Semiconductor device having a bonding pad

Abstract: A semiconductor device of a multilayer interconnection structure includes a plurality of insulating layers (7A,7B,7C) and a plurality of metal interconnection layers (11A,11B,11C). The uppermost metal interconnection layer is formed in a hall in the uppermost interlayer insulating layer. The uppermost interconnection layer is formed as a bonding pad portion and a part of the layer is formed into a ring-shaped portion (116) so as to cover the side portion of the hall.

Description: This invention relates to a semiconductor device and more particularly to a structure of a bonding pad portion of a semiconductor device having a metal interconnection or metallization structure. Until now, in semiconductor devices which have multilayer metal interconnection structure of this type, mainly aluminum or aluminum alloy such as Al-Cu, Al-Si-Cu or the like has been used as the metal for interconnections. However, electromigration, stress migration and other problems have occurred as interconnection widths and pitches become shorter and smaller. To solve these problems, gold or gold alloys have been used as the metal for interconnects. Generally, a lift-off method, an etching method, a resist-mask plating method or the like has been used to achieve fine gold interconnects, because of its dimensional accuracy and ease of processing. A brief description of that method is as follows: First, a layer of titanium, platinum or the like is formed all over an insulating layer as an electron-supplying layer. Then, a photoresist is applied except where interconnection patterns are required by the conventional photoresist process. Thereafter, the interconnection patterns are formed by a gold plating and then the photoresist is peeled-off or removed. Finally, the electron-supplying layer which remains between the interconnection patterns is removed by etching whereas the interconnection patterns serve as a mask and are unremoved. There are a number of etching methods. One is a chemical etching by a wet method. Another is dry etching or ion milling which makes use of reverse sputtering. The preferred method to make fine patterns is dry etching using reverse sputtering in an atmosphere of inactive gases, which produces little sideways etching or undercutting. However, there are some problems with this method. If the surface of the lower layers is uneven, ie. there are marked differences in level in the lower layers, some of the electron-supplying layer tends to remain unremoved even by etching and may cause a short circuit, by peeling-off or tearing-off and scattering in later stages of the processes. In order to avoid the formation of the uneven surface or steep differences in level in the lower layers, it has been suggested that organic insulating layers which can be formed by coating, such as polyimides that include silicon (called silicon polyimide below) or inorganic insulating layers, be used as interlayer insulating layers. Referring now to Figure 1, there is shown a cross-section of a bonding pad portion for wire bonding in a prior art semiconductor device, wherein interlayer insulating layers are used. On a semiconductor substrate 1, is a first metal interconnection layer which is not shown in the figure, on which a first interlayer insulating layer 3 is formed. A second metal interconnection layer which is not shown in the figure is formed thereon and furthermore a second interlayer insulating layer 7 is formed thereon. A layer formed by plasma CVD etc. is used as the first interlayer insulating layer 3 and an insulating layer which is coated and film-formed, such as silicon polyimide etc., is used as the second interlayer insulating layer 7. Then, a recess or hall 8 is made in the second interlayer insulating layer 7 and in the hall a third metal interconnection layer 11 is formed as a bonding pad. Referring now to Figure 2, there is shown a structure of another prior art semiconductor device. On a semiconductor substrate 1, is a first metal interconnection layer which is not shown in the figure, and on which a first interlayer insulating layer 3 is formed. A second metal interconnection layer 6 is formed thereon. An inorganic insulating layer formed by CVD, plasma CVD, etc. is used as the first interlayer insulating layer 3. Then, a second interlayer insulating layer is formed thereon and hall 8 is made, which exposes a part of the second metal interconnection layer 6 mentioned above. An organic insulating layer, which is coated and film-formed, such as silicon polyimide, etc. is used as the second interlayer insulating layer 7. Then, a third metal interconnection layer 11 is formed so that it covers the hall 8 made in the second interlayer