Effect of Crystal Orientation on Material Removal Characteristics in Sapphire Chemical Mechanical Polishing
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2017-06-30 |
| Journal | Journal of the Korean Society of Tribologists and Lubrication Engineers |
| Authors | SangâJin Lee, Sangjik Lee, Hyoungjae Kim, Chuljin Park, Keun-Yong Sohn |
| Citations | 1 |
| Analysis | Full AI Review Included |
Technical Documentation: Anisotropic Polishing Control in Wide Bandgap Materials
Section titled âTechnical Documentation: Anisotropic Polishing Control in Wide Bandgap MaterialsâSource Paper Analysis: Effect of Crystal Orientation on Material Removal Characteristics in Sapphire Chemical Mechanical Polishing (J. Korean Soc. Tribol. Lubr. Eng., Vol. 33, No. 3, June 2017).
Executive Summary
Section titled âExecutive SummaryâThis study provides critical insights into the anisotropic material removal characteristics during Chemical Mechanical Polishing (CMP) of wide bandgap substrates, specifically focusing on the influence of crystal orientation (C, R, and A planes) on surface quality and process efficiency.
- Orientation Dependence: Material Removal Rate (MRR) and Frictional Force (F) were strongly dependent on the crystal orientation, following the order: C-plane > R-plane > A-plane under identical processing conditions.
- Prestonâs Law Adherence: MRR correlated linearly with the product of pressure (P) and velocity (V), confirming adherence to the fundamental principles of the Preston equation across all orientations.
- Mechanical Correlation: Nano-indentation analysis demonstrated an inverse correlation between material hardness (A > R > C) and MRR/Friction Force (C > R > A). Softer planes were removed faster.
- Chemical Acceleration: Hydration (chemical reaction between the substrate and alkaline colloidal silica slurry) softened the surface across all planes, significantly accelerating MRR.
- Hardness Exacerbation: The chemical reaction amplified the intrinsic hardness differences between crystal orientations, primarily by increasing the indentation depth (h) on the C-plane more significantly than on the R or A planes.
- Relevance to Diamond: These findings underscore the necessity of strict crystal orientation control and optimized CMP recipes for processing highly anisotropic materials like Single Crystal Diamond (SCD) used in high-performance electronics.
Technical Specifications
Section titled âTechnical SpecificationsâThe following hard data points were extracted from the experimental conditions and measurement results:
| Parameter | Value | Unit | Context |
|---|---|---|---|
| Wafer Diameter | 2 | inch | Epi-ready substrate |
| Wafer Thickness | 430 | ”m | Initial substrate state |
| Initial Surface Roughness (Ra) | < 0.3 | nm | Epi-ready state |
| CMP Polishing Time | 30 | min | Constant process duration |
| Polishing Pressure Range (P) | 200, 300, 400 | gf/cm2 | Primary variable |
| Head & Platen Velocity Range (V) | 30, 60, 90, 120 | rpm | Primary variable |
| Slurry Flow Rate | 320 | ml/min | Alkaline colloidal silica (Compol-80) |
| Hardness (Bare C-plane) | 32.08 | GPa | Highest MRR orientation (before reaction) |
| Hardness (Reacted C-plane) | 31.12 | GPa | Hardness reduction due to hydration |
| Hardness (Bare A-plane) | 35.94 | GPa | Lowest MRR orientation (before reaction) |
| Maximum Load (Nano-Indentation) | 50 | mN | Mechanical characterization |
| Indentation Tip | Berkovich | - | Measurement geometry |
| Poissonâs Ratio (Assumed) | 0.30 | - | Used for hardness calculation |
Key Methodologies
Section titled âKey MethodologiesâThe experiment utilized a two-pronged approachâChemical Mechanical Polishing (CMP) integrated with real-time friction monitoring, followed by post-processing Nano-Indentation analysis.
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CMP Setup and Substrates:
- Equipment: Poli-500 (GNP Technology), modified with integrated temperature and frictional force monitoring devices.
- Substrate: Epi-ready 2-inch sapphire wafers of C(0001), R(1102), and A(11<20>) planes.
- Pad: Polyurethane impregnated felt pad (Suba-600).
- Slurry: Alkaline colloidal silica (Compol-80) diluted 1:1 with deionized water.
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CMP Process Parameters:
- Controlled Variables: Head/Platen Velocity (30 to 120 rpm) and Pressure (200 to 400 gf/cm2).
- Output Metrics: Material Removal Rate (MRR, measured by thickness change) and Frictional Force (measured in real-time).
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Nano-Indentation Sample Preparation:
- Bare Wafer: Epi-ready state, used as the baseline for intrinsic mechanical properties.
- Reacted Wafer: Bare wafers immersed in the CMP slurry solution for 12 hours prior to indentation, simulating the effect of surface hydration and chemical reaction.
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Nano-Indentation Analysis:
- Equipment: NHT-AE-0000 (Anton Paar) with a Berkovich diamond tip.
