of Chapter 1 - Silica, silicon nitride and oxynitride thin films - An overview of fabricationtechniques, properties and applications. Although thermal oxide remains an insulator of choice for silicon-based microelectronic devices, thin nitride and oxynitride films possess superior qualities for specific applications. In this chapter we describe both the main techniques used to manufacture thin nitrided insulator films and the main physical and electrical properties of the obtained films. The direct nitridation of silicon in ammonia, by thermal means, is difficult because it requires high temperature (> 950°C) and the obtained films are very thin ( Since the network of amorphous silicon nitride is denser than that of silica, it resists chemical etching (by HF solutions) better and behaves as a better barrier against diffusion. These properties are exploited in the LOCOS process. Unlike the oxide defects, the defects contained in nitrides behave mostly as electron traps. Thin oxynitride films can be fabricated by nitriding thin silica films in ammonia at high temperature (> 800°C). Nitridation may be performed at low pressure (P(NH3) The introduction of nitrogen atoms in silica, their concentration and their distribution modify in a complex fashion the physical and electrical properties of this material. The presence of nitrogen increases the dielectric strength of silica but increases the density of electron traps and introduces a hole conduction mode. It is also possible to fabricate thin oxide or nitride films, or to nitride thin silica films by using Rapid high Temperature Processes (based on the lamp heating of single wafers). The short process times used allow one to fabricate films whose properties are superior to those grown in furnace processes. To minimize the problems associated with the presence of hydrogen atoms introduced in nitrides during processing in ammonia, one can reoxidize these nitrided films. It is also possible to obtain virtually hydrogen-free nitride films by processing silicon surfaces directly in gaseous N2O or NO. The films thus obtained possess electrical properties which are superior to those of usual nitride films, and especially a greater dielectric strength and a better resistance to electrical stresses. It is also possible to fabricate nitride and oxynitride films at lower temperatures (and even at room temperature) by enhancing the reactivity of the species involved, by non-thermal means. These processes, briefly reviewed, use photons, electrons, ions or plasmas as an enhancement method, which allows one to reduce considerably the “thermal budget”. Thin nitride and oxynitride films have found numerous applications in microelectronic devices.

Chapter 1 Silica, silicon nitride and oxynitride thin films: An overview of fabrication techniques, properties and applications

Due to the fast development of microelectronics, quite an important number of the chemical aspects of component formation has been occulted. In particular just a few studies are related to thin film formation in the scope of chemical reactions and modelisation. Thermodynamics itself has been implemented rather ponctually and in an incomplete way. One of the Mayn reasons for this is that thin films are considered as standingly non equilibrium systems and that. thermodynamics, as a macroscopic science, has Maynly been considered as inadequate. Thus, we have decided to reconsider the problem of thin films formation from a strictly chemical point of view.Using a simple system (formation of silicon nitride on monocrystalline silicon), the chemical reactions have been investigated.
 Classical thermodynamics, though inaccurate and approximate for such systems is necessary to develop the first steps of a thermodynamical model describing the deposit formation. Using a computer program helping a global treatment of several chemical reactions confirms the conclusions obtained by classical thermodynamics. We have discussed the insufficiency of the classical model, and shown that, with respect to what was experimentally observed, it was nevertheless globally valid, and that the nitride formation should be regarded as a superposition of classical chemical reactions that occurred in "close to the equilibrium" states and globally following the classical laws of thermodynamics. Thus, we propose a model of formation for the first mono layer of Si 3 N 4 on monocrystalline silicon which is in total agreement to experimental observations.

Thermodynamical study of the thermal nitridation for the system NH3/monocristalline Si

Model of Formation of Thin Insulating Films on Silicon

An optical fiber sensor based on the resonant coupling between a surface plasmon wave and a guided mode of the optical fiber sensor has been reported. A technique based on the surface plasmon resonance phenomenon offers a sensitive method for studying the stability of optical sensors. In this work, the authors consider a layered structure consisting of three-layer optical waveguides incorporating silver-monolayer of bovine serum albumin coating layers. Tests include exposing these films to /spl beta/2-microglobulin have been studied. Experimental and theoretical results have been mutually compared, and the operation characteristics of this novel sensing device have been briefly described.

SPR sensor for detection of /spl beta/2-microglobulin

Boron was implanted in crystalline silicon through oxide layers with different thicknesses. The implantation is carried out at various doses and energies of interest in Ultra Large Scale Integration (ULSI) applications. Rapid thermal annealings (RTA) are used in a way to obtain shallow junctions and electrical activation of the B atoms. However, transient enhanced diffusion induced by implantation damage can be observed on boron profiles before and after annealing obtained with secondary ion mass spectrometry (SIMS). It is found that the diffusion transient in the tail region of the boron profile increases with decreasing oxide thickness. Even more, if the implantation damage concerns mostly the oxide, i.e. when the concentration peak is located into this oxide, the oxygen knocked into the silicon substrate could play an important role in restricting the boron diffusion.

J.C. Bureau

Papers

Model of Formation of Thin Insulating Films on Silicon

SPR sensor for detection of /spl beta/2-microglobulin

On the knocked oxygen contribution to low energy implanted boron diffusion retardation