Wafer boat system

Abstract

To provide a wafer boat system.SOLUTION: 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 shell connecting the first end member with the second end member, at least three circumferentially spaced apart axial series of ring support slots being provided to the shell, the ring support slots defining axially spaced apart holder ring positions; and a plurality of holder rings each engageable with the ring support slots to position the holder ring in the carrier at one of the holder ring positions, the holder ring being configured to support a wafer in the carrier. The shell circumferentially interconnects the axial series of slots, and axial series of gas transmission openings are formed in the shell between the axial series of slots.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] FIELD OF THEINVENTION The present invention relates to a wafer boat system comprising a carrier and a plurality of holder rings. The present invention further relates to the combination of such a carrier, such a holder ring, and a wafer boat system with an apparatus constructed and arranged to process a plurality of substrates. [Background technology]

[0002] Background of the disclosure Wafer boats are known for use in batch processing of semiconductor wafers, such as for deposition on the wafers. Wafer boats are typically primarily cylindrical structures capable of receiving multiple circular wafers spaced axially apart. The cylindrical axis of the wafer boat may be oriented vertically such that the wafers extend primarily horizontally.

[0003] US Patent No. 6,287,112 B1 describes the general problem that process gases may be non-uniform across the wafer surface when delivered 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 Patent No. 6,287,112 B1 also discusses the possible use of rings to enhance uniformity. In some variations, the wafer may be supported on such a ring, such that the ring may be considered as a holder ring.

[0004] While past developments have contributed to improved deposition uniformity across the wafer surface, further improvements remain desirable, while wafer processing is desired to be efficient. Summary of the Invention [Problem to be solved by the invention]

[0005] Disclosure Summary To improve deposition uniformity across the wafer surface while maintaining or improving wafer processing efficiency, aspects of the present invention provide a wafer boat system. [Means for solving the problem]

[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 with the second end member, wherein a series of at least three circumferentially spaced axial ring support slots are provided in the shell, the ring support slots defining axially spaced holder ring positions.

[0007] The wafer boat system includes a plurality of holder rings, each engageable with a ring support slot to position the holder ring at one of the holder ring positions within the carrier, the holder rings being configured to support a wafer within the carrier.

[0008] The shell circumferentially interconnects a series of axial slots and a series of axial gas permeable openings are formed in the shell between the series of axial slots.

[0009] Advantageously, the shell can eliminate the need for rods found in conventional wafer boat designs, such as those in U.S. Pat. No. 6,287,112 B1, thereby facilitating greater uniformity of deposition. In this regard, conventional rods are believed to typically result in non-uniformity, particularly due to the rods being relatively localized along the periphery of the wafer during use and disposed relatively radially close to the edge of the wafer. In contrast, the effect of the shell on deposition can be more distributed around the circumference and generally reduced, particularly due to the potentially larger radial distance of the shell relative to the wafer compared to the radial distance of a conventional rod relative to the wafer.

[0010] On the other hand, it has been found that the structural performance, e.g., stiffness and / or strength, of the carrier with the shell can be essentially maintained or improved compared to conventional carrier designs with rods. Without wishing to be bound by theory, it is believed that the maintained or improved structural performance may be particularly associated with a shell that circumferentially interconnects different axial series of slots, allowing the axial series of slots to derive stability and strength from each other through the shell, particularly at numerous axial positions between the first and second end members. Gas permeable openings in the shell facilitate the movement of process gas toward the wafer, while still allowing the shell to circumferentially interconnect the axial series of slots. During use, the holder ring with the wafer supported thereon can, for example, automatically move into or out of the carrier, thereby promoting efficiency. In contrast, the shell may allow transverse access into the carrier, specifically between two of the axial series of slots, as further described elsewhere herein.

[0011] Further aspects provide a carrier expressly configured for use as a carrier of a wafer boat system as described herein, and a holder ring expressly configured for use as one of the holder rings of a wafer boat system as described herein, The advantages of such a carrier and such holder ring correspond to those described above for a wafer boat system, in particular in the sense that such a carrier and / or such holder ring can be used to form such a wafer boat system or a similar wafer boat system.

