We investigated the deposition and the phase-change properties of In-doped GeTe thin films obtained by plasma enhanced metalorganic chemical vapor deposition and doped with indium using a solid delivery system. The sublimated indium precursor flow rate was calculated as a function of sublimation and deposition parameters. Indium related optical emission recorded by means of optical emission spectroscopy during deposition plasma allowed proposing the dissociation mechanisms of the [In(CH3)2N(CH3)2]2 solid precursor. In particular, using an Ar + H2 + NH3 deposition plasma, sublimated indium molecules are completely dissociated and do not induce by-product contamination by addition of nitrogen or carbon in the films. X-ray photoelectron spectroscopy evidences the formation of In-Te bonds in amorphous as-deposited In-doped GeTe films. The formation of an InTe phase after 400 °C annealing is also evidenced by means of X-ray diffraction analysis. The crystallization temperature Tx, deduced from monitoring of optical reflectivity of In-doped GeTe films with doping up to 11 at. % slightly varies as a function of the In dopant level with a decrease of Tx down to a minimum value for an In doping level of about 6–8 at. %. In this In doping range, the structure of crystallized In-GeTe films changes and is dominated by the presence of a crystalline In2Te3 phase. Finally, the Kissinger activation energy for crystallization Ea is showing to monotonically decrease as the indium content in the GeTe film is increased indicating a promising effect of In doping on crystallization speed in memory devices while keeping a good thermal stability for data retention.
Phase-change memory is one of the most promising technologies for the future non-volatile memories generation and the synthesis of highly conformal active material is one of the main challenges. Herein, we report the successful chemical vapor deposition of phase change materials conducted using original plasma enhanced pulsed liquid injection system. Smooth, conformal and amorphous as well crystalline GeTe layers were grown on large surfaces. Their phase-change characteristics present fast switch from amorphous to crystalline phases with high optical contrast between the two states. These properties are similar to those of sputtered films used in electronic devices. Moreover, thanks to appropriate process tuning, material structure and phase change properties can be tuned.Phase change memories (PCM) store information as resistive state using the high electrical contrast between amorphous and crystalline phase of chalcogenide alloys as GeTe. 1 Thanks to their outstanding properties, PCM are considered as serious candidates for the next non-volatile memories generation. 2 However this technology suffers from high power consumption, especially during the erasing step, where the current should be high enough to heat the material beyond its melting temperature. Nevertheless, it has been shown that confinement of phase change materials enhances Joule's effect efficiency: it was demonstrated that a current as low as 80 μA is obtained using dash confined structure. 3 Metal organic chemical vapor deposition (MOCVD) is known to produce highly conformal thin films and thereby is an efficient method to fill small cavities required for confined PCM.Number of studies focus on the deposition of phase-change materials by MOCVD 4-8 and most of them reports the difficulties to obtain homogenous and uniform thin films with smooth surface. [5][6][7] This problem is partially due to the metal organic precursors which present high decomposition temperatures, largely higher than the crystallization temperature of the targeted materials. In literature, it has been solved using innovative precursors 8 or additional process activation such as hot wire. 6,7 Here, we show results obtained thanks to an innovative plasma enhanced MOCVD (PE-MOCVD) process using pulsed liquid injection of precursors. Stoichiometric and smooth GeTe films are deposited on large surface area. Their phase change properties are similar to sputtered materials ones. The step coverage is evaluated thanks to lines patterned substrate. We demonstrate precise control of film properties through tuning of process condition. ExperimentalWe used a shower-head type 200 mm scale plasma enhanced pulsed liquid injection CVD reactor (AltaCVD200). 9 A scheme of the reactor is given in Figure 1. Metal organic precursors -Ge(NMe 2 ) 4 and Te(i-Pr) 2 -are introduced into the deposition chamber as vapors through a pulsed injection system and an evaporating furnace. Liquid precursors are pressurized with Ar. The injection stage is an original patented system where each injection head is...
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