Defect-free x-ray masks for 0.2-mu m large-scale integrated circuits

The x-ray mask fabrication process we developed can be used to make and maintain essentially defect-free masks consisting of Ta absorbers on SiN membrane. The surface of the deposited SiN substrates is polished to make them as smooth as possible. As Ta is chemically stable, mask fabrication processes are frequently followed with a wet-cleaning process using a strong acid solution. Inspection of resist patterns printed on a wafer confirms that there are less than 20 printable defects per mask, and there are no defects on the back surface. The inspection and repair are repeated until the mask is defect free. Defects caused by mask handling and x-ray exposure are immediately washed up by wet cleaning with strong acid. The resulting x-ray masks have been used in large-scale integrated circuits fabrication, and fully functional devices have been obtained. (C) 1996 American Vacuum Society.