Chemical mechanical polishing of Ba0.6Sr0.4TiO3 film prepared by sol–gel method

doi:10.1016/j.mee.2004.03.086

Microelectronic Engineering

Volume 75, Issue 2, August 2004, Pages 149-154

https://doi.org/10.1016/j.mee.2004.03.086 Get rights and content

Abstract

In this paper, we first applied the chemical mechanical polishing (CMP) process to the planarization of ferroelectric film in order to obtain a good planarity of electrode/ferroelectric film interface, and suggested the self-developed titania (TiO₂) abrasive slurry for ferroelectric random access memories (FRAM) applications. Ba_0.6Sr_0.4TiO₃ (shortly BST) ferroelectric film was fabricated by the sol–gel method. Then, we compared the structural characteristics before and after CMP process of Ba_0.6Sr_0.4TiO₃ films. Their dependence on slurry composition was also investigated. Our results will be useful guideline of global planarization for FRAM application in the near future.

Introduction

With the advent of integration of dynamic random access memories (DRAMs) and ferroelectric random access memories (FRAMs), the thickness of insulator in capacitors will approach the quantum limit. Using the conventional SiO₂ films, the thickness of the films can be less than 0.5 nm but the dielectric constant also will be lower. Therefore, the utilization of high dielectric constant materials will become inevitable [1]. The perovskite ferroelectric materials of the PZT [Pb(Zr,Ti)O₃], SBT (SrBi₂Ta₂O₉) and BST (Ba_0.6Sr_0.4TiO₃) series will attract much attention for application to ULSI devices. Among these materials, BST is a well-known dielectric material and has been attractive for the applications such as capacitors and FRAMs due to its high dielectric constant and high capacity of charge storage [2]. It is also a potential material for active microwave tunable devices because of its variable dielectric constant under external electric field [3]. Especially, BST thin films have a good thermal–chemical stability, insulating effect and variety of phases. However, BST thin films have problems of the aging effect and mismatch between the ferroelectric thin film and metal electrode. On the other hand, the degradation of device performances occurred due to the high defect-state density and surface roughness at grain boundaries and in the grains. In order to overcome these weaknesses, we first applied the chemical mechanical polishing (CMP) process [4], [5], [6] to the planarization of ferroelectric film. BST ferroelectric film was fabricated by the sol–gel method [7], [8]. Then, we compared the structural characteristics before and after CMP process of BST films. Finally, we have suggested the self-developed titania (TiO₂) abrasive slurry for FRAM applications. Our experimental results on the ferroelectric film are encouraging for next generation of FRAM applications.

Section snippets

Experiment

Fig. 1 shows the flow chart for preparation of BST film by sol–gel method. The precursor solutions for BST were prepared by the sol–gel method using barium acetate [Ba(CH₃COO)₂], strontium acetate [Sr(CH₃COO)₂] and titanium isopropoxide [Ti(OC₂H₄CH₃)₄] as the starting materials. The solid-state barium acetate, and strontium acetate, were initially dissolved in acetic acid (CH₃COOH) and then mixed to obtain a (Ba, Sr) stock solution. Titanium isopropoxide was dissolved in 2-methoxyethanol (CH₃OCH

Results and discussion

Until now, there was no commercial CMP slurry for ferroelectric material films. Therefore, we have first evaluated the planarization characteristics of a ferroelectric film using conventional silica (SiO₂) slurry for oxide CMP and alumina (Al₂O₃) slurry for metal CMP, and suggested the self-developed titania (TiO₂) abrasive slurry for FRAM applications. Table 2 shows the comparison of removal rates and within-wafer non-uniformity (WIWNU) as a function of different slurry and its hardness.

Conclusion

Chemical mechanical polishing results of BST films with silica-, alumina- and titania-based slurry have been demonstrated. Removal rate, WIWNU (%) and surface roughness have been found to depend on slurry abrasive types and their hardness, especially, surface roughness and planarity were strongly depend on the our self-developed titania-based slurry. A maximum in the removal rate is observed in the alumina slurry, in contrast with the minimum removal rate occurs at titania slurry. We found that

Acknowledgements

This work was supported by Korea Research Foundation Grant (KRF-2002-005-D00011).

