Patent ID: 7771897
Filing Date: 2010-08-10
Classification: G03F

Abstract:
1. A method of fabricating a photomask for forming a resist pattern by exposing a resist layer provided on an underlying layer to light transmitting through the photomask so that a resist pattern can be formed changing in film thickness on the overlying layer by performing development, the method comprising: a step of providing, in a position where to use the photomask, a virtual mask plane having a coordinate origin in a position corresponding to an on-resist reference point set on the resist layer; a step of setting a plurality of square cells in rows and columns by demarcating the mask plane with a plurality of straight lines orthogonal to each other at an equal interval, each of which has one side having a length provided smaller than a length of a resolution limit of an optical system of an exposure equipment for which the photomask is used; a step of setting four subcells by drawing virtual divisional lines in row and column directions and dividing each of the cells into two equal parts with respect to the row and column directions; a step of setting film thickness of the resist layer for positions corresponding to each of the subcells; a step of setting one of normalized light intensities of light transmitting through the subcells as a subcell intensity, the subcell intensity corresponding to the film thickness, the normalized light intensities having three or more different values in which a maximum value of the light transmitting through the subcells is normalized to 1; a step of setting each of the subcells with a preparatory cell intensity having a set of four values and having an average value giving the subcell intensity; a step of providing first to fourth transparent mask substrates; a step of setting mask cells corresponding to the cells in rows and columns by demarcating with a plurality of straight lines orthogonal to each other at an equal interval, on a surface of each of the first to fourth mask substrates; a step of setting sub-mask-cells corresponding to the subcells by a plurality of virtual divisional lines drawn in row and column directions and setting an on-mask reference point, on the surface of each of the first to fourth mask substrates; a step of aligning the on-mask reference point of the first mask substrate with the coordinate origin; a step of aligning the on-mask reference point of the second mask substrate with a position shifted a distance of ½ times the one-side length of the mask cell in a row direction from the coordinate origin; a step of aligning the on-mask reference point of the third mask substrate with a position shifted a distance of ½ times the one-side length of the mask cell in a column direction from the coordinate origin; a step of aligning the on-mask reference point of the fourth mask substrate with a position shifted a distance of ½ times the one-side length of the cell in the row and column directions from the coordinate origin; a step of providing the sub-mask-cells of the first to fourth mask substrates with preparatory cell intensities corresponding to the subcells, in greater order; a step of selecting one of the preparatory cell intensities of the sub-mask-cells belonging to each of the mask cells of the first to fourth mask substrates; a step of setting any one or both of a light-transmission area and a shade area to each of the mask cells of the first to fourth mask substrates, and defining the cell intensity with a light intensity through each of the mask cells to a corresponding area of the resist layer; and a step of forming a shade film over the shade areas of each of the first to fourth mask substrates, thereby obtaining first to fourth photomasks.