JPH09102498A - Forming method for solder bump electrode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a forming method for solder bump electrodes which can equally form the bump electrodes on all surface of a wafer without the semiconductor wafer warping by heating by the method of forming the solder bump electrode on electrodes of the semiconductor wafer. SOLUTION: This method provides a step of high melting point cream solder 6 being applied on a surface electrode of a semiconductor wafer 1 by screen printing method, a step of infrared beam irradiating all surface of the semiconductor wafer 1 by a near infrared beam halogen lamp, a step of the cream solder 6 applied on the electrode of the semiconductor wafer 1 being heated and melted by radiation heat of the infrared beam and a step of solder bump electrodes being formed.

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 solder bump electrodes on a semiconductor wafer.

[0002]

2. Description of the Related Art Currently, as a method for wirelessly bonding a semiconductor chip, a bump electrode, which is a metal protrusion, is formed on the semiconductor chip, and the external lead wire is directly connected to the semiconductor chip without using a bonding wire. Is used.

FIG. 8 is a sectional view of a semiconductor wafer on which solder bump electrodes are formed.
Solder bump electrodes 7 having a height of 50 μm to 100 μm are formed on the surface electrode 3 protected by.

As a method of forming the solder bump electrodes on the electrodes of the semiconductor wafer, there are a plating method, a vapor deposition method, a solder ball method, a reflow method and the like.

Among these methods, a method by reflow is disclosed in Japanese Patent Application Laid-Open No. 61-264743.
That is, after depositing the cream solder on the electrodes of the semiconductor wafer, the bump electrodes are formed by melting the solder by heating to a temperature above the melting point of the cream solder by reflow.

The method of heating and melting the solder by the above reflow is a method of heating the semiconductor wafer to a temperature above the solder melting point by a hot plate to melt the solder on the semiconductor wafer (hereinafter referred to as the hot plate method), and a heater. A method of heating the inside of the atmosphere furnace to raise the temperature of the entire furnace, and heating and melting the solder on the semiconductor wafer passing through the furnace (hereinafter referred to as the atmosphere furnace method) is known.

[0007]

In the hot plate method, the semiconductor wafer is heated from the back surface to a temperature equal to or higher than the solder melting point by the hot plate to heat and melt the solder attached to the electrodes of the semiconductor wafer. Therefore, the temperature of the semiconductor wafer itself rises before the solder is heated above the melting point. Since there is a difference in coefficient of thermal expansion between silicon which is a material of the semiconductor wafer and glass which is a protective film formed on the silicon, the semiconductor wafer may be warped.

When the semiconductor wafer is warped, the central portion of the semiconductor wafer is in contact with the hot plate, but the peripheral portion is not in contact with the hot plate. Therefore, a temperature difference may occur between the central portion and the peripheral portion of the semiconductor wafer, and the solder bump electrodes may not be uniformly formed on the entire surface of the semiconductor wafer. In addition, if you try to heat the solder on the periphery of the wafer that is not in contact with the hot plate to a temperature above the melting point, the solder in the center of the semiconductor wafer will be heated more than necessary. It also happens that the flux in the solder in some parts burns.

Particularly in recent years, since semiconductor wafers have tended to become larger and thinner, there is a strong demand for improvement in wafer warpage.

On the other hand, in the atmosphere furnace system, the temperature of the entire furnace is raised to a temperature above the solder melting point by a heater or the like to heat and melt the solder, so that the solder is heated even when the semiconductor wafer is warped. , Does not affect melting. However, this method has drawbacks in that it takes a relatively long time for a semiconductor wafer to pass through the furnace, and a large space is required for installing the furnace, resulting in poor mass productivity and cost.

Further, recently, as disclosed in Japanese Patent Application Laid-Open No. 7-37890, a method of forming bump electrodes by irradiating a chip with laser light to heat and melt solder is also known. . However, since laser light can be applied only within a narrow range and the solder on each chip is heated and melted, it is not possible to heat and melt all the solder on the semiconductor wafer, so this method also has good mass productivity. It can not be said.

Therefore, the present invention has been made in order to eliminate the above-mentioned problems, and the purpose thereof is to prevent the semiconductor wafer from being warped even when heated and to uniformly solder bump electrodes on the entire surface of the wafer. It is to provide a method for forming a solder bump electrode which can be formed and which is excellent in mass productivity.

[0013]

According to the method of forming a solder bump electrode of the present invention, after the cream solder is adhered to the electrode of the semiconductor wafer, infrared rays are radiated to the entire surface of the semiconductor wafer, and the semiconductor is radiated by the infrared rays. It heats and melts the cream solder attached on the electrodes of the wafer.

