Silver-tin solder film structure and preparation method thereof

Abstract

The invention discloses a silver-tin solder film structure and a preparation method thereof, the silver-tin solder film structure comprises a substrate, the upper surface of the substrate is provided with a seed layer, the upper surface of the seed layer is provided with a solder main body, the substrate is a silicon wafer, ceramic or metal material used for chip packaging, the seed layer is a multilayer film structure plated on the surface of the substrate, and the solder main body is arranged on the upper surface of the seed layer. The solder main body is a silver-tin alloy film; compared with a conventional Au80Sn20 solder, the solder has the remarkable advantages of being low in melting point, low in cost and environmentally friendly.

Description

Technical Field

[0001] The invention relates to a silver-tin solder film structure and a preparation method thereof, and in particular to the technical field of chip packaging. Background Art

[0002] The high temperature during chip packaging and bonding will have adverse effects on the various modules of the chip, so it is necessary to reduce the required temperature during packaging and bonding as much as possible, and the key is to reduce the melting point of the solder as much as possible. 80 Sn 20 ) is a common packaging solder. Although its melting point is only about 280℃, it still cannot meet the requirements of some high-demand packaging products. At the same time, because its raw materials require a large amount of gold, its cost has always been high. The melting point of lead-tin solder can be reduced to about 200℃, and the cost is lower, but the harmfulness of lead to the environment has led to very limited application of this solder. Summary of the invention

[0003] The invention provides a silver-tin solder film structure and a preparation method thereof, which are used to overcome the defect of lead-tin soldering in the prior art that it is highly harmful to the environment.

[0004] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0005] The invention discloses a silver-tin solder film structure, comprising a substrate, a seed layer is arranged on the upper surface of the substrate, and a solder body is arranged on the upper surface of the seed layer.

[0006] Furthermore, the substrate is an 8-inch single crystal silicon wafer, and patterning is completed by photolithography technology, and the thickness of the photoresist is 15±5 microns.

[0007] Furthermore, the seed layer is a multi-layer metal film structure, including Cr, Ni, and Cu metal films from bottom to top, with film thicknesses of 70±30, 70±30, and 500±200 nm, respectively, wherein the Cr film serves as a supporting layer to increase the bonding strength between the entire solder film and the substrate 100; the Ni film serves as a barrier layer to prevent the diffusion of Cr elements to the upper film; the Cu layer serves as a wetting layer to improve the film bonding strength between the solder body and the seed layer, while improving the stress and brittleness of the entire solder film.

[0008] Furthermore, the solder body is a silver-tin alloy thin film structure, with a periodic structure of Sn-Ag, Sn-Ag, Sn-Ag and Sn-Ag for a total of 4 times from bottom to top, with a total thickness of 4.5±0.5 microns, wherein the mass ratio of Sn to Ag is 96.5:3.5.

[0009] Furthermore, the preparation method of the silver-tin solder thin film structure comprises the following steps:

[0010] 1. Cleaning: Use degumming liquid to ultrasonically process the product for 30 minutes, then use deionized water to ultrasonically process for 30 minutes, and finally spin dry the product;

[0011] 2. Glue spraying: Use a fully automatic glue spraying machine to spray 15 micron thick negative photoresist on the surface of the product, and then bake it on a hot plate at 113℃ for 3 minutes;

[0012] 3. Photolithography: Use a semi-automatic proximity photolithography machine and the corresponding photolithography plate to expose the product, and then bake it on a hot plate at 113℃ for 3 minutes;

[0013] 4. Development: Use a fully automatic developing machine to develop the product and spin dry it;

[0014] 5. Hard film: Use a semi-automatic proximity photolithography machine, without placing a photolithography plate, to directly expose the product, and then bake it on a hot plate at 142°C for 6 minutes;

[0015] 6. Load the coating materials into the designated position of the coating machine, where the Cr layer is deposited by Cr powder resistor, with a mass of 1.0±0.5g, and placed at the No. 1 position of the evaporator; the Ni layer is deposited by Ni ingot electron gun, with a mass of >80g, and placed at the No. 1 position of the evaporator; the Cu layer is deposited by Cu block, with a mass of 8.0±2.0g, and placed evenly at the No. 2 and No. 3 positions of the evaporator; the Sn layer is deposited by Sn particle resistor, with a mass of 64±6g, and placed evenly at the No. 4-19 positions of the evaporator; the Ag layer is deposited by Ag particle resistor, with a mass of 4±1g, and placed at the No. 20 position of the evaporator;

[0016] 7. Place the product to be coated at the designated position in the coating machine, close the coating machine door, and click the coating program;

[0017] 8. The coating process is fully automatic, and the coating procedure is mainly divided into the following important components:

[0018] 1) Vacuuming: The vacuum degree is required to reach 4×10-4Pa or below;

[0019] 2) Ion bombardment: Use Ar ions to bombard the product surface for 10 minutes;

[0020] 3) Coating: Coating is carried out in the order of Cr, Ni, Cu, Sn, Ag, Sn, Ag, Sn, Ag, Sn, and Ag from bottom to top;

[0021] 4) Breaking vacuum: the vacuum degree is required to be restored to normal pressure;

[0022] 9. Open the coating machine door, take out the product, and complete the coating process;

[0023] 10. Use a fully automatic photoresist stripping machine to strip the photoresist and clean the product to obtain the final product.

