Method and apparatus for sputter coating

The present invention relates to a method for sputter coating workpieces, in which two opposing atomizing surfaces are atomized against each other and a gas flow is created between the atomizing surfaces and directed against at least one workpiece. Furthermore, the present invention relates to a sputter coating source with two opposing atomizing surfaces, an anode arrangement provided between the atomizing surfaces and a gas outlet arrangement acting in a gap defined between the atomizing surfaces, according to the preambles of claims 1 and 15, respectively. Furthermore, the present invention relates to a sputter coating system with such a source and uses of the method according to the invention, the source according to the invention or the system according to the invention.

It is known from US Pat. No. 4,094,764 to implement a gas flow over the atomizing surface for the sputter coating of a workpiece in order to drive the flowing inert or noble gas against the workpiece with dusted target material. In this way, a significantly higher coating rate is achieved compared to conventional cathodic sputtering.

The procedure according to DE-PS 42 10 125 is very similar, in that a gas flow is not created over the atomizing surfaces of a flat target according to US Pat. No. 4,094,764, but along the inner surface of a hollow-cone-shaped target - a hollow cathode target - and the material dusted from the target is fed to a substrate workpiece by means of the flow.

In H. Koch et al. "Hollow cathode discharge sputtering device for uniform large area thin film deposition", J. Vac. Sci. Technol. A9 (4), Jul / Aug 1991, the advantages of such hollow cathode sputtering are discussed, in particular with regard to the use of the electrons for the ionization of the gas contained in the reaction volume. It is therefore proposed there to provide a transverse slot in a target block and to use a gas flow directed through this slot against a workpiece.

Two atomizing surfaces of the target are located close to each other at the slot, which minimizes the undesired reloading of system parts other than the target itself.

This is of particular importance in the case of reactive DC sputtering, in which electrically insulating reaction products are produced and re-used as coating material.

However, this procedure has the following disadvantage:

If the occupancy of the opposing sputtering surfaces with target material that has already reacted is to be minimized and the electron impact efficiency for ionization is to be maximized, the selected gap width and thus the distance between the two sputtering surfaces must be kept small. However, the formation of the gap with closely opposing atomizing surfaces requires correspondingly short gap width or end surfaces. This, in turn, is extremely disadvantageous with regard to the electron sauce yield, in that they are reflected in the slot end regions and, in the end, without being completely released by the shock cascade to the gas particles, are in some cases not fully dissipated via the anode. There is therefore basically the problem when using a hollow slot cathode of the type described in the above-mentioned article that the better the target assignment problem is solved along the sputtering surfaces, namely with the smallest possible slot width, the higher the loss of electron impact yield in the slot end areas. As a rule, there is an electron drift in the longitudinal direction of the slot, preferably towards a slot end, which leads to an uneven longitudinal plasma distribution and thus dust distribution.

The present invention aims to solve the above problems. This is achieved on the basis of the method of the type mentioned above in that the opposing atomizing surfaces are each self-contained and the gas flow is generated by a self-contained gap, essentially transversely to cutting planes, in which the gap appears to be closed, with which a closed one Plasma loop is created.

The fact that the gap is self-contained, realized by two mutually opposed, each self-contained atomizing surfaces, for example an inner cylinder target and an outer cylinder hollow target, means that the gap width can be dimensioned within wide limits and, in particular, can be made short, in particular the one mentioned Taking back problems into account, but thanks to the self-contained atomizing surfaces, Even if there are corners provided, as when using cuboid targets, there are no gap ends at the circumferential gap and thus the electrons that move along and within the plasma loop can circulate in them until they reach their energy by collisions with the gas particles have given as completely as possible, which leads to a more efficient plasma discharge. This is evident from the lower discharge voltages and the more stable operation.

If, as is preferably proposed, each of the self-contained atomizing surfaces is formed on its own target, this results in a preferably stable arrangement. Each of the intended targets can also be supplied with a separate generator arrangement in order to achieve optimum power balancing or to produce mixed materials with different target materials.

In particular due to the high plasma density in the circumferential gap, it is possible to further minimize the reoccupation problem of the sputtering surfaces, in particular with electrically insulating reaction products, during reactive sputtering, which makes the proposed procedure particularly suitable for coating with dielectric materials, in particular with oxides. In a preferred embodiment, therefore, at least one gas fraction is selected as the reactive gas, preferably with O₂, whereby good gas separation is ensured if the inert gas, for example Ar, is admitted into the gap and the reactive gas, removed from the target, into the chamber.

