An adjustable mass-resolving slit assembly includes an aperture portion and an actuation portion. The aperture portion includes first and second shield members that define an aperture therebetween for receiving an ion beam during semiconductor processing operations. The actuation portion is coupled to the aperture portion and selectively and independently adjusts the position of the first and second shield members along first and second non-parallel axes. Adjusting the position of the first and second shield members along the first axis adjusts a width of the aperture. Adjusting the position of the first and second shield members along the second axis adjusts a region of the first and second shield members impinged by the ion beam. Methods for using the adjustable mass-resolving slit assembly are also disclosed.