METHOD FOR PROVIDING A PROPORTIONED VAPOUR FLOW AND ALSO APPARATUS FOR CARRYING IT OUT

Abstract: Method for providing a proportioned gas flow essentially containing triisobutylaluminium (TIBA) prepared from liquid TIBA by evaporation. During this process isobutyl is produced and this is subsequently removed. The vapor flow of (TIBA) is metered by the controlled supply of liquid isobutylaluminium to an evaporator with short retention time.

Description: Method for providing a proportioned vapour flow and also apparatus for carrying it out The invention relates to a method for providing a proportion¬ ed gas flow essentially containing triisobutylaluminium (TIBA) prepared from liquid TIBA by evaporation, the isobutene produced in this process being removed. Such a method is known from EP-A-0,068,738, TIBA is used for depositing an aluminium layer on a substrate by chemical means. For this purpose, the TIBA should be present in a gaseous state. TIBA is delivered as a liquid product and consequently has to be evapo¬ rated. In this process, isobutene, inter alia, is released as an undesirable by-product. In the apparatus according to the prior art, the liquid TIBA is introduced into a vessel and gaseous TIBA is produced from it by evaporation. This method has a number of disadvantages. Firstly, the quantity of TIBA can be varied only by heating the vessel to a greater or lesser extent. On the other hand, it is necessary for the temperature of the TIBA to be within a very limited range in order to achieve optimum properties thereof. As a result of heating or cooling the vessel, this range is departed from, with the result that an optimum composition of the desired vapour is not obtained in this manner. Decomposition of the liquid TIBA occurs, especially if the TIBA is heated too much, and as a result of this the quality of the Al deposits on the substrate decreases dramatically. The object of the present invention is to avoid this disad¬ vantage. This object is achieved in a method as described above in that the gas flow is metered by the controlled supply of liquid TIBA to an evaporator with short retention time. As a result of supplying more liquid TIBA to the evaporator, a greater evapora¬ tion will immediately take place and this will result in a greater vapour flow. As has been described above, isobutene is produced during the evaporation. It is necessary to separate the isobutene from the TIBA which has to be supplied to a reactor or the like for the substrate to be treated. According to an advantageous embodiment of the invention, the TIBA is preheated before being supplied in a liquid state to the evaporator and the vapour produced in this process is removed. This vapour contains essentially isobutene and the liquid product which is passed through contains essentially *FIBA. Preferably, the preheating is carried out at 30-40 °C and the evaporation at 4θ-6θ°C. According to a further advantageous embodiment, the metered vapour flow containing essentially TIBA is fed to a reactor and the dischai-ge therefrom is combined with the vapour produced during the preheating and stored and cooled for removal. By combining the two vapour flows, it is possible to provide a single removal system. Such a removal system is of importance because, if the reactor employs reduced pressure, the outlet for used TIBA may take place via thδ pump connection. It is undesirable that TIBA reaches said pump Because the pump may be damaged thereby. In order to avoid this, the TIBA (or isobutene respectively) has to be removed before reaching the pump. This can be done by cooling the exhaust gases. This may be carried out in at least two steps. In this case, essen¬ tially all the TIBA is removed in the first step and essentially the isobutene in the second, colder step. The invention will be explained below in more detail with reference to an embodiment shown in the schematic block diagram. Here a substrate schematically indicated by 1 has to be treated in a reactor generally indicated by 2 in a manner such that an aluminium layer is deposited thereon. The reactor 2 may be a reactor such as is described, for example, in NL-A-8,900,544. For this purpose, the apparatus according to the invention comprises a source 3 of TIBA connected via a pipe 4 to a vessel _\ . The pipe 4 incorporates a filter 6 and a proportioning pump 7» Connected to pipe 4 is a flushing pipe 8 for, for example, N . After being passed through the wall of vessel 5. pipe 4 opens into chamber _). The said chamber 9 has a terraced bottom 10 in the centre of which an overflow 11 is fitted whose end 12 opens into a cavity 13 in the centre of a plate evaporator indicated as a whole by 14. Both the #late Evaporator 14 and container 15 in which chamber 9 is provided are provided with heating means 16 and 17. respectively. A thermal¬ ly insulating material may possibly be provided between container 15 and plate evaporator 14. Container 1 is provided with an outlet pipe 18 which is connected to outlet pipe 19 of vessel 2. An adjus¬ table shut-off valve 20 is fitted in outlet pipe 19. Outlet pipe 19 opens, on the other hand, into cooling vessel 21. This vessel is supplied via pipes 22, 23 with a coolant from cooling apparatus 25. A cooling plate 26 is fitted in cooling vessel 21 and an outlet 27 is embodied near the bottom. An outlet 28 projecting to some extent above the bottom of the vessel is connected to freezing vessel 30. Fitted in the latter are cooling plates _\1 which are cooled with liquid nitrogen supplied from source 43 via pipe 42. Connected to freezing vessel 30 is an outlet 45 which is connected to pump system _\2 which opens into removal system 33• Outlet pipe 27 is connected to vessel 35 which contains a cooling coil 36 which is also connected to cooling apparatus 25. Vessel 35 is provided with an outlet 38 at the bottom which converges with outlet 39 from the bottom of freezing vessel 30 and opens into the removal system 40 for used product. Vessel 5 is provided, in addition, with an outlet 4l which opens at the top of vessel 35• The apparatus described above operates as follows: After the system has been flushed with nitrogen originating from the flushing pipe 8 in order to expel the oxygen present from the system, the source 3 of TIBA is connected and TIBA is trans¬ ported via pump 7 into vessel 5- The TIBA entering chamber 9 of holder 5 moves according to a predetermined movement pattern via bottom 10 to overflow 11 with a fixed retention time. The TIBA contained in chamber 9 is heated by heating system 17 in a manner such that, on the one hand, the TIBA remains liquid but essentially all the isobutene present evaporates. This preheating is preferably carried out between 30 and 4θ°C. Then the liquid TIBA is introduced into cavity 13 and from there is spread directly over the plate evaporator 14, which is kept at a temperature of 4θ to 60° by heating. As a result of this, the TIBA evaporates and travels towards reactor 2 via a pipe 45. In reactor 2, the substrate 1 undergoes the desired treatment after possibly preheating the TIBA further. Used TIBA and isobutene are removed by, respectively, outlet pipe 19, 18 in the manner described below. This manner of evaporating TIBA has the advantage that the quantity of TIBA to be evaporated is determined exclusively by the quantity of TIBA sup¬ plied. The rate of evaporation is not controlled, as in the prior art, by controlling the temperature of heating system 16, 17, but by controlling the output of pump 7. Because both the TIBA removed and the isobutene are detrimen¬ tal to the functioning of pump system 32, means have to be provided to remove said vapours before they reach said vacuum pump system 32. For this purpose, cooling vessel 21 and freezing vessel 30 are present. In cooling vessel 21, the material entering it from pipe 18 and 19 is cooled in a manner such that essentially all the TIBA is liquefied in vessel 21. That is to say, it was found in a test that approximately 80/U of the material is liquefied therein. Said liquid product is removfed via outlet 27 to vessel 35. where it is kept cooled. At set times, if vessel 35 is getting full, the TIBA can be removed via pipe 38 to system 40. The gaseous product still present enters, via outlet 28, freezing vessel 30 and freezes at cooling plates 31- Because said cooling plates are appreciably cooled by means of liquid nitrogen originating from source 43 via pipe 42, product detrimental to pump system 32 will virtually no longer be present in the outlet 45. Because most of the material is removed in cooling vessel 21, freezing vessel 30 can be of compara¬ tively limited capacity, but it must be understood that material adhering to the cooling plates 31 remains there until the end of a processing cycle. When the freezing vessel 30 is unfrozen, liquid product is produced near the bottom and is passed via pipe 39 to removal system 40. Although the invention has been described above with referen¬ ce to a preferred embodiment, it must be understood that many changes which are obvious to those skilled in the prior art can be made thereto without departing from the scope of the invention of the type for which protection is claimed hereinafter. For example, instead of the pump 7. any other metering means known in the prior art can be used, such as a shut-off valve.

