technique to be effective referring now to fig2 a through 2d there are figures illustrating examples of how asymmetric opc structures are used in accordance with the present disclosure it has been determined that opc structures are not required to be symmetrical in size and shape in order to be effective for correcting line end distortions deviations asymmetric opc structures may be effective in correcting such line end distortions deviations when certain preferred orientations are utilized fig2 a illustrates an example of asymmetric opc structures used upon a portion of a mask pattern comprising of 4 line ends of which one pair of adjacent lines a and b are located opposing another pair of adjacent lines a u2032 and b u2032 in close proximity opc has been applied to the line ends of all 4 lines so that each has a u201c protruding portion u201d extending out from the ends the opc structures are noted as being asymmetric as the serifs applied to the line ends of lines a and b point towards a different direction than that applied to the line ends of lines a u2032 and b u2032 fig2 a specifically shows serifs applied only to the right side of the line ends of adjacent lines a and b along the x axis direction the opc serifs applied upon the adjacent line ends of lines a u2032 and b u2032 are located only onto the left side of the lines along.