Source: {"pile_set_name": "USPTO Backgrounds"}

A binary or phase shift photomask may include glass and chrome features which form a pattern. Light may pass through the clear glass areas and be blocked by the opaque chrome areas. Light that passes through the mask may continue into an imaging system that projects an image of the mask pattern onto a wafer. The wafer may be coated with a photosensitive film (photoresist), which undergoes a chemical reaction when exposed to light. After exposure, in a “positive” photoresist, the areas on the photoresist exposed to the light may be removed in a developing process, leaving the unexposed areas as features on the wafer. Alternatively, in a “negative” photoresist, the areas on the photoresist shielded from the light may be removed in a developing process, leaving the exposed areas as features on the wafer.
“Pitch” refers to the center-to-center distance between features in a pattern. The resolution of an imaging system determines the smallest pitch the system can resolve. If the pitch of the original pattern exceeds the resolution limits of the system, e.g., is too small, the pattern may not be clearly defined on the photoresist. This may produce defects in the final product.