반도체공정 과제

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1. Comparison of conventional MOSFET and Fin FET

MOSFET(Metal Oxide Semiconductor Field Effect Transistor)은 4개의 단자(source, drain, gate, 기판의 접지)로 구성되어 있으며 금속-산화물-반도체 구조로 이루어져 있습니다. 평면(2D) 구조를 가지고 있습니다. FinFET(Fin Field Effect Transistor)은 트랜지스터 모양이 물고기 지느러미를 닮아 붙여진 이름입니다. MOSFET의 집적도를 높이기 위해 채널 길이를 줄이다 보면 여러 문제점이 발생하는데, 이를 보완한 것이 3D 입체 구조를 가진 FinFET입니다. FinFET은 MOSFET보다 gate와 channel이 만나는 면적이 넓어 더 많은 carrier가 움직일 수 있게 되어 성능이 향상되었습니다.
2. MOSFET의 동작원리 및 특징

n채널 MOSFET의 경우 gate에 전압을 인가하면 수직방향으로 전기장이 형성되어 반도체 영역까지 영향을 미칩니다. 전압에 의해 p형 기판의 전자 또는 정공들이 끌려와 전자 또는 정공 층을 형성시킵니다. gate에 -전압을 인가하면 산화물 근처로 정공들이 쌓여 전자가 이동을 못하는 accumulation 상태가 되고, +전압을 인가하면 산화물 근처로 전자들이 쌓여 전자가 이동할 수 있는 inversion 상태가 됩니다. p채널 MOSFET의 경우 반대로 음의 전압을 걸어주면 정공층을 형성시켜 채널 영역이 형성됩니다.
3. FinFET의 동작원리 및 특징

FinFET의 동작원리도 MOSFET과 거의 유사합니다. FinFET은 p-channel과 n-channel에 대해 두 가지 모드로 기능할 수 있으며 enhancement mode와 depletion mode가 있습니다. gate 단자에 전압이 인가되지 않을 때 채널에 최대 전도도를 보여주며, - 또는 + 전압이 인가되어 변화함에 따라 채널의 전도율은 감소합니다. Enhancement mode에서는 gate 단자에 전압이 인가되지 않을 때 전도되지 않으며, depletion mode에 비해 enhancement mode에서는 gate 단자에 전압이 더 높을 때 장치가 더 잘 작동합니다.
4. MOSFET 공정 순서

MOSFET 공정 순서는 다음과 같습니다: Thermal oxidation - CVD nitride deposition - active area mask - boron field implant - thermal field oxidation - Remove nitride and oxide pad - Regrow thin gate oxide - Boron threshold adjustment implant - CVD polysilicon depostion - Gate defintion - Source/drain implantation - source/drain diffusion - Cvd oxide deposition - contact openings - metal depostion - pattern metal - etch metal - passication layer deposition - open bonding pads.
5. FinFET 공정 순서

FinFET 공정 순서는 다음과 같습니다: substrate - fin etching - oxide deposition - planarization - Recess etch - Gate oxide deposition of the gate. 마지막으로 높은 n+ 도핑된 폴리 실리콘 층이 핀 위에 증착되므로 최대 3개의 게이트가 채널 주위를 감싸고 있습니다. 채널의 상부에 산화물 층의 증착에 의해 상부 게이트의 영향도 억제될 수 있습니다.
6. Comparison of SOI and Bulk FinFET

Bulk FinFET의 경우 실리콘을 기판으로 사용하는 대신에 절연기판을 사용하여 기기 특성과 회로 성능을 개선할 수 있습니다. SOI FinFET의 경우 single-device로 구성되어 서로 절연되어 있는 특성을 가지고 있습니다. Bulk와 SOI 모두 gate에 의해 커패시턴스 역할을 합니다. SOI FinFET은 TRIANGLE Hfin#이 작은 장점이 있고, Bulk FinFET은 TRIANGLE Hfin#이 크다는 단점이 있습니다. Bulk가 SOI FinFET에 비해 싸고 열에 대해 문제점이 덜 하다는 것이 장점입니다.

