Patent ID: 8865008

Claim:
A method of reducing a critical dimension (CD) in a photoresist mask layer to a free layer width (FLW) in an underlying magnetic tunnel junction (MTJ) stack of layers, comprising: (a) providing a MTJ stack of layers on a substrate including a pinned layer, a free layer, and a non-magnetic spacer between the pinned layer and free layer; (b) coating a photoresist layer on a top surface of the MTJ stack and patterning the photoresist layer to form a parallel line pattern wherein each line has a first critical dimension (CD) that is a width along a first axis that is perpendicular to a lengthwise dimension of the lines in a second axis direction, a second MTJ critical dimension that is along the second axis direction is determined in a separate photoresist coating and etching sequence; (c) performing a first ion beam etch (IBE) process with ions having one or more incident angles less than about 40° with respect to a plane that is perpendicular to the substrate to transfer the line pattern in the photoresist layer through the MTJ stack of layers and thereby generate a plurality of lines in the MTJ stack such that each line has a top surface and first and second sidewalls wherein the sidewalls connect the top surface with the substrate, and the free layer in each line has a first width between the first and second sidewalls and along a plane that is parallel to the MTJ top surface; and (d) performing a second IBE process with a sweeping motion and with ions having one or more incident angles greater than about 60° with respect to a plane that is perpendicular to the substrate such that the free layer has a second width which is the FLW that is less than or equal to the first width, the second IBE process includes a first step wherein ions are directed with the sweeping motion comprising a counterclockwise movement and a clockwise movement only at the first sidewall, and includes a second step wherein ions are directed with the sweeping motion comprising a clockwise movement and a counterclockwise movement only towards the second sidewall, the first and second steps do not overlap so that the first and second sidewalls are trimmed during different time intervals.