The Crucial Role of Chemical Mechanical Polishing in Silicon Polishing

In the realm of integrated circuit manufacturing, the need for precision and flatness at the nanometer level is paramount, making Chemical Mechanical Polishing (CMP) an essential process.

Because the integrated circuit components generally use multi-layer three-dimensional wiring, the front process of integrated circuit manufacturing needs to carry out multi-layer cycle. In this process, the wafer surface needs to be flattened by the CMP process. CMP is a key technology that can effectively make the "floor" of integrated circuits reach the nanometer level. Integrated circuit manufacturing is the most important application scenario of CMP equipment, which is reused after film deposition and before photolithography. In addition to integrated circuit manufacturing, CMP devices can also be used in silicon wafer manufacturing and advanced packaging.

In silicon wafer processing, multi-line cutting, grinding and other processing processes, damage layer will be formed on the surface, so that the surface has a certain roughness. Polishing is the process of further obtaining a smoother and flat silicon single crystal surface through chemical mechanical grinding on the basis of grinding plate. The roughness of the silicon wafer before polishing is generally 10-20um, and it can reach tens of nanometers after polishing.

The CMP process has the advantages of both chemical and mechanical action, and can achieve extremely high surface flatness in a large range, which is the only large-area surface flattening polishing technology at present. The chemical mechanical polishing of alkaline SiO2 is generally used, and the roughness below 100 nm can be achieved on 12 and 18 inch silicon wafers. In the CMP process, a flat plate with a silicon chip is installed under the polishing machine disc, the upper plate can be lifted and adjusted pressure, the lower plate is a large diameter disc, the interior needs to be cooled by water, and the surface is covered with a tough porous polyester or polyurethane polishing cloth.

When polishing, the bottom plate rotates under the drive of the motor, and the plate with the silicon wafer can rotate around its own axis to ensure the uniform polishing. The polishing slurry is injected from the center of the bottom plate and spread around under the action of centrifugal force. The temperature of the plate is controlled by the thermometer during polishing. The alkali in the polishing slurry reacts chemically with the silicon surface layer, and generates a relatively loose silicate (adhering to the surface layer, hindering the deep reaction), and then breaks away from the surface through the mechanical friction of SiO2 colloids and polishing cloth pads, so as to achieve the surface peel, and then is taken away by the polishing liquid. This process is repeated, so that the silicon wafer is stripped layer by layer, so that the polishing effect of removing the surface damage surface is achieved, and the high-precision polishing of the silicon wafer is achieved.

Interestingly, some of our customers who polish silicon devices, such as silicon reflectors, prefer to use our nano-scale alumina polishes rather than silicon oxide polishes.