Arrangement and method for removing alkali- or alkaline earth-metals from a vacuum coating chamber

Description

The invention relates to an arrangement and a method according to the preambles of claims 1 and 11.

Modern lithium batteries are, as a rule, produced in a vacuum chamber, wherein a substrate is provided with a lithium layer. The lithium layer is formed, for example, through the deposition on the substrate of lithium in the vapor state. Since lithium is highly reactive, contact by the operating personnel after opening the vacuum chamber must be avoided. Even if the excess lithium has been pumped out of the vacuum chamber, it is still possible for lithium particles deposited on the inner wall of the vacuum chamber or on facings and/or maskings to harm the operating personnel.

Methods for the production of lithium batteries are already known in which lithium is converted in a vacuum chamber into vapor, which is subsequently deposited on a substrate (JP 59-060866, JP 2003-007290, JP 2003-234100, JP 2007-207663). Nothing is found in these publications regarding the cleaning of the vacuum chamber.

It is further known to eliminate undesirable depositions on the inside of a coating installation by means of a cleaning gas (JP 2003-229365). However, lithium or alkali metals are herein not listed.

Furthermore, cleaning a process chamber by means of a gas containing O2 is known (US 2007/0163617 A1 ). Herein the cleaning is carried out at increased temperature and under vacuum. The gas preferably also contains H radicals, since the cleaning process can also be carried out by means of a plasma. However, the walls of the process chamber are cleaned of tungsten and not of lithium or another aggressive material.

A further method for cleaning coating chambers is disclosed in DE 103 38 275 A1. In this method the process chamber is flushed with a conditioned purge gas before a

coating process. The purge gas is preferably comprised of O2 and N ₂ with a humidity value of maximally 30%. The coating chamber is cleaned before the coating process and the coating material is not lithium.

US 2002/0185067 A1 discloses a device and a method for the in situ cleaning of a throttle valve in a CVD system. Here a cleaning gas is introduced which can comprise F ₂ , C ₂ F ₆ , O ₂ or NF ₃ . Lithium is not discussed.

A cleaning process for a coating chamber is furthermore known in which inter alia N ₂ and O ₂ are employed as cleaning gases (EP 1 612 857 A1 ). These gases are converted to plasma and subsequently serve for cleaning the inner wall of a CVD chamber. High frequency is utilized for the generation of the plasma. However, not Li, but rather Si ₃ N ₄ or SiO ₂ are removed.

EP 0 441 368 A discloses a device and a method for eliminating excess material from a PVD chamber. During a cleaning cycle a vacuum is generated in the PVD chamber and a gas mixture with reactive gas is introduced into the PVD chamber. The reactive gas is herein activated through plasma discharge. The objects of the cleaning are also screenings. The eliminated material is Ti, W or Al, not however Li.

JP 2002-206160 discloses an apparatus for manufacturing a thin film of lithium metal or lithium alloy. To remove the lithium metal adhering to the inner wall of the apparatus, a heater is provided to melt the lithium metal adhering to the inner wall. By melting and removing the lithium metal adhering to the apparatus, the danger of ignition and explosion resultant from the reaction of the lithium metal with moisture when the apparatus is opened to the atmospheric air can be avoided.

The invention addresses the problem of cleaning such parts of a vacuum coating chamber which during the production of thin-film batteries are unintentionally coated, for example maskings, metal lining sheets and the like.

This problem is solved according to the features of claims 1 and 11.

The advantage attained with the invention comprises in particular that unintentionally

coated parts are cleaned in simple manner and the cycle times or service times are shortened. Since the cleaning can also be carried out cyclically, it is possible to operate a coating installation without interruption.

The invention consequently relates to a cleaning method in which from a vacuum coating chamber of a coating installation for the coating of substrates with alkali- or alkaline earth-metals, residues of alkali or alkaline earth-metals are removed. For this purpose into the chamber a gas from the group of N ₂ , O ₂ or air is introduced which reacts with the alkali- or alkaline earth-metals to form the corresponding solid compounds. Water can still also be additionally introduced into the vacuum coating chamber.

