Mechanism of a New Post CMP Cleaning for Trench Isolation Process
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using a conventional CMP method is contaminated with silica particles and chemical impurities. The contamination produces pattern and crystal defects in the wafer surface layer after oxidation. It is difficult to remove them by the conventional cleaning technique. Therefore we studied a new post CMP cleaning method using special organic surfactant from the view point of contamination adhesion mechanism. EXPERIMENT The schematic diagram of the polisher, EBARA EPO-112, used in this study is shown in Fig.2. The polisher consists of polishing zone and wafer cleaning zone. The polishing zone is composed of wafer carrier and turntable. The wafer cleaning zone is composed of PVA brush and spin-dry stations [6]. The wafer is hold on side spin chuck and is rotated for cleaning. In the first stage, cleaning liquid is dropped onto a rotating PVA roll-like brush. In the second stage, the electric decomposed water (anode water) is dropped onto a wafer and spin dried. A wafer was polished on the turntable with a Rodeal IC 1000/SUBA IV stacked polish pad and colloidal silica slurry of alkaline base and then, DI water was supplied on the turntable to polish the wafer only with water (We call this process water polish.). The films used in this study were PolySi, SiO2 (100 rum thick on Si). Remaining impurities on wafer after polishing and 253 Mat. Res. Soc. Symp. Proc. Vol. 566 ©2000 Materials Research Society
cleaning were evaluated by Vapor Phase Dissolution-Inductively Coupled Plasma/Mass Spectroscopy (VPD-ICPiMS) and TOF-SIMS(time of flight secondary ion mass spectrometry). Analyzed metallic elements were Fe, Cu and Cr and organic element was C. Number of particles were counted by a surface particle counter (SURFSCAN6200 and 6420 : Tencor instruments). Particles and their shapes analyzed EDX and AFM, respectively. Organic film thickness measured ellipse spectroscope. And transmittance of organic surfactant ware investigated by spectrophotometer. RESULTS AND DISCUSSION 1. Conventional cleaning method 1.1 Metallic Contamination after CMP We have first focused on metallic impurities on wafers after polishing. The concentrations of the metallic impurities in slurry used in our experiments are shown in Table 1. Fe was detected remarkably as metallic impurity. Many particles selectively located on the PolySi pattern region, because the wafer was only rinsed in DI water. Next, this wafer was oxidized as next process step. Many crystal defects were induced by metallic impurities. It is clear that crystal defects with 1E5 density produced dramatically in the wafer at the remaining Fe and Cu impurity contamination over 5El0 atoms/cm2. Therefor, it is necessary to keep the remaining metallic impurity below IEl0atoms/cm2 after polishing in order to establish the defect free wafer through the trench isolation process. [71 1.2 Particles after CM? There are many kinds of particles on the appeared film surfaces. The number of particles on Si wafer surface are strongly depend on the film termination after CMP process. Remaining impurities on
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