Interconnection structure

Abstract: By providing an interconnection structure (1) with strip-shaped elevations (11) which, in a plan view, are preferably asterisk-shaped, the contact face is cleaned during compression and an adhesive can easily flow away. The interconnection structure is very suitable for face-down bonding of drive ICs in a display device.

Description: The invention relates to a device according to the introductory part of Claim 1. The relevant conductor pattern may be provided on, for example, a semiconductor substrate (integrated circuit or a discrete semiconductor element) or form part of a wiring pattern provided on a first substrate of, for example, glass, quartz, ceramic material, polyimide or synthetic resin. An interconnection structure, also referred to as "bump", may be provided on a semiconductor substrate for mounting by means of the so-called flip-chip method (also referred to as face-down bonding). Such a structure is described in US-P 4,749,120. An IC provided with such bumps is mounted on a glass substrate by means of said flip-chip method. In one of the mounting methods described in US-P 4,749,120 an electrically conducting contact is first obtained between the bump and the conductor track by means of a pressure contact, whereafter the pressure of this contact is maintained by curing a resin layer provided between the substrate and the IC. Such a mounting method is used, inter alia, in the manufacture of display devices (LCDs) in which ICs are secured by means of said flip-chip method on a substrate of glass or quartz which also form apart of the actual (liquid crystal) display device. Conductor tracks continuing as far as the actual display section are provided with drive voltages via the integrated circuit which contact these conductor tracks by means of said bumps. Presence of the resin (or other adhesive) during compression prevents good contact if superfluous resin remains between the bumps and the conductor tracks. This remaining resin leads to bad contacts or high contact resistances. Moreover, if no special measures are taken, the actual contact of the interconnection structure with, for example, a thin connection conductor may remain limited to a very small area (for example, a projecting point of the bump), which also leads to a high contact resistance. This notably occurs when a low pressure is used for contacting. Such high contact resistances subsist after mounting. The present invention has for its object to eliminate the above-mentioned drawbacks as much as possible. To this end a device according to the invention is characterized according to the characterizing part of Claim 1. The invention is based, inter alia, on the recognition that superfluous resin or adhesive can be removed by giving the bump a special profile. In this way the contact resistance is decreased and simultaneously the reliability of the interconnection structure is enhanced. Since the elevations are spaced more and more apart towards the edges of the bump superfluous adhesive or resin is easily squeezed out during compression. Substantially no adhesive or resin is left between the bumps and the conductor tracks, leading to reliable contacts. JP-A-2142133 shows a bump having groove sections between elevations to extrude resin, if present. The elevations however are not spaced further apart at the circumference than at the central area. So during compression there is no preferred direction for the resin towards the circumference. Consequently squeezing out is not enhanced by this structure. JP-A-1098237 describes a method in which whiskers grow in a direction perpendicular to the surface of the bump while the surfaces of said elevations intended for interconnecting are not defined; during compression the material of these whiskers accumulates between the structure and a supporting body, thus preventing adhesive or resin to flow away during compression. EP-A-152972 shows a bump in which the elevations are mushroom-shaped; these elevations serve to maintain mechanically and electrically stable contacts at temperatures up to 300°C. In EP-A-352020 grooves are formed; as a consequence resin will fill these grooves and since no special measures are shown this resin will stay within the grooves and may even flow over their edges on to the contacting surfaces. As a consequence contacts are rather made worse in such an embodiment when using resins or adhesives. EP-A-303256 shows the use of resinous bumps for electrically connecting the electrodes of an electronic device without mentioning a particular shape of said bumps. The elevations are preferably raised at the area of the circumference. An advantage of raised portions of the elevations along the circumference (with respect to parts in the central portion) is that satisfactory electric contacts are obtained at the area of the circumference so that current