TWI477660B - Non cyanide gold plating bath for bump - Google Patents

Description

Non-cyanide electrolytic gold plating bath for bump forming

The present invention relates to a non-cyanide electrolytic gold plating bath for bump formation of a semiconductor wafer. More specifically, it relates to a non-cyanide electrolytic gold plating bath which forms a bump having a flat surface and a desired hardness. The bumps formed are suitable for circuit bonding using an anisotropic conductive adhesive.

The non-cyanide electrolytic gold plating bath generally contains a gold sulfite salt as a gold salt or a gold ammonium sulfite. The basic bath system is known as a gold salt, a water-soluble amine as a stabilizer for a gold complex, a trace amount of Tl, Pb, or As compound as a crystal modifier of an electroplated film, and further, sodium sulfite or sulfuric acid as an electrolyte. Sodium and buffer are the ones. (Japanese Patent Application No. 2005-286147 (Scope of Application for Patent Application), Japanese Patent Application No. 2005-145767 (Application for Patent Application)).

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

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

When a gold bump is formed on a semiconductor wafer, first, a short-axis columnar aluminum (Al) electrode 2 is formed on the semiconductor wafer 1 by sputtering or the like. A compound wafer such as tantalum wafer or GaAs is used on the semiconductor wafer 1. The surface of the wafer 1 is formed in advance with a circuit layer 1' including an integrated circuit. Next, the passivation film 3 is patterned. An opening 3a is formed above the passivation film 3-based Al electrode 2.

Thereafter, an under bump metal (UBM) layer 6 of bumps formed of a titanium-tungsten (TiW) sputter film 4 and a gold sputter film 5 is formed by sputtering. The UBM layer 6 is exposed to the Al electrode 2 of the passivation film 3 and its opening portion 3a. The UBM layer 6 is attached to the photoresist film 8 for shielding. An opening 8a is formed in the photoresist film 8 above the Al electrode 2. Next, in the opening 8a of the photoresist film 8, gold bumps 7 are formed by electrolytic gold plating. Thereafter, the field of the photoresist film 8 and the gold sputter film 5 (the region not covered by the gold bumps 7) and the Tiw sputter film 4 are removed. As a result, the passivation film 3 is exposed, and a wafer on which the gold bumps 7 are formed is obtained.

The semiconductor wafer (i.e., the semiconductor wafer) forming the gold bumps is mounted with the printed wiring substrate in the subsequent step. At the time of mounting, the substrate electrode of the wiring pattern formed on the printed wiring board is connected to the gold bump formed on the semiconductor wafer. The connection includes a wire bonding method in which wire bonding is performed using a metal wire, and a bump chip bonding method in which a bump is bonded to a substrate electrode without using a metal wire.

In recent years, in order to simplify the manufacturing steps of the semiconductor package and to perform the bonding reliably, a film-shaped anisotropic conductive adhesive is often used in the flip chip bonding method. The 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 nickel or gold are sequentially coated on the surface of the particles formed of the acrylic resin are used.

The shape and hardness of the bumps have a large influence on the bondability between the bumps and the substrate. The gold bumps are excellent in electrical conductivity and oxidation resistance, and are required to have a desired shape and hardness.

In Fig. 3, 7' indicates the surface of the gold bump (the bonding surface with the substrate electrode). This surface 7' is a plane which is not parallel to the surface of the wafer 1, and is a convex shape which protrudes above the center. In addition to the above, there are cases where the surface of the bump is a concave shape or a shape in which the peripheral portion is cut. When the bumps of these shapes are bonded to the substrate, the conductive particles in the adhesive also fall into the concave or peripheral portion of the surface of the bump. Therefore, the conductive particles are not uniformly dispersed and disposed on the surface of the bump, but are biased in a part of the surface. As a result, the joint area is reduced and the bonding force between the gold bump and the counter substrate is not strong. This situation is also caused by electrical defects due to wire breakage or poor joints after the installation step.

Further, when the hardness of the bump is lower than that of the conductive particles, the conductive particles are not on the bump side. As a result, the conductive particles are not thermally bonded between the gold bumps and the counter substrate, and the bonding cannot be maintained.

On the other hand, when the hardness of the bump is too high, only the conductive particles are crushed and cannot be joined, which causes disconnection or poor bonding, which causes electrical defects.

