Liquid processing equipment
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- ACM RES (SHANGHAI) INC
- Filing Date
- 2024-05-06
- Publication Date
- 2026-06-16
Smart Images
Figure 2026519578000001_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the field of semiconductor device manufacturing, and more specifically, to a liquid processing apparatus.
Background Art
[0002] The manufacturing process of semiconductor devices includes a photoresist coating and development process for substrates. In the photoresist coating and development process, a developer and deionized water are sprayed from a development nozzle onto the surface of the substrate and left standing, and by waiting for the developer to react, the reaction is made uniform on the surface of the substrate.
[0003] Currently, the internal flow path structure of commercially available development nozzles has only one cavity and is relatively simple. Therefore, when the nozzle sprays the developer onto the substrate surface, the flow rate of the developer in the length direction of the development nozzle is uneven, the reaction of the substrate during the development reaction is uneven, and it is not guaranteed that the development everywhere on the substrate is completely sufficient, resulting in a decrease in the product yield.
Summary of the Invention
[0004] The present invention has been made in view of the above problems, and an object thereof is to provide a liquid processing apparatus that improves the uniformity of liquid flow rate.
[0005] In order to achieve the above object, the present invention provides the following technical solutions. A liquid processing apparatus, comprising a liquid spray unit, two side cover plates, and two processing plates. The two processing plates are symmetrically arranged on the side surfaces of the liquid spray unit, and the two side cover plates are arranged on the sides of the two processing plates away from the liquid spray unit, Liquid inlets are opened at the tops of the two processing plates, and a liquid discharge port is opened at the bottom of the liquid spray unit. A first groove is provided on each of the opposing sides of the two processed plates and the two side cover plates, and the two side cover plates are arranged to cover the first groove to form a first chamber, and a first liquid discharge hole is provided in the two processed plates that communicates with the lower side of the first chamber. Groove-like structures are provided on the opposing sides of the liquid spray unit and the two processing plates, and the two processing plates are arranged to cover the groove-like structures to form a second chamber, the second chamber is in communication with the first liquid discharge hole, and the liquid spray unit has a second liquid discharge hole that is in communication with the top of the second chamber, and the second liquid discharge hole is in communication with the liquid outlet.
[0006] The present invention has the following beneficial effects compared to the prior art. A first liquid discharge port is provided at the bottom of the first chamber, and the second chamber and the first liquid discharge port are connected. A second liquid discharge port is provided at the top of the second chamber. The flow paths on each side are configured in a U-shape from the liquid inlet to the second liquid discharge port. Developer and deionized water are injected into the two liquid inlets, respectively. The flow paths on both sides are identical, and the developer and deionized water flow into the first chamber from their respective liquid inlets, then sequentially through the first liquid discharge port, the second chamber, and the second liquid discharge port. This U-shaped structure extends the liquid flow path and makes the liquid flow velocity more uniform at each point where it exits the liquid outlet. [Brief explanation of the drawing]
[0007] The features and performance of the present invention will be further described by the following embodiments and their drawings. [Figure 1] Figure 1 is a schematic diagram of an explosion of a liquid processing apparatus structure according to an embodiment of the present invention. [Figure 2] Figure 2 is a side view of a liquid processing apparatus structure according to an embodiment of the present invention. [Figure 3] Figure 3 is a cross-sectional view along line AA in Figure 2 according to an embodiment of the present invention. [Figure 4] Figure 4 is an enlarged schematic diagram of region C in Figure 3. [Figure 5] Figure 5 is a schematic diagram of one side of the processed plate according to the present invention. [Figure 6] Figure 6 is a diagram showing the configuration of the other side of the processed plate according to the present invention. [Figure 7] Figure 7 is a schematic diagram of the structure of the liquid spray unit according to the present invention. [Figure 8] Figure 8 is a side view of the quartz according to the present invention. [Figure 9] Figure 9 is a cross-sectional view along line BB in Figure 8. [Figure 10] Figure 10(a) is a cross-sectional view along line AA in Figure 2 according to another embodiment of the present invention. Figure 10(b) is a cross-sectional view along line AA in Figure 2 according to another embodiment of the present invention. [Explanation of Symbols]
[0008] Base 1, top cover plate 2, side cover plate 3, processed plate 4, quartz 5, first chamber 6, second chamber 7, mixing chamber 8, mixing tank 9, liquid outlet 11, second groove 12, second liquid discharge hole 21, third groove 22, liquid inlet 41, first groove 42, first liquid discharge hole 43, third liquid discharge hole 44, annular groove 45, bump 51, central region 52, edge region 53. [Modes for carrying out the invention]
[0009] To more clearly explain the technical concept of the embodiments of this application, the drawings necessary for describing the embodiments are briefly introduced below. Obviously, the drawings in the following description are only a few examples or embodiments of this application, and those skilled in the art may apply this application to other similar scenarios based on these drawings, without paying any labor of inventive step. Unless otherwise stated or as is evident from the locale, identical reference numerals in the drawings represent identical structures or functions.
