摘要:

When microfabricating semiconductor materials, it is necessary to reduce etching damage and to apply a high‐selectivity mask. A single‐grid ion beam etching system can generate much larger ion currents at low accelerator voltages than a dual grid system. In this experiment, a tenfold ion current as that from a dual grid system is extracted at accelerator voltages below 1000 eV. Here, GaAs samples are etched with an Ar ion beam in order to evaluate the physical etching damage, as measured from theI–Vcurves of a Schottky diode. The normalizednfactor, which indicates the amount of etching damage, is less than 1.2 for an accelerator voltage less than 100 eV. The ion current density can be increased without increasing the etching damage. Additionally, several mask materials for GaAs etching are examined. Ion beam sputtered carbon has the highest selectivity, about 15–20 atVabelow 150 eV, among the materials examined. The selectivities of Ti for a metal mask and Al2O3for a transparent mask are more than 10 atVabelow 100 eV, whereas the selectivity of SiO2is 2.6.

ISSN:1071-1023    

DOI:10.1116/1.586392

出版商:American Vacuum Society    

年代:1992

数据来源: AIP

摘要:

The surface structure, morphology, and crystallinity of high Miller index (511) and (711) GaAs epitaxial layers prepared by molecular‐beam epitaxy are studied with electron diffraction, scanning electron micorscopy, Raman scattering, and Rutherford backscattering. All A‐ and B‐(511) and (711) surfaces exhibit an ordered array of steps with (100) terraces and (111) risers. The (511)‐B layers exhibit the smoothest surface morphology, and the best surface and bulk crystallinity among these layers.

ISSN:1071-1023    

DOI:10.1116/1.586394

出版商:American Vacuum Society    

年代:1992

数据来源: AIP

摘要:

We present an excimer‐laser‐based doping process useful for shallow uniform and laterally gradedp‐type doping of GaAs substrates. Specifically, low power 248‐nm pulses from a KrF excimer laser are used to nonthermally photodeposit thin Zn layers (∼3–300 Å) from a dimethylzinc (DMZn) ambient onto selected GaAs surface regions. Uniform exposure of a sample to the laser pulses produces a source film which is laterally uniform in thickness, whereas variations in exposure time across a sample deposit a source film which is laterally graded in thickness. The surface is subsequently capped, and the Zn source is diffused into the GaAs using rapid thermal annealing. Secondary ion mass spectroscopy and spreading resistance measurements indicate that uniformly thick source depositions result in uniform diffusions with shallow junction depths and high surface concentrations. Alternatively, our measurements show that gradations in the dopant source profile translate into laterally graded doping profiles for appropriately chosen source thicknesses and diffusion parameters.

ISSN:1071-1023    

DOI:10.1116/1.586395

出版商:American Vacuum Society    

年代:1992

数据来源: AIP

摘要:

We have utilized the isothermal capacitance transient spectroscopy and modulated function waveform analysis to investigate the deep levels and DX centers in molecular beam epitaxially grown AlxGa1−xAs/GaAs Schottky diodes deposited onn+GaAs, with Al composition ranging fromx=0 to 0.5, and implanted with Si. In the concentration rangex=0.19 to 0.50, two major electron trap levels (E1andE2) were detected, which gradually changed with composition. For example,E1changed from 0.393 to 0.339 eV andE2changed from 0.136 to 0.287 eV. However, in pure GaAs, three major trap levels with energyE1(hole)=0.226 eV,E2(electron)=0.496 eV, andE3(EL2)=0.74 eV were observed. Apparently, these levels are governed by the deep levels known as DX centers.

ISSN:1071-1023    

DOI:10.1116/1.586396

出版商:American Vacuum Society    

年代:1992

数据来源: AIP

摘要:

The field effect has been investigated on the deep levels and DX centers in molecular‐beam epitaxilly‐grown AlxGa1−xAs onn+GaAs for several compositions. We have measured the isothermal and isofield capacitance transients for the major energy levels with the applied potential in the range from −0.1 to −3 V. In samples withx=0.5, two electron trap levels (E1andE2) were detected. WhileE1was strongly field dependent (changed from 0.499 to 0.287 eV)E2was practically unchanged (0.305 eV) with respect to energy, cross section, and peak broadening. Contrary to this in pure GaAs (samplesx=0), we observed three energy levels, one hole trap (E1=0.239 eV), one electron trap (E2=0.512 eV), and the usual EL2 trap (E3=0.72 eV). At this composition, however, levelsE1andE2were absent at low reverse fields (at −1 V) and EL2 remained unchanged at 0.72 eV. We have considered the recent theories of Pool–Frenkel effect and tunneling for electron–phonon interaction to interpret the results. In particular, for AlxGa1−xAs withx=0.5, the electron–phonon coupling factor (S) was found to be about 4 and the deep centers were identified as neutral to repulsive.

