MONOLITHIC MICROWAVE INTEGRATED CIRCUIT AND METHOD FOR SELECTING IT

Abstract: Monolithic microwave integrated circuits with resist­ ance-capacitance coupling include bonding or terminal pads 20, 22, 26, 27 and 28 such as pads for signals, for a power source, and for bias potentials. In addition contact pads 21, 23, 24 and 25 are provided to enable the direct current characteristics of the circuit to be measured. These contact pads 21, 23, 24 and 25 can be contacted by probes when the circuit still forms part of a wafer to enable circuits with the required direct current characteristics to be selected for final assembly and packaging. The contact pads 21, 23, 24 and 25 are provided by opening up contact windows over eiectrical­ ly conducting pans of the circuit elements such as over metal electrodes of capacitors 5, 6, 7 and 9 which avoids the need to add to the area of the electrical conductors and hence enables the selection to be performed without sacrificing or impairing the high frequency characteristics of the circuit.

Description: The present invention relates to a monolithic microwave integrated circuit which can be produced without a sacrifice in its frequency characteristics and circuits having the required characteristics can be selected easily. A monolithic microwave integrated circuit is produced by assembling MESFET's, metal Schottky barrier semiconductor field effect transistors, Schottky diodes, inductances and capacitances on the surface of a semiconductor substrate of, for example, GaAs. Therefore, as compared with a MIC (microwave integrated circuit) the monolithic microwave integrated circuit has advantages that it requires smaller numbers of bonding pads and bonds and less trimming of the elements of the chips and, accordingly, it can reduce the cost remarkably by mass production. In the existing technique for producing semiconductor devices, however, it was difficult to make monolithic microwave integrated circuits of equal characteristics in a high reproducibility and, therefore, a selection step to select usable chips was indispensable. Further, since the monolithic microwave integrated circuits handle high frequency signals, it is difficult to determine their performance when they form part of a wafer by methods such as connecting probes to them. WO 82/02603 describes a technique for determining the DC characteristics of a connecting grid of conductors which are formed on a substrate by connecting probes to them to ensure the continuity of the connecting grid before individual preselected integrated circuit chips are attached to the substrate carrying the connecting grid. Accordingly, with monolithic microwave integrated construction it was the practice to divide the chip into separate dice, assembly the separate dice into a monolithic microwave integrated circuit and then test them by measurement at high frequencies. Since large reductions in cost and time can be expected by simplifying this selection process, there is therefore a need for a monolithic microwave integrated circuit which can be selected easily and simply and for a simple method for selecting chips of a monolithic microwave integrated circuit having the required characteristics. According to one aspect of this invention a monolithic microwave integrated construction including a substrate, a plurality of separate and distinct circuits, similar to each other, integrated onto said substrate, each such circuit having at least two stages that are resistance-capacitance coupled to one another and bonding pads that are indispensable for normal operation of the circuit at microwave frequencies for connecting input and output signals and power supplies to the circuit, is characterised in that it also includes additional contact pads to enable the direct current characteristics of said circuit to be measured, the additional contact pads being provided by opening up contact windows to enable contact to be established with electrically conducting portions of electrodes of capacitors, so that the area of electrical conductors present is not increased substantially by them. According to another aspect of this invention, a method for manufacturing microwave integrated circuits comprising integrating a plurality of separate and distinct circuits, similar to one another, onto a single substrate, each such circuit having at least two stages that are resistance-capacitance coupled together and bonding pads that are indispensable for normal operation of the circuit at microwave frequencies for connecting input and output signals and power supplies to the circuit, is characterised in that the each circuit further includes additional contact pads formed by opening up contact windows to enable contact to be established with electrically conducting portions of electrodes of capacitors, so that the area of the electrical conductors present is not increased substantially by them, and in that the method includes a measuring and selection step in which the direct current characteristics of each of the circuits are measured by probing said additional contact pads to measure circuit characteristics of said separate and distinct circuits whilst connected to the same substrate, and selecting circuit chips for further manufacturing steps based on the results of the measurements obtained by probing. A particular example of a circuit and method in accordance with this invention will now be described with reference to the accompanying drawings, in which:- Figure 1 is a circuit diagram; and, Figure 2 is a mask pattern of the circuit. The present invention is not limited at all in material. The present invention is applicable to a wide range of general transistor materials such as elemental transistors and compound transistors. In the following description, however, the present invention will be explained with reference to GaAs which is one of compound transistors having an advantage of high operation speed as the transistor material. Fig. 1 shows a circuit diagram of an embodiment of a monolithic microwave integrated circuit according to the present invention, in which reference numerals 1 and 2 denote MESFET's,3 to 9 denote capacitances, and 10 to 17 denotes resistances. The interstage coupling in this circuit is the resistance-capacitance coupling. The method for selection according to the present invention is characterized in that the layout pattern of a monolithic microwave integrated circuit is added with structurally indispensable pads or pads for measurement and selection of direct current characteristics. Fig. 2 shows an example of the mask pattern of the monolithic microwave integrated circuit according to the present invention, in which reference numerals 1' and 2' denote MESFET's, 3'to 9' denote capacitances, and 10' to 17' denote resistances, corresponding respectively to component elements of Fig. 1. Reference numerals 20', 22' , 26' , 27' and 28' denote structurally indispensable bonding pads, and 21', 23', 24' and 25' denote direct current characteristics measuring and selecting pads. Since the monolithic microwave integrated circuit is of the resistance-capacitance coupling circuit construction, the direct current characteristics of MESFET can be measured by combination of these pads. For measuring MESFET 1' and 2', the pads 20', 21', 23' and 24', 25' , 27' are used. The pads 20' to 28' correspond to contact points of the corresponding number in the circuit shown in Fig. 1. Generally, variation in the characteristics of monolithic microwave integrated circuits are dependent greatly upon variation in the characteristics of active elements MESFET. Efficient selection taking notice to the fact mentioned above is made possible by measuring the direct current characteristics of MESFET using the added pads for measuring and selecting the direct current characteristics. The high frequency characteristics of the monolithic microwave integrated circuit, such as the gain of an amplifier circuit, can be easily estimated from the direct current characteristics of MESFET. Further, since the measurement described above does not use high frequency signals, it can be performed by probing or like method in the state of wafers without the need for division and final assembly of chips previously. This can realize a sharp reduction of producing steps and materials. Addition of the pads 21', 24' and 25' does not cause any deterioration of the high frequency characteristics because the newly added pads use effectively the metal surface on the upper side of the capacitor and the pad 23' is small in area. As described hereinabove, the monolithic microwave integrated circuit according to the present invention has a great industrial value in that selection of the circuits after production is made very easily without sacrificing the high frequency characteristics by adding the pads for measuring and selecting the direct current characteristics. Further, in the method according to the present invention, since the monolithic microwave integrated circuit is probed in the state of a wafer, it is made possible to select the circuits very easily, and to discriminate the quality of the chips before measurement of their high frequency characteristics after assembly steps (dicing, packaging), to thereby realize reduction in time and cost for production. While the present invention has been described with reference to a specific example of circuit, it is to be distinctly understood that the present invention is not limited thereto but may be otherwise variously applied to monolithic microwave integrated circuits of resistance-capacitance coupling construction.

