DE2727319A1 - Hump electrode for gang bonding semiconductor arrays - has two layers of gold with geometric configuration increasing tear strength - Google Patents

Abstract

A semiconductor substrate has at least one circuit element, and a main surface coated by an insulating film on which is a hump-shaped electrode connected via a conducting layer to the circuit element. Electrode has a metal layer on insulating film and in contact with the conducting layer; on top of the metal layer is a further metal layer which does not extend beyond the first layer, and has a smaller area than the first layer. On top of the second layer is a third layer with a smaller area than, but made of the same metal as, the second layer. Layers two and three are pref. gold. A gold-coated wire lead is pref. bonded to the top of hump electrode. Provides a hump electrode for gang bonding, used e.g. in large scale integration, where the hump electrode has increased mechanical strength.

Description

Semiconductor device

with a hump-shaped connection electrode The invention relates on a semiconductor device with metallic connection electrodes, on the metallic one Connection lines are bonded.

For establishing an electrical connection between connecting cables with metallic connection electrodes on a semiconductor arrangement are already different proposed new methods instead of traditional wire bonding been. A technique recently proposed for LSI application is so-called series bonding (gang bonding), in which the connection lines appear as strips of metal foil a plastic tape are provided and their end portions are made so thin are that they bsw directly and simultaneously to the metallic projections. Iontaktfl.oko (iiöcker) / be bonded to the connection electrodes of the integrated circuits can. Such serial bonding is suggested, for example, in U.S. Patent No. 3,763,404.

With conventional semiconductor technology for series bonding the interconnections and connection electrodes are made of aluminum, while the Bumps are made of gold.

The formation of the gold bumps directly on the aluminum connection electrodes however, has poor adhesion and a fragile metallic bond between the result of the two metals known as purple plague. Ss will therefore generally be a refractory or between the aluminum and the gold heat-resistant metal laid to solve these problems. In this improved However, a breakdown of the metallic bond still occurs in the structure Furpurpest on: the intermediate refractory metal layer breaks on some Set up due to the pressure exerted by the bonding on the soft underlying aluminum is exerted. To avoid this disadvantage, was already proposed the gold humps on extended outer conductors from solid metal rather than on the aluminum terminal electrodes. Included a combination of Ti-Pt-Au has proven to be a suitable metal for the extended Outer conductors proved to have improved mechanical strength and good conductivity to obtain.

Due to the gold stud structure for series bonding, widely manufactured connecting leads using tin-plated copper. The selection of this material is due to the fact that the gold-tin eutectic can be obtained at a low bond pressure at a relatively low temperature can. A sufficient mechanical bonding without breaking points can thus be achieved if the above-described gold bump structure and tin-plated copper wires be used. However, under certain operating conditions such Lines often oxidation, corrosion and whisker formation on. This represents the hair formation of the tin, which occurs with a large electrical Current flow and induced at high temperature conditions, the ernathafteate Problem. Individual crystalline tin hairs can create separate conductive areas bridge, which can lead to an electrical short circuit. It was already Hor found that adding a small amount of lead (Pb) to the tin and some other procedures the occurrence of the Decrease hair, but not can completely exclude.

Accordingly, tin-plated copper wires are electrochemical in terms of their properties Poor quality and must be replaced by other stable materials. In this regard, gold-plated copper cables are particularly suitable because they show no chemical degradation or hair formation. However, it was found that the gold plated copper wires compared to the tin plated copper wires need a larger bond pressure to create a sufficient mechanical connection to be able to produce with the gold studs. The differences in bonding seem to be due to the fact that the bonding of gold with gold is based on the plastic deformation of the metal is based, while the bonding of tin with gold is based on a eutectic Alloy formation based. Because of the higher bond pressure for the gold-gold connection is required, e.g., about 1200 kg / cm2 or more at e.g. one temperature of 3000C, mechanical cracks often occur in the silicon substrate below the golo bumps on. In addition, in the case of series bonding in an LSI structure, the usually has a few tens of bond points, the bond pressure is not evenly applied all places are exercised, due to the different thickness of the Gold bumps and the gold-plated wires. Consequently, a greater pressure than the average value applied to some bond points and thus the silicon substrate clearly disintegrated below these disturb. So there is one first requirement for a reliable gold-gold series bonding in a complete Elimination of silicon cracks.

furthermore, in the case of the series bonding method, in addition to bonding, between the connection leads and the connection electrodes (inner lead bonding) normally Another bonding is necessary to connect the connecting lines to external lines to an external one Housing or a ceramic substrate to be bonded (external line bonding). before For this outer wire bonding, the connecting wires must be cut off, bent and provided with a plastic coating. It must therefore be due to the strength of the internal conduction bonding must be large enough to accommodate the mechanical To be able to withstand stresses (2 20 g).

