JPH04282837A - Forming method for gold protrusion - Google Patents

Abstract

PURPOSE:To easily form a gold protrusion formed in an excellent shape having a projection at a center and no lateral extension to a peripheral edge in an opening to be plated by an electric plating method. CONSTITUTION:Reynolds number of liquid flow to be applied to plating solution is set to 50 or more, a current density to be applied between electrodes is 5mA/cm<2> or less, a diameter (d) f an opening 3 is set to 150mum or less, 30-100ppm of Tl or As is applied as an additive to the solution, and a gold protrusion 1 formed in an excellent shape as shown in Fig. (a) is formed.

Description

Description: FIELD OF THE INVENTION The present invention relates to a method for forming gold protrusions using electroplating. 2. Description of the Related Art As semiconductor products become more highly integrated, high-density connections between electrical components in semiconductor devices and their peripheral devices are required. In particular, in the connection between a semiconductor element and its peripheral equipment, as semiconductor elements become more highly integrated, the number of electrodes to be formed on the semiconductor element increases and the pitch between the electrodes tends to decrease. Conventionally, electrodes and peripheral devices were individually connected by wire bonding using gold wires, but each connection took time, and the reduction in the pitch between the electrodes caused short circuits between adjacent gold wires. In recent years, TAB (Taped) has been used instead of wire bonding.
Automatic bonding is used for electrical connections in semiconductor products. TAB is
This is a method in which protrusions (bumps) are formed by gold plating on the electrodes of the semiconductor element, and connections are made to peripheral devices through the protrusions. [0004] In order to prevent connection failures in such TABs, it is necessary to make the shape of the gold protrusions constant.Therefore, various methods have been used to form gold protrusions with a stable shape by gold plating. Proposed. For example, a method of removing the underlying metal layer directly under the gold protrusion (Japanese Unexamined Patent Publication No. 6
1-141157), a method of leaving a resist in the center of the opening (Japanese Patent Application Laid-Open No. 62-252951), a method of repeating the photolithography process and a gold plating process (Japanese Patent Application Laid-Open No. 63-175446), etc. has been done. [0005] However, each of the above-mentioned forming methods has the following problems. The method of removing the base metal layer directly under the gold protrusion requires a complicated removal process, and if it is removed in a liquid phase, the etching solution remains and this residue mixes with the gold plating solution, resulting in poor shape. . Furthermore, the method of leaving the resist in the center of the opening has a small contact area with the base metal layer, resulting in poor adhesion, which tends to lead to a decrease in the strength of the protrusion during bonding. Furthermore, the method of repeating the photolithography process and the gold plating process requires a long time as a whole,
It is difficult to align in the photolithography process, and it is difficult to control the height of gold plating in each process. The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a method for forming gold protrusions that can easily form gold protrusions having a stable shape by limiting electrolytic gold plating conditions. With the goal. Means for Solving the Problems The method for forming gold protrusions according to the present invention includes forming gold protrusions by growing gold in the openings by electroplating. The Reynolds number of the applied liquid flow is 50 or more, the current density applied between both electrodes is 5 mA/cm2 or less, the diameter of the opening is 150 μm or less, and 30% of Tl or As is added as an additive to the plating solution. ~100 ppm
It is characterized by adding. [Function] If the Reynolds number of the liquid flow applied during gold plating is less than 50, a depression will be formed in the center of the protrusion or it will spread laterally to the periphery, resulting in poor shape. In this case, the Reynolds number shall be 50 or more. Furthermore, if the current density during gold plating is higher than 5 mA/cm2, a depression will be formed at the center of the protrusion, so in the present invention, the current density is set to 5 mA/cm2 or less. Further, if the diameter of the opening to be plated is larger than 150 μm, a depression will be formed at the center of the protrusion, so in the present invention, the diameter is set to 150 μm or less. Furthermore, when Tl or As is added to the plating solution as an additive, an appropriate amount is required, and in the present invention, 30 to 100
Add Tl or As at a concentration of ppm. [Examples] Examples of the present invention will be described below. Gold is grown by electroplating in the openings formed by the photoresist in a predetermined pattern to form gold protrusions. Incidentally, in order to improve the reproducibility of the plating experiment, a rotating disk electrode (R.D.E.) is used as the electrode. The Reynolds number (NRe) of liquid flow in this case is expressed by the formula shown in (1) below. [0010]NRe=Ωr2/η
...(1) Ω: Rotation speed r: Rotation radius
