METHOD FOR FORMING AN LICOO2 FILM AND DEVICE FOR CARRYING OUT SAME

Abstract

A method for forming a film of LiCoO2 involves applying to a substrate a layer of LiCoO2 from a metallic target of cobalt (Co) in vapours of lithium (Li) by reactive magnetron sputtering in a vacuum chamber. Lithium vapours are fed in a regulated manner to the magnetron through a gas distributor, connected to a working gas inlet and to a lithium feed inlet, by feeding a flow of a carrier gas through a heated lithium-containing reservoir which is heated to the melting point of lithium. The regulated feed of the lithium vapours is achieved by adjusting the flow of carrier gas through the heated reservoir. A device for forming a film of LiCoO2 comprises a vacuum chamber, and a magnetron with a metallic target of cobalt. On one side or about the perimeter of the magnetron is a gas distributor that is connected to a working gas inlet and, via a tap and/or a valve, to a heated lithium-containing reservoir that is connected to a carrier gas inlet. The gas distributor can be cellular or convoluted. The heated lithium-containing reservoir can be disposed inside or outside the vacuum chamber. The result is an increase in the deposition rate of a LiCoO2 film, an increase in the efficiency of the equipment and a reduction in the cost of mass-producing thin-film solid-state batteries.

Claims

1. Method of LiCoO2 film formation involving the deposition of a LiCoO2 layer on a substrate, the deposition is conducted by reactive magnetron sputtering of a metal cobalt (Co) target in lithium (Li) vapor onto a substrate in a vacuum chamber, the lithium tank is heated to lithium melting point, a gas-carrier flow is fed through the heated lithium reservoir which results in the controlled feeding of lithium vapor to a magnetron system via a gas distributor, wherein the gas distributor is connected to a working gas input and a lithium tank input, wherein the regulated supply of lithium vapor is carried out by changing the gas-carrier flow and the lithium vapor is supplied from a heated tank.

2. A technological LiCoO2 film forming device comprising a vacuum chamber with a magnetron system with a cobalt metal target, wherein the device also contains a gas distributor, which is located on one side of the magnetron system or around its perimeter, and a heated lithium tank, wherein the gas distributor is connected to an input of working gas, which is connected to the heated lithium tank via a tap and/or valve, wherein the tank is connected to a gas-carrier input.

3. The device according to claim 2 characterized by having a heated lithium tank either inside or outside the vacuum chamber.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0026] FIG. 1Schematic diagram of the LiCoO2 layer forming device.

[0027] FIG. 2Schematic diagram of a lithium vapor tank.

[0028] The following positions are marked on the figures: [0029] 1vacuum chamber; [0030] 2magnetron (system); [0031] 3gas distributor; [0032] 4heated tank; [0033] 5spectrometer; [0034] 6door for loading/unloading the lithium cassette; [0035] 7lithium cassette; [0036] 8heater; [0037] 9nozzle for gas-carrier connection

EXECUTION OF THE INVENTION

[0038] The method for LiCoO2 thin film formation (deposition) on the substrate is a technology of reactive magnetron sputtering from metal cobalt target in lithium vapor. Sub-strates may be silicon wafers, mica sheets, or other materials.

[0039] FIG. 1 shows the technological device for LiCoO2 thin film formation (deposition). It includes vacuum chamber (1) with magnetron system (2) and metal cobalt target.

[0040] The magnetron system (2) is a DC/AC magnetron with a magnetic system and an magnetic field (e.g. over 800 Gs). A gas distributor (3) is installed around the perimeter or on one side of the magnetron. This gas distributor is heated to 600-800 degrees Celsius. In the simplest case it may be a cavity distributor. In more complex versions it may be a labyrinth distributor. This gas distributor is connected via valves and/or taps to the working gas inlet and to a heated lithium tank (4) (lithium source).

[0041] This tank can be installed either inside or outside of the vacuum chamber. The lithium source (FIG. 2) is a heated tank (4) heated to 600 degrees Celsius. It is a tank or reservoir for lithium evaporation. A gas-carrier may be pumped through this tank. It can be an inert gas such as argon, helium, etc. The tank (4) preferably contains a door (6) which can have a metal seal for high temperature protection. A lithium cassette (7) may be installed inside the tank (4). A heater (8) is installed outside of the tank (4). The tank also has a nozzle (9) (inlet) for the gas-carrier connection. The tank is filled with lithium (e.g., in the form of pellets) in an inert atmosphere. The vol-ume of lithium is calculated based on required period of device working. The time period is determined by the inter-service or process maintenance interval of the equipment. For mass production, the interval is from 7 days and longer. The tank is equipped with a system of high temperature valves. These valves isolate the tank from the outside atmosphere during maintenance and repair operations. A spectrometer (5) for spectral control of lithium and cobalt can be installed at the end of the magnetron.

