JP2000100850A - Formation of low-melting point metal bump - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide electroplating method for forming a practical bump, which can replace solder plating. SOLUTION: In this method for forming a low-temperature fusing metal bumps in a semiconductor chip or package through electroplating, silver-based alloy plating bath includes the following components of (a) 5-300 g/l of at least one kind of alkanesulfonic acid ions or alslkanole sulfonate ions, (b) 0.01-10 g/l of Ag ions, (c) 0.1-40 g/l of one kind of metallic ions selected from between Sn2+ and Bi3+, (d) 0.01-40 g/l of one kind of phosphor compound and 0.5-30 g/l of one kind of phosphor containing compound and (e) 0.5-30 g/l of non-ionic surface-active agent. The current is imparted by the repetition of rectangular pulse waves or the multistage rectangular waves.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a low melting point metal bump on a semiconductor chip, a wiring lead or a package by electroplating.
The present invention relates to a method for forming a low-melting metal bump containing no lead by electroplating.

[0002]

2. Description of the Related Art Conventionally, bumps are formed as connection electrodes on semiconductor chips, wiring leads or packages. For example, a semiconductor chip is formed on a silicon wafer by a fine processing technique, and each of them is provided with a bonding pad, on which a bump is formed via a barrier metal. The chip with bumps formed in this way is called a flip chip (FP).

At present, there are known methods for forming bumps by an electroplating method and an electroless plating method. Among these methods, the electroplating method forms a barrier metal on a bonding pad of aluminum by a method such as sputtering. And a metal layer such as solder is provided thereon by electroplating.

In forming a bump by electroplating, a thin photoresist layer of about 7 μm is provided on a base material having a conductive layer, and a metal deposit (mushroom bump) which bulges in a semicircular shape on a portion where there is no resist is formed. In some cases, a thick resist layer of about 50 μm is provided on the same base material, and metal deposition (straight wall bumps) in the form of a column or a square column is formed in a portion where there is no resist. In any case, from the next step,
It is required that the outside of the bump (the direction of metal deposition) be as flat as possible and free from abnormal deposition.

At present, bump formation by electroplating is performed by a solder plating bath because of its low melting point and low cost. However, this method has problems due to the presence of radioisotopes and environmental problems. was there. That is, the lead forming the solder contains a radioisotope at a certain ratio, and when this emits radiation, it may cause malfunction of the electronic device. In addition, since lead has toxicity, it is necessary to consider the effect on the human body and the environment, and it is necessary to carefully treat wastewater after plating.
For this reason, there has been a demand for the development of a technique of using a low-melting metal instead of solder as a bump by electroplating.

Since many electroplating methods for obtaining a low melting point metal are already known, it is easy to think of using them for forming bumps, but it is extremely difficult to put them to practical use, and it is very difficult to use solder plating. No alternative electroplating method for bump formation has been known to date. The reason for this is that other electroplating methods cannot cope with high-pin-count, miniaturized packaging, that is, high integration of semiconductors (fine pitch), which is required as electronic devices become smaller and lighter. . In other words, in order to cope with high integration of semiconductors, a uniform and smooth electroplating film at a microscopic level is required, but abnormal precipitation or granular precipitation occurs in any plating bath, The request could not be met.

[0007]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a practical electroplating method for forming bumps which can be substituted for solder plating.

[0008]

Means for Solving the Problems The inventor of the present invention has been diligently studying to solve the above-mentioned problems, and has selected silver alloy plating using a sulfonic acid bath as low-temperature melting metal deposition electroplating, and By adjusting the deposition current waveform, it has been found that abnormal deposition and granular deposition are suppressed, and a uniform and smooth electroplating film at a microscopic level can be obtained, and the present invention has been completed.

