In the thin film deposition process of solar cells, there are two thin film deposition methods: chemical vapor deposition (CVD) and physical vapor deposition (PVD). Solar cell manufacturers also need to make targeted choices based on the specific problems of solar cells in the deposition process, and After completing the film deposition process, system testing is carried out through high-tech testing equipment. To this end, Millennial Solar has produced Four-Point Probe Tester, which can obtain sheet resistance/resistivity distribution information at different sample locations and quickly and automatically scan samples up to 220mm to evaluate whether the cell has reached the ideal photoelectric conversion rate.

The difference between chemical vapor deposition and physical vapor deposition

Although chemical vapor deposition and physical vapor deposition are both processes that use substances in the gas phase to form thin films on solid surfaces, they are different in principles, characteristics and application methods.

Differences in principles between chemical vapor deposition and physical vapor deposition

The principle of chemical vapor deposition is to use gaseous or vaporous substances to undergo chemical reactions at the gas phase or gas-solid interface to generate solid deposits and form a thin film on the surface of the substrate. The reaction substances of chemical vapor deposition are usually compounds containing target elements, such as SiH4, NH3, CH4, etc., which decompose or react on the surface of the substrate under a certain temperature, pressure and catalyst, releasing hydrogen or other by-products , while depositing target elements or compounds. The CVD reaction can be carried out at normal pressure or low pressure, or methods such as plasma or light radiation can be used to enhance the reaction activity.

The principle of physical vapor deposition is to use physical methods, such as evaporation, sputtering, etc., to vaporize the coating material and deposit it on the surface of the substrate to form a film. Coating materials for physical vapor deposition are usually pure metals or compounds. They evaporate or sputter atoms or molecules from the source under vacuum or low pressure conditions through heating, electron beams, ion beams, lasers, etc., and then condense on the surface of the substrate to form a thin film. No chemical reaction occurs during the physical vapor deposition process, and the substances before and after deposition are the same.

Differences in characteristics between chemical vapor deposition and physical vapor deposition

 Chemical vapor deposition and physical vapor deposition also have great differences in characteristics.

 Film quality: Chemical vapor deposition can produce films with high purity, good lethality, low residual stress, and good crystallization, while physical vapor deposition can produce films with high hardness, high strength, good thermal stability, good wear resistance, and stable chemical properties. Film with low coefficient of friction. The film quality of chemical vapor deposition is affected by factors such as reaction conditions, reaction substances, and reaction mechanisms, while the film quality of physical vapor deposition is affected by factors such as deposition energy, deposition rate, and deposition temperature.

 Thin film uniformity: Chemical vapor deposition can obtain a film with uniform thickness and composition, while physical vapor deposition has poor film thickness and composition uniformity. The film uniformity of chemical vapor deposition mainly depends on the flow and diffusion of gas, while the film uniformity of physical vapor deposition mainly depends on the deposition angle and distance.

 Step coverage: Chemical vapor deposition can produce a film with good step coverage, while physical vapor deposition has poor step coverage. The step coverage of chemical vapor deposition mainly depends on the diffusion and reaction rate of reaction substances, while the step coverage of physical vapor deposition mainly depends on the directionality and energy of the deposited particles.

 Deposition rate: Physical vapor deposition can produce films with a high deposition rate, while chemical vapor deposition has a lower deposition rate. The deposition rate of physical vapor deposition mainly depends on the evaporation or sputtering rate of the source, while the deposition rate of chemical vapor deposition mainly depends on the supply of reactive species and the reaction rate.

 Deposition temperature: Chemical vapor deposition requires higher deposition temperatures, while physical vapor deposition can be performed at lower deposition temperatures. The deposition temperature of chemical vapor deposition mainly depends on the decomposition or reaction temperature of the reactive species, while the deposition temperature of physical vapor deposition mainly depends on the evaporation or sputtering temperature of the source.

 Environmental pollution: Chemical vapor deposition will produce some harmful gases or liquids, causing environmental pollution, while physical vapor deposition does not produce harmful substances during the process, and it is a green preparation technology. The environmental pollution of chemical vapor deposition mainly comes from the handling of reaction substances and reaction products, while the environmental pollution of physical vapor deposition mainly comes from the maintenance of the vacuum system.

Four-Point Probe Tester

E-mail:market@millennialsolar.cn

Four-Point Probe Tester can quickly and automatically scan samples up to 230mm to obtain sheet resistance/resistivity distribution information at different locations of the sample. It can be widely used in photovoltaics, semiconductors, alloys, ceramics and many other fields.

 ● Ultra-high measurement range, measuring 0.1MΩ~100MΩ

 ● High-precision measurement, dynamic repeatability can reach 0.2%

 ● Fully automatic multi-point scanning, multiple preset schemes can also be customized and adjusted

 ● Rapid material characterization and automatic correction factor calculation

 Chemical vapor deposition and physical vapor deposition are two different solar cell thin film preparation technologies. They each have their own advantages and disadvantages and are suitable for different materials, structures and applications. In the actual film preparation process, it is often necessary to select the preparation technology suitable for the specific situation according to specific needs to achieve high-quality production, and use Four-Point Probe Tester to test the film at the end of production to achieve scientific use!