Cassette

Abstract

To reduce the amount of waste generated due to scraping of a support portion of a cassette by a wafer.SOLUTION: A cassette in which a plurality of wafers are accommodated includes a pair of side walls arranged to face each other, an upper end fixing portion that fixes the respective upper end portions of the pair of side walls, a lower end fixing portion that fixes the respective lower end portions of the pair of side walls, and a plurality of shelf portions that are spaced apart from each other along a vertical direction of each side wall and protrude from the inner surface of each side wall. Each of the plurality of shelf portions has a support portion that supports one wafer when the wafer is supported by the support portion. The support portion has a top surface that contacts one wafer, and the material constituting at least the top surface of the support portion is harder than the material of the pair of side walls.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a cassette in which a plurality of wafers are accommodated. [Background technology]

[0002] Semiconductor wafers (hereinafter simply referred to as wafers) used in manufacturing semiconductor device chips, etc., are generally manufactured by cutting cylindrical ingots with a wire saw. When using a wire saw, a range of the ingot thickness corresponding to the diameter of the wire saw (e.g., about 300 μm) is removed, and both sides of the wafer need to be flattened to remove unevenness formed on both sides of the cut wafer.

[0003] Therefore, when manufacturing wafers from an ingot using a wire saw, the thickness of the ingot to be removed per wafer is relatively large, which is uneconomical. Therefore, a method of manufacturing wafers from an ingot by using a laser beam instead of a wire saw has been proposed.

[0004] Specifically, by positioning the focal point of the laser beam at a predetermined depth in the ingot and relatively moving the ingot and the focal point, a mechanically weak peeling layer is formed at the predetermined depth in the ingot, and then the wafer is peeled off from the ingot at the peeling layer. Next, one side of the wafer corresponding to the peeling layer and the other side of the ingot are ground.

[0005] By sequentially repeating the laser processing, peeling, and grinding, multiple wafers are manufactured from the ingot (see, for example, Patent Document 1). The thickness of the peeled layer is about 60 μm, which is sufficiently smaller than the range of the thickness of the ingot removed when using a wire saw. Therefore, the volume of the ingot discarded when manufacturing one wafer can be reduced compared to when using a wire saw.

[0006] Each wafer produced from an ingot is housed in a cassette (see, for example, Patent Document 2). The cassette has a pair of side walls arranged opposite each other. Each side wall is formed, for example, from a synthetic resin, and a shelf or groove for supporting the wafer is formed on the inner surface of each side wall along the depth direction of the side wall. The wafers housed in the wafer cassette are supported by supports constituting the shelf or groove.

[0007] Normally, both sides of a commercially available single crystal silicon wafer are chamfered (also called beveled), but the outer periphery of the wafer immediately after it is manufactured through the above-mentioned laser processing, peeling, and grinding is not chamfered and is sharp. Therefore, when the wafer moves slightly inside the cassette during transportation, etc., the outer periphery of the wafer may scrape off the support portion.

[0008] Furthermore, when the wafers are formed from single crystal substrates of a hard material, such as silicon carbide (SiC) or gallium nitride (GaN), which are harder than single crystal silicon substrates, even if the wafers have chamfered portions, the support portions may be scraped off by the wafers as they move within the cassette.

[0009] The debris generated by scraping the cassette support may adhere to the wafer. If the debris adheres to the wafer, it may cause defects in processing the wafer or defects in the semiconductor device chips manufactured from the wafer. In addition, debris may fall off the cassettes transported in the clean room and contaminate the clean room. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] JP 2019-12765 A [Patent Document 2] Japanese Patent Application Publication No. 9-27543 Summary of the Invention [Problem to be solved by the invention]

[0011] The present invention has been made in view of the above problems, and has an object to reduce the amount of scraps generated when the support portion of the cassette is scraped by the wafer. [Means for solving the problem]

[0012] According to one aspect of the present invention, there is provided a cassette for accommodating a plurality of wafers, the cassette comprising a pair of side walls arranged to face each other, an upper end fixing portion for fixing each upper end of the pair of side walls, a lower end fixing portion for fixing each lower end of the pair of side walls, and a plurality of shelf portions provided at a distance from each other along the vertical direction of each side wall and each protruding from an inner surface of each side wall, each of the plurality of shelf portions having a support portion for supporting a single wafer, the support portion having a top surface that contacts the single wafer when the single wafer is supported by the support portion, and a material constituting at least the top surface of the support portion being harder than the material of the pair of side walls.

