KR20070037312A - Non-cyanogen type electrolytic gold plating bath for bump forming - Google Patents

Abstract

assignment

Provided is a non-cyanide electrolytic plating bath capable of suppressing enlargement during plating of the mask material opening and forming bumps and wirings having dimensions that are not significantly different from the design dimensions.

Resolution

Gold sulfite alkali salts or gold ammonium sulfite as a gold source, water-soluble amines as stabilizers, crystal regulators, sulfite and sulfate salts as conducting salts, buffers, polyalkylene glycols and / or amphoteric surfactants A non-cyanide electrolytic gold plating bath for forming bumps. As for the compounding quantity of polyalkylene glycol, 0.1 mg-10 g / L is preferable, and it is preferable that the compounding quantity of an amphoteric surfactant shall be 0.1 mg-1 g / L. As an amphoteric surfactant, a carboxybetaine type can be used preferably.

Description

Non-cyanide electrolytic gold plating bath for bump formation {NON-CYANOGEN TYPE ELECTROLYTIC GOLD PLATING BATH FOR BUMP FORMING}

BRIEF DESCRIPTION OF THE DRAWINGS It is explanatory drawing which shows the opening length (a) and bump dimension (b) of the bump pattern measured in the Example.

* Description of the sign *

1: silicon wafer

3: photoresist

5: opening

7: bump

[Patent Document 1] Japanese Unexamined Patent Publication No. 2004-176171

[Patent Document 2] Japanese Unexamined Patent Publication No. 2003-7762

The present invention provides a bumpless non-cyanide electrolysis suitable for forming gold bumps or gold wirings on a silicon wafer or a Ga / As compound wafer having a bump pattern or a wiring pattern patterned by a novolac positive type photoresist. It relates to a gold plating bath and a bump forming method using the bath.

For non-cyanide electrolytic gold plating baths, for example, a plating bath using a chlorate or gold sulfite salt as a gold source and a compound such as thiouracil as a complex compound (stabilizer) is disclosed (Patent Document 1). Known. Moreover, the plating bath etc. which use gold sulfite alkali salt or gold ammonium sulfite as a gold source, and a water-soluble amine as a stabilizer are known for a non-cyanide type electrolytic gold plating bath.

As the latter electrolytic gold plating bath, a basic composition includes a gold sulfite alkali salt or a gold ammonium sulfite, a water-soluble amine, a trace amount of a Tl compound, a Pb compound or an As compound as a crystal regulator, sulfite and sulfate as a conducting salt, and a buffer It is conventionally used to make.

The plated film formed by this non-cyanide electrolytic gold plating bath is excellent in physical properties such as electrical conductivity and thermocompression resistance, and also excellent in chemical properties such as oxidation resistance and chemical resistance. For this reason, this plating bath is used for formation of bumps and wiring on compound wafers, such as a silicon wafer and a Ga / As wafer, for example. The method itself for forming gold bumps by electrolytic gold plating is well known, and for example, Patent Document 2 describes a method for forming gold bumps using gold cyanide.

By the way, the non-cyanide electrolytic gold plating bath which has the above-mentioned basic composition is used at the plating bath temperature of 50-65 degreeC normally, in order to acquire the required film | membrane characteristic. When forming a wiring pattern etc. by gold plating, the novolak-type positive photoresist general-purpose as a mask material receives a heat history in a plating bath when a bath temperature becomes 55 degreeC or more. For this reason, the mask opening part is enlarged and bumps or wiring of a size larger than a design dimension are formed. As a result, in this case, bump intervals and wiring intervals become narrow, and a short circuit occurs at the time of joining by thermocompression bonding performed when mounting an IC chip or the like.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and it is possible to suppress the enlargement of the opening of a mask pattern formed of a mask material and to form bumps or wirings having a size that does not have a large difference from the design dimensions. It is an object to provide a gold plating bath.

MEANS TO SOLVE THE PROBLEM As a result of repeating | researching in order to achieve the said objective, as a result of mix | blending a polyalkylene glycol and / or an amphoteric surfactant with the basic composition of the above-mentioned general non-cyanide type electrolytic gold plating bath, It turned out that the enlargement of an opening part is suppressed.

In the gold film formed by the non-cyanide electrolytic gold plating bath of the present invention, due to the effect of the addition of polyalkylene glycol or an amphoteric surfactant, agglomerates of metal particles having a prominent and elongated needle-like crystal tendency in the vertical direction with respect to the plating surface. (Iii) is formed. Therefore, at the time of plating, crystal growth is promoted in the direction perpendicular to the plating surface, and growth in the horizontal direction is suppressed. As a result, the inventors believe that the stress of expanding the mask material generated in the horizontal direction as the gold film grows is alleviated, and the enlargement of the opening of the mask pattern is suppressed.

