Vapour deposition processes

Thin films of metals, alloys and compounds of a few micrometres diickness, which play an important part in microelectronics, can be prepared by die condensation of atomic species on an inert substrate from a gaseous phase. The source of die atoms is, in die simplest circumstances, a sample of die collision-free evaporated beam originating from an elemental substance, or a number of elementary substances, which is formed in vacuum. The condensing surface is selected and held at a pre-determined temperature, so as to affect die crystallographic form of die condensate. If diis surface is at room teiiiperamre, a polycrystalline film is usually formed. As die temperature of die surface is increased die deposit crystal size increases, and can be made practically monocrystalline at elevated temperatures. The degree of crystallinity which has been achieved can be determined by electron diffraction, while odier properties such as surface morphology and dislocation sttiicmre can be established by electron microscopy. 

The individual processes which take part in diiii film production are dins  

Growtli of nuclei by surface diffusion of atoms to form a continuous layer. 

Establishment of the him morphology as determined by the hlm/subsuate physical relationships. 

It will be seen tliroughout this discussion of thermochemical processes tlrat these require a knowledge of botlr thermodynamic and kinetic data for their analysis, and while kinehc theory obviously determines the rate at which any process may be caiTied out, the thermodynamic properties determine the extent to which the process can occur. 

Establishment of the film morphology as determined by the film/substrate physical relationships. 

The simplest system in which useful products are obtained by thermochemical processing involves the evaporation of an element or elements in vacuum in order to produce thin films on a selected substrate. This process is usually limited to the production of thin films because of the low rates of evaporation of the elements into a vacuum under conditions which can be controlled. These rates can be calculated by the application of the kinetic theory of ideal gases. 

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A situation which is frequently encountered in tire production of microelectronic devices is when vapour deposition must be made into a re-entrant cavity in an otherwise planar surface. Clearly, the gas velocity of the major transporting gas must be reduced in the gas phase entering the cavity, and transport down tire cavity will be mainly by diffusion. If the mainstream gas velocity is high, there exists the possibility of turbulent flow at tire mouth of tire cavity, but since this is rare in vapour deposition processes, the assumption that the gas widrin dre cavity is stagnant is a good approximation. The appropriate solution of dre diffusion equation for the steady-state transport of material tlrrough the stagnant layer in dre cavity is... 

Maeda, M. et a ., Newly Developed Continuous Zinc Vapour Deposition Process. Paper to SITEV 86 (1986)... 

Boron fibres are made by means of a CVD process, a Chemical Vapour Deposition process. Boron trichloride is heated in an oven and as a result it breaks down ... 

Some kinetic considerations of chemical vapour deposition processes Ch. 17... 

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