Removal of detrimental metal ions from hydrofluoric acid solution for cleaning silicon surfaces

In a method of refining a hydrofluoric acid solution for use in the manufacturing of semiconductor devices to clean silicon surfaces by removing at least one detrimental metal ion from the acid solution by bringing the acid solution into contact with silicon granules for adsorption of the detrimental metal ion or ions on the surfaces of the silicon granules,

• the improvement comprising depositing a metal which is lower in ionization tendency than silicon on said silicon granules so as to partly cover the surface of each silicon granule by the deposited metal in advance of the contact of the silicon granules with the hydrofluoric acid solution,
• wherein said silicon granules are not larger than 1 mm in granule size, and
• wherein said metal is gold, the quantity of said gold being at least 0.1 mg per gram of said silicon granules.

In a method of refining a hydrofluoric acid solution for use in the manufacturing of semiconductor devices to clean silicon surfaces by removing at least one detrimental metal ion from the acid solution by bringing the acid solution into contact with silicon granules for adsorption of the detrimental metal ion or ions on the surfaces of the silicon granules,

• the improvement comprising depositing a metal which is lower in ionization tendency than silicon on said silicon granules so as to partly cover the surface of each silicon granule by the deposited metal in advance of the contact of the silicon granules with the hydrofluoric acid solution,
• wherein said silicon granules are not larger than 1 mm in granule size, and
• wherein said metal is silver, the quantity of said silver being at least 0.02 mg per gram of said silicon granules.

In a method of refining a hydrofluoric acid solution for use in the manufacturing of semiconductor devices to clean silicon surfaces by removing at least one detrimental metal ion from the acid solution by bringing the acid solution into contact with silicon granules for adsorption of the detrimental metal ion or ions on the surfaces of the silicon granules,

• the improvement comprising depositing a metal which is lower in ionization tendency than silicon on said silicon granules so as to partly cover the surface of each silicon granule by the deposited metal in advance of the contact of the silicon granules with the hydrofluoric acid solution, and
• further comprising the step of regenerating said silicon granules when the adsorption power of the silicon granules lowers, the regeneration step comprising cleaning said silicon granules with an acid solution which dissolves at least one detrimental metal adsorbed on the surfaces of the silicon granules without dissolving silicon and the metal initially deposited on the surfaces of the silicon granules.