During IC processing, the appearance of point defects may reduce the
yield of the process. The yield is defined as the fraction of operative
devices or chips to the total number of chips fabricated.
Yield may be measured for a given wafer or as the average value for
an IC process line.
In the later case, the yield figure may be concieved of as a quality
metric for the process line.
Point defects on a wafer may be random as well as non-random.
Among random defects, you may find uncorrelated as well as
correlated defects, e.g. if clustering of defects occurs.
This applet demonstrates the effect of random, uncorrelated (point)
defects on wafer yield.
For a wafer of a given size, the chip size determines the number of
die sites on the wafer.
The wafer yield is a stochastic variable determined by
the number of die sites on the wafer as well as
the density of defects (or the number of defects on a wafer).
Use the sliders to select the die size (width and height)
and the number of defects per wafer.
Next, press the Apply selected values button to
generate a wafer filled with chips of the selected size,
and the specified total number of defects (shown as black dots).
Good chips are marked green, while bad chips are shown in red.
Press the Apply selected values button again to generate a new wafer
with the same number of chips but different location of defects.
Use the Apply random values button to generate a wafer
with random chip size and random number of defects per wafer.
(Try to resize or maximize the browser window if the applet does
not react to the 'apply' buttons.)
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