JP2781213B2 - Method of forming bump - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for forming a bump used in a wireless bonding technique in a semiconductor device, for example, a tape automated bonding (TAB) method.

(Prior Art) Conventionally, as a technique in such a field, for example, there is a technique shown in FIG.

FIG. 2 is a cross-sectional view of a bump for illustrating a conventional general bump forming method.

In the figure, an electrode 3 of aluminum (Al) or the like is formed on a semiconductor substrate 1 via an oxide film 2. Further, an insulating film 4 is formed on the entire surface, and the electrode 3 is exposed from the opening.

In order to form the bumps 5 on the exposed electrodes 3 by using a plating method, after removing a natural oxide film on the electrodes 3, one to three layers of a base metal 6 are formed on the entire surface by vapor deposition. Thus, the electrode portion 7 is formed by the electrode 3 and the underlying metal 6 thereon. Next, after covering portions other than the electrode portions 7 with a resist (not shown), the bumps 5 are formed on the base metal 6 of the electrode portions 7 by, for example, solder plating. Thereafter, unnecessary portions of the resist and the base metal 6 are removed by etching.

Further, in order to form the bumps 5 by using the vapor deposition method, after forming the base metal 6 in the same manner as the plating method, the base metal 6 is patterned to leave only the base metal 6 on the electrode 3. Here, an electrode portion 7 composed of the electrode 3 and the base metal 6 is formed. Next, after covering a portion except the electrode portion 7 with a resist, the bump 5 is formed on the base metal 6 by vapor deposition.

Although the above two bump forming methods are general,
In any of these methods, it is necessary to form a mask using the base metal 6 and the resist, and there is a problem that the process is complicated. Further, since the end portion of the base metal 6 is exposed in a state where one to three layers of dissimilar metals are in contact with each other, it is easily corroded by corrosive ions from the outside, and the bumps 5 may be peeled off.

Further, when the solder bumps 5 are formed by plating, the bumps 5 may be eroded by the etchant when the base metal 6 is removed by etching. It was difficult to form the bump 5 having a eutectic composition of tin (Sn).

To solve such a problem, Japanese Patent Application Laid-Open No. Sho 62-104143
In the publication, a bump forming method as shown in FIG. 3 is proposed.

In this bump forming method, soldering is performed using ultrasonic waves, and a solder bath 11 is used. In the solder bath 11,
A solder return path 12 is provided, and a molten solder 13 is accommodated therein. The molten solder 13 is returned to the circulation path by the rotation of the stirring rod 14.
It is jetted upward from the liquid level via 12 and refluxed.

In order to form bumps using the solder bath 11, the wafer 15 is vertically immersed in the molten solder 13 to be jetted. The wafer 15 has an electrode portion exposed to an opening of an insulating film (not shown).
No underlying metal is formed. On the back side of the wafer 15,
A reinforcing glass plate (not shown) is adhered via a high-temperature double-sided adhesive tape.

After the wafer 15 is immersed in the molten solder 13, the ultrasonic vibrator 16 is inserted into the molten solder 13 in the vicinity thereof, and ultrasonic waves are applied. By this operation, the solder is directly bonded on the electrode portion of the wafer 15, and a bump is formed.

In the bump forming method described above, the ultrasonic wave is applied to the molten solder 13 to destroy the natural oxide film on the surface of the electrode portion, and the solder is directly attached to the electrode portion. This makes it possible to form bumps without using a base metal or a mask.

(Problems to be Solved by the Invention) However, the bump forming method shown in FIG. 3 has the following problems, which are difficult to solve.

(1) When a single wafer 15 is immersed in the solder bath 11 and subjected to ultrasonic treatment, it is easily broken. Therefore, it is necessary to attach the wafer 15 to a double-sided tape glass plate. However, the operation of removing the wafer 15 from the glass plate is extremely difficult, and there is a possibility that the wafer 15 may be broken.

(2) Since the molten solder 13 in the solder bath 11 needs to be heated to a high temperature of about 280 ° C., there is a problem in safety for workers.

(3) Since the entire wafer 15 is put into the high-temperature molten solder 13, not only the electrode portion but also the entire semiconductor element is exposed to a high temperature. Therefore, the characteristics of the semiconductor element may be changed.

SUMMARY OF THE INVENTION The present invention provides a bump forming method that solves the problems of the prior art, such as the possibility of damaging a wafer, the problem of safety for workers, and the fact that the characteristics of semiconductor elements vary. It provides a method.

(Means for Solving the Problems) In order to solve the above problems, in the first invention, an electrode portion of a semiconductor element is exposed to an opening of an insulating film covering a surface of a semiconductor substrate, and a back surface of the semiconductor substrate is exposed. In addition to generating Joule heat in the electrode portion by an electromagnetic induction phenomenon from the side, supplying metal powder to the electrode portion heated by the Joule heat, and attaching and depositing the molten metal powder on the electrode portion. This is a method for forming a bump.

