Patent Application
20140284404
This invention relates to a chemical vapour deposition injector.
Chemical vapour deposition (CVD) reactors, or more particularly metal organic chemical deposition (MOCVD) reactors are used in semiconductor industry to produce compound semiconductor devices such as laser diodes, light emitting diodes (LEDs) etc. Such reactors include a reaction chamber where precursors react with each other under certain temperature and pressure conditions to form a homogeneous gas mixture which is deposited as a thin film on a substrate placed in the reaction chamber.
For MOCVD, the two precursors are typically TMGa (or TMIn) and NH3 The reactor includes a gas injector for introducing the precursors into the reaction chamber. A first challenge in the design of the gas injector is to prevent pre-reaction between the two precursors. This is because if they are allowed to mix before entering the reaction chamber, the two precursors would mix and react with each other to form particles which condense on walls of the reactor (which would be colder than the precursors). Such condensation is a waste of the precursors and may also degrade the reactor.
Thus, the gas injector should deliver the two precursors separately until the two precursors enter the reaction chamber, where they are allowed to mix.
A second challenge is to achieve uniform flow rates for the two precursors as the gases leave the gas injector's outlets. As the two precursors are injected into the reaction chamber, uniformity of the flow rates of the two precursors from the gas injector's outlets is critical to achieving a preferred gas flow pattern.
There have been proposed reactors to address the above two challenges. However, most address one but not the other challenges and for those that attempt to address both of these challenges, none can meet these challenges in a cost effective way or they are difficult to maintain.
In a first aspect of the invention, there is provided a chemical vapour deposition gas injector, comprising a gas injector body having
An advantage of the described embodiment is that this achieves a more uniform flow rate for the gases and much easier to manufacture. Further, the arrangement ensures that the two gases do not mix until the gases reach the reaction chamber.
Preferably, the gas injector body may comprise a semi-annular channel for receiving the first gas from the first gas channel, the semi-annular channel being arranged to split the first gas into the separate flow paths.
Each of the discrete first and second conduits may include a flow development portion for reducing pressure of the first and second gas respectively as the gases exits to the reaction chamber. The development portion may have an opening for receiving the first or second gas and a discharge opening for discharging the first or second gas to the reaction chamber, wherein the discharge opening is larger than the first opening. The flow development portion is particularly advantageous to reduce turbulence of the gas flow.
The gas injector body may further comprise the first plenum and the second plenum. The gas injector body may further comprise a first gas distribution channel for receiving the first gas from a first gas inlet and the first gas distribution channel is arranged adjacent to and around the first gas plenum. The gas injector body may further comprise a first plenum wall separating the first gas distribution channel and the first gas plenum, and with the first plenum wall comprising a first continuous gap to enable the first gas to diffuse from the first gas distribution channel to the first gas plenum. In this way, this improves the circulation gas flow. The gap may be about 1 mm for optimum results but it should be appreciated that this dimension may be varied.
The gas injector may also comprise a second gas distribution channel for receiving the second gas from a second gas inlet, and the second gas distribution channel is arranged adjacent to and around the second gas plenum. The gas injector may further comprise a second plenum wall separating the second gas distribution channel and the second gas plenum, and with the second plenum wall comprising a second continuous gap to enable the second gas to diffuse from the second gas distribution channel to the second gas plenum. In this way, circulation of the second gas is improved. The gap may be about 1 mm for optimum results but it should be appreciated that other dimensions are possible too.
Preferably, centre-to-centre distance between one of the second conduits and an immediately adjacent first conduit may be about 5 mm. Preferably, centre-to-centre distance between two immediately adjacent second conduits may be about 5 mm.
Preferably, the gas injector body further comprises a heat exchanging fluid distribution element for controlling temperature of the first and second gases. The heat exchanging fluid distribution element may comprise a series of elongate heat exchanging fluid channels through which at least some of the first and second conduits pass. The series of elongate heat exchanging fluid channels may be arranged along a second longitudinal axis which transverses the longitudinal axis of the second gas channels.
Preferably, the first direction, the longitudinal axis and the second longitudinal axis may be orthogonal to each other.
Preferably, the gas injector body may be a unitary body.
In a second aspect, there is provided a chemical vapour deposition reactor comprising the chemical vapour gas injector of the above aspects.
It should be appreciated that features relating to one aspect may also be applicable to the other aspects.
An example of the invention will now be described with reference to the accompanying drawings, in which:
The first and second gas input and delivery members 300,400 are arranged to deliver and channel a first precursor gas and a second precursors respectively to the reaction chamber 202 and the third fluid input and delivery member 500 is arranged to deliver a heat exchanging fluid for controlling temperature of the first and second gas input and delivery members 300,400.
