ELSEVIER Surface and Coatings Technology 98 ( 1998) 1578-1583 SURfACE &COATINBS IFGIINOLOGY Study of oxygen/TEOS plasmas and thin SiO x films obtained in an helicon diffusion reactor F. Nicolazo *, A. Goullet, A. Granier, C. Vallee, G. Turban, B. Grolleau Laboratoire des Plasmas et des Couches Minces-Institut des Matl'!riaux de Nantes Universite de Nantes-CNRS, 2 rue de la Houssinere. 44072 Nantes, Cedex 03, France Abstract Thin films of silicon dioxide are deposited on Si substrates at ambient temperature in a 02/TEOS (tetraethoxysilane) helicon diffusion plasma. The plasma source is operated at 5 mTorr (0.7 Pa), 300 W rJ. power. The plasma composition and film properties are studied as functions of the TEOS to oxygen flow rate ratio R, which is varied from 0 to 0.5, at fixed total gas flow rate. The SiO", layers are analyzed by in situ ellipsometry and by ex situ quantitative Fourier Transform Infrared spectroscopy (FTIR). The plasma density, the electron temperature and the concentration of oxygen atoms are measured owing to Langmuir probes and optical emission spectroscopy. At low R the deposition rate is proportional to the TEOS flow rate, while at higher TEOS flow rates it saturates around 110 Amin -1, indicating that the deposition is limited by the availability of oxygen atoms. At very low R good quality Si0 2 films, with low silanol (SiOH) incorporation, are obtained. Correlations between CO and OH emission intensities in the plasma and the quantitative FTIR analysis of the films are investigated. © 1998 Elsevier Science S.A. Keywords: Plasma processing and deposition; Silicon oxide; Optical emission spectroscopy; Actinometry; Fourier Transform Infrared spectroscopy; Langmuir probe 1. Introduction Silicon dioxide (Si0 2 ) is commonly used as interlayer dielectric in integrated circuits and microelectronics devices. Plasma Enhanced Chemical Vapor Deposition (PECVD) allows to deposit good quality films at low substrate temperature « 200°C). Traditionally, PECVD Si0 2 thin films are processed from silane using 02/SiH4 or N 2 0/SiH 4 plasmas but TEOS (Si(OC 2 H s )4) can be preferred to silane since it is non toxic, easier to handle and yields better step coverage. This paper deals with the deposition of SiD", thin films in an 02/TEOS helicon diffusion plasma. Diagnostics of the excited and charged species of the plasma by optical emission spectroscopy (DES) and Langmuir probes are carried out simultaneously with the character• ization of the SiO", layers, in situ by ellipsometry and, ex situ, by quantitative Fourier Transform Infrared spectroscopy (FTIR) and chemical etching (p-etch). Correlations between semi-quantitative OES and the properties of SiO x films are investigated. • Corresponding author. 0257-8972/97/$17.00 © 1998 Elsevier Science SA All rights reserved. PH S0257-8972(97)00295-8 2. Experimental The helicon reactor consists of two adjacent parts (Fig. I): the plasma source and the diffusion chamber. The plasma is created in a glass tube ( 15 cm in diameter and 25 cm in height) via an external Helicon antenna (Boswell type [1)) which couples the r.f. (13.56 MHz) power to the plasma in the presence of an external axial magnetic field created by a solenoid (up to 120 G). No additional magnetic field is applied to the stainless steel diffusion chamber (30 em in height and diameter). The substrate holder is set 18 cm below the bottom of the plasma source, electrically grounded and neither heated nor biased. Liquid TEOS is heated (40°C) and its vapor is injected on one side of the diffusion chamber. The TEOS flow rate (QTEOS) is regulated by a MKS mass flow controller (0-20 sccm). O 2 is introduced from the top of the plasma source. The gases are pumped by a 330 1s -1 turbomolecular pump. The base pressure in the diffusion chamber is about 2x 10- 6 Torr (2.6 x 10- 4 Pal. The plasma can be operated in the pressure range I-50 mTorr (0.1-6.6 Pal. According to the r.f. power (0-500 W) and to the magnetic field, the discharge is either in a capacitive (low power) or in an