WO2008146126A2

WO2008146126A2 - Reactor for growing crystals with cooled inlets

Info

Publication number: WO2008146126A2
Application number: PCT/IB2008/001302
Authority: WO
Inventors: Sonia De Angelis; Ambrogio Peccenati; Giuseppe Tarenzi; Franco Preti; Vincenzo Ogliari
Original assignee: Lpe S.P.A.
Priority date: 2007-05-28
Filing date: 2008-05-25
Publication date: 2008-12-04
Also published as: ITMI20071075A1; WO2008146126A3

Abstract

The present invention relates to a reactor for growing crystals of a compound material; the reactor comprises: a substantially cylindrical reaction chamber (1 ), which is adapted to be arranged in a manner such that the cylinder axis is substantially vertical and which is provided with walls (2, 3), the inner surfaces of which define at least partly an inner cavity (10) of the chamber (1), means adapted to heat said reaction chamber (1), in particular said cavity (10); the reaction chamber (1 ) comprises inlet means (4, 8) for feeding several precursor gases of said compound material into said cavity (10), which are located in the lower zone of the chamber (1), an assembly (6) adapted to hold at its bottom a seed or a substrate on which said growth takes place and located in the upper zone of the chamber (1 ), so that at least said seed or substrate and the growing crystal are kept within said cavity (10), outlet means (5) for discharging exhaust gases from said cavity (10), which are arranged around said assembly (6) in the upper zone of said chamber (1); the inlet means (4, 8) comprise: an opening (4) obtained in a bottom wall (2) of the chamber (1 ), an injector device (8) arranged outside said cavity (10) and adapted to inject at least a first and a second precursor gases of said compound material simultaneously into said cavity (10) through said opening (4); said injector device (8) is adapted to keep said two precursor gases cold and separate from each other until injection takes place.

Description

TITLE

REACTOR FOR GROWING CRYSTALS

WITH COOLED INLETS

DESCRIPTION

The present invention relates to a reactor for growing crystals, in particular a reactor for the epitaxial growth of monocrystals of a compound material, preferably silicon carbide or a third-group nitride.

A reactor of this kind is described, for example, in international patent application WO 2004/11 1316, which is incorporated herein by reference.

Reactors of this kind suffer from problems of inlet and/or outlet clogging; such clogging may be caused by spurious growth and/or spurious deposition and/or spurious material accumulation; over time, said clogging may even blocks the inlets and/or outlets completely.

As far as the inlets are concerned, a clogging thereof will lead, among other things, to a reduction in the quantity of growth material fed into the reaction chamber of the reactor during the growth processes, resulting in a lower crystal growth rate. If the inlets get blocked, the growth process will stop, thus limiting the length of the grown crystal.

A solution to the inlet clogging problem is provided by patent application WO 2006/125777, which is incorporated herein by reference.

The general object of the present invention is to provide a solution to the inlet clogging problem.

A particular object of the present invention to provide a solution which is alternative to the solutions known in the art and which is more effective than the latter in terms of capability of feeding growth material into the reaction chamber. These and other objects are achieved by the reactor having the features set out in the appended claims, which are intended as an integral part of the present description.

The present invention is based on the idea of using an injector device adapted to inject at least a first and a second precursor gases simultaneously and to keep said two precursor gases cold and separate from each other until injection takes place.

The present invention will become more apparent from the following description to be considered in conjunction with the annexed drawings, wherein: Fig. l shows an embodiment of the reactor according to the present invention, Fig.2 is a side view of the injector device of the reactor of Fig. l ,

Fig.3 is a cross-sectional view (A-A) of the injector device of Fig.2,

Fig.4 is a top view of the injector device of Fig.2,

Fig.5 is a vertical sectional view of a detail of the injector device of Fig.2 after several growth processes, Fig.6 is a vertical sectional view (analogous to the view of Fig.5) of a detail of an injector device similar to that of Fig.2, but modified in a first manner, Fig.7 is a vertical sectional view (analogous to the view of Fig.5) of a detail of an injector device similar to that of Fig.2, but modified in a second manner, and Fig.8 is a vertical sectional view (analogous to the view of Fig.5) of a detail of an injector device similar to that of Fig.2, but modified in a third manner.

