JPH06204227A - Bump formation method - Google Patents

Abstract

PURPOSE:To provide a bump formation method capable of forming a fine bump while avoiding the sagging during baking step. CONSTITUTION:A metallic mask 5 provided with a hole 6 on the prospective bumps 7a forming positions is arranged on the surface of a substrate 1 so that a bump molding body may be formed by coating the hole 6 inside with a metallic paste by screen printing step to be baked later in the state of the substrate surface fitted with the metallic mask 5.

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. More specifically, the present invention relates to a method of forming bumps, which are metal protrusions for connection with external leads, on electrode pads provided on the peripheral portion of a substrate such as a semiconductor chip.

[0002]

2. Description of the Related Art With the recent miniaturization of electronic equipment, semiconductor devices incorporating integrated circuits (ICs) have become
It is not a resin molded lead wire,
As seen in COB, COG, TAB, etc., there is an increasing number of methods for directly connecting to wiring leads such as a printed circuit board in a so-called bare chip state in which bumps are formed on electrode pads of a semiconductor chip. In this method, bumps are generally formed on the electrode pads of the semiconductor chip, and the external leads are directly connected to the bumps. Conventionally, the bumps have been formed mainly by a plating method using electrolytic plating. However, a method of forming by screen printing has been studied for mass production. As a method using screen printing, as shown in FIG. 4, first, a passivation film on a substrate 21 is first formed.
The surface of 22 is masked with a metal mask 24 in which holes 25 are provided in the electrode pad 23 portion, and then a paste-like metal material for bumps is printed to form a metal paste molded body 26. Then, after removing the metal mask 24, the semiconductor substrate 21 is heated in an oven furnace or an annular furnace (not shown) to burn the metal paste molded body 26 to form bumps.

[0003]

However, in the heating means conventionally used for firing a metal paste molded body, from the ambient temperature to the firing temperature (for example, about 350 to 450 ° C. for a bump made of silver). A relatively long heating time is required to raise the temperature, and it takes a long time to lower the temperature to the ambient temperature.
Slump occurs on 26. Therefore, there is a problem that it is not possible to form a bump having a fine shape.

For example, in the case of a ring furnace, it takes about 1 hour to heat the silver paste to about 320 ° C., for example. After heating, since the entire substrate 21 must be left for about 30 minutes to cool, the time required for heating / cooling becomes very long, and the substrate 21 is exposed to a high temperature for a long time, so that sagging easily occurs.

It is an object of the present invention to solve the above problems, prevent sagging during firing, and provide a bump forming method capable of accurately forming fine bumps.

[0006]

According to a bump forming method of a first invention, a metal mask having a hole corresponding to an electrode pad provided on a substrate is aligned and arranged on the substrate,
It is characterized in that a metal paste is printed on the metal mask by screen printing, and then the metal paste molded body is fired with the metal mask attached to the surface of the substrate.

In the bump forming method of the second invention, a mask having holes corresponding to the electrode pads provided on the substrate is aligned and arranged on the substrate, and a metal is formed by screen printing on the mask. The method is characterized in that a paste is printed, and then the metal paste molded body is dried in a state where a metal mask is attached to the substrate surface, and then the metal mask is removed from the substrate surface and baked. .

[0008]

According to the bump forming method of the first aspect of the present invention, screen printing is performed to form a metal paste molded body, and then firing is performed with a metal mask attached to the substrate surface.
The metal paste molded body during firing is in a state of being confined inside the holes of the metal mask, and sagging does not occur even if the metal paste molded body melts.

Further, according to the bump forming method of the second invention, since the metal mask is provided until the metal paste molded body is dried, it is solidified to some extent and the bump can be formed without sagging during the subsequent firing. .

[0010]

The present invention will be described below with reference to the drawings. FIG. 1 is a cross-sectional explanatory view showing one step of the bump forming method of the present invention, FIG. 2 is a plan explanatory view of the step of FIG. 1, and FIG. 3 is an RT for explaining one embodiment of the bump forming method of the present invention.
It is a schematic sectional drawing of A apparatus.

The method for forming bumps according to the present invention will be described with reference to FIGS.
This will be described with reference to FIG. Similar to the semiconductor circuit, the bumps of the semiconductor chip are formed at once on the electrode pad portion of each chip in the state of the semiconductor wafer.

