High temperature surface Brillouin scattering study of mechanical properties of boron-doped epitaxial polysilicon
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2017-02-01 |
| Journal | AIP Advances |
| Authors | B.A. Mathe, JD Comins, A. G. Every, L. W. Hobbs |
| Institutions | University of the Witwatersrand, Massachusetts Institute of Technology |
| Citations | 4 |
| Analysis | Full AI Review Included |
Technical Documentation and Analysis: High Temperature Elastic Properties for MEMS
Section titled âTechnical Documentation and Analysis: High Temperature Elastic Properties for MEMSâThis documentation analyzes the application of surface Brillouin scattering (SBS) to determine the mechanical properties of thin, boron-doped polysilicon layers, a critical material for high-performance Micro-Electro-Mechanical Systems (MEMS). We leverage the findings to highlight the superior properties and customization capabilities of 6CCVDâs advanced diamond materials for next-generation devices.
Executive Summary
Section titled âExecutive SummaryâThis paper investigates the temperature-dependent mechanical properties of boron-doped epitaxial polysilicon layers, demonstrating the utility of non-contact Surface Brillouin Scattering (SBS) for materials characterization relevant to MEMS.
- Core Achievement: Determination of fundamental elastic constants ($C_{11}$, $C_{44}$) and engineering moduli (Youngâs, Bulk, Shear, Poissonâs ratio) for 50 ”m thick, 3000 ppm boron-doped polysilicon.
- Measurement Method: SBS utilized a non-destructive, laser-based technique suitable for high-temperature testing (20 °C to 110 °C).
- Temperature Stability: Youngâs Modulus (E) remained stable around 150 GPa up to 74 °C, decreasing slightly to 145 GPa at 110 °C.
- Material Limitation: While functional, polysiliconâs elastic modulus (150 GPa) and thermal stability limit high-stress and high-temperature MEMS applications.
- 6CCVD Value Proposition: 6CCVD provides heavily Boron-Doped Diamond (BDD) films and high-modulus SCD/PCD materials, offering 5x higher Youngâs modulus (E > 1000 GPa) and vastly superior thermal endurance, enabling extreme environment MEMS design.
- Replication/Extension: 6CCVD specializes in thin-film MPCVD diamond layers (down to 0.1 ”m), ideal for replicating or extending non-contact mechanical characterization studies like SBS on ultra-hard materials (e.g., diamond, SiC).
Technical Specifications
Section titled âTechnical SpecificationsâThe following hard data points were extracted from the research concerning the sample material and measured mechanical results.
| Parameter | Value | Unit | Context |
|---|---|---|---|
| Material Deposited | Boron-Doped Polysilicon | N/A | Epitaxial Layer on Si (100) Substrate |
| Layer Thickness (d) | ~50 | ”m | Used in MEMS applications |
| Boron Doping Concentration | 3000 (Approx 1019) | ppm (atoms per cm3) | p-type conductivity |
| Measurement Temperature Range | 20 to 110 | °C | High-temperature study |
| Density (Ï) | 2.33 | g/cm3 | Used for velocity calculations |
| Longitudinal Modulus (C11) | 199.5 ± 4% | GPa | Maximum value (20 °C) |
| Shear Modulus (C44) | 56.5 | GPa | Maximum value (20 °C) |
| Youngâs Modulus (Eiso) | 150.0 (Average) | GPa | Stable up to 74 °C |
| Bulk Modulus (Biso) | 124.2 | GPa | Maximum value (20 °C) |
| Poissonâs Ratio (Îœ) | 0.29 | None | Average (20 °C - 74 °C) |
| SBS Laser Wavelength | 514.5 | nm | Ar+ ion laser |
Key Methodologies
Section titled âKey MethodologiesâThe study relied primarily on high-temperature Surface Brillouin Scattering (SBS) to obtain mechanical constants without mechanical contact.
- Sample Preparation: A ~50 ”m epitaxial polysilicon layer was deposited onto a Si (100) substrate. Both sides were heavily boron-doped (3000 ppm).
- Characterization: Raman spectroscopy confirmed the Fano-line shape typical of p-type silicon created by boron doping. SBS angular dependence confirmed the polycrystalline nature of the film (little anisotropy).
- Furnace Environment: The sample was mounted in a specially designed furnace chamber, repeatedly flushed with argon, and evacuated to a pressure of less than 2.7 x 10-5 mbar.
- Thermal Control: Temperature was regulated by a Eurotherm 818P/TC controller with a steady ramp rate of 2.4 °C/hour between testing plateaus.