Reactive gas is most preferably not admitted through the gap, but directly into the coating room.

In a particularly preferred embodiment, the coating is carried out with a material with at least one ferromagnetic component or with a dielectric material, both coating materials, as is known, extremely critical for DC sputtering, which is also preferred here. In a further preferred embodiment, the coating is carried out with MgO or ITO, be it by reactive sputtering of metallic targets or, if appropriate, by additionally reactive sputtering of oxidic targets, in particular, as in the case of MgO, of materials which, owing to their extremely low conductivity, express for DC sputtering are problematic.

With the procedure according to the invention and due to the fact that the two opposing atomizing surfaces can each be realized on a target, there is also the possibility of using different materials for the two atomizing surfaces and thus of depositing more complex coating materials, in particular reactively.

In a particularly preferred embodiment, a magnetic field is generated in the gap, preferably in the manner of a magnetron field, by generating at least one magnetic field with a tunnel-shaped field line course on at least one, preferably along both atomizing surfaces, the tunnel axes running along and along the self-contained sputtering surfaces preferably also close.

If a substantial increase in the plasma density is achieved with the inventive provision of a closed, circumferential gap compared to slot targets, as mentioned in the above-mentioned article, then this plasma density is increased even further by providing the magnetic fields mentioned. This is partly due to the increasingly improved electron impact yield (continuously rotating electron traps).

Although it is entirely possible to operate the target (s) with AC in the procedure according to the invention, DC is used, above all for cost reasons, in a much preferred form of implementation, if necessary with superimposed AC, as in pulsed operation, in order to conduct the operation in a particularly stable manner .

A sputter coating source for solving the above object is characterized in that the atomizing surfaces each form self-contained surfaces, the gap is a self-contained gap that is open at least on one side, and the gas outlet arrangement is provided opposite the gap opening.

A sputter coating system according to the invention has at least one sputter coating source of the type mentioned and for the at least one target, preferably the at least two targets, a DC generator, optionally a generator arrangement for emitting a DC signal with a superimposed AC signal, preferably a pulsed DC signal. Signal.

The method according to the invention, the source according to the invention and the system according to the invention are particularly suitable for sputter coating with ferromagnetic materials or dielectric materials, in particular for MgO or ITO coatings or for coating plasma display panels where large areas have to be coated economically .

In this case, the substrates can be guided over the linear source arrangement, for example. It is also possible to arrange several linear sources at intervals suitable for distribution in order to increase the overall coating rate or to statically coat a large area.

Preferred embodiments of the method according to the invention are specified in claims 2 to 14, the source according to the invention in claims 16 to 23 and the system according to the invention in claims 24 and 25.

Particularly preferred uses of the invention are specified in claims 26 to 28.

The invention is subsequently explained, for example, using figures. These show:<dl id="dl0001"><dt>Fig. 1:</dt><dd>Perspectively and schematically, a cross section through a sputter source according to the invention, working according to the method according to the invention;</dd><dt>Fig. 2:</dt><dd>starting from the illustration in FIG. 1, a further variant for the electrical supply of the source mentioned;</dd><dt>Fig. 3:</dt><dd>a schematic cross-sectional view of a further atomizing surface arrangement according to the method according to the invention or at a source or plant according to the invention;</dd><dt>4 to 8:</dt><dd>further perspectively arranged arrangements of atomizing surfaces or targets in the procedure according to the invention;</dd><dt>Fig. 9:</dt><dd>schematically a sputter source according to the invention, operating according to the method according to the invention and used in a system according to the invention with a magnetic field which is preferably used;</dd><dt>Fig. 10:</dt><dd>starting from the illustration according to FIG. 9, a further embodiment of the magnetic field that is preferably used;</dd><dt>Fig. 11:</dt><dd>a further development of a preferably used magnetic field;</dd><dt>Fig. 12:</dt><dd>the DC plasma discharge voltage (a) using the state-of-the-art procedure above the power removed per atomization area unit,<ul id="ul0001" list-style="none"><li>(b) in the procedure according to the invention without a magnetic field,</li><li>(c) in the procedure according to the invention with a magnetic field and</li></ul></dd><dt>Fig. 13:</dt><dd>a slot target of known construction with definition of its geometrical sizes.</dd></dl>

The basic procedure according to the invention will be explained with reference to FIG. 1.