Claims: A monolithic microwave integrated construction including a substrate, a plurality of separate and distinct circuits, similar to each other, integrated onto said substrate, each such circuit having at least two stages that are resistance-capacitance coupled to one another and bonding pads (20, 22, 26, 27 and 28) that are indispensable for normal operation of the circuit at microwave frequencies for connecting input and output signals and power supplies to the circuit, characterised in that it also includes additional contact pads (21, 23, 24 and 25) to enable the direct current characteristics of said circuit to be measured, the additional contact pads (21,23,24 and 25) being provided by opening up contact windows to enable contact to be established with electrically conducting portions of electrodes of capacitors (5, 6, 7 and 9), so that the area of electrical conductors present is not increased substantially by them. A method for manufacturing microwave integrated circuits comprising integrating a plurality of separate and distinct circuits, similar to one another, onto a single substrate, each such circuit having at least two stages that are resistance-capacitance coupled together and bonding pads (20, 22, 26, 27 and 28) that are indispensable for normal operation of the circuit at microwave frequencies for connecting input and output signals and power supplies to the circuit, characterised in that the each circuit further includes additional contact pads (21, 23, 24 and 25) formed by opening up contact windows to enable contact to be established with electrically conducting portions of electrodes of capacitors (5, 6, 7 and 9), so that the area of the electrical conductors present is not increased substantially by them, and in that the method includes a measuring and selection step in which the direct current characteristics of each of the circuits are measured by probing said additional contact pads (21, 23, 24 and 25) to measure circuit characteristics of said separate and distinct circuits whilst connected to the same substrate, and selecting circuit chips for further manufacturing steps based on the results of the measurements obtained by probing.

Inventors: SUZUKI, TOMIHIRO C/O OSAKA WORKS OF SUMITOMO
Applicants: SUMITOMO ELECTRIC INDUSTRIES LIMITED
Application year: 1983
Main classification: H01L21
IPC codes: H01L23