In recent years, semiconductor materials, as an emerging industry, have gained an increasingly significant position in the fields of high technology and national economy. The efficient production of ultra-smooth and defect-free semiconductor wafers holds great scientific significance and market application potential.
Polishing solution is the core of chemical mechanical polishing technology. It plays a decisive role in the chemical and mechanical actions during the chemical mechanical polishing process. The quality of the polishing solution directly affects the quality of semiconductor wafers. Generally speaking, the polishing solution is composed of abrasive particles, oxidants, deionized water, and additives (dispersants, passivators, pH regulators, corrosion inhibitors, catalysts, chelating agents, etc.). The most commonly used abrasive particles mainly include three types: silica, cerium oxide, and aluminum oxide.
Take silicon dioxide as an example. Through the hydrolysis of sodium silicate and organic silicate, the desired particle size and uniform distribution of colloidal silicon dioxide particles can be obtained. The particles have a regular circular shape and are chemically stable with moderate hardness. However, the colloidal silicon dioxide solution inevitably contains a large amount of sodium ions. These sodium ions exist in the isolation oxide layer of the device, and a small amount of sodium ions can affect the stability of the integrated circuit voltage.
The concentration of abrasive particles affects the material removal rate and surface quality. In the CMP polishing process, the trend of the material removal rate changing with the abrasive particle concentration is basically consistent. However, due to process control limitations, the concentration of the synthesized silica sol is relatively low. To meet the requirements of subsequent processes, it is necessary to increase the concentration of the silica sol.
To address the issue of high metal ion concentration and low abrasive particle concentration in the polishing solution, Bonanza Technology adopted the cross-flow filtration method, conducted membrane selection and equipment selection, and developed membrane separation and membrane concentration processes. As a result, the metal ion concentration was reduced to the PPB level, and the abrasive particle concentration was increased to over 40wt%.
Counter-flow filtration is also known as cross-flow filtration or tangential flow filtration. This filtration method has the characteristics of low filtration resistance, light membrane surface fouling, high filtration efficiency, linear scalability, and suitability for industrial production. The particles in the polishing solution are generally at the micron or nanometer level. Direct-flow filtration or centrifugal methods cannot meet the requirements of industrial production. By using counter-flow filtration, the polishing solution is subjected to pressure and flows tangentially through the membrane surface. The permeate fluid passes vertically through the membrane surface, avoiding the phenomenon of gel formation of nanoparticles during the filtration process, achieving the purpose of concentrating abrasive particles and washing out metal ions.
In combination with membrane type selection, equipment type selection, material selection and filtration parameter determination, the design and manufacture of membrane filtration systems for pilot-scale, pilot-scale and production-scale were successfully achieved, and high-quality polishing liquid products were prepared.
Wuhan Bona has been deeply engaged in membrane separation technology and its application processes for many years. During the research and development process, we not only focused on the innovation of process development, but also committed to the optimization and upgrading of equipment and devices. Through years of unremitting efforts, we have accumulated rich experience in product purification and engineering-scale expansion, successfully overcoming a series of manufacturing challenges, and significantly improving the quality and purity of the final products. Our efforts have not only won wide recognition from customers, but also enabled mutual empowerment and win-win development with customers.
