In Situ Investigation of Slurry Flow Fields during CMP

Abstract

The objective of this work is to obtain in situ slurry fluid flow data during the chemical mechanical planarization ͑CMP͒ process. Slurry flow affects the material removal processes, the creation of defects, and consumable use during CMP, and therefore impacts the cost and quality of polishing. Wafer-scale flow visualization using seeded slurry was accomplished for a variable applied load ͑0.3-2.5 psi downforce͒, wafer rotation speed ͑0 and 33 rpm͒, slurry injection locations, and various pad types ͑flat, XY grooved, and AC grooved͒. In situ pad conditioning was employed in all experiments. The data indicated complex slurry flow fields on the pad surface in the wafer vicinity, which are influenced by slurry injection point, pad grooving, downforce, and wafer/conditioner rotation. Injection location and pad type were shown to have the strongest impact on the variation in the fluid flow fields obtained.The semiconductor industry relies heavily on chemical mechanical planarization ͑CMP͒ to create planar surfaces on silicon substrates during the integrated circuit ͑IC͒ manufacturing process. As the IC feature size continues to shrink, the need to create surfaces with micrometer-level global planarity is of utmost importance. 1-4 CMP is a complex, multimechanism process 1 in which the material removal mechanisms are not well characterized, 5 leading to a high reliance on indirect empirical data. 6 In situ data acquisition during CMP is difficult due to concurrent processes, complex geometries, and the combined opaque nature of the pads, wafers, and slurry during polish. In most cases, CMP data are gathered ex situ or obtained from oversimplified systems that may not fully represent industrially relevant polishing conditions. Mechanistic models have been developed to explain the phenomena, 3,6-9 but there are only limited empirical data available to test these models. The polishing parameters and their effect on polish quality, which is influenced by fluid transport and polishing components, must be better understood to advance the state of the art in CMP. 1,3,9 The slurry velocity flow fields at the wafer-slurry-pad interface have not yet been fully characterized and a repeatable and reliable method to measure these polishing indicators is lacking. 10 We present data from two flow characterization approaches in this paper: qualitative flow visualization and slurry velocity measurement using particle image velocimetry ͑PIV͒. ExperimentalA photograph of the polisher utilized in this work is presented in Fig. 1. The primary component is a modified half-scale Stuers RotoPol-31 CMP industrial polisher that is surrounded by an 80/20 aluminum frame. The polishing system sits atop a 136 kg solid steel isolation table. Optically clear BK-7 glass wafers 75 mm in diameter ͑3 in.͒ and 12.5 mm thick ͑0.5 in.͒ were rotated and loaded with downforce through the centrally located aluminum shaft driven by a 0.2 hp Dayton motor. A transparent glass wafer was used as a surrogate for a silicon wafer because it has similar polishing chara...

Measurement of Microscale Shear Forces during Chemical Mechanical Planarization

“…[1][2][3][4] Models of polish rate dependence on an important subset of the mechanical and chemical variables for certain polishing systems have been developed. As feature sizes continue to shrink and depth of focus in the optical lithography systems decreases, planarity plays an increasingly important role in successful lithography.…”

A review on chemical and mechanical phenomena at the wafer interface during chemical mechanical planarization

“…Mueller et al [127] used tracer particles to study fluid flow characteristics over pad asperities and recorded a video at 30 frames/s using high definition camera to obtain in situ slurry fluid flow data during polishing (Table 2) and manually analyzed the qualitative information of the slurry flow characteristics from the video. This tool and method enable to study wafer-scale slurry flow visualization depending on CMP conditions, slurry injection locations, and various pad types [127]. The studies that used dyes or tracer particles contain valuable information on slurry film thickness and flow characteristics [23,24,127].…”

Chemical mechanical polishing: Theory and experiment

“…The slurry plays an important role at the wafer-pad interface during CMP. The particles and chemicals are brought to the interface with the slurry flow [83]; the slurry can build a lubrication film and decrease the friction force, and the fluid pressure can bear some of the downforce, thus causing wafer to have a flexible landing on the pad. To experimentally determine the fluid behavior at the wafer-pad interface, several fluid pressure mapping studies were performed on the simplified experimental setups of CMP, using a disk to simulate the wafer and wafer carrier [84][85][86][87][88][89].…”