JPH0243747A - Semiconductor device - Google Patents

Abstract

PURPOSE:To obtain a semiconductor device provided with an electrode junction structure quite high in reliability by a method wherein a metal ball bonded to a semiconductor chip electrode layer has a structure plastically deformed so that a continuously, gently changing concave surface is present at its connection with a metal wire. CONSTITUTION:This is a semiconductor device with a metal wire 2 bonded to a semiconductor chip electrode layer 8, wherein a metal ball 4 is formed at the end of the metal wire 2 and bonded to the electrode layer 8, an alloy layer 17 is formed along the boundary between the metal ball 4 and the electrode layer 8, and the metal ball 4 is so plastically deformed that there is a continuously, gently changing concave surface 15 on its connection with the metal wire 2. For example, an electrode junction of a structure described above may be embodied using a capillary chip 1 as illustrated. Such a capillary chip 1 should have, along the circumference of the opening at its end, a chamfering section 13 equipped with a convex surface continuously, gently changing from the inner wall of an insertion hole 22 toward a load plane 14.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a semiconductor device, and particularly to the shape of a bonding portion in which a metal ball at the tip of a metal wire is bonded onto an electrode layer of a semiconductor device.

[Conventional technology]

Generally, this type of bonding is performed in FIGS.
).

First, the tip of a metal wire (2) made of copper or the like that is inserted into the capillary chip (1) is heated with a torch (3) to form a metal ball (4) (Fig. 6(a)). The chip (1) is lowered and the metal ball (4) is placed on the aluminum electrode layer (8) of the semiconductor chip (7) placed on the die pad (6) of the copper lead frame (5).
) and plastically deformed (No. 611(b)). At this time, the die pad (6) is placed on the heat block (9), and the semiconductor chip (7) is deformed by the heat block (9). The capillary chip (1) is heated to a temperature of 300 to 400°C, and ultrasonic vibration is applied to the capillary chip (1) by a vibration device (not shown). As a result, both the metal elements of the metal ball (4) and the electrode layer (8) interdiffuse,
The metal ball (4) is joined to the electrode layer (8).

Next, while raising the capillary tip (1), let out the metal wire (2) from its tip (Fig. 6 (C)).
), the capillary tip (1) is lowered onto the inner lead (10) of the lead frame (5) and the metal wire (2
) onto the wire connection surface (11) of the inner lead (10) and loop the metal wire (2) as shown in FIG. 6(d). At this time, the inner lead (10) is connected to the heat block (9). Placed on top temperature 300~400℃
At the same time, ultrasonic vibration is applied to the capillary tip (1) by a vibrator M (not shown). As a result, the metal elements of the metal wire (2) and the wire connection surface (11) of the inner lead (10) are interdiffused, and the metal wire (2) and the wire connection surface (11) are bonded.

Thereafter, while fixing the metal wire (2) with the clamper (12), the capillary tip (1) is raised to cut the metal wire (2) (FIG. 6(e)).

[Problem to be solved by the invention]

Wire bonding is performed in this way, and the tip of the conventional capillary tip (1) has a conical chamfered part (13) at an angle of 45°, as shown in FIGS. 7(a) and (b). Was.

Therefore, the metal ball (4) is formed by plastically deforming the metal ball (4) using such a capillary tip (1).
) and the electrode layer (8) had a structure as shown in FIG. That is, the metal ball (4) has a conical surface (15) and a flat surface formed by applying a load to the conical chamfer (13) and flat load surface (14) of the capillary tip (1), respectively. (16), and an alloy layer (17) made of a copper-aluminum alloy is formed below the metal ball (4). Note that an electrode base layer (18) such as Si or an insulating film is formed below the electrode layer (8).

By the way, when the metal ball (4) is pressed, the metal ball (4)
The vector (19) of the load applied to (7th (see 2I) is the vector (19) of the load applied to
14), and is directed toward the vicinity of the center of the joint at the chamfer (13) and perpendicular to the plane of the electrode layer (8) at the load surface (14). Therefore, the sliding direction of the metal element such as copper forming the metal ball (4) is uniquely fixed, and the back surface of the metal ball (4) before the alloy layer (17) is formed has a
As shown in FIG. 9, a large nucleus (20) with few slip lines was formed near the center of the joint.

As a result, the alloy 1 (17) formed by mutual diffusion due to the heating energy of the bipolar layer (8) and the ultrasonic vibration energy applied to the metal ball (4) becomes non-uniform, resulting in reliability of the joint. This had the problem of causing a decline in sexual performance.

