As semiconductor devices evolve toward three-dimensional and highly integrated structures, MEMS, 3D NAND memory and advanced packaging increasingly require silicon structures with higher aspect ratios. High-aspect-ratio silicon etching and drilling have become core bottlenecks limiting device performance. Higher aspect ratios can cause etch rate reduction, sidewall roughness and hole-shape distortion. Achieving high precision, high stability and low-damage processing has therefore become an urgent industry challenge.
Mainstream processes for high-aspect-ratio silicon etching and drilling can be divided into dry etching and laser drilling, each with advantages and limitations and both moving toward integrated optimization. In dry etching, the Bosch process is widely used. By alternating SF₆ etching and C₄F₈ passivation cycles, it can process structures with aspect ratios above 50:1. However, the alternating cycles can create scalloped sidewalls, and the equipment cost is high with limited process flexibility. Cryogenic deep reactive ion etching can effectively improve sidewall roughness and is suitable for optical devices that require high precision, but strict low-temperature control increases process complexity.
Laser drilling has become an important supplement for high-aspect-ratio silicon through-holes because of its high processing efficiency. Femtosecond laser processing, due to its non-thermal ablation characteristics, can achieve precision machining with a narrow heat-affected zone and avoid surface pits and damage caused by heat accumulation in nanosecond laser processing. However, single-pulse femtosecond processing may generate residual stress and plasma shielding effects, while burst-mode processing may cause surface defects due to heat accumulation. Both can affect processing quality.
The main challenges of high-aspect-ratio processing are concentrated in three areas. First is aspect-ratio-dependent etching: as depth increases, etching ions have difficulty reaching the bottom vertically, leading to rate reduction and tapered hole profiles. Second is sidewall quality control. Scalloping in the Bosch process and thermal damage in laser processing both affect the mechanical and electrical performance of devices. Third is insufficient uniformity and repeatability. Large-area wafer processing can produce regional differences that are difficult to meet industrial production requirements.
To address these challenges, the industry has developed several key technical breakthroughs. In process optimization, hybrid multi-step femtosecond laser drilling combines the advantages of single-pulse and burst modes. Through a three-step flow—guide hole formation, through-hole drilling and pit trimming—it can increase aspect ratio by 1.7 times and improve sidewall roughness by 59.3%, effectively reducing laser-processing defects. In etching processes, optimizing gas ratios and RF power, combined with atomic layer deposition hard-mask technology, can improve etch selectivity and reduce substrate damage.
Equipment and inspection improvements are also critical. High-precision plasma sources help maintain ion directionality, while zoned temperature-control systems improve wafer processing uniformity. Real-time monitoring and endpoint detection can precisely control processing depth and prevent over-etching or incomplete etching. In addition, pure laser processing without auxiliary equipment reduces cost and maintenance difficulty and is better suited for high-density semiconductor packaging needs.
In the future, as device integration continues to increase, high-aspect-ratio silicon etching and drilling will develop toward higher aspect ratios, lower damage and higher efficiency. The industrial application of new technologies such as atomic layer etching and electron-beam-induced etching will further break through current process limits. Process integration will become a major trend and provide core support for the miniaturization and performance improvement of semiconductor devices.
