To etch silicon oxide films, by including a process for etching thin oxide films while cooling them to a predetermined temperature.

Etching a BPSG film 42 by an anisotropic etching, contact holes reaching respectively n-type regions 38, 39 are created to remove thereafter a resist mask 44. After forming the contact holes passing through the BPSG film 42, naturally oxidized films 45 which may be formed on the bottom surfaces of the contact holes are removed by a plasma down flow processing wherein NF3 is added to the down flow of a gas containing hydrogen and steam. In this case putting a silicon wafer 31 on a cooled stage in a down flow processing chamber, a light etching of the wafer 31 by the down flow is performed while monitoring the average temperature of the wafer 31 by a laser thermometer. By setting the temperature of the wafer 31 to a low value, the etching amount of the BPSG film 42 is suppressed and the naturally oxidized films 45 on the bottom surfaces of the contact holes can be removed effectively.