Energy Continuous Adjustment Precision Analysis of High Voltage Power Supply for Wide Energy Range Ion Implanter
Ion implanters used in semiconductor manufacturing must be capable of operating across a wide range of energies to meet diverse doping requirements. The implant energy determines the depth of the dopant distribution, with energies ranging from sub kiloelectronvolt for shallow junctions to megaelectronvolt for deep implants. The high voltage power supply must provide continuous energy adjustment with precision sufficient to achieve the required implant depth control.
Ion implantation introduces dopant atoms into semiconductor wafers by ionizing the dopant, accelerating the ions to high energy, and directing them into the wafer. The ion energy, determined by the acceleration voltage, sets the mean depth of the implanted dopant. The energy must be precisely controlled to achieve the designed junction depths.
Wide energy range implanters cover energies from hundreds of electronvolts to several megaelectronvolts. This range spans four orders of magnitude, challenging the power supply design. Different acceleration stages may be used for different energy ranges, with the power supply providing voltage to each stage. The continuous adjustment across the range requires coordination of the multiple stages.
Energy precision refers to the accuracy and resolution of the energy setting. The energy is proportional to the voltage, so voltage precision directly translates to energy precision. For typical semiconductor applications, the energy precision requirement is a fraction of a percent, corresponding to voltage precision of parts per thousand or better.
Continuous adjustment requires that the energy can be set to any value within the range, not just discrete steps. The power supply must provide continuously adjustable output voltage. The adjustment resolution must be fine enough to achieve the smallest required energy increment. The adjustment mechanism must be smooth, without jumps or discontinuities that would affect the implant.
Voltage regulation accuracy affects the energy precision. The output voltage must match the commanded value within tolerance. The regulation must be maintained despite variations in load current, input voltage, and temperature. The feedback control must have sufficient gain and bandwidth to maintain regulation.
Voltage stability over time affects the implant reproducibility. The voltage must not drift during an implant or between implants. Drift causes energy variations that affect the implant profile. The power supply must have low drift, typically specified in parts per million per hour or per degree Celsius.
Energy switching between implants of different energies must be fast for high throughput. The power supply must transition from one voltage to another quickly and accurately. The transition time depends on the voltage difference, the output capacitance, and the available current. Fast transitions enable rapid change between implant recipes.
Calibration establishes the relationship between the commanded voltage and the actual ion energy. The calibration accounts for voltage drops in the acceleration column, space charge effects, and other factors that affect the energy. Regular calibration maintains the accuracy over time. The calibration data enables correction of any systematic errors.
Energy verification during implant confirms that the energy is correct. Faraday cups or other detectors can measure the beam energy. The measurement can be used for feedback control or for quality assurance documentation. The verification must be accurate and not interfere with the implant process.
Multi stage acceleration for high energies requires coordination between stages. The total energy is the sum of the voltages applied to each stage. The stages must be balanced to prevent voltage stress concentration. The control must coordinate the stage voltages to achieve the desired total energy while maintaining the proper distribution across stages.
