Integrated circuit device and method for fabricating integrated circuit device

Abstract: An integrated circuit device comprises a substrate (1); circuit elements including an active element (7) and a bias line (61 or 62) for applying a DC bias voltage to the active element (7), disposed on the substrate (1); a thermoplastic material layer (8) disposed on a region of the substrate (1); and a magnetic substance layer (9) disposed on a region of the substrate (1) including a required region on the bias line (61 or 62), and adhered to and supported by the thermoplastic material layer (8). In this structure, the magnetic substance layer (9) can be formed in an appropriate shape and at an appropriate position on the bias line (61 or 62) according to the oscillation characteristics of the active element (7), such as a transistor, and the magnetic substance layer (9) absorbs the frequency components of the oscillation of the active element (7), whereby the oscillation of the active element (7) is easily prevented. Further, since the magnetic substance layer (9) is disposed on the bias line (61 or 62), the unwanted increase in the chip area of the integrated circuit device due to the use of the prior art oscillation preventing circuit is avoided.

Description: The present invention relates to a method for fabricating a microwave semiconductor integrated circuit. Figure 7(a) is a plan view illustrating a prior art monolithic microwave semiconductor integrated circuit device. In the figure, reference numeral 1 designates a semiconductor substrate comprising GaAs, Si, or the like, numeral 3 designated via-holes, numeral 4 designates a capacitor comprising a lamination of metal/insulator/metal (hereinafter referred to as MIM capacitor), numeral 7 designates a transistor, such as a field effect transistor, numeral 21 designates an input electrode pad, numeral 22 designates ground electrode pads, numeral 23 designates a gate bias electrode pad, numeral 24 designates a drain bias electrode pad, numerals 51 and 52 designate signal transmission lines, numeral 61 designates a gate side bias line, and numeral 62 designates a drain side bias line. In this integrated circuit device, a microwave signal applied to the input electrode pad 21 is transmitted through the MIM capacitor 4 and the signal transmission line 51 to the gate of the transistor 7. An output signal from the drain of the transistor 7 is transmitted through the signal transmission line 52 to a subsequent stage circuit (not shown). On the other hand, a gate bias voltage applied to the gate bias electrode pad 23 is transmitted through the gate side bias line 61 and the signal transmission line 51 to the gate of the transistor 7, and a drain bias voltage applied to the drain bias electrode pad 24 is transmitted through the drain side bias line 62 and the signal transmission line 52 to the drain of the transistor 7. The via-holes 3 connect the ground electrode pads 22 to a metal layer (not shown) on the rear surface of the semiconductor substrate 1. The MIM capacitor 4 connected between the input electrode pad 21 and the gate of the transistor 7 is permeable to microwave signals and impermeable to DC signals. The above-described prior art semiconductor IC has a problem that the transistor easily oscillates at the application of the gate and drain bias voltages. In order to prevent this unwanted oscillation, as shown in figure 7(b), an oscillation preventing circuit 11 including an MIM capacitor 41 connected to the bias line 61 is included in the IC device. However, since a plurality of transistors 7 are simultaneously fabricated and the oscillation characteristics of individual transistors are varied due to variations in their transistor characteristics in the fabricating process, in order to prevent the unwanted oscillation of each transistor 7, it is necessary for the MIM capacitors 41 of the oscillation preventing circuits 11 corresponding to the respective transistors 7 to have different capacitances according to the different oscillation characteristics of the transistors 7. However, since the oscillation preventing circuits 11 are fabricated simultaneously with the transistors 7 and the bias lines 61, it is impossible to change the capacitances of the MIM capacitors 41 after the fabrication of the transistors and the bias lines and the evaluation of the oscillation characteristics of the transistors. Therefore, it is impossible to prevent the unwanted oscillations of all transistors by the oscillation preventing circuits 11. Further, since the oscillation preventing circuit 11 comprises the MIM capacitor 41 disposed on a region of the semiconductor substrate and a wiring connecting the capacitor 41 to the bias line 61 as shown in figure 7(b), the chip area of the IC device is unfavorably increased by the area of the oscillation preventing circuit 11. From Patent Abstracts of Japan, Vol. 17, No. 691 (E-1419) and JP-A-5 235 655 an integrated circuit device is known which comprises an active element and a bias line for applying a DC bias voltage to the active element, and a magnetic substance layer disposed on the substrate and across the bias line. From US-A-4 716 389 it is known to use a microwave lossy material which is preferably impregnated with ferrite particles, for example, this material could be a silicon rubber material in which ferrite particles are generally uniformly distributed. From EP-A-0 461 316 it is known to use a thermoplastic polyimide film as an adhesive for integrated circuit components. It is an object of the present