[0012] A still further aspect provides a combination of a wafer boat system as described herein with 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 off the process chamber while supporting the wafer boat system with a plurality of substrates therein. Such a combination advantageously allows the wafer boat system to be used for batch processing of semiconductor wafers, for example for deposition on wafers as substrates. In this way, the described advantages of improved uniformity can be exploited in a particularly relatively efficient manner. Advantageously, the apparatus may be of a type known in this way, so that the advantages of the wafer boat system can be exploited without necessarily requiring adaptation of the apparatus. Thereby, for example, the outer dimensions of the carrier of the present wafer boat system may substantially correspond to the outer dimensions of known carriers for use in such apparatus.

[0013] As will be further explained in the following detailed description, optional advantageous elaborations of the above aspects are provided by the subject matter of the dependent claims.

[0014] This Summary is provided to introduce a selection of concepts in a simplified form that are described in more detail below in the Detailed Description of Example Embodiments of the Disclosure. This Summary is not intended to identify 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.

[0015] BRIEF DESCRIPTION OF THE DRAWINGS The present invention will be further described below using the embodiment examples and drawings. The drawings are schematic and merely show examples. In the drawings, corresponding elements are provided with corresponding reference symbols. For clarity of the drawings, the reference symbols for some elements may be omitted in some drawings, for example, when the presence of those elements is otherwise clear from the same or similar elements provided with the reference symbols in the same or similar drawings. Although reference is made to the drawings showing the examples, the description of the embodiments herein may also be understood independently of the drawings, and it is to be understood that the described embodiments may be variously applied in combination with or without one or more other embodiments.

[0016] In the drawings the following is shown: [Brief description of the drawings]

[0017] [Figure 1] FIG. 1 shows a perspective view of a carrier without a holder ring. [Diagram 2] FIG. 2 shows a perspective view of the carrier of FIG. 1 with a holder ring. [Diagram 3] FIG. 3 shows a perspective view of one of the holder rings. [Figure 4] 4 and 5 show a cross-sectional perspective view and a cross-sectional top view, respectively, of the carrier with the holder ring of FIG. 2, specifically showing an axial section of the carrier with the holder ring including the second end member. [Diagram 5] 4 and 5 show a cross-sectional perspective view and a cross-sectional top view, respectively, of the carrier with the holder ring of FIG. 2, specifically showing an axial section of the carrier with the holder ring including the second end member. [Figure 6] FIG. 6 shows a highly schematic cross-sectional side view of an apparatus having a wafer boat system. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] It will be appreciated that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale, for example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help improve understanding of the illustrated embodiments of the present disclosure.

[0019] DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS Although certain specific embodiments and examples are disclosed below, it will be understood by those skilled in the art that the invention extends beyond the specifically disclosed embodiments and / or uses of the invention, and obvious modifications and equivalents thereof, and therefore it is not intended that the scope of the disclosed invention should be limited by the specific disclosed embodiments described below.

[0020] The illustrations presented herein are not meant to be actual representations of any particular materials, structures, or devices, but merely idealized representations used to describe embodiments of the present disclosure.

[0021] The particular implementations shown and described are illustrative of the invention and its best mode and are not intended to otherwise limit the scope of aspects and implementations in any way. Indeed, for the sake of brevity, conventional manufacturing, association, preparation, and other functional aspects of the system may not be described in detail. Furthermore, the connecting lines shown in the various figures are intended to represent example functional relationships and / or physical couplings between the various elements. Many alternative or additional functional relationships or physical connections may be present in an actual system and / or may not be present in some embodiments.

[0022] It should be understood that the configurations and / or approaches described herein are exemplary in nature, and that these specific embodiments or examples are not to be construed in a limiting sense, as numerous variations are possible. The specific routines or methods described herein may represent one or more of any number of processing strategies. Thus, the various illustrated operations may be performed in the order illustrated, in other orders, or omitted in some cases.

[0023] The subject matter of the present disclosure includes all novel and non-obvious combinations and subcombinations of the various processes, systems, and configurations, and other features, functions, operations and / or properties disclosed herein, as well as all equivalents.

[0024] The figure illustrates a wafer boat system 1 comprising a carrier 2 and a plurality of holder rings 7. The carrier 2 extends along a carrier axis C and comprises 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 shell 4 connecting the first end member 3a with the second end member 3b.

