Antistiction MEMS substrate and method of manufacture
A composite wafer for fabricating MEMS devices is provided with a plurality of antistiction bumps, buried under a device layer of the composite wafer. The antistiction bumps are prepared lithographically, by patterning an antistiction material prior to the assembly of the composite wafer.
1 . A composite wafer for fabricating a moveable device, comprising:
a layer of antistiction material formed over at least a portion of a substrate;
a sacrificial layer formed over the portions of the substrate not covered by the antistiction material; and
a device layer coupled to the sacrificial layer.
2 . The wafer of claim 1 , wherein the layer of antistiction material is patterned into regions of less than about 100 μm in at least one dimension.
3 . The wafer of claim 2 , wherein the regions occur randomly over the substrate.
4 . The wafer of claim 1 , wherein the antistiction material is silicon nitride, and the device layer is silicon.
5 . The wafer of claim 1 , wherein the sacrificial layer is silicon dioxide, and the substrate is silicon.
6 . The wafer of claim 5 , wherein the silicon dioxide is a thermally grown layer, with a thickness of between about 1 μm to about 2 μm.
7 . The wafer of claim 1 , wherein a moveable feature of the moveable device is formed in the device layer using photolithographic techniques.
8 . The wafer of claim 1 , wherein the layer of antistiction material is between about 500 Angstroms and about 3000 Angstroms thick and the sacrificial layer is about 1 μm thick.
9 . The wafer of claim 1 , wherein the moveable device is at least one of a sensor, motor, switch, accelerometer, gyro, and actuator.
10 . A method of manufacturing a wafer for fabricating a moveable device, comprising:
forming a layer of antistiction material over at least a portion of a substrate;
forming a sacrificial layer over the portions of the substrate not covered by the antistiction material; and
coupling a device layer to the sacrificial layer.
11 . The method of claim 10 , further comprising:
forming the moveable device in the device layer using photolithographic techniques.
12 . The method of claim 10 , wherein the substrate is silicon and forming the sacrificial layer over the portions of the substrate not covered by the antistiction material comprises thermally growing a layer of silicon dioxide on the silicon substrate to a thickness of between about 1 μm to about 2 μm.
13 . The method of claim 10 , wherein forming the layer of antistiction material over at least a portion of the substrate comprises at least one of forming the layer of antistiction material over a portion located to contact a surface of the moveable device, and forming the layer of antistiction material over randomly located portions of the substrate.
14 . The method of claim 11 , further comprising removing at least a portion of the sacrificial layer which is under a moveable feature of the moveable device.
15 . The method of claim 10 , wherein forming the layer of antistiction material over at least a portion of the substrate comprises depositing a layer of silicon nitride using chemical vapor deposition to a thickness of between about 500 and about 3000 Angstroms, and patterning the silicon nitride layer to form a plurality of regions which are between about 15 μm and about 100 μm in at least one dimension.
16 . The method of claim 15 , wherein forming the layer of antistiction material over at least a portion of the substrate comprises depositing a layer of silicon nitride to a thickness of about 2000 Angstroms, and patterning the silicon nitride layer to form a plurality of regions about 20 μm in at least one dimension.
17 . The method of claim 10 , wherein forming the moveable device in the device layer comprises etching a feature of the moveable device using deep reactive ion etching.
18 . The method of claim 10 , wherein forming the layer of antistiction material over at least a portion of the substrate comprises depositing a layer of polycrystalline silicon to a thickness of about 2000 Angstroms.
19 . The method of claim 10 , wherein the substrate and the device layer are both silicon.
20 . An apparatus for manufacturing a wafer for fabricating a moveable device, comprising:
means for forming a layer of antistiction material over at least a portion of a substrate;
means for forming a sacrificial layer over the portions of the substrate not covered by the antistiction material; and
means for coupling a device layer to the sacrificial layer.