Overview of the film growth process

The development process of film growth process

As a key process for adhering substances to the surface of substrate materials by physical or chemical methods, film growth has always been an important technical cornerstone in modern information technology, electronics, sensors, optics and solar energy since its rise in the 60s of the 20th century. In integrated circuit manufacturing, thin film deposition technology is mainly divided into three major systems according to the working principle: physical vapor deposition, chemical vapor deposition and epitaxial growth, and each system continues to break through the process boundaries with the evolution of technology.
In the early days, micron technology was mainly based on multi-chip atmospheric pressure chemical vapor deposition equipment, which had a chamber working pressure of about 1ATM, and the wafer transfer and process flow were carried out continuously. With the increase in wafer size and the advancement of IC technology, the single-chip single-chamber process has gradually become dominant. In the sub-micron technology generation, low-pressure chemical vapor deposition equipment has become the mainstream choice due to its reduced working pressure, which significantly improves film uniformity and trench coverage and filling capacity. After entering the 90nm node, plasma-enhanced chemical vapor deposition equipment plays a key role in the deposition of dielectric insulation, semiconductor materials, and metal film deposition through plasma-assisted reduction of chemical reaction temperature, enhancement of film purity and density. With the introduction of 65nm technology, the application of selective SiGe epitaxial process in the source and leak regions of devices has effectively improved the mobility of PMOS holes. After the 45nm node, in order to meet the demand for multi-nanoscale ultra-thin film deposition, the atomic layer deposition process has been introduced with its precise film thickness control and excellent uniformity, becoming the core support for high dielectric materials and metal gate processes.
In the field of physical vapor deposition, the 150nm wafer era is dominated by single-chip single-chamber form, and sputtering equipment has gradually replaced vacuum evaporation equipment due to the advantages of film uniformity, density, adhesion strength and purity. With the development of technology, PVD equipment needs to evolve from single-planar film preparation to complex three-dimensional structure coverage, promoting the adjustment of chamber working pressure from millitor level to sub-millitotor or tens of millitorestor range, the distance from the target to the wafer is significantly increased, and magnetron sputtering, RF PVD and ionized PVD equipment have developed one after another. Among them, the application of DC and RF hybrid power supply reduces the energy of incident particles and reduces device damage, and such ionized PVD chambers are widely used in copper interconnect and metal gate deposition. At the same time, the introduction of auxiliary magnetic fields, RF power supplies and collimators, combined with base heating/cooling, RF negative bias and anti-sputtering functions, further improves process flexibility. At present, ionized PVD chambers are being integrated with metal chemical vapor deposition and atomic layer deposition technologies to form a multi-process chamber integration platform to meet the structural needs of complex devices.

Classification of film growth process

As the core technology system of integrated circuit manufacturing, the thin film growth process covers four technical paths: physical vapor deposition, chemical vapor deposition, atomic layer deposition and epitaxial growth.

Physical vapor deposition (PVD) is a technology dominated by sputter coating, which realizes thin film deposition through physical processes such as vacuum evaporation and ion bombardment, and is widely used in the preparation of electrodes and metal interconnect layers.

In the era of 0.13μm copper interconnect, titanium nitride (TiN), tantalum nitride (TaN) and other barrier layer materials are realized through the reaction sputtering process - nitrogen gas (N₂) is introduced on the basis of argon (Ar), so that the target Ti/Ta reacts with N₂ to form a compound film, effectively inhibiting the diffusion of copper atoms. At present, PVD technology has developed three mainstream sputtering methods: DC, RF and magnetron, among which magnetron sputtering has advantages in fine structures such as copper interconnects and metal grids by virtue of its high ionization efficiency and low damage characteristics. With the increase in the number of multi-layer metal wiring layers, the PVD material system continues to expand, covering Al-Si, Al-Cu, Ti, Ta, Co, WSi₂ and other alloys and compounds, and the vacuum degree of the equipment is increased to the order of 1×10⁻⁷~9×10⁻⁹Torr to ensure gas purity and film uniformity, and the process window is accurately controlled through parameters such as dust quantity, resistance value, and stress.

