Apparatus and method for treating etching solution

Abstract

An apparatus and method for treating an etching solution, where the replacement frequency of the etching solution is reduced, while the inclusion of impurities in the treated etching solution is prevented. An apparatus for treating an etching solution in order to reuse the etching solution used in etching treatment of silicon, where the apparatus includes: membrane separation means 3 which performs membrane separation treatment on the etching solution supplied from an etching bath 2; and circulating means 6 which circulates a permeated solution supplied from the membrane separation means 3 to the etching bath 2. The membrane separation means 3 includes a UF membrane module 4 and an NF membrane module 5. Alkaline and organic substances may be added to the etching solution supplied from the membrane separation means 3.

Description

FIELD OF INVENTION[0001]The present invention relates to an apparatus and a method for treating an etching solution, and in particular, the present invention relates to an apparatus and a method for treating an etching solution preferable in the case of, for example, forming a texture surface by etching a surface of a crystalline silicon substrate.BACKGROUND OF INVENTION[0002]In a crystalline silicon substrate used for a solar cell substrate, the surface of the substrate is made to have a fine pyramidal texture in order to improve the power generation efficiency by increasing the optical path length of incident light. Such a substrate can be obtained by etching (texture etching), a surface of a silicon substrate with an etching solution which may be, for example, a mixture solution of an alkaline solution containing 0.05 to 2 mol / L of NaOH or KOH, and a surfactant whose primary ingredient is caprylic acid or lauric acid of 0.01 mol / L or higher (Patent Document 1). The etching soluti...

AI Technical Summary

Benefits of technology

[0022]The apparatus and method for treating an etching solution of the present invention remove an etching solution containing silicon components and / or dopants eluted from silicon by a membrane separation treatment, and circulate the etching solution to the etching bath, which allows the etching solution to be used for a longer period of time than conventional art and reduces the exchange frequencies of the etching solution.

[0023]That is, with the present invention, silicate ions and dopant ions which affect the etching rate can be separated efficiently, so an etching solution can be used without having to replace it for a long time. Moreover, since the etching solution does not need to be replaced for a longer time than conventional art, the amount of acid used to neutralize a highly concentrated waste alkali solution can be reduced.

[0024]The membrane separation means may be provided with a nanofiltration membrane which selectively removes multivalent ions having a valence of two or more. In this case, multivalent ions having a valence of two or more, for example, silicate ions (e.g., SiO32−), in the etching solution may be selectively separated while keeping the alkalinity of the etching solution, so the processing time for the texturing process may be stabilized and reduced.

[0025]The membrane separation means may be provided with a nanofiltration membrane which removes multivalent ions having a valence of two or more, alkali metal ions having a valence of one, and hydroxide ions. In this case, the etching solution which does not permeate the membrane separation means is alkaline, so silicic acid is ionized and fouling of the nanofiltration membrane can be prevented.

[0026]That is, under a neutral condition, silicate ions solate and reduce flux of the nanofiltration membrane, but by keeping the etching solution which does not permeate the membrane alkaline, solation of silicate ions can be prevented and thus fouling of the nanofiltration membrane can be prevented.

[0027]The membrane separation means may be provided with a nanofiltration membrane and an ultrafiltration membrane which is installed at an upstream side of the nanofiltration membrane. The etching solution may contain high molecular weight material produced by reactions of dopants, organic substances, silicate ions or the like. So, when the etching solution is directly supplied to the nanofiltration membrane, the high molecular weight material may deposit on the surface of the membrane and reduce the flux thereof. By installing the ultrafiltration membrane module at an upstream side of the nanofiltration membrane module for removing the high molecular weight material, fouling of the nanofiltration membrane can be prevented.

Problems solved by technology

Since the water temperature in the etching bath is around 80° C., water readily evaporates and the NaOH concentration rises, which makes concentration control significantly difficult.

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