This description and these drawings are to be considered for exemplification purposes only and thus non-limiting.

The present invention will now be described with reference to the embodiment shown in Figs. 1 to 4.

The reactor of Fig.1 is intended for growing crystals, in particular for the epitaxial growth of monocrystals of a material, said material being a compound, preferably silicon carbide or a third-group nitride; said reactor comprises:

• a substantially cylindrical reaction chamber 1 , which is adapted to be arranged in a manner such that the cylinder axis is substantially vertical and which is provided with walls (2 and 3), the inner surfaces of which define at least partly an inner cavity 10 of the chamber 1 , means adapted to heat said reaction chamber 1 , in particular said cavity 10, preferably to a temperature higher than l ,800°C, more preferably to a temperature between 2,000°C and 2,500°C; said reaction chamber 1 comprises: inlet means (4 and 8) for feeding several precursor gases of said compound material into said cavity 10, which are located in the lower zone of the chamber 1,

• an assembly 6 adapted to hold at its bottom a seed or a substrate on which said growth takes place, which is arranged in the upper zone of the chamber 1 in a manner such that at least said seed or substrate and the growing crystal are kept within said cavity 10; the seed or substrate is preferably held in a substantially horizontal position by the assembly 6, while the assembly 6 is typically adapted to rotate about a substantially vertical axis and is preferably adapted to translate upwards as said growth is taking place,

• outlet means 5 for discharging exhaust gases from said cavity 10, which are arranged around said assembly 6 in the upper zone of said chamber 1; the inlet means comprise:

• an opening 4 obtained in a bottom wall 2 of the chamber 1, • an injector device 8 located outside said cavity 10 and adapted to inject at least a first and a second precursor gases of said compound material simultaneously into said cavity 10 through said opening 4; the injector device 8 is adapted to keep said two precursor gases cold and separate from each other until injection takes place.

The injector device 8 comprises:

• at least one inner duct 841 for the first precursor gas,

• at least one inner duct 842 for the second precursor gas,

• a cooling element (81, 82, 83) arranged around said ducts 841 and 842 and adapted to cool said ducts 841 and 842, thereby also cooling the gases flowing therethrough; for clarity, it must be specified that the gaseous flows associated with the ducts 841 and 842 are separate from each other. The injector device 8 is positioned at a certain distance from the chamber opening; the optimal value of said distance will depend on many geometric and fluidodynamic factors, and can be determined experimentally.

The injector device 8 is surrounded by a tube, without however touching it; said tube is closed at the top by the bottom wall 2 and communicates with the cavity 10 through the opening 4; said tube is conceived for an axial gaseous flow consisting of one or more substances chosen from the group including helium, argon, hydrogen, a halogen, in particular chlorine, a halide, in particular hydrochloric acid; a converging element at the final portion of said tube (as shown in Fig.1) may advantageously be provided in order to guide the gas flow towards the chamber opening.

The reactor of Fig.1 comprises a plurality of inner ducts 842 for the second precursor gas; in Fig.3 there are four of these ducts (only one of which with reference numeral), but they may also be three, five, six or more.

If there is just one duct 842, it may be arranged around the duct 841 , thus enclosing the latter; in such a case, both ducts may have a circular cross-section and be concentric.

In the presence of a plurality of ducts 842, they may be arranged around the duct 841 so as to surround the latter, as shown in the example of Fig.3.

