JPH05235102A - Semiconductor device - Google Patents

Abstract

(57) [Summary] (Modified) [Purpose] A bump connecting portion of a semiconductor device is composed of a first material having a high melting point and a high melting point and a high melting point, and a second material having a low melting point. A semiconductor device having excellent heat dissipation and electrical conductivity and high reliability against thermal stress, and a method for manufacturing the same are realized. In a semiconductor device in which a semiconductor element 1 is connected face down, a mushroom type metal having a flattened portion in contact with an electrode 9 of a wiring board 8 having excellent thermal conductivity and electric conductivity, centering on a mushroom type metal A bump structure in which the periphery of metal is covered with a metal material having a low melting point is formed. [Effect] It becomes possible to obtain a semiconductor device which has excellent heat dissipation, high connection strength, high reliability of heat stress and humidity resistance and which can be thinned by a simple method.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor device, and more particularly to a semiconductor device having a structure in which semiconductor elements having mushroom structure bumps are connected face down on a substrate.

[0002]

2. Description of the Related Art In recent years, semiconductor devices have been highly integrated, and there is a demand for high-density mounting of the semiconductor devices, and a flip-chip connection method has recently been mainly used.

In order to enable this flip chip connection method, bumps having a protrusion shape are formed on the bonding pads of the semiconductor element. Various methods have been proposed for this bump forming method, and details are given in "Semiconductor Packaging Handbook" Science Forum pp131. For example, as shown in FIG. 4, there is one in which a barrier metal 4 is formed on a bonding pad 5 of a semiconductor element 1 and solder is formed thereon by electroplating, which is generally called a mushroom bump. Further, as shown in FIG. 5, a barrier metal 4 is formed on the bonding pad 5 of the semiconductor element 1, and a bump is vertically formed by electroplating or the like using a thick film resist having an opening in the bonding pad portion. Yes, it is generally called a straight wall bump. In FIGS. 4 and 5, 6 indicates a passivation film.

In the flip-chip connection, the bump and the terminal electrode of the substrate are aligned with each other, then mounted and reflowed for connection. FIG. 6 shows a cross-sectional structure of a connecting portion between a semiconductor chip and a circuit board when mounted by such a method. In many cases, soldering is performed either by pre-forming on the bumps or by supplying in the form of preliminary soldering on the wiring board, or by a combination of both. In flip-chip mounting, a method of installing a resin between the semiconductor element and the wiring board is generally used to prevent stress generated due to the difference in thermal expansion coefficient between the semiconductor element 1 and the wiring board 8 from concentrating on the bump. Has been done. It is not always sufficient to reduce the failures due to thermal expansion to some extent by installing this resin. In particular, when the semiconductor element and the wiring board have large thermal expansion coefficients, stress concentrates on the interface between the board and the resin, and the bump is broken. Since the bumps make electrical connection and mechanical connection at the same time, when they are destroyed, the electrical characteristics are immediately affected and the semiconductor device fails. Therefore, attempts have been made to bring the thermal expansion coefficient of the wiring substrate close to that of silicon, which is the base material of the semiconductor element.

For example, COW using silicon for the substrate
(Chip On Wafer) has been proposed,
In manufacturing the substrate, a complicated process equivalent to or more than that of the semiconductor element is required, and the cost becomes extremely high. On the other hand, in order to solve the breakage failure at the bump bonding portion due to the thermal stress, the bump structure is made to have a structure resistant to the thermal stress.

[0006] For example, IEICE Technical Report C
As shown in PM-19 to 24 (1987), the bumps are laminated by sandwiching a polyimide tape for the purpose of mitigating thermal stress, but this method may be done by making a so-called bump sheet separately. , The formation method is complicated,
This is a costly method.

Further, a failure due to thermal stress occurs in the vicinity of the interface of the bump contacting the semiconductor device, and therefore, a method of making the bump shape into a staggered shape in consideration of the connection method has also been proposed.

In this method, when a semiconductor element having bumps is connected, the bumps are melted, and the distance between the bumps and the semiconductor element once connected is increased to form a continuous type. This method has a problem that if the distance to be separated is not sufficiently calculated, connection failure may occur and shape control cannot be sufficiently performed.

Further, since the flip-chip connection is face-down mounting, the heat generation surface of the semiconductor element faces the wiring board, and the generated heat amount is likely to be accumulated in the semiconductor chip, and the accumulated heat amount causes failure of the semiconductor element. cause. In particular, when resin was sealed between the semiconductor element and the wiring board, the effect of heat storage was remarkable. Therefore, as a method of radiating the amount of heat generated, a method of providing a radiation fin has been considered, but there is a problem that it is not practical for a device that requires thinning.

