Semiconductor manufacturing is a highly precise and intricate process that demands rigorous cleaning steps to ensure the quality and functionality of the final product. Two primary cleaning methods employed in this industry are dry cleaning and wet cleaning. Each method has its unique characteristics and applications, making them indispensable in achieving the desired purity levels on semiconductor wafers.

Wet Cleaning: The Mainstay of Semiconductor Purity

Wet cleaning is the dominant cleaning technology in semiconductor manufacturing, accounting for over 90% of cleaning steps. This method involves the use of liquid chemicals and deionized water, often combined with physical methods such as ultrasonic waves, heating, and vacuuming, to remove contaminants from the wafer surface.

The primary objective of wet cleaning is to eliminate particles, natural oxide layers, organics, metal contaminations, sacrificial layers, and polishing residues that accumulate during the manufacturing process. Various wet cleaning techniques, such as RCA cleaning, diluted chemical cleaning, IMEC cleaning, and single-wafer cleaning, are utilized to target specific contaminants.

RCA cleaning, for instance, employs a mixture of ammonium hydroxide, hydrogen peroxide, and water (APM, also known as SC1 cleaning solution) and hydrochloric acid, hydrogen peroxide, and water (HPM, also known as SC2 cleaning solution) to remove organic materials and heavy ions, respectively. These solutions are applied with megasonic energy to reduce chemical usage, shorten etch times, and minimize the impact on circuit features.

IMEC cleaning, proposed by the Interuniversity Microelectronics Center, simplifies the process by using ozone and diluted chemicals to conserve resources. Single-wafer cleaning, on the other hand, focuses on minimizing cross-contamination and surface damage, thereby enhancing product yield and reducing costs.

Dry Cleaning: The Precision Tool for Advanced Nodes

Dry cleaning, in contrast to wet cleaning, does not utilize liquid chemicals. Instead, it relies on gas-phase chemical methods, such as plasma cleaning, supercritical carbon dioxide cleaning, and beam cleaning, to remove contaminants from the wafer surface.

Dry cleaning excels in its ability to create fine lines and geometric patterns due to its anisotropic etching characteristics. Plasma cleaning, for example, involves exciting inert gases into a plasma state using lasers, microwaves, or thermionic methods. These plasma particles react with surface molecules to form volatile products that detach from the surface.

Beam cleaning techniques, such as those employing capillary-formed fine beams of conductive cleaning agents, efficiently remove impurities by breaking the van der Waals bonds between impurities and atoms. Laser beam cleaning further enhances this process by effectively removing micrometer- and sub-micrometer-sized particles without damaging the silicon surface.

However, dry cleaning has limitations. It is primarily used for cleaning specific contaminants and is essential for logic and memory products at technology nodes of 28nm and below. The challenge lies in the selective reaction of the chemical vapor with surface metal contaminants, which can lead to unwanted reactions with the silicon surface and incomplete removal of all metal contaminants.