Method and apparatus for extending spatial frequencies in photolithography images

A method for obtaining a pattern wherein the Fourier transform of said pattern contains high spatial frequencies by combining nonlinear functions of intensity of at least two exposures combined with at least one nonlinear processing step intermediate between the two exposures to form three dimensional patterns comprising the steps of:

• coating a substrate with a first mask material and a first photoresist layer;
• exposing said first photoresist layer with a first exposure
• developing said photoresist to form a first pattern in said first photoresist layer, said first pattern containing spatial frequencies greater than those in a two dimensional optical intensity image imposed onto said photoresist layer in said first exposure as a result of a nonlinear response of said first photoresist layer;
• transferring said first pattern into said first mask material, said first mask material comprising at least one of SiO.sub.2, Si.sub.3 N.sub.4, a metal, a polysilicon and a polymer;
• coating said substrate with a second photoresist;
• exposing said second photoresist with a second exposure
• developing said second photoresist layer to form a second pattern in said second photoresist layer, said second pattern containing spatial frequencies greater than those in a two dimensional optical intensity image imposed onto said photoresist layer in said second exposure as a result of a nonlinear response of said second photoresist layer;
• transferring said first pattern and said second pattern into said substrate using a combined mask including parts of said first mask layer and said second photoresist;
• removing said first mask material and said second photoresist.

A method for increasing spatial frequency content of lithographic patterns comprising the steps of:

• depositing a material;
• depositing a photoresist on said material;
• exposing a periodic image in said photoresist, said periodic image having a pitch p.sub.min and a linewidth less than p.sub.min /2;
• developing said periodic image to form a periodic pattern in said photoresist;
• transferring said periodic pattern to said material;
• depositing a second photoresist layer on said material;
• offsetting said periodic pattern by p.sub.min /2;
• repeating said exposing, developing and transferring steps, thereby interpolating new said pattern midway between said pattern.

A method for multiplying the spatial frequency content of a one-dimensional line/space pattern consisting of the steps of:

• providing a substrate;
• depositing a material on said substrate;
• depositing a photoresist on said material;
• exposing and developing a periodic pattern in said photoresist, said periodic pattern having a pitch p.sub.min and a linewidth less than p.sub.min /2;
• transferring said periodic pattern into said material by a process step;
• removing said first photoresist layer;
• depositing a second photoresist layer;
• exposing said second photoresist layer with said periodic pattern offset by p.sub.min /2;
• repeating the exposing, developing and transferring steps N times with offsets of p.sub.min /N, thereby interpolating N new said patterns equally spaced midway between said pattern,
• etching exposed said material down to a predetermined depth, thereby transferring said pattern through said material;
• transferring said pattern into said substrate.