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Cz process operates with two opposite rotations (melt and seed's rotations). How these rotations prevent growing imposed by other facets' directions (Other than that perpendicular to the axis of rotation-of seed?

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    $\begingroup$ Do you mean to ask whether the rotation prevents crystal growth in directions along the axis of rotation, or do you know that this is the case, and you are interested in why this is the case? Please clarify your question. $\endgroup$ – flaudemus Feb 19 at 8:20
  • $\begingroup$ Yes why it does exclusively in the direction of axis? $\endgroup$ – Eddie Feb 19 at 12:28
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Any connection between the (ingot, crucible) rotation rates and crystal growth direction is a bit indirect. The first question to ask is why there is rotation at all. As it turns out, the rotation(s) perform two very important tasks, one of which is what your question is about.

  1. The major problem to be resolved in crystal growth is maintaining a constant temperature across the face of the crystal. The enthalpy of crystallization has to be removed from all across the interface, and this is a mixed thermal diffusion and fluid flow problem. The rotation speeds of the ingot and crystal are adjusted to enhance the fluid mixing and even out the thermal profile. Keeping the interface generally flat means that the ingot grows in the appropriate direction (which is what you asked about).

  2. The second major task is closely related, and that is maintaining an even distribution of impurities (mainly the dopants, but C and O also) across the diameter of the wafer. This is one reason that all large (150mm and larger) silicon wafers are doped with boron - it distributes better and results in more uniform doping across a wafer, quite important for modern CMOS technology. The uniform incorporation of C is critical as well, since it is required for mechanical strength (float zone silicon, low in carbon, cannot support itself in a hot furnace anneal at current wafer diameters).

An interesting read is Fumio Shimura's book 'Semiconductor Silicon Crystal Technology' (Academic Press, 1989).

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  • $\begingroup$ Oh! this is great I appreciate it. $\endgroup$ – Eddie Feb 19 at 18:11
  • $\begingroup$ You said maintaining constant temperature across the face of crystal. You mean this is important at the interface which is perpendicular to the axis of rotation? What about the other facets of the seed which have their own direction(s) and have interfaces with melt? Can you please elaborate on the two type of rotations what they bring to growth beside temperature homogenization? $\endgroup$ – Eddie Feb 19 at 18:21
  • $\begingroup$ Yes, you have to keep the temperature across the face of the crystal, perpendicular to the crystal pull direction, constant. If you have one crystal orientation for the solid-liquid interface you will tend to get one growth direction. (Note this is another reason for silicon wafers being all (100) now - it is the easiest facet to grow). $\endgroup$ – Jon Custer Feb 19 at 18:27

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