The first plenum circumferential wall 310 has a first flow restrictor 312 which is a small continuous gap of about 1 mm that separates the top edge of the first plenum circumferential wall 310 and the cover 1002 of the reactor 1000, and
The gas injector 100 includes a unitary injector body 104 bounded by the top surface 102 and a bottom surface 106 which is contiguous with the reaction chamber 202 and the unitary injector body 104 has a general disc shape.
Referring to
The fifth first gas delivery element 314a includes a row of holes 316a (see
Each of the first gas channels 320a extends into the injector body 104 in a first direction and is configured to branch into separate flow paths and in this embodiment, this is achieved by an elongate, semi-annular channel 322a which extends continuously along the longitudinal axis 318a (see also
The fifth first gas delivery element 314a further includes a plurality of discrete first conduits 328a with pairs of the first conduits 328a having their inlets 330a coupled to respective pairs of the gas outlets 326a i.e. one inlet 330a of one first conduit 328a to one gas outlet 326a. Each of the first conduits 328a has a main portion 332a of about 1.6 mm in diameter which connects the inlet 330a to a flow development portion 334a. The flow development portion 334a includes a first opening 336a, a first gas discharge opening 338a and a first conduit tapered section 340a. The first opening 336a is coupled to the main portion 332a of the first conduit 328a and has the same diameter as the main portion 332a. However, the first gas discharge opening 338a has a larger diameter than the first opening 336a and which is about 4 mm and this arrangement, together with the tapered section 340a, improves gas flow since it reduces pressure and creates less turbulence in the gas flow.
It should be apparent that the first gas discharge opening 338a are disposed on the bottom surface 106 of the gas injector body 104 and thus, discharges the first gas to the reaction chamber 202.
As shown in
The two second gas inlets 402,404 are about 14 mm in diameter and are connected to a second precursor gas source (not shown) for channeling a second precursor gas, such as Nitrogen into the second gas distribution channel 406. The second gas distribution channel 406 is about 18 mm wide by 23 mm in height and the second gas distribution channel 406 is arranged also as a continuous loop around the second gas plenum 408, separated by the second plenum circumferential wall 410, and this is shown more clearly in
Referring to
The fifth second gas delivery element 414c includes an elongate tubular channel 416c (see also
The tubular channel 416c further includes a plurality of second gas openings 418c which are connected to respective downstream second conduits 420c. Each of the second conduits 420c includes a main portion 422c of about 1.6 mm diameter and a flow development portion 424c for reducing the pressure of the second gas as it exits to the reaction chamber 202 and in this way, creates less turbulence. The flow development portion 424c includes a second opening 426c, a second gas discharge opening 428c and a second conduit tapered section 440c. The second opening 426c is coupled to one of the second gas openings 418c and has the same diameter as the main portion 422c. However, the second gas discharge opening 428c has a larger diameter than the second opening 426c and which is about 4 mm and this arrangement, together with the second conduit tapered section 440c, improves gas flow since it reduces pressure and creates less turbulence in the gas flow.
It should be apparent that, in this embodiment, the second conduits 420c are arranged in two rows along the longitudinal axis 318a and between the first conduits 328. Distance D2 between corresponding pairs of second conduits 420c and D1, between one of the second conduits 420c and an immediately adjacent first conduit 328a has been strategically selected and in this embodiment, D1 and D2 are both about 5 mm (measured between centre to centre) as shown in
The second gas discharge opening 428c is disposed on the bottom surface 106 of the gas injector body 104 and thus, discharges the second gas to the reaction chamber 202. It may be appreciated that due to the arrangement of the first gas delivery element 314 and the second gas delivery element 414 makes it possible to group each of the first and second gas delivery element 314,414 as sets or groups. In other words, one first gas delivery element 314 may be grouped with one second gas delivery element 414 to form a set which may be called a gas distribution element. It should also be appreciated that for one gas distribution element, the second conduits 420c (or rows of the second conduits) are arranged between the first conduits 328a (or rows of the first conduits), although this may not be the case for the extreme gas distribution elements—see
When the second precursor gas is introduced into the two second gas inlets 402,404, the second precursor gas travels along a path or distance, as shown by arrows E, defined by the second gas distribution channel 406 and also does not immediately flow to the second plenum 408 due to the presence of the second plenum circumferential wall 410. However, due to the presence of the second flow restrictor 412, as the second precursor gas travels along the second gas distribution channel 406, some of the second precursor gas is diffused or drawn into the second gas plenum 408 via the second flow restrictor 412 (see arrows F). With this arrangement, this also achieves a more uniform gas flow rate in an angular direction for the second precursor gas to fill the second plenum 408, and since the second plenum 408 is arranged as a continuous loop, the second precursor gas also circulates along the continuous loop (as shown by arrows G) until the second precursor gas is drawn into the tubular channel 416a (or generally 416 for all the tubular channels) as shown by arrow H of
In
The heat exchanging fluid inlet 502 and the heat exchanging fluid outlet 506 are each about 10 mm in diameter and the heat exchanging fluid inlet 502 is connected to a heat exchanging fluid source (not shown) for channeling a heat exchanging fluid into the injector body 104 for controlling temperature of the first and second precursors.
