DE4102380C1 - High temp. superconductor film mfr. - by heating substrate with laser beam - Google Patents

Abstract

High temp. superconductor film is mfd. by laser or pseudo-function ablation, with direction of a laser heating beam on to the substrate and the film growing on it as pulses in the micro-s range. The pulses are coordinated to produce heating when particles ablated by an ablation pulse have just been deposited, pounding energy to form the required crystal structure. The laser is pref. a CO2 laser. ADVANTAGE - Growth and quality of films are improved.

Description

The invention relates to a method for layer production, in particular of high-temperature superconductor layers, using pulsed Laser or pseudo-spark ablation or other ablation procedure ren. Furthermore, the invention relates to devices for Performing these procedures.

For the production of (thin) layers of good quality, the Usually in-situ processes are used because these processes are generally take little time and deliver good results. At Many substances also require very high sub in situ processes street temperatures to form the desired crystal structure door.

In addition, with many substances, the layers have to be deposited are post-annealed in order to completely remove the crystal structure form or to bring about a required phase change. Often Sometimes the layer has to be deposited in a reactive atmosphere and / or post-annealed to be a sufficient number to incorporate coherent gas particles in the layer or by a to achieve the desired layer composition.

The high-temperature superconductor Y₁Ba₂Cu₃O _{7- δ} gives the best layers in terms of high transition temperature, critical current density and smoothness of the surface with the following in-situ processes:
The layer is deposited by means of a PVD process (Physical Vapor Deposition) on a suitable single crystal substrate heated to 700-800 ° C, the highest possible (partial) oxygen prevailing in the coating chamber. This gives stoichiometric, c-axis-oriented Y₁Ba₂Cu₃O _{7- δ} films (δ≈0.5), which still contain too little oxygen and have a tetragonal crystal structure that is not superconducting. In order to convert these into oxygen-rich (δ≈0.1) layers of the superconducting orthorhombic phase with a high transition temperature, they have to be post-annealed at 400-500 ° C under increased oxygen (partial) pressure. Sputtering, evaporation from three sources and laser ablation with pulsed UV lasers have proven to be particularly suitable PVD processes. Suitable single crystal substrates for Y₁Ba₂Cu₃O _{7- δ} are in particular SrTIO₃, LaAlO₃, LaGaO₃, ZrO₃ and MgO. With the in-situ method described above, Y₁Ba₂Cu₃O _{7- δ} layers with high transition temperatures T _c of 87-91 K, very high critical current densities j _c of 1-6 _* 10⁶ A / cm², smooth surfaces are obtained on these substrates and c-axis orientation.

A deposition at lower temperatures of 550-600 ° C leads to a-axis-oriented layers that have lower critical current densities and are therefore not suitable for many applications. In addition, these a-axis-oriented crystallites are not oriented in parallel, but rather approximately statistically on the substrate, as a result of which these layers degrade relatively quickly. Deposition at even lower temperatures causes poor crystal formation; an amorphous layer is obtained below 400 ° C. Such layers have to be post-annealed in oxygen at very high temperatures of around 900 ° C. in order to achieve superconductivity. They are then polycrystalline with very rough surfaces and low j _c , ie largely unsuitable for applications.

An aftertreatment to achieve superconductivity also made in the process of DE-OS 37 37 142, in which a layer production using pulsed pseudo-sparking material removal, especially of oxide ceramic superconductor targets, is made and the layer for realizing superconductivity ability with another pseudo-spark electron beam can be treated.

In all of the PVD processes described above, the Coated layers after deposition at 400-500 ° C pert, firstly to incorporate enough oxygen and second, the phase change from tetragonal to orthorhombi complete grid. The duration of this after annealing at 400-500 ° C under increased oxygen pressure in addition to the temperature of the subsequent annealing, the layer thickness and  the oxygen content of the Layer off.

In particular, if it is possible to incorporate a lot of oxygen during the deposition, the post-annealing can be shortened considerably. However, there are physical limits to the incorporation of oxygen, which depend largely on the substrate temperature and the permissible (partial) pressure during the PVD process. At high substrate temperatures of 700-800 ° C, a maximum of O _6.3 (δ≈0.7) can be achieved, while at lower temperatures more oxygen can be installed. However, the problem of incorrect crystal orientation then arises. To a certain extent, this can be counteracted by using activated oxygen (ions and / or radicals), since the activated oxygen provides the layer with some energy. This makes it possible to lower the substrate temperature to 650-700 ° C for c-axis oriented films with high T _c and j _c . This measure also shortens the duration of the post-heating, since a lot of oxygen was already installed during the layer deposition.

