Miniature High Voltage Ionization Power Supply Design for Contamination Monitoring Sensor in Extreme Ultraviolet Lithography
Extreme ultraviolet lithography uses 13.5 nanometer wavelength light to pattern semiconductor devices with nanometer scale features. The EUV light is generated by plasma produced from tin droplets irradiated by high power laser pulses. Contamination in the lithography system can degrade the optical components and reduce the imaging quality. Contamination monitoring sensors detect contamination particles using ionization methods, requiring miniature high voltage power supplies that fit within the constrained sensor volume.
EUV lithography systems contain multiple mirrors that reflect and focus the EUV light. The mirrors have multilayer coatings that provide high reflectivity at the EUV wavelength. Contamination deposition on the mirror surfaces reduces reflectivity, decreasing the light intensity and affecting the imaging performance. Contamination sources include tin debris from the plasma generation, hydrocarbon deposition from residual gases, and other particles from the system environment.
Contamination monitoring sensors detect particles in the EUV system environment, enabling contamination control measures. The sensors may use ionization methods where particles are charged and detected through their electrical effects. Ionization requires high voltage to create the electric fields that charge particles. The sensors must be compact to fit within the lithography system without interfering with the optical path.
Particle charging through ionization uses corona discharge or field charging methods. Corona discharge creates ions through gas ionization near a high voltage electrode. The ions attach to particles, charging them. Field charging occurs when particles in a high electric field become polarized and attract ions. Both methods require high voltage electrodes that create the necessary electric fields.
Miniature high voltage power supply design for contamination sensors must achieve compact size while providing adequate voltage and current. The sensor volume may be severely constrained, requiring power supplies with minimal footprint. The voltage requirements depend on the ionization method, typically ranging from hundreds to thousands of volts. The current requirements depend on the ion generation rate, typically microamperes to milliamperes.
Compact high voltage generation uses specialized topologies that minimize component count and size. Charge pump circuits step up voltage using switched capacitors, eliminating the need for transformers. Cockcroft Walton multiplier circuits cascade multiple stages to multiply voltage from a lower input. These topologies enable compact implementation using integrated capacitors and switches.
Miniature transformers can provide voltage step up in compact packages. Planar transformers use flat windings on printed circuit boards, achieving low profile height. High frequency operation reduces the transformer size, as the magnetic core and windings scale inversely with frequency. Miniature transformers can provide thousands of volts output in packages of centimeter scale.
High voltage insulation in miniature packages requires careful design. The insulation must prevent arcing and breakdown at the operating voltage. The limited space constrains the insulation thickness and the spacing between conductors. Insulation materials with high dielectric strength enable thinner insulation. Potting materials encapsulate the high voltage components, providing insulation and mechanical support.
Power consumption of miniature ionization power supplies must be low to minimize thermal load on the sensor and the lithography system. The ionization process requires continuous high voltage, drawing continuous current. The power supply efficiency determines the input power required for the output voltage and current. High efficiency reduces the power consumption and the heat generation.
Thermal management in miniature power supplies addresses the heat generation from power conversion. The limited volume restricts the heat dissipation capability. The power supply must operate within acceptable temperature limits despite the confined space. Thermal paths must conduct heat from internal components to the external environment.
Integration with contamination sensor electronics combines the high voltage generation with the sensor detection circuits. The integrated package must fit within the sensor volume while providing both high voltage and signal processing functions. The integration must maintain electrical isolation between the high voltage circuits and the low voltage detection circuits.
Reliability requirements for contamination monitoring sensors require the power supply to operate continuously throughout the lithography system operation. The power supply must maintain output voltage and current without degradation over extended periods. The reliability must match the sensor lifetime requirements, which may be years of continuous operation.
Environmental conditions in EUV lithography systems include vacuum or low pressure, elevated temperature from plasma heating, and potential contamination exposure. The power supply must operate in these conditions without degradation. Vacuum operation affects heat transfer and may affect insulation characteristics. The design must account for the specific environmental conditions.
