Fengwen Mu

Single-Crystalline 3C-SiC anodically Bonded onto Glass: An Excellent Platform for High-Temperature Electronics and Bioapplications

Single-crystal cubic silicon carbide has attracted great attention for MEMS and electronic devices. However, current leakage at the SiC/Si junction at high temperatures and visible-light absorption of the Si substrate are main obstacles hindering the use of the platform in a broad range of applications. To solve these bottlenecks, we present a new platform of single crystal SiC on an electrically insulating and transparent substrate using an anodic bonding process. The SiC thin film was prepared on a 150 mm Si with a surface roughness of 7 nm using LPCVD. The SiC/Si wafer was bonded to a glass substrate and then the Si layer was completely removed through wafer polishing and wet etching. The bonded SiC/glass samples show a sharp bonding interface of less than 15 nm characterized using deep profile X-ray photoelectron spectroscopy, a strong bonding strength of approximately 20 MPa measured from the pulling test, and relatively high optical transparency in the visible range. The transferred SiC film also exhibited good conductivity and a relatively high temperature coefficient of resistance varying from -12 000 to -20 000 ppm/K, which is desirable for thermal sensors. The biocompatibility of SiC/glass was also confirmed through mouse 3T3 fibroblasts cell-culturing experiments. Taking advantage of the superior electrical properties and biocompatibility of SiC, the developed SiC-on-glass platform offers unprecedented potentials for high-temperature electronics as well as bioapplications.

Silicon carbide wafer bonding by modified surface activated bonding method

4H-SiC wafer bonding has been achieved by the modified surface activated bonding (SAB) method without any chemical-clean treatment and high temperature annealing. Strong bonding between the SiC wafers with tensile strength greater than 32 MPa was demonstrated at room temperature under 5 kN force for 300 s. Almost the entire wafer has been bonded very well except a small peripheral region and few voids. The interface structure was analyzed to verify the bonding mechanism. It was found an amorphous layer existed as an intermediate layer at the interface. After annealing at 1273 K in vacuum for 1 h, the bonding tensile strength was still higher than 32 MPa. The interface changes after annealing were also studied. The results show that the thickness of the amorphous layer was reduced to half after annealing.

Room-temperature wafer bonding of SiC–Si by modified surface activated bonding with sputtered Si nanolayer

A modified surface activated bonding (SAB) with Fe–Si multi-nanolayers is expected to achieve the wafer bonding of SiC to various materials. However, Fe diffusion, which affects device performance, cannot be avoided during some annealing processes. In this work, the room-temperature wafer bonding of SiC–Si by only one sputtered Si nanolayer was successfully achieved. The bonding interface was investigated. A uniform intermediate layer with a thickness of ~15 nm just containing Si, C, and Ar was found at the interface. The bonding strength between the SiC surface and the sputtered Si nanolayer could reach the bulk Si strength in accordance with the results of the strength test. This indicates that the wafer bonding of SiC to any other materials can be achieved easily if the material could be also strongly bonded to the sputtered Si nanolayer. In addition, the thermal and chemical reliabilities of the SiC–Si bonding interface were investigated by rapid thermal annealing and KOH etching, respectively.

A comparison study: Direct wafer bonding of SiC–SiC by standard surface-activated bonding and modified surface-activated bonding with Si-containing Ar ion beam

In this study, the results of direct wafer bonding of SiC–SiC at room temperature by standard surface-activated bonding (SAB) and modified SAB with a Si-containing Ar ion beam were compared, in terms of bonding energy, interface structure and composition, and the effects of rapid thermal annealing (RTA) at 1273 K in Ar gas. Compared with that obtained by the standard SAB, the bonding interface obtained by the modified SAB with a Si-containing Ar ion beam is ~30% stronger and almost completely recrystallized without oxidation during RTA, which should be due to the in situ Si compensation during surface activation by the Si-containing Ar ion beam.

SiC wafer bonding by modified suface activated bonding method

3-inch 4H-SiC wafer bonding has been achieved by the modified surface activated bonding (SAB) method without any chemical-clean treatment and high temperature annealing. Strong bonding of the SiC wafers, greater than 32MPa (tensile strength), was demonstrated at room temperature under 5kN force for 300 seconds. Almost the entire wafer has been bonded very well except the small outermost region and few voids. The interface structure was analyzed to explore the bonding mechanism. An amorphous layer was found to be as the intermediate layer at the interface. Furthermore, to verify the stability of the interface, the interface changes after annealing were studied.

Strain Effect in Highly-Doped n-Type 3C-SiC-on-Glass Substrate for Mechanical Sensors and Mobility Enhancement

This work reports the strain effect on the electrical properties of highly doped n‐type single crystalline cubic silicon carbide (3C‐SiC) transferred onto a 6‐inch glass substrate employing an anodic bonding technique. The experimental data shows high gauge factors of −8.6 in longitudinal direction and 10.5 in transverse direction along the [100] orientation. The piezoresistive effect in the highly doped 3C‐SiC film also exhibits an excellent linearity and consistent reproducibility after several bending cycles. The experimental result is in good agreement with the theoretical analysis based on the phenomenon of electron transfer between many valleys in the conduction band of n‐type 3C‐SiC. Our finding for the large gauge factor in n‐type 3C‐SiC coupled with the elimination of the current leak to the insulated substrate could pave the way for the development of single crystal SiC‐on‐glass based MEMS applications.

SiC wafer bonding using surface activation method for power device

This study compared the results of room temperature direct wafer bonding of SiC-SiC accomplished by standard surface activated bonding (SAB) and modified SAB with a Si-containing Ar ion beam, in terms of bonding energy, interface structure and composition as well as the effects of rapid thermal annealing (RTA). Compared with that obtained by standard SAB, the bonding interface of modified SAB with a Si-containing Ar ion beam could be ∼30% stronger and almost completely recrystallized by RTA without oxidation. The advantages of modified SAB with a Si-containing Ar ion beam are attributed to the assumed in-situ Si-compensation during surface activation.

Room temperature SiC-SiC direct wafer bonding by SAB methods

Room temperature direct wafer bonding of SiC-SiC by standard surface-activated bonding (SAB) and modified SAB with a Si-containing Ar ion beam were compared in terms of bonding energy, interface structure and composition. Compared with that obtained by standard SAB, the bonding interface obtained by modified SAB with a Si-containing Ar ion beam is >30% stronger, which should be due to the in situ Si compensation during surface activation by the Si-containing Ar ion beam.

Wafer bonding of SiC-SiC and SiC-Si by modified suface activated bonding method

SiC-SiC and SiC-Si wafer bonding has been achieved by two different modified surface activated bonding (SAB) methods without any chemical-clean treatment and high temperature annealing. Bonding strength of SiC-SiC is even higher than 32MPa. Bonding strength of SiC-Si bonded pair is also higher than the bulk strength of Si. The bonded wafers were almost completely bonded without some voids or peripheral area, which should be caused by some partilces and wafer warpage. The interfaces of bonded SiC-SiC and SiC-Si have been analyzed by high-resolution transmission electron microscopy (HRTEM) to verify the bonding mechanism.

Direct bonding of SiC by the suface activated bonding method

3-inch 4H-SiC wafer direct bonding has been achieved by the modified surface activated bonding (SAB) method without any chemical-clean treatment and high temperature annealing. Strong bonding of the SiC wafers, greater than 32 MPa (tensile strength), was demonstrated at room temperature under 5 kN force for 300 seconds. Almost the entire wafer has been bonded very well except the small outermost region and few voids. Moreover, the interface structure was analyzed to explore the bonding mechanism. An amorphous layer was found to be as the intermediate layer at the interface.