Dense coil preparation method and dense coil

Abstract

The embodiment of the invention provides a dense coil preparation method and a dense coil, and the method comprises the steps: providing a wafer, and enabling the functional surface of the wafer to be provided with a bonding pad; forming a seed layer on the functional surface of the wafer; a photoresist layer is formed on the seed layer, the photoresist layer is patterned to form a window, and the size of the cross section of the top wall of the window is smaller than that of the cross section of the bottom wall of the window; electroplating in the window by adopting first current density to form a first metal bump, wherein the first metal bump is electrically connected with the bonding pad through the seed layer; a second metal bump is formed on the first metal bump through electroplating by adopting a second current density, so that a coil body is formed, and the second current density is larger than the first current density; and removing the residual photoresist layer and part of the seed layer. The dense coil obtained through the dense coil preparation method can be prevented from falling off, and the reliability is high.

Description

Technical Field

[0001] The disclosed embodiments belong to the field of semiconductor process technology, and specifically relate to a dense coil preparation method and a dense coil. Background Art

[0002] like Figure 1 As shown in the figure, in the MEMS product design, there will be a large area of ​​dense Au coil design, and there will be independent standard Au wire design at both ends of the coil. The spacing between the Au wires in the dense Au coil is narrow, and the coil density is high (spacing ≤ 15um). The dense Au coil & independent standard Au wire design both have the characteristics of high aspect ratio (height: width ≥

[0003] The dense Au wire design will cause stress concentration between the Au wire and the UBM (electroplating seed layer), and the aspect ratio will cause the Au wire to have weak shear resistance. Both of these will cause the Au wire to fall off.

[0004] On the one hand, the stress can be effectively reduced by reducing the thickness of the UBM layer (electroplating seed layer), but as the thickness of the UBM layer decreases, the resistance value increases, and the conductivity deteriorates during the electroplating process, resulting in poor uniformity of the height of the Au wire, which cannot meet the height uniformity requirements. On the other hand, increasing the annealing temperature or extending the annealing time can help release the stress of the Au wire and the UBM layer, but it will reduce the hardness of the Au wire, resulting in low shear force of the Au wire.

[0005] In view of the above problems, it is necessary to propose a dense coil preparation method and a dense coil that are reasonably designed and effectively solve the above problems. Summary of the invention

[0006] The embodiments of the present disclosure aim to solve at least one of the technical problems existing in the prior art and provide a dense coil preparation method and a dense coil.

[0007] One aspect of an embodiment of the present disclosure provides a method for preparing a dense coil.

[0008] Preparation methods include:

[0009] Providing a wafer, wherein a functional surface of the wafer is provided with a bonding pad;

[0010] forming a seed layer on a functional surface of the wafer;

[0011] Forming a photoresist layer on the seed layer, and patterning the photoresist layer to form a window, wherein the cross-sectional dimension of the top wall of the window is smaller than the cross-sectional dimension of the bottom wall of the window;

[0012] Electroplating a first metal bump in the window using a first current density, wherein the first metal bump is electrically connected to the pad through the seed layer;

[0013] electroplating a second metal bump on the first metal bump with a second current density to form a coil body, wherein the second current density is greater than the first current density;

[0014] The remaining photoresist layer and a portion of the seed layer are removed.

[0015] Optionally, the first current density ranges from less than 0.3 ASD, and the second current density ranges from 0.5 ASD to 0.6 ASD.

[0016] Optionally, the height of the first metal bump is greater than or equal to 1 / 3 of the height of the coil body.

[0017] Optionally, patterning the photoresist layer to form a window includes:

[0018] Providing a mask, wherein the mask is provided with a preset shape matching the coil body;

[0019] placing the mask on the photoresist layer;

[0020] Using the mask as a mask, the photoresist layer is exposed and developed to transfer the preset shape to the photoresist layer to form the window on the photoresist layer; wherein,

[0021] The exposure focus height range is 50um to 70um.

[0022] Optionally, the cross-sectional size of the window gradually increases from its top wall to its bottom wall.

[0023] Optionally, removing part of the seed layer includes:

[0024] The seed layer is etched to remove a portion of the seed layer, so that the remaining seed layer is only connected to the first metal bump.

