FI111939B - Method and apparatus for manufacturing a glass coating - Google Patents

Description

111939

Method and apparatus for manufacturing a glass coating

The invention relates to a method according to the preamble of claim 1 for the production of a planar glass coating, particularly suitable for use in planar waveguides 5. The invention further relates to an apparatus according to the preamble of claim 10 for carrying out the above method.

The optical planar Waveguide is obtained by forming overlapping layers of glass having a different refractive index on a suitable substrate, for example a silicon wafer. Traditionally, so-called glass is initially formed on the top of a silicon wafer. an undercladding layer on which is formed a core layer with an optical refractive index slightly higher than the above layer. The desired waveguide pattern is formed in this core layer, for example, using photolithographic methods. A third so-called optical refractive index with a slightly lower optical refractive index is formed on the core layer. upper cladding. In the waveguide structure thus formed, light is ete-20 absorbed in the core layer in the same manner as in the optical fiber core.

Optical level waveguides are now widely used in a variety of applications. Examples of some of the most important applications of planar waveguides are computing and telecommunications ·. 25 and various measuring and sensor applications. Planar waveguides enable the packaging of optical structures and elements on the same substrate in a small space to form a compact unit which, in addition to being small in size, may have advantages, e.g. low optical signal losses and high operating speed. In this respect, flat waveguides can thus drive 30 Telia to the same benefits as traditional integrated circuits, which use only electronic components on the same substrate. Nowadays optical components and structures can be combined with optical flat waveguides on the same substrate as well as electrical components and '. 35 structures.

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One known and widely used method for forming the layers of glass required in optical flat waveguides is the so-called "glass". Flame Hydrolysis Deposition (FHD).

U.S. Patent No. 5,622,750 discloses one way of forming glass layers for use in planar waveguides using the FHD method. Em. in the process described in the patent, the starting materials required for the manufacture of glass are mixed together into a solution, which is formed into aerosol droplets, which aerosol droplets are introduced with the carrier gas into the burner and further to the flame. In a thermal reactor flame, aerosol droplets form aerosol particles, which aerosol particles are further directed to the substrate to be coated by thermophoresis to form a glass material coating. In order to provide a uniform and uniform coating layer, the substrate is moved back and forth in a plane transverse to the flame during coating. Once a suitable coating layer of glass material has been grown on the substrate by the FHD method, the above coating layer is sintered to a dense glass layer by heat treatment of the substrate at a high temperature in a separate furnace.

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The FFID process disclosed in U.S. Patent No. 5,622,750, as well as other known processes using a flame, plasma, or other thermal reactor to generate nanometer-sized aerosol particles from the starting materials, is guided by coating; 25 would consist of aerosol particles to be coated to substantially the thermophoresis effect. Ts. Due to the temperature gradient between the thermal reactor flame or the like and the significantly cooler substrate, the aerosol particles formed in the thermal reactor are shifted by their thermal motion and the resulting collisional meander toward the substrate. Due to the small size and low mass of the aerosol particles, the momentum (mass x velocity) towards the substrate resulting from their flame is of minor importance in transporting the aerosol particles to the surface of the substrate.

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The homogeneous quality of the layers of glass contained in the flat waveguide (desired glass layer thickness, desired glass layer composition, local defects in the glass 11113939 layer) plays a very important role in the optical properties of the flat waveguide and further in the usability of the flat waveguide. In addition to optical properties, the various layers of glass of a flat waveguide should be matched for mechanical properties such as thermal expansion, to provide durable structures. All of the above require very careful control of the manufacturing process.

The main object of the present invention is to provide a novel process based on the use of a thermal reactor for the production of a planar glass coating, particularly suitable for use in a planar waveguide, in which the control and adjustability of the manufacturing process is significantly better than currently known methods. To accomplish this purpose, the method according to the invention is essentially characterized in what is set forth in the characterizing part of independent claim 1.

It is a further object of the invention to provide an apparatus implementing the above method. Correspondingly, the apparatus according to the invention is essentially characterized by what is disclosed in the characterizing part of the independent claim 10.

