Analysis of thin film deposition equipment - Principle and application of PECVD/LPCVD/ALD equipment

Thin film deposition is the plating of a film on the main substrate material of a semiconductor. This film can have a variety of materials, such as the insulating compound silicon dioxide, semiconductor polysilicon, metal copper, etc. The device used for coating is called a film deposition device.

From the perspective of semiconductor chip manufacturing process, it is located in the former process.

The film preparation process can be divided into two categories according to its film forming method: physical vapor deposition (PVD) and chemical vapor deposition (CVD), of which CVD process equipment accounts for a higher proportion.

Physical vapor deposition (PVD) refers to the vaporization of the surface of the material source and the deposition on the surface of the substrate by low pressure gas/plasma, including evaporation, sputtering, ion beam, etc.

Chemical vapor deposition (CVD) refers to the process of deposting a solid film on the surface of a silicon wafer through a chemical reaction of gas mixing. According to the different reaction conditions (pressure, precursor), it is divided into atmospheric pressure CVD(APCVD), low pressure CVD(LPCVD), plasma enhanced CVD(PECVD), high density plasma CVD(HDPCVD) and atomic layer deposition (ALD).

LPCVD: LPCVD has excellent step coverage capability, good composition and structure control, high deposition rate and output, and greatly reduces particle pollution sources. Relying on heating equipment as a heat source to maintain the reaction, temperature control and air pressure are very important. It is widely used in the Poly layer manufacturing of TopCon batteries.

PECVD: PECVD relies on the plasma generated by RF induction to achieve the low temperature of the film deposition process (less than 450 degrees). Low temperature deposition is its main advantage, which saves energy, reduces costs, improves productivity, and reduces the decay of the life of the few particles in the silicon wafer caused by high temperature. It can be applied to the process of PERC, TOPCON, HJT and other battery cells.

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ALD: Good uniformity of film formation, dense no holes, good step covering characteristics, can be carried out at low temperature (room temperature - 400℃), can be simple and accurate control of film thickness, widely applicable to different shapes of the substrate, no need to control the uniformity of reaction material flow. But the disadvantage is that the film formation speed is slow. For example, zinc sulfide (ZnS) light-emitting layers for the production of nanostructured insulators (Al2O3/TiO2) and thin-film electroluminescent displays (TFEL).

Atomic Layer Deposition (ALD) is a vacuum coating process in which a substance is deposited on a substrate layer by layer in the form of a single atomic layer. Back in 1974, Finnish materials physicist Tuomo Suntola developed the technology and won the Million Euro Millennium Technology Prize. ALD technology was originally used in flat panel electroluminescent displays, but it has not been widely used. Until the beginning of the 21st century, ALD technology began to be adopted by the semiconductor industry, by manufacturing ultra-thin high-dielectric materials to replace traditional silicon oxide, successfully solved the leakage current problem caused by the reduction of the line width of the field effect transistor, and prompted Moore's law to further develop to a smaller line width. Dr. Tuomo Suntola has stated that ALD can significantly increase the integration density of components.

Compared with the traditional Chemical Vapor Deposition (CVD) and Physical Vapor Deposition (PVD), ALD has the advantages of excellent 3D conformal and large area uniformity in film formation. As well as precise thickness control, it is suitable for growing ultra-thin films on complex shape surfaces and high aspect ratio structures.

In the post-Moore era, the complexity and process amount of wafer manufacturing have greatly increased. Taking logic chips as an example, with the increase in the number of production lines of processes below 45nm, especially the production lines of processes below 28nm, the requirements for coating thickness and precision control are higher, and the number of processes and equipment required for ALD are greatly increased after the introduction of multiple exposure technology. In the field of memory chips, the mainstream manufacturing process has been developed from 2D NAND to 3D NAND structure, the number of internal layers continues to increase, and the components gradually show high density and high aspect ratio structure, and the important role of ALD has become prominent. From the perspective of the future development of semiconductors, ALD technology will play an increasingly important role in the post-Moore era.

For example, ALD is the only deposition technology that can meet the coating and film performance requirements of complex 3D stacked structures such as 3D-NAND. This can be seen vividly in the figure below, where the film deposited in CVD A (blue) does not completely cover the lower part of the structure; Even with some process adjustments to the CVD (CVD B) to achieve coverage, the film properties and chemical composition of the bottom region are poor (white area in the figure); In contrast, the use of ALD technology shows complete film coverage and achieves high quality and uniform film characteristics in all areas of the structure.