GB2396481A

GB2396481A - Laser annealing method and device

Info

Publication number: GB2396481A
Application number: GB0229427A
Authority: GB
Inventors: Paul Peter Donohue; Carl John Anthony; Michael Andrew Todd
Original assignee: Qinetiq Ltd
Current assignee: Qinetiq Ltd
Priority date: 2002-12-18
Filing date: 2002-12-18
Publication date: 2004-06-23
Also published as: WO2004055880A1; GB0229427D0; AU2003292427A1

Abstract

A method for annealing a thin film, such as a ferroelectric or magnetic thin film comprising the steps of (i) taking a thin film 4 carried on a temperature sensitive substrate 6. The thin film having a radiation absorbing structure formed thereon, and (ii) illuminating the radiation absorbing structure 20 with a pulse 2 of radiation produced by a laser. The radiation absorbing structure is heated sufficiently by the pulse of radiation to anneal all or some of the thin film without exceeding the temperature budget of the temperature sensitive substrate. The method is used to fabricate an infra-red detector.

Description

1 239648 1

Annealing Method and Device.

This invention relates to a method for annealing thin films, and in particular to a method for annealing ferroelectric thin films.

s Recently, there has been a considerable amount of research into the development of devices which utilise the thermal properties of ferroelectric materials. One example is the development of infrared (JR) imaging cameras based on two-dimensional arrays of ferroelectric thermal detectors. Such detectors have proved attractive due 10 to their near ambient temperature operation.

Thermal detectors used for infra-red imaging rely on the temperature change of the sensing material due to absorption of infra-red radiation. In the case of ferroelectric materials this radiation causes a change in the electrical polarization of the material 15 enabling the magnitude of the change in temperature to be detected.

In order to reduce the size of the detectors, integrated ferroelectric devices have been developed in which the ferroelectric material is combined with the electronic read out circuitry in a single device. Typically, these integrated circuit (IC) devices 20 comprise layered structures with a thin layer of ferroelectric sputtered or spin coated or otherwise deposited onto or above one or more base layers. Other examples of such integrated ferroelectric devices are thin film piezoelectric actuators and ferroelectric random access memories (FeRAM).

25 The combination of the ferroelectric material with the active circuitry in one package produces a more compact device than the provision of a separate read out circuit and improves yield, reduces cost and improves performance. However, a fundamental problem with such devices is the need to deposit the ferroelectric material within a thermal budget that is compatible with the integrated circuitry not 30 being damaged or destroyed by the elevated temperatures. It is widely recognised that exposure of an integrated circuit (e.g. a CMOS circuit) to temperatures above

450 C is a constraint on the processing of chips/materials with IC content, and this conflicts with the growth requirements of many ferroelectric layers.

A particularly important family of ferroelectric materials in use and under 5 investigation for IR detector, actuator or FeRAM applications is the perovskites.

This family include materials such as lead scandium tantalate (PST), lead zirconate titanate (PZT), barium strontium titanate (BST), lead titanate (PT) and others. For use as a ferroelectric the material layer must be in the perovskite phase. It can either be deposited directly into that phase at an elevated temperature or at a lower 10 temperature which is then subsequently annealed into the ferroelectric perovskite phase. Layers deposited at low temperatures are generally in an amorphous, pyrochlore or other phase which is incapable of exhibiting ferroelectricity. For PST, for example, the material must be deposited at temperatures in excess of 450 C to enter the perovskite phase. Direct depositing of these materials in a perovskite phase 15 is therefore incompatible with the temperature budgets of integrated circuitry.

One known way of providing a layer of ferroelectric material in the perovskite phase without damaging an IC provided on a base layer is to deposit the material in a non-

ferroelectric state at a low temperature (say less than 450 C). The material may then 20 be annealed using a laser to heat the layer sufficiently to convert the material into its perovskite phase.

In order to heat the ferroelectric layer sufficiently without damaging the underlying integrated Circuitry, a laser wavelength is chosen which is strongly absorbed by the 25 ferroelectric layer. Typically the laser radiation is pulsed and the temporal width of the pulse is kept sufficiently short such that the heat diffusion length is small enough to prevent the induced heat wave from penetrating through the various layers to the IC layer.