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1. Comparison of conventional MOSFET and Fin FET

The conventional MOSFET and FinFET are both important transistor structures in the field of semiconductor technology, but they have distinct differences in their design, fabrication, and performance characteristics. The conventional MOSFET has a planar structure with a single gate electrode, while the FinFET has a three-dimensional (3D) structure with a fin-shaped channel and multiple gate electrodes. The FinFET design offers better control over the channel, leading to improved short-channel effects, higher drive current, and better scalability compared to the conventional MOSFET. However, the fabrication of FinFETs is more complex and requires advanced lithography and etching techniques. The choice between the two transistor structures depends on the specific application requirements, such as power consumption, performance, and scalability. Both technologies have their own advantages and disadvantages, and the selection of the appropriate transistor structure is crucial for the continued advancement of semiconductor devices.
2. FinFET's operating principle and characteristics

The FinFET (Fin Field-Effect Transistor) is a three-dimensional (3D) transistor structure that has emerged as a solution to the scaling challenges faced by the conventional planar MOSFET. The FinFET's operating principle is based on the field-effect, similar to the MOSFET, but with a key difference in its structure. The FinFET has a fin-shaped channel, with the gate electrode wrapping around the fin, providing better control over the channel and improved electrostatic integrity. This 3D structure allows for better scaling, reduced short-channel effects, and higher drive current compared to the planar MOSFET. The FinFET's characteristics include improved subthreshold swing, higher on-current, and lower off-current, making it a more suitable choice for low-power and high-performance applications. The fabrication of FinFETs, however, is more complex and requires advanced lithography and etching techniques. Understanding the FinFET's operating principle and characteristics is crucial for the continued advancement of semiconductor technology and the development of high-performance, energy-efficient electronic devices.
3. FinFET fabrication process sequence

The fabrication process of a FinFET (Fin Field-Effect Transistor) is more complex compared to the conventional planar MOSFET, but it is necessary to overcome the scaling challenges faced by the latter. The typical FinFET fabrication process sequence includes the following key steps: 1. Substrate preparation: The process starts with a clean, high-quality semiconductor substrate, typically silicon. 2. Fin formation: Vertical fin structures are etched into the substrate using advanced lithography and etching techniques. 3. Isolation formation: The fins are isolated from each other using a shallow trench isolation (STI) process. 4. Gate stack formation: The gate oxide is grown or deposited, followed by the deposition and patterning of the gate electrode material, typically polysilicon or metal, which wraps around the fin. 5. Source/drain formation: Dopants are implanted into the fin structures to create the source and drain regions of the FinFET. 6. Silicidation: A metal-semiconductor alloy (silicide) is formed on the source, drain, and gate regions to reduce contact resistance. 7. Interconnect formation: Multiple layers of metal interconnects are fabricated to connect the FinFET to other components in the circuit. 8. Passivation and packaging: The device is encapsulated in a protective layer and packaged for integration into electronic systems. The FinFET fabrication process requires advanced techniques, such as fin patterning, gate-all-around (GAA) structure formation, and high-aspect-ratio etching, to achieve the desired 3D structure and performance characteristics. Understanding the FinFET fabrication process sequence is crucial for optimizing device performance, improving manufacturing yield, and driving the continued advancement of semiconductor technology.
4. Comparison of SOI and Bulk FinFET

The choice between SOI (Silicon-on-Insulator) and Bulk FinFET technologies is an important consideration in the design and fabrication of advanced semiconductor devices. Both technologies have their own advantages and disadvantages, and the selection depends on the specific application requirements. The key differences between SOI and Bulk FinFET include: 1. Substrate structure: SOI FinFETs are fabricated on an insulating substrate, typically a buried oxide (BOX) layer, while Bulk FinFETs are fabricated on a standard silicon substrate. 2. Isolation: SOI FinFETs have better isolation between devices due to the insulating BOX layer, which reduces parasitic capacitances and improves device performance. Bulk FinFETs rely on shallow trench isolation (STI) for device isolation. 3. Leakage and power consumption: SOI FinFETs generally have lower off-state leakage and power consumption compared to Bulk FinFETs, making them more suitable for low-power applications. 4. Fabrication complexity: The fabrication of SOI FinFETs is more complex and expensive compared to Bulk FinFETs, as it requires the creation of the SOI substrate. 5. Scalability: Both SOI and Bulk FinFET technologies have demonstrated scalability, but Bulk FinFETs may have a slight advantage in terms of cost-effective scaling. The choice between SOI and Bulk FinFET depends on the specific performance, power, and cost requirements of the application. SOI FinFETs are often preferred for high-performance, low-power applications, while Bulk FinFETs may be more suitable for cost-sensitive, high-volume applications. Understanding the trade-offs between these two FinFET technologies is crucial for the continued advancement of semiconductor devices and the development of innovative electronic systems.

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