Steven Verhaverbeke

New Wet Cleaning Strategies for Obtaining Highly Reliable thin Oxides

The effect of metal contamination and silicon surface defects on the gate oxide yield is investigated. The characteristics of various cleaning procedures are studied and correlated with the integrity of thin gate oxides. The standard wet cleaning recipe is optimized and a new cleaning strategy is proposed. Selective contamination experiments in chemicals and on Siwafers are used to investigate the effect of small amounts of metal contaminants on the gate oxide integrity. It is found that the characteristics of the silicon substrate play a dominant role in this. HF-last processes are investigated and a new wet cleaning strategy is proposed.

The Relationship of the Silicon Surface Roughness and Gate Oxide Integrity in NH4OH/H2O2 Mixtures

In this study some recent findings on the cleaning action of the NH4OH/H2O2 (SC1) step in a pre-gate oxidation cleaning (RCA cleaning) are given. An important parameter in this mixture is the NH4OH/H2O2 ratio. The Fe contamination on the silicon surface after this cleaning step is found to increase upon decreasing the NH4OH/H2O2 ratio. This can be attributed to the incorporation of Fe in the chemical oxide, grown by the hydrogen peroxide. The particle removal efficiency of the cleaning step is found to decrease upon decreasing the NH4OH/H2O2 ratio. On the other hand, using a lower NH4OH concentration results in a less severe silicon surface roughening. It is demonstrated in this study that the NH4OH/H2O2 ratio during the SC1 step of the cleaning is the determining parameter for the breakdown properties of a gate oxide. A (0.25/1/5) NH4OH/H2O2/H2O mixture at 75°C in our experimental conditions is suggested to be the best compromise between particle removal and surface roughness during the SC1 step.

Atomic Force Microscopy and Infrared Spectroscopy Studies of Hydrogen Baked Si Surfaces

A H2 pre-bake at temperatures over 1050°C is typically used prior to Si epitaxial growth. In this study surface microroughness probed with tapping mode Atomic Force Microscopy (AFM) is correlated with multiple internal reflection infrared spectroscopy measurements for the different steps involved before epitaxy. A novel sample preparation technique was used for the multiple internal reflection set-up. A strong correlation was found between the presence of surface terraces and the IR double monohydride peaks for H2 annealed Si surfaces. We therefore put forward that the terraces are due to the H2 pre-bake step. These terraces remain after epitaxial deposition.

Charge Trapping and Defect Generation in Thermal Oxide Layers

Thin thermal oxide layers are an important part of MOS-technologies because they are always related with the active parts of the device. An important reliability issue for these layers is the charge injection in the gate oxide as a result of the high fields in small geometry transistors. This causes charge build-up in the SiO2 layer and degradation of the Si/SiO2 interface. After a brief introduction to the charge injection techniques two aspects of charge trapping are discussed in this paper which have received much attention over the last few years : the oxide field dependence of the charge trapping and interface degradation and the effect of small amounts of chlorine and fluorine on the trapping properties of oxide layers.