That is, the present invention provides a method for forming a low-melting metal bump on a semiconductor chip or package by electroplating, wherein the electroplating bath comprises the following components:
(A) 5 to 300 g / l of at least one alkanesulfonic acid ion or alkanolsulfonic acid ion,
(B) 0.01 to 10 g / l of Ag ion, (c) Sn
One of the metal ions selected from ²⁺ and Bi ³⁺ is 0.1 to 40 g / L, and one of the sulfur-containing compounds (d) is 0.1.
0.01 to 40 g / l, and (e) 0.5 g of the nonionic surfactant.
A method for forming a low melting point metal bump, characterized in that a current is applied by repetition of a rectangular pulse wave or a multistage rectangular wave using a silver-based alloy plating bath containing up to 30 g / l.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The silver-based alloy plating bath used in the method for forming a low melting point metal bump of the present invention (hereinafter referred to as “bump forming method”) has been previously developed by the present inventors. The details are described in JP-A-9-143786.

The plating bath itself is made up of the following four components, (b) Ag ion, (c) Sn ²⁺ , in an aqueous solution acidified with sulfuric acid, alkanesulfonic acid, alkanolsulfonic acid or the like (component (a)). Cu ²⁺ , In ³⁺ , Tl ⁺ , Z
It is prepared by adding one or more metal ions selected from the group consisting of n ²⁺ and Bi ^3+, (d) one or more sulfur-containing compounds, (e) a nonionic surfactant and Which do not contain a cyanide compound.

However, for the purposes of the present invention, alkanesulfonic acid or alkanolsulfonic acid is used as the acidic component, and Sn ²⁺ and Bi ³⁺ are used as the component (c).
It is necessary to use, and the compounding amount of each component,
Alkanesulfonic acid ion or alkanolsulfonic acid ion in the range of 5 to 300 g / l, component (b) is 0.0
The content of component (c) is 0.1 to 40 g / l.
l, the component (d) is in the range of 0.01 to 40 g / l,
(E) is preferably in the range of 0.5 to 30 g / l.

Preferred examples of the alkanesulfonic acid or alkanolsulfonic acid as the acidic component include methanesulfonic acid and ethanesulfonic acid. The Ag + ion as the component (b) is a silver alkanesulfonic acid salt such as silver methanesulfonate or silver ethanesulfonate;
It is obtained by dissolving a water-soluble silver salt such as silver alkanolsulfonate such as silver isopropanolsulfonate or the like, silver oxide, silver chloride or silver nitrate in water. In addition, S of component (c)
n ²⁺ and Bi ³⁺ are tin methanesulfonate, tin ethanesulfonate, tin isopropanolsulfonate, stannous chloride, stannous oxide, stannic oxide, stannous sulfate, bismuth methanesulfonate, ethanesulfone It can be obtained from bismuth acid, bismuth isopropanol sulfonate, bismuth oxide, bismuth nitrate and the like.

Further, as the sulfur-containing compound and the nonionic surfactant to be added to the silver-based alloy plating bath used in the present invention, those disclosed in JP-A-9-143786 can be used. However, an example of this is as follows.

