Introduction to Wafer Cleaning Technology

Wafer cleaning is a critical process in semiconductor manufacturing, designed to remove particles, metal ions, organic contaminants, and oxide residues from the wafer surface. As device dimensions shrink into the nanometer range, even the tiniest impurities can lead to pattern defects, dielectric breakdown, or transistor performance fluctuations—directly impacting chip yield and reliability. Therefore, cleaning technologies must efficiently eliminate contaminants while simultaneously preventing damage to the wafer's delicate surface structure.

I. Types of Pollutants and Corresponding Cleaning Principles

• Particulate pollutants are removed by disrupting their electrostatic adhesion to surfaces—either through physical forces (such as ultrasonic cavitation) or with chemical solutions like SC-1.
• Metal ion contamination: Alkali metals (such as sodium) can trigger dielectric breakdown, while heavy metals (like iron and copper) increase leakage current, requiring removal with a hydrochloric acid/hydrogen peroxide mixture (SC-2).
• Organic contamination—such as oils and photoresist residues—can be decomposed using strong oxidizing agents (e.g., the sulfuric acid/hydrogen peroxide mixture SPM).
• Oxide Layer: The natural oxide layer requires etching with hydrofluoric acid (DHF or BHF) to ensure the interface integrity for subsequent processes.

II. Mainstream Cleaning Methods and Process Flow

1. RCA Cleaning

The RCA cleaning method is one of the most classic wafer-cleaning techniques in the semiconductor industry, developed by RCA Corporation. Primarily used to remove organic contaminants and metallic ion impurities, this method is typically carried out in two steps: SC-1 (Standard Cleaning 1) and SC-2 (Standard Cleaning 2).

• SC-1 (APM): Ammonia/Hydrogen Peroxide Mixture (NH₄OH:H₂O₂:H₂O = 1:1:5), which removes organic contaminants and particles at 20°C while simultaneously forming a protective oxide layer.
• SC-2 (HPM): Hydrochloric acid/hydrogen peroxide mixture (HCl:H₂O₂:H₂O = 1:1:6), used to remove metal ions and passivate the surface at 80°C.

2. Piranha Etch Clean Method

Use a mixed solution of sulfuric acid and hydrogen peroxide, typically in a ratio of 3:1 or 4:1. Due to the solution's extremely strong oxidizing properties, it can effectively remove large amounts of organic material and stubborn contaminants. This method must be carried out under strictly controlled conditions—particularly regarding temperature and concentration—to prevent damage to the wafer.

3. Physical-assisted Cleaning

• Megasonic cleaning: High-frequency sound waves generate cavitation effects, effectively removing sub-micron particles while minimizing surface damage.
• Ozone Cleaning (DIO3): Utilizes ozone to oxidize organic substances into CO₂ and H₂O, making it environmentally friendly and leaving no chemical residue.

4. Standardized Processes

• Pre-cleaning: Rinse with deionized water combined with ultrasound to remove loose particles.
• Chemical Cleaning: Select SC-1, SC-2, SPM, or DHF solutions based on the type of contaminant.
• Final Cleaning: Thoroughly rinse with deionized water, complemented by ozone-infused water for enhanced purification.
• Drying: Centrifuge spin-dry or nitrogen purging to prevent water marks from remaining.

III. Structure and Function of the Cleaning Equipment

Modern wafer cleaning machines achieve efficient operation through automation and precise control:

1. Automation System

Three sets of independently computer-controlled robotic arms perform the entire process—from picking and placing to cleaning and drying—minimizing human error.

Automatic loading and unloading station with PLC program control, supporting real-time monitoring and parameter adjustment via touchscreen.

2. Protective Design

Third-generation acid- and corrosion-resistant materials combined with a fully enclosed housing provide protection against highly corrosive chemicals such as HF and H₂SO₄.

Integrate a ventilation system to prevent chemical vapor leakage and ensure operational safety.

3. Process Module

Spinning Rinse Function: The robotic arm drives the wafer to rotate within the槽, ensuring even contact with the cleaning solution.

Purification and Drying Chamber: Combining centrifugal spin-drying with vacuum drying technology, it precisely controls temperature and humidity to prevent stress cracks.

Fully automatic liquid replenishment system: Monitors chemical solution concentration in real time and automatically adds more, ensuring process stability.

IV. Application Scenarios

From single-step processes to full-line integration, the cleaning equipment covers every stage of semiconductor manufacturing:

1. Furnace Front Cleaning

Before the diffusion process, the wafer is cleaned to remove surface contaminants, providing a pristine substrate for subsequent processes.

2. Post-Photolithography Cleaning

Remove the residual photoresist and its byproducts from the lithography process to ensure precise pattern transfer.

3. Pre-Extension Cleaning

Before epitaxial growth, remove the SiO2 layer remaining after buried-layer diffusion, as well as surface contaminants, to provide a clean substrate for epitaxial growth.

4. Cleaning after ion implantation

Remove the photoresist and SiO2 layer residues generated during ion implantation to ensure optimal implantation results.

5. Cleaning of Attachments and Tools

Clean the accessories and tools used in the production process to remove surface contaminants and residues, ensuring the cleanliness of the production environment.

Kexinwei Company – Leading the Innovation in Semiconductor Cleaning Technology

For more technical details, please consult our technical advisor: 13861996325!

▲ Technical Consulting ▲ Follow Kexinwei's WeChat Official Account