Why does a plasma treatment prior to the wafer direct bonding increase the bonding energy of silicon wafer pairs in the low-temperature range?

摘要

Applying a plasma treatment before wafer direct bonding of hydrophilic silicon wafers promise to be a successful approach to enhance the bonding energy in the low-temperature range. Unfortunately, a suitable interpretation is still missing which is able to explain the different results obtained. We have performed various investigations of plasma-treated surface and bonded interfaces by AFM, ellipsometry, TEM, IR-spectroscopy, and several chemical methods. The results of our study let us assume that the observed increase of bonding energy is caused by different effects which can be described by the microroughness of the silicon surface, the thickness and structure of the interfacial oxide, and the type and arrangement of the chemical interfacial species. The bonding energy strongly depends on how pronounced each single effect is and terms out to be a complex function of the parameters of the plasma treatment, the chemical precleaning, and the bonding conditions.