EP0865663A1

EP0865663A1 - HF-PLASMA COATING CHAMBER OR PECVD COATING CHAMBER, ITS USE AND METHOD OF PLATING CDs USING THE CHAMBER

Info

Publication number: EP0865663A1
Application number: EP96937971A
Authority: EP
Inventors: Jürgen WEICHART
Original assignee: Balzers AG
Current assignee: OC Oerlikon Balzers AG
Priority date: 1995-12-08
Filing date: 1996-11-27
Publication date: 1998-09-23
Also published as: US6432492B2; JP2000501785A; WO1997022136A1; US20010007245A1

Abstract

Proposed is a chamber designed to provide dielectric substrates with protective coatings, the chamber being capable of operating at short cycle times and at temperatures suitable for plastics. A high-frequency plasma is produced by passing HF energy from a generator (19) through the substrate (1), opposite walls of the coating chamber (20) being formed by the substrate surfaces to be coated, which essentially make a seal with the chamber.

Description

RF plasma treatment chamber or PECVD coating chamber, their uses and methods for coating storage disks

The present invention is based on problems and needs which have arisen in the production of CDs. The resulting solutions can, however, be used in a fundamental way for other applications. Therefore, in the present description, the needs and problems in CD production are specifically taken as a starting point. Approaches according to the invention are described in order to then, generally speaking, show how the principles found can generally be used.

It has become established in the manufacture of CDs to treat the individual plastic substrates with very short cycle times per processing step, in the range of seconds. Vacuum sputtering technology has become established for applying the reflective metal layer. The subsequent varnishing with a protective varnish is carried out in a wet coating process.

In particular the subsequent rapid hardening of the lacquer under ultraviolet light represents a problem with the reliability of the CD production.

With regard to the vacuum coating technology, which is usually used for metal coating, the aforementioned coating is also foreign to the species.

So that the very short metal coating cycle times are not negated by much longer wet coating process cycle times, the painting process is long to operate technical expenses.

It is an object of the present invention to provide a vacuum treatment chamber which makes it possible to implement the protective layers mentioned in a vacuum process which is related to sputter technology and which has the required short cycle times.

Processes are now well known from vacuum coating technology for depositing non-conductive layers, such as corrosion protection layers. Usually, however, much longer coating times are to be accepted than the required few seconds specified above.

If coating rates of approximately 40 nm / sec are possible in the interior of the plasma discharge, as in known, so-called plasma-enhanced chemical vapor deposition (PECVD) processes with microwave plasma discharges, the plasma densities required for this are nevertheless so high, that the resulting temperature loads do not allow coating on plastic substrates. In order to maintain the plastic (for example PMMA or polycarbonate) tolerable temperatures, the substrate would have to be moved so far out of the range of the highest plasma density that, due to the lower coating rate there, the required short cycle times would not be maintained could become.

In addition, experience has shown that layers which are deposited at a high rate in the edge region of microwave discharges are frequently of a loose structure and are therefore not suitable for use as corrosion barrier layers.

In summary, it can therefore be said that the joint fulfillment of the short cycle times, in the range of seconds with the required coating thickness, the temperature load to be maintained and the maintenance of a sufficient layer quality were previously considered to be impossible to achieve with vacuum coating methods.

Less generally known, further known high-frequency CVD methods have the disadvantage that not only the substrate but also RF coupling arrangements are coated, be it with microwave plasmas, dielectric coupling windows or, at lower frequencies, with metallic coupling electrodes . Cleaning with replacement of the parts mentioned or by plasma chemical in-situ cleaning is not compatible with the requirement of short cycle times to be maintained over long periods.

It is therefore a further object of the present invention to develop an apparatus and a method for the rapid and economical deposition of layers from the gas phase, a low loss of layer material and a high degree of homogeneity being required.

On a high-frequency plasma treatment chamber according to the preamble of claim 1, with a view to the CD production problems, then designed as a coating chamber, in this case also designed in particular for a PECVD process, the above-mentioned problems are dealt with in their formation according to the Characteristic of claim 1 solved, ie in that the high-frequency discharge circuit also includes the substrate as a capacitive coupling element.

