JP5336785B2 - Non-cyan electrolytic gold plating bath for bump formation and bump formation method - Google Patents

Abstract

A non-cyanide gold pleating bath for forming a bump is provided to manufacture the bump having proper hardness and an even surface by containing a surfactant or polyalkylene glycol. A non-cyanide gold pleating bath for forming a bump includes conducting salt of 5~150g/L consisting of gold sulfite alkaline salt or gold sulfite ammonium sulfate, crystal modifier, and potassium sulfite, polyalkylene glycol 1mg/L~6g/L of 200~6000 molecular weight and/or an amphoteric surfactant 0.1mg~1g/L and watersoluble amine and/or a buffer material. The bump is manufactured by processing over 5 minutes with the heat at 200~400°C after using the gold pleating bath on a wafer(1). Coat hardness of the bump is 50~90 Hv, height difference of a surface is 1.8 micron meters or less.

Description

  The present invention relates to a non-cyan electrolytic gold plating bath for bump formation of a semiconductor wafer. Specifically, the present invention relates to a non-cyan electrolytic gold plating bath for forming bumps having a flat surface and a predetermined hardness. The bump to be formed is suitable for circuit bonding using an anisotropic conductive adhesive.

  The non-cyan electrolysis gold plating bath generally contains gold sulfite alkali salt or gold gold sulfite as a gold salt. From these gold salts, a water-soluble amine as a stabilizer of a gold complex, a trace amount of Tl, Pb, or As compound as a crystal modifier of a plating film, sodium sulfite or sodium sulfate as an electrolyte, and a buffer. Basic baths are known (Patent Documents 1 and 2).

  Gold bumps formed on a semiconductor wafer using a gold plating bath have been widely used as IC and LSI electrodes in recent years.

  FIG. 3 is a cross-sectional view of a conventional gold bump formed on a semiconductor wafer.

  When forming gold bumps on a semiconductor wafer, a short-axis columnar aluminum (Al) electrode 2 is first formed on the semiconductor wafer 1 by sputtering or the like. As the semiconductor wafer 1, a silicon wafer or a compound wafer such as GaAs is used. A circuit layer 1 ′ including integrated circuits is formed on the surface of the wafer 1 in advance. Next, patterning is performed with the passivation film 3. An opening 3 a is formed in the passivation film 3 above the Al electrode 2.

  Thereafter, an under bump metal (UBM) layer 6 composed of a titanium-tungsten (TiW) sputtered film 4 and a gold sputtered film 5 is formed by sputtering. The UBM layer 6 covers the passivation film 3 and the Al electrode 2 exposed in the opening 3a. A mask is formed on the UBM layer 6 with a resist film 8. An opening 8 a is formed in the resist film 8 above the Al electrode 2. Subsequently, gold bumps 7 are formed in the openings 8a of the resist film 8 by electrolytic gold plating. Thereafter, the resist film 8, the region of the gold sputtered film 5 other than the region covered with the gold bump 7, and the TiW sputtered film 4 are removed. As a result, the wafer on which the passivation film 3 is exposed and the gold bumps 7 are formed is obtained.

  A semiconductor wafer (that is, a semiconductor chip) on which gold bumps are formed is attached to a printed wiring board in a subsequent process. At the time of attachment, a connection is made between the substrate electrode of the wiring pattern formed on the printed wiring board and the gold bump formed on the semiconductor wafer. The connection includes wire bonding using a wire and flip chip bonding for bonding a bump and a substrate electrode without using a wire.

  In recent years, a film-like anisotropic conductive adhesive has been frequently used for flip chip bonding for the purpose of simplifying the manufacturing process of a semiconductor package and ensuring bonding. An anisotropic conductive adhesive is one in which conductive particles are uniformly dispersed in an epoxy resin or the like. As the conductive particles, conductive particles in which the surfaces of particles formed of acrylic resin are sequentially coated with nickel and gold are used.

  The shape and hardness of the bump have a great influence on the bondability between the bump and the substrate. The gold bump is required to have a predetermined shape and hardness in addition to excellent electrical conductivity, oxidation resistance, and the like.

