Abstract: The invention is directed to a method for growing metal fluoride crystals suitable for use in below 200 nm optical lithography systems, the method comprising including at least the step of heating a crystal growth furnace to a temperature in the range of 1400-2000° C. to purify the furnace by removal of sulfur and chlorine prior to using the furnace for growing metal fluoride single crystals.

Abstract: An apparatus for making a crystal pre-melt includes a hermetically-sealed muffle furnace made of a non-porous refractory material, at least one port for entry and exit of gaseous substance within the muffle furnace, a temperature-controlled zone defined inside the muffle furnace, and a crucible for holding crystal raw material in solid or molten form inside the muffle furnace. The crystal pre-melt is made by disposing crystal raw material in loose powder, pressed powder, granular, or densified form in the temperature-controlled zone, heating the temperature-controlled zone to a treatment temperature that enables reaction between a fluorinating agent and oxides in the crystal raw material, reacting the fluorinating agent with the crystal raw material to produce volatile gases, removing the volatile gases from the muffle furnace, heating the crystal raw material to form a melt, and solidifying the melt to form the crystal pre-melt.

Abstract: The invention is directed to a method for growing metal fluoride crystals suitable for use in below 200 nm optical lithography systems, the method comprising including at least the step of heating a crystal growth furnace to a temperature in the range of 1400-2000° C. to purify the furnace by removal of sulfur and chlorine prior to using the furnace for growing metal fluoride single crystals.

Abstract: The invention is directed to a method of preparing metal fluoride crystals that are suitable for making optical elements that can be used in below 200 nm lithographic equipment and processes. In accordance with the invention, metal fluoride particles, substantially all of which have a size of 1 mm or greater, are treated with an oxygen scavenger material just prior to being melted and used to grow a metal fluoride single crystal. In one embodiment of the invention a metal fluoride raw material is treated with an oxygen scavenger to remove oxygen containing impurities, liquefied and cooled to form a premelt material. The premelt material is then broken into particles having a range of sizes and separated by sieving or other separation methods known in the art into at least a group of particles substantially all of which have a size of 1 mm or larger and a group of particles having a size of less than 1 mm.

Abstract: A method of making crystals includes suspending a porous preform made of a crystal raw material in a hermetically-sealed chamber, heating the porous preform to a selected treatment temperature that enables reaction between a fluorinating agent and oxide impurities in the porous preform and reacting the fluorinating agent with the oxide impurities at the selected treatment temperature for a selected time period, filling a crucible in the hermetically-sealed chamber with a melt formed from at least a portion of the porous preform, and progressively moving the melt through a temperature gradient zone defined inside the hermetically-sealed chamber.

Abstract: An apparatus for making a crystal pre-melt includes a hermetically-sealed muffle furnace made of a non-porous refractory material, at least one port for entry and exit of gaseous substance within the muffle furnace, a temperature-controlled zone defined inside the muffle furnace, and a crucible for holding crystal raw material in solid or molten form inside the muffle furnace. The crystal pre-melt is made by disposing crystal raw material in loose powder, pressed powder, granular, or densified form in the temperature-controlled zone, heating the temperature-controlled zone to a treatment temperature that enables reaction between a fluorinating agent and oxides in the crystal raw material, reacting the fluorinating agent with the crystal raw material to produce volatile gases, removing the volatile gases from the muffle furnace, heating the crystal raw material to form a melt, and solidifying the melt to form the crystal pre-melt.