[0024] Furthermore, the purity of the Cr, Ni, Cu, Sn and Ag coating materials is higher than 99.99%.

[0025] The beneficial effect achieved by the present invention is that the solder is better than conventional Au 80 Sn 20 Solder has the significant advantages of low melting point, low cost and environmental friendliness. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The accompanying drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention and do not constitute a limitation of the present invention. In the accompanying drawings:

[0027] Figure 1 It is a schematic diagram of the structure of the present invention;

[0028] Figure 2 It is a schematic diagram of the structure of the solder film of the present invention;

[0029] Figure 3 It is a cross-sectional image of the film layer of the actual solder product of the present invention;

[0030] Figure 4 is the solder melting point data measured by DSC of the present invention;

[0031] Figure 5 is an X-ray image of the present invention;

[0032] Figure 6 It is the infrared image of the present invention.

[0033] In the figure: 100, substrate; 200, seed layer; 300, solder body. DETAILED DESCRIPTION

[0034] The preferred embodiments of the present invention are described below in conjunction with the accompanying drawings. It should be understood that the preferred embodiments described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention.

[0035] Example 1

[0036] like Figure 1 As shown, a silver-tin solder thin film structure includes a substrate 100 , a seed layer 200 is provided on the upper surface of the substrate 100 , and a solder body 300 is provided on the upper surface of the seed layer 200 .

[0037] The substrate 100 is an 8-inch single crystal silicon wafer, and is patterned by photolithography technology, with a photoresist thickness of 15±5 microns.

[0038] The seed layer 200 is a three-layer metal film structure, which is Cr, Ni, and Cu metal films from bottom to top, with film thicknesses of 70±30, 70±30, and 500±200 nm, respectively. The Cr film is used as a support layer to increase the bonding strength between the entire solder film and the substrate 100; the Ni film is used as a barrier layer to prevent the diffusion of Cr elements to the upper film; the Cu layer is used as a wetting layer to improve the film bonding strength between the solder body 300 and the seed layer 200, and to improve the stress and brittleness of the entire solder film.

[0039] The solder body 300 is a silver-tin alloy thin film structure with a periodic structure of (Sn-Ag)-(Sn-Ag)-(Sn-Ag)-(Sn-Ag) four times from bottom to top, with a total thickness of 4.5±0.5 microns, wherein the mass ratio of Sn to Ag is 96.5:3.5.

[0040] The purity of the Cr, Ni, Cu, Sn and Ag coating materials is higher than 99.99%.

[0041] The method for preparing the silver-tin solder thin film structure comprises the following steps:

[0042] 1. Cleaning: Use degumming liquid to ultrasonically process the product for 30 minutes, then use deionized water to ultrasonically process for 30 minutes, and finally spin dry the product;

[0043] 2. Glue spraying: Use a fully automatic glue spraying machine to spray 15 micron thick negative photoresist on the surface of the product, and then bake it on a hot plate at 113°C for 3 minutes;

[0044] 3. Photolithography: Use a semi-automatic proximity photolithography machine and the corresponding photolithography plate to expose the product, and then bake it on a hot plate at 113℃ for 3 minutes;

[0045] 4. Development: Use a fully automatic developing machine to develop the product and dry it;

[0046] 5. Hard film: Use a semi-automatic proximity photolithography machine, without placing a photolithography plate, to expose the product directly, and then bake it on a hot plate at 142°C for 6 minutes;

[0047] 6. Load the coating materials into the designated position of the coating machine, wherein the Cr layer is deposited by Cr powder resistor, with a mass of 1.0±0.5g, and placed at the No. 1 position of the resistor; the Ni layer is deposited by Ni ingot electron gun, with a mass of >80g, and placed at the No. 1 position of the electron gun; the Cu layer is deposited by Cu block, with a mass of 8.0±2.0g, and placed evenly at the No. 2 and No. 3 positions of the resistor; the Sn layer is deposited by Sn grain resistor, with a mass of 64±6g, and placed evenly at the No. 4-19 positions of the resistor; the Ag layer is deposited by Ag grain resistor, with a mass of 4±1g, and placed at the No. 20 position of the resistor; the coating machine used in the embodiment of the present invention has the functions of resistor evaporation, electron gun evaporation and magnetron sputtering coating at the same time;

