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超LSIの微細化に伴い,シリコンウェーハ洗浄用薬品の高純度化,金属不純物及び微粒子の低減が必要とされている.金属不純物は16MビットDRAM(dynamic random acccss memory)以降の超LSIでは1ppb以下が要求される.又微粒子はウェーハ表面に付着するとパターン欠陥や電気特性劣化の原因となる.著者らはEPMAによって薬品中の微粒子の構成元素を分析し,検出された元素を容器からの溶出元素の面から検討した.その結果,微粒子の構成元素は主にSiで,その他にAl,Mg,Fe,Cr,Tiであった.これらは容器に含まれており,微粒子の発生源の一つに容器が考えられる.不純物濃度は硫酸の場合Siのみがわずか増加したが,その他の元素には変化が見られなかった.

The thickness of Al thin films on 1000A SiO2 was estimated by using X-ray fluorescence (XRF). It was found thatA when the films were less than 1000A thick, the number of Al XRF counts was directly proportional to the Al thickness. Therefore, Al thickness is given by t=a(If-Bg) within an error of 3.0%, where a and Bg are constant and background noise, and If is the Al XRF count. In the Al film thicknes range of 2000A to 1.2 μm, XRF counts vs. Al thickness becomes nonlinear due to Al self-absorption. The Al thickness was given by t=-a·ln(1-(If-Bg/Imax)), where Imax is maximum value measured by Al XRF. The maximum relative error was 1.6%. However, for the Al film thickness range of 1000A to 2000A, the relative error was 9.7%.

An Electron Microprobe Auger Spectroscopy was applied to investigate interactions between Al film and thermally grown silicon dioxide (SiO2) in order to examine the failure occurred for very thin Al film on SiO2 surface during heating and stressing tests. It was found that the oxidation mechanism of Al film was different on Al film surface from that at the interface between Al and SiO2 during heating in vacuum at 400-500°C for 30 min. Also, the depth of penetration of Al into SiO2 was found to be unexpectedly large. As a result of stressing test, chained hillocks appeared along the direction of electron flow in the case of very thin Al film. This Phenomenon may be due to diffusion of Si into Al film by heating during device process.