Contact through hole etching method

The invention provides a contact through hole etching method which is applicable to a composite layer structure formed by at least stacking a first material layer and a second material layer, wherein the first material layer and the second material layer are made of different materials. The contact through hole etching method comprises the steps as follows: a, using a Bosch etching process to etch the first material layer to form a contact through hole in the first material layer, wherein the Bosch etching process further comprises the following sub steps: a1, forming a polymer on the side wall and bottom of the contact through hole; a2, removing the polymer on the bottom of the contact through hole; a3, etching the inside of the contact through hole by a predetermined depth; and a4, repeating the sub steps a1 to a3 until the contact through hole reaches a specified depth in the first material layer; and b, using another etching process different from the Bosch etching process to etch the contact through hole reaching the specified depth to enable the contact through hole to extend into the second material layer under the first material layer. By adopting the method of the invention, the contact through hole formed though etching has a better shape.