Patent ID: 7124624

Claim:
A gas gauge lithography proximity sensor for sensing a difference between a reference surface standoff and a measurement surface standoff, comprising: a junction that divides gas input into the gas gauge proximity sensor into a reference channel and a measurement channel; a first porous flow restrictor placed along the reference channel, wherein said first porous flow restrictor evenly restricts gas flow through the reference channel; a second porous flow restrictor placed along the measurement channel, wherein said second porous flow restrictor evenly restricts gas flow through the measurement channel; a reference probe at an end of the reference channel, wherein gas exits the reference channel through the reference probe and travels across a reference standoff to impinge upon a lithographic reference surface; a measurement probe at an end of the measurement channel, wherein gas exits the measurement channel through the measurement probe and travels across a measurement standoff to impinge upon a lithographic measurement surface; and a mass flow sensor coupled between the reference and measurement channels for sensing the mass of gas flow therebetween.