[0025] Another aspect of the present disclosure provides a dense coil, the dense coil comprising:

[0026] A wafer, wherein a pad is disposed on a functional surface of the wafer;

[0027] A seed layer, disposed on the functional surface of the wafer;

[0028] The coil body is disposed on the seed layer and electrically connected to the pad through the seed layer, and the cross-sectional dimension of the top wall of the coil body is smaller than the cross-sectional dimension of the bottom wall of the coil body; wherein,

[0029] The coil body includes a first metal bump disposed on the seed layer and a second metal bump disposed on the first metal bump.

[0030] Optionally, the height of the first metal bump is greater than or equal to 1 / 3 of the height of the coil body.

[0031] Optionally, the cross-sectional dimension of the coil body gradually increases from its top wall to its bottom wall.

[0032] Optionally, the coil body is a gold coil.

[0033] The dense coil preparation method and dense coil of the embodiment of the present disclosure, in the dense coil preparation method, a window is formed by patterning a photoresist layer, and the cross-sectional size of the top wall of the window is smaller than the cross-sectional size of the bottom wall of the window, so that the cross-sectional size of the top wall of the coil body formed by electroplating in the window is smaller than the cross-sectional size of the bottom wall, thereby increasing the contact area between the coil body and the seed layer, making the coil body more firmly fixed to the seed layer, and reducing the stress concentration of the dense coil on the seed layer; a first current density is used to electroplating in the window to form a first metal bump, and a second current density is used to electroplating on the first metal bump to form a second metal bump to form the coil body, and the first metal bump formed by electroplating with a low current density has a slow deposition speed, so that the stress generated by the first metal bump is small, and the second metal bump is electroplated on the first metal bump with a normal current density, thereby reducing the stress generated by the coil body. The dense coil prepared by the embodiment of the present disclosure can prevent the coil from falling off and has high reliability. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 A schematic diagram of the structure of a dense Au coil designed for a MEMS product in the prior art;

[0035] Figure 2 It is a schematic flow chart of a method for preparing a dense coil according to an embodiment of the present disclosure;

[0036] Figures 3 to 11 A schematic diagram of a process for preparing a dense coil according to another embodiment of the present disclosure;

[0037] Fig.12 The reliability verification result of the relationship between the exposure focus height limit and the window size of the first embodiment of the present disclosure;

[0038] Fig.13 The reliability verification result of the relationship between the exposure focus height definition and the coil body of the second embodiment of the present disclosure;

[0039] Fig.14 A curve diagram showing a change in first current density and wafer warpage in the third embodiment of the present disclosure;

[0040] Fig.15 A schematic diagram comparing the first current density, the wafer warpage change, and the height of the first metal bump in the fourth embodiment of the present disclosure;

[0041] Fig.16 A curve diagram showing the change of the electroplating height of the first metal bump and the wafer warpage of the fifth embodiment of the present disclosure;

[0042] Fig.17 It is a schematic diagram of the reliability verification result of the coil body of the fifth embodiment of the present disclosure;

[0043] Fig.18 This is a schematic structural diagram of a dense coil in another embodiment of the present disclosure. DETAILED DESCRIPTION

[0044] In order to enable those skilled in the art to better understand the technical solutions of the embodiments of the present disclosure, the embodiments of the present disclosure are further described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0045] like Figure 2 As shown, one aspect of an embodiment of the present disclosure provides a method S100 for preparing a dense coil, wherein the coil has a high aspect ratio, and the method S100 for preparing a dense coil comprises:

[0046] S110, providing a wafer, wherein a functional surface of the wafer is provided with a pad.

[0047] Specifically, Figure 3 As shown, a wafer 110 is provided, and a bonding pad 111 is disposed on a functional surface of the wafer 110 .

[0048] S120 , forming a seed layer on the functional surface of the wafer.

[0049] Specifically, Figure 4 As shown, a seed layer 120 is formed on the functional surface of the wafer 100 by sputtering through a sputtering process, and the seed layer 120 is electrically connected to each pad 111 of the wafer 100 .

[0050] S130, forming a photoresist layer on the seed layer, and patterning the photoresist layer to form a window, wherein a cross-sectional dimension of a top wall of the window is smaller than a cross-sectional dimension of a bottom wall of the window.

