C. K. Maiti

Strained-Si heterostructure field effect transistors

The purpose of this review article is to report on the recent developments and the performance level achieved in the strained-Si/SiGe material system. In the first part, the technology of the growth of a high-quality strained-Si layer on a relaxed, linear or step-graded SiGe buffer layer is reviewed. Characterization results of strained-Si films obtained with secondary ion mass spectroscopy, Rutherford backscattering spectroscopy, atomic force microscopy, spectroscopic ellipsometry and Raman spectroscopy are presented. Techniques for the determination of bandgap parameters from electrical characterization of metal-oxide-semiconductor (MOS) structures on strained-Si film are discussed. In the second part, processing issues of strained-Si films in conventional Si technology with low thermal budget are critically reviewed. Thermal and low-temperature microwave plasma oxidation and nitridation of strained-Si layers are discussed. Some recent results on contact metallization of strained-Si using Ti and Pt are presented. In the last part, device applications of strained Si with special emphasis on heterostructure metal oxide semiconductor field effect transistors and modulation-doped field effect transistors are discussed. Design aspects and simulation results of n- and p-MOS devices with a strained-Si channel are presented. Possible future applications of strained-Si/SiGe in high-performance SiGe CMOS technology are indicated.

Properties of silicon dioxide films deposited at low temperatures by microwave plasma enhanced decomposition of tetraethylorthosilicate

Silicon dioxide films have been deposited at low temperatures (200–250 °C) by microwave plasma enhanced decomposition of tetraethylorthosilicate (TEOS). The effects of the presence of oxygen in the discharge in film deposition rate, mechanism, and the physical properties of the films have been investigated. Structural characterization of the deposited films has been carried out by etch rate measurements, infrared transmission spectra, x‐ray photoelectron spectroscopy, Auger, and secondary ion mass spectrometry analyses. Films deposited using TEOS and oxygen have confirmed a density comparable to standard silane‐based low‐pressure chemical vapor deposition and plasma enhanced chemical vapor deposition oxides, nearly perfect stoichiometry, extremely low sodium and carbon content, and the absence of many undesirable hydrogen related bonds. Various electrical properties, viz., resistivity, breakdown strength, fixed oxide charge density, interface state density, and trapping behavior have been evaluated by the...

Hole mobility enhancement in strained-Si p-MOSFETs under high vertical field

Abstract The growth of a high quality, step-graded lattice-relaxed SiGe buffer layer on a Si(100) substrate is investigated. p -MOSFETs were fabricated on strained-Si grown on top of the above layer. Carrier confinement at the type-II strained-Si/SiGe buffer interface is observed clearly from the device transconductance and C - V measurements. At high vertical field, compared to bulk silicon, the channel mobility of the strained-Si device with x =0.18 is found to be about 40% and 200% higher at 300 K and 77 K respectively. Measurements on transconductance enhancement are also reported. Data at 77 K provide evidence of two channels and a large enhancement of mobility at high transverse field.

Reliability of ultrathin (<2 nm) oxides on strained SiGe heterolayers

The influence of nitrogen incorporation on the reliability of ultrathin (<2 nm) rapid thermal oxides grown on strained Si/SiGe/Si heterolayers has been investigated. It is shown that rapid thermal oxidation using N2O followed by N2-annealing results in improved electrical properties and reliability in terms of stress induced leakage current, low bulk trap density, trap generation rate and high lifetime.

Electrical properties of oxides grown on strained SiGe layer at low temperatures in a microwave oxygen plasma

Microwave plasma oxidation of strained Si1−xGex layer has been carried out at low temperatures (150–200 °C). The chemical properties of the oxide investigated by x‐ray photoelectron spectroscopy show the formation of single phase mixed oxides consisting a SiO2 and GeO2, without any Ge pileup on the surface or at the substrate‐oxide interface. Electrical properties of the oxides show a moderately low value of fixed oxide charge and interface trap density. Grown oxides exhibit low leakage current (10−8 A/cm2) and high breakdown strength (5–10 MV/cm), and are useful for a gate dielectric in metal–oxide semiconductor field effect transistor.

Fluorine‐enhanced nitridation of silicon at low temperatures in a microwave plasma

A microwave plasma discharge at very low temperatures (200–250 °C) has been used for the growth of thin silicon oxynitride films suitable for gate dielectric applications. The addition of CHF3 as a source of fluorine enhances the growth rate. A x‐ray photoelectron spectroscopy study indicates the incorporation of fluorine (F/Si≂0.2) in the film. Electrical properties of the grown layers have been evaluated by the characterization of metal‐insulator‐semiconductor capacitors. Results have indicated the presence of negative charges in the insulator. The estimated charge density is lowest for the fluorinated film. The conduction mechanism in the films at room temperature appears to be Frenkel–Poole type.

Effect of reactive‐ion bombardment on the properties of silicon nitride and oxynitride films deposited by ion‐beam sputtering

Silicon nitride and oxynitride films of very low hydrogen content have been deposited on silicon at low temperatures (150–200 °C) using ion‐beam sputtering. A dual‐ion‐beam sputtering technique, making simultaneous use of an energetic argon‐ion beam to sputter silicon nitride from a target and a low‐energy oxygen or nitrogen ion beam to react with the sputtered films on the substrate, has been employed to control the composition of the films. A precise control of film composition independent of deposition rate has been achieved through the control of oxygen/nitrogen ion‐beam parameters and gas flow ratios. The films have been characterized by the measurement and study of refractive index, chemical etch rate, infrared absorption, and x‐ray photoelectron spectra. A direct correlation between film properties with oxygen content has been obtained for silicon oxynitride films. The electrical properties have been studied by the measurement of the characteristics of metal‐insulator‐semiconductor capacitors fabri...

Leakage current characteristics and the energy band diagram of Al/ZrO2/Si0.3Ge0.7 hetero-MIS structures

Zirconium oxide (ZrO2) films have been deposited on Ge-rich SiGe heterolayers at 150 ?C by the microwave plasma enhanced chemical vapour deposition (PECVD) technique using zirconium tetra-tert-butoxide. The possible conduction mechanisms in deposited ZrO2 films have been investigated at both room and high temperature. It is found that the conduction mechanism is dominated by Schottky emission at a low electric field (E 1.2 MV cm?1). The extracted trap energy is about 0.78 eV from the conduction band of ZrO2. It is shown that the current in ZrO2 films exhibits strong temperature dependence at a low electric field. The trapping behaviour of the charge carriers in thin ZrO2 gate dielectric stacks during constant gate voltage stress of metal?oxide?semiconductor capacitors has also been investigated.

Extraction of interface state density of Pt/p-strained-Si Schottky diode

Abstract Interface state density of Pt/p-strained-Si Schottky contacts has been determined using experimental forward bias current–voltage (J–V) and capacitance–voltage (C–V) techniques. The effects of interfacial oxide layers and series resistance present in the structure have been studied using a SEMICAD device simulator. It is shown that the interface state density can be obtained directly from the measure of C–V data and is found to decrease as the energy from the edge of the valence band increases.

Ultrathin oxides using N2O on strained Si1−xGex layers

Microwave N2O plasma oxidation of strained Si1−xGex layers at low temperature (<200 °C) is reported. The hole confinement in accumulation in a metal oxide semiconductor (MOS)‐gated SiGe/Si heterostructure has been confirmed by both simulation and experiments. Electrical properties are also discussed.