Device for introducing reagents into an organometallic vapour phase deposition apparatus

Abstract: The device for introducing reagents into an organometallic vapour phase deposition apparatus consits of a valve body comprising two chambers (C1, C2), each of them being suited to be placed in communication with a way (1) for the introduction of the reagent and being permanently connected with two ways (2, ...) traversed by carrier gas.

Description: The present invention regards the plant for fabricating semiconductor devices and more particularly it concerns a device for introducing reagents into an apparatus for deposition from vapour phase organometallic materials. As known, many electronic devices, and more particularly many optoelectronic devices used in optical fibre transmission systems, such as lasers, photodetectors, etc., consist of semiconducting material structures formed of various monocrystalline layers with different compositions within the Indium, Gallium, Arsenic and Phosphor system and with thicknesses comprised between fractions of a µm (micron) and a few µm (microns). The individual layers are obtained by depositing appropriate compounds on a starting substrate using for the operation different methods, among which MOCVD (Metal-Organic Chemical Vapour Deposition) is widely used. According to this method the sources of metals, like Ga, In, consist of organometallic compounds, while the precursors of nonmetals, like As, P, consist of the corresponding hydrides. During deposition, mixtures of the reagents above are transported by use of carrier gases, like H₂, Ar, in the reactor, wherein the starting substrate is present, kept at convenient temperature. As they arrive there, they react with each other, yielding the desired semiconducting material which is deposited on the substrate. To obtain different layers the flow of reagent with a certain composition is replaced by a flow of reagents with different composition, trying at the same time to keep all the other physical conditions unchanged, so as to avoid the formation of layers with uncontrolled composition. According to the so-called vent/run method, described in the article entitled "An ultra-fast gas delivery system for producing abrupt compositional switching in OMVPE", written by R.S.Sillmon et alii, issued on pages 73-78 of the Journal of Crystal Growth, No.77, 1986, the gaseous flow in the line of each reagent is never halted, but it is only switched either towards the reactor (run line) or towards an exhaust line (vent line). The changeover between the two directions is obtained by acting on valves, which by halting the reagent flow or by letting it through, allows the reagent to be routed towards the desired line, thus obtaining also the purging of manifolds prior to the immission of the new flow into the reactor. To obtain this, the valves are activated in opposite manner, i.e. when one is OFF, the other is ON. In addition, because it is of main importance that the composition of each layer is constant and the transition from one layer to another is well defined, flow changeover in the reactor must take place as quickly as possible, so as to reduce to the minimum reagent stagnation in dead spaces of valves and manifolds, which for this reason must present low volumes (see e.g. US-A-4 747 367). Reagent flow changeover can take place without abrupt pressure variation if pressures in vent and run lines are equal. Pressure balancing is usually obtained by an electronic control system using a differential manometer for measuring pressure differences and a flowmeter for adjusting carrier gas flow in an additional line. By this line, carrier gas is injected into the line at a lower pressure till pressure values are balanced again. However a certain delay in control system response cannot be avoided, especially if line volumes are not negligible. Furthermore, in known vent/run system the reagent stagnation problem is not completely solved, since two valves joined with a pipe segment of non negligible length are usually used for the operation, owing to valve dimensions. Since the portion of pipe segment leading to the valve switched OFF and dead spaces of the valve itself are cut off from the flow, stagnation of a certain amount of reagent is unavoidable. Said drawbacks are overcome by the device for introducing reagents into an organometallic vapour phase deposition apparatus, provided by the present invention as defined in Claim 1, which, comprising an only valve body and no longer requiring pipe segments, presents a considerable reduction in dead spaces, encumbrance and leakage losses through joints; it is submitted to continuous purging in all its internal zones, whether the reagent is sent to the exhaust line or to the reactor, or the flow is halted. The present device can directly replace the pair of valves usually used in a vent/run system. The present invention provides a device for introducing reagents into an organometallic vapour phase deposition apparatus which has just five ways for routing reagent and carrier gases and two inlets for letting in compressed air to control pneumatic actuators provided for switching flows between different ways. The foregoing and other characteristics of the present invention will be made clearer by the following description and by the annexed drawing wherein: Fig.1 is a perspective view of the device; Fig.2 is a partial longitudinal sectional view; Fig.3 is a partial longitudinal sectional view, perpendicular to that of Fig.2. The perspective view of Fig.1 shows the device, comprising a valve body provided with five ways 1,2,3,4 and 5 for reagent and carrier gas transit. Two inlets 6 and 7 allow compressed air to be let in for controlling pneumatic actuators, which switch flows between different ways. More particularly, the reagent, which can be pure or mixed with carrier gas, is injeced through input way 1. A carrier gas enters through way 2 and goes out through way 5 without undergoing any control inside the device. Analogously, a carrier gas enters through way 3 and goes out through way 4 without undergoing any control. Ways 3 and 4 can, e.g., be part of the exhaust line and ways 2 and 5 can be part of the line leading to the reactor. During the usual operation the actuators are activated by compressed air injected through inlets 6 and 7 so as to connect way 1 with the continuous flow traversing ways 2 and 5, thus sending the reagent to the reactor, or so as to put in communication way 1 with continuous flow traversing ways 3 and 4, thus venting the reagent towards the exhaust. When idle, the actuators cut off way 1, so that only the carrier gas flows into the device and the reagent is halted. In the sectional view, shown in Fig.2, the internal device structure can be seen, except actuators A1 and A2, which are of a type commercially available. Way 1 ends in the middle of the segment of a perpendicular pipe, generally closed at its ends by two stem tips G1 and G2, drawn to opening position by bellows S1 and S2 belonging to pneumatic actuators A1 and A2. If actuator A2 is activated, stem tip G2 opens and lets the reagent flow from way 1 to chamber C2. This chamber communicates permanently with way 2 and way 5, visible in Fig.3, wherethrough the carrier gas flows. If actuator A1 is activated and actuator A2 is reset, stem tip G1 opens and stem tip G2 closes, so that the reagent flow is diverted towards chamber C1. As this chamber communicates permanently with ways 3 and 4, shown in Fig.3, reagent mixes with the carrier gas flowing therein.

