High-Density Nanopatterning of SiGeAsTe Chalcogenide as Ovonic Threshold Switch Selectors for Memory Applications

Abstract

Cross-point memory architecture involves high-density, fast yet cost-effective storage class memories (SCM). As a result, ovonic threshold switches (OTS) are extensively researched as they are needed in series with the SCM-based memory element for its precise functioning. In addition, these OTS-based devices exhibit the potential to be self-selecting memories too. Hence, its integration-friendly patterning becomes pivotal for large-scale manufacturing. Chalcogenide-based alloys are often the desired candidate for OTS. Here, we study the patterning of one of the widely investigated chalcogenide alloys-SiGeAsTe. While the elements of the alloy generate highly volatile halogenated etch by-products, this material is also prone to severe etch-induced lateral undercuts and material damage. Thus, its high-density patterning is challenging. A conventional method to minimize this undercut damage is to increase the hydrocarbon passivation during the etch process to prevent the exposure of the chalcogenide's sidewalls (SWs) to any type of etchant. Inherently, this leads to the tapering of the OTS-based pillars, consequently becoming an impediment to their scaling at tighter pitches. Here, we clearly establish that OTS-based devices with well-preserved chemical and morphological properties can be fabricated using lower hydrocarbon passivation by tuning the ion energies during etching. Higher ion energies ensure better etch directionality. Concurrently, a well-controlled high energy ion bombardment is likely to enhance deposition of the passivating hydrocarbon from the etch front on to the chalcogenide's SWs. This is achieved without any unwanted redeposition from underlying layers in the OTS-based stack. We successfully demonstrate high-density nanopatterning of chalcogenide-based OTS devices of diameter similar to 65 nm at 200 nm wide pitch. This is also effectively reproduced on 300 mm semiconductor wafers. The electrically measured devices exhibit low leakage and high endurance. This distinctive yet uncomplicated etch tailoring is also discussed to be scalable for pitches <200 nm and for other chalcogenide compositions.