Directly measured interaction distance (or planarization length) from a step density test mask was constant independent of pattern variables such as pattern density and pattern shapes between line and area. Then, using chemical mechanical polishing (CMP) test mask and taking the experimentally obtained interaction distance into consideration, systematic exploration regarding density and pitch effects on the remaining nitride thickness in shallow trench isolation CMP was performed, comparing plasma enhanced tetraethyl orthosilicate and high density plasma oxide.