Uniform Growth of Two-inch MPCVD Optical Grade Diamond Film
At a Glance
Section titled “At a Glance”| Metadata | Details |
|---|---|
| Publication Date | 2023-01-01 |
| Journal | Journal of Inorganic Materials |
| Authors | S Y Chan, Juping Tu, Ke Huang, Siwu SHAO, Zhiliang Yang |
| Institutions | North China University of Technology, University of Science and Technology Beijing |
| Citations | 3 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled “Executive Summary”This research successfully optimized the Microwave Plasma Chemical Vapor Deposition (MPCVD) process for growing large-area, high-quality optical grade diamond films by systematically studying the effect of the deposition platform height ($h$).
- Core Achievement: Uniform growth of a 2-inch (50.8 mm diameter) polycrystalline optical grade diamond film.
- Optimization Parameter: COMSOL simulation and experimental validation identified the optimal deposition platform height as $h = 2$ mm.
- Performance Metrics: The resulting film achieved a maximum thickness of 337 µm with a thickness inhomogeneity of less than 11.0%.
- Optical Quality: High transmittance was confirmed in both visible (up to 70%) and infrared (70% at 10.6 µm) bands.
- Crystalline Uniformity: Raman spectroscopy showed excellent quality, with the Full Width at Half Maximum (FWHM) ranging narrowly from 3.27 cm-1 (center) to 3.91 cm-1 (edge).
- Mechanism Insight: Increasing the platform height significantly improved the uniformity of the electric field on the substrate surface, leading to a flatter plasma shape and more uniform distribution of H atoms and carbon-containing radicals.
Technical Specifications
Section titled “Technical Specifications”| Parameter | Value | Unit | Context |
|---|---|---|---|
| Substrate Diameter | 50.8 | mm | N-type (100) Si wafer |
| Optimal Platform Height ($h$) | 2 | mm | Based on E-field and plasma uniformity |
| Maximum Film Thickness | 337 | µm | After 200 h growth |
| Thickness Inhomogeneity (Δd/d) | <11.0 | % | Across 2-inch wafer |
| Average Growth Rate | 1.5 | µm/h | At optimal conditions |
| Max Visible Transmittance | 69-70 | % | In the 480-800 nm range |
| IR Transmittance | 70.1 | % | At 10.6 µm wavelength |
| Raman FWHM (Center) | 3.27 | cm-1 | Indicator of high crystalline quality |
| Raman FWHM (Edge) | 3.91 | cm-1 | Indicator of quality uniformity |
| Preferred Orientation (XRD) | (220) | N/A | S(220)/S(111) ratio = 76.62 |
| Temperature Uniformity (ΔT) | 21 | °C | Temperature difference at $h = 2$ mm |
| E-Field Inhomogeneity | 14.1 | % | At optimal height (2 mm) |
Key Methodologies
Section titled “Key Methodologies”The study utilized a combination of computational modeling and a 2.45 GHz, 6 kW quartz-plate MPCVD system to achieve uniform deposition.
1. Computational Modeling (COMSOL)
Section titled “1. Computational Modeling (COMSOL)”- Objective: Simulate the multi-physical fields within the reactor, focusing on the impact of platform height ($h$).
- Variables Studied: Electric field (E-field) distribution, plasma shape, and substrate surface temperature uniformity.
- Key Finding: As $h$ increased, the E-field uniformity improved significantly (inhomogeneity dropped from 57.4% at -2 mm to 14.1% at 2 mm), and the plasma sphere flattened, becoming nearly parallel to the substrate surface.
2. Substrate Preparation
Section titled “2. Substrate Preparation”- Material: 50.8 mm diameter, 4 mm thick N-type (100) silicon wafers.
- Pre-treatment: Mechanical grinding for 30 min using a mixture of 5, 10, and 20 µm diamond powder, followed by 5 min grinding with 0.5 µm powder to create uniform nucleation sites.
- Cleaning: Ultrasonic cleaning in acetone and alcohol (15 min each).
3. MPCVD Process Parameters (Optimal $h = 2$ mm)
Section titled “3. MPCVD Process Parameters (Optimal $h = 2$ mm)”| Phase | Power (kW) | Pressure (kPa) | Gas Composition (sccm) | Temperature (°C) |
|---|---|---|---|---|
| Nucleation | 4.7 | 21 | H2: 500, CH4: 35 | 880 |
| Growth | 4.7-4.9 | 21-22 | H2: 500, CH4: 25, O2: 5 | 870-880 |
4. Characterization
Section titled “4. Characterization”- Plasma Diagnostics: Optical Emission Spectroscopy (OES) was used to monitor the relative concentrations of key growth species (C2, CH, Hα, Hβ) and estimate electron temperature (Te).
- Structural Quality: X-ray Diffraction (XRD) confirmed the preferred (220) orientation, and Raman spectroscopy measured crystalline quality and uniformity (FWHM).
- Optical Performance: UV-VIS-NIR and Fourier Transform Infrared (FTIR) spectroscopy measured transmittance across the 200 nm to 20 µm range.
Commercial Applications
Section titled “Commercial Applications”The production of large-area, thick, uniform optical grade diamond films enables several high-demand engineering applications, leveraging diamond’s unique combination of optical transparency, high thermal conductivity, and mechanical strength.
- High-Power Laser Optics:
- Application: Output windows and beam splitters for high-power CO2 lasers and other industrial/military laser systems.
- Benefit: Diamond’s high thermal conductivity and low absorption minimize thermal lensing and damage under extreme power loads.
- Fusion Energy Research (ITER):
- Application: Microwave windows (e.g., gyrotron windows) for electron cyclotron resonance heating (ECRH).
- Benefit: Low microwave loss (low tan δ) and high thermal stability are critical for transmitting high-frequency, high-power microwave energy into the plasma confinement vessel.
- Infrared and Multispectral Windows:
- Application: Protective windows and domes for aerospace, defense, and harsh industrial environments.
- Benefit: Broad transparency from visible light through the far infrared (including the 10.6 µm CO2 laser wavelength).
- High-Frequency/High-Power RF Devices:
- Application: Heat spreaders and substrates for high-power radio frequency (RF) electronics and microwave components where thermal management is paramount.
View Original Abstract
1,2 ，李成明 1 (1.北京科技大学 新材料技术研究院，北京 100083；2.北京科技大学 顺德研究生院，佛山 528399；3.北方工 业大学 机械与材料工程学院，北京 100144) 摘 要: 大尺寸光学级金刚石膜的均匀生长一直是微波化学气相沉积(Microwave plasma chemical vapor deposition， MPCVD)金刚石研究领域的热点和难点之一，沉积台的结构与位置对于金刚石膜均匀性以及厚膜生长的长期稳定 性至关重要。本研究通过 COMSOL 模拟结合实验研究了沉积台高度对衬底表面电场均匀性、等离子体状态和温度 均匀性的影响规律，优化了光学级金刚石膜均匀生长的工艺参数，在最佳的沉积台(高度 2 mm)下沉积得到的 2 英 寸金刚石膜(最大厚度 337 μm)，厚度不均匀性＜11%，从膜中心到边缘的拉曼半峰全宽为 3~4 cm -1 ，可见光波段内 最高透过率为 69%~70%，10.6 μm 处红外透过率为 70%。结果表明：金刚石膜的厚度和品质较为均匀，实现了两