Hydrogen in Dielectric Film Formation from an Electron Cyclotron Resonance Plasma
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HYDROGEN IN DIELECTRIC FILM FORMATION FROM AN ELECTRON CYCLOTRON RESONANCE PLASMA J. C. BARBOUR AND H. J. STEIN Sandia National Laboratories, Albuquerque,
NM 87185
ABSTRACT The incorporation of hydrogen into silicon nitride films grown downstream from an electron cyclotron resonance (ECR) plasma decreased rapidly with increasing substrate temperature (I00-600°C). Fourier transform infra-red (FTIR) spectroscopy showed that the hydrogen in the as-grown material was primarily bonded to nitrogen. However, an applied bias of -200 V caused an increase in the number of Si-H bonds relative to N-H bonds, as a result of increased ion-beam damage. In addition, ion irradiation of an asgrown film with 175 keV Ar+ at room temperature showed that H transferred from N-H bonds to Si-H bonds without a loss of H. Elastic recoil detection (ERD) and FTIR of thermally annealed films showed that the stability of H incorporated during deposition increased with deposition temperature, and that the N-H bond was more stable than the Si-H bond above 700*C. Deuterium plasma treatments, at 600*C, of annealed films caused isotopic substitution with a conservation of bonds. Therefore, hydrogen loss from annealed films is apparently accompanied by a reduction in dangling bonds.
INTRODUCTION High-quality silicon nitride dielectric films are important for semiconducting electronic devices such as non-volatile memory metal-nitrideoxide-semiconductor (MNOS) structures. Further, the incorporation of hydrogen into MNOS structures is known to have a strong effect on the electronic properties. For example, the charge storage time for MNOS structures is modified considerably by high temperature annealing of the nitride; a process which changes the concentration of N-H and Si-H bonds in the film [1]. The conventional method of forming silicon nitride is by chemical vapor deposition (CVD) at high temperatures (greater than 600°). In order to make use of Si 3 N4 with compound semiconductors and other temperature sensitive materials, plasma enhanced-CVD processes have been developed for low temperature Si3N4 deposition. Reference [2] demonstrated the use of an electron cyclotron resonance (ECR) plasma to deposit SiNx films which are of sufficient quality for use as gate dielectrics on Si or InGaAs. The ECR process is important because it allows for low temperature formation with little ion-beam damage. For example, SiNx films have been deposited at room temperature to 150°C from ECR plasmas [3,4,5] in which the ion energy is only 20-40 eV. If ECR plasma-CVD silicon nitride is to be used in microelectronics, then an understanding of the incorporation and release of H from these materials is important. Our previous work [6] examined the growth of low temperature ECR deposited SiNx films and the effects of SiH4 /N 2 gas ratio, pressure and sample position on the stoichiometry and H content. A nearly stoichiometric Si3N4 film with a low H content was deposited at 200*C from a plasma with a SiH4/N2 flow ratio of =0.2 and an electrically isolated sample far from
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