  In FIG. 3, 7 'indicates a gold bump surface (bonding surface with the substrate electrode). The surface 7 ′ is not a plane parallel to the surface of the wafer 1, but has a convex shape with the center protruding upward. In addition to the above, the bump surface may have a concave shape, or the peripheral portion may be cut out. When bonding a bump and a board | substrate of these shapes, the electrically-conductive particle in an adhesive agent falls easily to the hollow of a bump surface, or a peripheral part. Therefore, the conductive particles are not uniformly distributed on the bump surface and are unevenly distributed on a part of the surface. As a result, the bonding area is reduced and the bonding force between the gold bump and the counterpart substrate is weakened. In this case, electrical defects due to disconnection or poor bonding are likely to occur after the assembly process.

  In addition, when the hardness of the bump is lower than that of the conductive particle, the conductive particle is buried on the bump side. As a result, the conductive particles are not thermocompression-bonded between the gold bump and the counterpart substrate, and the bonding cannot be maintained.

On the other hand, if the bump hardness is too high, the conductive particles are only crushed and not joined, causing electrical defects due to disconnection or joining failure.
Japanese Patent Application No. 2005-286147 (Claims) Japanese Patent Application No. 2005-145767 (Claims)

  As described above, when the bump surface is not flat, it is a convex or concave bump shape, or when the periphery of the bump is notched, the conductive particles of the anisotropic conductive adhesive are uniformly distributed on the bump surface. Instead, the arrangement is localized in part. As a result, the bonding area through the particles decreases and the bonding strength decreases.

  Therefore, when bonding is performed using an anisotropic conductive adhesive, it is necessary to form a gold bump having an appropriate hardness as described above and a flat surface having high smoothness as a bonding surface.

  When bumps are formed using a conventional electrolytic gold plating bath, the gold bump hardness cannot be set to a desired hardness. As a result, it is difficult to bond the bump and the substrate electrode through the conductive particles of the anisotropic conductive adhesive without causing an electrical defect.

  Accordingly, it is an object of the present invention to provide a non-cyan electrolytic gold plating bath for bump formation, which can obtain a gold bump having a hardness and shape suitable for joining by thermocompression bonding using an anisotropic conductive adhesive. .

  The inventor has studied to solve the above problems. As a result, it has been found that the hardness of the gold bumps can be controlled within a desired range by adjusting the amount of alkylene glycol or amphoteric surfactant having a predetermined molecular weight added to the plating bath. Furthermore, it discovered that a bump with a flat joint surface was obtained by using together potassium sulfite and the said alkylene glycol or a double-sided activator as a conductive salt.

  The present invention for achieving the above object is described below.

  [1] Alkali gold sulfite or ammonium ammonium sulfite, crystal modifier, potassium sulfite 5 to 150 g / L, polyalkylene glycol 1 to 4 g / L and / or amphoteric surfactant having a molecular weight of 200 to 6000 A non-cyan electrolytic gold plating bath for bump formation containing 0.1 mg to 1 g / L and a water-soluble amine and / or buffer.

  [2] Amphoteric surfactants are 2-alkyl-N-carboxymethyl-N-hydroxyethyl imidazolinium betaine, lauric acid amidopropyl hydroxysulfobetaine, fatty acid amidopropyl betaine, and fatty acid acyl-N-carboxyethyl- The non-cyan electrolytic gold plating bath for bump formation according to [1], which is one or more selected from N-hydroxyethylethylenediamine alkali salts.

  [3] The non-cyanide electrolytic gold plating bath for bump formation according to [1], wherein the crystal modifier is a Tl compound, a Pb compound, or an As compound, and the crystal modifier is blended in a metal concentration of 0.1 to 100 mg / L. .

  [4] After performing electrolytic gold plating on the patterned wafer using the non-cyan electrolytic gold plating bath for bump formation described in [1], heat treatment is performed at 200 to 400 ° C. for 5 minutes or more. A bump forming method for forming a bump having a film hardness of 50 to 90 Hv and a surface height difference of 1.8 μm or less.

