Palladium-plated silver-gold-coated bump structure and manufacturing method thereof

Abstract

The invention discloses a bump structure with silver and gold coated by chemical plating palladium and a manufacturing method of the bump structure, and relates to the technical field of semiconductor manufacturing, in particular to the bump structure with silver and gold coated by chemical plating palladium and the manufacturing method of the bump structure. Comprising a silicon wafer carrier, an aluminum pad conducting layer, an insulating layer, a sputtering UBM titanium tungsten layer, a sputtering UBM gold layer, an electrosilvering layer, an electrogilding layer and a chemical palladium plating layer which are arranged from bottom to top, according to the invention, the silver-gold bump is coated by a thin palladium plating layer, the cost can be reduced by about 4 times compared with a process of coating a gold plating layer again, and the novel bump structure can solve the problems of easy silver migration, easy color change and the like of a silver metal material under the condition of ensuring the excellent characteristics of high conductivity and high thermal conductivity of the silver material. And the palladium material has good electron migration resistance, so that stable current can still pass through the bump structure in an environment with higher current density and higher temperature, and the reliability of a product is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of semiconductor manufacturing, and in particular to a bump structure coated with silver and gold by electroless plating and a manufacturing method thereof. BACKGROUND

[0002] In the field of DDIC packaging bumps, the common method is to use pure gold bumps. However, due to the influence of international politics and finance, the price of gold has been at a high level since 2020. The manufacturing cost of pure gold bumps in the field of DDIC packaging has doubled, which has led to a decrease in the order quantity of customers to packaging factories.

[0003] Currently, silver-gold bump technology and electroless silver alloy technology are transferred from the PCB field to wafer-level packaging. The cyanide-free silver-gold co-plating bath passed the FAB reliability verification in 2022. The alkali resistance of photoresist was improved, and the problem of silver ion dendrite pollution was solved, so that the yield of 40 µm pitch and 25 µm height micro bumps was greater than 98%, which was the same as pure gold for the first time. The downstream COG / COF thermal compression bonding machine was generally upgraded to 180℃±2℃ and 0.8MPa segment pressure control, which could be compatible with silver-copper alloy (HV55-80) with slightly higher hardness, opening the process channel for mass production of silver-gold bumps. However, silver-gold bumps are still affected by the inherent corrosion tendency of silver metal, which is easy to oxidize and sulfide, and appears tarnishing and color spots in a high temperature and high humidity environment, which directly affects the reliability and service life of the bump. In view of the above problems, various solutions have appeared in the industry, such as adding a gold coating layer. However, this new gold coating layer structure still has some disadvantages. The addition of a new electroless plating gold process still increases the material cost. In addition, pure gold has almost no ability to resist electron migration. Under the conditions of high power and high current density, the current density window may be doubled, and the bump may be "long hollow" when the current is slightly large, and "broken neck" when the temperature is slightly high.

[0004] Therefore, the present application provides a bump structure coated with silver and gold by electroless plating and a manufacturing method thereof to solve the above problems. SUMMARY

[0005] The present application aims to provide a bump structure coated with silver and gold by electroless plating and a manufacturing method thereof. The silver-gold bump is coated with a thin layer of electroless plating palladium. Compared with the process of coating with a new electroless plating gold layer, the cost can be reduced by about 4 times. This new bump structure can solve the problems of silver migration and color change of silver material while ensuring the excellent properties of high electrical conductivity and high thermal conductivity of silver material. In addition, palladium material has good resistance to electron migration, so that the bump structure can still maintain stable current in a higher current density and higher temperature environment, thereby improving the reliability of the product. The technical problems in the background art are solved.

[0006] To achieve the above object, the present application provides the following technical solutions: A convex bump structure coated with palladium-plated silver and gold and a manufacturing method thereof, comprising a silicon wafer carrier, an aluminum pad conductive layer, an insulating layer, a sputtered UBM titanium tungsten layer, a sputtered UBM gold layer, an electroplated silver layer, an electroplated gold layer and a palladium-plated layer arranged from bottom to top. The top end of the silicon wafer carrier is provided with the aluminum pad conductive layer, and the top end of the aluminum pad conductive layer is provided with the insulating layer. The outer side of the sputtered UBM gold layer is formed into the electroplated silver layer through the electroplating process, and the outer side of the electroplated silver layer is formed into the electroplated gold layer through the electroplating process.

