Unlocking the potential of 3D ICs: Tackling atomic-level impurities in silicon surfaces

As semiconductor technology continues to push the boundaries of miniaturization, 3D integrated circuits (three-dimensional, 3D ICs) are emerging as a promising solution to deliver increased performance, energy efficiency and functionality. By stacking multiple layers of circuitry vertically, 3D ICs offer significant advantages over traditional ICs in two dimensions, such as reduced interconnect distances, improved signal speed and better thermal management. However, despite these benefits, there are plenty of challenges that are delaying the utilization of 3D ICs beyond advanced data center use. Furthermore, atomic- level defects and contamination in silicon surfaces can impede the full potential of these advanced chips.

The benefits and challenges of 3D ICs 

3D ICs are fundamentally transforming the way semiconductors are designed and manufactured. Some of their key benefits include increased performance, energy efficiency, and compactness and integration.  

By stacking chips vertically, 3D ICs minimize the physical distance between layers, resulting in faster data transfer speeds and lower latency. 3D ICs can incorporate more functionality within the same footprint, allowing for enhanced parallel processing and improved system throughput. 

Shorter interconnects lead to lower resistance and capacitance, reducing the amount of power needed for signal transmission. With better heat dissipation from the stacked layers, 3D ICs can be more efficient at managing power and heat. 

More transistors and components can be packed into a smaller space, enabling the development of more powerful and compact devices. Different types of chips (e.g., logic, memory, sensors) can be integrated within a single package, improving system-level performance and flexibility. 

3D structures face, however, major challenges, such as thermal management, reliability and manufacturing complexity. Due to stacking multiple layers, heat dissipation becomes difficult. Integrating multiple layers can increase chances of defects and failures, raising reliability concerns. The manufacturing process of 3D ICs is more complex than in traditional methods, requiring precise control and advanced equipment.  

Atomic-level defects and contamination in 3D components 

While 3D ICs promise tremendous advantages, achieving these benefits requires addressing several challenges—one of the root causes behind them are atomic-level defects and contamination on the silicon surfaces. 

Silicon surfaces, when exposed to environmental conditions or handling during fabrication, can suffer from atomic-scale defects, such as: Misalignments in the crystal lattice can create areas of stress, negatively impacting the electrical performance of transistors. Vacancies or interstitials in the silicon structure can alter the behaviour of electrical carriers and disrupt the functionality of devices. These defects can degrade the performance of the 3D ICs, causing issues such as increased leakage currents, slower switching speeds, and higher power consumption. 

Contaminants like metals, organic residues, and particles can adhere to silicon surfaces during manufacturing. These impurities cause significant issues: Contaminants can interfere with the formation of thin, uniform layers required for high-performance semiconductor devices. They can create localized electric fields, which trap charges and disrupt the behaviour of transistors, leading to increased noise, reduced reliability and lower yield. In a stacked configuration like 3D ICs, the impact of contamination is magnified due to the close proximity of layers and the increased complexity of interconnects between them. 

In the fabrication of 3D ICs, atomic-level defects and contamination on the silicon surfaces can create significant obstacles that hinder performance and reliability. These issues arise primarily during handling, processing and layering of the chips. For example, contaminants can prevent proper bonding between stacked layers of the 3D IC, causing delamination or poor interconnect performance, which further impacts device efficiency and yield. 

Current solutions and their limitations 

To tackle these issues, several cleaning and surface treatment methods, such as plasma etching and cleaning as well as chemical cleaning and annealing processes, have been developed. However, each comes with its own set of limitations. 

Plasma treatment can remove organic contaminants and etch silicon surfaces at the atomic level, improving adhesion between layers. Plasma cleaning can also introduce defects, such as ion bombardment-induced damage or surface roughening. Additionally, plasma methods often fail to fully address subatomic-scale contamination. 

Chemical solutions, such as HF-based treatments, can effectively remove organic residues and oxides from the surface. These chemicals are harsh and can etch or damage the silicon, leading to degradation in the material's structural integrity. Moreover, they may not be able to eliminate certain metal contaminants or restore the crystalline structure. 

High-temperature annealing can repair some of the atomic-level defects by allowing atoms to move into a more stable configuration. Annealing can also result in oxidation or other unwanted side reactions, and temperatures above 450°C can be detrimental to sensitive 3D IC structures, potentially causing warping or delamination. 

The SisuSemi process: A superior solution for 3D ICs 

SisuSemi takes a unique approach to silicon surface cleaning and treatment, leveraging an advanced technique that combines Ultra High Vacuum (UHV), elevated temperatures (< 450°C) and controlled oxidation. The process addresses key challenges faced by 3D ICs: 

The UHV environment ensures that the silicon surface is exposed to minimal contaminants during the cleaning process, eliminating airborne particles and chemical impurities that could compromise the integrity of the silicon. UHV allows for precise control of atomic interactions, ensuring that the silicon surface is thoroughly cleaned without introducing additional defects. 

By heating the silicon to controlled temperatures under UHV conditions, the surface atoms are able to move and reorganize, helping to restore the crystalline structure. This process helps eliminate dislocations and vacancies, leading to improved material properties. Temperatures below 450°C are carefully selected to prevent warping or damage to the sensitive 3D IC structures while still promoting the reordering of surface atoms. 

A very thin and controlled layer of silicon dioxide (SiO2) is formed on the silicon surface. This layer acts as a protective barrier, preventing further contamination and providing a stable foundation for additional processing steps. The SiO2 layer enhances adhesion and ensures that subsequent layers of material or devices integrate seamlessly with the silicon substrate, promoting better performance and reliability in the final 3D ICs. 

How SisuSemi’s process enhances 3D ICs 

By restoring the silicon surface's crystalline structure and forming a stable, protective SiO2 layer, SisuSemi's approach directly addresses the issues caused by atomic-level defects and contamination. The process ensures that: 

• The silicon surfaces are freed from contaminants that could degrade performance 

• The crystalline structure of the silicon is preserved, improving the integrity of the 3D ICs. 

• The thin oxide layer enhances the reliability and longevity of the ICs, ensuring that they deliver the promised benefits of 3D stacking—improved performance, energy efficiency and miniaturization. 

3D ICs offer incredible potential for next-generation electronics, but to realize these benefits, also the challenges of atomic-level defects and contamination must be addressed. While current solutions like plasma cleaning, chemical treatments, and annealing provide partial relief, they are often limited in their effectiveness. 

SisuSemi’s advanced cleaning process, utilizing Ultra High Vacuum, controlled temperatures and oxidation, offers a comprehensive solution to these issues, enabling the full potential of 3D ICs. By ensuring clean, defect-free silicon surfaces with a stable oxide layer, this process sets the stage for creating high-performance, energy-efficient and reliable 3D ICs that can meet the growing demands of modern electronics.