30 Commercially available excimer lasers generate ultraviolet (W) radiation of a wavelength that is strongly absorbed by typical ferroelectric layers such as PST and PZT. Typically such lasers generate pulses having relatively short pulse durations;

for example around 25ns. Although such short pulses can anneal thin PST layers (up to say lOOnm in thickness), the energy density required to generate sufficient temperature at the bottom of a thick layer of PST will significantly increase the surface temperature at the top (i.e. the irradiated surface) of that layer. The surface 5 heating effect can cause surface damage, poor crystallization and crystal quality, poor film physical integrity and loss of stoichiometry due to evaporation of volatile components. In addition to surface heating effects, known laser annealing techniques also lack 10 control over the orientation of the crystalline phase that is grown during the annealing process. For thicker films, nucleation will occur as a bulk effect in a similar fashion to bulk ceramic ferroelectric materials with the consequent random, or at least mixed, orientation of the grain crystal axes.

15 WO 00/54317 describes an annealing process in which a temporal extender is provided to deliver a laser pulse at a slower rate than is possible with a non-extended commercially available laser source. The extended pulse increases the diffusion length through the material thus allowing thicker films to be annealed without surface darnage. Although the pulse extension technique mitigates some of the 20 problems associated with excessive surface heating in thicker films, the problems associated with nucleation and growth control remain.

According to a first aspect of the invention, a method for annealing a thin film comprises the steps of (i) taking a thin film carried on a temperature sensitive 25 substrate, the thin film having a radiation absorbing structure formed thereon, and (ii) illuminating the radiation absorbing structure with a pulse of radiation produced by a laser, wherein the radiation absorbing structure is heated sufficiently by the pulse of radiation to anneal all or some of the thin film without exceeding the temperature budget of the temperature sensitive substrate.

The present invention thus permits a thin film to be annealed without any heat induced damage of the underlying substrate. Furthermore, the use of a radiation

absorbing structure to convert the incident radiation to heat minimises any damage to the surface of the thin film that may arise from excessive heating. The present invention is thus advantageous over the prior art techniques described above in

which surface heating of the thin film itself is used during the annealing process. In 5 particular, the present invention will permit thin films having a thickness greater than around lam to be annealed without any significant damage to the surface of the thin film.

Furthermore, the present invention provides absorption which is independent of the 10 thickness of the thin film. In other words, the thin film does not have to be a certain minimum thickness to ensure that there is sufficient absorption of the incident radiation. This is particularly advantageous in FeRAM applications where the layer of ferroelectric material used is typically very thin and would thus absorb only a small amount of any radiation directly incident on it.

Herein, the term anneal is used to mean the permanent alteration of the properties of a material by heating. For example, in the case of ferroelectric films, annealing includes converting all or some of a thin film from a non-ferroelectric state into a phase capable of exhibiting ferroelectricity. Annealing in the context of ferroelectric 20 films would also include improving the ferroelectricity being exhibited, for example by converting more of the film into a ferroelectric state.

A person skilled in the art would recognise that the term "thin film" means a layer, or a plurality of layers, of a material. In particular the term "thin" should not be 25 taken to mean a film of a particular thickness. Thin film is used herein to describe a layer of material formed (e.g. spin coated, sputtered or grown) on a substrate as opposed to a piece of bulk material.

It should be noted that the pulse of radiation with which the radiation absorbing 30 structure is illuminated may be produced by the laser in a number of ways. For example, a pulsed laser source may be used or the output from a CW laser could be intensity modulated (e.g. chopped). Alternatively, any other means of exposing a

s specific portion of the radiation absorbing structure to a short burst of radiation could be used. For example, a CW laser could be rapidly scanned across the radiation absorbing structure; this would also locally illuminate regions of the radiation absorbing structure with a short duration burst (i.e. a pulse) of radiation.

Conveniently, the radiation absorbing structure comprises a nucleation layer in contact with the thin film.

