High-temperature protection process for forming pure gold protection layer through secondary gold plating of alloy bump

Abstract

Aiming at the limitation of the existing metal bump high-temperature protection technology, the invention provides an innovative process: a pure gold protection layer structure is formed by adopting secondary electroplating pure gold with a gold-silver alloy ratio of 3: 7, and a high-density gold layer is preferentially concentrated on the top of a bump to form a high-temperature protection layer by accurately regulating and controlling the gold-silver alloy ratio and electroplating parameters; the problem that intermetallic compounds are prone to being generated in metal interconnection in a severe environment in the prior art is effectively solved, and comprehensive breakthrough of high-temperature protection performance, electrical characteristics and cost effectiveness is achieved through innovative gradient material design and precise process control.

Description

Technical Field

[0001] This article belongs to the semiconductor packaging technology in the electronic manufacturing process, specifically to a high-temperature protection process in which alloy bumps are secondary gold-plated to form a pure gold protective layer. Background Art

[0002] In semiconductor packaging technology, high-temperature protection performance directly affects the long-term reliability and efficiency of the chip. Since the packaged chip needs to operate in a high-temperature environment of 150-200°C, the high temperature of the metal interconnect structure may cause increased resistance, degraded signal transmission, and even device failure. Therefore, optimizing the high-temperature protection process of metal bumps has become the key to improving packaging reliability.

[0003] The current high-temperature protection technology for metal bumps in semiconductor packaging has the following limitations:

[0004] The bump structure constructed through multiple photolithography, etching, and electroplating processes focuses only on geometric shape control, without involving alloy electroplating or optimizing the high-temperature protection of the top gold layer. The pure copper or pure tin bumps formed by this method are susceptible to electrochemical corrosion and sulfidation, and may cause increased contact resistance or even circuit failure after long-term use.

[0005] When using electroplating to fill the metal layer, only the focus is on conductivity, without optimizing the metal gradient distribution or the top high-temperature protection layer design. Due to the lack of a precious metal protective layer, electroplated copper or silver bumps are easily oxidized in a humid environment, resulting in reduced signal integrity.

[0006] The process of directly electroplating pads on copper layers does not consider the optimization of alloy ratios, resulting in uncontrollable growth of intermetallic compounds. Pure copper bumps are prone to forming intermetallic compounds in high-temperature environments and are prone to electromigration under high current density, significantly shortening device life.

[0007] Conventional electroplating processes lack gradient metal layer design, and the high-temperature diffusion barrier effect is insufficient, and the coating is prone to failure under thermal cycling stress (-55℃~125℃).

[0008] The above technologies currently relied upon still have significant limitations, and new high-temperature protection processes need to be developed to solve reliability issues in high-temperature environments. Summary of the Invention

[0009] In view of the limitations of existing high-temperature protection technology for metal bumps, this paper proposes an innovative process: a pure gold protective layer structure is formed by secondary electroplating of pure gold with a gold-silver alloy ratio of 3:7;

[0010] A high-temperature protection process for alloy bumps that are plated with gold twice to form a pure gold protective layer. The bumps are cubic in shape and have five exposed surfaces. The process includes the following steps:

[0011] S1. Pretreatment of bump surface: Remove oil and impurities from the bump surface, and use acidic solution to clean it to remove the oxide layer and activate the surface. Acidic solution cleaning can completely remove organic pollutants and metal oxide layers on the bump surface, providing an ideal metal substrate for subsequent electroplating processes. This pretreatment can significantly improve the bonding strength between the plating layer and the substrate, preventing the plating layer from falling off or generating pores. Moreover, the acidic activation treatment can make the bump surface clean, ensuring the long-term stability of the device in high temperature and high humidity environments. The surface activated bump can increase the electroplating speed while reducing the consumption of electroplating solution. By controlling the processing time and solution concentration, it can also ensure compatibility with subsequent materials such as photoresist, avoiding graphical defects caused by surface residues. Although the pretreatment only adds a small amount of process time, the overall benefits it brings are significant, creating dual value for manufacturers and end users.

[0012] S2. Positioning of the No. 1 mask: Install the No. 1 mask around the periphery of the bump. The opening size of the No. 1 mask is 0.5-2μm larger than the outer size of the bump. The enlarged opening ensures that the plating solution fully contacts the edge of the bump and avoids the loss of the plating layer due to alignment error. The reserved space allows the metal ions to be evenly distributed during electroplating, eliminating the edge thickening effect.

