Wafer boat system

Abstract

A wafer boat system includes a carrier extending along a carrier axis and including a first end member at a first axial end of the carrier, a second end member at a second axial end of the carrier, and a housing connecting the first end member with the second end member, wherein at least three circumferentially spaced apart axial series of ring support slots are provided to the housing, the ring support slots defining axially spaced apart retainer ring positions; and a plurality of retainer rings each engageable with the ring support slots to position the retainer rings in the carrier at one of the retainer ring positions, where the retainer rings are configured to support a wafer in the carrier, where the housing circumferentially interconnects the axial series of slots, wherein an axial series of gas delivery openings are formed in the housing between the axial series of slots.

Description

Technical Field

[0001] The present invention relates to a wafer boat system comprising a carrier and a plurality of retainer rings. The present invention also relates to such a carrier, such a retainer ring and a combination of a wafer boat system and an apparatus constructed and arranged to process a plurality of substrates. Background Art

[0002] Wafer boats are known for batch processing of semiconductor wafers, for example for vapor deposition on wafers. Wafer boats are usually mainly cylindrical structures in which a plurality of axially spaced circular wafers can be accommodated. The cylindrical axis of the wafer boat can be oriented vertically so that the wafers extend mainly horizontally.

[0003] US 6,287,112 B1 explains the general problem that the wafer surface may be non-uniform when the process gas is supplied radially. In particular, so-called edge effects may occur, for example resulting in increased material deposition at the edge of the wafer compared to the center of the wafer. US 6,287,112 B1 also discusses the possible use of rings to increase uniformity. In some variants, the wafer may be supported on such a ring, so that the ring may be considered a retainer ring.

[0004] Although past developments have helped to increase the uniformity of deposition across the wafer surface, further improvements are needed. At the same time, it is desirable that wafer processing be efficient. Summary of the invention

[0005] In order to improve the uniformity of deposition on the wafer surface while maintaining or improving wafer processing efficiency, one aspect of the present invention provides a wafer boat system.

[0006] The wafer boat system includes a carrier extending along a carrier axis and including a first end member at a first axial end of the carrier, a second end member at a second axial end of the carrier, and a shell connecting the first end member to the second end member, wherein at least three circumferentially spaced axial series ring support grooves are provided to the shell, the ring support grooves defining axially spaced retainer ring positions.

[0007] The wafer boat system includes a plurality of retainer rings, each retainer ring engageable with a ring support groove to position the retainer ring in the carrier at one of the retainer ring positions, wherein the retainer ring is configured to support a wafer in the carrier.

[0008] The housing has a circumferentially interconnected axial series of grooves, wherein an axial series of gas delivery openings are formed in the housing between the axial series of grooves.

[0009] Advantageously, the housing may avoid the need for rods as found in conventional wafer boat designs such as US 6,287,112 B1, thereby promoting greater uniformity of deposition. In this regard, it is believed that conventional rods often lead to non-uniformity, particularly due to the rods being relatively localized along the circumference of the wafer during use and being arranged relatively close to the wafer edge in the radial direction. In contrast, the effect of the housing on deposition may be more distributed along the circumference and may be reduced overall due to the potentially greater radial distance of the housing to the wafer, particularly compared to the radial distance of conventional rods to the wafer.

[0010] At the same time, it has been found that the structural properties of a carrier with a housing, such as stiffness and / or strength, can be substantially maintained or improved compared to a conventional carrier design with a rod. Without wishing to be bound by theory, it is believed that the maintained or improved structural properties may be particularly relevant to a housing that circumferentially interconnects different axial series of grooves, allowing the axial series of grooves to gain stability and strength from each other through the housing, particularly at many axial positions between the first and second end members. Gas transfer openings in the housing facilitate movement of process gases toward the wafer while still allowing the housing to circumferentially interconnect the axial series of grooves. During use, a retainer ring on which a wafer is supported can, for example, be automatically moved in or out of the carrier, thereby improving efficiency. In addition, the housing may allow lateral access to the carrier, particularly between two of the axial series of grooves, as further explained elsewhere herein.