Further, in the second invention, the metal powder is supplied to the electrode part by diffusing the metal powder in an inert gas atmosphere in contact with the electrode part.

(Operation) According to the first aspect of the present invention, the method of forming the bump is configured as described above. Therefore, generating the Joule heat in the electrode portion by the electromagnetic induction phenomenon causes only the electrode portion to be mainly heated. To prevent heat influence on the semiconductor element and also ensure the safety of workers. In addition, metal powder is supplied to the heated electrode portion, and this is melted on the electrode portion.
Attaching serves to form tightly bonded bumps directly on the electrodes without using a base metal. Further, an excessive external force is not applied to the wafer, the use of a reinforcing glass plate or the like is not required, and the handling of the wafer is facilitated.

According to the second aspect, the metal powder that diffuses in the inert gas atmosphere is always in contact with the electrode portion with a uniform density distribution, and the growth of the bump is performed stably and efficiently. As a result, the bonding of the bump to the electrode is further strengthened, and a bump of high quality in shape and composition can be obtained.

 Therefore, the above problem can be solved.

(Embodiment) FIG. 1 is a schematic view showing a method of forming a bump in an embodiment of the present invention, and FIG. 4 is a principle view of electromagnetic induction heating. Hereinafter, a method for forming a bump will be described with reference to FIG.

First, a wafer 21 on which a predetermined electrode portion is formed is prepared. The wafer 21 has an oxide film 23 formed on a semiconductor substrate 22 made of, for example, silicon (Si), and an electrode portion 24 is provided at a predetermined position on the oxide film 23. Further, an insulating film 25 for passivation is formed on the entire surface, and the electrode section 24 is exposed from the opening of the insulating film 25. The electrode part 24 is constituted only by an electrode 24a made of iron (Fe) -based metal, aluminum-based metal, iron-based clad material, nickel (Ni), and the like.
No underlying metal is formed.

Next, the wafer 21 is accommodated in a reaction vessel (not shown) provided with the electromagnetic induction heating device 26, and is fixed on the top plate 27. The electromagnetic induction heating device 26 includes, for example, a top plate 27, a heating coil 28, and a drive circuit and a control circuit (not shown). The top plate 27 is made of tempered glass ceramic or the like, and
Is fixed by vacuum suction or a mechanical method. The heating coil 28 is provided below the top plate 27 so as to cover almost the entire area of the wafer 21.

The reaction vessel is used to keep the wafer 21 airtight from the external environment, and an inert gas such as helium (He) or a nitrogen gas (N ₂ ) is sealed inside the reaction vessel. Is formed.

Next, when a current is applied to the heating coil 28, a magnetic field is generated,
Eddy current is generated in the metal in the magnetic field, that is, the electrode 24a by the electromagnetic induction action. As a result, the electrode 24a generates Joule heat,
Heated. Almost simultaneously with this heating, the metal powder 29 is supplied to the electrode 24a. The metal powder 29 is made of fine particles such as solder, lead, tin, indium (In) or gold (Au) -tin alloy, and has a particle diameter of, for example, about 2 to 5 μm.

By supplying the metal powder 29 to the electrode 24A thus heated, the metal powder 29 is melted and deposited on the electrode 24a, and a desired bump is formed. For example, if a eutectic solder powder having a relatively low melting point is used as the metal powder 29, it can be melted at about 190 ° C. and a bump can be easily formed.

The supply method of the metal powder 29 may be locally supplied to the electrode 24a by using a bump or the like, but a method of supplying the metal powder 29 by diffusing the metal powder 29 into an inert gas atmosphere in a reaction vessel is used. It is particularly convenient. By doing so, all the electrodes 24a on the wafer 21 are simultaneously
In addition, the metal powder 29 can be supplied in a uniform and stable state. Diffusion of the metal powder 29 can be easily realized by stirring a gas such as an inert gas.

Next, the principle of electromagnetic induction heating will be briefly described with reference to FIG.

The heating by the electromagnetic induction action can be represented as a transformer model in which the heating coil 28 is a temporary coil and the electrode 24a is a secondary coil and a load resistance _RL . The resistance R _C on the primary side indicates the loss of the heating coil 28.

In such a model, if a high-frequency current is supplied to the heating coil 28 by a high-frequency inverter and a high-frequency magnetic field is generated around the coil, an eddy current flows on the electrode 24a side, and module heat is generated.

By the way, there is no problem when an iron-based metal or the like is used for the electrode 24a. However, when an aluminum-based metal or a copper (Cu) -based metal is used, aluminum or copper is nonmagnetic and has a low resistivity. Heating is more difficult than However, this difficulty can be solved by increasing the number of turns of the heating coil 28 or increasing the frequency.

