| 학회 | 한국재료학회 |
| 학술대회 | 2009년 봄 (05/21 ~ 05/22, 무주리조트) |
| 권호 | 15권 1호 |
| 발표분야 | 반도체재료 |
| 제목 | Effect of pH in Colloidal Silica Slurry on Polishing Rate Selectivity of Nitrogen-doped Ge2Sb2Te5 to SiO2 in Chemical Mechanical Polishing |
| 초록 | The Phase-change random-access memory (PRAM) has been investigated as one possible substitution of next generation nonvolatile memory (NVM) because of its high scalability, fast operation speed and good endurance as compared with conventional Flash memory. In spite of its many advantage, there are some problem such as high reset current, cross talk as the thermal stability in order to scale down below the 30nm design rule. Because of these problems, the PRAM structure was changed from the conventional-T shape structure to the confined structure by chemical vapor deposition of nitrogen doped Ge2Sb2Te5 (NGST). It is the use of a confined memory-cell structure that requires the chemical mechanical polishing (CMP) of GST film as an essential process for avoiding etching damage and facilitating easy mass production of PRAM devices. To obtain well defined structure, NGST CMP requires a high and controllable polishing rate selectivity of NGST film to SiO2 film. We investigated the effect of pH in colloidal silica slurry on polishing rate selectivity of NSGT film to SiO2 film in CMP. The electrostatic interactions between the slurry abrasives and film surface are important during CMP and these electrostatic interactions are strongly influenced by the pH of the slurry. The polishing rate of GST film is lowest at approximately pH ~8, and increased linearly as further decrease or increases the pH. The slightly increase in the GST polishing rate as the pH decrease is due to the agglomerated large abrasive particle, which is resulted from the low zeta potential at near neutral pH region. On the contrary, the increase in the GST polishing rate as the pH increase is mainly due to the chemical reaction between GST film and TMAH in the slurry. From the result of X-ray Photoelectric Spectroscopy, it is found that after dipping in the slurry, the Ge, Sb, and Te oxides peaks are obviously decreased. It demonstrates that TMAH can react with surface oxides of GST and facilitate the mechanical abrasion. SiO2 polishing rate, however, remained constant until pH ~9, and then slightly increased as further increase of the pH. This slight increase is due to the direct dissolution of SiO2 by the hydroxide ions. |
| 저자 | Woong-Jun Hwnag1, Jong-Yung Cho2, Hao Cui1, Jin-Hyung Park2, Ungyu Paik1, Jea-Gun Park2 |
| 소속 | 1Advanced Semiconductor Material & Device Development Center, 2Hanyang Univ. |
| 키워드 | PRAM; GST; CMP; polishing rate selectivity; pH |