References (8)

S.Y Kim et al.
Microelectron. Eng.
(2002)
Y.J Seo et al.
Microelectron. Eng.
(2003)
Y.J Seo et al.
Microelectron. Eng.
(2003)
K.T Kim et al.
Microelectron. Eng.
(2003)

There are more references available in the full text version of this article.

Cited by (21)

Achieving smooth PZT surface via chemical mechanical polishing with ethylenediamine dihydrochloride
2022, Ceramics International
Citation Excerpt :
There have been only a few attempts to apply CMP to process piezoelectric ceramics. Seo et al. [4] studied the CMP performance of Ba0.6Sr0.4TiO3. It was found that the MRR, within-wafer non-uniformity and surface roughness depended on the type and hardness of abrasive particles.
Lead zirconate titanate (PZT) has been widely used in microelectromechanical systems and ferroelectric memory, and a high-quality PZT surface is important to the device performance. In this study, chemical mechanical polishing (CMP) was introduced to process PZT-4 (Pb(Zr_0.44Ti_0.56)O₃). A complexing agent ethylenediamine dihydrochloride (EDA·2HCl) was used as a crucial chemical additive in slurries to improve the CMP performance of PZT-4 because it may chelate metal ions of PZT-4, such as Ti⁴⁺. The results show that the material removal rate (MRR) of PZT-4 decreases and the surface roughness S_a increases as pH increases. At pH 4.0, with the EDA·2HCl concentration increasing, the MRR first increases, reaches the summit of 498 nm/min at 0.75 mM, and then decreases and levels off. The S_a has a similar trend. With 50 mM EDA·2HCl, the S_a reaches the minimum value of 3.5 nm, and no processing damage occurs in the substrate. For the removal mechanism, EDA can be adsorbed on PZT-4 probably via forming complex with Ti⁴⁺. With a low content of EDA·2HCl, the adsorbates of EDA distribute discretely and can be removed easily, and thus the MRR is high. As the content of EDA·2HCl increases, a relatively continuous and uniform film is formed to suppress dissolution and abrasion, and thus the MRR decreases. A two-step CMP process was developed, and a smooth PZT surface can be rapidly achieved. This study provides mechanistic insight of the role of EDA in the CMP of PZT-4, and may open new avenues of developing CMP slurries for achieving smooth surfaces of PZT materials via screening prospective complexing agents.
A study on the chemical mechanical polishing of oxide film using a zirconia (ZrO<inf>2</inf>)-mixed abrasive slurry (MAS)
2008, Microelectronic Engineering
We have studied the chemical mechanical polishing (CMP) characteristics of mixed abrasive slurry (MAS) retreated by adding of zirconium oxide (ZrO₂) abrasives within 1:10 diluted silica slurry. These mixed abrasives in the MAS are evaluated with respect to their particle size distribution, surface morphology, and CMP performance such as removal rate and non-uniformity. As an experimental result, the comparable slurry characteristics when compared to the original silica slurry were obtained from the viewpoint of high removal rate and low non-uniformity for excellent CMP performance. Therefore, our proposed ZrO₂-MAS can be useful to save on the high cost of slurry consumption since we used a 1:10 diluted silica slurry.
Improving dielectric loss and enhancing figure of merit of Ba<inf>0.5</inf>Sr<inf>0.5</inf>Ti<inf>0.95</inf>Mg<inf>0.05</inf>O<inf>3</inf> thin films doped by aluminum
2008, Materials Chemistry and Physics
The different Al contents effects of Ba_0.5Sr_0.5Ti_0.95Mg_0.05O₃ (BSTM) thin films grown on Pt/TiN/SiO₂/Si substrates in the crystallographic structure, surface morphology, dielectric constant, loss tangent, leakage current, and figure of merit were investigated. The BSTM films properties are studied as a function of Al content and have remarkable improvements including dielectric loss, leakage current, and figure of merit (FOM) as well as films grain sizes. With increasing Al content, the dielectric constant (k), tunability (T), loss tangent (tan δ), and leakage current density (J_L) decrease while the FOM, defined as T/tan δ, and breakdown strength increases. The maximum dielectric