Accordingly, the frequency of the electromagnetic induction heating energy is controlled (usually about 20 to 50 KH
By controlling the number of turns of the heating coil 28 and the number of turns of the heating coil 28, accurate heating can be performed.

As described above, in the present embodiment, by using the electromagnetic induction heating device 26, all the electrodes 24a on the wafer 21
Is locally heated, and metal powder 29 is supplied thereto to melt and
Since the method of forming the bump to be deposited is adopted, the bonding force between the electrode 24a and the bump is increased as compared with the conventional plating method and the like,
A bump can be formed directly on the electrode 24a without using a base metal. Therefore, a bump excellent in corrosion resistance can be formed by a simple process.

In addition, since there is no possibility of generating excessive stress during the bump forming process, it is not necessary to attach a reinforcing glass plate to the wafer 21, and the handling of the wafer 21 is easy. Moreover, since it is not necessary to use a large amount of molten solder or the like, and the entire wafer 21 is not exposed to a high temperature, the safety of the worker is ensured, and the characteristic variation due to the high heat of the semiconductor element can be prevented.

In particular, when the metal powder 29 is supplied to the electrodes 24a by diffusing the metal powder 29 in an inert gas atmosphere, uniform and stable supply is performed to all the electrodes 24a, and high-quality Bumps are easily formed.

The present invention is not limited to the illustrated embodiment, and various modifications are possible, for example, the following modifications.

(I) Although the electromagnetic induction heating device 26 in FIG. 1 is provided inside the reaction vessel, it may be provided outside the vessel. Further, the top plate 27 may not be particularly provided, and the bottom of the reaction vessel may be used for this.

(Ii) If conditions are set such that the electrode 24a and the metal powder 29 are not oxidized, the reaction vessel does not necessarily need to be filled with an inert gas. Further, it is not necessary to use a reaction container.

(Iii) As a method of supplying the metal powder 29, the metal powder 29 may be naturally dropped from the upper part of the reaction vessel, or may be supplied in a spray form. Further, the metal powder 29 may be supplied by mixing materials having different materials and particle diameters.

(Vi) The particle size of the metal powder 29 was about 2 to 5 μm.
It is not limited to this. The optimum particle size may be selected in consideration of the bump growth rate, the diffusion state in an inert gas atmosphere, and the like.

(V) Although the electrode section 24 is constituted only by the electrode 24a, the present invention can of course be applied to an electrode section composed of the electrode 24a and a base metal.

(Vi) Although bumps are formed simultaneously on all the electrodes 24a on the wafer 21, they may be formed separately for each region.

(Vii) The electromagnetic induction heating device 26 is not limited to the illustrated one,
For example, an apparatus including a plurality of heating coils may be used. By selectively using a plurality of heating coils or by using a combination thereof, electrodes 24a of various materials can be used.
Can be handled.

(Effects of the Invention) As described in detail above, in the first invention, the bumps are formed by locally heating the electrode portion by the electromagnetic induction phenomenon and supplying metal powder thereto. High quality bumps can be formed by a simple process without forming a base metal on the electrodes. In addition, since it is not necessary to use a reinforcing glass plate or a large amount of molten solder, handling of the wafer is easy, worker safety is ensured, and fluctuations in the characteristics of the semiconductor element can be prevented.

Further, in the second invention, since the metal powder is diffused in an inert gas atmosphere and supplied to the electrode portion, uniform and stable supply is performed, and bumps with less variation in shape and composition can be formed. Also, it is possible to easily form a large number of bumps simultaneously.

Therefore, there is an effect that a highly reliable bump can be easily formed by an efficient and safe operation.

[Brief description of the drawings]

FIG. 1 is a schematic view showing a method of forming a bump in an embodiment of the present invention, FIG. 2 is a sectional view of a bump showing a conventional general method of forming a bump, and FIG. 3 is another conventional method of forming a bump. And FIG. 4 is a principle diagram of electromagnetic induction heating. 21 ... wafer, 22 ... semiconductor substrate, 24 ... electrode part, 24a
…… electrode, 25 …… insulating film, 26 …… electromagnetic induction heating device, 28
... heating coil, 29 ... metal powder.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H01L 21/321 H01L 21/60

Claims (2)

(57) [Claims] 1. An electrode part of a semiconductor element is exposed to an opening of an insulating film covering a surface of a semiconductor substrate, and Joule heat is generated in the electrode part by an electromagnetic induction phenomenon from a back side of the semiconductor substrate. A method for forming a bump, comprising: supplying a metal powder to the electrode section heated by the Joule heat; and depositing and depositing the molten metal powder on the electrode section. 2. The bump forming method according to claim 1, wherein the supply of the metal powder to the electrode portion is performed by diffusing the metal powder into an inert gas atmosphere in contact with the electrode portion. Forming method.