SE431321B - FORMULA WITH A FLUOREDOP STANNY OXIDE MOVIE AND PROCEDURE FOR ITS PREPARATION - Google Patents

Description

7810975-3 2 by first applying a coating of pure silica to the glass. However, the protective layer of silica is not very effective on glass with a high alkali content and a high coefficient of thermal expansion, such as ordinary soda-lime glass. In addition, these corrosive by-products attack metal parts of the apparatus and metal contaminants, such as iron, can be deposited in the coating, which has unfavorable effects on both the electrical conductivity and the transparency of the coating.

Another problem has been the loss of uniformity and reproducibility in the properties of the coatings.

U.S. Pat. No. 2,651,585 states that better uniformity and reproducibility are obtained if the moisture content of the device is controlled. The use of steam instead of liquid spraying, as described, for example, in German Patent Specification 1,521,239, also results in more uniform and more reproducible coatings. Even with these improvements, studies have recently been carried out using vacuum deposition methods, such as evaporation and cathodic sputtering to provide cleaner and more reproducible coatings. Despite the higher cost of these vacuum processes, it is believed that the reduction in the amount of corrosive by-products and unwanted contaminants introduced by the spraying methods constitutes improvements, especially in applications involving high-purity semiconductors.

Intentional addition of certain pollutants is important in these processes to achieve high electrical conductivity and infrared reflectivity. Thus, tin is incorporated as an impurity into indium oxide, while antimony is added to tin oxide (stannous oxide) for these purposes. In all cases, these desired impurities (doping substances) have the task of adding "extra" electrons, which contribute to the conductivity. The solubility of these contaminants is high and they can be added without difficulty using all the 3 application methods mentioned above. Fluorine has an advantage over antimony as a tin oxide dopant in that the transparency of fluorine doped tin oxide film is higher than that of antimony doped film, especially within the red end of the visible spectrum. This advantage of fluorine is significant for potential applications to solar cells and solar heat collectors. Despite this advantage with fluorine, antimony is used for most and possibly for all commercially available tin oxide coatings as a dopant. This may be because fluorine doping has only been demonstrated in connection with the less advantageous spray method, while the improved application methods (chemical vapor deposition, vacuum evaporation and cathodic sputtering) are not believed to have been shown to provide fluorine doping. In addition, a recent report by a committee of experts in The American Institute of Physics Conference Proceedings, No. 25, page 288 (1975), concludes that the equilibrium solubility of fluorine in tin oxide is inherently lower than the solubility of antimony. . Nevertheless, the lowest resistivity of tin oxide films has been disclosed in U.S. Pat. No. 3,677,814. Using a spray method, according to this patent, fluorine-doped tin oxide films having a resistance as low as 15 ohms per square were obtained using as a starting material a compound containing a direct tin-fluorine bond. The lowest resistance in a commercially available tin oxide coated glass is so far in the range of about 40 ohms per square. If one wishes to obtain coatings with a resistance as low as 10 ohms per square, one has hitherto been forced to use much more expensive materials, such as indium oxide.

It is an object of the present invention to provide a method for applying a layer or coating of fluorinated doped stannous oxide with high transparency within the visible range, high electrical conductivity and high reflectivity for infrared light. Furthermore, one can easily vary the electrical conductivity during the application of a single such layer and achieve very low volume resistivity * H G3 C3 \ Q \ 3 04 I 0% 4 and surface resistance. This results in a non-corrosive deposition atmosphere, from which such layers of high purity can be easily deposited without contaminating the substrate with contaminants or corrosive attack on the substrate or device. Furthermore, gaseous instead of liquid means are used for the production of coated products as described in connection with the invention. According to the invention, a process is provided which without difficulty gives such layers with highly uniform and reproducible properties within large areas without limitations which characterize spraying methods.

Such layers can be applied without difficulty inside pipes or pistons or on surfaces of complicated shape which cannot be easily coated by spraying. Improved objects can be provided, such as solar cells, other semiconductors useful in electrical circuits, heat-reflecting windows, improved sodium lamps and the like.

