Abul Kabir

Method of making high sensitivity micro-machined pressure sensors and acoustic transducers

A method of making a pressure sensor or acoustic transducer having high sensitivity and reduced size. A thin sensing diaphragm is produced by growing a single crystal, highly doped silicon layer on a substrate using a chemical vapor deposition process. The diaphragm is incorporated into a pressure sensor or acoustic transducer which detects pressure variations by a change in the capacitance of a capacitor which includes the diaphragm as a movable member. The thin diaphragm produces a highly sensitive device which can be fabricated in a smaller size than sensors or transducers having thicker diaphragms.

Phosphorus and arsenic profile control for high performance epitaxial base bipolar junction devices

In this study, we report on the incorporation behavior of n-type species in undoped layers grown subsequent to doped layers at low temperature (700–750 °C) reduced pressure chemical vapor deposition of silicon/silicon germanium (Si/Si1−xGex) performed in a single wafer epitaxial deposition system. Significant amounts of these species are observed even in an undoped layer grown subsequent to the doped layer. The presence of these dopants in the subsequently grown undoped layer is attributed to segregation at the moving growth interface. The arsenic segregation is confirmed to be significantly higher than phosphorus. In addition, an increase in both the phosphorus and arsenic incorporation is observed in the presence of a highly doped boron layer.

Formation of self-assembled Si1−xGex islands using reduced pressure chemical vapor deposition and subsequent thermal annealing of thin germanium-rich films

Abstract In this study, we report on the initial experimental results of formation of self-assembled Si1−xGex islands by the selective chemical vapor deposition of highly strained Si1−xGex thin films (with x∼0.4) on patterned silicon wafers and the subsequent annealing of these thin films. Unlike previous studies, islands are formed during the thermal annealing of these thin films after the growth of the smooth continuous selectively grown thin films and not by direct growth of the islands. 50–160 A Si0.6Ge0.4 films are selectively grown on silicon wafers with an oxide pattern using chemical vapor deposition from germane, silane and HCl at 650°C and 40 Torr. In situ annealing of the films at 650–750°C at 20–40 Torr for 6–25 min resulted in the formation of the islands. The size and distribution of the islands was found to be a function of the annealing conditions and an ordered pattern can be achieved with specific annealing conditions.

Tungsten silicide and tungsten polycide anisotropic dry etch process for highly controlled dimensions and profiles

Highly anisotropic dry etching of tungsten silicide an tungsten polycides is required for the realization of su micron low resistance gates and interconnects for use in performance complementary metal–oxide–semicondu ~CMOS! and BiCMOS technologies. 1 The current etch chemistries are not anisotropic, i.e., lateral etching of tungsten silicide takes place which results in undesirable loss. In many applications a spacer needs to be formed on polycide sidewall~Fig. 1!. Undesirable undercutting can re sult in nonideal spacer formation for further device fabric tion. Tungsten silicide etching has been described in litera using mixtures of SF 6, Cl2 , or CF4. 2–4 However, all these chemistries have excessive undercutting, no end point de tion, and poor control of sidewall profile. It is the purpose this brief to describe an etch chemistry using C 2F6, Cl2 , and O2 which forms polymer on the sidewall of the tungst silicide during the etch in order to avoid undercutting. 5 In addition, the etch chemistry allows increase of the criti dimension by controlling the polymer deposition on the sid wall.

Single crystal silicon beams formed by merged epitaxial lateral overgrowth (MELO) for optical reflectors

Single crystalline silicon has very well known and predictable mechanical, optical, and electrical properties and is easily manufactured with consistent results. It is also integrated circuit compatible and leads to incorporation of circuits and high quality piezoresistors which are available to monitor motion for self-testing. We present for the first time a novel surface micro-machining process using merged epitaxial lateral overgrowth (MELO) silicon to demonstrate the fabrication of single crystal silicon, free standing cantilever beams 1 mm long and 5 micrometers X 10 micrometers in cross section. These beams had no evidence of stress related bending and were free from the substrate, returning to its original position after numerous electrostatic deflections. MELO has also shown great potential for advanced BJT and MOSFET device applications, hence active devices can be incorporated into the deflecting beam arrays. Diodes fabricated in the beams show excellent characteristics with average ideality factors of 1.01. Note that the technology permits adding of single crystal silicon to selected areas, hence it is an additive process as compared to traditional subtractive methods that deposit films over the entire wafer.