Study on the Weakly Alkaline Slurry of Copper Chemical Mechanical Planarization for GLSI

Abstract

Copper has been widely used as the most fundamental interconnection metal material for Gita-large scale integrated circuits(GLSI). During the chemical mechanical polishing (CMP) process, the stability of slurry is crucial to copper polishing performance. Through selecting the important factors of influence slurry such as pH, surfactant and pH-regulator, the weakly alkaline copper slurry was investigated in this paper. As the weakly alkaline slurry becomes very promising and stringent to fit for the requirement of integrated circuits development, and according to the investigation of removal rate results, pH 8.5–9.5 was selected as the appropriate pH range. Comparing with nonionic surfactant, anionic surfactant exhibited preferable performance for stability of silica sol such as ammonium dodecyl sulfate (ADS) due to its unique structure and charged property in weakly alkaline solution. Meanwhile, using tetraethylammonium hydroxide (TEAH) as pH-regulator instead of KOH, the copper slurry exhibited the stability for 7 days with H2O2. In order to examine the effectiveness of such copper slurry, the copper blanket and pattern wafer were polished by the slurry settling for 7 days. The pH-value, mean particle size, ζ potential and viscosity of the slurry fluctuated slightly with the aging time. And from the results of copper removal rate, roughness of copper blanket wafer and the step height values of pattern wafer it indicates that the weakly alkaline copper slurry has stability and which has a guiding significance to the development of microelectronics industry.

Effect of Complexing Agent Choices on Dishing Control Level and the Shelf Life in Copper CMP Slurry

“…24 The powder dispersion is highly dependent on the zeta potential, and it is difficult to aggregation for the particles with the larger negative electrostatic repulsion. 3,25 Just as Fig. 11 and Fig.…”

“…2 The first step employs a slurry having a high Cu removal rate to remove the bulk of the metal overburden, which is followed by a second step (called "finish polishing") to remove the remaining Cu. 3,4 In order to ensure complete copper removal across the entire wafer, some over-polishing beyond end point is invariably required by a high copper to barrier material (Ta/TaN) selective slurry. 5 The introduction of copper dishing is inevitable during over-polishing, which can aggravate copper loss and reduce the reliability.…”

Effect of Alkali Metal Ion on Chemical Mechanical Polishing of LiTaO3

“…At this potential, the slurry is stable due to the strong electrostatic repulsion between silica (as shown in Fig. 6, it is generally believed that when the absolute value of zeta potential is greater than 30 mV, the colloid is stable, and the larger the absolute value, the more stable colloid is 24,25 ). It can be seen that as the amount of ionic concentrations increases from 0 to 0.21 M, the zeta potential of the silica sol surface in the slurry containing additive KCl and NaCl continuously increases from −44 mV to −31.2 mV, and to −32.9 mV, respectively.…”

Improvement of Barrier CMP Performance with Alkaline Slurry: Role of Ionic Strength

“…On the other way, an excess of potassium ion can accelerate peroxide failure which will also reduce copper MRR. 20,22 The influence of potassium ionic strength on TEOS removal rate.-TEOS is mainly composed of acidic oxides silica. During CMP, the TEOS surface may react with hydroxyl ions in the alkaline solution and form soluble silicate which will flow away with slurry.…”