Sadahiro Kishii

Reconditioning-free polishing for interlayer-dielectric planarization

In chemical mechanical polishing (CMP) using a colloidal silica slurry with a pH of 10–11 for interlayer-dielectric (ILD) planarization, the removal rate of the oxide film drops off rapidly because the pad surface becomes flat during a CMP process. Thus we must recondition the polishing pad surface in order to obtain the rough polishing pad surface. In result, we can maintain a constant removal rate of the oxide film during the life time of the pad. We clarified that the alteration of the polishing pad surface was caused by the KOH solution in a conventional slurry. We also found that our newly developed MnO2 slurry could prevent the alteration of the polishing pad surface in reconditioning-free CMP.

Tungsten Film Chemical Mechanical Polishing Using MnO2 Slurry

It has been demonstrated that MnO2 abrasive can polish tungsten films without using an oxidizer solution. The polishing rate of MnO2 slurry is 1.5 times higher than that of commercially available Al2O3 slurry. A W plug is formed without etching holes (keyholes) during chemical mechanical polishing with MnO2 abrasive slurry. With MnO2 slurry, no key holes were formed even after overpolishing by an additional 0.6 µm. On the other hand, with conventional Al2O3 slurry, keyholes were formed after overlpolishing by an additional 0.4 µm. The residual MnO2 abrasive on the surface after chemical mechanical polishing was completely removed by the cleaning process because MnO2 abrasive easily dissolves in a cleaning solution of HCl, H2O2, and H2O. These results indicate that, since MnO2 is in itself a solid oxidizer, MnO2 abrasive can polish W films without using an oxidizer solution and does not etch the seam.

Study on the Development of Resource-Saving High Performance Slurry - Polishing/CMP for Glass Substrates in a Radical Polishing Environment, Using Manganese Oxide Slurry as an Alternative for Ceria Slurry

While investigating polishing mechanism of glass substrates with ceria abrasives (CeO2), we found its oxidizing properties worked effectively for the polishing. This finding has inspired us to speculate about the possibility of the manganese oxide abrasives as an alternative for ceria as they also have oxidizing properties. Therefore, focusing on the valence of the manganese, we have experimentally manufactured MnO, MnO2, Mn2O3 and Mn3O4 abrasives, and conducted a comparison study of the characteristics obtained with ceria slurry and manganese oxide slurries. As a result, the surface roughness of below Ra 0.8nm obtained with Mn2O3 slurry was found better than that with the conventional ceria slurry, on top of which, its removal rate was as good as or equal to that of ceria. Using a novel, closed type CMP (Chemical Mechanical Polishing) machine, we conducted another glass polishing experiment with ceria and manganese oxide slurries. The inside of the CMP machine was filled with high-pressure gases such as oxygen, air and nitrogen and kept at 500kPa to make the polishing environment radical. Through this experiment, we found an effective polishing method for high-quality surface. The removal rates were several times better than that of the conventional polishing performed in an open CMP machine.

Al-interconnect/Cu-plug structure for FeRAM multilevel interconnect

An Al-interconnect/Cu-plug structure, whereby a plug is filled by electrochemical deposition (ECD) for FeRAM interconnection, has been developed. Conventionally sputtered Al for current FeRAM devices cannot fill high aspect ratio plugs. A high aspect ratio plug can successfully be filled by ECD Cu and PZT degradation with this structure is much less than that with an Al-interconnect/W-plug structure, which has been widely adopted for DRAM and logic devices.

Wide feature dielectric planarization using MnO/sub 2/ slurry

We used MnO/sub 2/ slurry for dielectric planarization. We found that MnO/sub 2/ slurry has an ample removal rate at a low polishing pressure, whereas conventional slurry does not. Therefore, MnO/sub 2/ slurry can planarize dielectric more completely, with less lower level removal than conventional slurry.

Mn2O3 Slurry Reuse by Circulation Achieving High Constant Removal Rate

Fumed silica is widely used in SiO2 chemical mechanical polishing (CMP). In semiconductor processes, only fresh slurry is used, and used slurry is disposed. Sustainable development demands a reduction in waste. Since reuse of slurry is effective for reducing the amount of used slurry generated, we investigated the reuse of Mn2O3 slurry and conventional fumed silica slurry. In both cases, abrasive concentration decreases as reuse time increases. The removal rate for Mn2O3 slurry maintains a value 4 times that of the conventional fumed silica slurry during slurry reuse, because the removal rate for Mn2O3 slurry is almost constant for solid concentrations between 1.0 and 10 wt %. Pad conditioning was not performed for Mn2O3 slurry. The removal rate for conventional slurry decreases as the number of times of reuse increases, even when pad conditioning is appropriately performed.

