The answer to your question depends on what you mean by a "sharp tip".
Many people have made a silicon tip consisting of a single atom although
the overall shape doesn't much resemble that of a needle. If you are
looking for a sharp tip that resembles a needle then that is probably
the work I was involved with at Bellcore (Marcus et al, Appl Phys Lett
56(3) (1990) 236). This work was the first, I believe, to use the
concept of "oxidation sharpening" to form an atomically-sharp point.
While it is true that the first precursors were etched silicon pyramids
obtained from Trujillo (as pointed out by one of the contributors to
this MEMS column), a critical step is oxidation sharpening which we
developed. The principle of "oxidation sharpening" is based on earlier
work done at Bell Labs in the late 1970s (Marcus & Sheng, J Electrochem
Soc, 129 (1982) 1278) which looked at the oxidation kinetics of non-
planar silicon and showed the slowing down of thermal oxidation at
regions of very high curvature. This work was subsequently confirmed
and theoretically modeled by others.

This work which started in Bell Labs in the late 1970s and continued at
Bellcore more than ten years later is continued at NJIT. The precursor
structure can be made by wet or dry etching, but people often find that
multiple tips form instead of a single atomically sharp tip. In a paper
to be presented at the upcoming meeting of the AVS (Zhang, Zhang,
Sriram and Marcus) we try to show how to effectively prepare the precursor
structure so that a single tip only forms.