That is, the sulfur-containing compound as the component (d) is a compound containing a sulfur atom in the molecule.
g ⁺ refers to a compound that functions as a substitution inhibitor, and examples thereof include thiourea, thiourea dioxide, and 1-acetyl-2.
-Thiourea, allylthiourea, ethylenethiourea, sy
m-di-o-tolylthiourea, sym.-di-p-tolylthiourea, 1,3-bis (hydroxymethyl) thiourea, 1-phenyl-3- (2-thiazolyl) -2-thiourea, hydrochloric acid Benzylisothiourea, 2-malonylthiourea, S-methylisothiourea sulfate, N, N'-diphenylthiourea, trimethylthiourea, N, N'-diethylthiourea, 1-naphthylthiourea, 1,3-bis (dimethyl Thiourea compounds such as aminopropyl) -2-thiourea and tributylthiourea; 2-mercaptobenzothiazole, dibenzothiazole disulfide, and cyclohexylamine salt of 2-mercaptobenzothiazole;
Thiazole compounds such as (N, N-diethylthiocarbamoylthio) benzothiazole, 2- (4′-morpholinodithio) benzothiazole; N-cyclohexyl-2
-Benzothiazolylsulfenamide, N-tert-
Butyl-2-benzothiazolylsulfenamide, N-
Sulfenamide-based compounds such as oxydiethylene-2-benzothiazolylsulfenamide, N, N-dicyclohexyl-2-benzothiazolylsulfenamide; tetramethylthiuram disulfide, tetraethylthiuram disulfide, tetrabutylthiuram disulfide,
Thiuram compounds such as tetrakis (2-ethylhexyl) thiuram disulfide, tetramethylthiuram monosulfide, dipentamethylenethiuram tetrasulfide; pentamethylenedithiocarbamic acid piperidine salt;
Dithiocarbamate compounds such as pipecolyldithiocarbamic acid pipecoline salt, sodium diethyldithiocarbamate and sodium dibutyldithiocarbamate;
Bisphenol compounds such as 4,4'-thiobis (3-methyl-6-tert-butylphenol); Benzimidazole compounds such as 2-mercaptobenzimidazole and 2-mercaptomethylbenzimidazole; Organic compounds such as dilauryl thiodipropionate Thioic acid compound; N-
Anti-scorch agents such as cyclohexylthiophthalimide;
Vulcanizing agents such as 4,4'-dithiomorpholine; smelting accelerators such as o, o'-dibenzamide diphenyl disulfide; other, 2-benzoxazolethiol, 2,5-dimercapto-1,3,4- Thiadiazole, 2,5-dimercapto-1,3,4-thiadiazole dipotassium, diethylammonium diethyldithiocarbamate, sodium diethyldithiocarbamate trihydrate, thioglycol, thioglycolic acid, thiodiglycolic acid, β-thiodiglycol And other sulfur-containing compounds.

The nonionic surfactant (e) is used to obtain a dense and smooth plated surface with good adhesion, and a preferred specific example is the following general formula (1): And compounds containing a compound represented by any one of (4) to (4) as a main component.

[0017]

Embedded image

Wherein R ₁ is an aliphatic alcohol having 8 to 22 carbon atoms, a phenol substituted with an alkyl group having 1 to 25 carbon atoms, and a β substituted with an alkyl group having 1 to 25 carbon atoms.
-Naphthol, alkoxylated phosphoric acid having 1 to 25 carbon atoms, sorbitan or styrenated phenol esterified with a fatty acid having 8 to 22 carbon atoms (the hydrogen of the phenol nucleus is substituted by an alkyl group having 1 to 4 carbon atoms or a phenyl group) Or a hydrogen atom obtained by removing a hydrogen atom of those hydroxyl groups from R ₂₎ , and R ₂ has 8 carbon atoms.
And R ₃ and R _{4 each} represent a hydrogen atom or an alkyl group having 1 to 5 carbon atoms, and A represents —CH ₂ CH
₂ O—, B represents —CH ₂ CH (CH ₃ ) O—, m
₁ and n ₁ represent an integer of 0 to 30, m ₂ , n ₂ , m ₃ and n ₃ represent an integer of 0 to 40, and m ₄ and n ₄ represent an integer of 0 to 20, respectively. However, m ₁ and n ₁ , m ₂ and n ₂ , m ₃ and n _3, and m ₄ and n ₄ are simultaneously 0.
And m _{1 to} m ₄ and n _{1 to} n ₄ mean the total number of the substituents, and the positions of A and B are not limited.]

All of these nonionic surfactants include the corresponding aliphatic alcohol, substituted phenol, alkyl-substituted β-naphthol, alkoxylated phosphoric acid, esterified sorbitan, styrenated phenol, ethylenediamine, monoalkylamine, It can be prepared by adding a predetermined number of moles of ethylene oxide and / or propylene oxide to a diphenol which may be alkyl-substituted, and is also easily available as a commercial product.

As an example of a commercially available product, pullulafaf LF401 (BASF
And Tetronic TR-702 (manufactured by Asahi Denka Kogyo Co., Ltd.) and the like represented by Formula (2), respectively, and those represented by Formula (3) are represented by Nymein L-
Examples of those represented by the formula (4) such as 207 (manufactured by NOF Corporation) include Liponox NC-100 (manufactured by Lion Corporation).