- Loading Cycle: Maximum load of 50 mN, loading/unloading rate of 100 mN/min, 3-second holding time.
- Analysis: Measured maximum depth (hmax), elastic deformation (he), permanent deformation (hf), and calculated Indentation Hardness (HIT).
6CCVD Solutions & Capabilities
Section titled â6CCVD Solutions & CapabilitiesâThis research highlights the critical challenge of material anisotropy in achieving predictable and uniform material removal during ultra-precision processing, a challenge directly addressed by 6CCVDâs expertise in customized MPCVD diamond synthesis and finishing.
Applicable Materials
Section titled âApplicable MaterialsâTo replicate or extend this research into next-generation high-performance applications (such as diamond electronics, high-power optics, or quantum computing), 6CCVD recommends:
- Optical Grade SCD (Single Crystal Diamond): Equivalent to the high-quality, epi-ready substrates used in the study. 6CCVD offers SCD with specific crystal orientations (<100>, <110>, <111>) essential for controlling anisotropic CMP effects.
- Direct Correlation: SCD exhibits significant mechanical anisotropy. Understanding the MRR dependence on crystal plane (like the C-plane sapphire results) is mandatory for achieving Ra < 1nm surfaces required in advanced applications.
- Ultra-Smooth Polycrystalline Diamond (PCD): For applications requiring large area coverage (up to 125mm) where anisotropic effects must be minimized across the substrate.
- Heavy Boron-Doped Diamond (BDD): Used in electrochemical applications where surface modification (similar to the chemical hydration observed) is leveraged for functional performance.
Customization Potential
Section titled âCustomization PotentialâThe study underscores the necessity of precise material engineering and finishing control. 6CCVD is uniquely positioned to supply the required specialized diamond substrates:
| Study Requirement/Finding | 6CCVD Capability | Application Benefit |
|---|---|---|
| Crystal Orientation Control (C, R, A planes) | SCD Orientation Specificity: Guaranteed growth and delivery of specific <100>, <110>, or <111> oriented SCD wafers. | Enables targeted research into anisotropic removal mechanisms for diamond CMP recipe development. |
| Ultra-low Surface Roughness (Ra < 0.3 nm used) | Precision Polishing Guarantee: SCD surfaces polished to Ra < 1 nm. Inch-size PCD polished to Ra < 5 nm. | Meets or exceeds the surface quality requirements for Epi-ready and high-power optical applications. |
| 2-inch Wafer Format | Large Diameter Capabilities: Plates/wafers available up to 125mm (5 inches) in PCD and large SCD tiles. | Supports scale-up and high-volume manufacturing (HVM) transitioning from R&D stages. |
| Post-Processing Analysis (Nano-Indentation) | QC and Material Characterization: In-house teams utilize similar advanced metrology techniques to confirm hardness, stress, and surface integrity prior to global shipment. | Ensures repeatable, certified mechanical properties aligned with researcher specifications. |
| Need for Metallization (Electronics) | Custom Metalization: Internal capability for deposition of Au, Pt, Pd, Ti, W, and Cu layers. | Supports the transition of finished diamond wafers into device fabrication for power electronics or sensors. |
Engineering Support
Section titled âEngineering SupportâThis research demonstrates that optimal processing of hard, anisotropic materials is a delicate balance between mechanical removal (P-V product) and chemical modification (slurry interaction). 6CCVDâs in-house PhD engineering team specializes in diamond material selection and processing science. We can assist clients in defining the precise crystal orientation and surface finish requirements for projects involving anisotropic CMP, friction monitoring, and enhanced material durability.
6CCVD offers reliable global shipping (DDU default, DDP available) for all custom diamond specifications.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
Sapphire is an anisotropic material with excellent physical and chemical properties and is used as a substrate material in various fields such as LED (light emitting diode), power semiconductor, superconductor, sensor, and optical devices. Sapphire is processed into the final substrate through multi-wire saw, double-side lapping, heat treatment, diamond mechanical polishing, and chemical mechanical polishing. Among these, chemical mechanical polishing is the key process that determines the final surface quality of the substrate. Recent studies have reported that the material removal characteristics during chemical mechanical polishing changes according to the crystal orientations, however, detailed analysis of this phenomenon has not reported. In this work, we carried out chemical mechanical polishing of C(0001), R(<TEX>$1{\bar{1}}02$</TEX>), and A(<TEX>$11{\bar{2}}0$</TEX>) substrates with different sapphire crystal planes, and analyzed the effect of crystal orientation on the material removal characteristics and their correlations. We measured the material removal rate and frictional force to determine the material removal phenomenon, and performed nano-indentation to evaluate the material characteristics before and after the reaction. Our findings show that the material removal rate and frictional force depend on the crystal orientation, and the chemical reaction between the sapphire substrate and the slurry accelerates the material removal rate during chemical mechanical polishing.