[0010] As set forth in this application and claims, unless the context explicitly indicates an exception, terms such as “one,” “one,” “one kind,” and / or “the said” do not refer to a singular number but may include multiple numbers. Generally speaking, the terms “equip” and “include” merely indicate that explicitly identified steps or elements are included, and these steps or elements do not constitute an exclusive list, and the method or device may include other steps or elements.
[0011] The relative arrangement of components and steps, numerical expressions, and numerical values described in these embodiments do not limit the scope of this application unless otherwise specified. It should be understood that, for ease of explanation, the dimensions of the parts shown in the drawings are not based on actual proportional relationships. While technologies, methods, and devices known to those skilled in the art may not be discussed in detail, where appropriate, such technologies, methods, and devices should be considered part of the patented specification. In all examples shown and discussed herein, any specific values should be interpreted as merely illustrative and not limiting. Therefore, other examples of exemplary embodiments may have different values. Similar reference numerals and letters represent similar terms in subsequent drawings; therefore, once a term is defined in a drawing, it does not need to be discussed further in subsequent drawings. Please note.
[0012] In the description of this application, the directions or positional relationships indicated by directional terms such as "front, back, up, down, left, right," "side, up, vertical, horizontal," and "top, bottar" are usually based on the directions or positional relationships shown in the drawings and are used solely to facilitate and simplify the description of this application. Unless otherwise stated, these directional terms do not indicate or imply that the device or element being referred to must be configured and operate in a specific direction or orientation, and therefore cannot be understood as limiting the scope of protection of this application. The directional terms "inside" and "outside" refer to the inside and outside of the contour of each part itself.
[0013] For the sake of clarity, spatially relative terms such as “above,” “above,” “top,” and “on top,” as shown in the diagram, may be used here to describe the spatial positional relationship between one device or feature and another device or feature. …It should be understood that spatially relative terms are intended to include different orientations in use or operation of a device other than the orientation described in the drawing. For example, if the device in the drawing is inverted, a device described as “above another device or configuration” or “on top of another device or configuration” is positioned as “below another device or configuration” or “below another device or configuration.” Thus, the exemplary term “above…” could include two orientations: “above…” and “below….” This device could also be positioned in other different ways (90-degree rotation or other orientations), which can be appropriately explained for the spatially relative descriptions used here.
[0014] Furthermore, it is necessary to explain that the use of terms such as "first," "second," etc., to define parts is solely for the purpose of facilitating the distinction between corresponding parts, and unless otherwise stated, these terms have no special meaning and should not be understood as limitations on the scope of protection of this application. In addition, while the terminology used in this application has been selected from publicly known terms, some of the terms described in this specification were selected at the applicant's discretion, and their detailed meanings are described in the relevant sections of this specification. Moreover, it is necessary to understand this application not only through the terms actually used, but also through the meanings contained within each term.
[0015] The technical aspects of the present invention will be further described below with reference to the drawings, using specific embodiments.
[0016] Referring to FIG. 1, the present embodiment provides a liquid processing apparatus, which includes a liquid spray unit, two side cover plates 3, and two processing plates 4. The liquid spray unit includes a base 1 and a top cover plate 2 that are detachably connected, and the top cover plate 2 is arranged to cover the base 1. Quartz 5 is provided inside the base 1, and the quartz 5 has an elongated structure. Two processing plates 4 are provided on each side surface of the base 1, and the side cover plate 3 described above is provided on the side of the processing plate 4 away from the base 1. The entire apparatus has an axisymmetric structure centered on the central position of the quartz 5.
