Patent ID: 11004726

Abstract:
A stack of sacrificial layers is formed in a set of N levels. A first etch-trim mask having spaced apart first and second open etch regions is formed over the set. Two levels are etched through using the first etch-trim mask in each of M etch-trim cycles, where M is (N−1)/2 when N is odd and (N/2)−1 when N is even. One level is etched through using the first etch-trim mask in one etch-trim cycle when N is even. The first etch-trim mask is trimmed to increase the size of the first and second open etch regions, in each of etch-trim cycles C(i) for i going from 1 to T−1, where T is (N−1)/2 when N is odd and N/2 when N is even. A second etch mask is formed over the set, covering one of the open etch regions. One level is etched through using the second etch mask.