Furthermore, with the recent increase in the density of semiconductor devices, the electrode portions for bonding are inevitably becoming smaller, and therefore bonding using smaller metal balls is required. However, as shown in Fig. 7, the direction of the load vector (one) changes rapidly at the boundary (21) between the chamfer (13) and the load surface (14) of the conventional capillary tip (1). Therefore, if the size of the metal ball (4) is small, the boundary part (21
) could break through the metal ball (4) and collide with the electrode layer (8).

The present invention was made to solve these problems, and an object of the present invention is to obtain a semiconductor device having a highly reliable electrode junction structure.

[Means to solve the problem]

The semiconductor device according to the present invention includes two semiconductor chips! A semiconductor device in which a metal wire is bonded to a pole layer, the metal ball being formed at the tip of the metal wire and bonded to the electrode layer, and the metal ball being formed at the boundary between the metal ball and the electrode layer. The metal ball is plastically deformed so that a continuously smoothly changing concave curved surface is formed at the connection portion with the metal wire.

[Effect]

In this invention, since the metal ball is plastically deformed to form a continuously smoothly changing concave curved surface at the connection part with the metal wire, slippage of the tL texture of the metal ball occurs over the entire joint part. . Therefore, a uniform alloy layer is formed between the metal ball and the object to be bonded.

〔Example〕

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

FIG. 1 is a sectional view of an electrode junction of a semiconductor device according to an embodiment of the present invention. An electrode layer (8) made of aluminum or the like is formed on an electrode base layer (18) made of an insulating film such as Si.
is formed, and a metal ball (4) such as a copper ball is bonded to this electrode layer (8).

The metal ball (4) has a flat shape substantially parallel to the surface of the electrode layer (8), and its lower part is embedded in the electrode layer (8). One end of a metal wire (2) made of copper is integrally connected to the upper center of the metal ball (4), and the other end of the metal wire (2) is connected to a lead frame (not shown). . The connection part between the metal ball (4) and the metal wire (2) has a radius of curvature R whose slope changes continuously and smoothly.
A concave curved surface portion (15) is formed, and this concave curved surface portion (15)
A flat surface portion (16) is formed on the outer metal ball (4). Further, an alloy layer (1
7) is formed.

The electrode joints with this structure are shown in Figures 2 (a) and (b).
It can be formed by using a capillary chip (1) as shown in FIG. This capillary tip (1)
A flat loading surface (14) is formed at the tip of the
Further, an insertion hole (22) having a hole diameter D1 is provided in the center for inserting the metal wire (2). This insertion hole (22) is open to the load surface (14), and a chamfered portion (13) is formed at the periphery of the opening. This chamfered portion (13) has a radius of curvature R smaller than the diameter D2 of the metal wire (2) inserted into the insertion hole (22).
2) has a convex curved surface that changes continuously and smoothly from the inner wall surface toward the load surface (14).

Using such a capillary chip (1), wire bonding was performed in the same manner as the steps shown in FIGS. 6(a) to 6(e) described above.

That is, first, the insertion hole (2) of the capillary tip (1) is opened.
2) Insert the metal wire (2) into the metal wire (
2) is heated with a torch (3) to form a metal ball (4) having a diameter of 1.5 to 2.5 times the diameter D2 of the metal wire (2). lowering the chip (1) and positioning the metal ball (4) on the aluminum electrode layer (8) of the semiconductor chip (7) placed on the die pad (6) of the copper-based lead frame (5); Furthermore, the capillary tip (1) is lowered to plastically deform the metal ball (4).

At this time, the chamfered portion (13) of the capillary tip (1)
has a convex curved surface that changes continuously and smoothly with a radius of curvature R, so the load (19
) will have a continuously smoothly changing direction. Further, the dice pad (6) is placed on a heat block (9), and the semiconductor chip (7) is heated to a temperature of 300 to 400°C by this heat block (9). In this state, ultrasonic vibration is applied to the capillary chip (1) by a vibrator (not shown). As a result, the metal elements of both the metal ball (4) and the electrode layer (8) interdiffuse, and the metal ball (4) is joined to the electrode layer (8).

Next, after raising the capillary tip (1) and letting out the metal wire (2) from its tip, the capillary tip (1) is lowered onto the inner lead (1o) of the lead frame (5) and the metal wire (2) is pressed onto the wire connection surface (11) of the inner lead (10), and the metal wire (2) is looped. At this time, the inner lead (10) is placed on the heat block (9). The capillary chip (1) is heated to a temperature of 300 to 400°C, and ultrasonic vibration is applied to the capillary chip (1) by a vibrating device (not shown).This causes the wire connection between the metal wire (2) and the inner lead (1o). Both metal elements on the surface (11) are interdiffused, and the metal wire (2) is connected to the wire connection surface (11).
is joined to.

Thereafter, the metal wire (2) is fixed by the clamper (12) while the capillary tip (1) is raised to cut the metal wire (2).

