Acceleration sensor and manufacturing method thereof

1. An acceleration sensor, comprising:

a weight;

a pedestal arranged around the periphery of said weight;

a support frame arranged along said pedestal and formed to have a width narrower than that of said pedestal all around its perimeter;

a mass attached to said weight to retain said weight inside said support frame; and

beams connecting said support frame and said mass, and overlapping said pedestal near their ends on the support frame side.

2. An acceleration sensor according to claim 1 , wherein

said support frame and said beams have substantially the same thickness, and

said acceleration sensor further comprises a peripheral interlayer arranged between said support frame and said pedestal to create a predetermined clearance between said pedestal and the parts of said beams that overlap said pedestal.

3. An acceleration sensor according to claim 1 , wherein said acceleration sensor is formed by etching a multilayer substrate.

4. An acceleration sensor according to claim 3 , wherein

the multilayer substrate is a substrate with first and second layers formed on both sides of a third layer,

said mass, said support frame, and said beams are formed in said first layer,

said weight and said pedestal are formed in said second layer, and

said peripheral interlayer is formed in said third layer.

5. An acceleration sensor according to claim 4 , wherein the multilayer substrate is an SOI substrate with first and second semiconductor films formed on both sides of a dielectric film.

6. An acceleration sensor according to claim 1 further comprising strain detection means arranged in said beams.

7. A manufacturing method of an acceleration sensor, comprising:

a first step of preparing a multilayer substrate with first and second layers formed on both sides of a third layer;

a second step of forming first grooves in the first layer to form a mass, a support frame surrounding the periphery of the mass, and beams connecting the mass and the support frame;

a third step of forming second grooves in the second layer to form a pedestal arranged along the support frame, and a weight secured to the mass inside the pedestal; and

a fourth step of removing parts of the third layer that are exposed through the first and second grooves and where in the second step the support frame is formed to have a width narrower than the width of the pedestal all around its perimeter so that the beams will overlap the pedestal near their ends on the support frame side.

8. A manufacturing method of an acceleration sensor according to claim 7 , wherein

in said second step, the mass and the support frame are formed to have substantially the same thickness, and

in said fourth step, a peripheral interlayer is formed between the support frame and the pedestal in a manner to create a predetermined clearance between the pedestal and the parts of the beams that overlap the pedestal.

9. A manufacturing method of an acceleration sensor according to claim 7 , wherein said third step further comprises

a step of forming a hard mask pattern that covers a region for pedestal formation on the surface of the second layer to form a resist pattern that covers regions for the formation of the hard mask pattern and the weight,

a step of etching using the resist pattern to form the second grooves in such a manner that a predetermined thickness remains intact in the second layer so as to separate the pedestal and the weight, and

a step of removing the resist pattern, etching the bottom faces of the second grooves and the weight in such a state to cover the pedestal with the hard mask pattern, and exposing corresponding parts of the third layer through the second grooves while forming a predetermined step height between the weight and the pedestal.

10. A manufacturing method of an acceleration sensor according to claim 9 , wherein the step height between the weight and the pedestal is substantially the same as a predetermined film thickness of the second layer remaining in the second grooves.

11. A manufacturing method of an acceleration sensor according to claim 7 , wherein the multilayer substrate is an SOI substrate with first and second semiconductor films formed on both sides of a dielectric film.

12. A manufacturing method of an acceleration sensor according to claim 7 further comprising a fifth step of forming strain detection means in the beams.