Recasting and heat treatment can be used to move the dislocations, vacancy clusters and impurities to areas where the do less harm than in the original metal. The term defect engineering is used for this activity, and it includes:

• Addition of gas during casting, to ensure a uniform distribution of dislocations and vacancies.
• Casting with application of thermal gradients, to steer the direction of directional solidification, for the same reason.
• Heat treatment to assemble vacancies.
• Additions of alloying elements that will form particles together with impurities during a subsequent heat treatment. The particles form on dislocations and grain boundaries, and are less harmful than elements in solid solution.
• Etching in (HF+HNO3) followed by heat treatment of wafers in gas (POCl3), to form particles that withdraw fast diffusing elements from the interior of the wafer, followed by another etching of the surface (so called phosphorous gettering).
• Addition of a surface aluminium layer, and heat treatment so that fast diffusing impurities go to the aluminium layer, while the slow-diffusing aluminium stays in place (so called aluminium gettering).
  

In the SINTEF/NTNU “Heliosi lab”, there is a state of the art Crystalox furnace for directional solidification of multi-crystalline silicon ingots. Directional casting from the bottom (with a thermal gradient in the melt) collects most of the impurities in the top of the casting.

There are some interesting new literature and patents about adding special trace elements to the liquid silicon and subsequently heat treating the solidified silicon above the temperature usually used for cell processing. The point of the heat treatment is to gather the impurities in particles together with the added trace elements on dislocations and cell boundaries, instead of having them in solid solution