Investigation on Surface Hardening of Polyurethane Pads During Chemical Mechanical Polishing (CMP)

Abstract

Temperature control to stabilize the microscale contact surface between the pad and wafer, especially to prevent pad surface degradation, plays an important role in chemical mechanical polishing (CMP) processing of sub-50-nm devices. In this work, we investigated the phenomenon of pad surface hardening for various process temperatures and developed an effective method to minimize changes of the mechanical properties of the pad surface using diamond conditioner. The pad hardening characteristics were measured based on the force-distance (F-D) curve obtained by atomic force microscopy (AFM), and thermogravimetric analysis (TGA). F-D curve data showed that the increase of the elastic modulus with pad usage time at high process temperature was $1.5 times higher than at low process temperature. Also, TGA of a used polishing pad revealed a link between the endothermic peak intensity at 600°C and pad surface hardening. To prevent surface glazing or hardening throughout the lifetime of a pad at high process temperature, the optimum diamond size was investigated. Pad wear was investigated for various diamond conditioners with diamond grit size ranging from 100 lm to 270 lm. The results of pad surface analysis using scanning electron microscopy (SEM) and three-dimensional optical profiling showed that the 210 lm grit size was best for removing deformed layers, with the pad surface remaining consistent during the lifetime of the pad as verified by TGA and the F-D curve. The results of pad surface analysis are important for the design of conditioners that can produce pads with stable dynamic mechanical properties and prolonged lifetime at high process temperature.

Fluid-Structure Interaction Modeling and Simulation of CMP Process for Semiconductor Manufacturing

“…This may help the hard pad-particle mixture to induce microscratch on the wafer surface more easily. Recently a few experimental researches have suggested the feasibility of pad-particle mixture or particle-coated pad [9,10]. This simulation work is in good agreement with the experimental works.…”

Trace Metals Optimization in Ceria Abrasive for Material Removal Rate Enhancement during ILD CMP

“…It can be seen that the mode particle size of ceria abrasive without trace metals was 49.6 nm and there was no noticeable change in the particle mode size of the ceria abrasives with FeCl 2 and CrCl 2 up to 100 ppm, nor was there any change in particle number concentration; for the concentrations above 100 ppm however, the number of particles was found to be drastically decreased. A possible cause of this is the reaction of trace metals with hydroxyl groups (-OH) of the base solution, which may result in various salts such as Fe(OH) 3 or Cr(OH) 3 . We attempted to measure the agglomerated ceria abrasive particle number concentration, however we could not measure particle sizes above 300 nm due to limitations of the SMPS used in this study.…”

“…1,2 The material removal rate (MRR) is highly important in CMP to reduce the cost of consumables such as pads, slurries, and conditioners, along with improvisation in the production yield. [3][4][5] For interlayer dielectric (ILD) CMP, the use of ceria-abrasive-based slurries is becoming more prominent because they provide superior CMP performances, including high selectivity, high removal rate, and high planarization efficiency. 6,7 Since ceriaabrasive-based slurries are expensive, their functionality performance needs to be improved via the addition of other materials into the slurries.…”

Scratch formation and its mechanism in chemical mechanical planarization (CMP)

“…Borken chatter type of scratches was easily formed when dry slurry paritcles were added but group chatter when pad debris were added. Yang et al [74] measured the pad surface hardening phenomenon based on force-distance (F-D) curves. It was found that the interaction between abrasive particle and polyurethane pad under tribo-mechanical action could change the pad surface hardness.…”