[0042] The method of LiCoO2 thin film formation (deposition) includes the deposition of LiCoO2 film on a substrate from metal cobalt (Co) target in lithium (Li) vapor by using of reactive magnetron sputtering in vacuum chamber. Deposition by reactive magnetron sputtering in a vacuum chamber. Control of lithium vapor flow is realized through the gas distributor (into the magnetron). The gas distributor is connected to the input of working gas and to the input of lithium vapor. The lithium vapor is preferably deliv-ered into the vacuum chamber by means of a gas-carrier flow e.g. through a heated tank with lithium. The tank with lithium is heated to a lithium melting point and preferably beyond for evaporation. The lithium vapor supply is controlled by changing the gas-carrier flow through the heated tank.

[0043] The invention is carried out as follows according to an embodiment of the invention. Preferably the lithium cassette is loaded into the tank. A e.g. cobalt target is placed in the magnetron system. The installation is pumped to high vacuum. Checking and degassing the targets and/or the lithium reservoir/tank are carried out. The lithium tank is then heated to lithium melting point (liquid state). The heating may be followed by fixing and maintaining this temperature for the duration of the operation. The valve in the gas distribution system for lithium vapor feeding and can remain closed. The entire gas distribution system may also be heated to the required temperatures.

[0044] Once the evaporation system and lithium vapor supply have reached the specified temperature, the working gas may be fed to the magnetron system. This is preferably an inert gas such as argon, helium, etc. The working gas flow then be switched on and can be brought up to set power parameters. Preferably after this, the lithium vapor valve (tap) may be opened to the magnetron. The opening can take place e.g. by means of the gas-carrier. By varying the gas-carrier flow through the lithium tank, the amount of lithium vapor to the magnetron system can be controlled. This will change the parameters of the discharge and the LiCoO2 film to be deposited. Deposition of the LiCoO2 film takes preferably place in the environment of Li+Ar+Ox+additional inert gas (optional). By changing the ratio of the working gases and lithium vapor, the stoichiometry of the LiCoO2 film can be changed within a very wide range.

[0045] The film deposition rate can also be varied. A spectrometer (5) can be used to control the deposition speed and stoichiometry of the LiCoO2 film. This spectrometer may be used for spectral control of the lithium and cobalt. This spectrometer can be mounted at the magnetron system end. Maintaining the Li/Co (Co/Li) ratio by magnetron discharge parameters (discharge voltage) and by the amount of lithium vapor, the required parameters of the deposited film and deposition rate are ensured. This enables a radical reduction in the cost of mass production of thin-film solid-state batteries (batteries) compared to the current magnetron technology.

[0046] The claimed method of LiCoO2 formation allows: [0047] 1. Increase the capacity of deposited material in comparison with composite LiCoO2 (LCO) target. [0048] 2. Increase the deposition rate by using a metal target. Metal target allows to use higher power densities. Increase the deposition rate by a greater variability in the using of the working gases. [0049] 3. It is simple and reproducible enough to create material concentration gradients in the same process over the layer thickness. [0050] 4. Decrease the production cost of a thin-film battery (cell) structure. Decrease the production cost by using simple deposition materials.

[0051] The production cost of mass-produced thin-film solid-state batteries (accumulators) is reduced by two factors: [0052] 1) Increased LiCoO2 film deposition rate (LCO) and hence an increased equipment productivity; [0053] 2) Using of more simple and cheap materials (metal cobalt targets and metal lithium pellets) instead of complex composite LiCoO2 targets. Increased deposition rate is possible because of using reactive magnetron sputtering of metal cobalt (metal cobalt target is more cheaper, than the composite LiCoO2 target, and cobalt deposition rate is 2.7 time higher, that LiCoO2 deposition rate, as metal cobalt target allows more power supply in comparison with LiCoO2 target) and delivering lithium vapor into area of cobalt magnetron sputtering (vacuum chamber) from the heated tank through gas distributor by using pumped gas-carrier (argon, helium, other).