The use of GeS2 thin films in various resistive memory devices has been widely studied with positive results. These films are generally deposited by chemical vapor deposition (CVD) or by one of its relatives. The process of CVD is an incredibly useful technique, but has a few shortcomings such as difficulties with depositing ultra-thin films, growth rates of films depend on many variables, and some difficulties in controlling film stoichiometry. Atomic layer deposition (ALD) is another form of deposition that is becoming widely used throughout the thin film industry. ALD deposits reactants atom layers one at a time by self-limiting surface reactions; the nature of the deposition causes a linear correspondence between film thickness and number of pulse cycles. The ALD process allows for precise control over film stoichiometry and film thickness. In this study, GeS2 films were deposited in the ALD fashion with a student designed, cold-wall reactor. GeCl4 vapors and H2S were pulsed sequentially with Ar purging cycles between each pulse. A direct RF plasma was applied during the reactant pulse cycles to aid in the deposition. Pulse times, pulse cycles, and pressure were kept constant throughout the depositions, but temperature, plasma power, and type of substrate was varied. Temperature ranged from 100-150 °C, plasma power ranged from 10-30 W, and various substrates were used. Ag, Au, Al, W, Si, and glass were used as substrates; Ag and Au are often used as substrates for ALD films throughout the literature, and Al, W, Si, and glass are substrates widely used throughout the semiconductor industry for resistive ram devices. The composition and structure of the resulting films were characterized by EDS, XRD, and XRF. Thickness data was obtained by AFM, and resistance was determined by a four point probe. The data collected show that the student-designed ALD chamber in fact deposited GeS2. The morphologies, stoichiometeries, and impurity content of these films were compared to similar films deposited by plasma-enhanced CVD.

Plasma-assisted atomic layer deposition of GeS2 thin films from GeCl4 and H2S precursors in a student designed PAALD chamber

253rd National Meeting (2017)

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