Formation of Dislocations During Phosphorus Doping in the Technology of Silicon p-i-n Photodiodes and their Influence on Dark Currents

In the manufacture of p-type silicon-based p-i-n photodiodes (PDs), it was found that when the time of phosphorus diffusion increases, the yield of fit products significantly decreases. Up to 10 % are the rejects as to external appearance, the rest – as to the spread of dark current levels of PD responsive elements (REs), since the double spread of dark currents is considered a defect. Probably, the above occurrence might be caused by non-uniform distribution of defects across REs because of the increase in phosphorus impurity. An additional investigation was required to find out the cause of non-uniform distribution of dark currents and to establish the optimal concentration of impurities, which would provide for a low dark current with minimum spread. To study the effect of the surface resistance of the n+-layer on the concentration of dislocations and their distribution, PDs were made with different duration of the predeposition, accordingly, with different values of the surface resistance. To reveal the nature of the distribution of dark currents on REs, defective crystals were studied using selective etching. It was established that conditions for the occurrence of structural defects within one ingot may be different due to the spread of specific resistance. The dependence of the dislocation density on the surface resistance after phosphorus diffusion was studied. It was noted that REs of a high level of dark currents were characterized by an increased concentration of dislocations as compared to the characteristic density for good crystals at a given surface resistance. The actual reasons for the dislocations distribution non-uniformity are the irregular distribution of point defects generated during oxidation and the presence of microdefects formed during mechanical or chemical-dynamic polishing. When locally increased numbers of growth defects and point defects acquired during the mechanical, chemical or thermal operations are superimposed, critical faults and spread of dark currents with maximum values are observed.