While in the specific application on metal-coated dielectric, in particular plastic substrates, such as in the CD production, a use of the substrate as a microwave coupling window is out of the question, under a general aspect of the present invention according to claim 1, the microwave coupling through the dielectric substrate is quite possible, even if the one carried out Coating is dielectric.

In principle, according to the invention, a metal-coated dielectric substrate also acts as an electrode with respect to high-frequency plasmas in the lower frequency range.

The basic finding according to claim 1 is that the required high-frequency power can thereby be kept low, which solves the problem of the temperature load. At the same time, however, such high coating rates are achieved that the required effective protective layers can be removed in extremely short coating times, even of one second.

It was also found that the so, i.e. in a high-frequency PECVD coating process with the chamber according to claim 1, deposited protective layers with a comparable layer thickness are even harder than conventional lacquer layers. Furthermore, the layers are deposited practically exclusively on the high-frequency coupling surface acting substrate surface to be coated.

More specifically, in a PECVD coating chamber according to the preamble of claim 2, the problems mentioned above can be remedied, for the time being independently of the proposal according to claim 1, by their formation according to the characterizing part of claim 2. For the time being, this training aims to coat the process chamber wall areas, in addition to the layering substrates to keep as low as possible. However, a disadvantage of this solution approach, taken on its own, is that the coating rate on process chamber walls which are not covered by the substrate remains high, so that problems caused by flaking layers arise during prolonged operation without cleaning. On the other hand, high coating rates are also achieved with this chamber at the required low loading temperatures.

A chamber which is optimized in every respect results from the simultaneous implementation of the coupling technique according to claim 1 on the chamber with minimum volume according to claim 2.

A protective coating method according to the invention for storage disks, in particular optical storage disks, such as CDs, is therefore also created, which is embodied in the continuous production process as a vacuum coating method and is therefore of the same type as the fast sputtering method usually provided for metal coating . Following the wording of claim 12, a high-frequency PECVD method is preferably used, in which the high-frequency plasma discharge energy is coupled into the process space via the substrate.

Preferred embodiments of the invention are subsequently explained on the basis of figures, starting from this, on the basis of further figures and moving away from the specific production of CD or storage disks, the principles according to the invention presented by the following further embodiments of the invention.

Particularly preferred embodiments are in claims 3 to 8 with respect to the treatment chamber according to the invention specified, their preferred uses in claims 9 and 10.

The figures show:

Fig. 1 with a specific for the CD protective coating

PECVD designed coating chamber according to the invention, schematically and in cross section;

2 shows a further coating chamber according to the invention specifically designed for the Hf-PECVD protective coating of CDs;

3, starting from the coating chamber according to FIG. 2, schematically, the RF coupling technology according to the invention for the treatment of non-metal-coated dielectric substrates in microwave plasma;

FIG. 4 schematically, in a representation analogous to FIG. 3, the coupling technique used in the chamber according to FIG. 2 on a substrate without a metal coating;

Fig. 5 in a representation analogous to Figs. 3 and 4, a further coupling technique according to the invention;

6 schematically, an Hf-PECVD coating chamber according to the invention, which, combined, has the features according to the invention of the chamber according to FIG. 1 and the chamber according to FIG. 2.

1, as a first example, specific for the protective coating of circular disc-shaped substrates 1 with a ner center opening, namely in particular of storage disks, in particular optical storage disks such as CDs, with a metal, for example aluminum, coating 3, the chamber according to the invention around the central axis C is extremely flat, in the special case as a flat cylinder. The two-dimensional chamber walls 5 lying opposite each other with respect to the central axis C are essentially identical and carry, centrally, each pumping nozzle 7, a receptacle 9 for the periphery of the substrates to be coated 1. Because the chamber itself is designed according to the invention, which is not the case when the substrates 1 to be coated are picked up, the substrates 1 are shown in dashed lines.

The receptacles 9 each define receptacle surfaces 11 for the substrates 1 to be raised. The pump nozzles 7 are designed such that they protrude through the openings provided in the substrate and, if necessary, also serve to hold or position the substrate with the receptacles 9.