concentration at one point is avoided. This advantage is notably achieved if the bump, in a plan view, is circular or octagonal, but good results are also achieved with regular or irregular polygons. The bump may also be, for example, star-shaped in a plan view. The elevations are preferably star-shaped or asterisk-shaped, so that test pins for testing an integrated circuit make a satisfactory contact (without a high series resistance) while these elevations satisfactorily withstand the plastic deformation. Moreover, they generally cover an area which is smaller than the tip of the test pin so that the underlying metal is not damaged. Possible damages by a test pin only cover a portion of the bump, the total surface area of which is much larger than the surface area of a test pin. The maximum height of an elevation, viewed in a cross-section, is preferably 5 µm. The bump can be manufactured by means of conventional galvanic structures. The bump is notably advantageous in a display device in which connection electrodes extending beyond the display device on a (glass) supporting body are contacted, for example, with an integrated circuit for drive purposes. The interconnection structure according to the invention is particularly suitable for substrates having connections arranged in a plurality of rows, as described in the non-prepublished Netherlands Patent Application no. 8900675 in the name of the Applicant. The interconnection structure is notably advantageous in a display device in which connection electrodes extending beyond the dislay device on a (glass) supporting body are contacted, for example, with an integrated circuit for drive purposes. The invention will now be described in greater detail with reference to an embodiment and the accompanying drawings in which Fig. 1 is a diagrammatic plan view of an interconnection structure according to the invention; Fig. 2 is a diagrammatic cross-section taken on the line II-II in Fig. 1; Fig. 3 is a diagrammatic cross-section taken on the line III-III in Fig. 1; Fig. 4 shows some modifications of the device of Fig. 1; and Fig. 5 shows diagrammatically a device in which interconnection structures according to the invention are used. The interconnection structure (bump) 10 of Figs. 1, 2 is present on a substrate 1, in this example an integrated circuit formed in silicon. The wiring pattern of the integrated circuit comprises, inter alia , bonding pads 2 for contacting the circuit. The silicon substrate 1 has a passivating layer 3 of silicon oxide, silicon nitride or a combination thereof, which covers the entire surface area of the substrate 1, with the exception of the bonding pads 2. The passivating layer 3 has a thickness of approximately 1 µm and at the area of the bonding pads 2 it is provided with windows 12 having a slightly smaller surface area. In this example the bonding pads 2 are octagonal and have a diameter of approximately 70 µm, while the windows 12 have a diameter of approximately 60 µm. The interconnection pattern has a double layer which comprises a first layer 4 of aluminium and a second layer 6 of gold with a total thickness of approximately 3 µm in this example. The thickness of the layer 4 is approximately 1 µm. In this embodiment the layers 4, 6 form part of an asterisk-shaped assembly of elevations 11. The interconnection structure (bump) 10 described above can be manufactured as follows. The method starts from a substrate 1 comprising an (integrated) circuit or another circuit element having bonding pads 2 and being coated with a passivating layer having windows 12 at the area of the bonding pads. Firstly, a layer of aluminium 4, 4' with a thickness of 1 µm is deposited on the whole assembly, which layer is used a short-circuit layer at a later stage for obtaining the further structure by electrodeposition. The layer 4 may have an anti-diffusion coating to prevent gold from diffusing into the aluminium if gold is used for the layer 6. Subsequently, a mask 5 of a photoresist is provided photolithographically, which defines the areas where electrodeposition can take place. This layer has a thickness of, for example 2 µm, while the apertures in the mask 5 constitute an asterisk-shaped pattern in this embodiment. During electrodeposition a metal layer (gold in this example) is deposited to a thickness of approximately 4 µm at a low electrodeposition current and at a temperature of approximately 45°C. The layer thus obtained is in compliance with the underlying profile, is substantially smooth and extends to some extent beyond the edges of the mask 5. The structure of Figs. 1 to 3 has the following advantages. Since the elevations extending from a central area 9 towards the edges 8 are more and more spaced apart, superfluous adhesive or resin is squeezed from below the structure when a conductor structure connection is established via