摘要:

We present a study of the electronic states of GeAs as a model for the ordered, anion‐stabilized surface phases which form on Ge when it is grown epitaxially on GaAs substrates using MBE. Angle‐resolved, normal emission photoelectron energy distribution curves for four different azimuthal orientations of the GeAs(2̄01) face (i.e., four different polarizations) have been measured using photon energies fromhν=10 to 28 eV. The valence band structure plots (binding energy versus photon energy) show behavior typical of a layered compound. A large number of valence band states (about 12) are observed, and they show essentially nohν dispersion in normal emission and very little dispersion with polar angle. The electronic states are therefore localized both within and normal to the layer. The excitation of the Ge 3dand the As 3dcore levels into conduction band states observed by measuring the core hole decay emission does not show any enhancement peaks as usually observed if empty surface states exist in the conduction band. This suggests that the GeAs(2̄01) surface may not have any surface states. Chemical bonding information was obtained by measuring the Ge 3dcore level binding energy. The Ge is more tightly bound compared to the bulk Ge as indicated by a 3dcore level chemical shift of 0.45±0.1 eV toward higher binding energy. 3dcore threshold emission for both the Ge and the As is used together with the line shape of the valence band edge emission to determine a forbidden band gap is 0.4±0.3 eV. These results support the Bauer/Mikkelsen hypothesis that the Ge:As surface phase that floats on top of the MBE GaAs/Ge heterojunction is energetically more favorable than the corresponding clean Ge surface having unsatisfied dangling bonds. The data on GeAs(2̄01) leads to a picture of an As‐terminated surface having highly directional oribtals and very low reactivity.

ISSN:0734-211X    

DOI:10.1116/1.582707

出版商:American Vacuum Society    

年代:1983

数据来源: AIP

摘要:

Electron stimulated desorption, Auger line shape analysis, and electron loss spectroscopy measurements are reported for the electron activated stepwise oxidation and nitridation of the Si(111) surface. In ESD it is found that appreciable levels of surface hydrogen can be present which can lead to hydroxyl formation upon oxidation. The hydroxyl rich films are unstable in an electron beam, while surfaces oxidized with activated oxygen, where no OH is formed, are much more stable. The nitrided films are always stable in the electron beam even though there too hydrogen is always found. On the OH‐free oxide, ESD shows two chemically distinct O species, one thought to be SiO2and the other adsorbed O2or a chemical intermediate. The Si(L23VV) Auger spectra for both the oxide and nitride are treated by background subtraction, integration, deconvolution, and subtraction of the elemental part of the spectrum, as a function of reaction time over a well controlled series of reaction steps. The Auger spectra for both oxide and nitride films suggest that in the earliest stages of reaction, the reacted film is made up of low coordination intermediates which gradually evolve to the stoichiometric compound as the coordination increases. In loss spectroscopy, both the Si(L23) core loss and the near elastic loss were measured. TheL23core loss shows the same gradual evolution to the oxide seen in the Auger results, with an intermediate oxidation state dominating in the early stages of reaction. The near elastic loss spectra, by contrast, quickly saturate in the early stages of reaction to the final oxide spectrum which is characterized by features both of the full oxide and a suboxide. Similar results are found for the nitride.

ISSN:0734-211X    

DOI:10.1116/1.582710

出版商:American Vacuum Society    

年代:1983

数据来源: AIP

摘要:

The efficiency of ablative photodecomposition of poly(methyl methacrylate) caused by pulsed radiation at 193 nm from an excimer laser (argon–fluorine fill) has been studied as a function of fluence. A threshold for the onset of the process lies at 10 mJ/cm2per pulse of 14 ns. The efficiency of the process increases rapidly with fluence up to 250 mJ/cm2per pulse after which it levels off sharply. The etch depth of ∼3100 Å/pulse at 250 mJ/cm2can be compared to a depth of 4800 Å/pulse at a fluence of>20 J/cm2/pulse. A model is suggested for the ablative photodecomposition of organic materials and the photochemistry of the process at different fluences is discussed. The variation in the efficiency with the composition of the polymer is briefly considered.

ISSN:0734-211X    

DOI:10.1116/1.582712

出版商:American Vacuum Society    

年代:1983

数据来源: AIP

摘要:

During oxygen and carbon tetrafluoride plasma etching of silicon nitride, a light blue and water soluble film is deposited upon the surface of the silicon nitride layer. Depending upon the thickness, this film retards or completely inhibits the desired etching process. This film has been identified by infrared spectrophotometry as ammonium fluoride. The thickness of the ammonium fluoride layer has been determined to be a function of the ammonia to dichlorosilane mole ratio of the gas flow into the LPCVD reactor during deposition. For mole ratios greater then 4.0, the ammonium fluoride film thickness was observed to decrease to approximately one‐third of the observed value at a mole ratio of 3.0. A possible mechanism for the formation of the ammonium fluoride layer is the reaction of ammonia molecules and hydrogen atoms (which have been occluded in the silicon nitride layer during deposition) with fluorine atoms from the plasma etching process. Increasing the mole ratio during deposition improves the stoichiometry of the silicon nitride layer and reduces the number of hydrogen atoms available for subsequent formation of ammonium fluoride during etching. The etching variations caused by ammonium fluoride deposition during plasma etching of silicon nitride can be minimized by optimizing the ammonia to dichlorosilane mole ratio during the deposition of the silicon nitride layer.

