An embodiment method for forming an image sensor includes forming an anti-reflective coating over a surface of a semiconductor supporting a photodiode, forming an etching stop layer over the anti-reflective coating, forming a buffer oxide over the etching stop layer, and selectively removing a portion of the buffer oxide through etching, the etching stop layer protecting the anti-reflective coating during the etching. An embodiment image sensor includes a semiconductor disposed in an array region and in a periphery region, the semiconductor supporting a photodiode in the array region, an anti-reflective coating disposed over a surface of the semiconductor, an etching stop layer disposed over the anti-reflective coating, a thickness of the etching stop layer over the photodiode in the array region less than a thickness of the etching stop layer in the periphery region, and a buffer oxide disposed over the etching stop layer in the periphery region.