invention to provide a method of fabricating an IC device that easily controls oscillation of a transistor. This object is solved by the subject matter of claim 1. Further advantageous modifications of the present invention are subject matter of the dependent claims. According to the subject matter of claim 1, since the magnetic substance layer absorbs the frequency components of the oscillation of the active element, the oscillation of the active element is prevented. Further, since the magnetic substance layer is formed on the bias line, the unwanted increase in the chip area of the integrated circuit device due to the use of the prior art oscillation preventing circuit is avoided. In the drawings: Figure 1 is a plan view illustrating a semiconductor IC device fabricated in accordance with a first embodiment of the present invention. Figure 2 is a plan view illustrating a process step in a method of fabricating the semiconductor IC device in accordance with the first embodiment of the present invention. Figure 3 is a plan view illustrating a semiconductor IC device fabricated in accordance with a second embodiment of the present invention. Figure 4 is a plan view illustrating a process step in a method of fabricating the semiconductor IC device in accordance with the second embodiment of the present invention. Figure 5 is a plan view illustrating a semiconductor IC device fabricated in accordance with a third embodiment of the present invention. Figure 6 is a plan view illustrating a process step in a method of fabricating the semiconductor IC device in accordance with the third embodiment of the present invention. Figures 7(a) and 7(b) are plan views illustrating a semiconductor IC device and a semiconductor IC device including an oscillation preventing circuit fabricated in accordance with the prior art. In the following a first embodiment of the present invention will be described Figure 1 is a plan view illustrating a monolithic microwave semiconductor IC device fabricated in accordance with the first embodiment of the present invention. In figure 1, the same reference numerals as those in figure 7(a) designate the same or corresponding parts. Reference numeral 8 designates thermoplastic polyimide layers and reference numeral 9 designates a magnetic substance layer. In the IC device shown in figure 1, a microwave signal applied to the input electrode pad 21 is transmitted through the MIM capacitor 4 and the signal transmission line 51 to the gate of the transistor 7. An output signal from the drain of the transistor 7 is transmitted through the signal transmission line 52 to a subsequent stage circuit (not shown). On the other hand, a gate bias voltage applied to the gate bias electrode pad 23 is transmitted through the gate side bias line 61 and the signal transmission line 51 to the gate of the transistor 7, and a drain bias voltage applied to the drain bias electrode pad 24 is transmitted through the drain side bias line 62 and the signal transmission line 52 to the drain of the transistor 7. The via-holes 3 connect the ground electrode pads 22 to a metal layer (not shown) on the rear surface of the semiconductor substrate 1. The MIM capacitor 4 connected between the input electrode pad 21 and the gate of the transistor 7 is permeable to microwave signals and impermeable to DC signals. The thermoplastic polyimide layers 8 are located on both sides of the gate side bias line 61. The magnetic substance layer 9 is adhered to the thermoplastic polyimide layers 8 across the gate side bias line 61, whereby the magnetic substance 9 is fixed to the semiconductor substrate 1. The magnetic substance layer 9 comprises thermoplastic polyimide containing ferrite grains, or ferrite in the shape of a plate or beads. A description is given of the method for fabricating the IC device shown in figure 1. Figure 2 is a plan view illustrating a process step in the fabricating method. In figure 2, the same reference numerals as in figure 1 designate the same or corresponding parts. Initially, the via-holes 3, the MIM capacitor 4, the transistor 7, the electrode pads 21 to 24, the signal transmission lines 51 and 52, and the bias lines 61 and 62 are fabricated on the semiconductor substrate 1. Thereafter, the thermoplastic polyimide layers 8 are formed on the semiconductor substrate 1 at the both sides of the bias line 61 as shown in figure 2. Then, DC bias voltage is applied to the gate and the drain of the transistor 7 to evaluate the oscillation characteristics of the transistor 7. The magnetic substance 9 which comprises thermoplastic polyimide containing ferrite grains, or ferrite in the shape of a plate or a bead is pressed onto the thermoplastic polyimide layers 8, and they are heated to adhere the magnetic substance 9 to the polyimide layers 8, whereby the magnetic substance 9 is fixed to the semiconductor substrate 1. In this way, the IC device shown in figure 1 on which the magnetic substance layer 9 for preventing oscillation of the transistor 7 is disposed across the gate side bias line 61 is fabricated. In this first embodiment of the invention, since the frequency components of the oscillation of the transistor 7 to which the DC bias voltage is applied are absorbed by the magnetic substance layer 9, the oscillation of the transistor 7 is prevented. Further, after the fabrication of the circuit elements, i.e., the transistor 7, the bias lines 61 and 62, the signal transmission lines 51 and 52, and the like on the semiconductor substrate 1, the transistor 7 is operated to evaluate the