The chamber walls 5 are spaced such that the receiving surfaces 11 for the substrates 1 are at a distance A which must be at least large enough to avoid uncontrollable cavity discharges between the plates, which is at least 10 mm. On the other hand, the deposition on the cylinder jacket surfaces should be as small as possible, so that the distance A should be smaller than the plate radius.

With regard to the receptacles 9 peripheral, gas feeds 13, which are connected to a reactive gas tank (not shown), open into the area of both walls 5, preferably distributed. Pump units (not shown) are connected to the pumping nozzle 7. The spacing of the walls 5 is ensured by insulation parts 15, between which, preferably all around, a metallic electrode 17 is embedded. The latter is connected to a generator 19 for maintaining the plasma discharge in the process space 20, as are preferably both walls 5.

Depending on the intended coating process, the generator 19 can be designed as a DC generator or as an AC generator or emit a superimposition of the DC + AC signal or can emit a pulsating signal.

As is readily apparent from FIG. 1, there is a homogeneous reactive gas admitted unused, radially inward, along the substrates to be coated here by PECVD to the pumping of remaining reactive gas and gaseous, non-deposited reaction products.

With a chamber, as shown schematically in FIG. 1, a protective coating on Al-coated polycarbonate CD substrates was implemented while maintaining the following sizes:

Distance of the substrate surfaces to be coated: 50mm

Reactive gases:

a) Monomer: Hexamethyldisiloxane Flow: ΘOsccm

b) 0 ₂ :

Flow: 40sccm Total pressure: 42Pa

Generator frequency: 100kHz

Generator power: 250W at the load

Process time: 15sec

Results:

The layer thickness, measured on a measuring circle with a radius of 20 mm on the CD, was 430 nm, and 436 nm on a measuring circle with a radius of 55 mm.

This corresponds to a growth or coating rate of 29nm / sec.

If one takes into account that layer thicknesses of already approximately 140 nm are sufficient, it can be seen that the required coating is possible within approximately 5 seconds with the chamber according to the invention according to FIG. 1.

The polycarbonate CD substrate showed no thermal impairment whatsoever.

A disadvantage of the chamber presented in FIG. 1 is that the preferably annular electrode 17 is also coated. The coating rate determined on the electrode 17 in the example mentioned above was approximately three times higher than on the substrate. In the event of prolonged operation without cleaning, problems can therefore arise as a result of flaking layers from the electrode, which can contaminate the substrate coating and / or disrupt the plasma discharge. These problems are solved in the second preferred chamber according to the invention according to FIG. 2.

This shows the chamber according to the invention, again specifically for the protective coating of circular disk-shaped dielectric substrates, in particular storage disks with plastic substrates, again in particular for CDs. The substrate 1 with the metal coating 3, again, since it is not part of the chamber according to the invention, entered in dashed lines, lies on the receiving surface 11 of the receptacle 9 provided for receiving the substrate 1 along the peripheral region of the chamber. The pumping nozzle 7 is designed such that it protrudes through the center opening of the inserted substrate 1. At the periphery, in the area of the receptacle 9, the reactive gas inlets 13 open, preferably distributed, whereby in the embodiment shown here, in contrast to that according to FIG. 1, which is not mandatory, however, a separate gas inlet 13a for the reactive gas 0 _{2 is provided} with a separate pump nozzle 7a.

The high-frequency coupling from the generator 19, which in this case must be a high-frequency generator, working into the microwave range, is connected to a coupling electrode 21, which is exposed on the receiving surface 11 for the substrate 1 and, preferably, in a ring shaped, is embedded in an insulation support 22. As shown, the remaining metallic parts of the chamber are connected to the reference potential, in particular ground potential. In this case, both socket 7 and flange 13a are preferably electrically insulated from the chamber wall or formed as an insulator (not shown), the chamber wall is at reference potential. Because the material of the substrate is dielectric, ie in the special case made of plastic, such as in particular PMMA or polycarbonate, the electrode 21 on the one hand, the plastic body of the substrate 1 on the other hand and the metal coating 3 act as coupling capacitance, through which the high-frequency energy is transmitted into the Reaction space 20 is coupled. The chamber according to FIG. 2, which represents a preferred form of the invention, was operated as follows:

Reactive gases:

a) Monomer: lOOsccm 1,3 divinyl-1, 1,3, 3-tetramethyldisiloxane

b) oxygen:

Flow: lOOsccm

Total pressure: 60Pa

Generator frequency: 13.56MHz

Generator power at the load (reflection approx. 5%): 450W

Process time: lsec

As a result, a layer with a thickness of 140 nm was deposited, which corresponds to a coating rate of 140 nm / sec.

