CMP process and post-cleaning technology in semiconductor manufacturing

Introduction

Wafers are the foundation of semiconductor integrated circuit manufacturing, and their surface quality directly affects circuit precision and device performance. As integrated circuits develop towards multilayer three-dimensional wiring, the demand for global planarization of the wafer surface becomes increasingly stringent. Chemical mechanical polishing (CMP) processes, through the synergistic action of chemical etching and mechanical polishing, can effectively eliminate surface irregularities. However, pollutants remaining from the CMP process must be removed through a highly efficient cleaning process to ensure the accuracy of subsequent processes and the long-term reliability of devices.

CMP Process Overview

1. CMP Process Principle

CMP combines chemical corrosion and mechanical friction. It uses polishing fluids and specialized equipment to polish the wafer surface, achieving global planarization of dielectric layers, metal layers, and thin-film materials. This process optimizes the surface morphology layer by layer through multiple cycles of operation and is an indispensable part of the semiconductor front-end process.

2. Challenges of CMP Process
The CMP process may introduce abrasive particles, chemical residues, and metal contaminants. If not thoroughly removed, these will lead to device defects. Therefore, post-CMP cleaning becomes a crucial step in ensuring wafer cleanliness.

Importance of Post-CMP Cleaning Process

Removal of residual contaminants: This includes abrasive particles, chemical reagent residues, and metal ions from the polishing fluid, avoiding their negative impact on circuit performance.

Improving device reliability: Reducing failures such as short circuits and leakage caused by contaminants, extending device lifespan.

Optimizing surface quality: Providing a smooth and clean substrate for subsequent processes such as lithography and film deposition, ensuring pattern transfer accuracy.

Main Steps of Post-CMP Cleaning Process

1. Pre-cleaning

Using acidic or alkaline solutions for soaking and rinsing to initially remove most of the surface impurities and contaminants.

2. De-gumming

Dissolving and removing the resin carrier remaining from the CMP process using organic solvents or alkaline solutions.

3. Removal of Metal Particles

Using acidic solutions to dissolve metal contaminants attached to the surface, preventing interference with the device's electrical performance.

4. Final Cleaning

Combining ultrapure water and organic solvents, using methods such as soaking, rinsing, and ultrasonic cleaning to thoroughly remove residues and ensure surface purity.

Main Cleaning Technologies and Methods

1. Mechanical Cleaning

Single-wafer scrubbing: Using rotating brush bristles to contact the surface, efficiently removing contaminants, and supporting automated production. Its advantages include flexible operation, adaptability to various wafer sizes, and the ability to optimize cleaning effectiveness by adjusting brush material.

2. RCA General Cleaning Method

Based on the synergistic action of solvents, acids, and surfactants, organic matter and metal ion contamination are removed through oxidation and etching steps. The core process includes SC1 (ammonia-hydrogen peroxide-water) and SC2 (hydrochloric acid-hydrogen peroxide-water) step-by-step processing, with thorough rinsing with ultrapure water after each step.

3. Chemical Dilution Method

On the basis of RCA, the SC1/SC2 solution is diluted (e.g., 1:1:50), significantly reducing chemical consumption (by 80%-90%), while maintaining effective removal of particles and hydrocarbons. Diluted hydrochloric acid (1:100) can prevent particle precipitation, further improving cleaning efficiency.

4. Megahertz Cleaning

Utilizing megahertz-level high-frequency sound waves (non-cavitation effect) to generate strong acoustic streaming impacting the surface, removing submicron particles. Compared to ultrasonic cleaning, megahertz technology combines the advantages of mechanical scrubbing and chemical dissolution, and avoids standing wave damage, suitable for high-precision cleaning requirements.

Future Outlook

As semiconductor technology develops towards smaller nodes and new materials, post-CMP cleaning processes face greater challenges:

Control of new pollutants: Specialized cleaning agents need to be developed for advanced materials (such as high-k dielectrics and cobalt interconnects).

Green process optimization: Reducing chemical and water consumption to promote sustainable manufacturing.

Intelligent integration: Combining online monitoring and AI algorithms to achieve real-time control and defect prediction of the cleaning process.

Conclusion

Post-CMP cleaning technology is a core process in semiconductor manufacturing to ensure wafer cleanliness and device performance. By optimizing cleaning steps and introducing advanced technologies (such as megahertz cleaning and diluted chemical methods), process efficiency and reliability can be significantly improved. Future innovations are needed to address the challenges of new materials and structures, providing technological support for the high-quality development of the semiconductor industry.

Kexin Microelectronics Co., Ltd. - Leading the Innovation of Semiconductor Cleaning Technology

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