Method for transforming a liquid flow into a gas flow, and device for implementing the method

Abstract: Method and device which is to be used for the implementation thereof for transforming a liquid flow into a gas flow, whereby the liquid flow is led into a space (24) in which the liquid evaporates and the vapour which thus arises is carried off mixed with a carrier gas (16). By ensuring that the carrier gas flow (16) is passed directly past the liquid inlet port (12), whereby a complete mixing of both is achieved, and by keeping the way to the evaporation space short, a stabile and continuous gas flow is obtained. The provisions for mixing and evaporation are integrated in the device.

Description: The invention relates to a method and a device for transforming a liquid flow into a gas flow, whereby the liquid flow is led into a space in which the liquid evaporates and the vapour which thus arises is carried off mixed with a carrier gas. Such methods and devices are known and are used, for example, in places where the gas or vapour flow concerned is necessary for implementing processes of chemical deposition, such as are carried out when making chips. A common method for achieving such a transformation is the so-called bubbler method. Thereby a carrier gas - for example, oxygen - is led into the liquid which is to be evaporated, for example, Tetra Ethyl Orto Silicate - TEOS. The carrier gas causes bubbles in the liquid. If the liquid is kept at a certain high temperature, a mixture will be formed of carrier gas and vapour in the - closed-off - space above the liquid surface. This mixture is then carried-off and can be used, for example, in the said deposition process. This known method has disadvantages: the outgoing gas flow - therefore, the mixture - is not continuous and not stabile. Large variations with regard to stability and continuity can arise and such a flow will even be entirely interrupted now and again by, for example, gas envelopes. The disadvantages are particularly salient if one works with weak liquid flows, such as of 10 - 500 gram/hour. The instability and the discontinuity is caused especially as a result of the fact that the temperature is such a critical parameter with regard to those units of size, but other parameters also influence both units to a considerable degree; such as the pressure, the size of the bubbles and the height of the liquid level. May it also be noted that this bubbler method may if necessary also be carried out without the use of a carrier gas. However, in that event a relatively high temperature - for TEOS approx. 110 °C - is necessary. Gas-liquid mixing with partial evaporation is also known from EP-A-0 488 909 (published on 3.06.92) and GB-A-578 783. According to these known methods and devices, the liquid flow is sucked by a gas impulse, the quantity of liquid being determined by the gas impulse. A complete evaporation cannot occur. The invention relates to a method and device as claimed, whereby the said disadvantages do not occur It is essential that the mixing and evaporation steps are carried out completely and in a controlled manner. For that purpose it is ensured that the liquid is mixed with the carrier gas "immediately", that is to say, before it has to travel a long way, and that the evaporation also takes place quickly after that. It is important, then, that as soon as a liquid which is to be evaporated appears in the space where mixing with the carrier gas occurs, it must be able to make extensive contact with the carrier gas. The carrier gas must therefore be led to and along the place where the liquid enters the mixing space and after that the mixture must be brought quickly - therefore, for example, moved across a short distance - into the evaporation space. Heat is necessary for evaporation. Depending on the liquid which is to be evaporated and the quantity, heat must either be added or must be absorbed from the surroundings without undesired effects. It appears that the stability and the continuity of the gas flow vary less than 1% in the event of application of the method according to the invention. According to the invention, the liquid is brought into the mixing space with the aid of an adjustable valve, and the mixture is transported under pressure to the evaporation space. Of course, if more than one liquid is being brought into the mixing space, several adjustable valves will be used: one for each liquid. The pressure under which the mixture is brought into the evaporation chamber is built-up with the aid of a nozzle which forms the exit of the mixing space. Liquids on which the method according to the invention are applied are, for example: trimethylphosphate (TMP) (CH 3 O) 3 P; trimethylborate (TMB; (CH 3 O) 3 B); tetra-ethylorthosilicate (TEoS; (CH 3 -CH 2 O) 4 -Si. Oxygen is used as a carrier gas for all three and in gas form they are used for the manufacture of semi-conductors. In an implementation example of the method according to the invention, whereby TEoS is used as a liquid, work was carried out with a liquid flow of 30 gram/hour and with a carrier gas flow of oxygen of 6 l/minute. In order to ensure a good evaporation 10 J/s of added heat was necessary (in the event of use of TMP and TMB extra addition of heat turned out not to be necessary). Another type of liquid for which the method according to the invention was used is TiCl 4 , whereby hydrogen is used as a carrier gas. In gas form this substance is applied for tempering metals, for example lathe tools. The invention also relates to a device for implementing the above described method. Such a device comprises a vessel which consists of a first space for contacting the liquid with the gas, a supply line for the liquid and a supply line for the gas both being situated in said first space, a second space for evaporating the liquid and an outlet for the gas and vaporised liquid. Said device is characterised in that the supply line of the liquid comprises one or more adjustable valves positioned near the end of the supply line, with a valve mouth opening into the first space and that the supply line of gas is situated such that the gas flow is led past the valve mouth such that the liquid flow is carried with the gas flow. A preferential design of a device according to the invention is characterized by the fact that the device consists of a container with a first passage in a wall for the valve, with a second passage in a wall for the supply of the carrier gas to immediately next to that first passage, with a mainly tubular part preferably approximately in the extension of that first passage which serves as a mixing space and which opens up via a nozzle into a closed evaporation space, one wall of which is equipped with an exit opening for the mixture of carrier gas and vapour/gas. The evaporation unit may be used in series, whereby the gas/vapour flow of the first one is used as a carrier gas for a subsequent one. The invention will be explained further with the aid of a drawing, in which: Fig. 1 schematically shows a known device for transforming the liquid flow into a gas flow; Fig. 2 schematically shows the part of a device according to the invention here the mixing of the liquid with the carrier gas takes place; Fig. 3 schematically shows a form of implementation of a device according to the invention. In the known device shown in Fig.1 - a so-called "bubbler" installation - the carrier gas is supplied via a dosing mechanism 1 in the direction of the arrow 2 via the pipe 3 to a container 4 in which the liquid 5 which is to be evaporated is situated. In the container 4 the mixing of the carrier gas with the liquid 5 takes place and the evaporation also takes place. With the aid of a heating- regulating mechanism 7 which is present in the container for that purpose it is ensured that the amount of heat is added which is desired in order to have evaporation take place. The mixture of carrier gas and vapour/gas which arises is caught- up above the surface of the liquid 5 and is led via an exit pipe 8 and a dosing mechanism 9 to the place where the vapour is necessary. The flow of the mixture which is generated in this known manner which leaves the device is not stabile and continuous. Fig.2 schematically shows an essential part of the device according to the invention, being that part in which the carrier gas is supplied to the opening-out of a valve in the mixing space. A carrier gas 10 flows in the direction of the arrow into the mixing space 11. The liquid which is to be evaporated flows into that mixing space 11 via the valve mouth 12. As a result of the fact that the carrier gas is led in a precise manner to the valve mouth, as soon as liquid threatens to "fall" into the mixing space 11 through the valve mouth, that liquid is "caught" by the carrier gas and is mixed thoroughly therewith. The mixture which is obtained in this manner is then led in the direction of the arrow 13 to the evaporation space. Fig.3 shows a sketch in more detail of a device according to the invention. The container 14 has an opening 15 in a wall, through which carrier gas 16 flows in the direction of the arrow to the mixing space 17. The carrier gas 16 is led to immediately under the exit opening 25 of the valve 19 (in general a magnetically operated valve), which opens out through an opening in a wall of the container 14 into the mixing space 17. May it be noted that, while only one valve is drawn in the drawing, a device according to the invention can have several intake valves, through which various liquids can be brought into the mixing space. In the mixing space 17 the complete mixing takes place. The mixture then flows into the mainly tubular shaped part 20 according to arrow 21. The mixture is then sprayed via the spray part 22 - see arrow 23 - into the evaporation space 24. In that space the evaporation then takes place and from there the mixture of carrier gas and vapour is carried to the place of destination.

