Micromachined capacitor structure and method for making
First Claim
1. A method for forming travel limit stops in a micromachined capacitor structure comprising the steps of:
- providing a substrate having a top surface;
covering the top surface with a first silicon nitride layer;
forming a first polysilicon layer on the first silicon nitride layer,patterning the first polysilicon layer to form a first anchor and a lower capacitor plate, wherein portions of the first silicon nitride layer are exposed by the patterning step;
covering the first patterned polysilicon and the exposed portions of the first silicon nitride with a first sacrificial layer comprising silicon oxide;
covering the first sacrificial layer with a second silicon nitride layer;
covering the second silicon nitride layer with a second sacrificial layer comprising silicon oxide;
etching a first hole in the second sacrificial layer, the second silicon nitride, and the first sacrificial layer to expose the first anchor;
etching a second hole in the second sacrificial layer over the lower capacitor plate;
forming a second polysilicon layer that fills the first and second holes and covers the second sacrificial layer;
patterning the second polysilicon layer to form a middle capacitor plate that is mechanically attached to the anchor, has a portion spaced from the lower capacitor plate by the thickness of the first and second sacrificial layers together with the second silicon nitride layer, and a travel stop portion which is spaced from the lower capacitor plate by the thickness of the first sacrificial layer and the second silicon nitride layer; and
performing a sacrificial etch of the first and second sacrificial layers using an isotropic etchant that etches the silicon oxide faster than silicon nitride, wherein only a portion of the second silicon nitride layer which is covered by the travel stop portion remains after the sacrificial etching.
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Accused Products
Abstract
A micromachined capacitor structure having integral travel stops (19, 22, 22'"'"') within an active region of the capacitor is provided. The capacitor structure is formed on a substrate (11) and includes a moving capacitor plate (15) supported by one or more flexing arms (17) mechanically anchored to the substrate (11). The moving capacitor plate (15) has an active region (15) substantially parallel to the substrate (11) and separated from the substrate (11) by a first spacing. A corrugation (19) is formed in the moving capacitor plate (15) over the substrate (11) and separated from the substrate (11) by a second spacing, wherein the second spacing is smaller than the first spacing.
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Citations
18 Claims
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1. A method for forming travel limit stops in a micromachined capacitor structure comprising the steps of:
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providing a substrate having a top surface;
covering the top surface with a first silicon nitride layer;forming a first polysilicon layer on the first silicon nitride layer, patterning the first polysilicon layer to form a first anchor and a lower capacitor plate, wherein portions of the first silicon nitride layer are exposed by the patterning step; covering the first patterned polysilicon and the exposed portions of the first silicon nitride with a first sacrificial layer comprising silicon oxide; covering the first sacrificial layer with a second silicon nitride layer; covering the second silicon nitride layer with a second sacrificial layer comprising silicon oxide; etching a first hole in the second sacrificial layer, the second silicon nitride, and the first sacrificial layer to expose the first anchor; etching a second hole in the second sacrificial layer over the lower capacitor plate; forming a second polysilicon layer that fills the first and second holes and covers the second sacrificial layer; patterning the second polysilicon layer to form a middle capacitor plate that is mechanically attached to the anchor, has a portion spaced from the lower capacitor plate by the thickness of the first and second sacrificial layers together with the second silicon nitride layer, and a travel stop portion which is spaced from the lower capacitor plate by the thickness of the first sacrificial layer and the second silicon nitride layer; and performing a sacrificial etch of the first and second sacrificial layers using an isotropic etchant that etches the silicon oxide faster than silicon nitride, wherein only a portion of the second silicon nitride layer which is covered by the travel stop portion remains after the sacrificial etching. - View Dependent Claims (2, 3, 4, 5)
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6. A method for forming travel limit stops in a micromachined capacitor structure comprising:
- providing a substrate having a top surface;
forming a plurality of polysilicon anchors on the top surface;
forming a lower capacitor plate on the top surface, wherein the lower capacitor plate has an active portion and a landing pad portion;
covering the top surface, the anchors, and the lower capacitor plate with a sacrificial layer;
etching a first set of holes extending through the sacrificial layer to expose the anchors;
etching a second set of holes extending partially through the sacrificial layer and positioned over the landing pad portion of the lower capacitor plate;
forming a middle polysilicon capacitor plate on the sacrificial layer and extending into the first and second sets of holes, wherein the middle capacitor plate is mechanically attached to at least one anchor through the first set of holes and has dimples where the capacitor plate extends into the second set of holes; and
etching the sacrificial layer to provide an air gap between the capacitor plate and the substrate. - View Dependent Claims (7, 8, 9)
- providing a substrate having a top surface;
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10. A micromachined capacitor structure having a travel limit stop, the structure comprising:
- a substrate;
a moving capacitor plate having an active area separated from the substrate by a first spacing and mechanically attached to the substrate by at least one anchor region, wherein the active region is substantially parallel to the substrate; and
a corrugation formed in the second capacitor plate, wherein the corrugation has a bottom surface located over the substrate and separated from the substrate by a second spacing, wherein the second spacing is smaller than the first spacing. - View Dependent Claims (11, 12, 13, 14, 15, 16)
- a substrate;
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17. A micromachined capacitor structure comprising:
- a substrate;
a first capacitor plate formed on the substrate;
a second capacitor plate supported by at least one flexing arm and having an active area formed over the first capacitor plate, an anchor area mechanically attached to the substrate and spaced away from and electrically isolated from the first capacitor plate, and a flexure portion mechanically coupling the active area to the anchor portion; and
a plurality of corrugations formed in the active area of the second capacitor plate, wherein the corrugations make the active portion more rigid in at least one dimension than the flexure portion. - View Dependent Claims (18)
- a substrate;
Specification