[0025] The carrier 2 may have a substantially cylindrical shape, with the first end member 3a and the second end member 3b defining substantially circular end faces of the substantially cylindrical shape, and the carrier axis C corresponding to the cylinder axis of the substantially cylindrical shape. Nevertheless, as further described elsewhere herein, it will be appreciated that various openings may be provided in or to the carrier 2 such that the carrier 2 need not form a perfect cylinder. The support legs may extend from a bottom side of the second end member 3b. The carrier 2 may be made from materials known as such for wafer boats, for example, from quartz glass, also known as fused quartz or fused quartz.

[0026] A series of at least three circumferentially spaced axially spaced apart ring support slots 6 5a, 5b, 5c are provided in the shell 4 defining axially spaced apart holder ring positions. Preferably, the ring support slots 6 may be formed as openings or recesses in the shell 4. Alternatively, or additionally, one or more of the ring support slots may be formed between projections extending radially inwardly from the shell 4.

[0027] The holder rings 7 are each engageable with a ring support slot 6 to position the holder ring 7 in the carrier 2 at one of the holder ring positions. In addition, as further described elsewhere herein, at a circumferential position S corresponding to the ring support slot 6, the outer diameter RO of the holder ring 7 may be relatively large, e.g., locally equal to the maximum outer diameter ROmax of the holder ring 7. The design of the slots 6 and the portion of the holder ring 7 intended to engage with the slots 6 preferably takes into account the transverse direction T in which the holder ring 7 may be moved into or out of the carrier 2. For a relatively secure engagement of the holder ring 7 with the slots 6, one or more mutually engageable retaining structures, such as ridges and / or grooves, may be provided on the holder ring 7 and on one or more of the respective slots 6, such that when mutually engaged, the retaining structures are arranged to resist accidental transverse movement of the holder ring 7 out of the carrier 2, while still allowing intentional movement of the holder ring 7 out of the carrier 2, e.g., by slightly lifting the holder ring 7 relative to the carrier 2, thereby disengaging the retaining structures.

[0028] The holder ring 7 is configured to support the wafer 8 within the carrier 2, at least when the holder ring 7 is positioned within the carrier 2. In this manner, the wafer 8 may be supported within the carrier 2 without having direct contact between the wafer and the carrier 2.

[0029] The shell 4 circumferentially interconnects the axial series of slots 5a, 5b, 5c. Specifically, the interconnections of the shell 4 provide force transmission between the axial series of slots 5a, 5b, 5c along a circumferential direction as defined relative to the carrier axis C, thereby enabling mutual reinforcement between different axial series of slots 5a, 5b, 5c through the shell 4. The circumferential interconnections of the axial series of slots 5a, 5b, 5c by the shell 4 are preferably substantially distributed over an axial range corresponding to the axial range of the axial series of slots 5a, 5b, 5c.

[0030] A series of axial 9a, 9b gas-permeable openings 10 are formed in the shell 4 between the series of axial slots 5a, 5b, 5c. Preferably, these gas-permeable openings 10 are formed as elongated openings having a relatively small axial dimension or width and extending mainly in the circumferential direction. The circumferential interconnection of the series of axial slots 5a, 5b, 5c by the shell 4 can then be realized relatively effectively between the gas-permeable openings 10, in particular by means of an arcuate narrow beam-like section of the shell 4, while still allowing a relatively large total surface area of ​​the gas-permeable openings 10. As a result, the gas-permeable openings 10 preferably extend along a relatively large circumferential section of the shell 4 between the series of axial slots 5a, 5b, 5c, corresponding, for example, to at least 80% or at least 90% of the circumferential distance between the series of axial slots 5a, 5b, 5c.

[0031] In some embodiments, the shell 4 is circumferentially joined at two external slots 5a, 5b of the axial series of slots to allow the holder ring 7 and wafer 8 to move into or out of the carrier 2 between the two external axial series of slots 5a, 5b in a transverse direction T relative to the carrier 2.

[0032] In this way, such movement of the holder ring 7 and the wafer 8 can be substantially unobstructed by the shell 4, in particular while the shell 4 can still circumferentially interconnect the axial series of slots 5a, 5b, 5c. In particular, the outer slots 5a, 5b of the axial series of slots may therefore be interconnected by the shell 4 via a further or inner slot 5c of the axial series of slots. In this respect, it will be appreciated that the axial series of slots 5a, 5b may be referred to as outer slots as opposed to inner slots 5c, essentially taking into account their circumferential position with respect to the shell 4, while each of the axial series of slots 5a, 5b, 5c may still be at equal radial positions relative to one another with respect to the carrier axis C.

