Cleaning Effects by NH₄OH Solution on Surface of Cu Film for Semiconductor Devices

Abstract

We investigated cleaning effects using <TEX>$NH_4OH$</TEX> solution on the surface of Cu film. A 20 nm Cu film was deposited on Ti / p-Si (100) by sputter deposition and was exposed to air for growth of the native Cu oxide. In order to remove the Cu native oxide, an <TEX>$NH_4OH$</TEX> cleaning process with and without TS-40A pre-treatment was carried out. After the <TEX>$NH_4OH$</TEX> cleaning without TS-40A pretreatment, the sheet resistance Rs of the Cu film and the surface morphology changed slightly(<TEX>${\Delta}Rs:{\sim}10m{\Omega}/sq.$</TEX>). On the other hand, after <TEX>$NH_4OH$</TEX> cleaning with TS-40A pretreatment, the Rs of the Cu film changed abruptly (<TEX>${\Delta}Rs:till{\sim}700m{\Omega}/sq.$</TEX>); in addition, cracks showed on the surface of the Cu film. According to XPS results, Si ingredient was detected on the surface of all Cu films pretreated with TS-40A. This Si ingredient(a kind of silicate) may result from the TS-40A solution, because sodium metasilicate is included in TS-40A as an alkaline degreasing agent. Finally, we found that the <TEX>$NH_4OH$</TEX> cleaning process without pretreatment using an alkaline cleanser containing a silicate ingredient is more useful at removing Cu oxides on Cu film. In addition, we found that in the <TEX>$NH_4OH$</TEX> cleaning process, an alkaline cleanser like Metex TS-40A, containing sodium metasilicate, can cause cracks on the surface of Cu film.