Study on the Mechanism of Nano-Flake Defect during Tungsten Contact Chemical Mechanical Polishing

Abstract

Tungsten chemical mechanical polishing (CMP) has been used for metal interconnect formation in semiconductor manufacturing for a long time. Its application continues to the advanced device manufacturing with transistor scaling. However, the defect concerns of the tungsten CMP process have become critical to manufacturing such as metal flake defects that can cause electrical shorts between contacts. Although there are many published studies on tungsten CMP fundamentals, process applications and CMP-induced defects, the mechanism of thin metal flake formation in nanoscale (nano-flake defect) has not been clearly known to industry. In this study, nano-flake defects are identified after tungsten contact CMP, and mechanism of its formation is explored. Significant CMP dishing at wide contact area removes all tungsten and open barrier metal. Friction force by 3-body interaction among wafer, abrasive particle and pad asperity breaks the adhesion of barrier material from intermetallic dielectric material. And it allows re-deposition of barrier metal to the wafer surface. Insufficient CMP in-situ cleaning results in residual nano-flake defects at the end of CMP process. Analysis of device macros, thickness of flake, cross sectional analysis by transmission electron microscope (TEM) and topographical analysis support this suggested mechanism.

Chemical Mechanical Planarization-Related to Contaminants: Their Sources and Characteristics

“…Some metallic contaminants directly come from the metal interconnect lines. After the Cu CMP process, pyramid-shaped Cu particles (Cu, CuO, and CuOH) detached from the Cu films are discovered on the surface [49] Metal flakes such as Ti or W-Ti on the top of the replace metal gate (RMG) after W RMG CMP process are observed [50,51]. Metals at partially filled can be broken during the RMG CMP process, and they are a source of metal flake.…”

“…These metal flakes are trapped inside the brush and re-deposit to the wafer surface by the cross-contamination process. In some cases, the delamination of metal films is occurred at the wafer edge due to the edge over erosion or a poor adhesion between metal and barrier film, which is another source of metal flakes [50,51]. These metal flakes are known as a potential killer defect in the current RMG technologies.…”

Recent advances and applications of abrasive processes for microelectronics fabrications

“…Also, the friction force among the pad, abrasive particle and wafer removed the barrier metal from the intermetallic dielectric material, causing re-deposition of the barrier metal on the wafer surface. Inefficient in situ cleaning led to flake defects (Kim et al, 2018c). Han et al (2017) developed slurries and conducted CMP to remove SiN films with high removal selectivity between oxide and SiN films for sub-10-nm semiconductor devices.…”

“…Besides Si, SiC is a key material for the next-generation semiconductor because of its excellent properties (Wang et al, 2017;Zhou et al, 2017). CMP of tungsten has also become an important process for advanced device manufacturing of metal interconnects and transistor formation (Kim et al, 2018a); the CMP defects are issues because metal flake defects lead to electrical shorts (Kim et al, 2018c). Cobalt is also a promising material for the interconnects (Tian et al, 2018).…”

Investigation of Particle Kinetic Energy for EKF-CMP Process

“…27 The controlling process for the abrasive nanoparticle size in slurry flow for tungsten contact CMP has been examined. 20,28 The research on the motion behavior of the particle using the dielectrophoresis technology has been studied by Zhao et al 29 The motion qualification of all the colloidal silica nanoparticles and their granular temperature in the slurry layer affected the material abrasive process on the wafer surface. 30,31 In order to increase the slurry flow velocity, we have applied the technique of the electro-kinetic force (EKF) in the CMP process, which is verified by using the three-dimensional electroosmotic flow (3D-EOF) cell model at high voltages.…”