Method of improving photomask geometry

In a photolithographic apparatus having an illuminator for directing light onto a photosensitive surface of a semiconductor, the improvement comprising a photomask for optically transferring a lithographic pattern corresponding to an integrated circuit (IC) from said mask onto a semiconductor substrate, said pattern including a plurality of densely spaced features and an isolated feature spaced from the densely spaced features, said isolated feature having at least one pair of assisting bars on opposite sides of said isolated feature and spaced equally from the corresponding side opposite the assisting bar, wherein the assisting bars alter the edge intensity gradient of edges of the isolated feature to reduce proximity effects wherein spacing the assisting bars in accordance with the pitch of the densely space features and a spatial frequency filter disposed between the source of light and the photomask for distributing diffraction energy.

In a projection lithography apparatus with a light source, an illumination stage for shaping the light source, and a lens for directing the shaped light onto a photomask for projecting a pattern on the mask to a photosensitive surface of a semiconductor wafer, a method for locating optical proximity correction features on the photomask comprising:

• providing a set of densely packed mask features on the photomask, said densely spaced features having a dense feature pitch;
• providing one of more isolated features on the photomask;
• locating one or more assist features adjacent the isolated features a distance selected in accordance with the pitch of the dense features.

In a projection lithography apparatus with a light source of known wavelength and a known numerical aperture, an illumination stage for shaping the light source, and a lens for directing the shaped light onto a photomask for projecting a pattern on the mask to a photosensitive surface of a semiconductor wafer, a method for locating optical proximity correction features on the photomask comprising:

• providing a set of densely packed mask features on the photomask,
• providing one of more isolated features on the photomask;
• locating one or more assist features adjacent the isolated features a distance selected in accordance with the wavelength and numerical aperture.

The method of claim 20 wherein there are m sets of assisting features and each set m of features is spaced a distance corresponding to the wavelength divided by the numerical aperture.

1. In a photomask for optically transferring a lithographic pattern corresponding to an integrated circuit (IC) from said photomask onto a semiconductor substrate, said pattern including a plurality of densely spaced features and one or more semi-isolated features spaced from the densely spaced features, said isolated feature having at least one pair of assisting bars on opposite sides of said isolated feature and spaced equally from the corresponding side of the isolated feature opposite the assisting bar, wherein the assisting bars alter the edge intensity gradient of edges of the isolated feature to reduce proximity effects, the improvement comprising:

• spacing the assisting bars in accordance with the pitch of the densely space features;
• and
• spacing the semi-isolated features at preferred duty ratios at odd multiples of the duty ratios of the dense features.