Patent ID: 7094662

Claim:
A method of forming an overlay mark, comprising: forming a first material layer on a substrate; forming a first trench serving as a first potion of a trench type outer mark in the first material layer; forming a first deposition layer on the first material layer, wherein the first trench is partially or incompletely filled with the first deposition layer; performing a first chemical mechanical polishing process on the first deposition layer until the first material layer is exposed leaving a remaining portion of the first deposition layer in the first trench; forming a second material layer to cover the first material layer and the first deposition layer, wherein a thickness of the second material layer is smaller than that of the first material layer; removing the second material layer on the trench type outer mark to form a second trench exposing at least a portion of the first deposition layer in the first trench, wherein the second trench serves as a second portion of the trench type outer mark; forming a second deposition layer on the substrate to cover the second material layer and the first deposition layer in the first trench; performing a second chemical mechanical polishing process on the second deposition layer until the second material layer in the second trench is exposed; forming a third deposition layer on the second material layer, wherein a step height is formed on the third deposition layer between the edge of the first trench and the center of the first trench; and forming a raised feature serving as an inner mark on the third deposition layer.