Fluid protective wall cover in a vapor deposition chamber

A method of producing a high vacuum in a vacuum container which has an exst connection line connected thereto and using an interior protective covering for the walls of the container and a protective gas comprises, applying covering to the interior of the container so as to shield the inner walls thereof and to also shield the exhaust connection thereto, directing a protective gas into the space between the covering the interior walls of the container, preferably during the flooding in which the container is opened, and thereafter evacuating the interior of the container through the exhaust connection and heating the covering. The vacuum treatment device, such as a device for evaporating materials from vapor deposition, comprises a closed container having interior walls with a thin-walled metal sheet forming a covering arranged in spaced relationship to the interior walls so as to shield a major area of the walls and to define a space between the walls and the covering. A connecting line for introducing a protective gas into the container in the space between the walls and the covering is provided, and in addition an exhaust gas line is connected to the container and to an evacuating pump for evacuating the container. A thin-walled metal screen is arranged in the container and shields at least a portion of the exhaust line, and heater means are provided for heating both the covering and the shield.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates in general to a vacuum treatment device and 
specifically to method of producing a high vacuum in a container which has 
an interior thin metal sheet spaced from the walls thereof on the inside 
of the container defining a space therebetween which is connected at one 
end to an exhaust connection which includes means for introducing a 
protective gas in the space between the sheet and the interior walls, and 
for heating the covering for the interior walls. 
2. Description of the Prior Art 
During the evacuation of a container, the pressure in the high vacuum range 
depends primarily on the suction capacity of the pumping system and on the 
amount of vapor (chiefly water vapor) which, during the preceding contact 
with vapor-containing air, has been sorbed to the inside walls of the 
container and is slowly released again under the high-vacuum conditions. 
For this reason, efforts in the high-vacuum technology have continually 
been directed to maximum possible suction capacity and a minumum possible 
amount of sorbed vapor. 
Opposed to the unlimited increase of the suction capacity, however, are not 
only the growing costs of larger pumps but also some undesirable 
consequences related to the vacuum technique. That is, the relative 
difference between the particle number density in the gas space reached in 
the container during the pumping, and the particle number density 
determined by the vapor amount sorbed by the container walls under 
equilibrium conditions, increases approximately proportionally to the 
increasing suction capacity. The local differences in the volumetric 
particle density or in the collision rate by surface within the container, 
caused by the geometry of the container and any built-in equipment, grow 
larger in the same proportion. Such differences, however, jeopardize a 
representative checking of the determinative parameters of the process 
(for example, the measuring of pressure). Thus, with the augmented suction 
capacity, the risk increases of unduly affecting the reproducibility of 
the results of the vacuum process (for example, of the optical properties 
of thin layers deposited by evaporation in vacuum), even if the 
differences are very small, such as caused by the spatial arrangement of 
the built-in equipment, the temperature distribution or temperature 
variation. 
Thus the reduction of the sorbed amount of vapor offers particular 
advantages over an enhancement of the suction capacity, which advantages, 
as mentioned above, not only include savings in the size of pumps but are 
also of a technological nature. 
A well-known manner of reducing the sorption is to prevent air from 
contacting the inside walls of the container and to introduce and remove 
the pieces to be treated through vacuum-tight air locks. The result 
obtained, however, does not always justify the high technical expenditures 
of pressure-tight locks and of auxiliary means for actuating the locks and 
transporting the pieces to be treated. That is, if during the maintenance 
or cleaning, the inside walls of the container come even only temporarily 
in contact with vapor-containing air, the reestablishment of constant 
process parameters requires a new, relatively long recovery time. 
It is known to prevent humid air from penetrating into an open container by 
flooding the inside walls thereof with a stream of dry gas (protective 
gas). In this method of the prior art, no pressure-tight locks are needed, 
however, there is a disadvantage in a large consumption of protective gas. 
