Apparatus for and method of sensing fluorine concentration

Patent metadata

Field	Value
Publication number	US-10228322-B2
Application number	US-201715648845-A
Country	US
Kind code	B2
Filing date	Jul 13, 2017
Priority date	Jul 13, 2017
Publication date	Mar 12, 2019
Grant date	Mar 12, 2019

Abstract

Disclosed is an apparatus for and method of measuring the concentration of F2 in the laser gas used in an excimer laser. Quartz Enhanced Photoacoustic Spectroscopy is used to obtain a direct measurement of F2 concentration quickly and using only a small sample volume.

First claim

What is claimed is:

1. Apparatus comprising:
a laser chamber adapted to retain a laser gas containing fluorine;
a gas cell in selective fluid communication with the laser chamber for retaining a sample of the laser gas;
a frequency generator for producing a frequency signal having a reference frequency;
a radiation source arranged to receive the frequency signal and to irradiate at least a portion of the gas sample with radiation modulated at the reference frequency to produce acoustic waves in the gas sample;
an acoustic resonator located in the gas cell and arranged to amplify the acoustic waves;
a piezoelectric quartz tuning fork located in the gas cell and having a resonant frequency substantially the same as the reference frequency and subjected to the acoustic waves in such a manner as to cause at least a portion of the piezoelectric quartz tuning fork to vibrate for generating an electrical signal indicative of a frequency at which the piezoelectric quartz tuning fork vibrates;
a preamplification circuit arranged to receive the electrical signal to produce an amplified electrical signal;
a lock-in amplifier arranged to receive the amplified electrical signal and for generating an output signal indicative of a magnitude of a frequency component of the electrical signal at the reference frequency;
a laser controller arranged to receive the electrical signal and adapted to determine based at least in part on the electrical signal a concentration of F2 in the sample gas and to generate an indication that it is necessary to add gas containing F2 to the laser chamber; and
a gas supply system responsively connected to the laser controller and adapted to supply gas containing F2 to the laser chamber based at least in part on the indication from the laser controller.

Assignees

• Cymer LLC

Inventors

• Duffey Thomas Patrick

Classifications

• G01N29/2425

  optoacoustic fluid cells therefor · CPC title

• G01N2021/1708

  with piezotransducers · CPC title

• G01N21/3151

  using two sources of radiation of different wavelengths (G01N21/33 - G01N21/39 take precedence) · CPC title

• G01N21/1702 Primary

  with opto-acoustic detection, e.g. for gases or analysing solids · CPC title

• G01N2021/1704

  in gases · CPC title