Plasma etching includes microwave electron cyclotron resonance plasma etching (ECR), reaction ion etching (RIE) and inductive coupled plasma etching (ICP)...
Plasma etching includes microwave electron cyclotron resonance plasma etching (ECR), reactive ion etching (RIE) and inductive coupled plasma etching (ICP)
The microwave energy is absorbed by the ionized gas to form a plasma. There are three absorption mechanisms of microwave in plasma: collision absorption, non-collision absorption and nonlinear anomalous absorption. The mode of absorption depends mainly on the pressure of the working gas and the nature of the plasma produced. The electron cyclotron resonance microwave plasma is collision-free absorption.
Picture 1
(schematic diagram of the overall structure of ECR)
The microwave is introduced to the ceramic window near the opening surface of the resonator through the transmission circuit. Meanwhile, the permanent magnetic steel on the ceramic window surface generates a high-strength magnetic field. Under the action of this magnetic field, the outer electrons of gas molecules in the cavity move in a circle. The ECR condition is true when the circular motion frequency of the electron is consistent with the microwave angular frequency.
Under this condition, the electrons can effectively absorb the microwave energy and be accelerated, ionizing the gas in large quantities. As a result of the collision of the electrons, the ionization efficiency is improved and more gas molecules are ionized. Therefore, in the case of no discharge electrode, the high-density and low-temperature plasma is generated by the plasma source alone. Due to the magnetic field gradient, the electron distribution in the plasma is generated and the plasma potential gradient is formed.
The advantage of ECR is that it can produce a high plasma density while maintaining a low ion bombardment energy, which solves the original contradiction between high etching rate and high selection ratio. Its disadvantages are the complex structure, the need for microwave power source, and the matching problem between microwave resonance and RF generator of sample substrate. This shortcoming is well addressed by solid-state power generator.
When the ECR system is started, the plasma has not yet formed, which is equivalent to the open state of the load. With the gradual formation of the plasma, the load state tends to improve. Therefore, whether it can adapt to load open circuit is the primary index to measure microwave power generator. The wattsine solid-state power source use the technical solution based on highly robust semiconductor power devices and adds a self-protection mechanism under extreme conditions to make it suitable for different application scenarios with dynamic load changes.
Adapting to different plasma resonators is another important index for evaluating microwave power sources. The solid–state microwave generator of Wattsine use VCO + PLL scheme with adjustable frequency to adapt to the different resonators through continuous optimization algorithm, so as to achieve the highest efficiency of microwave energy transmission in the reaction process.
Both etching methods utilize a power source with a frequency of 13.56Mhz. Wattsine's RF power equipment (power generator + matcher) has been released in August 2019. Please contact our staff for details.
Picture 2
(schematic diagram of reactive ion etching)
Picture 3
(schematic diagram of the overall structure of inductive coupled plasma etching system)
Note: part of the content is quoted from "materials man" "searching for the bottom -- plasma etching technology"
