There have been somewhat arbitrary design rules implemented over the years dealing with how much open (non-resist covered) area is required on a product layout at a given layer to ensure robust endpoint detection. Design rules have been used at the typical layers that employ endpoint detection, e.g. poly, isolation, metal, capacitor. A systematic study of the poly layer endpoint detection is discussed in this report. A photolithographic method is introduced to measure the open area required for endpoint detection. Two etchers are studied: Lam 4400 poly etcher and a higher plasma density Lam TCP 9400SE. The endpoint signal versus percent open area and etch rate versus percent open area are presented. The minimum reticle open area required for the Lam 4400 endpoint detection was determined to be 25% and for the Lam 9400 it was 30%. Neither etcher showed an etch rate dependence on the percent open area.