Evaluation of Mechanical and Tribological Behavior, and Surface Characteristics of CMP Pads

Abstract

Chemical Mechanical Planarization (CMP) occurs at an atomic level at the slurry/wafer interface and hence slurries and polishing pads play a critical role in the successful implementation of this process. Surface roughness, visco-elastic properties, thickness and pore size also play an important role in this process. Unfortunately the mechanical properties of polyurethane polishing pads used in CMP are poorly understood. Here we have studied the mechanical and visco-elastic properties and surface morphology of CMP pads using nano-indentation and dynamic mechanical analysis along with high resolution scanning electron microscopy. A state-of-the-art Universal Micro-Tribometer was used to measure the pad deformation behavior under load. A novel non-destructive scanning ultrasonic transmission technique was also used to characterize inhomogeneity of the visco-elastic properties of full-size CMP pads. Results obtained by different techniques were analyzed to demonstrate methods for quick and reliable evaluation of pad quality for current CMP technology.

Investigation of the nonuniformities in polyurethane chemical mechanical planarization pads

“…[29][30][31] The UST experiments were performed on the "as received" polishing pad with the plastic release liner underneath. The amplitude of the ultrasound permeability with in a pad obtained as a result of UST is normalized to against the average UST amplitude to estimate the comparative variations in specific gravity in the different regions of the same polishing pad.…”

“…31,32 The pad displays higher mechanical properties when the perforations or grooves are oriented parallel to the length of the coupon used in the DMA. It has been shown before, that orientation of the polishing pad grooves or the directional orientation of the pad surface perforations directly affect the values of loss and storage modulus of the pad materials that are evaluated using DMA.…”

“…Commercial polishing pads are of viscoelastic nature and consist either of a matrix of cast polyurethane foam with filler material to control hardness or polyurethane impregnated felts. [29][30][31] This technique works on the principle of ultrasound permeability through absorbing viscoelastic medium. At the pad wafer interface, the slurry acts on the wafer and forms a compound with the material that is being polished.…”

Novel ceria–polymer microcomposites for chemical mechanical polishing

“…A dual force sensor allows continuous monitoring of lateral and normal forces in situ at a total sampling rate of 20 KHz. Features of the bench-top tester are provided in detail in previous publication [30]. All the slurries were well agitated during experimentation to reduce sedimentation of the abrasive particles.…”

Wavelet-based identification of delamination defect in cmp (cu-low k) using nonstationary acoustic emission signal

“…A number of theories exist that attempt to characterize the exact mechanism of material removal. Some examples are shown in [12]- [21]. Several defects that commonly arise during CMP and the metrology used to detect are discussed next.…”