Such layers can be applied by standard manufacturing methods in the semiconductor industry and in the glass industry.

The invention relates to a method for applying a fluorine-doped stannous oxide film to a heated substrate, which is characterized in that a mixture containing (a) a gaseous compound containing tin and fluorine, which is free from direct fluorine, is applied to a surface of the substrate. tin-bonding, (b) a gaseous, oxidizable, tin-containing compound and (c) a gaseous oxygen source, with or without (d) an inert carrier gas, the proportions of components (a), (b) and (c) being adjusted so that they remain in the gas phase and (a) are converted upon heating to form a second fluorine-containing compound which exhibits a direct fluorine-tin bond when the temperature of the gaseous mixture approaches the temperature of the heated substrate and the the converted compound is retained in vapor phase until it, together with the oxidizable tin-containing compound, is oxidized by the gaseous oxygen source, to form a fluorine-doped stannous oxide, which is precipitated so as to m film on the heated substrate.

The tin-fluorine bond can be formed immediately before deposition.

The tin-fluoride material is kept in the vapor phase at such a low temperature that oxidation of the compound takes place only after the rearrangement to form a tin-fluorine bond has been obtained.

Films of thus produced fluorine-doped tin oxide have low electrical resistivity and high reflectivity for infrared light.

According to a first embodiment of the invention, an organotin monofluoride vapor is prepared in the heated deposition area by reforming the vapor of a more volatile compound containing both tin and fluoroalkyl groups attached to tin.

A second advantageous embodiment of the invention utilizes an organotin monofluoride, which is formed at or near the interface between gas and substrate by reactions comprising organotin vapor and certain fluorine-containing gases containing fluoroalkyl and / or fluorosulfur groups.

In both cases, the product layer is a uniform, hard, adhesive transparent coating, the electrical conductivity and infrared reflectance of which depend on the concentration of the fluorine-containing dopant.

The invention also relates to an object obtainable by this method and characterized in that it comprises a preferably transparent substrate, for example glass, and a fluorine-doped stannous oxide film thereon, the concentration of free electrons in the stannous oxide film being in the range 1020-1021 cm an infrared reflectivity of about 90% and / or a maximum surface resistance of about 5 ohms per square.

Fig. 1 schematically shows the device which is suitable for carrying out a process in which a fluorine-containing dopant consists of an organotin fluoroalkyl vapor which is transferred in vapor phase from liquid form.

Fig. 2 shows an exploded view of a second embodiment according to which the fluorine-containing dopant is formed by reaction with certain fluoroalkyl and / or fluorosulfur gases which are supplied from a cylinder with compressed gas.

Fig. 3 shows a simplified embodiment of the device for carrying out the first or the second embodiment of the invention.

Fig. 4 is a schematic section through a solar cell illustrating a use of the invention for semiconductors.

Fig. 5 shows a window 120 which is coated with a layer 118 according to the invention. Figures 6 and 7 are diagrams showing how the conductivity and reflectivity change with the fluorine doping content.

The process according to the invention comprises two main steps: (1) preparation of a reactive vapor mixture which on heating gives a compound with tin-fluorine bond, and (2) delivery of this vapor mixture to a heated surface, on which fluorine-doped tin oxide is deposited. The embodiments described below differ in the chemical source of the fhmnmnmünß substance in the reactive vapor mixture and also in the means by which the vapor mixture is prepared. The second step (deposition on the heated surface) is largely the same in all examples.

Tin is added as a volatile, oxidizable tin compound, for example tetramethyltin, tetraethyltin, dibutyltin diacetate, dimethyltin dihydride, dimethyltin dichloride, etc. The preferred compound is tetramethyltin because it is sufficiently volatile at room temperature, non-corrosive and easily corrosive. This volatile tin compound is introduced into a bubble bottle enclosed in the figures, and an inert carrier gas, for example nitrogen gas, is caused to bubble through the tin compound. For the highly volatile compounds, for example tetramethyltin and dimethyltin dihydride, the bubble bottle can be kept at room temperature, but for other less volatile compounds the bubble bottle and tubes must be heated to an appropriate degree as will be apparent to those skilled in the art. It is an advantage of the present invention that one can avoid the use of high temperature appliances and that simple cold wall equipment can be used. The vapor mixture must contain an oxidizing gas, for example oxygen, N 2 O, or the like. Oxygen is the preferred gas because this gas is readily available and works just as well as more expensive alternative oxidants.