Therefore, as shown in FIG. 7, there is a structure in which the metal 3 having a good thermal conductivity such as Cu is centered and the periphery thereof is covered with the solder 2. However, when this method is used, a certain heat dissipation effect can be expected. However, because the Cu formation method is complicated or uneven, solder remains between the Cu and the electrode surface,
There is a problem that the connection strength decreases, and it was not always sufficient for equipment that requires high reliability. Note that FIG.
The numbers in 7 indicate the same as those in FIGS.

[0011]

When the semiconductor element having the bumps formed on the bonding pads is mounted as described above, the bumps are exposed to the thermal stress due to the difference in the thermal expansion coefficient between the wiring board and the semiconductor element. There was a problem that breakage occurred. Therefore, there is COW in which a semiconductor element is mounted on a silicon wafer as one of attempts to make the coefficient of thermal expansion of the wiring board equal to that of the semiconductor element, but a very expensive process is required in manufacturing. .. On the other hand, a structure that relieves the stress applied to the bumps is used, such as using a polyimide tape on which the bumps are formed, and forming the bumps in multiple stages or making the bumps into a staggered type by controlling the mounting process. Even in such a case, although a strict control on bump fabrication is required, a connection failure may occur, which is not always a sufficient method. Further, the heat dissipation method of flip chip connection can be solved to some extent by attaching a heat dissipation fin to the back surface of the chip, but it is not practical for thinning.

There is also a method of embedding a metal having a high heat conductivity coefficient as a heat radiation path through the bumps, but it is difficult to form a straight shape metal, or solder remains between the electrode and the metal having a high heat conductivity coefficient. In addition, the connection resistance increased and the connection strength decreased.

The present invention has been made in view of the above problems, and in a semiconductor device in which a semiconductor element is mounted on a wiring board having a thermal expansion coefficient different from that of the semiconductor element, a mounting step or a post-mounting step is performed. Provided is a semiconductor device having a face-down structure having bumps which are excellent in heat dissipation structure and can be connected with a low contact resistance without causing breakage of a semiconductor element at a bump portion due to thermal stress.

[0014]

The present invention relates to a semiconductor device in which a semiconductor element having a mushroom structure bump formed of a metal or an alloy thereof on a bonding pad is connected to a terminal electrode on a wiring board in a face-down structure,
The bonding pad of the semiconductor element and the terminal electrode on the wiring board are electrically connected by the first metal or its alloy forming the bump, and the periphery of the first metal or its alloy is the second metal or its alloy. A portion of the first metal or its alloy that is in contact with the terminal electrode on the wiring board has a mushroom structure in which an area narrower than the pillar of the bump is flattened. It is a semiconductor device characterized by the above.

As the first metal or alloy having a mushroom structure, it is preferable to use a material having a smaller electric resistance, a larger thermal conductivity coefficient and a higher melting point than those of the second metal or alloy. The first metal or alloy contains Cu, Al, Ti, Pd, Ni, etc., and the second metal or alloy contains Pb, Sn, I.
It is preferable to use those containing n, Sb and the like.

Further, the formation amount of the second metal or its alloy is at least the amount below the space under the mushroom where the first metal or its alloy is formed, and the space between the semiconductor element and the wiring board. It is preferable to have a structure in which an insulating resin is permeated and hardened to seal. Further, as a method of manufacturing a semiconductor device according to the present invention, for example,
A resist film is formed on a semiconductor element, a first opening is formed in a portion of the resist where the first metal or an alloy thereof is formed, and a first metal having a mushroom structure or the first opening is formed in the opening. Forming an alloy, forming a second metal or an alloy thereof continuously after forming the first metal or an alloy thereof, removing the resist, and removing a flat portion of the first metal or a mushroom alloy thereof. After being aligned so as to correspond to the electrodes of the wiring board, the bumps are higher than the melting point of the second metal or alloy thereof,
The first metal or its alloy is heated at a temperature lower than the melting point of the first metal or its alloy to melt the second metal or its alloy, and the flattened portion of the first metal or its alloy having a mushroom structure is connected to the wiring. There may be mentioned a method of connecting the electrodes corresponding to the electrodes on the substrate.