As described above, the surface of the bump is not convex and is convex or concave. When the periphery of the bump is cut, the conductive particles of the anisotropic conductive adhesive are not uniformly dispersed and disposed on the surface of the bump. Partially localized configuration. As a result, the joint area of the particles is reduced and the joint strength is lowered.

Therefore, when bonding is carried out using an anisotropic conductive adhesive, it is necessary to form a gold bump having a high planarity with smoothness while having a moderate hardness as described above.

In the case where a bump is formed by a conventional electrolytic gold plating bath, the hardness of the gold bump cannot be made to have a desired hardness. As a result, the conductive particles passing through the anisotropic conductive adhesive do not cause electrical defects, but the bonding of the bumps to the substrate electrodes becomes difficult.

Accordingly, an object of the present invention is to provide a non-cyanide electrolytic gold plating bath for forming a bump, which can obtain a gold bump having a hardness and a shape suitable for bonding by thermal compression bonding using an anisotropic conductive adhesive.

The present inventors conducted research to solve the above problems. As a result, it was found that the hardness of the controllable gold bumps was within a desired range by adjusting the amount of addition to the plating bath of the alkanediol or amphoteric surfactant having a predetermined molecular weight. Further, as a conductive salt, by using potassium sulfite in combination with the above alkanediol or a double-sided active agent, it was found that a bump having a flat joint surface was obtained.

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

[1] A non-cyanide electrolytic gold plating bath for forming a bump, which comprises a gold sulfite base salt or a gold ammonium sulfite, a crystal modifier, a potassium sulfite 5 to 150 g/L, and a molecular weight of 200 to 6000. The alkanediol is 1 mg/L to 6 g/L and/or the amphoteric surfactant is 0.1 mg to 1 g/L, and is formed with a water-soluble amine and/or a buffer.

[2] The non-cyanide electrolytic gold plating bath for forming a bump according to [1], wherein the amphoteric surfactant is selected from the group consisting of 2-alkyl-N-carboxymethyl-N-hydroxyethylimidazolium betaine, lauric acid One or two or more kinds of amidoxime hydroxy sulfobetaine, a fatty acid guanamine propyl betaine, and a fatty acid sulfhydryl-N-carboxyethyl-N-hydroxyethylethylenediamine base salt.

[3] The non-cyanide electrolytic gold plating bath for forming a bump according to [1], wherein the crystal modifier is a T1 compound, a Pb compound, or an As compound, and a crystal modifier is blended at a concentration of 0.1 to 100 mg/L.

[4] A bump forming method characterized in that electrolytic plating of gold is performed on a patterned wafer using a non-cyanide electrolytic gold plating bath for forming a bump described in [1], and then passing through the battery at 200 to 400 ° C for 5 minutes. The above heat treatment forms a bump having a film hardness of 50 to 90 Hv and a surface 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 substrate and a gold bump formed on an integrated circuit on the semiconductor wafer are used by using an anisotropic conductive adhesive The connection structure of the connection is characterized in that the hardness of the gold bump is 50 to 90 Hv.

The non-cyanide electrolytic gold plating bath of the present invention contains a conductive salt, which is potassium sulfite without using sodium sulfite, and further contains an amphoteric surfactant or a polyalkylene glycol as an essential component. Thereby, when a bump is formed on a semiconductor wafer such as a semiconductor wafer or a Ga/As, it has a preferable hardness, and a bump formed of an electrolytic gold plating film having a flat surface having no unevenness can be produced. .

In particular, the molecular weight and the amount of addition of the polyalkylene glycol can be controlled by blending with potassium sulfite in an electroplating bath to control any range of 50 to 90 Hv suitable for thermocompression bonding with an anisotropic conductive adhesive. The value of the bump hardness.

The gold bumps formed by the electroplating bath of the present invention have a flat pressure-bonding surface and a desired hardness. Therefore, electrode bonding can be easily performed by an anisotropic conductive adhesive such as an anisotropic conductive film or an anisotropic conductive adhesive film used in the semiconductor manufacturing step. Moreover, the proportion of occurrence of disconnection or poor bonding is extremely small.

The gold bump formed by using the plating bath of the present invention is not only expanded on the side surface of the bump which is in contact with the photoresist film on the bonding surface, so that a gold bump which is shaped like the opening portion of the photoresist film can be formed. Therefore, the side surface and the upper surface form a gold column bump having a columnar shape or a polygonal column shape in a plane or a cylindrical gold bump which can form a uniform diameter.