The gas pressure is determined with regulators 25, and the flow of oxygen from a tank 20 and of carrier gas from a tank 21 is regulated with control valves 30 and measured with flow meters 40. The gas streams are then passed through tail valves 50 to a mixing pipe 60 and a funnel-shaped chamber 70. A tin oxide film is deposited on the hottest surface 80, which is heated with heater 90, usually to a temperature of about 400-60 ° C.

The general type of process described above is well known in the steam deposition art. Various modifications, such as arranging the substrate surface vertically and rotating or below the reaction chamber and rotating, are well known to those skilled in the art, and may be particularly suitable for use depending on the geometry of the substrate or the conditions affecting a particular use.

Rotation of the substrate is recommended in order to best move the sample through any convection currents that may occur in the apparatus and thereby in the best way ensure uniformity of the applied layers. Furthermore, according to the invention, it has been found that by applying the heated substrate facing downwards, very uniform coatings can be obtained in a simpler manner without rotation, since the gas, when heated from above, does not exhibit troublesome convection 7810973-5 "" 8 streams. Another advantage of having the substrate above the reactive vapors is that any dust and dirt or powder formed as a by-product by homogeneous nucleation in the gas does not fall on the growing film.

The invention described is an improved process by which controlled amounts of fluorine such as contaminant can be incorporated into the growing tin oxide film. According to a simplest aspect of the invention, the fluorine dopant is a vapor containing a tin-fluorine bond in each molecule. The other three tin valences are occupied by organic groups and / or halogens other than fluorine. Typical examples of such compounds are tributyltin fluoride. It has been found that fluorine which is bound in this way and made available to a hot surface in vapor form is not cleaved from tin during oxidation at a hot surface.

Unfortunately, all of the prior art compounds with such a direct tin-fluorine bond are not substantially volatile near room temperature.

A particular advantage of the invention is achieved by preparing the fluorine dopant from volatile compounds which do not exhibit the required tin-fluorine bond but which on heating undergo reaction or rearrangement to form a direct tin-fluorine bond. This redistribution suitably occurs at a temperature which is sufficiently high (for example> 100 ° C) so that the tin fluoride thus formed remains in the vapor phase, but also so low (for example <400 ° C) that the oxidation of the compound has room after redistribution. An example of such a compound is trimethyltrifluoromethyltin, (CH 3) 3 SnCF 3. Upon heating to a temperature of about 150 ° C in a heated zone adjacent the deposition surface 80, this compound undergoes redistribution to form a direct tin-fluorine bond, in (CH 3) 3 SnF vapor, which then reacts as a fluorine donor or dopant.

Other compounds which undergo similar redistributions at temperatures which, of course, vary to some extent from compound to compound have the general formula R 3 SnRF} wherein R -QIILBLTQÉÉ '7810973-3 draws a hydrocarbon group and RF is a fluorinated hydrocarbon group having at least one fluorine atom attached to the carbon atom attached to the tin. The main advantage of these fluorine dopants is that they consist of volatile liquids, so that they can easily give sufficient vapor pressure when evaporating at room temperature. This simplifies the construction of the device, as shown in Figure 1, by eliminating the need to maintain a hot zone between the bubble device 15 and the reaction chamber 70 to keep the fluorine dopant in the vapor phase.

Thus, the device may be of the type commonly referred to as a "cold wall type chemical vapor deposition reactor" which is widely used, for example in the semiconductor industry for the deposition of silicon, silica, silicon nitride, etc. Other essential properties of the "cold wall reactor" for semiconductor purposes are similarly, in the manufacture of glass, the gas mixture can be added to the annealing and cooling furnace at the stage when the glass has a suitable temperature, for example about 470 ° C for soft glass. .

