Electrochemical Technology CorporationDryScrub®

 

PECVD Problems Dealt With Today

As geometries become smaller, yield requirements are harder to achieve and equipment up time becomes more critical.

Electrochemical Technology Corporation has developed the DryScrub® system to reduce these problems.

Particles

With the decrease in linewidth size, particles become a more of a problem. In order to gain the correct process results in any CVD deposition, only about 5-20% of the gas is used to grow the film, the rest of this activated but undeposited gas flows through the system. Consequently any areas of the pumping system where similar conditions to the process tube exist are areas in which further deposition will take place.

When the ‘waste’ gases react in the vacuum plumbing away from the process area there is less control of conditions and nano-metre sized molecular particles can form. Although the general flow of the gases is towards and through the pump, these very small particles, because of their nano-metric size and high energy/weight ratio, are able to migrate back into the process area where they can deposit on wafers and the process chamber walls. Work has been carried out which suggests that these small particles also act as seeds upon which bigger "particles" grow (coagulation).

Larger particles not only cause defects on the wafer but also in the films that deposit on the process chamber wall. These particles may cause the premature build up of stresses in these films that can lead to flaking and as a consequence, a more regular regime of process chamber cleaning is required.

Vacuum System

As the gases reach the pump they effectively enter another "process area", here adiabatic compression causes the gases to react and further deposition takes place on the walls and rotors of the pumping chambers. This build up continues at all times when the deposition process gas is flowing. Vacuum Pumps require clearances to operate correctly and as the deposition takes place so these clearances are reduced leading ultimately to higher current consumption and eventual failure of the pump.

Clogging

The gases that have not reacted out after this stage flow through the exhaust system to any down line gas cleaning equipment. This down line equipment requires maintenance as the elements within the equipment start to clog. Some residual gases may pass through these systems and make their way into the environment.

The Solution

ETC has developed a proven solution to address these problems. The ETC Dryscrub® is a PECVD reactor placed in the vacuum line downstream of the process chamber and before the vacuum pump.

The Dryscrub® is effective in reacting the gases through to completion with an efficiency >99.5% for most processes. The Dryscrub® consists of a vacuum chamber and electrode that has been constructed to give both spiral and cross-flow patterns of gas flow. As the gases pass through the plasma the deposition of a compressive stable film is made on the Dryscrub® electrode.

Due it’s design, the Dryscrub® is transparent in operation. It has no effect on the process or upon the gas flows and pumping rates within the vacuum system thus leaving the current processing parameters unaffected.

By reacting the gases with an efficiency of >99.5% the Dryscrub® has a significant impact on increasing yield and decreasing equipment downtime by:-

  1. Capturing nano-metric sized particles on the electrode - preventing them from migrating back into the process area.
  2. Removal of reactive gasses - so increasing wet and dry pump reliability and period between maintenance events.
  3. Easing of requirements for maintenance on downstream treatment and scrubbing equipment.
  4. The reduction of gases vented to atmosphere where no other downstream equipment is used.

Benefits

ETC Dryscrub® provides a solution which:-

  1. Increases yields by reducing particles on the wafer.
  2. Longer quartzware lifetime due to reduced cleaning requirements.
  3. Decrease in pump and downstream gas treatment maintenance requirements.
  4. Allows easier conformance with today’s stringent environmental standards.


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