US 3646305 A
A method for reducing transition resistance between two superimposed conducting layers of a multilayered microelectronic circuit, in which there is applied to the two conducting layers an electrical energy having a magnitude below that causing a destruction of the conducting layers involved, such energy preferably comprising a potential within the range of 1 to 20 volts derived from an energy source comprising a charged electrical capacitor.
Description (OCR text may contain errors)
United I States Patent Schmidtke et al.
 PROCESS FOR REDUCING TRANSITION RESISTANCE BETWEEN TWO SUPERIMPOSED, CONDUCTING LAYERS OF A MICROELECTRIC CIRCUIT lnventors: Martin Schmidtke; Winfried Riittenauer,
oth. sMu a e mlfl neltlitififlt. Vollmer, both of Sta rnherg, all of iermany Assignee: Siemens Aktiengesellschait, Berlin and Munich, Germany Filed: July 25, 1969 Appl. No.: 845,004
Foreign Application Priority Data 51 Feb. 29, 1972 Primary ExaminerR. F. Staubly Assistant Examiner-Hugh D. Jaeger Attorney-Hill, Sherman, Meroni, Gross & Simpson  ABSTRACT A method for reducing transition resistance between two su- Aug. 27, 1968 Germany ..P 17 90 023.1 pefimPosed conducting layers Of a multilayer! micmlectronic circuit, in which there is applied to the two conducting layers an electrical energy having a magnitude below that U.S. Cl ..219/50, 29/584, 219/ l 13 au ing a destruction of the conducting layers involved, such Int. Cl ..B23k 11/00 energy f abl m ri ing a potential within the range of 1 Field of Search ..29/584, 586, 610, 620; 219/50, to 20 volts derived f an energy Source comprising a 13; 338/329 charged electrical capacitor.
3 Claims, 8 Drawing Figures LL/ 7 I BACKGROUND OF THE INVENTION Conductive line paths produced for use in microelectronic circuits such as integrated circuits, etc., may be produced in various way, for example, by vaporizing-on, cathode dusting, screening, chemical processes or electrolytic metal precipitation. As a result of the multilayered construction of the line paths the conductors must be produced by different operational or working steps, as a result of which the conductor or conductor sections produced in a subsequent working step must be conductively connected electrically with line paths already present. The simplest way of effecting such a connection is to permit the conductors involved to overlap one another. However, at such overlapping locations, at which line paths to be connected are disposed one upon the other, there frequently occur contact disturbances resulting from the creation of separating layers between the respective conductive layers.
Such separating layers occur, particularly those resulting from surface oxidation, mainly on the line formed by the first applied layer. Separating layers can also be formed, however, by other chemical processes during storage or during the application of subsequent layers. They may also arise through impurities, for example, in coverings or photolacquers, as a result of adsorbed gases and the like. Such separating layers can also reduce the adhesion of the subsequently applied layers, and furthermore, as a rule, increase the electrical resistance between the layers to be connected.
Underlying the present invention is the problem of producing a process by which undesirably high transition resistance at the connecting points of such conductive layers is materially reduced.
BRIEF SUMMARY OF INVENTION The problem involved is solved according to the invention by the application of an electrical potential to the two conductive layers, the magnitude of such potential being so selected that it is sufficiently high to effect the desired change, but not sufficiently high to destroy any of the conductive layers. It has proven especially advantageous to supply to both conducting layers, between which there is to be established a good conductive connection, a predetermined amount of electrical energy derived from the discharge of a capacitor. It has been ascertained that the transition resistance declines as a function of the applied potential to a value that is virtually equal to zero, while a further increase in the potential ultimately leads to the destruction of one of the conductors. The resistance, however, does not again increase following such treatment of the connection.
A special advantage of the invention is that it thereby becomes possible to use, for the production of conduction paths in microelectronic circuits, even substances which tend to exhibit surface changes during the production operations, for example substances which oxidize easily such as aluminum. As is known, such substances have especially good adhesive characteristics.
There is further achieved the possibility, in the production of such microelectronic circuits, of using processes in which impurities may be produced which cannot subsequently be completely removed or which alter the surfaces in some manner. A subsequent treatment according to the invention makes it possible to prevent the increases, otherwise here occurring, of the transition resistance between connecting points of conductive layers.
Furthermore, it is unnecessary during the production of such microelectronic circuits to employ production steps which serve the purpose of protecting the surfaces of the conduction paths from any change, especially from oxidation.
A further advantage derived from utilization of the invention resides in that there are also prevented variations with aging, resulting from changes occurring in the separating layers in the course of time.
