# Mitigation of Electro Magnetic Interference by Using C-Shaped Composite Cylindrical Device
###### Abstract  
The extremely low-frequency (ELF) and its corresponding electromagnetic field influences the yield of CMOS processes in the foundry, especially for high-end equipment such as scanning electron microscopy (SEM) systems, transmission electron microscopy (TEM) systems, focused ion beam (FIB) systems, and electron beam lithography (E-Beam) systems. There are several techniques to mitigate electromagnetic interference (EMI), among which active shielding systems and passive shielding methods are widely used. An active shielding system is used to generate an internal electromagnetic field to reduce the detected external electromagnetic field in electric coils with the help of the current. Although the active shielding system reduces the EMI impact, it induces an internal electromagnetic field that could affect the function of nearby tools and/or high-performance probes. Therefore, in this study, we have used a C-shaped cylindrical device combined with an active shielding system and passive shielding techniques to reduce EMI for online monitoring and to overcome the aforementioned issues. In this study, the active shielding system was wrapped with a permalloy composite material (i.e., a composite of nickel and iron alloy) as a tubular device. A C-shaped opening was made on the tubular structure vertically or horizontally to guide the propagation of the electromagnetic field. This C-shaped cylindrical device further reduced electromagnetic noise up to \(-5.06\) dB and redirected the electromagnetic field toward the opening direction on the cylindrical device. The results demonstrated a practical reduction of the electromagnetic field. p 2021 14 January 20221 14 January  
equipment to manufacture semiconductors equipment should perform an ELF and EMF audit before installing semiconductor manufacturing equipment to determine if the areas are compatible with the equipment's immunity limits to prevent having to relocate equipment due to interference generated by the facility infrastructure or other equipment [11]. After installing semiconductor manufacturing equipment, the user should perform an ELF and EMF audit again to determine if the areas are still compatible with the semiconductor-manufacturing equipment EMI immunity limits and that the equipment itself does not generate ELF EMFs to prevent interference with other nearby ELF-sensitive equipment. In addition, every tool or instrument that uses electricity generates associated electromagnetic fields. It might be ELF. For example, a 10-nanometer offset can be observed, if electron beams work with an acceleration voltage of 300 V under EMI with a field strength of 1 mG [12]. In general, there are two methods to reduce EMI, including the active shielding method and the passive shielding method [13; 14; 15; 16; 17; 18]. The passive shielding is to build an electromagnetic-free chamber for protecting delicate equipment. The appropriate materials are sheets of Mu-metal or permalloy. They have excellent shielding properties to absorb or reflect electromagnetic fields [19; 20]. The propagation of electromagnetic waves thus has an impedance discontinuity on the propagation path. The major drawback of the passive shielding method is that it is expensive and also inconvenient for large-scale coverage [21]. The active shielding method uses coils with a current-sensing field with a sensor and induces a man-made electromagnetic field to reduce the stray magnetic field. Upon data processing, the processor sends a signal which responds to the amplitude of the convertor for counteracting the outcoming electromagnetic field [22; 23]. The convertor immediately delivers a current to the electric coils which produces a corresponding anti-electromagnetic wave to counteract the sensed electromagnetic wave. Even the active shielding coils are strapped only to the frame of EMI-sensitive equipment; the disadvantage of the active shielding method is that it may be a new source of EMI [24]. Thus, it is necessary to develop better shielding devices for the irresistible ELF and EMI.