That is, this invention which solves the said subject is described below.

[1] Bump containing gold sulfite alkali salt or gold ammonium sulfite as gold source, water-soluble amine as stabilizer, crystal regulator, sulfite and sulfate salt as conducting salt, buffer, polyalkylene glycol and / or amphoteric surfactant Non-cyanide electrolytic gold plating bath for forming.

[2] The non-cyanide electrolytic gold plating bath for bump formation according to [1], which contains 0.1 mg to 10 g / L of polyalkylene glycol.

[3] The non-cyanide electrolytic gold plating bath for bump formation according to [1], which contains 0.1 to 50 mg / L of polyalkylene glycol having a molecular weight of less than 1000.

[4] The non-cyanide electrolytic gold plating bath for bump formation according to any one of [1] to [3], wherein the amount of the amphoteric surfactant is 0.1 mg to 1 g / L.

[5] The amphoteric surfactant is 2-alkyl-N-carboxymethyl-N-hydroxyethylimidazoliniumbetaine, lauric acid amidepropylhydroxysulfobetaine, fatty acid amidepropylbetaine, and fatty acid acyl-N The non-cyanide type electrolytic gold plating bath for bump formation in any one of [1]-[4] which is 1 type, or 2 or more types chosen from -carboxyethyl-N-hydroxyethylethylenediamine alkali salt.

[6] The non-cyanide electrolytic gold plating bath for bump formation according to any one of [1] to [5], wherein the crystal regulator is a Tl compound, a Pb compound, or an As compound.

[7] A method for forming a bump, wherein the bump is subjected to electrolytic gold plating on a patterned wafer using the non-cyanide electrolytic gold plating bath for bump formation described in [1].

Best Mode for Carrying Out the Invention

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 stabilizer, a trace crystallization agent, sulfite and sulfate as a conductive salt, and a buffer. It is an electrolytic gold plating bath characterized by containing a polyalkylene glycol and / or an amphoteric surfactant in a well-known basic bath. Hereinafter, essential components of the electrolytic gold plating bath of the present invention will be described for each component.

(1) Gold sulfite alkali salts, gold ammonium sulfite (Golden source)

As a gold sulfite alkali salt used for this invention, it can use without restricting a well-known gold sulfite alkali salt. Examples of the gold sulfite alkali salts include gold (I) sodium sulfite, gold (I) potassium sulfite and the like. These may be used individually by 1 type, or may use 2 or more types together.

In the electrolytic gold plating bath of the present invention, the above-described gold sulfite alkali salt or gold ammonium sulfite is used as a gold source, and the compounding amount is usually 1 to 20 g / L, preferably 8 to 15 g / L as the amount of gold. to be. When the compounding quantity of gold sulfite alkali salt or gold ammonium sulfite is less than 1 g / L, the film thickness of plating may become nonuniform. If it exceeds 20 g / L, there will be no problem in appearance, property, etc. of the plated film formed, but it will be economically burdensome.

(2) water-soluble amines (stabilizers)

As the water-soluble amine, for example, 1,2-diaminoethane, 1,2-diaminopropane, 1,6-diaminohexane and the like can be used. These may be used individually by 1 type and may use 2 or more types together.

The compounding quantity of water-soluble amine is 1-30 g / L normally, Preferably it is 4-20 g / L. When the compounding quantity of a water-soluble amine exceeds 30 g / L, the stability of a gold salt will increase, but on the other hand, a plating film may become too dense and a problem may arise in joinability. If it is less than 1 g / L, the limit current density may decrease, resulting in burnt deposits.

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

As a crystal | crystallization regulator used for the electrolytic gold plating bath of this invention, For example, Tl compounds, such as thallium formate, thallium malonate, thallium sulfate, and thallium nitrate; Pb compounds, such as lead citrate, lead nitrate, and alkane sulfonate; As compounds, such as a arsenic trioxide, are mentioned. These Tl compound, Pb compound, and As compound may be used individually by 1 type, and may be used in combination of 2 or more type.

The compounding quantity of a crystal regulator can be suitably set in the range which does not impair the objective of this invention. The compounding quantity of a crystal regulator is 0.1-100 mg / L normally, Preferably it is 0.5-50 mg / L, Especially preferably, it is 3-25 mg / L as a metal concentration. When the compounding quantity of a crystal regulator is less than 0.1 mg / L, plating adhesion, plating bath stability, and durability may worsen, and the component of a plating bath may decompose. When it exceeds 100 mg / L, deterioration of plating adhesion and appearance irregularity of the plating film may occur.

