Metal filling method for wafer through-hole structure

Abstract

The present invention discloses a metal filling method for a wafer through-hole structure, comprising the following steps: preparing a through-hole in a first wafer; depositing a photoresist layer and a conductive layer on the surface of a second wafer in sequence; fastening the first wafer and the second wafer together so that the conductive layer abuts against the bottom surface of the through-hole in the first wafer; placing the first wafer and the second wafer in an electroforming liquid for electroforming metal filling so that the electroforming metal is filled in the through-hole from the bottom to the top of the through-hole; immersing the first wafer and the second wafer in a debonding solvent for separation, removing the electroforming metal and the conductive layer outside the through-hole, and obtaining a wafer through-hole structure filled with electroforming metal. The metal filling method for a wafer through-hole structure provided by the present invention does not need to adopt a complex second wafer bonding process, can form a stable bottom surface support and conductive layer support structure, and the first wafer and the second wafer are easy to separate, and is suitable for metal filling of through-holes of any size and shape.

Description

Technical Field

[0001] The invention relates to the field of wafer through-hole structure preparation, and in particular to a metal filling method for a wafer through-hole structure. Background Art

[0002] MEMS (micro-electromechanical system) technology usually involves complex micro-mechanical processing technology, and sometimes it is necessary to make and fill through-hole structures on various types of wafers to achieve specific functions or for packaging interconnection. In the process of preparing some devices, it is necessary to use the through-hole structure on the fully metal-filled wafer as the lead column on the wafer, so that the metal structure can be vertically connected between the upper and lower surfaces of the wafer. This wafer with through-hole metal filling can be used in the packaging process of many MEMS devices, or vertical lead structure, to replace lead pads in certain specific application requirements. In addition, this wafer structure with metal filling can realize the lead-out of direct through-hole electrodes inside the cavity of some devices in combination with the wafer bonding process, which is one of the methods for electrical leads inside the MEMS sealed cavity.

[0003] At present, the commonly used methods for filling metal through holes in wafers include TSV process, slurry sintering filling technology, and second substrate bonding electroplating filling. The TSV process is based on a silicon-based through-hole structure, and generally uses an electroplating copper process to fill the hole. It is often used in the packaging of electronic circuits to achieve vertical interconnection of 3D structures. Generally, an etching process is used to form a narrow through-hole or blind hole structure, and a metal conductive layer is deposited on the inner wall surface of the hole, and then metal copper is filled through processes such as photolithography and electroplating. For example, an efficient TSV filling method disclosed in the invention patent CN10567901A is a rapid filling process based on the traditional TSV process and using a double-sided electroplating method. Since the TSV process is mainly for integrated circuit packaging applications, the inner side wall electroplating sealing method used in the process is more suitable for narrow and long hole structures with a large depth and width ratio.

[0004] The slurry filling process is commonly used in electronic packaging and printed circuit board hole filling, etc. It mainly uses appropriate organic mixed metal powder or molten metal as through-hole filler. Slurry electroforming metal generally must go through a sintering or curing process. Compared with electroforming hole filling, the hole filling process must be under appropriate heat treatment conditions, and the temperature difference is more likely to cause stress between the electroformed metal and the hole structure.

[0005] Bonding the second substrate to the wafer to be filled with holes, and using the bonding surface and the second substrate as the support structure of the bottom surface and the conductive layer is also an important process for the current wafer metal filling process. For example, in patent CN109037149A, a method for preparing a defect-free through-silicon via structure is disclosed. By bonding the first wafer and the second wafer together, the conductive layer in the second wafer is attached to the bottom of the through hole in the first wafer, so that the metal can gradually grow from the bottom to the top until the entire through hole is completely filled; however, after the through hole is filled in this technology, multiple corrosion and thinning process steps are required to remove the second wafer and the conductive layer, which prolongs the preparation time of the entire wafer through hole structure, and the subsequent multiple corrosion and thinning process steps will also affect the quality of the through hole structure, which is not conducive to the continuous maintenance of high-quality through hole structures. Summary of the invention

[0006] The present invention aims to solve at least one of the problems in the related art to a certain extent. To this end, the purpose of the present invention is to provide a method for metal filling of a wafer through-hole structure, which does not require a complex second wafer bonding process, can form a stable bottom surface support and conductive layer support structure, and the first wafer and the second wafer are easy to separate, and is suitable for metal filling of through-holes of any size and shape.

