Semiconductor manufacturing is divided into two parts: "front-end" and "back-end." Back-end semiconductor manufacturing refers to the processes that take place after all features and circuits have been created on the wafer. It requires a combination of extreme accuracy, precision, and high throughput, making it a highly advanced and demanding technology.
Servo drives are widely used in many back-end semiconductor manufacturing processes because they deliver excellent performance and repeatability—exactly what is required in high-end semiconductor fabrication.
Front-end and Back-end Processes
The semiconductor manufacturing process can be compared to creating business cards.
For business cards, the process begins with finalizing the design, followed by printing multiple copies on a large sheet of paper. The final step is cutting the sheet into individual cards.
Semiconductor manufacturing follows a similar workflow. It is divided into three main stages: design, front-end, and back-end processes. The design stage corresponds to the card design, while the front-end process is similar to printing on the sheet. The subsequent step involves cutting the wafer into individual units.
In semiconductor production, integrated circuits are first designed, and large-scale integrated circuits (LSIs) are formed on silicon wafers during the front-end process. These circuits are then separated into individual chips during the back-end process. This article focuses on the back-end process.
Outline of back-end process
Wafer Inspection
Optical wafer inspection is used to detect irregularities that may cause malfunctions in the final product. Defects can be identified down to 30 nm in size, with effective usability approaching 10 nm. Electron-beam (E-beam) inspection overcomes the limitations of optical methods and can achieve reliable detection at sub-3 nm resolution. However, while E-beam inspection is capable of identifying the smallest defects, it has lower throughput compared to optical inspection. Once defects are detected, they are mapped and either repaired or avoided.
Wafer Probe / Wafer Test
This is the first stage in the semiconductor fabrication process where the chips are tested to verify whether they function as designed. At this point, the chips are still on the wafer and are tested using a probe system with fine needles that make contact with the circuits on the chip surface. The probes send signals to the chips and measure their responses. Chips that fail testing may be repaired if possible; otherwise, they are discarded after the dicing process.
Wafer Dicing
In this back-end semiconductor manufacturing process, the completed wafer is cut into individual chips. Automated methods include mechanical sawing and laser cutting. Mechanical sawing is performed using a dicing saw equipped with a circular blade, capable of cutting dies ranging in size from 35 mm to 0.1 mm. Die-handling equipment is then used to transfer the separated chips to the die bonding process.
Servo motion is ideal for controlling the cutting blade, as well as for positioning both the dicing saw and the wafer.
Die Bond
Individual dies are too small and fragile to be handled independently. They must be protected, and an effective method is required to establish electrical connections. Die Bond, also known as Die Attach, is the process of securing the bare die onto a substrate.
In subsequent steps, the substrate serves as the interface between the microscopic scale of the chip and the macroscopic scale of electronics manufacturing. It also forms the foundation of the protective chip package used on printed circuit boards (PCBs).
Wire Bond
After die bonding, the wire bonding process connects each pad on the die to a corresponding pad on the substrate using a thin gold wire. This creates the electrical connection between the silicon die inside the chip package and the external pins.
Wire bonding is commonly used in traditional chip packages such as Dual In-line Packages (DIP), recognizable by their black rectangular shape with silver pins extending outward, as well as Plastic Leaded Chip Carrier (PLCC) packages, which have conductors on all four sides.
With a large number of connections required for each chip, wire bonders operate at extremely high speeds to maintain production throughput. In fact, this represents one of the highest bandwidth applications in our system.
Solder Bump / Flip Chip
A modern alternative to wire bonding, flip chips are mounted “upside-down,” which is how the term “flip chip” originates. Instead of using wires connected around the periphery of the chip, as in wire bonding, an array of solder bumps is formed directly on the surface of the chip. These bumps serve as the electrical connection points between the chip and the external package.
The advantages of flip chip technology include:
· Improved electrical performance compared to wire bonding, as the absence of long wires reduces added capacitance and inductance, enabling higher signal speeds
· Increased number of connection points, since the entire surface of the chip can be utilized rather than just the edges
· Faster production processes
· Smaller overall package size
The flip chip process is commonly used in the manufacturing of Ball Grid Array (BGA) packages.
Encapsulation
Concluding the back-end semiconductor manufacturing process, the bonded die and lead frame are sealed either with a molded plastic compound or by attaching a sealed lid. This step provides protection for the die and its connections. The silicon die is now ready for use in electronics manufacturing.
Precision Technology in Back-End Process
Dicing: Wafer cutting requires exceptional precision. Matsusada Precision’s high-performance high-voltage power supplies are used to ensure stability across various cutting technologies. In plasma dicing, electrostatic chucks are used to secure the wafer, requiring specialized high-voltage power supplies to generate the necessary clamping force.
Wire bonding: Lead frames used in wire bonding undergo electroplating to enhance conductivity and bonding reliability. In this process, the metal frame is immersed in a plating solution, and an electric current is applied to deposit metal onto its surface. Precision provides highly stable DC power supplies that are essential for this electroplating process.
Evaluation testing: Pre-shipment inspection includes dielectric breakdown testing, electrostatic discharge (ESD) testing, and non-destructive X-ray inspection. In dielectric breakdown testing, high voltage is applied to the insulating layer of the semiconductor to determine the voltage level at which insulation failure occurs.
To evaluate resistance to static electricity from human contact, ESD testing is performed. During this test, a capacitor is charged to a high voltage and then rapidly discharged to simulate a static pulse. Precision offers high-voltage power supplies optimized for both dielectric breakdown and ESD testing systems.
For internal quality verification, non-destructive X-ray inspection enables operators to examine the internal condition of sealed packages. Precision also provides a range of X-ray inspection systems specifically designed for high-resolution semiconductor analysis.
