# US 5,348,722 A · Removal of detrimental metal ions from hydrofluoric acid solution for cleaning silicon surfaces > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 5,348,722 A - Document ID: US5348722A - Status: Granted - Kind: A - Application number: 08/077,440 - Filed: 1993-06-17 - Granted: 1994-09-20 - Earliest claimed: 1992-06-17 - Assignees: NEC Corporation - Inventors: Tsugio Shimono; Kenichi Yamamoto - Web page: https://patentgrep.com/patent/US5348722A ## CPC - C01B 7/197: {by adsorption} - C01B: NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; {METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C} ## Abstract The invention relates to the removal of detrimental metal ions represented by Cu ion from a hydrofluoric acid solution for use in the manufacturing of semiconductor devices to clean silicon wafer surfaces. The acid solution is brought into contact with silicon granules which are used for the adsorption of the detrimental metal ions. To enhance the adsorption power and the rate of adsorption, the silicon granules are treated in advance to deposit a metal which is lower in ionization tendency than silicon on the surface of each silicon granule so as to partly cover the silicon granule surface by the deposited metal. Particularly Au or Ag is suitable as the metal deposited on the silicon granules. ## Claims ### Claim 1 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 placing said partly covered silicon granules in either an adsorption column or a filter unit for the contact of the silicon granules with the hydrofluoric acid solution. ### Claim 2 (depends on 1) A method according to claim 1, wherein said metal is selected from the group consisting of gold and silver. ### Claim 3 (depends on 1) A method according to claim 1, wherein said silicon granules in the range from about 0.01 mm to about 5 mm in granule size. ### Claim 4 (depends on 3) A method according to claim 3, wherein said silicon granules are not larger than 1 mm in granule size. ### Claim 5 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. ### Claim 6 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. ### Claim 7 (depends on 1) A method according to claim 1, wherein said at least one detrimental ion comprises copper ion. ### Claim 8 (depends on 1) A method according to claim 1, wherein the contact of the hydrofluoric acid solution with said silicon granules is accomplished by agitating a dispersion of said silicon granules in the hydrofluoric acid solution. ### Claim 9 (depends on 1) A method according to claim 1, wherein the hydrofluoric acid solution is brought into contact with said silicon granules by passing the hydrofluoric acid solution through an adsorption column packed with said silicon granules. ### Claim 10 (depends on 1) A method according to claim 1, wherein said metal is deposited on the surfaces of said silicon granules by treating said silicon granules with a hydrofluoric acid solution containing said metal in the form of ion. ### Claim 11 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. ### Claim 12 (depends on 5) A method according to claim 5, wherein said at least one detrimental ion comprises copper ion. ### Claim 13 (depends on 5) A method according to claim 5, wherein the contact of the hydrofluoric acid solution with said silicon granules is accomplished by agitating a dispersion of said silicon granules in the hydrofluoric acid solution. ### Claim 14 (depends on 5) A method according to claim 5, wherein the hydrofluoric acid solution is brought into contact with said silicon granules by passing the hydrofluoric acid solution through an adsorption column packed with said silicon granules. ### Claim 15 (depends on 5) A method according to claim 5, wherein said metal is deposited on the surfaces of said silicon granules by treating said silicon granules with a hydrofluoric acid solution containing said metal in the form of ion. ### Claim 16 (depends on 6) A method according to claim 6, wherein said at least one detrimental ion comprises copper ion. ### Claim 17 (depends on 6) A method according to claim 6, wherein the contact of the hydrofluoric acid solution with said silicon granules is accomplished by agitating a dispersion of said silicon granules int eh hydrofluoric acid solution. ### Claim 18 (depends on 6) A method according to claim 6, wherein the hydrofluoric acid solution is brought into contact with said silicon granules by passing the hydrofluoric acid solution through an adsorption column packed with said silicon granules. ### Claim 19 (depends on 6) A method according to claim 6, wherein said metal is deposited on the surfaces of said silicon granules by treating said silicon granules with a hydrofluoric acid solution containing said metal in the form of ion. ### Claim 20 (depends on 11) A method according to claim 11, wherein said metal is selected from the group consisting of gold and silver. ### Claim 21 (depends on 11) A method according to claim 11, wherein said silicon granules in the range from about 0.0 mm to about 5 mm in granule size. ### Claim 22 (depends on 21) A method according to claim 21, wherein said silicon granules are not larger than 1 mm in granule size. ### Claim 23 (depends on 22) A method according to claim 22, wherein said metal is gold, the quantity of said gold being at least 0.1 mg per said silicon granules. ### Claim 24 (depends on 22) A method according to claim 22, wherein said metal is silver, the quantity of said silver being at least 0.02 mg per gram of said silicon granules. ### Claim 25 (depends on 11) A method according to claim 11, wherein said at least one detrimental ion comprises copper ion. ### Claim 26 (depends on 11) A method according to claim 11, wherein the contact of the hydrofluoric acid solution with said silicon granules is accomplished by agitating a dispersion of said silicon granules in the hydrofluoric acid solution. ### Claim 27 (depends on 11) A method according to claim 11, wherein the hydrofluoric acid solution is brought into contact with said silicon granules by passing the hydrofluoric acid solution through an adsorption column packed with said silicon granules. ### Claim 28 (depends on 11) A method according to claim 11, wherein said metal is deposited on the surface of said silicon granules by treating said silicon granules with a hydrofluoric acid solution containing said metal in the form of ion.