Hazards of Static Electricity in Cleanrooms
1. Electrostatic Coulomb Force
Under the action of electrostatic Coulomb force, adsorbed dust and dirt cause increased leakage or short circuits in components, damaging performance and significantly reducing yield and reliability. For example, when the dust particle size is >100μm, the aluminum wire width is approximately 100μm, and the oxide film thickness is 50μm, the product is most likely to be scrapped. Now, with finer wire diameters and thinner oxide films, even very small dust particles can damage components. This often occurs during processes such as etching, cleaning, photolithography, spot welding, and packaging.
2. Electrostatic Discharge (ESD)
(1) The insulating oxide film of components is broken down, and the leads are burned or melted between wires. If a human body carries a static charge of 10KV (100PF), and touches a device pin, an ESD will occur. The instantaneous pulse discharge current to ground can reach a peak of 20A (10~100s). This is devastating, damaging not only high-density, fine-diameter, thin-film SiO2 devices like Lsi and Vlsi, but also general ICs and MOS devices. Generally, the withstand voltage of the device's insulating gate SiO2 film is E = (5-10) × 10⁶ V/cm. If the SiO2 film thickness is 1000, applying a static voltage of 50V-100V or higher to the device's input pin will cause breakdown. It is very common for a human body to carry static electricity exceeding 50V or 100V.
(2) Causing noise and electromagnetic interference
ESD-induced EMI has sharp peaks and strong signals, equivalent to several volts of energy in a circuit. The powerful noise, with frequencies spanning several MHz or even hundreds of MHz, can damage components, cause equipment and sensors to malfunction, and even cause equipment to crash. ESD-induced EMI can also cause erroneous signal input or latch-up phenomena. For example, in a cleanroom, if the EMI shield of a wafer is placed on a steel trolley, the ESD from the wafer will be transmitted to the trolley through inductance. Since the wheels are insulated, the diffusion of EMI can cause the wafer processing machine to crash.
(3) Electric Shock to the Human Body
ESD Human body static discharge ball
When ESD on the human body or ESD to the human body exceeds the human body's electric shock limit current by more than 5mA, people will experience various harmful sensations, causing emotional distress and operational errors among staff.
Despite significant efforts, static electricity problems in cleanrooms for semiconductors, flat panel displays, optoelectronics, etc., still affect production safety and product output, manufacturing costs and efficiency, and product quality and reliability. Foreign industrial experts estimate that the average annual product loss due to static electricity in the United States is 8-33%, and some estimate that the annual damage to the electronics industry caused by static electricity in the United States reaches $10 billion. In the 1980s, Japan analyzed scrapped electronic products and found that losses caused by ESD accounted for one-third. my country's semiconductor, flat panel LCD, and optoelectronic industries started relatively late, but electrostatic discharge (ESD) hazards still occur frequently, resulting in low yield rates. In banks, securities companies, confidential databases, monitoring centers, power dispatch rooms, and other similar settings, ESD can easily cause interference and data loss, leading to even more serious situations.