In this way, highly uniform films can be produced in normal glassmaking equipment.

The preferred compound for use in the embodiment of Figure 1 is (CH 3) 3 SnCF 3, as it is more volatile than compounds having more carbon atoms. This compound is a stable, colorless, non-corrosive liquid which does not decompose in air at room temperature and which reacts only extremely slowly with water.

A particularly advantageous second embodiment of the invention utilizes a fluorine-containing gas which reacts with an organotin vapor upon heating to form tin fluoride vapor. Thus, for example, d-fluoroalkyl halides, preferably those in which the alkyl group has 4 carbon atoms or less, such gases as iodine trifluoromethane, CF 3 I, CF 3 CF 2 I, C 3 F 7 I and the like, can be mixed with organotin vapors, for example tetramethylene vapor, (CH 3) 4 Sn, at room temperature. i.e. to 32 ° C, in particular to a temperature of 65 ° C, without reaction. Further., _ .., ._.... ........-. _ f -_ ~, ..> _. ». f» .r .--.>.> m <.: - ~. s- »nv-n: fl-.. They are less reactive and about 10 to 20 times more are required in the reactant gas, but they are much less expensive. This is particularly surprising since such compounds are said to be inert. Fluoroalkyl chlorides are not preferred for use, as these reactivity is significantly lower than that of bromides.

As such a vapor mixture approaches the heated surface, reaction takes place in the gas phase, so that the desired tin-fluorine bonds are finally formed. Although the reaction sequence is complicated, it is believed to begin with such reactions as CFBI + R 4 Sn-α R 3 SnCF 3 + R 1 to form organotin fluoroalkyl R 3 SnCF 3 in vapor in the region near the hot surface interface, where they act as fluorine dopants for the growing same tin oxide film. manner as in the first embodiment.

Some other fluorine-containing gases are also active according to this second embodiment of the invention. Thus, for example, sulfur chloride pentafluoride SF5Cl is an effective fluorine donor gas as is sulfur bromide pentafluoride SF5Br.

Similarly, trifluoromethyl sulfur pentafluoride CF3SF5 acts in gaseous form to form tin-fluoride bonds by gas phase reaction.

The advantage of this second embodiment is that the fluorine donor is a gas, and the process is further illustrated in Figure 2. The preferred gases are CF3I and CF3Br, which are non-corrosive, non-combustible, non-substantially toxic and commercially readily available. SF5Cl and SF5Br are highly toxic and are therefore less desirable for use. CF3SF5 is non-toxic but slightly less reactive than CF3I.

The deposition process can be further simplified, as shown in Figure 3, if the gas mixtures are premixed and stored in a pressure vessel. .... ~ ..... ._ u ... _......-_._.- 7816575-s ll gas cylinder 19. For safe storage and use, the oxidizable compound must of course be kept at such a concentration , that it can not form an explosive mixture. For example, the lower explosion limit for tetramethyltin in air is about 1.9%. Concentrations used for chemical vapor deposition are less than half of this content. In addition, the use of CF3I and CF3Br as fluorine dopants also acts as flame retardants.

Films made according to the invention have been found to have infrared reflectivity of 90% or more measured, as is known in the art, at the conventional light wavelength 10 .mu.m, which is characteristic of thermal infrared radiation at room temperature. This reflectivity of 90% can be compared with the reflectivity of 80%, which has hitherto been achieved using tin oxide coatings. In normal use, these infrared reflective layers have a thickness of about 0.2 to 1 / rm and thicknesses between 0.3 and 0.5 / am are typical.

