摘要:

A new power metal–semiconductor field effect transistor (MESFET) with employing the superlattice structure in the gate and buffer has been fabricated successfully by molecular‐beam epitaxy. The use of undoped GaAs–Al0.3Ga0.7As superlattice gate insulator results in much smaller gate to source parasitic capacitance (Cgs) and leakage current and higher gate to drain breakdown voltage (25–30 V) than conventional MESFET’s. Furthermore, the existence of graded superlattice buffer provides higher saturation current and much smaller velocity degradation region than those of AlGaAs buffer MESFET’s. By the improvement ofCgsand transconductance, the cutoff frequency is expected to be higher. Due to the increasing of gate breakdown voltage and saturation current, the output power drivability is improved. In summary, the demonstrated superlattice gate and graded superlattice buffer structure is suitable for low‐noise, high‐frequency, and high‐power application.

ISSN:0734-211X    

DOI:10.1116/1.584799

出版商:American Vacuum Society    

年代:1989

数据来源: AIP

摘要:

Growth of high‐quality ZnSe films on GaAs(100) substrates by conventional molecular‐beam epitaxy (MBE) and migration enhanced epitaxy (MEE) have been examined. We have found a self‐regulatory MEE process in the temperature range between 350 and 400 °C where a complete monolayer of ZnSe was achieved per three operational cycles of Zn+Sen. Thin films (<1 μm) grown by self‐regulatory MEE exhibited much higher structural perfection than MBE thin ZnSe films grown under closely identical conditions. The explanation for these structural differences must lie in details of how initial nucleation takes place in MBE and MEE. For thicker films (≂2 μm) no significant differences in structural or electrical properties were found for the two methods.

ISSN:0734-211X    

DOI:10.1116/1.584800

出版商:American Vacuum Society    

年代:1989

数据来源: AIP

摘要:

Thermal oxides were grown on different doped polysilicon thin films: (i) as‐grown polysilicon at 620 °C, (ii) as‐grown polysilicon and annealed at 1000 and 1100 °C in nitrogen, and (iii) as‐grown amorphous silicon films at 570 °C subsequently converted into polycrystalline form during doping. These films are qualitatively characterized by studying electrical properties, such as leakage current, breakdown field, the temperature dependence of current, and the time dependence of current. The electrical measurements of oxides grown on polysilicon converted from amorphous form show lower leakage current and higher dielectric breakdown than oxides grown on as‐deposited polysilicon films. The results were interpreted in terms of interface texture of polysilicon/polyoxide using the Fowler–Nordheim tunneling mechanism. The temperature dependence of current through the oxides shows little variation at low temperatures, but it increases exponentially at high temperatures. The oxides also exhibit a time‐dependent current. This dependence could be ascribed to ionic–Ohmic conduction of charge carriers in the polyoxide, at low fields and high temperatures.

ISSN:0734-211X    

DOI:10.1116/1.584801

出版商:American Vacuum Society    

年代:1989

数据来源: AIP

摘要:

Microstructural changes and the evolution of silicide phases initiating at the interface between thin films of Si and Ti have been investigated by transmission electron microscopy and diffraction. This configuration allows an unambiguous interpretation of the results since the reactions are not mediated by SiO2. Spontaneous formation of the TiSi phase of nominal thickness occurs at room temperature, which is however not the actual growth phase at intermediate annealing temperature (500

ISSN:0734-211X    

DOI:10.1116/1.584802

出版商:American Vacuum Society    

年代:1989

数据来源: AIP

摘要:

Because of their ability to both mill and deposit material with submicron resolution, focused ion beams are now used to repair photolithography masks and are of increasing technological interest in the repair of x‐ray lithography masks and in integrated circuit restructuring. With the latter two applications in mind, we have fabricated milled and deposited Au features with linewidths of ≤0.1 μm using a 40 keV Ga focused ion beam. In addition, we present the results of a study parameterizing focused ion beam induced Au deposition under conditions of practical interest. Milling is accomplished by simple physical sputtering. Examples of milled microfeatures include a grating with a 210 nm period milled through a 5000 Å thick evaporated Au film. Deposition is accomplished by ion bombarding a SiO2substrate on which a precursor gas, dimethyl gold hexafluoro acetylacetonate, is continuously being adsorbed. Examples of deposited Au features include a 3×3 μm patch 1‐μm‐thick with steep sidewalls. The deposition rate was measured at room temperature as a function of ion and precursor flux, and a simple model of the process is fitted to the data. Ion beam induced deposition efficiency is shown to depend critically on the time averaged beam current density and only weakly on the precursor flux. The maximum achievable growth rate is shown to be ∼10 Å/s. Deposited Au films contain 30–60 at. % carbon and have conductivities 200–600 times less than that of bulk Au. Those films formed using lower organometallic pressures or higher ion beam current densities are characterized by greater purity with more continuous microstructure.

