Name:________________________
PHGN/CHEN/MLGN435/535 Pre-lab #9
Due Tuesday, March 22, 2016 at the beginning of class
Topic: Ion implantation
Reading: Campbell chapter 5 (skip or skim 5.2, 5.6, and 5.8)
We have spent quite a bit of time leaning how to put dopants into our samples by
diffusion. You have experience with phosphorous and boron. This process is still used
for discrete power transistors (packaged individually, not in an integrated circuit) and for
some MEMS applications, but the industry by and large uses ion implantation. Ion
implanters are basically particle accelerators. This reading will teach you about what
process is actually used for doping in industry. This pre-lab assignment will emphasize
some of the more important concepts related to ion implantation.
1. An ion implanter starts with a source gas (BF2 for example). The gas is ionized, and
the ions are electrostatically accelerated. At this point, the accelerated beam will have the
species we want to implant (B+ for example), but also other species we don't want to have
hit our wafer. Explain in a few sentences how the ion implanter selects the species we
want while blocking the others?
2. In ion implantation we talk about the effect that channeling has on projected range. In
contrast to what one might suppose, channeling does not relate to the wafer being
possessed by a host from a former life. What do we mean by channeling? (Don’t copy
word for word what the textbook says- explain it in your own words for full credit!)
3. Ion implantation induces damage in the host crystals. These are typically removed by
a post implant anneal. Your text distinguishes between primary defects, and secondary
defects. In your own words, explain what we mean by both primary and secondary
defects, and give an example or two of each.
4. SIMOX is under a lot of study right now as one version of a material known as silicon
on insulator (SOI). We know how to make transistors smaller laterally using lithography,
but to have the transistors continue to work, they must also scale smaller in the vertical
direction, into the wafer. To some extent, this can be accomplished with shallow doping
profiles, but a lot of research is going into use of SOI where thin silicon sits on top of an
insulator that limits the vertical extent of the device.
Your book points out SIMOX is expensive in part because it takes a lot of implanter time
and special high current implanters are being produced to address this. Do Campbell
problem 5.11 for an estimate of how long the implantation takes. (The current here is
probably for a good high current implanter, but not one specially designed for SIMOX.)
Remember that an O+ atom carries a charge of 1.602x10-19 C. Be careful of units.
Express your answer in hours, and think about it to see if it makes sense.