[0051] Specifically, step S130 may include:

[0052] First, if Figure 5As shown, a photoresist is coated on the seed layer 120 to form a photoresist layer 130. It should be noted that the photoresist layer 130 can be a positive photoresist or a negative photoresist. The type of the photoresist layer 130 can be selected according to actual needs and is not specifically limited in this embodiment.

[0053] Secondly, if Figure 6 As shown, a mask 200 is provided, on which a preset shape matching the coil body is arranged.

[0054] Again, if Figure 6 As shown, the mask 200 is placed on the photoresist layer 130 .

[0055] Again, if Figure 7 As shown, the photoresist layer 130 is exposed and developed using the mask 200 as a mask, and the preset shape on the mask 200 is transferred to the photoresist layer 130 to form a window 140 on the photoresist layer 130 .

[0056] The exposure focus height range is 50um to 70um, and the exposure focus height can make the cross-sectional size of the top wall of the formed window 140 smaller than the cross-sectional size of the bottom wall thereof.

[0057] For example, Figure 7 As shown, the cross-sectional dimension of the window 140 gradually increases from the top wall to the bottom wall. Specifically, the side wall of the window 140 may be in a linear plane shape. As shown in the figure, in this embodiment, the longitudinal section of the window 140 is trapezoidal.

[0058] In this embodiment, a window is formed by patterning the photoresist layer, and the cross-sectional dimension of the top wall of the window is smaller than the cross-sectional dimension of the bottom wall of the window, so that the cross-sectional dimension of the top wall of the coil body formed by electroplating in the window is smaller than the cross-sectional dimension of the bottom wall, thereby increasing the contact area between the coil body and the seed layer, making the coil body more firmly fixed to the seed layer, reducing the stress concentration of the dense coil on the seed layer, and increasing the reliability of the dense coil.

[0059] S140, electroplating in the window with a first current density to form a first metal bump, the first metal bump being electrically connected to the pad through the seed layer.

[0060] Specifically, Figure 8 As shown, a metal liquid is electroplated in the window 140 through an electroplating process using a first current density to form a first metal bump 150 in the window 140 , wherein the first metal bump 150 is electrically connected to the pad 111 of the wafer 110 through the seed layer 120 .

[0061] It should be noted that, in this embodiment, the first metal bump 150 is a gold bump.

[0062] Preferably, in this embodiment, the range of the first current density is less than 0.3ASD, that is, the first current density is lower than the normal current density, and is a low current density.

[0063] In this embodiment, the deposition speed of the first metal bump formed by low current density electroplating is slow, so that the stress generated by the first metal bump is small, thereby reducing the stress generated by the entire coil body. In addition, when the first current density is less than 0.3ASD, the warpage of the wafer changes little, and the stress generated by the electroplating of the first metal bump is small.

[0064] It should be noted that if Figure 8 As shown, since the cross-sectional dimension of the top wall of the window 140 is smaller than the cross-sectional dimension of the bottom wall, the cross-sectional dimension of the top wall of the first metal bump 150 formed in the window 140 is smaller than the cross-sectional dimension of the bottom wall. Specifically, in this embodiment, the longitudinal section of the first metal bump 150 is also trapezoidal.

[0065] Exemplarily, the height of the first metal bump 150 is greater than or equal to 1 / 3 of the height of the coil body A. Specifically, in this embodiment, the total height of the coil body A is 15um, and the height of the first metal bump 150 is greater than or equal to 5um. The specific electroplating height of the first metal bump 150 is not specified in this embodiment and can be selected according to actual needs.

[0066] In this embodiment, the height of the first metal bump is greater than or equal to 1 / 3 of the height of the coil body A, so that the wafer warpage tends to be stable, that is, the electroplating stress of the first metal bump is close to the minimum.

[0067] S150, electroplating on the first metal bump with a second current density to form a second metal bump to form a coil body, wherein the second current density is greater than the first current density.

[0068] Specifically, Fig. 9 As shown, the second metal bump 160 is formed by electroplating on the first metal bump 150 using a first current density, and the first metal bump 150 and the second metal bump 160 together constitute the coil body A. The second current density is greater than the first current density.

[0069] It should be noted that the second metal bump 160 is also a gold bump, that is, in this embodiment, the coil body A is a gold coil.

