Vacuum chuck for wafer adsorption

Abstract

This utility model relates to a vacuum chuck structure and discloses a vacuum chuck for wafer adsorption. The vacuum chuck includes a chuck body and an adsorption groove on the working surface of the chuck that communicates with a negative pressure through hole (3). The working surface of the chuck is divided into a circular adsorption groove area (2) and an annular planar area (1) surrounding the adsorption groove area (2), with the outermost edge of the adsorption groove forming the boundary. The ratio of the area of ​​the adsorption groove area to the area of ​​the annular planar area is 1:0.95 to 1.05. Within the adsorption groove area, the adsorption contact area accounts for more than 50% of the area of ​​the adsorption groove area. It still has sufficient adsorption capacity for warped wafers, is reliable in use, and is easy to process.

Description

Technical Field

[0001] This utility model relates to a vacuum chuck for wafer adsorption. Background Technology

[0002] In the wafer fabrication process, vacuum chucks are typically used to transfer wafer fabrication stations.

[0003] like Figure 1 As shown, the vacuum suction cups in imported coating machines and developing machines, such as those from the AIO brand, typically have the following surface groove shape: multiple concentric circular grooves are distributed from the center to the edge. The outermost ring is connected to the remaining circular grooves through multiple centrally symmetrically distributed straight grooves, extending into the smallest circular groove. A negative pressure through hole is set in the smallest circular groove, through which a negative pressure generator is connected. These grooves are used for gas flow to form a vacuum, while the solid part of the surface is in contact with the wafer.

[0004] After multiple processing steps, the wafer will deform. When the processed wafer warps (the center of the circle is low and the edges are high), the vacuum chuck will not be able to hold the wafer.

[0005] Analysis revealed that this type of vacuum chuck has an excessively large working surface area—the area used for contact with the wafer. This large contact area cannot perfectly accommodate the irregular shape of the wafer surface, easily creating gaps between the chuck and the wafer, preventing a reliable seal and leading to vacuum leakage. When the chuck surface cannot effectively adhere to the warped wafer surface, a stable sealing space cannot be formed, resulting in insufficient and continuous vacuum suction. Ultimately, the vacuum chuck fails to hold the wafer. This problem affects subsequent wafer coating, developing, and other processing steps, and may even lead to wafer displacement, reduced processing accuracy, or even wafer damage.

[0006] Therefore, a vacuum chuck is needed that still has sufficient adsorption capacity for warped wafers.

[0007] TWM660633U discloses a wafer support sealing gasket for a vacuum chuck used to hold a wafer. The vacuum chuck includes a groove with its opening facing the wafer and located near the outer periphery of the chuck. The wafer support sealing gasket is formed as a closed annular structure with a protrusion. The wafer support sealing gasket can be accommodated in the groove and can protrude from the groove towards the wafer, abutting against the bottom surface of the wafer. The wafer support sealing gasket is made of rubber, whose elasticity allows the wafer to remain in contact with the wafer support sealing gasket even when warped. This chuck incorporates a wafer support sealing gasket to ensure an effective sealing space between the wafer and the chuck within a certain range, but the structure is relatively complex.

[0008] CN222950209U discloses a vacuum chuck for wafer coating equipment, comprising a chuck body and a support sleeve. The chuck body is mounted on the support sleeve and is a circular disc. A vacuum suction hole is located at the center of the chuck body. Multiple concentric support components are arranged from the center outwards on the upper surface of the chuck body. An arc-shaped adsorption groove is formed between radially adjacent support components. Each ring of support components includes multiple arc-shaped support protrusions evenly spaced circumferentially. A connecting groove is formed between adjacent arc-shaped support protrusions on the same circumference. Radially adjacent arc-shaped support protrusions are staggered. The vacuum suction hole, connecting groove, and arc-shaped adsorption groove are interconnected. The multiple arc-shaped adsorption grooves and connecting grooves form a labyrinth seal, which can balance the adsorption pressure on the wafer, making the adsorbed wafer more uniformly stressed and reducing deformation caused by uneven stress. However, the adsorption effect of this chuck on wafers that have already been deformed by previous processes remains questionable. Summary of the Invention

[0009] The technical problem to be solved by this invention is to provide a vacuum chuck that still has sufficient adsorption capacity for warped wafers.

