JPH0828366B2 - Method for forming electrode of semiconductor device - Google Patents

Description

The present invention relates to a method for forming bump electrodes on a semiconductor device.

[Technical Background of the Invention] -Conventional Technology- Conventionally, a method is known in which a bump electrode is formed on a semiconductor device and the bump electrode is directly bonded to a metal foil lead provided on a carrier tape. This method
It has been known as a TAB (Tape Automated Bonding) method for quite some time, but there is a demand for miniaturization of electronic devices.
With the rapid progress of photolithography technology, it has begun to be reviewed again in recent years. However, in this TAB method, the most important technical element is that bump electrodes are formed on the semiconductor device.

FIG. 8 shows a sectional view of a conventional bump electrode structure. In the figure, reference numeral 1 is a silicon wafer, and an electrode pad 2 made of aluminum or an aluminum alloy is formed on the silicon wafer 1. Although not shown, the electrode pad 2 is connected to an internal electrode such as a gate of the silicon wafer 1. A peripheral portion of the electrode pad 2 is covered with an insulating film 3 such as silicon nitride having an opening 3a formed so as to face the electrode pad 2.
A barrier metal layer 4a and an adhesive metal layer are formed on the electrode pad 2.
An under bump layer 4 composed of 4b is formed. The under bump layer 4 is formed by vapor deposition or sputtering, and is shown only on the electrode pad 2 and the insulating layer 4 around the electrode pad 2 in the figure, but in the actual process, the under bump layer 4 is formed on the insulating layer 4. After forming the bump electrode 5 on the entire surface, an etching process is performed as shown in the drawing. In this case, the under bump layer 4 is fixed to the electrode pad 2 and the insulating layer 4 around the electrode pad 2, and the large bonding area ensures sufficient bonding strength. A bump electrode 5 made of gold is formed on the under bump layer 4. Since the bump electrode 5 is formed by plating, a gold thin film layer 5a is formed on the adhesive plating layer 4 as a base thereof. It Then, as described above, the under bump layer 4 on the outer side of the bump electrode 5 is removed by etching using the bump electrode 5 as a mask.
In this case, isotropic wet etching is usually used.

-Problems of the prior art-In the above-described conventional technology, the bump electrode 5 is
Since the head has a large mushroom-like shape, it causes a large pitch, which makes it difficult to apply to recent semiconductor devices in which the pitch of the electrode pad 2 is extremely miniaturized. There is. Therefore, whether a study is currently underway to reduce the width (or diameter) of the bump electrode 5, or a major issue in this study is the development of a technique for reducing the width (or diameter) of the head of the bump electrode. When the width (or diameter) of the head of the electrode is reduced, how to secure the bonding strength between the electrode pad and the under bump layer, and between the under bump layer and the bump electrode The width (or diameter) of the head of the bump electrode is reduced In this case, how to secure the bonding strength between the bump electrode and the finger lead of the carrier tape adhered to this bump electrode can be mentioned. For this reason, the applicant of the present application has filed an application for one of the pillars of the above-mentioned subject, paragraph (1) and one of the methods for solving the subject of paragraph (1) on November 18, 1987 (Japanese Patent Application No. 62-289257). .

[Problems to be Solved by the Invention]

That is, in the conventional technique, the head of the bump electrode 5 is
Since it has a relatively large area, even if the bonding strength per unit area with the finger leads adhered to it is somewhat small, the overall bonding strength will be satisfactory for the time being. It was However, when the width (or diameter) of the head of the bump electrode 5 is reduced, there is a drawback that the bonding strength of the finger leads is insufficient.

Therefore, the present invention provides an electrode forming method for a semiconductor device that reduces the area of a bump electrode, a method for forming an electrode for a semiconductor device that can increase the bonding strength to a connected terminal, and an etching method used for the forming method. The purpose is to provide.

[Means for solving the problem]

In order to achieve the above object, in an electrode forming method of a semiconductor device of the present invention, an under bump layer is formed on an electrode pad, and a photoresist thicker than a bump electrode to be formed on the under bump layer is formed. And forming an opening at a portion of the photoresist facing the electrode pad, and forming a bump electrode on the under bump layer in the opening with a thickness of 10 μm or more and not protruding from the upper surface of the photoresist. A V-shaped groove is formed on the surface of the bump electrode by reactive ion etching.