The presence of a nucleation, or seeding, layer is advantageous because it helps to 10 initiate growth of the required crystalline phase of the thin film which is being annealed. Preferably, the nucleation layer comprises platinum.

15 Alternatively, the nucleation layer comprises a conducting oxide. For example, a layer of perovskite structure conducting oxide material such as Lanthanum Nickelate or Strontium Ruthenate may be used. Such materials can be closely lattice matched to perovskite ferroelectric materials and provide a suitable template for perovskite growth. Advantageously, the radiation absorbing structure comprises a dielectric layer. In other words, the radiation absorbing structure has a dielectric layer, preferably on its external surface (i.e. the surface furthermost from the substrate), to maximise the amount of energy from the pulse of radiation that is retained within the radiation 25 absorbing structure for conversion into heat.

Conveniently, the dielectric layer comprises one or more layers of Silicon Dioxide.

Preferably, the dielectric layer has a thickness substantially equal to one quarter of 30 the wavelength of the pulse of radiation within said dielectric layer. This ensures that the maximum amount of radiation is coupled into the dielectric layer and therefore that the maximum heating effect is obtained.

Advantageously, the radiation absorbing structure is a resonant absorber structure.

For example, the radiation absorbing structure may comprises both a nucleation layer and a dielectric layer. In such a structure, the dielectric layer is arranged to 5 maximise the amount of radiation absorbed by nucleation layer.

Conveniently, the method further comprises the initial step of depositing the radiation absorbing structure on the thin film that is carried on the temperature sensitive substrate.

The actual deposition process used will depend on the type of radiation absorbing structure required. As described above, the radiation absorbing structure may comprise a single layer, or a plurality of layers.

15 Preferably, the thin film is a mixed oxide ferroelectric thin film. It should be noted that the mixed oxide material may not actually exhibit ferroelectric properties when initially deposited on the substrate; i.e. it may be deposited at a low temperature and hence initially be in a nonferroelectric phase. However, the term ferroelectric thin film shall herein mean any thin film that is, or is capable of being annealed to 20 become, ferroelectric.

Advantageously, the ferroelectric thin film comprises low grade deposited perovskite phase material and the annealing step improves the quality of the perovskite material.

Conveniently, the thin film comprises material deposited substantially in the non-

perovskite phase and the annealing step converts some or all of the material into the perovskite phase.

30 The ferroelectric thin film is preferably any one of lead scandium tantalate (PST), lead zirconate titanate (PZT), strontium bismuth tantalate (SBT), barium strontium titanate (BST) or lead titanate (PT).

Advantageously, the method may further comprise the step of removing some or all of the radiation absorbing structure after the thin film has been annealed.

5 Conveniently, the substrate comprises an integrated circuit which may comprise Silicon. For example, it may comprise polysilicon on a glass substrate.

Advantageously, the substrate is flexible. For example, the substrate could comprise polyamide or a plastic.

Preferably, the step of illuminating the radiation absorbing structure with a pulse of radiation produced by the laser is repeated a plurality of times Conveniently, an excimer laser is used to produce the pulse of radiation.

15 Alternatively any other suitable pulsed laser source, such as a transverse excited atmospheric carbon dioxide (TEA C02) laser, may advantageously be used to produce the pulse of radiation.

Furthermore, the pulse of radiation may advantageously be produced by a pulsed 20 laser and pulse extension means. For example, a temporal pulse extender of the type described in WO 00/54317 could be used.

Conveniently, the thin film is carried by the substrate in a microbridge arrangement.

In other words, the entirety of the thin film may not be in contact the substrate; i.e. 25 an air gap may be provided to thermally isolate the thin film from the substrate.

According to a second aspect of the invention, a method of producing an infra-red detector comprises the method according to the first aspect of the invention 30 According to a third aspect of the invention, a method of producing a thin film device comprises the steps of (i) forming a thin film on a temperature sensitive substrate, and (ii) forming a radiation absorbing structure on the thin film, wherein

the radiation absorbing structure is adapted such that it can be heated sufficiently by a pulse of radiation of a given wavelength to anneal all or some of the thin film without exceeding the temperature budget of the temperature sensitive substrate.

