Semiconductors are the fundamental components of modern electronic goods. With the advent of the digital age and now the current «Internet of Things», smaller, faster, and more powerful processors are in constant demand for many goods and services.
To produce silicon semiconductor devices, the grown silicon ingot material has to be cut, shaped, polished, and cleaned for further processing. Polishing is a key step in obtaining high quality silicon wafers, since it achieves surface planarity for future lithographic steps.
Chemical Mechanical Planarization «CMP» is one of the main technologies used to smooth or polish the silicon wafer surface. Typically, this process consists of mixing deionized water, CMP slurry (a colloidal silicon or alumina liquid dispersion), and hydrogen peroxide (a strong oxidizing agent) in a slurry blending station at a fixed concentration and ratio. The blended slurry mixture is pumped to the day tank for storage or to multiple polishers as part of a chemical delivery unit «CDU».
Because hydrogen peroxide degrades over time, it is necessary to constantly monitor its concentration online to ensure the CMP process is efficient and repeatable. In this manner, product loss is limited by checking that the CMP slurry is always in specification, and adjusting the mixture if necessary.
In 2019, the Semiconductor Industry Association (SIA) claimed that the worldwide semiconductor sales had been increasing in the last couple of years, with an annual growth rate of 6.81% per year.
Pure silicon ingots, from which the wafers are cut, are incredibly expensive to create. Therefore, any unnecessary waste must be kept to a minimum during the subsequent processing steps.
In the CMP polisher, the slurry mixture comes into direct contact with a single silicon wafer, oxidizing the hard silicon surface to a softer silicon oxide layer, and increasing the polishing efficiency. This is kept in a precise balance with the mechanical polishing pad to achieve optimum polishing rates for increased wafer yields.
Hydrogen peroxide is the most widely used chemical oxidizer for the CMP process, and is added to the majority of semiconductor CMP slurries. However, because of its degradation properties over time, hydrogen peroxide concentrations must be measured continuously and throughout the slurry global distribution loop to assure in spec slurry purity before use. This demands quick online analysis with fast response times as part of chemical replenishment and process control.
Online monitoring of hydrogen peroxide, pH, conductivity, and temperature is possible with the 2060 Process Analyzer from Metrohm Process Analytics. The hydrogen peroxide concentration is measured titrimetrically with cerium(IV) using a Pt-ring electrode to determine the endpoint with dynamic endpoint titration (DET). The analysis frequency is typically less than 5 minutes, ensuring timely control of the slurry mixture.
Other combinations of measurements, as well as measurement points taken from a single process stream or even multiple streams, can be realized across the Metrohm Process Analytics product portfolio. All platforms guarantee fast, accurate results continuously available for true process control.
- Enhanced wafer yields with qualified CMP slurry compositions
- Increased product throughput with less wafer defects
- Greater mixing integrity and purity in the blending station
- Enhanced control of chemical reaction rates and polishing rates of the CMP polishing process
The Metrohm Process Analytics 2060 Process Analyzer can measure not only the concentration of hydrogen peroxide in CMP slurry, but also include pH, conductivity and temperature measurements to give an overall health status of the produced CMP slurry mixture without delay.
Other applications are available for the semiconductor industry like: copper, sulfuric acid, and chloride in acid copper baths, acidity in mixed acid etchants, hydrofluoric acid etch, ammonium hydroxide, and hydrochloric acid in standard clean baths.