Even this lowered temperature to 650-700 ° C is still too high to use technologically important substrates such as gallium arsenide, silicon or sapphire (Al₂O₃ single crystal). From GaAs arsenic evaporates from 400 ° C, ie at the high substrate temperatures for Y₁Ba₂Cu₃O _{7- δ} layers the substrate decomposes. Silicon and sapphire are unsuitable because at the high deposition temperatures silicon or aluminum diffuses into the Y₁Ba₂Cu₃O _{7- δ} layer. The resulting layers have significantly lower T _c and j _c values than layers on SrTiO₃ or LaAlO₃ single crystals. Silicon, sapphire and gallium arsenide can be provided with buffer layers (e.g. Si₃N₄, ZrO₂, SrTiO₃) to somewhat prevent the diffusion or evaporation of arsenic. However, the buffer layers have the disadvantage that they lengthen the process of layer production and make it difficult to grow epitaxial layers if they themselves have not been epitaxially deposited on the substrate. GaAs, silicon or sapphire substrates provided with buffer layers enable somewhat better Y₁Ba₂Cu₃O _{7- δ} layers than these substrates without buffer layers. However, the T _c and j _c values are still too low for most applications. In order to be able to use GaAs, silicon and sapphire as substrates (possibly with buffer layers) to obtain high-quality high-temperature superconductor layers, one has to develop a process that is suitable for c-axis-oriented layers with high T _c - and j _c - Values significantly lower substrate temperatures than the conventional method allows.

A method that uses more oxygen would also be advantageous is installed than is possible with the conventional methods is. In particular, a method should be sought in which the Incorporation of the oxygen can be used at the same time Lower the substrate temperature significantly.

For some years now, the method of pulsed laser ablation has been successfully used for the production of thin layers. For the high-temperature superconductor Y₁Ba₂Cu₃O _{7- δ} and other multi-element compounds with very different melting points and vapor impressions of the elements, especially pulsed excimer and frequency-multiplied Nd: YAG lasers with pulse lengths in the ns range have proven their worth. Recently, the above-mentioned inexpensive pseudo-spark ablation has been added, in which electron beam pulses are shot at a target.

An example of the use of focused YAG or excimer Laser radiation can be found in JP-A-3 09 956, Pat. Abstr. JP, C-694, Feb. 27, 90, Volume 14, No. 106. There is a stable, epi tactical growth of oxide ceramic superconductor layers wrote, in which by means of such focused radiation the ablation or target ablation occurs and defocused CO₂ Laser radiation for preheating and simultaneous irradiation of the Substrate is used during the layer deposition. Here however, substrate temperatures of 800 to 950 ° C testifies that according to the above remarks on several systems are not possible.  

Both laser and pseudo-spark ablation include that Disadvantage of droplet formation. Because of the high pulsed Energy supply to the target is not just individual atoms or molecule (fragments), but also target fragments animals that are deposited as "droplets" in the layer. Due to their size of approx. 100 to 1500 nm, they can Limit the use of layers produced by ablation ken. In microstructuring in particular, they require one high committee.

The size and number of droplets both depend on the target as well as from the process parameters and can partly by the following measures are reduced:

• 1. use of lasers with short pulses and wavelengths, especially excimer lasers;
• 2. Use of high density targets;
• 3. extensive reduction of the energy density at the target; and
• 4. Setting the largest possible target substrate Distance.

However, these measures cannot always be implemented. In addition, points 3 and 4 mean a reduction in the number of separations rate, which is often undesirable. With the reactive discharge tion is also the maximum possible target-substrate distance from necessary background printing.

The object of the invention is to improve laser or pseudo-fun ken ablation process for layer production, in particular of Specify high-temperature superconductor layers in which the Layer growth and the quality of the layers improved and / or with at least constant layer quality Substrate temperature can be reduced so far that even when Use of temperature-sensitive substrates usable layers arise.

The process according to the invention after all the solutions given is suitable for all substances which have to be deposited at high substrate temperatures in order to form the desired crystal structure. The method is particularly suitable for substances that need to be reactively deposited, such as. B. the high temperature superconductor Y₁Ba₂Cu₃O _{7- δ} , the layer growth and the layer quality are also improved here. In addition, according to another solution, the layer growth is improved in that the droplet formation mentioned can be avoided or at least greatly reduced.

A first solution to the problem according to the invention (claim 1) enables in particular special, the substrate only to a relatively low temperature heat in the case of temperature sensitive substrates  of the type mentioned above still no substrate replacement or Diffusion of substrate particles into the layer. The for the Crystal formation still lacking energy is measured by laser pulses in the µs range in the growing film or in the substrate upper surface coupled.

The use of laser pulses in the µs range includes the following the beneficial effects:

• 1. In this time range, the parts just deposited get Chen by heating the substrate surface or the growing layer already enough energy for training the desired crystal structure and
• 2. Due to the short pulses, the substrate or the Shift, quickly approaching the pre-heating cool given temperature, so that at temperature critical No decomposition or diffusion.

