In field-effect transistor (FET) manufacturing, controlling the short-channel effect is crucial for improving device performance and reliability. The short-channel effect arises when the channel length is shortened to a value equivalent to or less than the electron mean free path, weakening the gate's control over channel carriers and leading to problems such as decreased threshold voltage, increased leakage current, and degraded subthreshold swing. To address this challenge, the manufacturing process requires synergistic optimization across multiple dimensions, including materials, structure, doping, and process parameters.
Regarding material selection, the application of high-k materials significantly enhances the gate's electrostatic control over the channel. Traditional silicon dioxide gate dielectrics, due to thickness limitations, struggle to effectively penetrate the channel when the channel length shortens, exacerbating the short-channel effect. The introduction of high-k materials (such as hafnium oxide) increases the physical thickness while maintaining the same equivalent oxide layer thickness, reducing gate leakage current and enhancing the gate's control over the channel, thereby suppressing threshold voltage drift.
Innovation in device structure is one of the core directions for controlling the short-channel effect. Multi-gate structures (such as dual-gate, triple-gate, and gate-all-around (GAA) transistors significantly improve gate control by increasing the contact area between the gate and the channel, effectively enveloping the channel from multiple directions. For example, the GAA completely encloses the channel within the gate, ensuring a uniform gate electric field distribution around the channel and effectively suppressing short-channel effects, making it the mainstream structure for 5nm and below technology nodes. Furthermore, field effect transistors (FinFETs) increase the contact area between the gate and the channel by designing the channel in a fin shape, similarly achieving effective control of short-channel effects.
Channel doping engineering is a crucial method for optimizing short-channel effects. By using retrograde doping technology to form a high-concentration doped layer in the channel region, the scattering probability of channel carriers can be increased, and the carrier mobility reduced, thereby suppressing the increase in leakage current caused by short-channel effects. Meanwhile, halo implantation technology introduces a high-concentration doped region at the interface between the channel and the source/drain junction, forming a potential barrier that effectively blocks the drain electric field from penetrating to the source, further reducing the drain-induced barrier reduction (DIBL) effect and improving the device's subthreshold characteristics.
Ultra-shallow junction technology reduces the impact of the source/drain depletion region on the channel by precisely controlling the doping depth of the source/drain region. When the channel length shortens, the expansion of the source/drain depletion region significantly weakens the gate's control over the channel. Ultra-shallow junction technology maintains effective gate control over the channel by limiting the expansion range of the depletion region, thereby suppressing the short-channel effect. Furthermore, this technology can reduce source/drain resistance and increase the device's drive current.
Precise control of process parameters is equally crucial. During the gate oxide layer fabrication process, advanced processes such as atomic layer deposition (ALD) are required to achieve uniformity and precision in the gate oxide layer thickness, avoiding local electric field concentration caused by uneven thickness, which can lead to the short-channel effect. Meanwhile, optimization of the photolithography process ensures precise control of the channel length, avoiding performance inconsistencies caused by channel length deviations.
Silicon-on-insulator (SOI) technology achieves electrical isolation between the device and the substrate by forming a single-crystal silicon thin film on an insulating layer, effectively reducing parasitic capacitance and leakage current. In short-channel devices, the SOI structure can suppress the influence of the substrate electric field on the channel, reduce the DIBL effect, and improve the subthreshold characteristics and reliability of the device.