- SBS Instrumentation: Measurements were taken using a Sandercock-type (3+3) pass tandem Fabry-PĂ©rot interferometer with a 60 GHz Free Spectral Range.
- Laser Input: A ~280 mW, p-polarized 514.5 nm radiation (Ar+ ion laser) was used in a backscattering geometry.
- Data Calculation: The elastic constants $C_{11}$ (Longitudinal) and $C_{44}$ (Shear) were determined from the measured Rayleigh mode and longitudinal dip frequencies using the Landau and Lifshitz relation for isotropic media, allowing subsequent calculation of the engineering moduli.
6CCVD Solutions & Capabilities
Section titled â6CCVD Solutions & Capabilitiesâ6CCVD offers superior MPCVD diamond materials and precision engineering services to replicate, validate, and surpass the performance metrics established in this research, especially for extreme-environment MEMS applications.
Applicable Materials for MEMS & High-Modulus Applications
Section titled âApplicable Materials for MEMS & High-Modulus ApplicationsâThe polysilicon examined here has a Youngâs Modulus (E) of 150 GPa. 6CCVD specializes in MPCVD diamond, which offers substantial performance gains for next-generation devices.
| 6CCVD Material | Application Focus | Key Advantage over Polysilicon |
|---|---|---|
| Polycrystalline Diamond (PCD) | Standard MEMS components, protective coatings, acoustic devices (SAWs), cantilevers. | Youngâs Modulus E > 1000 GPa. Highest stiffness, intrinsic temperature stability (up to 700 °C in air). |
| Boron-Doped Diamond (BDD) | Piezoresistive sensors, thermal sensors, and electrochemical MEMS requiring integrated conductivity and hardness. | High conductivity and exceptionally high elastic modulus (E > 900 GPa). Direct replacement for B-Poly-Si where higher performance is required. |
| Optical Grade Single Crystal Diamond (SCD) | Waveguides, optical windows, extreme stiffness micro-optics. | Perfect crystal structure, ultra-low surface roughness (Ra < 1 nm), ideal for advanced SBS studies requiring minimal surface scattering noise. |
Customization Potential
Section titled âCustomization PotentialâThe polysilicon layer studied was 50 ”m thick and relied on specific boron doping and a specific surface finish. 6CCVD can replicate or modify these specifications in diamond films.
- Thickness Control: 6CCVD offers tight thickness tolerances for thin films, ranging from 0.1 ”m (ideal for acoustic wave studies similar to SBS) up to 500 ”m for both SCD and PCD.
- Custom Doping (BDD): We provide heavily boron-doped diamond (BDD) films, allowing researchers to explore the effect of incorporating higher performance materials into the electrically functional components studied in this paper.
- Custom Dimensions and Substrate Integration: While the paper used 4x4 mm samples, 6CCVD can produce PCD wafers up to 125 mm diameter, suitable for high-volume MEMS fabrication processes.
- Precision Finishing: We offer ultra-smooth polishing (Ra < 1 nm for SCD, Ra < 5 nm for inch-size PCD), which is essential for minimizing scattering noise in non-contact optical techniques like Surface Brillouin Scattering (SBS).
- Metalization Services: 6CCVD provides in-house metalization capabilities (Au, Pt, Pd, Ti, W, Cu) for creating contacts or integrated device layers necessary for MEMS devices built on diamond substrates.
Engineering Support
Section titled âEngineering SupportâThe successful determination of elastic constants via SBS requires precise material properties and reliable crystal growth.
- 6CCVDâs in-house PhD material scientists are experts in MPCVD growth recipes and defect engineering. We can assist researchers in selecting the optimal SCD or PCD grade and crystallographic orientation to achieve maximum stiffness and thermal stability for similar high-temperature mechanical property projects.
- We offer global shipping services (DDU default, DDP available) to ensure reliable delivery of custom diamond materials for time-sensitive research timelines.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
A study of the mechanical properties of a boron-doped epitaxial polysilicon layer deposited on a Si (100) substrate specimen has been carried out by surface Brillouin scattering at high temperatures. This type of specimen is widely used in micro-electro-mechanical systems (MEMS). By accumulating spectra with the Rayleigh mode and the Lamb continuum the isotropic elastic constants C44 and C11 were obtained, from which the values of the bulk, shear and Youngâs moduli and Poissonâs ratio for the layer were determined over a range of temperatures from 20 °C to 110 °C. By contrast, an examination of the literature on polycrystalline silicon shows that other methods each provide a limited range of the above properties and thus additional experiments and techniques were needed. The SBS method is applicable to other polycrystalline materials such as silicon carbide, silicon nitride, silicon germanium and amorphous diamond that have also been used for MEMS applications.