After the heat exchanging fluid inlet 502, the heat exchanging fluid travels along heat exchanging fluid distribution channel 504 as shown by arrows J and is drawn into the heat exchanging fluid tubular channels 506 via inlets 508 of the heat exchanging fluid tubular channels 506 with outlets 510 of the heat exchanging fluid tubular channels 506 discharging the heat exchanging fluid back to the heat exchanging fluid distribution channel 504 and eventually flowing out of the injector body 104 via the heat exchanging fluid outlet 506. Each heat exchanging fluid tubular channel 506 transverses the elongate tubular channels 416 of the second input and delivery member 400 (or that the heat exchanging fluid tubular channels 506 are orthogonal to the longitudinal axis 318a, although on different planes). Specifically, the first conduits 328 of the first gas delivery element 314 and the second conduits 420 of the second gas delivery element 414 passes orthogonally through the heat exchanging fluid tubular channels 506. In this way, as the first and second precursors flow respectively through the first and second conduits 328,420, they are cooled by the heat exchanging fluid flowing through the heat exchanging fluid tubular channels 506.
Flow paths of the first and second precursors will now be described with reference to Figures, and in particular,
When the second precursor gas is introduced into the two second gas inlets 402,404, as shown by arrows E, the second precursor gas travels along the second gas distribution channel 406 and gradually the second precursor gas is drawn into the second plenum 408 via the second flow restrictor 412 as shown by arrows F. At the second plenum 408, the second precursor gas is drawn into respective elongate tubular channels 416 and then into the second conduits 420.
When the first precursor gas and the second precursor gas is flowing through the first and second conduits respectively, heat exchanging fluid is passed through the heat exchanging fluid tubular channels 506 which cools the first and second precursors. Eventually, the first and second precursors are discharged out of the injection body 104 and into the reaction chamber 202 via the flow development portions 334,242.
When the first and second precursors are discharged from the injection body and into the reaction chamber 202, this is when the two precursors are allowed to mix with each other to deposit a thin film on the substrate 210.
It should be apparent that at the bottom surface of the 106 of the injector body 104, the outlets of the first and second gas delivery members 300,400 are an array of distinct and separate openings (in this embodiment, they are circular openings) for discharging the first and second precursors into the reaction chamber 202.
Based on the proposed arrangement of the injector 100 and the reactor 1000, it is much easier to manufacture the injector 100. This also makes it a cost effective solution for high volume manufacturing. The injector 100 and reactor 1000 are also easier to maintain and may result in higher production yield. It is also possible to achieve a uniform flow rate for the precursors into the reaction chamber 202 and this may achieve a uniform growth rate for the substrates.
The described embodiments should not be construed as limitative. For example, the dimensions indicated in the embodiment are typical values for a 7×2″ (7×50.8 mm) CVD reactor and for illustrative purposes only. Needless to say, the dimensions may be varied depending on size of the reactor and application etc. Further, the semi-annular channel 322 may not be annular and other shapes are possible as long as the flow paths of the first precursor has is split into separate flow paths. Similarly, the tubular channels 416 and the heat exchanging fluid tubular channels 506 may not be tubular and other shapes, such as a square cross-section rather than circular might be possible, although not preferred.
The described embodiment uses a CVD reactor as an example, but it should be apparent that this invention may also be used for specific types of CVD reactors such as metal organic chemical deposition (MOCVD) reactors. Further, the gas injector 100 may not have the flow development portions 334,424, just preferred to have these.
Having now fully described the invention, it should be apparent to one of ordinary skill in the art that many modifications can be made hereto without departing from the scope as claimed. For instance, although the injector body 104 has been described as a unitary body, it should be appreciated that the first and second gas input and delivery members 300, 400 may also be separate channels for delivery of the first and second precursors to the reaction chamber 202. Although it has been described that the injector body 104 comprises the heat exchanging fluid distribution element input and delivery member 500, it should also be appreciated that such an input and delivery member may also be omitted.