5 Conveniently, the method further comprises the step of illuminating the radiation absorbing structure with a pulse of radiation of the given wavelength.

Advantageously, the step of forming a radiation absorbing structure on the thin film comprises the step of depositing a nucleation layer directly on the thin film.

Preferably, the step of forming a radiation absorbing structure on the thin film comprises the step of depositing a dielectric layer.

Conveniently, the radiation absorbing structure formed is a resonant absorber 1 5 structure.

The thin film may conveniently be a mixed oxide ferroelectric thin film.

Preferably, the method may further comprising the step of removing some or all of 20 the radiation absorbing structure after the thin film has been annealed.

According to a fourth aspect of the invention, a device incorporates a thin film layer annealed using the method of the first or third aspect of the invention.

25 According to a fifth aspect of the invention, an intermediate thin film device comprises a pre-annealed thin film carried on a substrate comprising an integrated circuit wherein the thin film has a radiation absorbing structure formed thereon.

Preferably, the thin film is a ferroelectric thin film.

The invention will now be described, by way of example only, with reference to the following drawings in which; 5 Figure 1 illustrates a prior art annealing process;

Figure 2 illustrates an annealing process according to the present invention; Figure 3 shows the predicted absorption properties of a Silicon Nitride absorber 10 layer as a function of absorber layer thickness for 10.6,um radiation; Figure 4 shows the predicted absorption properties of a Silicon dioxide absorber layer as a function of absorber layer thickness for 10.6,um radiation; 15 Figure 5 shows the predicted absorption properties of a Silicon Nitride absorber layer as a function of absorber layer thickness for 308nm radiation; and Figure 6 shows the intensity of radiation as a function of depth through a structure of the type described with reference to figure 5.

Referring to figure 1, a typical prior art annealing technique is illustrated. A laser

pulse 2 is directed to the surface of a PST ferroelectric thin film 4 of thickness d which is located on a substrate 6.

25 The substrate 6 is formed from a number of layers, but only the uppermost electrode layer 8 is shown separately. A skilled person would recognise that the substrate 6 will comprise various adhesion and barrier layers and integrated circuitry (e.g. CMOS). As described above, it is the integrated circuitry of the substrate which is particularly temperature sensitive and may be destroyed, or damaged, if exposed to 30 an elevated temperature. In the case of CMOS circuitry, exposure to temperatures exceeding around 450 C causes permanent damage. In other words, the substrate 6 has a temperature budget that must not be exceeded during the anneahng process.

Substrates formed as so-called microbridge structures are also known. Typical microbridge structures are described in more detail with reference to figures 1 and 10 of WO 00/54317 the content of which is incorporated herein by reference thereto.

5 In a typical microbridge structure the ferroelectric thin film is deposited on a substrate having a sacrificial layer which can subsequently be removed to provide an air gap. This enhances the thermal isolation of the ferroelectric thin film from the substrate, thereby enhancing device performance. The term substrate as used herein should thus be taken to mean anything on or above which the ferroelectric thin film 10 is located.

The PST ferroelectric thin film 4 may be deposited on the substrate 6 using any one of a variety of known techniques. For example, chemical solution deposition, RF magnetron sputtering, metal-organic chemical vapour deposition or laser ablation.

15 To prevent thermal damage to the substrate 6, the PST ferroelectric thin film is deposited on the substrate at relatively low temperatures (typically less than 450 C).

The deposited PST layer is thus initially in an amorphous or pyrochlore phase that does not exhibit ferroelectricity.

20 The laser pulse 2 is typically produced by an excimer laser (e.g. a KrF excimer laser which produces radiation having a wavelength of 248nm) and is strongly absorbed by the PST ferroelectric thin film. The relatively short duration of the laser pulse results in localised heating of the ferroelectric thin film, primarily at its upper surface 10, without any significant heating of the substrate 6. This localised heating 25 causes the PST thin film layer to be converted from a non- ferroelectric state to a ferroelectric form; i.e. the ferroelectric thin film is annealed. As described in WO 00/54317, P. P. Donohue, PhD Thesis, University of Southampton, 2001 and Donohue and Todd, Integrated Ferroelectrics, Vol. 31, pp285-296, 2000, the laser pulse duration may also be extended which can reduce surface damage when thicker 30 thin films are annealed.