In order to more quantitatively characterize the fluorine dopant contents in the films, the infrared reflectivity was measured in the wavelength range 2.5; Lm to 40 .mu.m. By fitting these values into theoretical curves, as described in more detail by R. Groth, E. Kauer and P.C. van den Linden, "Optical Effects of Free Carriers in SnO2 Layers", Zeitschrift für Naturforschung, volym 179, sid. 789-793 (1962), values for the concentration of free electrons in the films were obtained. The values obtained ranged from 1020 cm-3 to 1020 cm-3 and increased regularly with increasing levels of the fluorine dopant. Theoretically, a free electron should be emitted for each fluorine atom that is replaced by an oxygen atom in the lattice. This hypothesis was verified by Auger Electron Spectroscopic measurements of the total fluorine content of some of the films, which gave fluorine contents consistent with the free electron concentrations within the limits of the experimental accuracy. This conformity indicates that the majority of the incorporated fluorine amount is electrically active. The infrared reflectivity at 10 .mu.m and also the electrical bulk conductivity of the films were found to be maximum at a doping content of about 1.2 - 2% fluorine substitution for oxygen.

These maxima are very broad and almost maximum conductivity and reflectivity are shown by films with 1 to 2.5% fluorine. Furthermore, there is also a weak, general absorption within the entire visible wavelength range, which increases directly with the fluorine content. Therefore, for the production of films with high electrical conductivity and high visible transparency, a fluorine content in the film of about 1% (ie the ratio of fluoric acid in the film 0.01) is particularly desirable. This optimum, however, varies to some extent depending on the spectral distribution of interest for a given use. By varying the content of fluorine dopants, it is possible with routine experiments to easily determine the optimal content for a certain use.

Concentrations of fluorine dopants in excess of 3% can be easily achieved in the films using methods according to the invention. The results of previously known methods have not exceeded 1% and in the previous opinion, as stated above, this has been considered to be the solubility limit for fluorine. Although such high doping levels are not required to produce optimum infrared reflectivity or electrical conductivity, the gray films produced at doping levels of 2% or more may be useful on glass for architectural purposes, to limit the supply of solar heat in air-conditioned buildings. In such use, the doping content at the surface of the film is suitably lowered to about 2% to achieve maximum infrared reflectivity.

Using the measured electron concentrations and the values of the electrical conductivity, the electron operating motives can be obtained. For different films, values from 50 to 70 cmz / volt-second were calculated in this way. Previously obtained mobility values for tin oxide films have varied from 5 to 35 cmz / volt-second. It is believed that films of the invention are the first films to exhibit mobility values. ......._........-_-..- ».. -: -. ~ ..->.« »~ --I- ~ V1. ... n-HW .. ma ... 7810973-3 13 exceeding 40 cm2 / volt-second. These values illustrate in another way the superior quality of the process according to the invention and the films produced therewith.

The method according to the invention is also highly suitable for use in the manufacture of new devices, for example those with electron-conducting layers in the manufacture of semiconductors (for example integrated circuits and the like) as well as the manufacture of heat-reflecting transparent objects, such as windows.

The most advantageous embodiment of the invention is an embodiment in which the organotin fluoride compound with tin-fluorine bond is caused to decompose at the substrate immediately after the formation. This decomposition preferably takes place in a narrow reaction zone, which is mainly heated to the decomposition temperature by heat from the substrate itself.

In order to further illustrate the invention, the following are exemplary embodiments of embodiments of the method according to the invention and the products produced therewith.

Unless otherwise indicated, the following examples were performed using the following general procedure: Example 1.

The process is exemplified by an experiment using the apparatus of Figure 1 to produce a gas stream containing 1% tetramethyltin (CH 3) 4 Sn, 0.02% trimethyltrifluoromethyltin (CH 3) 3 SnCF 3, 10% nitrogen as the carrier gas and the remainder oxygen. The resulting stream is passed over a pyrex glass plate having a diameter of 15 cm and kept at 500 ° C for about 5 minutes of deposition. The gas flow amounts to about 400 cm3 per minute. This gas flow corresponds to a gas exchange in the funnel 70 of about one gas exchange per two minutes. A transparent film with a thickness of about 11 m is deposited. The film exhibits an electrical resistance of 2 ohms per square corresponding to a volume resistivity of 0.0002 ohm-cm. This film is measured to have a fluoric acid ratio of about 0.017 and an operating mobility of about 50 cm 2 / volt-second.

Example 2.

When repeating the experiment of Example 1 using a sodium-free silicon substrate, the resistance value drops to about 1 ohm per square, i.e. about half the value of the resistivity achieved with a sodium-containing substrate.