First, a metal is formed on the surface of a semiconductor substrate 1 (hereinafter referred to as substrate 1) on which a semiconductor circuit is formed, and electrode pads 2 are provided on the peripheral edge for connecting terminals of the circuit to external leads. A mask 5 is covered, and a metal paste 8 which is a material for bumps is printed with a squeegee 9 or the like to form a metal paste molded body 7 on the electrode pad 2 (see FIG. 1).

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.

The material of the metal paste 8 is selected according to the purpose of the bump to be formed. For example, silver paste, solder paste, gold paste, copper paste, silver-
Palladium paste or the like is used. For example, 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. To be done.

When the metal paste 8 is printed on the electrode pad 2, the metal material used for the electrode pad 2 and the metal material for the bumps are not compatible (for example, the electrode pad made of aluminum wiring is soldered). In the case of forming the bumps), a barrier metal having a one-layer or multi-layer structure such as a three-layer film made of titanium-nickel-gold or the like is formed on the electrode pad 2 by a plating method or a vapor deposition method. The metal paste 8 for bumps is printed on.

Next, with the metal mask 5 attached,
The bump molded body is baked.

When the bump molded body is heated and fired by a heating means such as an RTA apparatus, an oven furnace, or an annular furnace, the bump molded body is sealed by the metal mask 5 even if it melts. No inconvenience such as body deformation or sagging occurs.

In particular, when the RTA apparatus is used as the heating means for firing, the surface is heated and it is not necessary to heat the entire body, so that heat energy can be efficiently applied only to the metal paste molded body. In addition, it is possible to fire in a short time and to form fine bumps.

RTA equipment (Rapid Thermal Anneal)
Is irradiated by irradiating 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. It means a device that can be heat-treated from the surface in a short time (usually within 10 nanoseconds to several minutes). 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.

FIG. 3 shows a schematic view of a heat treatment apparatus using, for example, a halogen lamp as the RTA apparatus. In FIG. 3, a quartz susceptor is provided inside the SUS chamber 10.
The quartz susceptor 11 has a SUS chamber 10
The first supply pipe 12, the opening pipe 13 for temperature measurement on the back surface of the substrate, and the exhaust pipe 14 are electrically connected from the outside through the wall of the. In addition, a halogen lamp for heating is provided around the quartz susceptor 11.
15 are provided.

When firing is performed using this RTA apparatus, first, the lid 10a at one end of the SUS chamber 10 is opened, and the quartz wafer susceptor 16 on which the semiconductor substrate 1 which has undergone the above-mentioned steps is placed is the quartz susceptor 11. Insert inside. Lid 10
After closing a, nitrogen gas is introduced into the quartz susceptor 11 from the first supply pipe 12 at a flow rate of, for example, about 4 l / min. The introduced nitrogen gas is continuously discharged from the exhaust pipe 14 provided at one end of the quartz susceptor 11. By turning on the halogen lamp 15 in a state where these gases are circulated, light is irradiated and the temperature of the portion that absorbs the light rises rapidly. That is, even when light is irradiated, the quartz susceptor 11 hardly absorbs light and transmits it. The light radiated into the quartz susceptor 11 reaches the semiconductor substrate 1 mounted on the quartz wafer susceptor 16. Even in the semiconductor substrate 1, the bump metal paste easily absorbs light and easily heats up. The temperature of the non-existing part is less likely to rise than that of the bump metal paste. Therefore, only the metal paste molded body 7 can be effectively raised to the firing temperature, and by turning off the light source such as a halogen lamp after firing, the temperature of the entire furnace does not rise like an oven furnace, Since the surface of the semiconductor substrate that has been irradiated with light or the like, especially the metal paste molded body portion that easily absorbs light when irradiated with light, has a particularly high temperature, the heat capacity is small and the temperature immediately drops to the ambient temperature. Therefore, the temperature raising time and the temperature lowering time are usually as short as about 1 to 5 seconds, and since the metal paste compact is rapidly heated and is usually fired in about 1 to 60 seconds, it is necessary to dry the metal paste. By attaching a mask, even if there is no metal mask at the time of firing, if it is a metal with a high melting point like silver bumps,
The bump molded body is baked with almost no sagging.
This firing is for improving the contact between the metal powders of the metal paste compact and improving the electrical conductivity. Therefore, in eutectic solder bumps, for example, it is baked by heating at 210 to 220 ° C for about 1 to 60 seconds, and becomes completely molten (melting point of eutectic solder is 183 ° C), then cooled and solidified. As a result, it becomes a mass of solder to improve the electrical conductivity. On the other hand, silver bumps are fired by heating at, for example, about 350 to 450 ° C. for about 5 to 120 seconds. At this temperature, the silver powder does not reach a molten state, but the solvent in paste form evaporates and The surfaces of the bumps 7a are connected to improve the electric conduction of the bumps 7a.