As described above, there are various problems associated with known laser annealing techniques. For example, it can prove difficult to provide full conversion to the required ferroelectric phase throughout the thickness of the ferroelectric thin film. In other words, existing techniques can only provide a limited depth of phase 5 conversion of the thin film, especially in lead containing ferroelectric thin films.

Although the conversion depth can be increased using pulse-extension, it remains limited. Another problem associated with known laser annealing techniques is the inability 10 to control the orientation of the required crystalline phase as it is grown. For thicker films, say greater than lam in thickness, nucleation occurs as a bulk effect in a similar fashion to bulk ceramic ferroelectric materials with the consequent random, or at least mixed, orientation of the grain crystal axes.

15 Referring to figure 2, an annealing technique of the present invention is illustrated.

Elements common to those described with reference to figure 1 are assigned like reference numerals.

In accordance with the invention, a dual layer radiation absorbing structure 20 is 20 located on the PST ferroelectric thin film 4. The radiation absorbing structure 20 comprises a first layer 22 and a second layer 24. The first layer 22 is formed from a quarter wavelength (at the laser wavelength) coating of silicon dioxide. The second layer 24 comprises a layer of Platinum that is sufficiently optically thick to prevent a significant amount of radiation passing to the underlying thin film 4.

The first and second layers in combination provide a structure that efficiently absorbs the incident laser radiation pulse 2, thereby heating the second layer 24 to a temperature that is sufficient to nucleate growth of the ferroelectric phase in the thin film 4. The ferroelectric phase then grows downwards (i.e. away from the interface 30 of the second layer 24 and the thin film 4) and preferably converts the entire thickness of the thin film. Using the method of the present invention thus prevents

the excessive surface heating of the ferroelectric thin film that is often associated with prior art direct heating techniques.

In this example, the second layer is formed from Platinum that will also act as a 5 seeding layer to aid nucleation and growth of the ferroelectric phase. The seeding effect reduces the activation energy, and hence the temperature to which the thin film must be heated, required to initiate growth of the ferroelectric phase.

Although platinum is preferred, the second layer 24 could alternatively comprise 10 another metal, a conducting oxide (such as lanthanum nickelate or strontium ruthenate) or an insulating oxide. The use of a material which acts as a seeding layer is preferred, but it is not essential.

The second layer 24 could alternatively comprise a material that provides control 15 over the orientation of the growth of the ferroelectric phase. For example, a seeding function similar to that obtained using Platinum would be provided by perovskite structure conducting oxides. Such conducting oxides can also be closely lattice matched to perovskite ferroe]ectrics, thus providing a growth template for the required perovskite growth. This template effect provides control over the 20 orientation of the grown ferroelectric phase. The ability to gain orientation control during ferroelectric film growth is particularly important in devices that rely on having a significant component of the polar axis of the ferroelectric in a particular direction. 25 It would be appreciated by the skilled person that the duration and intensity of the laser pulse 2 would be selected so as to heat the second (e.g. platinum) layer 24 sufficiently to anneal the underlying thin film 4 without exceeding the temperature budget of the substrate 6. If required, a laser pulse-extension technique of the type described in patent application W 000/54317 could be used.

After laser annealing, the first layer 22 could be removed using an appropriate micro-machining technique. The second layer 24 could also be removed or, if it is

sufficiently conducting, all or part of it could be retained to serve as a top electrode for the ferroelectric layer. Once an insulating, or poorly conducting, second layer has been removed a high conductivity metal electrode could subsequently be deposited to provide an electrical contact.

s To maximise absorption of laser radiation, the properties of the absorbing material (e.g. layer thickness) forming the first layer 22 are tailored to the particular wavelength of the laser used. Although silicon dioxide is described above, numerous alternative dielectric materials could be used (e.g. a silicon nitride etc). In fact, the 10 first layer could comprise any material which assist absorption of the incident radiation pulse. In particular it is advantageous, although not essential, to select a material for the first layer 22 which maximises absorption of the radiation by the second layer 24; this ensures as much heat as possible is coupled in to the thin film.