  [5] A connection structure in which a substrate electrode having a substrate wiring pattern formed on a printed wiring board and a gold bump of an integrated circuit formed on a semiconductor wafer are connected using an anisotropic conductive adhesive. A connection structure in which the film hardness of the gold bump is 50 to 90 Hv.

  The non-cyan electrolytic gold plating bath of the present invention uses potassium sulfite without using sodium sulfite as a conductive salt, and further contains an amphoteric surfactant or polyalkylene glycol as an essential component. Thereby, when forming a bump on a compound semiconductor wafer such as a silicon semiconductor wafer or Ga / As, it is possible to produce a bump made of an electrolytic gold plating film having a preferable hardness and a flat surface without unevenness. .

  In particular, by selecting the molecular weight and addition amount of polyalkylene glycol and blending it with a plating bath together with potassium sulfite, bump hardness of any value in the range of 50 to 90 Hv suitable for thermocompression bonding with anisotropic conductive adhesive Can be controlled.

  The gold bump formed by the plating bath of the present invention has a flat pressure-bonding surface and a predetermined hardness. Therefore, it is easy to perform electrode bonding via an anisotropic conductive adhesive such as an anisotropic conductive film or an anisotropic conductive adhesive film used in the semiconductor manufacturing process. In addition, the rate at which disconnections and poor bonding occur is extremely small.

  Since the gold bump formed using the plating bath of the present invention does not bulge not only on the bonding surface but also on the side surface of the bump in contact with the resist film, a gold bump can be formed following the shape of the opening of the resist film. Accordingly, a prismatic or polygonal gold bump having a flat side surface and an upper surface, or a cylindrical gold bump having a uniform diameter can be formed.

  The electrolytic gold plating bath of the present invention is a non-cyanide gold plating bath, which comprises a gold sulfite alkali salt or gold ammonium sulfite as a gold source, a water-soluble amine as a gold complex stabilizer, and a small amount of crystals. An electrolytic gold plating bath containing potassium sulfite as a conductive salt and polyalkylene glycol and / or an amphoteric surfactant in a bath composed of a conditioner and a buffer. It is substantially free of sodium sulfite as a conductive salt.

  Hereinafter, the essential components of the electrolytic gold plating bath of the present invention will be described for each component.

(1) Gold sulfite alkali salt, gold ammonium sulfite (gold source)
As the gold sulfite alkali salt used in the present invention, a known gold sulfite alkali salt can be used without limitation. Examples of the gold sulfite alkali salt include gold (I) sodium sulfite and potassium gold (I) sulfite. These may be used alone or in combination of two or more.

  In the electrolytic gold plating bath of the present invention, the gold sulfite alkali salt or gold ammonium sulfite described above is used as a gold source, and the amount thereof is usually 1 to 20 g / L, preferably 8 to 15 g / L as the gold amount. L. If the blending amount of the gold sulfite alkali salt or gold ammonium sulfite is less than 1 g / L, the thickness of the plating film may be uneven. If it exceeds 20 g / L, there is no problem in the properties of the plating film, but the production cost increases and this is an economical burden.

(2) Water-soluble amine (stabilizer)
As the water-soluble amine, a diamine having 2 or more carbon atoms, preferably 2 to 6 carbon atoms can be used. For example, 1,2-diaminoethane, 1,2-diaminopropane, 1,6-diaminohexane and the like can be used. Can be mentioned. These may be used alone or in combination of two or more.

  The amount of the water-soluble amine is usually 0.1 to 30 g / L, preferably 1 to 12 g / L. If the blending amount of the water-soluble amine exceeds 30 g / L, the stability of the gold complex salt increases, but on the other hand, the plating film becomes excessively dense, and there may be a problem with respect to bonding properties. If it is less than 0.1 g / L, the limit current density may be reduced, resulting in burnt plating.

