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Investigation On Damascene Structure And Mechanism Of Hafnium Oxide Chemical Mechanical Planarization

Posted on:2016-07-24Degree:MasterType:Thesis
Country:ChinaCandidate:Y L FengFull Text:PDF
GTID:2308330461489334Subject:Microelectronics and Solid State Electronics
Abstract/Summary:PDF Full Text Request
Hafnium oxide(Hf Ox), as one of the transition metal oxide, has been widely used in micro- and optoelectronics due to its extraordinary properties, and the relative high performance devices also have the strict requirements on the surface and the interface of the materials. Chemical mechanical planarization(CMP) is the only technology to ensure the global planarization of multi-layer materials and to achieve the damascene structure of the device. As one of the most promising candidates of non-volatile memory(NVM), Resistive Random Access Memory(RRAM) must be integrated with high density to give the superior advantages. At this condition, the CMP of the functional layer and relative electrode materials has become the key process to achieve the industrialization of RRAM(the important of the planarization process in NVM has also been predicted in ITRS-2005). Meanwhile, Hf Ox-based RRAM has been considered as the one which has the biggest chance to achieve industrialization. Based on this point, the key process of CMP for Hf Ox-based NVM device fabrication was investigated in this thesis. The influence of slurry components and polishing parameters on blanket wafer and via-structure wafer Hf Ox-CMP was mainly studied. The polishing mechanism was explored afterwards combined with the characterization of AFM and FTIR. Finally, the damascene/via-structure RRAM device was fabricated based on the process optimization.First of all, the p H values, additive(Na BF4) and abrasive particle size of the slurry were optimized with the evaluation criteria of polishing rate and surface root mean square(RMS) roughness as well as stability of the slurry. The result indicates that the polishing rate of 70.1nm/min and RMS roughness of 0.3nm as well as the selectivity to Si O2(>10) can be achieved when Hf Ox-CMP was conducted in p H=6 slurry with 39.9nm silica and 0.2wt% Na BF4. Meanwhile, we also investigated the effect of down force and platen rotation rate on polishing rate and RMS roughness based on the optimized slurry. The polishing increases linearly with the increasing down force and platen rotation rate, which accorded with the Preston equation, whereas has little variations on RMS roughness. Moreover, the results by observi ng the dishing with different via sizes post Hf Ox-CMP show that the dishing increases from 19.8nm to 60.85 nm with via size increases from 3um to 9um. However, the dispersity of the dishing was relatively small.Next, the polishing mechanism was explored based on the process investigation of Hf Ox-CMP. On one hand, the Preston equation was modified to cRR =k PV +R, according to the product fitting of down force and platen rotation rate. The intercept Rc was calculated to 5.58nm/min, which is consistent with experimental data(~5.2nm/min) and thus defined as the static etch rate. On the other hand, after AFM and FTIR characterization of the surface of Hf Ox pre- and post-polishing as well as corrosion, we inferred that a surface layer was formed during polishing, which softened the Hf Ox surface, improved the polishing efficiency. Consequently, the polishing mechanism of Hf Ox-CMP was concluded as the formation of the surface layer and its removal: the surface layer with relatively small hardness was formed firstly by the reaction of Na BF4 with Hf Ox followed by the abrasion of the abrasives. The two steps conducted alternately to achieve the planarization of Hf Ox.Lastly, the via-structure of Hf Ox-based RRAM device was fabricated based on the process optimization and mechanism analysis. The electrical properties were measured and compared to the device without structures. It turned out that the via-structure device has smaller Set voltage, the dispersity of Set voltage and high/low resistive state within one cell. Besides, the uniformity of Set voltages could be much better from cell to cell. From this judgment, the process optimization and investigation of Hf Ox-CMP in this thesis were effective and viable, which provides the schemes and experimental foundations to further improve the uniformity of the RRAM devices.
Keywords/Search Tags:Hafnium Oxide, Chemical Mechanical Planarization, Polishing Rate, Surface Roughness, Polishing Mechanism
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