A method of forming a memory device, comprising: forming a layer stack (13L, 14L, 15L) including a lower electrode layer, a selector material layer, an upper electrode layer, a refractory metal-containing etch stop layer, a ruthenium etch stop layer, a conductive material layer, and at least one memory material layer over a substrate; patterning the at least one memory material layer into a memory element; patterning the conductive material layer into a conductive pillar using the ruthenium etch stop layer as an etch stop by performing a first anisotropic etch process having a first etch chemistry that etches the conductive material layer selective to ruthenium; characterized by: patterning the ruthenium etch stop layer into an ruthenium plate using the refractory metal-containing etch stop layer as an etch stop by performing a second anisotropic etch process having a second etch chemistry that etches ruthenium selective to a material of the refractory metal-containing etch stop layer; patterning the refractory metal-containing etch stop layer into refractory metal-containing etch stop plate by performing a third anisotropic etch process having a third etch chemistry that etches a material of the refractory metal-containing etch stop layer selective to a material of the upper electrode layer without etching through the upper electrode layer; and anisotropically etching the upper electrode layer, the selector material layer, and the lower electrode layer by performing additional anisotropic etch processes; wherein: an ovonic threshold switch selector element is formed by anisotropically etching the selector material layer; the refractory metal-containing etch stop layer consists essentially of tantalum, tungsten, rhenium, niobium, molybdenum, intermetallic alloy thereof, or a conductive metallic nitride thereof; and the third anisotropic etch process is a timed based etch process which employs a fluorine-based plasma which is timed to etch through the refractory metal-containing etch stop layer without etching all the way through the upper electrode layer, such that the ovonic threshold switch material is not exposed to the fluorine-based plasma. forming a layer stack (13L, 14L, 15L) including a lower electrode layer, a selector material layer, an upper electrode layer, a refractory metal-containing etch stop layer, a ruthenium etch stop layer, a conductive material layer, and at least one memory material layer over a substrate; patterning the at least one memory material layer into a memory element; patterning the conductive material layer into a conductive pillar using the ruthenium etch stop layer as an etch stop by performing a first anisotropic etch process having a first etch chemistry that etches the conductive material layer selective to ruthenium; characterized by: patterning the ruthenium etch stop layer into an ruthenium plate using the refractory metal-containing etch stop layer as an etch stop by performing a second anisotropic etch process having a second etch chemistry that etches ruthenium selective to a material of the refractory metal-containing etch stop layer; patterning the refractory metal-containing etch stop layer into refractory metal-containing etch stop plate by performing a third anisotropic etch process having a third etch chemistry that etches a material of the refractory metal-containing etch stop layer selective to a material of the upper electrode layer without etching through the upper electrode layer; and anisotropically etching the upper electrode layer, the selector material layer, and the lower electrode layer by performing additional anisotropic etch processes; an ovonic threshold switch selector element is formed by anisotropically etching the selector material layer; the refractory metal-containing etch stop layer consists essentially of tantalum, tungsten, rhenium, niobium, molybdenum, intermetallic alloy thereof, or a conductive metallic nitride thereof; and the third anisotropic etch process is a timed based etch process which employs a fluorine-based plasma which is timed to etch through the refractory metal-containing etch stop layer without etching all the way through the upper electrode layer, such that the ovonic threshold switch material is not exposed to the fluorine-based plasma.