Measuring and testing – With fluid pressure – Dimension – shape – or size
Reexamination Certificate
2000-03-10
2001-05-08
Raevis, Robert (Department: 2856)
Measuring and testing
With fluid pressure
Dimension, shape, or size
Reexamination Certificate
active
06227035
ABSTRACT:
FIELD OF INVENTION
The invention relates to test equipment for a gas module, and more specifically the invention relates to test equipment for gas supply systems in gas discharge lasers.
BACKGROUND
Gas discharge lasers, such as excimer lasers, are used in industrial applications. These applications include use in stepper systems for ultra large scale integrated circuit manufacturing. In such industrial applications it is extremely important to precisely control laser beam pulse energy and wavelength in order to ensure consistent processing quality for each wafer. Laser beam quality is critically dependent on accurate and precise control of gas mixture and pressure in the laser discharge chamber.
FIG. 1
shows an excimer laser system used as a stepper system illumination source. Gas control unit (or gas module)
101
in laser system
102
is subject to testing by the present invention. Laser system
102
produces laser output beam L used by stepper
103
. Stepper control unit
104
uses a signal to trigger laser control unit
105
to generate a laser pulse. Laser control unit
105
then signals power source
106
to provide a controlled voltage pulse to lasing unit
107
. Lasing unit
107
comprises a laser chamber, optical resonator, and other conventional laser beam generation components. Lasing unit
107
sends signals to laser control unit
105
that indicate the status of lasing unit
107
components and gas mixtures.
The laser chamber in lasing unit
107
is filled with a laser gas having a precise pressure and mixture. Gas mixtures are typically krypton-fluorine or other conventional rare gas/halide laser gas mixtures. Control circuits excite the laser gas mixture by applying a voltage discharge pulse of predetermined width and interval across electrodes (not shown). The voltage discharge pulse excites an oscillation in the resonating chamber and thereby creates a laser beam.
Gas control unit
101
helps to ensure constant laser beam energy and bandwidth by replacing laser chamber gases consumed during laser beam generation. Gas control unit
101
receives control signals from control unit
105
to supply the proper gas mixture and pressure to lasing unit
107
. Laser control unit
105
receives signals from gas control unit
101
indicating operating status and gas pressures in gas control unit
101
. Gas control unit
101
must limit mass flow rates and control the mixture ratio of gases supplied to the laser chamber. In addition, gas control unit
101
must provide a capability for handling dangerous gases, such as fluorine, typically used in gas discharge lasers. And, gas control unit
101
must provide for gas evacuation from the laser beam generation equipment in lasing unit
107
under both normal and emergency conditions.
To Applicants' knowledge, no procedures or equipment were developed to characterize and test the critical gas control unit
101
prior to the present invention. In addition, no single piece of test equipment existed that was capable of performing a comprehensive test of a gas module such as gas control unit
101
.
The challenge, therefore, was to create a test fixture and evaluation methods capable of ensuring proper gas control unit function during production operations using the laser beam. A further challenge was to create a test fixture and evaluation methods that allow gas module tests and measurement for use during engineering development.
SUMMARY
One embodiment of the present invention provides apparatus and methods for testing a gas discharge laser gas control module. Testing may be accomplished in accordance with the present invention by using a single test fixture. A test operator may test a gas module using automatic or manual functions, or a combination of both. Functional tests include evaluating gas control module leakage, valve logic, electrical wiring and connections, valve operation, pump operation, and metering orifice diameters. Test data are acquired, stored, manipulated, and displayed to produce information useful during both production and engineering development.
Gas module leakage may be tested by pressurizing gas module components using nitrogen gas and monitoring for pressure drops. Additional leak tests may be accomplished in embodiments having a built-in helium detector for use in conventional helium leak testing.
Valve logic and electrical circuit tests ensure a given control signal activates the proper valve. A pressurized gas may be applied to a closed valve. When a control signal is applied to open the valve, either directly as in a solenoid valve or indirectly as in a pneumatically actuated valve, gas pressure is monitored to check proper valve function.
Check valves and pressure relief valves may be tested both for leakage (reverse flow pressure test) and for correct opening pressure (forward flow pressure test). Opening pressure may be checked by applying an increasing pressure ramp to the valve under test and monitoring the pressure difference between upstream and downstream pressure readings of gas flow through the valve. The increasing pressure ramp may be supplied using a controlled gas fill rate into a ballast tank.
Orifice diameter testing may be done by monitoring either the gas fill or discharge rate of a gas container through the orifice under test. Gas pressures above and below the orifice under test may be monitored and compared to known calibration readings. From this pressure information a computing system may calculate an accurate average diameter of the orifice under test.
Information such as analog output signals from pressure transducers may be sampled and stored in a test fixture memory storage area. This information may be used to calculate test results that are subsequently displayed in graphic format.
Test fixture control may be accomplished through a computer graphical user interface. In some embodiments, a schematic of the gas control module and the test fixture is displayed. These embodiments may include capability for operating both gas module and test fixture components using the graphic interface. An operator may monitor automatic test sequences by viewing the display as well. Test fixture operation may be accomplished using a computer control system that controls the gas-related plumbing and monitors data collection devices with electronic interfaces.
REFERENCES:
patent: 4527415 (1985-07-01), Chabat-Courrede
patent: 4574617 (1986-03-01), Hetznecker et al.
patent: 4598579 (1986-07-01), Cummings et al.
Rice Gregory D.
Shogren Peter K.
Allenby, Esq. Christopher
Cymer Inc.
Raevis Robert
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