(4) sulfite, sulfate (conductive salt)

Examples of the sulfite and sulfate used as the conductive salt in the present invention include sulfites such as sodium sulfite, potassium sulfite, sodium pyrosulfite and sodium hydrogen sulfite; Sulfates, such as sodium sulfate, are mentioned. Especially, the combination of sodium sulfite and sodium sulfate is suitable.

Although it can set suitably in the range which does not impair the objective of this invention as a compounding quantity of the said sulfite and sulfate in the electrolytic gold plating bath of this invention, it is preferable to set it as the following compounding quantities.

The amount of sulfite is in a normally 5~100g / L as the amount of SO ₃ ^2-, preferably 10~80g / L, and particularly preferably 20~60g / L. If the compounding quantity of sulfite is less than 5 g / L, adhesiveness and liquid stability may worsen and decomposition of a plating bath may occur. When it exceeds 100 g / L, a limit current density may fall and it may become a carbon plating layer.

The amount of the sulfate salt is usually 1 to 120 g / L as the amount of SO ₄ ^2- , preferably 1 to 60 g / L, and particularly preferably 1 to 40 g / L. If it is less than 1 g / L, liquid stability may deteriorate, and plating bath may decompose, and if it exceeds 120 g / L, a limit current density may fall and it may become a carbon plating layer.

(5) buffer

The buffer 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 borate salts, organic acids such as citrate, phthalate, and ethylenediamine tetraacetate. (Carboxylic acid, hydroxycarboxylic acid) salts and the like can be used.

The compounding amount of the buffer in the non-cyanide 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. If the amount of the buffer is less than 1 g / L, the pH decreases, so that the liquid stability may deteriorate, and if the content of the buffer agent exceeds 30 g / L, the limiting current density may decrease, resulting in a carbon plating layer.

(6) polyalkylene glycols, amphoteric surfactants

Polyethylene glycol, polypropylene glycol, etc. are mentioned as a polyalkylene glycol mix | blended with the non-cyanide type electrolytic gold plating bath of this invention.

As an amphoteric surfactant, betaine type amphoteric surfactants, such as 2-alkyl-N-carboxymethyl-N-hydroxyethyl imidazolinium betaine, laurate amide propyl hydroxy sulfobetaine, and fatty acid amide propyl betaine. ; Aminocarboxylate-based amphoteric surfactants such as fatty acid acyl-N-carboxyethyl-N-hydroxyethylethylenediamine alkali salts; And imidazoline derivative-based amphoteric surfactants.

As a compounding quantity of polyalkylene glycol, it is 0.1 mg / L-10 g / L normally, Preferably it is 0.5-100 mg / L, Especially preferably, it is 0.5-50 mg / L. On the other hand, the compounding quantity of the amphoteric surfactant is usually 0.1 mg / L to 1 g / L, preferably 1 to 100 mg / L, particularly preferably 5 to 20 mg / L.

Only one of the polyalkylene glycol and the amphoteric surfactant may be used. By using both in combination, the effect of suppressing expansion of bumps and the like can be enhanced, and a film can be formed with bumps or wiring sizes without a great difference from the design dimensions.

When a standard is formed in the film hardness after heat treatment of the gold plating bumps, the film hardness can be adjusted by blending polyalkylene glycol having a molecular weight of 1,000 or less and adjusting the compounding amount. For example, when making the film hardness after heat processing into 60 HV or less, it can achieve by making the compounding quantity of polyalkylene glycol of molecular weight 1000 or less into 0.1-50 mg / L, Preferably it is 0.1-5 mg / L. In this case, the blending amount of the amphoteric surfactant is preferably 0.1 to 20 mg / L, more preferably 1 to 10 mg / L.

When performing gold plating on bumps, wirings, etc. on a silicon wafer and a compound wafer by plating using the non-cyanide type electrolytic gold plating bath of this invention, plating operation may be performed according to a conventional method. For example, after masking using a mask material on a wafer on which Ti-W, Au sputter coating, or the like is formed thereon as UBM (under bump metal; base metal of bump), the wafer is electroplated as a plated object. Then, the method of dissolving and removing a mask material in a solvent, etc. can be used.

A novolak positive photoresist can be used for a mask material. As a commercial item, LA-900, HA-900 (above, Tokyo-Oukawa Co., Ltd. product) etc. are mentioned, for example.

