Scales for the Semiconductor Fabrication Industry

We meet the needs of the semiconductor fabrication industry by providing reliable, accurate and safe methods to weigh chemicals and gases used for the manufacturing of integrated circuits and silicon wafers, including those in electronics assembly operations.

Arlyn Scales is the leader in corrosion resistant technology for weighing scales used in harsh environments. We manufacture a complete line of scales and accessories designed for weighing and monitoring the usage, feed rate, and inventory of corrosive chemicals and/or materials.

Chemicals/Materials include:

• Atmospheric gases (argon, helium, hydrogen, oxygen, nitrogen)
• Corrosive gases (chlorine, hydrogen bromide, and chloride)
• Dopant gases (arsine, phosphine)
• Etchant gases (halocarbons, hydrogen chloride, and fluoride)
• Reactant gases (ammonia, carbon dioxide, nitrous oxide, tungsten hexafluoride)
• Precursor gases (silane, dichlorosilane, trichlorosilane, silicon tetrachloride)
• Soldering and cleaning gases (nitrogen, carbon dioxide)

Meeting the Weighing Needs of the Semiconductor Manufacturing Industry

Weighing technology from Arlyn Scales ensures reliable and accurate measurement of chemical gases during the production processes to maintain high levels of product purity. From silicon wafer fabrication and integrated circuit production facilities to PC board manufacturing and electronic assembly operations, producing an integrated circuit requires over 30 different gases (examples seen above). Processes include chemical vapor deposition, etching, oxidation, doping, and inerting applications. During this time, monitoring the supply of liquefied gases via weight is critical.

Measuring the Contents of Gas in Semiconductor Fabrication

Chemicals used during these processes are typically stored in cylinders or dewars. In order to store a significant amount of the gas, it is often pressurized, liquefied and stored in a high-pressure tank. Valves are then used to dispense the gas in the order, and in the amount that is required.

While measuring the gas pressure through the valve may be the least expensive and most convenient method, it is also thoroughly inaccurate. Knowing how much gas is remaining in each cylinder so that the supply does not run out helps avoid shutting down production lines. In addition, damage caused to products by excessive or interrupted gas flow during the production process can be extremely costly

Liquefied gas boils into the gaseous state and is then dispensed. Therefore, the gas pressure valve may remain constant as long as there is liquid remaining. As soon as the last of the liquid boils off, the gas pressure will decrease to zero. There will be no warning that the liquid content is nearing the empty point. The only practical means of accurately measuring the contents of gas remaining is to weigh the entire cylinder.

Cylinder, Platform, and Electronic Scales

Corrosive-Resistant, High Capacity Scales

After compensating for the weight of the cylinder itself, an electronic scale reading will show the amount of liquefied gas remaining. The output of the scale is often tied into other processing equipment, which is used to alert the operator of the condition of the cylinder.

One of the most common gasses used is liquefied chlorine. Since this material is very harsh on the surrounding equipment, platform scales that hold the gas cylinder should be manufactured from stainless steel to prevent corrosion. Also, consider that the weight of a full canister can be more than one ton. For this purpose cylinder scales supplied by Arlyn Scales have capacities over a ton – some even more than 3000 lbs.

Stainless Steel Shielding

One of the most difficult environmental issues that are often found in these facilities is electronic interference. This includes both electromagnetic and radio frequency interference. This may be caused by a wide variety of process and communication equipment and electronic scales are generally very sensitive to all types of electronic noise.

Load sensors on the scale use signals in the millivolt range. This signals must travel over fairly long wire lengths. These wires can act as an antenna for any type of electronic signals that may be in the area. That will cause distortions to the desired signals and errors in the weight results.

To avoid these problems, scales for semiconductor fabrication should be designed with very extensive shielding and filtering. Stainless steel has very good blocking properties for scales used in these environments, Arlyn Scales places their stainless steel load sensors inside stainless steel tubes in the frame of the scale. Then the ends of the tubes are closed with a stainless steel plate while the plates are attached to the tubes with a continuous stainless steel weld.

All of these efforts will provide extensive shielding for the load cells and load cell cables. The load cells themselves should be carefully grounded to the stainless steel frame. A braided copper strap is used for this purpose. It is bolted to both the load cell and the frame with stainless steel hardware. The load cell cable running internally in the tubing is wrapped around a ferrite core. This also helps to attenuate interference signals. The access to the load cell is covered with a removable stainless steel plate, which is also bolted to the tubular frame. Graphite impregnated gasket material is used to ensure excellent contact between the plates and the frame.

Output Communications

The scales must output the weight information to other process equipment that will monitor this weight. A standard method of communication is a 4-20 ma current loop. The cable that runs out of the scale is also susceptible to interference signals. Again, a ferrite core is used to suppress this interference.

Whether the application requires a standard or custom weighing system, Arlyn Scales’ engineers will help find the right solution to best meet your weighing needs. Learn why our industrial scales are best suited for this environment and process and then contact us for help with your decision or possibly for a custom solution.