MEMS package, semiconductor structure and method of forming same

Various embodiments of the present invention are directed to methods of roughening a crystalline layer. A crystalline layer is deposited over the substrate. The mask material diffuses into the crystalline layer along a grain boundary of the crystalline layer. For example, the crystalline layer and the mask material may be polysilicon and silicon oxide respectively, or include polysilicon and silicon oxide, respectively. However, other suitable materials are also feasible. Etching is performed on the crystalline layer with an etchant having high selectivity to the crystalline layer with respect to the mask material. The mask material defines a micromask embedded in the crystalline layer along the grain boundary. The micromask protects portions of the underlying crystalline layer during etching such that etching forms trenches in the crystalline layer that are not masked by the micromask. The embodiment of the invention also relates to a MEMS package, a semiconductor structure and a forming method thereof. 本发明的