Two self-contained atomizing surfaces 3a and 3b are provided in such a way that they define between them a gap 5 which is open and closed at least on one side at a circumferential opening 10. The atomizing surfaces 3a or 3b, as shown in dashed lines in FIG. 1, can be formed by incorporating the gap 5 into a uniform target block, but preferably the atomizing surfaces 3a and 3b are atomizing surfaces each of a target, namely an external target 6a and an all-round or essentially rod target 6b.

At one end area of ​​the gap 5, an anode arrangement 8 is provided which, as shown, can be formed from a common anode for both targets 6a or 6b, but can optionally also comprise two separately feedable anode rings. The anode can, however, also advantageously be placed on the outlet side (10) and at the same time enclose the cathode from the outside with a dark space distance, or else be mounted insulated. It can also be designed as a slit diaphragm at the same time. Anodes are preferably operated at ground. Bias feeding to control the particle energy is also possible. Such an anode arrangement is shown in dashed lines in FIG. 2 at 8a.

A gas flow G is generated along the gap 5, essentially transversely to the cutting surface, such as E, in which the gap 5 appears to be closed all the way round. With the gas flow G, coating particles are carried out of the gap 5 through the gap opening 10 against one or more workpieces 12 and deposited there gently. With reactive sputtering, a reactive gas is only admitted there.

The one or, as shown, the two targets 6a, 6b defining the atomizing surfaces 3a and 3b are preferably supplied individually with DC or optionally with DC and superimposed AC, each from an assigned generator 14a or 14b. Alternatively, as shown in FIG. 2, they are optionally fed by a common generator 14c.

The workpiece 12 or a workpiece carrier (not shown) provided for this purpose in the system according to the invention is floating in a vacuum chamber of the sputtering system according to the invention with the source 16 just described, or at reference potential, such as ground, or at a bias potential, preferably DC Potential, or a DC potential with superimposed AC potential, as is shown schematically in Fig. 1 with the possibility switch 20.

A further arrangement of the atomizing surfaces 3a and 3b according to FIG. 1 is shown schematically in cross-section in FIG. 3. In this case, the gap 5 ′ tapers towards the gas outlet opening 10, whereby an accelerated gas flow G against the workpiece 12 is achieved, similar to a compression stage. As further shown in dashed lines in FIG. 3, this can be seen from FIG. 1 extend the principle on which the present invention is based, insofar as the interior 22 can optionally also be used with an additional atomizing surface 3c for coating purposes - as a hollow cathode - and / or by providing additional atomizing surfaces 3d and correspondingly surrounding columns 10a, an increasingly complex source according to the invention is realized in a space-saving manner can be.

Without showing further details in FIGS. 4 to 8, apart from the arrangement of the atomizing surfaces and, correspondingly, the design of the one or two targets provided in the minimal configuration, these figures show different design variants of the circumferential gap 10 and thus of the circumferential gap which also defines it Atomizing surfaces 3a and 3b.

In FIG. 4, the circumferential gap 10 is rectangular, in the form of a frame, according to FIG. 5 circular or elliptical, the atomizing surfaces defining the gap in FIGS. 4 and 5 being parallel to a center axis A and equidistant. The sputtering surfaces according to FIGS. 4 and 5, namely, cuboid surfaces or cylinder surfaces or cylinder-like surfaces 3a, 3b.

In the arrangement according to FIG. 6, the sputtering surfaces 3a, 3b span truncated pyramid surfaces, according to FIG. 7 essentially circular-conical or ellipsoid-conical surfaces.

6, 7 and 8, despite the constant evaporation surfaces, the gas flow cross section of the gap towards the opening 10 is reduced even more markedly in the embodiment according to FIG. 3. On the one hand, this results in an increasingly intensive contact of gas flow with the atomization surfaces and a gas flow -Acceleration against the workpiece. This effect can - as mentioned with reference to Fig. 3rd - In all the embodiments according to FIGS. 4 to 8, the atomization surfaces are not arranged equidistantly, but approach the outlet opening 10, preferably steadily. In the embodiment according to FIG. 8, which differs from that of FIG. 7 is shown as an example of how a pronounced pressure stage can be realized between gap 5 and workpiece coating space B with a corresponding increase in the gas outflow speed towards the workpiece 12 shown in FIG.

1 to 8 it is clear to the person skilled in the art how the atomizing surfaces are to be designed and arranged in principle and according to the invention, and this opens up further possibilities for saving gas or even better separating inert gas and reactive gas.

FIG. 9 shows a cross-sectional illustration of a system according to the invention with a sputtering source according to the invention, which works according to the method according to the invention, wherein further, most preferably used measures are to be described, which of course are preferably also implemented in all the embodiments of the invention described so far.

