JP3171477B2 - Semiconductor device - Google Patents

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 a semiconductor element having a mushroom structure bump is connected face-down on a substrate.

[0002]

2. Description of the Related Art In recent years, there has been a trend toward higher integration of semiconductor devices, and there has been a demand for mounting the semiconductor devices at high density. Recently, flip-chip connection methods have been mainly used.

In order to enable this flip chip connection method, bumps having a protruding shape are formed on bonding pads of a semiconductor element. Various methods have been proposed for this bump formation method, which are described in detail in "Semiconductor Packaging Handbook" Science Forum pp131. For example, as shown in FIG. 4, there is a type in which a barrier metal 4 is formed on a bonding pad 5 of a semiconductor element 1 and a 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 a bonding pad 5 of the semiconductor element 1, and a bump is formed vertically 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. 4 and 5, reference numeral 6 denotes a passivation film.

[0004] In flip-chip connection, after the positions of the bumps and the terminal electrodes of the substrate are aligned, mounting is performed and reflow is performed to perform connection. FIG. 6 shows a cross-sectional structure of a connection portion between the semiconductor chip and the circuit board when mounted by such a method. In many cases, soldering is performed either in advance of forming on bumps or in the form of preliminary soldering on a wiring board, or in a combination of both. In flip-chip mounting, generally, a method of installing a resin between the semiconductor element and the wiring board in order to prevent stress generated from a difference in thermal expansion coefficient between the semiconductor element 1 and the wiring board 8 from being concentrated on the bumps. Is being done. It is not always sufficient to install this resin to reduce the number of failures due to thermal expansion to some extent. In particular, when the thermal expansion coefficients of the semiconductor element and the wiring board are significantly different, stress concentrates on the interface between the board and the resin, and the bump is broken. Since these bumps perform electrical connection and mechanical connection at the same time, breaking them immediately affects the electrical characteristics and causes a failure of the semiconductor device. Attempts have been made to make the thermal expansion coefficient of the wiring board close to that of silicon as the base material of the semiconductor element.

[0005] For example, COW using silicon for a substrate
(Chip On Wafer) has been proposed,
In manufacturing the substrate, a complicated process equivalent to or more than that of a semiconductor element is required, and the cost becomes extremely high. On the other hand, in order to solve a breaking failure at a bump bonding portion due to thermal stress, a bump structure having a structure resistant to thermal stress has been used.

For example, IEICE technical report C
As shown in PM-19 to 24 (1987), for the purpose of relieving thermal stress, bumps are laminated with a polyimide tape interposed therebetween. In this method, a bump sheet is separately formed. , The formation method is complicated,
It is a costly method.

[0007] In addition, since fracture failure due to thermal stress occurs near the interface of the bump in contact with the semiconductor device, a method has been proposed in which the bump shape is concavo-convex in consideration of the connection method.

According to this method, when a semiconductor element having a bump is connected, the bump is melted so that the distance from 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, poor connection may occur and shape control may not be sufficiently performed.

Further, since the flip-chip connection is a face-down mounting, the heat generation surface of the semiconductor element faces the wiring board, and the amount of heat generated easily accumulates in the semiconductor chip. cause. In particular, when resin was sealed between the semiconductor element and the wiring board, the effect of heat storage was significant. For this reason, as a method of dissipating the heat generated, a method of providing a radiating fin has been considered, but there is a problem that it is not practical for a device requiring a reduction in thickness.

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

[0011]

As described above, when a semiconductor device having a bump formed on a bonding pad is mounted, the bump portion is formed at a bump portion due to a thermal stress caused by a difference in thermal expansion coefficient between the wiring board and the semiconductor device. There was a problem that breakage occurred. Therefore, as one of attempts to make the thermal expansion coefficient of the wiring substrate equal to the thermal expansion coefficient of the semiconductor element, there is COW in which the semiconductor element is mounted on a silicon wafer, but a very expensive process is required in manufacturing. . On the other hand, using a polyimide tape on which bumps are formed, a structure that relieves stress applied to the bumps is used, such as using bumps in multiple stages or forming bumps in a continuous shape by controlling the mounting process. Even in such a case, although strict control is required in the production of bumps, a connection failure occurs and the method is not always sufficient. 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 thermal conductivity as a heat radiating path through the bump. However, it is difficult to form a straight-shaped one or solder remains between the electrode and the metal having a high thermal conductivity. In addition, the connection resistance increases and the connection strength decreases.

