摘要:

Compositional grading at the emitter‐base junction ofNpnheterojunction bipolar transistors (HBTs) has been achieved by using a nine period graded gap AlInAs/GaInAs superlattice of 300 Å thickness. The as designed 500 Å base region was doped using Be fluxes that ranged from 0.8×1012to 1.4×1012atoms/cm2 s. Growth over this flux range resulted in a base doping of 4.5×1019cm−3with the highest flux producing an additional 160 Å of Be penetration into the graded region as compared with the lowest flux. The dc and rf characteristics of the graded emitter‐base HBTs are found to be tolerant to this degree of Be outdiffusion.

ISSN:1071-1023    

DOI:10.1116/1.586065

出版商:American Vacuum Society    

年代:1992

数据来源: AIP

摘要:

Two ohmic contact systems for quantum effect devices and heterojunction bipolar transistors (HBTs) were investigated and compared. Ni/Ge/Au/Ti/Au and Pd/Ge/Ti/Al were characterized for diffusion length after annealing and specific contact resistivity on chemical beam epitaxially grown In0.53Ga0.47As. It was found, in general, that the diffusion length could be controlled by varying the total metal thickness and that the specific contact resistivity maintained reasonably low values as long as the compositional ratio of each system remained constant. The diffusion length for Ni/Ge/Au/Ti/Au ranged from 1000 to 2000 Å and that of Pd/Ge/Ti/Al was ∼300 Å. In both cases the specific contact resistivity onn‐type InGaAs was 5×10−7Ω cm2. Furthermore, the Pd/Ge/Ti/Al was applied top‐type InGaAs and showed a specific contact resistivity of 3×10−6Ω cm2. Finally, both systems were used to fabricate an InGaAs/InP hot electron transistor and an InAlAs/InGaAs HBT with excellent direct‐current results.

ISSN:1071-1023    

DOI:10.1116/1.586067

出版商:American Vacuum Society    

年代:1992

数据来源: AIP

摘要:

A trilevel resist scheme using low temperature (≤50 °C) deposited SiNxrather than Ge for the transfer layer has been developed. This allows use of an optical stepper for lithographic patterning of the emitter‐base junctions in GaAs/AlGaAs heterojunction bipolar transistors where a conventional lift‐off process using a single level resist often leads to the presence of shorts between metallizations. The plasma‐enhanced chemically vapor deposited (PECVD) SiNxshows a slightly larger degree of Si–H bonding compared to nitride deposited at higher temperature (275 °C), and is under compressive stress (∼5×1010dyn cm−2) which is considerably relieved upon thermal cycling to 500 °C (∼1.5×1010dyn cm−2after cooldown). This final stress is approximately a factor of 2 higher than conventional PECVD SiNxcycled in the same manner. The adhesion of the low temperature nitride to the underlying polydimethylglutarimide base layer in the trilevel resist is excellent, leading to high yields in the lift‐off metallization process. These layers are etched in electron cyclotron resonance discharges of SF6or O2, respectively, using low additional dc bias (≤−100 V) on the sample. Subsequent deposition of the HBT base metallization (Ti/Ag/Au) and lift‐off of the trilevel resist produces contacts with excellent edge definition and an absence of shorts between metallization.  

ISSN:1071-1023    

DOI:10.1116/1.586068

出版商:American Vacuum Society    

年代:1992

数据来源: AIP

摘要:

Epitaxially grownn‐type GaAs was sputtered by bombarding it with Ar ions at energies of between 0.5 and 5 keV at a dose of 1013ions/cm2. The fabrication of Au Schottky barrier contacts followed directly after the sputtering. The electrical characteristics of the the sputter induced defects were studied using deep‐level transient spectroscopy (DLTS). Several defects with discrete defect levels ranging from 0.05–0.70 eV below the conduction band, as well as defects with continuously distributed energies in the conduction band, were introduced during sputtering. Concentration depth profiling revealed that whereas some defects are located very close to the interface, others were detected several microns below the interface. The depth of some of these deep lying defects increased with sputter voltage. A possible explanation of the reduction in EL2 DLTS signal previously observed after sputtering is shown to be the sputter induced barrier height lowering.

ISSN:1071-1023    

DOI:10.1116/1.586069

出版商:American Vacuum Society    

年代:1992

数据来源: AIP

摘要:

The adsorption and thermal desorption of chlorine on GaAs(100) surfaces prepared either As‐rich or Ga‐rich has been studied using Auger electron spectroscopy, thermal desorption spectroscopy (TDS), and low‐energy electron diffraction (LEED). The initial adsorption occurs more rapidly on the Ga‐rich surfaces, however saturation coverages appear equal on both As‐ and Ga‐rich surfaces. Monitoring the As and Ga Auger signals during adsorption reveals a consistent drop in the As signal while the Ga signal remains constant, which may be a result of a replacement reaction between Cl and As. Sputter damaged surfaces result in more exposed Ga, and hence, 20% more chlorine can be adsorbed onto this surface. LEED and TDS experiments on clean surfaces reveal that desorption of As2closely follows observed reconstruction changes. Chlorine saturated surfaces, however, show no noticeable reconstruction change from that of the clean surface, and upon heating the saturated surface, only GaCl and As2are seen as desorption products. Both the adsorption and desorption behavior of chlorine suggest a preferential formation of a Ga–Cl bond at the GaAs surface.