9, a source 16 according to the invention is provided in a treatment chamber 30 of a system according to the invention. It lies opposite a workpiece carrier 32, shown schematically. It can be designed according to one of the different variants shown with reference to FIGS. 1 to 8. The gap area opposite the gas outlet opening 10 of the gap 5 is closed and carries a circumferential anode ring 34. A gas distribution space 38 is provided in the gap closure 36, which is fed, for example, by means of a circumferential ring line 40 from a gas tank arrangement 42, which preferably contains an inert gas, such as an inert gas, for example Ar.

In addition, and as the preferred variant shown in all the variants according to FIGS. 1 to 8, a magnetic field H is generated in the gap 5. Permanent and / or electromagnet arrangements 44 are provided, which generate atomizing surfaces 3a and 3b on at least one, as shown on both, atomization surfaces 3a and 3b, preferably in a tunnel-like manner, the tunnel axes, as in A_T 9, also revolve along the circumferential, self-contained atomizing surfaces and are preferably also self-contained.

FIG. 10 shows another arrangement of the tunnel magnetic fields and consequently the magnet orders 44, from which it is obvious to the person skilled in the art that depending on the gap expansion and the desired effect, the preferred tunnel fields on the two atomizing surfaces differ, as shown for example in FIG. 10 , can be realized staggered locally. Homogeneous fields from target to target are particularly suitable for ferromagnetic targets, for example can be achieved by yoke arrangements according to FIG. 11, or mixed forms of homogeneous and inhomogeneous fields.

The method according to the invention or the source or system therefor are particularly suitable for sputter coating workpieces with materials which have at least one ferromagnetic component or with dielectric materials. At least one, preferably both, of the atomizing surfaces and consequently the associated targets are therefore preferably formed from a ferromagnetic material or from a dielectric material if the latter is not reactively formed and deposited. In particular for the deposition of dielectric layers, the gas G is additionally or instead of the provision of dielectric targets_r or at least one component of this gas can be formed by a reactive gas from the tank arrangement 43, in addition to the inert gas G from the tank arrangement 42. For example, and in the particularly preferred application, an MgO layer can be deposited, be it by sputtering MgO targets, if appropriate with subsequent post-oxidation in an O₂ containing gas G_r, or by sputtering from metallic Mg targets and reacting with the O₂ containing gas G_r. In particular, the design of the source as a circular source makes it possible to sputter-coat circular substrate disks, such as, for example, storage disks of all known types.

The following are necessary for the operation of a source according to the invention <u>parameter</u> advised:<ul id="ul0002" list-style="none" compact="compact"><li><u>Total pressure</u> in coating room B: 0.1 to 10 mbar</li></ul>

For <u>reactive sputtering</u> from Oxyden:<ul id="ul0003" list-style="none" compact="compact"><li><u>Partial pressure</u> O₂: up to 10% of the total pressure in coating room B with inlet 0₂ (G_r) in room B.</li></ul>

<u>Outlet flow</u> of the gas G from the opening 10 into the treatment room B:

The Ar gas flow G in the gap is realized in the Knudsen or viscous range. The following applies<ul id="ul0004" list-style="none"><li>Knudsen area:<maths id="math0001" num=""><math display="block"><mrow><msup><mrow><mtext>10</mtext></mrow><mrow><mtext>-2</mtext></mrow></msup><mtext> mbar cm ≤ p · Φ ≤ 0.6 mbar · cm</mtext></mrow></math><img file="EP0803587A1_D0001.tif" /></maths></li><li>Viscous range:<maths id="math0002" num=""><math display="block"><mrow><mtext>0.6 mbar cm &lt;p · Φ,</mtext></mrow></math><img file="EP0803587A1_D0002.tif" /></maths></li></ul> with p as the total pressure in the gap and Φ (see Fig. 9) as the gap width.

