Electrochemical Technology CorporationDryScrub

 

Why Dryscrub?

There are many problems involved in the CVD, PECVD and Etching of today's semiconductor wafer processing.
The DryScrub
system is a simple, effective solution in eliminating some of these problems at their source.

Particles

Inspection of the exhaust from any CVD, PECVD or Etching system will show particles deposited internally, these particles are visible (>0.4m) and are loosely attached in the form of a powder. A major symptom of visible particles is smaller particles grouping together through collisional attachment, these smaller particles can be large enough to cause significant yield problems. In terms of volume, a 0.4m particle will require approximately eight 0.2m particles to form, for each visible particle found it can be deduced that there will be many invisible smaller particles in the surrounding space. Particles will form wherever the correct physical and chemical conditions are met.

In the wafer processing chamber, reaction conditions are manipulated for the correct process to occur, beyond the chamber, conditions will change and uncontrolled reactions occur causing molecular clusters of particles to form. These nano-metric sized clusters, as they collide with each other, rapidly multiply in size to become larger and larger particles. One way of treating this symptom is to heat the forelines so that deposits are formed further away from the wafer processing chamber.

It is mainly mechanical forces (dynamic flow, gravity, etc.) which govern the movement of larger particles, but, quantum forces (random movement, electrostatic charge, etc.), which operate at the molecular level, progressively emerge as a factor for smaller sized particles such that they start to act like gas molecules. As the particles become smaller they become highly mobile and have the ability to backstream and diffuse into the wafer processing chamber, here they act as seeds for initiating larger particles to grow which may eventually deposit on the wafer and the process chamber walls.

Environmental and Safety impacts

Only 5-20% of the reactive gases are used to obtain the required process results, a portion of this unreacted gas will pass through the exhaust, pumps and any abatement system before being vented to atmosphere. These reactive gases have the potential to cause serious environmental and safety problems. Additionally, some processes produce powder in the exhaust lines which may be toxic, pyrophoric or even explosive.

Maintenance


Deposits on downstream control valves can cause malfunction through blockage of the control valves or leakage of sealing surfaces, similarly deposits within the exhaust system will eventually cause clogging as the amount of powder accumulates. Reactive gasses and powder reaching the downstream abatement systems will reduce their intended efficiencies by limiting the active reagent or contact area available.

Vacuum pumps create an environment suitable for the formation of deposits, this is caused by the heat generated in the rapid compression changes (adiabatic compression). These deposits will eventually cause excessive wear or seizure of the rotor and/or the clogging of manifolds.

All of these problems can be easily eliminated by the use of the DryScrub System.

DryScrub is a highly efficient Plasma Reactor that reacts residual process gases virtually to completion, installed in the exhaust line adjacent to the wafer processing chamber it is sited immediately next to the point of use. It 'scrubs' the reactive molecular clusters and depletes the solid components of the process gas by converting them into a stable film and less hazardous gases. In doing so a near particle free space and gas stream is generated which extends from the wafer processing chamber to the pumps and beyond.

The DryScrub with a reaction efficiency >99.5%, deposits a stable solid film within the system similar to that produced on the wafer, the properties of this film ensure that it is environmentally safer and allows easier handling for waste management. Powder deposited in the exhaust system is reduced to almost zero and any resultant gases are able to flow through the exhaust system to be more effectively abated by the downstream equipment. As this equipment no longer has to cope with the large volumes of reactive waste material the cost of ownership is reduced.

The stable solid film, along with the reduction of powder deposits and less hazardous waste gasses ensures that environmental and safety risks are reduced to a minimum.

Reduction of deposits downstream from the DryScrub reduce the requirement for maintenance on control valves, pumps, exhaust lines and abatement equipment.

The DryScrub offers many benefits in the treatment of the waste gasses from CVD, PECVD and Etching processes. As well as providing reduced particle counts for increased yields, reduction of environmental and safety risks and reduction in the costs of ownership of control valves, pumps and other equipment it also has implications for the wafer processing chamber itself. As the highly mobile nano-metric particles are eliminated, the film that deposits on the wafer processing chamber walls will have fewer defects and can be grown thicker before there is a requirement for cleaning or replacement.


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