Laser Grinding of Single-Crystal Silicon Wafer for Surface Finishing and Electrical Properties

At a Glance

Metadata	Details
Publication Date	2021-03-04
Journal	Micromachines
Authors	Xinxin Li, Yimeng Wang, Yingchun Guan
Institutions	Beihang University, University of Nottingham Ningbo China
Citations	6
Analysis	Full AI Review Included

Technical Analysis and Documentation: Laser Grinding for Surface Finishing

This document analyzes the research paper “Laser Grinding of Single-Crystal Silicon Wafer for Surface Finishing and Electrical Properties” and connects the findings to the advanced material solutions offered by 6CCVD.

Executive Summary

This study successfully demonstrates the use of nanosecond pulsed laser grinding as a highly efficient, non-contact method for improving the surface quality and electrical properties of diamond-sawn single-crystal silicon (Si) wafers.

Feature	Detail
Core Achievement	Efficient removal of mechanically induced surface damage (SiO₂ layer, amorphous/polycrystalline Si, and carbon pollutants).
Surface Quality	Arithmetic roughness (Ra) reduced by over 81%, dropping from 0.4 µm (as-received) to 0.075 µm (75 nm) after laser grinding.
Microstructure Recovery	Detrimental polycrystalline silicon (poly-Si) layers, caused by mechanical sawing, were completely transformed back into a perfect single-crystal structure.
Electrical Improvement	Resistivity (ρ) decreased significantly from 0.572 Ω·cm to 0.417 Ω·cm, attributed directly to the elimination of the high-resistance polycrystalline phase.
Methodology	Utilized a 1064 nm nanosecond laser (220 ns pulse width) in an inert Argon (Ar) shield environment to prevent re-oxidation.
Relevance to 6CCVD	The challenges addressed (subsurface damage, high roughness, crystallinity defects) are critical in MPCVD diamond processing, highlighting 6CCVD’s capability to deliver ultra-smooth, high-crystallinity SCD/PCD materials.

Technical Specifications

The following hard data points were extracted from the experimental results and optimal process parameters:

Parameter	Value	Unit	Context
Initial Surface Roughness (Ra)	0.4	µm	As-received Si wafer
Final Surface Roughness (Ra)	0.075 (75)	µm (nm)	After laser grinding
Roughness Reduction	>81	%	Macro-scale measurement
Initial Resistivity (ρ)	0.572	Ω·cm	As-received Si wafer
Final Resistivity (ρ)	0.417	Ω·cm	Laser-grinded Si wafer
Laser Wavelength	1064	nm	Nanosecond pulsed laser
Laser Pulse Width	220	ns	Optimal setting
Optimal Laser Intensity	6.75 x 10⁶	W/cm²	Optimal process condition
Optimal Scanning Speed	3000	mm/s	Optimal process condition
Optimal Laser Frequency	100	kHz	Optimal process condition
Wafer Dimensions	4	inch diameter	Single-crystal Si wafer
Boron Doping Concentration	10¹⁶/cm³	N/A	P-type Si wafer

Key Methodologies

The experiment focused on optimizing nanosecond laser parameters under an inert atmosphere to achieve high-quality surface finishing and microstructure recovery.

Material Selection: Single-crystal silicon wafers (525 µm thick, <100> orientation, Boron-doped 10¹⁶/cm³) were used, initially damaged by diamond sawing.
Laser System: A 1064 nm nanosecond pulsed laser (100 W maximum power) with a 220 ns pulse width was employed.
Beam Delivery: A two-mirror galvanometric scanner and an F-theta objective lens achieved a focal beam diameter of 35 µm.
Environmental Control: The grinding process was performed within an Argon (Ar) shield environment to prevent atmospheric oxygen from reacting with the molten silicon, thereby minimizing the formation of new SiO₂.
Damage Removal Mechanism: The process involves two steps:
- Step 1 (Ablation): High-energy laser absorption by the surface oxide layer creates rapidly expanding plasma and shock waves, fragmenting and removing pollutants and scratches.
- Step 2 (Melting/Regrowth): Thermal accumulation melts the silicon surface, allowing molten Si to redistribute via surface tension and the Marangoni effect, followed by bottom-up epitaxial regrowth from the single-crystal substrate, restoring crystallinity.
Characterization Techniques: Surface morphology, chemical composition, and crystallinity were verified using LSCM, SEM, EDS, XPS, XRD, and Raman spectroscopy. Electrical properties were measured using the four-probe method.

