Deposition is the general term for the process of forming a thin film on the surface of a wafer.

 

The types of films formed are extremely varied, including:

・Insulating films (SiO₂, SiN, low-k materials)

・Metal films (Cu, Al, Ti, W)

・Barrier films (TiN, TaN)

・Gate materials (W, HfO₂)

・Protective films (SiN)

 

In semiconductor processing, the ability to form the right film, in the right place, at the right thickness and quality, is what ultimately determines device performance.

Deposition methods fall broadly into two categories:

(1) CVD (Chemical Vapor Deposition)

A method in which a film is deposited through a chemical reaction between gaseous source materials.

 

(2) PVD (Physical Vapor Deposition)

A method in which a film is formed by physically evaporating or ejecting material from a source.

 

Understanding this basic distinction is the key to understanding deposition technology.

CVD can be further divided into the following methods:

LPCVD (Low Pressure CVD)

・Achieves high film uniformity through low-pressure processing.

・Used for polysilicon and SiN films, among others.

・Operates at high temperature (600–800°C).

 

PECVD (Plasma Enhanced CVD)

・Uses plasma to enable deposition at lower temperatures (300–400°C).

・Widely used for BEOL processing and passivation films.

・Its low-temperature process makes it compatible with glass substrates and multilayer structures.

 

MOCVD (Metal-Organic CVD)

・Essential for GaN, LEDs, and compound semiconductors.

・Used for growing epitaxial films such as AlGaN/GaN HEMT structures.

 

ALD (Atomic Layer Deposition)

・Builds films one atomic layer at a time — the ultimate in thin-film control.

・Essential for high-k gate layers and barrier films in 3D structures.

・Enables atomic-level control over film thickness.

 

As miniaturization progresses further, the importance of ALD and MOCVD continues to grow.

Sputtering

・Forms a film by using ions to knock atoms off a target (a metal source).

・Used for Cu, Ti, TiN, Al, and other wiring and barrier films.

・Operates at relatively low temperature and high speed.

 

Evaporation

・Forms a film by heating a material until it evaporates and deposits onto the wafer.

・Used in research applications and for certain specific metal films.

・In industrial mass production, sputtering remains the dominant method.

The thin films formed during this process must satisfy several requirements:

・Film thickness uniformity (across-wafer uniformity)

・Density (higher density means higher reliability)

・Step coverage

・Barrier properties (preventing copper from diffusing into silicon)

・Dielectric constant (using low-k materials to reduce signal delay)

・Mechanical strength and stress

 

In particular, low-k materials — insulating films with a low dielectric constant — are critical for fine-pitch wiring, because they reduce RC delay in the wiring and improve operating speed.

Representative materials for each application include:

Insulating films

・SiO₂

・SiN

・Low-k materials (SiOC, SiOF)

 

Metal wiring

・Cu (copper)

・Al

・W (tungsten) — used as a contact material

 

Barrier films

・TiN

・TaN

・Manganese-based barriers (a next-generation option)

 

Gate materials

・High-k materials (HfO₂)

・Metal gates (TiN, W)

 

As wiring continues to shrink, barrier film and low-dielectric-constant film technology become increasingly critical.

Adapting to 3D structures

As structures grow more complex — moving from FinFET to GAA to 3D NAND — ALD has become essential for depositing uniform films along sidewalls.

 

Research into barrier-free wiring

As copper wiring approaches its own limits, research is progressing into alternatives such as ruthenium, cobalt, and graphene-based barriers.

 

Mechanical strength challenges with low-k materials

Because lowering a material’s dielectric constant tends to make it more brittle, controlling stress and developing hybrid materials remain key challenges.

・Deposition is the core process for forming thin films, built around the two fundamental methods of CVD and PVD.

・ALD becomes increasingly important as devices continue to shrink.

・Materials are clearly matched to specific applications.

・As wiring shrinks and 3D structures become more common, the importance of deposition technology continues to grow.

・Barrier films and low-k films will play a decisive role in the future speed of wiring.

1.Explain the difference between CVD and PVD.

2.Why has ALD become increasingly important?

3.What is the purpose of using low-k materials?

 

Column Supervisor: Koji Kakumoto (Otis Group Co., Ltd.)

After studying abroad and working in planning and development at a trading company, he joined Otis Group Co., Ltd. in 2011. While primarily working in the Corporate Planning Department, he has also served concurrently in manufacturing and technical divisions, and since 2018 has served as Representative Director, working to drive business growth and strengthen the organization.

 

This article is a general technical explanation intended for educational purposes and does not refer to any specific company, product, or technology.