Pad Wear Rate Research Articles

Pad Conditioning Density Distribution in CMP Process With Diamond Dresser

In the chemical-mechanical polishing (CMP) process, the pad conditioning density distribution plays a crucial role in the pad wear. A precise model and detailed analysis of a conditioning density function are required. To this end, at first we construct the mathematical model of polishing trajectories on the pad, then under the assumptions that the diamond grains are uniformly distributed and a slow sweeping motion is applied during dressing, the conditioning density distribution for a pad in CMP process is determined. This conditioning density function is verified through numerous numerical examples. In the mean time, it was also observed that to have a flat distribution of pad wear rate we have to make the ratio of disk-radius to pad-radius small, and the effect of the pattern of grain distribution on conditioning density function is insignificant, which agrees with known results from literature.

Computational Solid Mechanics Modeling of Asperity Deformation and Pad-Wafer Contact in CMP

ABSTRACTAsperity-scale pad deformation and dynamic pad-wafer contact area are crucial to the fundamental understanding of material removal and defect formation mechanisms in CMP. Pad asperity stress and strain are also central to characterizing pad wear rate during polishing and cut rate during conditioning. While it is very difficult to isolate and measure stress and strain in individual asperities, finite element modeling may be used in conjunction with experimental surface characterization to predict asperity-scale deformation and pad-wafer contact. Asperity sub-domains up to 1270 microns across are reproduced from three-dimensional point cloud data on porous polyurethane CMP pads obtained by confocal microscopy, meshed to high resolution, and analyzed using ABAQUS finite element software. Physical properties are derived from dynamic mechanical experiments. Pad stacks are simulated both with and without sub-pads. Results show that while a sub-pad increases pad-wafer contact area overall, it limits the local spreading of individual contact regions as polishing load increases. This finding identifies a direct mechanical origin of the trade-off in pad design between wafer-scale and die-scale planarity. As expected, the real contact area between a pad and wafer is much smaller than the cross-sectional or “bearing” area, but the difference is notably greater when a sub-pad is present. Values of asperity stress and strain under typical CMP polishing pressures reveal that plastic deformation takes place both on and beneath the contacting surface. Hence upon release of the polishing load the asperities do not fully rebound to their pre-compressed shapes. Each pass under the wafer thus reshapes the pad asperities such that a slightly different texture is presented upon the next pass. These deformation mechanics clarify the impact of top pad and sub-pad properties on real contact area, allowing better optimization of CMP pad performance.

Tire Model To Predict Treadwear

Abstract This study examines treadwear on tires caused by low severity cornering during free roll. The authors previously proposed a method to predict treadwear using rubber pad wear tests. This method required measurements from actual tires to obtain the tread frictional parameters, i.e., the sliding distance, sliding velocity, and contact pressure. The present study proposes an analytical tire model for predicting treadwear that does not require measurements from actual tires. This enables treadwear prediction during the tire design stage, prior to test tire construction. A continuous tread model for lateral tread deformation is described to evaluate the frictional parameters. The treadwear is then predicted from the parameters and the rubber pad wear rate. The predicted treadwear rates are compared with actual treadwear rates and are found to be valid in the tread center area.