POROUS GAS-BEARING BACKER
A gas-levitated substrate backing system includes a gas-levitating backer structure which is used for providing a non-contact force onto a surface. The gas-levitating backer structure has an output face, and includes a gas manifold and a porous material layer of a porous material. Gas enters the gas-levitating backer structure from a gas source, and passes through the gas manifold. A gas flow through the output face is controlled by controlling a pressure of the gas in the gas manifold. The porous material layer has an outer surface facing the surface and an inner surface facing the gas manifold, wherein at least a portion of the porous material layer is a porous membrane having a permeability-to-thickness ratio of at least 1×10-9 inches.
1 . A gas-levitated substrate backing system for providing a non-contact force onto a surface of a substrate, comprising:
a gas-levitating backer structure having an output face including:
a gas manifold, through which gas enters the gas-levitating backer structure from a gas source, and wherein a gas flow through the output face is controlled by controlling a pressure of the gas in the gas manifold; and
a porous material layer of a porous material, the porous material layer having an outer surface facing the surface and an inner surface facing the gas manifold, and wherein the output face corresponds to the outer surface of the porous material layer, wherein at least a portion of the porous material layer is a porous membrane having a permeability-to-thickness ratio of at least 1×10 −9 inches.
2 . The gas-levitated substrate backing system of claim 1 , wherein a pressure between the output face and the surface of the substrate is uniform to within 15% across at least 80% of a width of the output face.
3 . The gas-levitated substrate backing system of claim 2 , wherein the pressure between the output face and the surface of the substrate is uniform to within 5% across at least 80% of the width of the output face.
4 . The gas-levitated substrate backing system of claim 1 , wherein the gas-levitating backer structure is freely moveable in a direction normal to the surface of the substrate.
5 . The gas-levitated substrate backing system of claim 4 , further including a lateral constraint system that constrains the gas-levitating backer structure from moving in a plane parallel to surface of the substrate while enabling the gas-levitating backer structure to move freely in a direction normal to the surface of the substrate.
6 . The gas-levitated substrate backing system of claim 5 , wherein the gas-levitating backer structure fits within an opening in the lateral constraint system.
7 . The gas-levitated substrate backing system of claim 5 , wherein the lateral constraint system includes a flexure attached to the gas-levitating backer structure.
8 . The gas-levitated substrate backing system of claim 5 , wherein the flexure includes a means for conveying energy to the gas-levitating backer structure or conveying electrical signals to or from the gas-levitating backer structure.
9 . The gas-levitated substrate backing system of claim 5 , wherein the lateral constraint system includes a gas supply tube which supplies gas to the gas-levitating backer structure.
10 . The gas-levitated substrate backing system of claim 1 , wherein the non-contact force applied to the surface of the substrate is no more than 1.0 pounds per square inch of the output face.
11 . The gas-levitated substrate backing system of claim 1 , wherein the porous material layer is a porous graphite material.
12 . The gas-levitated substrate backing system of claim 1 , wherein the inner surface of the porous material layer includes a rib structure.
13 . The gas-levitated substrate backing system of claim 12 , wherein the rib structure includes a pattern or ribs, and wherein the outer surface of the porous material layer includes vent grooves that are aligned with the ribs.
14 . The gas-levitated substrate backing system of claim 12 , wherein the rib structure includes a pattern of ribs having a rib width which is within a factor of 2× of a thickness of the porous membrane.
15 . The gas-levitated substrate backing system of claim 1 , wherein the inner surface of the porous material layer includes an array of blind holes that extend partway through a thickness of the porous material layer.
16 . The gas-levitated substrate backing system of claim 15 , wherein the outer surface of the porous material layer includes a cross-hatch pattern of vent grooves such that the blind holes are aligned with land areas between the vent grooves.
17 . The gas-levitated substrate backing system of claim 16 , wherein surfaces of the vent grooves are covered by a coating that reduces their porosity.
18 . The gas-levitated substrate backing system of claim 1 , further including a heater for heating the gas-levitating backer structure.
19 . The gas-levitated substrate backing system of claim 18 , wherein the gas-levitating backer structure heats the surface by conductive heating.
20 . The gas-levitated substrate backing system of claim 1 , wherein the surface of the substrate is oriented in a horizontal orientation.
21 . The gas-levitated substrate backing system of claim 20 , wherein the gas-levitating backer structure applies a net force on the surface of the substrate corresponding to a weight of the gas-levitating backer structure.
22 . The gas-levitated substrate backing system of claim 1 , wherein a gas flow through the output face is controlled to lift the gas-levitating backer structure away from the surface of the substrate such that a gap between the output face and the surface of the substrate is no more than 50 μm.
23 . The gas-levitated substrate backing system of claim 1 , wherein the substrate is a flexible substrate.
24 . The gas-levitated substrate backing system of claim 1 , further including a vacuum-preloaded gas bearing having an output face, the vacuum-preloaded gas bearing being positioned in a fixed location on an opposite side of the substrate from the gas-levitating backer structure with the output face of the vacuum-preloaded gas bearing facing the opposite side of the substrate.
25 . The gas-levitated substrate backing system of claim 24 , wherein the vacuum-preloaded gas bearing is a thin film deposition head which deposits a thin film of material onto the opposite side of the substrate.
26 . The gas-levitated substrate backing system of claim 25 , further including a substrate positioning system that moves the substrate in a lateral direction parallel to the output face of the gas-levitating backer structure according to a specified motion pattern.