Preventing Contamination in High-Purity CVD Coated Parts Storage

The problem of producing clean High purity CVD SiC raw material parts, and keeping them clean from manufacturing to the installation in an epitaxy system, is also significant. An insignificant amount of dust and contamination that accumulates during storage can result in defects on wafers, and decrease the yield during production when the system starts. Often, problems originate from storage, not the manufacturing process itself. As an example of storage contamination, engineers noticed the cleaned susceptor parts had been contaminated when being stored by an open workshop door; instability during production ensued when the equipment was brought back on-line.

Cleanroom Packaging Standards for CVD SiC and CVD TaC Coating Parts

The proper packaging of high purity Cvd sic coating or CVD TaC coated parts is more than just preventing physical damage; it is to protect the clean surface achieved during coating. Trace particulate which cannot be seen by the eye can negatively impact the quality of the wafer during epitaxy.

The first step of any packaging procedure should occur in a clean room, which has a positive pressure, and a clean environment maintained with high efficiency air filters. Clean room clothing should always be worn, including masks, and powder-free gloves must be worn at all times to avoid transferring skin particles, dust or fibers to the components.

Materials used for packaging are also critical. Typically two layers of cleanroom plastic bags will be used to double protect components; however, for extremely delicate parts vacuum or nitrogen packaging may be employed to further minimize both moisture and atmospheric contaminants. Protective foam used should also be constructed of cleanroom safe, low outgassing material to avoid any additional contaminants being released from storage to component.

Once sealed, the components should only be removed from the packaging environment in the clean room, and not in an open workshop. Opening an inordinately packaged component may re-contaminate it to a point where the component must be re-cleaned.

By properly packaging, components will remain clean for use in production.

Proper Handling Methods for High-Purity Graphite Epitaxial Parts

Although the high purity graphite parts appear very durable, they are prone to trapping dirt, oil and moisture on their surface. These contaminants can remain undetected throughout the parts' life span but can affect epitaxy at later stages.

Handling of parts must always be done while wearing powder-free, clean nitrile gloves. Bare hands should never come into contact with any of the parts, as skin oils will attach themselves to the surface of the part in very minute quantities and can be difficult to remove from the surface later on.

Parts should also be handled carefully. Simply picking them up off a table by their edges can leave microscopic cracks in the part which may not be evident immediately but may appear after a few cycles of heating, and although you cannot always see it there may be particles generated within the reactor.

You should also be in an environment which is both suitable and clean for the particular application to handling. If parts are handled and left on the workbench you must not allow them to sit on a metal table, cardboard or raw plastic surface as these may shed dust and fibres onto the part.

The airflow should also be considered during handling of parts.dust being blown onto the part from a fan, or if a door is open, can accumulate on the parts, and hence many facilities perform their parts handling operations under a laminar flow bench or in a clean area.

Moisture and Oxidation Risks During Long-Term Component Storage

While the parts (which were made of high purity graphite) seemed to be of a very high quality; it is relatively easy to get dirt, oil and moisture trapped onto the surface of the parts and to remain undetectable throughout the parts life but influencing the epitaxy at a later stage.

Always handling of parts must be with powder free, clean, nitrile gloves. The parts must never be touched by bare hands, as skin oils will attach to the surface of the part in very minute amounts, and are extremely hard to get off again at a later date.

Also parts must always be handled with a great degree of care. Even just picking up parts off the bench from the edges might result in microscopic cracks being created in the part which would not be visible until the part has been through a few thermal cycles, and while you would be unable to see the cracks it might result in particles being produced within the reactor.

Also you should try to be in a proper, clean environment for the application at hand. Handling and leaving the parts lying on the bench are only acceptable if not left on a metal bench, cardboard or an unprepared plastic surface, since dust particles will shed onto the part.

Airflow must also be considered, dust particles being blown onto the part via the fan, or from the outside due to an open door could attach themselves to the part, and thus many companies are using Laminar Flow benches or a clean room to perform these parts handling processes under.

Transportation Protection for Large Susceptors and Gas Floating Disks

Large susceptors and gas floating disks, while being large components, can still be damaged during shipping if they are not supported correctly.

The majority of shipping damage comes from vibration and uneven pressure as opposed to a large accident. The large components need to be fully supported in the shipping container and any tilting or even pressure to one side while traveling for extended periods of time can cause warping of the component which will be harmful to the reactor.

To protect the large parts they need to be fully supported with clean packaging material to distribute the load throughout the whole component inside the crate and packaged to absorb vibration.

Moisture protection also needs to be considered. By including sealed inner bags and desiccant one can avoid condensation build up during the process of packing, unpacking, and shipment.

Crates should also be moved via forklifts and lift equipment while being kept relatively level as well as maintaining pressure on the crate to not shift the internal load during the transport phase.

Incoming Inspection Standards Before Epitaxy Reactor Installation

The last chance to catch problems with a part before putting it into an epitaxy reactor is when the part is received.

Though a part looks clean after being stored and shipped, there could still be contaminants or small defects present that might not be discovered until the reactor is hot.

The inspection process should take place in a clean area, where packaging can be opened without creating dust. The part can then be viewed closely under a strong light to look for defects, discoloration, chipped corners, or damaged coatings.

Large components such as gas floating disks and susceptors also need to be inspected for flatness and proper dimensions because small changes to either may cause performance problems. Many facilities will check surface cleanliness, as well, just before putting the part into the reactor.

Having detailed records for each part, including serial numbers and pictures, can also be a great aid when a part eventually fails or causes problems later on.

Thorough incoming inspection does not just involve refusing to accept bad parts. It allows the engineer to find minor problems before they become production concerns, allowing for better process stability, fewer unexpected failures, and higher wafer yield.