In the method of forming a low melting point metal bump of the present invention, it is important to use the above-mentioned plating bath and to set a current waveform for electroplating. That is, in order to form a bump by the method of the present invention, it is necessary to use (1) a repetitive multistage rectangular wave or (2) a repetitive pulse rectangular wave as a plating current waveform.

Of these, the repetitive multistage rectangular wave of (1) is:
FIG. 1 shows a waveform obtained by repeatedly performing a multi-step rectangular wave in which the current density is changed in a stepwise manner. In order to carry out the bump forming method of the present invention, the number of steps of the multi-stage rectangular wave may be about 4 to 100 steps, and the current density range of each step is about 0.1 to 30 A / dm ² ,
The difference between the current densities at each stage is from 0.1 to 5 A / dm ²
The plating time at each current density is as follows:
The time may be set to about 0.001 to 10 seconds, preferably about 0.01, and this may be repeated for an appropriate time until the bump is formed.

On the other hand, the repetitive pulse rectangular wave of (2) is a waveform that repeatedly turns on and off at a constant current density, and an example is shown in FIG. In order to carry out the bump forming method of the present invention using this waveform, the current density at the time of ON is determined as
0.1 to 30 A / dm ² and the on-time is 0.00
The off time may be set to about 1 to 1 second and the off time may be set to about 0.001 to 1 second, and this may be repeated for an appropriate time until the bump is formed.

The current having the above-mentioned waveform can be obtained by using a rectifier having a current waveform programming mechanism. By combining with the above-mentioned electroplating bath, a low melting point metal bump which can be replaced by a solder plating bump is obtained. Can be In the method of the present invention, even when the electroplating bath is used, when a multi-stage rectangular wave (FIG. 3) or a DC waveform (FIG. 4) without repetition is used instead of the current waveform,
Granular precipitation or bump deposition results, and a bump having a good shape cannot be obtained.

[0025]

Next, the present invention will be described in more detail with reference to examples and test examples, but the present invention is not limited to these examples.

Example 1 Preparation of tin-silver alloy plating bath: Two types of tin-silver alloy plating baths were prepared with the following compositions. [Tin-silver alloy plating bath 1] (Composition) Tin methanesulfonate 110 g / l Silver methanesulfonate 0.8 g / l Methanesulfonic acid (free acid) 160 g / l Thiourea 5 g / l N, N-diethylthiourea 5g / l Ethylene 8g / l Oxide 7mol adduct of alkylamine Ethyl Alkylphenol 1g / l Renoxide 10mol adduct

[Tin-silver alloy plating bath 2] (Composition) Tin methanesulfonate 110 g / l Silver methanesulfonate 0.2 g / l Methanesulfonic acid (free acid) 160 g / l Thiourea 5 g / l N, N -Diethylthiourea 5 g / l Ethylene 8 g / l oxide 7 mol adduct of alkylamine Ethyl 1 g / l ethylene oxide 10 mol adduct of alkylphenol

EXAMPLE 2 Electroplating by repeated multi-stage rectangular waves: (a) As a plating sample, hundreds of pads (signal terminals) were formed by photolithography microfabrication technology, and 50 to 50 pads were formed on the pads with photoresist. A semiconductor chip provided with an opening of 80 microns was used. Using the tin-silver alloy plating bath 1 prepared in Example 1, the sample was plated by the repetitive multistage rectangular wave shown in FIG. The current densities of the multi-stage rectangular wave were 4, 5, 6, 7, and 8 A / dm, respectively.
² , and each current density was taken for 1 second. Then, the multi-stage rectangular wave is repeated, and plating is performed until the total reaches 60 minutes. The other conditions of the electroplating were as follows:
The liquid was stirred with a squeegee (12 m / min), and a tin anode was used as the anode.

(B) Plating is performed on the semiconductor chip provided with the 50-80 micron opening under the same conditions as in (a) above, except that the current density of the repetitive multi-stage rectangular wave is taken every 0.01 second. went.