[0017] In accordance with FIGS. 2 to 6, a liquid inlet 41 is opened in each processing plate 4. A first groove portion 42 is opened on the surface of the processing plate 4 on the side facing the side cover plate 3, and the side cover plate 3 is fitted into the first groove portion 42 to form a first chamber 6. The cross section of the side cover plate 3 has a fan-shaped structure, and the cross section of the formed first chamber 6 also has a fan-shaped structure. The liquid inlet 41 communicates with the first chamber 6. Further, a plurality of first liquid discharge holes 43 are opened in the processing plate 4, and the plurality of first liquid discharge holes 43 communicate with the lower side of the first chamber 6. The adjacent first liquid discharge holes 43 are spaced at the same distance. Also, a third liquid discharge hole 44 that communicates with the top of the first chamber 6 is opened in the processing plate 4, and the third liquid discharge hole 44 communicates with the liquid inlet 41. Liquid is injected from the liquid inlet 41, and the liquid enters the first chamber 6 from the third liquid discharge hole 44 and diffuses to the lower first liquid discharge holes 43 due to the influence of gravity. Since the cross sections of the side cover plate 3 and the first chamber 6 are fan-shaped structures, the liquid can be quickly diffused to the first liquid discharge holes 43 along the inclined surface.
[0018] Referring to FIGS. 3 and 7, a groove-like structure is formed on the side facing the liquid spray unit and the processing plate 4. The groove-like structure includes a second groove portion 12 and a third groove portion 22. Specifically, the second groove portion 12 is formed on the side surface of the base 1 facing the processing plate 4, and the third groove portion 22 is formed on the side surface of the top cover plate 2 facing the processing plate 4. The processing plate 4 is installed to cover the second groove portion 12 and the third groove portion 22, and a second chamber 7 is formed. Since the first liquid discharge hole 43 communicates with the second chamber 7, the first chamber 6 and the second chamber 7 communicate with each other. A plurality of second liquid discharge holes 21 are formed inside the third groove portion 22, and the adjacent second liquid discharge holes 21 are spaced at the same distance. The second liquid discharge holes 21 communicate with the top of the second chamber 7. The liquid flows from the first chamber 6 into the second chamber 7 through the first liquid discharge hole 43.
[0019] Referring to FIGS. 3 to 4, a gap is formed between the quartz 5 and the inner wall of the base 1 with a preset distance. This gap communicates with the second liquid discharge hole 21, and a liquid discharge port 11 is provided at the bottom of the base 1. The liquid flows from the second chamber 7 into the gap through the second liquid discharge hole 21.
[0020] In the photoreceptor coating and development process, the liquids on both sides are developer and deionized water respectively. The developer and deionized water are injected into the two liquid inlets 41 respectively. The flow paths on both sides of the liquid treatment device are the same. The developer and deionized water flow into the corresponding first chamber 6 from the corresponding liquid inlets 41 respectively, and then flow sequentially through the first liquid discharge hole 43, the second chamber 7, and the second liquid discharge hole 21. Since a height difference is formed between the quartz 5 and the second liquid discharge holes 21 on both sides respectively, a height difference is formed between the upper surface of the base 1 and the upper surface of the quartz 5, and a mixing chamber 8 is formed between the inner wall of the base 1 and the top of the quartz 5. The developer and deionized water are mixed above the quartz 5, that is, inside the mixing chamber 8, after flowing out from the second liquid discharge holes 21, and the mixed liquid flows from the gaps on both sides of the quartz 5 to the liquid discharge port 11.
[0021] From the liquid inlet 41 to the second liquid outlet 21, the flow paths on both sides of the liquid processing device are formed in a U-shape, extending the liquid flow path and making the flow velocity of the mixed liquid more uniform at each point after it flows out from the liquid outlet 11.
[0022] Quartz 5 is hydrophilic, and the liquids on both sides flow out in a curtain-like manner from the sides of Quartz 5, further improving the uniformity of the outflow rate of the mixed liquid.
[0023] In the photoreceptor coating and development processes, the liquids on both sides are deionized water and developer, respectively. The wafer is first wetted using another wetting device, and then the deionized water and developer are simultaneously injected into the apparatus from the liquid inlets 41 on both sides. In other embodiments, the deionized water and developer may be injected into the apparatus from the liquid inlets 41 on both sides at regular time intervals. Deionized water is injected to wet the wafer, and then a developer of a predetermined concentration is injected.