[0013] S3. Alloy plating solution filling: The first mask is filled with a gold-silver alloy plating solution with a mass ratio of 3:7. By filling the first mask with a 3:7 alloy plating solution, while ensuring excellent conductivity, the chemical inertness of gold is utilized to form a basic high-temperature protective layer, significantly reducing material costs compared to the pure gold solution.

[0014] S4, first electroplating: Perform the first electroplating to form alloy bumps. After completion, remove the first photomask. By precisely controlling the electroplating parameters, an alloy coating is formed on the surface of the bumps. After electroplating, remove the first photomask to avoid residual contamination of the photomask, and proceed directly to subsequent patterning processing.

[0015] S5, Graphical processing: The surface of the alloy bump is subjected to processes such as glue coating, exposure, and development, and the second photomask is installed. After the trimming is completed, the secondary electroplating area is defined. Through precise photolithography and accurate positioning of the second photomask, a precise deposition area is created for the secondary pure gold electroplating;

[0016] S6, gold plating solution filling: Fill the second mask with pure gold plating solution to provide a high-quality material foundation for the formation of the final high-temperature protective layer;

[0017] S7, second electroplating: the second electroplating is performed to form a pure gold layer, which is called a pure gold protective layer;

[0018] S8, post-processing: removing the second photomask to obtain alloy bumps that are electroplated with pure gold for the second time to form a pure gold protective layer.

[0019] Furthermore, in step S4, the alloy bumps are formed using the following electroplating parameters:

[0020] Alloy bump height: 5-12μm;

[0021] Current density: 0.2-0.8ASD;

[0022] Electroplating time: 1000-2400 seconds;

[0023] Plating solution flow rate: 10-15L / min;

[0024] Plating tank shaking frequency: 10-30Hz;

[0025] The electroplating process adopts a pulse current mode with a duty cycle of 30%-50% and a frequency of 50-100Hz to improve the density and composition uniformity of the coating.

[0026] Furthermore, in step S5, the patterning process of the alloy bumps before secondary electroplating includes the following steps:

[0027] S5.1 Glue Coating: Spin-coat negative photoresist on the surface of the alloy bump and remove excess photoresist. By establishing a high-precision temporary pattern carrier, a spatial positioning reference is provided for selective electroplating, which is a key step in ensuring the accuracy of the high-temperature protection structure.

[0028] S5.2 Spinning: Spin the photoresist again at a certain speed to ensure uniform surface coverage and redistribute the photoresist into a molecularly uniform film, establishing an ideal dielectric layer for nanoscale pattern transfer. This is a key pre-processing step to ensure the edge accuracy of the final gold wrapping layer.

[0029] S5.3 Replacing the Photomask: Replace the second photomask and adjust the chip bump size deviation to expand the exposure area. Through the intelligent size deviation compensation design, it not only solves the tolerance problem of multiple process stacking, but also creates ideal space conditions for forming a fully wrapped high-temperature protection structure.

[0030] S5.4 Exposure: UV exposure is performed to define the secondary electroplating area, which directly determines the dimensional accuracy and coverage integrity of the final high-temperature protection structure;

[0031] S5.5 Development: Dissolve the photoresist in the unexposed areas. The optimized development process ensures complete coverage and clear edges of the subsequent electroplated gold layer.

[0032] S5.6 Baking: Baking on a hot plate at a certain temperature to cure the photoresist.

[0033] The graphic processing in step S5 is used to correct the positioning deviation of the second mask to ensure accurate coverage of the secondary electroplating area.

[0034] Furthermore, in step S7, the pure gold protective layer formed by the second electroplating satisfies the following conditions:

[0035] Use a current density of 0.5-1ASD and an electroplating time of 1800-3600 seconds;

[0036] Forming a pure gold wrapping layer with a thickness of 0.1-0.5 μm on five exposed surfaces around the alloy bump;

[0037] The purity of the gold layer is ≥99.99%;

[0038] After high temperature storage test (150℃ / 1000h), the contact resistance change rate is less than 3%;

[0039] No delamination after thermal shock test (-65℃~150℃, 500 times);

[0040] After 1000h in 85℃ / 85%RH environment, the corrosion area is less than 0.05%;

[0041] The wrapping layer completely covers the five surfaces of the cubic bump, wherein the five surfaces are four side surfaces and one top surface, and there is no missing plating area.