According to the present invention, the solder bump electrodes can be formed uniformly on the entire surface of the semiconductor wafer without warping of the semiconductor wafer.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION The invention according to claim 1 of the present invention is that, after cream solder is attached to the electrodes of silicon and compound semiconductor wafers by a method such as screen printing, the entire surface of the semiconductor wafer is irradiated with infrared rays, The radiant heat of the infrared rays heats and melts the cream solder adhered on the electrodes of the semiconductor wafer to form solder bump electrodes.

Infrared rays do not pass through the solder but pass through silicon and glass. Therefore, only the solder portion can be heated and the temperatures of the semiconductor wafer and the glass do not rise, so that the semiconductor wafer is not warped.
Further, even if the warp occurs, the solder on the entire surface of the semiconductor wafer can be heated to a substantially constant temperature without affecting the warp.

Further, since the solder on the entire surface of the wafer can be instantly heated by the infrared rays, the bump electrodes on the entire surface of the wafer can be formed in a short time.

Further, infrared rays have a wavelength of about 0.76 μm.
An electromagnetic wave of up to 1 mm, and the radiant energy of infrared rays is converted into thermal energy is that heat is generated by exciting molecules of the object. Therefore, the energy loss when passing through the air is extremely small, and the penetrating force is large, so that heat is generated more effectively from inside the substance.

Therefore, the solder is not extremely softened, bubbles are formed, and cracks are not generated.

FIG. 1 shows an embodiment of the present invention.
From now on, a detailed description will be given with reference to FIG. 7.

(Embodiment 1) FIG. 1 is an explanatory view showing a method of heating a semiconductor wafer with an infrared lamp after a cream solder is attached on a surface electrode of the semiconductor wafer.

An infrared lamp 11 is arranged above the semiconductor wafer transfer path 21, and when the semiconductor wafer 1 passes under the infrared lamp 11, infrared rays are radiated to the entire surface of the semiconductor wafer 1 to heat and melt the cream solder 6. Then, solder bump electrodes are formed.

FIGS. 2A to 2D are explanatory views showing the overall steps of the method for forming solder bump electrodes according to the present invention.

FIG. 2A is a cross-sectional view of a semiconductor chip 2 of a mesa type diode obtained by a well-known manufacturing method. Both electrodes of the front surface electrode 3 and the back surface electrode 4 are a nickel layer or a gold layer in addition to this. It is composed of.

In FIG. 2B, the opening 9 of the metal mask 8 is brought into contact with the surface electrode 3 on which the solder bump electrode is to be formed by the screen printing method, and then a metal mask is formed by using a squeegee (not shown). 8 is a cross-sectional view of the semiconductor chip 2 formed by inserting the cream solder 6 prepared above 8 into the opening 9. FIG. The cream solder refers to a flux-containing high melting point solder, and in the present embodiment, the composition is Pb (90 wt%) / Sn (8 wt%) / Ag (2
wt%) and a melting point of 295 ° C. were used.

FIG. 2C is a cross-sectional view of the semiconductor chip 2 in which the cream solder 6 is attached on the surface electrode 3 on which the solder bump electrode is to be formed by removing the metal mask 8.

FIG. 2D is a sectional view of the semiconductor chip 2 in which the solder bump electrodes 7 are formed by irradiating the cream solder 2 with infrared rays and heating and melting the infrared rays.

In this embodiment, the temperature is equal to or higher than the melting point of the solder powder in the cream solder, that is, Pb (90 wt).
%) / Sn (8 wt%) / Ag (2 wt%) with a melting point of 2
320 ℃ at 95 ℃ (However, temperature at which solder oxidization and flux carbonization in cream solder do not occur)
It was heated for 10 seconds by the radiant heat of a near infrared halogen lamp.

(Second Embodiment) FIG. 3 is an explanatory view showing another embodiment of a method for heating a semiconductor wafer.

The carrier plate 22 on which the semiconductor wafer 1 is mounted is reciprocally moved by a motor 23 and serves as a mechanism for carrying the wafer at 5 mm / sec. The upper part of the wafer transfer path 21 is separated by 10 mm to 20 mm from the semiconductor wafer 1 and has a length of 2 mm.
Two infrared lamps 11 having a width of 00 mm and a width of 50 mm are arranged side by side without a gap. The wafer has a diameter of 100 mm, and the entire surface of the wafer is within the infrared irradiation range. The lamp uses a near infrared halogen lamp, 100V, 98
A current of 6.2 A to 9.2 A was applied at 0 W.

(Embodiment 3) FIG. 4 is an explanatory view showing still another embodiment of a method for heating a semiconductor wafer.

