The low-temperature doping of silicon by radiation-induced diffusion

Abstract

Low-temperature doping of silicon by the radiation-induced diffusion (RID) is investigated theoretically and experimentally. It is estimated that RID of impurities diffusing on interstitial sites in silicon can occur in accordance with impurity recharging models. The possibil .ity of Pd or Co doping of silicon at 46 "C using CoB0 y-radiation (1800 Rs-') is confirmed experimentally.Es wird die Tiefteniperaturdotierung von Silizium durch strahlungsinduzierte Diffusion (RID) theoretisch und experimentell untersucht. Dabei wird angenommen, dal3 RID von Storstellen, die iiber Zwischengitterpliitzen diffundieren, im Einklang mit Storstellenumladungsmodellen auftreten kann. Die Moglichkeit einer Pd-oder Co-Dotierung von Silizium bei 45 "C mit CoGo-y-Strahlung (1800 Rs-l) wird experimentell bestatigt. Regularities of RID in SiliconRadiation-induced diffusion (RID) in silicon has been observed as well a t high energy radiation as a t subthreshold irradiation [l to 101. Recently systematic investigations of RID [8 to lo] have shown the following:1. The integral effect of impurity transport by RID a t temperatures from 77 to 400 K is equivalent to thermal diffusion a t 500 to 1300 K. 2.The rate of gold and zinc diffusion is independent of the irradiation dose. During RID of indium or gallium the diffusion rate increases with dose.3. With Co* y-irradiation or low energy electron irradiation the gold diffusion rate in p-silicon is about one order of magnitude larger than in silicon.4. The gold RID coefficient depends on the defect concentration in silicon [ 111. For example, the gold RID coefficient increases with the concentration of dislocations.6. RID in silicon depends weakly on the irradiation temperature. The observed dependence [8] is caused by the rate of production and annealing of Frenkel defects.6 . I n silicon the dependence of RID on irradiation flux density I can be written as D N I" and N , -Ik, where N , is the subsurface impurity concentration. The values of n and k depend on the experimental conditions [8].The experimental data on low-temperature RID permit to make conclusions about the impurity migration mechanism. It is estimated, that Au, Zn, Cu [B], Ki, Pd [12], and Co migrate in silicon by a dissociative mechanism, whereas In and Ga are mobile via a vacancy mechanism, as presented in [13]. TheoryExperimental values of RID coefficients are in agreement with theoretical models [14 to 221, which take into account the influence of recharging of impu-29 physlcs (a) 38/2