η: coefficient of kinematic viscosity [0011] In order to make the flow conditions uniform, a gold protrusion is formed at a position 8 mm from the center of the rotating shaft, and a sulfite-based gold plating solution is used. [0012] The shape of the gold protrusion thus formed is as follows:
Observe with a scanning electron microscope. FIG. 1 is a cross-sectional view showing the shape of the formed gold protrusion. In the figure, reference numeral 2 denotes a photoresist, and the photoresist 2 in a predetermined pattern is provided with an opening 3 that serves as a gold plating site, and a gold protrusion 1 is formed in the opening 3. Note that d indicates the diameter of the opening 3. The shapes of the formed gold protrusions can be classified into three types as shown in FIG. FIG. 1A shows an ideal shape that is convex upward, and such a shape will be referred to as A hereinafter. FIG. 1(b) shows a defective shape with a depression in the center of the protrusion, and this shape will be referred to as B hereinafter. Figure 1(c)
) is a defective shape in which lateral expansion has occurred toward the periphery of the protrusion, and such a shape is hereinafter referred to as C. Next, gold protrusions 1 were formed by changing the electrolytic gold plating conditions.
An experimental example in which . [Reynolds number and shape of gold protrusion] Opening part 3
The diameter d of is 10 μm, 15 μm, 30 μm, 50 μm,
The photoresist 2 was patterned to have a diameter of 80 μm, 100 μm, and the Reynolds number (NRe) was set to 0, 10, 30, 50, 100,
200, and a gold protrusion 1 was formed. Note that the current density is 4
An amount of electricity of 25 C/cm2 was given as mA/cm2. The formed gold projections 1 were then observed using a scanning electron microscope. The observation results are shown in Table 1 below. [0016] Reynolds number (NRe) is 3
In the case of 0, if the diameter d of the opening 3 is 30 μm or more, the shape is defective. On the other hand, when NRe is 50 or more, the shape is ideal in all cases. From these results, it can be seen that the NRe boundary that determines the good shape and bad shape of the gold protrusion 1 is 50. [Current density and shape of gold protrusion] NRe was set to a constant value of 50, and a constant amount of electricity of 25 C/cm2 was applied.
Current density is 1mA/cm2, 2mA/cm2, 3m
A/cm2, 4mA/cm2, 5mA/cm2
, 8 mA/cm2 to form gold protrusions 1. Note that the diameter d of the opening 3 was kept constant at 80 μm. The observation results in this case are shown in Table 2 below. [0020] Current density is 6 mA/cm2
In this case, defective shapes of B and C types occur. Therefore, it is preferable that the current density is 5 mA/cm2 or less. [Diameter of the hole and shape of the gold protrusion] NRe is set to a constant value of 50, a constant amount of electricity of 25C/cm2 is applied, and the current density is set to a constant value of 4mA/cm2.
The diameter d of is 15μm, 30μm, 50μm, 100μm
Gold protrusions 1 were formed by changing the thickness to m, 150 μm, and 200 μm. The observation results in this case are shown in Table 3 below. [0023] The diameter d of the opening 3 is 200
If it is more than μm, the shape will be defective. Therefore, it is preferable that this diameter d is 150 μm or less. [Additive and shape of gold protrusion] NRe is set at a constant value of 50, a constant amount of electricity is applied at 25 C/cm2, the current density is set at a constant level at 4 mA/cm2, and the diameter d of the opening 3 is set at 80 μm. The Tl added to the plating solution is kept constant and is 0.
ppm, 10ppm, 30ppm, 60ppm, 90p
pm, 100ppm, 500ppm, 1000ppm
The gold protrusion 1 was formed by changing the following. The observation results in this case are shown in Table 4 below. In addition, NRe was set to a constant value of 50, a constant amount of electricity of 25C/cm2 was applied, and the current density was set to a constant value of 4mA/cm2.
The diameter d of the opening 3 is kept constant at 80 μm, and the amount of As added to the plating solution is 0 ppm, 10 ppm, and 30 ppm.
, 60ppm, 90ppm, 100ppm, 500ppm
Table 5 below shows the observation results when gold protrusions 1 were formed by changing the amount of gold to 1,000 ppm. As can be seen from the results in Tables 4 and 5, when the amount of additive added to the plating solution is 30 to 100 ppm, gold protrusions 1 with good shapes can be obtained. Effects of the Invention As described above, in the method for forming gold protrusions of the present invention, the Reynolds number is set to 50 or more, and the current density is set to 5 m
A/cm2 or less, and the diameter of the opening is 150 μm.
As shown below, Tl or As is added to the plating solution as an additive.
Since gold protrusions are formed by containing 0 to 100 ppm, it is possible to avoid shape defects due to depressions at the center of the protrusions or lateral expansion to the periphery of the protrusions, thereby forming gold protrusions with extremely good shapes. be able to.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view showing the shape of a formed gold protrusion.

[Explanation of symbols]

1 Gold protrusion 2 Photoresist 3 Opening part d Diameter of opening

Claims (1)

[Claims] Claim 1. A method for forming a gold protrusion in which gold is grown in an opening by electroplating to form a gold protrusion, wherein the Reynolds number of the liquid flow applied to the plating solution is 50 or more,
The current density applied between both electrodes is 5 mA/cm2 or less, the diameter of the opening is 150 μm or less, and 30 to 100 p of Tl or As is added as an additive to the plating solution.
A method for forming gold protrusions, characterized by adding pm.