insulating layer 7, and is configured as a bonding pad. In Figures 1 and 2, a field insulating layer and an electron supplying layer are omitted. Thus, in prior art structures, a combination of a conventional insulating layer formed by coating and an interconnecting method in which remnants of a gold layer or electron supplying layer may easily remain at the locations where a steep difference in level exists in the lower layer or at a deep vertical gap, causes the following conflicting problems. When steps are taken to avoid cracking of the insulating layer, there is a possibility of a short circuit due to peeling-off of pieces of the gold or electron supplying layers remaining on vertical or step edges due to poor etching. On the other hand, if the structure in such as to avoid short circuits due to such etching debris, there is a possibility of cracking of the insulating layer. For example, in Figure 1, the third metal interconnection film 11 is formed as a bonding pad in a recess or hall 8 of the second interlayer insulating layer 7. In this case, even if mechanical pressure or impact on bonding is applied to the third metal interconnection layer 11, pressure is not applied to the second interlayer insulating layer 7 and thus cracking in this layer 7 can be avoided. However, in this structure, the gold-plating layer or electron supplying layer which forms the third metal interconnection layer 11 tends to remain on the side 8a of the hall 8 on etching of the third metal interconnection layer 11. Thus, there is a possibility of a short circuit due to its peeling-off in the subsequent processes. On the other hand, in the structure as shown in Figure 2, since the third metal interconnection layer 11 is so formed as to cover the hall 8, no etching is carried out at the side 8a of the hall 8 and no peeling-off at the side 8a takes place. However, there is a possibility of cracking in the second interlayer insulating layer 7 by mechanical pressure during bonding and it will cause the in-service reliability of the products to be reduced. Figures 1 and 2 are examples of a three-layer interconnection (metallization) structure. Not only the three-layer structure but also two-layer or multilayer (four and more) structures suffer the same problem when the use of coated and film-formed insulating layers which easily crack under mechanical pressure is combined with the interconnecting techinque by which the gold layer or electron supplying layer may remain on vertical and near-vertical surfaces in the lower layers. EP-A-0 177 251 and EP-A-0 395 072 each disclose semiconductor devices in which cracking of the upper insulating layer on applying the bonding stress is reduced. It is an object of the invention to provide a semiconductor device which does not suffer from these problems. According to the invention there is provided a semiconductor device comprising a semiconductor substrate; an insulating layer covering said semiconductor substrate; a recess selectively formed in said insulating layer, said insulating layer having an edge portion defining said recess; a metal interconnection layer comprising a bonding pad portion, said metal interconnection layer comprising gold or gold alloy, wherein the bonding pad portion is disposed in said recess and is spaced from said edge portion of said insulating layer; said metal interconnection layer further comprising a ring-shaped portion of said metal interconnection layer covering said edge portion of said insulating layer to surround said bonding pad portion and spaced from said bonding pad portion. The interconnection structure may comprise a plurality of said insulating layers and a plurality of said metal interconnection layers insulated by these insulating layers, a part of the uppermost metal interconnection layer being formed as the bonding pad portion, and the recess being formed in the uppermost insulating layer. A metal interconnection layer which is bigger than the recess in the insulating layer may be formed under the recess. By the use of the invention, by establishing an interconnection layer shaped portion separated from the bonding-pad portion, the residue of metal interconnection layer on etching thereof at the side of the hole of the insulating layers can be avoided. Also, cracks which occur when bonding pressure is applied to the interlayer insulating layers can be avoided. The invention will now be described, by way of example only with reference to the accompanying drawings, in which: Figures 1 and 2 are sectional views which show different conventional structures, as already discussed; Figure 3(a) is a plan view of a first embodiment of this invention and Figure 3(b) is a longitudinal sectional view thereof; Figures 4(a) to 4(d) are