The supply of pulsed energy for layer production is in itself known from semiconductor technology. So-called companies called "Rapid Annealer" that offered intense light pulses give up, whereby the substrate or the layer temporarily strong is heated. The disadvantage of "rapid annealers" is their relative long pulse duration in the ms to s range. With a temp sensitive substrate often sets diffusion in the Layer one as it cannot cool down fast enough. From the Research into high temperature superconductors is also a ver drive known in which the beam of an excimer laser to a Part on the target and the remaining part on the substrate is directed (Otsubo et al., Japanese Journal of Applied Phy sics, volume 28, No 11 (November), 1898, pages 2211-2218). At However, crystal growth is only negligible in this process sufficiently supported because, on the one hand, the ns pulses are too short and on the other hand the penetration depth of the UV light is too small. The main disadvantage of this method is also a lack of time coordination between the ablation pulse and the heating pulse.  

In the method according to the invention, these disadvantages are on the one hand avoided by the µs-long laser pulses. In addition, at some temperature sensitive substrates, such as GaAs, for the short duration of the µs pulse over the substrate surface Decomposition temperature of the substrate can be heated without the substrate decomposes or the surface of its crystal loses order. The prerequisite for this that the sub cool down quickly below the critical temperature can be achieved according to the invention by the short pulse length.

To form the desired crystal structure of the layer the particles just separated need a minimum energy, the in the case of simple processes via a stationary heater becomes. It is crucial for the formation of the crystal structure the surface temperature when the deposited part hits Chen and in the subsequent period that the particles for Need orientation. By coordinating the timing Heating impulses with the ablation pulses are successful with the invention method, the average substrate temperature increases considerably reduce. The heating impulses are controlled in terms of time and intensity bar, so that the ablated particles are sufficient hot surface to be deposited, which is just before or during is heated pulsed during the deposition. Due to the short pulse duration of the heating pulse relatively little energy is transferred to the substrate surface or the layer is coupled in, so that the substrate subsequently can cool down quickly. In particular, this can temperature sensitive substrates quickly under one for that Cool the substrate or the critical temperature layer so that Decomposition and diffusion can be avoided. This is particularly successful especially in the case of one coordinated in time with the ablation pulses Delivery of heating pulses, because then the ablated particles the optimal surface temperature for the substance on the Substrate are deposited.  

The main advantage of the first solution above is the lowering of the mean substrate temperature by the time coordinate tion of the ablation pulses with the specified heating pulses Length is reached. In particular the use of temperature this enables sensitive substrates. Self for substances that are longer than a few µs for the arrangement or orientation of the particles in the desired crystal lattice the process can be successfully further developed, in this case by applying additional heating pulses to the substrate gives. The first of these additional pulses should preferably be short after the deposition of the particles just ablated, the sub reach strat. The subsequent pulses can usually have significantly lower intensity since they have a maximum of Temperature difference between the current temperature and the maxi must compensate for the temperature at the first heating pulse. If the Lasers for this training are not sufficiently high pulse frequency two lasers should co-ordinate be kidneyed. This applies in particular to substances where the first two heating pulses occur at intervals of a few µs should.

The inventive method according to the above solution is suitable basically for all substances that are usually found at high Substrate temperatures need to be deposited to the ge wanted to get crystal structure. It enables in particular lowering the average substrate temperature, which otherwise unsuitable temperature-sensitive substrates successfully turned on can be set, d. H. the layer quality corresponds to that of Layers on temperature-insensitive substrates conventional methods were produced. With temperature-insensitive sensitive solution, the solution is also advantageous because through the pulsed heating the formation of the desired kri stall structure and thus the layer growth can be accelerated. In the case of many substances, this allows the same layer quality increase the maximum deposition rate.  

Layer growth can still be improved if one uses a laser whose light is not just the one you want Generates heating pulses, but also the ablated particles or the added gas particles in the case of reactive ablation stimulates.

The above procedure is basically suitable for all single cri stallinen, polycrystalline and amorphous substrates. At polykri The stable and amorphous substrates are the deposited ones As a rule, layers are not single-crystal, but polycrystalline lin. The properties of polycrystalline layers are mostly significantly worse than that of single-crystal layers, whereby their quality largely depends on the size of the crystallites. However, this achievable quality is not always sufficient. A Continuing the above solution involves improving Layer quality especially of polycrystalline films polycrystalline or amorphous substrates. This training includes a layered structure of the entire layer in the following Wise:

• 1. It becomes a very thin film of at most a few nm Thickness deposited using the heating pulses:
• 2. The deposition is interrupted to give the particles more time to give to the formation of crystallites; and
• 3. The remaining layer is applied in one step using heating pulses to the desired thickness, or steps 1 and 2 are repeated as often as required. During step 2 , heating pulses can continue to be applied to the substrate or the layer in order to shorten this step in time. For substances that also have to incorporate gas particles, the most favorable parameters for the installation should be selected during step 2 , ie generally a different substrate temperature and a significantly increased (partial) pressure of the gas to be installed. With these substances, too, further heating pulses during step 2 are generally advantageous, since in addition to the formation of the crystal structure, they also accelerate the incorporation of the gas particles. Whether you can deposit the layer directly to the desired thickness after step 2 , or whether you have to repeat steps 1 and 2 , depends largely on how quickly the substance to be deposited can form the desired crystal structure and how good the layer will be got to.

