The Adsorption Behaviors of Citric Acid on Abrasive Particles in Cu CMP Slurry
- PDF / 149,410 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 99 Downloads / 236 Views
W7.5.1
The Adsorption Behaviors of Citric Acid on Abrasive Particles in Cu CMP Slurry Young-Jae Kang, Yi-Koan Hong, Jae-Hoon Song, In-Kwon Kim and Jin-Goo Park
Div. of Materials and Chemical Engineering, Hanyang University, Ansan, 426-791, Korea ABSTRACT The interaction between Cu surface and abrasive particles in slurry solution was characterized. The adsorption behavior of the citrate ions was dependent on the pH of the slurry and the concentration of the citric acid. The adsorption of citrate ions generated a highly negative charge on the alumina surface and shifted isoelectric point (IEP) to lower pH values. The Cu removal rate of alumina slurry was higher than that of colloidal silica based slurry in the investigated pH ranges. Although lower friction forces of Cu were observed in alumina based slurry of pH 4, 6 and 8, a higher friction force was observed at pH 2. This high friction force was attributed to the positive zeta potential and greater adhesion force of particle. It indicates that the magnitudes of particle adhesions on Cu surfaces in slurries can be directly related to the frictional behavior during CMP process. 1. INTRODUCTION Cu CMP slurry is consisted of two major components; abrasive particles and chemical solutions. Chemical solution always contains both the complexing agent and oxidant. The oxidant reacts with Cu in the slurry and Cu2+ ions are formed. As complexing agents, organic acids (carboxylic acids), amino acids with both carboxyl and amine groups and amine types are widely used to formulate Cu slurry. Hydrogen peroxide is widely used as an oxidant due to its high oxidizing power [1]. The nature and the properties of the oxidized surface layer for Cu vary with changes in the chemistry and the pH of the slurry [2]. The adsorption behavior of citric acid is dependent on the pH of the suspension and the concentration of the citric acid. Citric acid is also known to be a chealating agent for Cu2+ ions [3]. The maximum amount of citric acid adsorbed on the alumina surface was 2.17 μmol/m2 at pH 3 and decrease to 1.17 μmol/m2 at pH 8 [4]. Citric acid has been used as a chelating and etching chemical in Cu slurry formation. The adsorption of citrates on Cu and slurry particles could affect the polishing behavior. 2. EXPERIMENTS Slurry preparation γ- alumina (Degussa, 99.99% primary particle size,13nm) and colloidal silica (ACE Hightec, mean particle size, 40 nm) particles were used for the slurry preparation. Hydrogen peroxide based slurry was used for the polishing test. NH4OH was used as a pH adjustor. Removal rates A copper disc (99%, diameter 100 mm) was used as a polishing substrate. Removal rate was evaluated by measuring the weights before and after the polishing using a microbalance with a
W7.5.2
sensitivity of 0.1 mg. Polishing tests were performed on a rotational friction polisher (G&P Tech., POLI-500 Korea)using Ronm&Hass IC 1400 k-groove pad. The polishing was done for 1 min at a slurry flow rate of 140 ml/min at a process pressure 4.2 psi. The polisher head and platen velociti
Data Loading...