(3) Tl compound, Pb compound, As compound (crystal modifier)
Examples of the crystal adjusting agent used in the electrolytic gold plating bath of the present invention include Tl compounds such as thallium formate, thallium malonate, thallium sulfate, and thallium nitrate; Pb compounds such as lead citrate, lead nitrate, and lead alkanesulfonate; Examples include As compounds such as diarsenic trioxide. These Tl compounds, Pb compounds and As compounds may be used alone or in combination of two or more.

  The compounding amount of the crystal modifier can be appropriately set within the range not impairing the object of the present invention, but the metal concentration is usually 0.1 to 100 mg / L, preferably 0.5 to 50 mg / L, particularly preferably 3 to 25 mg / L. L. When the blending amount of the crystal modifier is less than 0.1 mg / L, there are cases where the components around the plating bath are deteriorated due to deterioration of the plating around, plating bath stability and durability. When it exceeds 100 mg / L, deterioration around the plating and uneven appearance of the plating film may occur.

(4) Potassium sulfite (conductive salt)
In the electrolytic gold plating bath of the present invention, potassium sulfite is used as a conductive salt.

  The blending amount of potassium sulfite in the electrolytic gold plating bath of the present invention can be appropriately set within the range not impairing the object of the present invention, but is preferably the following blending amount.

  The blending amount of potassium sulfite is usually 5 to 150 g / L, preferably 10 to 150 g / L, more preferably 50 to 100 g / L, and particularly preferably 60 to 90 g / L. When the blending amount of potassium sulfite is less than 5 g / L, the bump surface cannot be sufficiently bulged to make the bump surface flat. Further, the surroundings of the plating and the liquid stability are deteriorated, and the plating bath may be decomposed. If it exceeds 150 g / L, the limit current density may be reduced, resulting in burnt plating.

  The plating bath of the present invention is substantially free of sodium salts such as sodium sulfite and sodium sulfate as conductive salts. Sodium contained in the plating bath is limited to that derived from sodium gold sulfite as a gold source.

(5) Buffer Agent The buffer agent used in the present invention is not particularly limited as long as it is usually used in an electrolytic gold plating bath. For example, inorganic acids such as phosphates and borates, organic acids such as citrates, phthalates and ethylenediaminetetraacetates (divalent to pentavalent polycarboxylic acids, hydroxycarboxylic acids) May be used, or two or more kinds may be used.

  The blending amount of the buffer in the non-cyan electrolytic gold plating bath of the present invention is usually 1 to 30 g / L, preferably 2 to 15 g / L, particularly preferably 2 to 10 g / L. When the blending amount of the buffering agent is less than 1 g / L, the solution stability may deteriorate due to a decrease in pH, and the plating bath components may be decomposed. If it exceeds 30 g / L, the limit current density may be reduced, resulting in burnt plating.

(6) Polyalkylene glycol, amphoteric surfactant Examples of the polyalkylene glycol blended in the non-cyan electrolytic gold plating bath of the present invention include polyethylene glycol and polypropylene glycol.

  Examples of amphoteric surfactants include betaine amphoteric surfactants such as 2-alkyl-N-carboxymethyl-N-hydroxyethylimidazolinium betaine, amidopropyl hydroxysulfobetaine laurate, and fatty acid amidopropyl betaine; Examples thereof include aminocarboxylate-based amphoteric surfactants such as N-carboxyethyl-N-hydroxyethylethylenediamine alkali salts; imidazoline derivative-based amphoteric surfactants.

  The blending amount of the polyalkylene glycol is 1 mg / L to 6 g / L, preferably 20 to 3000 mg / L, particularly preferably 100 to 1000 mg / L. On the other hand, the compounding amount of the amphoteric surfactant is usually 0.1 mg / L to 1 g / L, preferably 5 to 500 mg / L, particularly preferably 10 to 300 mg / L. When the blending amount of the polyalkylene glycol and the amphoteric surfactant is less than the above range, the film hardness of the bump after heat treatment is less than 50 Hv, and the bump surface cannot be made flat. When exceeding the above range, the film hardness of the bump after the heat treatment is 90 Hv or more, and a hardness suitable for bonding cannot be obtained.

