Methods and apparatus for controlling and delivering a vaporous element or compound, for example, selenium or sulfur, from a solid source to a work piece are provided. The methods and apparatus may be used in photovoltaic cell manufacturing. The apparatus may comprise a treatment chamber, for example, a box furnace or a tube furnace. The chamber may include an inner enclosure, an outer enclosure, and heating sources capable of independent thermal control, for example, in compliance with a predetermined heating schedule. The apparatus include devices and mechanisms for isolating the treatment chambers from the ambient environment. The methods and apparatus may be adapted to control metalloid vapor delivery in photovoltaic cell processing, for example, the processing of CIGS and CIGSS photovoltaic cells.