[0013] Preferably, each of the multiple shelf portions protrudes from the inner surface of each side wall and has a horizontal portion extending along a width direction perpendicular to the depth direction and up-down direction of the space defined by the pair of side walls, the upper end fixing portion and the lower end fixing portion, and a convex portion provided at the tip of the horizontal portion and protruding toward the upper end fixing portion, and the convex portion is the support portion that supports the single wafer.

[0014] In addition, preferably, each of the multiple shelf portions protrudes from the inner surface of each side wall and has a horizontal portion extending along a width direction perpendicular to the depth direction and the up-down direction of the space defined by the pair of side walls, the upper end fixed portion and the lower end fixed portion, and the horizontal portion is the support portion.

[0015] Preferably, the material constituting the top surface of the support includes metal, diamond, or hard ceramics, and the material constituting the pair of side walls is a synthetic resin.

[0016] Preferably, the material constituting each of the upper end fixing portion and the lower end fixing portion is a synthetic resin.

[0017] Preferably, the material constituting the top surface of the support is silicon carbide. Effect of the Invention

[0018] The support part of the cassette according to one embodiment of the present invention has a top surface that contacts one wafer, and at least the top surface of the support part is made of a material harder than the material of the pair of side walls. Therefore, the amount of scrap generated by the support part being scraped by the wafer can be reduced compared to when the top surface of the support part is made of the same material as the pair of side walls. [Brief description of the drawings]

[0019] [Figure 1] FIG. [Diagram 2] FIG. 2(A) is a front view of the cassette, and FIG. 2(B) is a rear view of the cassette. [Diagram 3] FIG. 13 is an enlarged perspective view of a plurality of shelves. [Figure 4] FIG. 2 is a partial cross-sectional side view of a side wall and multiple shelves. [Diagram 5] FIG. 2 is a cross-sectional view of one sidewall element. [Figure 6] FIG. 2 is a front view of a cassette containing a plurality of wafers. [Figure 7] FIG. 7(A) is a perspective view of the wafer, and FIG. 7(B) is a cross-sectional view of the wafer. [Figure 8] 13 is a partial cross-sectional side view of a side wall and a number of shelves of a cassette according to a first modified example. FIG. [Figure 9] 13 is a partial cross-sectional side view of a side wall and a number of shelves of a cassette according to a second modified example. FIG. [Figure 10] FIG. 13 is a partial cross-sectional side view of a side wall and a number of shelves of a cassette according to a third modified example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] An embodiment according to one aspect of the present invention will be described with reference to the accompanying drawings. Fig. 1 is a perspective view of a cassette 2, Fig. 2(A) is a front view of the cassette 2, and Fig. 2(B) is a rear view of the cassette 2.

[0021] 1, 2(A) and 2(B), the width direction A1, the depth direction A2 and the height direction (up-down direction) A3 of the cassette 2 are perpendicular to each other. The cassette 2 has a pair of side walls 4 each having a rectangular plate shape.

[0022] The pair of side walls 4 are made of a synthetic resin such as polypropylene (PP), perfluoroalkoxyalkane (PFA), polyetheretherketone (PEEK), polycarbonate (PC), polyetherimide (PEI), or polybutylene terephthalate (PBT).

[0023] The pair of side walls 4 have approximately the same shape and thickness, and are arranged to face each other in the width direction A1. The upper ends 4a of the pair of side walls 4 are fixed to each other by a rectangular top plate (upper end fixing portion) 6. The material constituting the top plate 6 is the same synthetic resin as that of the side walls 4.

[0024] The upper ends 4a of the pair of side walls 4 may be fixed by a cylindrical or prismatic rod or a thin, elongated plate extending in the width direction A1, instead of the top plate 6. The longitudinal portion of the rod or thin, elongated plate does not necessarily have to be arranged parallel to the width direction A1.

[0025] An upper protrusion 4c is provided on the upper end 4a of the side wall 4. The upper protrusion 4c is a rectangular column extending along the depth direction A2, and is made of the same synthetic resin as the side wall 4. The upper protrusion 4c is provided so that one cassette 2 can be stably placed on top of another cassette 2.

