Coating processes – Coating by vapor – gas – or smoke
Reexamination Certificate
2001-10-25
2004-12-28
Hiteshew, Felisa C. (Department: 1765)
Coating processes
Coating by vapor, gas, or smoke
C117S084000, C117S088000, C117S089000, C117S090000, C117S091000, C117S092000
Reexamination Certificate
active
06835414
ABSTRACT:
FIELD AND BACKGROUND OF THE INVENTION
The present invention relates to a method for producing material-charged substrates in which
a) at least one substrate is introduced into an evacuated vacuum container;
b) the surface of the substrate to be charged is exposed to a reactive gas which is adsorbed on the surface;
c) the exposure of the surface to the reactive gas is terminated,
d) the reactive gas adsorbed on the surface is allowed to react.
Such a method is prior known from U.S. Pat. No. 5,916,365. Therein a substrate is introduced into an evacuated vacuum container with a container wall comprised of ceramics, delimiting the process volume against the environment.
The surface to be coated of the substrate is exposed to a first reactive gas, which is adsorbed on said surface. The exposure of the surface to the reactive gas is terminated by subsequently pumping off the reactive gas.
A second reactive gas is subsequently introduced and, by means of a coil configuration provided outside of the vacuum container, an electromagnetic high-frequency field is generated in the container. Thereby at least a portion of the introduced second reactive gas is activated to form radicals, and the first reactive gas adsorbed on the surface, is allowed to react exclusively with said radicals generated by the effect of the high-frequency field.
The present invention addresses the problem of proposing a method of the above listed type, which builds on the deposition of a monolayer of atoms on the surface of the substrate to be coated, but has a substantially expanded flexibility of application with respect to the variety of monolayers which can be deposited.
SUMMARY OF THE INVENTION
We are herein addressing charging with materials for the reason that said monolayer does not need to be deposited as a continuous layer in the sense of a coating, but rather the density of deposited atoms can be far lower than is necessary for the formation of a continuous layer. But, if desired, the material charging can readily take place such that a continuous monolayer is formed, in this case in the sense of a coating.
This is attained according to the invention thereby that
d
1
) the surface with the adsorbed reactive gas is exposed to a low-energy plasma discharge with ion energy E
I0
on the surface of the substrate of
0<E
I0
≦20 eV
and an electron energy E
eo
of
0 eV<E
eo
≦100 eV,
d
2
) the adsorbed reactive gas is allowed to react at least with the cooperation of plasma-generated ions and electrons.
In contrast to said U.S. Pat. No. 5,916,365 where the adsorbed gas is exclusively allowed to react with radicals, which by definition are electrically neutral, according to the invention the reactive gas adsorbed on the surface is also allowed to react mildly through the effect of ions and electrons generated by low-energy plasma discharge. Therewith the feasibility is given of properly stabilizing the adsorbed gas also without effect of radicals of a further reactive gas on the surface, solely through “mild” interaction with low-energy inert gas ions and electrons or through such effect by other reactive gas ions.
Although the cited U.S. Pat. No. 5,916,365 explains that it was prior known to deposit thin coatings with the inclusion of a glow discharge in an atmosphere of a mixture of reactive gases, but which did not lead to satisfactory coating formation, in the course of the present description it will be explained how the plasma discharge employed according to the invention must be implemented in order, in addition to the generation of the effect of ions and electrons onto the adsorbed reactive gas or gas mixture, to activate in the plasma discharge also a second reactive gas or reactive gas mixture to form radicals and ions and to bring the adsorbed reactive gas or gas mixture additionally into interaction with the radicals generated by plasma activation, and per se electrically neutral radicals, as well as reactive gas ions.
Since in any event electrically charged particles participate in the reaction of the adsorbed gas, the reaction and in particular also its distribution can be controlled by electric and/or magnetic fields, whereby, however, the behavior of radicals alone would not be influenced.
In a preferred embodiment the ion energy E
I
on the surface of the substrate is further reduced to the range
0 eV<E
I
≦15 eV.
Further, the adsorbed reactive gas can also be a reactive gas mixture. The plasma discharge is furthermore, either maintained in an inert gas atmosphere, therein preferably in an argon atmosphere, or the plasma discharge is generated in an atmosphere which contains a further reactive gas or gas mixture. This further reactive gas or gas mixture preferably comprises at least one of the following gases:
hydrogen, nitrogen, oxygen, preferably hydrogen, or it consists of hydrogen gas.
In a further preferred embodiment of the method according to the invention the vacuum container is evacuated to a pressure p
v
for which applies:
10
−11
mbar≦p
v
≦10
−6
mbar.
This ensures that virtually no contaminants are deposited from the vacuum atmosphere into which the substrate is introduced, and disturb the surface.
In a further preferred embodiment the reactive gas or gas mixture, which is to be adsorbed on the surface, is introduced up to a partial pressure p
p
for which applies:
10
−4
mbar≦p
p
≦1 mbar.
To a certain extent the quantity of the reactive gas or gas mixture adsorbed on the surface can be controlled by the time period between exposing said surface and terminating this exposure. It is essentially possible therein to assume an exponential function coursing towards a saturation value with a time constant characteristic for the dynamics of the saturating-out. This time constant can therein, if required, be controlled by heating or cooling the surface.
In a further preferred embodiment of the method according to the invention, the exposure of the surface to the reactive gas or reactive gas mixture to be adsorbed is terminated thereby that the substrate is transferred from the evacuated vacuum container with the reactive gas or gas mixture into a further evacuated vacuum container. The remaining process steps are completed in the further evacuated vacuum container. This has the advantage that a first vacuum container serves exclusively for the gas adsorption and therewith remains free of contamination, while the further vacuum container is employed for the plasma discharge reaction of the adsorbed gas.
In this approach it is possible, for example, to provide centrally a further vacuum container for the plasma discharge further treatment of the substrates, which previously had possibly adsorbed different reactive gases or reactive gas mixtures, in the specific “adsorption” container grouped about the central further vacuum container. Therewith complex coating systems comprised of even a multiplicity of different atom monolayers can be built layer by layer.
In many cases for the sequential deposition of differing or identical atomic monolayers in the central plasma reaction container using said low-energy discharge the same second reactive gas or reactive gas mixture can be employed, namely in particular preferred nitrogen and/or hydrogen and/or oxygen, therein in particular preferred is hydrogen. Conversely, it is also possible to assign several of the further vacuum containers for the reaction of the adsorbed reactive gases or gas mixtures in plasmas to an “adsorption” container, namely primarily when the adsorption step is shorter in time than the reaction step in the plasma.
In a further preferred embodiment of the method according to the invention, the exposure of the surface to the reactive gas or reactive gas mixture to be adsorbed is terminated by pumping out the remaining reactive gas or gas mixture from the evacuated vacuum container.
This pumping-out is therein preferably carried out until a total pressure p
v
′ has been reached in the vacuum container, for which applies:
10
−11
mbar≦p
v
′≦10
−8
mba
Hiteshew Felisa C.
Notaro & Michalos P.C.
Unaxis Balzers Aktiengesellschaft
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