[0011] A further aspect provides for: a carrier, which is notably configured for use as a carrier for a wafer boat system as described herein; and a retainer ring, which is notably configured for use as one of the retainer rings for a wafer boat system as described herein. The advantages of such a carrier and such a retainer ring correspond to the above advantages for a wafer boat system, in particular in the sense that such or similar wafer boat systems can be formed using such a carrier and / or such a retainer ring.

[0012] Yet another aspect provides a combination of a wafer boat system as described herein and an apparatus constructed and arranged to process a plurality of substrates. The apparatus comprises: a process tube creating a process chamber; and a door configured to close the process chamber while supporting the wafer boat system with a plurality of substrates therein. This combination advantageously allows the wafer boat system to be used for batch processing of semiconductor wafers, for example for vapor deposition on wafers as substrates. In this way, the advantages of the improved uniformity described can be exploited, in particular relatively efficiently. Advantageously, the apparatus can be of a known type, so that the advantages of the wafer boat system can be exploited without the need for modifications to the apparatus. Furthermore, for example, the outer dimensions of the carrier of the present wafer boat system can correspond substantially to the outer dimensions of known carriers used in such an apparatus.

[0013] The subject matter of the dependent claims provides optional advantageous elaborations of the above-mentioned aspects, which will be further explained in the following detailed description.

[0014] This summary is provided to introduce some concepts in a simplified form. These concepts are further described in detail in the detailed description of the example embodiments disclosed below. This summary is not intended to identify the key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Below, the present invention will be further explained using examples of embodiments and drawings. The drawings are schematic and only show examples. In the drawings, corresponding elements have corresponding reference numerals. For the clarity of the drawings, the reference numerals of some elements may be omitted in some drawings, where the presence of these elements is obvious, such as in the same or similar drawings, where the same or similar elements have reference numerals. Although reference will be made to the drawings showing examples, the description of the embodiments herein may also be understood independently of the drawings, and it should be understood that the described embodiments may be applied differently in combination or not in combination with one or more other embodiments.

[0016] In the attached picture:

[0017] Figure 1 shows a perspective view of the carrier without the retainer ring;

[0018] Figure 2 Shown is a retainer ring Figure 1 A perspective view of a carrier;

[0019] Figure 3 A perspective view of one of the retainer rings is shown;

[0020] Figure 4 and Figure 5 They are shown respectively Figure 2 A cross-sectional perspective view and a cross-sectional top view of a carrier with a retainer ring, particularly showing an axial section of the carrier with a retainer ring including a second end member; and

[0021] Figure 6 A highly schematic cross-sectional side view of an apparatus having a wafer boat system is shown.

[0022] It should be understood that the elements in the drawings are shown for simplicity and clarity and are not necessarily drawn to scale. For example, the size of some elements in the drawings may be exaggerated relative to other elements to help improve the understanding of the illustrated embodiments of the present disclosure. DETAILED DESCRIPTION

[0023] Although certain embodiments and examples are disclosed below, those skilled in the art will appreciate that the invention extends beyond the specifically disclosed embodiments and / or uses of the invention and their obvious modifications and equivalents. Therefore, it is intended that the scope of the disclosed invention should not be limited by the specifically disclosed embodiments described below.

[0024] The illustrations presented herein are not meant to be actual views of any particular material, structure, or device but are merely idealized representations used to describe embodiments of the present disclosure.

[0025] The specific embodiments shown and described are illustrations of the present invention and its best mode and are not intended to limit the scope of these aspects and embodiments in any way. In fact, for the sake of brevity, the traditional manufacturing, connection, preparation and other functional aspects of the system may not be described in detail. In addition, the connecting lines shown in the various figures are intended to represent exemplary functional relationships and / or physical connections between various elements. Many alternative or additional functional relationships or physical connections may exist in actual systems, and / or may not exist in some embodiments.

