Doping Step Research Articles

Minimal ohmic contact resistance limits to n-type semiconductors

An exact general formula for the lower contact resistance limit is derived, giving the lowest possible ohmic contact resistance for nondegenerate and degenerate metal-semiconductor contacts. Calculations for nondegenerate semiconductors include the nonparabolic nature of the conduction-band electrons and full Fermi–Dirac statistics. A discussion of standard emission theories shows that they are not applicable in the ohmic contact limit because of ‘‘electron tail lowering’’ and the negligence of quantum-mechanical reflections due to occupied states on the opposite side of their derivation. Together with a proof that an abrupt n-n+ doping step is governed by thermionic emission, the ohmic contact resistance of a general ohmic contact is determined and it is shown that the n-n+ doping step is responsible for this limitation. Thus, the lowest possible contact resistance is determined by the bulk doping of the semiconductor for a large variety of different alloyed and nonalloyed contact structures and not by the surface doping concentration. The theory predicts a lowest possible contact resistance in the 1 × 10−8 Ω cm2 region for parabolic III-V semiconductors and of about 3 × 10−9 Ω cm2 for Si and Ge.

Flow of PECVD Oxide Films Doped with POCl3

In this work plasma‐enhanced CVD oxide layers doped by a conventional liquid‐dopant‐source have been evaluated for use as planarization and intermetal dielectric films. The results obtained for the tangential angle of flow show that the use of a doping step in a atmosphere followed by a flow step in an oxidizing ambient gives rise, down to 850°C, to acceptable planarized surfaces to ensure continuity of subsequently deposited metal layers. Although a highly doped layer exists at the surface of the obtained films, the etching of these layers by reactive ion etching leads to contours acceptable for planarization purposes and as a consequence they can be implemented in a CMOS technology.

A shallow junction submicrometer PMOS process without high temperature anneals

A PMOS process resulting in very shallow, low-leakage source-drain junctions without high-temperature annealing following doping is discussed. The doping is performed using gas immersion laser doping which relies on a melt/regrowth process, initiated by a pulsed excimer laser (XeCl, lambda =308 nm), to drive in the dopant species. The properties of the resulting source/drain layers are discussed. A significant feature of this process is that unwanted diffusions are eliminated because no high-temperature anneals are used after the doping step. Submicrometer PMOS devices fabricated using this process exhibit excellent short-channel behavior with some process conditions resulting in very little or no threshold-voltage shift down to submicrometer gate lengths. >

Electrochemical oxidation of (CH) x in sulphuric acid

Polyacetylene reacts with pure and water- or nitromethane-diluted sulfuric acid. Two reversible doping steps have been evidenced by cyclic voltammetry techniques. A preliminary EPR study effected on heavily-doped samples shows the metallic character of these materials.

Kinetics of Antimony Doping in Silicon Molecular Beam Epitaxy

A new kinetic model for Sb doping into the Si MBE layer is proposed. In this model, Sb doping steps are assumed as follows: a fraction of impinging Sb4 molecules adsorbs on the growing Si surface (adlayer) and monoatomic Sb desorbs from the adlayer into vapor; a fraction of monoatomic Sb in the adlayer is incorporated into the bulk, so that surface-concentration of Sb atoms may be in equilibrium with bulk-concentration of Sb. According to this model, calculated results successfully represent the present experimental data on relations between incident Sb4 flux, Sb concentration in the adlayer and that in bulk. As a result, it is indicated that doping levels in MBE layers are uniquely determined by Sb concentration in the adlayer, and not by Sb4 flux/Si flux ratio, when Si growth rate is lower than 1 Å/s.

Improved frequency stability of PZT resonators by manganese doping and special process steps

Abstract For different applications, e.g., resonators in oscillator circuits, professional filters and frequency discriminators, high stability of resonance frequency is needed.

AES Study of Boron Diffusion in Silicon from a Boron Nitride Source with Hydrogen Injection

Boron diffusion in silicon from a boron nitride source with a doping step in hydrogen was characterized with Auger electron spectrometry and depth profiling. The thickness and the composition of the boron‐rich layer (BRL) which grows in this process were studied as a function of the oxygen concentration in the gas phase in the final cooling step. Oxygen diffuses to and through the BRL to the BRL/Si interface: The silicon in the boron‐rich layer is preferentially oxidized, and a silicon dioxide layer grows for a high enough oxygen concentration. A chemical etch in hydrofluoric acid can then remove this oxide layer and lift away the remaining BRL. A range in oxygen concentration was found for which the doping level is practically the same as for sample diffused with no oxygen in the cooling step, but subjected to an oxidation at low temperature, which is the usual method for the BRL removal.

Depletion-Layer Capacitance of p+n Step Junctions

It is shown that when the contribution of holes in a p+n junction to the space charge in the n region adjacent to the doping step is considered, the capacitance C as function of applied voltage Va is given by C−2=[2(ND+NA)/qεNDNA](Va+Vx).Here NA and ND are acceptor and donor concentrations and Vx, called the offset voltage, has the classical value of built-in voltage minus 2kT/q for nearly symmetrical junctions, independent of applied voltage. For large doping ratios NA/ND, the offset voltage is nearly independent of built-in voltage but increases nearly logarithmically with applied voltage. For forward bias the present treatment gives capacitance values considerably larger than those resulting from the widely accepted treatment which neglects the charge of holes on the n side.