One-Step laser process achieves compatibility between semiconductor characteristics and CMOS process

A new type of laser technology can regulate semiconductor conductivity characteristics in a fast and low-cost manner, which will revolutionize the manufacturing process of CMOS circuits and make them more simplified and efficient.

Laser-induced oxidation and doping integration (LODI), a technology developed by researchers at Daegu Gyeongbuk Institute of Science and Technology (DGIST), enables precise, p-type doping in titanium oxide (TiO2), an n-type semiconductor, by adjusting laser power to control dopant diffusion and oxidation at the same time. LODI achieves simultaneous oxidation and doping with just one laser irradiation.

TiO2 is valued for its non-toxicity, abundance, and superior chemical and thermal stability. Its wide, but relatively small, bandgap endows it with tunable properties that, combined with high transparency, make it suitable for applications in gas sensors, thin film transistors, memory devices, and transparent displays.

Concept of laser oxidation and surface analysis of titanium oxide (TiO2)

But, because TiO2 works as an n-type semiconductor, there are significant constraints on using it with CMOS circuits, which require both n-type and p-type conductivity to achieve balanced, efficient performance. CMOS circuitry is used to power many advanced electronic devices, including smartphones and computers.

To obtain stable p-type conductivity in TiO2, the researchers placed an aluminum oxide (Al2O3) film on top of a thin metal film of titanium (Ti) and irradiated it with a continuous wave laser for a few seconds. Aluminum (Al) ions diffused inside the lattice as the Ti combined with oxygen (O) to convert into TiO2. The balance of electrons broke down during this process, creating holes and then forming a p-type semiconductor in which holes, instead of electrons, carried current.

The researchers confirmed the formation of TiO2 and the incorporation of Al dopants using x-ray photoelectron spectroscopy and energy dispersive spectroscopy transmission electron microscopy. In addition, they fabricated laser-oxidized, Al-doped TiO2 thin film transistors to demonstrate that Al doping improved hole current and photostability.

The conventional approach to converting TiO2 semiconductors into p-type conductors is a complex, hours-long process that requires high-temperature thermal treatment and vacuum ion implantation. It also involves expensive equipment and a high vacuum environment, which limits its potential for commercialization.

The LODI process offers significant advantages over conventional methods. LODI allows for rapid fabrication under ambient conditions while minimizing thermal damage to the substrate and surrounding materials, preserving the integrity of underlying layers. It eliminates the need for separate photolithography and deposition processes, which are typically required for oxide channel formation. Oxidation is completed within seconds, significantly accelerating the process compared to traditional techniques.

By integrating lithography, oxide deposition, and doping into one process, LODI streamlines semiconductor fabrication, achieving the same effect as traditional methods in just a few seconds and with just one laser. Considered by the research team to be a next-generation semiconductor manufacturing technology, LODI performs oxidation, doping, and patterning simultaneously and significantly lessens process time and cost. It provides an easy, simple, efficient, and controllable method to convert TiO2 for CMOS technology and advanced electronic devices.

“This study holds significance as it converts titanium oxide semiconductors, which have been mainly used in the n-type, to the p-type while streamlining the conventional complex process into a single laser process,” professor Hyukjun Kwon said. “This original technology, that can precisely control the conductivity type of oxide semiconductors, will serve as a foundation for implementing next-gen, highly integrated, and reliable devices.”

Source: photonics