The effect of airborne contaminants in the cleanroom for ULSI manufacturing process

In this paper we report on the effect of airborne organic contaminants in actual cleanrooms. We have developed methods for the analysis of contaminants adsorbed on wafer surfaces, including thermal desorption-gas chromatography/mass spectrometry (TD-GC/MS) and thermal desorption-atmospheric pressure ionization mass spectrometry (TD-APIMS). From the results of analysis using TD-GC/MS, TD-APIMS, and ion chromatography (IC), we demonstrate that several specific organic compounds in cleanroom air tend to adsorb on silicon wafers. These include dioctyl-phthalate (DOP), other esters, and amines. We have also found that these organic contaminants adsorbed on the wafer surface cause a reduction in the breakdown field strength of an insulating SiO₂ layer. The origin of DOP and the other esters is the plasticizer added to many polymeric materials. DOP exists in the cleanroom inlet atmosphere, and there are additional outgassings from many polymeric materials in the cleanroom itself. The major source of amine contaminants is chemicals added to the steam which is used for humidity control in the cleanroom. We show that organic contaminants from the wafer carriers and boxes also cause a reduction in the breakdown field strength of a SiO₂ layer. We also succeed in decreasing organic contaminants by use of adopting charcoal air filtering.