A new technique for slicing diamonds into thin wafers is paving the way for their adoption as a next-generation semiconductor material.
While silicon-based materials are currently the undisputed leaders in the field of semiconductors, scientists across the globe are continually seeking superior alternatives for next-generation electronics and high-power systems.
Interestingly, diamonds are among the most promising materials for applications such as fast telecommunications and power conversion in electric vehicles (EVs) and power plants, due to their exceptional properties. A diamond’s dielectric breakdown strength is three times higher than in silicon carbide (SiC) and more than 30 times higher than in silicon (Si). In addition, unlike most other wide band gap (WBG) semiconductors, the carrier mobility is very high for both carrier types, and the thermal conductivity is unmatched.
Despite these attractive properties for the semiconductor industry, the applications of diamonds have so far been limited due to a lack of techniques capable of slicing them into thin wafers efficiently. As a result, diamond wafers must currently be synthesised one by one, making fabrication costs prohibitive for most industries.
LASERS HOLD THE ANSWER
Now, a research team from Japan, led by Professor Hirofumi Hidai from the Graduate School of Engineering at Chiba University, has unveiled a solution to this problem. The team has developed a novel laser-based slicing technique that can be used to cleanly slice a diamond along the optimal crystallographic plane to produce smooth wafers. According to the researchers, their findings will help in making diamonds cost-effective semiconductors for highly efficient power conversion in EVs and high-speed communication technologies.
The properties of most crystals, including diamonds, vary along different crystallographic planes – imaginary surfaces containing the atoms that make up the crystal. For instance, a diamond can easily be sliced along the (111) surface. However, slicing (100) is challenging because it also produces cracks along the (111) cleavage plane, increasing kerf loss.
To prevent the propagation of these undesirable cracks, the researchers developed a diamond processing technique that focuses short laser pulses onto a narrow cone-like volume within the material. “Concentrated laser illumination transforms diamond into amorphous carbon, whose density is lower that that of diamond,” says Professor Hidai. “Hence, regions modified by laser pulses undergo a reduction in density and crack formation.”
By shining these laser pulses onto the transparent diamond sample in a square grid pattern, the researchers created a grid of small crack-prone regions inside the material. If the space between the modified regions in the grid and the number of laser pulses used per region are optimal, all modified regions connect to each other through small cracks that preferentially propagate along the (100) plane. As a result, a smooth wafer with (100) surface can be easily separated from the rest of the diamond block by simply pushing a sharp tungsten needle against the side of the sample.
The Chiba University team believes its technique offers a pivotal step towards making diamonds a suitable semiconductor material for future technologies, particularly those that will aid in creating a more sustainable future.
“Diamond slicing enables the production of high-quality wafers at low cost and is indispensable in fabricating diamond semiconductor devices,” says Professor Hidai. “Therefore, this research brings us closer to realising diamond semiconductors for various applications in our society, such as improving the power conversion ratio in EVs and trains.”
Click here for more information, read the full paper ‘Laser slicing of a diamond at the (100) plane using an irradiation sequence that restricts crack propagation along the (111) plane,’ published in the Diamond & Related Materials Journal