[0042] Furthermore, in step S5.1, the negative photoresist is an epoxy resin-based photoresist with a thickness of 5-15 μm;

[0043] Furthermore, in step S5.2, the speed of the coating is 1000-3000 rpm;

[0044] Furthermore, the exposure energy in step S5.4 is 150-250 mJ / cm 2 ;

[0045] Furthermore, in step S5.5, 2.38% tetramethylammonium hydroxide solution is used for development for 45-90 seconds;

[0046] Furthermore, the baking condition in step S5.6 is baking on a hot plate at 100-120° C. for 60-120 seconds.

[0047] The second electroplating process adopts a pulse reverse electroplating process, with forward power on for 10ms, reverse power off for 2ms, forward current density of 0.5-1ASD, and reverse current density of 0.1-0.3ASD.

[0048] The acidic solution is 10% sulfuric acid or 5% nitric acid solution, and the activation treatment time is 30-60 seconds.

[0049] Beneficial effects:

[0050] Compared with traditional processes, this process improves the high-temperature contact resistance stability by 5 times, extends the thermal cycle life by 300%, and extends the high-temperature bias failure time from 500 hours to 2000 hours. The high-density gold layer is preferentially enriched on the top of the bump to form an efficient high-temperature protective layer. It not only effectively solves the industry problem that traditional metal interconnects are easily damaged in high-temperature environments, but also achieves synergistic breakthroughs in high-temperature protection performance, electrical characteristics and cost-effectiveness through innovative gradient material design and precise process control. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1 It is a high temperature protection process of No. 1 mask positioning with secondary gold plating of alloy bumps to form a pure gold protective layer.

[0052] Figure 2 It is a high temperature protection process for the second mask positioning of alloy bumps with secondary gold plating to form a pure gold protective layer.

[0053] Figure 3 This is a cross-sectional view of a secondary electroplated alloy bump that is a high-temperature protection process in which the alloy bump is plated twice with gold to form a pure gold protective layer.

[0054] Figure 4 This is a process flow chart of a high-temperature protection process in which alloy bumps are plated twice with gold to form a pure gold protective layer.

[0055] In the figure: 1. Photomask No. 1, 2. Bump, 3. Alloy plating, 4. Package substrate, 5. Photomask No. 2, 6. Alloy bump, 7. Photoresist coating, 8. Gold plating. DETAILED DESCRIPTION

[0056] In order to deepen the understanding of the present invention, the present invention will be further described in detail below with reference to the embodiments and drawings. The embodiments are only used to explain the present invention and do not constitute a limitation on the scope of protection of the present invention.

[0057] No. 1 photomask 1, bump 2, alloy plating 3, packaging substrate 4, No. 2 photomask 5, alloy bump 6, photoresist coating 7, gold plating 8.

[0058] like Figure 1 、 2 , 3, and 4

[0059] A high-temperature protection process for alloy bumps with secondary gold plating to form a pure gold protective layer. The bump 2 is a cubic structure with five exposed surfaces. The process includes the following steps:

[0060] S1, pretreatment of the surface of the bump 2: removing oil and impurities on the surface of the bump 2, cleaning with an acidic solution to remove the oxide layer and activate the surface;

[0061] S2, positioning the first photomask 1: installing the first photomask 1 on the periphery of the bump 2, wherein the opening size of the first photomask 1 is 0.5-2 μm larger than the periphery size of the bump 2;

[0062] S3, alloy plating solution filling: fill the first mask 1 with a gold-silver mixed alloy plating solution, wherein the mass ratio of gold to silver is 3:7;

[0063] S4, first electroplating: Perform the first electroplating to form the alloy bump 6, and remove the first photomask 1 after completion;

[0064] S5, graphic processing: the surface of the alloy bump 6 is subjected to processes such as gluing, exposure, and development, and the second photomask 5 is installed. After the trimming is completed, the secondary electroplating area is defined;

[0065] S6, gold plating solution filling: fill the second mask 5 with pure gold plating solution;

[0066] S7, second electroplating: the second electroplating is performed to form a pure gold layer, which is called a pure gold protective layer;

[0067] S8, post-processing: removing the second photomask 5, and obtaining the alloy bump 6 which is electroplated with pure gold twice to form a pure gold protective layer.

