Chemical Mechanical Planarization Mechanism for Nitrogen-Doped Polycrystalline Ge₂Sb₂Te₅ Film Using Nitric Acidic Slurry Added with Hydrogen Peroxide

Abstract

We investigated the chemical mechanical planarization (CMP) mechanism of nitrogen-doped polycrystalline Ge 2 Sb 2 Te 5 (pc-GST) using nitric acid slurry without or with 1.0 wt % hydrogen peroxide (H 2 O 2 ). Without H 2 O 2 , the pc-GST film surface undergoes selective corrosion of Ge and Sb, resulting in pitting corrosion. Otherwise, with H 2 O 2 , the pc-GST film surface produces a Ge, Sb, Te oxide layer, thereby introducing a cyclic polishing process such as chemical oxidation, chemical and mechanical polishing, and sequential chemical oxidation. As a result, the polishing rate increased up to $1000 Å /min and the surface roughness decreased to 0.858 nm.Phase change memory (PRAM) is one of the most promising nonvolatile memories due to its large signal sensing margin, fast writing speed, outstanding endurance, long data retention time, and most importantly, scalability, for commercial high density production. 1-3 Recently, PRAM has been successfully manufactured with high density, which is quite close to commercial NOR flash memory. 4,5 To facilitate mass production of the high density PRAM, chemical mechanical planarization (CMP) has been employed to develop smooth and defect-free surface of Ge 2 Sb 2 Te 5 (GST) after gap filling in the confined cell structure. 4,6,7 Here, a polycrystalline state was preferable for the deposited GST rather than an amorphous state in order to achieve a higher speed and wider sensing margin. Moreover, polycrystalline GST (pc-GST) was inevitably used to avoid incomplete contact between electrodes and amorphous GST because amorphous GST shrinks by 5-7% in volume as it switches from an amorphous to a crystalline state due to the thermal process. 8 Hydrogen peroxide (H 2 O 2 ) is commonly used as the oxidizer in various CMP slurries because it has high oxidizing ability and does not generate ionic byproducts. Our group 9,10 has reported the CMP mechanism of nitrogen-doped pc-GST film in an alkaline slurry in which H 2 O 2 has been added. We found that the polishing rate of the pc-GST film increased as the H 2 O 2 concentration was increased. However, this resulted in severe pitting corrosion because the chemical passivation layer on the pc-GST film was difficult to form in the alkaline solution with H 2 O 2 . On the contrary, Zhong et al. 8 and Wang et al. 11 have conducted amorphous GST CMP with acidic slurries added with H 2 O 2 and some surfactant, and found enhanced CMP performance such as a higher amorphous GST polishing rate and lower surface roughness without inducing pitting corrosion. However, the CMP mechanism of the GST film with H 2 O 2 in the acidic environment was not discussed in detail. Moreover, the pitting corrosion on the pc-GST film surface was much more severe than that for the amorphous GST film surface, and the polishing rate of the pc-GST film was slower than that of the amorphous GST film. 9,10,12 Thus, in our work, we investigated the detailed CMP mechanism of the pc-GST film in an acidic slurry without or with 1.0 wt % H 2 O 2 , by analyzing the corrosion...

Effect of the Hydrogen Peroxide on the Ti0.4Sb2Te3Chemical Mechanical Polishing in Acidic Slurry

“…The decrease in polishing rate with increase of H 2 O 2 concentration beyond 0.5 wt% was believed to be due to the stronger passivation of the TST surface. 8 This effect could be contributed to the formation of oxide in peroxide solutions or the adsorption of OH radicals on the TST surface. 9 In the future study, we will be proposing a possible mechanism of the TST film polishing rate with various H 2 O 2 concentrations.…”

Mechanism of amorphous Ge2Sb2Te5removal during chemical mechanical planarization in acidic H2O2slurry

“…With regard to the component of the chemical oxide layer on the a-GST surface, Zhong et al [13] reported that it was GeO 2 , Sb 2 O 5 , and TeO 2 formed in the a-GST film surface in the acidic condition with 2.0 wt% H 2 O 2 . In our study, according to Pourbaix diagrams in a water system in the standard condition [14] for Ge, Sb, and Te, the corrosion potential of a-GST (less than 0.02 V) below 0.5 wt% H 2 O 2 is located in the domain of GeO 2 , Sb/Sb oxide boundary, and Te. In contrast, for above 0.…”

“…Their results show that GeO 2 , Sb 2 O 5 , and TeO 2 were formed on the a-GST surface after a-GST was dipped in the slurry for 10 min, but no detailed discussion about the removal mechanism was given. Cui et al [14] investigated CMP of N-GST using nitric acidic slurry with 1.0 wt% H 2 O 2 and found the addition of H 2 O 2 could suppress selective pits corrosion of N-GST, and removal of N-GST followed a cyclic polishing mechanism with 1.0 wt% H 2 O 2 . However, few studies were reported on other concentrations of H 2 O 2 such as that below 1.0 wt% in the acidic slurry.…”

Effect of β-cyclodextrin and Citric Acid on Chemical Mechanical Polishing of Polycrystalline Ge2Sb2Te5in H2O2Containing Slurry

“…The detailed peak identification and its binding energy were referred to from some previously reported results. [18][19][20] For the pc-GST film dipped in the H 2 O 2 containing solution without CA, GeO 2 , Sb 2 O 5 , and TeO 2 peaks were found due to the oxidizing power of H 2 O 2 in a slurry. As the CA concentration increased to 0.1 wt%, the TeO 2 peak decreased and Te-metal (homopolar bonds of Te, Te-Sb, or Te-Ge) peaks increased.…”