Nanoscale tribological aspects of chemical mechanical polishing: A review

The semiconductor industry is the backbone of exponentially growing digitization. Countries from the east and the west both are investing significantly to accelerate this growth. Chemical mechanical planarization (CMP) is one of the crucial technologies for expediting this growth. In 1986, IBM first developed CMP for the polishing of oxide layers. In 1988, it was deployed for the polishing of tungsten. Very soon, the CMP process became popular among the academic researchers and industries due to its global as well as local surface planarization capacity. As the number of active components in a wafer is increasing significantly, the feature size is decreasing for developing high performance integrated circuit (IC) chips. Along with the reducing feature sizes, multiple levels are being implemented. These additional levels necessitate multilevel interconnection. To accommodate all these features, CMP has become an inevitable process for both the semiconductor and solar cell wafer manufacturing industries. The CMP provides a critical support for achieving good surface finish at various levels of IC fabrication. Furthermore, the CMP is also used for the surface polishing of a wide range of materials including sapphire wafers, titanium based biomedical implants, aluminium, copper, YAG crystals, zirconium ceramics, cobalt, molybdenum etc. After its development, ample studies have been carried out for further improvement of CMP processes. However, the intricacy of the process parameters for different wafer & pad materials and slurry composition makes it difficult to indiscriminately apply to any wafer or alloys. Most of the studies have been discretely carried out either on a specific wafer material or based on controlled investigations of certain parameters. In this review paper, CMP has been analysed holistically based on its nanoscale tribological aspects. Several studies have been discussed for the relevant parameters at nano and microscale level including morphology, type, and size of abrasive particles, as well as the arrangement of polishing pad asperities and their conditioning to explore the nanotribological characteristics of CMP. Subsequently, atomic force microscopy (AFM) based studies on CMP have been discussed to correlate it with macroscale CMP. As our mother nature is facing environmental crisis world-wide, research communities should develop environment friendly processes for production. In this regard, the scientists are developing environment friendly CMP process to mitigate the burden of environment. At the same time, researchers can save a mammoth quantity of laboratory resources by carrying out the nanoscale studies of CMP using molecular dynamics simulation approach. In this review, both the green CMP and molecular dynamics studies related to CMP have been discussed. Moreover, the readers can grasp the challenges, difficulties, and achievements of CMP from the nanotribological point of view. Finally, the review presents some insights that can be implemented for further improvements of CMP process.