The third requirement for reliable bonding is complete Elimination of the possible silicon cracks caused by thermal stress may occur under some operating conditions even if the internal wire bonding fulfills the first and second requirements. These types of cracks can be due to intentional Destruction of the connection due to a tear-off stress can be determined. at This simple test can disconnect the connection in four different places at the connection line, at the line-hump interface, at the interface Humps Substrate and on the silicon substrate. Comparing these four Types of fracture, the first shows a sufficiently good connection, the second and third type, however, a bad connection of the hump with the line or a poor adhesion of the cusp with the substrate. The fourth type of breakage or damage, i.e., the occurrence of silicon cracks as a result of the deliberate pull-off stress of more than 20 g, corresponds to a possible silicon crack or break.

In contrast, the invention fulfills the three requirements mentioned above to a sufficient extent.

An object of the invention is to provide a semiconductor device in which the bump terminal electrodes are required for series bonding have improved mechanical strength.

The semiconductor arrangement according to the invention with a hump-shaped Terminal electrode comprising a semiconductor substrate with at least one circuit element and a main surface, an insulating film formed on the main surface, and a has formed on the insulating film bump terminal which has a conductive Layer is connected to the circuit element is characterized in that the stud terminal electrode has a first, a second and a made of the same material like the second existing third metal layer, the first metal layer on the Insulating film is formed and connected to the conductive sheet electrode is connected, the second metal layer directly on the surface of the first metal layer is arranged, it does not extend beyond this and its area is smaller is than that of the first metal layer, and wherein the third metal layer directly arranged on the surface of the second metal layer and its area smaller is than that of the second metal layer.

Accordingly, the invention provides a connection electrode for a semiconductor device with a bump terminal electrode, the first, second and third Iwletallschicht and thereby forms a step-like profile. The hump terminal electrode has improved mechanical strength for series bonding.

Embodiments of the invention are explained in more detail with reference to the drawings described. 1 shows a cross section through a semiconductor arrangement with a bump electrode which is connected to a connecting lead; Figure 2A an enlarged top plan view of a conventional bump structure; Fig. 2D is a cross-section along the line B-B of FIG. 2A; Fig. 3 is a diagram in which shows the results of a tear-off test on a line connected to the conventional hump structure of Figures 2A and 2B is bonded; Figures 4A, 4B and FIG. 4C is schematic sectional views of a conventional hump structure and FIG two hump structures in which the stress is distributed; Fig. 5 shows an embodiment of the hump structure according to the invention, FIG. 5A being a top view and FIG. 5B Figure 5 is a cross-section along the line B-B of Figure 5A; Fig. Ü a diagram, which shows the results of the Abreil3 test of a line that is connected to the hump structure according to the invention shown in FIG. 5 is bonded; Fig. 7A is a top view of an alternate embodiment of a hump structure; Fig. 7B shows a cross section along the line B-B of FIGS. 7A and 7 Fig. 8 is a graph showing the results of a line tear test which is bonded to the hump structure of FIG.

The integrated semiconductor device shown in Fig. 1 with a Bump connection electrode has a main section of a copper connection line 1, a surface covering 2 made of a plated gold layer on the copper connection line, a conventional gold bump 3, Au, Pt and Ti layers 4, 5 and 6 for the extended ones Outer conductor, an SiO2 layer 7 for insulating the various metal layers, Aluminum intermediate layers 9, an SiO2 layer 10 for surface passivation, an impurity diffusion region 11 and an Si substrate 12, which in turn have circuit elements, such as a transistor or resistor. One the loosener connection electrode Part 20 including the arrangement of FIG. 1 is shown in FIGS. 2A and 2B. A main surface of the substrate 12 is covered with the SiO 2 layer 10, which preferably by a thermal growth process followed by a chemical one Daiipf deposition process, is formed. When the bumps are formed first a Ti layer 6 and a Ut layer 5 and sprayed in the shape of the elongated Outer conductor brought. Then a thinner gold layer 4 (about 2 µ) is applied, to increase the electrical conductivity of the extended outer conductor. In the end becomes a gold bump 3 by applying a thick layer of gold (about 15) formed. This gives the gold bump electrode shown in Fig. 2, wherein the Ti layer 6, the Pt layer 5 and the gold layer 4 are multilayered one on top of the other are arranged and their peripheral edges are aligned.

