Optimizing Stressor Film Deposition Sequence in Polish Rate Order for Best Planarization

ABSTRACTChemical Mechanical Polish (CMP) is one of the key technologies for the development of modern high performance integrated circuits. The requirements for the CMP uniformity get extremely demanding in order to meet the litho requirements for 32nm technology node and beyond. In this paper, two kinds of orders related to the stressor films that affect the CMP uniformity are revealed. The first is the stressor films deposition order according to the CMP polish rate of each stressor film. The second is the stress gradients order that formed inside the films sitting on top of the stressors. Through the optimization of the order, we show successfully removal of couple hundreds angstroms stressor step heights within 300mm wafer range. The method developed here can also find applications in microelectromechanical systems and 3D integration circuits.

The Role of Arginine as a Complexing Agent in Copper CMP

Chemical mechanical polishing (CMP) of copper was investigated in hydrogen peroxide and arginine slurries. Arginine was found to be a complexing agent for the copper in peroxide based slurries, in the alkaline region. The copper polish rate was measured in a Struers LaboPol-5 and LaboForce-3 CMP polishing tool. Static etch rate experiments of copper discs (25.4 mm Dia × 10 mm) were carried in 200 ml beakers with different combinations of hydrogen peroxide and arginine concentrations. Peroxide concentration was varied from 0 to 10 vol%, while the arginine concentration was varied from 0 to 1 wt% for both static etch and polish rate experiments. Fumed silica used as the abrasive medium for polishing.The electrochemical processes involved in oxidative dissolution of copper were investigated by the Tafel corrosion plots and OCP measurements, using the Princeton Applied Research potentiostat. Three electrode corrosion flat cell was used for the electrochemical measurements. Corrosion current density and open circuit potentials (OCP) were used to elucidate the oxidative behavior of peroxide and the complexing role of arginine. Surface characteristics of the polished copper surface were analyzed with the Digital Instruments NanoScope AFM. Polishing with these chemicals resulted in smooth finish.These results indicated that the arginine curtails the formation of oxidative layer on the copper surface and the removal rate was increased by forming complex with the copper.

A Predictive Model for Controlling Wafer Level Polish Rate Uniformity in Oxide CMP

A stress based engineering model has been developed that predicts the removal rate profile across the wafer as a function of the principal and shear stresses on the wafer. The model reproduces the form of the radial variation in polish rate that is seen without back side air for the current set of consumable conditions and the changes in the polish rate profile that occur when back side air pressure is used on an IPEC-472 tool. The model which is GUI based and can be run in the fab, returns the optimum recipe setting to maximize polish rate uniformity based on the current tool performance. Implementing this model in production resulted in a 50% improvement in within wafer uniformity statistics.

Polish profile control using magnetic control head

Magnetic bearing technology is widely used in various technical fields, and is particularly appreciated in the semiconductor industry, where it is applied to the turbo molecular pump and wafer transfer system due to the excellent controllability it provides, even at speeds as high as 50,000 rpm. This report discusses the adoption of magnetic bearing technology to control the wafer carrier tilt angle during polishing. When the wafer is polished on a viscoelastic pad, the wafer carrier is inclined and pressed into the pad. Therefore, the reaction force on the wafer from the pad is concentrated at the wafer edge, increasing the polish rate at the edge relative to the rest of the wafer. Modification of the tilt angle is thought to offer a possible means of normalizing the distribution of the reaction force from the pad and correcting the nonuniformity of the polish rate. The wafer carrier was confirmed to press slightly into the pad and to be tilted 18 × 10-5 rad by the viscoelasticity of the pad (without tilt angle control). Constant current control led to better control of the polish rate profile relative to feedback control. The polish rate in the outer area of the wafer was increased by tilting the carrier to the positive side, and the polish rate of the wafer center area could be reduced by tilting it to the negative side. The best profile was obtained with control current of Im = -0.4 A. When the wafer carrier was tilted in the reverse direction, the polish rate became almost zero. It was concluded that hydro-planing occurred between the wafer and the pad. Accordingly, this report demonstrates the possibility of improving the polish rate profile by maintaining the wafer carrier in a horizontal position using magnetic control.

Mechanism and an empirical model of the fixed abrasivepolishing process on a web-format tool

Several chemical–mechanical planarization characterization test wafers were polished to understand the polishing mechanism of the fixed abrasive process. Oxide thickness removal in the “active” (up) and the “recessed” (down) regions of the wafer was monitored for different times of polish. It was found that there was no significant removal in the recessed areas until the step height was reduced to about 100 Å, and the polish rate in the active area decreased rapidly once this critical step height had been attained. At this critical step height, the polish rate of the down areas started to increase and approached that of the up area, with both eventually reaching the negligibly low removal rate of the blanket wafer. The drop in the polish rate of the up area, after planarity had been attained, was fitted to an exponential model.

Chemical mechanical polishing of thermal oxide films using silica particles coated with ceria

Thermal oxide covered silicon wafers were polished with slurries containing either nano-sized ceria (CeO2) or newly prepared uniform colloidal silica particles coated with ceria. The polish rate of the latter was significantly higher than that of pure ceria. The experiments were carried out using different concentrations of the abrasives at pH 4 and 10. Little effect on the polishing rates was noted when the conditions of the slurries were varied, which was explained by the compensation of two opposite polishing mechanisms.