Defects formation on the surface of Si-substrates during thermal sputtering of gold

Abstract

Silicon photodetectors, in particular p–i–n photodiodes, are widely used as sensors of optical radiation. With technological advances, the requirements for the parameters and reliability of these elements of solid-state electronics are increasing sharply, thus improving these characteristics is an important task. During the production of silicon photosensors, parameters were observed to degrade after the stage of forming contact pads by thermal sputtering of chrome-gold. Examination of the samples in the selective etchant allowed discovering the complexes of structural defects, which contributed to the deterioration of the parameters, in particular, the growth of dark currents. When investigating the causes of the appearance of these defects, it was established that they were formed as a result of local melting of silicon when gold “drops” hit it with a temperature higher than the melting temperature of silicon due to boiling in the evaporator. It was established that the use of wire is accompanied by a more intensive appearance of gold drops than when using beads. It was also noticed that the roughness of the morphology in the case of sputtering from a wire is significantly higher than in the case of sputtering from beads. It is noted that after the metallization is formed, photolithography is performed on the front side of the substrates to form contact pads, and considering the possibility of etching due to the presence of gold thickenings, it is better to spray on the front side from crowns. Wire spraying should be used for the reverse side of substrates, where defect formation is less critical. The formation of the described defects can be minimized by using spraying from closed evaporators or by increasing the time of spraying on the shutter during gold melting.