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

[0014]

According to the present invention, there is provided 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 a first metal or an alloy thereof constituting the bump, and the periphery of the first metal or the alloy thereof is a second metal or an alloy thereof. A portion of the first metal or its alloy that is in contact with the terminal electrode on the wiring substrate has a mushroom structure in which an area smaller than a pillar of the bump is flattened. A semiconductor device.

As the first metal or alloy having a mushroom structure, it is preferable to use a material having a lower electric resistance, a larger heat conduction coefficient and a higher melting point than the second metal or alloy. As the first metal or alloy, one containing Cu, Al, Ti, Pd, Ni, or the like, and as the second metal or alloy, Pb, Sn, I
It is preferable to use one containing n, Sb, or the like.

Further, the formation amount of the second metal or the alloy thereof is at least equal to or larger than the gap under the mushroom where the first metal or the alloy thereof is formed, and the gap between the semiconductor element and the wiring board is formed. It is preferable to adopt a structure in which an insulating resin is penetrated and hardened for sealing. 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 a first metal having a mushroom structure is formed in the opening. An alloy is formed, a second metal or an alloy thereof is continuously formed after the formation of the first metal or the alloy thereof, the resist is removed, and a flat portion of the first metal or the mushroom alloy thereof is removed. After alignment to correspond to the electrode of the wiring board, higher than the melting point of the second metal or the alloy thereof of the bump,
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 the mushroom structure is connected to the wiring A method of making connection corresponding to the electrode of the substrate can be given.

[0017]

According to the present invention, a metal having a mushroom structure or an alloy thereof has a structure in which a portion in contact with a terminal electrode of a wiring board is flattened, so that a heat radiation path can be enlarged. The heat dissipation characteristics can be significantly improved as compared with the above, and the second metal or alloy wraps around the gap below the mushroom, and the bonding strength with the bonding pad of the semiconductor element or the barrier metal provided thereon is increased. Becomes extremely high. The reason why the area of the flat portion is made smaller than that of the mushroom structure is due to easiness in a manufacturing process and easiness of contact with a terminal electrode of a wiring board. Further, when the thermal conductivity of the first metal or alloy is 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 formed by the first metal or alloy having a high thermal conductivity. Is connected and the surrounding area is
Is connected by the shape covered by the metal or alloy, heat generated from the semiconductor element is radiated to the wiring board by the first metal or alloy having a high heat conduction coefficient, and heat is accumulated in the chip. Flip-chip connection can be performed without attaching a heat radiation fin, and failure of a semiconductor element due to heat storage can be prevented, and thinning can be achieved. In addition, the second metal or the alloy thereof is heated at a temperature higher than the melting point of the first metal or the alloy and lower than the melting point of the first metal or the alloy to melt the second metal or the alloy thereof. The metal or its alloy melts, but the first metal or its alloy does not. Therefore, the second metal or the alloy of the second metal can be maintained in a flat structure at a portion in contact with the wiring board.
Since the metal or its alloy is melted, a required amount of gap 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 is covered with the second alloy made of solder, even if a brittle intermetallic compound is formed at the interface, the mushroom is formed. The umbrella portion plays a role of "trapping", thereby preventing a decrease in connection strength. Further, the first metal or its alloy that plays a role of electrical connection and heat dissipation can be prevented from being corroded by an external atmosphere.

As described above, according to the present invention, a semiconductor device that is flip-chip connected to a chip having a bump formed on a bonding pad and has a thin structure, excellent heat dissipation, and a low connection resistance that is strong against thermal stress. Becomes possible,
A semiconductor device with excellent connection reliability can be realized.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS.

FIG. 1 shows one embodiment of a semiconductor device according to the present invention, FIG. 2 shows a cross-sectional structure showing a bump structure provided on a semiconductor element according to the present invention, and FIG. 3 shows the semiconductor device shown in FIG. It is a process sectional view for realizing a device. Figure 1,
2 and 3, reference numeral 1 denotes a semiconductor element, and 2 denotes, for example, Pb.
/ Sn = 40/60 eutectic solder, second metal or alloy, 3 is, for example, first metal or alloy made of Cu, 4 is barrier metal, 5 is bonding pad, 6 is passivation film, 7 is Bumps made of 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 a semiconductor device having the above bumps will be described with reference to FIG. First, in FIG. 3, a barrier metal 4 is formed on a wafer on which a bonding pad 5 is formed on a semiconductor element 1 and a passivation film 6 is formed except for a part of the bonding pad.
For example, a Ti / Cu laminated body is entirely deposited. (Fig. 3-a)