After the alkali- or alkaline earth-metals have reacted with the gas, the corresponding solid compound is removed from the vacuum coating chamber.

An embodiment example of the invention is shown in the drawing and will be described in further detail in the following. In the drawing depict:

Fig. 1 a vacuum chamber for coating a substrate by means of a vaporized material.

A coating installation 1 , in which a substrate 2 can be coated, is shown in Figure 1 in sectional view. This coating installation 1 includes a vacuum coating chamber 3, of which two side-walls 4, 5 are evident. Masking 6 is disposed between the substrate 2 and a vapor feed system 7, which comprises a vaporizer crucible 8, a valve 9 and a vapor inlet 10 to 13. The end of the vapor inlet is formed by a linear distributor 14 implemented as a vertically oriented tube with linearly disposed openings. These openings are located opposite the masking 6. By 15, 16 are denoted covers in the vacuum chamber 3.

In the vaporizer crucible 8 is melted, for example, lithium for the production of thin- film lithium batteries and vaporized. Instead of lithium, another reactive metal from the group of alkali- and alkaline earth-metals, for example cesium, could also be utilized.

The vaporized material arrives via the vapor inlet 10 to 13 at the distributor 14 and from here, via the masking 6, which does not need to be provided in every case, at the substrate 2. In addition, the vaporized material also reaches the covers 15, 16 and other parts which it is not intended to reach.

When the coating of substrate 2 is completed, the unintentionally coated parts must be freed of the coating in order for the operating personnel not to be harmed by the reactive lithium when opening the vacuum chamber 3 and removing the coated substrate 2.

However, in order for a person not to come into contact with the lithium or other alkaline earth- or alkali-metals, these metals must be removed from the installation. The removal of these reactive metals from the installation takes place after the coating process has been terminated and the substrates have been transferred from the coating installation 1 via a vacuum lock, not shown in Figure 1. After the substrates have been removed from the coating installation 1 , one or several gases are introduced into the vacuum chamber 3 before the opening the vacuum chamber 3.

For this purpose, outside of vacuum chamber 3 several gas containers 20, 21 , 22 are provided which contain the gases N ₂ , O ₂ or air. Activation of the gases is not absolutely required. These gas tanks 20, 21 , 22 are connected via supply pipes 23, 24, 25 and valves 26, 27, 28 with the vacuum chamber 3. If N ₂ is introduced into the vacuum chamber 3, the N ₂ molecules combine with lithium according to the equation 6 Li + N ₂ □ 2 Li ₃ N. This end product is a solid which falls from the vertical surfaces to the bottom of the vacuum chamber 3 or adheres at the site of the reaction.

If O ₂ is introduced into the vacuum chamber 3, based on the expression 4 Li + O ₂ the colorless powdery solid compound Li ₂ O is formed, which is also nontoxic and falls from vertical parts.

It is understood that instead of pure oxygen, air can also be introduced into the vacuum chamber 3. This air can herein be enriched with O ₂ . Since air contains both nitrogen as well as also oxygen, lithium consequently reacts with the nitrogen as well

as also with the oxygen. It is here advantageous if the air has a certain humidity. To this end the air can additionally be enriched with water. If there is also water contained in the air, the following reaction takes place: Li + H ₂ O D LiOH + D H ₂ .

When air and water are introduced, in addition to Li ₃ N and Li ₂ O, LiOH and Li ₂ COs are also formed.

For instance, Li ₂ COs is formed through the following reaction: 2 LiOH + CO ₂ D Li ₂ CO ₃ + H ₂ O.

At high temperatures Li ₂ CO ₃ breaks down again into Li ₂ O and CO ₂ . The same applies also to LiOH which breaks down into Li ₂ O and H ₂ O. The lithium compounds must in every case be nontoxic and remain stable in air.

Since the reactions of H ₂ O, O ₂ and N ₂ are exothermic, it is advantageous to cool the vacuum chamber 3. This can be carried out by means of a cooling system, not depicted in Figure 1.

