Hydroxyl Radical Formation in H[sub 2]O[sub 2]-Amino Acid Mixtures and Chemical Mechanical Polishing of Copper

Abstract

Chemical mechanical polishing (CMP) has become the key planarization technology in ultralarge scale integration (ULSI) silicon device manufacturing to fabricate sub-quarter-micrometer metal and dielectric lines. [1][2][3][4] In the CMP process, planarization is achieved by polishing a wafer with uneven topography using a colloidal slurry consisting of sub-micrometer sized abrasive particles. The particles are dispersed in an aqueous solution containing various chemicals, which make up the slurry. These chemicals, depending on their identity, play different roles such as oxidizers [Fe(NO 3 ) 3 , (NH 4 )S 2 O 8 , H 2 O 2 ], passivating agents (benzotriazole, benzimidazole), slurry stabilizers [poly(ethylene glycol), arabic gum], etc. While several slurry chemistries are available for Cu CMP and significant progress has been made in utilizing them in manufacturing, very little fundamental information about them is available in the published literature.Copper CMP in a highly acidic pH regime leads to corrosion problems, while Cu CMP in alkaline conditions is faced with an unfavorable polish rate selectivity with respect to SiO 2 , leading to interlayer dielectric (ILD) erosion. Thus, an intermediate pH range 4-7 appears to be a better choice for Cu CMP. 5-7 One of the more attractive slurries in this intermediate pH range consists of hydrogen peroxide, glycine (an amino acid), and an abrasive. Hirabayashi et al. 8,9 demonstrated that slurries containing hydrogen peroxide, glycine, and silica particles (abrasive) can be used for Cu CMP. They successfully fabricated inlaid copper wiring using the damascene process with very little dishing (less than 60 nm in the linewidth range of 0.5-100 m) with the above slurry. The mechanism, as proposed by them, consists of the oxidation of Cu to copper oxide by H 2 O 2 in the recessed region, thereby preventing the dissolution of Cu from the recessed areas of the wafer. The oxide formed in the protruded regions, on the other hand, is removed by the abrasives exposing the underlying metallic Cu surface to the slurry. According to Hirabayashi et al. copper is then converted into Cu(H 2 O) 4 2ϩ by the hydrogen peroxide in the slurry which in turn reacts with glycine (also in the slurry) to form a Cu 2ϩ -glycine chelate that is soluble in water. Thus, while the formation of copper oxide prevents the direct etching of Cu in the low lying regions, Cu in the protruded regions is removed by both direct dissolution as well as by the removal of the oxide formed. However, they did not describe the interaction between the Cu 2ϩ -glycine complex and hydrogen peroxide and its effect on Cu removal or the role of hydroxyl radicals. It has been well established that the decomposition of hydrogen peroxide leads to the formation of hydroxyl radicals (*OH) which are a much stronger oxidizing agent than hydrogen peroxide itself. 10,11 There is also a rich collection of information concerning the catalytic generation of *OH from hydrogen peroxide, with various metal ions and metal ion complexes acting ...

Key Chemical Components in Metal CMP Slurries

“…The electrochemical data generated by Brusic and coworkers [16] suggested that H 2 O 2 and glycine promote the formation and removal of a Cu(II) oxide film. Li and coworkers [17] further investigated the formation of the Cu-glycine complex and its effect on the copper film removal rate and static state dissolution rate. It was concluded that the Cu-glycine complex formed during CMP enhanced the decomposition of H 2 O 2 to give hydroxyl radical (*OH).…”

“…Although the function of hydrogen peroxide as an oxidizer is well known, the role of glycine in Cu CMP was somewhat less clear. In a study reported by Li and coworkers [17], the main role of glycine was defined as a chelating agent to form a complex with the Cu 2+ ions generated during the polishing process. The complex can catalyze the decomposition of hydrogen peroxide leading to the formation of hydroxyl radicals (*OH).…”

Chemical-mechanical planarization of Cu and Ta

“…However, the copper-polish rate with H 2 O 2 -only slurries is low and complexing agents are usually added to improve the dissolution of copper. Among the potential candidates, amino acids 14,15 have been extensively studied. Copper-polish rates increase significantly with addition of glycine to H 2 O 2 -containing slurries, as shown in Table I, due to the formation of soluble copper 2+ -glycine chelate which catalyzes the decomposition of H 2 O 2 to yield *OH radicals.…”

“…Copper-polish rates increase significantly with addition of glycine to H 2 O 2 -containing slurries, as shown in Table I, due to the formation of soluble copper 2+ -glycine chelate which catalyzes the decomposition of H 2 O 2 to yield *OH radicals. 15 However, an inherent problem arising from the enhanced dissolution rate is copper-line corrosion and dishing. As a solution, inhibitors are introduced to prevent etching of the low-lying features without significantly sacrificing the removal rate.…”

Effect of Linear Aliphatic Polyamines on Copper Removal Rate in Chemical Mechanical Planarization (CMP)

“…Hydrogen peroxide (H 2 O 2 ) is the oxidant most widely used to 'extract' electrons from copper. [1][2][3][4][5][6] The resulting ions easily hydrolyze at neutral and alkaline pH forming insoluble oxide films that hinder the oxidation. The role of complexing agents is to dissolve the oxides and ensure the access of H 2 O 2 molecules to the metal.…”