GB2220679A - Apparatus for thin film deposition of aerosol particles by thermolytic decomposition - Google Patents

Abstract

The apparatus comprises aerosol generator means (1) for forming an aerosol of particles to be deposited on a substrate, particle size selector means (2) for controlling the size of the particles in the aerosol, a thermal reaction zone (4) in which the substrate is coated, and exhaust control means (6), the thin film deposition apparatus being such that in operation the substrate to be coated moves transversely of the direction of flow of the particles to the reaction zone (4). <IMAGE>

Description

THIN FILM DEPOSITION APPARATUS This invention relates to thin film deposition apparatus.

Known thin film deposition apparatus is such that the deposited film are often not uniform, especially when the deposited films are deposited over a relatively large area.

It is an aim of the present invention to obviate or reduce the above mentioned problem.

Accordingly, this invention provides thin film deposition apparatus comprising aerosol generator means for forming an aerosol of particles to be deposited on a substrate, particle size selector means for controlling the size of the particles in the aerosol, a thermal reaction zone in which the substrate is coated, and exhaust control means, the thin film deposition apparatus being such that in operation the substrate to be coated moves tranversely of the direction of flow of the particles through the reaction zone.

The thin film deposition apparatus of the present invention may be effective to give uniformly deposited thin films of constant chemical composition. The thin films may be of up to optical quality. Any of the existing materials that are deposited in thin film technology may be used in the thin film deposition apparatus of the present invention.

A typical example of one such material is zinc. The deposited thin films can be insulating/dielectric, conducting, for example magnetic, or semiconducting. The thickness of the material deposited can be from substantially zero upwards.

The transverse movement of the substrate with respect to the direction of flow of the particles through the thermal reaction zone enables the apparatus to be constructed such that loss of toxic hazards during the deposition process is minimised, and also such that cross contamination from two or more adjacent thermal reaction zones is also minimised. This may be effected by controlling the space around the thermal reaction zone with a neutral gas bearing or with a reduced pressure gap.

The particle size selector means may comprise a relatively coarse particle size pre-selector section and a relatively fine particle size selector section. The particle size selector means should be such that the particles in the aerosol are sufficiently fine not to produce spotty zones on the substrate being coated.

The relatively coarse particle size pre-selector section may be an impacter.

The relatively fine particle size selector section may be a parallel array of tubes, or an array of tubes which are staggered to form geometric shapes such for example as diamond shapes. Alternatively, the relatively fine particle size selector section may comprise curved shapes, packed spheres or products of shapes other than spheres, or baffles.

The thermal reaction zone may include an infra red heater, a resistive type of heater, or a radio frequency heater. Generally, any suitable and appropriate type of heater may be employed. The thermal reaction zone may be of varying cross sectional sizes and shapes. The thermal reaction zone is preferably rectangular.

The exhaust control means may be employed to produce an appropriate pressure in the thermal reaction zone. The exhaust control means can enable the apparatus of the invention to have a relatively short thermal reaction zone and this in turn enables the apparatus to be constructed of a compact size.

Preferably, the thermal reaction zone is an axially uniform thermal reaction zone.

The thin film deposition apparatus of the invention preferably has the facility for chemical purity control.

The apparatus preferably thus includes a recovery section.

The recovery section may be effective to enable the recovery of one or more of a propellant chemical, a solvent chemical, a solute chemical, and waste chemicals.

All of these various chemicals may be employed in the apparatus to enable the thin film coating of substrates.

The thin film deposition apparatus may be in modular form for allowing a plurality of coatings sequentially to be applied to a substrate. Thus, as many coatings as may be required may be applied to a substrate.

For applying a plurality of coatings to one or more substrates, the thin film deposition apparatus may include a plurality of thermal reaction zones. Alternatively, a plurality of pieces of the thin film deposition apparatus may be connected together so that each separate piece of thin film deposition apparatus Sas its own single thermal reaction zone.

The apparatus of the invention may include an aerosol generator.

The aerosol generator may include one or more atomiser devices.

The thin film deposition apparatus may be regarded as spray pyrolysis apparatus.

The thin film deposition apparatus may be used in the production of dielectric mirrors and dielectric filters.

These mirrors and filters may be multilayer mirrors and filters. The mirrors and filters may be used in the tuning and modulating of lasers. The apparatus may also be used in the production of capacitive components and display devices such as electroluminescent panels. Electroluminescent panels may be used for microcomputer displays. Alternating current luminescent displays may also be produced.

