Energy stabilized gas discharge laser

An excimer or molecular fluorine laser system for generating an output beam at a specified energy, comprising:

• a discharge chamber initially filled with a gas mixture at least including molecular fluorine and a buffer gas, and a trace amount between 10 ppm and 2000 ppm of an attenuating gas additive for attenuating the output beam to said specified energy;
• a plurality of electrodes in the discharge chamber connected to a discharge circuit for energizing the gas mixture by applying electrical pulses at predetermined driving voltages to the electrodes at a repetition rate of at least one kilohertz;
• a resonator including a line-narrowing and wavelength tuning module and the discharge chamber for generating said output beam at said specified energy;
• a gas supply unit coupled with the discharge chamber and configured to permit a quantity of a molecular fluorine/buffer gas mixture less that two mbar to inject into said discharge chamber at selected intervals;
• an energy detector for monitoring energies of the output beam;
• a wavelength meter for monitoring wavelengths of the output beam;
• a processor for receiving values of the energies and wavelengths and including a signal indicative of a concentration of the molecular fluorine in the gas mixture, the processor controlling the line-narrowing and wavelength tuning module to tune the wavelength, the discharge circuit to control the energy of the output beam and the gas supply unit to control the concentration of the molecular fluorine in the gas mixture, and
• wherein values of the predetermined driving voltages are selected by the processor based on the received values of the energies, and wherein the trace amount of the attenuating gas additive is selected to provide enhanced pulse-to-pulse energy, stability, such that the overall stability of output beam parameters including pulse-to-pulse energy stability and wavelength is enhanced, and wherein the selected values of the predetermined driving voltages are increased due to the presence of the attenuating gas additive for providing the output beam at the specified energy.

An excimer or molecular fluorine laser, comprising:

• a discharge chamber initially filled with a gas mixture at least including molecular fluorine, a buffer gas and a trace amount of a gas additive, wherein the concentration of the gas additive in the gas mixture is actively adjusted during laser operation to control a parameter of the output beam;
• a plurality of electrodes in the discharge chamber connected to a discharge circuit for energizing the gas mixture by applying predetermined driving voltages to the electrodes at a repetition rate of at least one kilohertz;
• a resonator including a line-narrowing and wavelength tuning module and the discharge chamber for generating an output laser beam at a specified energy,
• a gas supply unit coupled with the discharge chamber and configured to permit a quantity, of a molecular fluorine/buffer gas mixture less than two mbar to inject into said discharge chamber at selected intervals;
• an energy detector for monitoring energies of the output beam;
• a wavelength meter for monitoring wavelengths of the output beam;
• a processor for receiving values of the energies and wavelengths and including signals indicative of a concentration of the molecular fluorine in the gas mixture and the output beam parameter that is controlled by said active adjustment of the concentration of the gas additive, the processor controlling the line-narrowing and wavelength tuning module to tune the wavelength, the discharge circuit to control the energy of the output beam and the gas supply unit to control the concentration of the molecular fluorine in the gas mixture and the additive gas species concentration to control said parameter of the output beam, and
• wherein values of the predetermined driving voltages are selected by the processor based on the received values of the energies, and wherein the trace amount of the gas additive is selected to control said output beam parameter, such that the overall stability of output beam parameters including said parameter, energy and wavelength is enhanced, and wherein the selected values of the predetermined driving voltages are influenced by the presence of the gas additive for providing the output beam at the specified energy.

A method of initializing and operating an excimer or molecular fluorine laser having a gas mixture at least including molecular fluorine, a buffer gas, and a trace amount of a gas additive species for generating an output laser beam in burst mode, comprising the steps of:

• selecting a value of a parameter of the output laser beam;
• filling a gas mixture into the laser including a selected amount of the energy attenuating gas for controlling the parameter to the selected value;
• operating the laser at a repetition rate of at least one kilohertz;
• monitoring the concentration of and periodically replenishing the molecular fluorine of the gas mixture during operation of the laser based on the monitored concentration;
• monitoring an energy of the output beam and adjusting values of input driving voltages for maintaining the energy at a specified energy based on the monitoring of the energy;
• monitoring a wavelength of the output beam and controlling a line-narrowing and wavelength tuning unit for controlling the wavelength based on the monitoring of the wavelength;
• wherein values of the input driving voltages are selected by the processor based on monitored values of the energy, and wherein the trace amount of the gas additive is selected to control said output beam parameter, such that the overall stability of output beam parameters including said parameter, energy and wavelength is enhanced, and wherein the selected values of the predetermined driving voltages are influenced by the presence of the gas additive for providing the output beam at the specified energy.