[0068] Furthermore, in step S4, the alloy bump 6 is formed using the following electroplating parameters:

[0069] Alloy bump 6 height: 5-12 μm;

[0070] Current density: 0.2-0.8ASD;

[0071] Electroplating time: 1000-2400 seconds;

[0072] Plating solution flow rate: 10-15L / min;

[0073] Plating tank shaking frequency: 10-30Hz.

[0074] The electroplating process adopts a pulse current mode with a duty cycle of 30%-50% and a frequency of 50-100Hz to optimize the density and composition uniformity of the coating.

[0075] In step S5, the patterning process of the alloy bump 6 before the secondary electroplating includes the following steps:

[0076] S5.1 Glue coating: Spin-coat a negative photoresist on the surface of the alloy bump 6 and remove excess photoresist;

[0077] S5.2 Spinning: Spin the photoresist again at a certain speed to ensure uniform coverage of the surface;

[0078] S5.3 Replace the photomask: Replace the second photomask 5 and adjust the size deviation of the chip bump 2 to expand the exposure area;

[0079] S5.4 Exposure: Perform UV exposure to define the secondary plating area;

[0080] S5.5 Development: dissolve the photoresist in the unexposed areas;

[0081] S5.6 Baking: Baking on a hot plate at a certain temperature to cure the photoresist.

[0082] Furthermore, the graphic processing in step S5 is used to correct the positioning deviation of the second mask 5 to ensure accurate coverage of the secondary electroplating area.

[0083] Furthermore, in step S7, the pure gold protective layer formed by the second electroplating satisfies the following conditions:

[0084] Use a current density of 0.5-1ASD and an electroplating time of 1800-3600 seconds;

[0085] Form a pure gold wrapping layer with a thickness of 0.1-0.5 μm on the five exposed surfaces around the alloy bump 6;

[0086] The purity of the pure gold layer is ≥99.99%;

[0087] After high temperature storage test (150℃ / 1000h), the contact resistance change rate is less than 3%;

[0088] No delamination after thermal shock test (-65℃~150℃, 500 times);

[0089] After 1000h in 85℃ / 85%RH environment, the corrosion area is less than 0.05%;

[0090] The wrapping layer completely covers the five surfaces of the cubic bump 2 , which are four side surfaces and one top surface, without any missing plating areas.

[0091] Furthermore, in step S5.1, the negative photoresist is an epoxy resin-based photoresist with a thickness of 5-15 μm;

[0092] Furthermore, in step S5.2, the speed of the coating is 1000-3000 rpm;

[0093] Furthermore, the exposure energy in step S5.4 is 150-250 mJ / cm 2 ;

[0094] Furthermore, in step S5.5, 2.38% tetramethylammonium hydroxide solution is used for development for 45-90 seconds;

[0095] Furthermore, the baking condition in step S5.6 is baking on a hot plate at 100-120° C. for 60-120 seconds.

[0096] The second electroplating process adopts a pulse reverse electroplating process, with forward power on for 10ms, reverse power off for 2ms, forward current density of 0.5-1ASD, and reverse current density of 0.1-0.3ASD.

[0097] The acidic solution is 10% sulfuric acid or 5% nitric acid solution, and the activation treatment time is 30-60 seconds.

[0098] Implementation Example

[0099] In the first step, surface pretreatment is performed to remove oil and impurities on the surface of the bump 2, and an acid solution is used to clean it to remove the oxide layer and activate the surface;

[0100] The second step is to carry out the first electroplating. First, install the No. 1 mask, then fill the plating solution, and finally start the pulse electroplating.

[0101] The third step is to carry out graphic processing, including glue coating, glue leveling, changing the mask, exposure, development and baking;

[0102] The fourth step is to perform the second electroplating. First, install the second mask 5, then fill it with pure gold plating solution, and finally perform pulse reverse electroplating.

[0103] The fifth step is to conduct high temperature storage test, thermal cycle test and high temperature and high humidity test.

