Nikon I-Line Steppers in Semiconductor Manufacturing

1. Introduction

Nikon has long been a leader in the development and production of photolithography equipment, a key technology in the semiconductor manufacturing process. Among their contributions, the NSR-i series of I-Line steppers has been instrumental in enabling the production of semiconductor devices across a wide range of process nodes, from legacy to advanced nodes. These steppers are used primarily for photolithography processes, where light is projected onto a photoresist-coated wafer to create intricate circuit patterns essential for modern electronic devices.

The I-Line steppers are built on the foundation of Nikon’s experience in producing high-precision lithography systems. These systems are vital for fabricating semiconductors used in applications ranging from microprocessors and memory chips to increasingly complex devices like logic ICs. With an emphasis on high resolution, accuracy, and throughput, the NSR-i series offers a variety of models to meet the needs of different manufacturing nodes.

This article provides a detailed exploration of the Nikon NSR-i series models—NSR-2005i, NSR-2205i, NSR-2210i, NSR-2245i, NSR-2255i, and NSR-2305i—highlighting their individual features, comparing their capabilities, and examining the technological advancements that have shaped their evolution.

2. What is I-Line Lithography?

I-Line lithography refers to a specific photolithographic process that uses light with a wavelength of 365 nm to transfer patterns onto a silicon wafer. This wavelength falls in the ultraviolet (UV) spectrum and is commonly used for semiconductor nodes at 180nm, 130nm, and 90nm, with certain models like the NSR-2255i and NSR-2305i extending capabilities to smaller nodes.

In semiconductor photolithography, the light is passed through a mask containing the desired circuit pattern and then projected onto a photoresist-coated wafer. The photoresist undergoes chemical changes upon exposure, and the exposed regions are developed to create the final pattern. The precision and resolution of this process are critical for achieving the miniaturized transistors that define modern semiconductor technology.

Key Characteristics of I-Line Lithography:

• Wavelength: 365 nm
• Resolution: Ideal for producing nodes from 180nm to 90nm (for advanced models)
• Masking and Alignment: I-Line steppers use advanced mask aligners and precise wafer handling systems to ensure high-quality pattern transfer.
• Depth of Focus: One of the critical parameters in I-Line lithography that ensures consistent focus across the wafer.

I-Line lithography is known for its balance of high resolution and cost-effectiveness, particularly when compared to KrF (248 nm) and ArF (193 nm) lithography technologies, which are more commonly used in the production of advanced nodes below 45nm.

3. Detailed Overview of Nikon’s NSR-i Series Models

Nikon’s NSR-i series represents a progression of I-Line steppers designed to handle increasingly demanding semiconductor production requirements. Over the years, Nikon has improved both optical systems and wafer handling to meet the needs of different nodes. Let’s explore the key models in this series:

NSR-2005i

• Introduction: The NSR-2005i was an early model in Nikon's I-Line stepper lineup, primarily designed for legacy node production. It is well-suited for 180nm and 130nm processes, with a focus on memory and logic applications.
• Key Features:
  • Throughput: High throughput for medium-sized wafers.
  • Resolution: Good resolution for larger nodes (down to 180nm).
  • Wafer Size: Typically supports 200mm wafers.
• Applications: Primarily used in the production of DRAM, flash memory, and other less complex logic devices.
• Limitations: Less capable for smaller nodes below 90nm.

NSR-2205i

• Introduction: Building on the performance of the NSR-2005i, the NSR-2205i introduced improvements in exposure accuracy and throughput. This model was designed for the 130nm to 90nm process nodes and continued to be a staple in memory IC production.
• Key Features:
  • Resolution: Capable of resolving critical layers at 90nm.
  • Exposure Accuracy: Improved exposure systems to ensure precise pattern transfer.
  • Throughput: Enhanced throughput suitable for medium-volume production.
• Applications: Widely used for the production of logic ICs, microprocessors, and non-volatile memory.
• Limitations: Though it can handle smaller nodes, it is less efficient for cutting-edge, high-volume applications.