The next step is a gold-plated copper wire 1 attached to the gold bump 3 and then thermocompression (1200 kg / cm2 at 3000C) exerted on the hump 3 via the connecting line 1.

The strength of the connection is measured by a tension meter, by pulling line 1 upwards until the connection is disconnected will. The test result is shown in Fig. 3, with the tensile strength on the x-axis, at which the separation occurs, and the number of separations is plotted on the y-axis is. With 36 are the number of separations due to silicon cracks and with 37 denotes the number of other types of separation.

It can be seen from this that most of the connections are caused by silicon cracks be separated. Another disadvantage can also be seen from the diagram, namely that many connections have a strength less than 20 g.

From this it must be concluded that the conventional gold hump only can be bonded very poorly to the gold-plated wire and that a such hump Terminal electrode not for series bonding can be used.

For a better understanding of this fracture behavior, we will now consider bonding and take a closer look at the stress concentration.

It is obvious that when bonding to the surface of the gold-plated pipe average pressure exerted (usually 1200 kg / cm2 at a temperature of 3000C) does not affect the compressive strength of silicon (approx 3500 kg / cm2). However, it appears that the bump edge is on the silicon substrate applied concentrated stress in some cases affects the compressive strength of the silicon exceeds, which can be attributed to the deformation of the hump structure during bonding is. Under these circumstances, the silicon crystal may be destroyed (cracked).

One of the easiest ways to reduce the above concentrated stress consists in making the bump surface larger than the bond area to shape with the connecting cable. This means a reduction in the line width relative to the hump size. A maximum hump size is usually determined by the economic Determined from the point of view of the LSI production. The current maximum is Bump size usually at 100 P x 100 and the future trend is moving in Direction towards a reduction of this maximum cusp size. The applicant has with Tests carried out with a gold bump size of 100 P x 100 P and found that the width of the connecting line must be reduced to below 40 P to to completely eliminate the silicon cracks. To avoid possible misalignment when bonding a connection line with respect to the hump surface should be charged this value can be further reduced for a suitable maximum line width. A connecting line with such a small width is, however, seen mechanically very weak.

From this it can be concluded that this method is unsuitable.

Another attempt at stress distribution can consist of that the conventional hump structure is modified so that the concentrated stress is minimized. This is achieved by the hump structure according to the invention.

hen a hump with a flat surface on a flat plane is formed and it is subjected to a uniform pressure over the entire surface the resulting stress concentration will generally be below the The edge of the cusp is determined by the shape and material of the cusp. Regarding the Stress concentration can be said here that with a solid surface, soil interface and cusp height is the maximum stress yrnax that acts on the plane below, with an increase in curvature radius of the side surface g decreases. So results for the humps shown in FIGS. 4A, 4B and 4C, namely the conventional bumps 41 and the improved bumps 42 and 43 at each Curvature of the side surface «b or

where γb <γc ', on the corresponding substrates 44, 45 and 46 have the following relationship: a max> #bmax> #cmax where a max '# b max and #c max denote the maximum voltage that is applied to the substrate 44, 45 or 46 acts.

With a series of humps 41, 42 and 43 were on an equal Silicon substrate 44, 45 and 446 based on the above-mentioned principle experiments made to find out ura a stress-relieved structure that matches the conventional one Technology is compatible.

A preferred embodiment of a hump electrode arrangement according to the invention is shown in Figs. 5A and 5B, the composition of the metallic materials is the same as in Fig. 2. The geometric structure of the bump electrode assembly is in the vertical direction, however characterized in that they has two stages which approximate the curve shape shown in FIG represents.

A preferred manufacturing method will now be described with reference to FIG a hump structure according to the invention described.

On the Si3N4 layer 52 formed on the silicon substrate 51 is first a 1000 i thick titanium layer 53 and then a 1500 i thick platinum layer 54 sprayed on.

This double metal layer applied to the electrode area is then made into a 100p x 100p square shape.

