Chemical mechanical planarization of silicon wafers at natural pH for green manufacturing

Abstract

In order to eliminate the disposal issues of toxic chemicals in chemical mechanical planarization, a water-based ultra-polishing experiment with alumina abrasives was investigated for silicon wafer based on Box-behnken theory. It was found that the material removal rate (MRR) was sensitive to pH value, more sensitive to the slurry flow rate, and most sensitive to the oxidizer concentration. Under the optimal conditions of oxidizer concentration (0.44%), slurry flow rate (71.86 mL/min), and natural pH (pH: 7), the highest MRR was derived. Finally, a confuse-understanding of pH on material removal was addressed as well. It was pointed out that the increase in pH leads to the initial decrease in MRR, followed by a rapid increase as pH exceeds 11.

Surface Modification Using Assisting Electrodes in Wire Electrical Discharge Machining for Silicon Wafer Preparation

“…Note that the high skewness topography provides pockets capable of retaining the chemical agents used in chemicalmechanical planarization (CMP) to enhance the polishing performance. Figure 3a presents the target workpiece of polycrystalline silicon (156 × 100 × 156 mm 3 ) sandwiched between assisting electrodes of aluminum alloy (160 × 100 × 0/15/25 mm 3 ) during a discharging action. Table 2 details the physical and engineering properties of the target workpiece, the wire electrode, and the assisting electrodes used in the experiments.…”

“…Figure 3d illustrates the set-up used for the measurement of the electrical signals (voltage and amperage wave forms) throughout the test intervals. Specimens cut from the stacked workpiece had cubic dimensions of 5 × 1 × 156 mm 3 . The specimens were carefully examined to reveal indications of surface deposits, alloying with source materials, the removal of source and target materials, and the topography of the machined surfaces.…”

“…When comparing the effects of the drawn currents between the 15 and 25-mm assisting electrodes, the PCR (86.44%) of the open voltage greatly surpassed the other variables. The influence of electrical resistance and pulse-on time were overridden by those of source material thickness and open voltage, so long as the discharging energy was within the preferable range of 42.11-151.52 mJ/mm3 . Extending the pulse-on time and reducing resistance could theoretically increase the current draw; however, these actions did not have a significant effect, perhaps due to the secondary deposition of aluminium and its effect on operating efficiency.…”

Computational analysis and chemical mechanical polishing for manufacturing of optical components

“…When the pH is increased from 7 to 11, the MRR is decreased. However, after reaching the minimized MRR at pH of 11, the MRR increases when pH increase from 11 to 12 [87]. For silicon dioxide, the formation of Si(OH) 4 , which is the result of the reaction of Si and OH-in the water, is noticeably enhanced at a pH more than 11.…”

“…Schematic of a) a conventional nozzle, b) a new nozzle with a height of 10 mm, c) a new nozzle with a height of 30 mm, and d) a new nozzle with a height of 50 mm [9].The particle size is not constant in the CMP processes. pH value increasing can make the particle size increases[87]. Surface roughness is proportional to the mean particle size.…”