NSR-2210i

• Introduction: The NSR-2210i introduced Nikon’s more advanced optical systems and alignment accuracy capabilities, making it ideal for 90nm and 65nm nodes.
• Key Features:
  • Resolution: Excellent resolution at 90nm, with higher precision alignment and depth of focus improvements.
  • Optical Performance: Advanced lens and exposure system for finer detail reproduction.
  • Wafer Handling: Features a more robust and stable wafer handling system for high-volume production.
• Applications: Primarily used for microprocessor, logic IC, and flash memory manufacturing at 65nm and 90nm nodes.
• Limitations: While suitable for these nodes, it struggles with the most advanced processes below 45nm.

NSR-2245i

• Introduction: The NSR-2245i was designed with a focus on 65nm to 45nm nodes, featuring advanced optical and alignment technologies that improve pattern fidelity.
• Key Features:
  • Resolution: Excellent performance for 45nm nodes, offering high precision in pattern transfer.
  • Exposure Control: Highly precise exposure systems for critical layer lithography.
  • Wafer Size: Capable of handling 300mm wafers.
• Applications: Ideal for high-performance logic ICs, DRAM, and other complex devices at 45nm nodes and higher.
• Limitations: Limited capability in nodes smaller than 45nm due to the resolution constraints of I-Line technology.

NSR-2255i

• Introduction: The NSR-2255i represents Nikon's entry into the sub-45nm territory, offering improvements in exposure control and process optimization for cutting-edge semiconductor manufacturing.
• Key Features:
  • Resolution: Strong performance at 45nm and below, with high resolution and stable imaging.
  • Throughput: High throughput, suitable for advanced memory and logic devices at these nodes.
  • Optical System: Enhanced optics for better depth of focus and imaging precision.
• Applications: Primarily used for advanced logic ICs, flash memory, and system-on-chip (SoC) applications.
• Limitations: Although it handles 45nm nodes effectively, it faces challenges in sub-45nm production where EUV or immersion lithography would be more suitable.

NSR-2305i

• Introduction: The NSR-2305i is the most advanced model in the NSR-i series, designed for the most demanding applications at sub-45nm nodes.
• Key Features:
  • Resolution: High-resolution capabilities for sub-45nm and even 28nm process nodes.
  • Advanced Optical Systems: Cutting-edge optics for superior imaging performance, critical for advanced node manufacturing.
  • Throughput: High throughput for volume production of advanced semiconductors.
• Applications: Ideal for high-performance logic ICs, memory chips, and system-on-chip (SoC) devices at the smallest process nodes.
• Limitations: While it can handle the most advanced nodes, it still faces competition from newer EUV technology for nodes below 28nm.

4. Model-by-Model Comparison

When selecting a Nikon I-Line stepper for a specific semiconductor manufacturing process, it’s crucial to compare key features such as resolution, throughput, optical performance, and wafer handling capabilities. Below is a detailed comparison of the models in the NSR-i series, highlighting their strengths and how they cater to different production needs.

Resolution and Accuracy

One of the most critical aspects of an I-Line stepper is its ability to resolve fine features on the wafer. The I-Line wavelength of 365nm inherently limits the resolution compared to shorter wavelengths like KrF (248nm) or ArF (193nm), but Nikon has advanced the resolution capabilities of each NSR-i model for specific applications.

As we can see, NSR-2305i stands out as the most advanced in terms of resolution, enabling production at nodes down to 28nm, making it suitable for the most advanced semiconductor processes.

Throughput and Efficiency

Throughput is critical for high-volume production, particularly in industries like memory manufacturing. Nikon’s NSR-i series models provide excellent throughput, with later models offering better efficiency for smaller nodes, but typically with trade-offs in terms of exposure time and alignment precision.

Later models like the NSR-2255i and NSR-2305i significantly enhance throughput, critical for high-demand, high-volume production environments.

Optical Systems

Each model in the NSR-i series boasts improvements in optical performance over its predecessors, particularly in terms of lens quality, depth of focus, and light source stability. As nodes get smaller, these features become essential for ensuring pattern fidelity across the wafer.

