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Measuring the Resistance of Very Thin Layers

IP.com Disclosure Number: IPCOM000034048D
Original Publication Date: 1989-Jan-01
Included in the Prior Art Database: 2005-Jan-26
Document File: 3 page(s) / 33K

Publishing Venue

IBM

Related People

Euen, W: AUTHOR [+2]

Abstract

The proposed method is based on the four-point method for Rs measurement and uses a very thin oxide layer on top of the implanted layer to be characterized, so that the points of the needles penetrate the center of the thin layer to a particular depth. The parameters of implantation in the dose range of about - 1 E 13 cm-2 are controlled by measuring the layer resistance of the implanted wafer after an activation anneal step. The dose range, for which this measuring method is suitable, may be extended to about - 2 E 11 cm-2, if extremely low-doped substrates of about 100 to 400 ohm cm are used and surface states are prevented from forming by cleaning the surface following the activation anneal step. However, the dose range may only be extended for lower doses if the implantation energy for boron is, for instance, - 50 keV.

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Measuring the Resistance of Very Thin Layers

The proposed method is based on the four-point method for Rs measurement and uses a very thin oxide layer on top of the implanted layer to be characterized, so that the points of the needles penetrate the center of the thin layer to a particular depth. The parameters of implantation in the dose range of about - 1 E 13 cm-2 are controlled by measuring the layer resistance of the implanted wafer after an activation anneal step. The dose range, for which this measuring method is suitable, may be extended to about - 2 E 11 cm-2, if extremely low-doped substrates of about 100 to 400 ohm cm are used and surface states are prevented from forming by cleaning the surface following the activation anneal step. However, the dose range may only be extended for lower doses if the implantation energy for boron is, for instance, - 50 keV. Correspondingly higher limits exist for arsenic and phosphorus. At lower energies, the needles of the four- point measuring head penetrate the implanted layer, so that the resistance of the substrate but not that of the implanted layer is measured. For producing a monitor for characterizing low implantation doses of about - 1 E 12 cm-2 and energies which are equally low, a method is proposed which does not remove the oxide layer prior to measuring the layer resistance. By thus simplifying the production of the monitor, the following advantages are obtained:
1. The points of the measuring head penetrate the

implanted

layer less deeply, avoiding faulty measurements. 2. There is no time-dependent change of the layer resistance

by the formation of surface states, since the

surface is passivated by the oxide. 3. The time elapsing between implantati...