1. Why establish an electrostatic protection system?
With the increasing development of semiconductor manufacturing technology, the width and spacing of interconnecting wires are getting smaller and smaller, and the integration density of integrated circuits is getting higher and higher. At the same time, the problem is that the electrostatic breakdown voltage of the device is getting lower and lower. In the development and production of semiconductor devices, we must pay attention to the problem of static electricity and take electrostatic protection measures.
This article will give the causes and characteristics of static electricity in the production of semiconductor devices, and comprehensively analyze the methods and measures of static electricity protection. Electrostatic damage in production is one of the important factors affecting the reliability of the device. The manufacturer must establish an electrostatic protection system for comprehensive protection.
2. Hazards of static electricity
Electrostatic adsorption: In the process of device production, due to the extensive use of utensils and materials made of quartz and macromolecular substances, their insulation is very high, and some inevitable friction during use will cause the surface charge to accumulate continuously, and the potential will become more and more high. Due to the mechanical effect of static electricity, the floating dust in the workplace is adsorbed on the surface of the chip, thereby changing the impedance between the lines and affecting the function and life of the semiconductor device.
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(Picture: Damage to the internal circuit of the chip)
Electrostatic discharge (ESD): The electrical breakdown of components caused by electrostatic discharge is the main way of electrostatic hazard. The main mechanisms of device damage are thermal secondary breakdown, metal coating melting, dielectric breakdown, arc discharge, surface breakdown, body breakdown, etc. Electrostatic discharge can cause hard or soft breakdown of the device.
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(Picture: IC plastic encapsulation material causes ablation during electrostatic discharge)
3. What are the types of electrostatic protection measures?
① Internal protection method of the device: In most cases, electrostatic discharge breakdown components mainly occur near the input end of the device, so the usual protection method is to make a protection circuit in the part related to the input end. In unipolar integrated circuits (MOS circuits), high voltages are prone to appear at the input due to the high input impedance. Therefore, the protection circuit is essential. The commonly used methods are to use diodes, triodes, Zener diodes and spark gap protection.
②The external protection method of the device: The easiest way to protect the external device is to connect a resistor in series or a diode in parallel at the input end of the device. The role of the resistor is to limit the excessive electrostatic discharge current, increase the discharge time constant, and reduce the amplitude of the current pulse, while the diode can bypass the electrostatic energy. After the above protection methods are adopted, the IC's anti-breakdown voltage capability can generally be increased by 2-6 times, which protects the device from damage to a certain extent.
③ Protection of devices by anti-static system: The specific measures to establish an anti-static system are generally to set up an anti-static work area. In this work area, all personnel must wear anti-static overalls, shoes, and hats. The operator must operate on a workbench equipped with various static elimination devices. At present, the common antistatic devices on the market include ion air nozzles, ion fans, and ion air rods. How to choose these three devices depends on the location where the equipment is installed and the range of static electricity removal. Only have a good understanding of electrostatic hazard devices and take active precautions to effectively protect semiconductor devices from electrostatic hazards.
4. Closing Statement
Only by taking electrostatic protection measures and establishing a periodic monitoring system in all aspects of design, production, delivery, packaging, inspection, storage and transportation, can we achieve effective protection of electrostatic sensitive components and provide users with high-quality and highly reliable devices. Meet the high reliability requirements of semiconductor devices in various industries.