[0070] Preferably, in this embodiment, the second current density is in the range of 0.5 ASD to 0.6 ASD. That is, the second current density adopts a normal current density, and the second metal bump 160 is formed by electroplating on the first metal bump 150 with the normal current density.

[0071] It should be noted that, since the cross-sectional dimension of the top wall of the window 140 is smaller than the cross-sectional dimension of the bottom wall, the cross-sectional dimension of the top wall of the second metal bump 160 formed in the window 140 is smaller than the cross-sectional dimension of the bottom wall. Specifically, in this embodiment, the longitudinal section of the second metal bump 160 is also trapezoidal.

[0072] S160, removing the remaining photoresist layer and part of the seed layer.

[0073] Specifically, Fig.10 As shown, the residual photoresist layer 130 is removed by etching process. Fig.11 As shown, the seed layer 120 is etched to remove the seed layer 120 on the wafer 110 that is not connected to the first metal bump 150, so that the remaining seed layer 120 is only connected to the first metal bump 150, preventing electrical short circuit between the coil bodies due to the existence of the seed layer 120.

[0074] The dense coil preparation method of the disclosed embodiment forms a window by patterning the photoresist layer, the cross-sectional size of the top wall of the window is smaller than the cross-sectional size of the bottom wall of the window, so that the cross-sectional size of the top wall of the coil body formed by electroplating in the window is smaller than the cross-sectional size of the bottom wall, increasing the contact area between the coil body and the seed layer, making the coil body more firmly fixed to the seed layer, and reducing the stress concentration of the dense coil on the seed layer; using a first current density to electroplate in the window to form a first metal bump, using a second current density to electroplate on the first metal bump to form a second metal bump, so as to form the coil body, the first metal bump formed by electroplating with a low current density has a slow deposition speed, so that the stress generated by the first metal bump is small, and using a normal current density to electroplate on the first metal bump to form the second metal bump, reducing the stress generated by the coil body. The dense coil prepared by the disclosed embodiment can prevent the coil from falling off and has high reliability.

[0075] like Figures 12 to 17 As shown, the reliability of the dense coil preparation method provided by the embodiment of the present disclosure is described below in combination with several specific embodiments. The coil body A is described by taking a gold coil as an example.

[0076] Example 1

[0077] Conduct reliability verification of exposure focus height range limitation. Fig.12As shown, the DOE experiment with different focus heights is set based on the reference exposure focus height (10um). The photoresist type used in the photoresist layer 130 is: negative photoresist (JSR121, NEPES NNBP-103T); exposure energy: JSR121 400±100mj, NNBP-103T 500±100mj. Fig.12 It can be seen that for the two photoresists JSR121 and NNBP-103T, the trapezoidal morphology of the photoresist window 140 can be stably presented in the exposure focus height range of 50um to 70um. Since the risk of overdevelopment is too great when the focus height deviation is higher, and 20um is sufficient for the focus window, the exposure focus height range for exposing the photoresist layer 130 can be set at 50um to 70um, which can make the top wall cross-sectional size of the window 140 smaller than the bottom wall cross-sectional size of the window 140, so that the longitudinal section of the window 140 is trapezoidal.

[0078] Example 2

[0079] like Fig.13 As shown, the photoresist type used in the photoresist layer 130 is: JSR121, NEPES NNBP-103T, the exposure energy is: JSR121 400±100mj, NNBP-103T 500±100mj; the exposure focus heights are: 10um, 50um, 60um and 70um respectively. Fig.13 It can be seen that for the two photoresists JSR121 and NNBP-103T, the trapezoidal morphology of the coil body A can be stably presented in the exposure focus height range of 50um to 70um. When the exposure focus height is 50um to 70um, the upper surface size of the coil body A is not significantly different from the normal exposure focus height of 10um, but the bottom size of the coil body A is larger (0.6um), making the structural reliability of the coil body A stronger.

[0080] Example 3

[0081] The relationship between the first current density and stress is verified. Fig.14 As shown, multiple sets of current densities are designed based on the reference electroplating current density (0.5ASD), and the consistency of the electroplating height (15um) is maintained. The change in the warpage of the wafer 110 is monitored to characterize the generation of electroplating stress during the electroplating process: the greater the electroplating stress, the greater the warpage of the wafer 110. Fig.14 It can be seen that as the first current density decreases, under the same electroplating height, the change in the warpage of the wafer 110 during the electroplating process becomes smaller, that is, the stress generated by the electroplating becomes smaller. After the first current density drops to 0.3ASD, the change is smaller, and the warpage of the wafer 110 tends to be stable. Therefore, the selection interval of the first current density should be ≤0.3ASD.