Best form for implementing the invention

The electrolytic gold plating bath of the present invention is a non-cyanide gold plating bath, and is a water-soluble amine or a trace amount of a crystal modifier which is a gold salt of sulfite or gold ammonium sulfite as a gold source, a stabilizer for gold salt. The bath formed with the buffer contains an electrolytic gold plating bath as a conductive salt of potassium sulfite, a polyalkylene glycol, and/or an amphoteric surfactant. The conductive salt system is substantially free of sodium sulfite.

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

(1) gold sulfite alkali salt, gold ammonium sulfite (gold source)

The gold sulfite salt used in the present invention is not limited to the use of a known gold sulfite salt. Examples of the gold sulfite base salt include sodium (I) sulfite and potassium (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 above-mentioned gold sulfite salt or gold ammonium sulfite is used as the gold source, and the blending amount thereof is generally 1 to 20 g/L, preferably 8 to 15 g/L. . When the blending amount of the gold sulfite alkali salt or the gold ammonium sulfite is less than 1 g/L, the thickness of the plating film may not be uniform. When it exceeds 20 g/L, there is no problem in the characteristics of the plating film, etc., but the manufacturing cost becomes high and it becomes an economic burden.

(2) Water-soluble amine (anti-setting agent)

As the water-soluble amine, a diamine having 2 or more carbon atoms and preferably 2 to 6 carbon atoms can be used, and examples thereof include 1,2-diaminoethane, 1,2-diaminopropane, and 1,6-di. Aminohexane and the like. These may be used alone or in combination of two or more.

The blending amount of the water-soluble amine is usually from 0.1 to 30 g/L, preferably from 1 to 12 g/L. When the blending amount of the water-soluble amine exceeds 30 g/L, the stability of the gold-salt salt increases, but on the other hand, the plating film is excessively densified and the bonding property is poor. When the current density is less than 0.1 g/L, the current density is lowered to become a case of burnt plating.

(3) Tl compound, Pb compound, As compound (crystal modifier)

Examples of the crystal modifier used in the electrolytic gold plating bath of the present invention include T1 compounds such as cesium formate, strontium malonate, barium sulfate, and cesium nitrate; and Pb such as lead citrate, lead nitrate, and lead alkane sulfonate. a compound; an As compound such as arsenic trioxide. These T1 compounds, Pb compounds, and As compounds may be used alone or in combination of two or more.

The blending amount of the crystal modifier may be appropriately set within a range not detracting from the object of the present invention, but the metal concentration is generally 0.1 to 100 mg/L, preferably 0.5 to 50 mg/L, particularly preferably 3 to 25 mg/ L. When the blending amount of the crystal modifier is less than 0.1 mg/L, plating adhesion, plating bath stability, and durability are deteriorated, and the constituent components of the plating bath are decomposed. When it exceeds 100 mg/L, there is a case where the plating adhesion is deteriorated and the appearance of the plating film is uneven.

(4) Potassium sulfite (conductive salt)

In the electrolytic gold plating bath of the present invention, potassium sulfite is used as the conductive salt.

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

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, particularly preferably 60 to 90 g/L. When the blending amount of potassium sulfite is less than 5 g/L, the expansion of the bump shape cannot be sufficiently suppressed, and the surface of the bump is flat. Further, the plating adhesion and the liquid stability are deteriorated, and the decomposition of the plating bath is caused. When it exceeds 150 g/L, there is a case where the limit current density is lowered and it becomes a burnt plating.

In the plating bath of the present invention, the conductive salt is substantially free of a sodium salt such as sodium sulfite or sodium sulfate. The sodium contained in the electroplating bath is limited to gold sodium sulfite from the gold source.

(5) Buffer

The buffer used in the present invention is not particularly limited as long as it is a user of a general electrolytic gold plating bath. For example, an organic acid such as a mineral acid salt such as a phosphate or a borate, a citrate salt, a citrate salt or an ethylenediaminetetraacetate salt (a polyvalent carboxylic acid of 2 to 5 or a hydroxycarboxylic acid) may be used alone. It is also possible to use two or more types.

The blending amount of the buffering agent in the non-cyanide electrolytic gold plating bath of the present invention is generally 1 to 30 g/L, preferably 2 to 15 g/L, particularly preferably 2 to 10 g/L. When the blending amount of the buffer is less than 1 g/L, the liquid stability is deteriorated due to a decrease in pH, and decomposition of the plating bath component occurs. When it exceeds 30 g/L, the boundary current density is lowered to become a case of burnt plating.

