Method for correcting local loading effects in the etching of photomasks
A method for correcting local loading-effects in photomask etching includes the steps of determining the location-dependent density of structures of a mask; determining the location-dependent strength of the loading effect with the aid of the structure density; and determining location-dependent correction values for the mask structures with the aid of the strength of the loading effect for the purpose of compensating the loading effect. It is recognized that the strength of location-dependent loading effects can be predicted with the aid of the location-dependent structure density and therefore compensated.
1. A method for correcting local loading effects during etching of photomasks, which comprises the following steps:
determining a location-dependent density of mask structures resulting in a structure density, the determining step including:
forming a density function d(x,y) for determining the location dependent density of the mask structures;
determining a location-dependent strength of a loading effect with an aid of the structure density, the determining step including:
determining the location-dependent strength of the loading effect by a convolution of the density function with a Gauss function; and
determining location-dependent correction values for the mask structures using the location-dependent strength of the loading effect for compensating for the loading effect.
2. The method according to claim 1 , which further comprises determining the location-dependent density of the mask structures by analyzing a location-dependent bright field proportion of a mask surface that is to be generated.
3. The method according to claim 1 , which further comprises determining a location-dependent shift of edges of the mask structures with an aid of the location-dependent strength of the loading effect, the location-dependent correction values compensating for the location-dependent shift of the edges of the mask structures.
4. The method according to claim 3 , which further comprises using an equation for the location-dependent shift of the edges at point (x,y) on the mask surface being:
s ( x,y )= m ( t 0 −p σ ( x,y )),
whereby p σ (x,y) is a density pseudo-function, and model parameters σ, m and t 0 are determined with an aid of measurements of uncorrected masks.
5. The method according to claim 4 , which further comprises calculating the density pseudo-function p σ (x,y) by convolution of the density function d(x,y) of the mask structures with the Gauss function of a range σ.
6. The method according to claim 4 , which further comprises determining the location-dependent correction values by use of a correction function formed by inverting a sign of m from a function s(x,y).
7. The method according to claim 1 , which further comprises:
partitioning a mask surface into subregions; and
assigning a location-dependent correction value to each of the subregions.
8. The method according to claim 7 , which further comprises creating a table for allocating the location-dependent correction value to each of the subregions.
9. A computer program for configuring a layout of a mask and correcting mask structures: comprising:
computer executable instructions for carrying out the method according to claim 1 .