[0026] It should be understood that the configuration and / or method described herein are exemplary in nature, and these specific embodiments or examples should not be considered restrictive, because many variations are possible. The specific routine or method described herein can represent one or more of any number of processing strategies. Therefore, the various actions shown can be performed in the order shown, in other orders, or omitted in some cases.

[0027] The subject matter of the present disclosure includes all novel and nonobvious combinations and subcombinations of the various processes, systems and configurations, and other features, functions, acts and / or properties disclosed herein, and any and all equivalents thereof.

[0028] The drawings show a wafer boat system 1 including a carrier 2 and a plurality of retainer rings 7. The carrier 2 extends along a carrier axis C and includes a first end member 3a at a first axial end of the carrier 2, a second end member 3b at a second axial end of the carrier 2, and a housing 4 connecting the first end member 3a and the second end member 3b.

[0029] The carrier 2 may have a generally cylindrical shape, wherein the first and second end members 3a, 3b define generally circular end faces of the generally cylindrical shape, and wherein the carrier axis C corresponds to the cylinder axis of the generally cylindrical shape. However, as further explained elsewhere herein, it should be understood that various openings may be provided in or to the carrier 2 such that the carrier 2 need not form a complete cylinder. The support legs may extend from the bottom side of the second end member 3b. The carrier 2 may be made of materials known for use in wafer boats, such as quartz glass, also known as fused quartz or fused silica.

[0030] At least three circumferentially spaced axial series 5a, 5b, 5c of ring support grooves 6 are provided to the housing 4, the ring support grooves 6 defining axially spaced retainer ring positions. Preferably, the ring support grooves 6 may be formed as openings or recesses in the housing 4. Alternatively or in addition, one or more ring support grooves may be formed between projections extending radially inwardly from the housing 4.

[0031] Each retainer ring 7 can engage with the ring support groove 6 to position the retainer ring 7 in the carrier 2 at one of the retainer ring positions. In addition, as further explained elsewhere herein, at the circumferential position S corresponding to the ring support groove 6, the outer diameter RO of the retainer ring 7 can be relatively large, such as locally equal to the maximum outer diameter ROmax of the retainer ring 7. The design of the groove 6 and the portion of the retainer ring 7 for engaging the groove 6 preferably takes into account the lateral direction T in which the retainer ring 7 can be moved into or out of the carrier 2. For relatively secure engagement of the retainer ring 7 with the groove 6, one or more mutually engageable retaining structures, such as ridges and / or grooves, can be provided for the retainer ring 7 and one or more corresponding grooves 6, and when mutually engaged, the retaining structures are arranged to prevent the retainer ring 7 from accidentally moving laterally out of the carrier 2, while still allowing the retainer ring 7 to be intentionally moved out of the carrier 2, such as by slightly lifting the retainer ring 7 relative to the carrier 2 to disengage the retaining structure.

[0032] The retainer ring 7 is configured to support the wafer 8 in the carrier 2 at least when the retainer ring 7 is positioned in the carrier 2. In this way, the wafer 8 can be supported in the carrier 2 without direct contact between the wafer and the carrier 2.

[0033] The housing 4 circumferentially interconnects the axial series of grooves 5a, 5b, 5c. In particular, the interconnected portion of the housing 4 provides force transmission between the axial series of grooves 5a, 5b, 5c along a circumferential direction defined relative to the carrier axis C, thereby allowing mutual reinforcement between different axial series of grooves 5a, 5b, 5c via the housing 4. The circumferential interconnection of the axial series of grooves 5a, 5b, 5c by the housing 4 is preferably substantially distributed over an axial range corresponding to the axial range of the axial series of grooves 5a, 5b, 5c.

