Historical overview of silicon crystal pulling development

The first silicon single crystals were grown by crucible pulling in 1950, 2 years after the invention of the transistor, which was first made from germanium. Two years later, the crucible-free float zone pulling was invented. In this stage, the low purity of the starting polysilicon for the crystal pulling was the biggest problem. A great help in the purification of polysilicon were the very low distribution coefficients of most of the impurities. This effect was used in the refining of silicon by repeated crucible-free zone melting (zone refining). However, boron cannot be sufficiently removed by this technique. Since 1961, the raw silicon is first transformed into a silane, then the silane is purified by distillation and adsorption, and finally retransformed to elemental silicon by chemical vapor deposition. This purification technique yields a polysilicon that needs no further purification by zone refining. A big step forward was the invention of the dislocation-free crystal growth in 1958, an absolute necessity for the manufacturing of highly integrated devices. The first crystals were small with about 0.5′′ diameter and about 100 g weight. Predominantly for economical reasons, the size of the crucible pulled crystals increased stepwise about every 4 years to 12′′ diameter (for 300 mm wafers) and to 250 kg in weight until today. The maximum diameter of float zone grown crystals is only 6′′ at present, because there was no need for larger float zone-Si diameters in the past. But this has changed recently.