Thereafter, a thin gold layer 55 with a thickness of 2 to 3 p locally electroplated around an elongated outer conductor terminal in the mold a square of 80 P x 80 P to form. Eventually the 10 to 15 P becomes thick Gold layer applied locally and forms the gold bump 56 in the shape of a square von 60 P x 60 After the production of this double step structure, the The tear-off test described above was carried out on a gold-plated copper line, which was bonded to the hump 55. The result of these tests is shown in the diagram 6 shown. It can be seen from this that none of the bumps tested had a Silicon crack occurred. Almost all disconnections occurred due to a line break and the tensile strength was more than 30 g in each case. This Result clearly shows a substantial improvement in strength and reliability of the connection in comparison with the conventional one shown in Figs. 2A and 213 Structure.

As a further approximation to the waveform shown in FIG with a curved side surface, a hump structure shown in FIG. 7 was included a single stage. In this example the lower layers, namely, the Ti layer 73, the Pt layer 74, and the Au layer 75 in the shape of one Square of 150 x x 150 and the overlying cusp structure 76 in the dorlaa a square of 80 P x 80 P brought. The result of the maturity3 test of a Line bonded to the hump structure shown in FIG. 7 is shown in FIG.

From this it can be seen that the single-stage structure is arguably the reliability of gold-gold bonding is improved, but it cannot eliminate the Si cushion, even if the step edge is chosen to be greater than 35 P on each side. From it it can be concluded that a step-like hump structure with no less than two levels is sufficient.

Regarding the cusp structure with two steps, it was found that a minimum step margin of 5 P is required for each step in order to achieve a favorable one ensure the effect of the gradation. Am maximum step edge of about 25th P is favorable both in terms of an axial axial size of the cusps that is tolerable in an LI structure as well as a required minimum cusp size for a sufficient mechanical Strength. In a preferred embodiment of the invention, the thickness is the titanium layer 53 500 to 1500 i, that of the flatin layer 54 1000 to 3000 i, the of the gold layer 55 1 to 3 μ and that of the gold bump 56 5 to 30 As described above the bump structure of the present invention is capable of high stress to resist. With this the bonding of a gold line to a gold bump was realized, without deteriorating the semiconductor device. By exchanging the previously used tin-plated connecting wire through the gold-plated wire an improvement in reliability was achieved, which is due to the elimination of the Hair formation and corrosion is attributed. This enables the inventive Bump structure ensures reliable bonding of the LSI connection electrodes to the connection lines.

Changes and refinements to the described embodiments are easily possible for the person skilled in the art and fall within the scope of the invention. So the principle of the double-stage hump can also be applied to other metals such as applied to a copper bump, as well as to others Semiconductor arrangements, such as a single transistor, a single diode, and an integrated semiconductor device.

Claims (7)

Claims 1. Semiconductor arrangement with a hump-shaped connection electrode, which is a semiconductor substrate with at least one circuit element and a main surface, an insulating film formed on the main surface and one on the insulating film has formed bump connection, cter via a conductive layer with the Circuit element is connected, thereby g e k e n n z e i c h n e t that the bump terminal electrode a first, a second, and one made of the same material as the second third metal layer, the first metal layer on the insulating film is formed and electrically connected to the conductive layer, the second Uetallschicht is arranged directly on the surface of the first metal layer, it does not extend beyond this and its area is smaller than that of the first metal layer, and the third metal layer directly on the surface of the second @; Metal layer arranged and its area is smaller than that of the second metal layer. 2. Semiconductor arrangement according to claim 1, characterized in that g e -k e n n z e I do not know that the second and third metal layers are made of gold. 3. Semiconductor arrangement according to claim 1, characterized in that between the edge of the second metal layer and that of the third metal layer There is a distance of more than 5 µ. 4. Semiconductor arrangement according to claim 1, characterized in that ge-Ei e n n,. e i c h n e t that between the edge of the first metal layer and that of the second There is a distance of more than 5 µ between the metal layer. 5. A semiconductor arrangement according to claim 1, characterized in that ¼ e -k e n n z e i c h n e t that it also has a metal connection line, one of which End is bonded to the hump connection electrode. 6. Semiconductor arrangement according to As claim 5, characterized in that the metal connection line has a surface coating made of gold. 7. A semiconductor arrangement according to claim 1, characterized in that it is -k e n n z e i n e t that the first metal layer is wider than the conductive layer. U. Semiconductor arrangement according to Claim 7, characterized in that that the first metal layer is square in plan view.