compression. Simultaneously, the surface area to be contacted is cleaned, as it were. The ultimate compression of the bump is therefore exclusively defined by plastic properties of the bump material. As a result of this and of the strip-shaped structure, a maximum lateral widening of the elevation is possible, leading to a maximum contact surface area and an optimum cleaning. Moreover, the strip-shaped elevations 11 can be tested by means of a probe without damaging the underlying contact surface area 2. Since the elevations 11 are raised at the area of the edges 8, the smallest risk of poor cleaning and hence poor contacts exists at that area. This prevents electric currents from flowing substantially through one point in the finished product. The elevations 11 have, for example, a width of 4 µm and a height of 4 µm (Fig. 3a). The length of the elevations 11a is approximately 70 µm and that of the elevations 11b is approximately 20 µm. These elevations are preferably square or rectangular, as viewed in a cross-section, but they may also be mushroom-shaped (Fig. 3b) or semi-circular, pointed, or have another shape (Fig. 3c .... Fig. 3e). Fig. 4 shows some alternative shapes of the elevations 11. For example, they may have the shape of a cross (which is closed or not closed), as is shown in Fig. 4a. Instead of an uninterrupted strip or elevation, the elevation may alternatively comprise an assembly of, for example, cylindrical or mushroom-shaped elevations which are arranged, for example, in a line configuration. The interconnection structure or "bump" may also be round (Fig. 4a) or square (Fig. 4b). Fig. 5 shows a substrate 1 with, for example, a control circuit which establishes an electrically conducting contact with conductor tracks 17, 18 on a supporting body 13 of, for example, glass (or quartz) via such interconnection structures 10 and by means of pressure contacts. Together with a sealing edge 15, the glass plate 13 and a second glass plate 14 enclose a liquid crystal material 16 and thus form a part of a liquid crystal display device. (Further components such as polarizers, lighting elements, etc. have been omitted for the sake of simplicity in Fig. 5). To be able to drive the display device, it has connection electrodes which are formed by conductor tracks 17 of, for example, indium tin oxide which extend beyond the edge 15 in this example and are connected in an electrically conducting manner to the control circuit in the substrate 1 via interconnection structures (bumps) 10. External signals are applied to this control circuit via aluminium tracks 18 and interconnection structures (bumps) 10. A possible difference in thickness between the conductor tracks 16 and 18 (exaggerated in Fig. 5) is compensated for, because the bumps 10 can be depressed over a large part of their thickness without any influence on the electric contact. The pressure for these pressure contacts is maintained by an adhesive bond 19 in the relevant example. The following variations are possible within the scope of the invention. The bumps 10 may also be formed on the supporting body. In Fig. 5 the liquid crystal may be replaced by other electro-optical media such as electrochromic or electrophoretic materials. More generally, the invention is applicable to chip-on-glass techniques, for memories or to face-down bonding techniques on ceramic material, polyimide. Interconnection structures according to the invention may also be used advantageously in control circuits for thin display devices as described in NL 8700486.

Claims: A device comprising an integrated circuit (1) having a bonding pad (2) and a substrate having a conductor track, an interconnection structure interconnecting the bonding pad in an electrically conducting manner to the conductor track, an adhesive bonding the substrate and the integrated circuit together, characterized in that a passivating layer (3) covers the integrated circuit and has a window (12) at the area of the bonding pad (2), the interconnection structure being formed by electrically conducting strips (11), each electrically conducting strip extending within the window and partly beyond the edge of the window in the passivating layer, the strip, being more spaced apart towards the edge, to enable the squeezing out of superfluous adhesive during manufacture. A device as claimed in claim 1, characterized in that the electrically conductive strips (11) have a length to width ratio of at least 4 : 1. A device as claimed in claim 1 or 2, characterized in that the electrically conductive strips (11) are star-shaped or asterisk-shaped.

Inventors: PLANGGER GUIDO, SCHRAIVOGEL RAINER ANANDA, PLANGGER, GUIDO, SCHRAIVOGEL, RAINER ANANDA
Applicants: FASELEC AG, KONINKL PHILIPS ELECTRONICS NV, FASELEC A.G., KONINKLIJKE PHILIPS ELECTRONICS N.V.
Application year: 1991
Main classification: H01L21
IPC codes: G02F1, H01L21, G09F9, H01L23