(6) Polyalkylene glycol, amphoteric surfactant

Examples of the polyalkylene glycol blended in the non-cyanide electrolytic gold plating bath of the present invention include polyethylene glycol and polypropylene glycol.

Examples of the amphoteric surfactant include beta-alkyl-N-carboxymethyl-N-hydroxyethylimidazolium betaine, guanamine propyl hydroxythiobetaine, and fatty acid amidinopropyl betaine. An amphoteric surfactant; an aminocarboxylate-based amphoteric surfactant such as a fatty acid oxime ester-N-carboxyethyl-N-hydroxyethylethylenediamine base salt; an imidazoline derivative-based amphoteric surfactant.

The blending amount of the polyalkylene glycol is from 1 mg/L to 6 g/L, preferably from 20 to 3,000 mg/L, particularly preferably from 100 to 1,000 mg/L. On the other hand, the blending amount of the amphoteric surfactant is generally from 0.1 mg/L to 1 g/L, preferably from 5 to 500 mg/L, particularly preferably from 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 the heat treatment is less than 50 Hv, and further, the surface of the bump cannot be made flat. When it exceeds the above range, the hardness of the film of the bump after heat treatment becomes 90 Hv or more, and the hardness suitable for joining cannot be obtained.

The polyalkylene glycol and the amphoteric surfactant may be used alone or in combination. When both are used together, the blending amount of the two is suitably adjusted within the above respective ranges for the purpose of blending.

When the polyalkylene glycol is used, the film hardness of the gold bump after the heat treatment is suitable for 50 to 90 Hv of the bonding of the adhesive film for the anisotropic conductive, and the molecular weight is 200 to 6000, preferably 400 to 2000, more preferably 400 to 1000. When the molecular weight exceeds 6,000, in order to make the film hardness after heat treatment 50 to 90 Hv, it is necessary to make the blending amount to an extremely low concentration of less than 1 mg/L. It is difficult and practical to manage the concentration of the plating solution at such a low concentration.

The hardness of the film formed by electroplating can be adjusted to a desired value in the range of 50 to 90 Hv by adjusting the blending amount of the polyalkylene glycol having a molecular weight of 6,000 or less. In the case of a low molecular weight polyalkylene glycol, the amount of blending is increased, and in the case of a high molecular weight, by reducing the blending amount, a film hardness of 50 to 90 Hv can be obtained. In any of the molecular weights, the hardness of the film is increased by increasing the blending amount, and a relatively high hardness of approximately 90 Hv can be obtained.

For example, when the film hardness after heat treatment is 70 Hv, the blending amount of the polyalkylene glycol having a molecular weight of 6,000 or less is 1 mg/L to 6 g/L, preferably 20 to 3000 mg/L. Further, the blending amount of the amphoteric surfactant is preferably from 10 to 300 mg/L.

Generally, by increasing the blending amount of the polyalkylene glycol or the amphoteric surfactant, the decrease in the hardness of the film due to the heat treatment is reduced. Further, in the case where potassium sulfite is blended without polyalkylene glycol or an amphoteric surfactant, the height difference of the bump surface cannot be sufficiently reduced. When only potassium sulfite, polyalkylene glycol or an amphoteric surfactant is added, both the height difference of the surface of the bump and the hardness of the film may be desired.

In the non-cyanide electrolytic gold plating bath of the present invention, other components such as a pH adjuster may be suitably used insofar as the object of the present invention is not impaired.

Examples of the pH adjuster include sulfuric acid, sulfurous acid water, phosphoric acid, and the like; alkali potassium hydroxide, ammonia water, and the like.

When the bump is formed on the semiconductor wafer by electroplating using the non-cyanide electrolytic gold plating bath of the present invention, the plating operation is preferably carried out in accordance with a usual method. For example, a Ti-W sputter film is used as the UBM layer, and a wafer on which an Au sputter film or the like is formed is masked using a photomask. Thereafter, electrolytic plating of gold is performed using the wafer as a material to be plated. Next, there is a method of dissolving the photomask in a solvent to remove it. After the photomask is removed, the portion not covered by the gold bumps of the UBM layer is removed by etching and heat treatment of the wafer is performed.

