JPH06204229A - Bump formation method and semiconductor device - Google Patents

Abstract

PURPOSE:To provide the easily forming method of a lot of tall fine bumps by screen printing step. CONSTITUTION:Molded bodies 13 are formed by screen-printing an electrode pad 2 on the surface of a substrate 1 with a metallic paste 9 and after finishing the drying-up step, the screen printing step and the drying-up step are repeated. Later, bumps 14 are to be formed by baking the metallic paste molded bodies 13 using an RTA device irradiating the substrate 1 with the beams of a halogen lamp, etc.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bump forming method for forming bumps, which are metal projections provided for connection with external leads, on electrode pads provided on the peripheral portion of a substrate such as a semiconductor chip. And a semiconductor device using the method. More specifically, it relates to a bump forming method using screen printing.

[0002]

2. Description of the Related Art With the recent miniaturization of electronic equipment, semiconductor devices incorporating integrated circuits (ICs) have not been molded with resin and lead wires have been led out.
A semiconductor chip (so-called bare chip) in which bumps, which are metal projections for external connection, are formed directly on the electrode pads of the semiconductor chip, such as G or TAB, has been used. This type of semiconductor chip is used by directly connecting it to wiring leads such as a printed circuit board (so-called wireless bonding), and is therefore convenient and convenient for downsizing electronic devices.

A bump portion of such a semiconductor chip is shown in FIG.
This will be described with reference to the sectional view shown in FIG. The electrode terminals for external connection of the semiconductor circuit of the semiconductor substrate 1 are aluminum wiring or the like and are led out to the peripheral portion of the semiconductor chip to form the electrode pads 41. Metal bumps 44 are formed on the electrode pads 41. However, in many cases, since the electrode pad 41 is made of aluminum and does not adhere to the solder and the like that form the bump 44, the bumps 44 are usually formed by interposing a plurality of layers of the barrier metal 42. The portion where no bump is formed is covered with a passivation film 43 made of a silicon oxide film, a silicon nitride film, or the like.

Conventionally, such bumps 44 are generally formed by electrolytic plating. Other, screen printing,
Methods such as transfer and vapor deposition are also being studied. When forming bumps by the screen printing method, it is necessary to dry and bake the printed metal paste molded body, which is usually dried and baked in an oven or the like.

[0005]

However, when the metal paste is printed, dried and fired, the solvent and residual gas in the metal paste escape from the surface and shrink and dry. As a result, it is not possible to obtain a sufficient height (30 μm or more), and when connecting to external leads, it may come into contact with other leads on the board, or the bumps may not be connected enough to cause poor conduction. There is a problem that. Also, if the residual gas in the metal paste does not escape sufficiently, voids are generated inside and the electrical resistance increases.

On the other hand, it is possible to increase the thickness of the mask in order to obtain bumps of sufficient height even after drying, but there is also the problem that the aspect ratio cannot be increased and fine processing is difficult. is there.

According to the present invention, there is provided a bump forming method which solves such a problem, can form bumps of sufficient height without forming voids in the bumps, and can easily form bumps by screen printing. The purpose is to provide.

[0008]

According to a first aspect of the present invention, there is provided a bump forming method, comprising: (a) arranging a mask having holes corresponding to electrode pads provided on a substrate in alignment with the substrate. , (B) printing a metal paste by screen printing on the mask, drying the metal paste,
(C) Further, at least the step of (b) is repeated once or more, and (d) is followed by firing.

Further, in the bump forming method according to the second aspect of the present invention, (a) a mask having holes corresponding to the electrode pads provided on the substrate is aligned and disposed on the substrate,
(B) A metal paste is printed on the mask by screen printing, (c) the metal paste is dried and then fired, and (d) the steps of (b) and (c) are repeated at least once. It is a thing.

Further, the semiconductor device of the present invention is a semiconductor device in which bumps are formed, and the bumps are formed by repeating screen printing twice or more.

[0011]

According to the bump forming method of the present invention, bumps can be easily formed in a short time by screen printing, and a metal paste is screen-printed and dried on the metal paste molded body that has shrunk during drying. However, since the baking is performed, tall bumps can be easily formed in a short time. In addition, by repeating screen printing after firing and further repeating firing, bumps having a sufficient height can be formed. Therefore, a semiconductor device having bumps formed by this method can form bumps with a small width and a sufficiently high height, and can maintain a sufficiently high reliability even for high integration.

