Overview of Key CVD Technologies in Semiconductor Research

Chemical Vapor Deposition (CVD) is the most widely used technology in the semiconductor industry for depositing various materials, including a wide range of insulating materials and most metal and metal alloy materials.

CVD is a traditional thin film preparation technique that utilizes gaseous precursors. Through chemical reactions between atoms and molecules, certain components of the precursors decompose, forming a thin film on the substrate. The basic characteristics of CVD include: the generation of chemical changes (chemical reactions or thermal decomposition); all materials in the film originate from external sources; reactants must participate in the reaction in gas phase.

Low Pressure CVD (LPCVD), Plasma Enhanced CVD (PECVD), and High-Density Plasma CVD (HDP-CVD) are three common CVD technologies that differ significantly in material deposition, equipment requirements, and process conditions. Below is a brief explanation and comparison of these three technologies.

1. LPCVD (Low Pressure CVD)  

Principle: LPCVD is a CVD process conducted under low-pressure conditions. It involves injecting reactant gases into a reaction chamber under vacuum or low pressure and using high temperatures to decompose or react the gases to form solid thin films deposited on the substrate surface. The low pressure reduces gas collisions and turbulence, enhancing the uniformity and quality of the films. LPCVD is widely used for various films, including silicon dioxide (LTO, TEOS), silicon nitride (Si₃N₄), polysilicon (POLY), phosphosilicate glass (BSG), boron-phosphosilicate glass (BPSG), doped polysilicon, graphene, and carbon nanotubes.

Characteristics: 

- Process Temperature: Typically between 500-900°C; relatively high process temperatures.

- Pressure Range: Low pressure environment of 0.1-10 Torr.

- Film Quality: High quality, good uniformity, and density with few defects.

- Deposition Rate: Slow deposition rate.

- Uniformity: Suitable for large substrates with good uniformity.

- Advantages & Disadvantages: Capable of depositing very uniform and dense films; performs well on large substrates and is suitable for batch production; relatively low cost; high temperature makes it unsuitable for heat-sensitive materials; slower deposition rate results in lower yield.

2. PECVD (Plasma Enhanced CVD)  

Principle: PECVD utilizes plasma to activate gas phase reactions at lower temperatures. The plasma ionizes and decomposes molecules in the reactant gases, leading to the deposition of films on the substrate surface. The energy from the plasma can significantly lower the temperature required for the reaction, allowing for a wide range of applications in the preparation of various metal, inorganic, and organic films.

Characteristics: 

- Process Temperature: Typically between 200-400°C; lower temperatures compared to LPCVD.

- Pressure Range: Usually in the range of hundreds of mTorr to a few Torr.

- Film Quality: While uniformity is good, the plasma may introduce defects, resulting in lower density and quality compared to LPCVD.

- Deposition Rate: Higher deposition rates, leading to improved production efficiency.

- Uniformity: Slightly less uniform on large substrates compared to LPCVD.

- Advantages & Disadvantages: Allows for film deposition at lower temperatures, suitable for heat-sensitive materials; fast deposition rates, ideal for high-efficiency production; process flexibility to control film properties via plasma parameters; however, plasma may introduce defects like pinholes or non-uniformity, and film density and quality may be slightly inferior to LPCVD.

3. HDP-CVD (High Density Plasma CVD)  

Principle: HDP-CVD is a specialized form of PECVD that achieves higher plasma density and quality at lower deposition temperatures than conventional PECVD systems. HDP-CVD provides nearly independent control over ion flux and energy, enhancing the filling capabilities for trenches or holes, and is used for high-performance film deposition, such as antireflective coatings and low dielectric constant materials.

Characteristics: 

- Process Temperature: Between room temperature and 300°C; very low process temperatures.

- Pressure Range: Between 1 and 100 mTorr; lower than PECVD.

- Film Quality: High plasma density leads to superior film quality and uniformity.

- Deposition Rate: Deposition rates are between LPCVD and PECVD, slightly higher than LPCVD.

- Uniformity: Excellent film uniformity due to high-density plasma, suitable for complex substrate shapes.

- Advantages & Disadvantages: Capable of depositing high-quality films at lower temperatures, very suitable for heat-sensitive materials; exceptional film uniformity, density, and surface smoothness; higher plasma density improves deposition uniformity and film properties; however, equipment is complex and more expensive; deposition rates may be slower, and higher plasma energy can introduce minimal damage.