[0082] Example 4

[0083] The relationship between the first current density and the uniformity of the electroplating height is verified. Fig.15 As shown, multiple sets of current densities are designed based on the reference electroplating current density (0.5ASD) to maintain the uniformity of electroplating height (15um). The height of all gold wires in the wafer 110 is measured to confirm the uniformity of electroplating height. Fig.15 It can be seen that under the same electroplating height, as the first current density decreases, the gold wire height distribution becomes more convergent and the uniformity becomes better. The first current density tends to be stable after it drops to 0.3ASD, which is consistent with the electroplating stress trend. Therefore, the first current density can be limited to ≤0.3ASD.

[0084] Example 5

[0085] Verification of the relationship between the first current density and the height of the first metal bump 150. Fig.16 As shown, a plurality of different first metal bump 150 heights are designed based on the first current density 0.3ASD, and the total electroplating height of the gold coil is kept consistent (15um). The electroplating stress generated during the electroplating process is characterized by monitoring the change in the warpage of the wafer 110: the greater the electroplating stress, the greater the warpage of the wafer 110. Fig.16 It can be seen that as the height of the first metal bump 150 increases, the warpage of the wafer 110 decreases significantly. When the height of the first metal bump 150 satisfies ≥0.5 um, the warpage of the wafer 110 tends to be stable, that is, the electroplating stress is close to the minimum at this time.

[0086] Example 6

[0087] Verify the reliability of the coil body. Fig.17 As shown, when the exposure focus height is in the range of 50um to 70um (with 60um as the baseline) and the first current density is 0.3ASD, and the electroplating height of the first metal bump 150 is greater than or equal to 0.5um, the coil body passes the shear force test, no gold wire falls off, and the reliability is good.

[0088] like Fig.18 As shown, another aspect of the embodiment of the present disclosure provides a dense coil 100, the coil has a high aspect ratio, and the dense coil 100 includes a wafer 110, a seed layer 120 and a coil body A. In this embodiment, the coil body A is a gold coil. The dense coil 100 of the embodiment of the present disclosure is prepared by the dense coil preparation method S100 described above. The specific process of the dense coil preparation method S100 has been described in detail above and will not be repeated here.

[0089] The functional surface of the wafer 110 is provided with a pad 111, and the seed layer 120 is provided on the functional surface of the wafer 110. The coil body A is provided on the seed layer 120 and is electrically connected to the pad 111 through the seed layer 120, and the cross-sectional dimension of the top wall of the coil body A is smaller than the cross-sectional dimension of the bottom wall of the coil body. The coil body A includes a first metal bump 150 provided on the seed layer 120 and a second metal bump 160 provided on the first metal bump 150.

[0090] In the dense coil of the disclosed embodiment, the cross-sectional dimension of the top wall of the coil body is smaller than the cross-sectional dimension of the bottom wall of the coil body, thereby increasing the contact area between the coil body and the seed layer, making the coil body more firmly fixed to the seed layer and reducing the stress concentration of the dense coil on the seed layer.

[0091] Exemplarily, the height of the first metal bump 150 is greater than or equal to 1 / 3 of the height of the coil body A. Specifically, in this embodiment, the total height of the coil body A is 15um, and the height of the first metal bump 150 is greater than or equal to 5um. The specific electroplating height of the first metal bump 150 is not specified in this embodiment and can be selected according to actual needs.

[0092] In this embodiment, the height of the first metal bump is greater than or equal to 1 / 3 of the height of the coil body A, so that the wafer warpage tends to be stable, that is, the electroplating stress of the first metal bump is close to the minimum.

[0093] Exemplarily, the cross-sectional dimensions of the coil body A gradually increase from the top wall to the bottom wall. Specifically, the side wall of the coil body A may be in a linear plane shape. Fig.18 As shown, in this embodiment, the longitudinal section of the coil body A is trapezoidal.