[0033] In some embodiments, the two series of external axial slots 5a, 5b are formed as toothed edges of the shell 4, each having an axial series of teeth 11 with interdental spaces 12 between the teeth 11 which form the respective slot 6.

[0034] In this way, the series of two external axial slots 5a, 5b can be formed particularly effectively, allowing not only the engagement of the holder ring 7 but also a transverse movement of the holder ring 7 into or out of the carrier 2, while still allowing a relatively good separation from the wafer 8 of the engagement between the holder ring 7 and the series of external axial slots 5a, 5b.

[0035] In some embodiments, each of the holder rings 7 has an annular body 13. In particular, the holder rings 7 may be substantially formed by the annular body 13, apart from optional ring protrusions 14 described elsewhere herein. The annular body 13 may be formed as a flat disk, for example having a thickness similar to that of the wafer 8, thereby being relatively compact in terms of axial dimension and thus allowing for gas transmission between the holder rings 7, while still allowing for a relatively large number of holder rings 7 in the carrier 2.

[0036] In some embodiments, the outer radius RO of the holder ring 7, and in particular the outer radius RO of the annular body 13, varies along its circumference between a maximum outer radius ROmax and a minimum outer radius ROmin. As will be further explained elsewhere herein, various advantages can be obtained by such a variable outer radius RO. In a general sense, such a variable outer radius RO allows taking into account the potential effect of the carrier 2 on the deposition uniformity, in a compensatory manner that promotes a particularly high level of deposition uniformity, while also taking into account structural and spatial constraints. In this respect, without wishing to be bound by theory, it is believed that the effect of surrounding structures such as the holder ring and the carrier on the uniformity of the deposition on the wafer may depend at least in part not only on the local surface area of ​​those structures, but also on the distance between those structures and the edge of the wafer 8. Therefore, for a relatively uniform deposition, in particular with respect to the radial direction, it is preferred that the surfaces of such structures are 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 effect of the surrounding structures on the deposition is similar all along the circumference of the wafer 8.

[0037] In some embodiments, the outer radius RO is smaller than the maximum outer radius ROmax and preferably larger than the minimum outer radius ROmin at circumferential positions G corresponding to the gas permeable openings 10 when the holder ring 7 engages with the ring support slots 6. Since the gas permeable openings 10 extend into the shell 4, which interconnects a series of axial slots 5a, 5b, 5c, some material of the shell 4 may be present at these positions G and affect the deposition uniformity. By having the outer radius RO smaller than the maximum outer radius ROmax at these positions G, the ring 7 can essentially provide at least partial compensation of local potential effects from the shell 4. On the other hand, if the outer radius RO at these positions G is larger than the minimum outer radius ROmin, the compensation effect, as described elsewhere herein, can be evaluated relatively well, specifically being relatively moderate, compared to the possible larger effect at positions S of the slots 6.

[0038] In some embodiments, the outer radius RO is greater than the minimum outer radius ROmin and preferably less than or equal to the maximum outer radius ROmax at circumferential positions F that are not radially adjacent to the shell 4 when the holder ring 7 engages the ring support slots 6. In this way, the effect of the holder ring 7 on the deposition uniformity can be greater at positions F where the shell 4 has no effect on the deposition uniformity. Therefore, the combined effect of the shell 4 and the holder ring 7 on the local deposition uniformity can be approximately the same all along the circumference of the wafer 8. If the outer radius RO at positions F is less than the maximum outer radius ROmax, the outer radius RO at these positions F can still be moderated relatively well.

[0039] In some embodiments, the outer radius RO at a circumferential position F that is not radially adjacent to the shell 4 is larger than the outer radius RO at a circumferential position G that corresponds to the gas permeation openings 10. In this way, essentially the surface area of ​​the holder ring 7 at said circumferential position F can therefore be similar to the combined surface area of ​​the holder ring 7 and the gas permeation openings 10 at said circumferential position G, which can promote a particularly uniform deposition.

[0040] In some embodiments, the maximum outer radius ROmax is present at a circumferential position S corresponding to the ring support slot 6, allowing the holder ring 7, specifically the annular body 13, to extend into and / or engage with the ring support slot 6. A relatively stable and reliable engagement can thus be obtained without necessarily requiring a large local surface area of ​​the carrier 2 and / or the holder ring 7, specifically close to the wafer 8. In other words, the engagement between the holder ring 7 and the carrier 2 can be relatively well spaced from the wafer 8, thereby facilitating a relatively high level of deposition uniformity.

