JP2782869B2 - Manufacturing method of solder bump - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Summary] The present invention relates to a method of manufacturing solder bumps by a transfer method, which aims at forming solder bumps without damaging a semiconductor integrated circuit, and in which a large number of integrated circuits are provided on a semiconductor wafer. On the electrode pad of the integrated circuit, a solder bump formed in advance on a transfer substrate that does not react with solder is aligned and abutted, and the semiconductor wafer is heated so that the solder bump is formed on the electrode pad. In the method of forming solder bumps to be transferred to a semiconductor device, the solder bumps are transferred onto the electrode pads in a state where the semiconductor wafer is fitted and fixed to a holder made of a metal having excellent heat conductivity. A method for manufacturing solder bumps is characterized in that the solder bumps are placed in a cleaning container with the surface on which the solder bumps are formed facing downward, and flux cleaning is performed.

[Industrial Application Field] The present invention relates to a method for manufacturing a solder bump.

Due to the need to process large amounts of information at high speed, information processing equipment has been increasing in capacity, and semiconductor devices, which are the main components of this equipment, have been reduced in size and capacity, and integrated circuits such as LSI and VLSI have become practical. Has been

Here, a conventional integrated circuit is a semiconductor chip having a size of several mm square (hereinafter simply abbreviated as a chip) in which semiconductor elements such as a unit transistor are formed in a matrix.
The circuit is connected to the electrode pads provided around the chip.After the chip is mounted on a ceramic multilayer circuit board, circuit connection is made by wire bonding with the electrode pads patterned on the circuit board. It was done.

However, for large-capacity elements such as LSIs, such a method is difficult. Instead, a flip-chip structure in which solder bumps are arranged in a matrix on the chip surface is used, and this is used for the multilayer ceramic circuit board. A flip-chip method has been adopted in which positioning is performed on a large number of pads of a conductor line provided in an upper layer and directly welding is performed.

[Conventional technology]

Most of the chips on which LSIs and VLSIs are formed have a size of 10 mm square or less, and a large number of solder bumps are formed thereon in a matrix, but this size is extremely small.

For example, as an example of an LSI, there is a 10 mm square silicon (Si) chip in which a total of 441 solder bumps each having a length of 200 μm and a height of 100 μm, 21 vertically and horizontally, are formed.
In this case, the gap between the solder bumps is only 120 μm.

As a method of forming such a solder bump, a vacuum evaporation method,
Although there are a solder ball method, a plating method and the like, none of them is practical.

That is, it is difficult to perform mask evaporation to a thickness of about 100 μm with a positional accuracy of several μm in the vacuum evaporation method.

Further, in the solder ball method, it is not economical to precisely align and weld a large number of solder balls to pad positions, which requires a large number of steps.

Further, the plating method is not preferable because the semiconductor element is chemically affected.

As a method for solving these problems, the inventors have proposed a method for forming a solder bump by a transfer method. (Japanese Patent Laid-Open No. 64-689942, published on July 31, 1988) FIGS. 2A to 2E show this process. First, a transfer such as Si or Al (aluminum) that does not react with solder is performed. Solder 2 for bump by mask evaporation on substrate 1
Is formed.

Next, a three-layer structure of, for example, titanium (Ti) / platinum (Pt) / gold (Au) is formed at a solder bump forming position on the Si wafer 3 on which a large number of integrated circuits are formed by a vacuum evaporation method. Is provided.

Here, the Ti layer is for improving the adhesion to the Si substrate, the Au layer is for improving the solderability, and the Pt layer is for improving the bonding property of the Au layer to the Ti layer. . Next, the pad 4 of the flux-coated Si wafer 3
Then, bump solder 2 formed on transfer substrate 1 shown in FIG.

Next, by heating the Si wafer 3, the solder for bumps 2 moves onto the pads 4 of the Si wafer 3 to form the solder bumps 5.

In this state, the solder bumps 5 and the transfer substrate 1 are merely joined by flux. Next, when this is immersed in a flux cleaning solution for cleaning, the transfer substrate 1 is separated, and a wafer having hemispherical bumps can be obtained.