Furthermore, the apparatus may be used to give optical coatings, electrical coatings and protective finishes such for example of polytetrafluoroethylene. As indicated above, the films that are deposited can generally be insulating, conducting or semiconducting. Depending upon the type of thin film required, the flow characteristics of the aerosol/gas/vapour can be controlled by inlet nozzles/baffles, the geometry of the thermal reaction zone (which may be in the form of a channel) and the exhaust control means (which may be in the form of a nozzle).

Embodiments of the invention will now be described solely by way of example and with reference to the accompanying drawings in which: Figure 1 shows first thin film deposition apparatus; Figure 2 shows a perspective view of the thermal reaction zone employed in Figure 1; Figure 3 is a side view of the thermal reaction zone; Figures 4,5 and 6 illustrate how aerosol/gas containment can be effected in the reaction zone; Figure 7 illustrates what happens in the thermal reaction zone; Figure 8 illustrates the geometry of the reactor; Figure 9 illustrates the flow profile of the channel reactor; Figure 10 illustrates a growth pattern on a substrate; Figure 11 is a plan view of second thin film deposition apparatus; and Figure 12 shows a third thin film deposition apparatus.

Referring to Figure 1, there is shown thin film deposition apparatus which uses thermolysis of.aerosols containing coating precursor in solution or suspension, or in vapour form. The precursor may be an organometallic compound or a mixture of organometallic compounds. In Figure 1, there is shown an aerosol generator 1, a particle size selector 2, an inlet nozzle 3, a channel reactor 4, a reaction/deposition zone 5, and an exhaust nozzle 6.

The aerosol generator may include a plurality of atomisers.

Inside the aerosol generator is provided particle size selector means for controlling the size of the particles in the aerosol. The particle size selector means comprises a relative coarse particle size pre-selector in the form of a virtual impactor, and relatively fine particle size selector means in the form of an array of tubes.

The apparatus also includes an exhaust treatment section for enabling the recovery of propellant the recovery of solvent, the recovery of solute, and the recovery of waste. The apparatus further comprises a heater 8, a compressor 9, and a purge gas/start up container 10.

In a modified form of the apparatus, the compressor 9 may be substituted by a blower and unused aerosol may be recirculated. The direction of flow of the aerosol is indicated by the arrow. The direction of propellant flow is also indicated by the arrow.

Referring now to Figure 2, there is shown in enlarged detail the channel reactor 4 which forms the thermal reaction zone. It will be seen from the arrows that the direction of movement of the substrate is transverse to the direction of movement of the aerosol and also to the longitudinal axis of the channel reactor which, as shown, is rectangular.

Figure 3 shows a side view of the reactor and it will be seen that there is shown an adjustable gap 12 and a substrate 14.

Referring now to Figures 4,5 and 6, there is illustrated how a gas wall is used to provide containment of fluid, that is aerosol or gas. The gas wall may be replaced with a partial vacuum to provide alternative containment. The gas wall may be operated at higher pressure than the aerosol/gas pressure, thereby injecting gas into the reactor zone. Figure 4 shows the substrate 14, a heater 16, and the channel 4. In addition there is a space 18 in which inert gas is injected. The space 18 is defined by an outer wall 20. Figure 5 shows a gap 22 between the reactor and the substrate 14.

Equal pressure occurs at point 24. Because of the containment system, the coating surface of the substrate remains free of mechanical damage.

If desired, various pieces of the apparatus may be ganged together on a production line to produce multilayer coating. The following conditions may exist in the reaction zone,namely reducing conditions, oxidising conditions, and inert conditions. The enclosure pressures may be effected at above atmospheric pressure, below atmospheric pressure or at atmospheric pressure. The gas wall may be effective to substantially eliminate cross contamination between machines.

Referring to Figure 6, the use of resistance (gas) may be used to effect containment in some circumstances. In Figure 6, there is shown the wall of the reactor 4 and an aerosol/gas space 26. A gap 28 provides resistance to free flow i.e. leakage. The substrate is shown as substrate 14.

Figure 7 illustrates how the apparatus produces a coating. In Figure 7 there is shown the roof 30 of the channel reactor 4. There is shown a reaction boundary 32 and the substrate 14. A heat source is represented as heat source 34. The size sorted droplets in the aerosol approach the heated substrate. A reaction zone forms above the surface and the coating material deposits uniformly. By arranging for an even arrival rate at the reaction zone along the gas flow axis, a uniform deposit is formed in this direction. By moving the substrate under this constant deposition profile at a fixed speed, areas of constant thickness are produced.

Taking any section through the deposition zone, a constant deposition profile occurs.

Figure 8 shows the geometry of the thermal reaction zone used to produce the films.