[0010] The inventors noted that while the wafer surface is theoretically a flat plane, it undergoes continuous deformation during processing. However, the deformation at the wafer's center is relatively small, while the warping deformation increases towards the wafer's edge. Therefore, the inventors considered directly applying sufficient suction power to the vacuum chuck near the wafer's center. The technical solution adopted by this invention to solve its technical problem is: a vacuum chuck, comprising a chuck body and suction grooves on its working surface for communication with negative pressure through-holes. The working surface of the chuck is divided into a circular suction groove area and an annular planar area surrounding the suction groove area, with the outermost edge of the suction groove serving as the boundary. The ratio of the area of ​​the suction groove area to the area of ​​the annular planar area is 1:0.95 to 1.05. The design concept is to shrink the area where the adsorption trenches are arranged towards the center of the suction cup, and to avoid the outer periphery of the wafer with large warpage as much as possible, so as to ensure a tight seal between the suction cup support and the wafer within the adsorption area and prevent negative pressure leakage. When the area where the adsorption trenches are arranged shrinks towards the center of the suction cup, the width of the adsorption trenches needs to be appropriately widened to maintain sufficient suction. Through calculations and experiments by the inventors, it is found that maintaining the area of ​​the adsorption trenches within a radius of approximately 0.7D (where D is the diameter of the suction cup) centered on the center of the suction cup is most suitable.

[0011] Furthermore, based on suction calculations, it is recommended that the adsorption contact area account for more than 50% of the adsorption trench area. The adsorption contact area refers to the area that can theoretically contact the wafer during adsorption and is located within the adsorption trench area. The sum of this area and the area projected onto the disk surface by the slotted portion is the adsorption trench area.

[0012] The adsorption trench area is provided with 3 to 4 annular trenches, and a negative pressure through hole is provided at the center of the adsorption trench area. All the annular trenches are connected to the negative pressure through hole through radial straight trenches.

[0013] The radial straight groove includes a short straight groove used only to connect two adjacent annular grooves and a perforated straight groove extending from the innermost annular groove to the negative pressure through hole.

[0014] There are four perforated straight grooves, and the short straight grooves are distributed on six to eight straight segments that radiate outward from the center of the suction cup.

[0015] The working surface diameter of the suction cup does not exceed 120mm, the width of the annular groove does not exceed 4mm, the width of the radial straight groove does not exceed 2mm, and the depth of the annular groove and the radial straight groove does not exceed 4mm.

[0016] The working surface diameter of the suction cup is 117.6 mm. There are three annular grooves, each with a width of 4 mm. The width of the radial straight groove is 1.5 mm. The diameter of the negative pressure through hole is 1.5 mm. The depth of the annular groove and the radial straight groove is 3 mm. From the center outwards, the center distances between the inner edge of the first annular groove, the inner edge of the second annular groove, and the inner edge of the third annular groove and the center of the suction cup are 11 mm, 23.55 mm, and 36.1 mm, respectively.

[0017] The advantages of this invention are: it still has sufficient adsorption capacity for warped wafers, is reliable in use, and is easy to process. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the groove distribution on the surface of an existing vacuum chuck.

[0019] Figure 2 This is a schematic diagram of the groove on the working surface of the vacuum suction cup of this utility model.

[0020] Figure 3 This is a schematic diagram of the suction cup body of the vacuum suction cup of this utility model.

[0021] Figure 4 This is a schematic diagram (another view) of the suction cup body of the vacuum suction cup of this utility model.

[0022] Figure 5 This is a dimensional schematic diagram of one example of the vacuum suction cup of this utility model.

[0023] The markings in the figure are: 1-circular planar area, 2-adsorption groove area, 3-negative pressure through hole, 4-circular groove, 5-radial straight groove, 51-straight groove with hole, 52-short straight groove. Detailed Implementation

[0024] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0025] like Figure 2 , Figure 3 , Figure 4 and Figure 5 As shown, the vacuum chuck of this invention for wafer adsorption includes a chuck body and an adsorption groove on the working surface of the chuck that communicates with a negative pressure through-hole 3. The working surface of the chuck is divided into a circular adsorption groove region 2 and an annular planar region 1 surrounding the adsorption groove region 2. The two are defined by the outermost edge of the adsorption groove in the circle (see reference). Figure 2The area of ​​the adsorption trench region is divided by a non-black circle, and the ratio of the area of ​​the adsorption trench region to the area of ​​the annular plane region is 1:0.95 to 1.05. To avoid the chuck coming into contact with the warped area near the edge of the wafer, which would prevent the formation of a stable sealing space, the distribution area of ​​the adsorption trench is designed to be the area in the middle of the chuck, i.e., the adsorption trench region. Calculations show that if the diameter of the chuck is D, the diameter of the adsorption trench region is generally recommended to be around 0.7D. At the same time, the distribution and size (groove shape, groove depth, groove width) of the adsorption trench are calculated and determined according to the principle of having an appropriate safety factor for the suction force. It is generally recommended that the adsorption contact area should account for at least 50% of the area of ​​the adsorption trench region.

