Contamination Control System

Electrostatic Control Program

A Well Designed Contamination Control Vacuum System should have an effective Electrostatic Control Program in it. Electrostatic Control Program is no longer an optional consideration, but an essential and integrated part of any modern day contamination control system.

Shrinking Geometries & Technology

Every reduction in size increases susceptibility to lower voltage levels. Sometime ago, some wafers could withstand 1500Volts without incidence. Today, with the SEMI E78 standard (Semiconductor Equipment Material International), semiconductor industry strive to keep static charge below 100Volts, and the recommendated Volt is likely to be 25Volts.

To put it in perspective, the average volt a person gets after a walk on the carpet, follow by a touch on a doorknob is 4000Volts.

Electrostatic discharge event is rapid, spontaneous transfer of electrostatic charge by an electrostatic field between two objects that have different electrostatic potentials. The resulting current produces radio waves, interfere with equipment operation; causing microprocessor lock-ups, corrupting memory, or altering datas in the process of being analyzed. Thus, equipment lockup, misdiagnosed as a software or hardware problem is usually a result of it. Electro-Magnetic Inteference (EMI) produced by Electrostatic discharge (ESD); both radiated and conducted from the site of the occurrence; are especially difficult to locate, often reducing equipment availability and production capacity.

Static discharges that are too small to be noticed by personnel can instantly melt metal lines or silicon; break through oxide layers or cause other damage. ESD events can damage production tools and create random defects in products, eg. damage features of photo masks used for ‘printing’ patterns on wafers. In wafers production facility, ESD events can result in latent failures that does not impact functionality immediately, it doesn’t kill, it wounds. For example, products can make the way through the production process and quality checks, but only to fail six months later at the client site. When these happen, it will cost a lot more and also the loss of client’s confidence.

Fire & Explosion Hazard

Pulverized materials that passes through chutes or pneumatic conveying systems; steam, air or gas flowing from any opening in a pipe or hose; where the steam is wet or the air or gas stream contain particulate matter are common static electricity generation sources.

It is also noted from NFPA’s observation that humidification is not a cure for all static problems. For example, some plastics are capable of accumulating static charges even though the atmosphere might have a relative humidity of up to 100 percent.

Static Electricity if not managed, is often the Ignition Source for an ignitable mixture, such as in high speed dust conveying situation.

A nuisance & a maintenance cost?

The presence of static draws dust particle within its field, therefore increasing the need to clean and maintain the internal surface of the pipes or ducts that are used to transport these captured dust. More so in situations where dust particles may contain toxic or might have pathogen, (especially in system serving life science research or facilities), it is not wise to leave it unattended for too long too.