Liquid level detection device, method of detecting liquid level, high temperature plasma raw material supply device and extreme ultra violet light source device

A liquid level detection device for detecting a liquid level, comprising:

• a reservoir configured to contain a high temperature plasma raw material in a liquid state for generating a high temperature plasma;
• an electrode rod arranged on the reservoir and having a front edge thereof arranged to be positioned at a same or a substantially same height as a first liquid level and a surface constituted with a conductive material inert with respect to the high temperature plasma raw material;
• a tubular member configured to be fitted onto the electrode rode such that the front edge of the electrode rode is exposed toward a liquid surface of the high temperature plasma raw material and constituted with a material having an anticorrosion property and an electrically insulating property to the high temperature plasma raw material;
• a conductive circuit configured to be in an electrically conducive state when the front edge of the electrode rod contacts the liquid surface of the high temperature plasma raw material;
• and
• a temperature sensor arranged in the reservoir and configured to be positioned at a same or a substantially same height as a second liquid level that is lower than the first liquid level,
• a titanium oxide coating being applied to a surface of stainless steel of the electrode rod, and
• a material of the tubular member being aluminum oxide.

A method of detecting a liquid level, comprising:

• detecting, using a first liquid level sensor, that a liquid level of a high temperature plasma raw material in a liquid state for generating a high temperature plasma is elevated to reach a first liquid level that is an upper limit level to allow the high temperature plasma raw material to be contained in a reservoir;
• and
• detecting, using a second liquid level sensor, that the liquid level of the high temperature plasma raw material is lowered to reach a second liquid level that is lower than the first liquid level, wherein
• the first liquid level sensor is an electrode rod arranged in the reservoir and having a front edge positioned at a same or a substantially same height as the first liquid level, and
• the second liquid level sensor is a temperature sensor arranged in the reservoir and configured to be positioned at a same or a substantially same height as the second liquid level.