BRIEF DESCRIPTION OF THE DRAWINGS Other objects, features and advantages of the invention will be readily apparent from the following description of a preferred embodiment thereof, taken in conjunction with the accompanying drawing, although variations and modifications may be effected without departing from the spirit and scope of the novel concepts of the disclosure, and in which:
FIG. 1 illustrates the overlying of two conductors;
FIG. 2 illustrates the crossing of two conductors;
FIG. 3 illustrates the underpassing of two conductors;
FIG. 4 illustrates the contacting of a conductor;
FIGS. 5 and 6 illustrate connections of conductors respectively arranged in X- and Y-directions;
FIG. 7 illustrates an arrangement for performing the method of the invention; and
FIG. 8 illustrates a circuit suitable for use in method of the invention.
practicing the DETAILED DESCRIPTION OF THE INVENTION Referring to FIG. 1, the conductors l and 2 overlap one another at the location 3 and at the meeting surfaces thereat there occur separating layers, particularly oxide layers, which increase the transition resistance. I have found that this transition resistance can be considerably reduced by the application of an electrical potential to the respective conductors involved. For example, in the case of an overlapping of two conductive line paths, each of which has a width of 50 p. and a thickness of from 1 to 2 p. by connecting the two conductors l and 2 with a capacitor of l00;1.f., which had previously been charged to a voltage of from 4 to 8 volts, it was possible to reduce the transition resistance from an initial 50,000 ohms to a few milliohms. It is apparent that while the transition resistances occurring before the use of the treatment according to the invention are objectionably high, following use of the method of the invention, such resistances are reduced to extremely low values.
FIG. 2 illustrates a conductive line crossover in which the line paths formed by the conductors l, 2 and the conductor bridge 4 passes over the line 5. Electrical insulation between the conductor 5 and the line path 1, 2 and 4 is provided by insulating layer 6. In this case, there likewise occur at the connection points between the bridge 4 and the conductors l and 2 separating layers which can be considerably reduced by applying an electrical potential to the conductors l and 2 or to the conductor bridge 4 and to each one of the conductors l and 2.
FIG. 3 illustrates a conductor underpass, which is otherwise generally constructed analogously to the conductor overpass of FIG. 2, and in which there likewise occur between the line section 4 and the conductors l and 2 separating layers which can be considerably reduced by application of the method of the invention.
For the connection of individual points of a circuit with supply potentials, etc., which require large areas in a single plane, there can be produced, in a similar manner, contacting portions such as those illustrated in FIG. 4, in which the conductor 7 extends through an opening in the insulating layer 8 into direct contact with the layer 9 forming, for example, a potential supply conductor. The separating layers occurring between the layer 9 and conductor layer 7 may, as previously described, be eliminated by applying a potential to the supply layer 9 and the conductor layer 7.
FIGS. 5 and 6 illustrate connections between a conductor 10 extending in X-direction and conductors such as the conductors ll, 11' arranged thereabove and separated therefrom by respective insulating layers, such as the layers 13,13 extending in Y direction, as illustrated in FIG. 5, or a continuous insulating layer 13 as illustrated in FIG. 6, by means of connecting sections 12. Separating layers occurring at the common surfaces of the lines 10,11 and the line sections 12 may be eliminated according to the invention by applying a suitable potential to the lines and 11, as previously described.
As illustrated in FIG. 7, the application of an electrical potential to the line paths 1 and 2 for the elimination of transition resistance at the overlap 3 can be accomplished with the aid of probes l4, 15, connected with a suitable electrical potential source, which probes are pressed in contacting relation with the conducting layers 1 and 2.
FIG. 8 illustrates a suitable circuit arrangement for the practice of the invention, comprising a potential source 16 which, for example, can be applied over a series resistor 18 and a switch 21 to a capacitor 17 to effect a charging of the latter. By actuation of the switch 21, the energy stored in the capacitor 17 may then be applied, possibly over a series resistor 19, to the transition site, represented in FIG. 8 by its substitution resistance 20.
It will be appreciated from the above description that we have provided a very simple yet highly effective method of eliminating undesirably high transition resistances between conductor paths which are to be conductively connected, which method may be readily adapted for use in production line techniques and the like We claim as our invention:
1. A method of reducing transition resistance at the electrical connection between two conductor sections cooperable to form a composite conductor for connecting elements of a mu]- tilayered microelectronic circuit, which conductor sections are in the form of respective relatively thin conductive layers disposed on a suitable supporting member in sequential operations with portions of said layers superimposed upon each other to form said electrical connection, and in the course of which operations such transition resistance is created by the formation of separating layers between opposed connecting faces of said conductive layers, comprising the step of applying to the two conductive layers so formed an electrical energy having a magnitude that is sufficient to substantially eliminate such separating layers between such opposed connecting faces of said superimposed conductive layers and thereby materially reduce said transition resistance therebetween to a negligible operative value as compared to a corresponding continuous element-connecting conductor, but insufficient to cause a destruction of the relatively very thin conductive layers forming said conductor sections.
2. A method according to claim 1 wherein said energy is derived from an energy source comprising a charged electrical capacitor.
3. A method according to claim 2, wherein said applied energy comprises an initial potential within the range of l to 20 volts.