Quartz plates are extensively utilized in a variety of disciplines, including optoelectronics, lasers and sensors, owing to their exceptional optical properties and chemical stability. In such applications, silicon-coated films (Si films) on quartz plates have been demonstrated to have the capacity to enhance material performance, for example by increasing reflectivity of light, reducing light loss, and improving electrical characteristics.

1. How to select materials before coating

Quartz plates are usually made from high-purity silicon dioxide (SiO₂), which offers excellent light transmittance, particularly in the ultraviolet to visible light spectrum, as well as a low coefficient of thermal expansion and superior chemical stability. When choosing quartz plates, it is important to make sure they have a high light transmittance rate and a low impurity content.

The performance of silicon films on quartz plates is directly determined by their characteristics. The performance of different silicon films (such as amorphous silicon, crystalline silicon, and microcrystalline silicon) is different, and will be introduced one by one below.

-Amorphous silicon (a-Si): It has a relatively low cost and is suitable for large-area coating, but its electrical performance is poor.

-Crystalline silicon (c-Si): It has superior photoelectric performance. However, it usually has high requirements for temperature and environment during the deposition process.

-Microcrystalline silicon: It combines the advantages of both amorphous silicon and crystalline silicon, offering good stability and performance.

2. Pre-treatment operation before coating

(1) Cleaning

Before coating a silicon film on a quartz plate, it is vital to clean and pretreat the surface of the quartz plate. Selecting the appropriate cleaning method is essential for removing surface contaminants and ensuring good adhesion between the film and the substrate.

-Ultrasonic cleaning

Remove surface contaminants using the energy of ultrasonic waves. This method is suitable for use on large-area films.

-Acid pickling

Acidic solutions such as dilute nitric acid and hydrofluoric acid can be used to remove organic matter and metal ions on the plate surface.

-Deionized water rinsing

Rinse the cleaned quartz plate with deionized water to remove any residual chemicals.

(2) Surface treatment

-Hydrogen treating

The surface of quartz plates is treated with a hydrogen atmosphere to create hydrogenated silicon-like groups. This improves the film’s adhesion and electrical properties.

-Plasma processing

Plasma treatment technology can be used to remove organic matter and pollutants, thereby enhancing the surface’s hydrophilicity.

3. Selection of coating technology

There are many methods of depositing silicon thin films. The most commonly used methods include chemical vapour deposition (CVD), physical vapour deposition (PVD) and magnetron sputtering. When choosing a coating technology, the following factors should be taken into consideration.

(1) Chemical vapour deposition

CVD is a commonly used silicon film deposition technology, which has the advantages of good uniformity and high film quality.

-Advantages: It is suitable for large-area coating and can be carried out under low pressure, which makes it easy to control the composition and thickness of the film.

-Disadvantages: The generation of by-products during the reaction process can be a problem, so it is necessary to control the gas flow rate and reaction temperature properly.

(2) Physical vapor deposition

PVD involves transforming a solid or liquid into a gas through physical means, which is then deposited onto the surface of the substrate.

-Advantages: It is suitable for depositing high-purity materials and can combine various materials, offering strong application flexibility.

-Disadvantages: The coating pressure is relatively high and requires a considerable amount of equipment resources.

4. Post-treatment after coating

Following the completion of the coating process, it is often necessary to apply additional treatments to enhance the performance and stability of the film.

(1) Heat treatment

The silicon film after deposition often requires heat treatment to enhance its crystallinity and electrical conductivity.

-Temperature range:The commonly used temperature range is 400℃ to 1000℃, which is determined by the type of film layer and application requirements.

-Heat treating atmosphere:It is carried out under the protection of nitrogen or argon to prevent the oxidation of the film.

(2) Surface finishing

Finishing the surface of the coated film can remove surface defects and stresses, enhancing its performance and service life.