Staircase etch control in forming three-dimensional memory device

Abstract

Embodiments of three-dimensional (3D) memory devices and methods for controlling a photoresist (PR) trimming rate in the formation of the 3D memory devices are disclosed. In an example, a method includes forming a dielectric stack over a substrate, measuring a first distance between the first trimming mark and the PR layer along a first direction, and trimming the PR layer along the first direction. The method also includes etching the dielectric stack using the trimmed PR layer as an etch mask to form a staircase, forming a second trimming mark using the first trimming mark as an etch mask, measuring a second distance between the second trimming mark and the trimmed PR layer, comparing the first distance with the second distance to determine a difference between an actual PR trimming rate and an estimated PR trimming rate, and adjusting PR trimming parameters based on the difference.

1 - 20 . (canceled) 
     
     
         21 . A method for forming a three-dimensional (3D) memory structure, comprising:
 forming a dielectric stack over a substrate, the dielectric stack comprising a plurality of sacrificial material layers and a plurality of insulating material layers arranged alternatingly;   etching the dielectric stack to form a first trimming mark;   forming a photoresist (PR) layer covering the dielectric stack but exposing the first trimming mark;   trimming the PR layer using a first PR trimming rate based on a location measurement of the first trimming mark; and   etching the dielectric stack, using the trimmed PR layer as an etch mask, to form a first staircase.   
     
     
         22 . The method of  claim 21 , wherein the first trimming mark has a protruding structure and a recessed structure. 
     
     
         23 . The method of  claim 22 , wherein the protruding structure includes a height of a thickness of a staircase and the recessed structure includes a depth of the thickness of the staircase. 
     
     
         24 . The method of  claim 21 , wherein the protruding structure comprises a sacrificial material layer and an insulating material layer. 
     
     
         25 . The method of  claim 21 , wherein the recessed structure comprises a trench embedded in a sacrificial material layer and an insulating material layer. 
     
     
         26 . The method of  claim 21 , further comprising:
 etching the dielectric stack to form a second trimming mark, using the first trimming mark as an etch mask;   trimming the PR layer using a second PR trimming rate based on a location measurement of the second trimming mark; and   etching the dielectric stack, using the trimmed PR layer as an etch mask, to form a second staircase.   
     
     
         27 . The method of  claim 26 , further comprising:
 measuring a first distance between the first trimming mark and the PR layer;   measuring a second distance between the second trimming mark and the trimmed PR layer;   comparing the first distance with the second distance to determine a PR trimming rate adjustment; and   modifying one or more PR trimming parameters of the PR trimming process to change the first PR trimming rate to the second PR trimming rate based on the PR trimming rate adjustment.   
     
     
         28 . The method of  claim 25 , wherein:
 the second trimming mark and the first trimming mark are formed by a same patterning process; and   the second trimming mark and the first trimming mark are located on different staircases.   
     
     
         29 . The method of  claim 21 , further:
 determining a first distance in a first direction between the first trimming mark and a first side of the PR layer along a second direction;   determining a third distance in the second direction between the first trimming mark and a second side of the PR layer along the first direction; and   trimming the PR layer along the first direction and the second direction simultaneously, wherein the first PR trimming rate applied along the first direction is determined based on the first distance, and a third PR trimming rate applied along the second direction is determined based on the third distance.   
     
     
         30 . The method of  claim 29 , further comprising:
 measuring a second distance in the first direction between the second trimming mark and a first side of the trimmed PR layer along the second direction;   comparing the first distance with the second distance to determine a first PR trimming rate adjustment along the first direction;   measuring a fourth distance in the second direction between the second trimming mark and a second side of the trimmed PR layer along the first direction;   comparing the third distance with the fourth distance to determine a second PR trimming rate adjustment along the second direction; and   modifying one or more PR trimming parameters of the PR trimming process to change the first PR trimming rate to a second PR trimming rate along the first direction based on the first PR trimming rate adjustment, and to change the third PR trimming rate to a fourth PR trimming rate along the second direction based on the second PR trimming rate adjustment.   
     
     
         31 . A method for controlling a photoresist (PR) trimming rate in a PR trimming process, comprising:
 (i) providing an estimated PR trimming rate;   (ii) determining an actual PR trimming rate during the PR trimming process applied on a PR layer;   (iii) comparing the actual PR trimming rate and the estimated PR trimming rate to determine a difference between the actual PR trimming rate and the estimated PR trimming rate;   (iv) in response to the difference being greater than a threshold, adjusting one or more PR trimming parameters for the PR trimming process so that an adjusted actual PR trimming rate is nominally the same as the estimated PR trimming rate.   
     
     
         32 . The method of  claim 31 , wherein an adjustment of the PR trimming parameters is proportional to a value of the difference. 
     
     
         33 . The method of  claim 31 , wherein operation (ii) comprises:
 measuring a first distance in a first direction between a first trimming mark and a first side of the PR layer along a second direction to determine the actual PR trimming rate of the PR trimming process along the first direction.   
     
     
         34 . The method of  claim 33 , further comprises:
 after trimming the PR layer along the first direction using the adjusted actual PR trimming rate, repeating operations (ii), (iii) and (iv).   
     
     
         35 . The method of  claim 34 , wherein repeating operation (ii) comprises:
 measuring a second distance in the first direction between a second trimming mark and a first side of the trimmed PR layer along the second direction to determine the actual PR trimming rate of the PR trimming process along the first direction.   
     
     
         36 . The method of  claim 33 , further comprises:
 (I) providing an second estimated PR trimming rate;   (II) determining a second actual PR trimming rate of the PR trimming process along the second direction;   (III) comparing the second actual PR trimming rate and a second estimated PR trimming rate to determine a second difference between the second actual PR trimming rate and the second estimated PR trimming rate; and   (IV) in response to the second difference being greater than the threshold, adjusting one or more PR trimming parameters for the PR trimming process so that a second adjusted actual PR trimming rate along the second direction is nominally the same as the second estimated PR trimming rate.   
     
     
         37 . The method of  claim 36 , wherein determining the second actual PR trimming rate comprises:
 measuring a third distance in the second direction between the first trimming mark and a second side of the PR layer along the first direction to determine the second actual PR trimming rate of the PR trimming process along the second direction.   
     
     
         38 . The method of  claim 37 , further comprises:
 trimming the PR layer along the first direction using the adjusted actual PR trimming rate; and   simultaneously trimming the PR layer along the second direction using the second adjusted actual PR trimming rate.   
     
     
         39 . The method of  claim 38 , further comprises:
 after trimming the PR layer, repeating operations (ii), (iii), (iv) and (II), (III), (IV).   
     
     
         40 . The method of  claim 34 , wherein repeating operation (II) comprises:
 measuring a fourth distance in the second direction between the second trimming mark and a second side of the trimmed PR layer along the first direction to determine the second actual PR trimming rate of the PR trimming process along the second direction.