3″(76.2mm) Vacuum Chuck for KW Spin Coater

Once the basic unit is selected, one must consider the appropriate “chuck” for holding the substrate being coated. Furthermore, there are available optional purge cabinets, glass lids, and optional 10″ bowls and lids to accommodate even larger substrates to be coated.

A few words about chuck size generally:

Generally speaking, the wafer size should be at least 0.25″ (6 mm) larger than the chuck. Yet one should not have the wafer too much larger than the chuck size either or else performance will suffer. You should select the chuck precisely on the basis of the wafer size being coated. This might mean more than one chuck size would be purchased. It is also important that the entire chuck surface is completely covered with the wafer, otherwise, the coating formulation will be literally sucked into the vacuum system and everything will clog up.

Family of precisely machined vacuum chucks:

Although the bowl, especially with the optional 10″ bowl is much larger than the largest mentioned wafer size, there is the temptation to think that larger than 6″ wafers can be coated. This is not correct. Although some space is indeed needed between the bowl and the outer circumference of the wafer to avoid the phenomenon of “splash-back”, a perhaps even more important reason is that the motor in the unit is just not sized to take an 8″ wafer and performance will suffer. The exception would be if a thinner-than-normal wafer is being coated. But in order to do that, one would need the 8″ chuck.

A few words about PTFE chucks:

In general, most users do not need to incur the added expense of a PTFE coated chuck. However, it is recommended for those who absolutely can not tolerate any metal or metal ions in these finished coatings. Note also the PTFE (e.g. polytetrafluoroethylene) is a “soft” polymer and will not last forever. How long it lasts for a particular user will depend on how carefully it is handled and to what it is being exposed and at what temperatures.