Potential-pH Diagrams of Interest to Chemical Mechanical Planarization of Copper

Recently, stainless steel has been widely used as the solar cell substrate. In this paper, chemical mechanical polishing technique was employed to prepare the ultra-smooth 316L stainless steel surface for such application. The effects of solid content, pH, H 2 O 2 and benzotriazole (BTA) on the polishing performance of 316L stainless steel were investigated. The results indicated that, at pH 4.00, with the increase in the H 2 O 2 concentration, the MRR first dramatically increases due to the fact that, with the addition of small amount of H 2 O 2 , a porous outer layer mainly consisting of iron-enriched oxides with relatively low mechanical strength of the bilayer-structure oxide film is rapidly formed on the surface. After reaching the maximum value, the MRR gradually decreases since the outer layer gradually grows compact by the transformation of γ-FeOOH into α-FeOOH and even into α-Fe 2 O 3 . With the addition of BTA, the MRR can be suppressed, which is probably attributed to the formation of BTA passivating film on the top surface. Finally, a two-step polishing method was proposed, by which the ultra-smooth 316L stainless steel surface with the surface roughness R a about 2.0 nm can be achieved within 30 min and it can be subsequently used for thin-film solar cells. Stainless steel plays an important role in the mechanical industry due to the excellent mechanical properties, the high thermostability and the strong corrosion resistance. Recently, various types of stainless steels have been intensively used in precise devices, 1-4 especially been used as the substrate for thin-film solar cells. [5][6][7][8][9][10] In order to achieve satisfactory performance of solar cells, low roughness, low defects as well as excellent flatness of the stainless steel substrate are intensively demanded and even indispensable. It is reported that, by improving the surface roughness of stainless steel substrate from 38 nm to 23 nm, the conversion efficiency of hydrogenated amorphous silicon thin-film solar cells can greatly increase to 5.4%. 10 As is revealed, chemical mechanical polishing (CMP) combines the synergetic effects of chemical corrosion and mechanical abrasion, and can achieve both local and global planarization of the substrate surface. 11-14Hu et al.2 used colloidal silica as the abrasive and investigated the effects of pH and oxidizer on the polishing performance of stainless steel, and it was reported that the combination of oxidizer and strong acidity was the prerequisite for high material removal rate (MRR). However, the microscopic defects of 1-2 μm in size cannot be effectively avoided on the polished surface. Lee et al.10 used electrochemical mechanical polishing technique, which applied an additional anodic potential on the stainless steel substrate besides CMP, to polish the stainless steel surface, and it was reported that the polished surface roughness was reduced from about 38 nm to about 23 nm. However, more detailed polishing performance and the mechanism of chemical reactions during the polishing pr...

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“…immunity, corrosion or passivation. [17][18][19] The effect of pH on the polishing performance of 316L stainless steel is shown in Fig. 2.…”

Section: Resultsmentioning

confidence: 99%

Chemical Mechanical Polishing of Stainless Steel as Solar Cell Substrate

Jiang

Yang

2015

ECS J. Solid State Sci. Technol.

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“…[40][41][42][43][44] For pH < 2, no complex was observed as the citric acid largely favored its neutral, non-dissociated form. However, once pH>2, citric acid dissociated to H 2 45 Complex formation can be ob- served through UV-vis spectroscopy, with absorption at 800 nm being associated with hydrated, non-complexed Cu ions, and a blueshift and intensity increase being associated with complex formation. 31 We observed a similar behavior at various citric acid concentrations, providing fundamental information as to the possible function of citrate as a suppressor in Cu superfilling.…”

Section: Resultsmentioning

confidence: 99%

Electrochemical Behavior of Citric Acid and Its Influence on Cu Electrodeposition for Damascene Metallization

Kim

Choe

Kim

et al. 2015

J. Electrochem. Soc.

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The electrolyte for Cu superfilling generally consists of copper sulfate, sulfuric acid, a chloride ion, an accelerator, and a suppressor. In this study, the characteristics of citric acid-based electrolytes and the interaction between citrate species and accelerators are investigated, with the ultimate goal being the replacement of both sulfuric acid and the suppressor with citric acid. Electrochemical impedance measurements were adopted to measure the changes in solution and charge transfer resistances with respect to citric acid and accelerator concentrations. In addition to a decrease in solution resistance resulting from the addition of citric acid, charge transfer inhibition was observed during Cu electrodeposition, which is likely the result of adsorption of citrate species onto Cu surface. A competitive adsorption between the citrate species and the accelerator was also observed and the new additive system was applied to the feature filling in the absence of the conventional polyethylene glycol suppressor. Using this new copper sulfate, citric acid, chloride ion, and accelerator system, trenches were successfully bottom-up filled, resulting in no internal defects.

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“…[3] Citric acid, which is well known as a complexing agent for copper ions and is widely used in the cleaning process due to its high complexing ability with metallic ions, also acts as an inhibitor of copper etching. [4,5] Monoethanolamine (MEA) also has the ability to form a complex with copper ions and can act as a cupric chelating agent as well as a copper corrosion inhibitor. [6,7] In this study, aqueous solutions including citric acid and MEA have been evaluated for their ability to remove PER copper such as copper oxides.…”

Section: Introductionmentioning

confidence: 99%

Effects of pH variation in aqueous solutions on dissolution of copper oxide

Lee

2010

Surface & Interface Analysis

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Dissolution characteristics, such as the solubility of copper oxides and the complexation stability between copper ions and aqueous solutions, were analyzed under various pH values of citric acid or monoethanolamine (MEA) aqueous solution, which are known as complexing agents for copper. The dissolution characteristics of the aqueous solutions were measured in terms of the solubility of copper oxides and metallic copper. The citric acid solution had a good solvent property for copper oxides in the range of acidic conditions, whereas the MEA solution showed the same property in the basic region. The surface roughness of copper film treated with solutions having different pH values strongly depended on the solubility of copper oxides. The treatment of citric acid and MEA of different pH values has an influence on the oxidation status of copper surface, which is confirmed with X-ray photoemission spectroscopy and electrochemical impedance.

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Potential-pH Diagrams of Interest to Chemical Mechanical Planarization of Copper

Cited by 131 publications

References 18 publications

Chemical Mechanical Polishing of Stainless Steel as Solar Cell Substrate

Chemical Mechanical Polishing of Stainless Steel as Solar Cell Substrate

Electrochemical Behavior of Citric Acid and Its Influence on Cu Electrodeposition for Damascene Metallization

Effects of pH variation in aqueous solutions on dissolution of copper oxide

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