(C) Plating is performed on the semiconductor chip provided with the opening of 50 to 80 μm under the same conditions as in (a) except that the tin-silver alloy plating bath 2 prepared in Example 1 is used. went.

(D) Using the tin-silver alloy plating bath 2 prepared in Example 1, each current density of the repetitive multi-step rectangular wave was set to 0.1.
Plating was performed on the semiconductor chip provided with the opening of 50 to 80 μm under the same conditions as in (a) except that it was taken every 01 second.

EXAMPLE 3 Electroplating by repeated multi-stage rectangular waves: (a) As a plating sample, hundreds of pads (signal terminals) were formed by photolithography fine processing technology, and 50 to 50 pads were formed on the pads using a photoresist. A semiconductor chip provided with an opening of 80 microns was used. Using the tin-silver alloy plating bath 1 prepared in Example 1, the sample was plated by the repetitive multistage rectangular wave shown in FIG. The current densities of the multi-stage rectangular wave are 1, 2, 3, 4, and 5 A / dm, respectively.
^2. Each current density is taken for 1 second. Then, this multi-stage rectangular wave is repeated, and plating is performed for a total of 120 minutes. In addition,
The other conditions of the electroplating were as follows: the liquid temperature was 40 ° C., the liquid was stirred by squeegee (12 m / min), and a tin anode was used as the anode.

(B) Plating is performed on the semiconductor chip provided with the opening of 50 to 80 μm under the same conditions as in (a) above, except that the current density of the repetitive multi-stage rectangular wave is taken every 0.01 second. went.

(C) Plating is performed on the semiconductor chip provided with the opening of 50 to 80 μm under the same conditions as in (a) except that the tin-silver alloy plating bath 2 prepared in Example 1 is used. went.

(D) Using the tin-silver alloy plating bath 2 prepared in Example 1, each current density of the repetitive multi-step rectangular wave was set to 0.3.
Plating was performed on the semiconductor chip provided with the opening of 50 to 80 μm under the same conditions as in (a) except that it was taken every 01 second.

Example 4 Electroplating by Repetitive Pulse Square Wave: (a) Using the tin-silver alloy plating bath 1 prepared in Example 1, the repetition pulse square wave shown in FIG.
Plating was performed on the semiconductor chip provided with the same 50-80 micron opening as used in (a). The current density of the pulse rectangular wave is 12 A / dm ² , and the on-time and the off-time each take 0.005 seconds. And
This pulse rectangular wave is repeated, and plating is performed until a total of 60 minutes is reached. The other conditions of the electroplating are as follows:
The solution was stirred at ℃ with a squeegee (12 m / min), and a tin anode was used as the anode.

(B) The above (a) except that the on-time and off-time of the pulse rectangular wave are each 0.01 seconds.
Plating was performed on the semiconductor chip provided with the opening of 50 to 80 microns under the same conditions as described above.

(C) Plating is performed on the semiconductor chip having the opening of 50 to 80 μm under the same conditions as in (a) except that the tin-silver alloy plating bath 2 prepared in Example 1 is used. went.

(D) Using the tin-silver alloy plating bath 2 prepared in Example 1, under the same conditions as in (a) above, except that the on-time and off-time of the pulsed square wave are each 0.01 seconds. Plating was performed on the semiconductor chip provided with the opening of 50 to 80 microns.

Comparative Example 1 Electroplating by Multi-Square Waves: (a) Using the tin-silver alloy plating bath 1 prepared in Example 1 and the multi-step rectangular waves shown in FIG. Plating was performed on a semiconductor chip provided with the same 50-80 micron opening as used. The current densities of the multi-stage rectangular wave were 4, 5, 6, 7, and 8 A / dm ² respectively, and each current density was taken for 12 minutes, and plating was performed for a total of 60 minutes. Other conditions of the plating are the same as those in Example 1 (a).

(B) Plating was carried out in the same manner as in (a) except that the tin-silver alloy plating bath 2 prepared in Example 1 was used.

Comparative Example 2 Electroplating by rectified wave: (a) Using the tin-silver alloy plating bath 1 prepared in Example 1 and applying a direct current having a current density of 4 A / dm ² ,
Plating was performed on the semiconductor chip provided with the same 50-80 micron opening as used in (a). The plating time was 90 minutes in total.

