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Sacrificial Etching Guard Ring

IP.com Disclosure Number: IPCOM000079241D
Original Publication Date: 1973-Jun-01
Included in the Prior Art Database: 2005-Feb-26
Document File: 2 page(s) / 44K

Publishing Venue

IBM

Related People

Chappelow, RE: AUTHOR [+4]

Abstract

Nonuniform etching of uniform composition materials ordinarily is encountered, whenever the etching solution used is rate-limited by dilution of an active, necessary component. Nonuniform etching is avoided in such cases, by placing the object being etched in a sacrificial holder made of the same material being etched. The holder is arranged to extend the perimeter of the object being etched, in effect, so that the region of nonuniform etching occurs in the sacrificial holder and not in the object being etched.

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Sacrificial Etching Guard Ring

Nonuniform etching of uniform composition materials ordinarily is encountered, whenever the etching solution used is rate-limited by dilution of an active, necessary component. Nonuniform etching is avoided in such cases, by placing the object being etched in a sacrificial holder made of the same material being etched. The holder is arranged to extend the perimeter of the object being etched, in effect, so that the region of nonuniform etching occurs in the sacrificial holder and not in the object being etched.

In an exemplary case, polycrystalline silicon is selectively etched using the composition HNO(3)/HF/CH(3)COOH. The HF concentration is kept very low so that reasonable etching rates are attained. In gross respects, HNO(3) oxidizes the silicon and the oxide is simultaneously removed by the HF. The latter reaction is deliberately attenuated by the availability of HF, whereby the total etch rate is controlled. At localized areas of the polycrystalline silicon being etched, the HF is used up as the etching proceeds and must be replenished from the bulk etching solution. HF concentration gradients exists because of this action.

Fig. 1 illustrates a typical planar wafer, whose polycrystalline layer 1 is to be etched away from underlying silicon nitride layer 2 on silicon substrate 3. Point A receives HF from the local etching solution, as do all adjacent points such as B and C. Similarly, reaction products diffuse from A to the local bulk etching solution, which also receives reaction products from all adjacent points such as B and C. In contrast to this, point D receives HF from a localized region of the bulk etching solution which supplies much fewer adjacent...