Types and Applications of Wet Etching Solutions

Despite limitations in precise linewidth control, wet etching demonstrates significant advantages that make it indispensable for certain applications.

1.1 Significant cost-effectiveness

Dry-etching equipment involves complex vacuum, plasma, and control systems, resulting in high equipment acquisition costs, as well as substantial expenses for electricity, specialized gases, and routine maintenance during operation. In contrast, wet-etching equipment typically consists of simple structures—such as chemical solution tanks equipped with auxiliary units like heating and ultrasonic systems—making it much more affordable to purchase and maintain. Additionally, the raw material costs for the chemical etching solutions used in wet etching are significantly lower than the costs of the high-purity gases required for dry etching.

1.2 Simple process with high efficiency

Wet etching technology has a relatively low technical barrier, is simple to operate, and easy to maintain. Its etching rate is typically much higher than that of dry etching, making it ideal for mass production applications where high anisotropy in the etching direction isn't critical. This approach effectively boosts throughput while reducing the manufacturing cost per individual chip.

1.3 Etching Requirements for Specific Materials

Certain critical materials cannot be processed using dry etching, while wet etching often yields superior results. For instance, etching metal copper (Cu) typically requires wet-process techniques. Therefore, in device fabrication involving such materials, wet etching is the inevitable choice.

2. The Differences Between Wet Etching and Wet Cleaning Processes

In semiconductor manufacturing, wet processes are used for both etching and cleaning, yet the purposes of the two are entirely different:

• Wet etching: Its primary purpose is to selectively remove unwanted thin-film materials, achieving material thinning or patterning through chemical reactions.
• Wet cleaning primarily aims to remove contaminants from the wafer surface—such as particles, organic residues, metal impurities, or remnants from previous process steps—without damaging the wafer material itself or the underlying circuit patterns. For instance, post-chemical mechanical polishing (CMP) cleaning is designed to eliminate polishing particles, while pre-diffusion SC-1/SC-2 cleaning is used to thoroughly clean the silicon wafer surface.

The wet etching process has a wide range of applications, primarily focusing on the following areas:

3.1 Non-Integrated Circuit Chip Manufacturing

In fields where feature size requirements are relatively relaxed (typically referring to line widths ≥3 micrometers), wet etching can replace dry etching. This covers most non-integrated-circuit products, including:

• MEMS sensors
• Optoelectronic devices (such as LEDs)
• Discrete devices (such as power diodes, thyristors)

3.2 Wafer-Level Packaging and Advanced Interconnects

In the back-end processes of integrated circuits, wet etching is one of the key technologies:

• Wafer-level packaging facilities widely employ wet etching—for instance, after bump formation—to remove the seed layer left behind by the electroplating process.
• TSV (Through-Silicon Via) interposer manufacturing: Wet etching also plays a crucial role in this process.

Wet etching solutions can be classified according to the type of material being etched, and the following lists commonly used and heavily consumed types in semiconductor manufacturing:

4.1 Conductive Material Etching Solution

Used for etching a variety of metals and conductive layers, including: copper (Cu) etchant, aluminum (Al) etchant, chromium (Cr) etchant, titanium (Ti) etchant, gold (Au) etchant, nickel (Ni) etchant, tin (Sn) etchant, tantalum (Ta) etchant, cobalt (Co) etchant, indium (In) etchant, germanium (Ge) etchant, platinum (Pt) etchant, molybdenum (Mo) etchant, zinc (Zn) etchant, and more.

4.2 Etchant for Insulator Materials

Used for etching dielectric layers, passivation layers, and other insulating materials, these primarily include: silicon dioxide (SiO₂) etchants, silicon nitride (Si₃N₄) etchants, aluminum oxide (Al₂O₃) etchants, sapphire etchants, carbon etchants, epoxy resin etchants, as well as photoresist stripping solutions designed to remove patterned photoresist after lithography.

4.3 Semiconductor Material Etching Solution

Used for etching various semiconductor substrates and functional layers, these include: silicon (Si) etchants, silicon carbide (SiC) etchants, germanium (Ge) etchants, gallium arsenide (GaAs) etchants, indium phosphide (InP) etchants, indium tin oxide (ITO) etchants, zinc oxide (ZnO) etchants, as well as etchants specifically designed for the piezoelectric material PZT.