the silicon substrate 12 is a thermally grown sio 2 layer 14 also referred to as a pad oxide layer formed over the silicon substrate 12 surface the pad oxide layer 14 is preferably grown by a conventional thermal oxidation process to a thickness of about 25 angstroms to about 150 angstroms for example the pad oxide layer 14 is grown in rapid thermal oxidation process rto or in a conventional furnace annealing process including oxygen at a temperature of about 800 u00b0 c to about 1150 u00b0 c formed over the pad oxide layer 14 is a hardmask metal nitride layer 16 also referred to as a pad nitride layer preferably silicon nitride e g si 3 n 4 deposited by a cvd for example an lpcvd process it will be appreciated that other silicon oxynitride e g sion may be used or included in the hardmask layer 16 the hardmask layer 16 for example may include an uppermost layer to improve critical dimension control during a subsequent trench etching process for example formed of lpcvd sion or sio 2 for example the hardmask layer 16 is formed to have a thickness of between about 500 angstroms and 3000 angstroms in addition an organic or inorganic anti reflective coating arc e g sion 16 b is preferably formed over the hardmask layer 16 to reduce light reflections in a subsequent photolithographic process referring to fig1 b following formation of the hardmask layer 16 the hardmask layer is first photolithographically patterned and etched to form an etching mask for etching an sti trench e.