Laser activated flow of phosphosilicate glass in integrated circuit devices

The use of a cw CO2laser to flow phosphosilicate glass for the planarization of p+/n diode arrays is demonstrated. A power density flow threshold of 110 kW cm^-2at a wavelength of 9.26 µm is estimated and found to be essentially invariant to the thickness of the glass (1.0 to 1.5 µm) and to the phosphorus concentration of the glass (3 to 9% wt). This laser activated process results in glass flow without impurity diffusion in the active device area and is therefore compatible with VLSI.