[0007] In order to achieve the above-mentioned purpose, the present application adopts the following technical solution: A metal filling method for a wafer through-hole structure comprises the following steps:

[0008] S1: preparing a through hole in a first wafer; and sequentially depositing a photoresist layer and a conductive layer on a surface of a second wafer;

[0009] S2: fastening the first wafer and the second wafer together so that the conductive layer abuts against the bottom surface of the through hole in the first wafer;

[0010] S3: placing the first wafer and the second wafer in the electroforming liquid to perform electroforming metal filling, so that the electroforming metal is filled in the through hole from the bottom of the through hole to the top of the through hole;

[0011] S4: Soaking the first wafer and the second wafer in a degumming solvent to separate them, removing the electroformed metal and the conductive layer outside the through hole, and obtaining a wafer through hole structure filled with the electroformed metal.

[0012] Furthermore, step S2 uses a fastening tool to fasten the first wafer and the second wafer together, and the fastening tool is provided with a groove for placing the first wafer and the second wafer, and an upper cover is provided on the top of the groove. When the upper cover covers the outer periphery of the top end of the first wafer, the upper cover and the first wafer are sealed by a rubber ring.

[0013] Furthermore, the upper cover of the fastening tool is fixed to the top of the groove by a fastener, a rubber ring is used to seal between the fastener and the upper cover, and a rubber ring is used to seal between the upper cover and the top of the groove.

[0014] Furthermore, in step S3, after the first wafer and the second wafer are placed in the electroforming liquid to be filled with electroforming metal, the height of the electroforming metal in the through hole is greater than the height of the through hole.

[0015] Furthermore, before separating the first wafer from the second wafer in step S4, the top of the first wafer is flattened by mechanical grinding and polishing to remove excess electroformed metal.

[0016] Furthermore, after the first wafer and the second wafer are separated in step S4, the bottom end of the first wafer is flattened by mechanical grinding and polishing to remove the conductive layer.

[0017] Furthermore, in the mechanical grinding and polishing method, aluminum oxide and silicon oxide are used as abrasives in sequence for mechanical grinding and polishing, and the height difference between the wafer and the electroformed metal surface after mechanical grinding and polishing is 6-8 microns, and the roughness Ra is less than or equal to 20nm.

[0018] Furthermore, the thickness of the photoresist layer is greater than 80 microns.

[0019] Furthermore, in step S1, a conductive layer is deposited on the photoresist layer by physical vapor deposition, and the conductive layer is a TiCu layer or a TiAu layer or a CrCu layer or a CrAu layer.

[0020] Furthermore, the diameter of the second wafer is greater than the diameter of the first wafer, and in step S2, the centers of the first wafer and the second wafer are overlapped and fastened together.

[0021] The above technical solution provided by the embodiment of the present application has the following advantages compared with the prior art: in the present application, the first wafer and the second wafer are fastened together by external force without the need for bonding, and in the process of electroforming metal, since the conductive layer on the surface of the second wafer is placed below the through hole in the first wafer, the electroformed metal filling the hole will gradually grow upward from the bottom of the through hole; regardless of the aperture size and shape of the through hole, even an irregular through hole structure can be uniformly filled, and the defective structure that is easily formed by sidewall growth filling and the complex electroforming parameter control requirements can be avoided. After the electroplating metal filling is completed in the present application, it is only necessary to dissolve the photoresist layer to separate the first wafer from the second wafer, and then the wafer through-hole structure can be obtained by surface processing the first wafer. The present application avoids the process steps of wafer bonding in the prior art, and only adopts the method of tooling locking and fixing to maintain the relative position and gap between the upper and lower wafers during the electroplating process. The second wafer as a conductive substrate is not affected by any process in the above process, which is a lossless process, and therefore can continue to be recycled as a substrate, which improves the utilization rate of the second wafer, simplifies the entire process steps, and improves the electroplating efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the invention and, together with the description, serve to explain the principles of the invention.