In particular in the case of precoating with a metallic layer made of Al, it is advisable to precede the aforementioned PECVD protective coating with a short oxygen treatment of approximately 0.2 seconds; even layer thicknesses of more than 7μm can be adhered in this way to CD substrates in a pulsating operating mode. In the continuous operating mode, the process time for CDs is limited to 10 to 20 seconds for thermal reasons. This is understandable if one assumes that if only a fraction of 100W is injected into a CD with a mass of 16g for 15sec, its temperature will increase by 80 °.

Because, as can be seen from FIG. 2, the metal layer 3 or its surface acts as an equipotential surface, the uniformity of the coating thickness distribution is very good, for example with deviations of at most 4% from the mean. The deposition rate on reactor parts not to be coated was measured at a distance of 1/30 of the CD coating rate at a distance from the CD surface to be coated.

The following process size ranges are particularly recommended for the protective coating of optical storage disks, such as CDs:

Base pressure: <8Pa, which can be achieved in a very short time with a two-stage rotary vane pump.

Pump cross section: according to the center opening of the

Storage disk and, according to FIG. 2, optionally via additional pump lines above the substrate to be coated.

Process pressure: 30 to 10OPa, preferably approx. 60Pa.

Monomer: preferably a siloxane compound, such as, for example, hexamethyldisiloxane or divinyltetramethyldisiloxane _c, preferably supplied on the circumference of the substrate to be coated.

Another reactive gas: preferably oxygen, not necessarily supplied at the periphery of the substrate to be coated.

Plasma operating frequency: 1 to 500 MHz, preferably 13.56 MHz for reasons of availability.

Power: 200 to 1000W RF.

Process time: 1 to 15sec. A plasma pretreatment in pure oxygen is preferably carried out for a process time of 0.1 to isec.

The coating process carried out with the chambers according to the invention runs at relatively high pressure and is not sensitive to residual air, i.e. as mentioned, a two-stage rotary vane pump is sufficient for pumping.

The high-frequency power required is low, for example 600W, which enables corresponding savings, inter alia when the generator is provided. Effective corrosion protection layers can be produced in very short process cycle times of lsec. With a comparable layer thickness, the layers are harder than wet-applied lacquer layers. The deposition takes place practically only as desired on the substrate. The chambers, both according to Fig. 1 and Fig. 2, can be easily set up for automatic handling.

In particular, the procedure according to FIG. 2 with high-frequency coupling through the substrate can be used for many other high-frequency plasma treatment methods, e.g. be used for reactive etching processes of the substrate, further e.g. for the deposition of dielectric intermediate layers or metal organic compounds as metallic layers on dielectric substrates.

Compared with the known protective coating techniques, in particular for CDs, there is a higher reliability and higher layer hardness; this results in a lower consumption of coating material and a lower environmental impact.

As the person skilled in the art immediately recognizes, the RF coupling technique, as was explained specifically for the CD application with reference to FIG. 2, fundamentally offers a wide variety of possibilities.

According to FIG. 3, microwave energy can be injected into the process space 20 through the dielectric substrate 1, provided that it is not metallically coated, where the substrate 1 is non-conductively coated or etched.

4, a non-metallic precoated substrate 1 can be treated by coupling the high-frequency energy of the generator 19 into the process space 20 via the electrode 21 and thereby acting as a capacitance counterelectrode with respect to the electrode 21. It should be emphasized that, as shown specifically in FIG. 5, in the chamber according to FIG. 2 as well as in FIG. 4 the electrode 21 does not have to be exposed against the process space 20 in order to contact the substrate 1 directly. It can be covered electrically.

