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Contactless Photovoltage VS Bias Method for Determining Flat-Band Voltage

IP.com Disclosure Number: IPCOM000099535D
Original Publication Date: 1990-Feb-01
Included in the Prior Art Database: 2005-Mar-15
Document File: 4 page(s) / 123K

Publishing Venue

IBM

Related People

Fung, MS: AUTHOR [+2]

Abstract

A tool has been developed to measure fixed and mobile charges in semiconductor monitor wafers without the need for metal contacts. The contactless method provides for the real measurement of charges for all types of insulators in semiconductors and is independent of insulator thickness and integrity. (Image Omitted)

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Contactless Photovoltage VS Bias Method for Determining Flat-Band Voltage

       A tool has been developed to measure fixed and mobile
charges in semiconductor monitor wafers without the need for metal
contacts.  The contactless method provides for the real measurement
of charges for all types of insulators in semiconductors and is
independent of insulator thickness and integrity.

                            (Image Omitted)

      The proposed method is based on the conventional capacitance vs
voltage (C-V) method for charge measurements (1). It also examines
silicon surface bandbending (Ds) as a function of surface potential
(Vs) be it oxide, nitride, polyimide, and obtains the flat-band
voltage (Vfb) of interest defined as the value of Vs corresponding to
Ds = 0.

      For conventional C-V, a calculated flat-band capacitance is
used as the indicator of Ds = 0.  This proposal uses the behavior of
surface photovoltage (SPV) as the zero bandbending indicator.  When a
silicon surface is neither accumulated, depleted or inverted, no
silicon surface field will exist to separate photo-induced
electron-hole pairs.  Hence, SPV will become zero at flat-band and
undergo an easily recognizable phase change on either the
accumulation or depletion side of flat-band (2,3).

      The significant aspect of the photovoltaic method proposed is
its being contactless.  An oxide monitor wafer 1(Fig. 1) with its
oxide layer 2 is held on a thermal vacuum chuck 3 which resides on a
slide 4.  The slide alternately moves along a slide track 5 to
position the wafer at the bias station 6 or measurement station 7.
The bias station is equipped with an ionization chamber 9 from which
ionized room air is directed toward the wafer.  Vs is varied by
charging the dielectric of interest across an air gap with a charging
bias 11 and the ionized air.

      At the measurement station 7 a transparent metallic electrode
pickup plate 12 is located above the oxide surface 2.  The plate is
connected to an ultra-high input impedance metal oxide semiconductor
field-effect transistor (MOSFET) 13.  A mechanical vibrator 14 sets
the electrode into motion, and Vs is determined as the value of null
bias supply voltage 15 required to null the resultant AC signal at
the output of the MOSFET buffer.  The mechanical vibration is
switched off, and a pulsed illumination source 16 traveling through a
light pipe 17 is used to generate electron-hole pairs.  These are
separated by the surface field of the silicon and result in an SPV 18
when the silicon surface is not in...