PVD Processes

Physical Vapor Deposition Processes. The three physical vapor deposition (PVD) processes are evaporation, ion plating, and sputtering... 

Vacuum Deposition. Vacuum deposition, sometimes called vacuum evaporation, is a PVD process in which the material is thermally vaporized from a source and reaches the substrate without coUision with gas molecules in the space between the source and substrate (1 3). The trajectory of the vaporized material is therefore line-of-sight. Typically, vacuum deposition takes place in the pressure range of 10 10 Pa (10 10 torr), depending on the level of contamination that can be tolerated in the resulting deposited film. Figure 3 depicts a simple vacuum deposition chamber using a resistively heated filament vaporization source. 

It i s not restricted to a line-of-sight deposition which is a general characteristic of sputtering, evaporation and other PVD processes. As such, CVD has highthrowingpower. 

The deposition rate is high and thick coatings can be readily obtained (in some cases centimeters thick) and the process is generally competitive and, in some cases, more economical than the PVD processes. 

CVD does not usually require the low pressures which are necessary with sputtering, MBE, and other PVD processes. Consequently the vacuum system is simpler and less costly. Mechanical pumps are adequate for many operations. Vane pumps, built with corrosion resistant material, are preferred. If properly maintained, these pumps will operate for long periods of time. 

Thermal CVD, reviewed above, relies on thermal energy to activate the reaction, and deposition temperatures are usually high. In plasma CVD, also known as plasma-enhanced CVD (PECV) or plasma-assisted CVD (PACVD), the reaction is activated by a plasma and the deposition temperature is substantially lower. Plasma CVD combines a chemical and a physical process and may be said to bridge the gap between CVD andPVD. In this respect, itis similar to PVD processes operating in a chemical environment, such as reactive sputtering (see Appendix). 

Both CVD and PVD are used extensively in the production of coatings for cutting-tool applications. The PVD processes include mag-... 

Chemical vapor deposition competes directly with other coating processes which, in many cases, are more suitable for the application under consideration. These competing processes comprise the physical vapor deposition (PVD) processes of evaporation, sputtering, and ion plating, as well as the molten-material process of thermal spray and the liquid-phase process of solgel. A short description of each process follows. For greater detail, the listed references should be consulted. 

The PVD process by means of electric arc evaporation has attained a high degree of importance in deposition of hard layers on an industrial scale. The hardness achieved is a minimum of 2100 HV. Compare this to the standard nitriting process which provides a hardness of about 900 HV or the stelliting process which offers about 500-600 HV. Extmsion screws treaded with this special process in the tire industry have seen a much improved wear life when processing highly filled silica compounds or very hard apex compounds. 

The CBD CdS on CIGS or CIS devices produce superior solar cells relative to solar cells made by dry chemical vapor deposition (CVD) or physical vapor deposition (PVD) of CdS. Several groups15-20 put forward plausible reasons for the superior performance, including selective etching or removal of native oxides by ammonia and also that the CBD process does not cause any physical damage, which could occur during CVD or PVD processes. 

Most people have likely never heard of the PVD process, but surely use PVD products. The general concept of putting a protective coating on a surface is not entirely unknown. Paint contains chemicals that deposit a protective layer on the surface of objects. Electroplating uses electricity to deposit a layer of metal on the surface of tableware, jewelry, and coins. The PVD process uses phase changes to deposit layers on the surface of objects. 

Figure 9.3 This microchip has been coated using the PVD process. The coating provides protection for the information stored in the chip.

PVD of a ceramic layer involves the introduction of an additional gas. However, the energy of the gas is much too low to form a ceramic reaction product. For example, the formation of TiN from Ti and N2 needs much higher temperatures than the normal PVD process temperatures. 

Handbook of Physical Vapor Deposition (PVD) Processing Film Formation, Adhesion, Surface Preparation and Contamination Control, D. M. Mattox (Ed.). Noyes, Westwood, NJ, 1998. 

One way to observe and quantify the type of growth is to deposit material into a deep trench cut into the substrate. In the PVD process the total deposit in the trench is proportional to the area of the top opening because it is flux-limited, and when the trench is deep and narrow, the film will be thin. In contrast, the deposit in a CVD process is proportional to the substrate surface area, so that the film in the trench is the same thickness as on the top surface. These two situations are illustrated in Fig. 2.7. 

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