This is performed by forming photo resist over the structure except for where the trenches are to be formed, followed by a dry etch (e.g. RIE) with a relatively soft mask material that is laterally etched as the trench is formed (e.g. etch rate of less than about 2 to 1, versus an etch rate of traditional mask materials that is typically greater than 5 to 1), such that trench 38 is formed with slo