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Case study: Plasma Cleaning for the Semiconductors Industry

Updated: Oct 20, 2023

Plasma treatment is driving change in industries. It offers enhanced cleaning, surface modification, and advanced etching processes. By utilizing ionized gas, this method not only removes contamination with incredible efficiency but also manipulates the surface condition to foster improved adhesion.

Industries ranging from manufacturing to semiconductor development are realizing the benefits of plasma's highly reactive ions and molecules. These ensure that surfaces are not only immaculately clean but also optimized for specific applications. In this article, we will explore plasma treatment and its indispensable role in the semiconductor industry.

What is Plasma Treatment?

Plasma cleaning is defined as a process that uses an ionized gas to interact with a substrate in order to remove contamination and/or modify its surface.

Plasma cleaning, therefore, is much more than just a cleaning process, it is also a surface modification process and an etching process. In a more general way, we can say that most plasma cleaning applications are methods to promote adhesion between two items by:

  • Simple decontamination of their interfacing surfaces

  • Generating a modified surface condition such as increasing the surface roughness

  • Increasing the surface energy

  • Rendering the surface hydrophilic

  • Rendering the surface hydrophobic

  • Removing metal oxides by physical and/or chemical interaction

One of the primary applications of plasma treatment is surface cleaning. In this process, plasma is used to effectively remove contaminants from the surfaces of materials. It is a popular cleaning method in many industries due to its effectiveness and efficiency. The highly reactive ions and molecules in the plasma can break down organic contaminants and residues, resulting in a clean, pure surface.

Surface activation is another common application. In this process, the plasma treatment is used to increase the surface energy of materials to improve adhesion. This is particularly useful in the bonding, painting, and coating of materials, where enhanced adhesion can improve the quality and durability of the final product.

Plasma treatment can also be used for surface coating. In this method, plasma is employed to apply coatings that can protect, enhance, or modify the surface properties of materials. It ensures uniform coating and can be used for various purposes, including improving resistance to wear, corrosion, and environmental impacts.

Plasma Cleaning for the Semiconductors Industry

Plasma treatment is widely used for a range of applications, including cleaning, etching, and deposition processes. These treatments are crucial for the manufacturing and development of semiconductor devices like integrated circuits (ICs), microelectromechanical systems (MEMS), and other nano-scale devices.

Plasma cleaning is used to remove organic and inorganic contaminants from the surface of semiconductor wafers. Utilizing a combination of reactive ions and ultraviolet light, plasma cleaning effectively eliminates residues, ensuring a clean and defect-free surface. This is highly useful when looking at semiconductors industry analysis.

Plasma etching is one of the most critical applications in semiconductor fabrication. It's a process where selective material is removed from the surface of a wafer, leaving behind well-defined patterns that are integral to the functionality of semiconductor devices.

There are several benefits to using plasma treatment in the semiconductor industry.

Plasma treatments offer a high degree of control, enabling the creation of intricate patterns and structures with extreme precision. It is a highly efficient process, essential for achieving the cleanliness and pattern resolutions required in semiconductor fabrication. The ability to use different gases and parameters allows for a wide range of modifications to the surface properties.

Plasma Cleaning Use Cases: Semiconductors Industry

1. Plasma Cleaning and Wire Bonding Yield

In the semiconductor industry a typical application is preparing the surface of a lead frame, and the dies mounted on it, with plasma cleaning. This is typically done prior to the wire bonding process with the purpose of increasing the bonding yield. It is also done before the molding process to ensure the removal of voids and delamination, thus increasing the package yield.

Semiconductor manufacturing processes are intended to build each individual die so that it performs according to specification. However, manufacturing issues during processing, variation in the process variables and cross contamination from other processes may cause some die to fail due to a phenomenon called NSOP (Non Stick on Pad).

NSOP defines the event detected by the wire bonder when it senses that the bond just created was unsuccessful (no adhesion between the wire and the die’s pad surface).

2. Surface Preparation

Surface preparation is a critical step in wire bonding and package yield within the electronics and semiconductor industry, and plasma treatment plays a pivotal role in ensuring that these processes are conducted effectively.

Wire bonding is a method used to connect semiconductor devices to their packages, and it involves the use of fine wires to create electrical connections. Surface preparation is essential in this process to ensure that the surface is clean, free of contaminants, and adequately activated to promote strong adhesion between the wires and the semiconductor device.

The reason proper surface preparation is so vital is that any contamination on the surface can significantly hinder the wire bonding process. Contaminants can lead to poor adhesion. And a uniform surface ensures consistent wire bonds, reducing variability and enhancing the overall reliability of the semiconductor device.

3. Yield Issues

Another example of how plasma cleaning can help solve this problem comes from an experiment where a gold-coated palladium bonding pad has been developed to reduce silicon cratering. The assembly, while improving on its hardness, has shown a high rate of NSOP due mainly to the presence of surface oxides. To reduce or eliminate these oxides, a plasma of Ar/H2 was used to form hydrogen radicals and react chemically with the metal oxide. The removal of metal oxides is more effective and faster using Ar/H2 compared to pure argon ion bombardment.

An experiment was defined using pure Ar and Ar/H2 plasma cleaning. A significant reduction of the NSOP rate was observed using Ar/H2compared to Ar alone and Ar/H2 contributed to achieve higher wire bonding yield. In other cases, argon alone is also very effective, especially if argon plasma is generated at lower pressures.

To summarize in simpler terms, the bonding pad is made of gold-coated palladium and is meant to be sturdy but has issues with something called NSOP, caused by the presence of surface oxides (rust-like compounds).

To solve this issue, a mix of argon and hydrogen gases is turned into plasma, which is a supercharged gas that can clean and modify surfaces. This plasma mix helps remove the surface oxides effectively. When the bonding pad is cleaned with this plasma mix, the NSOP issue is significantly reduced. Thus showing the clear benefits and uses of plasma treatment.

4. Increasing Bondability

As we can see, plasma cleaning can substantially modify the surface of a metal substrate or a die’s pad. By effectively eliminating the cause of NSOP, plasma cleaning can participate actively in increasing the wire bonding yield.

Preparing the surfaces of the dies and lead frames with plasma cleaning will increase the bondability of that specific assembly. Removing organic contamination or oxides left behind by previous process steps like die attach or snap curing are an easy task for a good plasma cleaning system.

The wire bond pull and shear forces will increase, creating a much more reliable bond improving the overall bonding yield. An increased yield means a higher ROI for that particular product – so much so that the investment for a plasma cleaner could amortize rapidly.

Find Out More About Plasma Cleaning and the Semiconductor Industry

Plasma treatment is reshaping industries with its advanced cleaning, surface modification, and etching capabilities. In the semiconductor world, it's a game-changer, ensuring clean surfaces and precise patterns. By tackling issues like NSOP through effective oxide removal, plasma boosts the reliability of semiconductor devices. As more sectors tap into its potential, plasma treatment promises a bright, efficient future.

SCI Automation, with its trademark SCIPLASMA, has been in the market of experience in designing and manufacturing plasma cleaning systems since 2000.

If you have any questions or want to learn more about how we can help you, please do not hesitate to contact us today.


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