The invention is essentially based on the idea that when using a thermal reactor, such as a flame, to form a glass surface. 25 aerosol particles needed to provide the coating, so that the aerosol particles would move substantially / * / · onto the substrate to be coated. Because of the forces generated only by thermophoresis, the flow of aerosol particles and gases from said reactor towards the 30 substrates is arranged by a suitable pressure difference. In this case, the aerosol particles traveling with the gas flow due to the pressure difference have a significant amount of momentum exceeding the thermophoretic forces, whereby this momentum causes the aerosol particle / * cartridges to collide and adhere to the substrate, i.e. glass coating on the substrate. based on impact. Impact. The gas flow required to provide 35 is achieved by providing *: a suitable pressure difference between the thermal reactor and the substrate over the set 4111939 nozzle portion which is permeated by said gas flow of said nozzle portion.

The movement of the aerosol particles with the gas flow through the nozzle part 5 allows for a much better control of the coating process, since according to the invention, the aerosol particles can now be . Em. size classification can be carried out on the basis of aerodynamic size separation, the physical principles of which are known per se, e.g. apparatus for measuring and separating aerosol particles.

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In a preferred embodiment of the invention, the aerosol particles generated in the thermal reactor are guided through the gas flow through the flow control nozzle portion to impart a particle jet to the surface of the substrate, whereby this effect significantly facilitates thermophoresis coating formation. Em. the coating layer provided in accordance with the invention can be used to form a very homogeneous final glass layer in connection with Sintra.

·. 25

If necessary, the nozzle part design can influence the particle jet hit on the surface of the substrate, the shape and velocity of its cross-section so that, for example, the particle jet can be limited to a desired location on the substrate. In this case, the substrate ·; ' With respect to the particle beam, moving across the direction of the particle beam may provide either a uniform coating layer over the entire surface area of the substrate, or by appropriately moving the substrate relative to the particle beam, the coating layer may also be adjusted differently at different positions; 35 surfaces.

5, 111939

By adjusting the velocity of the gas stream flowing into the substrate, aerosol particles that can be imparted to the substrate can be further categorized by their aerodynamic size such that only particles larger than a certain size will impact the substrate to form a coating. Em. size categorization, similar to a high-emission particle filter, makes the size distribution of the aerosol particles involved in coating formation narrower, thus preventing the participation of aerosol particles smaller than a certain size in the coating formation. As a result, the resulting coating is of a more homogeneous quality.

In another embodiment of the invention, before directing the gas flow from the thermal reactor through the nozzle portion toward the surface of the substrate, the gas flow and the aerosol particles contained therein are first controlled by a so-called. through pre-separation. This pre-separation stage acts as a low-emission particle filter, removing larger than certain aerosol particles from the gas stream before guiding the gas stream and the aerosol particles contained therein through the nozzle portion to form a coating on the actual substrate. The pre-separation rate can be used to prevent too large particles from the thermal reactor from reaching the substrate. Such particles can be generated, for example, when the gas burner used to generate the flame, which is used as a thermal reactor, slags, and the slag bodies further detach according to the gas flow.

Where appropriate, the above-described high-pass and low-pass according to the invention. By combining solutions similar to emission particulate filters, the size distribution of the aerosol particles involved in coating formation can be adjusted to the desired level, so that the aerosol particles involved in coating formation are as homogeneous as possible in composition and thus obtain a homogeneous composition.

Thus, the present invention provides considerable prior art methods based on the use of a thermal reactor. 35 for better control and control of the manufacturing process'; in the manufacture of flat glass coatings. This enables, for example, the production of higher quality optical flat waveguides.

The following more detailed description of the invention, by way of example, will further illustrate to the person skilled in the art the preferred embodiments of the invention as well as the advantages of the invention over the prior art.

The invention will now be described in more detail with reference to the accompanying drawings, in which Figure 1 illustrates in principle a preferred embodiment of the invention; Fig. 4 illustrates in principle another embodiment of the invention, and Fig. 5 illustrates the size distribution of aerosol particles, pellets that hit the substrate in the situation of Fig. 4.