[0012]

The present invention will be described below with reference to the drawings. FIG. 1 is a diagram for explaining a series of steps of printing, drying, and baking a metal paste in one embodiment of the bump forming method of the present invention, and FIG. 2 is a metal when the printing and drying steps are repeated. It is a figure explaining the change of the height of a paste molding.

In FIG. 1, 1 is a substrate such as a semiconductor substrate or circuit board, 2 is an electrode pad, 5 is a metal mask, and 6 is a hole. The electrode pad 2 is exposed at the peripheral edge of the substrate 1, 6 is opened in the metal mask 5 at a position corresponding to the electrode pad 2.

Here, the metal mask 5 is made of a thin film of stainless steel, nickel, tungsten or the like, and the holes 6 are formed corresponding to the electrode pads 2 provided on the substrate 1 on which bumps are to be formed. This metal mask 5 is usually 50-30
It is formed with a thickness of 0 μm. Hole 6 if too thick
Is not formed vertically, and if it is too thin, the formation height of the bump becomes low and it becomes impossible to project it from another film or the like.

First, as shown in FIG. 1 (a), the substrate 1 is placed on the fixing jig 3 and aligned, and then the suction holes 4 opened on the upper surface of the fixing jig 3 are used. Evacuate,
The substrate 1 is firmly fixed onto the fixing jig 3.

Next, as shown in FIG. 1B, the holes 6 of the metal mask 5 are aligned with the electrode pads 2 of the substrate 1, and the metal paste 9 is printed by a screen printer. The material of the metal paste 9 is selected according to the purpose of the bump to be formed. For example, silver paste,
Solder paste, gold paste, copper paste, etc. are used. The silver paste is made by mixing silver powder and glass powder with the solvent butyl carbitol acetate (BCA) to make a paste, and the solder paste is made by mixing eutectic solder powder with a flux to make a paste. It As a specific example, after the holes 6 of the metal mask 5 are firmly aligned so that they are on the electrode pads 2, the metal paste 9 is fixed to the holes 6 with a rubber squeegee 8 after being fixed from three sides with a fixture 7. The metal paste molded body 13 is embedded. At this time, the metal paste 9 is prevented from remaining on the metal mask 5. When the metal mask 5 is removed during drying and firing, the metal paste 9 may remain on the metal mask 5.

Next, as shown in FIG. 1C, the substrate 1
Then, the metal mask 5 is removed from the screen printing machine and heated from below by a heater 10 such as a hot plate. Then, the metal paste molded body 13 starts to dry from the lower side facing the substrate 1, and the metal paste molded body 13 is dried.
The solvent in the inside evaporates and escapes from the open upper side.
Dry as shown in (d). This drying is not limited to heating from the lower side, and may be an oven furnace, a ring furnace, an RTA device, or the like.

Here, the RTA device is, for example, a light source such as a halogen lamp, a xenon lamp, an optical lamp such as an arc lamp or a discharge lamp, a laser beam, an electron beam (EB) or a heat source such as a carbon heater, a heat ray, or a beam. A device that can perform heat treatment from the irradiated surface in a short time (usually within 10 ns to a few minutes) by irradiation (Rapid Therma
l Anneal). According to this RTA device, the surface is irradiated with light or a beam and is heated, and the temperature rises. Further, when there is a difference between the transmissivity and the absorptivity depending on the material to which light or the like is irradiated, the light received by the material having the good absorptivity is converted into heat, and the temperature rises especially.

In FIG. 1 (c), since the metal mask 5 is for preventing sagging of the metal paste molded body 13, the metal paste molded body 13 having a certain degree of viscosity.
When using, the metal mask 5 may be removed and dried.

After drying as described above,
When the mask is aligned or when the mask is dried with the metal mask attached, the steps from the screen printing to the drying are repeated one or more times, and then the RTA device 15 as shown in FIG. The paste molded body 13 is fired to form bumps 14. This firing is for improving the contact between the metal powders of the metal paste compact and improving the electrical conductivity. Therefore, with eutectic solder bumps, for example, at about 210 to 220 ° C,
It is baked by heating for about 60 seconds to become completely in a molten state (melting point of eutectic solder: 183 ° C), and then cooled and solidified to form a lump of solder for good electric conduction. On the other hand, for silver bumps, for example, 350-
It is fired by heating at about 450 ° C for about 5 to 120 seconds. At this temperature, the silver powder does not reach a molten state, but the solvent made into a paste evaporates, and the surfaces of the powders are connected to form bumps. Has good electrical conductivity.