constant at zero bias, tunability, dielectric loss, FOM, and leakage current density of 1 mol% Al-doped BSTM films at 280 kV cm⁻¹ are 248, 40%, 0.0093, 43, and 3.76 × 10⁻⁷ A cm⁻², however, the same measured conditions of undoped BSTM films are 341, 54%, 0.0265, 20, and 1.19 × 10⁻⁶ A cm⁻², respectively. The dc resistivity increases from 2.33 × 10¹¹ Ω cm of the BSTM film to 6.08 × 10¹² Ω cm of the 5 mol% Al-doped BSTM film at 280 kV cm⁻¹. In addition, the tolerance factor (t) of Al-doped BSTM perovskite thin films is 0.97 as compared to 0.87 of the undoped BSTM thin films. The increasing of tolerance factor value indicates that the specimens with Al-doped BSTM films are more stable than undoped specimens.
Chemical mechanical polishing of PZT thin films for FRAM applications
2006, Microelectronic Engineering
In this paper, we first applied the chemical mechanical polishing (CMP) process to the planarization of PZT film in order to obtain a good planarity of the ferroelectric film surface. Pb_1.1(Zr_0.52Ti_0.48)O₃ (shortly PZT) ferroelectric film was fabricated by the sol–gel method. And then, we compared the structural characteristics before and after CMP process of PZT films. Their dependence on slurry composition and pH change was also investigated. Removal rate, within-wafer non-uniformity (WIWNU%) and surface roughness have been found to depend on slurry abrasive types and their hardness, especially, surface roughness and planarity strongly depend on its pH value.
Chemical mechanical polishing of BTO thin film for vertical sidewall patterning of high-density memory capacitor
2006, Thin Solid Films
Most high-k materials cannot to be etched easily. Problems such as low etch rate, poor sidewall angle, plasma damage, and process complexity have emerged in high-density DRAM fabrication. Chemical mechanical polishing (CMP) by the damascene process has been used to pattern high-k materials for high-density capacitor. Barium titanate (BTO) thin film, a typical high-k material, was polished with three types of silica slurry having different pH values. Sufficient removal rate with adequate selectivity to realize the pattern mask of tetra-ethyl ortho-silicate (TEOS) film for the vertical sidewall angle was obtained. The changes of X-ray diffraction pattern and dielectric constant by CMP process were negligible. Planarization was also achieved for the subsequent multilevel processes. Our new CMP approach will provide a guideline for effective patterning of high-k materials by CMP.
Chemical mechanical polishing of polymeric materials for MEMS applications
2006, Microelectronics Journal
Polymeric materials such as polycarbonate (PC) and poly-methyl methacryate (PMMA) are replacing silicon as the major substrate in microfluidic system fabrication due to their outstanding features such as low cost and good chemical resistance. In this study, chemical mechanical polishing (CMP) of PC and PMMA substrates was investigated. Four types of slurry were tested on CMP of the polymers under the same process conditions. The slurry suitable for polishing PC and PMMA was then chosen, and further CMP experiments were carried out under different process conditions. Experimental results showed that increasing table speed or head load increased the material removal rates of the polymers. The polymeric surface quality after CMP was acceptable to most MEMS applications. Analysis of variance was also carried out, and it was found that the interaction of head load and table speed had a significant (95% confidence) effect on surface finish of polished PMMA. On the other hand, table speed had a highly significant (99% confidence) effect on surface finish of polished PC.

View all citing articles on Scopus

View full text

Chemical mechanical polishing of Ba0.6Sr0.4TiO3 film prepared by sol–gel method

Abstract

Introduction

Section snippets

Experiment

Results and discussion

Conclusion

Acknowledgements

Microelectron. Eng.

Microelectron. Eng.

Microelectron. Eng.

Microelectron. Eng.

Chemical mechanical polishing of Ba_0.6Sr_0.4TiO₃ film prepared by sol–gel method