Gas inlet assembly for epitaxial reactor

Abstract

A gas inlet assembly for a reactor (10) for epitaxial growth of semiconductor wafers, the gas inlet assembly comprising: an inlet (12) for introduction of process gases into the reactor (10); a gas conduit (25) having a first end (26) arranged to be connected to a growth chamber of the reactor (10) and a second end (27) arranged adjacent to the inlet (12) to provide fluid communication between the inlet (12) and the growth chamber (16); and a sealing device (30) attached to the inlet (12) and to the second end (27) of the gas conduit (25) to provide a gastight barrier therebetween, the sealing device (30) being configured to allow movement of the second end (27) of the gas conduit (25) in relation to the inlet (12).

Description

GAS INLET ASSEMBLY FOR EPITAXIAL REACTORCross Reference to Related Applications

[0001] This application is based on and claims priority to Swedish Application No. 2451083-6, filed November 4, 2024, the entire contents of which is incorporated by reference herein as if expressly set forth in its respective entirety herein.Technical Field

[0002] The present invention relates to a gas inlet assembly for reactors for epitaxial growth of semiconductor wafers. More specifically, it relates to a sealing device for obtaining gastight connection between the gas inlet and the growth chamber of an epitaxial reactor. Background

[0003] Silicon carbide is becoming a more and more important semiconductor material, replacing silicon in important applications. High-quality silicon carbide is produced in an epitaxial process at high temperature in a graphite reactor by means of chemical vapor deposition (CVD). A precursor gas is introduced in the reactor and undergoes a chemical reaction upon contact with a thin substrate or wafer. The high-quality silicon carbide is thus formed on top of the wafer, also made of silicon carbide.

[0004] The precursor gas is typically introduced through an inlet and is then directed through a liner funnel to reach the growth chamber, as shown in e.g. US2015013595A1. Tire liner funnel ensures that the precursor gas does not leak into the space surrounding the growth chamber. Another example is a feed pipe for a gas inlet to a CVD furnace as shown in US20070204848A1.

[0005] In MOCVD / CVD / VPE reactors for high temperatures of up to 1800 °C, made for epitaxial growth of homoepitaxy SiC with 4H crystal orientation, the substrate holder and growth chamber are typically made of graphite with a protective coating of for example, poly SiC or TaC. The graphite is typically heated by resistance or RF heaters to the target temperature between 1600 and 1800 °C. During operation of the reactor, the graphite is thus subjected to temperatures ranging from room temperature up to process temperatures between 1600-1800 °C. The coefficient of linear thermal expansion (CLTE) for graphite is typically in the range of 5,0–5,7 × 10-6 / K. This causes a linear expansion of the growth chamber by a factor of approximately 1,008–1,01. This leads to a relative expansion of a 400 mm long graphite susceptor at room temperature of about 3.2 to 4 mm at processtemperature. If the center of the growth chamber is fixed by its support in the center of the cooled reactor, both sides of the susceptor will expand by about 1.6 to 2 mm in this example.

[0006] Thermal expansion also affects the thickness of the graphite in the growth chamber. A susceptor with a thickness of 50 mm at room temperature will be 50.4 to 50.5 mm at process temperature. When located at the bottom of the cooled reactor cell it will move up by about 0.4 to 0.5 mm in this example.

[0007] The gas inlet which is integrated in the wall of the cooled reactor chamber is typically at a much lower temperature of about 20-100 °C. At this temperature there is nearly no expansion and therefore the distance from the gas inlet to the growth chamber will be reduced. Which means that the connection from the cold gas inlet to the hot zone will change its relative location by 1.6 to 2.0 mm in a horizontal direction and 0.4-0.5 mm in a vertical direction in the exemplary case.

[0008] In known reactors, there is a designed gap between the gas inlet and the growth chamber to allow for thermal expansion which means it is not gastight. Another known solution is a contact between the growth chamber and a liner tube made of quartz having a porous graphite insulation in contact directly with the hot growth chamber. The insulation is required as quartz can only withstand temperatures up to 1200 °C. But there is still always a gap at room temperature which results in a non-gastight situation.

[0009] Hence, there is a need to develop improved solutions for making the growth chamber gastight.Summary of Invention

[0010] An objective of the present disclosure is therefore to provide an improved gas inlet assembly for an epitaxial reactor to solve the problems identified above.

