Semiconductor manufacturing is divided into two parts - "front-end" and "back-end". Back end semiconductor manufacturing refers to the fabrication processes after all of the features/circuits have been created on the wafer. A combination of extreme accuracy and precision combined with high throughput, makes for exciting technology.
Servo drives are used in many processes in back end semiconductor manufacturing because they provide excellent performance and repeatability; exactly what's needed in high-end semiconductor fabrication.
Wafer Inspection
Optical wafer inspection looks for irregularities that can cause malfunctions in the final end-product. Defects and nuisances are easily identified down to 30nm in size with effective usability down to 10nm. Electron-beam inspection overcomes the limitations of optical inspection and is reliable down to sub-3nm resolution. Although E-beam inspection finds the smallest defects, it has a lower throughput when compared with optical inspection. Once defects and nuisances are identified they are mapped and either repaired or avoided.
Wafer Probe / Wafer Test
This is the first time in the semiconductor fabrication process that the chips are tested to see if they work as designed. The chips are still on the wafer and are functionally tested using a test fixture with needles that make contact with the circuits on the surface of the chip. Probes send and measure signal responses from the chips. Chips that fail are repaired if possible, otherwise they are discarded after the dicing process.
Wafer Dicing
In this back end semiconductor manufacturing process the completed wafer is sliced into individual chips. Automated methods include mechanical sawing and laser cutting. Mechanical sawing is accomplished with a dicing saw that uses a circular dicing blade to cut the die into sizes ranging from 35mm to 0.1mm. Die-handling equipment is then used to transfer the chips to the die-bonding process.
Servo motion is ideal for controlling the cutting blade as well as for positioning the dicing saw and the wafer.
Die Bond
Individual die are too small and delicate to be handled on their own. They need to be protected and there also needs to be an easy way to electrically interface with the die. Die Bond, also called Die Attach, is the process of securing the bare die to a substrate.
In later steps the substrate will act as the interface between the microscopic scale of the chip and the macroscopic scale of electronics manufacturing. It will also be the foundation of the protective chip package seen on PC boards.
Wire Bond
After die bond, the wire bond process connects each pad on the die to a corresponding pad on the substrate via a thin gold wire. This forms the electrical connection between the silicon die inside the chip package and the pins on the outside. The wire bond process is used on classic chip packages such as dual in-line package or DIP, with the familiar black oblong rectangle with silver pins sticking out like bug legs, as well as PLCC packages with conductors on all four sides.
With so many connections to be made on each chip, wire-bonders move with lightning speed to maintain throughput. In fact this is one of our highest bandwidth applications!
Solder Bump / Flip Chip
A modern alternative to wire bonding, flip chips are mounted "upside-down". Hence the name "flip chip". Instead of wires connected around the periphery of the chip as in wire bonding, an array of "bumps" are formed on the surface of the chip. These bumps are then used as connection points from the chip to the outer package. The advantages of flip chip technology include:
- Better connections to the chip as opposed to wire bonding where the wires add extra length, capacitance and inductance that limit signal speed.
- More attachment points available since the whole area of the chip is available instead of just the edges
- Faster production
- Smaller overall package size
The flip chip process is used to make Ball Grid Array chip packages, also called a BGA package.
Encapsulation
Wrapping up the back end semiconductor manufacturing process the bonded die and frame are sealed - either by a molded plastic compound, or by the attachment of a sealed lid. The silicon die is now ready to be used in electronics manufacturing.