[0034] The axial series 9a, 9b of gas transfer openings 10 are formed in the housing 4 between the axial series of grooves 5a, 5b, 5c. Preferably, such gas transfer openings 10 are formed as mainly circumferentially extending elongated openings, having a relatively small axial dimension or width. The circumferential interconnection of the axial series of grooves 5a, 5b, 5c by the housing 4 can then be achieved relatively efficiently between the gas transfer openings 10, in particular by the arcuate narrow beam-like portions of the housing 4, while still allowing a relatively large total surface area of ​​the gas transfer openings 10. Therefore, the gas transfer openings 10 preferably extend along a relatively large circumferential portion of the housing 4 between the axial series of grooves 5a, 5b, 5c, for example corresponding to at least 80% or at least 90% of the circumferential distance between the axial series of grooves 5a, 5b, 5c.

[0035] In an embodiment, the housing 4 is circumferentially defined at two outer axial series of grooves 5a, 5b of the axial series of grooves to allow the retainer ring 7 and the wafer 8 to be moved into or out of the carrier 2 between the two outer axial series of grooves 5a, 5b in a transverse direction T relative to the carrier 2.

[0036] In this way, such movement of the retainer ring 7 and the wafer 8 can be substantially unimpeded by the housing 4, in particular when the housing 4 can still circumferentially interconnect the axial series of grooves 5a, 5b, 5c. In particular, the outer axial series of grooves 5a, 5b of the axial series of grooves can thus be interconnected by the housing 4 via the other or inner axial series of grooves 5c of the axial series of grooves. In this regard, it should be understood that the axial series of grooves 5a, 5b can be referred to as the outer axial series of grooves, as opposed to the inner axial series of grooves 5c, mainly in view of their circumferential position relative to the housing 4, while each of the axial series of grooves 5a, 5b, 5c can still be in a mutually equal radial position relative to the carrier axis C.

[0037] In the embodiment, the two outer axial series of grooves 5 a, 5 b are formed as toothed edges of the housing 4 , each having an axial series of teeth 11 with inter-tooth spaces 12 between the teeth 11 , wherein the inter-tooth spaces 12 form the respective groove 6 .

[0038] In this way, the two outer axial series of grooves 5a, 5b can be formed particularly effectively, allowing the engagement of the retainer ring 7 and the lateral movement of the retainer ring 7 into or out of the carrier 2. At the same time, the engagement between the retainer ring 7 and the outer axial series of grooves 5a, 5b can still be relatively well spaced from the wafer 8.

[0039] In an embodiment, each retainer ring 7 has an annular body 13. In particular, apart from the optional annular protrusions 14 explained elsewhere herein, the retainer ring 7 may be substantially formed by the annular body 13. The annular body 13 may be formed as a flat disk, for example with a thickness similar to that of the wafer 8, thereby being relatively compact in terms of axial dimensions and thus allowing gas to be transferred between the retainer rings 7 while still allowing a relatively large number of retainer rings 7 in the carrier 2.

[0040] In an embodiment, the outer diameter RO of the retainer ring 7, in particular the annular body 13, varies along its circumference between a maximum outer diameter ROmax and a minimum outer diameter ROmin. Various advantages can be obtained by such a variable outer diameter RO, which will be further explained elsewhere herein. In a general sense, such a variable outer diameter RO allows the potential impact of the carrier 2 on the deposition uniformity to be taken into account, in particular in a compensating manner that promotes a high level of deposition uniformity, while also taking into account structural and spatial limitations. In this regard, without wishing to be bound by theory, it is believed that the impact of surrounding structures (such as retainer rings and carriers) on the deposition uniformity on the wafer may depend at least in part on the local surface area of ​​these structures and the distance between these structures and the edge of the wafer 8. Therefore, for relatively uniform deposition, in particular with respect to the radial direction, it is preferred that the surface area of ​​such structures is relatively small and / or relatively far away from the wafer 8. At the same time, in order to promote uniformity in the circumferential direction, it is preferred that the combined local impact of the surrounding structures on the deposition is similar along the entire circumference of the wafer 8.

