Fabricating microlens arrays of single-crystal silicon by slow-tool-servo diamond turning
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2016-01-01 |
| Journal | Seisan Kakou, Kousaku Kikai Bumon Kouenkai kouen rombunshuu/Seisan Kako, Kosaku Kikai Bumon Koenkai |
| Authors | Mao Mukaida, Jiwang Yan |
| Institutions | Keio University |
| Analysis | Full AI Review Included |
6CCVD Technical Analysis & Documentation: Ultra-Precision Diamond Turning of Silicon Microlens Arrays
Section titled â6CCVD Technical Analysis & Documentation: Ultra-Precision Diamond Turning of Silicon Microlens ArraysâReference: Fabricating microlens arrays of single-crystal silicon by slow-tool-servo diamond turning (M. Mukaida et al., Keio University, 22-23 Oct 2016)
Executive Summary
Section titled âExecutive SummaryâThis research successfully demonstrates the fabrication of highly accurate concave microlens arrays on single-crystal silicon (SCS) wafers using Slow-Tool-Servo (STS) ultra-precision diamond turning. The findings underscore the critical role of premium Single Crystal Diamond (SCD) tooling in achieving nanometer-scale surface finishes on brittle materials.
- Application Focus: Advanced Infrared (IR) optics and image sensor components requiring high-density microlens arrays on SCS substrates.
- Core Achievement: Successful fabrication of spherical dimples with exceptional precision, achieving a form error (PV) of approximately 300 nm and a final surface roughness (Sa) of 6 nm.
- Tooling Requirement: A high-quality single crystal diamond R-bite tool (1 mm nose radius, -30° rake angle) was necessary to enable ductile-mode cutting.
- Process Optimization: Ductile-mode machining was confirmed to occur reliably at tool feed rates (f) below 5 ”m/rev.
- Material Science Insight: The study quantified the dependence of brittle fracture and amorphous silicon (a-Si) phase transformation on crystal orientation (<110> vs. <100>) and tool feed rate.
- 6CCVD Relevance: The results validate the necessity of 6CCVDâs optical grade, sub-nanometer polished SCD for ultra-precision tooling required in next-generation optics manufacturing.
Technical Specifications
Section titled âTechnical SpecificationsâThe following hard data points were extracted detailing the machining parameters and achieved performance metrics.
| Parameter | Value | Unit | Context |
|---|---|---|---|
| Workpiece Material | Single-Crystal Silicon (SCS) | N/A | (001) wafer orientation |
| Tool Material | Single Crystal Diamond (SCD) R-Bite | N/A | Rake Angle: -30° |
| Tool Nose Radius | 1.0 | mm | Required for STS envelope generation |
| Dimple Diameter | 320 | ”m | Size of the microlens element |
| Dimple Depth | 5 | ”m | Max depth of cut during dimple fabrication |
| Cutting Speed | 4.5 | mm/s | Constant surface speed maintained by spindle adjustment |
| Optimal Feed Rate (Ductile Mode) | 1 | ”m/rev | Achieved best surface quality and form accuracy |
| Critical Feed Rate (Ductile/Brittle Transition) | 4 | ”m/rev | Above this rate (fâ„5 ”m/rev), brittle fracture dominates |
| Achieved Surface Roughness (Sa) | 6 | nm | At f = 1 ”m/rev (Ductile Cut) |
| Achieved Form Error (PV) | 300 | nm | At f = 1 ”m/rev (Deviation from ideal spherical surface) |
| Preferred Direction for Brittleness | <110> | N/A | Increased brittle fracture and lower critical depth of cut |
| Phase Transformation Product | Amorphous Silicon (a-Si) | N/A | Generated significantly at higher feed rates (higher pressure) |
Key Methodologies
Section titled âKey MethodologiesâThe experiment focused on validating the effects of tool feed rate and crystal orientation on achieving ductile-mode cutting of single-crystal silicon using Slow-Tool-Servo (STS) diamond turning.