[Operation] According to the method of the present invention, 10 μm is formed on the under bump layer in the opening facing the electrode pad of the photoresist.
It is possible to form a bump electrode having a thickness of m or more and not protruding from the upper surface of the photoresist. Since this bump electrode has a thickness of 10 μm or more, it is possible to directly bond it to the connection terminal. In addition, since the thickness is such that it does not protrude from the upper surface of the photoresist, it does not grow in the direction of the adjacent bump electrodes when it is formed by plating, so it can be formed with a fine pitch. Further, since the V-shaped groove is erased on the surface of the bump electrode by the reactive ion etching, the contacting oil agent such as solder for joining the bump electrode and the connected terminal is formed in the V-shaped groove of the bump electrode. It is filled so as to bite into it and enhances the bonding strength.

〔Example〕

 Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a bump electrode structure of a semiconductor device. In this figure, 10 is a silicon wafer, which usually has a diameter of 4 to
An 8-inch one is used. An internal electrode 11 such as a gate and an insulating film 12 made of silicon oxide are formed on the silicon wafer 10. An electrode pad 13 connected to the internal electrode 11 is formed on the insulating screen 12. This electrode pad 13 is made of aluminum (Al), aluminum (A
l) -Silicon (Si), Aluminum (Al) -Copper (Cu)-
It is made of aluminum alloy such as silicon (Si). An insulating film 14 of silicon nitride is formed on the peripheral portion of the electrode pad 13 and the insulating film 12. An opening 14a is formed in a portion of the insulating film 14 corresponding to the electrode pad 13. The electrode pad 13 facing the opening 14a and this electrode pad 13
An intermediate connection film (under bump layer) 15 is formed on a portion of the insulating film 14 which covers the peripheral edge of the. The intermediate connection film 15 is made of an alloy of a barrier metal and an adhesive metal, for example, an alloy of titanium (Ti) -tungsten (W), platinum (pt) -titanium (Ti), palladium (Pd) -titanium (Ti), or the like. . Such an alloy of a barrier metal and an adhesive metal has not only a barrier function even in a single layer, but also a function of ensuring the bonding strength between the gold bump 16b and the electrode pad 13. Preferably, a titanium-tungsten alloy in which titanium is mixed in an atomic weight ratio of 10% and a weight ratio of 30% is used, and the titanium-tungsten alloy is formed to a thickness of several thousand Å by sputtering. The outer end of the intermediate connection film 15 is positioned between the outer end of the electrode pad 13 and the opening 14a of the insulating film 14. An external electrode (bump electrode) 16 made of gold (Au) is formed on the intermediate connection film 15 in a protruding shape. The external electrode 16 is a gold thin film 16a and a gold bump 1
6b and has a total thickness of about 10 to 25 μm, and its outer end is substantially flush with the outer end of the intermediate connecting film 15.

The gold thin film 16a is an underlayer for plating of the gold bumps 16b formed by plating, and is attached to the intermediate connection film 15 by a spatter. A fine V-shaped groove 17 is formed on the head surface of the gold bump 16b. The feature of the present invention is that the gold bump 16
These fine V-shaped grooves 17 are formed on the entire surface of the head portion of b, and the details of the forming method will be described later.

First, a method of forming the external electrodes 16 on the silicon wafer 10 will be described with reference to FIGS.

First, as shown in FIG. 2 (A), a silicon wafer 10
An internal electrode 11 and an insulating film 12 of silicon oxide are formed on the upper surface, and an electrode pad 13 made of aluminum or an aluminum alloy is formed thereon. Next, a silicon nitride insulating film 14 is formed over the electrode pad 13 and the insulating film 12. An opening 14a which is slightly smaller than the outer shape of the electrode pad 13 is formed in the insulating film 14 by etching so that the electrode pad 13 is exposed from the opening 14a. In this state, by sequentially spattering an intermediate connection alloy made of an alloy such as titanium-tungsten and gold, the intermediate connection film 15 and the gold thin film are spread over the entire surface of the electrode pad 13 and the insulating film 14 on the silicon wafer 10. Each 16a is formed to a thickness of several thousand Å. However, the thickness of the gold thin film 16a is several hundred Å
It may be a degree. In this case, spattering is optimal in order to make the adhered metal particles uniform. Before performing this process, a removal process for removing the aluminum oxide film is performed, if necessary.

