Surface-Tensile-Stress Induced Polishing-Voids Suppression via H₂O₂Oxidizer Effect in Cross-Point Phase-Change-Memory-Cells

Abstract

The chemical-mechanical-planarization (CMP) of the Ge-doped SbTe (Ge-ST) film deposited by atomic layer deposition (ALD) is essentially necessary for 3-dimensional (3D) cross-point phase-change-memory (PCM) array, producing indispensably the surface-tensile-stress inducing polishing-voids due to the corrosion of the Ge-ST film and structural tensile stress in the confined memory-cells with ∼20-nm-diameter. The oxidizer (i.e., H2O2) in a CMP slurry played an important role to suppress the generation of the polishing voids via strong chemical oxidation of Sb2O5 and TeO2 of the Ge-ST film surface to avoid a corrosion process during CMP. The suppression efficiency of the polishing voids greatly depended on the H2O2 concentration in a ALD Ge-ST-film CMP of the confined memory-cell array; i.e., the polishing voids could disappear completely greater than a specific H2O2 concentration (i.e., 4wt%).

Fenton Reaction for Enhancing Polishing Rate and Protonated Amine Functional Group Polymer for Inhibiting Corrosion in Ge1Sb4Te5 Film Surface Chemical-Mechanical-Planarization

“…Generally, a Ge x Se y Te z film surface CMP slurry uses an oxidizer to enhance the polishing rate, inducing corrosion pits on the Ge x Se y Te z film surface after CMP [22,23]. To enhance the Ge x Se y Te z film surface polishing rate and to avoid corrosion pits simultaneously, the Fenton reaction between the ferric-ionic catalyst and oxidizer was introduced for a Ge x Se y Te z film surface CMP slurry.…”

“…Although the Fenton reaction in a Ge 1 Sb 4 Te 5 film surface CMP slurry can significantly suppresses CMP-induced corrosion on the Ge 1 Sb 4 Te 5 film surface, as shown in Figure 3, an actual Ge 1 Sb 4 Te 5 film surface CMP process using a Fenton reaction-based CMP slurry can also result in CMP-induced corrosion, producing a polishing-induced void or a recess at a nanoscale confined-structure PCRAM-cell [22,23]. Thus, to avoid corrosion at the nanoscale confined-structure PCRAM-cell after Ge 1 Sb 4 Te 5 film surface CMP, a corrosion inhibitor was mixed with the Ge 1 Sb 4 Te 5 film surface CMP slurry using the Fenton reaction.…”

“…These results indicate that the addition of a corrosion inhibitor (i.e., PEI) in the CMP slurry evidently suppresses the degree of corrosion-induced surface roughness. In general, a PRAM cell is fabricated with a confined hole structure with a high aspect ratio (i.e., 4-nm in diameter and 60.7-nm height), as shown in Figure 9 [22,23]. The polishing rate of the Ge 1 Sb 4 Te 5 film surface without a confined-hole structure PRAMcell array pattern in Figure 8 would be lower than that of the Ge 1 Sb 4 Te 5 film surface with a confined-hole structure PRAM-cell array pattern, because the polishing-rate of the Ge 1 Sb 4 Te 5 film surface in a confined-hole structure PRAM-cell array pattern could be enhanced because of the confined memory cell structure-induced stress [22,23].…”

“…To fabricate a confined PCRAM-cell structure, a PCRAM material such as Ge x Sb y Te z or Ge or N 2 doped Sb y Te z , etc., called a GST film, should be filled in the confined hole structure with a high aspect ratio of >10 [22]. Thus, sputtering followed by annealing, chemical vapor deposition (CVD), or atomic layer deposition (ALD) of a GST film in a confined-hole structure is utilized.…”

“…To avoid corrosion or polishing-void, the addition of an oxidizer (i.e., H 2 O 2 ) in the GST film surface CMP slurry is essential, which can passivate the GST film surface by forming a chemical oxidizer layer on the GST film surface. However, an oxidizer significantly reduces the polishing-rate of the GST film surface and cannot completely prevent the generation of a corrosion or polishing-induced-void on the GST film surface after a CMP [22,23]. In addition, the research has been reported for enhancing the GST film surface polishing-rate, presenting that the pH design of the GST film surface CMP slurry would be a key parameter to determine the GST-film surface polishing-rate [24,25].…”