  Only one of the polyalkylene glycol and the amphoteric surfactant may be used, or both may be used in combination. When both are used in combination, the blending amount of both is appropriately adjusted in accordance with the purpose within the above ranges.

  When polyalkylene glycol is used, the molecular weight is 200 to 6000, preferably 400 to 2000, more preferably in order to set the film hardness of the gold bump after heat treatment to 50 to 90 Hv suitable for bonding of the anisotropic conductive adhesive film. The thing of 400-1000 is used. When the molecular weight exceeds 6000, in order to make the film hardness after heat treatment 50 to 90 Hv, it is necessary to make the concentration very low with a blending amount of less than 1 mg / L. A plating solution having such a low concentration is difficult to control the concentration and is not practical.

  By adjusting the blending amount of polyalkylene glycol having a molecular weight of 6000 or less, it is possible to adjust the hardness of the film formed by plating to a desired value in the range of 50 to 90 Hv. In the case of a low molecular weight polyalkylene glycol, a coating hardness of 50 to 90 Hv can be obtained by increasing the blending amount, and in the case of a high molecular weight, decreasing the blending amount. In any molecular weight, the film hardness is increased by increasing the blending amount, and a relatively high hardness close to 90 Hv can be obtained.

  For example, when the film hardness after heat treatment is 70 Hv, it can be achieved by setting the blending amount of polyalkylene glycol having a molecular weight of 6000 or less to 1 mg / L to 6 g / L, preferably 20 to 3000 mg / L. . Furthermore, in this case, the amount of amphoteric surfactant is preferably 10 to 300 mg / L.

  In general, increasing the amount of polyalkylene glycol or amphoteric surfactant reduces the decrease in film hardness due to heat treatment. Furthermore, when potassium sulfite is blended and polyalkylene glycol or amphoteric surfactant is not blended, the bump surface height difference is not sufficiently reduced. Only when both potassium sulfite and polyalkylene glycol or amphoteric surfactant are added, both the height difference of the bump surface and the film hardness become desirable values.

  In the non-cyan electrolytic gold plating bath of the present invention, other components such as a pH adjuster may be appropriately used within a range not impairing the object of the present invention.

  Examples of the pH adjuster include sulfuric acid, aqueous sulfite, phosphoric acid and the like as acid, and potassium hydroxide, aqueous ammonia and the like as alkali.

  When bumps are formed on a semiconductor wafer by plating using the non-cyan electrolytic gold plating bath of the present invention, the plating operation may be performed according to a conventional method. For example, masking is performed on a wafer having a Ti—W sputtered film as an UBM layer and an Au sputtered film formed thereon as a mask material. Thereafter, electrolytic gold plating is performed using the wafer as an object to be plated. Next, there is a method of removing the mask material by dissolving it in a solvent. After removing the mask material, the portion of the UBM layer that is not covered with the gold bumps is removed by etching or the like, and the wafer is heat-treated.

  A novolac positive photoresist can be used as the masking agent. As a commercial item, LA-900, HA-900 (above, Tokyo Ohka Kogyo Co., Ltd. make) etc. can be mentioned, for example.

  The plating temperature is usually 40 to 70 ° C, preferably 50 to 65 ° C. If the temperature of the plating bath is out of the range of 40 to 70 ° C., the plating film may be difficult to deposit, or the plating bath may become unstable and decomposition of the plating bath components may occur.

The set current density used for plating is difficult to determine uniquely because the appropriate range varies depending on the conditions such as the composition and temperature of the plating solution. Under conditions of a gold concentration of 8 to 15 g / L and a plating bath temperature of 60 ° C., it is usually 2.0 A / dm ² or less, preferably 0.2 to 1.2 A / dm ² . If the set current density is out of the above range, workability may be deteriorated, the appearance of the plating film and the plating film characteristics may be abnormal, or the plating bath may become extremely unstable, resulting in decomposition of the plating bath components. .

  The pH of the non-cyan electrolytic gold plating bath of the present invention is usually 7.0 or higher, preferably 7.2 to 10.0. If the pH of the non-cyan electrolytic gold plating bath is less than 7.0, the plating bath may become extremely unstable and decomposition may occur. On the other hand, if the pH exceeds 10.0, the mask material may be dissolved and a desired gold bump or the like may not be formed.

