A wet chemical method for the determination of thickness of SiO2 layers below the nanometer level

A wet chemical procedure has been elaborated to measure the thickness of th in silicon dioxide layers. The procedure is based on the etching of the SiO 2 layer by HF and the determination of Si concentration in the microgam per liter range in the HF containing etch solutions. Two analytical techniques were optimized for this purpose: a spectrophotometric technique, the so-ca lled molybdenum blue method and inductively coupled plasma mass spectrometr y (ICP-MS). In the first method a detection limit of 3.3 mu g/L Si could be achieved with a sensitivity of (780 +/- 8.7) x 10(-6)/(mu g/L Si). Interfe rence by HF up to 0.1% v/v (volume/volume %) HF could be eliminated by addi ng boric acid to the solution. In the second method Si was determined by IC P-MS using the Si-28 isotope. The detection limit in bidistilled water was 1.2 mu g/L Si with a sensitivity of (5807 +/- 98) cps/(mu g/L Si). The pres ence of HF increased the background signal of Si due to the etching of the quartz plasma torch. In 0.005% v/v HF a detection limit of 5.9 mu g/L Si co uld be achieved. For silicon dioxide layers below 1 nm, a reproducibility b etter than 5% was obtained. (C) 1999 The Electrochemical Society. S0013-465 1(98)07-054-2. All rights reserved.