Also known is to apply a higher, constant temperature, in order to reduce 
the water adsorption on a container wall. In this method, because of the 
increased saturation pressure of the water vapor, the relative humidity of 
the air is reduced (ratio of the partial pressure of the water vapor to 
the saturation pressure thereof), whereby the amount of sorbed water is 
also reduced. However, since at a higher temperature the sorbed water 
amount equilibrates a larger volumetric particle number in the gas space, 
the obtained effect is relatively small. 
Better results are obtained by alternately heating and cooling the inside 
walls during the evacuation. The temperature is varied periodically in 
accordance with the cycle of consecutive evacuation processes, 
predominantly with the aid of fluid heat carriers. During the flooding, 
the temperature is kept above the dew point given by the air humidity, but 
mostly not above 60.degree. C., in order not to complicate the maintenance 
and not to intensify the corrosion. 
A further improvement is obtained by heating the container walls during the 
evacuation to temperatures above 60.degree. C. To accelerate the 
temperature variation and save energy, it has also been provided to cover 
the inside walls of the container with heatable protective screens, for 
example, metal foils, spaced therefrom. The intention was to protect the 
inside walls from vapor deposition. In this way, particuarly in vacuum 
coaters, the porous, strongly sorbing vapor-deposited layers can be 
prevented from forming on the inside walls, while the protective screens 
coated with such layers may easily be outgassed by heating during the 
evacuation and thereby regenerated, or they may be exchanged. Experience 
has been made, however, that the pressure drop thereby obtained in the 
container is still substantially smaller than that which could 
theoretically be expected on the basis of the temperature drop. 
SUMMARY OF THE INVENTION 
The present invention is directed to measures for increasing the pressure 
drop produced by heating and cooling. 
To this end, the inventive method of producing high vacuum in a container 
into which, at least during the period of flooding, a protective gas is 
introduced to protect the inside wall from being charged with vapor, 
providing that the inside wall is largely screened by a covering and the 
protective gas is introduced into the intermediate space formed between 
the container wall and the covering, and that during the following 
evacuation, the covering is heated. 
The protective gas is introduced primarily during the flooding of the 
container and while the container is open. During the following 
evacuation, the gas feed may be throttled and then, upon accomplishing the 
heating, shut off. 
It is advisable to shield also the exhaust connection against the 
penetration of vapor-containing air, by a heatable, thin-walled flap or 
movable screen, as well as by suitably directing the vapor-free protective 
gas, with the flap or movable screen being fully opened during the 
heating, but brought, after the heating, into a position in which it is 
adjusted to a gas conductance at which the pressure in the container 
assumes a minimum value, and closed during the flooding. 
Another improvement may be obtained by designing the exhaust connection or 
the covering placed in front of the inside wall thereof, as a cool trap, 
sorption trap, or decomposition trap, for example. 
The protective gas consumption may be reduced by minimizing the width of 
the exit slits from the screened cavities between the inside walls of the 
container and the covering. But on the other hand, the exit slits must be 
sufficiently large to permit a satisfactorily quick pressure equalization 
and to prevent damaging of the thin covering by too high differential 
pressures during the evacuation or flooding. As far as possible, the 
covering should screen the inside wall of the container completely, 
without contacting it, and all portions thereof should be heatable. 
Further, the covering is to be as thin-walled as possible, to ensure a 
quick drop of its temperature and of the pressure in the container after 
the heat supply is switched off. For example, with coverings of a 0.01 mm 
thick copper foil, the cooling period up to reaching a substantially 
constant pressure amounts to 20 seconds at most. In contradistinction 
thereto, a sheet metal covering having a thickness of 1 mm requires a 10 
to 20 times longer cooling time and a much higher wattage to obtain the 
same pressures. 
For the heat supply, electrically heated radiation sources for example 
electric heating wires of up to 2 mm in diameter, are particuarly 
suitable, because they cool down sufficiently quick after the current is 
switched off. 
The heating of the 0.01 mm thick copper foil to temperatures between 
100.degree. and 200.degree. C. requires only a few minutes, taking into 
account a wattage of 1 to 2 kW per m.sup.2 of the surface area of the 
covering. By heating such a thin covering in accordance with the disclosed 
method, not only the pressure in the container but also the pumping time 
is reduced to fractions of the comparable values in isothermal processes. 