The injector device 8 comprises metallic elements adapted to transfer cold by conduction to said duct 841 for the first precursor gas. In the example of Fig.3, there is a circular cross-section metallic core in which the ducts 841 and 842 are obtained, e.g. by drilling and/or milling; a portion of the core metal is thus used for cooling the duct 841 directly. The axes of said ducts 841 and 842 are substantially parallel to each other and are substantially parallel to the axis of said chamber 1.

The first precursor gas may be a silane or a chlorosilane or an organosilane. The second precursor gas may be a hydrocarbon. In this case, the crystal material is silicon carbide. The first precursor gas and/or the second precursor gas may be mixed with one or more substances chosen from the group including helium, argon, hydrogen, a halogen, in particular chlorine, a halide, in particular hydrochloric acid.

The cooling element of the injector device 8 comprises a shell 81 which encloses, wholly or partly, said ducts 841 and 842.

Said shell 81 delimits a cavity 80, and said cooling element comprises means (82 and 83) through which a cooling fluid is fed into, circulated within and discharged from the cavity 80.

Said cooling fluid is preferably a liquid, in particular water (or an aqueous solution); as an alternative, it may also be a gaseous fluid.

The aforementioned means of the cooling element may comprise an inlet opening and an outlet opening for the cooling fluid, said openings being obtained in said shell 81.

Said shell 81 has a substantially cylindrical shape; the axis of said shell 81 and the axes of said ducts 841 and 842 are substantially parallel to one another and substantially parallel to the axis of said chamber 1.

Said shell 81 ends with a cap 811 (see Fig.2 and Fig.4) on the side facing said opening 4 (see Fig.l ).

Said ducts 841 and 842 open on said cap 81 1 (see Fig.4). The number of mouths may match the number of ducts, as in the example of Fig.2 and Fig.3 and Fig.4; if there is a single duct 842 enclosing the duct 841 , the duct 842 may however have a plurality of separate mouths in the cap 81 1 (as shown in Fig.4).

The above-mentioned inlet and outlet openings may be obtained on the side of the shell 81 opposite to said cap 811.

Said cooling element comprises a first circulation duct 82 connected to said inlet opening and preferably extending from said inlet opening to said cap 811 in said cavity 80 within said shell 81. Said first circulation duct 82 may also extend outside said shell 81 on the side of the shell 81 opposite to said cap 811 ; in the illustrated example, the inner duct 82 is connected to the outer duct 85.

Said cooling element comprises a second circulation duct 83 connected to said outlet opening and extending from said outlet opening in said cavity 80 within said shell 81 , preferably for a limited length.

Said second circulation duct 83 may also extend outside said shell 81 on the side of the shell 81 opposite to said cap 811 ; in the illustrated example, the inner duct 83 is connected to the outer duct 88.

In the illustrated example, the inner duct 841 is connected to the outer duct 86, and the inner ducts 842 are connected together to the outer duct 87.

Outside the chamber 1, at the opening 4 there is the device 8; the device 8 does not touch the wall 2; an annular zone is defined between the upper end of the device 8, i.e. the cap 811 , and the wall 2.

The device 8 is surrounded by a tube, without however touching it; the tube is closed at the top by the wall 2 and communicates with the cavity 10 through the above-mentioned annular zone.

It is appropriate to position the injector device 8 according to the present invention in a manner such that its inner ducts for the precursor gases end at said opening 4.

The gas flow along the tube may be used for cooling the injector device 8, in particular the shell 81 thereof, from the outside.

Furthermore, the gas flow along the tube can be used for providing thermal and/or physical insulation of the gases, in particular the precursor gases, coming out of the injector device from the surfaces that delimit the inlet opening in the wall of the reaction chamber; for this purpose, the diameter of the injector device is equal or close to the diameter of the inlet opening in the wall of the reaction chamber. Experiments carried out with the reactor of Fig.1 and the injector device of Fig.2, Fig.3, Fig.4 have shown that material (in particular silicon) grows/deposits on the cap 811, in particular at the mouth of the duct 841, as shown by way of non- quantitative example in Fig.5; this phenomenon may lead to clogging of the duct 841 after several growth processes or during very long growth processes; it seems to be due to the central area of the cap 811 becoming hot (because it is irradiated from the chamber through the opening 4) and to contact with the precursor gases; it should be noted that the duct 841 is rather small, since its inner diameter is typically between 4 mm and 8 mm.