  The heat treatment temperature of the gold bump is 200 to 400 ° C., preferably 200 to 300 ° C. The heat treatment time is 5 minutes or longer, preferably 30 to 60 minutes. The heat treatment is performed using a fine oven or the like that can hold the interior of the chamber at a set temperature for a certain period of time.

  The non-cyan electrolytic gold plating bath of the present invention has two turns (one turn when the entire amount of gold in the plating bath is consumed for plating) by supplementing and managing the gold source and other components constituting the plating bath. You can achieve the above use.

  The non-cyan electrolytic gold plating bath of the present invention is not selected as long as the substrate is metallized and conductive. It can be particularly suitably used when bumps are formed on a compound wafer such as a silicon wafer or a Ga / As wafer patterned using a novolac positive photoresist as a mask material.

  FIG. 1 is a cross-sectional view showing an example of gold bumps formed on a semiconductor wafer using the gold plating bath of the present invention. In FIG. 1, 1 is a semiconductor wafer, 1 ′ is a circuit layer including an integrated circuit formed on the surface of the semiconductor wafer, 2 is an Al electrode, 3 is a passivation film, 3a is an opening of the passivation film, and 4 is TiW sputtering. Film 5 is a gold sputtered film, 6 is a UBM layer composed of a TiW sputtered film 4 and a gold sputtered film 5, 7 is a gold bump, 7 'is a surface of the gold bump 7, 8 is a resist film, and 8a is an opening of the resist film. Part. The surface 7 ′ of the gold bump is formed flat, and the height difference (the difference in distance from the wafer 1) between the central portion 7′a and the peripheral end portion 7′b in contact with the resist film is within 1.8 μm. It is preferably within 1.7 μm, more preferably within 1.6 μm, and particularly preferably within 1.5 μm.

  FIG. 2 is a cross-sectional view showing a state in which the semiconductor chip on which the gold bump shown in FIG. 1 is formed is attached to a printed wiring board. The same parts as those in FIG. 1 are denoted by the same reference numerals, and the description thereof is omitted.

  A board wiring pattern 12 made of a conductive material such as copper is formed on the hard board 11 of the printed wiring board 10. A substrate electrode 14 made of a conductive material such as gold is formed on the substrate wiring pattern 12. On the other hand, a gold bump 7 is formed on the semiconductor chip 16 attached to the substrate 10 in parallel with the printed wiring board 10 so as to face the substrate electrode 14. The substrate electrode 14 and the gold bump 7 are joined by an anisotropic conductive adhesive 20. A space between the hard substrate 11 and the semiconductor wafer 1 is sealed with a sealing material 18.

  The material of the hard substrate 11 is not particularly limited as long as it is used for a hard printed wiring board, and examples thereof include glass fiber reinforced epoxy resin and ceramic. As the sealing material 18, known resins that are usually used for sealing semiconductor chips can be used. The substrate wiring pattern 10 and the substrate electrode 14 are formed on the hard substrate 11 by vapor deposition, plating, etching of a metal thin film, application of a conductive paint, or the like.

  A method of attaching the semiconductor chip 16 onto the printed wiring board 10 is performed as follows. First, the semiconductor chip 16 is positioned so that the gold bump 7 is positioned above the substrate electrode 14, and the semiconductor chip 16 is placed on the printed wiring board 10 with the film-like anisotropic conductive adhesive 20 interposed therebetween. Next, the gold bump 7 and the substrate electrode 14 are thermocompression bonded via the anisotropic conductive adhesive 20. By attaching the semiconductor chip 16 to the printed wiring board 10, the gold bumps 7 as the electrodes of the integrated circuit formed in the circuit layer 1 ′ and the substrate electrodes 14 formed on the board wiring pattern 12 are anisotropic. The conductive conductive adhesive 20 is connected.

