Spinner manual (PDF)

Spinning Resist
If one should consider blowing up a balloon, he/she would find that the rubber or
latex material in the balloon skin has very uniform thickness and material properties. It is
this uniformity that allows each square of the material to expand exactly the same amount
as every other square. It is this uniformity that allows the size of the enclosed volume to
increase many times before the balloon pops. We can recognize this truth by introducing
an imperfection in the form of a needle, a knife, or non-uniform pressure exerted on
some, but not all, areas of the balloon skin. The balloon analogy may prove useful to
students while learning to spin acceptable polymer coatings on substrates.
The polymer solution under consideration is considerably less robust than a
balloon skin because only the surface tension of the liquid polymer solution (and not the
elastic properties of rubber or latex) maintains the liquid film’s surface. Because of this
fact, dust and/or chemical contaminants will suffice to destroy the students’ films; no
needles or knives are necessary. An expanding balloon skin has two-dimensional
symmetry about each point that causes the equal expansion of all squares mentioned
above. The balloon pops when the elastic strength of the material becomes insufficient to
compensate for fluctuations in the balloon’s skin. Once the two-dimensional symmetry is
broken, a rupture very quickly expands outward to yield a very large hole in the balloon
skin. Similarly, a spinning substrate coated with polymer solution has two-dimensional
symmetry about each point and the introduction of a discernable fluctuation will cause
very large and unacceptable thickness variations in the polymer film. It is only in the
absence of “nucleation centers” that the liquid’s surface tension can pull the surface into a
beautiful plane without disrupting the surface. In the absence of nucleation centers, the
“centrifugal force” of the spinning substrate will remove material uniformly from each
square of the film and will leave the student with a beautiful, uniform film suitable for
exposure.
The instructions listed below are designed to aid the student in substrate
preparation and spinning technique so that he/she can obtain suitable resist coats with
some practice.
Cleaning the Substrates
Cleaning the Spinner
The environment around the spinner is relatively dusty compared to the specially
cleaned rooms that are normally used for processing samples for production. Because of
this dirty environment, the student must exercise more care when preparing his/her spincoating
process. The most effective step in a successful process is the careful cleaning of
the spinner interior. The second most effective step is using a clean wafer. The third
most effective step is using uniform liquid and progressing steadily so that the liquid
solvents cannot evaporate from the surface and leave behind substantial non-uniformities.
While the spinner is in motion the spindle stirs the air inside substantially. If any
dust or chemical contaminants are within the spinner, the motion of the air will certainly
deposit some of them on the coating and destroy the needed 2D symmetry. Because of
this it is necessary to remove or to glue down all sources of contamination within the
spinner’s interior prior to attempting to spin-coat any substrates. This step is particularly

important if the spinner has been idle (and is therefore more dusty). Additionally, the
spinner interior will acquire dust at a lower rate if the contents of the fume hood are also
clear of dust and contamination.
1) Open the vacuum valve that connects the spinner to the house
vacuum.
2) Open the nitrogen tank main valve and set
the nitrogen pressure to 65 psi.
Increase
Decrease
3) Put on a clean pair of gloves and verify
that sufficient acetone and isopropyl alcohol are
available.
4) Before bringing chemicals near the spinner, completely
cover the o-ring with a waste wafer fragment and
activate the vacuum chuck to keep it firmly in
place. This wafer, if correctly installed, will
prevent chemicals from entering the spinner
vacuum port and spoiling the spinner’s bearing
lubrication. Do not use the spinner if it is possible
that chemicals have been admitted to the vacuum
port… doing so will ruin the spinner and will
yield very poor results.
5) To clean the spinner spindle, soak the outside
portion of the substrate holder with acetone and
keep wet for 20 s. Use as little acetone as
possible while keeping the surface wet. Acetone
will dissolve the rubber o-ring, so be careful that
the two do not meet.
No
Acetone

6) After 20 s acetone soak, flood the spindle with
isopropyl alcohol (IPA) beginning at the waste
wafer center and working outward. Begin this
step while the acetone is wet and keep the spindle
wet for 30 s so that the IPA can dissolve the
acetone residue.
Alcohol
7) Close the lid and start the spinner.
8) After the spinner stops, lift the lid, deactivate the
vacuum chuck, and
carefully remove the
waste wafer and the
o-ring. Please do not
scratch the o-ring
grooves because any
scratches will
prevent a good
vacuum seal and will
tilt the substrates in the future.
9) Carefully and thoroughly wipe the spindle and o-
ring groves with tissue or cloth. If any loose
polymer ends are observed, carefully pull away
as much old polymer as possible with tweezers
and discard in the trash. Wipe the waste wafer
and o-ring clean with tissue or cloth.
O-Ring
Grooves
10) Using the nitrogen nozzle, blow away debris from
the o-ring groves and spindle. If any loose polymer ends are observed, carefully
pull away as much old polymer as possible with tweezers and discard in the trash.

11) Carefully replace the o-ring in its groove and replace the waste wafer fragment so
that the o-ring is completely covered. Re-engage the vacuum chuck.
12) Wipe the remaining spinner interior clean with tissue or cloth. If poor results are
observed, dampen the tissue with DI water before wiping the spinner interior. For
more extreme cases, use Liquinox and water to wash the interior before
thoroughly rinsing away the Liquinox with DI water. Acetone will dissolve the
plexiglass top, so do not use acetone close to the spinner top.
13) Allow solvents to evaporate. If no other cause can be found for poor results,
suspect the presence of solvents and allow more drying time.

Applying PMMA
14) De-activate the vacuum chuck and replace the waste wafer with a clean substrate.
Reactivate the vacuum chuck. Blow away debris from the top and bottom of the
spinner interior using the pressurized nitrogen nozzle. Close the spinner lid.
15) Remove the stopper in the spinner top and blow
away debris from the substrate and spindle.
16) With minimal delay, apply several drops of PMMA
to the substrate so that the surface is completely
covered, start the spinner, and replace the stopper in
the spinner hole.

17) Examine the completed coat for defects. A good coat will have uniform color
(usually blue, green, or purple depending upon the coat thickness) except very near
the substrate edges. Proceed to baking or to cleaning and re-coating as the spin
quality dictates.
18) Dispose of waste. Place glass and sharp objects like razor blades in the safety
approved container. Place paper, old gloves, etc. in the wastebasket. Place waste
chemicals in the gallon container provided. Wash glassware with soap and water in
the sink, rinse thoroughly, and wipe dry.