Figure 1 shows a first embodiment of the invention. The thermal reactor 10 is closed to the first chamber 11. The first chamber 11 is connected by a nozzle member 12 to the second chamber 13 such that the first chamber 11 and the second chamber 12 together form a gas-tight system separated from the surrounding atmosphere.

The thermal reactor 10 may be a burner which generates a flame. 35 and oxidizing combustion gases 14, to which the flame starting materials 15 for glass formation are introduced, for example, as aerosol droplets with the carrier gas, from which said aerosol droplets 7111939 further form aerosol particles 16 for the glass coating formation. oxygen.

For example, silicon or germanium tetrachloride, or chlorine-free starting materials such as TEOS or tetraethoxygermanium GEOS in suitable forms may be used as starting materials. In addition to the above, the starting materials 15 may also contain, in appropriate form, rare earth metals and lanthanides such as, for example, erbium and / or neodymium, as well as aluminum, phosphorus, boron and / or fluorine to form so-called multi-component glass.

Preferably, the thermal reactor 10 is a flamethrower as disclosed in Finnish Patent No. 98832 or International Patent Application PCT / FI99 / 00818 15, wherein a portion of the precursors 15 required to form the glass material can be led to the flame 10 in liquid form by aerosolizing said precursor (s). 10 immediately prior to their introduction into the flame 10. This provides the significant advantage that the individual aerosol droplets fed to the flame 10 contain precisely the various constituents of the liquid precursor used. in the original proportions of the ingredients, since the different vapor pressures of these ingredients do not affect the composition of the aerosol droplets. If aerosol droplets are formed elsewhere, for example 25 farther from the flame 10 in a separate container from which they are further conveyed by the carrier gas to the flame 10, the higher vapor pressure components will be fed more efficiently to the lower vapor pressure components, of the composition. When using carrier gas, small aerosol droplets also vaporize the ingredients in an inhomogeneous proportion, depending on differences in vapor pressures of said ingredients, whereby the composition of the aerosol droplets changes as they are carried by the carrier gas.

35 The use of a flame spray as disclosed in the above-mentioned Finnish Patent No. 98832 or International Patent Application No. 8 111939 PCT / FI99 / 00818 as a thermal reactor further has the advantage that larger amounts of material can be fed to flame 10 compared to methods of aerosol droplet formation from 10 with carrier gas. At high feed rates of liquid starting materials 15, when using carrier gas, the size of the aerosol droplets during transport tends to increase e.g. due to coagulation and agglomeration before the aerosol droplets reach the flame 10. In addition, losses occur on the walls of the transport channel used, for example piping, and thereby the transport channel also tends to become dirty, further complicating process control. Aerosol droplets produced from aerosol droplets as disclosed in Finnish Patent No. 98832 or International Patent Application PCT / FI99 / 00818 as a thermal reactor 10 typically have a size in the range of 20 to 80 nm, with a narrow size distribution of 15 aerosol particles. the growth rate.

However, the invention is not limited to the use of the aforementioned flame spray 20 as a thermal reactor 10. The thermal reactor 10 may also be any other method apparent to one skilled in the art for providing a high local temperature where the corresponding aerosol particle generating reactions are accomplished. Such possibilities include, for example, various plasmas, which can be achieved, for example, by means of electric current or laser light. The starting materials 15 required to form the glass material may also be introduced into the process by any means known per se.

The aerosol particles from the starting materials 15 in the thermal reactor 10 move through the nozzle portion 12 from the first chamber 11 to the second chamber 13 and toward the substrate 17 with the gas stream 18 which is provided by providing a suitable pressure differential between the first chamber 11 and the second chamber 13 . Preferably, the aforementioned pressure difference is achieved by means of a suction pump 19, which suction pump 19 removes gas from the second chamber 13. It is, of course, obvious that a differential pressure can also be obtained by applying excess pressure to the first chamber 11 relative to the second chamber 13.

9 111939 The gas can then flow out of the other chamber even without the suction pump 19.

