Maybe you should talk to the Si supplier about:
- Crystal defect density (stacking fault, dislocations, etc.); usually
very low in today's materials; maybe also sub-surface polishing damage.
- Oxygen content and chemical state (dissolved, precipitated through
thermal treatment) can affect some mechanical properties like resistance
to fracture. CZ crystal growth process typically introduces tens of ppm
of oxygen in the silicon; FZ process typically has ppb or lower oxygen
in the silicon.
- It is possible that heavily doped Si (~ 0.01 Ohm-cm) has different
mechanical properties than lightly doped (~ 1 Ohm cm) since doping
impurities stress the Si lattice because they do not "fit" as well as Si
atoms in the crystal structure; B and P stress in opposite directions;
Sb stress is low because it fits better than B or P.

Regards,
Pierre x286