No abstract

No abstract

The organic oxidizing agents 1,4-benzoquinone and its nontoxic derivative 2,3,5,6-tetrachloro-1,4-benzoquinone have been shown to be alternatives to the toxic and carcinogenic hexavalent chromium which is routinely used in most etching solutions. The newly developed etching solutions delineate both grown-in and process-induced defects in silicon-on-insulator substrates fabricated by the Smart-Cut technology and show a good correlation to the defect densities obtained with a dilute Secco ͑0.04 M͒ etching solution serving as a reference. In combination with an aqueous solution of the nontoxic fluorinating agent tetrafluoroboric acid, which has been introduced as an alternative to the very toxic solution of hydrofluoric acid ͑49%͒, a completely nontoxic etching solution is presented. An etching mechanism will be discussed, explaining the generation of elemental hydrogen which is formed during the etching process.

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.

Protruding etch features, some of which may be related to crystal defects and some to artifacts, were obtained on Si surfaces after wet chemical etching with defect etching solutions containing certain amounts of potassium iodide or potassium dichromate. It will be shown that the potassium ions play a decisive role in the formation of these etch features. Surface sensitive and non-surface sensitive methods were used to study the chemical nature and therewith the origin of the etch features.