FAQ

A wobbly spin chuck can result in poor coatings on a spin coater. If you are experiencing this issue, it will need to be resolved. Below are some typical causes of this issue.

• Spindle shaft is bent – A bent spindle shaft should be easily observed by spinning the spindle shaft by hand without the chuck attached. It should be noted that this is a serious problem which always happens as the result of some sort of misuse or physical abuse of the tool, or possibly improper assembly methods after being serviced. If you believe your spindle shaft to be bent, contact Cee® Support to determine what the next best step is to resolve your specific situation.
• The chuck is not sitting correctly on the spindle – All Cee® spin coater equipment utilizes a spindle which has a pin/key that engages a slot on the inside of the chuck. If these are not lined up and the chuck is fixed with the screw, the chuck will not sit flush and level with the top of the shaft.
• The wafer is not centered on the chuck – Cee® offers handheld centering devices to center substrates onto chucks. The handheld centering device can be used for specific sizes and is very cost-effective. This component will positively mate to the side of a specific chuck and allow for quick alignment of the referenced size. Handheld devices are available for 2- and 3-inch and 100-, 125-, 150-, 200-, and 300-mm sizes. Custom wafer sizes are available upon request.

For best results, we recommend that the vacuum chuck diameter be slightly less than the diameter of the substrate. Below is a chart showing the recommended spin chuck size to substrates size.

If this sizing chart is not followed there may be negative impacts to the quality of your coated wafers.

• First, material may migrate between the chuck and the substrate causing backside contamination on substrates, dirty chucks, and vacuum issues from the material getting drawn into the spin coater’s vacuum system.
• Secondly, the substrate may not create enough of a seal to achieve optimum vacuum which can result in the wafer being dislodged from the chuck under hard acceleration or deceleration of the spin process.

The vacuum chucks for all Cee® spin coaters are designed with maximum vacuum contact to the wafer in mind. If the substrate is not large enough to make a proper seal, the spin coater will detect a vacuum error and will halt the coating process.

Standard circular vacuum chucks are capable of processing substrates with a diameter of no more than twice the spin chuck surface diameter. For example, a 4 inch chuck would not be recommended for substrate sizes larger than 8 inches (200 mm) in diameter or 8 inches square.

As substrate size increases, the use of a centering device, and/or verification of optimal centering of the substrate, becomes increasingly critical for maintaining positive contact between the substrate and the vacuum surface. With standard-thickness (275-750 μm) substrates that are centered properly, a maximum spin speed range of 3,000 to 6,000 rpm and accelerations of 3,000 to 6,000 rpm/s are recommended. As thickness increases, the maximum speed and acceleration must be decreased for safe operation. To process beyond these parameters, captive or recessed spin chucks are recommended.

We offer custom and specialized spin chucks to accommodate many substrate types, shapes, and sizes. We have an extensive library of over 700 unique spin chucks designed for specialized applications and substrate configurations.

For a unique and custom spin chuck, designed for your specific substrate and/or application, sizes can range from 1/8-inch in diameter to 14-inches square, with 3/8-, 1/2-, and 3/4- inch spindle diameters. In-house mechanical engineers are available to modify existing concepts or create custom spin chuck designs, per specific customer requests.

There may be numerous reasons why your spin coater is making weird noises while spinning. The following suggestions may help you determine what the problem is and how best to approach solving it.

• Unplug your Cee® spin coater and spin the spindle shaft by hand. The spindle should turn smoothly and freely by hand, with a minimum of drag. If you feel strong resistance, or hear sounds during this test, the spindle bearings may be faulty. The most common cause of bearing failure is process chemical contamination by way of the chemicals making their way down around the spindle of the spin coater and past the bearing shields / seals. Replacement bearing kits are available through Cee® Support.
• The next item to check is the spindle drive belt which over a period of years can and will become worn, possibly requiring replacement. Additionally, in much the same way that the spindle bearings can become damaged from chemical infiltration, the belt can also be similarly damaged from excessive exposure to process chemicals.
• The drive belt can be inspected for wear or damage by unplugging your Cee® spin coater and removing the back cover of the spin coater cabinet. Spinning the shaft by hand will allow you to inspect the belt surfaces inside and out. Improper belt tension, any observable cracks in the belt, or other physical damage like fraying edges indicate a work belt which should be replaced. Contact Cee® Support for replacement belts.
• The last item that may be the cause of a noisy spin coater are the drive servo PID (Proportional-Integral-Derivative) settings. All Cee® spin coaters use a sophisticated PID servo control system to ensure precise spin speed control, and repeatable spin coat recipe execution. This is an electronic system that is adaptive and capable of learning which means that under widely varying conditions of performance such as large differences in substrate weights or other process parameters, the system may require a few process cycles to learn and adapt to a new set of optimal parameters for any changed conditions it has encountered. If repeated attempts to run the system under a controlled condition do not result in the elimination of the noise, these parameters can be reset manually to a default condition which will provide a new starting point for the system to learn and optimize the PID control parameters. These can be reset by acquiring the proper instruction for your spin coater from Cee® Support.

