Electron temperature measurement in a slot antenna 2.45 GHz microwave plasma source* J. Cotrino, a) A. Palmero, and V. Rico Departamento de Fı ´sica Ato ´mica, Molecular y Nuclear, Facultad de Fı ´sica, Avda. Reina Mercedes s/n, Universidad de Sevilla, 41080 Sevilla, Spain A. Barranco, J. P. Espino ´ s, and A. R. Gonza ´ lez-Elipe Instituto de Ciencias de Materiales (CSIC-Univ. Sevilla), Avda Ame ´rico Vespucio s/n, 41092 Sevilla, Spain Received 26 May 2000; accepted 5 February 2001 The electron temperature in a low-pressure microwave electron cyclotron resonance slot antenna produced plasma is obtained. The upper excited atomic level populations have been measured through atomic emission spectroscopy. It has been shown that the Corona balance provides a good description of such levels and, based on this fact, a simple argon collisional-radiative model has been used in the temperature determination. © 2001 American Vacuum Society. DOI: 10.1116/1.1358881 I. INTRODUCTION Microwave plasma excitation with 2.45 GHz offers a simple and cheap method to obtain significantly higher de- grees of ionization and ion concentrations (10 11 – 10 12 cm -3 ) than plasma excitation with radio frequency (13.56– 27.12 MHz. Furthermore, the concentration of chemically active radicals is comparatively high 1 and the electron energy dis- tribution function shows a larger number of highly energetic electrons. 2 The reason for these effects can be found in the more effective power coupling of the microwave field with the plasma. In recent years there has been a renewed interest in the generation and use of plasmas in connection with many tech- nological applications. By the use of microwave fields, sur- face wave sustained discharges constitute the most promising method for the production of large volume plasmas. The first applications of surface waves were developed in the 1970’s, 3,4 and new devices are in development today. The recently developed source slot antenna SLAN plasma de- vice that enables the generation of 2.45 GHz discharges into large volume reactors. 5 At present it is used in our laboratory for the preparation of SiO 2 thin films by plasma enhanced chemical vapor deposition. Due to its structure based in a slotted annular wave guide, the SLAN exhibits the same in- dependence on discharge radius than that reported for Lisi- tano coils. 6 The combination of this feature with the surface wave operation mode provides an efficient applicator for the generation of very large volume plasmas. The electron cyclotron resonance ECR plasma-heating principle has been proved to be a very efficient method of extending the operating range of microwave discharges to- wards low-pressure regions. Thus, ECR plasma sources can be used for applications down to the 10 -5 Torr pressure range, while still yielding comparatively high ion densities and low electron energies. 7 The ECR microwave plasma source concept used here is based on the SLAN principle. It offers a solution for many of the problems that occur with conventional microwave sources. The magnetic field in the ECR version of SLAN is produced by SmCo permanent magnets. They are placed between the microwave applicator and the quartz bell jar, to favor a compact structure. 8 The wide range of potential applications of ECR plasma sources, have motivated considerable experimental effort aimed at de- termining how excited particles produced in ECR plasmas depend on external parameters. Understanding the basic physic of the ECR plasmas include the determination of the electron temperature T e and the plasma density n e . Both parameters have been measured previously, radial and down- stream, in a similar SLAN source using double-Langmuir- probe techniques. 8 In this article we present a different method to determine the value of T e . The procedure is based on the use of optical emission spectroscopy to characterize the argon plasma as a function of pressure and a simple collisional-radiative model for the argon atom. The following three reasons have motivated this article: i to develop a nonperturbative method to determine the electron temperature T e in a SLAN device based in atomic emission spectroscopy, ii to provide an experimental con- firmation of a Corona balance regime for the argon upper excited states in the experimental conditions of this work, and iii to show indirect evidence of Maxwellian electron energy distribution functions in an ECR SLAN plasma. II. EXPERIMENTAL DETAILS A. Vacuum system The vacuum system is a  • 35 2 • 30 cm 3 stainless steel cylinder. The plasma source is mounted to the chamber via an ISO-K 250 flange. The pumping system consists of two stages. The first stage is a rotatory pump with a pumping speed of 6 m 3 /h. The second stage is a turbomolecular pump with a pumping speed of 230 l/s. The achievable final pres- sure is below 10 -6 Torr. Argon is supplied through a gas manifold connected to a dosing ring placed into the plasma chamber of the source. The Ar supply is controlled by mass flow controllers UNIT. Pressure measurement are made *No proof corrections received from author prior to publication. a Electronic mail: cotrino@cica.es 410 410 J. Vac. Sci. Technol. B 19„2…, MarÕApr 2001 1071-1023Õ2001Õ19„2…Õ410Õ5Õ$18.00 ©2001 American Vacuum Society