[0048] 7. Place the product to be coated at the designated position in the coating machine, close the coating machine door, and click the coating program;

[0049] 8. The coating process is fully automatic, and the coating procedure is mainly divided into the following important components:

[0050] 1) Vacuuming: The vacuum degree is required to reach 4×10-4Pa or below;

[0051] 2) Ion bombardment: Use Ar ions to bombard the product surface for 10 minutes;

[0052] 3) Coating: Coating is carried out in the order of Cr, Ni, Cu, Sn, Ag, Sn, Ag, Sn, Ag, Sn, and Ag from bottom to top;

[0053] 4) Breaking vacuum: the vacuum degree is required to be restored to normal pressure;

[0054] 9. Open the coating machine door, take out the product, and complete the coating process;

[0055] 10. Use a fully automatic degumming machine to strip the photoresist and clean the product to obtain the final product.

[0056] like Figure 2 As shown, where:

[0057] S101 is a substrate 100 , and single crystal silicon is used in this example.

[0058] S201 is a support layer in the seed layer 200 , and in this example 1, a Cr metal film is used.

[0059] S202 is a barrier layer in the seed layer 200 , and in this example 1, a Ni metal film is used.

[0060] S203 is the wetting layer in the seed layer 200 , and in this example 1, a Cu metal layer is used.

[0061] S301 , S303 , S305 , and S307 are Sn metal layers in the solder body 300 , and the thicknesses and coating parameters of the four Sn metal layers are consistent.

[0062] S302 , S304 , S306 , and S308 are Ag metal layers in the solder body 300 , and the thicknesses and coating parameters of the four Ag metal layers are consistent.

[0063] like Figure 3 As shown in the figure, it is obtained through focused ion beam (FIB) testing. The position and morphology of each film layer can be clearly distinguished in the figure. The red solid line in the figure is added later to assist observation, rather than the solder itself. Among them:

[0064] The Cr metal layer of S201 is relatively flat, with a clear boundary line from other film layers. The film thickness is 70nm, which is in line with the theoretical design value.

[0065] The Ni metal layer of S202 is relatively flat, with a clear boundary line from other film layers. The film thickness is 70nm, which is in line with the theoretical design value.

[0066] The Cu metal layer of S203 diffuses into the Sn metal layer of S301 to form irregularly shaped Cu-rich phases and Sn-rich phases. This result enhances the bonding force between the solder body and the seed layer, while improving the product performance of the solder body.

[0067] The surface morphology of the Sn metal layer of S301, S303, S305, and S307 is relatively rough.

[0068] The Ag metal layers of S302, S304, S306, and S308 show island-like enrichment phenomenon, which is because the film thickness is relatively thin, while the surface morphology of the Sn metal layers of S301, S303, S305, and S307 is relatively rough, so a continuous film morphology cannot be formed. However, this does not affect the mass ratio of silver and tin, so the impact on solder performance can be ignored.

[0069] like Figure 4 As shown, the peak starting point is 216.4°C and the peak value is 220.4°C, which perfectly meets the theoretical design value.

[0070] like Figure 5 As shown, the results show excellent packaging performance and stability, without any packaging defects such as cracks or holes.

[0071] like Figure 6 As shown, the results also show excellent packaging performance and stability, without any packaging defects such as cracks and holes.

[0072] It should be noted that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention is described in detail with reference to the above embodiments, it is still possible for those skilled in the art to modify the technical solutions described in the above embodiments, or to replace some of the technical features therein by equivalents. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention. The terms used in the description of this application are only for describing specific implementations, and are not intended to limit the exemplary implementations according to the present application. For ease of description, the sizes of the various parts shown in the drawings are not drawn according to the actual proportional relationship. The techniques, methods and devices known to ordinary technicians in the relevant fields may not be discussed in detail, but where appropriate, the techniques, methods and devices should be regarded as part of the authorization specification. In all examples shown and discussed here, any specific value should be interpreted as merely exemplary and not as a limitation. Therefore, other examples of the exemplary embodiments may have different values. It should be noted that similar reference numerals and letters represent similar items in the following drawings, so once an item is defined in one drawing, it does not need to be further discussed in subsequent drawings.

[0073] It should be noted that the terms "first", "second", etc. in the specification and claims of the present application are used to distinguish similar objects, and are not used to describe a specific order or sequence. It should be understood that the data used in this way can be interchangeable under appropriate circumstances, so that the embodiments of the present application can be implemented in an order other than those illustrated or described here, and the objects distinguished by "first", "second", etc. are generally of one type, and the number of objects is not limited. For example, the first object can be one or more. In addition, "and / or" in the specification and claims represents at least one of the connected objects, and the character " / " generally indicates that the objects associated with each other are in an "or" relationship.

