Browse Prior Art Database

Method for Characterizing Low Concentration Ion Implantations

IP.com Disclosure Number: IPCOM000052190D
Original Publication Date: 1981-May-01
Included in the Prior Art Database: 2005-Feb-11
Document File: 3 page(s) / 76K

Publishing Venue

IBM

Related People

Elliott, BJ: AUTHOR [+4]

Abstract

Ion implantation has taken the place of many standard diffusions in hig density large-scale integrated circuit process lines. The advantages of control, low concentration and low junction depth profiles are the key to the success of these processes.

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Method for Characterizing Low Concentration Ion Implantations

Ion implantation has taken the place of many standard diffusions in hig density large-scale integrated circuit process lines. The advantages of control, low concentration and low junction depth profiles are the key to the success of these processes.

The 10/12/-10/13/ dose levels, resulting in high sheet resistivities and shallow junctions, are well beyond the capability of the standard characterization approaches. A capacitively coupled time domain reflectometer (TDR) method has been developed to nondestructively characterize such low doping levels.

The method combines two classical measurement techniques: fast pulse, baseband time domain reflectometry and spreading resistance. A picosecond pulse TDR is combined with a special coaxial probe to measure the local resistivity in the region of the semiconductor sample that is immediately adjacent to the probe's surface. Provided the risetime of the TDR is short enough, and provided the coupling capacitance is large enough, i.e., close spacing of probe to surface, about 5 Mum, is maintained, the initial value of the reflected wavefront will be proportional to the reflection coefficient of the sample which terminates the transmission line. In fact, the spreading resistance, Rho over 4a will be related to the reflection coefficient, h, through the transmission line formula H = Z(L)-Z(0) over Z(L)+Z(0) where Z(0) is the transmission line impedance, a is the radius of the inner electrode of the coaxial

probe, in cm,

Z(L) approx. equal to Rho over 4a is the load impedance

except for minor geometrical corrections, and

Rho is the bulk resistivity in ohm-cm.

The TDR...