Application of 160kV DC High Voltage Power Supply in Electron Beam Physical Vapor Deposition
Electron beam physical vapor deposition uses a focused electron beam to heat and evaporate source material in vacuum, depositing thin films on substrates positioned above the source. The technique achieves high deposition rates and can evaporate refractory materials that are difficult to process by other methods. The 160 kilovolt DC high voltage power supply provides the electron accelerating potential, with the voltage level affecting the electron penetration, the evaporation efficiency, and the film properties.
The electron beam evaporation process begins with thermionic emission of electrons from a heated cathode. The electrons are accelerated by a high voltage potential, gaining kinetic energy equal to the product of the electron charge and the accelerating voltage. At 160 kilovolts, electrons have energy of 160 kiloelectron volts, sufficient to penetrate into the source material and deposit energy through scattering and stopping. The energy deposition heats the source material to evaporation temperature.
The electron beam is focused and deflected by magnetic fields to create a small spot on the source material surface. The power density in the spot can reach megawatts per square centimeter, producing localized heating and evaporation. The evaporated material expands into the vacuum, traveling to substrates positioned around the source. The deposition rate depends on the evaporation rate, the source to substrate geometry, and the sticking coefficient of the evaporant on the substrate.
The accelerating voltage affects the electron range in the source material, the depth to which electrons penetrate before stopping. Higher voltages produce longer ranges, depositing energy deeper in the source. For 160 kilovolt electrons, the range in typical metals is tens of micrometers. The energy deposition profile affects the temperature distribution in the source and the evaporation characteristics. Surface evaporation occurs when the energy is deposited near the surface, while deeper energy deposition can cause different evaporation behavior.
The electron beam power, the product of accelerating voltage and beam current, determines the total energy delivered to the source. Higher power produces higher evaporation rates, enabling faster deposition. The power is limited by the ability to dissipate heat in the source material without causing splashing or other defects. The power density, the power per unit area in the beam spot, affects the local heating and the evaporation dynamics.
Beam scanning over the source surface improves the utilization of the source material and prevents deep crater formation. Without scanning, the beam creates a deep pit in the source, reducing the effective evaporation area and potentially causing source damage. Scanning the beam in a pattern across the source surface distributes the heating and produces more uniform erosion. The scanning pattern and frequency are optimized for the source geometry and material.
The high voltage power supply must provide stable voltage with low ripple for consistent electron energy and beam focusing. Voltage variations cause variations in electron energy, affecting the range and the energy deposition profile. Voltage ripple at frequencies within the bandwidth of the beam control system can cause beam position variations. The power supply design must achieve the stability required for the deposition process.
Arc detection and suppression are critical for protecting the electron gun and the power supply. Arcs can occur in the electron gun or in the process chamber when conditions allow electrical breakdown. The high voltage and the presence of evaporant vapor create conditions favorable for arcing. The power supply must detect arcs quickly and reduce or remove the voltage to extinguish the arc. Fast arc suppression prevents damage and enables rapid recovery to resume deposition.
Film properties affected by the electron beam parameters include the deposition rate, the film density, the microstructure, and the stoichiometry for compound materials. The deposition rate scales with the beam power. The film density depends on the energy of arriving atoms and the substrate temperature, with higher energy generally producing denser films. The microstructure depends on the deposition conditions including rate and temperature. For compound materials, the stoichiometry depends on the evaporation behavior of the different components.
Multi source configurations enable co deposition of multiple materials for alloy or composite films. Each source has its own electron beam and power supply, allowing independent control of the evaporation rate from each source. The relative power to each source determines the composition of the deposited film. The power supplies must be controlled in coordination to achieve the desired composition and to compensate for any differential depletion of the sources.