Mn2O3 Slurry Achieving Reduction of Slurry Waste

Fumed silica is widely used for SiO2 chemical mechanical polishing (CMP). In semiconductor processes, only fresh slurry is used, the used slurry being disposed of. We have demonstrated that Mn2O3 abrasive slurry polishes dielectric SiO2 film, giving 4 times the removal rate of conventional fumed silica slurry. The higher removal rate reduces the total amount of slurry used, consequently reducing the amount of used slurry waste. The removal rate of Mn2O3 slurry remains constant for solid concentrations between l and 10 wt %, and stays constant without pad conditioning. These characteristics are very useful for slurry reuse. Remanufacture of Mn2O3 slurry from used slurry has been demonstrated, and the removal rates of the remanufactured and fresh slurries are the same. Reuse and remanufacturing drastically reduce the amount of waste.

Dielectric SiO2 Planarization Using MnO2 Slurry

MnO2 slurry can polish SiO2 film faster and planarize wide feature steps (2 ×2 mm2) to a lower height than conventional silica slurry. A comparison of Gibbs free energies indicates that the MnO2 abrasive directly reacts on the SiO2 film. In post-Chemical mechanical polishing (CMP), the MnO2 abrasive can be completely removed by dipping it in mixed solutions of inorganic acids and H2O2 followed by scrubbing and dipping in HF solution. A comparison of Gibbs free energies clarifies that the MnO2 abrasive on the wafer is easily dissolved in a mixed solution of an inorganic acid and H2O2.

Study of Manganese Oxide Slurries for Chemical Mechanical Polishing

of Thesis (English) In this paper, manganese oxide slurries have been studied for chemical mechanical polishing (CMP) in semiconductor process for the first time. In semiconductor process, Al2O3 slurry is used for tungsten film CMP. It has been demonstrated that MnO2 abrasive can polish tungsten films without using an oxidizer solution. The polishing rate of MnO2 slurry is 1.5 times higher than that of commercially available Al2O3 slurry. A W plug is formed without etching holes (keyholes) during chemical mechanical polishing with MnO2 abrasive slurry. With MnO2 slurry, no key holes were formed even after overpolishing by an additional 0.6 um. On the other hand, with conventional Al2O3 slurry, keyholes were formed after overlpolishing by an additional 0.4 um. The residual MnO2 abrasive on the surface after chemical mechanical polishing (CMP) was completely removed by the cleaning process because MnO2 abrasive easily dissolves in a cleaning solution made of HCl, H2O2, and H2O. These results indicate that, since MnO2 is in itself a solid oxidizer, MnO2 abrasive can polish W films without using an oxidizer solution and does not etch the seam. In semiconductor process, fumed silica (SiO2) slurry is used for silicon dioxide (SiO2) film CMP. In semiconductor processes, only fresh slurry is used, the used slurry being disposed of. We have demonstrated that Mn2O3 abrasive slurry polishes dielectric SiO2 film, giving 4 times the removal rate of conventional fumed silica slurry. The higher removal rate reduces the total amount of slurry used, consequently reducing the amount of used slurry waste. The removal rate of Mn2O3 slurry remains constant for solid concentrations between l and 10 wt%, and stays constant without pad conditioning. These characteristics are very useful for slurry reuse. Remanufacture of Mn2O3 slurry from used slurry was demonstrated, and the removal rates of the remanufactured and fresh slurries are the same. Reuse and remanufacturing drastically reduce the amount of waste. Since manganese oxide slurry polishes several materials such as tungsten, copper, SiO2, and low dielectric constant materials, further studies on manganese oxide slurries are expected to reduce the amount of slurry waste in semiconductor processes.

Dielectric SiO

MnO2 slurry can polish SiO2 film faster and planarize wide feature steps (2 ×2 mm2) to a lower height than conventional silica slurry. A comparison of Gibbs free energies indicates that the MnO2 abrasive directly reacts on the SiO2 film. In post-Chemical mechanical polishing (CMP), the MnO2 abrasive can be completely removed by dipping it in mixed solutions of inorganic acids and H2O2 followed by scrubbing and dipping in HF solution. A comparison of Gibbs free energies clarifies that the MnO2 abrasive on the wafer is easily dissolved in a mixed solution of an inorganic acid and H2O2.