Carrier lifetime of silicon wafers doped by neutron transmutation

Contactless techniques of infrared and microwave absorption by free carriers for the monitoring of silicon structures are described. Theoretical principles of photoconductivity decay analysis and methodology for the determination of recombination parameters are given for both homogeneous and non-homogeneous excess carrier generation. Different approximations (the methods of decay amplitude-asymptotic lifetime analysis, the simulation of the whole decay curve, the variation of effective lifetime with wafer thickness and the asymptotic lifetime measurement for stepwise varying parameters in layered structure) corresponding to real experimental conditions for various structures and treatments of materials, which are important for microelectronics, are discussed.The determined recombination parameters in the range of bulk lifetime 0.0006-230 µs, velocity of surface recombination 600-5 × 10 4 cm s −1 and diffusion coefficient 0.015-18 cm 2 s −1 are illustrated for Si wafers obtained by various doping and preparation processes. The necessity to consider carrier trapping effects and nonlinear recombination processes is demonstrated by the analysis of experimental results obtained at different excitation levels for carrier concentrations in the range 10 13 -10 18 cm −3 . The possibility of extracting the parameters of the traps (with activation energy values 0.16 ± 0.02 eV, 0.20 ± 0.02 eV and 0.28 ± 0.04 eV) from the temperature-dependent asymptotic carrier lifetime measurements is illustrated for neutron transmutation doped wafers.

Section: Trapping Impactmentioning

confidence: 95%

Investigation of recombination parameters in silicon structures by infrared and microwave transient absorption techniques

Gaubas

Kaniava

Vaitkus

1997

“…In other words, Auol/u and Auo2/a denote the the injection levels of minority carriers for weak and strong illumination intensities. These simple relationships of equation ( 4) are applicable to sample wafers of high-quality single crystal free of trapping centres [9]. However, it is known that the effect of trapping centres can be eliminated by a steady background light illumination [2].…”

Section: (3)mentioning

confidence: 99%

Contactless measurement of bulk carrier lifetime in thick silicon wafers by an induced eddy current

Maekawa¹,

Fujiwara²,

Yamagishi³

1995

Self Cite

In order to examine the bulk carrier lifetime in a silicon single crystal, a contactless method of determining the carrier lifetime for wafers up to 20 mm thick has been developed. This method is based on the measurement of the photoconductive decay of the eddy current induced in a wafer by a high-frequency magnetic flux. The experimental results show that the maximum values of measurable bulk carrier lifetime are longer than the known values for high-quality silicon crystals. The measurable maximum values are comparable with those satisfying the American Society for Testing and Materials designation, i.e. 11 ms for p-type and 32 ms for n-type wafers, The minimum value of measurable bulk carrier lifetime is found as a function of the wafer thickness. This functional dependence of the minimum value on the wafer thickness Is also examined and discussed in some detail.

“…To reduce the impact of these radiation defects on the carrier lifetime and on the mobility, various annealing treatments are carried out after neutron irradiation. It has been shown [4] that different processes cause recovery of the conductivity or carrier lifetime due to the removal of defects within the bulk of the wafer and on its surface. So, the separation of the impact of the surface and bulk defects on the wafer quality is important.…”

Section: Introductionmentioning

confidence: 99%

Study of recombination properties of neutron transmutation doped silicon wafers

Gaubas

Vanhellemont

Simoen

et al. 1997

The asymptotic lifetime dependency on temperature, excitation depth and intensity, and on continuous-wave bias illumination have been investigated for the simultaneous determination of the recombination parameters to characterize neutron transmutation doped silicon by the microwave absorption transient technique. These experiments also reveal trapping effects. Defects, which are characterized by activation energies of 0.16 ± 0.02 eV, 0.20 ± 0.02 eV and 0.28 ± 0.04 eV, are controlling both bulk and surface recombination. The traps E C − 0.23 eV, E C − 0.28 eV and E C − 0.53 eV, which are revealed by deep-level transient spectroscopy, confirm the presence of these defects.