sectional views to show the process of making the structure of Figures 3(a) and 3(b); Figure 5(a) is a plan view of a second embodiment of this invention and Figure 5(b) is a sectional view thereof; and Figure 6(a) is a plan view of a third embodiment of this invention and Figure 6(b) is a sectional view thereof. Referring now to Figures 3(a) and 3(b), there are shown a plan view of a first embodiment of this invention and a longitudinal sectional view thereof. Regarding these figures, on a semiconductor substrate 1, a field insulating layer 2 is formed, on which a first metal interconnection layer not shown in the figures is formed. Then, thereon, a first interlayer insulating layer 3 is formed, on which is formed a second metal interconnection layer 6 which comprises an electron supplying layer 4 and a gold-plating layer 5. Furthermore, thereon, a second interlayer insulating layer 7 is coated and formed. In the second interlayer insulating layer 7, a hall 8 is made on the above second metal interconnection layer 6. In addition, in the hall 8 a third metal interconnection layer 11, which comprises an electron supplying layer 9 and a gold-plating layer 10, is formed as a bonding pad portion 11a. At the same time, a ring-shaped portion 11b is formed so as to cover the side 8a of the hall 8 using a part of the third metal interconnection layer 11, and is spaced from the bonding pad 11a. Referring to Figures 4(a) to 4(d), there are shown sectional views which show the structure of Figure 3 in processwise sequence. First, as shown in Figure 4(a), a field insulating layer 2 is formed on a semiconductor substrate 1 and on the field insulating layer 2 a first metal interconnection layer not shown in the figure is formed. Then, on it, a first interlayer insulating layer 3 is formed by CVD or plasma CVD. Concerning the first interlayer insulating layer 3, for example, approximately 1.0µ thick layer of plasma oxide is formed. At this time, a flat and smooth surface can be made by Silica-Coating, Etching-Back, etc. Second, as shown in Figure 4(b), after an electron supplying layer 4 is formed over a whole surface, a photoresist pattern 12 for a plating is formed around the area for a bonding pad. A combination of Pd, Pt, Au or the like and Ti, TiW, TiN or the like is chosen as the electron supplying layer 4, considering the adhesion to the lower layer and the easiness of plating. When a composition of a second metal interconnection layer mentioned below is different from that of a third metal interconnection layer mentioned below, it is necessary to consider the extent of the barrier. Third, as shown in Figure 4(c), a gold-plating layer 5 is formed using the above-mentioned photoresist 12 for a mask to form a second metal interconnection layer 6, a part of which is processed as a ground part of a bonding pad to a required pattern. Then, after the photoresist 12 is removed, unnecessary part of the electron supplying layer 4 is removed by etching. Fourth, as shown in Figure 4(d), an insulating layer, which can be coated and formed, such as siliconpolyimide etc., is formed all over the top surface. The thickness of the layer is preferably about 1.0 - 1.5µm at a flat surface portion. Or, before a formation of the coating layer, for example, an insulating layer may be formed by plasma CVD or other methods. As a result, a second interlayer insulating layer 7 is formed. Then, on it, is formed a photoresist pattern not shown in the figure and a hall 8 is made in the insulating layer 7 to expose the ground part of the bonding pad formed in the second metal interconnection layer. Thereafter, (referring back to Figure 3) an electron supplying layer 9 is formed over the entire top surface. By using the electron supplying layer 9, a gold-plating layer 10 is formed to thereby form a third metal interconnection layer 11. Then, a pattern of the third metal interconnection layer 11 is formed by the pattern of photoresist not shown in the figure. In the above semiconductor device, the third metal interconnection layer 11 is patterned so that a bonding pad portion 11a, which is formed in the hall 8 mentioned above, is separated from a ring-shaped portion 11b, which covers a side 8a of the hall 8. Also, another layer which covers the top surface can be formed for purposes of passivation and mechanical protection. According to this structure, the ring-shaped portion 11b remains unetched; that is, parts besides the one covering the side 8a of the hall 8 are etched. Thus, in the third metal interconnection layer 11, there is no debris due to etching on the side 8a of the hall 8. Also, since the bonding pad portion 11a is formed only inside the hall 8, pressure on bonding is not applied to the second interlayer