LOW-TEMPERATURE WAFER DIRECT BONDING

A pronounced increase of interface energy of room temperature bonded hydrophilic Si/Si, Si/SiO2 and SiO2/SiO2 wafers after storage in air at room temperatue-150 degrees C for 10-400 h has been observed. The increased number of OH groups due to a reaction between water and the strained oxide and/or silicon at the interface at temperatures below 110 degrees C and the formation of stronger siloxane bonds above 110 degrees C appear to be the main mechanisms responsible for the increase in the interface energy. After prolonged storage, interface bubbles are detectable by an infrared camera at the Si/Si bonding seam. Desorbed hydrocarbons as well as hydrogen generated by a reaction of water with silicon appear to be the major contents in the bubbles. Design guidelines for low temperature wafer direct bonding technology are proposed.