Aiming at solving the general problem of spurious growths/depositions on the outer surface of an injector device at the mouth of a duct, some appropriate solutions have been conceived by the Applicant.

A first solution will be illustrated below by referring to Fig.6 and by taking into consideration the cap 811 and the duct 841 of the above-described example of Fig.2, Fig.3, Fig.4.

A second solution will be illustrated below by referring to Fig.7 and by taking into consideration the cap 811 and the duct 841 of the above-described example of Fig.2, Fig.3, Fig.4.

A third solution will be illustrated below by referring to Fig.8 and by taking into consideration the cap 811 and the duct 841 of the above-described example of Fig.2, Fig.3, Fig.4.

According to the first solution, within the duct 841 , which may be called "main duct", there is a duct 843, which may be called "auxiliary duct", concentric to the duct 841. The auxiliary duct preferably ends shortly before the main duct, i.e. it is somewhat set back from the outer surface of the injector device; thus, the auxiliary duct will be heated less by the chamber.

The setback may be, for example, a distance 0.5 to 2.0 times the main duct diameter. The auxiliary duct is used for carrying a flow of a precursor gas, in particular a mixture consisting of a precursor gas and one or more substances chosen from the group including helium, argon, hydrogen, a halogen, in particular chlorine, a halide, in particular hydrochloric acid; the main duct is used for carrying a flow of one or more substances chosen from the group including helium, argon, hydrogen, a halogen, in particular chlorine, a halide, in particular hydrochloric acid, around the auxiliary duct.

The gaseous flow in the main duct contributes to cooling and/or cleaning the walls of both the main duct itself (in particular the final portion thereof) and the auxiliary duct (thus cooling the gas flowing therein).

Furthermore, the gaseous flow in the main duct (which is preferably faster than the gaseous flow in the auxiliary duct) contributes to confining the gaseous flow in the auxiliary duct centrally and axially (even past the duct end) and to preventing this latter flow from coming in contact with the final portion of the main duct and with the outer surface of the injector device.

The outer diameter of the auxiliary duct is smaller than the inner diameter of the main duct; for example, the outer diameter of the auxiliary duct may be 0.7 to 0.9 times the inner diameter of the main duct.

According to the second solution, within the duct 841 , which may be called "main duct", there is a duct 844, which may be called "auxiliary duct", concentric to the duct 841 ; the outer diameter of the auxiliary duct is slightly smaller than the inner diameter of the main duct; for example, the outer diameter of the auxiliary duct may be 0.90 to 0.98 times the inner diameter of the main duct.

The auxiliary duct repeatedly (e.g. periodically) performs a short reciprocating axial motion during the growth processes (as schematized in Fig.7), so that any spurious growths/depositions occurring at the mouth of a main duct (as schematized in Fig.5) will be removed (broken and/or detached) thanks to the direct mechanical action exerted by the moving auxiliary duct. In the idle position, the auxiliary duct preferably ends shortly before the main duct, i.e. it is somewhat set back (e.g. at a distance 1.0 to 4.0 times the main duct diameter) from the outer surface of the injector device; thus, the auxiliary duct will be heated less by the chamber.

Fig.7 shows two preferred end-of-stroke positions taken by the auxiliary duct during said reciprocating motion: the first position (drawn with a continuous line) is set back (e.g. by 5 mm to 30 mm) relative to the outer surface of the injector device, whereas the second position (drawn with a dashed line) is slightly protruding (e.g. by 2 mm to 5 mm) above the outer surface of the injector device.

The reciprocating motion of the auxiliary duct may be of various types.