ISSN:1071-1023    

DOI:10.1116/1.586070

出版商:American Vacuum Society    

年代:1992

数据来源: AIP

摘要:

The characteristics of plasma etching of InP, InAs, InSb, GaAs, AlGaAs, GaSb, AlInAs, InGaAs, and AlInP in microwave (2.45 GHz) discharges of methyl‐, ethyl‐, and propyl‐iodide have been examined with respect to etch rates, surface morphology, damage introduction, and etch anisotropy. The etch rates for all of these semiconductors are somewhat faster than for conventional CH4‐based discharges under the same conditions of direct‐current bias, pressure, and microwave power, but are not as fast as with HI discharges. Polymer deposition on the mask and within the chamber occurs as with CH4‐based mixtures, but is minimized at low pressure (≤10 mTorr) and with H2dilution. The etched surface morphologies are smooth over a wide range of plasma parameters and show roughness only under conditions of significant polymer deposition. Chemical analysis by Auger electron spectroscopy and x‐ray photoelectron spectroscopy also shows that the near surface of the etched samples retains its stoichiometry under most conditions. While the etch rates are slower than for HI‐based discharges, the halocarbon iodides are significantly less corrosive and much more stable.

ISSN:1071-1023    

DOI:10.1116/1.586071

出版商:American Vacuum Society    

年代:1992

数据来源: AIP

摘要:

An expanding cascaded arc is used as a fluorine atom source for fast etching of silicon. Extremely high etch rates up to 1.3 μm/s have been obtained. A reactor parameter study has been performed. The obtained selectivity Si/SiO2is ∼11 for substrate temperatures of 600 °C, increasing to ∼20 at 100 °C. The etching proces is fully isotropic.

ISSN:1071-1023    

DOI:10.1116/1.586072

出版商:American Vacuum Society    

年代:1992

数据来源: AIP

摘要:

A direct process for fabricating nanometer size trenches in Si3N4using high voltage electron beam lithography and CHF3/O2reactive ion etching has been developed and characterized. The process can be used on both bulk and thin membrane substrates and has demonstrated a feature resolution of better than 20 nm. An extension of this process allows 15 nm wide slots to be fabricated in a metal film without performing any metal etching.

ISSN:1071-1023    

DOI:10.1116/1.586073

出版商:American Vacuum Society    

年代:1992

数据来源: AIP

摘要:

Surface residues and near‐surface damage present in the surface and near‐surface regions of Si after reactive ion etching with CF4, CF4+H2, and CHF3were investigated with secondary ion mass spectrometry, laser ellipsometry, x‐ray photoelectron spectroscopy, and cross‐sectional transmission electron microscopy. Specifically, the change in the thickness and composition of the deposited residues with changes in the backfill gas chemistry was investigated. A fluorocarbon (FC) residue was found to develop on all etched samples, with thicknesses ranging from a few angstroms to microns. Two regimes of FC deposition were identified, where (a) a steady‐state FC layer quickly develops during etching, and the net FC deposition rate drops to zero thereafter, and (b) the FC deposition continues at a constant rate throughout the etch. F was found to diffuse to the Si surface to form a fluorinated Si layer between the deposited FC layer and the bulk Si. This layer was taken to be the reaction layer resulting from diffusion‐limited kinetics in this etch system. The diffusion of F or C into the near‐surface region of Si was not observed to change with increasing H2additions. A simple quantitative model was developed based on rate‐limiting Fickian diffusion through the deposited FC layer. The model was found to agree well the available etch rate data. Si etching with CHF3was found to behave similiarly to CF4+H2etching in the steady‐state FC layer regime.

ISSN:1071-1023    

DOI:10.1116/1.586074

出版商:American Vacuum Society    

年代:1992

数据来源: AIP

摘要:

The appearance of striations on dry etched semiconductor laser mesas is a common feature of these structures. We describe a number of different methods of reducing the extent of this roughness, including the choice of dielectric etch chemistry, modification of the initial resist processing, and deposition of a SiN sidewall to prevent additional roughening during the plasma etch step. SF6is found to be preferable to CF4for dielectric etching because of an absence of polymer formation. This produces smoother SiO2sidewalls. Flood exposure of theinitial photoresist mask and optimization of the postbake temperature also produces smoother sidewalls on the subsequently etched SiO2. The sidewall can also be protected from roughening that occurs during the dry etch step by coating it with a low temperature SiN layer. A combination of all of these methods produces sidewalls with morphological variations of ≤500 Å.

ISSN:1071-1023    

DOI:10.1116/1.586075

出版商:American Vacuum Society    

年代:1992

数据来源: AIP