Evaporation by induction heating produces significant degree of metal ionization, enhancing degree of penetration of evaporant on substrate

Brainard, W. A.

Spalvins, T.

English

NASA Technical Reports Server

.December 1975
	
B75-10288 
NASA TECH BRIEF	 C' Lewis Research Center 
NASA Tech Briefs announce new technology derived from the U S. space proriram They are issued to encourage 
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Induction Heating Simplifies 
Metal Evaporation for Ion Plating 
.
10-kV  
power
I supply
Specimen 
(cathode) - 
Pyrex 
cylinder—	 ili 2 
Crucible with 
evaorant__------f
Removable 
/ aluminum cover 
Induction coil with 
coaxial feedthrough 
induction 
generator 
/ /
Basep late 	 Load coil 
transformer 
To vacuum pumps 
Ion plating with induction heating source. 
The Problem: 
Because of its simplicity and convenience, the vapor 
source most commonly used in ion plating is resistance 
heating, utilizing a refractory metal boat or filament. 
However, resistance heating cannot be used for 
evaporating metals which at high temperatures in their 
molten state react with the boat or for evaporating metals 
with very high melting points. To vaporize such materials, 
other evaporation methods have been tried, some 
successfully. For example, electron beam evaporation has 
tilled many of the needs which could not be performed by
resistance heating. The main reason why electron beam 
evaporation is not utilized on a larger commercial scale in 
ion plating is because the operations are highly compli-
cated. Other methods which have been tried on a limited 
scale are arc discharges and sputtering targets. Each of 
these techniques has its advantages and disadvantages 
which essentially depend on the particular application. 
(continued overleaf( 
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The Solution: 
The use of induction heating as the evaporation source 
under glow discharge conditions offers a simplified 
approach. By utilizing a bare induction coil without any 
shielding, the evaporant source can be heated directly in 
the glow discharge region with no arcing. 
Metals which cannot be evaporated by resistance 
heating can easily and quickly be evaporated by induction 
heating. The unique characteristics of ion plating are 
retained in terms of throwing power and penetration or 
alloying affects which are responsible for strong 
adherence. 
How It's Done: 
A schematic diagram of ion plating by induction 
heating is shown in the figure. The apparatus consists 
essentially of the specimen (cathode) to be coated and the 
evaporation source which is an inductively heated ceramic 
crucible containing the evaporant material. The specimen 
is an integral part of the high voltage ceramic-metal 
vacuum feedthrough and is connected to the negative 
terminal of the high voltage power supply. The positive 
terminal of the high voltage power supply is grounded. 
The plating conditions used were those most 
commonly utilized in industrial • ion plating; negative 
potential 3-5 kv, argon pressure 15-20 p, and the current 
density 0.3 to 0.8 ma/cm 2 . A conventional induction 
generator of a frequency of 450 KHz cannot be utilized in 
ion plating since severe arcing of the coil takes place in the 
glow discharge. To overcome this difficulty, the frequency 
was reduced to about 75 KHz. 
As shown in the figure, an induction generator in 
conjunction with a load-coil transformer supplies power 
through the coaxial feedthrough to a four-turn induction 
coil (voltage across coil is 70 volts RF) which 
accommodates a 2.5 cm (1 in) diameter ceramic crucible. 
At these frequencies and voltages, the induction coil does 
not require any external shielding and a bare copper coil is 
used.
A number of metals which were practically impossible 
to deposit by resistance heating evaporation due to severe 
alloying with the refractory boat can now effectively be 
evaporated and deposited by induction heating in any 
desired thickness. Metals, particularly metals such as 
nickel and iron, have been deposited up to thickness of 50 
pm (2 mils), with the strong adherences normally 
obtained in ion plating. High temperature melting 
materials such as refractories can also be evaporated by 
induction heating, utilizing the appropriate capacity 
induction generator. 
Evaporation by induction heating in ion plating has an 
additional feature which resistance and electron beam 
methods do not possess. It produces a significant degree 
of ionization of the evaporant metal. The additional 
amount of the ionized metal evaporant is of great 
importance in ion plating since this enhances the degree of 
penetration of the evaporant on the substrate. 
Notes: 
1. The low operating frequency of 75 KHz is the basic 
requirement for operating a bare induction coil in a 
glow discharge region. 
2. No additional documentation is available. Specific 
technical questions, however, may be directed to: 
Technology Utilization Officer 
Lewis Research Center 
21000 Brookpark Road 
Cleveland, Ohio 44135 
Reference: B75-10288 
Patent Status: 
NASA has decided not to apply for a patent. 
Source: . T. Spalvins and W.A. Brainard

Lewis Research Center

(LEW-12595)
fl 
B75-10288	 Category 03


Induction heating simplifies metal evaporation for ion plating

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