Contact or proximity printing using a magnified mask image
Improvements in the fabrication of integrated circuits are driven by the decrease of the size of the features printed on the wafers. Current lithography techniques limits have been extended through the use of phase-shifting masks, off-axis illumination, and proximity effect correction. More recently, liquid immersion lithography has been proposed as a way to extend even further the limits of optical lithography. This invention described a methodology based on contact or proximity printing using a projection lens to define the image of the mask onto the wafer. As the imaging is performed in a solid material, larger refractive indices can be obtained and the resolution of the imaging system can be increased.
1. A method for manufacturing integrated circuits, comprising:
providing a sample having a layer adapted to be developed in response to radiation having a wavelength;
providing a layout object to be projected on said layer;
placing said layer on said sample a) in contact with a lens element of a projection lens or b) in close proximity with the lens element of the projection lens with a spacing between the lens element and the sample not greater than approximately the wavelength of the radiation divided by five and without an immersion lens between the lens element and the sample, wherein said lens element comprises a material having an index of refraction for said radiation greater than 1; and
imaging the object onto said layer through said projection lens.
2. The method of claim 1 , including imaging the object at an image plane so that evanescent waves emanating from the lens element transfer an image of the object to said layer.
3. The method of claim 1 , including imaging the object at an image plane near a top surface of said layer.
4. The method of claim 1 , including preventing adhesion of said lens element to said layer.
5. The method of claim 1 , including placing a mask including said layout object in contact or close proximity with another lens element of a projection lens, wherein said another lens element comprises a material having an index of refraction for said radiation greater than 1.
6. The method of claim 1 , including laying out a layout pattern on a mask including the layout object to be imaged on said layer, said laying out including applying proximity correction using a lithography model comprising, for an incident material different than air characterized by its refractive index and absorption coefficient, calculating fields in said layer, accounting for the incident material refractive index and absorption coefficient, performed using thin film optics or by solving Maxwell equations.
7. The method of claim 1 , including laying out a layout pattern on a mask including the layout object to be imaged on said layer, said laying out including applying proximity correction using a lithography model comprising, for an incident material different than air characterized by its refractive index and absorption coefficient, calculating fields in said layer, accounting for the incident material refractive index and absorption coefficient, performed using thin film optics or by solving Maxwell equations, and accounting for a gap between the incident material and resist using thin film modeling or by solving Maxwell equations.
8. The method of claim 1 , including laying out a layout pattern on a mask including the layout object to be imaged on said layer, the layout pattern comprising an alternating aperture phase-shifting mask layout, said laying out including applying proximity correction using a lithography model comprising, for an incident material different than air characterized by its refractive index and absorption coefficient, calculating fields in said layer, accounting for the incident material refractive index and absorption coefficient, performed using thin film optics or by solving Maxwell equations.
9. The method of claim 1 , including laying out a layout pattern on a mask including the layout object to be imaged on said layer, wherein said imaging the object on said layer through said projection lens, includes applying an off-axis setting for the projection lens, the off-axis setting obtained using a lithography model comprising, for an incident material different than air characterized by its refractive index and absorption coefficient, calculating fields in resist, accounting for the incident material refractive index and absorption coefficient, performed using thin film optics or by solving Maxwell equations.
10. The method of claim 1 , including laying out a layout pattern on a mask including the layout object to be imaged on said layer, the layout pattern comprising an assist feature having a size and a distance from a corresponding main feature, said laying out including determining said size and said distance using a lithography model comprising, for an incident material different than air characterized by its refractive index and absorption coefficient, calculating fields in said layer, accounting for the incident material refractive index and absorption coefficient, performed using thin film optics or by solving Maxwell equations.
11. The method of claim 1 , including laying out a layout pattern on a mask including the layout object to be imaged on said layer, the layout pattern comprising an attenuated phase-shifting mask having sizing parameters, said laying out including determining said sizing parameters using a lithography model comprising, for an incident material different than air characterized by its refractive index and absorption coefficient, calculating fields in said layer, accounting for the incident material refractive index and absorption coefficient, performed using thin film optics or by solving Maxwell equations.
12. The method of claim 1 , wherein the sample comprises a wafer including a plurality of materials forming a wafer stack, and including laying out a layout pattern on a mask including the layout object to be imaged on said layer, said laying out including applying proximity correction using a lithography model comprising, for an incident material different than air characterized by its refractive index and absorption coefficient, dividing refractive indices and absorption coefficients of all the materials in the wafer stack by the refractive index of the incident material.