Example 3.

An advantageous embodiment of the method can be illustrated by a process using the device shown in Figure 2. The resulting gas mixture consists of 1% tetramethyltin (CH3) 4Sn, 0.2% iodine trifluoromethane CF3I, 20% nitrogen carrier gas and the remainder oxygen. Films deposited on pyrex glass substrates showed the same electrical properties as in Example 1.

Example 4.

The simplified device according to Figure 3 was used, preparing the mixture described in Example 3 in a pressurized gas cylinder 19. The results are identical to those obtained according to Example 3. After one month of storage in the gas cylinder, the experiment was repeated to obtain identical results. This shows the stability and shelf life of the mixture.

Example 5.

The experiment of Example 3 is repeated except that the deposition is interrupted when the stannous oxide film has a thickness of 0.5 .mu.m. The obtained stannous oxide film has an infrared reflectivity of about 90%.

Examples 6 - 13.

The gases listed below were all used as a replacement, in equimolar amounts, for CF3I in the procedure of Example 3 (except that the concentration of fluorine dopant was increased 15-fold according to Examples 6, 7, 8 and 13). Very good conductivity and reflectivity for i, c, ..., - .. i, _.> _-_. ~ _. _. . , eaaq-a -n-w. .www-- w-n - .vnøvn fl unvuwfqxïqrm fl ßlhiæråä "751 0973-3 15 infrared radiation is obtained.

Example Gas Example Gas 6 CF3Br 10 C3F7I 7 C2F5Br ll SF5Br 8 C3F7Br 12 SF5Cl 9 CZFSI 13 CF3SF5 Conventional photoelectric cells with silicon ("so1 cells") have hitherto shown typical surface resistance values of 50 - 100 ohms per square. In order to obtain an acceptably low total cell resistance, a metal grid with a spacing of 1 or 2 mm is deposited on the silicon surface. By depositing a fluorine-doped tin oxide layer with a layer resistance of about 0.5 ohm per square (about 2 / nn thick) on the cell surface, the gap in the metal grid can be increased to about 10 mm with a corresponding reduction in the cost of the grid. Alternatively, the grid size can be kept small and the cell can function efficiently even when the sunshine is concentrated by a factor of about 100, provided that satisfactory cooling of the cell is maintained.

A schematic section 100 through such a cell is shown in Figure 4, with a layer 102 having a thickness of 2 .mu.m of n-SnO2 (fluorine-doped material according to the invention being used), a layer 104 having a thickness of 0.4 .mu.m of n-silicon (phosphorus-doped silicon of the prior art type), a layer 106 with a thickness of 0.1 mm of β-silicon (boron-doped silicon of known type) are joined to an aluminum layer 108, which acts as an electrode. Metal grilles 110 are arranged with a mutual distance of about 10 mm. Despite this, very good results are obtained.

The applied layers can be used in the manufacture of other semiconductor products, for example conductors or resistors. Tin oxide coatings have been used for this purpose in integrated circuits. The improved conductivity allows more extensive use of this material. Thus, not only can the layer resistance range be extended to much lower values (e.g. about 5 ohms per square or less) than has hitherto been possible, but one can also achieve deposition of the layer in the same device used for growth, for example. of epitaxial silicon. This eliminates costly and cumbersome emptying, cleaning and loading as a step between the deposition operations.

The resistivity values obtained for the fluorine-doped tin-4 Ohm-cm, which is the comparative oxide on silicon substrate, are about 10-bar with the value for vaporized tantalum metal, which in some cases is used as a connection in integrated circuits. The good agreement between the coefficients of thermal expansion of tin oxide and silicon allows the deposition of thick layers without significant stresses.

Figure 6 shows the electrical conductivity of the fluorine-doped stannous oxide film as a function of the measured fluorine: oxygen ratio in the film for deposition temperatures of 480 and 50 ° C.

Figure 7 shows the infrared reflectivity of the fluorine-doped stannous oxide films as a function of the measured fluorine-oxygen ratio in the film for the deposition temperatures of 480 and 50 ° C.