[0007] As a further technical solution of the present application, the following steps are included: S1: wafer pretreatment, confirming the wafer chip model, checking the appearance, removing dust on the wafer surface by using two-fluid cleaning, and removing oxide on the surface of the wafer insulating layer and the aluminum pad by using high-frequency etching; S2: sputtering process, forming a dense and strong adhesion titanium tungsten film on the AL pad window through physical vapor deposition technology to form a sputtered UBM titanium tungsten layer; and sputtering a gold film layer on the titanium tungsten layer through this technology to form a sputtered UBM gold layer; S3: spin coating photoresist, realizing spin coating of the photoresist through a coating machine, the thickness of spin coating being 15-20 um, soft baking after spin coating, the soft baking temperature being 90-120°, the time being 30-90 s, and cooling after baking; S4: exposure and development: through an exposure machine, a light source projects a pattern onto the surface of the photoresist through a mask plate, a chemical reaction occurs at the place where the photoresist contacts the light, and after soaking in a developing solution, the desired pattern size before electroplating is left; S5: Descum, removing the residual photoresist scum after development through plasma treatment; S6: electroplating process, wet electrochemical deposition, taking the wafer workpiece as a cathode and a target metal as an anode, under the action of pulse current, metal ions are reduced into atoms to form a dense and thickness-controllable metal layer on the surface, through this technology, a silver layer is electroplated on the surface of the wafer, and a gold layer is subsequently electroplated on the surface of the electroplated silver layer 6; S7: etching, after the above electroplating is completed, the exposed gold layer and titanium tungsten layer after the removal of the photoresist are selectively removed, and only the UBM stack layer below the convex bump is retained; S8: plating process: on the surface of the above structure, palladium metal is deposited on the surface of the UBM stack layer through a chemical reduction reaction to form a palladium-plated layer.

[0008] As a further technical solution of the present invention, the appearance inspection in step S1 includes the detection processes of whether the vacuum aluminum foil bag is damaged, whether nitrogen is leaking, and whether the HIC humidity card is >10%RH.

[0009] As a further technical solution of the present invention, the etching in step S7 includes the following operation steps: 1) Resin removal: Acetone is used to remove residual photoresist and etching byproducts; 2) Pre-cleaning: Use plasma cleaning to remove organic matter, metal ions and particles from the surface; 3) Gold layer etching: using a concentration of 0.01-0.03 g / L -1 The gold layer is removed by a chemical reaction using an alkaline potassium cyanide solution. 4) Rapid rinsing: Immediately rinse the etching residue with ultrapure water with a resistivity ≥18.2 MΩ·cm; 5) Titanium-tungsten layer etching: The etching rate is controlled by a hydrofluoric acid-based solution to remove the titanium-tungsten layer; 6) Ultrapure water cleaning: Residual etching agent is removed by rinsing with ultrapure water combined with ultrasonic assistance, so that the surface particles are controlled to ≤0.2μm.

[0010] As a further technical solution of the present invention, the chemical reduction reaction in step S8 uses a concentration of 1-2 g / L. -1 Palladium chloride was added as the main salt at a concentration of 8 g / L. - Sodium hypochlorite was used as a reducing agent at a concentration of 15-25 g / L. -1 Disodium ethylenediaminetetraacetate was used as a complexing agent, and ammonia was added to maintain the pH at 8.5 ± 0.2, with a concentration of 0.05-0.1 g / L. -1 Maleic acid was added as a stabilizer at a concentration of 0.01-0.03 g / L. -1 Cell granulation was performed using indium trichloride at a concentration of 0.5-1 g / L. -1 Glycine is used to assist in complexation and stress reduction; finally, the temperature of the entire solution is controlled at 50-60℃ to carry out the chemical reduction reaction.

[0011] As a further technical solution of the present invention, the mass percentages of palladium chloride, sodium hypochlorite, disodium ethylenediaminetetraacetate, maleic acid, indium trichloride and glycine can be calculated. Based on the density of pure water at 25°C ρ≈1.00kgL⁻¹, the mass percentage wt% is obtained by dividing the concentration by 10.