The substrate 17 may be silicon, glass, quartz, or other suitable material. The substrate 17 is preferably in the form of a thin circular disk, for example a silicon wafer, but other forms of substrate are also possible.

Upon contact with the substrate 17, the gas stream 18 changes sharply 10 in its direction. Thus, the smallest aerosol particles 16 having an aerodynamic size such that they are able to follow the rapidly changing gas flow 18 as it encounters and rotates the substrate 17 do not hit the substrate 17 at all and thus do not contribute to the formation of the coating. Em. larger size aerosol particle cartridges, respectively, are unable to follow the gas flow 18 and are impregnated into the substrate 17 to form a coating. The velocity of the gas flow 18 into the substrate 17, and thus the size rating (overflow) of the aerosol particles can be adjusted by changing the distance of the nozzle portion 12 from the substrate 17 and / or varying the size of the 20 orifices 20 in the nozzle portion 12 The physical basis of aerodynamic size classification is well known per se and therefore it is not appropriate to go into further detail here.

Fig. 2 shows the size distribution of the aerosol particles 16, which in principle affect the substrate 17 and form the glass coating in the situation shown in Fig. 1. Only aerosol particles larger than a certain threshold of aerodynamic size (high emission), which fall within the area marked by the 30 lines in Fig. 2, will be able to influence the substrate 17.

The nozzle member 12 may include one or more apertures 20 for directing the gas flow toward the substrate 17. Figures 3a-3c are a top view, i.e., viewed from the direction of travel of the gas flow 18. ·. 35 basically a few examples of the positioning of the aperture (s) 20; 3a-3c, the position of the circular sub-substrate 17 relative to the nozzle portion 12 is shown in principle by a dashed line I · · · 10111939. By moving the nozzle member 12 (and also the thermal reactor 10) relative to the substrate 17, either a uniform coating layer can be provided over the entire surface area of the substrate 17, or the thickness of the coating layer may also be adjusted differently at different locations on the substrate 17 surface.

3a-3c, the nozzle member 12 may also be substantially smaller than the substrate 17, if necessary, to allow the jet of particles to be more precisely targeted to the desired substrate 17. This allows the coating layer to be patterned by moving the nozzle member 12 and the substrate 17 relative to one another. In addition to the thickness of the coating layer, the local properties of the coating layer may also be changed, if necessary, by varying the feed / composition of the starting materials 15 when moving the nozzle member 12 relative to the substrate 17. Em. it is also possible to produce a uniform coating layer in which the composition of the glass material and consequently the properties of the glass material vary locally.

The coating process and the properties of the coating formed on the surface of the substrate 17 may also be influenced by changing the distance of the substrate 17 from the nozzle portion 12. This first affects the aerodynamic size classification of the aerosol particles 16 impinging on the substrate 17 as the gas flow between nozzle 12 and substrate 17 the residence time of the aerosol particles 16 in the gas stream 18. Em. the residence time affects the properties of the aerosol particles 16, and thus also the properties of the coating formed on the substrate 17.

Movement of the substrate in the second chamber 13 relative to the nozzle portion 12 may be accomplished by any of the methods known per se. It is also possible that the relative movement between the nozzle member 12 and the substrate 17 is effected by moving the nozzle member 12 and the thermal reactor 10 relative to the second chamber 13 to which:. 35 relative to the chamber 13, the substrate 17 is then held in place.

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The nozzle member 12 of Fig. 3c allows one layer of glass of variable thickness transversely to the aperture 20 (direction z in Fig. 3c) to be formed on the surface of the substrate 17 by moving the nozzle member 12 and the substrate 17 relative to each other in said z direction. In this way, it is possible to form, for example, so-called. a taper element that allows the optical plane waveguide light channel, i.e., the thickness of the core layer, to be slowly changed over a given distance (in the z direction) so that light propagating through the core layer does not escape to the surrounding skin layers. In this way, different types of light conductors (e.g., fiber optic) or light sources (e.g., semiconductor laser) can be matched to the edge of the planar waveguide with good efficiency by matching the size of the light channels.

