Measurement of pitch dependency of overlay errors under OAI by using the electric CD measurement technique.

Pattern displacement error under off axis illumination (OAI) was evaluated by using an electrical critical dimension measurement method at various pitches. Two major phenomena were observed which should be considered in order to control overlay accuracy between layers. One is the difference of pattern displacements between sub-micron device level patterns and large micron optical overlay measurement patterns, which is correctable by making correction tables between the layers. The other is pattern displacement error distribution within a field, which is not correctable and limits the usage of the field size and pattern pitches for minimal overlay control. The latter is more important and should be investigated in detail for systems with given pitch sizes before the devices are integrated.