Doping media for the local doping of silicon wafers

Process for the preparation of printable, high-viscosity oxide media, having a viscosity >500 mPas, in the form of doping media, comprising carrying out an anhydrous sol-gel-based synthesis by condensation of alkoxysilanes and/or alkoxyalkylsilanes with

• a) one or more symmetrical or asymmetrical carboxylic anhydrides
• i. in the presence of boron-containing compounds and/or
• ii. in the presence of phosphorus-containing compounds or
• b) one or more strong carboxylic acids
• i. in the presence of boron-containing compounds and/or
• ii. in the presence of phosphorus-containing compounds or
• c) with a combination of variants a) and b)
• i. in the presence of boron-containing compounds and/or
• ii. in the presence of phosphorus-containing compounds,
• to provide an oxide medium,
• and preparing a paste-form, high-viscosity doping media by controlled gelling of the oxide medium, which comprises:
• gelling the oxide medium to give a high-viscosity, approximately glass-like material;
• and either redissolving the resultant product by addition of a solvent or retransforming the resultant product to a sol state by high-shear mixing;
• and allowing the dissolved or sol state resultant product to retransform to a gel by partial or complete structure recovery.