Figures 6 and 7 also show (1) the conductivity of previously known expensive indium oxide materials and as described in Philips Technical Review, vol. 29, p. 17 (1968) by van Boort and Groth and (2) the best previously known values for conductivity and reflectivity of doped stannous oxide coatings. Although a number of embodiments according to the invention have been described and illustrated, it will be apparent to those skilled in the art that a variety of changes and modifications may be practiced without departing from the spirit of the invention.

Claims (20)

rr, _ / a1n97s-3 PATENTKRAV 1. An article, characterized in that it comprises a preferably transparent substrate, for example glass, and a fluorine-doped stannous oxide film thereon, the concentration of free electrons in the stannous oxide film being in the range 1029-1021 cm -1 and the object having an infra - red reflectivity of about 90% and / or a maximum surface resistance of about 5 ohms per square. 2. An article according to claim 1, characterized in that the article exhibits an infrared reflectivity of about 90%, the film having a fluoric acid ratio of between about 0.007 and 0.03. A semiconductor article according to claim 1 of the type used in electronic circuits and exhibiting a coating of fluorine doped stannous oxide, characterized in that the article exhibits a resistance of less than about 5 ohms per square and a bulk resistivity in the coating of about 10-4 ohm-cm. 4. A method of applying a fluorine-doped stannous oxide film to a heated substrate, characterized in that a mixture containing (a) a gaseous compound containing tin and fluorine, which is free from direct contact, is applied to a surface of the substrate. fluorine-tin bonding, (b) a gaseous, oxidizable, tin-containing compound and (c) a gaseous oxygen source, with or without (d) an inert carrier gas, the proportions of components (a), (b) and (c) being adjusted so that they remain in the gas phase and (a) are subjected to conversion upon heating to form a second fluorine-containing compound which exhibits a direct fluorine-tin bond as the temperature of the gaseous mixture approaches the temperature of the heated substrate and the The converted compound is retained in the vapor phase until it, together with the oxidizable tin-containing compound, is oxidized by the gaseous oxygen source to form a fluorine-doped stannous oxide which is precipitated so as to m film on the heated substrate. 5. A process according to claim 4 for the production of transparent stannous films on a heated substrate, characterized in that a gas mixture is used which initially contains (1) a first fluorine-containing organotin compound which is free from direct tin. fluorine bond, (2) an oxidizable tin compound and (3) an oxidizing gas, 7 comprising the steps of: (a) converting the first fluorine-containing organotin component of the gas mixture to a second gaseous tin-organic fluoride with a direct tin-fluorine bond; , (b) immediately oxidizes this second fluoride compound in the immediate vicinity of the substrate, so that a fluorine dopant is obtained in the gas mixture, and (c) prepares a fluorine doped stannous oxide film on the heated substrate by co-depositing thereon the oxidizable tin compound and the fluorine dopant. 6. A process according to claim 5, characterized in that the first gaseous fluorine-organotinic compound is prepared by heating a gas mixture containing (a) a gas selected from the group consisting of CF 3 I, CF 3 Br and homologous alkyl-fluorinated compounds of CF 3 I, CF 3 Br and CF 3 SF 5, SF 5 Br and SF 5 Cl, or mixtures of these substances, and (b) the oxidizable tin compound, wherein (a) and (b) are substantially inert to each other at temperatures below about 65 ° C. Process according to Claim 5 or 6, characterized in that the conversion of the first volatile fluorine-containing organotin compound, which is free from direct tin-fluorine bonding, into the gaseous organotin fluoride compound with direct tin-fluorine bonding , is achieved by heating the substrate. A method according to claim 4 for depositing fluorine-doped stannous oxide films on a heated substrate, characterized in that a) a gaseous, fluorine-containing component is mixed and b) a gaseous, oxidizable tin-containing component and c) a gaseous, oxygen-containing component and, optionally, d) inert carrier gas, these components being selected to remain in the gas phase at the mixing temperature and the component (a) and component (b) reacting to form a compound having a tin-fluorine bond only when the gas mixture is heated