IPA溶液的界面和电动特性

In this study, the interfacial and electrokinetic phenomena of mixtures of isopropyl alcohol  IPA and deionized  DI water in relation to semiconductor wafer drying is investigated. The dielectric constant of an IPA solution linearly decreased from 78 to 18 with the addition of IPA to DI water. The viscosity of IPA solutions increased as the volume percentage of IPA in DI water increased. The zeta potentials of silica particles and silicon wafers were also measured in IPA solutions. The zeta potential approached neutral values as the volume ratio of IPA in DI water increased. A surface tension decrease from 72 to 23 dynes/cm was measured when the IPA concentration increased to 30 vol %. The surface excess of IPA at the air–liquid interface reached a maximum at around 20 vol % IPA. The adhesion forces of silica particles on silicon wafers were measured using atomic force microscopy in IPA solutions. The adhesion force increased as the volume percent of IPA in water increased. Lower particulate contamination was observed when the wafers were immersed and withdrawn from solutions containing less than 25 vol % IPA.

Wet chemical processes are indispensable in wafer cleaning due to their effectiveness in removing contaminants. Recently, wet cleaning and drying have become more important than ever due to increases in pattern density and wafer size and rapid decreases in pattern sizes below 0.13  m. Spin and hot isopropyl alcohol  IPA vapor drying have been displaced by Marangoni-type IPA drying,1 which utilizes the surface pressure gradient at the air–liquid interface at room temperature.

IPA has been utilized in wet cleaning and drying to increase the surface wettability and to enhance wafer drying because of its low surface tension, high vapor pressure, and high solubility in water.2,3 Even though studies evaluating a thin IPA layer on deionized  DI water have been performed in order to elucidate the wafer drying phenomena,4,5 few studies have been conducted evaluating the interfacial and electrokinetic phenomena of IPA solutions from the point of view of semiconductor wet processing. In this study, electrokinetic and interfacial characterization of IPA solutions was conducted in order to elucidate the role of IPA in solutions in semiconductor cleaning and drying processes.

Experimental 

Pure IPA  semiconductor grade, Dongwoo Fine Chemicals Co. was mixed with ultrahigh-purity DI water and left for 5 h in a closed system for complete mixing. In order to characterize the properties of the mixture of IPA and DI water, the viscosity and surface tension of the mixed solutions were measured as a function of IPA concentration using a viscosity meter  Brookfifield DV-II, Brookfifield Engineering Laboratory, Inc. and a Wilhelmy-type6 surface tension analyzer  DCA 315, Cahn Co. , respectively, at room temperature.

Fumed silica   50 nm, Degussa Co. particles were used for measuring its zeta potential and particle size. The zeta potential and mean particle size were measured by a laser electrophoretic zeta potential analyzer  LEZA-600, Otsuka Electronics Co. at various concentrations of IPA solution. Silicon particles  −325 mesh, 99.9%, Sigma-Aldrich Co. were used to measure the zeta potential instead of the Si wafer surface.

The adhesion force between a silica particle and the Si surface was measured using atomic force microscopy  AFM, AutoProbe CP Research, PSIA Co. at different concentrations of IPA solutions.7,8 A 40  m diam spherical soda lime silica particle  Duke Scientifific Co. was attached on a Si3N4 tipless cantilever. Silicon wafers were precleaned in SPM  H2SO4·H2O2 = 4:1 vol %, 120°C and APM  NH4OH·H2O2:H2O = 1:1:5 vol %, 80°C cleaning solutions for 10 min. After cleaning, the wafers were rinsed using DI water for 3 min. Then the wafers were fifinally cleaned with dilute hydroflfluoric acid solution  0.5% DHF for 5 min and rinsed with DI water.

Six-inch wafers were used for the drying and particle adhesion experiments in various concentrations of IPA solutions. The wafers were dipped into the IPA mixtures contaminated with silica particles  0.5  m, Duke Scientifific Co. for 2 min 30 s. After dipping, the wafers were withdrawn very slowly at a speed of 2.4 mm/s. The wafers were dried by hot N2 blowing. The number of particles on the wafer surfaces was measured using a laser particle scanner  Surfscan 5500, KLA Tencor Co. before and after drying the wafers.