Bevel contamination management in 3D integration by localized SiO2 deposition

Abstract

This paper investigates silicon oxide bevel deposition to manage contamination in 3D integration with intermediate Back-End Of Lines (iBEOL) levels. Bevel etching and cleaning techniques are now sufficiently mature to remove efficiently contamination on wafer bevel area. However, 3D integration with iBEOL could require encapsulating metal lines, which emerge on the bevel area. This paper explores the efficiency of bevel deposition to answer contamination issues in 3D integration. Films are deposited on the bevel area of 300 mm wafers thanks to a torus shaped Plasma Enhanced Chemical Vapor Deposition (PECVD) configuration allowing encapsulation of the last few mm of the wafer frontside, backside and the apex in a single processing step. Deposition is carried out at 350 °C from mixture of SiH4 and N2O at 2 Torr. When the gap between wafer and top insulator increases from 0.4 to 0.7 mm, the frontside deposition profile is shifted by 0.5 mm inward. In accordance with refractive index of 1.55 measured by ellipsometry, surface analysis by X-ray Photoelectrons Spectroscopy (XPS) show a film composition of SiO1.8N0.3 with a quasi-constant composition from 147 to 149 mm wafer radius. The film resistance, evaluated by wet etch in 2% HF, leads to Wet Etch Rate (WER) ratio to thermal oxide of 4–5. We demonstrate that such films are compatible with oxide bonding. Thanks to a proper integration scheme, minimal impact on the bonding edge quality with bonding limit of 147.7 mm on real product Complementary Metal Oxide Semiconductor with 4 Metal levels (CMOS+M4) is reported. Finally, the effectiveness of the strategy to keep the metallic contamination at 1 × 1010 at.cm-2 or below is verified by either specific Liquid Phase Decomposition bevel Inductively Coupled Plasma Mass Spectrometry (LPD bevel-ICPMS) on BEOL wafers or by Vapor Phase Decomposition (VPD)-ICPMS standard process control on Front-End Of Line (FEOL) wet tool just after having cleaned BEOL wafers.