[0026] A pair of handles 8 are provided between the pair of upper protrusions 4c and on the top surface of the top plate 6, which are used when an operator holds the cassette 2 by hand. The pair of handles 8 are made of the same synthetic resin as the side walls 4, and are rotatable around a rotation axis 8a indicated by a dashed line in FIG.

[0027] The pair of handles 8 shown in FIG. 1 are arranged substantially parallel to the A1-A2 plane (i.e., lying down), but the operator can rotate the pair of handles 8 around the rotation axis 8a to arrange them substantially parallel to the A2-A3 plane (i.e., standing up).

[0028] The lower ends 4b of the pair of side walls 4 are fixed to each other by a rectangular bottom plate (lower end fixing portion) 10. The material constituting the bottom plate 10 is also the above-mentioned synthetic resin, the same as that of the side walls 4. By using a synthetic resin for the pair of side walls 4, the top plate 6, the bottom plate 10, etc., there is an advantage in that the cassette 2 can be made lighter than when a metal material such as stainless steel is used.

[0029] The lower ends 4b of the pair of side walls 4 may be fixed by a cylindrical or prismatic rod or a thin, elongated plate extending in the width direction A1, instead of the bottom plate 10. The longitudinal portions of the rod or thin, elongated plate do not necessarily need to be arranged parallel to the width direction A1.

[0030] Lower protrusions 4d protruding in the height direction A3 are provided below the lower end portion 4b of the side wall 4. The pair of lower protrusions 4d are rectangular columns extending in the depth direction A2 and function as legs of the cassette 2.

[0031] The material constituting the lower protrusion 4d is also the above-mentioned synthetic resin, which is the same as that of the side wall 4. Note that, instead of the prismatic lower protrusion 4d, a plurality of legs having any shape, such as a cylinder, a disk, or a rectangular parallelepiped, may be provided discretely along the depth direction A2.

[0032] The rectangular parallelepiped space defined by the pair of side walls 4, the top plate 6, and the bottom plate 10 serves as a storage space 2a for storing a plurality of objects (i.e., wafers 11 (see FIGS. 7(A) and 7(B))). The front end of the cassette 2 in the depth direction A2 defines an opening 2b through which the wafers 11 pass when they are inserted into the cassette 2 (see FIGS. 1 and 2(A)).

[0033] A rectangular back plate 12 (see FIG. 2(B)) is provided at the rear end of the cassette 2 located on the opposite side to the opening 2b along the depth direction A2. The back plate 12 is also made of the same synthetic resin as the side wall 4.

[0034] In this embodiment, the back plate 12 covers the entire rear end of the cassette 2, as shown in FIG. 2(B). However, the back plate 12 does not necessarily have to cover the entire rear end of the cassette 2 as long as it can prevent the wafers 11 from falling out of the cassette 2.

[0035] In addition, instead of the rectangular back panel 12, one or more cylindrical or prismatic rods, one or more elongated thin panels, etc. may be provided in the center of the rear end of the cassette 2 in the width direction A1, extending from the top panel 6 to the bottom panel 10.

[0036] 2(A), each side wall 4 is provided with a number of shelves 14 each protruding from an inner surface 4e of the side wall 4. The shelves 14 are spaced apart from one another at predetermined intervals, such as 6.35 mm, 10 mm, etc., along the height direction A3 of each side wall 4.

[0037] A pair of shelves 14 at corresponding positions in the height direction A3 support one wafer 11. In the cassette 2 of the present embodiment, 12 pairs (i.e., 12 sets) of shelves 14 are provided, but the number of pairs of shelves 14 is not limited to this.

[0038] Next, the multiple shelves 14 will be described in more detail with reference to Figures 3, 4, and 5. Figure 3 is an enlarged perspective view of a portion of the multiple shelves 14 located on one side in the width direction A1. Figure 4 is a partial cross-sectional side view of the side wall 4 and the multiple shelves 14 located on one side in the width direction A1. Figure 5 is a cross-sectional view of one side wall element 18.

[0039] Each of the shelves 14 has a horizontal portion 14a that protrudes from the inner surface 4e of the side wall 4 and extends along the width direction A1. The amount of protrusion of the horizontal portion 14a from the inner surface 4e is approximately constant throughout the depth direction A2.

