Kinetics and thermodynamics constraints in Pt gettering by P diffusion in Si

Abstract

We have explored the mechanisms underlying the gettering of Pt atoms dissolved in crystalline Si. By using Pt implantation at different fluences followed by a thermal process at 970 °C for 5 h we were able to prepare crystalline silicon wafers containing a uniform Pt concentration in the range 2×1012–2×1014 atoms/cm3. Subsequently, a heavily doped n-type region was produced on one side of the wafer by P diffusion at 900 °C. Following this deposition process we have studied the kinetics of Pt gettering to the P-doped region in the temperature range 700–970 °C and for annealing times ranging from 30 min to 48 h. Lifetime measurements by means of a contactless technique were used to detect the depletion of Pt in the bulk of the wafer due to the gettering process. The large range of initial Pt concentrations that we have explored allowed us to identify and separate the kinetics and thermodynamics constraints that determine the gettering efficiency and to propose a phenomenological model for the gettering of Pt. In particular, it has been found that the kinetics of the gettering process are driven by the dissolution of immobile substitutional Pt atoms into interstitial sites. This process is assisted by Si self-interstitials and characterized by an activation energy of 0.4 eV. Moreover, the equilibrium distribution of Pt is thermodynamically determined by a segregation coefficient of the Pt atoms between the gettering sites and the silicon matrix. This segregation coefficient, and hence the gettering efficiency, decrease when the temperature of the gettering process is increased and is described by an activation energy of 2.5 eV.

Damage engineering and proximity gettering of metals studied by electrical measurements on Pt-contaminated diodes

“…A possible explanation of this discrepancy could be Pt segregation in the phosphorus-doped region. Indeed, Pt segregation in the P-doped region created by POCl 3 backside deposition has been observed during lifetime engineering in Pt-doped power devices [17,18]. Assuming that only 3% of the Pt dose is segregated in the P-doped region (≈1 µm), the Pt concentration would rise from 10 14 cm −3 to 1.5×10 15 cm −3 , with a consequent decrease of τ R from 0.5×10 −6 s to 0.025×10 −6 s [17].…”

A Review of Platinum Diffusion in Silicon and Its Application for Lifetime Engineering in Power Devices

“…It can be used to further tailor the platinum profiles and the charge-carrier lifetime adjustment, and thereby to further optimize the performance of silicon power devices in terms of soft switching. [1,2] In this article, we review how the platinum is introduced into silicon power devices, how the relevant processes are modeled, and how the calibration of these models has made contributions to basic research, including an establishment of more narrow limits for the equilibrium concentrations of vacancies and self-interstitials in silicon, as well as an improved parameterization of the transport capacity of interstitial platinum.…”

“…σ n and σ p denote the capture cross sections for electrons and holes, and v n and v p the respective thermal velocities. According to Coffa et al, [2] the first fraction takes a value of 1.33 Â 10 7 s cm À3 . How V f is calculated is described by, for example, Lutz et al [3] Lifetimes of 100 ns to a few 100 ns are expected for components with platinum (symmetrical U-shaped profiles), whereas components without platinum have lifetimes up to some 100 μs, depending of course on the wafers used.…”

Procesos de extracción de impurezas contaminantes y aplicación a estructuras de células solares

“…-En el caso del oro y del platino, que son impurezas sustitucionales que difunden por mecanismo de expulsión, se observa que el proceso de extracción es reversible (tras un proceso de extracción, recocidos a temperaturas mayores redistribuyen el metal hacia el volumen de la oblea, recocidos a temperatura moderada lo vuelven a confinar en la capa rica en fósforo) [74], [80], [82].…”

“…Hay un amplio acuerdo en considerar el mecanismo de extracción por fósforo como un mecanismo inducido por segregación, en el que la extracción se produce durante el proceso de alta temperatura y no durante el enfriamiento posterior. Así lo comprueban Cofia et al [82] para la extracción de platino, midiendo la misma eficiencia de extracción para procesos con tasa de enfriamiento de 3°C/min y de 30°C/min. Sin embargo, afirman que en el caso de otras impurezas, como el cobre y el hierro, la extracción ocurre durante el enfriamiento, debido a la alta dependencia de sus solubilidades sólidas con la temperatura y al alto valor de sus difusividades, incluso a baja temperatura.…”