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VLSI Class Notes Fall 2010, Class 3
Homework #1 Due August 30, 2010: See VLSI Class notes #2
Reading Today, Jaeger Chap. 5.1, 5.2, and 5.3
Reading Friday/Monday Chap. 4.1, 4.2, 4.3, 4.4, 4,5 and 4.6
Homework #2, Due Wednesday, Sept. 1, 2010.
1) Standard implant problem: a) What energy is necessary to make a Boron implant
through a 110nm layer of gate oxide if the peak of the implant is supposed to be at the
surface? b) Sketch the impurity concentration versus depth for Boron implant in part
a). What is the implant straggle?
2) What the process engineer really wants is to have 95% of the Boron just below the
oxide. However there is an oxide thickness and tolerance of 110nm +- 4nm. Also, there is
an implanter voltage reduction of up to 8% from the nominal voltage because the
implanter high voltage source gradually reduces voltage until the machine power supply
is serviced annually. (This is a low cost implanter).
So what is the minimal implanter energy that you need to implant the Boron under these
conditions to guarantee that 95% of the Boron is below the oxide (SiO
). What is the
Review the pictures of the ion implantation system, profiles of Ion implanted
dopants, masking of Ion implantation, and sheet resistance of implanted regions in
Jaeger, Chapter 5.
Ion implementation is a method of doping semiconductors to turn them into and n-
type or p-type.
Undoped silicon or pure silicon is like an insulator even at room
Dopants in silicon (Atomic Mass)
P-type, Boron (11), [Al(27), In(115) are dopants but are not used in modern ICs]
N-type, Phosphorus (31), Arsenic (75), Antimony (122)
The machine that performs ion implantation is called an ion implanter.
implanter the dopant species are ionized, that is to make them charged. Once they are
charged they are accelerated to specified kinetic energies.
Then the dopant ions lead
the accelerator and impact the silicon lattice. Figure 5.1 in Jaeger shows the ion
implanter block diagram