[0024] In other embodiments, the liquids on both sides may be the same solution. For example, in the photoreceptor coating and developing process, pre-diluted developer is injected into both sides, and it is not necessary to inject deionized water.
[0025] Referring to Figure 8, in one embodiment, bumps 51 are provided at both ends of the quartz 5, and correspondingly, clutch grooves are provided on the inner wall of the base 1, and the bumps 51 engage with the clutch grooves to fix the quartz 5 to the base 1.
[0026] In other process operations, the developer and deionized water are flowed to the liquid outlet 11 separately without mixing above the quartz 5. As shown in Figures 8 and 9, the top surface of the quartz 5 is stepped. The quartz 5 has a central region 52 and edge regions 53 on its top surface, with the edge regions 53 positioned on both sides of the central region 52. The central region 52 is higher than the edge regions 53 and contacts the bottom surface of the top cover plate 2. Selectively, the central region 52 is in contact with the bottom surface of the top cover plate 2. The central region 52 is for separating the developer and deionized water, and the developer and deionized water flow from the edge regions 53 into the gap, respectively.
[0027] In this application, the number of first liquid discharge holes 43 and second liquid discharge holes 21 is not specifically limited. Preferably, a plurality of first liquid discharge holes 43 are provided in the first chamber 6 and a plurality of second liquid discharge holes 21 are provided in the second chamber 7 to make the flow velocity of the liquid at each point flowing out from the liquid discharge port 11 more uniform.
[0028] The spacing between adjacent second liquid discharge holes 21 and between adjacent first liquid discharge holes 43 is not limited to the setting method described above. The multiple first liquid discharge holes 43 along the length of the first chamber 6 from the edge to the center, and the multiple second liquid discharge holes 21 along the length of the second chamber 7, may be arranged from dense to sparse.
[0029] In some embodiments, the base 1 and the top cover plate 2 are designed as an integral part of the structure.
[0030] In other embodiments, quartz 5 is not provided inside the base 1, and the base 1 is a cavity. After the developer and deionized water on both sides are mixed inside the base 1, the mixture flows from the cavity to the liquid outlet 11 and is discharged outside the device.
[0031] In other embodiments, the cross-section of the side cover plate 3 is not limited to a fan-shaped structure. The side cover plate 3 may have an elongated structure, and the side cover plate 3 may cover the first groove 42 to form the first chamber 6.
[0032] Referring to Figure 5, an annular groove 45 is provided on the side of the processed plate 4 facing the base 1. The annular groove 45 is provided corresponding to the inner circumference of the groove-shaped structure, and a rubber ring (not shown) is fitted inside the annular groove 45. After the processed plate 4 covers the liquid spray unit, the rubber ring is locked to the inner circumference of the second groove 12 and the third groove 22, improving the airtightness of the second chamber 7.
[0033] In one embodiment, referring to Figure 10(a), the liquid spray unit has a separate mixing tank 9 above the quartz 5, the top or side of the mixing tank 9 is in communication with a second liquid discharge hole 21, and a long groove is provided at the bottom of the mixing tank 9, the groove is in communication with a gap, and the mixed liquid flows from the groove into the gap between the quartz 5 and the base 1 and flows to the liquid discharge port 11.
[0034] In another embodiment, referring to Figure 10(b), two or more quartz crystals 5 are arranged side by side along the width direction of the base 1, and the liquid spray unit has a mixing tank 9 above the quartz crystals 5. Grooves are made at the bottom of the mixing tank 9, corresponding to different quartz crystals 5. After mixing the liquids on both sides in the mixing tank 9, the mixture flows down in a curtain-like manner from the sides of the two or more quartz crystals 5 to the liquid discharge port 11, and the uniformity of the flow velocity of the mixture can be further improved by dispersing the mixture into multiple flow paths.