Claims: CLAIMS 1. Method for providing a proportioned gas flow essentially containing triisobutylaluminium (TIBA) prepared from liquid TIBA by evaporation, wherein the isobutene produced in this process is removed, characterized in that the vapour flow is metered by the controlled supply of liquid TIBA to an evaporator with short retention time. 2. Method according to Claim 1, wherein the TIBA is preheated before being supplied in the liquid state to the evaporator and the vapour produced in this process is removed. 3. Method according to Claim 2, wherein the preheating is car¬ ried out at 30-4θ β C. 4. Method according to one of the preceding claims, wherein the evaporation is carried out at 4θ-6θ β C. 5- Method according to one of the preceding claims, wherein the proportioned vapour flow containing essentially TIBA is fed to a reactor and the discharge therefrom is combined with the vapour according to Claim 2 and stored and cooled for removal. 6. Method according to Claim 5. wherein the exhaust gases are cooled in at least two steps. 7. Apparatus for carrying out the method according to one of the preceding claims, comprising a preheating apparatus having a cham¬ ber for receiving the liquid TIBA introduced and provided with overflow means opening onto a plate evaporator. 8. Apparatus according to Claim 7, wherein the chamber for receiving TIBA is provided with means for regulating the retention time thereof.

Inventors: GRANNEMAN ERNST HENDRIK AUGUST, KWAKMAN LAURENS FRANS TAEMSZN, PIEKAAR HANS WILLEM, SLUIJK BOUDEWIJN GIJSBERT, GRANNEMAN, ERNST, HENDRIK, AUGUST, KWAKMAN, LAURENS, FRANS, TAEMSZN, PIEKAAR, HANS, WILLEM, SLUIJK, BOUDEWIJN, GIJSBERT
Applicants: ASM EUROP, ASM EUROPE B.V.
Application year: 1990
Main classification: C23C16
IPC codes: C23C16, H01L21