15 Figure 3 shows the predicted absorption (curve 30) as a function of Si3N4 layer thickness for 10.6'um radiation incident on Si3N4 topped stack. The stack comprises an Si3N4 layer (which is illuminated with the 10.6pm radiation) located on a 0.1pm thick layer of platinum which is carried by a PST thin film.

20 It can be seen that Si3N4 layers of a thickness greater than around lam provide absorption in excess of 30%. Furthermore, such absorption is almost independent of layer thickness for any layer thickness greater than around 2pm. The thickness of the layer can thus be selected to provide the required (e.g. maximum) amount of absorption. It should be noted that the choice of Si3N4 layer thickness will also 25 require consideration to be given to its heat capacity; i.e. a thicker layer wild have a heat capacity that limits the temperature rise in the underlying layers.

Referring to figure 4, the predicted absorption (curve 40) as a function of SiO2 layer thickness for 10.6,um radiation incident on SiO2 topped stack is shown. The stack 30 comprises an SiO2 layer (which is illuminated with the 10.6pm radiation) located on a 0.1pm thick layer of platinum which is carried by a PST thin film. Local

absorption maxima are observed for stacks comprising SiO2 layers around 1. 8m and 4.5pm in thickness. Again, the layer thickness can be selected to provide the desired level of absorption bearing in mind the heat capacity of the material.

5 A TEA CO2 laser can be used to produce radiation having a wavelength of 10.6m.

Typical TEA CO2 lasers can output relatively high optical powers and have a pulse duration that is controllable and can be significantly longer than typical excimer laser devices.

10 A standard excimer laser may also be used to illuminate the first layer, and figure 5 shows the absorption properties (curve 50) as a function of Si3N4 layer thickness for 308nm radiation incident on Si3N4 topped stack. The silicon nitride layer is located on a O.lum thick layer of platinum which is carried on a PST thin film. It can be seen that the absorption maxima of the stack approaches 90% at this wavelength, 15 however the optical power that can be output by a typical excimer laser is generally significantly lower than that produced by a typical TEA CO2 laser.

Referring to figure 6, the intensity of 308nm radiation as a function of depth for a stack of the type described with reference to figure 5 is shown. A first region 60 20 corresponds to the silicon nitride layer, a second region 62 corresponds to the O.lm platinum layer and third region 64 is the PST thin film.

It can be seen that the majority of the radiation is absorbed at the surface of the Platinum layer (i.e. in the second region 62). In this manner, the platinum layer is 25 heated thereby nucleating growth of the perovskite phase of the PST thin film.

In accordance with the teachings contained herein, the skilled person would select a laser wavelength and absorbing material that are optimised for the particular thin film to be annealed. It would also be appreciated by a person skilled in the art that 30 radiation absorbing structures other than the dual layer resonant structure described above could be used to implement the present invention. For example, a single layer of material that strongly absorbs the laser radiation could be employed.

Alternatively, a multiple layer stack (e.g. a stack comprising three or more layers) could be used.

Although ferroelectric films are described in the above examples, it should be noted 5 that the annealing technique of the present invention is equally applicable to other types of thin film. For example, the presentinvention could be used to anneal magnetic thin films etc. Alternatively, the annealing of amorphous Silicon thin films carried on glass or plastic substrates as used in thin film transistor (TFT) liquid crystal display applications would be possible.

Claims

1. A method for annealing a thin film comprising the steps of; (i) taking a thin film carried on a temperature sensitive substrate, the thin film having a radiation absorbing structure formed thereon, and (ii) illuminating the radiation absorbing structure with a pulse of radiation produced by a laser, wherein the radiation absorbing structure is heated sufficiently by the pulse of radiation to anneal all or some of the thin film without exceeding the temperature budget of the temperature sensitive substrate.

2. A method according to claim 1 in which the radiation absorbing structure comprises a nucleation layer in contact with the thin film.

