A method for manufacturing a magnetoresistive read sensor that allows the sensor to be constructed with clean well defined side junctions, even at very narrow track widths. The method involves using first and second etch mask layers, that are constructed of materials such that the second mask (formed over the first mask) can act as a mask during the patterning of the first mask (bottom mask). The first mask has a well defined thickness that is defined by deposition and which is not affected by the etching processes used to define the mask. This allows the total ion milling etch mask thickness to be well controlled before the ion milling process used to define the sensor side walls.