In the case of the photomask, a novolak-based positive photoresist can be used. Examples of the commercially available product include LA-900 and HA-900 (above, manufactured by Tokyo Ohka Kogyo Co., Ltd.).

The plating temperature is usually 40 to 70 ° C, preferably 50 to 65 ° C. When the temperature of the plating bath is out of the range of 40 to 70 ° C, there is a case where the plating film is hard to be precipitated, or the plating bath is unstable, and decomposition of the plating bath component occurs.

The set current density used in the plating is different depending on the composition of the plating solution, the temperature, and the like, and is therefore difficult to determine by one meaning. Gold concentration at 8 ~ 15g / L, the plating bath under the conditions of a temperature of 60 deg.] C, typically based 2.0A / dm ² or less, preferably 0.2 ~ 1.2A / dm ^2. When the current density is set to be out of the above range, the workability may be poor, or the appearance of the plating film or the plating film characteristics may be abnormal, or the plating bath may become unstable and the plating bath component may be decomposed.

The pH of the non-cyanide electrolytic gold plating bath of the present invention is generally 7.0 or more, preferably 7.2 to 10.0. When the pH of the non-cyanide electrolytic gold plating bath is less than 7.0, there is a case where the plating bath becomes unstable and decomposes. On the other hand, when the pH exceeds 10.0, the photomask is dissolved and a desired gold bump or the like cannot be formed.

The heat treatment temperature of the gold bumps 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 carried out using a precision thermostat (Fine Oven) or the like which can hold the inside of the chamber for a certain period of time at a set temperature.

The non-cyanide electrolytic gold plating bath of the present invention can achieve the use of 2 turns (consumption of the amount of gold in all plating baths as 1 turn in plating) by supplementing and managing other components constituting the gold source and the plating bath.

In the non-cyanide electrolytic gold plating bath of the present invention, if the material is metallized to be conductive, the object to be plated is not selected. The photomask is made of a novolak-based positive photoresist, which is particularly suitable for forming bumps on patterned wafers such as patterned wafers or Ga/As wafers.

Fig. 1 is a cross-sectional view showing an example of forming a gold bump on a semiconductor wafer using the gold plating bath of the present invention. In the first drawing, 1 is a semiconductor wafer, 1' is a circuit layer including an integrated circuit formed on a semiconductor wafer, 2 is an Al electrode, 3 is a passivation film, 3a is an opening of a passivation film, and 4 is TiW. The sputter film, 5 is a gold sputter film, 6 is a UBM layer formed of the TiW sputter film 4 and the gold sputter film 5, 7 is a gold bump, 7' is a gold bump surface, and 8 is an opening of the photoresist film. 8a is an opening of the photoresist film. The surface 7' of the gold bump is formed flat, and the height difference (distance difference from the wafer 1) of the contact center portion 7'a and the peripheral end portion 7'b of the photoresist film is within 1.8 μm, and is within 1.7 μm. Preferably, it is preferably within 1.6 μm and preferably within 1.5 μm.

Fig. 2 is a cross-sectional view showing a state in which a semiconductor wafer in which the gold bumps shown in Fig. 1 are formed is mounted on a printed wiring board. The same portions as those in Fig. 1 are denoted by the same reference numerals, and their description will be omitted.

A substrate wiring pattern 12 formed of a conductive material such as copper is formed on the rigid substrate 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, in the semiconductor wafer 16 mounted on the substrate 10 in parallel with the printed wiring board 10, gold bumps 7 opposed to the substrate electrodes 14 are formed. The substrate electrode 14 and the gold bump 7 are joined by the anisotropic conductive adhesive 20. The hard substrate 11 and the semiconductor wafer 1 are sealed by a sealing material 18.

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

The method of mounting the semiconductor wafer 16 on the printed wiring board 10 is performed as follows. First, the position of the gold bump 7 is placed above the substrate electrode 14, and the position of the semiconductor wafer 16 is determined, and the semiconductor wafer 16 is placed on the printed wiring board 10 via the film-shaped anisotropic conductive adhesive 20. Next, the gold bump 7 and the substrate electrode 14 are thermally pressed by the anisotropic conductive adhesive 20. The gold bumps 7 formed on the electrodes of the integrated circuits in the circuit layer 1' are attached to the substrate electrodes 14 formed on the substrate wiring pattern 12 by mounting toward the semiconductor wafer 16 of the printed wiring substrate 10. The directional conductive adhesive 20 is connected.