ISSN:1071-1023    

DOI:10.1116/1.586397

出版商:American Vacuum Society    

年代:1992

数据来源: AIP

摘要:

We have studied the low temperature magnetoresistance of In1−xEuxSb for a range of europium concentrations. We find that the addition of the rare earth element reduces the carrier mobility substantially and alters dramatically the character of the magnetoresistance. In particular, we observe negative magnetoresistance for 0.012

ISSN:1071-1023    

DOI:10.1116/1.586308

出版商:American Vacuum Society    

年代:1992

数据来源: AIP

摘要:

The successful preparation of double‐heterostructure (DH) distributed‐feedback (DFB) PbEuSe lasers using an embossing technique for the DFB sub‐micrometer grating is reported here for the first time. The submicrometer grating was performed in (111) oriented silicon wafers by holographic exposure and argon ion milling. Using a hydrostatic press this grating was embossed into a lead chalcogenide wafer, covered by a DH structure grown by molecular beam epitaxy. Lasers made from wafers with grating periodicities of 0.678 and 0.755 μm show DFB characteristics at the corresponding emission wavenumbers around 1420 and 1590 cm−1.

ISSN:1071-1023    

DOI:10.1116/1.586309

出版商:American Vacuum Society    

年代:1992

数据来源: AIP

摘要:

Using a 50 keV, fine diameter electron beam lithography system, and a substrate consisting of a 10 nm‐thick gold plating base on a 1 μm‐thick, 2 cm‐diam SiNxx‐ray mask membrane, we have successfully exposed interdigitated electrode patterns for quantum‐effect devices having lines and spaces of 50 nm. The resist is a single layer of polymethyl methacrylate (PMMA), 496 K molecular weight, 250 nm thick. That such fine features are achievable in a single layer of thick resist is attributed to: (1) reduced backscattering from the very thin plating base (10 nm Au versus the standard 30 nm) and thin substrate (1 μm‐thick SiNx); (2) a well focused beam; (3) proximity‐effect correction; and (4) precise exposure and development control. Once developed and ‘‘de‐scummed,’’ 200 nm‐thick gold is electroplated into the PMMA mold, yielding high contrast (∼12 dB) x‐ray masks suitable for the CuLlines at 1.3 nm. To avoid problems of distortion and peeling of the 50 nm‐wide lines, the plating was done under current–density andpH conditions that produce zero stress. The x‐ray masks were replicated onto substrates and ‘‘daughter’’ x‐ray mask membranes and electroplated, yielding ‘‘polarity reversal.’’ These polarity reversed masks, with 50 nm line‐and‐space features, can then be exposed onto device substrates using either contact or proximity x‐ray lithography. This overall process takes advantage of the best aspects of electron‐beam and x‐ray nanolithographies, i.e., the capabilities of the former to create patterns of arbitrary geometry, and the robustness and high process latitude of the latter.

ISSN:1071-1023    

DOI:10.1116/1.586284

出版商:American Vacuum Society    

年代:1992

数据来源: AIP

摘要:

Electron beam (EB) direct‐writing lithography with intraproximity effect correction has been developed for fabricating contact holes having deep submicron size. The dimensional accuracy of contact holes is strongly influenced by the intraproximity effect. In delineating contact hole patterns by using EB direct writing, it is necessary to increase the exposure dose a great deal. This is because the effect of backscattered electrons on the smaller hole patterns is decreasing. It was found that the forward scattering parameter in proximity function should be optimized in order to obtain high dimensional accuracy for contact holes with the minimum feature size of 0.2 μm. The accuracy within ±0.03 μm was realized for contact holes with their dimensions from 1.0 to 0.2 μm at the same time by using present intraproximity effect correction and noncharging trilayer resist process. When this high‐performance EB direct writing was applied to fabricate 0.2 μm size contact holes, the yield of the 104contact hole chains was improved to over 95% by using selectively deposited W film on the bottom of the contact holes.

ISSN:1071-1023    

DOI:10.1116/1.586285

出版商:American Vacuum Society    

年代:1992

数据来源: AIP

摘要:

Photoactive parameters of contrast enhancement material CEM 420 for Dill’s model were measured to analyze the contrast enhancement lithography (CEL) process. Then using the three‐dimensional photolithography simulator RESPROT, photoresist images in the CEL process were analyzed and compared with images got in a conventional process. The nature of the photosensitizer concentration distribution in contrast enhancement material (CEM) differs from that in conventional photoresist. The former has a higher contrast distribution. In the CEL process, the sidewall of the photoresist image has a steeper slope than that in the conventional one, and the depth of focus is improved 25% for the former. When defocus is 2.0 μm in the conventional process, the photoresist holes do not open but in the CEL process they do. The contrast of an aerial image in the photomask pattern is improved in the CEL process. For a three‐line pattern in the conventional process, the center photoresist line is narrow and low, but in the CEL process, all three lines have the same height and width. For a double elbow pattern in the conventional process, photoresist thicknesses differ inside and outside of the two elbow photoresist lines after development, however, they are the same in the CEL process.

ISSN:1071-1023    

DOI:10.1116/1.586286

出版商:American Vacuum Society    

年代:1992

数据来源: AIP