[0012] Compared with the prior art, the beneficial effects of the present invention are: The present application adopts a thin palladium layer to cover the silver-gold bump, and compared with the process of covering the gold layer, the cost can be reduced by about 4 times, the new bump structure can solve the problems of silver migration and color change of the silver material under the guarantee of the excellent properties of high conductivity and high thermal conductivity of the silver material, and the palladium material has good electron migration resistance, so that the bump structure can still maintain stable current under higher current density and higher temperature environment, and the reliability of the product is improved. BRIEF DESCRIPTION OF DRAWINGS

[0013] Figure 1 is a structural schematic diagram of the present application.

[0014] Figure 2 is a comparison diagram of the conductivity of each metal in the present application.

[0015] Figure 3 is a comparison diagram of the thermal conductivity of each metal in the present application.

[0016] Figure 4 is a comparison diagram of the plating stress of each metal in the present application.

[0017] 1, silicon wafer carrier; 2, aluminum pad conductive layer; 3, insulating layer; 4, sputtering UBM titanium tungsten layer; 5, sputtering UBM gold layer; 6, electroplated silver layer; 7, electroplated gold layer; 8, electroplated palladium layer. DETAILED DESCRIPTION

[0018] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0019] Please refer to Figures 1-4 In the embodiments of the present application, a bump structure of palladium-coated silver-gold and a manufacturing method thereof include a silicon wafer carrier 1, an aluminum pad conductive layer 2, an insulating layer 3, a sputtering UBM titanium tungsten layer 4, a sputtering UBM gold layer 5, an electroplated silver layer 6, an electroplated gold layer 7, and an electroplated palladium layer 8 arranged from bottom to top. The top end of the silicon wafer carrier 1 is provided with the aluminum pad conductive layer 2, and the top end of the aluminum pad conductive layer 2 is provided with the insulating layer 3, the outer side of the insulating layer 3 is formed by a physical vapor deposition technology to form the sputtering UBM titanium tungsten layer 4, and the outer side of the sputtering UBM titanium tungsten layer 4 is formed by a physical vapor deposition technology to form the sputtering UBM gold layer 5; The outer side of the sputtered UBM gold layer 5 is formed by electroplating a silver layer 6, and the outer side of the silver layer 6 is formed by electroplating a gold layer 7; the surface of the gold layer 7 is deposited with a palladium layer 8 by chemical reduction reaction.

[0020] This embodiment includes the following steps: S1: Wafer preprocessing, confirming the wafer chip model, inspecting the appearance, and using two-fluid cleaning to remove dust from the wafer surface, and using high-frequency etching to remove oxides from the wafer insulating layer and aluminum pad surface; S2: Sputtering process, through physical vapor deposition technology, a dense and strongly adherent titanium-tungsten film is formed on the AL pad window to form a sputtered UBM titanium-tungsten layer 4; then a gold film layer is sputtered on the titanium-tungsten layer to form a sputtered UBM gold layer 5. S3: Spin-coating photoresist. The photoresist is spin-coated using a coating machine. The spin-coating thickness is 15-20µm. After spin-coating, the photoresist is soft-baked at a temperature of 90-120°C for 30-90 seconds. After baking, the photoresist is cooled. S4: Exposure and Development: Through the exposure machine, the light source passes through the mask to project the pattern onto the photoresist surface. The photoresist undergoes a chemical reaction where it comes into contact with the light. After being soaked in the developing solution, the desired pattern size is left behind before electroplating. S5: Descum, which removes residual photolithography slag after development through plasma treatment, improving the uniformity and quality of subsequent processes; S6: Electroplating process, wet electrochemical deposition, using the wafer workpiece as the cathode and the target metal as the anode. Under the action of pulsed current, metal ions are reduced to atoms, forming a dense metal layer with controllable thickness on the surface. Silver layer 6 is electroplated on the surface of the wafer using this technology, and then gold layer 7 is electroplated on the surface of the silver layer 6. S7: Etching. After the above electroplating is completed, the gold layer and titanium-tungsten layer exposed after the adhesive is removed are selectively removed, leaving only the UBM stack under the bump. S8: Chemical plating process: On the surface of the above structure, palladium metal is autocatalytically deposited on the surface of the UBM stack through a chemical reduction reaction to form a chemically plated palladium layer 8.