A non-cyan electrolytic gold plating bath was prepared with the formulation shown in Tables 1-4. The unit of blending concentration of each raw material is g / L unless otherwise specified. However, Na ₃ Au (SO ₃ ) ₂ and gold ammonium sulfite indicate the concentration with respect to the amount of Au.

As the object to be plated, a silicon wafer having a bump opening patterned with a novolac positive photoresist (base cross-sectional composition is a gold sputtered film / TiW / SiO ₂ ) was used. An object to be plated was immersed in 1 L of the prepared non-cyan electrolytic gold plating bath and energized to form a gold plating film having a thickness of 15 μm. The current efficiency of the non-cyan electrolysis gold plating bath is usually 100% under normal plating operation conditions.

  After forming a film with a predetermined film thickness, the mask material is removed, the shape of the formed bump, bath stability, plating film appearance, film hardness (after non-heat treatment and heat treatment at 300 ° C. for 30 minutes), iodine in the Au sputtered film The etching property by the system etchant was evaluated by the following method and criteria. A result is combined with Tables 1-4 and shown.

[Bump surface height difference (μm)]
As shown in FIG. 1, patterning having a rectangular opening with a long side of 80 to 20 μm and a short side of 80 to 20 μm was performed on the silicon wafer 1 using a novolac positive photoresist 8. After plating using an electrolytic gold plating bath, a novolac positive photoresist was dissolved with methyl ethyl ketone as a solvent. About the obtained bump, the difference between the highest point on the upper surface of the bump and the lowest point on the outer surface of the upper surface was measured as a height difference using a laser microscope VK-9710 manufactured by Keyence, and used as an index of smoothness. The height difference usually required for bump plating is 3 μm or less, preferably 2 μm or less, and more preferably 1.5 μm or less.

[Bath stability]
The state of the plating bath after plating the object to be plated was observed and evaluated according to the following criteria.
Decomposition: The components in the plating bath were decomposed.
X: Precipitation of gold was observed in the plating bath at a level that can be seen with the naked eye.
Δ: Slight gold precipitation was observed in the plating bath. Level that can be observed by filtering with 0.2μm membrane filter.
○: No precipitation of gold was observed in the plating bath.

[Appearance of plating film]
The appearance of the surface film of the gold bump formed on the object to be plated was observed and evaluated according to the following criteria.
X: The color is red, dendrite-like precipitation is observed, unevenness is observed, or burns occur.
Δ: No abnormal precipitation, but a glossy appearance.
○: The color tone is lemon yellow and it has a non-semi-glossy uniform appearance.

[Film hardness (Vickers hardness; Hv)]
Using a specific bump portion formed on the object to be plated, the film hardness (unheated and after heat treatment at 300 ° C. for 30 minutes) was measured with a Vickers hardness meter. As a characteristic required for bumps for medium hardness, the film hardness after annealing is about 70 Hv. The measurement conditions were based on the condition that the measurement indenter was held at 25 gf load for 10 seconds.

[Etching property of Au sputtered film with iodine-based etchant]
The object to be plated was immersed in an iodine-based etchant sufficiently stirred at room temperature for 90 seconds, washed with an alcohol-based rinse solution, sprayed with ethanol and dried with a dryer. Thereafter, the surface state of all the bumps formed on the object to be plated was observed at a magnification of 50 to 200 times using a metal microscope, and evaluated according to the following criteria.
X: Unevenness is observed on the surface of bumps of 50% or more.
Δ: Unevenness is observed on the surface of the bump in a limited area.
○: Unevenness is not observed on the surface of all the bumps on the workpiece.

〔Comprehensive evaluation〕
From the above evaluation results, the evaluation was made according to the following evaluation criteria.
X: Unfavorable results were included in the evaluation results regarding the formed gold plating film (gold pump) and the non-cyan electrolysis gold plating bath after the plating treatment.
Δ: Although the above evaluation results regarding the formed gold plating film (gold pump) and the non-cyan electrolysis gold plating bath after the plating treatment were generally good, some unfavorable results were included.
○: The above-described evaluation results regarding the formed gold plating film (gold pump) and the non-cyan electrolysis gold plating bath after the plating treatment were all good results.

