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Investigation of flat-band voltage distributions over the gate area of Al-SiO2-Si structures

Krzysztof Piskorski ,  Henryk M. Przewłocki 

Institute of Electron Technology (ITE), al. Lotników 32/46, Warszawa 02-668, Poland

Abstract

Extraction of MOS system parameters is very important in modeling and device optimization for modern integrated circuits. Having a possibility to make very accurate measurements of some electrical parameters of MOS systems, it is possible to use these results as a diagnostic tool on technological line for control purposes.

In this research we have developed a new, high precision photoelectric measurement method of the local flat-band voltage VFB values in MOS structures. This method, called SLPT (Scanning Light Pulse Technique) consists in scanning the whole gate area with the small light spot, which allows determination of the local VFB value distribution over the gate area. It was found that in Al-SiO2-Si structures the local values of VFB in the central part of the metal gate are higher than at gate corners. This characteristic non-uniform, dome-like shape of VFB(x,y) distribution over the gate area was obtained for many MOS structures made in different technological processes.

To confirm these results the measurements of the VFB voltage by classical C(V) characteristics method (without any illumination) were performed. It turned out that VFB values (for the entire gate area) decrease monotonically with the R-ratio of the gate perimeter to gate area. Such behavior confirms that local VFB values in the vicinity of gate edges are lower than in the central part of the gate.

In our previous investigations we proved that the effective contact potential difference fMS, and the barrier height at the metal gate – dielectric interface EBG, both have a similar dome-like shapes of distributions over the gate area. It supports our hypothesis that the mechanical stress existing in the oxide under the metal gate has a dominating influence on the shape of distributions of the above mentioned electrical parameters.
 

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Related papers
  1. Development of a photoelectric method to measure the MOS system flat-band voltage

Presentation: Poster at E-MRS Fall Meeting 2008, Symposium B, by Krzysztof Piskorski
See On-line Journal of E-MRS Fall Meeting 2008

Submitted: 2008-05-15 11:52
Revised:   2009-06-07 00:48