this ppt is covering the fundamebtals of the diffusion in the fabrication of IC technology.... hope it'ld be a useful for u. thnx

1. Report On
Diffusion & Measurement Of
Sheet Resistance
By:- Prateek Agrawal
ECE/67/08

2. Diffusion
 Diffusion can be defined as the
random walk of an ensemble of
particles from regions of high
concentration to regions of lower
concentration.
 In integrated circuit fabrication,
diffusion is used to introduce dopants
in controlled amounts into the
semiconductor substrate.

3. Laws Of Diffusion
First law Of Diffusion
According to the First Law of
Diffusion, the transfer of solute atoms
per unit area in a one-dimensional
flow can be described by the following
equation:

4. where J is the particle flux,
C is the concentration of the solute,
D is the diffusion coefficient,
x is the distance into the substrate, and
t is the diffusion time.
The negative sign indicates that the diffusing mass flows
in the direction of decreasing concentration.
From the Conservation of Mass, we also know that:

5. Second Law Of Diffusion
If we combine this relationship with the 1st
Law of Diffusion, then we have derived the
2nd Law of Diffusion (otherwise known as
Fick's Law), which states:
Two solutions to Fick's Law are generally
encountered in IC fabrication: infinte-source
and limited-source diffusion

6. Sheet Resistance And Its
Measurement
 Sheet resistance is a measure of resistance of thin
films that are nominally uniform in thickness. It is
commonly used to characterize materials made by
semiconductor doping, metal deposition, resistive
paste printing, and glass coating. Examples of these
processes are: doped semiconductor regions
(e.g., silicon or polysilicon), and the resistors that are
screen printed onto the substrates of thick-film hybrid
microelectronic.

7. Methods To Measure The Resistance
 Thereare mainly two methods
a) Four Probe Method
b) Van Der Pauw Method

8. Four Probe Method
 A four point probe is used to avoid contact resistance,
which can often be the same magnitude as the sheet
resistance.
 Typically a constant current is applied to two probes and
the potential on the other two probes is measured with a
high impedance voltmeter.
 The key advantage of four-terminal sensing is that
the separation of current and voltage electrodes
eliminates the impedance contribution of the wiring
and contact resistance

9. Operating Principle
 Ckt Diagram  When a Kelvin
connection is used,
current is supplied via
a pair
of force connections
(current leads). These
generate a voltage
drop across the
impedance to be
measured according
to Ohm’s Law V=RI.

10. Van Der Pauw Method
The van der Pauw Method is a technique
commonly used to measure the
Resistivity and the Hall Coefficient of
a sample. Its power lies in its ability to
accurately measure the properties of a
sample of any arbitrary shape, so long
as the sample is approximately two-
dimensional (ie. it is much thinner than it
is wide) and the electrodes are placed
on its perimeter.

11. Vander Pauw Contact
Placement

12. THANX FOR YOUR ATTENTION
Presented By:-
Prateek Agrawal
ECE/67/08