[0041] In some embodiments, the minimum outer radius ROmin is present at a circumferential position S that corresponds to one or more of the ring support slots 6, in particular at a circumferential position that is circumferentially between one or more of the ring support slots 6 and an adjacent one of the gas permeation openings 10. In this way, the minimum outer radius ROmin that is essentially present between the ring support slots 6 and the gas permeation openings 10 can provide a locally reduced surface area of ​​the holder ring 7, which can at least partially compensate for the local absence of gas permeation through the shell 4, thus promoting a particularly uniform deposition. Although in FIG. 5 as an example, a minimum outer radius ROmin is shown to be present at each of the three positions S, it will be appreciated that the minimum outer radius ROmin may alternatively be present only at one or some of these positions S, while in other such positions the local outer radius RO may, for example, be slightly larger than the minimum outer radius ROmin.

[0042] In some embodiments, gas transmission openings 10 are disposed axially between the holder ring positions, i.e., between the positions at which the holder ring 7 may be positioned as defined by the ring support slots 6. In this manner, gas transmission openings 10 may be axially aligned with the wafer 8 on the holder ring 7, thereby facilitating relatively free movement of gas to the wafer 8.

[0043] In some embodiments, the shell 4 has a uniform thickness apart from the slots 6 and the gas permeable openings 10. In this manner, construction of the shell may be relatively simple. Of course, for example, in view of FIG. 1, elements of the carrier 6 may nevertheless extend radially inwardly from the shell 4, for example where the shell 4 connects with the end members 3a, 3b.

[0044] In some embodiments, the system 1 is configured such that the engaged holder ring 7 is spaced from the shell 4 except for the ring support slots 6, which can promote a relatively uniform transfer of gas to the wafer 8.

[0045] In some embodiments, the shell 4 is connected to the first and second end members 3a, 4a at their respective outer edges to form a cylindrical wall section of the carrier 2. In this manner, the shape of the shell 4 may essentially follow the circular edge of the wafer 8 such that the shell 4 can be radially spaced from the wafer 8 in a substantially uniform manner about the circumference. Nevertheless, as explained elsewhere herein, the shell 4 preferably does not extend along the complete circumference of the wafer 8 such that the holder ring 7 and wafer 8 can be moved relatively easily into and out of the carrier 2 in the transverse direction T.

[0046] In some embodiments, the holder rings 7 each have a ring protrusion 14 that protrudes from the annular body 13. In some embodiments, the ring protrusion 14 is disposed to contact the wafer 8 and space the wafer 8 away from the annular body 13 when the wafer 8 is supported by the holder rings 7 in the carrier 2.

[0047] Such a ring protrusion may advantageously eliminate the need for direct wafer contact with the carrier, which could otherwise contribute to non-uniformity, while by spacing the wafer away from the annular body, the ring protrusion allows an end effector of a wafer positioning robot to reach underneath the supported wafer without interference from the annular body.

[0048] In some embodiments, at the ring protrusion 14, the inner radius RI of the annular body 13 is locally enlarged, in particular increased compared to the circumferential average or median value of the inner radius RI of the annular body 13. In this way, local non-uniformity effects from the presence of the ring protrusion 14 may be at least partially compensated for by the locally reduced surface area of ​​the annular body 13.

[0049] 6 illustrates a possible combination of a wafer boat system 1 as described herein with an apparatus 15 constructed and arranged to process a plurality of substrates, specifically wafers 8. The apparatus 15 may be of a type known as such and includes a process tube 16 creating a process chamber 17 and a door 18 configured to close off the process chamber 17 while supporting the wafer boat system 1 having a plurality of substrates, specifically wafers 8, therein.

[0050] In FIG. 6, for clarity of the drawing, the wafer boat system 1 is shown very diagrammatically and does not show, for example, the engagement between the carrier 2, the holder ring 7, and the wafer 8, although it will be appreciated that the wafer system 1 of FIG. 6 may be essentially configured as shown in FIGS. 1-5, by way of example only.