In principle, the metal Li, or also the other alkali- and alkaline earth-metals, can be made to react with other substances, such as, for example, with halogens or hydrogen compounds of these halogens.

However, since these halogens or halogen compounds are highly reactive and can also chemically attack the chamber, it is necessary when employing these compounds to build the chamber of a material that is chemically inert relative to these compounds.

Although activation of the gases is not absolutely required, it is nevertheless advantageous to carry out the reaction at increased temperatures. A temperature in the range from 30° C up to 200° C can be selected, at which the reaction is started. It is obvious that at higher temperatures the reaction proceeds faster. It is of advantage if the reaction takes place at a pressure of up to 100 mbar. The choice of temperature as well as of pressure depends substantially on the design of the

vacuum chamber 3. If only pure oxygen is utilized as the gas, the temperature can be, for example, 80° C and the pressure of the oxygen 100 mbar. This ensures optimal reaction conditions.

It is advantageous if during the cleaning process the reaction is monitored by means of a gas sensor 32. A gas sensor 32 to be considered is, for example, a mass spectrometer, a lambda probe or an IR or NIR spectrometer. Via these measuring devices the gas composition can be determined during the process. If a lambda probe is employed, oxygen is preferably added to the gas or gas mixture. In this case the oxygen content can be determined during the process. As long as there is still lithium in the chamber and reacts with the gases, the concentration of the reactive gases is below the concentration of the gases before their introduction into the vacuum chamber 3 vitiated with lithium. As soon as the lithium has reacted with the gases, the concentration of the gases reaches the starting value again. This indicates that the reaction process has been completed. The gas composition, which had been determined by means of the gas sensor 32, is supplied to an evaluation instrument 33. When the process is completed, by means of a pump 30 and an extraction fitting 31 the powder on the bottom of the vacuum chamber 3 can be suctioned out. It is also possible to vent the vacuum chamber 3 and subsequently to remove the powder by means of a dust extractor. It is herein advantageous to remove the lithium salt adhering on the walls of the vacuum chamber 3 by means of ultrasound such that it falls to the bottom. This facilitates the cleaning work considerably. By setting parameters such as, for example, pressure, temperature or the moisture content in the form of water in the gas or the gas mixture, the reaction with the lithium can be accelerated. In order to enrich gases with moisture, water is introduced into the vacuum chamber 3 via a feed pipe 35.

Whether the lithium salts remain adhered to the surface after the cleaning process or spall off and consequently fall to the bottom of the vacuum chamber 3 depends substantially on the layer thicknesses of the formed lithium salts. If the lithium layers formed in the coating reaction are very thin, salts with a very small grain diameter are formed in the cleaning process. Such lithium layers remain preferably well adhered on the walls of the vacuum chamber 3. If during the coating process thick lithium layers have been formed on the walls of the vacuum chamber, layers are formed in

the cleaning reaction with the gases, which layers are under mechanical stress, which can lead to the spalling of the coating. For this reason it can be advantageous to remove the salt residues still adhering on the walls of the vacuum chamber 3 by means of ultrasound.

Those skilled in the art can readily recognize that numerous variations and substitutions may be made in the invention, its use and its configuration to achieve substantially the same results as achieved by the embodiments described herein. Accordingly, there is no intention to limit the invention to the disclosed exemplary forms. Many variations, modifications and alternative constructions fall within the scope and spirit of the disclosed invention as expressed in the claims.

Reference numerals

1 coating installation

2 substrate

3 vacuum coating chamber

4 side-wall

5 side-wall

6 masking

7 vapor feed system

8 vaporizer crucible

9 valve

10 vapor inlet

11 vapor inlet

12 vapor inlet

13 vapor inlet

14 linear distributor

15 cover

16 cover

20 gas container

21 gas container

22 gas container

23 supply pipe

24 supply pipe

25 supply pipe

26 valve

27 valve

28 valve

30 pump

31 extraction fitting

32 gas sensor

33 evaluation instrument

35 feed pipe