Defect delineation by chemical etching techniques in silicon and engineered silicon substrates: Novel chemistries and basic aspects

Preferential etching techniques in combination with light optical microscopy are still the workhorse for the evaluation of defect types and area densities in engineered silicon substrates such as silicon-on-insulator (SOI) wafers. Most etching recipes are based on chromium (VI) compounds as oxidizing agent. Since in the meantime the use of carcinogenic Cr (VI) compounds is restricted by law there is a need for Cr-free recipes with adequate or superior defect delineation performance. We present novel Cr-free etching chemistries based on organic peracids or on organic oxidizing agents (OOE) such as benzoquinone and derivatives in organic solvents. Some of these have very low removal rates (nm/min at 25 °C), are very defect sensitive and are especially suitable for the application on thin (<50 nm) SOI films. Preferential etching solutions can be characterized by parameters like removal rate, activation energy for the etching process and selectivity. The selectivity describes the ratio of the removal at the crystal defect and at the perfect crystal. In this work the selectivity was determined experimentally on dislocations for various defect etching chemistries. Dislocations were generated by damaging silicon substrates by controlled indentation with a diamond tip and subsequent annealing at 1000 °C. After preferential etching the depth of etch pits was measured by an atomic force microscope. The activation energy was evaluated via an Arrhenius plot of the temperature dependent etch rates. At the dislocations the activation energies are reduced by about 5%. For the various defect etching chemistries selectivities in the range of 1.5–2.5 were found.