Liquid flow proximity sensor for use in immersion lithography
AssigneeASML Holding N.V.
InventorKevin Violette
Life of this patent
Estimating the term…
Abstract
An apparatus and method for precisely detecting very small distances between a measurement probe and a surface, and more particularly to a proximity sensor using a constant liquid flow and sensing a liquid mass flow rate within a bridge to detect very small distances. Within the apparatus the use of a flow restrictor and/or snubber made of porous material and/or a liquid mass flow rate controller enables detection of very small distances in the nanometer to sub-nanometer range. A further embodiment wherein a measurement channel of a proximity sensor is connected to multiple measurement branches.
Claims20
A liquid flow proximity sensor, comprising:
- a junction that divides liquid input into the liquid flow 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 liquid flow through the reference channel;
- a second porous flow restrictor placed along the measurement channel, wherein said second porous flow restrictor evenly restricts liquid flow through the measurement channel;
- a reference probe at an end of the reference channel, whereby liquid exits the reference channel through the reference probe and travels across a reference standoff to impinge upon a reference surface;
- a measurement probe at an end of the measurement channel, whereby liquid exits the measurement channel through the measurement probe and travels across a measurement standoff to impinge upon a measurement surface;
- and
- a liquid mass flow sensor coupled between the reference and measurement channels for sensing the flow of liquid therebetween, whereby, the difference in standoffs between the reference and measurement surfaces can be sensed.
A bridge for use in a liquid flow proximity sensor comprising:
- a junction that receives a liquid flow and divides that liquid flow 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 liquid flow through the reference channel;
- and
- a second porous flow restrictor placed along the measurement channel, wherein said second porous flow restrictor evenly restricts liquid flow through the measurement channel.
A method for sensing a difference in a reference standoff and a measurement standoff, comprising the steps of:
- (a) distributing a flow of liquid between a measurement channel and a reference channel;
- (b) restricting the flow of liquid substantially evenly across cross-sectional areas of both the measurement and reference channels;
- (c) forcing the flow of liquid through porous restrictors located in the measurement and reference channels;
- (d) outputting liquid from the reference and measurement channels through nozzles to impinge upon a reference surface and a measurement surface, respectively;
- and
- (e) sensing a liquid mass flow rate across a bridge channel that connects the reference and measurement channels, the liquid mass flow rate being representative of the magnitude of a difference between a measurement standoff and a reference standoff.
Dependencies are inferred from the claim text.