Formation of Silicon Nitride Films Newly Developed by the Ion and Vapour Deposition Method
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ABSTRACT The Ion and vapour deposition method ( IVD method ) has been used for the first time to form silicon nitride films. Silicon nitride formation using IVD method, which consists of a nitrogen ion implantation and a simultaneous electron beam evaporation of silicon, has been confirmed. These silicon nitride films formed by IVD method have been characterized using FTIR , ellipsometry and AES analyses. It has been observed that these IVD silicon nitride films characteristics are sensitive to the nitrogen ion implantation conditions and the silicon evaporation rate. Applications of these IVD films to selective oxidation have exhibited a good resistance to oxidation. It has also permitted the bird's beak to be reduced. INTRODUCTION Silicon nitride formed by LP-CVD or PE-CVD has extensively been used as oxidation mask, gate dielectric and passivation film for VLSI process. Recently, various isolation methods [ 1,2,3 ] have been developed to reduce the lateral oxide extension( bird's beak ), which prevents higher packing density in VLSI. One approach is the formation of an insulator layer ( silicon nitride or silicon oxide ) on the silicon surface [ 4,5,6 ] or in the silicon substrate [ 7,8 ) by nitrogen or oxygen ion implantation. Formation of silicon nitride by implantation appears to be the better method because it is cleaner and generates a gradual transition between silicon and silicon nitride. This film shows a strong adhesion, so applications to local oxidation of silicon ( LOCOS ) process exhibit bird's beak free profiles.[ 4,5 ] But an increase of leakage current or defects density have been reported. [ 6,9 ] So we thought that the IVD method , which had been used for surface modification or film formation[ 10,11 ] , could provide a good solution to form silicon nitride film: while it keeps the advantages of ion implantation, the film characteristics can be changed by separately monitoring nitrogen ion implantation and silicon vapour deposition conditions. The purpose of this paper is to characterize silicon nitride films formed by IVD method and optimize the IVD conditions for applications to LOCOS. For film characterization, Fourier transform infrared ( FTIR ), ellipsometry and Auger electron spectroscopy ( AES ) analyses were used before and after nitridization annealing. EXPERIMENTAL PROCEDURE FIg.l shows a schematic diagram of the IVD machine. The machine consists of a rectangular bucket type multiapertures ion source, an evaporator with electron-gun, rotary wafer holder with water cooling and a
Mat. Res. Soc. Symp. Proc. Vol. 54. ý 1986 Materials Research Society
536
film thickness monitor. Details of this apparatus was explained in a previous paper [ 11 ). The experiments employed ( 100 ) p-type oriented 6-9 ohm-cm SUBSTRATE silicon wafers. The sample chamber tas pumped down to below wInH EVAPORATOR 2 x 10 Torr and then, during \ ELECTRON BEAM film preparation, its pressure was approximately 8 x 10 Torr. Nitrogen ions were implanted in an energy range from 5 to 20 keV and a beam current range fro
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