Effects of OH Radicals on Formation of Cu Oxide and Polishing Performance in Cu Chemical Mechanical Polishing

Abstract

The amount of OH radicals generated varied according to the complexing agent or Cu ion, and the accelerating effect of OH radicals on the rate of Cu oxide formation was found in acidic pH. When Cu͑I͒ ions and oxalic acid were added to H 2 O 2 -based slurry, the decreases in etch and removal rates of Cu were observed because more generation of OH radicals resulted in the formation of thicker Cu oxide compared to additive-free slurry. Therefore, proper control of the formation and dissolution of Cu oxide led to an increase in etch and removal rates.Cu has been introduced as an interconnection material due to its low electrical resistance and high resistance to electromigration compared to W or Al. 1-3 The damascene process based on chemical mechanical polishing ͑CMP͒, which is used to remove the protruding part and planarize the whole wafer surface, makes it possible to use Cu as an interconnection material.During Cu CMP, the Cu surface is oxidized by an oxidizing agent through the oxidation of Cu to cuprous or cupric ions ͑Eq. 1͒. Among such oxidizing agents, hydrogen peroxide ͑H 2 O 2 ͒ is widely used for Cu CMP and its properties have been widely investigated. 4-8 Also, various organic additives were added into the slurry to maximize specific characteristics during the Cu CMP. To inhibit Cu corrosion, benzotriazole ͑BTA͒ or 5-aminotetrazole ͑ATRA͒ is commonly used. 9-11 An organic additive of the carboxylic group was added as a complexing agent to improve the removal rate of Cu. At present, citric acid, 12-14 oxalic acid, 15 and glycine 16-18 were introduced as the complexing agent and their properties and performance investigated. The complexing agents react with oxidized Cu and form complexes on the Cu surface. In an acidic pH, Cu cations, especially Cu͑I͒ ions, react with H 2 O 2 and then H 2 O 2 is converted into OH radicals and hydroxyl ions through the so-called Fenton reaction ͑Eq. 2͒. 19 The oxidation potential of the OH radical is higher than that of H 2 O 2 , which is well known to be one of the most powerful oxidizing agents Cu → Cu + + e or Cu 2+ + 2e ͓1͔It has been reported that OH radicals enhanced the removal rates of Cu in an H 2 O 2 -based slurry, including an amino acid at alkaline solution, 16 and that citric acid and oxalic acid improved the removal rate of Cu in the acidic solution. When using citric acid and oxalic acid as the complexing agent in weak acidic pH, the effect of OH radicals in the slurry on Cu CMP performance has not been reported. Therefore, the objective of this study is to understand the effect of OH radicals on Cu CMP. ExperimentalElectrochemical measurements.-For the electrochemical experiments, a 99.9% Cu rod with a surface area of 0.5 cm 2 was used. A Pt electrode and a saturated calomel electrode ͑SCE͒ were used as a counter and a reference electrode, respectively. Potentiodynamic studies were performed with an EG&G model 263 potentiostat/ galvanostat corrosion measurement system. The potentiodynamic polarization measurements were obtained with a scan rate of 10 mV/s a...

Ultra‐small CuO nanoparticles with tailored energy‐band diagram synthesized by a hybrid plasma‐liquid process

“…The plasma‐ethanol interface is also known to produce radicals leading to the formation of hydrogen peroxide (H 2 O 2 ) and we have confirmed that also in our case H 2 O 2 is produced and consumed by equation (see Supporting Information) . The interaction of locally produced (i.e., close to the interface) H 2 O 2 with reduced copper atoms then leads to the formation of CuO, where the very high reaction rates of solvated electrons and the non‐acidic state (>6 pH; measured before and after synthesis, see Supporting Information) prevents Fenton‐like reactions with the Cu‐ions . The size of the NPs is then determined by the local concentration of coalescing CuO.…”

A modified Damascene electrodeposition process for bottom-up filling of recessed surface features

“…The citric acid and H 2 O 2 are well-known as a complexing agent and oxidizer, respectively. The combination has been effectively used for chemical mechanical polishing (CMP) of Cu [27,28]. Following etching, the specimens were rinsed with 18 M cm DI water, dried with N 2 gas flow, and then immediately immersed into the plating bath with the potential applied.…”

Local Corrosion of the Oxide Passivation Layer during Cu Chemical Mechanical Polishing

“…Oxalic acid produced a thicker oxide film than the citric-acid-based solution or H 2 O 2 -only solution. 19 The stress determined by the measurement of the wafer curvature is biaxial stress, which is intrinsically gener-ated from the chemical modification. During the polishing process, the pressure to push the wafer to the pad was applied normal to the surface.…”

“…[14][15][16][17][18] The differences could induce different polishing rates according to the slurry pH, oxide formation character differences, and deviations in the radical formation rate. 19 However, there has been little research into the correlation between the difference in oxide formation and the corrosion character of various slurries. In this research, the stress evolution due to the oxide formation by the slurry and its effect on the corrosion fit generation was intensively studied.…”