ISSN:0734-211X    

DOI:10.1116/1.582714

出版商:American Vacuum Society    

年代:1983

数据来源: AIP

摘要:

Plasma‐enhanced CVD requires close control of the plasma power density for reproducibility of both deposition rate and spatial uniformity in a radial‐flow reactor. Frequently the low rf power levels needed are not adequately controlled by the output power control of the relatively high power rf generator found in most commercial multipurpose plasma etch/deposition systems. This paper describes very simple and inexpensive broadband optical monitoring of the plasma emission for improved control sensitivity. The technique has the advantage of directly monitoring the plasma intensity, avoiding effects of variable power transmission losses between the rf generator and the plasma. Application to the control of low power plasma‐enhanced CVD of ‘‘SiO2’’ from Ar:SiH4:N2O plasmas, where the monitor signal is almost entirely due to near infrared Ar emission, is described.

ISSN:0734-211X    

DOI:10.1116/1.582716

出版商:American Vacuum Society    

年代:1983

数据来源: AIP

摘要:

In anticipation of the continued size reduction of switching elements to the molecular level, new approaches to materials, memory, and switching elements have been developed. Two of the three most promising switching phenomena include electron tunneling in short periodic arrays and soliton switching in conjugated systems. Assuming a three‐dimensional architecture, the element density can range from 1015to 1018per cc. In order to make the fabrication of such a molecular electronic device computer feasible, techniques for accomplishing lithography at the molecular scale must be devised. Three approaches possibly involving biological and Langmiur–Blodgett materials are described.

ISSN:0734-211X    

DOI:10.1116/1.582717

出版商:American Vacuum Society    

年代:1983

数据来源: AIP

摘要:

Microfabrication processes based on focused laser‐beam activation of surface chemistry are reviewed with an emphasis on the classification of the diverse chemical processes used. Surface reactions are divided according to their method of activation and the material phase most important in the chemical kinetics. Examples of reaction mechanisms and means of confining reaction dimensions are given. New results demonstrating that linewidths for deposition and etching of Si can be<0.4 μm are described. The ultimate limits to spatial resolution are explored in terms of an effective contrast (γ*) for laser–microchemical processes. Enhanced diffusive transport, characteristic of laser microreactions, and its effect on ultimate reaction rates are also analyzed.

ISSN:0734-211X    

DOI:10.1116/1.582718

出版商:American Vacuum Society    

年代:1983

数据来源: AIP

摘要:

Microfocused heavy ion beams obtained from liquid metal ion sources of gallium, indium, and tin are bombarded onto silicon and gallium arsenide substrates, and the amorphous regions created are selectively dissolved in suitable etchants (ion bombardment enhanced etching). The area exposure doses required to etch to the depth of the calculated projected range of the incident ions are in the region of 5×10−6∼1×10−5C/cm2at accelerating voltages of 30∼50 kV,and the dose dependencies of the etched depths show rapid increases in specified dose regions. Widths of etched depths obtained in line delineations depend on a line exposure dose, and the minimum linewidth clearly obtained is 20∼40 nm for all the ion beams. From measurements of the dose dependencies of linewidth, the beam diameters are evaluated for various conditions of the source operation and of a lens acceptance half‐angle. The virtual crossover diameters that are independent of the half‐angle, are found to be 40∼50 nm for the gallium source and 67 nm for the indium source at the emission current of 4∼12 μA. In the case of the tin ion beam, each line is split into two distinct lines about 100 nm apart at 50 kV. This effect is caused by the separation of singly and doubly charged atomic ions in some stray magnetic field of the order of 50 mG. From variations of the width of grooves produced by the bombardment with the doubly charged ion beam, the crossover diameter for the tin source is estimated to be 56∼67 nm.

ISSN:0734-211X    

DOI:10.1116/1.582719

出版商:American Vacuum Society    

年代:1983

数据来源: AIP

摘要:

In electron beam direct writing, a capability of ‘‘one chip within one deflection field’’ can reduce time wasted in stage moving, and eliminate field stitching errors in a chip. These advantages lead to high throughput and high overlay accuracy for successful VLSI fabrications. A large angle electrostatic deflection, variable shaped, electron beam exposure system (EB57) has been developed to achieve this capability. The key EB57 technologies are a large angle electrostatic deflection and high speed deflection control. Newly developed multiple electrostatic deflectors were designed using an in‐lens, dual channel deflection method. In this method, two types of field and subfield deflectors are equipped inside a projection lens. Deflectors free of third and fifth θ components can provide a large angle of deflection with a 10 mm2field. 18‐bit digital‐to‐analog converters, and ±800 V amplifiers effect this large field deflection. The high breakdown voltage for the amplifiers is attained by connecting vertical power MOSFETs in series. The settling time of the amplifiers is less than 10 μs at 1/64 full scale. Amplifiers for subfield scanning and beam shaping have a 250 ns settling time at full scale. To correct chip distortions, deflection distortions, and stage positioning errors, a new data correction method that takes rounding off errors into consideration has been applied to a high speed arithmetic unit. This EB57 system can write from 7 to 10 4‐in. wafers per hour with 0.5 μm lithography.

ISSN:0734-211X    

DOI:10.1116/1.582720

出版商:American Vacuum Society    

年代:1983

数据来源: AIP

摘要:

Some of the basic considerations in the design of the electron optics of a variable line scanning (VLS) system, a particular form of variable‐shape electron‐beam lithography system, are discussed. In the VLS system, the electron beam is projected on the resist‐coated wafer in the form of a narrow line whose length and position can be varied simultaneously as it is scanned. The writing is done as the stage is moved in a serpentine fashion under laser control with the pattern features placed using both raster and vectorial placement techniques. The line can be produced in either of two orthogonal directions in order to maximize the exposure rate. In general, the required source brightness is greater than that of a more conventional‐shaped‐beam system, however, this can be achieved readily with LaB6at a desirable operating temperature. Exposed and developed patterns demonstrate the resolution capabilities of the optics.

ISSN:0734-211X    

DOI:10.1116/1.582721

出版商:American Vacuum Society    

年代:1983

数据来源: AIP