Computer Controlled Pulsed Pecvd Reactor for Laboratory Scale Deposition of Plasma Polymerized Thin Films
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ABSTRACT A pulsed PECVD reactor has been successfully constructed for laboratory scale studies of plasma polymerized thin films. A computer control system based on National Instrument's LABVIEW software controls power supply sequence, feed injection, and introduction of RF energy. An optical fiber and a photo diode allow the user to monitor the emitted light for each pulse. A fast ionization gauge is used to characterize the pressure evolution over time, subsequent to acetylene gas injection. Substrates with diameter as large as 10 cm can be accommodated within the reactor. Both aniline liquid and acetylene gas have been used as reactor feed. The deposited plasma-polymerized films were characterized using AFM and SEM. Electrical conductivity of plasma polymerized acetylene film was also measured INTRODUCTION As device sizes shrink and new applications are being found for thin films, plasma enhanced chemical vapor deposition (PECVD) is becoming more and more popular as a thin film deposition technique. In this technique plasma is used to decompose feed chemicals into reactive species which then deposit onto the substrate. Plasma processing offers such advantages as low temperature processing, film smoothness and uniformity, ease of deposition, and the ability to polymerize a wide variety of organic compounds. At the present time, continuous plasma discharges are almost universally used in industry. Pulsed plasma deposition, however, offers significant advantages in terms of better control of the process and film structure. Additional advantages include possible reductions in raw material usage, and process emissions. Pulsed plasma reactors have been used in the past to grow Si0 2 and silicon nitride films [1,21, and to deposit hydrocarbon [3,4], halogenated hydrocarbon [5,6], and amorphous silicon films [7]. In this paper a laboratory scale pulsed plasma reactor is described. In our studies the reactor has been used for deposition of acetylene (gas) and aniline (liquid) polymer films. The films were characterized using AFM and SEM. Electrical properties of the films were also measured. Several diagnostic tools were employed to characterize plasma and pre-plasma conditions in the reactor. Fast ionization gauge (FIG) was used for measurement of transient pressures in the reactor. Plasma light emission was measured at different
reactor locations and pressures using a photodiode detector. Data obtained from the above measurements are presented and discussed here.
EXPERIMENTAL SETUP The schematic of the reactor is shown in Figure 1. Gas or liquid monomer is pulse-fed into the
reaction chamber using a conventional automotive gasoline fuel injector. The setup for gas and liquid injection was different in the way the monomer was supplied to the injector. Liquid is delivered to the injector from a syringe storing a small (1-10 mL) volume of liquid monomer. Gaseous monomer is delivered from a compressed gas cylinder through a regulator and a valve. The amount of monomer delivered to the system is set by the duration of vol
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