TECHNICAL FIELD

The present disclosure relates to a laser apparatus.

BACKGROUND ART

The recent miniaturization and increased levels of integration of semiconductor integrated circuits have led to a demand for increases in resolutions of semiconductor exposure apparatuses. A semiconductor exposure apparatus is hereinafter referred to simply as “exposure apparatus”. Accordingly, exposure light sources to output light at shorter wavelengths have been under development. As the exposure light sources, gas laser apparatuses instead of conventional mercury lamps are typically used. The gas laser apparatuses for exposure include a KrF excimer laser apparatus that outputs an ultraviolet laser beam at a wavelength of 248 nm and an ArF excimer laser apparatus that outputs an ultraviolet laser beam at a wavelength of 193 nm.

As a current exposure technology, immersion exposure has been put to practical use. In the immersion exposure, a gap between a projection lens and a wafer in an exposure apparatus is filled with a fluid such as water to change refractive index in the gap such that an apparent wavelength of the light from the exposure light source is shortened. In a case where immersion exposure is performed using an ArF excimer laser apparatus as an exposure light source, a wafer is irradiated with ultraviolet light whose wavelength in water is equivalent to 134 nm. This technology is referred to as “ArF immersion exposure”. The ArF immersion exposure is also referred to as “ArF immersion lithography”.

Spectrum line widths of KrF and ArF excimer laser apparatuses in natural oscillation are as wide as approximately 350 pm to 400 pm. This causes a chromatic aberration of a laser beam (ultraviolet light) that is subjected to reduced projection onto a wafer by a projection lens in an exposure apparatus. The chromatic aberration thus causes a reduction in resolving power. Accordingly, spectrum line width of a laser beam that is outputted from a gas laser apparatus needs to be narrowed to such an extent that the chromatic aberration can be ignored. The spectrum line width is also referred to as “spectrum width”. To narrow the spectrum width, a laser resonator of a gas laser apparatus is equipped with a line narrow optical system (line narrow module) having a line narrow element. The line narrow element may be an etalon, a grating, or the like. A laser apparatus whose spectrum width is narrowed in this way is referred to as “line narrowed laser apparatus”.

Patent Document 1: International Publication No. WO2015/098985 A

Patent Document 2: US Patent Application Publication No. 2015/0188274 A

Patent Document 3: US Patent Application Publication No. 2013/0100980 A

Patent Document 4: International Publication No. WO01/028048 A

Patent Document 5: Japanese Patent Application Publication No. H04-102383 A

Patent Document 6: Japanese Patent Application Publication No. 2012-018979 A

SUMMARY

An aspect of the present disclosure relates to a laser apparatus including a chamber in which a pair of discharge electrodes is provided, a gas supply device configured to supply first laser gas including halogen gas and second laser gas having a halogen gas concentration lower than the first laser gas to the chamber, an exhausting device configured to exhaust laser gas in the chamber, a pressure sensor configured to measure gas pressure in the chamber, and a controller configured to select one of a first gas control and a second gas control based on the gas pressure measured by the pressure sensor. Here, the first gas control causes at least one of the first laser gas and the second laser gas to be supplied to the chamber such that the gas pressure in the chamber after the first gas control is higher than the gas pressure in the chamber before the first gas control, and the second gas control causes at least the first laser gas to be supplied to the chamber and causes a part of the laser gas in the chamber to be exhausted such that a difference between the gas pressure in the chamber before the second gas control and the gas pressure in the chamber after the second gas control is smaller than a difference between the gas pressure in the chamber before the first gas control and the gas pressure in the chamber after the first gas control.

Another aspect of the present disclosure relates to a laser apparatus including a chamber in which a pair of discharge electrodes is provided, a gas supply device configured to supply first laser gas including halogen gas and second laser gas having a halogen gas concentration lower than the first laser gas to the chamber, an exhausting device configured to exhaust laser gas in the chamber, and a controller configured to execute a first process to execute a gas control more than once to supply at least one of the first laser gas and the second laser gas to the chamber such that gas pressure in the chamber increases at a substantially constant rate per elapsed time, and a second process to execute a gas control more than once after the first process to supply at least the first laser gas to the chamber and exhaust a part of the laser gas in the chamber such that the gas pressure in the chamber is substantially kept at a first constant value regardless of the elapsed time.

