Managing Wafer Fabrication

June 27, 2005

6 Min Read
Managing Wafer Fabrication

The semiconductor industry uses wafer fabrication technology that produces highly sophisticated electronic logic and control devices known as integrated circuits (IC). This process involves silicon, the basic element in sand, provided in thin disks or wafers, and modifies if through a process that involves a vacuum, heat, and the implantation of atoms by chemical and gaseous means creating sub-micron circuits of miraculous structure. Once the process is complete, you'll have a wafer of pure silicone with millions of devices in its makeup. The devices are identical so the next step is to dice the disks into thousands of IC devices. It is packaged with electrical connections and rigorously tested. The "front end" is the technology used during the creation of the disk and the remaining portion is the "back end."

Wafer fabrication equipment includes furnaces that heat the silicone into a crystal that is drawn into a log-like structure. This structure is then cut into disks. The next step involves lithography and chemical or gas deposition, which creates the electronic architecture that will become the finished wafer.

Shock Absorber

In wafer fabrication, shock absorbers provide controlled, predictable deceleration. These products work by converting kinetic energy to thermal energy. More specifically, motion applied to the piston of a hydraulic shock absorber pressurizes the fluid and forces it to flow through restricting orifices, causing the fluid to heat rapidly. The thermal energy is then transferred to the cylinder body and harmlessly dissipated to the atmosphere. This process allows for safe deceleration of moving loads in a relatively short distance at the end of the machine cycle.

Shock absorbers come in adjustable and non-adjustable varieties. The hydraulic devices generally use Krytox as the fluid in many semiconductor applications. These semiconductor units are usually miniature and not adjustable. The two most common types of dampening are dashpot and the progressive type of deceleration. Dashpot or constant orifice area dampening provide the largest shock force at the beginning of the stroke and provide high-energy absorption in a small economical design. Progressive dampening provides deceleration with a gradually increasing shock load. The initial minimal resistance at impact protects delicate loads and machinery from damage. Progressive dampening shock absorbers also have built in self-compensation for a wide range of weights and velocities. This type of dampening provides smooth decelerations in applications where energy conditions are unknown.

Often when the dampening profile is not known on a new design, adjustable units rather than non-adjustable are used to determine the best profile. The principle reasons for using non-adjustable units is that they are tamper-resistant and less costly.

Many applications are simple X and Y types of motion that use pneumatic cylinders or slides to create the back and forth or up and down motion. Most slide manufacturers offer shock absorbers as an option. Pneumatic cylinders use internal cushions, which are not very precise in providing smooth stops. For precision stops on cylinder applications, the shocks are mounted in the device in motion and used to provide a soft stop.

Pneumatic Rotary Actuator Pneumatic rotary actuators are also used to provide up to 360 degrees of motion. These devices also use shocks to provide smooth stops and, in some cases, adjust the stroke of a unit.
Servo- and stepper-driven stages will use shocks as an emergency stops. Usually these motor-driven units cycle back and forth as dictated by the motion profile and going into a hard stop is not good practice. If a travel overrun does occur, then a shock absorber can supply a smooth deceleration and provide a soft stop. Shock absorbers designed for this type of emergency stop are either one-shot shocks or designed for very limited cycle life. Front end processes—where the disks are created—employ shock absorbers to smooth the point-to-point transfer of wafers. Wafer boats carry them between process stations. Loads at the front end are generally light and velocites there usually low. The same can be said for loaders and unloaders. Back end processes are generally light loads but they are of high and varying velocities. Dicing saws, packaging equipment, and test equipment are usually servo motor-driven with pneumatics on doors and transfer mechanisms. Shock absorbers continue to be economical, efficient ways of converting kinetic energy created during process to eliminate damage to equipment.
Rate Controls Rate devices control the rate of the total travel of the mechanical motion. They are linear or rotary. These linear devices are hydraulic and control motion on the extend stroke, the retract stroke, or both directions. They are available as adjustable or non-adjustable. Rotary Viscous Damper (RVD)
An RVD consists of an outer housing that is stationary and an inner disk that rotates via shaft connection to the rotating load. The device is filled with silicone fluid whose viscosity matches the application. As the disk rotates, it shears the silicon fluid and produces controlled rotary motion in both directions. Applications for these devices involve pneumatically or manually generated motions that require economical motion controls. Process chambers that are opened by hand, as well as roll feeders and pneumatic loaders, are machines on which such devices are used. Wire Rope Isolator Wire rope isolators are simple devices made of stainless steel stranded cable and retaining bars. They provide a high performance level of shock and vibration isolation. They are not affected by temperature and are environmentally stable.   Vibrations from pumps, fans, motors, and other rotating devices can be a source of problems and downtime. Imagine a service cart moving between stations, that slight movement can produce intermittent difficulties that are hard to identify. These problems consist of calibration, sensor accuracy, false process alarms, and long-term damage to solder joints and connectors. Wire ropes are a good alternative to elastomer type units that age and harden. Wire rope isolators are also used in shipping containers and skids to eliminate damage caused by shock and vibration to equipment during transport. About Enidine. With its world headquarters located in Orchard Park, NY, Enidine Inc. specializes in the design and manufacture of standard and custom energy absorption and vibration isolation product solutions within the industrial, aerospace, defense, and rail markets. Enidine products include shock absorbers, rate controls, air springs, wire rope and compact wire rope isolators, heavy industry buffers, and emergency stops. Its facilities are located throughout the U.S., Germany, U.K., Japan, Korea, and China.

Sign up for the Design News Daily newsletter.

You May Also Like