A high-resolution spectrometer monitored changes in argon emission after different gases were added to a closed-reaction plasma chamber. Plasma characteristics derived from these measurements can be used for monitoring plasma processes.
Background
Plasma is an energized, gas-like state where a fraction of the atoms has been excited or ionized to form free electrons and ions. As the electrons of excited neutrals return to the ground state, the plasma emits light at wavelengths specific to the atoms present in the plasma. The spectral profile of the emitted light is used to determine the composition of the plasma. Plasma is formed using a range of high energy methods to ionize the atoms including heat, high powered lasers, microwaves, electricity and radio frequency.
Plasma is used in industries including semiconductor manufacturing for applications including elemental analysis, film deposition, plasma etching and surface cleaning. Precise monitoring of plasma-based processes can help to minimize wafer contamination, improve quality and optimize production yields.
Plasma Monitoring
Plasma monitoring via the emission spectrum measured for the plasma sample can provide detailed elemental analysis and determination of critical plasma parameters required for controlling a plasma-based process. The wavelengths of the emission lines identify the elements present in the plasma, with emission line intensity used to quantify particle and electron densities in real time for process control.
Parameters including gas mixture, plasma temperature and particle density are critical for controlling the plasma process. Changes to these parameters via introduction of various gases or particles to the plasma chamber will change the plasma characteristics, impacting the plasma-substrate interaction. The ability to monitor and control the plasma in real time leads to improved processes and outcomes.
For example, plasma monitoring is important for process control in plasma-based etching processes. In the semiconductor industry, wafers are fabricated and manipulated using lithography techniques. Etching is a major part of this process in which materials can be layered to a very specific thickness. As the layers are etched on the wafer surface, plasma monitoring is used to follow the etching through the wafer layers and determine when the plasma has completely etched a specific layer and reached the next. By monitoring the emission lines generated by the plasma during etching, the etching process can be followed precisely. This endpoint detection is critical to the production of semiconductor materials using plasma-based etching processes.