insulating layer 7 and thus cracking at the second interlayer insulating layer 7 can be avoided. It is desirable that there should be at least an 1µm distance between the bonding pad portion 11a and the ring-shaped portion 11b although it depends on the strength of pressure on bonding. Referring now to Figures 5(a) and 5(b), there are shown plan and sectional views of a second embodiment of the present invention, respectively. The difference between this embodiment and the above first embodiment is that the second metal interconnection layer is not formed under the hall 8 of the second interlayer insulating layer 7 in this embodiment. In this structure, pressure which is applied to the bonding pad portion 11a on bonding is not further conveyed to the second interlayer insulating layer 7 and cracking on the second interlayer insulating layer 7 can be thereby avoided. Referring to Figures 6(a) and 6(b), there are shown plan and sectional views of a third embodiment of the present invention, respectively. In this embodiment, the same structure as the first embodiment is repeatedly made from the second interconnection to the fifth interconnection. In this case, the ring-shaped portion 11b, which is formed from a part of the metal interconnection layers 11A, 11B and 11C which are composed of each of electron supplying layers 9A, 9B and 9C and each of gold-plating layers 10A, 10B and 10C, are patterned so that the lower layer is in turn put in the inner place. In this structure, pressure on bonding is not transmitted directly to the interlayer insulating layers 7A, 7B and 7C and cracking can be avoided. As explained above, in the described embodiments, the bonding pad portion is formed by the formation of the uppermost metal interconnection layer or layers in the hall or halls made in the uppermost interlayer insulating layer and a part of this metal interconnection layer is formed in the shape of a ring so that it covers the side of the hall. As a result, the bonding pad portion is separated from the ring-shaped portion. Therefore, transmission of pressure applied to the bonding pad portion on bonding to the interlayer insulating layer can be avoided and cracking in the interlayer insulating layer can be avoided. Furthermore, a short circuit by the remnants of incomplete etching of the metal interconnection layer from vertical surfaces can be avoided because of the ring-shaped portion, which preferably is spaced from the bonding pad by at least 1µm.

Claims: A semiconductor device comprising; a semiconductor substate (1); an insulating layer (7) covering said semiconductor substrate (1); a recess (8) selectively formed in said insulating layer (7), said insulating layer (7) having an edge portion (8a) defining said recess (8); a metal interconnection layer (11) comprising a bonding pad portion (11a), said metal interconnection layer (11) comprising gold or gold alloy (10), wherein the bonding pad portion is disposed in said recess and is spaced from said edge portion (8a) of said insulating layer (7); said metal interconnection layer further comprising a ring-shaped portion (11b) covering said edge portion (8a) of said insulating layer (7) to surround said bonding pad portion (11a) and spaced from said bonding pad portion; A semiconductor device according to Claim 1, comprising: a field insulating layer (2) disposed on an upper surface of said substrate (1); a further metal interconnection layer disposed on an upper surface of said field insulating layer (2); a interlayer insulating layer (3) formed on an upper surface of said further metal interconnection layer; a second further metal interconnection layer (6) formed on an upper surface of said interlayer insulating layer, and upon which said insulating layer (7) is disposed. A semiconductor device as claimed in Claim 1 characterised in that the device is multilayered and comprises a plurality of said insulating layers and a plurality of said metal interconnection layers insulated by these insulating layers, a part of the uppermost metal interconnection layer (11) being formed as the bonding pad portion, and the recess (8) being formed in the uppermost insulating layer (7). A semiconductor device according to Claim 1 characterised in that under the recess (8) in the insulating layer, there is a metal interconnection layer which is bigger than the recess. A semiconductor device according to any one of the proceeding claims characterised in that the distance between said bonding pad portion and said ring-shaped portion of the interconnection layer spaced therefrom is at least 1µm.

Inventors: KANO ISAO, KANO, ISAO
Applicants: NIPPON ELECTRIC CO, NEC CORPORATION
Application year: 1991
Main classification: H01L23
IPC codes: H01L21, H01L23