ISSN:0734-211X    

DOI:10.1116/1.584803

出版商:American Vacuum Society    

年代:1989

数据来源: AIP

摘要:

The intensity of an AsCl2signal obtained from a mass spectrometer showed the most remarkable increase during etching of GaAs with CCI2F2/He. It was shown that etching of GaAs/AlGaAs/GaAs and GaAs/InAs(3 monolayers)/GaAs could be precisely monitored with the signal intensity of AsCl2.Even etch‐stop on the 3 monolayers InAs was directly observed, showing that precise control of the etching on a monolayer scale is possible. The technique can be used to selectively etch III–V compound semiconductor heterostructures which contain As.

ISSN:0734-211X    

DOI:10.1116/1.584804

出版商:American Vacuum Society    

年代:1989

数据来源: AIP

摘要:

We have demonstrated a low‐temperature cleaning technique for removing both carbon and oxygen from a Si surface. It uses a combination ofexsituwet chemical clean and aninsituremote rf plasma‐excited hydrogen clean in an ultrahigh vacuum chamber. Since a remote rf plasma is used, there is insignificant plasma damage or other deleterious effects on surface morphology. A combination ofinsituAuger and RHEED analysis has been used to confirm the removal of surface contaminants and the reconstruction of the Si surface. From mass spectroscopy studies, we believe that the hydrogen cleaning is due to a chemical etching of the Si by atomic hydrogen produced by the plasma. This clean is compatible with UHV processing and yields Si substrates that can be used for successful very low temperature (220–400 °C) Si homoepitaxy by remote plasma‐enhanced chemical vapor deposition.

ISSN:0734-211X    

DOI:10.1116/1.584805

出版商:American Vacuum Society    

年代:1989

数据来源: AIP

摘要:

The reactive ion etching of titanium is described using rf discharges of CCl4and O2with additions of fluorine containing gases. Because of these additions the titanium etch rate increases substantially in comparison with the pure CCl4/O2plasma. This is presumably due to a shift of equilibrium reactions within the discharge towards the production of the volatile etch product. Process parameters are given for which the reactive ion etching of titanium with a photoresist mask is highly anisotropic and an etch end point control by optical emission spectroscopy is possible.

ISSN:0734-211X    

DOI:10.1116/1.584806

出版商:American Vacuum Society    

年代:1989

数据来源: AIP

摘要:

This paper describes x‐ray spectra variation caused by x‐ray absorption in columnar high‐density plasma which is employed as an x‐ray source for x‐ray lithography. In the axial direction of the columnar plasma, it is found that x‐ray emission from Ne+8ions is absorbed more intensely than from Ne+9ions. Thus, the x‐ray spectral features vary from the primary profile due to x‐ray absorption by high‐density plasma. For x‐ray lithography, it is necessary to produce high‐density plasma near the x‐ray extraction side electrode in order to prevent the x‐ray output attenuation caused by absorption. An external magnetic field is employed to control the pinched plasma. High‐density plasma is localized near the extraction side electrode by the magnetic field. However, pinching becomes weak and x‐ray outputs decrease simultaneously. Shortening the electrode gap is effective to prevent the x‐ray output attenuation, because plasma density near the extraction side electrode becomes high substantially. However, discharges become unstable if the gap is too narrow. At the optimized electrode gap, x‐ray output fluctuation is low and high‐density plasma is produced stably. Accordingly, it is necessary to optimize the electrode gap in the plasma source for x‐ray lithography.

ISSN:0734-211X    

DOI:10.1116/1.584620

出版商:American Vacuum Society    

年代:1989

数据来源: AIP

摘要:

An attempt was made to design a high‐performance positive photoresist from the standpoint of the image formation process. There are a lot of trade‐off relationships among performance of a positive photoresist. A study was made to raise performance without the decrease in other performances. It was necessary to design a new type of novolak resin that has a molecular structure different from the existing materials. Many kinds of cresol–formaldehyde type novolak resins were synthesized and evaluated lithographically. Such items as molecular weight, molecular weight distribution, isomeric structure of cresol, the position of methylene bond, and the content of quinonediazide in a positive photoresist were investigated. Three methods were found useful: (i) to apply high‐ortho novolak resins that have a high content of ortho–ortho’ methylene bonds (ii) to optimize molecular weight distribution of novolak resins, and (iii) to optimize the content of quinonediazides in a photoresist. These results are explained in terms of a simple model for positive photoresist development, which we call ‘‘stone wall model’’. This model is applicable to design a high‐performance positive photoresist.

ISSN:0734-211X    

DOI:10.1116/1.584621

出版商:American Vacuum Society    

年代:1989

数据来源: AIP