With this development of the above method, many substances can be deposited on inexpensive polycrystalline or amorphous substrates, which otherwise cannot be used due to a lack of layer quality. This further development is also advantageous for the deposition on single-crystalline substrates, in particular if one wishes to deposit at high rates. Step 1 is then preferably carried out at a reduced deposition rate in order to produce the best possible single-crystal film on which the layer can then continue to grow epitaxially at a high deposition rate. The first thin film thus serves to induce the correct crystal structure and to compensate for any mismatch between the lattice parameters of the substrate and those of the substance to be deposited.

The method according to the invention is based on pulsed deposition, especially on pulsed laser or pseudo-spark ablation. The problem with these methods is droplet formation. These are particles ablated from the target, which are known as "droplets chen "in the film and the use of the abla tion layers produced. This also applies to polykri stalline layers, in contrast to single-crystal layers there are no very high quality requirements. A Reduction or even avoidance of droplets by choice Process parameters are only partially possible. To avoid or at least largely reducing the droplets prevent these ablated particles from reaching the layer.  

For this purpose, the invention provides a second solution (claim 6), in which this Verify particles on the way to the substrate with a laser beam be steamed. The laser beam from a continuous wave laser is blasted through the plasma cloud (with plasma cloud is the whole Space meant by the ablated particles on the way to the Traverse substrate, d. h the "ablation cloud"). this is the simplest way to implement this solution according to the invention, and has the advantage that all particles are independent of their Speed can be detected. The laser beam is preferred not just once, but several times (at least twice) the plasma cloud blasted. To do this, he is mirrored into the Plasma cloud reflected back, making the probable ability to evaporate particles increases.

In the case of multiple reflection, an alternative can also be preferred as long as possible pulsed laser used with good success because the covered speed window is big enough. However, you also need a syn Chronization of ablation and particle evaporation. in the the following are the pseudo-radio source or the laser Ablation referred to as an ablation laser and the laser for Particle evaporation as an evaporation laser.

The first solution can be advantageously with this combine second solution. With such a combination a pulsed laser for heating the substrate surface, or the growing layer provided anyway (hereinafter as heating laser), which synchronizes with the ablation laser becomes. This is suitable due to the pulse length of a few µs Lasers also good for particle evaporation, i.e. H. the ray of the Heat lasers can be split and partially onto the substrate as well partially blasted through the plasma cloud. Ideally the (first) heating pulse occurs at a time when the Particles from the previously branched laser beam from the heating laser  to fly. This can result in an optical delay of the evaporator tion laser pulses are avoided, otherwise to synchronize with particle movement is required.

Instead of the heating laser, a branched part of the Laser beam from the ablation laser for particle evaporation be set. Because of the usual pulse durations in the ns range however, this requires a more complex multiple reflection and optical delay of this sub-beam. If available, should one can use three lasers (ablation, heating, evaporation La ser), the synchronization of which is hardly more complex than the syn Chronization between ablation and heating lasers. Advantages here of are avoiding a mostly necessary optical Delay and above all the optimization of each laser beam for its purpose. In the case of a continuous wave laser to the party There is no evaporation when combined with the first solution even synchronization.

The second solution according to the invention can be produced any substance using laser or pseudo-spark ablation apply with the result of the layer improvement. Especially their use in the ablation of ceramic has been successful Targets, e.g. B. the high-temperature superconductors, the ferroelectric ka or the dielectrics.

The second solution according to the invention is particularly suitable for Improve the quality and growth of Layers that invent simultaneously using the first Solution according to the invention are prepared. The second solution can but can also be used to improve layers with usual ablation methods, d. H. without pulsed time coordinator heating the substrate surface.

In an article "Particulates reduction in laser-ablated Y₁Ba₂Cu₃O _{7- δ} thin films by laser-induced plume heating" by G. Koren et. al ,. Applied Physics Letters, Vol. 56 (21), May 21, 1990, pages 2144-2146, it is described that Y₁Ba₂Cu₃O _{7- δ} layers have droplets when that of a pulsed Nd: YAG laser (1.06 µm) generated plasma cloud is irradiated with the light of a pulsed excimer laser (KrF 248 nm). However, the layers obtained have significantly more small droplets and still considerable unevenness compared to layers which have been produced by ablation with the KrF laser. It is pointed out that progress should be possible by optimizing the laser intensity, wavelength, alignment with regard to the plasma cloud and time delay compared to the ablation laser. On the other hand, the measures according to the invention bring the decisive progress that as many particles as possible are recorded in the plasma cloud.

The invention sees one applicable to the above solutions Continuing education, especially in the case of reactive ablation Layer growth and layer quality improved. At this The reactive gas to be built into the layer is further developed offered by means of gas pulses. These gas pulses allow local on Substrate or the growing layer for the short duration of Gaspulses a significantly higher gas pressure than it does with a continuous gas supply is possible. The advantage of gas pulses comes especially with a time coordination with the Ablation pulses to wear. The one is particularly advantageous set of gas pulses when the reactive gas is at least partially in activated form z. B. is offered as ions or radicals. Details about the use to improve the layer quality and layer growth are in a not pre-published German patent application by the applicant (P 40 35 073.8) ge describes.