[0035] In one embodiment, there is no gap between the quartz 5 and the inner wall of the base 1, and the liquid spray unit has a separate mixing tank 9 above the quartz 5, with the top or side of the mixing tank 9 communicating with a second liquid discharge hole 21. A through hole or through groove is provided in the center of the quartz 5 along the height direction of the base 1, and the through hole or through groove communicates with the mixing tank 9 and the liquid discharge port 11, respectively. After the liquids on both sides are mixed in the mixing tank 9, the mixture flows from the through hole or through groove to the liquid discharge port 11. Optionally, in this embodiment, a certain gap may be set in advance between the quartz 5 and the inner wall of the base 1. Optionally, a separate mixing tank 9 is not provided above the quartz 5, and the through hole or through groove communicates with the mixing chamber 8 and the liquid discharge port 11, respectively, and the liquids on both sides are mixed in the mixing chamber 8.
[0036] As described above, the liquid processing apparatus of the present invention has a plurality of first liquid discharge holes 43 at the bottom of the first chamber 6, the second chamber 7 is in communication with the first liquid discharge holes 43, and the second liquid discharge hole 21 is provided at the top of the second chamber 7. The flow paths on each side are configured in a U shape from the liquid inlet 41 to the second liquid discharge hole 21. Developer and deionized water are injected into the two liquid inlets 41, respectively. The flow paths on both sides are the same, and the developer and deionized water flow into the first chamber 6 from their respective liquid inlets 41, then sequentially flow through the first liquid discharge hole 43, the second chamber 7, and the second liquid discharge hole 21 before flowing out of the liquid discharge port 11 and being sprayed onto the substrate surface. The U-shaped structure on both sides effectively extends the liquid flow path and makes the liquid flow velocity more uniform at each point where it flows out from the liquid discharge port.
[0037] While the basic concepts have been explained above, it is clear that for those skilled in the art, the above disclosure is merely an example and does not constitute a limitation of this application. Although not explicitly stated here, those skilled in the art may make various modifications, improvements, and alterations to this application. Since such modifications, improvements, and alterations are proposed in this application, such modifications, improvements, and alterations still fall within the spirit and scope of the model embodiment of this application.
[0038] At the same time, the present application uses specific terminology to describe embodiments of the present application. For example, “one embodiment,” “one embodiment,” and / or “some embodiments” mean features, structures, or characteristics relating to at least one embodiment of the present application. Therefore, it should be emphasized and noted that “one embodiment,” “embodiment,” or “alternative embodiment” mentioned more than once in different places in this specification do not necessarily mean the same embodiment. Furthermore, specific features, structures, or characteristics in one or more embodiments of the present application may be combined as appropriate.
[0039] Similarly, it should be noted that, in order to simplify the language of the disclosure and thereby aid in understanding one or more embodiments of the invention, multiple features may be combined into a single embodiment, drawing, or description in the descriptions of the embodiments described herein. However, this method of disclosure does not mean that there are more features required for the subject matter than those described in the claims. In fact, the features of an embodiment are fewer than the features of each individual embodiment disclosed above combined.
[0040] In some embodiments, numbers are used to describe the number of components or attributes, and it should be understood that in some examples, the numbers used in such embodiment descriptions are modified with the modifiers “about,” “approximate,” or “nearly.” Unless otherwise specified, “about,” “approximate,” or “nearly” indicates that a variation of up to 20% is permitted in the number. Thus, in some embodiments, all numerical parameters used in the specification and claims are approximations, and these approximations may vary depending on the desired characteristics of the individual embodiments. In some embodiments, numerical parameters need to employ a general digit preservation method, taking into account a specified number of significant digits. While the numerical ranges and parameters used to confirm their breadth in some embodiments of this application are approximations, in certain embodiments, such numbers are set as precisely as possible within the available range.
Claims
1. A liquid processing apparatus, The device comprises a liquid spray unit, two side cover plates (3), and two processing plates (4), wherein the two processing plates (4) are symmetrically positioned on the sides of the liquid spray unit, and the two side cover plates (3) are positioned on the sides of the two processing plates (4) away from the liquid spray unit. Liquid inlet (41) is provided at the top of both of the aforementioned processing plates (4), and a liquid outlet (11) is provided at the bottom of the liquid spray unit. A first groove (42) is provided on each of the opposing sides of the two processed plates (4) and the two side cover plates (3), and the two side cover plates (3) are arranged to cover the first groove (42) to form a first chamber (6), and a first liquid discharge hole (43) is provided in the two processed plates (4) that communicates with the lower side of the first chamber (6). A liquid processing apparatus characterized in that groove-like structures are provided on the opposing sides of the liquid spray unit and the two processing plates (4), the two processing plates (4) are arranged to cover the groove-like structures to form a second chamber (7), the second chamber (7) communicates with the first liquid discharge hole (43), the liquid spray unit has a second liquid discharge hole (21) that communicates with the top of the second chamber (7), and the second liquid discharge hole (21) communicates with the liquid outlet (11).
