In the case of the semi-insulating polycrystalline silicon ͑SIPOS͒ SiO x low-pressure chemical vapor deposition ͑LPCVD͒ process, the influence of the two most important operating parameters, gas inlet composition and process temperature, on the evolutions of the deposition rate and of the film oxygen content along the reactor load and on-wafer, has been experimentally studied. This set of experimental results was then used as a database to develop a new kinetic model, using a local numerical simulation code for LPCVD reactors, named CVD2. This new kinetic model certainly summarizes numerous poorly known gas phase and surface reactions involved in SIPOS deposition. Its validation has been successfully performed by comparison with specific experimental data, both along the load and on-wafer. An efficient mathematical tool is then available to better control and optimize the performances of SIPOS low-pressure deposition processes.The acronym SIPOS, for semi-insulating polycrystalline silicon, is used to refer to silicon thin films doped with oxygen. These layers are characterized by a global average composition SiO x with x varying between 0 ͑polycrystalline silicon layer͒ and 2 ͑stoichiometric oxide͒. Because of its efficiency in improving the breakdown characteristics of high-voltage bipolar transistors when used as a passivating layer, 1,2 SIPOS has been dealt with in many studies during the last several years. This material has a complex internal nanometer-scale organization and is composed of several phases. There are reports of silicon both in the amorphous form 3-6 and as small microcrystallites 3,7,8 of silica 3 and substoichiometric oxide SiO x . Many compositions have been experimentally obtained such as SiO, 9 Si 2 O 3 , 9 SiO 0.86 , 3 or SiO 1,4 , 7 depending on the operating conditions. The quantity of oxygen atoms incorporated into the layer during the deposition mainly determines the physicochemical 10 and electrical properties of the layer, 3,8,11,12 and, consequently, any variation of this oxygen content can decrease the entire component reliability. This is why a strict control of the oxygen content incorporated during deposition must be exerted. The most widely used process in the microelectronic industry for SIPOS elaboration is chemical vapor deposition under low-pressure conditions ͑LPCVD͒, because it can process conveniently several tens of wafers by run. The SIPOS process deposits results from the reactions of two gaseous sources, usually silane (SiH 4 ) and nitrous oxide (N 2 O). It is well known that the oxygen concentration can be varied by modifying the entrance gas composition 8,10 and that it is a nonlinear function 10 of the molar fraction ␥ ϭ N 2 O/SiH 4 . The process temperature has also been found to exert an important influence on the layer composition. 10 In addition, heterogeneities on any of the wafers and from wafer to wafer all along the load have been observed 13 which limits the number of wafers per run and, hence, the reactor productivity. For instance, a SIPOS layer grown ...
To improve mastery of the low pressure chemical vapor deposition semi-insulating polycrystalline silicon ͑SIPOS͒ SiO x process, a local kinetic model describing homogeneous and heterogeneous phenomena is used to analyze the influence of some key operating parameters and of the main geometrical reactor features on the process behavior. In particular, the gas hydrodynamics near an interwafer space is detailed, and the role of each chemical species involved in the deposit formation is investigated, with special attention paid to the two radicalar molecules silylene and silanone. This analysis has allowed us to explain the origins of the radial heterogeneities on wafers for each of the parameters investigated, thus opening possible ways of process optimization. This study demonstrates how efficient such a modeling tool can be for improving the existing process performances, or even for designing reactors. Such a mathematical approach is certainly a possible answer to the increasingly drastic industrial requirements of the microelectronic field.
A characterization of Semi-insulating Polycrystalline Silicon (SIPOS) layers deposited from SiH4 on SiO2 is presented, as a function of growth and annealing conditions (time and temperature), in order to better understand the processes involved in nucleation of silicon nanocrystals. Correlation between optical and XPS measurements allows determination of the starting composition of the amorphous material. After annealing, Fourier transform infrared (FTIR), ultraviolet-visible and Raman spectroscopies have been used to determine the structural and optical characteristics of the resulting material. Thermal treatment promotes a phase separation, modifying the layer properties and degrading the electrical insulation characteristics. Concentration of the silicon dioxide phase increases, whereas elemental silicon precipitates into nanocrystals which nucleate near the interface with the underneath SiO2. Their density depends of the initial silicon content in the SIPOS layer, and some directions such as <1I1> and <220> grow preferentially whereas other directions such as <311> show a slower growth. As the percentage of oxygen increases, the formation of precipitates is less marked.
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