[0040] 5, a screw hole 14b is provided in the base end portion 14a1 of the horizontal portion 14a. The screw hole 14b is a hole having a threaded groove for fastening the bolt 16. Two or more screw holes 14b are provided along the depth direction A2.

[0041] A protruding portion 14c is provided at a tip portion 14a2 of the horizontal portion 14a, protruding substantially perpendicularly from a top surface 14a3 of the horizontal portion 14a toward the top plate 6. In this embodiment, the top of the protruding portion 14c has a semi-cylindrical shape with its longitudinal direction aligned along the depth direction A2.

[0042] The convex portion 14c is provided across the depth direction A2, similar to the horizontal portion 14a. In this embodiment, the convex portion 14c functions as a support portion that contacts one wafer 11 and supports the one wafer 11. When one wafer 11 is supported by the convex portion 14c, the convex portion 14c and the wafer 11 contact each other in a linear region located at the top of the semi-cylindrical shape.

[0043] In this way, by contacting the convex portion 14c and the wafer 11 in a linear region, the contact area between the shelf portion 14 and the wafer 11 can be reduced compared to when the horizontal portion 14a and the wafer 11 are in surface contact without providing the convex portion 14c.

[0044] The protruding portion 14c has a top surface 14d that contacts one wafer 11 when the wafer 11 is supported by the protruding portion 14c. In this embodiment, the top surface 14d of the protruding portion 14c that contacts one wafer 11 is a region that corresponds to the outer circumferential side surface of the semi-cylindrical shape.

[0045] The material constituting the top surface 14d is harder than the material (i.e., synthetic resin) constituting the side walls 4. Therefore, the amount of waste generated when the convex portion 14c is scraped off the wafer 11 can be reduced, compared to when the top surface 14d of the convex portion 14c is made of the same material as the pair of side walls 4.

[0046] The material constituting the top surface 14d of the protrusion 14c includes a hard material such as a metal such as stainless steel or cemented carbide, diamond, or hard ceramics. As the hard ceramics, a material having a Vickers hardness of 12 GPa or more is selected.

[0047] For example, silicon carbide, alumina (i.e., aluminum oxide (e.g., Al2O3)), silicon nitride (e.g., Si3N4), and zirconia (i.e., zirconium oxide (e.g., ZrO2)) are selected as hard ceramics. Note that silicon carbide, which has a relatively high hardness and does not contain metal elements, is preferable as the hard ceramics.

[0048] These hard materials cover the top surface 14d of the protrusion 14c as a hard film. The thickness of the film is not particularly limited, but is appropriately adjusted within the range of, for example, 100 μm to 1000 mm. The film of the hard material is not limited to a single layer, and may have a multi-layer structure.

[0049] It is sufficient that at least the top surface 14d of the convex portion 14c is formed of this hard material, but the entire outer surface of the horizontal portion 14a, including the top surface 14a3 and the bottom surface 14a4, and the entire outer surface of the convex portion 14c may be coated with the above-mentioned hard material.

[0050] As shown in Figures 3 and 4, each shelf 14 forms a portion of a side wall 4. In this embodiment, one side wall element 18 includes one shelf 14 and a portion of a side wall 4, as shown in Figure 5.

[0051] The side wall element 18 is entirely made of the above-mentioned synthetic resin, except for the top surface 14d of the protruding portion 14c. As shown in Fig. 5, the side wall element 18 has an inner wall portion 18a that protrudes from the base end portion 14a1 of the horizontal portion 14a toward the bottom plate 10 along the height direction A3.

[0052] In addition, in Fig. 5, the boundary between the integrally formed inner wall portion 18a and the horizontal portion 14a is shown by a dashed line for convenience. The inner wall portion 18a is a rectangular plate-shaped region extending along the depth direction A2. The surface of the inner wall portion 18a that contacts the storage space 2a becomes the above-mentioned inner surface 4e.

[0053] The corner where the upper end of the inner surface 4e of the inner wall portion 18a and the bottom surface 14a4 of the horizontal portion 14a are connected is rounded. By providing the rounded corner, the connection strength between the inner wall portion 18a and the horizontal portion 14a can be improved compared to when the corner is not rounded.

[0054] An outer wall portion 18b is provided on the opposite side of the inner wall portion 18a from the inner surface 4e in the width direction A1. The outer wall portion 18b is a rectangular plate-shaped region extending along the depth direction A2. In FIG. 5, the boundary between the inner wall portion 18a and the outer wall portion 18b, which are integrally formed, is shown by a dashed line for convenience.

