Characterization of high density matrix microwave argon plasmas by laser absorption and electric probe diagnostics

Abstract

Microwave plasma sources distributed on a planar matrix configuration can produce uniform bi-dimensional plasmas free from magnetic field in the 100 Pa pressure range. In argon, such uniform sheets of plasma have been obtained with ion densities in the range of 1012 to 1013 cm−3 with microwave power ranging from 0.4 to 2 kW. The electrical characterization of the plasma has been investigated using a cylindrical Langmuir probe. A first feature concerns the plasma potential that exhibits quite high values due to the large increase in the electron temperature towards the source plane where the microwave electric field is applied. Secondly, the decrease in the electron temperature observed when increasing the microwave power can be justified by the apparition of multi-step ionization mechanisms via metastable and higher excited states of Ar atom. The concentration and temperature of Ar(3P2) metastables have been measured by laser diode absorption spectroscopy. The results indicate that the presence of Ar(3P2) metastables is significant at 2 cm from the source plane with concentration and temperature values varying from 1010 to 1011 cm−3 and from 500 K to 1300 K, respectively, as functions of argon pressure and microwave power. An analytical model using a few simplifying assumptions provides a plasma picture in good agreement with the experimental results.

Measured density of copper atoms in the ground and metastable states in argon magnetron discharge correlated with the deposition rate

“…A very reliable method to obtain the gas temperature is from the linewidth of the Doppler-broadened absorption profile of a specific line, measured with a single-mode tunable diode laser. Absorption from argon metastable atoms is particularly popular in pure argon plasmas 17,18,19,20 or by adding a small amount of argon to the halogen based plasmas 21 . Another commonly used technique consists of adding a small amount of a diatomic molecule, very often N 2 , to the plasma and on the measurement of its rotational temperature.…”

High deposition rates of uniform films in tetramethylsilane-based plasmas generated by elementary microwave sources in matrix configuration

“…7 in Ref. [8]). The electron temperature T e sharply decreases away from the source plane, where the microwave electric field is applied, and becomes nearly constant in the central volume of the plasma.…”

“…Assuming an ambipolar diffusion of the plasma, the floating potential (equal ion and electron current densities) at the source plane is thus equal to the wall potential, generally at the ground potential. Since the electron temperature is maximum at the source plane, the difference V p − V f is also maximum, so that the plasma potential reaches a quite high initial value at the reactor wall [8]. Fig.…”

“…The solution recently proposed is the generalization of the concept of plasma source distribution applied to ECR sources [5] to microwave plasma sources free from magnetic field. This novel kind of plasmas [7,8], so-called matrix plasmas, can generate uniform sheets of plasma over a wide range of argon pressure, from 7.5 to 750 Pa with densities between 10 12 and 10 13 cm − 3 at 20 mm from the source plane [7].…”

Investigation of Nucleation and Growth of Nanocrystalline Diamond Films Deposited at Low Temperature Using In Situ Laser Reflectance Interferometry

“…Among these new technologies, distributed antenna array (DAA) microwave system was developed to provide high density microwave plasma sources for large area depositions while ensuring relatively low substrate temperatures, below 400 °C. This new concept to realize a planar reactor comprises a 2‐dimensional matrix of several single microwave plasma source elements without using magnetic fields . A DAA reactor using a 4 × 4 microwave antenna matrix has been successfully used at low pressure (<1 mbar) to deposit NCD films on 4‐inch silicon wafers with low surface roughness (<20 nm) and low grain size (<20 nm), while keeping a good thickness uniformity (∼10 %), at growth rates up to 60 nm h −1 .…”