[0041] In an embodiment, when the retainer ring 7 is engaged with the ring support groove 6, the outer diameter RO is less than the maximum outer diameter ROmax, and preferably greater than the minimum outer diameter ROmin, at circumferential positions G corresponding to the gas delivery openings 10. Since the gas delivery openings 10 extend in the housing 4, and the housing 4 interconnects the axial series of grooves 5a, 5b, 5c, some material of the housing 4 is present at these positions G, potentially having an impact on deposition uniformity. By making the outer diameter RO less than the maximum outer diameter ROmax at these positions G, the ring 7 can generally provide at least partial compensation for the local potential impact from the housing 4. At the same time, when the outer diameter RO at these positions G is greater than the minimum outer diameter ROmin, the compensating impact can be relatively well measured, especially relatively modest compared to the potentially larger impact at the positions S of the groove 6, as explained elsewhere herein.

[0042] In an embodiment, when the retainer ring 7 is engaged with the ring support groove 6, the outer diameter RO is greater than the minimum outer diameter ROmin, and preferably less than or equal to the maximum outer diameter ROmax, at circumferential positions F that are not radially adjacent to the housing 4. In this way, the influence of the retainer ring 7 on the deposition uniformity can be greater at the positions F where the housing 4 has no influence on the deposition uniformity. Therefore, the combined influence of the housing 4 and the retainer ring 7 on the local deposition uniformity can be approximately the same along the entire circumference of the wafer 8. When the outer diameter RO at the positions F is less than the maximum outer diameter ROmax, the outer diameter RO at these positions F can still be relatively well moderated.

[0043] In an embodiment, the outer diameter RO at a circumferential position F which is not radially adjacent to the housing 4 is greater than the outer diameter RO at a circumferential position G which corresponds to the gas transfer opening 10. In this way, a particularly uniform deposition can be promoted, mainly because the surface area of ​​the retainer ring 7 at said circumferential position F can thus be similar to the combined surface area of ​​the retainer ring 7 and the gas transfer opening 10 at said circumferential position G.

[0044] In an embodiment, the maximum outer diameter ROmax exists at a circumferential position S corresponding to the ring support groove 6 to allow the retainer ring 7, in particular the annular body 13, to extend into and / or engage the ring support groove 6. In this way, a relatively stable and secure engagement can be obtained, in particular without requiring a large local surface area of ​​the carrier 2 and / or the retainer ring 7 to be close to the wafer 8. In other words, the engagement between the retainer ring 7 and the carrier 2 can be relatively well spaced from the wafer 8, thereby promoting a relatively high level of deposition uniformity.

[0045] In an embodiment, the minimum outer diameter ROmin is present at adjacent circumferential positions S corresponding to the one or more ring support grooves 6, in particular at circumferential positions located circumferentially between the one or more ring support grooves 6 and adjacent gas transmission openings in the gas transmission openings 10. In this way, a particularly uniform deposition can be promoted, mainly because the presence of the minimum outer diameter ROmin between the ring support groove 6 and the gas transmission opening 10, resulting in a locally reduced surface area of ​​the retainer ring 7, can at least partially compensate for the local lack of gas transmission through the housing 4. Although in Figure 5 In the figure, as an example, it is shown that the minimum outer diameter ROmin exists at each of the three positions S, but it should be understood that, alternatively, the minimum outer diameter ROmin may exist only at one or some of these positions S, while at other such positions, the local outer diameter RO may be, for example, slightly larger than the minimum outer diameter ROmin.

[0046] In an embodiment, the gas delivery openings 10 are disposed axially between retainer ring locations, i.e., between locations where the retainer ring 7 may be positioned, as defined by the ring support grooves 6. In this manner, the gas delivery openings 10 may be axially aligned with the wafer 8 on the retainer ring 7, thereby facilitating relatively free movement of gas to the wafer 8.

[0047] In an embodiment, the housing 4 has a uniform thickness except for the slots 6 and the gas transfer openings 10. In this way, the construction of the housing can be relatively simple. It will be appreciated that, for example, Figure 1 However, elements of the carrier 6 may extend radially inwardly from the housing 4, for example where the housing 4 is connected to the end members 3a, 3b.