According to an advantageous possibility, the auxiliary duct is kept in the idle position for a long time interval (e.g. from a minimum of one minute to a maximum of one hour), and then performs a fast forward and backward movement (lasting from a minimum of 0.2 sec to a maximum of 2.0 sec).

The auxiliary duct is used for carrying a flow of a precursor gas, in particular a mixture consisting of a precursor gas and one or more substances chosen from the group including helium, argon, hydrogen, a halogen, in particular chlorine, a halide, in particular hydrochloric acid; in the main duct surrounding the auxiliary duct there is virtually no flow, due to the extremely small cross-section.

The concepts of the first and second solutions may also be combined together; in other words, with reference to the example of Fig.6, the duct 843 may repeatedly perform a short reciprocating axial motion.

According to the third solution, within the duct 841 there is a core 845 which is concentric to the duct 841 ; the core typically has a circular cross-section, and its outer diameter may, for example, be 0.3 to 0.7 times the duct inner diameter; the external shape of said core may be such as, for example, to affect the shape and direction of the gas flow within the duct.

Said core repeatedly (e.g. periodically) performs a short alternate axial motion during the growth processes (as schematized in Fig.8), so that any spurious growths/depositions occurring at the mouth of a main duct (as schematized in Fig.5) will be removed (broken and/or detached) thanks to the direct mechanical action exerted by the moving core.

As regards the axial positioning and axial motion of the core, substantially the same considerations and teachings expressed above with reference to the auxiliary duct will still apply.

Of course, in case of a moving auxiliary duct or core, it will be necessary to provide the reactor with suitable moving means, e.g. pneumatic means.

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Claims

1. Reactor for growing crystals of a material, said material being a compound, comprising: a substantially cylindrical reaction chamber (1), which is adapted to be arranged in a manner such that the cylinder axis is substantially vertical and which is provided with walls (2, 3), the inner surfaces of which define at least partly an inner cavity (10) of the chamber (1 ),

• means adapted to heat said reaction chamber (1), in particular said cavity (10); wherein said reaction chamber (1) comprises: inlet means (4, 8) for feeding several precursor gases of said compound material into said cavity (10), which are located in the lower zone of the chamber

(1),

• an assembly (6) adapted to hold at its bottom a seed or a substrate on which said growth takes place, which is located in the upper zone of the chamber (1) in a manner such that at least said seed or substrate and the growing crystal are kept within said cavity (10),

• outlet means (5) for discharging exhaust gases from said cavity (10), which are arranged around said assembly (6) in the upper zone of said chamber (1); characterized in that said inlet means (4, 8) comprise:

• an opening (4) obtained in a bottom wall (2) of the chamber (1),

• an injector device (8) located outside said cavity (10) and adapted to inject at least a first and a second precursor gases of said compound material simultaneously into said cavity (10) through said opening (4); said injector device (8) being adapted to keep said two precursor gases cold and separate from each other until injection takes place.

2. Reactor according to claim 1 , wherein said injector device (8) comprises:

• at least one inner duct (841) for the first precursor gas,

• at least one inner duct (842) for the second precursor gas, a cooling element (81, 82, 83) arranged around said ducts (841 , 842) and adapted to cool said ducts (841 , 842), thereby also cooling the gases flowing therethrough.

3. Reactor according to claim 2, characterized by comprising a plurality of inner ducts (842) for the second precursor gas.

4. Reactor according to claim 2 or 3, wherein said duct(s) (842) for the second precursor gas is(are) arranged around said duct (841 ) for the first precursor gas.

5. Reactor according to claim 4, wherein said injector device (8) comprises metallic elements (84) adapted to transfer cold by conduction to said duct (841) for the first precursor gas. u

6. Reactor according to claim 2 or 3, wherein the axes of said ducts (841 , 842) are substantially parallel to each other and substantially parallel to the axis of said chamber (1 ).

