CMP, that is, Chemical Mechanical Polishing, chemical mechanical polishing.
CMPPAD, that is, Chemical Mechanical Polishing Pad, chemical mechanical polishing pad.
1. Basic principles of CMP
Macroscopically speaking, the basic principle of CMP is: the rotating polished wafer is pressed on the elastic polishing pad of the CMP pad that rotates in the same direction, and the polishing slurry flows continuously between the wafer and the base plate.The upper and lower discs operate in reverse at high speed, and the reaction product on the surface of the polished wafer is constantly peeled off, and the new polishing slurry is added, and the reaction product is taken away with the polishing slurry.The newly exposed wafer plane undergoes a chemical reaction again, and the product is then peeled off and circulated back and forth, forming an ultra-fine surface under the combined action of the substrate, abrasive particles and chemical reaction agent.
2. Application of CMP
The concept of CMP technology was first proposed by Monsanto in 1965.This technology was originally used to obtain high-quality glass surfaces, such as military telescopes.In 1988, IBM began to apply CMP technology to the manufacture of 4M DRAM, and since IBM successfully applied CMP to the production of 64M DRAM in 1991, CMP technology has developed rapidly around the world.Unlike traditional purely mechanical or purely chemical polishing methods, CMP uses a combination of chemical and mechanical effects to avoid surface damage caused by simple mechanical polishing and shortcomings such as slow polishing speed, poor surface flatness and polishing consistency that are easily caused by simple chemical polishing.It uses the principle of "soft grinding and hard" in wear, that is, softer materials are used for polishing to achieve high-quality surface polishing.Under a certain pressure and the presence of polishing slurry, the polished workpiece moves relative to the polishing pad. By means of the organic combination between the grinding effect of the nano-particles and the corrosive effect of the oxidant, a smooth surface is formed on the surface of the polished workpiece.The most widely used application of CMP technology is the polishing of silicon wafers of matrix materials in integrated circuits (IC) and ultra-large-scale integrated circuits (ULSI).It is generally believed internationally that when the characteristic size of the device is below 0.35µm, global planarization must be carried out to ensure the accuracy and resolution of lithographic image transmission, and CMP is currently almost the only technology that can provide global planarization, and its application range is expanding day by day.
At present, CMP technology has developed into a CMP technology with chemical mechanical polishing machine as the main body, integrating online detection, end-point detection, cleaning and other technologies. It is the product of the development of integrated circuits to micro-refinement, multilayer, thinning, and flattening processes.At the same time, it is also a necessary process technology for the transition of wafers from 200mm to 300mm and even larger diameters, to increase productivity, reduce manufacturing costs, and flatten the substrate globally.
3. CMP technical equipment and consumables
CMP, that is, Chemical Mechanical Polishing, chemical mechanical polishing.The equipment and consumables used in CMP technology include: polishing machine, polishing slurry, CMP pad polishing pad, post-CMP cleaning equipment, polishing end point detection and process control equipment, waste treatment and testing equipment, etc.Polishing machine, polishing slurry and CMPPAD polishing pad are the three key elements of the CMP process, and their performance and mutual matching determine the level of surface flatness that CMP can achieve.Among them, the polishing slurry and CMPPAD polishing pad are consumables.
Fourth, the main problems in the CMP process
The ultimate goal of polishing slurry research is to find the best combination of chemical and mechanical effects, so that a polishing slurry with high removal rate, good flatness, good film thickness uniformity and high selectivity can be obtained.In addition, issues such as ease of cleaning, corrosion to equipment, waste disposal costs and safety must be considered.
Reducing defects is an eternal topic in the CMP process and even the entire chip manufacturing.The semiconductor industry also has corresponding "unspoken rules" for the CMP process, that is, the material loss of the device after the CMP process should be less than 10% of the thickness of the entire device.In other words, slurry must not only make the material effectively removed, but also be able to accurately control the removal rate and final effect.As the characteristic size of the device continues to shrink, the impact of defects on process control and final yield becomes more and more obvious. The size of fatal defects requires at least 50% of the device size.
V. Development prospects of CMP
The third-generation wide bandgap semiconductor material represented by gallium nitride (GaN) has developed rapidly in recent years. Gallium nitride (GaN)-based semiconductor materials have the characteristics of high luminous efficiency, good thermal conductivity, high temperature resistance, radiation resistance, high strength and high hardness, and can be made into high-efficiency blue and green light-emitting diodes and laser diodes (also known as lasers).However, gallium nitride (GaN) materials cannot grow single crystals by themselves, and must be grown on a substrate material similar to their structure.At present, the internationally recognized substrate material is sapphire crystal.With the growth of the market demand for gallium nitride (GaN) materials, the demand for sapphire will also grow rapidly.