The RTA device 15 includes a SUS chamber 16 and a SUS chamber 16 that can be sealed and has a lid 16a.
And a quartz susceptor 17 which is a cylindrical body provided inside the halogen lamp 21 so as to open toward the lid 16a.
A first supply pipe 18 is provided at 16a, an open pipe 19 for measuring the temperature of the back surface of the substrate 1 is provided below the quartz susceptor 17, and an exhaust pipe 20 is provided at the side opposite to the open end. With this device, the lid 16a is opened and the substrate 1 is placed on the quartz wafer susceptor 22.
Is placed inside the quartz susceptor 17, and the lid 16a
Close. After that, the halogen lamp 21 is turned on, and the temperature of the metal paste molded body 13 is set to a firing temperature suitable for the metal material to perform firing, whereby the bumps 14 are formed.

As a specific example, a silver paste is used as the above-mentioned metal paste 9, and a hot plate at about 150.degree.
Place it for about 5 minutes to dry, repeat silver paste printing and drying once, and then use an RTA device for about 350
Baking was performed at ℃ for about 1 to 60 seconds.

The height of the metal paste molded body 13 when screen printing and drying are repeated will be described with reference to FIG.

As shown in FIG. 2A, the metal paste compact 13a after the first screen printing has a height H1. However, the height of the metal paste 13a after heating and drying the substrate 1 is H as shown in FIG. 2 (b).
It has been reduced to 2. Therefore, as shown in FIG.
Is again fixed to the jig 3, and the second screen printing is performed so that the holes 6 of the mask 5 are aligned with the metal paste molded body 13a as shown in FIG. 1 (b). Then, FIG. 2 (c)
As described above, the molded body 13b having the height H3 is formed on the molded body 13a. The molded body 13b is also reduced to the height H4 after drying. However, a molded body having a height of H2 + H4 can be combined with the molded body 13a. By repeating this and further firing, the bumps 14 having a required height can be formed.

By using as the substrate 1 a semiconductor substrate on which a semiconductor circuit is formed by an ordinary semiconductor wafer process method, a semiconductor device including a bare chip on which bumps are formed can be obtained.

The mask 5 may be removed from the substrate 1 depending on the viscosity of the metal paste 9 after the drying or after the firing. However, when the screen printing is repeated, it is preferable from the viewpoint of alignment of the screen printing to finish the drying of at least the first time and keep the mask on the substrate until the metal paste is screen printed again.

In the above-mentioned embodiment, the steps from mask alignment or screen printing to drying were repeated, and then firing was carried out, but some shrinkage in the firing step is also compensated (most shrinkage occurs in the drying step). It is more effective to repeat the steps from mask alignment or screen printing to baking a plurality of times.

Further, when the screen printing is repeated and a mask having small holes is used, the metal mask can be overlaid on the molded body and higher bumps can be formed.

[0029]

According to the bump forming method of the present invention, at least the steps from screen printing of the metal paste to drying or firing are repeated, so that a large number of high bumps can be easily formed. As a result, when connecting the leads to the bumps, the work is easy and the connection is reliable, and
The connection lead can avoid contact with other circuit wiring parts, improving reliability. Further, even in a highly integrated semiconductor device, a semiconductor device having a miniaturized tall bump can be obtained.

[Brief description of drawings]

FIG. 1 is a diagram illustrating a series of steps of screen printing, drying, and firing in one example of a bump forming method of the present invention.

FIG. 2 is a diagram illustrating a change in height of a metal paste compact when the process of FIG. 1 is repeated.

FIG. 3 is a cross-sectional explanatory view of an example of a firing device.

FIG. 4 is a cross-sectional explanatory diagram of a bump portion formed on a substrate.

[Explanation of symbols]

 1 substrate 2 electrode pad 5 metal mask 6 hole 9 metal paste 13 metal paste molded body 14 bump

Claims (3)

[Claims] 1. (a) A mask having holes corresponding to electrode pads provided on a substrate is aligned and disposed on the substrate, and (b) a metal paste is printed on the mask by screen printing. A bump forming method, characterized in that the metal paste is dried, (c) the step of (b) is repeated at least once, and (d) then baked. 2. (a) A mask having holes corresponding to electrode pads provided on the substrate is aligned and arranged on the substrate, and (b) a metal paste is printed on the mask by screen printing. (C) A method of forming a bump, characterized in that the metal paste is dried and then fired, and (d) the steps of (b) and (c) are repeated at least once. 3. A semiconductor device having bumps, wherein the bumps are formed by repeating screen printing twice or more.