A high density plasma chemical vapor deposition (HDP-CVD) process is used to
deposit
silicon dioxide in trenches of various widths. The thickness of the silicon dioxide
filling both narrow and wide trenches is made more uniform by reducing an HDP-CVD
etch to deposition ratio. The lowered etch to deposition ratio is achieved by lowering
a ratio of oxygen to silane gas, by lowering the power of a high frequency bias
signal, and by lowering the total gas flow rate.