Many issues can interrupt vacuum or cause vacuum errors. All Cee® spin coaters monitor the vacuum being applied to the substrate through the spin chuck and will report an error if insufficient vacuum exists for the spin coater to safely and reliably carry out the intended process. If your Cee® spin coater reports a vacuum error, which you believe to be incorrect, a list of troubleshooting checks (to be performed in the order listed) are listed below.

• Check incoming vacuum – The incoming vacuum supply should not be less than 20 inHg (33 kPa) and a minimum flow rate of 15 l/min.
• Check vacuum at the spindle – Remove the vacuum chuck and cover the vacuum hole of the spindle with a piece of tape. If you are getting sufficient vacuum at the spindle to satisfy the vacuum interlock the vacuum system of the spin coater is fine and the issue is with the chuck. If there is no vacuum at the spindle, then the issue is with the vacuum system of the spin coater.
• Check vacuum at the chuck – If the vacuum check at the spindle is bad, then skip this section. Inspect the chuck for any defects such as burrs, cuts, material build up, or anything else that will not allow the substrate sit flat on the chuck. If you chuck has an o-ring, inspect the o-ring. If the chuck has gouges or cuts, a new chuck may be necessary. If the chuck has burrs or material build up, we recommend running a glass microscope slide over the surface at a 45 ° angle. This will easily remove the material without risk of damaging the chuck further. Once you can run the microscope slide across the entire surface without feeling resistance, recheck the vacuum on the chuck.
• Check vacuum switch/sensor – All Cee® spin coaters are equipped with either a vacuum sensor or switch. If this has failed, the interlock will never switch to allow the process to run. If the chuck is holding a wafer and can not be easily removed when vacuum is turned on, this is likely the issue.
• Check vacuum trap – All Cee® spin coaters have a vacuum trap installed. This allows any material pulled down through the vacuum system to be separated from the stream before the vacuum goes to the valve. If this is full or otherwise blocked, a vacuum error will be reported.
• Check all vacuum lines – Inspect all vacuum lines for blockage or damage. Any of these can cause vacuum issues.
• Check vacuum at the valve – Remove the vacuum line from the spindle side of the vacuum valve. Check vacuum at the valve. If there is no vacuum at the valve, the valve is most likely to have a blockage or damaged.
• Check vacuum going into the spindle assembly – If there is sufficient vacuum present at the spindle assembly, the most likely issue is a failure of the vacuum seal at the bottom of the spindle shaft. After years of wear or material contamination, this seal can fail. We recommend replacing the seal any time that other service is being performed on the drive system such as belt or bearing replacement. Spindle service kits containing both bearings and a replacement vacuum seal are available for purchase.

We recommend a minimum vacuum of 20 inches of Mercury (Hg) (32 kPa) and a minimum flow rate of 15 L/min

Coating defects can be caused by several factors. Cee® has published a separate document describing the theory of spin coating and troubleshooting. You can find the guide here on our Spin Coat Theory page.

Cee® offers a programmable exhaust option for our spin coaters and developers. This option allows the user to program the amount of exhaust flow at each step of the recipe. This capability can be very beneficial for controlling the solvent enrichment in the bowl during the casting and spreading steps, as well as for exhausting solvent fumes from the bowl at the completion of the recipe. This option is very critical for achieving optimal coating uniformity (such as total thickness variation, or TTV) for medium- to thick-film resists.

The programmable exhaust will also allow the user to set a predetermined default position and subsequently control the exhaust load/flow during ambient conditions. This capability may be beneficial for controlling or conserving the overall volume of air in the ambient lab conditions and/or for creating the optimal solvent enrichment for subsequent processes.

You can contact Customer Support for more information and pricing for the programmable exhaust module.

Cee® process equipment can accommodate this requirement through our purged bowl / hood accessory option. This optional extra is available on all Cee® spin coaters and bake plates at the time of purchase. Alternatively, this option can also be fitted to an existing machine any time.

For a spin coat process, four diffusers mounted in the spin bowl cover and allows a user to purge a (regulated) nitrogen (or other inert gas) supply into the bowl environment. The Cee® dispense control box can be used to regulate the nitrogen flow rate and minimize the oxygen levels in the spin bowl. This feature offers a complementing programmable exhaust option for creating positive pressure inside the bowl chamber.

For a bake plate process, diffusers similar to those used in a spin bowl purge process are fitted to the bake plate exhaust hood. These nozzles are connected to a nitrogen (or other inert gas) supply to create an area immediately above the wafer that is purged free of oxygen.