Aufschleudern - Spin coating

Beginner's Guide to Spincoating

Relation between layer thickness and time, exhaust volume and speed.

If you are completely new to spincoating, then you can find here some basic hinds to get your sample coated. This shall help you to understand the process and possible mistakes. A practical example you can find below. You can try it yourself, but first we suggest you to be always nice to the cleanroom staff and ask them for help.

At a glance: you have a solid material solved in a solvent with a specific ratio. You apply this solution on a surface and let the solvent evaporate. The remains are the solid material you want as the layer.

At first, we will show you the realations between thickness of your coated layer as a function of time, exhaust volume and speed. You can optain these parameters by googl'ing, asking the cleanroom staff, from papers or the manual of your coating. If you want to find them out yourself, then keep the relation in figure 1 in mind. You want a specific, reproducable layer thickness. The spinspeed causes centripetal acceleration, which spread the material over the sample surface. Higher speed means more force which can act against the viscosity, surface tension and adhesion forces. So the higher speed will result in a thinner layer.

Over spintime the centripetal forces (depending on the speed) stay active. Imagine a water droplet with sugar, pinned in the middle of a roationg plate: the droplet flattens while the plate rotate but it will immediately turn into the normal state, after stopping the rotation. You need to wait, until the water is evaporated or at least so viscous, that the fluid keeps flat.

The acceleration ramp over time for a spincoating process.

The evaporation rate depends on the solvents properties, the temperatur, the humidity and on the exhaust volume. While the solvents properties are kind of stable/known and the humidity and temperatur cannot be controled, you can control the exhaust volume. If the volume is closed, the airflow and the turbulence is minimized and therefore reproducable.

Another important factor is the acceleration. The solvent of a thin film may evaporate within seconds. Therefore you need to reach the desired spinspeed in time.

Troubleshooting

Layer to thin	Solution
Spinspeed too high	...lower it
Spintime too long	Decrease time during high speed step
material not appropriate for thick layers	try another material or solvent-solid-ratio

Layer to thick	Solution
Spinspeed too low	...boost it
Spintime too short	Increase time during high speed step
Exhaust volume too high	Adjust exhaust lid or house exhaust damper
material not appropriate for thin layers	try another material or solvent-solid-ratio

Problem description	Layer appearance
Air bubbles on wafer surface Air bubbles in dispensed fluid (resin) Dispense tip is cut unevenly or has burrs or defects
Comets, streaks, or flares luid velocity (dispense rate) is too high Spin bowl exhaust rate is too high Resist sits on wafer too long prior to spin Spin speed and acceleration setting is too high Particles exist on substrate surface prior to dispense Fluid is not being dispensed at the center of the substrate surface
Swirl pattern Spin bowl exhaust rate is too high Fluid is striking substrate surface off center Spin speed and acceleration setting is too high Spin time too short
Center circle (chuck mark) If the circle is the same size as the spin chuck, switch to a Delrin spin chuck
Uncoated areas Insufficient dispense volume
Pinholes Air bubbles Particles in fluid If old resist, try ultrasonic bath the resist for 15 min to dissolve solid residues If new resist, try a syringe with a filter Particles exist on substrate surface prior to dispense

Poor reproducibility
Variable exhaust or ambient conditions	Adjust exhaust lid to fully closed
Substrate not centered properly	Center substrate before operation
Insufficient dispense volume	Increase dispense volume
Inappropriate application of resin material	Contact resin cleanroom staff or manufacturer
Unstable balance in speed / time parameters	Increase speed / decrease time or visa versa

Poor film quality
Exhaust volume too high	Adjust exhaust lid or house exhaust damper
Acceleration too high	Select lower acceleration
Unstable balance in speed / time parameters	Increase speed / decrease time or visa versa
Insufficient dispense volume	Increase dispense volume
Inappropriate application of resin material	Contact resin manufacturer or cleanroom staff

Copyright

Kann man auch genauso nachlesen auf: http://www.brewerscience.com/spin-coating-theory . Aber ich dachte, es sei ganz praktisch, dass auch mal hier zu haben.

Wird immer mal wieder ergänzt :) Sebastian vdE

Small chips

1. Keep your equipment clean.
2. Prepare everything you need.
   • Pipette
   • pipette holder (if available)
   • chips which you want to spin-coat
   • paper towels for cleaning and putting equipement on it
   • aceton for cleaning the spin coater in between separate spin coating step
3. Warm up hotplate (if necessary)
4. Put your programme into the spincoater.
   • Check speed, lid position, accelaration for all steps.
5. Put your chip on a suitable holder.
   • To put it on a wafer holder you can use a Capron foil with a hole for the vacuum.
6. Vacuum on.
7. Put resist in pipette (how -to will be in new wiki-site (how -to -use a pipette) later on.
8. Now the important steps.
   1. Put 1-2 drops in the spin-coater and keep the pressure on the pipette. Makes the air bubbles out.
   2. In the next steps, try not to touch the chip surface with the pipette.
   3. Put a big drop which is half as big as the chip in the middle of your chip with your pipette very close and leave your pipette in the fluid.
   4. With the pipette in the fluid move round the corner of your chip slowly dripping more resist onto the chip (I will put a photograph in here later.)
   5. At the end you chip should be coated with resist completely, especially all the edges.
   6. Start spin-coater immediately.
9. If not so: Vacuum off.
10. Carefully remove chip from spincoater and put on the hotplate (or in the chip box).
11. Clean the spin-coater after each chip with a bit of aceton. There should be no threads from the resist and no big drops in the relevant area.
12. If finished: Clean the whole spin-coater very, very good. The next people will hold you responsible otherwise.

Just a info: Chip boxes can be fetched from Nina Giraud (SP403818.00)

PS. Noch nicht fertig. Ich schreib noch weiter, aber ihr dürft gerne helfen. Gruß Kira