During the coating process, the substrate 17 is sealed onto the substrate 15 21 to provide good thermal conductivity between said substrate 21 and the substrate 17. Em. the attachment may be effected in a manner known per se, for example by suctioning the substrate 17 under reduced pressure onto the substrate 21, or the attachment may also be by any other means apparent to one skilled in the art.

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The substrate 21 may be arranged to be heated and / or cooled, whereby the substrate 17 may be controlled by the substrate 17 to control the coating process.

By raising the temperature of the substrate 17 by heating the substrate 21, it is possible, if necessary, to prevent the smallest aerosol particles 16 from adhering to the substrate 17, since the hot substrate 17 then causes so-called.

inverse thermophoretic phenomenon, as a result of which the vigorous heat movement of the smallest aerosol particles 16 prevents them from attaching to the substrate 17.

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In order to prevent the aerosol particles 16 from adhering to the walls of the first chamber 11 and / or the second chamber 13, the walls of said chambers are arranged to be heated as necessary by means of electrical resistors. It is still possible that also '; the nozzle part 12 is arranged to be heated.

I · 12 111939

Figure 4 illustrates another embodiment of the invention wherein, prior to directing the gas flow 18 from the thermal reactor 10 through the nozzle portion 12 towards the surface of the substrate 17, the gas flow 18 is first controlled through a pre-separation stage 41.42. The pre-separation stage consisting of a flow guide 41 and a collection-5 substrate 42 acts as a low-emission particle filter, removing from the gas stream 18 aerosol particles 16 of a certain size which are impacted and adhered to the collecting medium 42.

10 A pre-separation rate of 41.42 can prevent too large aerosol particles 16 from the reactor 10 from reaching the substrate 17. Such particles may be generated by a normal amount of aerosol particles forming process, or may be generated from time to time during normal process operation. Such a disturbance situation may arise, for example, when a gas burner used to generate a flame is slagged and the slag bodies detached according to the gas flow 18, or, for example, using laser ablation, i.e., laser light generated plasma to vaporize precursors from Aero-20 solids.

Figure 5 illustrates the size distribution of the aerosol particles 16 which are substantially activatable to the substrate 17 and form the glass coating in the situation shown in Figure 4. The substrate 17 has access to the impacted nucleus only in a specific size range of aerodynamic size; t 30 is marked by curve 1 (see Figure 2).

· ·

Em. the pre-separation degree 41.42 may also include, if necessary, a plurality of discrete and sequential impeller stages formed by the flow controller 41 and the collecting tray 42. Particle size classification based on the use of the impeller stages, including the design and operation of such an impactor; as well as a more precise definition of the aerodynamic size of aerosol particles. * 13 131939 are known to those skilled in the art, and are therefore not discussed further herein as being outside the scope of the invention.

If necessary, the pre-separation stage 41.42 may be arranged to be heated, for example electrically, to prevent unwanted adhesion of the aerosol particles 16 to the surfaces of the various components of the pre-separation stage 41.42.

Once the desired embodiments of aerosol particles have been formed on the surface of substrate 10 using the above embodiments of the invention, formation / growth of the coating layer is terminated either by shutting down the thermal reactor 10 completely or by discontinuing the over.

Subsequently, the coating layer on the surface of the substrate 17, which at this stage is still a porous layer consisting only of partially adhered particles, is sintered into a compact glass material with a story of substrate 21 such that the particles imparted to the substrate melt together to form a homogeneous glass layer. Alternatively, the substrate 17 for sintering by heating may also be transferred to a separate furnace where sintering is carried out using techniques known per se.

v. 25

In summary, the process and apparatus of the invention provide significantly improved control and controllability of the manufacturing process based on the use of a thermal reactor. According to the invention, the aerosol particles 16 forming the coating on the substrate 17 can be guided more precisely to the desired location on the substrate 17, and by moving the substrate 17 relative to the nozzle part 12, a uniform coating layer i · * can be obtained over the entire surface of the substrate 17. or a coating layer, the thickness of which is controlled in a controlled manner at various points on the substrate 17. Further, when the feed / composition of the starting materials 15 is changed by moving the nozzle part 12,

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14 111939, the coating 17 can be coated at various points with different properties.