[0011] According to a first aspect of the present disclosure, there is provided a gas inlet assembly for a reactor for epitaxial growth of semiconductor wafers, the gas inlet assembly comprising: an inlet for introduction of process gases into the reactor; a gas conduit having a first end arranged to be connected to a growth chamber of the reactor and a second end arranged adjacent to the inlet to provide fluid communication between the inlet and the growth chamber; and a sealing device attached to the inlet and to the second end of the gas conduit to provide a gastight barrier therebetween, the sealing device being configured to allow movement of the second end of the gas conduit in relation to the inlet

[0012] By means of the sealing device, gas leakage between the process gas volume and outer reactor volume is prevented whilst at the same time allowing for thermal expansion of components exposed to high temperatures.

[0013] In one embodiment, the sealing device comprises a planar sheet having a throughgoing opening arranged to receive the second end of the gas conduit. The planar sheet acts as a gastight membrane which facilitates mounting to the respective components.

[0014] In one embodiment, the inlet comprises a flange extending in a direction substantially perpendicular to a longitudinal extension of the inlet and the gas conduit comprises a flange extending in a direction substantially perpendicular to a longitudinal extension of the gas conduit, wherein the flanges of the inlet and the gas conduit are arranged parallel and aligned with each other, and wherein the sealing device is attached to the respective flanges. This arrangement enables the sealing device to bend in the direction of the longitudinal extension of the gas conduit to follow the linear expansion, whilst maintaining rigidity in the perpendicular direction to properly align the gas conduit with the inlet.

[0015] In one embodiment, the sealing device is made of graphite foil or metal. The membrane is preferably made of a thin graphite foil (graphite thickness at equal to or less than 0.5 mm or below 0,5 mm) but it could also be made from a metal like stainless steel alloys or titanium alloys, with smaller thicknesses compared to a graphite foil. The relative softness of the graphite foil or metal enables deformation of the membrane without breaking and keeps the gastight characteristics.

[0016] In one embodiment, the inlet comprises at least one central conduit for directing process gases and a peripheral conduit surrounding the at least one central conduit for directing a cooling fluid therethrough. By means of the peripheral conduit, the inlet can be cooled to maintain a low temperature of the process gas until it reaches the growth chamber.

[0017] In one embodiment, the inlet extends through the gas conduit and terminates adjacent the first end of the gas conduit. Preferably, the inlet comprises a plurality of conduits arranged for introduction of separate process gases or a mixture of process gases. By extending the inlet and its plurality of conduits towards the growth chamber, separation of the process gases is achieved such that mixing only occurs when they reach the hot growth chamber.

[0018] In one embodiment, the inlet further comprises a conduit for introduction of purge gas, the purge gas conduit being separate from a main conduit for introduction of process gases. By means of the purge gas inlet, quick and efficient purging of the growth chamber is achieved.

[0019] In a second aspect of the present disclosure, there is provided a reactor for epitaxial growth of semiconductor wafers, comprising: an outlet for exhaust gases to exit the reactor; a growth chamber delimited by chamber walls; a wafer carrier positioned within the growth chamber for supporting a semiconductor wafer, the semiconductor wafer comprising an epitaxial surface side on which material deposition takes place; one or more heating elements; and a gas inlet assembly according to the first aspect.Brief Description of Drawings

[0020] The disclosure is now described, by way of example, with reference to the accompanying drawings, in which:Fig. la illustrates a schematic cross-sectional view of an epitaxial reactor;Fig. lb illustrates a close-up view of the reactor shown in Fig. la showing a gas inlet assembly according to the present disclosure in an initial state of the reactor at room temperature;Fig. 1c illustrates a close-up view of the gas inlet assembly in an operating state of the reactor at an elevated temperature;Fig. 2a illustrates a schematic cross-sectional view of an epitaxial reactor;Fig. 2b illustrates a close-up view of the reactor shown in Fig. 2a showing a gas inlet assembly according to one embodiment of the present disclosure;Fig. 3 illustrates a perspective view of a sealing device; andFig. 4 illustrates a perspective cross-sectional view of the sealing device in Fig. 3 mounted in a gas inlet assembly according to the present disclosure.Detailed Description

[0021] In the following, a detailed description of a gas inlet assembly for an epitaxial growth reactor according to the present disclosure is presented. In the drawing figures, like reference numerals designate identical or corresponding elements throughout the several figures. It will be appreciated that these figures are for illustration only and do not in any way restrict the scope of the present disclosure. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of ‘including’, ‘comprising’, or ‘having’ and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. Unless specified or limited otherwise, the terms ‘mounted’, ‘connected’, ‘supported’, and ‘coupled’ and variations thereof are used broadly and encompass both direct and indirectmountings, connections, supports, and couplings. Further, ‘connected’ and ‘coupled’ are not restricted to physical or mechanical connections or couplings.