After that, as shown in FIG. 2B, a photoresist solution is dropped on the gold thin film 16a and spin coating is performed to form a thick photoresist film 19. The photoresist film 19 has a viscosity of several hundred to several thousand and several hundreds of CPS (centipoise) in order to have a thickness of about 20 to 30 μm, which is several to several tens of times higher than that of ordinary spin coating (for example, BMR1000 manufactured by Tokyo Ohka Kogyo Co., Ltd. is used. The rotation speed is several hundred rpm. In this case, if the photoresist has a viscosity of 100 CPS or less, it cannot be made to have a predetermined thickness.

Next, after the photoresist film 19 thus formed is dried, a mask (not shown) is aligned on the upper surface thereof. The transparent portion of this mask is formed in such a size that the outer edge portion of the transparent portion is located between the outer edge portions of the electrode pad 13 and the opening 14a of the insulating film 14. Then, the photoresist film 19 is exposed through this mask and developed to form an opening 19a in the photoresist film 19 as shown in FIG. 2 (C). Next, by electroplating gold on the gold thin film 16a exposed through the opening 19a, the gold bump 1
Form 6b. Stop the gold bump 16b where its upper surface does not protrude from the upper surface of the photoresist film 19 and adjust its thickness.
20 to 30 μm. As a result, the upper surface of the gold bump 16b becomes substantially flat. The developer used for developing the photoresist film 19 is an organic solvent containing xylene as a main component (for example, C-3 manufactured by Tokyo Ohka Kogyo Co., Ltd.).

After that, as shown in FIG. 2D, the photoresist film 19 is made of ethyl cellosolve, an organic solvent containing dichlorobenzene as a main component (for example, a stripping solution S manufactured by Tokyo Ohka Kogyo Co., Ltd.).
Peel it off. Then, in this state, the gold thin film 16a is etched with an iodine-based etching solution to remove an unnecessary portion, that is, a portion of the gold thin film 16a that does not correspond to the gold bump 16b. This state is shown in FIG. After that, the silicon wafer 10 (the drawing shows only the enlarged portion of the bump electrode structure, but actually, a disk shape of 4 to 8 inches) is stored in the sputter device 20 shown in FIG.
Etching. Sputter (Etching) device 20
Is equipped with plates 22 and 23 in a vacuum chamber 21, and the wafer 1
0 is arranged on the plate 23. Plate 22 has 13, 56M
A high frequency signal of Hz is applied via a matching box 24 and a block capacitor 25. The inside of the vacuum chamber 21 is maintained at a high degree of vacuum by a vacuum pump (not shown), and the reactive ion gas 28 is introduced into the vacuum chamber 21 by opening the valve 26. By measuring the inflow amount of the reactive ion gas 28 with the flow meter 27 and controlling the opening / closing of the valve 26, the inside of the vacuum chamber 21 is 15 to
The gas pressure is set to 30 Pa (1 Pascal = 1/133 Torr). A mixed gas of a halogenated gas and a chlorine-based gas is used as the reactive ion gas. As the halogenated gas, CF ₄ , C ₂ F ₆ , C ₃ F ₈ , CHF ₃ , SF ₆ or the like can be used. In addition, as chlorine-based gas, CF ₃ Cl, CF ₂ Cl ₂ , CFC
l ₃ , Cl ₂ , SiCl ₄ , BCl ₃ , HCl, CCl ₄ or the like can be used. A typical combination is SF ₆ + CFCl ₃ .

When the reactive ion etching is performed under the above conditions, the sputtering effect of the reactive ions acts on the intermediate connection film 15 and the gold bumps 16b, and the anisotropic etching progresses. In this case, the thickness of the gold bumps 16b is extremely larger than that of the intermediate connection film 15, so that the intermediate connection film 15 is completely removed, but all the bumps 16b are fine, but due to the spattering on the surface of the head. A relatively deep V-shaped groove is formed.

FIG. 6 is a photomicrograph of the gold bump 16b in a state when the gold bump 16b is formed by plating, that is, in the state of FIGS. 2 (C) to (E). Fine irregularities are also observed on the surface of the head of the gold bump 16b in FIG. However, on the surface of the head of the gold bump 16b in this state, a minute convex portion in which the tip side is raised in a spherical shape is formed. Further, FIG. 7 shows the state of the gold bump 16 after the reactive ion etching, that is, the state shown in FIG.
It is a micrograph of b. On the surface of the head of the gold bump 16b in this state, a minute ridge having a sharp tip is observed.