[0094] It should be noted that, in the present embodiment, the first metal bump 150 is formed by electroplating at a first current density, wherein the first current density is less than 0.3 ASD, and the first current density is lower than a normal ionization density, i.e., a low current density.

[0095] In this embodiment, the deposition speed of the first metal bump formed by low current density electroplating is slow, so that the stress generated by the first metal bump is small, thereby reducing the stress generated by the entire coil body. In addition, when the first current density is less than 0.3ASD, the warpage of the wafer changes little, and the stress generated by the electroplating of the first metal bump is small.

[0096] It should be further explained that the second metal bump 160 is formed by electroplating with a second current density, wherein the second current density ranges from 0.5ASD to 0.6ASD. In other words, the second current density adopts a normal current density, and the second metal bump 160 is formed by electroplating on the first metal bump 150 with a normal current density.

[0097] In the dense coil of the embodiment of the present disclosure, the cross-sectional dimension of the top wall of the coil body is smaller than the cross-sectional dimension of the bottom wall of the coil body, thereby increasing the contact area between the coil body and the seed layer, making the coil body more firmly fixed to the seed layer, reducing the stress concentration of the dense coil on the seed layer, and increasing the reliability of the coil body.

[0098] It is to be understood that the above embodiments are merely exemplary embodiments used to illustrate the principles of the embodiments of the present disclosure, but the embodiments of the present disclosure are not limited thereto. For those of ordinary skill in the art, various modifications and improvements can be made without departing from the spirit and essence of the embodiments of the present disclosure, and these modifications and improvements are also considered to be within the protection scope of the embodiments of the present disclosure.

Claims

1. A method for preparing a dense coil, characterized in that: The preparation method comprises: Providing a wafer, wherein a functional surface of the wafer is provided with a bonding pad; forming a seed layer on a functional surface of the wafer; Forming a photoresist layer on the seed layer, and patterning the photoresist layer to form a window, wherein the cross-sectional dimension of the top wall of the window is smaller than the cross-sectional dimension of the bottom wall of the window; Electroplating a first metal bump in the window using a first current density, wherein the first metal bump is electrically connected to the pad through the seed layer; electroplating a second metal bump on the first metal bump with a second current density to form a coil body, wherein the second current density is greater than the first current density; The remaining photoresist layer and a portion of the seed layer are removed.

2. The method for preparing a dense coil according to claim 1, characterized in that: The first current density is in a range of less than 0.3 ASD, and the second current density is in a range of 0.5 ASD to 0.6 ASD.

3. The method for preparing a dense coil according to claim 2, characterized in that: The height of the first metal bump is greater than or equal to 1 / 3 of the height of the coil body.

4. The method for preparing a dense coil according to any one of claims 1 to 3, characterized in that: The step of patterning the photoresist layer to form a window comprises: Providing a mask, wherein the mask is provided with a preset shape matching the coil body; placing the mask on the photoresist layer; Using the mask as a mask, the photoresist layer is exposed and developed to transfer the preset shape to the photoresist layer to form the window on the photoresist layer; wherein, The exposure focus height range is 50um to 70um.

5. The method for preparing a dense coil according to any one of claims 1 to 3, characterized in that: The cross-sectional size of the window gradually increases from the top wall to the bottom wall.

6. The method for preparing a dense coil according to any one of claims 1 to 3, characterized in that: The removing part of the seed layer comprises: The seed layer is etched to remove a portion of the seed layer, so that the remaining seed layer is only connected to the first metal bump.

7. A dense coil, characterized in that: The dense coil comprises: A wafer, wherein a pad is disposed on a functional surface of the wafer; A seed layer, disposed on the functional surface of the wafer; The coil body is disposed on the seed layer and electrically connected to the pad through the seed layer, and the cross-sectional dimension of the top wall of the coil body is smaller than the cross-sectional dimension of the bottom wall of the coil body; wherein, The coil body includes a first metal bump disposed on the seed layer and a second metal bump disposed on the first metal bump.

8. The dense coil according to claim 7, characterized in that: The height of the first metal bump is greater than or equal to 1 / 3 of the height of the coil body.

9. The dense coil according to claim 7, characterized in that: The cross-sectional dimension of the coil body gradually increases from the top wall to the bottom wall.

10. The dense coil according to claim 9, characterized in that: The coil body is a gold coil.

Images