Example

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

As the object to be plated, a ruthenium wafer having a bump opening portion (a texture cross-section composition of a gold sputter film/TiW/SiO ₂ ) patterned with a novolac-based positive resist was used. The plated material was immersed in 1 L of the prepared non-cyanide electrolytic gold plating bath, and a gold plating film having a film thickness of 15 μm was formed by applying electricity. Further, the current efficiency of the non-cyanide electrolytic gold plating bath is generally 100% under normal plating operation conditions.

After forming a film having a predetermined film thickness, the mask material is removed, the shape of the bump formed, the bath stability, the appearance of the plating film, the film hardness (after heat treatment and heat treatment at 300 ° C for 30 minutes), and the iodine of the Au sputtering film. The etchability of the etchant was evaluated by the following method and standard. The combined results are shown in Tables 1-4.

[High and low difference (μm) of the surface of the bump]

As shown in Fig. 1, a phenol varnish-based positive resist 8 is used on the ruthenium wafer 1, and a rectangular opening having a long side of 80 to 20 μm and a short side of 80 to 20 μm is patterned. After electroplating was carried out using an electrolytic gold plating bath, a novolac-based positive photoresist was dissolved in methyl ethyl ketone as a solvent. Using the laser microscope VK-9710 manufactured by KEYENCE, the difference between the highest point on the bump and the lowest point on the upper side of the bump was measured as a height difference and an index of smoothness was obtained. Further, generally, the height difference obtained in the bump plating application is 3 μm or less, preferably 2 μm or less, and more preferably 1.5 μm or less.

[Bath stability]

The appearance of the plating bath after the plating was applied to the object to be plated was observed and evaluated on the basis of the following criteria.

Decomposition: decomposition of components in the electroplating bath.

×: The precipitation of gold in the plating bath was observed to the extent that it was judged by the naked eye.

△: A small amount of gold precipitated in the plating bath was confirmed. The degree of observation can be filtered by a 0.2 μm membrane filter.

○: No precipitation of gold in the plating bath was observed.

[Electroplating film appearance]

The appearance of the surface film of the bump formed on the object to be plated was observed and evaluated on the basis of the following criteria.

×: The color tone was observed to be red and dendritic, and unevenness was confirmed, and scorching occurred.

△: There was no abnormal precipitation, and it was a glossy appearance.

○: The hue is lemon yellow and has a uniform appearance of no-half gloss.

[Film hardness (Vickers hardness; Hv)]

The film hardness (after heat treatment and heat treatment at 300 ° C for 30 minutes) was measured using a Vickers hardness test using a specific bump portion formed on the object to be plated. The characteristics obtained by the bumps for medium hardness use are about 70 Hv after annealing. Further, the measurement conditions were such that the indenter was held under a load of 25 gf for 10 seconds.

[Etching property of iodine-based etchant by Au plating film]

The object to be plated was immersed in an iodine-based etchant which was sufficiently stirred at normal temperature for 90 seconds, washed in an alcohol-based rinsing liquid, and then sprayed with ethanol to dry with a hair dryer. Thereafter, the surface state of the entire bump formed on the object to be plated was observed with a metal microscope at a magnification of 50 to 200 times, and evaluated based on the following criteria.

×: It was observed that the surface of the bumps of 50% or more was uneven.

△: It was observed that the surface of the bump of only a part of the area was uneven.

○: No unevenness in the surface of the entire bump on the object to be plated was observed.

[Total assessment]

From the above evaluation results, the evaluation is performed on the basis of the following evaluation criteria.

X: The above evaluation results of the formed gold plating film (gold bump) and the non-cyanide electrolytic gold plating bath after the plating treatment contained poor results.

△: Among the above evaluation results of the formed gold plating film (gold bump) and the non-cyanide electrolytic gold plating bath after the plating treatment, the results were partially satisfactory.

○: Good results were obtained in the above evaluation results of the formed gold plating film (gold bump) and the non-cyanide electrolytic gold plating bath after the plating treatment.

By comparing the examples and the comparative examples, it is clearly as follows.

(1) The potassium sulfite system is based on the effect of reducing the height difference of the surface of the bump. The height difference of Examples 1 to 20 containing potassium sulfite was 1.01 to 1.56, and the height difference of the surface of the bump was significantly higher than the height difference of 1.85 to 3.11 of Comparative Examples 2 to 12 containing sodium sulfite. small.

