Patent ID: 7105404

Claim:
Method for fabricating a semiconductor structure having the steps of: providing a semiconductor substrate ( 1 ) made of silicon with a first hard mask layer ( 10 ; 10 ′) made of silicon oxide and an overlying second hard mask layer ( 15 ; 15 ′) made of silicon; providing a masking layer ( 30 ; 30 ′) made of silicon oxide above and laterally with respect to the second hard mask layer ( 15 ; 15 ′) made of silicon and above an uncovered edge region (RB) of the semiconductor substrate ( 1 ); providing a photoresist mask ( 25 ) above the masking layer ( 30 ; 30 ′) with openings corresponding from trenches (DT) to be formed in the semiconductor substrate ( 1 ); opening the masking layer ( 30 ; 30 ′) in a first plasma process using the photoresist mask ( 25 ), the edge region (RB) being covered by a shielding device (AR); opening the first hard mask layer ( 10 ; 10 ′) and second hard mask layer ( 15 ; 15 ′) in a second and third plasma process; and forming the trenches (DT) in the semiconductor substrate ( 1 ) in a fourth plasma process using the opened first hard mask layer ( 10 ; 10 ′); the edge region (RB) not being covered by the shielding device (AR) in the second to fourth plasma processes.