Carrier illumination (CI) is a photoelectrothermal modulated optical reflectance (PMOR) technique for the one dimensional active doping profile characterization of ultrashallow junctions. The specificity of CI as a PMOR technique is to exploit the probe differential reflectance nonlinearity as a function of the pump laser irradiance . The probe differential reflectance as function of the pump power is called a power curve, and its interpretation provides information on the underlying active doping profile. In a previous work [F. Dortu et al., J. Vac. Sci. Technol. 24, 375 (2006)], the independent extraction of the active doping concentration and the metallurgical junction of a chemical vapor deposited boxlike profile was based on two features of the power curve, namely, the inflexion power and the signal at end of range power. However, this method suffers from the difficulty to extract accurately the second derivative and has a limited extraction range (, ). In the present work, we present a method making use of the power curve’s first derivative at low and high illumination powers. This method, in principle, allows a much broader extraction range (, ) provided that the signal time dependence due to the native silicon oxide charging under intense illumination is taken into account properly. The present work is supported by a two-layer diffusionless nonlinear analytical model, which provides the basic insights of the method, and three dimensional axisymmetric numerical simulations in the framework of the drift-diffusion equations. A procedure to remove the time dependent charging effect is also presented.
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The evaluation of the analytical solution of Eq. (6) is not straightforward due to numerical errors caused by the large range spanned by the polynomial coefficients. An arbitrary precision software is preferably used.
Note that, in principle, one could use the signal itself instead of the derivative but as the signal always tends toward zero at low power (contrary to the derivative), the precision of the extraction would be extremely low.
Although the depletion region completely vanishes due to the high carrier injection level, the electric field remains nonzero at the metallurgical junction and plays an important role in the carrier exchange between the doped layer and the substrate
The values in microvolts used in Ref. 13 have to be divided by in order to obtain the present . multiplies the root mean square value returned by the lock-in amplifier in order to obtain the first harmonic signal amplitude. is a gain applied to the detector signal for measuring the first harmonic. When the signal dc part is measured no pregain is applied
Least-squares fitting with three breakpoints, more breakpoints leading to spurious oscillations.