[0021] In this embodiment, the visual inspection in step S1 includes checking whether the vacuum aluminum foil bag is damaged, whether nitrogen is leaking, and whether the HIC humidity card is >10%RH.

[0022] In this embodiment, the etching in step S7 includes the following steps: 1) Resin removal: Acetone is used to remove residual photoresist and etching byproducts to avoid contaminating subsequent processes; 2) Pre-cleaning: Plasma cleaning is used to remove organic matter, metal ions and particles from the surface to ensure the cleanliness of the substrate; 3) Gold layer etching: using a concentration of 0.01-0.03 g / L -1 The gold layer is removed by a chemical reaction using an alkaline potassium cyanide solution. 4) Rapid rinsing: Immediately rinse the etching residue with ultrapure water with a resistivity ≥18.2 MΩ·cm to prevent byproduct redeposition; 5) Titanium-tungsten layer etching: The etching rate is controlled by a hydrofluoric acid-based solution to remove the titanium-tungsten layer and ensure pattern accuracy; 6) Ultrapure water cleaning: Residual etching agent is removed by rinsing with ultrapure water combined with ultrasonic assistance, so that the surface particles are controlled to ≤0.2μm.

[0023] In this embodiment, the chemical reduction reaction in step S8 uses a concentration of 1-2 g / L. -1 Palladium chloride was added as the main salt at a concentration of 8 g / L. - Sodium hypochlorite was used as a reducing agent at a concentration of 15-25 g / L. -1 Disodium ethylenediaminetetraacetate was used as a complexing agent, and ammonia was added to maintain the pH at 8.5 ± 0.2, with a concentration of 0.05-0.1 g / L. -1 Maleic acid was added as a stabilizer at a concentration of 0.01-0.03 g / L. -1 Cell granulation was performed using indium trichloride at a concentration of 0.5-1 g / L. -1 Glycine is used to assist in complexation and stress reduction; finally, the temperature of the entire solution is controlled at 50-60℃ to carry out the chemical reduction reaction.

[0024] In this embodiment, the mass percentages of palladium chloride, sodium hypochlorite, disodium ethylenediaminetetraacetate, maleic acid, indium trichloride, and glycine can be calculated. Based on the density of pure water at 25°C ρ≈1.00kgL⁻¹, dividing the concentration by 10 yields the mass percentage wt%.

[0025] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0026] Furthermore, it should be understood that although the specification is described in terms of embodiments, not every embodiment includes every feature or implementation described herein. The specification can include implicit combinations of explicitly mentioned features and / or implicit combinations of implicitly mentioned features. Such combinations are also expressly included within the scope of the specification and an equivalent scope appropriate to each element. Such combinations are only expressly excluded where it is clear that the combination with the explicitly recited combination would not work, or where the disclosure explicitly teaches away from the combination.

Claims

1. A palladium-plated silver-gold coated bump structure, characterized in that: The structure includes, from bottom to top, a silicon wafer carrier (1), an aluminum pad conductive layer (2), an insulating layer (3), a sputtered UBM titanium tungsten layer (4), a sputtered UBM gold layer (5), an electroplated silver layer (6), an electroplated gold layer (7), and a chemically plated palladium layer (8). The top of the silicon wafer carrier (1) is provided with an aluminum pad conductive layer (2), and the top of the aluminum pad conductive layer (2) is provided with an insulating layer (3). The outer side of the insulating layer (3) is formed by physical vapor deposition technology to form a sputtered UBM titanium tungsten layer (4), and the outer side of the sputtered UBM titanium tungsten layer (4) is formed by physical vapor deposition technology to form a sputtered UBM gold layer (5). The outer side of the sputtered UBM gold layer (5) is formed by electroplating silver layer (6), and the outer side of the electroplated silver layer (6) is formed by electroplating gold layer (7); the surface of the electroplated gold layer (7) is deposited with a chemically plated palladium layer (8) by chemical reduction reaction.