[0023] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0024] In the attached figure:

[0025] Figure 1 This is a flow chart of the metal filling method of the wafer through-hole structure in the present application;

[0026] Figure 2 A schematic diagram for selecting a first wafer;

[0027] Figure 3 is a schematic diagram of preparing a through hole in a first wafer;

[0028] Figure 4 A schematic diagram for selecting a second wafer;

[0029] Figure 5 is a schematic diagram of depositing a photoresist layer on a second wafer;

[0030] Figure 6 is a schematic diagram of depositing a conductive layer on a second wafer;

[0031] Figure 7 A schematic diagram of bonding a first wafer to a second wafer;

[0032] Figure 8 is a schematic diagram of a first wafer and a second wafer being fastened by a fastening tool;

[0033] Fig. 9 is a schematic diagram of a first wafer and a second wafer being electroformed with electroformed metal;

[0034] Fig.10 This is a schematic diagram of the first mechanical grinding and polishing;

[0035] Fig.11 Schematic diagram of separating the first wafer from the second wafer

[0036] Fig.12 It is a schematic diagram of the second mechanical grinding and polishing;

[0037] Reference numerals: 1. first wafer; 2. through hole; 3. second wafer; 4. photoresist layer; 5. conductive layer; 6. fastening tooling; 61. upper cover; 62. rubber ring; 63. electrical pad; 64. fastener; 7. electroformed metal. DETAILED DESCRIPTION

[0038] In order to have a clearer understanding of the technical features, purposes and effects of the present invention, the specific embodiments of the present invention are now described in detail with reference to the accompanying drawings. In the following description, it should be understood that the directions or positional relationships indicated by "front", "back", "up", "down", "left", "right", "longitudinal", "horizontal", "vertical", "horizontal", "top", "bottom", "inside", "outside", "head", "tail", etc. are based on the directions or positional relationships shown in the accompanying drawings, are constructed and operated in a specific direction, and are only for the convenience of describing the present technical solution, rather than indicating that the mechanism or element referred to must have a specific direction, and therefore cannot be understood as a limitation to the present invention.

[0039] It should also be noted that, unless otherwise clearly specified and limited, the terms such as "installed", "connected", "connected", "fixed", "set" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral one; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. When an element is referred to as being "on" or "under" another element, the element can be "directly" or "indirectly" located on the other element, or there may be one or more intermediate elements. The terms "first", "second", "third", etc. are only for the convenience of describing the present technical solution, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first", "second", "third", etc. can explicitly or implicitly include one or more of the features. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to the specific circumstances.

[0040] In the following description, specific details such as specific system structures, technologies, etc. are provided for the purpose of illustration rather than limitation, so as to provide a thorough understanding of the embodiments of the present invention. However, it should be clear to those skilled in the art that the present invention may be implemented in other embodiments without these specific details. In other cases, detailed descriptions of well-known systems, mechanisms, circuits, and methods are omitted to prevent unnecessary details from obstructing the description of the present invention.

[0041] Example 1

[0042] See also Figure 1-Figure 12 The present application provides a method for metal filling of a wafer through-hole structure, comprising the following steps:

[0043] S1: preparing a through hole in a first wafer; and sequentially depositing a photoresist layer and a conductive layer on a surface of a second wafer;

[0044] S2: fastening the first wafer and the second wafer together so that the conductive layer abuts against the bottom surface of the through hole in the first wafer;

[0045] S3: placing the first wafer and the second wafer in the electroforming liquid to perform electroforming metal filling, so that the electroforming metal is filled in the through hole from the bottom of the through hole to the top of the through hole;

[0046] S4: Soaking the first wafer and the second wafer in a degumming solvent to separate them, removing the electroformed metal and the conductive layer outside the through hole, and obtaining a wafer through hole structure filled with the electroformed metal.

