Role of Heating on Plasma-Activated Silicon Wafers Bonding

Abstract

This paper reports on a comparative study of silicon wafer bonding using reactive ion etching (RIE) vs sequential plasma-activated bonding (SPAB). The study shows the measurement of silicon surface roughness and the investigation of heating influences on the bonding strength and microstructures of silicon∕silicon bonded interfaces as a function of the plasma processing parameters such as plasma time and gas pressure. In SPAB, the surfaces were activated using nitrogen radicals after treatment with RIE plasma for . The surface roughness created via RIE plasma is higher than that of the nitrogen radical. In both methods, although high strength bonding of silicon∕silicon interfaces was achieved before heating, bonding strength was reduced after heating except for the specimens activated for 10 and heated at in the RIE method. This reduction may be attributed to the growing number of voids generated across the bonded interface. High resolution transmission electron microscope observations showed a silicon oxide interfacial layer in the SPAB-processed silicon∕silicon interface, which is thicker than that of the RIE-processed interface without heating. After heating (at for in air), the thicknesses of the interfacial oxide layers were increased for both processes. The increased oxide layer thicknesses after heating are a result of the addition of thermally activated oxygen from water absorbed by the silicon bulk wafers and oxygen intrinsic to bulk silicon.