The gas flow in the Knudsen area is preferably selected. The following also preferably applies:<maths id="math0003" num=""><math display="block"><mrow><msup><mrow><mtext>10th sccm / cm</mtext></mrow><mrow><mtext>2</mtext></mrow></msup><msup><mrow><mtext> ≤ F ≤ 200 sccm / cm</mtext></mrow><mrow><mtext>2</mtext></mrow></msup><mtext>,</mtext></mrow></math><img file="EP0803587A1_D0003.tif" /></maths> with F as the working and possibly reactive gas flow per stomata area unit,<ul id="ul0005" list-style="none" compact="compact"><li>preferably 20 sccm / cm² ≤ F ≤ 50 sccm / cm².</li></ul>

<u>Gap width</u> or target distance Φ (see Fig. 9):<maths id="math0004" num=""><math display="block"><mrow><mtext>5 mm ≤ Φ ≤ 40 mm,</mtext></mrow></math><img file="EP0803587A1_D0004.tif" /></maths><ul id="ul0006" list-style="none"><li>preferably Φ ≤ 25mm</li><li>preferably 8 mm ≤ Φ ≤ 20 mm.</li></ul>

<u>Gap height</u> H_S (see Fig. 9):<maths id="math0005" num=""><math display="block"><mrow><msub><mrow><mtext>1 cm ≤ H</mtext></mrow><mrow><mtext>S</mtext></mrow></msub><mtext> ≤ 20 cm.</mtext></mrow></math><img file="EP0803587A1_D0005.tif" /></maths>

<u>Magnetic field:</u> Measured parallel to the atomizing surfaces in the middle of the gap 5:<maths id="math0006" num=""><math display="block"><mrow><mtext>150 Gauss ≤ H ≤ 1200 Gauss,</mtext></mrow></math><img file="EP0803587A1_D0006.tif" /></maths><ul id="ul0007" list-style="none"><li>preferably H ≥ 300 Gauss,</li><li>preferably 300 Gauss ≤ H ≤ 800 Gauss.</li></ul>

A system according to the invention with a round source, constructed essentially according to FIG. 9, has the following dimensions and was operated as follows:<ul id="ul0008" list-style="dash"><li>Distance opening level to substrate (D, Fig. 9): 40 mm</li><li>total target area: 301.4 cm²</li><li>Gap height H_S: 40 mm</li><li>Gap width φ: 30 mm</li><li>Outlet area 10: 113 cm²</li><li>average gap diameter: 120 mm</li><li>Gap length: 377 mm</li><li>Argon flow: 2825 sccm</li><li>Pressure in coating room B: 0.6 mbar</li><li>Power: 9 kW</li><li>Power per target area unit: 29.9 W / cm²</li><li>Argon flow per exit area unit: 25 sccm / cm²</li><li>Field strength H, parallel to the atomizing surface, on the target: 300 Gauss</li></ul>

Result:<ul id="ul0009" list-style="none"><li>Al coating rate: 22 Å kWs</li><li>Fe coating rate: 16 Å kWs</li><li>MgO coating rate (Mg target</li><li>with O₂Share in B approx. 2%): 18 Å kWs</li></ul>

By increasing the gas flow, the coating rate can be increased by a factor of 2 to 3.

12 shows the dependence of the discharge power P on the DC operating voltage U.<ul id="ul0010" list-style="none" compact="compact"><li>(a) represents the course on an Al slot target according to the above-mentioned article H. Koch et al. with the following slot dimension (see Fig. 12):<ul id="ul0011" list-style="none"><li>Slot length L: 10 cm</li><li>Slot width Φ_S: 30 mm</li><li>Slot height H_Sat: 40 mm</li></ul></li></ul>

<u>Ar flow:</u><ul id="ul0012" list-style="none" compact="compact"><li>Gas flow in coating room per</li><li>Slot area unit: 33 sccm / cm²</li><li>Total pressure in coating room B: 0.6 mbar</li></ul><ul id="ul0013" list-style="none"><li>(b): Operation and dimensioning of the system according to the invention, as specified above, but without a magnetic field H and with an argon flow G per opening area unit of 35 sccm / cm².</li><li>- (c) to the system operated as under (b), a single tunnel-shaped magnetic field was then created in the gap 10 on each target, which in the center of the target, where the field runs parallel to the target and measured on the target surface, gave a magnetic field strength of 300 Gauss .</li></ul>

As can be seen from FIG. 11, the operating voltage required for a required output, starting from the known slot target (a), drastically decreases via an arrangement according to the invention according to (b) without a magnetic field and finally according to (c) with a magnetic field. This shows the surprisingly high effect of closing the respective atomizing surfaces. Furthermore, it can be seen how the characteristic curve asymptotically approaches a limit value in magnetic sputtering according to (c), which is typical for a magnetron characteristic curve, whereas it increases exponentially according to (a) and (b), which is typical for cathode sputtering without a magnetron field. Low firing voltages are essential for high-quality dielectric layers, such as for MgO, as mentioned.

To generate the gas jet G, it is necessary to work at pressures which are unusually high for cathodic sputtering.