Polyimide Film Properties and Selective LPCVD of Tungsten on Polyimide

Abstract

du Pont PI‐2575‐D polyimide films were characterized to determine their suitability for use as an interlevel dielectric with a selective tungsten via fill process. Polyimide films cured at 400° and 440°C were found to breakdown at voltages greater than . The pinhole density, when processed in a non‐cleanroom environment, is below 1 per cm2. The dielectric constant for 1.6 μm films is 3.9. Adhesion to thermal oxide is 100% for films in boiling water up to 1h. The maximum moisture absorption is 1.7 w/o at 90% relative humidity. Perfect tungsten selectivity was achieved in the absence of nearby tungsten surfaces at 216°C, 0.75–7.5 torr total pressure, 15:1 and times to 210 min. When the polyimide was exposed to adjacent tungsten surfaces, tungsten did deposit on the polyimide, resulting in a moving metal front. The activation energy for the rate of progress of the tungsten film front is 16 kcal/mol.