Advantageously, the gas pulses with the first Lö solution combined with pulsed heating. the big advantage this training compared to the exclusive use of gas or heating pulses is possible significant reduction in substrate temperature. These  additional reduction of the maximum substrate surface temperature temperature or layer temperature is determined by the combination of the tempe measures to reduce heating and gas pulses (activate tem) reactive gas is reached, which is time-coordinated with the ablation pulse. This can make even more temperature sensitive Substrates are used as when applying the first Solution or you can often on otherwise necessary buffers do without layers.

But even when depositing substances at high temperature on non-temperature-critical substrates, the above development is particularly advantageous if the reactive gas is installed stoichiometrically at a lower temperature than that at which the substance adopts the correct crystal structure (generally the maximum deposition temperature). With many substances, such as. B. the high-temperature superconductor Y₁Ba₂Cu₃O _{7- δ} , the reactive gas is only far below the usual deposition temperature of 700-800 ° C at about 400-500 ° C stoichiometrically properly installed. Due to the pulsed heating, the average substrate surface temperature can be in this low temperature range. If you give oxygen pulses to the substrate in this temperature range, the gas particles are well built in, especially if they are activated. In the subsequent ablation pulse, the layer is brought to a higher temperature by appropriately controlled heating pulses, so that the particles which have just been deposited receive enough energy to arrange themselves in the desired crystal lattice. This makes it possible to improve the layer growth and the layer quality with a significantly reduced average substrate temperature, so that on the one hand temperature-sensitive substrates such as silicon can be used successfully without buffer layers, and on the other hand the layers can crystallize directly in the superconducting orthorhombic phase. In other words, the twin formation of the layers is greatly reduced.

The invention also sees the combination of the gas pulses with the Particle evaporation for those substances where it it is not a question of a drop in temperature, but of possible best possible installation of gas particles and freedom from droplets Films. A possible formation of this solution is as follows not described. You can by from the above Combination can be easily derived.

Further training is also not described in detail, which is a combination of the heating pulse and gas pulse with the droplet represents vaporization. This training takes place preferred use wherever layers using of heating and gas pulses are produced, too many droplets e.g. B. for microstructuring. Hereby it succeeds droplet-free layers with reduced substrate temperature and separating particularly good installation of reactive gas particles.

The further development of the first solution with the advantageous one layer-by-layer deposition to improve the layer quality and layer growth, in particular on polycrystalline or amorphous substrates can also be used successfully with the others Apply solutions and developments according to the invention.

Another advantage of the invention is the possibility of large areas substrates even at low substrate temperatures coat. This is particularly the case with reactive ablation promoted by the use of gas pulses.

Are for the heating pulse laser, the evaporation laser and / or the Ablation laser used wavelengths that ablated Excite particles and / or the gas pulse particles, so that can Further improve layer growth.

In itself, every solution or further education improves that Layer growth and layer quality, the first solution preferred to lower the substrate temperature at the non  active ablation (especially in high vacuum) is suitable, the The second solution is to avoid droplets, the further development of the first solution with the gas pulses in the reactive Ablation to lower the substrate temperature and improve it The installation of the gas particles is used, the training the second solution with the gas pulses especially for manufacturing droplet-free layers with improved incorporation of the gas particles suitable is; and advanced training that combines all solutions for the production of droplet-free layers with reduced sub street temperature and improved incorporation of gas particles is set.

The invention is particularly suitable for the layer production of high-temperature superconductors, ferroelectrics or dielectrics and also metal alloys. Examples include the following substances: ReBa₂Cu₃O _7-x (Re = rare earth element or yttrium, lead zirconate, PZT, PZT with lanthanum (PLZT), Bleitita nat, ZrO₂, SrTiO₃, LaAlO₃, NdGaO₃.

The method according to the invention is also not only suitable for improved growth of thin layers and climb layer properties, especially when the sub is lowered street temperature, but also for structuring the layers during growth. In-situ structuring is known in which the layer is structured during the deposition is that light contributes to local heating of the layer and thereby a different crystal structure in the irradiated part of the Layer is caused as in the unirradiated part. With the elder ren German application P 39 25 085.7 of the applicant Light from a continuous wave heating laser through a mask onto that Substrate or the growing layer. The crystal formation necessary temperature is only reached where the laser light falls on the substrate, so that the desired structure in a planar layer. The layer produced in this way exists e.g. B. from areas with the desired superconducting crystal structure and other areas of non-superconducting crystal  structure. Furthermore, laser healing is generally known in which the crystal structure of a film is laser-irradiated lung is changed. By imaging a mask or by Writing with the laser can be the desired structure if necessary, also achieve during the deposition.