[0047] In the present application, the first wafer and the second wafer are fastened together by external force without bonding. In the process of electroplating metal, since the conductive layer on the surface of the second wafer is placed below the through hole in the first wafer, the electroplated metal filling the hole will gradually grow upward from the bottom of the through hole; regardless of the aperture size and shape of the through hole, even the irregular through hole structure can achieve uniform filling, and can avoid the defect structure easily formed by the side wall growth filling hole and the complex electroplating parameter control requirements. After the electroplating metal filling of the present application is completed, it is only necessary to dissolve the photoresist layer to achieve the separation of the first wafer and the second wafer, and then the wafer through hole structure can be obtained by surface treatment of the first wafer. The present application avoids the process steps of wafer bonding in the prior art, and only adopts the method of tooling locking and fixing to maintain the relative position and gap between the upper and lower wafers during the electroplating process. The second wafer as a conductive substrate is not affected by any process in the above process, which belongs to a non-destructive process, so it can continue to be recycled as a substrate, that is, the utilization rate of the second wafer is improved, and the entire process steps are simplified, and the electroplating efficiency is improved.

[0048] Example 2

[0049] See also Figure 1 The present application provides a method for metal filling of a wafer through-hole structure, comprising the following steps:

[0050] S1: preparing a through hole in the first wafer; and sequentially depositing a photoresist layer and a conductive layer on the surface of the second wafer.

[0051] like Figure 2 As shown, the material of the first wafer 1 can be any material, such as a 500 micron thick four-inch silicon wafer as the first wafer. Commonly used first wafer materials can be, for example, silicon wafers, quartz wafers, silicon carbide wafers, aluminum oxide wafers, gallium arsenide wafers, etc. The specific material can be selected according to the applicable occasion of the wafer through-hole structure.

[0052] like Figure 3 As shown, in the preparation process of the through hole 2 in this step, there are different through hole preparation methods for different wafers. For example, commonly used through hole preparation methods include dry etching, wet etching, ultrasonic drilling, laser drilling, micromechanical drilling and other processing methods. The micro-process involved in the hole making process mentioned here is not the scope of protection involved in this patent.

[0053] like Figure 4 As shown, the main function of the second wafer 3 is to provide a substrate for the first wafer during the electroforming process. The diameter of the second wafer is slightly larger than the diameter of the first wafer, ensuring that the second wafer can evenly provide a substrate for each through hole in the first wafer. The material of the second wafer in this application can specifically be quartz glass.

[0054] like Figure 5As shown, a photoresist layer 4 is formed on the surface of the selected second wafer 3 by spin coating photoresist or dry film pasting, and the photoresist layer is pre-heated at an appropriate temperature. The photoresist layer has the characteristic of being easily soluble in the corresponding degumming solvent, and the thickness range of the photoresist layer finally formed should be controlled to be above 80 microns.

[0055] like Figure 6 As shown, a conductive layer 5 is deposited on the photoresist layer 4. The conductive layer 5 is a TiCu layer, a TiAu layer, a CrCu layer, or a CrAu layer. Common deposition methods include physical vapor deposition, such as magnetron sputtering.

[0056] S2: Fasten the first wafer and the second wafer together so that the conductive layer abuts against the bottom surface of the through hole in the first wafer.

[0057] like Figure 7 As shown, the centers of the first wafer 1 and the second wafer 3 are aligned and bonded together, and then fastened together. Note: During the bonding process, the conductive layer faces a side surface of the through hole in the first wafer.

[0058] Specifically, Figure 8 As shown, the present application uses a fastening tool 6 to fasten the first wafer 1 and the second wafer 3 together. The fastening tool 6 is provided with a groove for placing the first wafer 1 and the second wafer 3. The top of the groove is provided with an upper cover 61, and the upper cover 61 is used to fasten the first wafer 1 and the second wafer 3 inside the groove. In addition, the fastening tool also includes a rubber ring 62 for sealing and a conductive power pad 63.

[0059] When the upper cover covers the periphery of the top of the first wafer, the upper cover and the first wafer are sealed by a rubber ring. At the same time, the upper cover of the fastening tool is fixed to the top of the groove by a fastener 64, and a rubber ring is used to seal the fastener 64 and the upper cover, and the upper cover and the top of the groove are sealed by a rubber ring. The fastener 64 can be a locking screw. The electrical gasket 63 is connected to the conductive layer 5 of the second wafer 3. When the wafers are placed, the second wafer is located below the first wafer, and the through hole is located at the top of the groove.