By comparing the two in this way, it is recognized that the structure of the head surface of the gold bump 16b is completely different before and after the reactive ion etching treatment is performed.

Next, with reference to FIG. 4 and FIG. 5, a case where finger leads are connected to the bump electrodes of the semiconductor device configured as described above will be described.

First, the silicon wafer 10 is cut by dicing and separated into a plurality of semiconductor chips 30. A large number of the above-mentioned external electrodes 16 are arranged on one of the semiconductor chips 30. For the finger lead 41, tape the copper foil to the carrier.
After being laminated on 40, it is formed into a predetermined shape by etching, and solder 42 is plated on each finger lead 41. One end of each finger lead 41 projects into a square hole 43 formed in the center of the tape carrier 40, and each projecting end portion is arranged corresponding to each external electrode 16 of the semiconductor chip 30. In this case, the solder 42 that is plated on the surface of the finger lead 41 contains tin (Sn) and lead (Pb) 8:
It is composed of about 2 alloys and its thickness is about 0.2 to 0.6 μm.

When the finger leads 41 are connected to the external electrodes 16 of the semiconductor chip 30, the finger leads 41 are associated with the external electrodes 16 and thermocompression bonded. The conditions of this thermocompression bonding are as follows: the temperature is 200-400 ℃, the crimping force is 30-360g / mm ² , and the time is 1
~ 5 seconds. In this way, the finger lead is attached to the external electrode 16.
When 41 is thermocompression bonded, gold bump 16b and finger lead 41
Solder 42 on the surface of is subjected to Au-Sn eutectic bonding.

Moreover, the gold bump 16b has a fine V-shaped groove 17 formed therein, and the solder 42 bites into the V-shaped groove 17,
An anchor effect of the solder on the rough surface of the gold bump is obtained, and highly reliable bonding is achieved. In the examples, the gold thin film
The reason why wet etching is used for 16a is to collect the gold removed by etching and reuse it.
As with the under bump layer, it is naturally possible to remove this etching simultaneously by reactive ion etching.

〔The invention's effect〕

As described in detail above, according to the method of the present invention,
A bump electrode having a thickness of 10 μm or more that does not protrude from the upper surface of the photoresist can be formed on the under bump layer in the opening facing the electrode pad of the photoresist. Since it is as thick as 10 μm or more, it can be directly bonded to the connection terminal, and since it is a thickness that does not protrude from the upper surface of the photoresist, it does not grow in the direction of the adjacent bump electrode when formed by plating. It can be formed with a fine pitch. Further, since the V-shaped groove is erased on the surface of the bump electrode by the reactive ion etching, the contacting oil agent such as solder for joining the bump electrode and the connected terminal is formed in the V-shaped groove of the bump electrode. It is filled so as to bite in, and has the effect of increasing the bonding strength.

[Brief description of drawings]

1 to 7 show an embodiment of the present invention, FIG. 1 is an enlarged sectional view showing a bump electrode structure, and FIG.
(E) is an enlarged cross-sectional view showing each forming step, FIG. 3 is a cross-sectional view of an etching device used for forming the bump electrode of the present invention, and FIG. 4 is a plan view of a semiconductor chip mounted on a tape carrier. 5 and 5 are enlarged cross-sectional views showing a state in which finger leads are bonded to the bump electrodes shown in FIG. 1,
Fig. 6 is a micrograph of the grain structure of the bump electrode before reactive ion etching, Fig. 7 is a micrograph of the grain structure of the bump electrode after reactive ion etching treatment, and Fig. 8 is an enlargement of the conventional bump electrode structure. A sectional view is shown. 10 ... Silicon wafer, 13 ... Electrode pad, 15 ... Under bump layer, 16 ... Bump electrode, 17 ... V-shaped groove, 20 ...
… Reactive ion etching equipment, 28 …… Reactive ion gas, 41 …… Fingerlead, 42 …… Solder.

Claims (1)

[Claims] 1. An under-bump layer is formed on an electrode pad, a photoresist having a thickness thicker than a bump electrode to be formed on the under-bump layer is formed, and an opening is formed in a portion of the photoresist facing the electrode pad. A bump electrode is formed on the under-bump layer in the opening so as to have a thickness of 10 μm or more and does not protrude from the upper surface of the photoresist, and V-shaped is formed on the surface of the bump electrode by reactive ion etching. A method for forming an electrode of a semiconductor device, which comprises forming a groove.