If you let the light of the Heizla sers fall through a mask onto the layer in the process according to the invention, a sharper structure is obtained than in the process according to the above application. The reason for this is the only strong local warming in such a short time that the heat conduction is negligible. This achieves a high temperature with little energy and creates a steep temperature gradient at the edge of the irradiated areas. The transition zone from a certain (e.g. superconducting) crystal structure to another (e.g. normally conducting) crystal structure is very small. This not only makes the structure sharp, but can also be small overall. The crystal formation is completed before the heat conduction takes effect. The heat conduction interweaves the temperature profile. Essentially, the high-temperature modification is frozen in the irradiated zone, while there is no structural change in the unirradiated area because of the low temperature increase. This structuring also produces a planar layer, which is often an advantage. For cases in which only the structure is to remain on the substrate, the invention provides the following development:
The intensity of the heating pulses is set so that it is sufficient to ablate the particles that have just been deposited again from the substrate. Wherever the layer is to be grown, the intensity of the heating pulses is reduced to such an extent by means of a partially permeable mask that the energy is sufficient to achieve the desired crystal structure (analogous to the first solution according to the invention). In other words, the light from the heating laser passes through a special mask that partially lets the light through where the desired layer structure is to remain on the substrate. The light from the heating laser is completely let through where no layer should grow.

In the following the invention with reference to the drawings explained. In detail shows

Figure 1 shows an embodiment of an apparatus for performing the inventive method according to the first solution.

FIG. 2 shows a possible temporal temperature profile of the substrate surface according to the exemplary embodiment from FIG. 1;

FIG. 3 shows an alternative temporal temperature profile of the sub stratoberfläche;

Figure 4 shows an embodiment of an apparatus for performing the inventive method according to the second solution or according to a combination of the first and second solution.

FIG. 5 shows a modified exemplary embodiment of the device from FIG. 4;

Fig. 6 shows an embodiment of a device according to a further development of the first solution;

FIG. 7 possible temporal temperature and gas pressure profiles on the substrate surface according to the exemplary embodiment from FIG. 6;

Fig. 8 is an alternative temporal temperature and gas pressure characteristics at the substrate surface; and

Fig. 9 shows an embodiment of a device according to a development of the first and second solution.

In Figs. 1, 4-6 and 9, all of which in each case 1 show a Beschich processing chamber for carrying out the method according to the invention, a pulsed laser beam is, for ablation. B. from an excimer laser always indicated with 2 . This laser beam is always directed (focused) onto the target 3 , whereupon a plasma cloud 4 is formed from the ablated particles. A substrate 5 to be coated is arranged opposite the target and can be heated by means of a heating device 6 . This device is used to carry out the generally known method of laser ablation. Instead of the laser beam 2 , z. B. also uses a pseudo-spark beam or any other pulsed ablation beam for ablation. (These embodiments are not drawn.)

In Fig. 1, an embodiment is shown according to the first solution. In addition to the known ablation, the substrate surface or the growing layer is briefly heated by means of short heating pulses above a relatively low mean temperature, which is predetermined by the heating. The approx. 1-10 µs long heating pulses are generated with a TEA-CO₂ laser beam 7 . These heating pulses are coordinated with the ablation pulses. Using a mask 8 , the layer can be structured in situ during the deposition. Due to the mask, different crystal structures arise in the planar layer, e.g. B. superconducting in addition to normal conducting.

In Fig. 2 shows a possible time coordination between heating pulse and Ablationspuls is shown, which is ideal for most substances. In the upper diagram of FIG. 2, the intensity I _{s of} the ablated particles on the substrate is plotted against time, in the lower diagram the substrate surface temperature T _{s is} plotted against time. The heating pulse takes place in such a way that the maximum substrate surface temperature is reached approximately at the maximum intensity of the ablated particles on the substrate. The heating pulse is longer than the pulse of the ablated particles on the substrate, so that the particles reach a briefly heated substrate. Due to the short pulses, the substrate surface temperature quickly falls back to the average (uncritical) temperature T _n due to the heat emission.

In Fig. 3, a modified time coordination between ablation and heating pulses is shown, in which a heating pulse approximately at the same time with and another heating pulse shortly after reaching the ablated particles on the substrate to heat this to a maximum. This exemplary embodiment of the first solution is particularly advantageous when the particles to be separated preferably have to strike a strongly heated, ie thermally excited surface and at the same time additionally require a relatively long time to arrange. The second pulse occurs during this time, so that the particles have enough energy to arrange them.

Other designs, not shown, see additional heating pulses between the ablation pulses.

With the arrangement shown, the above-mentioned is further formed process with initial formation of a very thin one Film and subsequent interruption of the deposition feasible. In this case, the heating laser can be used in addition to the phases in to which the layers are applied, even during the Interrupted phase of formation of the crystal structure can be controlled to the formation of the crystal accelerate structure. By varying the heating pulse parameters Intensity and frequency can be the substrate temperature to an optimum value for the formation of the crystal structure change, i. a. lower.