2. A liquid processing apparatus according to claim 1, The liquid spray unit comprises a base (1) and a top cover plate (2), the top cover plate (2) being detachably attached to the base (1), A liquid processing apparatus characterized in that a second groove (12) is provided on each of the opposing sides of the base (1) and the two processing plates (4), a third groove (22) is provided on each of the opposing sides of the top cover plate (2) and the two processing plates (4), and the two processing plates (4) are arranged to cover the second groove (12) and the third groove (22), respectively, to form a second chamber (7).
3. A liquid processing apparatus according to claim 2, A liquid processing apparatus characterized in that a quartz (5) is provided inside the base (1), a gap is formed between the quartz (5) and the inner wall of the base (1) at a predetermined distance, and the gap is for the liquid to flow to the liquid discharge port (11).
4. A liquid processing apparatus according to claim 1, A liquid processing apparatus characterized in that a plurality of first liquid discharge holes (43) are provided along the longitudinal direction of the first chamber (6), and adjacent first liquid discharge holes (43) are spaced at the same distance apart.
5. A liquid processing apparatus according to claim 1, A liquid processing apparatus characterized in that a plurality of second liquid discharge holes (21) are provided along the longitudinal direction of the second chamber (7), and adjacent second liquid discharge holes (21) are spaced at the same distance apart.
6. A liquid processing apparatus according to claim 3, A liquid processing apparatus characterized in that bumps (51) are provided at both ends of the quartz (5), clutch grooves are provided on the inner wall of the base (1) corresponding to the bumps (51), and the bumps (51) engage with the clutch grooves to fix the quartz (5) to the base (1).
7. A liquid processing apparatus according to claim 1, A liquid processing apparatus characterized in that the first groove (42) has a fan-shaped structure, and the first chamber (6) has a fan-shaped cross-section.
8. A liquid processing apparatus according to claim 1, The liquid processing apparatus is characterized in that the two side cover plates (3) have a fan-shaped cross-section.
9. A liquid processing apparatus according to claim 3, A height difference is formed between the upper surface of the quartz (5) and the upper surface of the base (1), and a mixing chamber (8) is formed between the inner wall of the base (1) and the top of the quartz (5). A liquid processing apparatus characterized in that the mixing chamber (8) and the second liquid discharge hole (21) are in communication, and the liquids from the second liquid discharge holes (21) on both sides are mixed through the mixing chamber (8) and then flow from the gap to the liquid discharge port (11).
10. A liquid processing apparatus according to claim 3, The liquid spray unit is characterized in that a mixing tank (9) is provided above the quartz (5), the top or side of the mixing tank (9) communicates with the second liquid discharge hole (21), and an elongated groove is provided at the bottom of the mixing tank (9), and the groove communicates with the gap.
11. A liquid processing apparatus according to claim 10, A liquid processing apparatus characterized in that at least two of the quartz (5) are arranged along the width direction of the base (1), and grooves are provided at the bottom of the mixing tank (9) corresponding to different quartz (5).
12. A liquid processing apparatus according to claim 10, A liquid processing apparatus characterized in that a through hole or through groove is provided in the center of the quartz (5) along the height direction of the base (1), and the mixed liquid flows from the through hole or through groove to the liquid discharge port (11).
13. A liquid processing apparatus according to claim 1, A liquid processing apparatus characterized in that each processed plate (4) has an annular groove (45) provided corresponding to the inner circumference of the groove-shaped structure, a rubber ring is fitted inside the annular groove (45), and the rubber ring is to be locked to the inner circumference of the groove-shaped structure after each processed plate (4) is positioned to cover the groove-shaped structure.
14. A liquid processing apparatus according to claim 3, The liquid processing apparatus is characterized in that the upper surface of the quartz (5) has a central region (52) and edge regions (53) provided on both sides of the central region (52), the central region (52) is higher than the edge regions (53), and the central region (52) is in contact with the bottom surface of the top cover plate (2).