Aspects of the disclosure provide a method of forming a semiconductor apparatus. A stack of dielectric layers is formed over a semiconductor layer on a substrate of the semiconductor apparatus. Multiple openings are formed in the stack of dielectric layers. Multiple pillars including first sub-pillars and second sub-pillars are formed in the multiple openings. A cantilever structure that includes a first cantilever beam and a second cantilever beam is formed. A cantilever supporting structure that includes a portion of a first subset of the multiple pillars is formed. The first cantilever beam connects the second cantilever beam and the cantilever supporting structure. One of the stack of dielectric layers is removed to expose first portions of the first sub-pillars and second portions of the second sub-pillars. Isolation structures are formed between the first sub-pillars and the respective second sub-pillars.