[0017]

According to the present invention, since the metal or its alloy having a mushroom structure has a structure in which the portion of the wiring board that contacts the terminal electrode is flattened, the heat dissipation path can be made large. The heat dissipation characteristics can be significantly improved as compared with the above, and the second metal or alloy wraps around in the space under the mushrooms to bond with the bonding pad of the semiconductor element or the barrier metal provided on the bonding pad. Is extremely high. The area of the flat portion is made narrower than the pillar of the mushroom structure because of the ease of the manufacturing process and the contact with the terminal electrodes of the wiring board. Further, when the thermal conductivity coefficient of the first metal or alloy is made larger than that of the second metal or alloy, the bonding pad of the semiconductor element and the terminal electrode of the wiring board are made by the first metal or alloy having a high thermal conductivity coefficient. Is connected to the second
Since they are connected by the shape covered with the metal or alloy, the heat generated from the semiconductor element is radiated to the wiring board by the first metal or alloy having a high thermal conductivity coefficient, and the amount of heat is accumulated in the chip. In addition, flip-chip connection can be performed without further attaching a heat radiation fin, failure of the semiconductor element due to heat accumulation can be prevented, and thinning is possible. In addition, the bumps are formed in order to melt the second metal or its alloy by heating it at a temperature higher than the melting point of the second metal or its alloy and lower than the melting point of the first metal or its alloy. The first metal or its alloy is not melted but the first metal or its alloy is melted. Therefore, the structure in which the portion of the first metal or its alloy that contacts the wiring board is flattened is maintained
Since the metal or the alloy thereof is melted, a necessary amount of space can be easily maintained between the semiconductor element and the wiring board, and a bump structure excellent in heat dissipation and reliability can be easily realized.

Further, since the periphery of the first metal having a mushroom structure made of Cu, for example, is covered with the second alloy made of solder, even if a brittle intermetallic compound is formed at the interface, the mushroom is mushroomed. The umbrella portion of the can play a role of “grabbing” and prevent a decrease in connection strength. Furthermore, the first metal or its alloy that plays a role of electrical connection and heat dissipation can be prevented from being corroded by the external atmosphere.

As described above, according to the present invention, a semiconductor device for flip-chip connecting chips having bumps formed on bonding pads is thin, has excellent heat dissipation, and has a structure with a low connection resistance that is strong against thermal stress. Is possible
It is possible to realize a semiconductor device having excellent connection reliability.

[0020]

Embodiments of the present invention will be described below with reference to FIGS. 1, 2 and 3.

FIG. 1 is an embodiment showing a semiconductor device according to the present invention, FIG. 2 is a sectional structure showing a bump structure provided in a semiconductor element according to the present invention, and FIG. 3 is a semiconductor shown in FIG. It is process sectional drawing for implement | achieving an apparatus. Figure 1,
2 and 3, 1 is a semiconductor element, 2 is, for example, Pb
/ Sn = 40/60 second metal or alloy made of eutectic solder, 3 first metal or alloy made of Cu, for example, 4 barrier metal, 5 bonding pad, 6 passivation film, 7 second The bumps made of the first and second metals or alloys, 8 is a wiring board, and 9 is a terminal electrode.

Next, an embodiment of a method of manufacturing the semiconductor device having the above bump will be described with reference to FIG. First, in FIG. 3, the barrier metal 4 is formed on the wafer in which the bonding pad 5 is formed on the semiconductor element 1 and the passivation film 6 is formed except for the bonding pad portion.
As an example, a Ti / Cu laminated body is vapor-deposited on the entire surface. (Fig. 3-a)

Next, a thick film resist AZ4903 (Hoechst Japan) is spin-coated to form a resist 31 having a film thickness of 5 μm, and an opening having a dimension of 70 μm, which is smaller than the bonding pad 100 μm on one side by 30 μm, is formed by exposure and development. Is formed on the resist. (Fig. 3-b)

Thus, the wafer in which the resist is opened in a size smaller than that of the bonding pad corresponding to the bonding pad is immersed in a solution of copper sulfate 250 g / l and sulfuric acid (specific gravity 1.84) 50 g / l, At a bath temperature of 25 ° C., the above Ti / Cu was used as a cathode, a high-purity copper plate was used as an anode, and a current density was 5 A / dm ^2. Copper isotropically plated with a height of 30 μm and a lateral direction of 30 μm while applying and gently stirring to form a first metal or alloy 3 having a mushroom structure having a flat portion on the top. (Fig. 3-c)

