Nirmal B. Chakrabarti

Strained silicon heterostructures : materials and devices

* Chapter 1: Introduction * Chapter 2: Strained Layer Epitaxy * Chapter 3: Electronic Properties of Alloy Layers * Chapter 4: Gate Dielectrics on Strained Layers * Chapter 5: SiGe Heterojunction Bipolar Transistors * Chapter 6: Heterostructure Field Effect Transistors * Chapter 7: BICFET, RTD and Other Devices * Chapter 8: MODFETs * Chapter 9: Contact Metallization on Strained Layers * Chapter 10: Si/SiGe Optoelectronics

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.

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.

TEOS-based PECVD of silicon dioxide for VLSI applications

Silicon dioxide films deposited from tetraethylorthosilicate (TEOS) using plasma-enhanced chemical vapour deposition (PECVD) are reviewed. The effect of the presence of oxygen on the film deposition rate and mechanism and the physical properties of the films, particularly the step coverage properties (conformality), are discussed in detail. Structural characterisation of the films has been carried out via etch rate measurements, infrared transmission spectroscopy, X-ray photoelectron spectroscopy (XPS) and Auger and secondary ion mass spectroscopy (SIMS) analysis. Electrical properties, i.e. resistivity, breakdown strength, fixed oxide charge density, interface state density and trapping behaviour, have been evaluated using metal-oxide-semiconductor (MOS) structures fabricated using the deposited oxides. Films deposited by microwave plasma-enhanced decomposition of TEOS in the presence of oxygen have been found to be comparable with standard silane-based low-pressure chemical vapour deposition (LPCVD) and PECVD oxides. It has been shown that films deposited on thin native oxides grown by either in situ plasma oxidation or low-temperature thermal oxidation exhibit excellent electrical properties.

Low-temperature deposition of dielectric films by microwave plasma enhanced decomposition of hexamethyldisilazane

Hexamethyldisilazane (HMDS) has been used as an organosilicon source for the deposition of dielectric films at low temperatures (200-250° C) by microwave plasma enhanced CVD technique. Hydrogenated films of variable composition of silicon carbonitride, silicon oxynitride and silicon dioxide have been deposited by decomposition of HMDS in the presence of additive gases like NH3, O2 and H2 under different process conditions. Deposited films have been characterized by the measurement of refractive index and buffered HF etch rate, and by the analysis of XPS and infrared transmission spectra. An increase in HMDS partial pressure generally results in the decrease of refractive index. The films show stable C-V characteristics of metal-insulator-semicon-ductor (MIS) capacitors with positive insulator charge density.

Estimation of hole mobility in strained Si1−xGex buried channel heterostructure PMOSFET

Abstract Fabricated strained Si/Si0.8Ge0.2/Si heterojunction PMOSFET devices have been used to calculate the hole mobility in surface-Si and buried-SiGe channels. A simple analysis based on the inversion layer mobility model has been used to find the current contribution of the buried-SiGe channel to the total drain current. The ‘true’ effective mobility enhancement in the buried channel of the fabricated Si0.8Ge0.2 PMOSFET device has thus been extracted over a temperature range of 77–300 K. The validity of the model has been verified by calculating the drain current as a function of drain voltage at different values of gate bias considering the estimated effective mobility of both parasitic-Si and buried-SiGe channels.

Deposition of composition‐controlled silicon oxynitride films by dual ion beam sputtering

Silicon oxynitride films of controlled composition have been deposited on silicon by dual ion beam sputtering (DIBS) making simultaneous use of an energetic argon ion beam to sputter silicon nitride from a target and a low‐energy oxygen ion beam to react with the sputtered film on the substrate. The correspondence between film properties and oxygen beam parameters has been studied from measurements of refractive index, chemical etch rate, infrared absorption, and x‐ray photoelectron spectroscopy spectra. In situ ion beam oxidation of silicon prior to oxynitride deposition results in a film with a low insulator charge density (3.5×1011 cm−2) and interface trap density (4×1011 cm−2 eV−1).

Thick-Film Ferrimagnetic Pastes Using Lithium Ferrite

The preparation of a thick-film ferrimagnetic paste using lithium ferrite powders and its physical, electrical, and magnetic properties are described. A resonance technique for the measurement of the dielectric constant, saturation magnetization, loss tangents, and resonance linewidth of the ferrite films at microwave frequencies is presented. Applicability of the ferrite pastes developed for the fabrication of nonreciprocal microwave components such as isolators and circulators is described.

Silicon heterostructure devices for RF wireless communication

Wireless communication of high speed data in UHF-microwave region, requires RFIC implementation of the front end for low cost consistent with high performance. The suitability of silicon based devices and circuits, in particular Si/SiGe heterostructures, is examined in this paper. Issues related to the change of technology for RFICs are considered and it is shown that scaled SiGe-HBTs satisfy the requirements of transconductance/gain, f/sub T//f/sub max/ and noise figure. Results of simulation of SiGe-HBT devices, amplifiers using them, and also the noise figure have been presented.