Boron Ion-exchange Monitoring Analytics

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Abstract

The presence of boron in ultrapure water (UPW*) for semiconductors has until recently been monitored only to determine the regeneration status of ion-exchange (IX) beds because of low resin affinity for the specie. However, because of its difficulty of removal and its newly suspected potential to lower semiconductor production yield, boron has increasingly become a contaminant of concern in UPW. It typically exists in feedwater as boric acid (H3BO3), which dissociates to form borate (B(OH)4-) at high pH. It is not well eliminated in reverse osmosis or IX, owing to its small molecular size and its weak acid characteristics, which cause it to remain largely undissociated at pH below 8 (1-3). Because the element is a common dopant used to make P-N junctions, its presence in semiconductor rinse water can interfere with the proper performance of the finished chips (2). Boron may deposit onto wafer surfaces at high pH conditions (i.e., SC1 cleans). Therefore, understanding its behavior in UPW production is essential.

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