[0026] For small-diameter vacuum suction cups, 3 to 4 annular grooves 4 are provided in the adsorption groove region 2, and a negative pressure through hole 3 is provided at the center of the adsorption groove region 2. All the annular grooves 4 are connected to the negative pressure through hole 3 through radial straight grooves 5.

[0027] Similar to existing technologies, the radial straight groove 5 includes a short straight groove 52 used only to connect two adjacent annular grooves and a perforated straight groove 51 extending from the innermost annular groove to the negative pressure through hole.

[0028] To maintain uniform suction, there are four perforated straight grooves 51, and the short straight grooves 52 are distributed on six to eight straight segments that radiate outward from the center of the suction cup.

[0029] To avoid wafer deformation caused by suction cup adsorption, it is recommended that the working surface diameter of the suction cup not exceed 120mm, the width of the annular groove 4 not exceed 4mm, the width of the radial straight groove 5 not exceed 2mm, and the depth of the annular groove 4 and the radial straight groove 5 not exceed 4mm.

[0030] Example: A factory has a negative pressure main pipeline with a nominal diameter of 100mm and a pressure of -80Kpa. It wants to modify its existing wafer vacuum chuck to maintain reliable suction for 8-inch warped wafers. The existing vacuum chuck uses a negative pressure connecting tube with a nominal diameter of 6mm. The modified chuck will still use this connecting tube, and the calculated suction force should be greater than -21kPa. Figure 2 , Figure 3 and Figure 4As shown, a vacuum chuck for adsorbing 8-inch wafers includes a chuck body and adsorption grooves on the working surface of the chuck that communicate with negative pressure through-holes 3. The working surface of the chuck is divided into a circular adsorption groove region 2 and an annular planar region 1 surrounding the adsorption groove region 2, with the outermost circle of the adsorption groove as the boundary. Three annular grooves 4 are provided in the adsorption groove region 2. A negative pressure through-hole 3 with a diameter of 1.5 mm is provided at the center of the adsorption groove region 2. All the annular grooves 4 are connected to the negative pressure through-holes 3 through radial straight grooves 5. The radial straight grooves 5 include grooves only used to connect two adjacent annular grooves. The suction cup consists of four short straight grooves 52 and four perforated straight grooves 51 extending from the innermost annular groove to the negative pressure through-hole. The short straight grooves 52 are distributed on eight radially arranged straight segments radiating outwards from the center of the suction cup. The working surface diameter of the suction cup is 117.6 mm. The width of the annular groove 4 is 4 mm, the width of the radial straight groove 5 is 1.5 mm, and the depth of both the annular groove 4 and the radial straight groove 5 is 3 mm. From the center outwards, the center distances between the inner edge of the first annular groove, the inner edge of the second annular groove, and the inner edge of the third annular groove and the center of the suction cup are 11 mm, 23.55 mm, and 36.1 mm, respectively. The above suction cup adsorption groove design is based on the following concept.

[0031] I. Vacuum and Pressure Calculations in Fluid Mechanics First, according to the ideal gas law pV=nRT (where p is pressure, V is volume, n is amount of substance, R is universal gas constant, and T is thermodynamic temperature), when the gas inside the suction cup is extracted to form a vacuum, the pressure difference Δp inside and outside the suction cup is the key factor in generating the suction force F. The suction force F can be calculated by the formula F=Δp×S (where S is the effective adsorption area of ​​the suction cup).

[0032] To ensure proper suction, the vacuum level within the suction cup must be maintained stably during operation. This necessitates considering the impact of the channel on gas flow. The channel must allow for smooth gas extraction, but it should not be too wide or deep, which could lead to excessive vacuum leakage and compromise the maintenance of the vacuum level.

[0033] II. The Influence of Channel Dimensions on Airflow Width w: From the perspective of gas flow, according to the pipe flow theory in fluid mechanics, the channel can be regarded as a pipe with a rectangular cross-section. For laminar flow, the flow rate Q is related to the channel width w, depth h, and pressure difference between the two ends. To ensure that the gas can be quickly extracted, the channel width cannot be too small, otherwise it will increase the flow resistance; but it also cannot be too large, otherwise it will reduce the contact area between the suction cup and the adsorbed surface, affecting the effective adsorption area S, and thus affecting the suction force F.

[0034] Depth h: If the depth is too shallow, it will increase the flow resistance and make it difficult for gas to be discharged; if the depth is too deep, it will affect the rigidity of the suction cup and may cause the channel to be easily blocked during adsorption, or prevent the suction cup from adsorbing the surface well, thus affecting the maintenance of vacuum.

