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Bulk Lifetime Measurements in Heavily Doped Substrates

IP.com Disclosure Number: IPCOM000120135D
Original Publication Date: 1991-Mar-01
Included in the Prior Art Database: 2005-Apr-02
Document File: 3 page(s) / 76K

Publishing Venue

IBM

Related People

Paz, O: AUTHOR [+3]

Abstract

Present methods of measuring lifetime cannot be used when the doping concentration exceeds 5 1017 cm-3 . The depletion layer is too shallow for MOS lifetime measurements and even the SPV (surface-photo-voltage) method is limited in this range.

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Bulk Lifetime Measurements in Heavily Doped Substrates

      Present methods of measuring lifetime cannot be used when
the doping concentration exceeds 5 1017 cm-3 .  The depletion layer
is too shallow for MOS lifetime measurements and even the SPV
(surface-photo-voltage) method is limited in this range.

      The method that we developed is based on generation of excess
carriers in the substrate by electron beam (generated by a SEM)
excitation.  The generated carriers diffuse to the collecting
junction that can be a Schottky barrier diode, or a P-n junction
(implanted or diffused).  The substrate concentration does not have a
limiting effect on this operation by simply determining the injection
level (high or low).

      To arrive at a lifetime value, the number of collected carriers
is determined from the ratio of two currents:  the collection current
and the sample current (Fig. 1).  The number of collected carriers
can also be calculated.  It is a function of the diffusion length
(and, therefore, the lifetime).  The lifetime can be determined by
adjusting until:
      N calculated = N measured

      Fig. 2 is an illustration of two structures that can be used to
characterize the memory epi program.  In Fig. 2A the epi is left on
and the lifetime is measured in both the epi layer and the substrate.
Or the substrate alone can be measured (Fig. 2B).  In this case a
diffused or implanted P-n junction is required.

      Lifetime was meas...