A flow of oxygen gas activated by passing through a microwave discharge plasma in a 100 and 200 W field was introduced into a deposition cham ber for tantalum oxide deposition by KrF laser photolysis of Ta(OCH3)(5), and the change of the non-stoichiometry of deposit was examined under the laser condition of 120 Hz and 200 Jm(-2). The stoichiometry of the deposit could be improved to a value of about 90% under the condition of rather low supply rate of Ta(OCH3)(5) (100 mg h(-1)). An effect of post-treatment laser following chemical vapour deposition (CVD) by KrF laser and/or microwave discharge of oxygen gas was also investigated, and it was found that activated oxygen species formed by KrF laser irradiation in an oxygen gas atmosphere which passed through a microwave discharge was effective in enhancing the oxidation of non-stoichiometric tantalum oxide prepared by KrF laser CVD.