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Process for Producing a Precision Filter

IP.com Disclosure Number: IPCOM000036123D
Original Publication Date: 1989-Sep-01
Included in the Prior Art Database: 2005-Jan-28
Document File: 2 page(s) / 71K

Publishing Venue

IBM

Related People

Euen, W: AUTHOR [+2]

Abstract

A process sequence is described which permits producing filters with pore sizes down to 5 nm and the respective pore size to be kept with an accuracy of - 3%. The filters thus produced may be used to filter fluids and gases in semiconductor technology but also for separating viruses.

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Process for Producing a Precision Filter

A process sequence is described which permits producing filters with pore sizes down to 5 nm and the respective pore size to be kept with an accuracy of - 3%. The filters thus produced may be used to filter fluids and gases in semiconductor technology but also for separating viruses.

A P- Si substrate 1 (Fig. 1) comprises a boron implantation 2 with a drive-in which determines the thickness of the filter membrane. For this purpose, the fact is utilized that silicon with boron concentrations of > 1 x 1019 cm-3 is not attacked by the etch solution. The described process is suitable for producing a filter thickness of about 2 mm. For thicker membranes, the implanted layer may be replaced by a grown epitaxial layer with the necessary boron concentration and the desired thickness. Trenches 3, produced by RIE (reactive ion etching), are a prerequisite for defining the pore size. The thickness of a thermally grown oxide 4 or an oxide 4 applied by CVD (chemical vapor deposition) directly determines the pore size. This means, an oxide thickness of 5 nm yields a filter pore size of the same value, with the tolerance of the pore size being > - 3% for thermal oxides. Then, trenches 3 are filled with polysilicon 5 (Fig. 2).

The further process steps are: planarizing the surface by RIE or chemical/mechanical polishing (Fig. 3), adjusting the filter thickness by etching the back side (Fig. 4), and etching oxide 4 for generating filter po...