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METHOD OF CUTTING DOUBLE-POLY CAPACITORS USING A FOCUSED ION BEAM MACHINE

IP.com Disclosure Number: IPCOM000008263D
Original Publication Date: 1997-Sep-01
Included in the Prior Art Database: 2002-May-31
Document File: 4 page(s) / 260K

Publishing Venue

Motorola

Related People

Wayland Seifert: AUTHOR [+4]

Abstract

Focused Ion Beam (FIB) machines have found extensive use in the semiconductor industry in the area of post processing analysis or failure analysis (FA). Frequently, the analog circuits on early samples of an integrated circuit require a trim because of unanticipated process variations. Having the ability to trim a capacitor's top poly without generating new masks would allow verification of the trim while saving valuable time and money.

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@ MofoRoLA

Technical Developments

METHOD OF CUTTING DOUBLE-POLY CAPACITORS USING A FOCUSED ION BEAM MACHINE

by Wayland Selfert, David Perrin, Carlo6 Grewem, Mat Ryblckl

BACKGROUND

  Focused Ion Beam (FIB) machines have found extensive use in the semiconductor industry in the area of post processing analysis or failure analysis (FA). Frequently, the analog circuits on early samples of an integrated circuit require a trim because of unanticipated process variations. Having the ability to trim a capacitor's top poly without generating new masks would allow verification of the trim while saving valuable time and money.

METHOD OF CUTTING POLY

  By skillfully combining a FIB machine cut and a chemical etch allows double-poly capacitors to be trimmed post processing. This invention, depicted in the four figures below, combines both of these steps to successfully and repeatably cut double-poly capacitors.

  After selecting the portion of the double-poly capacitor that must he removed, a small trench is cut through all surface layers above the double-poly capacitor using a focused gallium ion beam (see Figures 1 and 2). The depth of the trench is cut just to the surface of the top plate of the double-poly capacitor using an end-point measurement which is available on most FIB machines. The length of this trench must extend beyond the edges of the top poly plate to prevent shorting of the poly plates or an incomplete cut. The next step is to chemically etch away any top poly that remains and some of the inter-poly oxide as shown in Figure 3. In this described procedure, a one second room tempera- ture Wright Etch (described in the Appendix below) was used, however other etch solutions may work as well. A Wright Etch was chosen because of its preferential etching of poly-silicon and not the interpoly oxide. This allowed etching of the top plate without etching through the interpoly oxide into the bottom plate. As a final step, a rinse with

de-ionized water is applied to clean any remaining etch solution from the cut. The final partitioned double-poly capacitor is shown in Figure 4.

  Alternative methods of cutting the initial trench could be applied to achieve various results such as finer or higher accuracy trims. The etch solution is not limited to the Wright Etch composition described below, but could be composed of any variety of chemical etches used in the industry today. Even the more recently developed "dry" etches or plasma etches could be applied. By varying the...