To illustrate the method of the invention, there is provided a vacuum 
treatment device which comprises a closed container having an interior 
walls with thin-walled metal sheet forming a covering arranged in spaced 
relationship to the walls to as to shield the major area of the walls, and 
to define a space between the walls and the covering with means for 
introducing a protective gas into the space with an exhaust gas line 
connected into the container with evacuating pump means associated 
therewith for evacuating the container wherein there is a thin-walled 
metal screen in the container shielding at least a portion of the exhaust 
line, and there are heating means for heating the covering and the shield. 
A further object of the invention is to provide a method of producing high 
vacuum in a vacuum container which has an exhaust connection line 
connected thereto, using an interior protective covering and a protective 
gas which comprises applying the covering to the interior of the container 
so as to shield the inner walls thereof and at least a portion of the 
exhaust connection and directing a protective gas into the space between 
the covering and the interior walls of the container, and thereafter 
evacuating the interior of the container through the exhaust connection 
and heating the covering. 
The various features of novelty which characterize the invention are 
pointed out with particularity in the claims annexed to and forming a part 
of this disclosure. For a better understanding of the invention, its 
operating advantages and specific objects attained by its uses, reference 
is made to the accompanying drawing and descriptive matter in which a 
preferred embodiment of the invention is illustrated.

GENERAL DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring to the drawings in particular, the apparatus embodied therein 
comprises a vacuum treatment device generally designated 50 which may be 
used for carrying out the method of the invention for producing a high 
vacuum in a vacuum container, comprising a container 1 as shown in FIG. 1. 
The container 1 is connected, through an exhaust connection 2, to a high 
vacuum pumping system 3. The inside walls of the container and exhaust 
connection are screened by thin metal sheets 4, 5. As a further portion of 
the screening or covering, an adjustable thin-walled screen 7 is provided 
between exhaust connection 2 and the space 6. Through a valve 8 and a 
connecting line 9, protective gas can be fed into the cavities formed 
between sheets 4, 5 and the inside walls of the container and the exhaust 
connection. The covering is advantageously heated by means of a suitable 
heater 10. The heater 10 comprises an electric radiating heating body 
which is energized from a supply unit 11 through a line 12 passed through 
the container wall. 
FIG. 2 shows an embodiment of a vacuum coater designed for carrying out the 
inventive method. Corresponding elements are designated as in FIG. 1 but 
with primes. Here again, the container walls are largely covered with thin 
metal sheets 4', so that only suction slits are left between the 
individual parts of the covering, to be able to evacuate or flood the 
intermediate space. 
As heating elements, electric heating wires 13 are shown in FIG. 2 which 
extend in the intermediate space. An adjustable flap 7.sup.1, comparable 
to the screen 7 of FIG. 1 and representing a portion of the covering, is 
also equipped with such heating wires, at its side remote from space 6'. A 
plurality of protective gas connections 9' is provided, to be able to 
bring the protective gas securely in contact with all portions of the 
inside wall of the container. In an exhaust connection 2', a cool trap 14 
is provided which can be supplied with a coolant through a funnel 15. For 
its operation as a vapor-depositing unit, the apparatus is equipped with 
an evaporation device 16 known per se which is supplied with current from 
a power source 18, through lines 17. Opposite to the evaporation device, a 
rotary supporting structure 19 of spherical shape is provided for the 
substrates to be treated. Further shown in s removable cover 20 for 
opening the apparatus, provided with an inspection glass 21. 
By sorption, in connection with this specification, any kind of fixing gas 
to the walls in a reversible manner is understood. Such a gas fixation is 
frequently described as adsorption when a fixing to the surface is 
assumed, or as absorption when it is assumed that the fixed gas has 
penetrated deeper into the wall, or also as chemisorption when the 
fixation is attributed to a reversible chemical reaction taking place on 
the surface or in the interior of the wall. 
While specific embodiments of the invention have been shown and described 
in detail to illustrate the application of the principles of the 
invention, it will be understood that the invention may be embodied 
otherwise without departing from such principles.