Wafer rinsing process
Under wafer rinsing ( English wafer rinse ) are combined a group of treatment methods, by means of which impurities from the wafer surface to be removed. The flushing procedures are generally part of windscreen cleaning procedures such as RCA cleaning . There they should remove the contaminants that were dissolved or bound in the previous cleaning steps and the chemicals used there. This requires a continuous supply of the flushing medium - often deionized water (DI water).
The rinsing process can also be used to end a processing step. For example, by diluting and rinsing a hydrofluoric acid solution with water, the etching process is stopped and the etching medium is removed
Overflow rinse
The most commonly used method is overflow rinse , in which DI water is introduced into the container in which the wafers are located; this washes around the substrates to be cleaned and thus pulls the particles with it. The water runs over the edge of the container or an overflow. The process can be supported by introducing nitrogen (bubbler) to support the mixing of the water with the chemicals and particles.
The goals of overflow flushing are high flow rates and no dead spots where contaminants can collect.
The disadvantage of overflow rinsing is the very high DI water consumption, which is why cascaded baths are sometimes used, with the overflow always flowing into the next, deeper bath. The wafers run through the baths from bottom to top into the cleanest bath.
Spray rinse
In the case of spray rinse , the wafer is sprayed with the cleaning medium. DI water is usually used as the cleaning medium, but other solvents such as isopropanol or corresponding mixtures can also be used, with isopropanol often being used to accelerate and improve the drying of the wafer.
Hot DI flush
Rinsing with DI water at a temperature of approx. 70–80 ° C ( hot-rise ) is a very widespread process. The advantages of this process are the reduction of drying times (e.g. after H 2 SO 4 treatment), the disinfection of supply and discharge lines in which bacteria can collect (DI water is not germ-free) and the reduction in temperature shocks , for example after RCA cleaning steps that take place at up to 180 ° C.
Drain flushing
With the dump rinse , DI water is sprayed onto the wafer and the tank is filled in the process. Once a certain level is reached, the drain is opened and the tank is quickly emptied, which should carry away impurities. This process is repeated several times.
As with overflow purging, a gas, for example nitrogen , can be introduced to support the process in order to increase the removal of particles.
literature
- Michael Quirk, Julian Serda: Semiconductor manufacturing technology. Prentice Hall, Upper Saddle River (NJ) 2001, ISBN 0-13-081520-9 .
- Werner Kern: Handbook of semiconductor wafer cleaning technology - Science, technology, and applications. Noyes Publications, Park Ridge, (NJ) 1993, ISBN 0815513313 .