The semiconductor wafer 1 conveyed by a conveyor mechanism (not shown) is irradiated with infrared rays from the infrared lamp 12 arranged under the semiconductor wafer to the back surface of the semiconductor wafer 1 to heat the semiconductor wafer. Next, an infrared lamp 13 arranged above the semiconductor wafer irradiates the surface of the semiconductor wafer 1 to heat the cream solder 6.

(Embodiment 4) FIG. 5 is an explanatory view showing still another embodiment of a method for heating a semiconductor wafer.

A round infrared lamp 14 is arranged above the semiconductor wafer 1 conveyed by a conveyor mechanism (not shown) to irradiate and heat the entire surface of the conveyed semiconductor wafer 1.

(Embodiment 5) FIG. 6 is an explanatory view showing still another embodiment of a method for heating a semiconductor wafer.

Semiconductor wafer 1 carried in quartz tube 24
In addition, the infrared lamp 11 arranged on the upper side is a mechanism for irradiating and heating.

(Embodiment 6) FIG. 7 is an explanatory view showing still another embodiment of a method for heating a semiconductor wafer.

The semiconductor wafer 1 is taken out from the case 25 and fixed at a predetermined position. The infrared lamp 11 moves from the upper part of the semiconductor wafer 1 and is irradiated and heated while reciprocating on the semiconductor wafer 1, and then the semiconductor wafer 1 is housed in a housing 26.

[0039]

As described above, in the method for forming solder bump electrodes of the present invention, after the cream solder is adhered on the electrodes of the semiconductor wafer, the entire surface of the semiconductor wafer is irradiated with infrared rays and the infrared rays are radiated by the infrared rays. Since the cream solder adhered on the electrodes of the semiconductor wafer is heated and melted, 1) Due to the heating by infrared rays, the semiconductor wafer is less likely to warp. 2) Even if the semiconductor wafer is warped, bump electrodes can be uniformly formed on the entire surface of the wafer. 3) The flux does not burn even if cream solder is used. 4) Since semiconductor wafers can be instantly heated by infrared rays, mass productivity is excellent. 5) Cracks do not occur in the solder due to the properties peculiar to infrared rays. It brings such a great effect.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing an embodiment of a method for heating a semiconductor wafer in a method for forming a solder bump electrode according to the present invention.

FIG. 2 is an explanatory view showing an embodiment of a method for forming a solder bump electrode according to the present invention, in which (a) is a cross-sectional view of a mesa type diode semiconductor chip and (b) is a cross-sectional view of the chip after cream solder is inserted. (c) is a cross-sectional view of the chip after adhesion of cream solder (d) is a cross-sectional view of the chip after solder melting

FIG. 3 is an explanatory view showing another embodiment of a method for heating a semiconductor wafer in the method for forming solder bump electrodes of the present invention.

FIG. 4 is an explanatory view showing still another embodiment of a method for heating a semiconductor wafer.

FIG. 5 is an explanatory view showing still another embodiment of a method of heating a semiconductor wafer.

FIG. 6 is an explanatory view showing still another embodiment of a method of heating a semiconductor wafer.

FIG. 7 is an explanatory view showing still another embodiment of the method of heating the semiconductor wafer.

FIG. 8 is a sectional view of a semiconductor wafer on which bump electrodes are formed.

[Explanation of symbols]

 1 Semiconductor Wafer 2 Semiconductor Chip 3 Front Surface Electrode 4 Back Surface Electrode 5 Glass 6 Cream Solder 7 Solder Bump Electrode 8 Metal Mask 9 Opening 11 Infrared Lamp 12 Infrared Lamp 13 Infrared Lamp 14 Round Infrared Lamp 21 Wafer Conveying Path 22 Wafer Conveying Plate 23 Motor 24 Quartz tube 25 Wafer case 26 Wafer storage

Claims (6)

[Claims] 1. A method of depositing solder on an electrode of a semiconductor wafer, irradiating infrared rays to the entire surface of the semiconductor wafer, and heating and melting the solder attached to the electrode of the semiconductor wafer by radiant heat of the infrared ray. Forming method of solder bump electrode. 2. The method for forming a solder bump electrode according to claim 1, wherein the semiconductor wafer is a wafer made of silicon and a compound semiconductor. 3. The method for forming a solder bump electrode according to claim 1, wherein the solder is a high melting point cream solder. 4. The method of forming a solder bump electrode according to claim 1, wherein the solder attachment is a screen printing method. 5. The method of forming a solder bump electrode according to claim 1, wherein the lamp is irradiated with infrared rays. 6. The method for forming a solder bump electrode according to claim 5, wherein the lamp is a near infrared halogen lamp.