Highly repeatable dry etch corner rounding solution for 0.11 μm shallow trench isolation

Abstract

A highly repeatable dry etch corner rounding solution for 0.11 μm shallow trench isolation (STI) without increasing additional process steps was proposed. It is mentioned for the first time that the two-step silicon nitride over etching method is used in the STI etching to get the corner rounding effect, in which the gas combination is CF4 + CH2F2. The top rounding can be achieved by properly adjusting the proportion of two-step etching gas. The STI prepared by this method has a perfect top rounding morphology in both dense and isolate areas. The subsequent TEM images show that the thickness of gate oxide at the thinnest part increased from 40 to 52 A, an increase of 30%. The results of the gate oxide integrity test confirmed that the value of breakdown voltage is greatly improved by using the new etching methods regardless of n-MOS or p-MOS. In terms of the breakdown voltage, the improvement level of n-MOS is higher than that of p-MOS. The breakdown voltage of n-MOS is increased by 10% and that of p-MOS is increased by 7%. With the further reduction of semiconductor size, the increase in gate oxide thickness in corner of STI is very important for the improvement of device reliability and performance.