Choosing the Best CMP Slurry

There is a definitive method when it comes to selecting the right polishing media for your workflow. Firstly, all solutions should be purchased on an application-specific basis. Some manufacturers categorise different product lines by their intended end-use, but it is more common to define solutions by composition rather than application. This means that process engineers require a decent understanding of what goes into their polishing slurries in order to make informed decisions about new products.

Let us say you work with chemical mechanical planarization and need to choose a cost-effective CMP slurry that combines rapid removal rates with high planarization efficiency. Where should you start?

A Brief Introduction to CMP Slurries

Briefly, CMP slurries are heterogeneous dispersions comprised of micro-abrasive particles dispersed in a chemically active mobile phase. They are used in conjunction with lapping or rotary buffing equipment to remove small volumes of surface material from typically hard, crystalline workpieces.

The performance of your CMP slurry is based on various interconnected factors including its chemical specificity, which is largely determined by the type of substrates you will be working with. Examples include, but are by no means limited to:

• Electronic wafers
• Hard disk drives (HDDs)
• Optical substrates
• Photovoltaic panels

CMP Slurry Formats

The next step in the buyer’s journey is determining the format of your CMP slurry, which largely depends on your processing capabilities and inclination. Buying premixed solutions is the simplest option, but some CMP slurry providers may be unable to offer highly specific configurations, grains, or performance qualities. On the other hand, buying dry abrasives and batch-mixing solutions in-house can be challenging and time-consuming in getting the best dispersion. Understanding the performance characteristics of different grain types can help you decide on the right CMP slurry format for your supply chain.

Grain Types

There are several different overarching grain types commonly used for CMP slurry micro-abrasives. At Saint-Gobain Surface Conditioning, we leverage a choice of engineered grains based on precision alumina or synthetic diamond.

• Alumina: Aluminium oxide (Al₂O₃) is an extremely hard-wearing ceramic with good engineering capabilities and ready material availability. It forms the basis of a wide range of common CMP slurry products.
• Zirconia: Zirconium oxide (ZrO+)
• Diamond: Bond mesh diamond is a synthetic monocrystalline abrasive with extreme toughness and unmatched hardness, making it a critical superabrasive in various machining applications.

Each of these can be suspended in a variety of alcohol, water, or oil-based lubricants depending on key performance properties. These are the most important parameters to consider when you come to choosing the right CMP slurry.

Performance Properties

The performance of your CMP slurry comes down to a combination of factors, but you can generally correlate these close to your choice of micro-abrasive. More specifically, how well a CMP slurry planarizes your substrate depends on several key physical characteristics including density, particle friability, particle size distribution (PSD), solution pH level, surface tension, and so on. Each of these interconnected physical properties correlates to a range of important performance drivers:

• Defectivity: Explains the extent to which your CMP slurry will impart surface defects such as micro-scratches. Larger PSDs typically translate to higher defectivity.
• Planarization efficiency: Defines the efficacy of a CMP slurry in terms of removing selectively and uniformly removing surface material. 
• Removal rate: Refers to the rate at which the CMP slurry removes surface material from a substrate. Smaller grains usually mean lower removal rates.
• Selectivity: Explains the chemical specificity of your CMP slurry.

CMP Slurries from Saint-Gobain

This article is intended to share a few of the important things to bear in mind when selecting a CMP slurry for your polishing process. It is not a definitive guide, and we appreciate you may have questions about one or more aspect of the selection process. Contact us today and we would be happy to provide any answers.