However, in the conventional method, since the Si wafer is handled in a bare state, the exposed portion is large, and there is a high risk that the semiconductor element may be damaged.

Further, in the flux cleaning step shown in FIG. 2E, the transfer substrate 1 separated from the Si wafer 3 floats in the cleaning liquid and rubs with the Si wafer 3, thereby damaging the integrated circuit and manufacturing. There was a problem that the yield was reduced, and measures were needed.

[Problems to be solved by the invention]

As described above, the present inventors have proposed a method of forming solder bumps on a Si wafer on which an integrated circuit is formed by a transfer method, but wash the Si wafer after the transfer of the solder bumps. At this time, there is a problem that the integrated circuit is damaged by rubbing with the transfer substrate, and this problem is solved.

[Means for solving the problem]

The above-described problem is that after the solder bumps are transferred onto the electrode pads in a state where the semiconductor wafer is fitted and fixed to a holder made of metal having excellent heat conductivity, the holder is placed on the lower side with the solder bump forming surface facing downward. The method can be solved by configuring a method for manufacturing solder bumps, characterized in that the method is set in a cleaning container and flux cleaning is performed.

[Action]

The present invention employs a method in which a holder to which a wafer is fitted is formed using a metal having good thermal conductivity such as copper (Cu), and the holder is heated to transfer solder for bumps to pads on a Si wafer. This improves workability and eliminates the occurrence of defects due to contact or the like.

In addition, when cleaning is performed by placing the holder upside down in a cleaning solution and performing cleaning, the transfer substrate is separated and sinks, so that solder bumps can be formed without damaging the integrated circuit. It is.

〔Example〕

1 (A) to 1 (D) are cross-sectional views for explaining an embodiment according to the present invention.

First, there was prepared a Cu holder 9 capable of screwing the outer periphery of a Cu container 8 with a cylindrical frame 7 having a fixing portion protruding inward.

Then, an integrated circuit was formed, and the Si wafer 3 having a large number of pads 4 in a matrix was fitted into the container 8 of the holder 9 and then fixed by the frame 7.

Next, flux is applied on the Si wafer 3 and then formed on the transfer substrate 1 on the pad 4.
The bump solder 2 having a thickness of 100 μm was aligned and contacted.

Next, the Si wafer 3 is passed through the container 8 of the holder 9 at 220 ° C.
Then, the solder 2 was transferred onto the pad 4 of the Si wafer 3 by heating for 10 minutes.

Next, the holder 9 is turned upside down, and the frame 7 is placed in the cleaning container 10 with the frame 7 facing downward.
When the substrate was immersed in 11 to perform flux cleaning, the flux was dissolved and the transfer substrate 1 dropped to the bottom of the container 8. Next, the holder 9 was pulled up, the frame 7 was removed, and the Si wafer 3 was taken out to obtain a Si wafer provided with solder bumps.

〔The invention's effect〕

By implementing the present invention, the chance of touching the wafer is reduced and the collision of the transfer substrate is eliminated in the flux cleaning step, so that the production yield when mounting the flip type IC can be improved.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view for explaining the present invention, and FIG. 2 is a cross-sectional view of a bump forming method proposed by the inventors. In the figure, 1 is a transfer substrate, 2 is a solder for a bump, 3 is a Si wafer, 4 is a pad, 5 is a solder bump, 7 is a frame, 8 is a container, 9 is a holder, 10 is a cleaning container, and 11 is a cleaning container. Washing liquid,

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-3-145135 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) H01L 21/321 H01L 21/60

Claims (1)

(57) [Claims] 1. A method in which a plurality of integrated circuits are provided on a semiconductor wafer, and solder bumps formed in advance on a transfer substrate which does not react with solder are positioned on electrode pads of the integrated circuits. Contacting and heating the semiconductor wafer to transfer the solder bumps onto the electrode pads. In the method for forming a solder bump, the semiconductor wafer is fitted and fixed to a holder made of a metal having excellent heat conductivity. A method of manufacturing a solder bump, comprising transferring a bump onto an electrode pad, placing the holder in a cleaning container with the surface on which the solder bump is formed facing downward, and performing flux cleaning.