NOVELTY - Selenization or sulfurization of roll-to-roll metal substrate involves introducing (402) a substrate having precursor material deposited on surface into a zone (Z1) of a vacuum chamber, heating (404) precursor material at 270-490 degrees C to target reaction temperature, maintaining (406) selenium vapor or sulfur vapor in a zone (Z2) of the vacuum chamber and introducing (408) the precursor material and substrate to the zone (Z2) of the vacuum chamber. The precursor material comprises copper, indium, and at least one of gallium, sodium, selenium, sulfur, aluminum, and silver.    USE - Selenization or sulfurization of roll-to-roll metal substrate comprising stainless steel, non-stainless steel, aluminum and other metal films (all claimed) used for forming copper indium gallium selenide film for solar cells.    ADVANTAGE - The copper indium gallium selenide film having excellent surface smoothness is formed on roll-to-roll metal substrate by using selenization or sulfurization method.    DETAILED DESCRIPTION - Selenization or sulfurization of roll-to-roll metal substrate involves introducing a substrate having a precursor material deposited on surface into a zone (Z1) of a vacuum chamber, heating the precursor material at 270-490 degrees C to a target reaction temperature, maintaining one of a selenium vapor or sulfur vapor in a zone (Z2) of the vacuum chamber and introducing the precursor material and the substrate to the zone (Z2) of the vacuum chamber. The precursor material comprises copper, indium, and at least one of gallium, sodium, selenium, sulfur, antimony, boron, aluminum, and silver. An INDEPENDENT CLAIM is included for non-transitory computer readable medium storing instructions that when executed by a control system cause the control system to perform selenization or sulfurization.    DESCRIPTION OF DRAWING(S) - The drawing shows a flow chart explaining the method for processing a precursor material.    Processing of precursor material (400)    Introduction of substrate (402)    Heating the precursor material (404)    Maintaining selenium vapor in zone of vacuum chamber (406)    Introduction of precursor material (408)