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Chemical vapor deposition (CVD) is a chemical reaction of vapor reactants on the surface of a substrate to form solid thin films, which is widely used in the deposition of oxides, nitrides, carbides, polysilicon and other materials.

According to the pressure classification, atmospheric pressure (APCVD), sub-atmospheric pressure (SAPCVD), and low pressure (LPCVD) have their own characteristics: LPCVD has become the mainstream of submicron nodes by reducing the working pressure to improve film uniformity and trench filling ability. By energy, technologies such as plasma enhancement (PECVD), high-density plasma (HDPCVD), rapid heat (RTCVD), and fluidity (FCVD) continue to innovate, among which FCVD shows unique advantages in three-dimensional structures with its excellent gap filling ability. Typical reactions such as silane (SiH₄) and oxygen (O₂) to form SiO₂, or doping with phosphane (PH₃) and borane (B₂H₆) to form functional films, and the reaction source is also extended to N₂O, TEOS, WF₆, etc., to meet the requirements of different dielectric constants, stresses and breakdown voltages. Selective epitaxy technologies such as SiGe source-leak epitaxy, which continue lattice growth on single crystal substrates through CVD to improve PMOS hole mobility, have become a key process after the 65nm node.
Atomic layer deposition (ALD) is the preferred technology for ultrathin film layers such as high-k-gate media, metal gates, and copper interconnect barrier layers with self-limiting single-layer growth mechanism as the core, and achieves atomic-level thickness control and excellent step coverage through alternating pulsed precursors. Its self-limiting properties stem from the chemisodestion and reaction saturation mechanism of the precursor on the substrate surface, ensuring that the deposition thickness of each layer is accurate to the sub-nanometer level. In 3D structures such as FinFET and 3D NAND, ALD supports the fine structure preparation of gate side walls, high aspect ratio vias, and other fine structures with excellent trench filling uniformity. With the advancement of technology nodes, the research and development of ALD precursors continues to make breakthroughs, such as the optimization of precursors for hafnium-based and zirconium-based high-k materials, and the application of metal-organic precursors in metal gate deposition, which promotes the simultaneous improvement of film properties and process stability.

The epitaxial process realizes lattice matching and defect control by growing orderly single crystal layers on single crystal substrates, and is widely used in silicon epitaxial wafers, embedded source and leak, LED substrates and other fields. Solid-phase epitaxy realizes amorphous layer recrystallization through ion implantation and thermal annealing, and restores the single crystal structure. Chemical vapor phase epitaxy (CVD epitaxy) is dominated by high-quality single crystal growth through ultra-clean cavity and low-temperature process (600~700°C). The epitaxial silicon layer improves yield with high purity and low defects, and optimizes device performance through flexible design thickness and doping concentration. Embedded source-drain epitaxy is introduced through the germanium-silicon (SiGe) stress layer to improve the mobility of channel carriers and reduce parasitic resistance, which has become a key technology for advanced logic devices. With the development of 3D integration technology, epitaxial processes have expanded to 3D epitaxy, low-temperature epitaxy, etc., supporting the innovation of new device structures.

Facing the future, the thin film growth process continues to evolve in the direction of new material adaptation, low-temperature technology, three-dimensional structure coverage and interface performance control. accelerate the research and development of deposition processes for emerging thin film materials such as two-dimensional materials and superconducting materials, and promote collaborative innovation of equipment and processes; Tightening thermal budget restrictions drive technological breakthroughs such as low-temperature ALD and plasma-assisted CVD. The complexity of the structure of 3D devices requires film growth to have a higher aspect ratio, trench filling ability and film thickness control accuracy. The improvement of system integration and the progress of automation control technology promote the development of multi-process chamber integration platforms in the direction of intelligence and modularization, realize the collaborative optimization of multi-material and multi-process, and finally achieve a balance breakthrough between performance, cost and reliability.