[0022] Referring now to Fig. la, there is shown cross-sectional views of an epitaxial reactor 10 for growing semiconductor wafers. The reactor 10 comprises an outer enclosure 11 accommodating a hot cell or growth chamber 16 therein. The growth chamber 16 is delimited by a top wall 17 and a bottom wall 18. The walls 17, 18 are made by a very heat-resistant material, e.g. graphite. The growth chamber 16 is surrounded by an insulation 24 with an upper heater 21 and a lower heater 22 arranged to heat the growth chamber 16. A wafer carrier or susceptor 20 is arranged in or at the bottom wall 18. The wafer carrier 20 may be rotatably arranged flush with the bottom wall 18 or protruding from the latter. During operation, a semiconductor wafer is placed on the wafer carrier 20 to allow for epitaxial growth of semiconductor material through CVD by flowing process gases over the wafer and heating the growth chamber 16 to an operating temperature of about 1600-1800 °C.

[0023] To this end, the reactor 10 is provided with a gas inlet assembly comprising an inlet 12 for introducing process gases into the growth chamber 16 and an outlet 14 for evacuating gas from the growth chamber 16. The gas inlet assembly is mounted such that the inlet 12 extends through an opening in the enclosure 11 and is aligned with the growth chamber 16. To ensure that the process gases flow directly into the growth chamber 16, the gas inlet assembly further comprises a liner funnel or gas conduit 25 for providing fluid communication between the inlet 12 and the growth chamber 16. A first end 26 of the gas conduit 25 is arranged to be connected to the growth chamber 16 in a gastight manner whereas a second end 27 is arranged adjacent to the inlet 12 in such a manner that the second end 27 is allowed to move in relation to the inlet 12. As shown in Fig. lb, a portion of the second end 27 may extend into an interior channel or central conduit 15 of the inlet 12, but without being attached thereto.

[0024] To ensure a gastight connection between the inlet 12 and the gas conduit 25 and thereby prevent leakage of process gases, there is provided a membrane or sealing device 30 which is attached to the inlet 12 and to the second end 27 of the gas conduit 25. The sealing device 30 exhibits a degree of flexibility and resilience to allow relative movement between the inlet 12 and the gas conduit 25 through deformation of the sealing device 30. When the growth chamber 16, and to a lesser degree the gas conduit 25, undergo linear thermal expansion due to heating of the growth chamber 16 to elevated temperatures, the second end 27 of the gas conduit 25 is displaced left towards the inlet 12, as shown in Fig. 1c. At thesame time, the sealing device 30 moves with the second end 27 as it bends without breaking, keeping the gastight connection intact.

[0025] Referring to Fig. 3, the sealing device 30 may comprise a planar sheet with a throughgoing opening 32. The opening 32 is arranged to receive the second end 27 of the gas conduit 25 therethrough. For fastening, the sealing device 30 may comprise a plurality of holes 31 distributed around a peripheral edge of the planar sheet as well as around the opening 32. The sealing device 30 may be made of a thin graphite foil having a thickness of about 0.5 mm or less. Alternatively, the sealing device 30 may be made of a metal sheet, such as stainless steel or titanium alloy and having a smaller thickness compared to the graphite foil.

[0026] The attachment between the sealing device 30 and the inlet 12 may be achieved by means of a flange 13 extending outward from the inlet 12 in a direction perpendicular to the longitudinal extension of the inlet 12. The flange 13 may be a separate component attached to the inlet 12, e.g. by means of screws, or may be integrally formed with the inlet 12 in one piece. Similarly, the sealing device 30 may be attached to the second end 27 by means of a flange 28 extending outward from the second end 27 of the gas conduit 25 in a direction perpendicular to the longitudinal extension of the gas conduit 25. The sealing device 30 may then be attached to the respective flanges 13, 28 by fastening elements 33 (e.g. screws) extending through the holes 31 and suitable clamping members 29, 34 as shown in Fig. 4, thereby obtaining a gastight seal.

[0027] Due to its flexibility and resiliency, the sealing device 30 may bend or bulge in the direction of the longitudinal extension of the gas conduit 25 to follow the linear thermal expansion, as may be seen in Fig. 1c, whilst maintaining rigidity in the perpendicular direction to properly align the gas conduit 25 with the inlet 12. In order to accommodate the movement of the gas conduit 25 due to linear thermal expansion, there is foreseen a gap between the inlet 12 and the second end 27 of the gas conduit 25, as may be seen in Fig. lb. The orifice in the second end 27 may be beveled, with a corresponding shape provided in the inlet 12 to ensure that the two components mate when the gas conduit 25 moves towards the inlet 12.