Next, the plating bath was set to 40 g / l of total tin, the first
Tin 35g / l, Lead 44g / l, Free boric acid 40g /
l, boric acid 25 g / l, glue 3.0 g / l, instead of Ti / Cu as the cathode,
Current density of 3.2 A / dm ² with 40% tin as anode Pb / Sn =
40/60 alloy isotropically, height 35μm, lateral direction 3
5 μm continuous plating was performed to form solder as the second metal or alloy 2. (Fig. 3-d)

The copper and solder (Pb / Sn alloy) as bumps thus formed are removed from the wafer provided on the surface of the barrier metal 4 on the bonding pad by using acetone to remove the plating resist AZ-4903. (Fig. 3
-E)

The positive resist OFPR-800 (Tokyo Ohka Kogyo Co., Ltd.) is coated again, and the resist is patterned using solder / Cu and a bump of 200 μmφ as a mask. Using the patterned resist as a mask, first, Cu in the barrier metal 4 is etched with a mixed solution of ammonium persulfate, sulfuric acid and ethanol, and then the barrier metal 4 is treated with a solution of EDTA, ammonia and hydrogen peroxide solution.
After the Ti in the inside is etched to pattern the entire barrier metal, the resist is removed with acetone. (Figure 3-
f)

By performing the above steps, a bump having the structure shown in FIG. 2 can be obtained. A method of connecting the semiconductor element having the bumps made of the first metal or alloy and the second metal or alloy having the mushroom structure thus manufactured to the wiring board will be described below.

In this method, the semiconductor element is kept face down relative to the wiring board, and the bumps of the semiconductor element and the terminal electrodes of the wiring board are aligned by a known method using a half mirror. The bumps of the semiconductor element and the terminal electrodes 9 made of thick film wiring of the alumina substrate 8 are brought into contact with each other via the barrier metal 4. (Fig. 3-g)

At this time, the wiring substrate is held on a stage having a heating mechanism and preheated to 280 ° C., which is higher than the melting point of the eutectic solder formed on the bumps and lower than the melting point of Cu.

The collet holding the chip in a state where the bump of the semiconductor element is in contact with the terminal electrode of the wiring board is heated in a nitrogen atmosphere at the same temperature as the stage on which the wiring board is mounted, 280 ° C., to form the bump. It is electrically connected to the semiconductor element by melting the solder. (Fig. 3-h)

At this time, Cu / T which becomes the barrier metal 4
Since i is larger than the Cu core by the solder coating area, the contact angle between the second metal or alloy and the bonding pad is about 60 °, and the bump shape has a structure resistant to thermal stress. When the contact angle with the bonding pad is less than 90 °, a highly reliable connection with respect to thermal stress can be obtained. Then, a silicon resin or the like is filled in a gap between the semiconductor element and the wiring board so as to cover the semiconductor element, thereby forming a semiconductor device.

When the thermal resistance value of the semiconductor device having the bump structure shown above was evaluated, when mounted on an alumina substrate, a 5 mm chip was naturally cooled to 20.
The value of ° C / W was obtained. For comparison, in the case of a semiconductor device having only solder bumps not centered on Cu,
The value of 0 ° C./W is shown, and the heat dissipation characteristics are improved by a factor of two.

Further, in order to improve the thermal resistance value of the semiconductor device having only the bumps of solder to 20 ° C./W, the same effect can be obtained unless the heat radiation fin having five fins is provided on the back surface of the chip. However, the thickness could be reduced to 1/10 when the thermal resistance values were made equal. Further, the connection resistance between the bump and the terminal electrode of the wiring board was 0.005 Ω / pad, which was able to be reduced to about 1/2 of that in the conventional method shown in FIGS. 6 and 7.

Further, the connection structure of FIG. 1 is placed on an alumina substrate 6.0 to 6.5 × 10 ⁻⁶ / ° C., which has a thermal expansion coefficient about twice that of silicon (semiconductor element), 3.5 × 10 ⁻⁶ / ° C. As a result of flip-chip connection with, the contact angle between the bump and pad becomes 60 ° on both the semiconductor device side and the substrate side, and a temperature cycle test (-55 ° C (30 min) to 25 ° C (5 min) to 1
300 at 50 ° C (30 min) to 25 ° C (5 min))
No fracture was observed at the connection point even after 0 cycles. Further, the semiconductor device according to the present invention was flip-chip connected to a wiring board, and a high temperature and high humidity storage test was conducted.
No failure was recognized up to H. Further, when a resin was sealed between the semiconductor element and the wiring board, no failure was observed up to 5000H.

