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2005
Conference Paper
Titel
Thermal process control for laser radiation bonding of silicon and glass
Abstract
Selective Laser Radiation Bonding (SLB) is an innovative method for the selective joining of silicon and glass and other material pairs. SLB is based on the transmission heating of the interface of both joining partners using the thermo-chemical principles of Silicon Direct Bonding with covalent oxygen-bonds. With this method the laser beam is transmitted through the glass and absorbed by the silicon at the silicon-glass interface. The laser radiation is converted into heat energy directly at the interface. SLB is very promising with regard to applications in the packaging of micro systems. The sealing of sensors on silicon-based conductors, the sealing of micro cavities, e.g. for medical and biological technology and the selective bonding of silicon-glass for Silicon on Insulator (SOI) are potential applications. Furthermore, it is possible to use SLB on other material combinations to assemble complex hybrid systems. Depending on the selected wavelength of the laser radiation, material combinations like sapphire/Al203, glass/ceramics can be bonded. Bonding of very small, complex joining geometries need exact heat control at the interface. In this work the experimental results based on the usage of thermal process control for SLB will be presented. While bonding silicon and glass along a complex joining geometry e.g. sealing a micro mixer along the channel contour with a channel width of approximately 100 µm in a multi-s-shaped geometry with constant laser power, overheating can occur. This is caused due to the heat accumulation in the bond front. To avoid heat accumulation and to assure a constant bond temperature, it is necessary to use a thermal process control to re-adjust the laser power online. For this purpose a pyrometric sensor was installed in the laser processing head, and a software based control loop was implemented. Experimental tests were carried out to compare thermal process control with the process of constant laser power.