[0055] The top of the outer wall portion 18b is located between the top and bottom of the inner wall portion 18a, and the bottom of the outer wall portion 18b protrudes toward the bottom plate 10 further than the bottom of the inner wall portion 18a in the height direction A3.

[0056] In the outer wall portion 18b, a first hole 18b1 for accommodating the head of the bolt 16 and a second hole 18b2 for inserting the shaft of the bolt 16 are provided between the bottom of the inner wall portion 18a and the bottom of the outer wall portion 18b. The first hole 18b1 and the second hole 18b2 are not threaded, but the second hole 18b2 may be threaded.

[0057] The first hole 18b1 and the second hole 18b2 are disposed approximately coaxially and form a through hole in the outer wall portion 18b. Furthermore, two or more pairs of the first hole 18b1 and the second hole 18b2 are provided along the depth direction A2.

[0058] With the two side wall elements 18 stacked along the height direction A3, the outer wall portion 18b of the upper side wall element 18 and the inner wall portion 18a of the lower side wall element 18 are fixed to each other with bolts 16 (see Figure 4).

[0059] In this manner, by stacking and fixing a plurality of side wall elements 18 in the height direction A3, the side wall 4 and a plurality of shelves 14 are formed as shown in Figures 1 to 4. The cassette 2 accommodates a plurality of wafers 11.

[0060] 6 is a front view of a cassette 2 containing a plurality of wafers 11. Each wafer 11 is supported by a pair of shelves 14 located at the same height in the height direction A3. In this embodiment, the outer periphery of each wafer 11 on both sides is not chamfered.

[0061] Fig. 7(A) is a perspective view of a wafer 11 in which the front surface 11a and the back surface 11b are not chamfered, and Fig. 7(B) is a cross-sectional view of this wafer 11. As shown in Fig. 7(B), the outer periphery 11a1 of the front surface 11a and the outer periphery 11b1 of the back surface 11b are not chamfered and are sharp.

[0062] However, in this embodiment, the material constituting the top surface 14d of the convex portion 14c is harder than the material constituting the pair of side walls 4 (i.e., synthetic resin), and therefore the amount of debris generated when the convex portion 14c is scraped off the wafer 11 can be reduced compared to when the top surface 14d of the convex portion 14c is formed from the same synthetic resin as the pair of side walls 4.

[0063] (First Modification) Next, a first modification will be described with reference to Fig. 8. Fig. 8 is a partial cross-sectional side view showing a side wall 4 and a plurality of shelves 14 of a cassette 2 according to a first modification. In the first modification, instead of a side wall element 18, a plurality of shelves 14 are fixed to an inner surface 4e of a solid plate side wall 4 using bolts 16. This point differs from the above-described embodiment.

[0064] In the first modification, the side wall 4 is entirely made of the above-mentioned synthetic resin, and the shelf 14 is entirely made of the above-mentioned synthetic resin, except for the top surface 14d of the protrusion 14c. By making at least the top surface 14d of the protrusion 14c out of the above-mentioned hard material, the amount of scrap generated by the wafer 11 being scraped off the protrusion 14c can be reduced.

[0065] (Second Modification) Next, a second modification will be described with reference to Fig. 9. Fig. 9 is a partial cross-sectional side view showing the side wall 4 and multiple shelf portions 14 of a cassette 2 according to the second modification. In the second modification, similar to the above-described embodiment, the side wall 4 and multiple shelf portions 14 are formed by fixing multiple side wall elements 18 in a stacked state along the height direction A3.

[0066] Each shelf 14 has a horizontal portion 14a. However, the tip 14a2 of the horizontal portion 14a does not have a protruding portion 14c. This is different from the above-described embodiment. In the second modification, the horizontal portion 14a contacts one wafer 11 and functions as a support portion that supports the wafer 11.

[0067] The horizontal portion 14a has a top surface 14e that comes into contact with one wafer 11 when the wafer 11 is supported by the horizontal portion 14a. Since the top surface 14e is made of the above-mentioned hard material, the amount of scraps generated when the horizontal portion 14a is scraped by the wafer 11 can be reduced compared to when the top surface 14e is made of the same synthetic resin as the pair of side walls 4.

