Low-temperature direct bonding of InP and diamond substrates under atmospheric conditions
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2021-05-27 |
| Journal | Scientific Reports |
| Authors | Takashi Matsumae, Ryo Takigawa, Yuichi Kurashima, Hideki Takagi, Eiji Higurashi |
| Institutions | Kyushu University, National Institute of Advanced Industrial Science and Technology |
| Citations | 15 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThis research demonstrates a robust, low-temperature method for directly bonding Indium Phosphide (InP) substrates to diamond heat spreaders, critically addressing thermal management issues in high-performance InP devices.
- Core Achievement: Successful direct bonding of InP (100) to diamond (111) substrates achieved through surface activation and low-temperature annealing (250 °C).
- Thermal Management: The technique utilizes diamond (2200 W/mK) to replace the low thermal conductivity InP (68 W/mK) substrate, enabling efficient heat dissipation for high-power density devices.
- Bonding Interface Quality: The substrates are bonded via an ultra-thin (~3 nm) amorphous intermediate layer composed of In, P, O, and C, avoiding the high thermal resistance associated with conventional thick metal bonding layers (2-4 ”m).
- Mechanical Strength: The resulting bond exhibits a shear strength of 9.3 MPa, which meets standard die shear strength requirements (MIL STD 883E).
- Process Simplicity: The method relies on standard industrial processes: NH3/H2O2 cleaning for diamond and oxygen plasma activation for InP, followed by annealing under atmospheric conditions.
- Surface Requirements: Both surfaces maintained atomic smoothness (RMS roughness < 3.1 A) after activation, confirming suitability for direct bonding.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Bonding Temperature | 250 | °C | Low-temperature annealing step |
| Annealing Duration | 24 | h | Time under load |
| Applied Load (Annealing) | ~1 | MPa | Pressure applied during annealing |
| Bond Shear Strength | 9.3 | MPa | Measured on 3x3 mm2 diamond die |
| Intermediate Layer Thickness | ~3 | nm | Amorphous layer at InP/Diamond interface (TEM analysis) |
| InP Thermal Conductivity | 68 | W/mK | Reference value (low thermal dissipation) |
| Diamond Thermal Conductivity | 2200 | W/mK | Reference value (highest thermal conductivity solid) |
| InP RMS Roughness (Before O2) | 2.76 ± 0.3 | A | Atomic Force Microscopy (AFM) measurement |
| InP RMS Roughness (After O2) | 3.03 ± 0.3 | A | Activated surface condition (required < 5 A) |
| InP Wafer Thickness | 500 | ”m | Starting substrate thickness |
| Diamond Substrate Size | 3 x 3 | mm2 | Die size used for bonding test |
Key Methodologies
Section titled âKey MethodologiesâThe direct bonding process involves surface preparation to generate hydroxyl (OH) groups, followed by contacting and low-temperature thermal annealing.
| Step | Substrate | Process/Recipe Parameter | Result/Purpose |
|---|---|---|---|
| 1. Diamond Cleaning | Diamond (111) | Cleaned for 10 min at 75 °C using a mixture of 10 mL NH3 (28%), 10 mL H2O2 (35%), and 50 mL DI water. | Generates C-OH groups (OH-termination) on the diamond surface. |
| 2. InP Activation | InP (100) | Activated using Reactive Ion Etching (RIE) with O2 plasma. | Plasma parameters: 200 W power, 30 s duration, 60 Pa O2 pressure, 20 mL/min O2 flow. Generates In-OH/P-OH groups. |
| 3. Contacting | Both | InP substrate cooled to 14 °C (Peltier cooler) for ~30 s, then diamond placed on InP in a clean room (23 °C, 40% RH). | Cooling promotes condensed water molecules, facilitating initial hydrogen bond networks between the surfaces. |
| 4. Annealing (Bonding) | Specimen | Annealed at 250 °C for 24 h under a load of approximately 1 MPa. | Thermal dehydration reaction forms covalent atomic bonds (InP-O-C-Diamond) across the interface. |
| 5. Interface Analysis | Specimen | TEM and EDX analysis performed after grinding InP thickness down to 10 ”m. | Confirmed 3 nm amorphous layer composed of In, P, O, and C, and absence of cracks or nanovoids. |
Commercial Applications
Section titled âCommercial ApplicationsâThis low-temperature direct bonding technology is crucial for manufacturing next-generation devices requiring high power density and superior thermal management.
- High-Frequency Electronics:
- Application: Fabrication of InP High Electron Mobility Transistors (HEMTs) and Heterojunction Bipolar Transistors (HBTs) designed for THz monolithic integrated circuits (TMICs).
- Benefit: Enables sustained high-frequency operation (fmax > 1 THz) by effectively removing localized heat, preventing performance degradation and failure.
- High-Power RF/Microwave Devices:
- Application: High-power InP-based amplifiers and microwave power transistors.
- Benefit: Provides a robust, low-thermal-resistance path to the diamond heat spreader, allowing for increased power density and improved reliability compared to devices bonded with conventional metal layers.
- Photonic Integrated Circuits (PICs):
- Application: Integration of InP lasers, modulators, and photodetectors for next-generation optical communications systems (e.g., 1.55 ”m systems).
- Benefit: Mitigates temperature-induced wavelength shifts and efficiency drops in high-power optical components, crucial for miniaturization and high-power operation.
- Heterogeneous Integration:
- Application: Wafer-level bonding of III-V semiconductors (like InP) onto high-thermal-conductivity materials (like diamond) using scalable, low-temperature processes.
- Benefit: Simplifies manufacturing by utilizing standard cleaning and atmospheric annealing steps, contributing to higher integration density and lower manufacturing costs for advanced semiconductor devices.