1. Product Overview

The CMP polishing pad (Chemical Mechanical Polishing Pad) is one of the most critical consumables in the chemical mechanical polishing process, widely applied in semiconductor wafer fabrication, optical component finishing, and advanced material surface treatment.

CMP technology integrates two synergistic mechanisms: chemical reactions that soften or modify the surface layer of the material, and mechanical abrasion that removes the loosened particles. Together, these actions enable global planarization, superior surface flatness, and nanometer-level roughness.

The polishing pad is the medium that directly interfaces with the wafer and the slurry, making it central to the success of CMP. Typically made of polyurethane or composite polymers, pads are engineered with a porous structure and designed with specialized groove patterns. These structural features help to evenly distribute slurry, discharge debris, manage heat dissipation, and maintain consistent material removal rates.

Different types of CMP pads are optimized for different materials. For example:

• Silicon wafers in integrated circuit production require pads with excellent planarization uniformity.

• Sapphire substrates used in LED manufacturing need harder pads to handle high hardness.

• SiC and GaN substrates demand pads with high durability due to their extreme mechanical properties.

• Glass and hard disk substrates benefit from pads engineered for smooth finishing and scratch-free surfaces.

2. Structure and Working Principle

Structure

CMP polishing pads are composed of multiple functional layers, each contributing to polishing performance:

1. Backing/Substrate: Provides mechanical support, stiffness, and dimensional stability.

2. Polishing Layer: The functional surface in direct contact with the wafer; determines removal rate and surface quality.

3. Pores: Micro-porous structures that retain slurry and increase the number of abrasive contact points.

4. Grooves: Engineered patterns such as concentric circles, radial lines, or crosshatch grids that allow slurry flow, debris evacuation, and thermal balance.

5. Adhesive Layer: Ensures firm attachment of the pad to the polishing platen while enabling easy replacement.

Working Principle

During CMP, the pad rotates against the wafer under controlled downforce. The slurry, containing abrasives and reactive chemicals, fills the micro-pores and grooves of the pad surface. Abrasive particles are pressed between the wafer and the pad, enabling controlled material removal. At the same time, chemical reactions soften the surface material to enhance polishing efficiency.

The combination of pad elasticity, slurry retention, groove design, and applied pressure determines critical process outcomes such as:

• Removal rate (RR)

• Within-wafer non-uniformity (WIWNU)

• Defectivity and scratch levels

• Surface roughness

3. Key Features

CMP polishing pads are engineered with specific properties to meet the demanding requirements of semiconductor and advanced material industries.

• Superior Planarization: Optimized porosity and groove designs ensure uniform material removal across the wafer surface.

• High Process Compatibility: Pads are suitable for silicon wafers, sapphire, SiC, GaN, glass, and metal films, and compatible with a wide variety of slurries including SiO₂, CeO₂, and diamond suspensions.

• Customizable Performance: Hardness, elasticity, thickness, groove design, and pad diameter can be customized to match process-specific requirements.

• Durability and Stability: Manufactured with high-quality polyurethane or composite polymers, pads offer excellent wear resistance, chemical stability, and consistent performance during extended runs.

• Conditioning Compatibility: Pad surfaces can be periodically reconditioned using a diamond conditioner to restore surface roughness and extend service life.

• Low Defectivity: Engineered to minimize microscratches, dishing, and erosion, ensuring excellent surface integrity.

• Scalability: Available in various diameters, ranging from 14 inches to over 42 inches, for compatibility with multiple CMP tools.

4. Applications

CMP polishing pads have a broad range of applications in different industries:

• Semiconductor Manufacturing

  • Planarization of silicon wafers during front-end-of-line (FEOL) and back-end-of-line (BEOL) processes.

  • Copper interconnect CMP in advanced integrated circuits.

  • SOI wafer processing.

• Compound Semiconductors

  • GaN-on-sapphire substrate polishing for LED production.

  • SiC wafer planarization for power devices.

  • GaAs and other III-V compound semiconductor processing.

• Optical Components

  • Precision polishing of sapphire windows, infrared lenses, and optical filters.

  • Fabrication of high-clarity, defect-free optical components.

• Data Storage Industry

  • Polishing of glass and aluminum hard disk substrates to nanometer-level flatness and smoothness.

• Advanced Materials Research

  • Planarization of advanced ceramics, composite materials, and single crystals used in aerospace, defense, and scientific research.

5. Standard Specifications

• Material: High-purity polyurethane or polyurethane composites.

• Hardness: Available in soft, medium, and hard grades depending on application.

• Diameter: 14 – 42 inches (custom sizes available).

• Thickness: Typically 1.0 – 2.0 mm, customizable per requirements.

• Groove Patterns: Concentric, spiral, radial, crosshatch, or customer-specific designs.

• Porosity: Controlled open-pore structures for slurry retention and uniform removal.

• Backing Options: With or without adhesive backing.

• Color/Identification: Available in multiple colors for process identification.

6. Advantages of CMP Polishing Pads

• Precision: Achieves sub-nanometer surface roughness and excellent planarization.

• Versatility: Suitable for multiple materials and process nodes.

• Reliability: Stable performance across extended polishing cycles.

• Cost-effectiveness: Long pad lifetime with the ability to be reconditioned.

• Process Control: Supports tight control of removal rates and uniformity.

7. Frequently Asked Questions (FAQ)

Q1: How long does a polishing pad last?
The lifetime depends on the material and process. On average, one pad can polish between 200 and 500 wafers before replacement is required. Lifetime is influenced by factors such as downforce, rotational speed, slurry chemistry, and conditioning frequency.

Q2: What happens when the pad surface becomes smooth or glazed?
When the pad surface becomes too smooth, removal rates decrease. Regular conditioning with a diamond conditioner restores surface asperities and maintains pad effectiveness.

Q3: Can the pad be customized?
Yes. Pads can be customized in terms of hardness, thickness, groove patterns, and diameter to fit specific CMP tools and process requirements.

Q4: How does slurry compatibility affect pad performance?
Slurry chemistry and abrasives must be matched to the pad. For example, ceria-based slurries often require different pad hardness compared to silica-based slurries. Proper pairing ensures high removal rates and low defectivity.