Changes in the silicon thermal donor energy level as a function of anneal time

Abstract

A deep level transient spectroscopy (DLTS) study of 450 °C annealed Czochralski silicon is presented. Particular attention is given to the relative concentrations of the two thermal donor energy levels Ec−0.15 eV and Ec−0.07 eV. Relative concentrations of the Ec−0.15 eV and Ec−0.07 eV energy levels indicate that there are fewer of the more shallow level. Also there is anomalous motion of the energy levels with anneal time indicating the gradual accretion of the thermal donor complexes. The suggested correlation with infrared absorption (IR) studies is that the nine double-donor defects found by IR form sequentially in the material and the DLTS energy level obtained merely reflects the most abundant of the nine distinct complexes. This indicates that the nine thermal donors are formed by the addition of some constituent to an earlier complex. As the thermal donor complex accretes the associated energy levels change, moving to shallower energies as anneal time increases. These findings tend to contradict the simple thermal donor models.

What Do We Know about Hydrogen-Induced Thermal Donors in Silicon?

“…30 It has been noted in the past that there can be a difference between the free carrier concentration in CZ material heat treated around 450°C to create OTDs and the resulting concentration derived from DLTS, the latter method yielding lower values in many cases. 5,30,[37][38][39][40] Especially when the OTD concentration is higher than the background doping concentration, capacitance DLTS will underestimate the true OTD concentration for several reasons. One is the fact that the OTDs are attractive deep levels for electrons, so that they exhibit a Poole-Frenkel shift of the peak position to lower temperatures ͑en-ergies͒ with increasing electric field.…”

Evolution of shallow donors with proton fluence in n-type silicon

“…It is worthwhile to note the difference between the actual donors and the shallow thermal donors found in Czochralsky ͑Cz͒ silicon after annealing at about 450°C. 6 Since the former are due to a combination of hydrogen implantation and post thermal annealing at temperatures higher than or equal to 300°C, the latter are the result of annealing effects and are related to the oxygen complex. 7,8 It is therefore obvious that the actual shallow donors are not just a manifestation of the best known oxygen thermal donors, but are induced by the isolated hydrogen atoms at a specific lattice site or the hydrogen-point defect.…”

What do We Know About Hydrogen-Induced Thermal Donors?

“…Unfortunately, this simple picture is not supported by the DLTS results on the same material, demonstrating OTD concentrations which amount to only 20 % of the added shallow donors [30]. It has been noted in the past that there can be a difference between the free carrier concentration in Cz material heat treated around 450 o C to create OTDs and the resulting concentration derived from DLTS, the latter method yielding lower values in many cases [5,30,[37][38][39][40]. Especially when the OTD concentration is higher than the back-ground doping density, capacitance DLTS will underestimate the true OTD concentration for several reasons.…”