Plasma Enhanced Chemical Vapor Deposition of Conformal GeTe Layer for Phase Change Memory Applications

Abstract

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...

Phase-change materials for non-volatile memory devices: from technological challenges to materials science issues

“…Thanks to the plasma assistance, the substrate temperature can be reduced to temperatures near or below the crystallization temperature of the material, which favors the deposition of a smooth amorphous material. This can be observed in figure 11 for a GeTe film deposited in the same reactor either in a CVD or PECVD mode (see [85] for experimental details). Only the PECVD mode with a substrate temperature lower than 200 °C gives the amorphous GeTe necessary for filling the high aspect ratio trench.…”

“…Plasma assistance brings major improvement over the CVD deposition of PCMs that results in polycrystalline films with large grains and rough surfaces at high temperature and the incorporation of some ligands or organic groups from the precursor when the temperature is lowered. Indeed, a smooth material with moderate contamination can be deposited using plasma assistance for precursor dissociation in a 13.56 MHz capacitively-coupled reactor [83][84][85][86]. In this case, PCM precursors are diluted in H 2 /Ar (or He) gases, which favor low-temperature dissociation of precursors and etching of organic groups during film growth.…”

Phase Change Memories challenges: A material and process perspective

“…The main challenges are the development of such processes. In our work two routes have been explored: metal organic CVD (MOCVD) [16] and Atomic Layer Deposition (ALD) [17]. Regarding MOCVD, we were able to perform high deposition rate of GeTe alloy using plasma enhanced pulsed liquid injection.…”

“…The crystallization temperature can be explained by the C content. Insert, SEM images showing the low roughness of the film and its good step coverage [16]. GST deposited by ALD.…”