7. Reactor according to claim 2 or 3, wherein said first precursor gas is a silane or a chlorosilane or an organosilane.

8. Reactor according to claim 2 or 3, wherein said second precursor gas is a hydrocarbon.

9. Reactor according to claim 7 and/or 8, wherein said first precursor gas and/or said second precursor gas are mixed with one or more substances chosen from the group including helium, argon, hydrogen, a halogen, in particular chlorine, a halide, in particular hydrochloric acid.

10. Reactor according to claim 2, wherein said cooling element comprises a shell (81) which encloses said ducts (841 , 842).

11. Reactor according to claim 10, wherein said shell (81) delimits a cavity (80), and said cooling element comprises means (82, 83) through which a cooling fluid is fed into, circulated within and discharged from the cavity (80).

12. Reactor according to claim 1 1 , wherein said cooling fluid is a liquid, in particular water.

13. Reactor according to claim 11 or 12, wherein said means comprise an inlet opening and an outlet opening, said openings being obtained in said shell (81 ).

14. Reactor according to any of claims 10 to 13, wherein said shell (81 ) has a substantially cylindrical shape, and wherein the axis of said shell (81) and the axes of said ducts (841 , 842) are substantially parallel to one another and substantially parallel to the axis of said chamber (1).

15. Reactor according to claim 14, wherein said shell (81) ends with a cap (811) on the side facing said opening (4).

16. Reactor according to claim 15, wherein said ducts (841, 842) end at said cap (81 1).

17. Reactor according to claims 13 and 15, wherein said openings are obtained on the side of the shell (81) opposite to said cap (81 1).

18. Reactor according to claim 13, characterized in that said cooling element comprises a first circulation duct (82) connected to said inlet opening and preferably extending from said inlet opening to said cap (811) in said cavity (80) within said shell (81).

19. Reactor according to claim 18, wherein said first circulation duct (82) also extends outside said shell (81) on the side of the shell (81) opposite to said cap

(811).

20. Reactor according to claim 18 or 19, characterized in that said cooling element comprises a second circulation duct (83) connected to said inlet opening and preferably extending for a limited length from said inlet opening in said cavity (80) within said shell (81).

21. Reactor according to claim 20, wherein said second circulation duct (83) also extends outside said shell (81) on the side of the shell (81) opposite to said cap (811 ).

22. Reactor for growing crystals of a material, in particular according to any of the preceding claims 1 to 21 , comprising an injector device (8) adapted to inject at least one precursor gas of said material into the reaction chamber (1) of the reactor, wherein said injector device (8) comprises a first duct (841) for said precursor gas, characterized by comprising a second duct (843, 844) inside of and preferably concentric to the first duct (841 ).

23. Reactor according to claim 22, wherein said second duct (843, 844) ends before said first duct (841).

24. Reactor according to claim 22 or 23, wherein said second duct (843, 844) is adapted to carry a flow of a precursor gas, in particular a mixture consisting of a precursor gas and one or more substances chosen from the group including helium, argon, hydrogen, a halogen, in particular chlorine, a halide, in particular hydrochloric acid, and said first duct (841) is preferably adapted to carry a flow of one or more substances chosen from the group including helium, argon, hydrogen, a halogen, in particular chlorine, a halide, in particular hydrochloric acid, around it.

25. Reactor according to claim 22 or 23 or 24, wherein said second duct (844) is adapted to perform repeatedly a short reciprocating axial motion.

26. Reactor for growing crystals of a material, in particular according to any of the preceding claims 1 to 21 , comprising an injector device (8) adapted to inject at least one precursor gas of said material into the reaction chamber (1) of the reactor, wherein said injector device (8) comprises a duct (841 ) for said precursor gas, characterized by comprising a core (845) inside of and preferably concentric to said duct (841 ), said core (845) being preferably adapted to perform repeatedly a short reciprocating axial motion.

27. Reactor according to claim 26, wherein said core (845) ends before said duct (841).

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