- Machine & Setup: Utilized a 4-axis simultaneous control free-form surface machining center (Nanoform X, Precitech). Cutting was performed in a dry environment.
- Tool Specification: A high-precision, single crystal diamond R-bite tool was used, specified with a 1 mm nose radius and a negative rake angle of -30°.
- STS Implementation: The tool was advanced along the X-axis while simultaneously oscillating in the Z-axis using STS to generate the spherical dimple envelope.
- Process Control: A constant cutting speed of 4.5 mm/s was maintained across the tool path by continuously modulating the spindle rotation speed.
- Parameter Variation: Six different tool feed rates (f = 1, 2, 3, 4, 5, 6 ”m/rev) were tested to identify the ductile-to-brittle transition point.
- Orientation Study: Dimples were processed with the cutting direction aligned along the <110> and <100> crystal orientations.
- Analysis: Evaluation included SEM analysis of chip morphology (distinguishing flow-type vs. powder-type chips), white light interferometry for shape/form error, and Micro Raman Spectroscopy for mapping the intensity of generated amorphous silicon (a-Si).
6CCVD Solutions & Capabilities
Section titled â6CCVD Solutions & Capabilitiesâ6CCVD provides the high-performance MPCVD diamond materials and engineering expertise necessary to replicate and advance this ultra-precision diamond turning research, particularly in the realm of custom optics tooling.
| Research Requirement | 6CCVD Solution & Value Proposition |
|---|---|
| Material: Ultra-Hard SCD Tooling | Optical Grade Single Crystal Diamond (SCD): We supply highly stable, low-defect SCD material crucial for fabricating the critical -30° rake angle R-bite tools. Our SCD ensures the chemical purity and mechanical integrity required for nanometer-scale material removal. |
| Finish: Achieving Nanometer Roughness (6 nm Sa) | Premium Polishing Services (Ra < 1 nm): The success of ductile-mode cutting relies entirely on the stability and quality of the diamond cutting edge. 6CCVD provides polished SCD wafers and plates with certified surface roughness down to Ra < 1 nm (SCD) and Ra < 5 nm (PCD), guaranteeing superior edge quality. |
| Dimensions: Specific Tool Geometry (1mm Radius) | Custom Dimensions and Precision Cutting: 6CCVD offers custom laser cutting and dimensional services for diamond plates (PCD and SCD) up to 125 mm. We can supply the base material precisely cut and polished to meet demanding specifications for tool fabrication (e.g., specific angles, radii, and thickness up to 500 ”m). |
| Metallization: Integration for Tool Mounting/Sensing | In-House Metallization Services: Should tool mounting or integrated sensing be required for force monitoring (as utilized in the paper), 6CCVD offers proprietary metalization layers including Au, Pt, Pd, Ti, W, and Cu, ensuring robust bonding and electrical access. |
| Engineering Support: Optimization of Cutting Recipe | Expert Engineering Consultation: Our in-house PhD material scientists specialize in understanding the complex mechanics of diamond-material interaction, including the transition between ductile and brittle regimes and amorphous phase generation. We assist researchers in selecting the optimal crystal orientation and material grade for ultra-precision cutting experiments. |
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly. We ship globally (DDU default, DDP available).
View Original Abstract
Microlens arrays of single-crystal silicon are required increasingly in advanced IR optics. In this study, we attempted to fabricate concave microlens arrays on a single-crystal silicon wafer by slow-tool-servo diamond turning. The form error, surface topography, material phase transformation and cutting force characteristics were investigated experimentally. It was found that brittle fracture occurred preferentially at one side (the exit side of tool feed) of the lens dimples when cutting direction is along <110> and tool feed rate is high. Amorphous silicon phase was generated significantly at the exit side of tool feed of the dimples as tool feed rate increased. The peak values of cutting forces changed with tool feed rate and crystal orientation. Spherical microlens arrays with a form error of ~300 nmPV and surface roughness of ~6 nmSa were successfully fabricated.