[0051] The present invention has been described herein using example embodiments and drawings, which do not limit the scope of the invention as defined by the claims, within which numerous variations, combinations and extensions are possible, as would be apparent to one of ordinary skill in the art having the benefit of this disclosure. [Explanation of symbols]

[0052] List of reference symbols 1. Wafer Boat System 2. Career 3a. First end member 3b. Second end member 4. Shell 5a. A series of external axial ring support slots 5b. A series of external axial ring support slots 5c. A series of internal axial ring support slots 6. Ring support slot 7. Holder ring 8. Wafer 9a. A series of axial gas permeable openings 9b. A series of axial gas permeable openings 10. Gas permeable openings 11. Teeth 12. Interdental Spaces 13. Annular body 14. Ring protrusion 15. Equipment 16. Process tube 17. Process chamber 18. Door C. Carrier axis F. Circumferential locations that are not radially adjacent to the shell G. Circumferential location corresponding to gas permeable opening RI. Inner radius RO.Outer radius ROmax. Maximum outer radius ROmin. Minimum outer radius S. Circumferential position corresponding to the ring support slot T. Transverse

Claims

1. 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 said carrier, a second end member at a second axial end of said carrier, and a shell connecting said first end member with said second end member, a series of at least three circumferentially spaced axial ring support slots provided in said shell, said ring support slots defining axially spaced holder ring positions; a plurality of holder rings, each engageable with the ring support slot to position the holder ring in one of the holder ring positions within the carrier, the holder rings configured to support a wafer within the carrier; The wafer boat system, wherein the shell circumferentially interconnects the axial series of slots, and a series of axial gas permeable openings are formed in the shell between the axial series of slots.

2. 2. The wafer boat system of claim 1, wherein the shell is circumferentially coupled at two outer slots of the axial series of slots to enable a holder ring and wafers to be moved into or out of the carrier in a transverse direction relative to the carrier between the series of the two outer axial slots.

3. 3. The wafer boat system of claim 2, wherein the two series of external axial slots are formed as toothed edges of the shell, each toothed edge having an axial series of teeth with inter-tooth spaces between the teeth, the inter-tooth spaces defining a respective one of the slots.

4. 2. The wafer boat system of claim 1, wherein an outer radius of the holder ring varies along its circumference between a maximum outer radius and a minimum outer radius, and wherein, when the holder ring engages the ring support slots, at a circumferential location corresponding to the gas permeable opening, the outer radius is less than the maximum outer radius and preferably greater than the minimum outer radius.

5. 5. The wafer boat system of claim 4, wherein, when said holder ring engages said ring support slots, said outer radius is greater than said minimum outer radius and preferably less than or equal to said maximum outer radius at a circumferential location not radially adjacent said shell.

6. 6. The wafer boat system of claim 5, wherein the outer radius at the circumferential location not radially adjacent the shell is greater than the outer radius at the circumferential location corresponding to the gas permeable opening.

7. 5. The wafer boat system of claim 4, wherein the minimum outer radius is at an adjacent circumferential position corresponding to one or more of the ring support slots, specifically, at a circumferential position that is circumferentially between one or more of the ring support slots and adjacent ones of the gas permeation openings.

8. The wafer boat system of claim 1 , wherein the gas transmission openings are disposed axially between the holder ring positions.

9. 2. The wafer boat system of claim 1, wherein said shell has a uniform thickness apart from said slots and said gas transmission openings.

10. 2. The wafer boat system of claim 1, wherein the engaged holder ring is configured to be spaced from the shell except for the ring support slot.

11. 2. The wafer boat system of claim 1 , wherein the shell is connected to the first and second end members at outer edges of each of the first and second end members to form a cylindrical wall section of the carrier.

12. each of the holder rings has an annular body and a ring protrusion protruding from the annular body, the ring protrusion disposed to contact the wafer and space the wafer away from the annular body when the wafer is supported by the holder ring in the carrier; 2. The wafer boat system of claim 1, wherein at the ring protrusion, an inner radius of the annular body is locally enlarged, specifically larger than a circumferential average or median value of the inner radius of the annular body.

13. A carrier explicitly configured for use as a carrier for a wafer boat system according to any one of claims 1 to 12.

14. A holder ring explicitly configured for use as one of said holder rings of a wafer boat system according to any one of claims 1 to 12.

15. 13. A combination of the wafer boat system of claim 1 with an apparatus constructed and arranged to process a plurality of substrates, the apparatus comprising: a process tube creating a process chamber; a door configured to support the wafer boat system having a plurality of substrates therein while enclosing the process chamber.

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