6CCVD Solutions & Capabilities

The research highlights the critical need for ultra-low roughness and perfect crystallinity in advanced semiconductor materials. 6CCVD specializes in providing MPCVD diamond materials (SCD and PCD) that inherently meet these stringent requirements, often eliminating the need for complex, secondary laser recovery processes.

Applicable Materials for High-Performance Applications

The challenges of subsurface damage (SSD) and roughness addressed in this Si study are directly relevant to high-power electronics, thermal management, and quantum applications utilizing diamond.

Material Solution	Description & Relevance to Research
Optical Grade SCD	Required for applications demanding the highest crystallinity and lowest defect density (analogous to the recovered single-crystal Si). 6CCVD provides SCD with Ra < 1 nm standard, surpassing the 75 nm achieved by laser grinding Si.
Electronic Grade SCD	Ideal for high-power devices and sensors where low resistivity and perfect crystal structure are paramount. Our SCD is optimized for minimal SSD, ensuring superior electrical performance compared to mechanically processed materials.
Large-Area PCD Wafers	The Si wafer used was 4 inches. 6CCVD offers Polycrystalline Diamond (PCD) plates up to 125 mm (nearly 5 inches) in diameter, suitable for scaling up thermal management or large-area detector applications.
Boron-Doped Diamond (BDD)	For applications requiring controlled conductivity (like the Boron-doped Si wafer), 6CCVD offers custom BDD materials, allowing engineers to precisely tune resistivity for electrochemical or electronic devices.

Customization Potential & Engineering Support

6CCVD’s in-house capabilities are perfectly suited to support researchers replicating or extending this type of surface engineering work onto diamond substrates.

Capability	Benefit to Researchers
Ultra-Low Roughness Polishing	6CCVD guarantees SCD surfaces with Ra < 1 nm and inch-size PCD surfaces with Ra < 5 nm. This high initial quality minimizes the need for post-processing steps like the laser grinding described in the paper.
Custom Dimensions & Thickness	We provide SCD and PCD wafers in custom dimensions up to 125 mm, with thicknesses ranging from 0.1 µm to 500 µm, and substrates up to 10 mm thick. This supports both thin-film device fabrication and robust substrate requirements.
Advanced Metalization Services	The paper discusses electrical testing. For building functional devices on diamond, 6CCVD offers in-house metalization (Au, Pt, Pd, Ti, W, Cu) crucial for creating low-resistance ohmic contacts or robust thermal interfaces.
Expert Engineering Support	The transformation of polycrystalline material back to single-crystal structure is a key finding. 6CCVD’s in-house PhD team specializes in controlling MPCVD growth and post-processing to ensure high-purity, low-defect SCD, assisting clients with material selection for similar high-frequency, quantum, or thermal management projects.

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

View Original Abstract

In this paper, we first report the laser grinding method for a single-crystal silicon wafer machined by diamond sawing. 3D laser scanning confocal microscope (LSCM), X-ray diffraction (XRD), scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), laser micro-Raman spectroscopy were utilized to characterize the surface quality of laser-grinded Si. Results show that SiO2 layer derived from mechanical machining process has been efficiently removed after laser grinding. Surface roughness Ra has been reduced from original 400 nm to 75 nm. No obvious damages such as micro-cracks or micro-holes have been observed at the laser-grinded surface. In addition, laser grinding causes little effect on the resistivity of single-crystal silicon wafer. The insights obtained in this study provide a facile method for laser grinding silicon wafer to realize highly efficient grinding on demand.

Tech Support

Original Source

DOI: https://doi.org/10.3390/mi12030262

References

2001 - Fine grinding of silicon wafers [Crossref]
2004 - An experimental investigation into soft-pad grinding of wire-sawn silicon wafers [Crossref]
2006 - Simultaneous double side grinding of silicon wafers: A literature review [Crossref]
2009 - Recovery of microstructure and surface topography of grinding-damaged silicon wafers by nanosecond-pulsed laser irradiation [Crossref]
2017 - Analytical modeling of grinding-induced subsurface damage in monocrystalline silicon [Crossref]
2018 - Formation of subsurface cracks in silicon wafers by grinding [Crossref]
2008 - Grinding of silicon wafers: A review from historical perspectives [Crossref]
2018 - Effect of heat treatment on the microstructural evolution of a nickel-based superalloy additive-manufactured by laser powder bed fusion [Crossref]
2017 - Laser polishing of 3D printed mesoscale components [Crossref]