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Apparatus for Verifying Lifetime Profiles in 5" Wafers by Very Low Level MOS Leakage Measurements

IP.com Disclosure Number: IPCOM000047201D
Original Publication Date: 1983-Oct-01
Included in the Prior Art Database: 2005-Feb-07
Document File: 2 page(s) / 52K

Publishing Venue

IBM

Related People

Paz, O: AUTHOR [+2]

Abstract

An apparatus for measuring low level oxide leakage in MOS capacitors is described. This measurement is useful in verifying generation lifetime depth profiles that are used to determine the depth of the defect-free zone (DFZ) in Czochralski-grown wafers. This method that is aimed at characterizing the silicon substrate underneath the oxide presupposes leakage-free oxide, since a leaky oxide may lower the lifetime and distort the lifetime profile in the substrate. The technique of determining the depth of the DFZ using lifetime depth profiling entails plotting lifetime vs. depletion layer width of a MOS capacitor (Fig. 1). A depth profile 1 was produced by pulsing the gate of a MOS capacitor, located in the area of interest, with progressively larger voltage pulses.

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Apparatus for Verifying Lifetime Profiles in 5" Wafers by Very Low Level MOS Leakage Measurements

An apparatus for measuring low level oxide leakage in MOS capacitors is described. This measurement is useful in verifying generation lifetime depth profiles that are used to determine the depth of the defect-free zone (DFZ) in Czochralski-grown wafers. This method that is aimed at characterizing the silicon substrate underneath the oxide presupposes leakage-free oxide, since a leaky oxide may lower the lifetime and distort the lifetime profile in the substrate. The technique of determining the depth of the DFZ using lifetime depth profiling entails plotting lifetime vs. depletion layer width of a MOS capacitor (Fig. 1). A depth profile 1 was produced by pulsing the gate of a MOS capacitor, located in the area of interest, with progressively larger voltage pulses. As a result, the depletion layer widens, effectively changing the depth of the substrate where the lifetime is being measured. As the depletion layer moves away from the surface, it approaches a region in the bulk of the substrate known to contain a high density of defects and the lifetime rapidly declines. This region marks the end of the defect-free zone. The depth at which the lifetime reduces to 1 msec or less is used to define the DFZ width 2. Since the depth of the DFZ often exceeds 10 mm, gate voltage levels of 100 v and higher are needed in order to widen the depletion layer sufficiently. The high e...