Patent ID: 8293639

Claim:
A method for controlling an ADI-AEI CD difference ratio of openings having different sizes, wherein the openings are formed with steps comprising: forming an etching resistive layer, an Si-containing material layer and a patterned photoresist layer on a target material layer in sequence, wherein the patterned photoresist layer has therein a first opening pattern and a second opening pattern with different sizes, and the size of the first opening pattern is larger than the size of the second opening pattern; and performing steps of etching the Si-containing material layer, the etching resistive layer and the target material layer in sequence to form a first opening and a second opening respectively corresponding to the first opening pattern and the second opening pattern in the target material layer, wherein a difference between a size of the first opening and a size of the first opening pattern is a first dimension difference, a difference between a size of the second opening and a size of the second opening pattern is a second dimension difference, and a ratio of the first dimension difference to the second dimension difference is called an ADI-AEI CD difference ratio, the method comprising: performing a trimming step to the patterned photoresist layer before the steps of etching the Si-containing material layer, the etching resistive layer and the target material layer; performing a first etching step using the trimmed photoresist layer as a mask to pattern the Si-containing material layer and form a patterned Si-containing material layer, wherein a polymer layer is formed on sidewalls of the trimmed photoresist layer and the patterned Si-containing material layer; performing a second etching step using the trimmed photoresist layer, the patterned Si-containing material layer and the polymer layer as masks, so as to remove exposed portions of the etching resistive layer and the target material layer; and adjusting at least one parameter among trimming parameters of the trimming step and etching parameters of the first etching step, so as to obtain a predetermined ADI-AEI CD difference ratio.