[0048] In an embodiment, the system 1 is configured such that the engaged retainer ring 7 is spaced apart from the housing 4 except at the ring support groove 6. Relatively uniform movement of gas to the wafer 8 may thereby be facilitated.

[0049] In an embodiment, the shell 4 is connected to the first and second end members 3a, 4a at their respective outer edges to form a cylindrical wall portion of the carrier 2. In this way, the shape of the shell 4 can substantially follow the circular edge of the wafer 8, so that the shell 4 can be radially spaced from the wafer 8 in a substantially uniform manner with respect to the circumferential direction. However, as explained elsewhere herein, the shell 4 preferably does not extend along the entire circumference of the wafer 8, so that the retainer ring 7 and the wafer 8 can be moved into and out of the carrier 2 in the transverse direction T relatively easily.

[0050] In an embodiment, each retainer ring 7 has a ring protrusion 14 protruding from the ring body. In an embodiment, when the wafer 8 is supported by the retainer ring 7 in the carrier 2, the ring protrusion 14 is arranged to contact the wafer 8 and space the wafer 8 from the ring body 13.

[0051] Such an annular protrusion can advantageously eliminate the need for direct contact between the wafer and the carrier, which would otherwise result in non-uniformity. At the same time, by spacing the wafer from the annular body, the annular protrusion allows the end effector of a wafer positioning robot to reach under the supported wafer without interference from the annular body.

[0052] In an embodiment, at the annular protrusion 14, the inner diameter RI of the annular body 13 is locally enlarged, in particular larger than the circumferential average or median value of the inner diameter RI of the annular body 13. In this way, the local adverse uniformity effects due to the presence of the annular protrusion 14 can be at least partially compensated by the locally reduced surface area of ​​the annular body 13.

[0053] Figure 6A possible combination of a wafer boat system 1 and an apparatus 15 as described herein is shown, the apparatus 15 being constructed and arranged to process a plurality of substrates, in particular wafers 8. The apparatus 15 may be of a known type and comprises: a process tube 16 creating a process chamber 17; and a door 18 configured to close the process chamber 17 while supporting the wafer boat system 1 with a plurality of substrates, in particular wafers 8, therein.

[0054] exist Figure 6 In the drawings, for the sake of clarity, the wafer boat system 1 is shown highly schematically, for example without showing the engagement between the carrier 2, the retainer ring 7 and the wafer 8, wherein it should be understood that, as an example, Figure 6 The chip system 1 in the embodiment can be basically as follows Figures 1 to 5 Configure as shown.

[0055] Although the present invention has been described herein using the examples of embodiments and drawings, these do not limit the scope of the invention which is determined by the claims. Many variations, combinations and extensions are possible within the scope, which will be apparent to those skilled in the art having benefit of this disclosure.