to about the temperature of the heated substrate, and that the compound with tin-fluorine bond and the oxygen-containing component subsequently reacts to deposit the fluorine-doped stannous oxide film on the heated substrate. Process according to Claim 4, for depositing fluorine-doped stannous oxide films on a heated substrate, characterized in that a) a gaseous, fluorine-containing component is mixed and b) a gaseous, oxidizable tin-containing component and c) a gaseous, oxygen-containing component and, optionally, d) inert carrier gas, these components being selected to remain in the gas phase at the mixing temperature and component (a) and component (b) reacting to form a compound with a tin-fluorine bond only when the gas mixture is heated to about the temperature of the heated substrate, and the compound with tin-fluorine bond and the oxygen-containing component thereafter reacts to deposit the fluorine-doped stannous oxide film on the heated substrate, and component (a) contains a volatile organotin-fluorine-containing compound which is free from direct tin-fluorine bonding but which on heating undergoes redistribution to form a direct tin-fluorine bond at such a high temperature that the newly formed association with 9.. Direct tin-fluorine bonding remains in the vapor phase until it reacts with the oxidizable tin compound to deposit a fluorine-doped tin oxide film. 10. A process according to claims 4 - 9, characterized in that tetramethyltin vapor, in a concentration of up to about 1%, constitutes the volatile oxidizable tin compound, and that oxygen with a partial pressure up to about an atmosphere used as oxidizing gas; and that stannous oxide was deposited on a surface heated to about 500 ° C. 11. ll. Process according to Claim 4, characterized in that the first fluorine-containing compound consists of a volatile tin compound which decomposes on heating to form an organotin monofluoride vapor, preferably trimethyltrifluoromethyltin or trimethylpentafluoroethyltin. 12. A process according to claim 5, characterized in that a mixture of (a) and (b) is used, which is stable at about 32 ° C, in which a reaction of (a) and (b) is thermally initiated and forming an organotin monofluoride vapor, this vapor being a source of controlled addition of fluorine contaminant to the film of stannous oxide, preferably the fluorine dopant is formed by reacting trifluoroiodomethane and an organotin compound containing at least one tin-carbon bond per molecule, such as by reacting tri fluorodiodomethane gas and tetramethyltin. 13. A method according to claim 12, characterized in that iodine is replaced by bromine. 14. A process according to claim 12, characterized in that the fluorine dopant is prepared by reacting sulfur chloride pentafluoride gas or trifluoromethyl sulfur pentafluoride gas and an organotin compound containing at least one tin-carbon bond per molecule, preferably tetramethyltin. 15. A method according to any one of claims 4 to 14, characterized in that the amount ratio of fluorine dopant oxidizable tin compound is selected so that the concentration of free electrons in the film is in the range of about 1020 cm -1 - 321 cm -1. A method according to any one of claims 4 to 15, characterized in that the levels of fluorine dopant in the stannous oxide film are about 1-3% fluorine as a replacement for oxygen. 17. A process according to claim 8, characterized in that component (a) contains reactive fluoroalkyl groups, such as fluoroalkyl halides or mixtures thereof, preferably a gas selected from the group consisting of CF 3 compounds or mixtures thereof, or contains Br , CF3I and homologous or substituted fluorinated reactive fluorosulfur groups, such as SF5Cl, SF5Br or SFSCF3 and homologous or substituted compounds or mixtures thereof, or mixtures of these substances. 18. A process according to any one of claims 4 to 17, characterized in that component (a) contains a fluoroalkyl group or substituted fluoroalkyl group attached to a tin atom, preferably trimethyltrifluoromethyltin or trimethylpentafluoroethyltin. 19. A process according to any one of claims 4 to 18, characterized in that component (b) comprises a compound containing at least one carbon-tin bond, preferably tetramethyltin or dimethyltin dichloride. Process according to one of Claims 4 to 19, characterized in that component (b) contains oxygen, nitrogen or argon. Zl. A method according to any one of claims 4 to 20, characterized in that the substrate to be coated is turned downwards and that the gas mixture is directed upwards towards the substrate surface.