Characterization of the Diamond Wire Sawing Process for Monocrystalline Silicon by Raman Spectroscopy and SIREX Polarimetry

At a Glance

Metadata	Details
Publication Date	2017-03-23
Journal	Energies
Authors	Sindy Würzner, Martin Herms, Thomas A. Kaden, H. Bjerrum Møller, Matthias Wagner
Institutions	Technologiezentrum Halbleitermaterialien
Citations	23
Analysis	Full AI Review Included

6CCVD Technical Analysis & Documentation: Stress and Damage Control in Diamond Processing

Executive Summary

This research characterizes the sub-surface damage (residual stress, amorphous phase, microcracks) induced in monocrystalline silicon wafers during diamond wire sawing, providing key insights valuable for optimizing diamond material quality in extreme wear applications.

Critical Material Link: The degree of amorphization (a-Si/c-Si ratio, $r$) and the homogeneity of residual stress are proven to correlate directly with diamond wire wear and cutting ability.
Fresh Diamond Performance: Sharp diamond grains (fresh wire) maximize brittle material removal, resulting in the lowest amorphization (min. 8 nm depth) and the shallowest microcracks (min. 1.1 µm), crucial for increasing fracture strength.
Worn Diamond Damage: Used (worn) diamond wire leads to a significant increase in the amorphous silicon layer thickness (up to 38 nm) and intensifies localized compressive stresses (up to 1.8 GPa).
Methodological Value: The complementary use of Raman spectroscopy (absolute stress $\sigma_R$ and phase ratio $r$) and SIREX polarimetry (stress difference $\Delta\sigma$) establishes high-resolution, non-destructive optical inspection as a standard for sub-surface damage qualification.
Process Optimization: Increasing wire velocity reduces crack depth (down to 1.1 µm at 20 m/s), while utilizing fresh, high-quality diamond material minimizes detrimental phase transformations that impact subsequent solar cell texturing and etching processes.
6CCVD Value Proposition: The findings underscore the industrial necessity for high-purity, ultra-wear-resistant diamond materials—a core specialization of 6CCVD’s MPCVD manufacturing.

Technical Specifications

Parameter	Value	Unit	Context
Material Sawn	Monocrystalline Si ({001} orientation)	N/A	PV-grade Cz-silicon, p-type
Wafer Dimensions	156 x 156 x 0.22	mm³	Sample size
Wire Core Diameter	120	µm	Sawing Tool Specification
Diamond Size Distribution	8-16	µm	Fixed abrasive particle size
Linear Diamond Density	330	diamonds per mm²	Wire surface density
Wire Velocities Tested	10, 15, 20	m/s	Sawing parameter (constant feed rate 0.6 mm/min)
Max Residual Compressive Stress ($\sigma_R$)	Up to 1.8	GPa	Found parallel to sawing grooves (used wire)
Minimum Microcrack Depth	1.1	µm	Observed depth range (high velocity, fresh wire)
Maximum Microcrack Depth	13.2	µm	Observed depth range (low velocity, used wire)
Amorphous Layer Depth (Minimum)	8	nm	Corresponds to $r = 0.16$ (10 m/s, fresh wire)
Amorphous Layer Depth (Maximum)	38	nm	Corresponds to $r = 1.29$ (15 m/s, used wire)
Raman Excitation Wavelength	532	nm	For detecting stress and a-Si/c-Si ratio
Laser Penetration Depth (Si)	Approx. 800	nm	Used for Raman analysis
SIREX $\Delta\sigma$ Detection Limit	Approx. 0.05	MPa	Sensitivity for in-plane stress difference

Key Methodologies

The study utilized controlled diamond wire sawing parameters followed by advanced, non-destructive optical characterization to map sub-surface damage.

Diamond Sawing Process:
- Equipment: Meyer Burger DS264 wire saw.
- Wire Condition: Un-dressed wire utilized to observe significant wire wear effects (comparing fresh wire vs. used wire sides of the brick).
- Process Inputs: Wire velocities maintained at 10, 15, and 20 m/s. Feed rate held constant at 0.6 mm/min.
Post-Sawing Cleaning:
- Wafers treated with a standard alkaline cleaning medium (surfactant with sodium hydroxide, pH ~12).
- Steps included thermal ultrasonic cleaning (up to 70 °C, 20-30 min, 25-120 kHz). (Note: This cleaning etched away ~50% of the initial amorphous layer.)
Raman Spectroscopy (Bruker Optik GmbH):
- Purpose: Local detection of total residual material stress ($\sigma_R$) and amorphous-to-crystalline phase ratio ($r = I_{a-Si}/I_{c-Si}$).
- Parameters: Excitation laser 532 nm, Power 1.2 mW. Spatial resolution 5 µm.
- Calibration: Raman shift of ±3.2 cm^-1 corresponds to ±1 GPa stress.
SIREX Polarimetry (PVA TePla):
- Purpose: Reflection-based measurement of photo-elastic properties to map the in-plane difference of principal stress components ($\Delta\sigma$).
- Method: Measures depolarization of an initially linearly polarized infrared laser beam after reflection. High spatial resolution used for stress imaging.
Microcrack Depth Analysis (CLSM):
- Preparation: Bevel-cut samples (1º inclination) prepared via mechanical polishing.
- Etching: Samples etched for 30 s with Secco etch (hydrofluoric acid/potassium dichromate) to reveal damage structure.
- Measurement: Confocal Laser Scanning Microscopy used to measure the difference in height between the original surface and the point where the last microcrack vanishes.

