洁度,说明腐蚀速率是获得高光洁度表面的关键。实验还证明碘在热碱溶液中的稳定性和持久性要高于现在已被大量研究的双氧水和过硫等,尤其是对硅(110)表面光洁度的改善具有积极的促进作用。     

An investigation of steady-state velocity overshoot in silicon

Electron dynamics in silicon is investigated by means of improved momentum- and energy-balance equations including particle diffusion and heat flux. The resulting system of partial differential equations is numerically solved in a variety of field configurations including strong discontinuities, in order to enhance velocity overshoot effects. It is found that diffusion, usually neglected in previous studies, plays a major role, and considerably modifies the features of the velocity vs distance curve, leading to an increase of the carrier drift velocity in the low-field region, i.e. before experiencing the effect of the strong field. In addition, it is found that, in order to take full advantage of velocity overshoot effects in MOSFET's, a structure must be designed having the strongest possible field at the source-end of the channel, where carrier density is controlled by the gate.     

Characterization of silicon metallization systems using energetic ion backscattering

Silicon metallization systems have become increasingly sophisticated in order to tailor contact properties such as adhesion, electrical conductivity, barrier height, and long-term reliability. These contact properties are highly susceptible to solid-solid reactions, typically involving atom migration over distances less than 1 µm. Analysis by monoenergetic ion beam irradiation is a valuable new materials characterization technique to optimize process parameters and contact lifetime. Energy analysis of the backscattered ions allows nondestructive determination of the depth distribution of the atomic composition of thin multilayered systems. Recent application of this technique has provided extensive data on the energetics and kinetics of interdiffusion and compound formation for thin-film metallizations on silicon, particularly those used in silicon device technology. After a brief introduction to the technique, the results of these studies are reviewed and systematized. Interdiffusion results are treated for silicon-metal and metal-metal reactions. Distinction is made between cases where internal surface transport effects dominate and cases where compound formation dominates. Examples are taken from each of these areas and are discussed in terms of metallurgical properties.     

An RF concentrating method using inductive aperture-typeapplicators

A method for concentrating electromagnetic (EM) energy of a low frequency in hyperthermia is proposed. The phantom together with boli are placed between a pair of inductive aperture-type applicators. The calculated results show that the method can heat the deep portion of the phantom without overheating the fat layers excessively     

Investigation of oxygen annealing effects on RF sputter deposited SiC thin films

Amorphous silicon carbide films were deposited by RF sputtering technique using a SiC target. These films were annealed in dry oxygen ambient in the temperature range of 400–700 °C. Subsequently the films were characterized using X-ray photoelectron spectroscopy (XPS) to investigate the chemical composition at each annealing temperature. XPS indicated that increasing the anneal temperature results in a decrease in SiC phase, and an increase in SiO_x. Surface morphology of the oxidized films was characterized using atomic force microscope. Optical absorption studies indicated blue shifting effects as the annealing temperature was increased.     

Mobility study on RIE etched silicon surfaces usingSF6/O2 gas etchants

A methodology for the measurement of the inversion layer mobility on trench gate structures, which allows independent measurement of the sidewall and bottom surface mobilities, is described. Using this method, the inversion layer mobility has been experimentally studied for trenches formed using the SF₆/O₂ method on diffused base regions of power UMOSFETs. The effect of several post RIE surface treatments on the surface mobility is reported. The measured sidewall mobilities have been found to be comparable to those previously reported for other RIE etchants. These results are of interest for the design of devices using the trench gate (UMOS) technology     

多孔硅制备中醇对形貌的影响

实验研究了无光照情况下多孔硅制备中不同单羟基正醇对形貌的影响。实验结果表明,随着醇碳链的增长,多孔硅孔密度减小,枝杈变长,枝杈的尖端变得尖锐。在孔的生长过程中,十字枝杈首先沿着晶格方向快速生长,然后晶格方向的生长速率减小,而非晶格方向则持续生长直到空穴耗尽。本实验增进了对硅溶解动力学中醇作用机理的理解。     

Reactive sputter etching of silicon with very low mask-material etch rates

Directional etching of deep structures in silicon is often made difficult by a high mask erosion rate. Recent results have given a Si/SiO2etch rate ratio of up to 8 without the undercut problems associated with other selective etches. In this paper a new selectivity mechanism is described which can reproducibly give Si/SiO2etch rate ratios of more than 100 with a nonloading target, and more than about 50 with a loading target. Similar etch ratios are also obtained with masks of MgF2, Al2O3, Al, and Cr. The inherently high Si/SiO2etch rate ratio obtained in Ar/Cl2discharges is here enhanced by causing selective deposition of SiO2onto slowly etched materials. The silicon may be obtained from the target, or, for easier control, from input gases such as SiCl4. The deposition rate is controlled by the oxygen concentration. The results of etching deep grooves in Si are presented. Etch-mask faceting and Si surface decoration appear to limit the attainable etch rate ratios with fine structures; however, 18-µm-deep gratings of 4.5-µm period have been etched in Si.     

Residual damage effects on gate contacts formed on SiC surfaces etched by using the amorphization technique

A trench fabrication process has been proposed and experimentally demonstrated for silicon carbide using the amorphization technique. In the present work, the quality of gates [oxide for metal oxide semiconductor field-effect transistors (MOSFETs) and Schottky barrier contacts for metal semicondcutor field-effect transistors (MESFETs)] fabricated on the etched surfaces are compared with those formed on the as-grown silicon carbide surface. The resistivity and breakdown electric field of the thermal oxide grown on the etched surface was found to be comparable to that of thermal oxide grown on silicon. However, a large concentration of acceptor type interface states (0.5-1 x 10¹³ cm⁻²eV⁻¹) was observed. This results in a large negative interface charge at room temperature and a significant shift in flat band voltage as a function of temperature, which makes the process unsuitable for formation of gates in UMOSFETs. Titanium Schottky contacts formed on the etched surface showed superior reverse current-voltage characteristics and higher breakdown voltages than the Schottky diodes formed on unetched surface with similar doping concentrations. This indicates that the argon implant process for trench formation is suitable for fabrication of gate regions in high voltage vertical MESFETs (or SITs).