THE BASIC AIM OF THIS PROJECT DERIVES FROM THE CONVICTION THAT ANY SUBSTANTIAL PROGRESS, CONCERNING THE QUALITY OF THE MATERIAL AND THE DEPOSITION RATE, CAN ONLY BE BASED ON A MORE COMPLETE COMPREHENSION OF THE PROCESS MECHANISMS. FOR THIS PURPOSE THERE IS A NEED OF UNIVERSAL PROCESS EVALUATION PROCEDURES, BASED ON MORE EFFICIENT DIAGNOSTIC TECHNIQUES. IN THIS DIRECTION WE ARE APPLYING SPATIALLY RESOLVED OPTICAL METHODS, LIKE LASER INDUCED FLUORESCENCE (LIF) AND OPTICAL EMISSION SPECTROSCOPY (OES). THESE METHODS PERMIT SIMULTANEOUS IN-SITU DETECTION OF GROUND STATE AND ELECTRONICALLY EXCITED SPECIES, IN ACTUAL DEPOSITION CONDITIONS, WITHOUT DISTURBING THE PLASMA. THE SPATIAL CONCENTRATION PROFILES THUS OBTAINED ARE STRONGLY CORRELATED WITH THE ELECTRICAL AND GEOMETRICAL CHARACTERISTICS OF THE DEPOSITION CHAMBER. THE EXPERIMENTAL METHOD IS FURTHER SIMPLIFIED AND IMPROVED BY SUPERIOR ALIGNMENT TECHNIQUES AND EXTENSIVE USE OF DIGITAL SIGNAL PROCESSING.
A kinetic study has been conducted of the deposition process of glow discharge hydrogenated amorphous silicon using laser induced fluorescence (LIF) and optical emission spectroscopy (OES) techniques for the simultaneous detection of ground state silicon hydride and electronically excited silicon hydride radicals. These methods were used for recording axial intensity profiles of silane radicals between the 2 electrodes in various working conditions.
It was concluded that the spatial concentration profiles of silicon hydride represent stationary generation rates of the silane radicals.
Ground and excited state silicon hydride radicals have different spatial distribution and different response to the discharge parameters. This is due to the fact that the generation rate of silicon hydride radicals is influenced by the characteristics of the sheath, whereas the generation rate of silicon hydride depends mainly on the bulk power density. So it is suggested that LIF profiles can be used as the spatially distributed source of radicals.
The use of those profiles, instead of a homogeneous radical production in space, can increase the accuracy of kinetic calculations.
The use of OES profiles can induce considerable errors on amorphous silicon deposition kinetic calculations.
THE MAIN PROBLEM, IN THIS DIRECTION, IS THE ELUCIDATION OF BOTH, GAS-PHASE REACTION AND PLASMA-SURFACE INTERACTION MECHANISM.
IN THIS PROJECT WE USE LASER INDUCED FLUORESCENCE SPECTROSCOPY, IN COMBINATION WITH OPTICAL EMISSION SPECTROSCOPY, IN ORDER TO EVALUATE THE CONTRIBUTION OF VARIOUS RADICAL SPECIES TO THE FILM GROWTH. ANOTHER PROBLEM IS THE PRESENTLY VERY LOW DEPOSITION RATE. WE PLAN TO OVERCOME THIS DIFFICULTY BY USING ALTERNATIVE SOURCE GASES (DISILANE). DURING THE FIRST SIX MONTHS THE GOALS DESCRIBED IN OUR PROPOSAL PLAN HAVE BEEN ACCOMPLISHED.
THE PLASMA DEPOSITION CHAMBER AND VACUUM LINE CONSTRUCTION WAS COMPLETED. ALSO THE SPECTROSCOPY SETUP WAS INTERFACED TO A MICRO COMPUTER FOR DATA ACQUISITION AND DEVICE CONTROL. THE CAPABILITY OF THIS SYSTEM ON RECOVERING WEAK SIGNALS WAS TESTED BY RECORDING WELL KNOWN LIF AND OES SPECTRA. IN ADDITION A THEORETICAL APPROACH TO THE PROCESS, BY COMPUTER SIMULATION, IS UNDER DEVELOPMENT.