[0074] It should be noted that, in the description of the present application, the orientation or positional relationship indicated by terms such as "front, back, up, down, left, right", "lateral, vertical, perpendicular, horizontal" and "top, bottom" are usually based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description. Unless otherwise stated, these orientation words do not indicate or imply that the device or element referred to must have a specific orientation or be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the scope of protection of the present application; the orientation words "inside and outside" refer to the inside and outside relative to the contour of each component itself.

Claims

1. A silver-tin solder film structure, characterized in that: The invention comprises a substrate, wherein a seed layer is arranged on the upper surface of the substrate, and a solder body is arranged on the upper surface of the seed layer.

2. The silver-tin solder thin film structure according to claim 1, characterized in that: The substrate is an 8-inch single-crystal silicon wafer, and is patterned by photolithography technology, with a photoresist thickness of 15±5 microns.

3. The silver-tin solder thin film structure according to claim 1, characterized in that: The seed layer is a multi-layer metal film structure, which includes Cr, Ni, and Cu metal films from bottom to top, with film thicknesses of 70±30, 70±30, and 500±200 nm, respectively. The Cr film serves as a supporting layer to increase the bonding strength between the entire solder film and the substrate 100; the Ni film serves as a barrier layer to prevent the diffusion of Cr elements to the upper film; the Cu layer serves as a wetting layer to improve the film bonding strength between the solder body and the seed layer, while improving the stress and brittleness of the entire solder film.

4. The silver-tin solder thin film structure according to claim 1, characterized in that: The solder body is a silver-tin alloy thin film structure, with a total of 4 periodic structures of Sn-Ag, Sn-Ag, Sn-Ag and Sn-Ag from bottom to top, with a total thickness of 4.5±0.5 microns, and the mass ratio of Sn to Ag is 96.5:3.

5.

5. The silver-tin solder thin film structure according to claim 1, characterized in that: The purity of the Cr, Ni, Cu, Sn and Ag coating materials is higher than 99.99%.

6. A method for preparing a silver-tin solder thin film structure, used for preparing the silver-tin solder thin film structure as claimed in any of claims 1 to 5, characterized in that: The method comprises the following preparation steps:

1. Cleaning: Use degumming liquid to ultrasonically process the product for 30 minutes, then use deionized water to ultrasonically process for 30 minutes, and finally spin dry the product; 2. Glue spraying: Use a fully automatic glue spraying machine to spray 15 micron thick negative photoresist on the surface of the product, and then bake it on a hot plate at 113℃ for 3 minutes; 3. Photolithography: Use a semi-automatic proximity photolithography machine and the corresponding photolithography plate to expose the product, and then bake it on a hot plate at 113℃ for 3 minutes; 4. Development: Use a fully automatic developing machine to develop the product and spin dry it; 5. Hard film: Use a semi-automatic proximity photolithography machine, without placing a photolithography plate, to directly expose the product, and then bake it on a hot plate at 142°C for 6 minutes; 6. Load the coating materials into the designated position of the coating machine, where the Cr layer is deposited by Cr powder resistor, with a mass of 1.0±0.5g, and placed at the No. 1 position of the evaporator; the Ni layer is deposited by Ni ingot electron gun, with a mass of >80g, and placed at the No. 1 position of the evaporator; the Cu layer is deposited by Cu block, with a mass of 8.0±2.0g, and placed evenly at the No. 2 and No. 3 positions of the evaporator; the Sn layer is deposited by Sn particle resistor, with a mass of 64±6g, and placed evenly at the No. 4-19 positions of the evaporator; the Ag layer is deposited by Ag particle resistor, with a mass of 4±1g, and placed at the No. 20 position of the evaporator; 7. Place the product to be coated at the designated position in the coating machine, close the coating machine door, and click the coating program; 8. The coating process is fully automatic, and the coating procedure is mainly divided into the following important components: 1) Vacuuming: the vacuum degree reaches 4×10-4Pa or below; 2) Ion bombardment: Use Ar ions to bombard the product surface for 10 minutes; 3) Coating: Coating is carried out in the order of Cr, Ni, Cu, Sn, Ag, Sn, Ag, Sn, Ag, Sn and Ag from bottom to top; 4) Breaking vacuum: the vacuum degree is required to be restored to normal pressure; 9. Open the coating machine door, take out the product, and complete the coating process; 10. Use a fully automatic photoresist stripping machine to strip the photoresist and clean the product to obtain the final product.

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