Acoustic sensor and manufacturing method of the same
An acoustic sensor is provided for improving shock resistance performance, along with a method for manufacturing the acoustic sensor. In the acoustic sensor, a fixing plate is provided by a semiconductor manufacturing process, a frame wall has a curved shape in at least a portion of the periphery of the fixing plate, the frame wall being coupled to the semiconductor substrate. A sacrifice layer removed from the inner side of the fixing plate in the manufacturing process remains at least on a portion of the inner side of the frame wall. Roughness of the remaining sacrifice layer is smaller than roughness of a sound shape reflecting structure in which a shape similar to the external shape of sound holes is repeated. Roughness of the sound shape reflecting structure is formed when removing the sacrifice layer using etching liquid supplied from the plurality of sound holes in the semiconductor manufacturing process.
1. An acoustic sensor that detects acoustic vibration by converting the acoustic vibration into change in electrostatic capacitance between a vibration electrode film and a fixed electrode film, comprising:
a semiconductor substrate having an opening in a surface thereof;
a back plate composed of a fixing plate and the fixed electrode film provided on the fixing plate, the fixing plate being arranged to face the opening of the semiconductor substrate and having a plurality of sound holes and the fixed electrode film provided on the fixing plate; and
the vibration electrode film arranged between the back plate and the semiconductor substrate so as to face the back plate across a gap,
wherein the fixing plate is provided by a semiconductor manufacturing process, and a frame wall is constituted with a curved shape in at least a portion of a periphery of the fixing plate, the frame wall being coupled directly or indirectly to the semiconductor substrate, and
a sacrifice layer removed from an inner side of the fixing plate in the semiconductor manufacturing process remains at least on a portion of an inner side of the frame wall, with roughness of an inward surface of the remaining sacrifice layer being smaller than roughness of a sound hole shape reflecting structure in which a shape similar to an external shape of the sound holes is repeated, the roughness of the sound hole shape reflecting structure being formed in a case of removing the sacrifice layer using an etching liquid supplied from the plurality of sound holes in the semiconductor manufacturing process.
2. The acoustic sensor according to claim 1 ,
wherein the plurality of sound holes are arranged inward of the opening of the semiconductor substrate as viewed from the normal direction of the fixing plate.
3. The acoustic sensor according to claim 1 ,
wherein the semiconductor manufacturing process includes:
a step of depositing, on the surface of the semiconductor substrate before the opening is formed, a first sacrifice layer and a second sacrifice layer covering the first sacrifice layer;
a step of forming the vibration electrode film on the second sacrifice layer;
a step of depositing a third sacrifice layer so as to cover the vibration electrode film;
a step of removing the first sacrifice layer; and
a step of removing a portion of each of the second and third sacrifice layers,
wherein the sound holes are arranged inward of an external shape of the first sacrifice layer as viewed from the normal direction of the fixing plate.
4. The acoustic sensor according to claim 1 ,
wherein the sacrifice layer is composed of at least two layers vertically, and
a material of the sacrifice layer is selected such that an etching rate of a lower sacrifice layer is higher than an etching rate of an upper sacrifice layer in the semiconductor manufacturing process.
5. The acoustic sensor according to claim 1 ,
wherein an opaque thin film is further deposited above at least a portion of the fixing plate on which the sacrifice layer remains, as viewed from the normal direction of the fixing plate.
6. The acoustic sensor according to claim 1 ,
wherein the vibration electrode film has a vibration portion that is substantially quadrilateral as viewed from the normal direction of the fixing plate, and
an average thickness of portions of the sacrifice layer remaining on areas of the frame wall facing sides of the vibration portion is greater than an average thickness of portions of the sacrifice layer remaining on other areas of the frame wall.