When the chip wafer is manufactured, it is necessary to make conductive metal layers for each module or area, and there is a metallization process in the IC field.
Methods of Metal Deposition
Metal deposition needs to consider how to form a high-quality metal film with good step coverage, good contact and uniformity on the surface of the silicon wafer. Physical vapor deposition is the most commonly used method for metal deposition.
Physical vapor deposition (PVD) refers to the use of a certain physical process to realize the transfer of substances, that is, atoms or molecules are transferred from the source to the surface of the substrate (silicon) and deposited to form a thin film. There is no chemical reaction in this process.
Therefore, the sputtering method has basically replaced the evaporation method in the manufacture of VLSI; however, evaporation is still widely used in discrete devices (diodes, triodes, etc.) and small and medium-sized integrated circuits with low requirements. Such as LED, LD, Vcsel and so on.
Evaporation: The process by which vapor is produced when a material melts.
Vacuum evaporation is to use the saturated vapor pressure of evaporation materials at high temperature to prepare thin films.
In other words, evaporation refers to heating the evaporation source under vacuum conditions, heating the material to be deposited to emit steam, and the steam atoms move in a straight line through the cavity to the surface of the substrate (silicon wafer), and condense to form a solid film.
Because the main physical process of the vacuum evaporation method is to evaporate the material by heating to evaporate its atoms or molecules, so it is also called thermal evaporation.
Advantages and disadvantages
The equipment is simple and easy to operate, the prepared thin film has high purity, fast film forming rate and simple growth mechanism.
The formed thin film has low adhesion to the substrate and poor step coverage.
Evaporation stage is mainly used in the manufacture of small-scale integrated circuits and discrete devices. It is also applied to gold plating on the back to better improve the ohmic contact and the adhesion of chips and packaging materials.
Vacuum system: provide a vacuum environment for the evaporation process.
The vacuum evaporation process must be carried out in a high vacuum environment, otherwise the evaporated atoms or molecules collide with a large number of residual gas molecules, which will seriously pollute the film, and even form oxides or it is difficult to form a uniform and continuous film due to the barrier of residual molecules.
Heating evaporation system: the device for placing the evaporation source, as well as the heating and temperature measuring device.
For multi-layer electrode films, multi-crucible equipment is required to achieve continuous coating.