By comparing the examples and comparative examples, the following is clear.
(1) In principle, potassium sulfite has the effect of reducing the height difference on the bump surface. The height difference of 1.01 to 1.56 of Examples 1 to 20 containing potassium sulfite is compared with the height difference of 1.85 to 3.11 with Comparative Examples 2 to 12 containing sodium sulfite instead of potassium sulfite. The bump surface height difference is clearly small.
(2) Polyalkylene glycols and amphoteric surfactants have the effect of reducing the decrease in film hardness after heat treatment at 300 ° C. In Examples 1 to 20 containing a polyalkylene glycol or an amphoteric surfactant, the film hardness after heat treatment at 300 ° C. is moderate (50 to 90 Hv). On the other hand, the hardness of the comparative examples 1 and 2 which does not contain polyalkylene glycol and an amphoteric surfactant is as low as 45Hv and 43Hv.
(3) However, simply adding potassium sulfite does not sufficiently reduce the bump surface height difference. Although the comparative example 1 has added the same amount of potassium sulfite as Examples 1-20, the difference in elevation is large (1.83). By adding polyalkylene glycol or amphoteric surfactant to potassium sulfite, the difference in height becomes 1.56 or less (Examples 1 to 20) for the first time.

It is sectional drawing which shows an example of the gold bump formed using the gold plating bath of this invention. It is sectional drawing which shows an example of the state which attached the semiconductor chip which has a gold bump shown in FIG. 1 to the printed wiring board. It is sectional drawing which shows the gold bump formed using the conventional gold plating bath.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Semiconductor wafer 1 'Circuit layer 2 Al electrode 3 Passivation film 3a Passivation film opening 4 TiW sputter film 5 Gold sputter film 6 UBM layer 7 Gold bump 7' Surface of gold bump 8 Resist film 8a Resist film opening 10 Print Wiring substrate 11 Hard substrate 12 Substrate wiring pattern 14 Substrate electrode 16 Semiconductor chip 18 Sealing material 20 Anisotropic conductive adhesive

Claims (5)

1 to 20 g / L of gold sulfite alkali salt or gold ammonium sulfite as a gold amount, 5 to 150 g / L of a conductive salt composed of a crystal modifier and potassium sulfite alone, and 1 mg / L of a polyalkylene glycol having a molecular weight of 200 to 6000 A non-cyan electrolysis gold plating bath for bump formation containing ˜6 g / L and / or amphoteric surfactant 0.1 mg to 1 g / L, and a water-soluble amine and / or buffer ,
A non-cyan electrolytic gold plating bath for bump formation which does not contain sodium sulfite other than sodium sulfite derived from the gold sulfite alkali salt. Amphoteric surfactants include 2-alkyl-N-carboxymethyl-N-hydroxyethyl imidazolinium betaine, lauric acid amidopropyl hydroxysulfobetaine, fatty acid amidopropyl betaine, and fatty acid acyl-N-carboxyethyl-N-hydroxy. The non-cyan electrolytic gold plating bath for bump formation according to claim 1, which is one or more selected from ethylethylenediamine alkali salts. The non-cyan electrolytic gold plating bath for bump formation according to claim 1, wherein the crystal adjusting agent is a Tl compound, a Pb compound, or an As compound, and the crystal adjusting agent is blended in an amount of 0.1 to 100 mg / L as a metal concentration. A film hardness is obtained by performing heat treatment at 200 to 400 ° C. for 5 minutes or more after performing electrolytic gold plating on the patterned wafer using the non-cyan electrolytic gold plating bath for bump formation according to claim 1. A bump forming method for forming a bump of 50 to 90 Hv and a surface height difference of 1.8 μm or less. A substrate electrode having a substrate wiring pattern formed on the printed circuit board; and a gold bump of an integrated circuit formed on the semiconductor wafer using the non-cyan electrolytic gold plating bath for bump formation according to claim 1; Is a connection structure in which a film hardness of the gold bump is 50 to 90 Hv.

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