Ion beam etching of STT-RAM structures

A method of patterning STT-RAM structures arranged in a square pattern defining a reference orientation of 0°, each STT-RAM structure having a magnetic tunnel junction (MTJ) stack, the method comprising:

• (a) etching the structures just past the MTJ stack where the etching is performed at a near normal incidence angle;
• (b) performing a clean-up etch at an angle greater than near normal incidence angle to remove redeposited material from sidewalls of the MTJ stack, the projection of the clean-up etch ion beam in the wafer plane being at 90° increments starting at 45° relative to the reference orientation of 0° as defined by the direction of rows in the square pattern when the structure is rotated;
• (c) depositing electrically insulating etch stop material over the cleaned up etched MTJ sidewalls to form re-entrant insulating sidewalls;
• (d) etching the remainder of the structure at a near normal incidence angle while ensuring that the re-entrant insulating sidewall of the MTJ stack is mostly preserved;
• and
• (e) performing a second clean-up etch at an angle greater than near normal incidence to remove a majority of redeposited materials from the sidewalls of the MTJ stack, at 90° increments starting at 45° relative to the reference orientation of 0° when the structure is rotated.

A method of patterning an STT-RAM structure having a magnetic tunnel junction (MTJ) stack comprising:

• (a) providing an initial structure comprising an MTJ stack;
• (b) etching the structure to a pre-determined depth to provide etched sidewalls;
• (c) depositing an encapsulation layer over the etched sidewalls to form re-entrant encapsulation layer sidewalls;
• and
• (d) etching the structure having the encapsulation layer.