By the way, as mentioned above, the vector (19) of the load applied to the metal ball (4) when the metal ball (4) is pressed is the convexly curved chamfered portion (13) of the capillary tip (1).
The direction changes gradually and smoothly continuously (see Figure 2). This distributed load is caused not only by the metal element near the joint surface of the metal ball (4) with the capillary tip (1) but also by the metal element. It also acts on the metal elements inside the ball (4),
As shown in FIG. 3, slip lines appear over a wide range on the back surface of the metal ball (4) before the alloy layer (17) is formed, and the core (20) with few slip lines becomes small. As a result, as shown in FIG. 1, the alloy layer (17) is formed almost uniformly over the entire joint between the metal ball (4) and the electrode layer (8).

Incidentally, wire bonding was performed by changing the hole diameter of the insertion hole (22) of the capillary chip (1) and the diameter D2 of the copper wire, /D2, and each alloy layer <17
), the results shown in Figure 4 were obtained. In other words, if 102 is less than 13, the metal wire cannot move smoothly in the insertion hole (22) and cannot be looped, and if it is larger than 1.5, the metal wire cannot move smoothly in the insertion hole (22), and if it is larger than 1.5, the metal wire cannot move smoothly in the insertion hole (22). Therefore, the ratio DI/D between the hole diameter D1 and the metal wire diameter 02
The optimal range for 2 is 1.3 to 1.5.

In addition, the radius of curvature R of the concave curved surface portion (15) of the metal ball (4), that is, the chamfered portion (13) of the capillary tip 1)
It was confirmed that the uniformity of the alloy layer (17) is excellent when the radius of curvature R of the convex curved surface is smaller than the diameter D2 of the metal wire (2).

Furthermore, the relationship between the height H of the metal ball (4) after bonding and the thickness T of the alloy layer (17) is determined by the curve (23) in FIG.
), however, the bonding load is 130 gm,
Ultrasonic vibration frequency 60KHz and application time 30m5e
I went with c. As can be seen from Fig. 5, the convex curved chamfer (13) of the capillary tip (1) and the flat load surface (14) are connected smoothly, so the size of the metal ball (4) Even if the height is small, the load will not concentrate and break through the metal ball (4), and normal bonding can be performed even if the height H of the metal ball (4) after bonding is reduced to about 6μ. . Therefore, it is possible to maximize the effect of ultrasonic vibration energy. For comparison reference, FIG. 5 shows the relationship between the height H of the metal ball (4) and the thickness T of the alloy layer (17) at the Ti junction of a conventional semiconductor device. ! (24)
It is shown in

Note that the metal wire (2) and the metal ball (4) may be formed from a metal other than copper, and the electrode layer (8) may also be formed from a metal other than aluminum.

〔Effect of the invention〕

As explained above, according to the present invention, a metal ball formed at the tip of a metal wire and bonded to an electrode layer, and an alloy layer formed at a boundary between the metal ball and the electrode layer. The metal ball is plastically deformed so as to form a continuously smoothly changing concave curved surface at the connection part with the metal wire, so that the alloy formed at the boundary between the metal ball and the electrode layer The uniformity of the layer is improved, and the reliability of the electrode joint is improved.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing an electrode junction of a semiconductor device according to an embodiment of the present invention, and FIGS. 3 is a diagram showing the sliding line of the metal element on the back surface of the metal ball in FIG. 1, and FIG. 4 is a diagram showing the hole diameter of the insertion hole of the capillary tip in the example, A graph showing the uniformity of the alloy layer with respect to the ratio DI/D2 with the diameter D2 of the wire, FIG. 5 is a graph showing the relationship between the height H of the metal ball after bonding and the thickness T of the alloy layer, and FIG. a) to (e) are process diagrams showing a general wire bonding method, FIGS. 7(a) and (Jb) are a sectional view and an end view showing the main parts of a conventional capillary chip, respectively, and FIG. 8 is a conventional FIG. 9 is a cross-sectional view showing the electrode junction of the semiconductor device shown in FIG. In the figure, (2) is a metal wire, (4) is a metal ball, (8) is an electrode layer, (15) is a concave curved surface portion, and (17) is an alloy layer. Note that the same reference numerals in each figure indicate the same or corresponding parts.

Claims (1)

[Scope of Claims] A semiconductor device in which a metal wire is bonded to an electrode layer of a semiconductor chip, comprising: a metal ball formed at the tip of the metal wire and bonded to the electrode layer; and the metal ball. an alloy layer formed at a boundary with the electrode layer, and the metal ball is plastically deformed so as to form a continuously smoothly changing concave curved surface at the connection with the metal wire. Characteristic semiconductor devices.