Corrosion Inhibitor for Cu CMP Slurry

Abstract

Copper chemical-mechanical planarization (Cu CMP) is a rapidly growing segment in the fabrication process of today's semiconductor devices [1]. Copper CMP slurry typically contains an oxidizer that chemically converts the metal film for easy removal, abrasive particles that enhance the abrasiveness of the pad, a complexing agent that enhances the solubility of the abraded metal/ metal oxide, a passivating agent that protects the lower lying areas, a pH regulating agent, and a surfactant [2]. The main function of the passivating agent is to protect the copper film from aggressive chemical attack that may lead to isotropic dissolution of the copper film. With the protection of such passivating agent, ideally, only the copper film in the protruded area is selectively removed by mechanical force, thus yielding a step height reduction. It is commonly observed that a passivating agent in a Cu CMP slurry will lower not only the static etch rate but also the removal rate. As a strong corrosion inhibitor, benzotriazole (BTA) is the most commonly used passivating agent in Cu CMP slurry. A vast number of publications and reports have been devoted to the use of BTA in metal CMP slurry [3][4][5][6][7][8][9][10][11][12][13][14][15][16]. The study of BTA analogs for CMP application, however, has been relatively limited in open literature. In this chapter, the role of corrosion inhibitor in Cu CMP slurry is first described. As a case study, the relative effectiveness of some tetrazoles such as 5-aminotetrazole monohydrate (ATA), 5-phenyl-1H-tetrazole (PTA), and 1-phenyl-1H-tetrazole-5-thiol (PTT) as corrosion inhibitor in Cu CMP slurry will be discussed.

Chemical Mechanical Planarization: Slurry Chemistry, Materials, and Mechanisms

“…Benzotriazole (BTA) is by far the most widely used adsorbate or inhibitor, even though other triazoles and several organic compounds that are known to adsorb on Cu have been investigated. 99 Earlier slurries did not have strong chelating agents in the formulation because in acid pH highly soluble Cu 2+ ions are the dominant species and achieving high rates is not a problem. Since the Cu polish rates are low in neutral and alkaline slurries, strong chelating agents were added to increase the rate.…”

“…Anionic surfactants like sodium or ammonium dodecyl sulfate or cationic surfactants like cetyl trimethyl ammonium bromide (CTAB), dodecyl trimethyl ammonium bromide, and cetyl pyridinium chloride have been reported. 99 The adsorption of these molecules can be classified as physical adsorption and often exhibits Langmuir isotherm behavior. Very often they also adsorb onto the abrasives and cause slurry instability.…”

“…The silica abrasives have appreciable polish rates for Ta/TaN barrier and need additional components in the slurry to suppress liner erosion. Benzotriazole (BTA) is by far the most widely used adsorbate or inhibitor, even though other triazoles and several organic compounds that are known to adsorb on Cu have been investigated . Earlier slurries did not have strong chelating agents in the formulation because in acid pH highly soluble Cu 2+ ions are the dominant species and achieving high rates is not a problem.…”

“…Surfactants have been used in Cu CMP slurries to modify and alter the BTA films or as better alternatives to BTA films. Anionic surfactants like sodium or ammonium dodecyl sulfate or cationic surfactants like cetyl trimethyl ammonium bromide (CTAB), dodecyl trimethyl ammonium bromide, and cetyl pyridinium chloride have been reported . The adsorption of these molecules can be classified as physical adsorption and often exhibits Langmuir isotherm behavior.…”

5-Phenyl-1-H-Tetrazole as a Low-pH Passivating Agent for Copper Chemical Mechanical Planarization

“…In addition to pKa effects, PTA also has lower solubility in acidic Cu CMP slurries than BTA, suggesting that it can form a more stable passive film. 24 The passive film formed from PTA-based Cu CMP slurries is also more hydrophobic than the passive film formed from BTA-based slurries, as shown by contact angle measurements, and this may also contribute to the improved stability of the passive film. 24 The BTA film formed at low pH is thicker and more porous than that obtained at high pH.…”