Photolithography process using multiple anti-reflective coatings

A method for fabricating a memory cell, the method comprising the steps of:

• providing a substrate;
• forming a structure on the substrate, the structure comprising
• at least two active areas in the substrate;
• a gate stack between the active areas;
• and
• a capacitor in electrical contact with one of the active areas;
• depositing a first anti-reflective coating having a first index of refraction, a first absorption, a first thickness, and an upper surface defining a first interface over the structure;
• depositing a second anti-reflective coating having a second index of refraction, a second absorption, a second thickness, and an upper surface defining a second interface at least partially on the upper surface of said first anti-reflective coating;
• depositing an insulating layer over the structure;
• and
• patterning the insulating layer using a photo-lithographic process, wherein the first index of refraction is different from the second index of refraction.

An integrated circuit comprising:

• a reflective layer having a reflective surface;
• a first anti-reflective coating over the reflective surface, the first coating having a first index of refraction, a first absorption, a first thickness, and an upper surface defining a first interface;
• and
• a second anti-reflective coating at least partially on the upper surface of said first anti-reflective coating, the second anti-reflective coating having a second index of refraction, a second absorption, a second thickness, and an upper surface defining a second interface, wherein the first index of refraction is different from the second index of refraction.

A memory cell comprising:

• a structure on a substrate, the structure comprising
• at least two active areas formed in the substrate;
• a gate stack between the active areas;
• and
• a capacitor in electrical contact with one of the active areas;
• a first anti-reflective coating over the structure, the first anti-reflective coating having a first index of refraction, a first absorption, a first thickness, and an upper surface defining a first interface;
• a second anti-reflective coating on at least a portion of the first anti-reflective coating, the second anti-reflective coating having a second index of refraction, a second absorption, a second thickness, and an upper surface defining a second interface;
• and
• a patterned insulating layer over the structure, the insulating layer being patterned by a photo-lithographic process, wherein the first index of refraction is different from the second index of refraction.

An integrated circuit comprising:

• at least one memory cell, the memory cell comprising
• a structure on a substrate, the structure comprising
• at least two active areas formed in the substrate;
• a gate stack between the active areas;
• and
• a capacitor in electrical contact with one of the active areas;
• a first anti-reflective coating over the structure, the first anti-reflective coating having a first index of refraction and a first absorption;
• a second anti-reflective coating on at least a portion of the first anti-reflective coating, the second anti-reflective coating having a second index of refraction and a second absorption;
• and
• a patterned insulating layer over the structure, the insulating layer being patterned by a photo-lithographic process, wherein the first index of refraction is different from the second index of refraction.

A computer system comprising:

• a processor;
• and
• a memory, the memory comprising at least one memory cell, the memory cell comprising
• a structure on a substrate, the structure comprising
• at least two active areas formed in the substrate;
• a gate stack between the active areas;
• and
• a capacitor in electrical contact with one of the active areas;
• a first anti-reflective coating over the structure, the first anti-reflective coating having a first index of refraction and a first absorption;
• a second anti-reflective coating formed on the first anti-reflective coating, the second anti-reflective coating having a second index of refraction and a second absorption;
• and
• a patterned insulating layer over the structure, the insulating layer being patterned by a photo-lithographic process, wherein the first index of refraction is different from the second index of refraction.

A method for forming a memory cell, the method comprising the steps of:

• depositing a first anti-reflective coating over a reflective surface;
• depositing a second anti-reflective coating over and in contact with the first anti-reflective coating;
• depositing a dielectric material over and in contact with the second anti-reflective coating;
• and
• etching the dielectric material, using the anti-reflective coating as an etch stop.

A computer implemented method for designing anti-reflective coating layers with desirable properties comprising:

• a) modeling a first anti-reflective coating with a first index of refraction, a first absorption, and a first thickness, wherein the first thickness is slightly less than a total maximum allowable thickness for said anti-reflective coating layers based on the requirements of a desired integrated circuit fabrication process;
• b) modeling a second anti-reflective coating with a second index of refraction, a second absorption, and a second thickness, wherein the first and second indices of refraction are different, and the combined thicknesses of the first and second anti-reflective coatings is approximately equal to said total maximum allowable thickness;
• c) modeling the reflective properties of the anti-reflective coatings using a lithography modeling program;
• d) evaluating the reflective properties of said first and second anti-reflective coatings relative to a set of desired reflective properties;
• e) adjusting the thicknesses, indices of refraction, and absorptions of the anti-reflective coatings based on said evaluating step;
• f) repeating steps c, d, and e to arrive at a solution for anti-reflective coating layers which provide desired reflective properties.