Fig. 4 shows a further solution to improve the layer qualities and layer growth. In this second solution, in addition to the known ablation, the laser beam 9 of a continuous wave laser is radiated through the plasma cloud. By this measure, ablated particles are evaporated, whereby the formation of droplets is prevented or at least greatly reduced. In many cases, this second solution alone is preferable to the combination of the first and second solution, in which heating pulses are added to the substrate in addition to the particle evaporation. (In the second solution without a combination, the laser beam 7 and the mask 8 which may be present are omitted).

FIG. 5 shows a modified exemplary embodiment from FIG. 4, in which the laser beam 9 for particle evaporation is reflected several times by the plasma cloud. The mirrors 10 required for this can also be replaced by curved mirrors or arranged outside the coating chamber. Instead of the laser beam from a continuous wave laser, the beam of a pulsed laser can also be used in this embodiment, the pulse length of which should be as large as possible in order to cover a large speed window with regard to the ablated particles. The lasers for particle evaporation and for heating the substrate can originate from a split laser beam. However, this generally requires a somewhat complex optical delay of a partial beam. When using an evaporation laser suitable wavelength, it is also possible to excite the ablated particles in the plasma cloud.

FIG. 6 shows a preferred development of the first solution for substances which (must) be deposited reactively. In addition to the process according to the first solution, the reactive gas to be installed is applied to the substrate by means of gas pulses. These gas pulses are coordinated with the ablation and heating pulses in such a way that the installation of the gas particles is optimally supported and the temperature of the substrate surface can be further reduced. The gas pulses 12 are applied to the substrate via a nozzle 11 . The gas is preferably activated beforehand, ie it has a high proportion of activated particles (ions and / or radicals). Instead of the reactive gas to be incorporated, a gas can also be used with certain substances which splits off or breaks down into gas particles to be incorporated.

Fig. 7 shows a possible time coordination between ablation, heating and gas pulses to the substrate. In the upper diagram the intensity I _{s of} the ablated particles on the substrate, in the middle diagram the temperature T _{s of} the substrate surface and in the lower diagram the gas pressure P _s on the substrate are plotted against time. In this embodiment, the heating pulse occurs approximately simultaneously with the reaching of the ablated particles on the substrate and the gas pulse thereafter. The timing is coordinated in such a way that the ablated particles are deposited on a heated surface from which they receive enough energy to arrange themselves in the correct crystal lattice. The gas pulse occurs shortly afterwards at a point in time at which the temperature has already decayed to such an extent that a larger proportion of gas particles can be incorporated than at the maximum temperature. On the other hand, activated gas particles in particular bring their own energy, which is used to arrange the particles. As a result, the average temperature T _{m can be} lower than in the method according to the first solution without this combination. The gas pulses can briefly generate a much higher pressure on the substrate than would be possible in the stationary case (P _m ). The background pressure P _h can in turn be much lower than in conventional reactive ablation, so that even larger substrates can be coated.

In Fig. 8 a modified temporal coordination between the ablation, heating and gas pulses is shown which is particularly suitable for substances that require a relatively large amount Zeut to the correct crystal structure take and install many particles of the reactive gas at a low temperature. The temporal co-ordination between the pulses takes place in such a way that first a heating pulse heats the substrate or the layer already formed strongly, the ablated particles being deposited on the hot surface at about the same time. Shortly after the ablated particles are separated, a gas pulse reaches the layer. In order to properly install the ablated particles and the gas particles in the desired crystal lattice, a second heating pulse is carried out in such a way that the temperature maximum is reached simultaneously with the intensity maximum of the gas pulse. This combination of heating and gas pulses, which are coordinated in time with the abla tion pulses, the mean substrate temperature T _{m can} in turn be lower than in the exemplary embodiment according to FIG. 1 or the ablation with gas pulses alone. Especially when the gas particles have been activated, T _{m can be} significantly reduced. For many substances, the reactive gas is only properly installed stoichiometrically at a temperature that is much lower than the temperature required for crystal formation. The development according to FIG. 8 takes this into account by adding further gas pulses between the ablation pulses to the substrate when the substrate surface temperature or the layer temperature has dropped at least approximately to the low mean temperature T _m . Only one further gas pulse is shown in FIG. 8. Of course, between the ablation pulses, many gas pulses can reach the substrate with different intensities. Likewise, further heating pulses with generally lower energy between the gas pulses are conceivable, which take place in such a way that the gas particles are installed at an accelerated rate.

The development according to FIG. 8 is in principle suitable especially for materials such as high-temperature superconductors Y₁Ba₂Cu₃O _{7- δ.} With this substance, the temperature for the formation of the desired crystal structure is very high (650-800 ° C), the stoichiometrically correct incorporation of oxygen, however, only takes place below 500 ° C. By means of the method according to the invention, the average substrate temperature can be set to values below 500 ° C., preferably below 400 ° C. The heating pulses briefly heat the substrate to values of 650-800 ° C (depending on the degree of activation of oxygen and the temperature sensitivity of the substrate). Since the gas pulses increasingly generate very high pressures on the substrate for a short time, it is thus possible to grow Y₁Ba₂Cu₃O _{7- δ} directly in the superconducting orthorhombic phase. That is, the otherwise necessary tetragonal-orthorhombic phase change can be omitted, which reduces the formation of twins. In addition, this method is particularly suitable for the deposition of Y₁Ba₂Cu₃O _{7- δ} on temperature-sensitive substrates such as sapphire, silicon and gallium arsenide.