The NSR-2305i model integrates the most advanced optical technologies, ensuring the best possible performance for next-gen semiconductor production.

5. Applications of Nikon I-Line Steppers in Semiconductor Manufacturing

The Nikon I-Line Steppers are integral to several key semiconductor manufacturing processes, especially for nodes above 28nm. While EUV (Extreme Ultraviolet Lithography) is increasingly used for sub-28nm nodes, I-Line steppers remain essential in the production of various devices. These include memory ICs, logic ICs, microprocessors, system-on-chip (SoC) devices, and power devices.

Memory Devices

I-Line lithography is widely used for the production of dynamic random-access memory (DRAM) and flash memory chips, especially at the 130nm to 65nm nodes. The NSR-2205i and NSR-2210i are commonly employed for high-volume memory production due to their ability to provide excellent resolution and throughput.

For flash memory, the NSR-2245i and NSR-2255i are more commonly used, as they offer superior performance for nodes below 90nm, which is critical for high-density flash memory chips.

Logic ICs

Logic integrated circuits (ICs), including processors and other computing devices, require precise patterning capabilities to ensure proper function at smaller nodes. The NSR-2255i and NSR-2305i are the ideal candidates for high-performance logic IC production, with 28nm or 22nm nodes, where fine feature resolution is crucial.

Additionally, SoC (System on Chip) devices, which are essential in modern consumer electronics, are manufactured using I-Line steppers. These devices often integrate multiple functionalities like processing, memory, and communications into a single chip, requiring high precision in the photolithography process.

Power Devices and Sensors

Power devices, such as MOSFETs (Metal-Oxide-Semiconductor Field-Effect Transistors), which are critical for power management in electronic systems, also benefit from the high-resolution capabilities of Nikon I-Line steppers. The NSR-2210i and NSR-2305i are suitable for these applications, supporting high-voltage and high-current process requirements at 65nm and 45nm nodes.

Sensors, including MEMS (Micro-Electro-Mechanical Systems) devices, which are used in automotive and industrial applications, also leverage the resolution capabilities of I-Line lithography, making Nikon's steppers key players in their production.

6. Advantages of Nikon I-Line Steppers

Nikon’s I-Line steppers, particularly those in the NSR-i series, provide several distinct advantages over other lithography tools, especially in mid-range nodes. These advantages include:

Cost-Effectiveness

Compared to the more advanced EUV or immersion lithography systems, Nikon’s I-Line steppers are more cost-effective, especially for legacy nodes (above 28nm). The cost of acquiring and maintaining an I-Line system is significantly lower, making it an attractive option for manufacturers focused on high-volume, cost-sensitive applications such as memory production.

High Throughput

Nikon’s I-Line steppers, particularly the NSR-2305i, are known for their high throughput, making them ideal for high-volume production. The throughput can be enhanced through continuous advancements in optical systems, exposure techniques, and alignment systems that allow the systems to handle complex patterns with minimal downtime.

Precision and Resolution

The NSR-2255i and NSR-2305i models are capable of achieving high pattern fidelity even at smaller nodes, ensuring the production of high-quality ICs. For applications requiring precision such as SoC or logic ICs, the ability to resolve fine features with minimal defects is crucial for yield optimization.

Versatility

One of the standout features of the I-Line stepper is its ability to cover a wide range of applications and node sizes, from 130nm to 28nm. The flexibility to support different production needs, including both memory and logic ICs, is a significant advantage over more specialized lithography tools.

7. Conclusion

Nikon's I-Line stepper series, particularly models like the NSR-2005i, NSR-2205i, NSR-2210i, NSR-2245i, NSR-2255i, and NSR-2305i, have been instrumental in the evolution of semiconductor photolithography. Despite the rise of advanced technologies like EUV, these I-Line systems remain indispensable for a wide range of applications, from legacy node production to high-performance logic and memory ICs.

The precision, throughput, and cost-effectiveness of Nikon's I-Line steppers will continue to support semiconductor manufacturers, particularly as they transition to advanced packaging and heterogeneous integration processes. These tools will remain an integral part of the semiconductor production ecosystem for years to come.