Ingrid Cornelissen

A Detailed Study on the Growth of Thin Oxide Layers on Silicon Using Ozonated Solutions

The oxidation of silicon using ozonated, deionized water solutions was investigated as a function of several parameters: reaction time, pH, ozone concentration, temperature, and influence of anions. The oxidation of silicon was dependent on ozone concentration especially near neutral pH. This concentration dependence disappears at concentrations greater than 15 mg/L ozone. No temperature effect was found between 20 and 50°C. Lowering the pH leads to a less pronounced concentration dependence with no specific anion effect between HCl or . The oxidation of silicon by ozonated solutions does not lead to extensive roughening of the silicon surface as shown by atomic force microscopy measurements. Various thermal oxidation models were evaluated and the Fehnler expression represents the experimental data fairly well. The overall oxidation thus follows logarithmic growth kinetics. It is proposed that ozone dissociates at the interface in a one‐step reaction forming the oxidizing species, namely, . This radical diffuses through the layer under the influence of an electric field which develops over the oxide layer. The field‐imposed drift is the limiting factor in the oxidation process. The bulk chemistry of the ozonated solutions is of no importance to the oxidation of silicon. The initial oxidation rate, defined at an oxidation time of 6 s, was dependent on the ozone concentration below 15 mg/L and leveled off above this concentration as it was limited by the field‐imposed drift of the oxidation precursor.

Cost-effective cleaning and high-quality thin gate oxides

Some recent findings in the area of wafer cleaning and thin oxide properties are presented in this paper. Results are shown for a practical implementation of a simplified cleaning concept that combines excellent performance in terms of metal and particle removal with low chemical and DI-water consumption. The effect of organic contamination on ultrathin gate-oxide integrity is illustrated, and the feasibility of using ozonated DI water as an organic removal step is discussed. Metal outplating from HF and HF/HCI solutions is investigated. Also, the final rinsing step is critically evaluated. It is demonstrated that Si surface roughness without the presence of metal contaminants does not degrade gate-oxide integrity. Finally, some critical remarks on the reliability measurements for ultrathin gate oxides are given; it is shown that erroneous conclusions can be drawn from constant-current charge-to-breakdown measurements.

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 thin silicon dioxide layers. The procedure is based on the etching of the layer by HF and the determination of Si concentration in the microgram per liter range in the HF containing etch solutions. Two analytical techniques were optimized for this purpose: a spectrophotometric technique, the so‐called molybdenum blue method and inductively coupled plasma mass spectrometry (ICP‐MS). In the first method a detection limit of 3.3 μg/L Si could be achieved with a sensitivity of . Interference by HF up to 0.1% v/v (volume/volume %) HF could be eliminated by adding boric acid to the solution. In the second method Si was determined by ICP‐MS using the Si isotope. The detection limit in bidistilled water was 1.2 μg/L Si with a sensitivity of (5807 ± 98) cps/(μg/L Si). The presence 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 μg/L Si could be achieved. For silicon dioxide layers below 1 nm, a reproducibility better than 5% was obtained.

A novel resist and post-etch residue removal process using ozonated chemistries

A novel, environmentally friendly process is successfully applied for the removal of photoresist and organic post-etch residues from silicon surfaces. The moist ozone gasphase process described, greatly increases the organic removal efficiency. Improved performance over traditional processes is due to enhanced reactive ozone availability near the wafer surface. Additionally, OH radical scavengers such as acetic acid chemically enhance the process efficiency even further.

Cost-effective cleaning for advanced Si-processing

The effect of various metal contaminants on the thin gate oxide integrity is investigated and a classification is made according to their final position in the structure. A simplified cleaning strategy is presented which is highly performant and at the same time cost-effective and has less environmental impact than the traditional cleaning sequences. Finally, a novel environmentally friendly ozone/DI-water process for the removal of photoresist and organic post-etch residues is proposed.