3. A method according to claim 2 in which the nucleation layer comprises platinum.

4. A method according to claim 2 in which the nucleation layer comprises conducting oxide.

5. A method according to any one of the preceding claim in which the radiation absorbing structure comprises a dielectric layer.

6. A method according to claim 5 in which the dielectric layer comprises one or more layers of Silicon Dioxide.

7. A method according to any one of claims 5 to 6 in which the dielectric layer has a thickness substantially equal to one quarter of the wavelength of the pulse of radiation within said dielectric layer.

8. A method according to any one of the preceding claims in which the radiation absorbing structure is a resonant absorber structure.

9. A method according to any one of the preceding claims and further comprising the initial step of depositing the radiation absorbing structure on the thin film that is carried on the temperature sensitive substrate.

10. A method according to any one of the preceding claims in which the thin film is a mixed oxide ferroelectric thin film.

11. A method according to claim 10 in which the ferroelectric thin film comprises low grade deposited perovskite phase material and the annealing step improves the quality of the perovskite material.

12. A method according to claim 10 in which the thin film comprises material deposited substantially in the non-perovskite phase and the annealing step converts some or all of the material into the perovskite phase.

13. A method according to any one of claims 10 to 12 in which the ferroelectric thin film is any one of lead scandium tantalate (PST), lead zirconate titanate (PZT), strontium bismuth tantalate (SBT), barium strontium titanate (BST) or lead titanate (PT).

14. A method according to any one of the preceding claims and further comprising the step of removing some or all of the radiation absorbing structure after the thin film has been annealed.

15. A method according to any one of the preceding claims in which the substrate comprises an integrated circuit.

16. A method according to claim 15 in which the integrated circuit comprises Silicon

17. A method according to any one claims 1 to 14 in which the substrate is flexible.

18. A method according to any one of the preceding claims wherein the step of illuminating the radiation absorbing structure with a pulse of radiation produced by the laser is repeated a plurality of times.

19. A method according to any one of the preceding claims in which an excimer laser is used to produce the pulse of radiation.

20. A method according to any one claims 1 to 18 in which a transverse excited atmospheric carbon dioxide (TEA C02) laser is used to produce the pulse of radiation.

21. A method according to any one of the preceding claim wherein the pulse of radiation is produced by a pulsed laser and pulse extension means.

22. A method according to any one of the preceding claims in which the thin film is carried by the substrate in a microbridge arrangement.

23. A method of producing an infra-red detector comprising the method according to any one of preceding claims.

24. A method of producing a thin film device comprising the steps of; (i) forming a thin film on a temperature sensitive substrate, and (ii) forming a radiation absorbing structure on the thin film, wherein the radiation absorbing structure is adapted such that it can be heated sufficiently by a pulse of radiation of a given wavelength to anneal all or some of the thin film without exceeding the temperature budget of the temperature sensitive substrate.

25. A method according to claim 24 and further comprising the step of illuminating the radiation absorbing structure with a pulse of radiation of the given wavelength.

26. A method according to any one of claims 24 to 25 in which the step of forming a radiation absorbing structure on the thin film comprises the step of depositing a nucleation layer directly on the thin film.

27. A method according to any one of claims 24 to 26 in which the step of forming a radiation absorbing structure on the thin film comprises the step of depositing a dielectric layer.

28. A method according to any one of claims 24 to 27 in which the radiation absorbing structure formed is a resonant absorber structure.

29. A method according to any one of claims 24 to 28 in which the thin film is a mixed oxide ferroelectric thin film.

30. A method according to any one of claims 24 to 29 and further comprising the step of removing some or all of the radiation absorbing structure after the thin film has been annealed.

31. A device incorporating a thin film layer annealed using the method as claimed in any one of the preceding claims.

32. An intermediate thin film device comprising a pre-annealed thin film carried on a substrate comprising an integrated circuit wherein the thin film has a radiation absorbing structure formed thereon.

33. A device according to claim 32 wherein the thin film is a ferroelectric thin film.

34. A device according to any one of claims 32 to 33 wherein the radiation absorbing structure comprises a nucleation layer in contact with the thin film.

35. A method as hereinbefore described with reference to figure 2.