[0060] In the present application, the rubber ring enables sealing between the first wafer and the upper cover, sealing between the upper cover and the groove, and sealing between the fastener 64 and the upper cover 61, ensuring that when the fastening tool 6 is placed in the electroforming liquid in the next step, the electroforming liquid can only contact the conductive layer from the position of the through hole.

[0061] S3: Fig. 9 As shown, the first wafer 1 and the second wafer 3 are placed in an electroforming liquid for electroforming metal filling, so that the electroforming metal 7 is filled in the through hole from the bottom to the top of the through hole.

[0062] This application can use conventional copper electroforming solution, and control the current density to 15mA / cm 2 The electroforming time is 6 to 8 hours. Metal copper is electroformed into the through-hole until the 400-micron-deep through-hole is filled with metal copper, and all the electroformed metal in the hole is 20 to 30 microns higher than the wafer surface.

[0063] S4: Soak the first wafer and the second wafer in a degumming solvent to separate them, remove the electroformed metal and the conductive layer outside the through hole, and obtain a wafer through hole structure filled with electroformed metal. The specific steps include:

[0064] S41: Fig.10 As shown, the stacked wafers after the electroforming holes are taken out and the fastening tooling is removed. At this time, the two wafers cannot be separated temporarily due to the electroforming metal filling. Before the first wafer 1 and the second wafer 3 are separated, the electroforming metal 7 that is higher than the surface of the first wafer after the electroforming holes are filled is flattened by mechanical grinding and polishing.

[0065] Specifically, the top of the first wafer can be flattened by mechanical grinding and polishing to remove excess electroformed metal. For example, use 20 micron aluminum oxide abrasives for grinding for 20 minutes, then use 9 micron aluminum oxide abrasives for grinding for 15 minutes, and use nano silicon oxide polishing liquid to polish the surface for 30-40 minutes. The height difference between the wafer and the metal surface is 6-8 microns, and the roughness Ra value is about 20nm.

[0066] S42: Fig.11 As shown, the stacked wafers that have been polished for the first time are placed in an acetone solution, and ultrasonic vibration is used to dissolve the photoresist layer in the acetone, so that the first wafer 1 and the second wafer 3 are separated. The first wafer is taken out, and the residual acetone solution of the first wafer is rinsed with deionized water. At this time, the conductive layer 5 of the second wafer will be connected to the first wafer due to the dissolution of the photoresist layer.

[0067] S43: Fig.12 As shown, after the first wafer 1 and the second wafer 3 are separated, the bottom of the first wafer 1 is flattened by mechanical grinding and polishing to remove the conductive layer. Aluminum oxide abrasive with a particle size of 9 microns is used for grinding for 15 minutes, and nano silicon oxide polishing liquid is used for polishing the surface for 30-40 minutes. The height difference between the wafer and the metal surface is 6-8 microns, and the roughness Ra value is about 20nm.

[0068] S44: cleaning the first wafer after the secondary planarization process, and drying it in an oven at 110° C. for 20 minutes to obtain a metal copper-filled through-hole silicon-based wafer structure with planarization on both sides.

[0069] The shape, size, hole depth, etc. of the wafer holes filled by electroforming in this application are not limited by the process itself. Different from the electroforming growth method of the metal conductive layer on the side in the commonly used TSV process, the TSV process fills the holes by electroforming the hole wall toward the center of the hole, mainly for narrow holes with large depth and small aperture. Since the conductive layer on the surface of the second wafer is placed below the wafer to be filled, the electroformed metal to fill the hole will gradually grow from the bottom of the through hole. Regardless of the size and shape of the hole, even irregular hole structures can be filled, and the defective structure that is easily formed by sidewall growth filling and the complex electroforming parameter control requirements can be avoided.