Of course, the coupling method according to the invention can also be carried out if, as with the CD, the surface to be coated and / or the back of the substrate is metal-coated. Here the dielectric carrier of the substrates takes on the function of a coupling capacitance in an HF discharge. The resulting soap-bias voltage on the metal layer has an advantageous effect on increasing the coating rate and its uniformity - by forming an equipotential surface.

With regard to the dimensioning of the electrode surfaces of the electrodes 21 and the dielectrics lying between the latter and the process space 20 and their thicknesses as well as the operating frequencies used, the person skilled in the art knows the corresponding laws. In order in particular to achieve the coupling into the metal layer on the CD, the electrode surface or its projection should not be larger than the surface of the metal layer.

FIG. 6 shows a further preferred embodiment of a chamber according to the invention, which results from the consideration of FIGS. 1 and 2 without further explanation.

The coupling principle via the substrate 1 according to FIG. 2 is used on the chamber according to FIG. 1. As a result, with a view of FIG. 1, there is no electrode 17, which is excessively hard-coated on the embodiment according to FIG. 1. Of course, the two coupling electrodes 21 provided on the chamber according to FIG. 6 are preferably operated by the same high-frequency generator if a symmetrical discharge, as in the vast majority of cases, is to be achieved, as shown in dashed lines at 19a. With regard to the potential connection of a chamber housing (not shown here), the flanges 13a and the connecting piece 7, what has been said in relation to FIG. 2 applies.

Claims

Claims:

1. RF plasma treatment chamber for at least one dielectric substrate (1) with an RF generator (19) for the plasma discharge and an associated coupling arrangement for RF energy into the chamber (20) as well as at least one receiving surface for the substrate (1) defining substrate receptacle (9), characterized in that the receptacle (9) and the RF connection to the generator (19) are arranged in such a way that the RF discharge circuit depletes the substrate (1) as a capacitor capacitive coupling element.

2. PECVD coating chamber for at least two flat substrates with a generator (19) for the plasma discharge and an associated coupling arrangement for the discharge energy into the chamber (20) and with at least two receiving surfaces (11) for one of the substrates (1) defining substrate receptacles (9) and with a gas inlet (13) - and a gas pumping (7) arrangement on the chamber, characterized in that the receiving surfaces (11) lie opposite one another and, essentially conclusively, opposing process space Define boundary surfaces that the following also applies to the distance A of these surfaces:

A <10mm.

3. Treatment chamber according to the features of claim 1 with substrate receptacles according to claim 2.

4. Chamber according to one of claims 1 or 3, characterized gekenn¬ characterized in that the RF generator (19) is a microwave generator and the substrate forms the coupling window.

5. Chamber according to one of claims 1, 3 or 4, characterized in that the coupling arrangement has a, in the area of the receiving surface (11) arranged, for this purpose essentially plane-parallel, metallic electrode surface (21) which against the chamber interior (20) is exposed or is dielectrically covered.

6. Chamber according to one of claims 1 to 5, characterized gekenn¬ characterized in that the receptacle (9) or the receptacles (9) for circular disk-shaped substrates (1) is or are, a gas inlet arrangement (13) in the peripheral region of the jewei¬ leaigen defined receiving surface (11), preferably distributed, opens and a gas pumping arrangement (7) opens centrally with respect to the receiving surface (11) in the chamber.

7. Chamber according to one of claims 2 to 6, characterized in that the coupling arrangement comprises an electrode (17) which is arranged on a chamber wall section (15, 17) spacing the receiving surfaces (11), preferably as a circumferential ring electrode (15 ).

8. Chamber according to one of claims 1, 3 to 7, characterized ge indicates that it is designed as a PECVD chamber and for this purpose has a gas inlet arrangement (13) and a gas pumping arrangement (7).

9. Use of the chamber according to one of claims 1 to 8 for the treatment of substrates with a plastic base body.

10. Use according to claim 9 for the protective coating of a metal-coated substrate surface, preferably on an optical storage disk, preferably on a CD.

11. Process for the protective coating of metallically coated storage disks in a continuous process, characterized in that a vacuum coating process is used for this.

12. The method according to claim 11, characterized in that a PECVD method is used.

13. The method according to any one of claims 11 or 12, characterized in that an RF plasma is generated for the coating and the RF energy is coupled into the process space for this purpose via the substrate.