Figure 9 shows a flow profile in the thermal reaction zone i.e. in the channel reactor. The flow profile shows the aerosol operated in a laminar flow region.

Figure 10 illustrates the growth pattern on a substrate.

The film profile can be made uniform about an axis by ensuring uniform velocity profile, and ensuring that the substrate is in a flat velocity region. The composition of the film is uniform because the composition of the aerosol is fixed at the time of generation. This contrasts strongly with the variations in known films produced by CVD, where cracking of components from the vapour stream leads to variable deposits. By selecting low particle size, no spots form on the deposited film.

Figure 11 shows second thin film deposition apparatus having three thermal reaction zones 4. Each thermal reaction zone 4 may be regarded as a unit having its own control heater and gap adjustment. Also shown in Figure 3 is a region 36 of programmed cooling and intermediate programmed heaters 38. Further included in the apparatus shown in Figure 11 are exhaust control and precursor sections 40, generator and size selectors 42, a substrate magazine 44 giving autoload and unload, and a treated substrate section 46. The units 4 form a plurality of spray pyrolysis reactor assemblies. A basic frame may be able to accept varying numbers of the assemblies at varying spaced apart widths. The entire machine may be enclosed in a cabinet, having an inner atmosphere. A stepper motor may be employed to control the rate of feed of one or more substrates.

Referring to Figure 12, there is shown third thin film deposition apparatus 48 having an exhaust and recovery section 50 which includes cold traps. There is also a generator and reactor section 52. A compressor 54 is further employed. The apparatus shown in Figure 12 may be a closed system where only small volumes of propellant gas are lost for each run. Thus, if a reducing environment were required, hydrogen could be used, oxidising pure oxygen or oxygen enriched air or simply air. The advantages of a closed system are as follows: 1. A reduction of costs by not requiring large quantities of bottled gas.

2. Toxic vapours are not released to atmosphere.

3. Recovery of solvent and solute is allowed and this is especially advantageous if expensive materials are used.

4. Uncontrolled draughts are excluded.

The various types of thin film deposition apparatus described may be used to give large areas of constant quality and thickness deposited films. Providing the solution being sprayed remains homogenic, there is substantially no limit to the composition being sprayed. In other words, compound films may be grown, the composition of which can be accurately controlled.

It is to be appreciated that the embodiments of the invention described above with reference to the accompanying drawings have been given by way of example only and that modifications may be effected. Thus, for example, the thermal reaction zone may have other shapes so that it could, for example be a cylindrical reactor.

The invention also extends to parts of the described apparatus, taken separately, or in any combination.

Claims (14)

1. Thin film deposition apparatus comprising aerosol generator means for forming an aerosol of particles to be deposited on a substrate, particle size selector means for controlling the size of the particles in the aerosol, a thermal reaction zone in which the substrate is coated, and exhaust control means, the thin film deposition apparatus being such that in operation the substrate to be coated moves transversely of the direction of flow of the particles through the reaction zone.

2. Thin film deposition apparatus in which the particle size selector means comprises a relatively coarse particle size pre-selector section and a relatively fine particle size selector section.

3. Thin film deposition apparatus according to claim 2 in which the relatively coarse particle size pre-selector section is an impacter.

4. Thin film deposition apparatus according to claim 2 or claim 3 in which which the relatively fine particle size selector section is a parallel array of tubes, or an array of tubes which are staggered to form geometric shapes.

5. Thin film deposition apparatus according to any one of the preceding claims in which the thermal reaction zone includes an infra red heater, a resistive type of heater, or a radio frequency heater.

6. Thin film deposition apparatus according to any one of the preceding claims in which the thermal reaction zone is rectangular.

7. Thin film deposition apparatus according to any one of the preceding claims in which the thermal reaction zone is an axially uniform thermal reaction zone.

8. Thin film deposition apparatus according to any one of the preceding claims and including a facility for chemical purity control.

9. Thin film deposition apparatus according to any one of the preceding claims and including a recovery section.

10. Thin film deposition apparatus according to any one of the preceding claims and which is in modular form for allowing a plurality of coatings sequentially to be applied to a substrate.

11. Thin film deposition apparatus according to any one of the preceding claims and which is for applying a plurality of coatings to one or more substrates, and in which the thin film deposition apparatus includes a plurality of thermal reaction zones.

12. Thin film deposition apparatus according to any one of the preceding claims and including an aerosol generator.

13. Thin film deposition apparatus according to claim 12 in which the aerosol generator includes one or more atomiser devices.

14. Thin film deposition apparatus substantially as Therein described with reference to the accompanying drawings.