The size classification of the aerosol particles 5 forming the coating 17 on the substrate makes it possible to obtain coatings of a higher quality than those of the prior art. For example, in prior art methods, small particles arriving at the substrate 17 differ in composition from the larger particles having the desired size distribution because their process of condensation / coagulation / agglomeration of the various components on the surface of the particles differs from that of larger aerosolized particles. Small particles can also cause bubbles or similar errors when sintering the glass layer. For the same reason, larger aerosol particles may also have a different composition due to the different origin process and may also cause local errors during the sintering step. In particular, large particles caused by slagging or other malfunctioning of the equipment cause defects in the coating. By means of the invention, the size distribution of the aerosol particles forming the coating on the substrate 17 can be narrowed, whereby said aerosol particles are of a more uniform composition, and thus the coating formed therefrom is also very uniform.

It will, of course, be apparent to one skilled in the art that various combinations of the methods, procedures, and apparatus structures set forth above in connection with the various embodiments of the invention may provide various embodiments of the invention that are within the spirit of the invention. Therefore, the foregoing examples should not be construed as limiting the invention, but embodiments of the invention may freely vary within the scope of the inventive features set forth in the claims below.

·. It will, of course, be obvious to one skilled in the art that the following * ·. the drawings are intended only to illustrate the invention, 35 and, therefore, the structures and components shown therein are not drawn in the correct mutual dimensions thereof.

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Claims (21)