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

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

Next, the plating bath was changed to a total tin of 40 g / l,
Tin 35 g / l, lead 44 g / l, free boric acid 40 g /
l, boric acid 25 g / l, and glue 3.0 g / l, and Ti / Cu was used as a cathode in the same manner as in the previous case.
Current density 3.2 A / dm ² with 40% tin as anode Pb / Sn =
40/60 alloy isotropically 35 μm high, 3 lateral directions
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 formed in this manner remove the plating resist AZ-4903 from the wafer provided on the surface of the barrier metal 4 on the bonding pad with acetone. (FIG. 3
-E)

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

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

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

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

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

At this time, Cu / T serving as barrier metal 4 is used.
Since i is larger than the Cu core by the solder covering 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. If the contact angle with the bonding pad is less than 90 °, a highly reliable connection can be obtained against thermal stress. Next, a semiconductor device is formed by filling a gap between the semiconductor element and the wiring board with silicon resin or the like so as to cover the semiconductor element.

The thermal resistance of the semiconductor device having the bump structure described above was evaluated.
C / W values were obtained. For comparison, in a semiconductor device having only solder bumps without Cu as the center, 4
The value of 0 ° C./W was shown, and the heat radiation characteristic was improved by a factor of two.

Furthermore, in order to improve the thermal resistance of a semiconductor device having only solder bumps to 20 ° C./W, the same effect can be obtained unless a heat radiation fin having five fins is provided on the back surface of the chip. When the thermal resistance was made equal, the thickness could be reduced to 1/10. The connection resistance between the bump and the terminal electrode of the wiring board was 0.005 Ω / pad, which was reduced to about １ ／ as compared with the conventional method shown in FIGS.

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

Accordingly, 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 embodiment, but can be variously modified without departing from the gist thereof.

For example, an alloy having a different melting point to be formed is C
It is not limited to u and Pb / Sn, but for example, In, Sb, etc. may be added to the second metal or its alloy, or an alloy containing these as a main component may be used. Further, the thickness is not limited.

Further, the dimensions, thickness and configuration of the barrier metal serving as the cathode during plating shown in the examples are not limited, and the resist is not limited either.

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

[0040]

According to the present invention, the first metal having a mushroom structure or its alloy has a structure in which the portion of the wiring board in contact with the terminal electrode is flattened, thereby increasing the heat radiation path. The heat dissipation characteristics can be significantly improved, and the contact resistance can be extremely reduced.

Further, since the periphery of the first metal or the alloy thereof having the mushroom structure is covered with the second metal, even if a brittle intermetallic compound is formed near the interface, the umbrella of the mushroom is formed. The portion plays a role of “jam”, so that a decrease in connection strength can be prevented.

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

Further, when a material having a higher thermal conductivity 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 higher thermal conductivity. Since the electrodes are connected to each other and the periphery thereof is connected by a shape covered with the second metal or alloy, heat generated from the semiconductor element is generated by the first metal or alloy having a high heat conduction coefficient with respect to the substrate. Heat is dissipated, heat is not accumulated in the chip, and flip-chip connection can be made without attaching a heat radiation fin, thereby preventing failure of the semiconductor element due to heat storage and making it possible to reduce the thickness.

Further, when a material having a higher melting point than the second metal or alloy is used as the first metal or alloy,
In addition, the second metal or the alloy thereof is heated at a temperature higher than the melting point of the first metal or the alloy and lower than the melting point of the first metal or the alloy to melt the second metal or the alloy thereof. Metal or its alloy melts, but the first
Is not melted. Therefore, the first
Since the second metal or its alloy is melted while maintaining the structure where the portion of the metal or its alloy that comes into contact with the wiring substrate is flattened, a required amount of gap can be easily formed between the semiconductor element and the wiring substrate. Can be maintained and heat dissipation and reliability are improved.

[Brief description of the drawings]

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

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

FIG. 3 is a process sectional view for illustrating the method for manufacturing the semiconductor device shown in FIG.

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

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

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

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

[Explanation of symbols]

 REFERENCE SIGNS LIST 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

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H01L 21/60

Claims (1)

(57) [Claims] In 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 semiconductor element bonding pad and the wiring board The first electrode or the alloy thereof is electrically connected to the terminal electrode of the first metal or an alloy thereof, the periphery of the first metal or the alloy thereof is formed so as to be covered by the second metal or the alloy thereof, and A portion of the first metal or an alloy thereof in contact with the terminal electrode on the wiring substrate has a mushroom structure in which an area smaller than a pillar portion of the bump is flattened. .