(B) Plating was carried out in the same manner as in (a) above, except that the current density was 8 A / dm ² and the plating time was 60 minutes in total.

(C) Plating was carried out in the same manner as in (a) above, except that the tin-silver alloy plating bath 2 prepared in Example 1 was used.

(D) Using the tin-silver alloy plating bath 2 prepared in Example 1, the current density was 8 A / dm ² , and the plating time was 60 minutes in total. Plating.

Test Example 1 The shapes of the mushroom bumps and the straight bumps formed by plating in Examples 2 and 3 and Comparative Examples 1 and 2 were observed using a scanning electron microscope (SEM). Each of the deposited plating films was dissolved in aqua regia, and the composition of the components was analyzed by an emission spectrophotometer (ICP). Table 1 shows the results.

[0047]

[Table 1]

As is apparent from the results, in Examples 2 and 3 using the repetitive multi-stage rectangular wave and Example 4 using the repetitive pulse rectangular wave, bumps having a good mushroom shape and straight shape were obtained. . On the other hand, in Comparative Example 1 using a simple multi-stage rectangular wave and Comparative Example 2 using a direct current, a bump having a preferable shape could not be obtained.

[0049]

According to the method for forming a low melting point metal bump of the present invention, a bump having a good shape can be formed without using lead. Since the pump obtained by the method of the present invention does not contain lead, it does not cause an erroneous operation such as inverting a semiconductor memory element by α-rays, and is also advantageous from the viewpoint of environmental pollution. Therefore, the method of the present invention is extremely advantageous as a method for forming bumps on a semiconductor chip or a package by electroplating.

[Brief description of the drawings]

FIG. 1 is a drawing showing a repetitive multi-stage rectangular wave

FIG. 2 is a drawing showing a repetitive pulse wave.

FIG. 3 is a drawing showing a multi-stage rectangular wave.

FIG. 4 is a drawing showing a DC wave.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H01L 21/288 H01L 21/288 M 21/92 603A F term (Reference) 4K023 AB34 AB40 CB05 CB11 CB13 4K024 AA15 BB12 CA01 CA02 CA06 CA07 GA16 4M104 BB36 CC01 DD52 5F044 KK19 QQ03 QQ04

Claims (6)

[Claims] 1. A method for forming a low-melting metal bump on a semiconductor chip or a package by electroplating, wherein the electroplating bath comprises the following components: (a) at least one alkanesulfonic acid ion or alkanolsulfonic acid ion of 5 to 5%; 300 g / l, (b) 0.01 to 10 g / l of Ag ion, (c) 0.1 to 40 g / L of one metal ion selected from Sn ²⁺ and Bi ³⁺ , (d) sulfur-containing compound (E) A silver-based alloy plating bath containing (e) a nonionic surfactant in a concentration of 0.5 to 30 g / l, and a current is repeated as a rectangular pulse wave or a multistage rectangular wave. Forming a low melting point metal bump. 2. The method according to claim 1, wherein the repetition period of the rectangular pulse wave or the multistage rectangular wave is 0.001 to 10 seconds. 3. The method for forming a low melting point metal bump according to claim 1, wherein the multi-stage rectangular wave is a step-like rectangular wave in which the current increases stepwise. 4. The current density at each stage of the multi-stage rectangular wave is 0.1.
4 to 30 A / dm ² , and the stepwise rectangular wave generation time is 0.001 to 10 seconds.
The method for forming a low-melting metal bump according to any one of the above items. 5. The method for forming a low melting point metal bump according to claim 1, wherein the ratio between the pulse time of the rectangular pulse wave and the pause time is 1: 1 to 10: 1. 6. The method according to claim 1, wherein the current density at the time of the pulse of the rectangular pulse wave is 0.1 to 30 A / dm ² , and the rectangular pulse wave generation time is 0.001 to 10 seconds. 6. The method for forming a low-melting-point metal bump according to claim 5.