Process for fabricating a microelectromechanical structure
First Claim
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1. A process for fabricating a microelectromechanical (MEM) structure on a device side of a substrate, comprising steps for:
- (a) partially building up the MEM structure by depositing and patterning a plurality of layers of polysilicon on the device side of the substrate with each adjacent pair of polysilicon layers being separated by a layer of a sacrificial material, and with the layers of polysilicon and the sacrificial material having an accumulated stress of a sufficient magnitude after a step for annealing the substrate to produce a bowing of the substrate characterized by a radius of curvature of the substrate which is less than a critical value;
(b) depositing a stress-compensation layer on a backside of the substrate opposite the device side to reduce the bowing of the substrate, with the radius of curvature of the substrate being increased to more than the critical value; and
(c) depositing and patterning at least one additional layer of polysilicon on the device side of the substrate to complete building up the MEM structure.
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Abstract
A process is disclosed for forming a microelectromechanical (MEM) structure on a substrate having from 5 to 6 or more layers of deposited and patterned polysilicon. The process is based on determining a radius of curvature of the substrate which is bowed due to accumulated stress in the layers of polysilicon and a sacrificial material used to buildup the MEM structure, and then providing one or more stress-compensation layers on a backside of the substrate to flatten the substrate and allow further processing.
37 Citations
36 Claims
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1. A process for fabricating a microelectromechanical (MEM) structure on a device side of a substrate, comprising steps for:
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(a) partially building up the MEM structure by depositing and patterning a plurality of layers of polysilicon on the device side of the substrate with each adjacent pair of polysilicon layers being separated by a layer of a sacrificial material, and with the layers of polysilicon and the sacrificial material having an accumulated stress of a sufficient magnitude after a step for annealing the substrate to produce a bowing of the substrate characterized by a radius of curvature of the substrate which is less than a critical value;
(b) depositing a stress-compensation layer on a backside of the substrate opposite the device side to reduce the bowing of the substrate, with the radius of curvature of the substrate being increased to more than the critical value; and
(c) depositing and patterning at least one additional layer of polysilicon on the device side of the substrate to complete building up the MEM structure. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12)
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13. A process for fabricating a microelectromechanical (MEM) structure on a device side of a substrate, comprising steps for:
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(a) partially building up the MEM structure by depositing and patterning a plurality of alternating layers of polysilicon and a sacrificial material;
(b) measuring a radius of curvature of the substrate by reflecting a light beam off the substrate, with the radius of curvature being due to a bowing of the substrate that arises from an accumulated stress in the layers of polysilicon and the sacrificial material which cannot be completely eliminated by a step for annealing the substrate;
(c) depositing a stress-compensation layer on a backside of the substrate opposite the device side when the measured radius of curvature is less than a critical value; and
(d) repeating steps (a)-(c) at least one more time to complete the buildup of the MEM structure. - View Dependent Claims (14, 15, 16, 17, 18, 19, 20, 21, 22)
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23. A process for fabricating a microelectromechanical (MEM) structure on a device side of a substrate, comprising steps for:
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(a) depositing and patterning a plurality of alternating layers of polysilicon and a sacrificial material to partially build up the MEM structure on the device side of the substrate, with the layers of polysilicon and the sacrificial material having an accumulation of stress therein resulting in a bowing of the substrate;
(b) depositing a stress-compensation layer on a backside of the substrate opposite the device side when a radius of curvature of the substrate due to the bowing of the substrate is below a critical value, with the stress-compensation layer increasing the radius of curvature above the critical value; and
(c) repeating steps (a)-(c) at least one more time to complete the buildup of the MEM structure on the substrate. - View Dependent Claims (24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36)
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Specification