[0068] The hard material only needs to be provided in a region of the top surface 14e that contacts one wafer 11, and the hard material does not necessarily need to be provided on the top surface 14e located directly above the inner wall portion 18a in the height direction A3.

[0069] (Third Modification) Next, a third modification will be described with reference to Fig. 10. Fig. 10 is a partial cross-sectional side view showing the side wall 4 and multiple shelves 14 of a cassette 2 according to the third modification. In the third modification, similar to the above-mentioned first modification (see Fig. 8), the multiple shelves 14 are fixed to the inner surface 4e of the side wall 4, which is made of a single plate, by using bolts 16.

[0070] However, each shelf portion 14 in the third modified example does not have a protrusion 14c at the tip portion 14a2 of the horizontal portion 14a, similar to the second modified example (see FIG. 9). Therefore, the horizontal portion 14a contacts one wafer 11 and functions as a support portion that supports the wafer 11.

[0071] In the third modified example as well, the amount of debris generated by the horizontal portion 14a being scraped off by the wafer 11 can be reduced compared to when the top surface 14e of the horizontal portion 14a is formed from the same synthetic resin as the pair of side walls 4.

[0072] In addition, the structures, methods, etc. according to the above-mentioned embodiments can be modified as appropriate without departing from the scope of the present invention. In the above-mentioned embodiment and the first modified example, the top surface 14d of the convex portion 14c is provided with a hard coating, but the horizontal portion 14a and the convex portion 14c may be entirely made of the above-mentioned hard material. In the second and third modified examples, the horizontal portion 14a may be entirely made of the above-mentioned hard material. [Explanation of symbols]

[0073] 2: Cassette, 2a: Containment space, 2b: Opening 4: side wall, 4a: upper end, 4b: lower end, 4c: upper protrusion, 4d: lower protrusion, 4e: inner surface 6: Top plate (upper end fixing part), 8: Handle, 8a: Rotation axis, 10: Bottom plate (lower end fixing part) 11: ウェーハ、11a: surface、11a1: outer periphery、11b: back、11b1: outer periphery 12: back plate, 14: shed 14a: horizontal part, 14a1: base end, 14a2: tip end, 14a3: top surface, 14a4: bottom surface 14b: Neji hole, 14c: convex part (support part), 14d, 14e: top surface 16: ボルト, 18: Side wall element, 18a: Inner wall part 18b: outer wall, 18b1: first hole, 18b2: second hole A1: Banner direction, A2: Olympic direction, A3: High direction (up and down direction)

Claims

1. A cassette for accommodating a plurality of wafers, A pair of side walls arranged to face each other; an upper end fixing portion that fixes each upper end of the pair of side walls; a lower end fixing portion that fixes each lower end of the pair of side walls; a plurality of shelves provided along the vertical direction of each side wall and spaced apart from one another, each protruding from an inner surface of each side wall; Equipped with each of the plurality of shelves having a support for supporting a wafer; the support has a top surface that contacts the one wafer when the one wafer is supported by the support; A cassette according to claim 1, wherein a material constituting at least the top surface of the support portion is harder than a material constituting the pair of side walls.

2. Each of the plurality of shelves comprises: a horizontal portion protruding from the inner surface of each side wall and extending along a width direction perpendicular to the depth direction and the up-down direction of a space defined by the pair of side walls, the upper end fixing portion, and the lower end fixing portion; a protruding portion provided at a tip end of the horizontal portion and protruding toward the upper end fixing portion; having 2. The cassette according to claim 1, wherein the protrusion is the support portion for supporting the one wafer.

3. Each of the plurality of shelf portions protrudes from the inner surface of each side wall and has a horizontal portion extending along a width direction perpendicular to a depth direction and a vertical direction of a space defined by the pair of side walls, the upper end fixing portion, and the lower end fixing portion; 2. A cassette as claimed in claim 1, wherein said horizontal portion is said support portion.

4. the material constituting the top surface of the support portion includes metal, diamond, or hard ceramics; 4. A cassette according to claim 1, wherein the pair of side walls are made of a synthetic resin.

5. 5. The cassette according to claim 4, wherein the material constituting each of the upper end fixing portion and the lower end fixing portion is a synthetic resin.

6. 5. A cassette as claimed in claim 4, wherein the material comprising said top surface of said support is silicon carbide.

Images