Fig. 9 shows a preferred development of the first and two th solution, in which particles are vaporized with a further laser beam in addition to the heating and gas pulses coordinated in time with the ablation pulses. In this embodiment example, the beam 9 of a continuous wave laser is used. The time coordination between the pulses can e.g. B. as in Fig. 7 or Fig. 8. This training is particularly suitable for ceramic substances, for. B. in the high temperature superconductors, where the droplet formation occurs interfering.

Claims (20)

1. A process for the production of layers, in particular of high-temperature superconductor layers by means of pulsed ablation, in particular laser or pseudo-spark ablation, characterized in that laser heating radiation is directed onto the substrate surface or the layer growing there in a manner known per se, which, however, consists of laser heating pulses of a pulse length in the microsecond range, which are timed in relation to the ablation pulses in such a way that they cause temporary heating of the substrate surface or the growing layer when the particles abla tated by an ablation pulse are deposited there are given energy from this temporary heating to form a desired crystal structure. 2. The method according to claim 1, characterized, that ver to generate the heating pulses as a pulsed CO₂ laser is applied. 3. The method according to claim 1 or 2, characterized, that especially for substances where the time is Formation of the crystal structure takes a relatively long time or several additional heating pulses after the deposition of the Particles are directed onto the substrate. 4. The method according to any one of the preceding claims, characterized in that

• a) first a very thin film of a maximum of a few nm is deposited,
• b) the deposition is interrupted for a predetermined time during which the respective crystal structure forms to the desired extent and
• c) the layer to be produced is applied to the desired total thickness either in a deposition step or by repeating steps a) and b) accordingly.

5. The method according to claim 4, characterized, that even during process step b) heating pulses on the thin film. 6. Process for the production of layers, in particular of high temperature ratur superconductor layers by means of pulsed ablation, ins special laser or pseudo-spark ablation, characterized, that the light of a continuous wave laser or a pulsed one Lasers through the plasma cloud resulting from the ablation is blasted with the light of the pulsed laser in each Case and that of the continuous wave laser preferably several times is reflected by the plasma cloud. 7. The method according to claim 6, characterized, that the light of the pulsed laser for the irradiation of the Plasma cloud by dividing and redirecting the pulsed laser is generated for ablation. 8. The method according to any one of claims 6 or 7, characterized, that the reflection takes place so that the plasma cloud as possible is completely irradiated by the laser beam.   9. The method according to any one of claims 6 to 8, characterized, that the laser beam and / or the reflected laser beams radiated through the plasma cloud near the target surface will be. 10. The method according to any one of claims 6 to 9, characterized, that the laser beam and / or the reflected laser beams parallel or almost parallel to the target surface by the Plasma is being blasted. 11. The method according to any one of claims 6 to 10, characterized, that a laser wavelength for irradiating the plasma cloud is used with the ablated particles and / or gas particles are excited. 12. The method according to any one of claims 1 to 5, characterized, that in addition to the direction of the heating pulses on the substrate radiation of the plasma cloud according to one of the claims 6 to 11 is carried out. 13. The method according to claim 12, characterized, that to generate the heating pulses on the substrate and A pulsed laser is used to irradiate the plasma cloud whose beam is divided and deflected accordingly. 14. The method according to any one of claims 1 to 13, characterized, that one or more gas pulses are timed to the Substrate are directed that they this shortly before and / or after reaching the ablated particles.   15. The method according to claim 14 when it is related back to Claim 4 characterized, that in process step b) further gas pulses on the sub to be judged. 16. The method according to claim 14 or 15, characterized, that gas pulses are generated that consist of particles, which are to be installed in the layer to be produced or split off atoms or molecules to be installed there or in decompose such. 17. The method according to claim 14 to 16, characterized, that the gas pulses with a high proportion of activated part chen in the form of excited atoms or molecules, ions and / or radicals are generated. 18. The method according to any one of claims 14 to 17, characterized, that generate a laser wavelength for the pulsed laser The heating pulses used to ablate and / or excites the particles of the gas pulses. 19. The method according to any one of claims 1 to 5 and 12 to 18, characterized, that in the beam path of the pulsed laser to generate the Heating pulses one of the desired structure of each Layer corresponding mask is arranged.   20. The method according to claim 19, characterized in
that a mask is used which has partial and fully permeable areas for the wavelength of the laser for generating the heating pulses, and
that the intensity of the heating pulses is set so that the deposited particles under the fully permeable areas of the mask are ablated from the substrate and the areas separated from the partially permeable masks absorb sufficient energy for crystal structure formation.