2. The method for fabricating the palladium-plated silver-gold-coated bump structure according to claim 1, characterized in that: Includes the following steps: S1: Wafer preprocessing, confirming the wafer chip model, inspecting the appearance, and using two-fluid cleaning to remove dust from the wafer surface, and using high-frequency etching to remove oxides from the wafer insulating layer and aluminum pad surface; S2: Sputtering process, through physical vapor deposition technology, a dense and strongly adherent titanium-tungsten film is formed on the AL pad window to form a sputtered UBM titanium-tungsten layer (4); through this technology, a gold film layer is sputtered on the titanium-tungsten layer to form a sputtered UBM gold layer (5). S3: Spin-coating photoresist. The photoresist is spin-coated using a coating machine. The spin-coating thickness is 15-20µm. After spin-coating, the photoresist is soft-baked at a temperature of 90-120°C for 30-90 seconds. After baking, the photoresist is cooled. S4: Exposure and Development: Through the exposure machine, the light source passes through the mask to project the pattern onto the photoresist surface. The photoresist undergoes a chemical reaction where it comes into contact with the light. After being soaked in the developing solution, the desired pattern size is left behind before electroplating. S5: Descum, which removes residual photolithography residue after development through plasma treatment; S6: Electroplating process, wet electrochemical deposition, using the wafer workpiece as the cathode and the target metal as the anode, under the action of pulse current, metal ions are reduced to atoms, forming a dense metal layer with controllable thickness on the surface. A silver layer (6) is electroplated on the surface of the wafer through this technology, and a gold layer (7) is electroplated on the surface of the silver layer (6). S7: Etching. After the above electroplating is completed, the gold layer and titanium-tungsten layer exposed after the adhesive is removed are selectively removed, leaving only the UBM stack under the bump. S8: Chemical plating process: Palladium metal is autocatalytically deposited on the surface of the above structure through a chemical reduction reaction to form a chemically plated palladium layer (8).

3. The method for fabricating the palladium-plated silver-gold-coated bump structure according to claim 2, characterized in that: The visual inspection in step S1 includes checking whether the vacuum aluminum foil bag is damaged, whether nitrogen is leaking, and whether the HIC humidity card is >10%RH.

4. The method for manufacturing the palladium-plated silver-gold-coated bump structure according to claim 2, characterized in that: The etching process in step S7 includes the following steps: 1) Resin removal: Acetone is used to remove residual photoresist and etching byproducts; 2) Pre-cleaning: Use plasma cleaning to remove organic matter, metal ions and particles from the surface; 3) Gold layer etching: using a concentration of 0.01-0.03 g / L -1 The gold layer is removed by a chemical reaction using an alkaline potassium cyanide solution. 4) Rapid rinsing: Immediately rinse the etching residue with ultrapure water with a resistivity ≥18.2 MΩ·cm; 5) Titanium-tungsten layer etching: The etching rate is controlled by a hydrofluoric acid-based solution to remove the titanium-tungsten layer; 6) Ultrapure water cleaning: Residual etching agent is removed by rinsing with ultrapure water combined with ultrasonic assistance, so that the surface particles are controlled to ≤0.2μm.

5. The method for fabricating the palladium-plated silver-gold-coated bump structure according to claim 2, characterized in that: The chemical reduction reaction in step S8 uses a concentration of 1-2 g / L. -1 Palladium chloride was added as the main salt at a concentration of 8 g / L. - Sodium hypochlorite was used as a reducing agent at a concentration of 15-25 g / L. -1 Disodium ethylenediaminetetraacetate was used as a complexing agent, and ammonia was added to maintain the pH at 8.5 ± 0.2, with a concentration of 0.05-0.1 g / L. -1 Maleic acid was added as a stabilizer at a concentration of 0.01-0.03 g / L. -1 Cell granulation was performed using indium trichloride at a concentration of 0.5-1 g / L. -1 Glycine is used to assist in complexation and stress reduction; finally, the temperature of the entire solution is controlled at 50-60℃ to carry out the chemical reduction reaction.

6. The method for manufacturing the palladium-plated silver-gold-coated bump structure according to claim 5, characterized in that: The mass percentages of palladium chloride, sodium hypochlorite, disodium ethylenediaminetetraacetate, maleic acid, indium trichloride, and glycine can be calculated. Based on the density of pure water at 25°C ρ≈1.00kgL⁻¹, dividing the concentration by 10 yields the mass percentage wt%.

Images