Dao, T.; Tamminga, Y.; Tak, van der, K.; Roozeboom, F.; Augendre, E.

Fluorine-enhanced boron diffusion in germanium-preamorphized silicon J. Appl. Phys. 98, 073521 (2005); 10.1063/1.2084336Recrystallization, redistribution, and electrical activation of strained-silicon/Si 0.7 Ge 0.3 heterostructures with implanted arsenicWe have studied impurity redistribution due to low-temperature crystallization of amorphous silicon. Many impurities move ahead of the amorphous-crystalline interface and relocate closer to the surface. In general, redistribution is more likely at high impurity concentrations. By investigating a wide range of concentrations for indium, lead, and antimony, we demonstrate the direct correlation between the magnitude of this redistribution effect and the impurity metastable solubility limit in crystalline silicon. At low concentrations, it is less likely for impurities to redistribute. However, in this regime we show that indium experiences concentration-independent segregation, and that boron profiles are also affected by the crystallization process.

No abstract

The use of silicon substrate preamorphization in ultrashallow junction formation has increased in recent years. The reduction of channeling during impurity implantation, coupled with higher-than-equilibrium metastable solubility levels, produces scaled junctions with low resistances. However, a number of physical phenomena arise that must be considered for proper impurity profile and device optimization.With respect to impurity solubility advanced annealing techniques such as solid-phaseepitaxial-regrowth (SPER), flash, and laser annealing, can place impurity atoms on substitutional sites in the silicon lattice to extremely high concentrations when combined with preamorphization. In this context there is a relationship between the equilibrium distribution coefficient and metastable solubility. The long-established equilibrium distribution coefficient of an impurity, extracted in the liquid to solid phase transformation, can make a prediction of metastable solubility after transformation of amorphous silicon into crystalline silicon during SPER, flash, and laser annealing.With respect to impurity redistribution the significant effects can be split into 3 categories, namely before, during, and after recrystallization. Before recrystallization impurity diffusion in the amorphous region may occur. Boron is particularly susceptible to this effect, which is very significant for the formation of p-type junctions. During recrystallization many impurities move ahead of the amorphous-crystalline (a/c) interface and relocate closer to the surface. In general redistribution is more likely at high impurity concentrations. For lowtemperature SPER there is a direct correlation between the magnitude of this redistribution effect and the impurity metastable solubility. After recrystallization, with SPER, flash, and laser annealing commonly leaving residual damage in the silicon substrate, interstitial-diffusers are especially vulnerable to preferential diffusion toward the surface, where impurity atoms may be trapped, ultimately leading to a more shallow profile. METASTABLE SOLUBILITYIn the 1940s & 1950s many equilibrium impurity solubilities in silicon were determined experimentally. In a review paper by Trumbore [1] this body of work is nicely summarized, and the graph therein of impurity solubility versus temperature is frequently reproduced in textbooks. Above-equilibrium levels of solubility, allowing for advanced device scaling and greater freedom for process optimization, are known to be generated by SPER, flash, and laser anneal.