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Monitor for Surface Potentials to Be Used for Ion Implantation

IP.com Disclosure Number: IPCOM000046424D
Original Publication Date: 1983-Jul-01
Included in the Prior Art Database: 2005-Feb-07
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Elsner, G: AUTHOR [+4]

Abstract

The accurate compensation of potentials on SiO2 surfaces is determined by analyzing the shift of lithium or sodium doping profiles under the influence of surface charges.

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Monitor for Surface Potentials to Be Used for Ion Implantation

The accurate compensation of potentials on SiO2 surfaces is determined by analyzing the shift of lithium or sodium doping profiles under the influence of surface charges.

To compensate for charge build-up on isolating surfaces during ion implantation, the surface is conventionally flooded by an additional electron beam; this method is, however, insufficient for structures with thin SiO2 layers, where even a few remaining volts of surface potential cause dielectric breakdown.

To adjust the electron beam for improved compensation, it is proposed to use a monitor wafer with an SiO2 structure identical with the wafers to be implanted and to generate in the monitor wafer a well-defined concentration profile of lithium or sodium ions by ion implantation (at a small dose of about l0l2/cm2 and to a small depth of about 5 nm). These ions have a high mobility even at moderate temperatures (about 50OEC), so that small surface potentials cause them to migrate to the SiO2/Si boundaries. The resulting Li+ or Na+ concentration profile is analyzed by secondary mass ion spectroscopy (SIMS) or capacitance measurements, using Hg contacts.

Optimum compensation conditions are determined by varying the energy and current of the compensating electron beam as well as its impact area until no further shift in the ion concentration profile can be detected. Surface potentials can thus be reduced to less than l V over large area...