Dépôt chimique CVD de silicium dopé in situ au phosphore. Partie 1: Etude expérimentale

The fabrication of silicon layers doped in situ with phosphor using CVD technique is still poorly controlled by the microelectronics industry. Significant thickness heterogeneities are noticeable on circuit and load, which greatly limits the process utilization. An experimental study of this deposition was carried out. The influence of many parameters (temperature, pressure, feed composition) was studied in terms of deposition thickness and uniformity as well as crystalline structure and resistivity. The advantages and involved mechanisms are presented.     

Une nouvelle technologie d'appareils de dépôt chimique en phase vapeur. Partie 2 : Modélisation du dépôt de silicium pur à partir de silane et de silicium dopé in situ au phosphore

A better understanding of Chemical Vapour Deposition (CVD) process can be obtained by modelling the phenomena involved in CVD reactors. The established model is then a useful tool for industrial equipment design and for the optimization of operating conditions. The research for optimal operating conditions is done by a more rational and efficient way using a model. The specific case of the polycristalline silicon deposition from silane in a new technology of LPCVD reactor is used to illustrate the approach. Hypotheses and methods necessary for the development of the model are presented and discussed first, then results are described and compared to experimental data. Finally, the more complex case of in situ phophorus doped polysilicon is discussed.     

Influence des principaux paramètres opératoires sur le dépôt de silicium à partir de silane par CVD en lit fluidisé en vue de limiter les problèmes d'agglomération

Chemical vapour deposition of silicon from silane on fluidized powders is an efficient and flexible surface modification technology; however, its main drawback is the agglomeration of the fluidized particles beyond a critical initial concentration of silane. To clarify this phenomenon, we have studied the influence of operating conditions covering temperatures lower than 550°C, both experimentally and theoretically using the simulation model of Kato and Wen (1969). The influence of the main operating parameters has been accurately determined not only on the process throughput but also on the thermal behaviour of the bed, which is directly linked to the solid phase motion and then to the possible agglomeration of particles.     

Méthodologie d'étude et de modélisation de la déphosphatation d'effluents aqueux

Due to phosphorus impact on water pollution, a P‐recovery process by calcium phosphate precipitation was developed. The reactor process is a fluidized bed in which phosphate precipitates continuously and coats sand grains. The pilot unit can treat synthetic wastewater flow rates ([P] = 50 mg/l) of about 0.1 m3/h. A two‐stage methodology is proposed to understand the physicochemical phenomena. Fluidized bed precipitation modeling involves thermodynamical concepts taking into account the various calcium phosphates that can precipitate vs. operating conditions (PH, [P], [Ca], T). Coating modeling is performed by a first‐order kinetics reaction between fines and sand grains, combined with a network of ideal reactors representing system hydrodynamics.     

Analyse des interactions fluide-paroi dans un système ouvert a partir de la connaissance de la distribution des temps de sejour. Application aux dépôts d'aérosols par thermophorèse

In an open material system where the residence time distribution of a fluid is known, it is possible, using micromixing Zwietering' model to predict the results of linear interaction between the fluid and the wall of system but also for the aerosol particles transported by the fluid flow. This methodology is applied for aerosol deposition by thermophoresis in cylindrical pipe with constant wall temperature. The interpretation of experimental results in laminar flow shows that, for Knudsen numbers between 0.2 and 1.0, the thermophoresis coefficient must be calculated by Talbot' correlation. Finally, in transition flow, the aerosol mass deposition by thermophoresis and turbulent diffusion becomes probably minimal.     

Modélisation d'un four de calcination du coke de pétrole: I. Le modèle

In this first of a two-article series, a one-dimensional steady-state mathematical model has been developed to simulate the process of calcination of petroleum coke in a rotary kiln. The model is made of 14 ordinary differential equations describing the conservation of energy and mass in the coke bed and in the freeboard gas. They are solved simultaneously using the 4th-order Adams-Moulton numerical method. The model calculates the various temperature profiles and the mass concentration profiles of the different chemical species. Special emphasis is laid on the usual process variables such as calcined coke recovery factor, and the loss of coke in the form of dust exhausted with the gas. In the second article, a complete simulation will be presented and the results discussed. Also, a comparison with existing models will be made.     

Evaluation des dépôts d'aérosols par thermo et diffusiophorèse lors de l'ecoulement dans une conduite cylindrique — applications aux essais tuba diffusiophorèse

In the hypothesis of a severe accident on a pressurized water nuclear reactor, the aerosols created and carried by a gas flow consist of steam and incondensable gases which can settle by different mechanisms on the walls of the primary circuit. In particular, in the tubular bundle of steam generator, on contact with the wall cooled by the water flowing at the outside of the bundle, the aerosols are transferred and fixed on the wall by thermo and diffusiophoresis. A model of the deposition on a vertical cylindrical tube based on the mass and energy balances allows us to show that the efficiency of the deposit depends only on two thermohydraulic parameters. The theoretical relations of the efficiency applied to the Institut de Protection et de Sûrete Nucleaire experimental program “Tuba diffusiophoresis” agreed with experimental results and confirm that the efficiency of deposition by thermo and diffusiophoresis must be evaluated simultaneously rather than independently.     

Contrǒle hydrodynamique en convection mixte de l'épaisseur de dépǒts en phase gazeuse de semi-conducteurs sur des corps à symétrie de révolution

The authors solve using an finite difference method the equations of steady-state laminar boundary layer around a body of revolution (sphere, extended and flattened ellipsoids). Hydrogen gas at 25°C flows upward around the body. Its nose faces downward, the temperature of its surface is 500°C and it rotates about its vertical axe at a constant velocity. The variability of the physical properties of the fluid as a function of temperature is considered as well as the resulting natural convection. It is revealed that flow, heat and mass transfers depend of the physical properties of the gas. It is possible to control the development of thermal and diffusional boundary layers through the operational conditions, specially the contour of the body.     

Étude comparative de flux et de performances lors du traitement d'effluent papetiers par bioréacteur à membranes

The goal of this study was to evaluate the role of the membrane within a membrane bioreactor (MBR) and to model the flux. Two models developed for external membrane bioreactor enabled the evaluation of the importance of mixed liquor suspended solids. The effect of backwash was also quantified. A performance comparison of two membrane bioreactors using membranes with different pores demonstrated the predominant importance of the sludge layer (deposited at their surface and inside of the membranes) versus the pore size.