[0104] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A high-temperature protection process for alloy bumps to form a pure gold protective layer by secondary gold plating, wherein the bumps are in the shape of a cube and have five exposed surfaces, characterized in that: This process includes the following steps: S1. Bump surface pretreatment: remove oil and impurities from the bump surface, use acidic solution to clean to remove the oxide layer and activate the surface, and control the surface roughness to Ra ≤ 0.1μm; S2, positioning the first photomask: installing the first photomask on the periphery of the bump, wherein the opening size of the first photomask is 0.5-2 μm larger than the outer size of the bump; S3, alloy plating solution filling: fill the first mask with a gold-silver mixed alloy plating solution, where the mass ratio of gold to silver is 3:7; S4, first electroplating: perform the first electroplating to form alloy bumps, and remove the first photomask after completion; S5, Graphic processing: The surface of the alloy bump is subjected to processes such as gluing, exposure, and development, and a second photomask is installed. After trimming is completed, the secondary electroplating area is defined; S6, gold plating solution filling: fill the second mask with pure gold plating solution; S7, second electroplating: the second electroplating is performed to form a pure gold layer, which is called a pure gold protective layer; S8, post-processing: removing the second photomask to obtain alloy bumps that are electroplated with pure gold for the second time to form a pure gold protective layer.

2. The high temperature protection process for forming a pure gold protective layer by secondary gold plating of alloy bumps according to claim 1, characterized in that: In step S4, the alloy bumps are formed using the following electroplating parameters: Alloy bump height: 5-12μm; Current density: 0.2-0.8ASD; Electroplating time: 1000-2400 seconds; Plating solution flow rate: 10-15L / min; Plating tank shaking frequency: 10-30Hz. The electroplating process adopts a pulse current mode with a duty cycle of 30%-50% and a frequency of 50-100 Hz to optimize the density and composition uniformity of the coating.

3. The high temperature protection process for forming a pure gold protective layer by secondary gold plating of alloy bumps according to claim 1, characterized in that: In the step S5, the patterning process of the alloy bumps before the secondary electroplating comprises the following steps: S5.1 Glue coating: Spin-coat negative photoresist on the surface of the alloy bump and remove excess photoresist; S5.2 Spinning: Spin the photoresist again at a certain speed to ensure uniform coverage of the surface; S5.3 Replace the photomask: Replace the second photomask and adjust the chip bump size deviation to expand the exposure area; S5.4 Exposure: Perform UV exposure to define the secondary plating area; S5.5 Development: dissolve the photoresist in the unexposed areas; S5.6 Baking: Baking on a hot plate at a certain temperature to cure the photoresist.

4. The high temperature protection process for forming a pure gold protective layer by secondary gold plating of alloy bumps according to claim 1, characterized in that: The graphic processing in step S5 is used to correct the positioning deviation of the second mask to ensure accurate coverage of the secondary electroplating area.

5. The high temperature protection process for forming a pure gold protective layer by secondary gold plating of alloy bumps according to claim 1, characterized in that: In step S7, the pure gold protective layer formed by the second electroplating satisfies the following conditions: Use a current density of 0.5-1ASD and an electroplating time of 1800-3600 seconds; Forming a pure gold wrapping layer with a thickness of 0.1-0.5 μm on five exposed surfaces around the alloy bump; The purity of the pure gold layer is ≥99.99%; After high temperature storage test (150℃ / 1000h), the contact resistance change rate is less than 3%; No delamination after thermal shock test (-65℃~150℃, 500 times); After 1000h in 85℃ / 85%RH environment, the corrosion area is less than 0.05%; The wrapping layer completely covers the five surfaces of the cubic bump, wherein the five surfaces are four side surfaces and one top surface, and there is no missing plating area.

6. The high temperature protection process for forming a pure gold protective layer by secondary gold plating of alloy bumps according to claim 3, characterized in that: In step S5.1, the negative photoresist is an epoxy resin-based photoresist with a thickness of 5-15 μm; In step S5.2, the speed of the coating is 1000-3000 rpm; The exposure energy in step S5.4 is 150-250 mJ / cm 2 ; In step S5.5, 2.38% tetramethylammonium hydroxide solution is used for development for 45-90 seconds; The baking condition in step S5.6 is baking on a hot plate at 100-120° C. for 60-120 seconds.

7. The high temperature protection process for forming a pure gold protective layer by secondary gold plating of alloy bumps according to claim 5, characterized in that The second electroplating process adopts a pulse reverse electroplating process, with forward power on for 10ms, reverse power off for 2ms, forward current density of 0.5-1ASD, and reverse current density of 0.1-0.3ASD.

8. The high temperature protection process for forming a pure gold protective layer by secondary gold plating of alloy bumps according to claim 1, characterized in that The acidic solution is 10% sulfuric acid or 5% nitric acid solution, and the activation treatment time is 30-60 seconds.

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