Therefore, from the above results, the reliability of the semiconductor device according to the present invention was sufficient. The present invention is not limited to the above-mentioned embodiments, and various modifications can be made without departing from the scope of the invention.

For example, alloys having different melting points to form are C
Not limited to u and Pb / Sn, In, Sb, etc. may be added to the second metal or its alloy, or may be an alloy containing these as the main components. Further, its thickness is not limited.

Further, the size, thickness and constitution of the barrier metal which becomes the cathode at the time of plating shown in the examples are not limited, and the resist is not limited either.

The method of forming the bumps is also not limited to electroplating, and the first metal or its alloy may be subjected to a flattening treatment after the formation of the bumps, or electroless plating may be used. The method for forming the metal is not limited. Further, in the embodiments, the case of mounting on a wiring board made of alumina is described, but the board may be made of silicon and the material thereof is not limited.

[0040]

According to the present invention, the first metal or its alloy having a mushroom structure has a structure in which the portion of the wiring board that contacts the terminal electrodes is flattened, so that the heat dissipation path is enlarged. Therefore, the heat dissipation characteristics can be remarkably improved, and the contact resistance can be made extremely small.

Further, since the periphery of the first metal or its alloy having a mushroom structure is covered with the second metal, even if a brittle intermetallic compound is formed near the interface, the mushroom umbrella The part plays the role of "hooking" and can prevent the decrease in connection strength.

Furthermore, since the second metal or its alloy covers the circumference of the first metal or its alloy that plays a role of electrical connection and heat dissipation, the first metal or its alloy is corroded by the external atmosphere. Can be prevented.

Further, when a material having a larger heat conductivity coefficient than the second metal or alloy is used as the first metal or alloy, the bonding pad of the semiconductor element and the substrate are formed by the first metal or alloy having a higher heat conductivity coefficient. Since the electrode is connected and the periphery thereof is connected by the shape covered with the second metal or alloy, the heat generated from the semiconductor element is applied to the substrate by the first metal or alloy having a high thermal conductivity coefficient. The chip is not radiated and the amount of heat is not accumulated in the chip, and the flip-chip connection can be performed without attaching the radiating fin, and the failure of the semiconductor element due to the accumulated heat can be prevented and the thickness can be reduced.

When a material having a melting point higher than that of the second metal or alloy is used as the first metal or alloy,
In addition, the bumps are formed in order to melt the second metal or its alloy by heating it at a temperature higher than the melting point of the second metal or its alloy and lower than the melting point of the first metal or its alloy. Metal or its alloy melts, but
The metal or its alloy is not melted. Therefore, the first
Since the second metal or its alloy is melted while maintaining the structure in which the portion of the metal or its alloy that comes into contact with the wiring substrate is flattened, a necessary amount of space can be easily formed between the semiconductor element and the wiring substrate. It can be maintained and heat dissipation and reliability are improved.

[Brief description of drawings]

FIG. 1 is a schematic view of a bump portion of a semiconductor device according to the present invention.
Sectional drawing which shows an Example.

FIG. 2 is a sectional view of a bump portion of a semiconductor device according to the present invention.

3A to 3D are process cross-sectional views for explaining the method for manufacturing the semiconductor device shown in FIG.

FIG. 4 is a bump cross-sectional view for explaining a conventional technique.

FIG. 5 is a bump cross-sectional view for explaining a conventional technique.

FIG. 6 is a bump cross-sectional view for explaining a conventional technique.

FIG. 7 is a bump cross-sectional view for explaining a conventional technique.

[Explanation of symbols]

 1 Semiconductor Element 2 Solder 3 Cu 4 Barrier Metal 5 Bonding Pad 6 Passivation Film 7 Bump 8 Wiring Board 9 Terminal Electrode 31 Plating Resist

Claims (1)

[Claims] 1. A semiconductor device in which a semiconductor element having a mushroom structure bump formed of a metal or an alloy thereof on a bonding pad is connected to a terminal electrode on a wiring board in a face-down structure. Is electrically connected to the terminal electrode of the first metal or an alloy thereof forming the bump, and the periphery of the first metal or an alloy thereof is formed to be covered with a second metal or an alloy thereof, and And a portion of the first metal or alloy thereof in contact with the terminal electrode on the wiring substrate has a mushroom structure in which an area narrower than a pillar portion of the bump is flattened. ..