Impact of doping level on the metal assisted chemical etching of p-type silicon

The impact of doping level on the metal assisted chemical etching of p-type silicon using silver particles is investigated. 12 boron doped wafers with doping levels ranging from 1012 up to 1019 cm−3 were used. Silver particles generated from a sputter-deposited thin film via a dewetting procedure act as catalyst in a HF:H2O2 etch mixture. The characteristics of the etch rate as a function of time was investigated, revealing in addition an enhanced material removal at the beginning (i.e. in the range of several seconds) and an undesired etching of silver free regions at longer etch times (i.e. >15 min). Furthermore, a strong decrease in etch rate at doping levels exceeding 1016 cm−3 is observed. Only at these highly doped samples, a porous sub-structure is detected located adjacent and in-between the pores which are generated by the Ag particles. It is assumed that the injected holes representing majority charge carriers in p-type silicon diffuse at higher doping levels faster and more efficiently away from the metal-semiconductor interface into the silicon sample resulting in a decreased etch rate.