Comparison of Glycine and Citric Acid as Complexing Agents in Copper Chemical-Mechanical Polishing Slurries

Abstract

Two complexing agents, glycine and citric acid, in hydrogen peroxide based slurries for planarizing copper have been compared. Copper dissolution and polish rates and in situ electrochemical experimental results at various slurry pH values and hydroxyl radical concentrations at pH=8.4 are presented. It was observed that the pH of the slurry has a strong influence on copper dissolution and polish rates. While high copper removal rates were observed with citric acid-peroxide solutions at low pH values, glycineperoxide system yielded high Cu removal rates at alkaline pH values. Copper dissolution rates in both the systems at pH 4 and 8 were consistent with the electrochemical measurements. The concentration of hydroxyl radicals generated in citric acid-peroxide system was less than that of those generated in glycine peroxide system at pH=8.4 indicating low copper removal rates at alkaline conditions in the former system.

Role of the Functional Groups of Complexing Agents in Copper Slurries

“…Certain complexing agents can also form Cucomplex films [12][13][14] that can be abraded at low polishing pressures. Glycine, [15][16][17][18][19][20][21][22][23] citric acid, 19,21,24,25 ethylene diamine, 26 ethylene diamine tetraacetic acid, 27 phthalic acid, 28 and oxalic acid 12 are some of the many complexing/chelating agents that have been investigated in Cu CMP slurries. However, there has been no systematic evaluation of the role of the molecular structure of the complexing agents-different functional groups ͑e.g., -NH 2 vs -COOH͒, their relative positions, the length of the carbon chain, etc.-in controlling Cu dissolution and polish rates.…”

Chemical Mechanical Planarization for Cu Through-Wafer Interconnects

“…It has been well-documented that slurry pH and H 2 O 2 concentration of the slurry dictate the type of species formed on the Cu surface. [9][10][11][12] Although a wealth of information on the effect of slurry pH and H 2 O 2 concentration, 9-12 inhibitors, 13,14 and complexing agents 13,[15][16][17][18][19] on the Cu CMP process has been reported, limited information is known about the interactive effects between slurry pH and H 2 O 2 concentration and their combined effect on Cu removal rate and uniformity. As with any CMP process, machine parameters and slurry chemistry are paramount in obtaining desired removal rates and uniformity.…”