(2) The polyalkylene glycol and the amphoteric surfactant are based on the effect of reducing the hardness of the film after heat treatment at 300 °C. Examples 1 to 20 containing a polyalkylene glycol or an amphoteric surfactant were suitable for film hardness after heat treatment at 300 ° C (50 to 90 Hv). On the other hand, the hardness of Comparative Examples 1 and 2 which did not contain a polyalkylene glycol and an amphoteric surfactant was the low of 45 Hv and 43 Hv.

(3) However, it is not sufficient to add only potassium sulfite to reduce the height difference of the surface of the bump. Although Comparative Example 1 was added with the same amount of potassium sulfite as in Examples 1 to 20, the height difference was still large (1.83). When the polyalkylene glycol or the amphoteric surfactant was added to the potassium sulfite, the height difference was changed to 1.56 or less (Examples 1 to 20).

1. . . Semiconductor wafer

1'. . . Circuit layer

2. . . Al electrode

3. . . Passivation film

3a. . . Passivation film opening

4. . . TiW sputtering film

5. . . Gold splash coating

6. . . UBM layer

7. . . Gold bump

7’. . . Gold bump surface

8. . . Photoresist film

8a. . . Opening of the photoresist film

10. . . Printed wiring substrate

11. . . Hard substrate

12. . . Substrate wiring pattern

14. . . Substrate electrode

16. . . Semiconductor wafer

18. . . Sealing material

20. . . Anisotropic conductive adhesive

Fig. 1 is a cross-sectional view showing an example of a gold bump formed using the gold plating bath of the present invention.

Fig. 2 is a cross-sectional view showing an example of a state in which a semiconductor wafer having gold bumps shown in Fig. 1 is mounted on a printed wiring board.

Figure 3 shows a cross-sectional view of a gold bump formed using a conventional gold plating bath.

1. . . Semiconductor wafer

1'. . . Circuit layer

2. . . Al electrode

3. . . Passivation film

3a. . . Passivation film opening

4. . . TiW sputtering film

5. . . Gold splash coating

6. . . UBM layer

7. . . Gold bump

7’. . . Gold bump surface

7’a. . . Central department

7’b. . . Week end

8. . . Photoresist film

8a. . . Opening of the photoresist film

Claims (5)

The invention relates to a non-cyanide electrolytic gold plating bath for forming a bump, which is characterized in that it contains gold alkali sulfite or gold ammonium sulfite, a crystal modifier, a conductive salt formed only by potassium sulfite, 5 to 150 g/L, and a molecular weight of 200. ~6000 polyalkylene glycol 1mg / L ~ 6g / L and / or amphoteric surfactant 0.1mg ~ 1g / L and water-soluble amine and / or buffer, and does not contain the aforementioned gold sulfite salt Sodium sulfite other than sodium sulfite. A non-cyanide electrolytic gold plating bath for forming a bump according to claim 1, wherein the amphoteric surfactant is selected from the group consisting of 2-alkyl-N-carboxymethyl-N-hydroxyethylimidazolium betaine, bismuth laurate One or two or more kinds of the amine propyl hydroxy sultaine, the fatty acid guanamine propyl betaine, and the fatty acid sulfhydryl-N-carboxyethyl-N-hydroxyethyl ethylenediamine base salt. A non-cyanide electrolytic gold plating bath for forming a bump according to the first aspect of the invention, wherein the crystal modifier is a T1 compound, a Pb compound, or an As compound, and a crystal modifier is blended at a metal concentration of 0.1 to 100 mg/L. A bump forming method for performing electrolytic gold plating on a patterned wafer using a non-cyanide electrolytic gold plating bath for bump forming according to item 1 of the patent application, and then passing it at 200 to 400 ° C for 5 minutes or more After heat treatment, a bump having a film hardness of 50 to 90 Hv and a surface height difference of 1.8 μm or less is formed. A connection structure for a substrate electrode having a substrate wiring pattern formed on a printed wiring substrate, and a patent application scope number 1 a gold bump in which an integrated circuit formed on a semiconductor wafer is formed by a non-cyanide electrolytic gold plating bath for bump formation, and a connection structure in which an anisotropic conductive adhesive is used is connected, and the gold bump is coated. The hardness is 50~90Hv.