Front-End Process in Chip Manufacturing: Thin Film Deposition

Front-End Process in Chip Manufacturing: Thin Film Deposition

Integrated circuits are composed of many complex and refined fabrication steps, among which thin film desposition is one of the most critical technologies. The purpose of thin film deposition is to build multilayer stacks in semiconductor devices and ensure insulation between layers of metal. Multiple conductive metal layers and dielectric insulating layers are alternately stacked on the wafer surface. These are then selectively removed via repeated etching processes to form a 3D structure.

The term thin typically refers to films with a thickness of less than 1 micron, which cannot be produced by conventional mechanical machining. The process of attaching these molecular or atomic films onto the wafer surface is called desposition.

Depending on the underlying principle, thin film deposition techniques are generally categorized into:

• Chemical Vapor Deposition (CVD)

• Physical Vapor Deposition (PVD)

• Atomic Layer Deposition (ALD)

As thin film technology has evolved, various deposition systems have emerged to serve different steps of wafer fabrication.

▌Physical Vapor Deposition (PVD)

PVD refers to a group of vacuum-based processes that use physical means to vaporize the target material (solid or liquid) into atoms or molecules, or partially ionize them, and transport them through low-pressure gas or plasma to deposit functional films onto the substrate.

Common PVD methods include:

• Evaporation deposition

• Sputter deposition

• Arc plasma deposition

• Ion plating

• Molecular beam epitaxy (MBE)

PVD is characterized by:

• High film purity

• Stable film quality

• Lower processing temperatures

• High deposition rates

• Relatively low manufacturing cost

PVD is mainly used for depositing metal films, and not suitable for insulating films. The reason is that when positive ions bombard an insulating target, they transfer kinetic energy to the target surface, but the positive ions them mainly used for depositing metal filmsselves accumulate on the surface. This charge buildup generates an electric field that repels incoming ions and eventually halts the sputtering process.

● Vacuum Evaporation

In a vacuum environment, the target material is heated and evaporated. Atoms or molecules vaporize from the surface and travel with minimal collision through vacuum to deposit on the substrate. Common heating methods include:

• Resistive heating

• High-frequency induction

• Electron beam, laser beam, or ion beam bombardment

● Sputter Deposition

In vacuum, high-energy particles (typically Ar⁺ ions) bombard the target surface, causing atoms to be ejected and deposited onto the substrate.

● Ion Plating

Ion plating uses plasma to ionize the coating material into ions and high-energy neutral atoms. A negative bias is applied to the substrate, attracting the ions to deposit and form a thin film.

▌Chemical Vapor Deposition (CVD)

CVD utilizes chemical reactions to deposit thin films. Reactant gases are introduced into a reaction chamber and activated using heat, plasma, or light. These gases react chemically to form the desired solid film on the substrate, while by-products are exhausted from the chamber.

CVD includes many variants depending on the conditions:

• Atmospheric Pressure CVD (APCVD)

• Low Pressure CVD (LPCVD)

• Plasma Enhanced CVD (PECVD)

• High Density PECVD (HDPECVD)

• Metal-Organic CVD (MOCVD)

• Atomic Layer Deposition (ALD)

CVD films generally exhibit:

• High purity

• Superior performance
  It is the mainstream method for fabricating metal, dielectric, and semiconductor films in chip manufacturing.

● APCVD

Performed at atmospheric pressure and 400–800 °C, used for producing films such as:

• Single-crystal silicon

• Polycrystalline silicon

• Silicon dioxide (SiO₂)

• Doped SiO₂

● LPCVD

Applied in >90nm processes for producing:

• SiO₂, PSG/BPSG

• Silicon nitride (Si₃N₄)

• Polysilicon

● PECVD

Widely used in 28–90 nm nodes for depositing dielectric and semiconductor materials.
Advantages:

• Lower deposition temperatures

• Higher film density and purity

• Faster deposition rates
  PECVD systems have become the most widely used thin film tools in fabs compared to APCVD and LPCVD.

▌Atomic Layer Deposition (ALD)

ALD is a special type of CVD that enables ultra-thin film growth by depositing one atomic layer at a time via self-limiting surface reactions.

Unlike conventional CVD, ALD alternates precursor pulses. Each layer is formed by a sequential surface reaction with the previously deposited layer. This enables:

• Atomic-scale thickness control

• Conformal coverage

• Pinhole-free films

ALD supports deposition of:

• Metals

• Oxides

• Carbides, nitrides, sulfides, silicides

• Semiconductors and superconductors

As integration density increases and device sizes shrink, high-k dielectrics are replacing SiO₂ in transistor gates. ALD’s excellent step coverage and precise thickness control make it ideal for advanced device fabrication and is increasingly adopted in cutting-edge chip production.

▌Comparison of Deposition Technologies

● Film Deposition Performance

(Here you may insert a comparative table of conformality, thickness control, step coverage, etc.)

● Technologies and Applications

(Insert table showing PVD vs. CVD vs. ALD use cases)

● Equipment & Capabilities

(Insert table comparing deposition rates, temperatures, uniformity, costs)

Conclusion

The advancement of thin film deposition technologies is essential to the continued development of the semiconductor industry. These processes are becoming more diverse and specialized, enabling further innovation and refinement in integrated circuit manufacturing.