ETCH “sandbox”: Controlled release dimensions through atomic layer deposition etch stop with trench refill and polish

We report on the demonstration of a microfabrication process which allows the release of suspended films or structures of varying sizes in which the release volume is predefined by i) lithographic patterning, ii) etch-stop deposition by atomic layer deposition (ALD), iii) refilling sacrificial layer into the empty volume, and iv) subsequent chemical mechanical planarization (CMP). We refer to this as an “etch sandbox,” which allows the user to process devices on a planarized substrate after completion of the sandbox. We demonstrate micrometer scale Al₂O₃ suspended membranes utilizing Al₂O₃ as the etch-stop and polysilicon as the refill/sacrificial etch material. Within a single substrate and single release, defined etch volumes up to differing by up to a factor of 10⁴ can be realized. Considering the flexibility of this process, suspended membranes with more complicated structure and composition could be developed in the future.