Overview of Ultra Short Pulse Laser Processing of Wide Bandgap Semiconductor Materials

Professor Zhang Peilei's team from Shanghai University of Engineering and Technology, in collaboration with the research team from Warwick University and Autuch (Shanghai) Laser Technology Co., Ltd., published a review paper titled "A review of ultra shot pulse laser micromachining of wide bandgap semiconductor materials: SiC and GaN" in the international journal Materials Science in Semiconductor Processing. The paper reviewed and summarized the current status and challenges of using ultra short pulse lasers to process wide bandgap semiconductor materials.

In the past few decades, semiconductor devices based on silicon (Si) have long dominated. But with the increasing demand for higher current, voltage, packaging density, and temperature, silicon-based power devices have gradually begun to approach their performance limits. At the same time, wide bandgap (WBG) semiconductors have begun to become a potential alternative technology. Wide bandgap (WBG) materials have excellent semiconductor and physicochemical properties. Silicon carbide (SiC) and gallium nitride (GaN), as typical representatives of third-generation semiconductor materials, can be applied to high-temperature, high-frequency, radiation resistant, and high-power devices, and are emerging materials in the power electronics industry. However, due to the brittle nature of the material, traditional mechanical processing methods are no longer able to meet higher processing quality requirements. At the same time, the high precision and non-contact nature of laser processing make it a suitable processing method. In this context, the article reviews the application of ultra short pulse lasers in processing WBG materials, including SiC and GaN semiconductor materials.

Figure 1 Comparison of Material Properties of Silicon, Silicon Carbide, and Gallium Nitride

Figure 2 Common Processing Methods for Silicon Carbide and Gallium Nitride Materials

Figure 3 Schematic diagram of nanosecond laser and ultrafast laser ablation

Figure 4: Ultra fast laser processing of SiC microstructure: (a) Femtosecond laser microfabrication of rotor; (b) Through-hole array on 3C SiC chip; (c) ArF laser microfabrication of grooves; (d) Femtosecond laser microfabrication of holes

Figure 5: Ultra fast laser ablation of GaN thin film: (a) Photo of a separated LED device; (b-c) patterned GaN thin film attached to TRT substrate; Optical images of purple blue EL emitted by separated LED devices in different bending states (d-f)

The article summarizes the application of ultra short pulse lasers in processing silicon carbide and gallium nitride materials, as well as the physical mechanisms of their interaction with semiconductor materials. Ultra short pulse lasers can effectively reduce thermal effects due to their ultra short operating time. With the increasing demand for efficient and precise manufacturing in the semiconductor industry, ultrafast laser processing technology is expected to be widely applied. Traditional semiconductor material processing methods are often limited by material properties, processing equipment, and other factors, making it difficult to meet specific processing requirements. Ultra fast laser processing technology has higher flexibility and controllability, and can adjust laser parameters according to different processing needs to achieve diversified processing effects. In summary, both picosecond and femtosecond ultra short pulse lasers can be used as the first choice for processing WBG semiconductor materials such as SiC and GaN. Picosecond and femtosecond ultra short pulse lasers have low thermal effects, small heat affected zones, and precise control of processing geometry, making them excellent choices for micro and nano processing.

There are still some difficulties and challenges in the research of ultrafast laser processing of wide bandgap semiconductor materials in the future:

1. At the same laser energy density, femtosecond laser is more precise and picosecond laser is more efficient. For femtosecond pulses, mode locking is almost the only means of implementation, so the cost is relatively lower compared to picosecond lasers. When ultra short pulse lasers interact with transparent media, nonlinear effects such as multiphoton ionization dominate. Femtosecond lasers are more likely to reach nonlinear thresholds and are better suited to the absorption characteristics of materials. Therefore, femtosecond pulse lasers have more advantages in transparent medium processing and other applications. In the selection of laser parameters, factors such as thermal effects, cost, and application scenarios should be comprehensively considered, and an appropriate pulse width should be chosen in a balance between efficiency and accuracy;

2. The development trend of femtosecond laser technology is high-precision processing, but the disadvantage is that it cannot achieve large-scale processing comparable to traditional microelectronics/microelectromechanical manufacturing technology. Exploring new strategies such as parallel multi beam processing and volumetric manufacturing technology to improve processing efficiency is also in line with the standards of large-scale production;

3. Currently, most research focuses on distributing laser energy density in the spot according to Gaussian distribution, and there is little research on other types of beam processing;

4. Whether it is picosecond or femtosecond, the interaction mechanism between ultrafast lasers and semiconductor materials is still unclear, which requires further research on the interaction mechanism and the proposal of more accurate physical models.

Source: Yangtze River Delta Laser Alliance