Plating temperature is 40-70 degreeC normally, Preferably it is 50-65 degreeC. When the plating bath temperature is out of the range of 40 to 70 ° C, the plating film is difficult to precipitate, or the plating bath may become unstable and decomposition of the plating bath components may occur.

Moreover, as a current density which can be used, under the conditions of the plating bath temperature of gold concentration of 8-15 g / L and 60 degreeC, for example, it is usually 2.0 A / dm 2 or less, preferably 0.2 to 1.2 A / d M 2. If the current density is out of the above range, the workability may deteriorate, abnormality may occur in the appearance of the coating film and the coating film properties, or the plating bath may become unstable remarkably, resulting in decomposition of the plating bath component.

The pH of the non-cyanide electrolytic gold plating bath of the present invention is usually 7.0 or more, preferably 7.2 to 10.0. If the pH of the non-cyanide electrolytic gold plating bath is less than 7.0, the plating bath may become remarkably unstable and decomposition may occur. On the other hand, when pH is 10.0 or more, a mask material may melt | dissolve and a desired gold bump etc. may not be formed.

In the non-cyanide electrolytic gold plating bath of the present invention, other components such as a pH adjuster and a stabilizer may be suitably used within a range that does not impair the object of the present invention.

As a pH adjuster, sodium hydroxide, potassium hydroxide, aqueous ammonia, etc. are mentioned as alkali, for example as sulfuric acid, sulfurous acid water, phosphoric acid, etc. as an acid.

Heavy metal (Tl, Pb, As, etc.) ions etc. are mentioned as a stabilizer.

In the non-cyanide electrolytic gold plating bath of the present invention, by supplementing and managing gold sulfite alkali salts and other components constituting the plating bath, two turns (when all the gold amount in the plating bath is consumed for plating is turned into one turn) It can be used over.

The non-cyanide electrolytic gold plating bath of the present invention does not select a plated object if the base is metallized (conductor thin film is formed on the base) or can conduct. For example, it can apply especially suitably for formation of bump, wiring, etc. on compound wafers, such as a silicon wafer and Ga / As wafer patterned using the novolak-type positive photoresist for a mask material.

Example

Examples 1-17, Comparative Examples 1-11

The non-cyanide electrolytic gold plating bath was adjusted by the formulation shown in Tables 1-4. The unit of the compounding density | concentration of each raw material is g / L unless there is particular notice. Na ₃ Au (SO ₃ ) ₂ is Au, Na ₂ SO ₃ is SO ₃ Volume, Na ₂ SO ₄ SO ₄ The concentration with respect to quantity is shown.

As the plated material, a silicon wafer having bump openings patterned with a novolak-based positive photoresist was used. The cross-sectional composition of the silicon wafer is a gold sputtered film / TiW / SiO ₂ . The plated film having a film thickness of 15 µm was formed by immersing the plated object in 1 L of the adjusted non-cyanide electrolytic gold plating bath and conducting electricity. In addition, the current efficiency of the non-cyanide electrolytic gold plating bath is usually 100% under normal plating operation conditions.

After forming the film having a predetermined film thickness, the mask material was removed, and the extent of expansion of the formed bumps, bath stability, plating film appearance, film hardness, and etching property of the iodine-based etchant of the Au sputtered film were as follows. Evaluation was performed. The results are shown in Tables 1 to 4 together.

[Bump Expansion Degree (μm)]

As shown in Fig. 1 (a), patterning having rectangular openings of 80 to 20 µm long sides and 80 to 20 µm short sides using the novolac positive photoresist 3 on the silicon wafer 1 Was carried out. Next, the dimension (design dimension) of the opening part of the corner bump of the bump pattern formed on the silicon wafer which is to-be-plated was measured. The measurement of the opening part was performed about the length of the long side (arrow X direction) and the short side (arrow Y direction) of the opening part using the scale attached to a metal microscope. After plating to a to-be-plated object using the electrolytic gold plating bath, the novolak-type positive photoresist was dissolved in methyl ethyl ketone which is a exclusive solvent. The dimension of the finishing bump of the corner bump of the same position obtained above was measured using the scale with a metal microscope. The dimension of the completed bump was made into the maximum length of the long side direction (arrow X direction) and the short side direction (arrow Y direction) of bump 7 as shown to FIG.

For each of the X direction and the Y direction, the value obtained by subtracting the design dimension before plating was calculated from the dimensions of the completed bumps, and was defined as the bump expansion degree (µm). In addition, the specification of bump expansion degree required for bump plating applications is 3 micrometers or less normally.

[Bath stability]

The state of the plating bath after plating to-be-plated was observed, and the following references | standards evaluated.

