The landscape of semiconductor technology is undergoing significant transformations, particularly in the realm of transistor design and ESD (electrostatic discharge) protection mechanisms. As reported by In Compliance Magazine, the shift from conventional planar transistors to advanced multi-gate architectures has been pivotal, especially with the mainstream adoption of bulk FinFET structures for mobile System on Chips (SoCs).
Historically, Moore's Law, which observes that the number of transistors on a microchip doubles approximately every two years, relies heavily on the capability to scale transistor geometries. The current trend has seen the emergence of bulk Gate-All-Around (GAA) technology beyond the 3nm node. GAA technology has been gaining traction due to its enhanced electrostatic control and reduced leakage, promising significant improvements in performance for future devices.
A crucial factor in advancing these technologies is the implementation of double-sided connectivity through Backside Power Delivery Networks (BS-PDN). Introduced as a part of design technology co-optimization (DTCO), BS-PDN aims to improve the functional performance of logic scaling by enabling better separation of signal pathways from power delivery, thereby enhancing signal integrity across the chip assembly.
Achieving optimal performance with BS-PDN requires the utilisation of high-density through-silicon vias (TSVs) for connectivity between the front and back sides of silicon wafers. This need for high-density connections necessitates that silicon substrates be thinned to just a few hundred nanometers. However, this reduction brings about notable challenges, particularly in maintaining effective electrostatic discharge (ESD) protection, as adequate silicon volume is essential for proper discharge and heat dissipation.
Investigations into the effects of substrate thinning on ESD performance have highlighted differences between shallow trench isolation (STI) diodes and gated diodes. Simulations indicate that STI diodes made with extremely thin substrates are prone to failure under stress, while gated diodes exhibit comparatively improved resilience. The heightened current density observed in thinned STI structures underscores the fragility of ESD protection as dimensions shrink.
To counteract the challenges posed by thinner silicon substrates, a novel approach involving active backside (BS) technology has been proposed. This strategy introduces a p+ epitaxial layer and patterns for backside contacts, creating vertical diodes that promote area efficiency and enhance ESD current uniformity, thereby improving thermal dissipation.
Looking forward, the integration of GAA technology continues to evolve, with innovative designs such as the fork-shaped transistor architecture aimed at minimising spacing between p-type and n-type MOSFETs, thereby enhancing scalability beyond current nanosheet designs. Concurrently, the proposed complementary FET (CFET) technology, which involves stacking n-type on top of p-type MOSFETs, represents a significant shift in transistor architecture. However, CFET poses unique challenges for ESD security due to thin structural elements and the complexities introduced in designing compatible ESD protection mechanisms.
As these advancements unfold, the semiconductor industry stands on the brink of new capabilities that promise to reshape the future of AI automation and business integration, necessitating ongoing evaluation of the implications they carry for operational practices and system design.
Source: Noah Wire Services