Next, a specific example will be described. First,
A wafer-shaped semiconductor substrate on which a semiconductor circuit and electrode pads 2 are formed is placed on a fixed base 17 having a vacuum chuck, aligned, and sucked using a vacuum in which air is exhausted from an exhaust hole 18, Fix it. Next, after the metal mask 5 attached to the fixing base 17 and having the holes 6 formed in advance corresponding to the electrode pads 2 of the semiconductor substrate 1 is covered, the metal mask 5 is fixed from the three side surfaces by the fixing brackets 19,
The silver paste 8 is screen-printed with a squeegee 9.
The silver paste may have various mixing ratios depending on the purpose. For example, the silver powder and the glass powder are mixed at a weight ratio of 3: 1 (solvent: 50% by weight) to form a paste. I used one.

Next, the semiconductor substrate with the metal mask 5 attached is placed in an RTA apparatus having a halogen lamp 15, and the halogen lamp 15 is turned on to irradiate the semiconductor substrate 1. The temperature was raised from about 20 ° C. to about 350 ° C. in about 1 second, and, for example, heating was continued at 350 to 450 ° C. for about 5 to 120 seconds.
After that, turn off the halogen lamp, for example 5
The temperature was lowered to 50 ° C or lower in about 180 seconds, the temperature was lowered from the RTA device, and the metal mask was removed. As a result, burned bump-free bumps were formed.

In the above embodiment, the bumps formed on the semiconductor chip were formed in the state of the semiconductor wafer, but the bumps are not limited to the semiconductor chip, and lead bumps such as leadless resistors and capacitors connected to a circuit board or the like may be used. The present invention can be applied to other electronic components as well. Further, the bumps may be formed not only on the electronic components but also on the connection parts such as the circuit board, and the present invention can be applied to any of the bumps.

As another manufacturing method, RT is performed in a state where a metal mask is attached to the surface of the semiconductor substrate as a pre-step of firing.
The metal paste molded body may be dried by A, and then the metal mask may be removed from the surface of the semiconductor substrate and baked. Specifically, after using a silver paste to form a metal paste molded body by screen printing, with a metal mask attached to the surface of the semiconductor substrate, R
Using a TA unit, for example, at a drying temperature of about 120 ° C.
Dry for about 20 minutes. After that, firing is performed in the same manner as described above. According to this manufacturing method, thermal energy can be efficiently applied to the metal paste molded body by drying the metal paste molded body with an RTA device or the like, and the metal paste molded body can be dried in a short time. Therefore, even if the metal mask is removed from the surface of the semiconductor substrate and firing is performed, sagging does not occur.

[0026]

According to the present invention, the occurrence of sagging is prevented,
Fine bumps can be formed accurately and easily. Moreover, if the metal paste compact is fired by the RTA device, thermal energy can be efficiently applied, so that it can be fired in a short time, the metal mask can rotate quickly, and mass production can be performed.

Therefore, since it is possible to easily form fine bumps, it is possible to cope with the recent increase in the density of semiconductor integrated circuits.

[Brief description of drawings]

FIG. 1 is an explanatory cross-sectional view showing one step of a bump forming method of the present invention.

FIG. 2 is a plan explanatory view of the process of FIG.

FIG. 3 is a schematic sectional view of an RTA apparatus for explaining an example of a bump forming method of the present invention.

FIG. 4 is a cross-sectional view of a semiconductor substrate having bumps.

[Explanation of symbols]

 1 substrate 2 electrode pad 5 metal mask 6 hole 7a bump

Claims (2)

[Claims] 1. A metal mask having a hole corresponding to an electrode pad provided on a substrate is aligned and disposed on the substrate, a metal paste is printed on the metal mask by screen printing, and then the substrate is printed. A method for forming bumps, characterized in that a metal paste compact is fired with a metal mask on the surface. 2. A metal mask having holes corresponding to electrode pads provided on the substrate is aligned and disposed on the substrate, a metal paste is printed on the metal mask by screen printing, and then the substrate is printed. With the metal mask on the surface, dry the metal paste molded body,
After that, the metal mask is removed from the surface of the substrate, and baking is performed.