and 14 which are formed for example on a quartz mask substrate 16 as shown in fig4 b the pitch of the features utilized in the example of fig4 a is 300 nm further in the exemplary illustration the quasar illumination setting is 0 85 outer 0 55 inner 30 degree as illustrated in fig5 it is shown that essentially three distinct u201c regions u201d of aerial image slope can be observed a 1 st region with a positive aerial image slope a 2 nd region with a near zero aerial image slope and a 3 rd region with a negative aerial image slope the first region is characteristic of a cpl feature having a small width where the two phase edges are close to each other as shown in fig5 in the first region as the cd of the feature increases the cd of the resulting feature imaged on the wafer also increases in a substantially linear manner in the first region two phase edges interact closely to form a single line pattern the second region designates the maximum feature size that can be achieved using two adjacent chromeless phase edges as shown in fig5 in the second region the slope of the aerial image is near zero as such as the feature width continues to increase the width of the resulting feature imaged on the wafer no longer increases in a linear manner i e the width of the imaged feature essentially remains the same regardless of the variation of the feature width this is due to the fact that in the second region the two phase edges begin to lose the interactivity necessary for proper image formation in the third region the.