Claims: A device for introducing reagents into an organo-metallic vapour phase deposition apparatus, comprising a first way (1) which is the input way for reagent injection and which comprises stem tips (G1, G2); a second way (2) which allows the injection of a carrier gas outgoing through a third way (5) without any control inside the device; and a fourth way (3) which allows the injection of a carrier gas outgoing through a fifth way (4) without any control inside the device; which device consists of a valve body which just has these five ways (1, 2, 3, 4, 5) for routing reagent and carrier gases and two pneumatic actuators (A1, A2) with inlets (6, 7) for letting in compressed air to control the pneumatic actuators (A1, A2) provided for switching or stopping flows between said different ways. A device as in claim 1, characterized in that said first way (1) ends in the middle of the segment of a pipe perpendicular to the first way (1) and usually closed at its end faces by the first and the second stem tip (G1 and G2), drawn to opening position by the first and the second pneumatic actuator (A1, A2), respectively. A device as in claim 2, characterized in that the ways comprise a first chamber (C1), which permanently communicates with said fourth and fifth ways (3, 4) and which communicates through said first stem tip (G1), when it is opened by said first pneumatic actuator (A1), with said first way (1). A device as in claim 2 or 3, characterized in that the ways comprise a second chamber (C2), which permanently communicates with said second and third ways (2, 5) and which communicates through said second stem tip (G2), when it is opened by said second pneumatic actuator (A2), with said first way (1).

Inventors: BERTONE DANIELE, BERTONE, DANIELE
Applicants: CSELT CENTRO STUDI LAB TELECOM, CSELT CENTRO STUDI E LABORATORI TELECOMUNICAZIONI S.P.A.
Application year: 1992
Main classification: C23C16
IPC codes: C23C16, C30B25