One illustrative method disclosed herein includes, among other things, forming an initial patterned etch mask above a feature-formation etch mask, the initial patterned etch mask including a plurality of laterally spaced-apart features having a non-uniform spacing, and performing at least one first etching process to remove an entire axial length of at least one of the plurality of features so as to thereby form a modified final patterned etch mask comprised of a plurality of features with a uniform spacing that defines a feature-formation pattern. In this example, the method also includes performing at least one second etching process so as to form a patterned feature-formation etch mask comprising the feature-formation pattern and performing at least one third etching process so as to form a plurality of features in a first layer, the features being formed with the feature-formation pattern.