Method for removing a contamination layer by an atomic layer etching process

Method for at least partial removing a contamination layer from an optical surface of an optical element that reflects extreme ultraviolet (EUV) radiation, comprising:

• taking the optical element from a selected optical arrangement, in which the optical surface of the optical element is exposed to EUV radiation, into a process chamber of an atomic layer etching apparatus, which process chamber is external to the selected optical arrangement;
• subsequent to said taking step performing, an atomic layer etching process in the process chamber, for at least partially removing the contamination layer from the optical surface, wherein said performing step comprises:
• in a surface modification step, exposing the contamination layer to a surface-modifying reactant, and
• in a material detachment step, exposing the contamination layer to a material-detaching reactant, wherein, in said surface modification step, the surface-modifying reactant comprises oxygen (O2) and wherein, in said material detachment step, the material-detaching reactant comprises hydrogen (H2);
• and
• subsequent to said performing step, installing the optical element in a further optical arrangement.

Method for at least partially removing a contamination layer from an optical surface of an optical element that reflects extreme ultraviolet EUV radiation, comprising:

• taking the optical element from a selected optical arrangement, in which the optical surface of the optical element is exposed to EUV radiation, into a process chamber of an atomic layer etching apparatus, which process chamber is external to the selected optical arrangement;
• subsequent to said taking step, performing an atomic layer etching process in the process chamber, for at least partially removing the contamination layer from the optical surface, wherein said performing step comprises:
• in a surface modification step, exposing the contaminnation layer to a surface-modifying reactant, and
• in a material detachment step, exposing the contamination layer to a material-detaching reactant,
• wherein, in said surface modification step, the surface-modifying reactant comprises an organic compound, and wherein, in the material detachment step, the material-detaching reactant comprises oxygen (O2));
• and
• subsequent to said performing step, installing the optical element in a further optical arrangement.

Method for at least partially removing a contamination layer from an optical surface of an optical element that reflects extreme ultraviolet (EUV) radiation, comprising:

• taking the optical element from a selected optical arrangement in which the optical surface of the optical element is exposed to EUV radiation;
• subsequent to said taking step, performing an atomic layer etching process for at least partially removing the contamination layer from the optical surface,
• wherein said performing step comprises:
• in a surface modification step, exposing the contamination layer to a surface-modifying reactant, and
• in a material detachment step, exposing the contamination layer to a material-detaching reactant;
• and
• subsequent to said performing step, installing the optical element in a further optical arrangement,
• wherein either:
• (i) in said surface modification step, the surface-modifying reactant comprises oxygen (O2) and, in said material detachment step, the material-detaching reactant comprises hydrogen (H2),
• or (ii) in said surface modification step, the surface-modifying reactant comprises an organic compound and, in said material detachment step, the material-detaching reactant comprises oxygen (O2).

Method for at least partially removing a contamination layer from an optical surface of an optical element that reflects extreme ultraviolet (EUV) radiation, comprising:

• taking the optical element from a selected optical arrangement in which the optical surface of the optical element is exposed to EUV radiation;
• subsequent to said taking step, performing an atomic layer etching process for at least partially removing the contamination layer from the optical surface, wherein said performing step comprises:
• in a surface modification step, exposing the contamination layer to a surface-modifying reactant, and
• in a material detachment step, exposing the contamination layer to a material-detaching reactant,
• wherein at least one of said surface modification step and said material detachment step is plasma-assisted;
• generating the plasma in a dielectric barrier discharge plasma source of an atomic layer etching head,
• wherein said generating step comprises generating the plasma at a pressure between 100 mbar and 2000 mbar;
• and
• subsequent to said performing step, installing the optical element in a further optical arrangement.

Method for at least partially removing a contamination layer from an optical surface of an optical element that reflects extreme ultraviolet (EUV) radiation, comprising:

• taking the optical element from a selected optical arrangement in which the optical surface of the optical element is exposed to EUV radiation;
• subsequent to said taking step, performing an atomic layer etching process for at least partially removing the contamination layer from the optical surface, wherein said performing step comprises:
• in a surface modification step, exposing the contamination layer to a surface-modifying reactant, and
• in a material detachment step, exposing the contamination layer to a material-detaching reactant;
• and
• producing a temperature change (ΔTu, ΔTd) between said surface modification step and said material detachment step;
• and
• subsequent to said performing step, installing the optical element in a further optical arrangement.