ild o the siro layer typically has a r i greater than 1 6 such as greater than 1 7 e g 1 7 to 2 0 the present invention achieves such objectives by a plasma enhanced chemical vapor deposition technique conducted at an elevated temperature such as a temperature of 450 u00b0 c to 550 u00b0 c e g 500 u00b0 c and at a silane flow rate of 100 to 150 sccm such as 125 sccm such deposition may be conducted at a n 2 o flow rate of 165 to 195 sccm e g 180 sccm a pressure of 1 8 to 2 2 torr e g 2 0 torr and an rf power of 110 to 140 watts e g 125 watts the spacing distance between the wafer and shower head from which gases exit may be maintained at about 625 to 675 mils e g 650 mils the deposition process may be conducted for 3 to 15 seconds resulting in the deposition of an siro film having a thickness of 400 u00e5 to 600 u00e5 e g 500 u00e5 such a plasma enhanced chemical vapor deposition technique is effective to deposit the siro layer with an increase silicon content such that the r i is elevated to greater than 1 6 such as greater than 1 7 e g 1 7 to 2 0 whereas typical silicon oxide layers exhibit a r i of 1 45 to 1 46 the use of a siro film in accordance to the present invention provides tighter vt distribution than obtained employing conventional fabrication techniques an embodiment of the present invention is schematically.