[0035] Channel placement design: The channel placement typically considers the uniform discharge of gas, generally radiating outwards from the center of the suction cup towards the edges. This design allows gas in the central area to flow evenly towards the edges through the channels, ensuring uniform vacuum levels throughout the suction cup and thus uniform suction distribution, avoiding localized insufficient or excessive suction.

[0036] III. Based on the above calculation formulas, design a vacuum chuck suitable for use with 8-inch wafers.

[0037] like Figure 5 As shown, for an 8-inch wafer with a maximum warpage of 0.78 mm, the overall contact area between the wafer and the chuck needs to be appropriately reduced to avoid vacuum leakage due to warpage. Experimental data indicates that to achieve an adsorption force greater than -21 kPa, the maximum diameter of the chuck should be designed to be 117.6 mm. Three concentric annular grooves should be designed from the center outwards, with the largest annular groove having a diameter 80.2 mm greater than its outer edge. The center-to-center distances of the inner edges of the first, second, and third grooves are 11 mm, 23.55 mm, and 36.1 mm, respectively. The three concentric annular grooves are 4 mm wide and 3 mm deep, divided into eight equal sections, with a designed vacuum contact area of ​​approximately 2220 ± 5 mm². 2 The outermost ring to the edge of the suction cup is a solid plane, and there are corresponding requirements for the flatness of the plane. The width of the solid contact protrusion in the vacuum contact area is 8.55mm, and the total area, S, is approximately 2823±5mm². 2 The ratio of the area of ​​the adsorption trench region to the area of ​​the annular plane region is approximately 1:1, and the adsorption contact area accounts for about 56% of the area of ​​the adsorption trench region.

[0038] When the aforementioned suction cups were used in production, it was found that they still had sufficient adsorption capacity for warped wafers, and their use was reliable.

[0039] For larger wafers, such as 12-inch wafers, the above design concept can be used to calculate the suction force and propose a suitable trench distribution diagram. For example, there can be 5 to 8 annular trenches.

Claims

1. A vacuum chuck for wafer adsorption, comprising a chuck body and an adsorption groove disposed on the working surface of the chuck and connected to a negative pressure through hole (3), wherein the working surface of the chuck is divided into a circular adsorption groove region (2) and an annular planar region (1) surrounding the adsorption groove region (2), the two being demarcated by the outermost circle containing the outer edge of the adsorption groove, characterized in that: The ratio of the area of ​​the adsorption trench region to the area of ​​the annular plane region is 1:0.95 to 1.

05.

2. The vacuum chuck for wafer adsorption as described in claim 1, characterized in that: Within the adsorption trench area, the adsorption contact area accounts for more than 50% of the total area of ​​the adsorption trench area.

3. The vacuum chuck for wafer adsorption as described in claim 1, characterized in that: The adsorption groove area (2) is provided with 3 to 4 annular grooves (4), and a negative pressure through hole (3) is provided at the center of the adsorption groove area (2). All the annular grooves (4) are connected to the negative pressure through hole (3) through radial straight grooves (5).

4. The vacuum chuck for wafer adsorption as described in claim 3, characterized in that: The radial straight groove (5) includes a short straight groove (52) used only to connect two adjacent annular grooves and a perforated straight groove (51) extending from the innermost annular groove to the negative pressure through hole.

5. The vacuum chuck for wafer adsorption as described in claim 4, characterized in that: There are 4 perforated straight grooves (51), and the short straight grooves (52) are distributed on 6 to 8 straight segments that radiate outward from the center of the suction cup.

6. The vacuum chuck for wafer adsorption as described in claim 3, characterized in that: The width of the annular groove (4) is no more than 4 mm, the width of the radial straight groove (5) is no more than 2 mm, and the depth of the annular groove (4) and the radial straight groove (5) is no more than 4 mm.

7. The vacuum chuck for wafer adsorption as described in claim 6, characterized in that: The working surface diameter of the suction cup is 117.6 mm. There are 3 annular grooves (4). The width of the annular grooves (4) is 4 mm. The width of the radial straight grooves (5) is 1.5 mm. The diameter of the negative pressure through hole (3) is 1.5 mm. The depth of the annular grooves (4) and the radial straight grooves (5) is 3 mm. From the center outward, the center distances between the inner edge of the first annular groove, the inner edge of the second annular groove, and the inner edge of the third annular groove and the center of the suction cup are 11 mm, 23.55 mm, and 36.1 mm, respectively.

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