Decomposition: The components in the plating bath decomposed.

X: The precipitation of gold in the plating bath was observed by the visually understandable level.

(Triangle | delta): The precipitation of gold was observed slightly in a plating bath. A level that can be observed by filtration with a 0.2 μm membrane filter.

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

[Plating film appearance]

The surface coating appearance of the gold bump formed on the to-be-plated object was observed, and the following reference | standard evaluated.

X: Hue is red, dendrite precipitation is seen, and a stain is observed or burnt.

(Triangle | delta): Although there is no abnormal precipitation, it is a glossy appearance.

(Circle): A hue is lemon yellow and it is a uniform appearance with no gloss.

[Film Hardness (Vickers Hardness; Hv)]

Using the specific corner bump area formed on the to-be-plated object, the film hardness was measured with the Vickers hardness tester. The measurement of the film hardness was performed about the thing which was not heat-treated and heat-processed at 300 degreeC for 30 minutes.

Usually, as a characteristic calculated | required by bump plating use, the film hardness after annealing is 60 Hv or less. In addition, the measurement conditions were based on the conditions which hold the measurement indenter at 25 gf load for 10 second.

[Etchability by Iodine Etchant of Au Sputter Film]

The plated object was immersed in a sufficiently stirred iodine etchant at room temperature for 90 seconds, washed with an alcohol-based rinse solution, sprayed with ethanol and dried with a dryer. Then, the surface state of the whole bump formed on the to-be-plated object was observed by the metal microscope using 50-150 times magnification, and the following reference | standard evaluated.

X: Smudge is observed on 50% or more of bump surface.

(Triangle | delta): An unevenness is observed in the bump surface of some defined area.

○: No stain is observed on the entire bump surface on the plated object.

[General evaluation]

From each said evaluation result, it evaluated by the following evaluation criteria.

X: Unfavorable result was contained in the said evaluation result about the formed gold plating film (gold pump) and the non-cyanide type electrolytic gold plating bath after plating process.

(Circle): The said evaluation result about the formed gold plating film (gold pump) and the non-cyanide type electrolytic gold plating bath after plating process was all a favorable result.

Buffer A: Sodium Ethylenediaminetetraacetic acid

Buffer B: Sodium Phosphate

Polyethylene Glycol A: Average Molecular Weight 400

Polyethylene glycol B: average molecular weight 1000

Polyethylene glycol C: average molecular weight 6000

Amphoteric Surfactant A: Nippon Oil Oil Co., Ltd. make, Nissan Anon BDL (carboxybetaine type)

Amphoteric Surfactant B: manufactured by Cao Corporation, Anhitol 20YB (carboxybetaine)

The non-cyanide electrolytic gold plating bath of this invention has the outstanding liquid stability and liquid life, and it is possible to form the film of a uniform, dense, and favorable appearance to a to-be-plated object. According to the electrolytic gold plating bath of the present invention, gold bumps and gold wirings having a flat surface can be formed in a design size while maintaining good film hardness and share strength characteristics.

Claims (7)

Bich for forming bumps containing gold sulfite alkali salts or gold ammonium sulfite as a gold source, water-soluble amines as stabilizers, crystal regulators, sulfites and sulfates as conducting salts, buffers, polyalkylene glycols and / or amphoteric surfactants An-based electrolytic gold plating bath. The method of claim 1, A non-cyanide electrolytic gold plating bath for bump formation containing 0.1 mg / L to 10 g / L of the polyalkylene glycol. The method of claim 1, A non-cyanide electrolytic gold plating bath for bump formation containing 0.1 to 50 mg / L of said polyalkylene glycol having a molecular weight of less than 1000. The method according to any one of claims 1 to 3, The non-cyanide type electrolytic gold plating bath for bump formation whose compounding quantity of the said amphoteric surfactant is 0.1 mg / L-1 g / L. The method according to any one of claims 1 to 4, The amphoteric surfactant is 2-alkyl-N-carboxymethyl-N-hydroxyethylimidazolinium betaine, lauric acid amide propyl hydroxy sulfobetaine, fatty acid amide propyl betaine, and fatty acid acyl-N-carboxy A non-cyanide electrolytic gold plating bath for bump formation, which is one or two or more selected from ethyl-N-hydroxyethylethylenediamine alkali salts. The method according to any one of claims 1 to 5, The crystal regulator is a non-cyanide electrolytic gold plating bath for bump formation is a Tl compound, Pb compound or As compound. A bump formation method for electrolytic gold plating on a patterned wafer using the non-cyanide electrolytic gold plating bath for bump formation according to claim 1.

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