111939 A method for forming a planar glass coating, particularly suitable for use in planar waveguides, wherein a thermal reactor (10), such as a flame or plasma, is used to generate aerosol particles (16) from the feedstocks (15) which are applied to the surface of the substrate (17) , characterized in that the aerosol particles (16) formed from the starting materials (15) in the thermal reactor (10) are guided by a gas stream (18) passing through the nozzle part 10 (12) to impart a particle jet to the substrate (17). over the nozzle part (12). Method according to Claim 1, characterized in that the gas flow (18) and the aerosol particles (16) contained therein are directed to influence the substrate (17) by shaping and / or positioning the nozzle part (12) with respect to the substrate (17). . Method according to Claim 1 or 2, characterized in that by shaping and / or positioning the nozzle part (12) with respect to the substrate (17) and the velocity of the gas flow passing through the nozzle part (12) by differential pressure affecting the gas flow (18) and aerosol particles 16) directing the substrate (17) in a desired manner to categorize the particles to be impacted on the substrate (17) based on their aerodynamic size in the manner of a high-emission particulate filter:. > »« A method according to any one of claims 1 to 3, characterized in that before guiding the gas flow (18) and the aerosol particles (16) therein through the nozzle part (12). the stream (17), the gas flow (18) and the aerosol particles (16) contained therein are guided through one or more low-pass particulate filter pre-separation stages (41,42), each pre-separation stage comprising a flow controller (41) and a collecting tray (42) therewith. . 111939 Method according to one of the preceding claims 1 to 4, characterized in that a flame spray is used as the thermal reactor (10), in which part of the starting materials (15) required for the formation of glass material is fed to the flame (10) in liquid form. the substances (15) are dropped into Aero sol droplets only in the immediate vicinity of the flame (10) just before they are introduced into the flame (10). Process according to any one of Claims 1 to 5, characterized in that silicon tetrachloride, germanium tetrachloride, TEOS (tetraethyl orthosylicate) or GEOS (tetraethoxygermanium) is used as the starting material (15) or an ingredient thereof. Process according to any one of claims 1 to 6, characterized in that the starting material (15) or one of its constituents for the formation of multicomponent glass contains erbium, neodnium, other lanthanide, aluminum, phosphorus, boron and / or fluorine. Method according to one of Claims 1 to 7, characterized in that the nozzle part (12) and the substrate (17) are moved relative to one another in a plane substantially parallel to the surface of the substrate (17) so that the thermal reactor (10) 12) in a constant position. Method according to one of claims 1 to 8, characterized in that the nozzle part (12) and the substrate (17) are moved substantially perpendicular to the surface of the substrate (17) in relation to the surface of the nozzle part (12) and the substrate (17). ) to change the distance. 30 10. Apparatus for use in planar, in particular planar waveguides ···. for forming a suitable glass coating, the apparatus comprising a thermal reactor (10), such as a flame or plasma, for generating aerosol particles: * (16) from the starting materials (15), and means for conducting aerosol particles 35 (16) on the substrate (17) , characterized in that said apparatus comprises at least 111939 - a first chamber (11) and - a second chamber (13), and - a nozzle part (12) connecting the first (11) and the second (13) chamber such that the first (11) and the second (13) the chamber 5 is arranged to form a substantially gas-tight system separated from the surrounding atmosphere, and - a thermal reactor (10) located in the first chamber (11), and - a substrate (17) located in the second chamber (13); means (19) for providing a differential pressure across the nozzle portion (12), thereby generating aerosol particles from the starting materials (15) in the thermal reactor (10) the cartridges (16) are guided by a gas stream (18) generated by the differential pressure and passing through the nozzle member (12) to impart a jet of particles to the substrate (17). Apparatus according to Claim 10, characterized in that the nozzle part (12) is shaped and / or positioned with respect to the substrate (17) to direct the gas flow (18) and the aerosol particles (16) contained therein to impact the desired substrate and / or desired area. 17). Apparatus according to Claim 10 or 11, characterized in that the nozzle part (12) is arranged in a configuration and / or position relative to the substrate (17) to control the gas flow caused by the differential pressure; the backing (18) and the aerosol particles (16) contained therein to meet the substrate (17) in the desired manner to classify the particles which are to be impacted on the substrate (17) by their aerodynamic size, like a high-pass particle filter. 30 Apparatus according to any one of claims 10 to 12, characterized in that said apparatus further comprises one or more · pre-separation stages *: * (41,42) acting as a low-pass particulate filter, each stage comprising a flow controller (41) and 35 in the gas flow direction. the following collection tray (42), and which "pre-separation degree (s) (41,42) are disposed in the direction of flow of gas flow (18) ♦ · · 111939 before the nozzle portion (12), and which pre-separation degree (s) are arranged to act as a low emission particulate filter. as filters. Apparatus according to one of the preceding claims 10 to 13, characterized in that the thermal reactor (10) is a flamethrower, in which a portion of the precursors (15) required to form the glass material is fed to the flame (10) in liquid form, (15) is dropped into aerosol droplets only in the immediate vicinity of the flame (10) just before they are introduced into the flame (10). Apparatus according to any one of claims 10 to 14, characterized in that said apparatus further comprises means for moving the nozzle part (12) and the substrate (17) relative to one another in a plane substantially parallel to the surface of the substrate (17) such that the thermal reactor (10) remains at a constant position with respect to the nozzle portion (12). Apparatus according to any one of claims 10 to 14, characterized in that said apparatus further comprises means for moving the nozzle member (12) and the substrate (17) substantially perpendicular to the surface of the substrate (17) and the substrate (12). (17). Apparatus according to one of the preceding claims 10 to 16, characterized in that said apparatus further comprises means for heating the walls of the first chamber (11) and / or the second chamber (13). Apparatus according to one of the preceding claims 10 to 17, characterized in that said apparatus further comprises means for heating the nozzle part (12) and / or components (41,42) of the pre-separation stage (s). The apparatus according to any one of claims 10 to 18, characterized in that said apparatus further comprises means for heating and / or cooling the substrate (17). »T · 1 · 111939 Apparatus according to one of the preceding claims 10 to 19, characterized in that the nozzle part (12) comprises one or more openings (20) of circular and / or rectangular cross-section. Apparatus according to one of the preceding claims 10 to 20, characterized in that the nozzle part (12) comprises a single slit aperture (20) on the surface of the substrate (17) to form a glass layer of variable thickness transverse to said aperture (20). »· · ·» • · 20 111939