In the processing of semiconductor silicon materials, there is an ‘unassuming yet indispensable’ role – surfactants. Unlike photolithography machines and etching machines, which are frequently mentioned, surfactants ‘silently exert their influence’ in every critical step of slicing, grinding, polishing, and cleaning: reducing knife marks, minimizing damage, improving flatness, and removing impurities… Without them, silicon wafers could be riddled with defects, significantly reducing chip yield. Today, we will dissect the working logic of this ‘invisible assistant’ and see how it transforms silicon from ‘rough crystal rods’ into ‘mirror substrates.’

1. Understanding First: Why Does the Semiconductor Industry Prefer ‘Non-Ionic’ Surfactants?

The core capability of surfactants is to ‘reduce surface tension’, but the semiconductor industry has particularly stringent requirements – they must not introduce metal ions (which can lead to leakage in devices), and they must be easy to clean and highly stable. Therefore, non-ionic surfactants have become the preferred choice, offering four major advantages:

1. No Metal Contamination: Exists in molecular form in water, free of ions, and does not introduce harmful metals like sodium and calcium;
2. High Stability: Unaffected by acids, bases, or electrolytes, maintaining stable performance in the complex environment of semiconductor processing;
3. Easy to Clean: Physically adsorbed on the silicon wafer surface, easily removed later without residue;
4. High Surface Activity: Low critical micelle concentration (CMC), allowing significant reduction of surface tension with a small amount added, forming a dense adsorption layer.

The commonly used non-ionic surfactants in the industry are mainly divided into polyol types (such as the FA/O polyamine type invented by Professor Liu Yuling from Hebei University of Technology, which won a national invention award) and polyether alcohol types. The former has stronger permeability and wettability and is also biodegradable.

2. Step-by-Step Breakdown: The ‘Precise Assistance’ of Surfactants

Every step in silicon wafer processing has its pain points, and the role of surfactants is to ‘target and solve problems’, being present throughout the entire process from crystal rod slicing to final cleaning.

1. Slicing Process: The ‘Lubricant’ that Reduces Knife Marks

Slicing is the first step in transforming silicon rods into silicon wafers, but due to the high hardness of silicon, three major problems arise during cutting: high friction heat, numerous knife marks, and high stress (which can easily lead to wafer breakage or dislocation). The solutions provided by surfactants are:

• Lubrication and Cooling: Forms a ‘lubricating film’ between the tool and the silicon wafer, turning the friction between metal and silicon into internal friction between the molecules of the lubricating film, reducing friction heat (cutting point temperature drops from several hundred degrees), and minimizing knife marks and micro-cracks;
• Reducing Wear: Increases the contact area between the tool and the silicon wafer, dispersing stress to avoid ‘adhesive wear’ caused by localized high pressure, extending tool life and reducing tool repair rates;
• Practical Case: The FA/O cutting fluid developed by Hebei University of Technology, after adding surfactants, improved slicing efficiency by 30%, reduced knife marks by 50%, and significantly increased yield.

2. Grinding Process: The ‘Dispersant’ that Removes Damage

The surface of silicon wafers after slicing has three layers of defects: the broken layer, the damaged layer, and the stress layer. These defects can lead to high device noise and leakage current, necessitating removal through grinding. The core role of surfactants is ‘penetration + dispersion’:

• Penetration ‘Splitting’: Surfactant molecules penetrate the gaps between abrasive particles and the silicon wafer, acting like a ‘wedge’ to open micro-cracks (the ‘splitting wedge effect’), making it easier for the broken layer to fall off without damaging the underlying layer;
• Dispersing Abrasives: Adsorbs on the surface of abrasive particles, forming a ‘spatial barrier’ to prevent particle agglomeration, allowing abrasives to act uniformly on the silicon wafer, reducing localized over-grinding and decreasing the thickness of the damaged layer. Without it, grinding could become rougher, or even leave particles that affect subsequent polishing.

3. Polishing Process: The ‘Regulator’ for Achieving Flattening

Chemical mechanical polishing (CMP) is key to the global flattening of silicon wafers, but to achieve ‘no damage and high flatness’, surfactants are essential. Their role lies in the details:

• Controlling Removal Rate: Forms different adsorption layers at the uneven areas of the silicon wafer – thin adsorption at raised areas leads to strong mechanical grinding and fast removal; thick adsorption at recessed areas leads to weak grinding and slow removal, achieving flattening through ‘rate differences’ (as shown in Figure 1, accelerated removal at raised areas 1-3, and slow removal at recessed areas 4-7);
• Reducing Surface Tension: Prevents localized aggregation of polishing liquid that causes the ‘orange peel effect’ (high-temperature non-uniform corrosion), ensuring uniform temperature across the silicon wafer surface and reducing damage haze;
• Easy Cleaning Protection: Prioritizes adsorption on the newly generated high-energy surface of the silicon wafer, forming a physical adsorption layer that reduces surface energy and is easy to clean later, leaving no residue.

4. Cleaning Process: The ‘Cleaner’ that Removes Impurities

After grinding and polishing, the surface of the silicon wafer will retain tiny particles and metal ions (sodium, calcium, etc.), which can lead to device leakage and reduced breakdown voltage, necessitating thorough removal. The ‘dual cleaning power’ of surfactants:

• Removing Particles: Non-ionic surfactants penetrate between particles and the silicon wafer, ‘lifting’ the particles away from the silicon wafer while forming a protective layer on the particle surface to prevent re-adsorption;
• Removing Metal Ions: Some surfactants (such as chelating agents) can wrap metal ions using N and O atoms in their molecules through ‘chelation’, forming soluble complexes that are carried away with the cleaning solution (Note: Traditional chelating agent EDTA contains sodium ions, which can contaminate devices, so sodium-free types should be selected).

3. Future Trends: Composite Surfactants as a New Direction

As silicon wafer diameters progress to 300mm and 450mm, and chip processes advance to 2nm and 1nm, the requirements for surfactants are becoming increasingly stringent: they must not only have strong single functions but also ‘collaborate’ – for example, composite surfactants that possess lubrication, dispersion, and chelation capabilities simultaneously.Composite surfactants can be formulated by combining polyol-type surfactants with chelating agents in CMP polishing liquids, improving flatness while simultaneously removing metal ions; in slicing liquids, combining components with strong lubrication and penetration further reduces stress damage.

The development of these new surfactants will become the ‘invisible driving force’ behind breakthroughs in semiconductor processes towards higher precision.

Conclusion: Small Additives, Big Impact

Surfactants in semiconductor processing act as a ‘bridge between fine chemicals and semiconductor processes’ – they solve the pain points of mechanical processing with their chemical properties, transforming silicon wafers from ‘rough’ to ‘perfect’. From reducing knife marks during slicing to achieving nanometer-level flattening during polishing, and ensuring impurity-free cleaning, every step of progress relies on their ‘assistance’.

In the future, as semiconductor technology continues to upgrade, this ‘invisible assistant’ will play an even greater role, becoming an important part of driving breakthroughs in chip processes.