Document: Chemical Mechanical Polishing (CMP) Technology for Nanocrystalline Diamond Films
Table of Contents
Introduction
Application Requirements
System Specifications
Processing Flow
Results
Customer Case
Introduction
Nanocrystalline Diamond (NCD) films retain the high Young's modulus (1,100 GPa) of single-crystal diamond while offering the advantage of low-temperature (<450 °C) growth. This makes them highly promising for applications in Micro-Electro-Mechanical Systems (MEMS), Surface Acoustic Wave (SAW) devices, thermal management, and tribological coatings. However, due to competitive grain growth, the surface roughness of NCD films increases with thickness, limiting their use in devices requiring ultra-smooth surfaces. Chemical Mechanical Polishing (CMP), as a low-temperature, low-pressure, high-precision surface planarization technique, can effectively reduce NCD film roughness and enhance their suitability for such devices.
Application Requirements
NCD wafer processing must achieve the following objectives:
Surface Roughness: Post-polishing Ra ≤ 2 nm
Total Thickness Variation (TTV): Final wafer TTV ≤ 2 µm
Thickness Control: Subject to customer requirements
No Surface Damage: Avoid defects such as micro-cracks and graphitization
High Yield: Suitable for bowed wafers, avoiding breakage
System Specifications
The HSM Precision Grinding and Polishing System provides a full-process solution.
Processing Flow
Sample Preparation
Prepare CVD-grown NCD films with a thickness of 1.5 µm.
Clean the silicon substrate using a cleaning solution.
Polishing Preparation
Replace the grinding platen with a polishing pad. Pre-condition the pad for 30 minutes and switch the abrasive to HSM specialized polishing slurry.
Control key parameters via the graphical interface:
Polishing platen speed: ≤ 100 rpm
Slurry flow rate: Monitored by a real-time drip feed control system (reduces waste)
Pressure load: 3-4 psi
Target: Remove sub-surface damage and achieve an atomically smooth surface (Ra ≤ 2 nm).
Results
NCD films processed by the HSM-CMP system achieved the following performance:
Customer Case
A customer used the HSM-CMP system for CMP processing of a 2-inch NCD film as follows:
Initial State: RMS = 18.3 nm, showing distinct grain faceting.
After 4 hours of polishing: RMS = 1.7 nm, with localized areas reaching 0.42 nm.
Surface Composition: XPS showed no graphitization, with a moderate increase in oxygen content.
Suitability: Effective for bowed wafers with no risk of fracture.
Cleaning Effect: SC-1 cleaning removed most surface contaminants.
Technical Validation
Schematic: Surface morphology of the NCD film after processing by the HSM-CMP system.
Notes:
Measurement Equipment: ER230 White Light Interferometer
