Use of a Quartz Crystal Microbalance with Dissipation Monitoring to Study Adsorption Phenomena Relevant to Semiconductor Wet Processing

Abstract

In silicon processing, contamination control is very important in each of the processing steps to ensure device reliability and enhance yield. There are many different types of contamination that are introduced at different processing steps from different sources. Industrial practice regarding contamination control, while effective, is not guided by a fundamental understanding of the systems involved. The objective of this work is to utilize the capability of a quartz crystal microbalance with dissipation monitoring (QCM-D) to investigate the fundamentals of contaminant adsorption and desorption, taking sulfate ion and benzotriazole (BTA) as examples, where the sulfate is a type of ionic contaminant and BTA is an organic contaminant. The study of sulfate adsorption onto silicon dioxide films was investigated in the context of front-end-of-line (FEOL) wet cleaning, specifically organic removal with a sulfuric acid/peroxide mixture (SPM). During SPM cleaning, high concentrations of sulfuric acid are used, and residual sulfate on the surface is generally removed by deionized (DI) water rinsing. The amount of sulfate adsorbed from potassium and sodium sulfate solutions was studied with QCM-D. The adsorption of sulfate was shown to result in the formation of multilayers with co-adsorption of cations. This adsorbed sulfate multilayered film was shown to be viscoelastic. The amount adsorbed increases linearly with sulfate concentration in the solution. The effect of temperature was studied, and sulfate uptake decreased with temperature, indicating sulfate adsorption is an exothermic reaction with a heat of adsorption in the range of −15 ~ −11 kJ/mole. The desorption kinetics of sulfate during DI water rinsing was also investigated, and desorption rate constants were calculated to be 0.04 s−1 and 0.12 s−1, respectively, at two different DI water flow rates of 0.2 mL/min and 1.0 mL/min. The effect of temperature on sulfate desorption was shown to be minimal in the range of 22 to 50 °C. The study of BTA adsorption onto copper surfaces was investigated in the context of back-end-of-line (BEOL) wet processing, especially barrier chemical mechanical planarization (CMP) and post-CMP cleaning. BTA inhibits copper corrosion during barrier CMP by adsorbing onto copper surfaces to form a complex with copper. BTA adsorption from alkaline solutions was studied with QCM-D. Two types of oxides, Cu2O and CuO, were investigated. It was determined that BTA adsorption was highly dependent on the oxidation state of copper. BTA adsorbed much more onto the Cu2O surface than onto the CuO surface, indicating Cu(I)-BTA complex formation is the dominating passivation factor for copper. For both type of oxides, Cu2O and CuO, the adsorbed BTA layers were shown to be rigid and compact. The adsorption of BTA onto Cu2O in the presence of hydrogen peroxide was also measured. BTA complexing with Cu(I) dominated over the oxidation of Cu(I). BTA removal was studied by rinsing with tetramethylammonium hydroxide (TMAH) and acetohydroxamic acid (AHA), and the QCM-D results indicate that BTA removal by pH 10 TMAH was not complete, whereas 1 ppm AHA solution was able to completely remove BTA in ~10 min.