Coating apparatus – Gas or vapor deposition – With treating means
Patent
1994-09-22
1997-09-02
Niebling, John
Coating apparatus
Gas or vapor deposition
With treating means
118723HL, C23C 1600
Patent
active
056627416
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a process for the ionization of material vapors generated thermally at reduced pressure and a device for conducting the process.
It is generally known that the use of ionized material vapors in coating substrates from a vapor phase results in significant improvement of various layer characteristics. In particular, by using plasma- and ion-based processes, higher adherence of the coating on substrate surfaces as well as higher compactness of the layer structure may be achieved. Furthermore, there is the possibility of conducting reactive coating processes.
In order to generate ionized material vapors, electrical discharges are used. Here, according to physical aspects, a distinction is made between glow discharges and arc discharges.
Glow discharges include cathode sputtering. Arc discharges are classified as discharges constrained to process gas using hollow cathodes according to U.S. Pat. No. 3,562,141 or glow cathodes according to U.S. Pat. No. 4,197,175, and vacuum arc discharges with self-consuming cathode according to U.S. Pat. No. 4,562,262, or self-consuming cathode and hot self-consuming anode according to U.S. Pat. No. 4,917,786.
Further, from DE-A-30 42 337, there is known a vacuum arc discharge having a controlledly adjustable degree of ionization. In the process described therein, vapor deposition rate and degree of ionization are highly interdependent in order to control the latter. Furthermore, the control of the degree of ionization described therein requires mechanical motion in vacuum.
All the above-mentioned processes have in common that the vaporization material must be arranged in a process-specific fashion. Conventional thermal vaporizers are not part of the processes mentioned. These include resistance- or induction-heated crucibles or vaporizer helices as well as material vaporization using an electron beam. Material vapors generated by thermal vaporizers are non-ionized. Several methods for the ionization of such material vapors are already known.
The DE-A-39 31 565 describes a method according to which the thermally generated vapor is admixed with ions of a gaseous starting material, typically argon or nitrogen. These ions are generated in a separate ion source. Therefore, the issue concerned here is not ionization of material vapor but material vapor which is admixed with ions of a gaseous starting substance.
U.S. Pat. No. 4,039,416 and U.S. Pat. No. 4,342,631 describe processes for generating ionized material vapors, wherein the material vapors are generated by means of thermal vaporization (induction or resistance heating). Ionization of these material vapors in the vicinity of the workpiece to be coated is effected by the coupling of high frequency electromagnetic waves (RF heating). The advantage in this method is that pure plasma of the material vapor is produced without employing a process gas. However, RF discharges are difficult to control, particularly on a larger industrial scale, and require shielding measures to avoid spurious radiation.
Furthermore, from U.S. Pat. No. 3,756,193 and U.S. Pat. No. 4,461,689, there is known a process wherein the material vapor generated by an electron beam is ionized by means of a d.c. glow discharge. In order to maintain such glow discharge, the material vapor must be admixed with a process gas. The principle of this process called "ion plating" was first described in U.S. Pat. No. 3,329,601.
A drawback in ion plating is that in practice, this process is restricted to a laboratory scale. With increasing size of the vaporization apparatus or the substrate surface, the tendency of a d.c. glow discharge to turn into an arc discharge is greatly increased. At a critical size of apparatus and thus, above a critical value of the discharge current, the arc will always be the form of discharge preferred over the glow discharge. This changing into an arc discharge may result in considerable damage in vapor source or substrate. Another drawback is the use of high voltage and the use of a process gas which frequently adver
REFERENCES:
M. Mausbach et al., "Relations between plasma properties and properties of thin copper films produced by an anodic vacuum arc", Materials Science & Engineering, vol. A140 (1991), 825-829.
Chang Joni Y.
Niebling John
Plasco Dr. Ehrich Plasma-Coating GmbH
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