[0070] The method of providing support and conductive layer for the second wafer in the present application avoids the bonding process steps in existing similar processes. Existing bonding processes all require specific process steps, such as vacuum hot pressing and other methods, to bond the upper and lower wafers through the surface metal layer. And finally, after the hole filling process is completed, the corresponding substrate removal means must be used to remove the second substrate, making the overall manufacturing process relatively complicated. However, the present application is combined with a fastening tooling, and only uses the tooling locking and fixing method to maintain the relative position and gap between the upper and lower wafers during the electroplating process, without the need for complex wafer bonding processing.

[0071] The separation process of the first wafer and the second wafer after the hole filling is completed in this application is simple, and the second wafer can be reused. Since the two wafers are not connected by a bonding process, a relatively thick photoresist layer is first prepared on the surface of the second wafer as an isolation layer, and then a conductive layer is prepared as a substrate. Therefore, after the hole filling process is completed, the thick photoresist layer on the surface of the second wafer can be dissolved by simply soaking in a degumming solution, thereby separating it from the hole-filling wafer. As a conductive substrate wafer, it is not affected by any process in the above process, and it is a lossless process, so it can continue to be reused as a substrate wafer.

[0072] It can be understood that the above embodiments only express the preferred implementation modes of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the patent scope of the present invention. It should be pointed out that, for ordinary technicians in this field, the above technical features can be freely combined without departing from the concept of the present invention, and several deformations and improvements can be made, which all belong to the protection scope of the present invention. Therefore, all equivalent changes and modifications made to the scope of the claims of the present invention should belong to the coverage of the claims of the present invention.

Claims

1. A metal filling method for a wafer through-hole structure, characterized in that: The steps include: S1: preparing a through hole in a first wafer; and sequentially depositing a photoresist layer and a conductive layer on a surface of a second wafer; S2: fastening the first wafer and the second wafer together using a fastening tool so that the conductive layer abuts against the bottom surface of the through hole in the first wafer; The fastening fixture is provided with a groove for placing the first wafer and the second wafer, and an upper cover is provided on the top of the groove. When the upper cover covers the periphery of the top of the first wafer, the upper cover and the first wafer are sealed by a rubber ring to ensure that the electroforming liquid can only contact the conductive layer from the position of the through hole; The upper cover of the fastening tool is fixed to the top of the groove by a fastener, the fastener and the upper cover are sealed with a rubber ring, and the upper cover and the top of the groove are sealed with a rubber ring; the electrical pad is connected to the conductive layer of the second wafer; S3: placing the first wafer and the second wafer in the electroforming liquid to perform electroforming metal filling, so that the electroforming metal is filled in the through hole from the bottom of the through hole to the top of the through hole; S4: The top of the first wafer is flattened by mechanical grinding and polishing to remove excess electroformed metal; the first wafer and the second wafer are separated by immersing in a degumming solvent to remove the electroformed metal outside the through hole, and the bottom of the first wafer is flattened by mechanical grinding and polishing to remove the conductive layer to obtain a wafer through hole structure filled with electroformed metal.

2. The metal filling method of a wafer through-hole structure according to claim 1, characterized in that: In step S3, after the first wafer and the second wafer are placed in the electroforming liquid to be filled with electroforming metal, the height of the electroforming metal in the through hole is greater than the height of the through hole.

3. The metal filling method of a wafer through-hole structure according to claim 1, characterized in that: In the mechanical grinding and polishing method, aluminum oxide and silicon oxide are used as abrasives in sequence for mechanical grinding and polishing, and the height difference between the wafer and the electroformed metal surface after mechanical grinding and polishing is 6-8 microns, and the roughness Ra is less than or equal to 20nm.

4. The metal filling method of a wafer through-hole structure according to claim 1, characterized in that: The thickness of the photoresist layer is greater than 80 microns.

5. The metal filling method of a wafer through-hole structure according to claim 1, characterized in that: In step S1, a conductive layer is deposited on the photoresist layer by using a physical vapor deposition method, and the conductive layer is a TiCu layer or a TiAu layer or a CrCu layer or a CrAu layer.

6. The metal filling method of a wafer through-hole structure according to claim 1, characterized in that: The diameter of the second wafer is greater than the diameter of the first wafer, and in step S2, the centers of the first wafer and the second wafer are overlapped and fastened together.

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