Claims: Method for transforming a liquid flow into a gas flow, in which the liquid flow is brought with a gas flow into a mixing space (11, 17), followed by leading said gas and liquid into an evaporation space (24) in order to evaporate said liquid at least partially, and that finally that flow leaves the evaporation space (24), characterized in that the liquid is brought into the mixing space (11, 17) via a valve mouth (12, 25), the flow of the liquid being regulated by one or more adjustable valves and that the gas comprises a carrier gas, the flow of which is led past the outlet of said valve mouth such that substantially the entire liquid flow is carried with the gas flow to the evaporation space. Device for implementing the method according to claim 1, comprising a vessel which consists of a first space (11, 17) for contacting the liquid with the gas, a supply line for the liquid and a supply line for the gas both being situated in said first space, a second space (24) for evaporating the liquid and an outlet for the gas and vapourised liquid, characterized in that the supply line of the liquid (12, 25) comprises one or more adjustable valves positioned near the end of the supply line, with a valve mouth opening into the first space (11, 17) and that the supply line of gas is situated such that the gas flow is led past the valve mouth such that the liquid flow is carried with the gas flow. Device according to claim 2, characterized in that the device consists of a container (14) with a first passage (25) in one wall for a valve for the liquid flow, with a second passage in a wall for leading the gas (16) to the liquid flow from the outlet of said first passage (25), with a mainly tubular part (20) preferably approximately in the extension of said first passage (25) which serves as a mixing space and which opens up via a nozzle (22) into a closed evaporation space (24), one wall of which is equipped with an exit opening for the gas and vapourised liquid.

Inventors: BOER HENDRIK JAN, BOER, HENDRIK JAN
Applicants: BERKIN BV, BERKIN B.V.
Application year: 1993
Main classification: B01D1
IPC codes: C23C16, H01L21, B01D1, B01D3, B01F3, B01J7