6CCVD Solutions & Capabilities

The findings clearly establish that the integrity and consistency of the diamond material used for abrasive processes are paramount to minimizing sub-surface damage, residual stress, and undesirable phase transformations (amorphization). 6CCVD’s specialized MPCVD technology provides the foundation for materials that can replicate and significantly extend the high-performance results demonstrated with fresh diamond wire.

Applicable Materials for Advanced Sawing/Grinding:

To replicate the “sharp diamond” performance achieved in this research—and sustain it over extended operational periods—ultra-high purity and wear-resistant diamond material is essential.

Application/Requirement	6CCVD Material Recommendation	Rationale
Extreme Wear/Consistent Abrasive Performance	High-Purity Polycrystalline Diamond (PCD)	Optimized grain size and density (up to 125mm size) ensures superior toughness and minimal abrasive particle wear, sustaining cutting ability and reducing stress inhomogeneity over time.
High Thermal Stability/Low Stress Interface	Optical Grade Single Crystal Diamond (SCD)	Excellent thermal conductivity and purity minimize thermal stress during high-velocity cutting, crucial for maintaining optimal material removal mechanisms.
Electrochemical/Etching Optimization	Boron-Doped Diamond (BDD) Films	While not directly used in sawing, BDD can be used for reference electrode manufacturing or advanced tooling that requires high chemical resistance and conductivity, complementing the analysis of Si solar cell texturing performance.

Customization Potential for Replication and Research Extension

The research relied heavily on precise surface preparation and high-resolution optical analysis. 6CCVD offers customized material processing essential for advancing similar engineering efforts:

Precision Polishing for Optical Characterization: The SIREX and Raman methods require highly consistent surfaces for reliable measurement. 6CCVD provides industry-leading polishing services:
- SCD Polishing: Achieved surface roughness Ra < 1 nm.
- PCD Polishing: Achieved surface roughness Ra < 5 nm (on inch-size wafers).
Custom Dimensions and Substrate Sizing: While the paper used 156 mm Si wafers, 6CCVD can supply large-area PCD plates up to 125mm diameter and SCD wafers up to 10mm thickness, ideal for developing custom tooling or calibration standards used in stress mapping.
Advanced Metalization: For integrating stress sensors or creating custom tools, 6CCVD offers in-house deposition of metals including Au, Pt, Pd, Ti, W, and Cu, supporting complex device architectures and metrology setups.

Engineering Support & Global Reach

6CCVD’s in-house team of PhD material scientists can provide expert consultation on material selection for projects focused on minimizing sub-surface damage in semiconductors, high-precision machining, and optical metrology. We specialize in tailoring MPCVD diamond properties (thickness, purity, doping) to meet demanding industrial and research requirements. We facilitate global supply, offering worldwide shipping (DDU default, DDP available) to ensure your critical materials arrive efficiently.

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.

View Original Abstract

A detailed approach to evaluate the sub-surface damage of diamond wire-sawn monocrystalline silicon wafers relating to the sawing process is presented. Residual stresses, the presence of amorphous silicon and microcracks are considered and related to diamond wire velocity and cutting ability. In particular, the degree of amorphization of the wafer surface is analyzed, as it may affect the etching performance (texturing) during solar cell manufacture. Raman spectroscopy and Scanning Infrared Stress Explorer (SIREX) measurements are used independently as non-destructive, contactless optical characterization methods to provide stress imaging with high spatial resolution. Raman mappings show that amorphous silicon layers can occur inhomogeneously across the surface of diamond wire-sawn wafers. The Raman and SIREX results reveal a connection between a higher fraction of the amorphous phase, a more inhomogeneous stress distribution and a lower peak maximum of the stress difference on wafers, depending on both the wire wear and the wire velocity. SIREX line scans of the in-plane difference of the principal stress components ∆σ taken across the sawing grooves show significant differences in magnitude and periodicity. Furthermore, the results are compared with the microcrack depth from the same investigation areas. The possibility to optimize the diamond wire sawing processes by analyzing the sub-surface stress of the wafers is offered by complementary use of both Raman and SIREX measurements.

Tech Support

Original Source

DOI: https://doi.org/10.3390/en10040414

References

2015 - Surface damage and mechanical strength of silicon wafers
2016 - Comparative investigations of the surface damage of monocrystalline silicon wafers by Scanning Infrared Reflection Examination and Raman spectroscopy
2006 - Photoelastic characterization of residual stress in GaAs-wafers [Crossref]
1996 - Micro-Raman spectroscopy to study local mechanical stress in silicon integrated circuits [Crossref]
2007 - Grain orientation, texture, and internal stress optically evaluated by micro-Raman spectroscopy [Crossref]
1999 - Raman microspectroscopy study of processing-induced phase transformations and residual stress in silicon [Crossref]
2008 - Nondestructive measurement of machining-induced amorphous layers in single-crystal silicon by laser micro-Raman spectroscopy [Crossref]
2015 - Determination of the impact of the wire velocity on the surface damage of diamond wire sawn silicon wafers [Crossref]
1972 - Dislocation etch for (100) planes in silicon [Crossref]