[0028] The inlet 12 comprises a main, central conduit 15 for guiding process gases. Additionally, the inlet 12 may comprise a peripheral conduit 19 surrounding the central conduit 15. The peripheral conduit 19 is closed at one end and may be used to introduce a fluid (e.g. water) for cooling the inlet 12 and thus maintaining a low temperature of the process gases to prevent premature chemical reactions and deposition before reaching thegrowth chamber 16. The inlet 12 may also comprise an additional conduit 23 for introducing purge gas into the growth chamber 16, the purge gas conduit 23 being separate from the central conduit 15.

[0029] Referring now to Figs. 2a and 2b, there is shown an alternative embodiment of the inlet 12 with the remaining components similar or identical to the ones described above in relation to Figs, la and lb. In this embodiment, the inlet 12 extends substantially all the way through the gas conduit 25 and terminates adjacent the first end 26. The inlet 12 further comprises a plurality of conduits 15a-15d arranged for introduction of separate process gases or a mixture of process gases, each conduit 15a-15d extending substantially the entire length of the inlet 12. With this configuration, different process gases may be maintained separated from each other until they reach the growth chamber 16, to prevent premature chemical reactions through mixing. The conduits 15a-15d may have the same or different cross-sectional areas and the flow of process gas through each conduit 15a-15d may be controlled independently of each other through valves or similar to achieve a desired concentration and mixture of process gases.

[0030] Embodiments of an epitaxial reactor according to the present disclosure have been described. However, the person skilled in the art realizes that this can be varied within the scope of the appended claims without departing from the inventive idea.

[0031] All the described alternative embodiments above or parts of an embodiment can be freely combined without departing from the inventive idea as long as the combination is not contradictory.

Claims

CLAIMS1. A gas inlet assembly for a reactor (10) for epitaxial growth of semiconductor wafers, the gas inlet assembly comprising:an inlet (12) for introduction of process gases into the reactor (10);a gas conduit (25) having a first end (26) arranged to be connected to a growth chamber of the reactor (10) and a second end (27) arranged adjacent to the inlet (12) to provide fluid communication between the inlet (12) and the growth chamber (16); anda sealing device (30) attached to the inlet (12) and to the second end (27) of the gas conduit (25) to provide a gastight barrier therebetween, the sealing device (30) being configured to allow movement of the second end (27) of the gas conduit (25) in relation to the inlet (12).

2. The gas inlet assembly according to claim 1, wherein the sealing device (30) comprises a planar sheet having a throughgoing opening (32) arranged to receive the second end (27) of the gas conduit (25).

3. Tire gas inlet assembly according to claim 2, wherein the inlet (12) comprises a flange (13) extending in a direction substantially perpendicular to a longitudinal extension of the inlet (12) and the gas conduit (25) comprises a flange (28) extending in a direction substantially perpendicular to a longitudinal extension of the gas conduit (25), wherein the flanges (13, 28) of the inlet (12) and the gas conduit (25), respectively, are arranged parallel and aligned with each other, and wherein the sealing device (30) is attached to the respective flanges (13, 28).

4. Tire gas inlet assembly according to claim 2 or 3, wherein the sealing device (30) has a thickness equal to or less than 0.5 mm.

5. The gas inlet assembly according to any one of the preceding claims, wherein the sealing device (30) is made of graphite foil or metal.

6. The gas inlet assembly according to any one of the preceding claims, wherein the inlet (12) comprises at least one central conduit (15) for directing process gases and a peripheral conduit (19), surrounding the at least one central conduit (15), for directing a cooling fluid therethrough.

7. Tire gas inlet assembly according to any one of the preceding claims, wherein the inlet (12) extends through the gas conduit (25) and terminates adjacent the first end (26) of the gas conduit (25).

8. The gas inlet assembly according to claim 7, wherein the inlet (12) comprises a plurality of conduits (15a–15d) arranged for introduction of separate process gases or a mixture of process gases.

9. The gas inlet assembly according to any one of the preceding claims, wherein the inlet (12) further comprises a conduit (23) for introduction of purge gas, the purge gas conduit (23) being separate from a central conduit (15) for introduction of process gases.

10. A reactor (10) for epitaxial growth of semiconductor wafers, comprising:an outlet (14) for exhaust gases to exit the reactor (10);a growth chamber (16) delimited by chamber walls (17, 18);a wafer carrier (20) positioned within the growth chamber (16) for supporting a semiconductor wafer, the semiconductor wafer comprising an epitaxial surface side on which material deposition takes place;one or more heating elements (21, 22); anda gas inlet assembly according to any one of the preceding claims.

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