[0056] Reference numerals list

[0057] 1 Wafer Boat System

[0058] 2 Bearings

[0059] 3a First end member

[0060] 3b Second end member

[0061] 4 Housing

[0062] 5a External axial series ring support groove

[0063] 5b External axial series ring support groove

[0064] 5c Internal axial series ring support groove

[0065] 6 Ring support groove

[0066] 7 Retainer ring

[0067] 8 chips

[0068] 9a Axial series gas delivery openings

[0069] 9b Axial series gas delivery openings

[0070] 10 Gas delivery openings

[0071] 11 teeth

[0072] 12 Interdental Space

[0073] 13 Ring body

[0074] 14 Ring protrusion

[0075] 15 Equipment

[0076] 16 Processing tube

[0077] 17 Processing Room

[0078] 18 doors

[0079] C Bearing axis

[0080] F is not radially adjacent to the circumferential position of the shell

[0081] G corresponds to the circumferential position of the gas delivery opening

[0082] RI Inner Diameter

[0083] RO outer diameter

[0084] ROmax Maximum outer diameter

[0085] ROmin Minimum outer diameter

[0086] S corresponds to the circumferential position of the ring support groove

[0087] T Horizontal direction

Claims

1. A wafer boat system, comprising: - a carrier extending along a carrier axis and comprising a first end member at a first axial end of the carrier, a second end member at a second axial end of the carrier and a housing connecting the first end member with the second end member, wherein at least three circumferentially spaced axial series of ring support grooves are provided to the housing, the ring support grooves defining axially spaced retainer ring positions; and - a plurality of retainer rings, each retainer ring engageable with the ring support groove to position the retainer ring in the carrier at one of the retainer ring positions, wherein the retainer ring is configured to support a wafer in the carrier, Therein, the housing has a circumferentially interconnected axial series of slots, wherein an axial series of gas transfer openings are formed in the housing between the axial series of slots.

2. The wafer boat system of claim 1, wherein: The housing is circumferentially defined at two outer ones of the axial series of grooves to allow a retainer ring and wafer to be moved into or out of the carrier in a lateral direction relative to the carrier between the two outer ones of the axial series of grooves.

3. The wafer boat system of claim 2, wherein: The two outer axial series of grooves are formed as toothed edges of the housing, each toothed edge having an axial series of teeth with inter-tooth spaces between them, wherein the inter-tooth spaces form the respective grooves.

4. A wafer boat system according to any one of the preceding claims, wherein: When the retainer ring is engaged with the ring support groove, the outer diameter of the retainer ring varies along its circumference between a maximum outer diameter and a minimum outer diameter at a circumferential position corresponding to the gas delivery opening, wherein the outer diameter is smaller than the maximum outer diameter and preferably larger than the minimum outer diameter.

5. A wafer boat system according to claim 4 as appended to claim 2, wherein: When the retainer ring is engaged with the ring support groove, the outer diameter is greater than the minimum outer diameter and preferably less than or equal to the maximum outer diameter at a circumferential location not radially adjacent to the housing.

6. A wafer boat system according to claim 5 as appended to claim 4, wherein: The outer diameter at a circumferential position not radially adjacent to the housing is greater than the outer diameter at a circumferential position corresponding to the gas delivery opening.

7. The wafer boat system according to any one of claims 4 to 6, wherein: The minimum outer diameter exists at adjacent circumferential positions corresponding to one or more of the ring support grooves, in particular at a circumferential position circumferentially located between one or more of the ring support grooves and an adjacent one of the gas delivery openings.

8. A wafer boat system according to any one of the preceding claims, wherein: The gas delivery opening is disposed axially between the retainer ring locations.

9. A wafer boat system according to any one of the preceding claims, wherein: The housing has a uniform thickness except for the slots and the gas delivery openings.

10. A wafer boat system according to any one of the preceding claims, configured such that the engaged retainer ring is spaced apart from the housing except at the ring support groove.

11. The wafer boat system according to any one of the preceding claims, wherein: The housing is connected to the first and second end members at respective outer edges of the first and second end members to form a cylindrical wall portion of the carrier.

12. A wafer boat system according to any one of the preceding claims, wherein: Each retainer ring has an annular body and an annular protrusion protruding from the annular body, the annular protrusion being arranged to contact and space the wafer from the annular body when the wafer is supported by the retainer ring in the carrier, Therein, at the annular protrusion, the inner diameter of the annular body is locally enlarged, in particular, larger than a circumferential average value or a median value of the inner diameter of the annular body.

13. A carrier, notably configured for use as a carrier for a wafer boat system according to any one of the preceding claims.

14. A retainer ring, notably configured for use as one of the retainer rings of a wafer boat system according to any one of claims 1-12.

15. A wafer boat system according to any one of claims 1 to 12 in combination with an apparatus constructed and arranged to process a plurality of substrates, the apparatus comprising: - Process tubes to create process chambers; as well as - A door configured to close the processing chamber while supporting a wafer boat system having a plurality of substrates therein.

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