A. Turn on Ellipsometer by fully turning key clockwise (key is on back right
hand side of unit). The unit really isn't stable until it has warmed up, so
it's good to have it on for half an hour before taking critical data. For most
things in our lab, it begins to work adequately right away.
B. Place sample to be measured on the measurement platform (its a vacuum chuck
but we typically don't use the vacuum). On the back of the output detector,
there is a switch with M, A/M and A. Set it to the middle position, A/M Also,
open the shutter at the laser output point.
C. Now we must level the sample. Begin by looking through the eyepiece. You
will see two cross hairs, a broad set and narrow set. Adjust eyepiece in/out
(it just slides) to focus narrower cross hairs. In general you won't need to
do this as they will be in focus from the last user.
D. Below the sample chuck are a locking screw to hold the chuck fixed, two leveling
screws toward the front and right, and a height adjustment screw toward the
back. Loosen the locking screw. Adjust the leveling screws to center narrow
cross hairs within wider cross hairs.
E. There is a signal monitor just below the eyepiece (a bar output). Rotate
the output polarizer (its just in front of the detector) until the signal is
either maximum, or if the output overloads, until the signal is about 2/3 of
full scale. Now use the height adjustment screw to find the height where this
signal is maximized. Tighten the locking screw on the sample chuck. Your sample
should now be aligned at the right height and with the right (and equal) angles
of incidence and reflection.
F. Switch to "A" setting on the back of the output detector. As you
proceed at some point you will see the analyzer (output polarizer) begin to
rotate.
G. On computer open Ellipsometer file
H. Run Standard program from computer (STD)
I. Using the PF keys, choose "SPECIP", then your desired wavelength
(6328 is a good start), then pick the setting for the kind of film you would
like to tell the computer you have. The "OXIDE" choice assumes oxide
on a silicon substrate. It calculates thickness and index of refraction, but,
if the index is uncertain, will assume the index of silicon dioxide. There is
also a silicon nitride setting, a setting where the instrument must calculate
the index as an unknown, and a setting which forces the instrument to assume
an oxide or nitride index even if it feels it can calculate a better one. This
program always assumes a silicon substrate. After you choose oxide or another
setting, the instrument will make a measurement and output thickness and index.
J. When you have finished your measurements the PF10 key will take you to the
initial STD program screen, and then allow you to quit. Turn off the computer
monitor but leave the computer running.
K. Remove your sample, turn off the ellipsometer at the key, put on the instrument
cover, and sign the logbook noting in particular any difficulties.
Some additional details that may be useful.
-To verify the ellipsometer is working correctly you can measure the test sample.
A. Place the pre-calibrated wafer on sample chuck. (Be very careful handling
it. It can be damaged by fingerprints, dust, and especially by dropping.)
B. Follow the procedure above to measure the bluish region in the center of
the test wafer using the "OXIDE" setting.
C.Sample should be about 900 angstroms.
D. Carefully return test wafer to its wafer container.
-The ellipsometer is very good at measuring index, but only gets film thickness
to within a multiple of a quantity related to the film thickness, optical wavelength,
and sample index of refraction.
A. If you get an answer where you know the thickness is wrong, but where the
measurement seems to be stable and should work, try hitting the PF key that
gives a list. This is a list of possible thicknesses that could go with your
measurement. Your correct thickness is probably in the list.
B. Two other modes of operation are available with the standard program that
can help decide which thickness is right. The two wavelength option essentially
gives two lists, one for each wavelength, and chooses the thicknesses from the
two lists which are in closest agreement. The two angle measurement holds the
wavelength constant but makes measurements at both 70 and 50 degrees, again
giving two lists and matching them. The two angle approach is really quite good
and typically spot on. Before using either the two wavelength, or two angle
methods, you MUST be trained and approved for these two modes. In particular
you should not attempt to modify the system setup from the basic one angle measurement
described above without being approved to do so. See the lab coordinator to
obtain training and approval.