oscillation characteristics and, thereafter, the magnetic substance layer 9 is formed across the gate side bias line 61. Therefore, the shape and the position of the magnetic substance layer 9 can be appropriately selected according to the oscillation characteristics of the transistor 7, so that the oscillation of any transistor can be easily prevented. Furthermore, the magnetic substance layer 9 is disposed on the bias line 61, and the thermoplastic polyimide layers 8 for firing the magnetic substance layer 9 to the semiconductor substrate 1 are disposed on the minimum regions required for fixing the magnetic substance layer 9 at the both sides of the bias line. Therefore, the undesired increase in the chip area of the IC device due to the use of the prior art oscillation preventing circuit 11 shown in figure 7(b) is avoided. Although the magnetic substance layer 9 is disposed on the gate side bias line 61, it may be disposed on the drain side bias line 62 or on both of these bias lines. Alternatively, a plurality of magnetic substance layers may be adhered to the thermoplastic polyimide layers 8. In the following a second embodiment of the present invention will be described. Figure 3 is a plan view illustrating a monolithic microwave semiconductor IC device fabricated in accordance with the second embodiment of the present invention. In figure 3, the same reference numerals as those in figure 1 designate the same or corresponding parts. In the IC device shown in figure 3, the microwave signal transmission path and the DC bias voltage application path are the same as those already described in the first embodiment. The thermoplastic polyimide layer 8 is disposed on the drain side bias line 62, and two magnetic substance layers 9 comprising thermoplastic polyimide containing ferrite grains, or ferrite in the shape of a plate or a bead are disposed on the thermoplastic polyimide layer 8. The magnetic substance layers 9 are adhered to the thermoplastic polyimide layer 8, whereby the magnetic substance layers 9 are fixed to the semiconductor substrate 1. Although in the above-described first embodiment the thermoplastic polyimide layer 8 is not present on the bias line, in this second embodiment it is disposed across the bias line. A description is given of the method for fabricating the IC device shown in figure 3. Figure 4 is a plan view illustrating a process step in the fabricating method. In figure 4, the same reference numerals as in figure 3 designate the same or corresponding parts. Initially, the via-holes 3, the MIM capacitor 4, the transistor 7, the electrode pads 21 to 24, the signal transmission lines 51 and 52, and the bias lines 61 and 62 are fabricated on the semiconductor substrate 1. Thereafter, the thermoplastic polyimide layer 8 is formed on the semiconductor substrate 1 across the bias line 62 as shown in figure 4. Then, DC bias voltage is applied to the gate and the drain of the transistor 7 to evaluate the oscillation characteristics of the transistor 7. The magnetic substance 9 which comprises thermoplastic polyimide containing ferrite grains, or ferrite in the shape of plates or beads is pressed onto the thermoplastic polyimide layer 8, and they are heated to adhere the magnetic substance 9 to the polyimide layer 8, whereby the magnetic substance 9 is fixed to the semiconductor substrate 1. In this way, the IC device shown in figure 3 on which the magnetic substance layers 9 for preventing oscillation of the transistor 7 are disposed across the drain side bias line 62 is fabricated. In this second embodiment of the invention, as in the above-described first embodiment, since the frequency components of the oscillation of the transistor 7 are absorbed by the magnetic substance layers 9, the oscillation of the transistor 7 is prevented. Further, since the magnetic substance layers 9 are formed on the drain side bias line 62 after the evaluation of the oscillation characteristics of the transistor 7, the shape and the position of the magnetic substance layers 9 can be appropriately selected according to the oscillation characteristics of the transistor 7. Therefore, it is possible to prevent the oscillation of any transistor. Further, the magnetic substance layers 9 are disposed on the bias line 62, and the thermoplastic polyimide layer 8 is disposed on the minimum region, including a region on the bias line 62, required for fixing the magnetic substance layers 9. Therefore, the undesired increase in the chip area of the IC device due to the use of the prior art oscillation preventing circuit 11 shown in figure 7(b) is avoided. Although the magnetic substance layer 9 is disposed on the drain side bias line 62, it may be disposed on the gate side bias line 61 or on both of these bias lines. Alternatively, the magnetic substance and the thermoplastic polyimide layer according to this second embodiment may be disposed on one of the bias lines 61 and 62 while the magnetic substance and the thermoplastic polyimide layer according to the above-described first embodiment are disposed on the other bias line. Although two magnetic substance layers are adhered to the thermoplastic polyimide layer 8, a single magnetic substance layer or three or more magnetic substance layers may be adhered. In the following a third embodiment of the present invention will be described. Figure 5 is a plan view illustrating a monolithic microwave semiconductor IC device fabricated in accordance with the third embodiment of the present invention. In the figure, the same reference numerals as those in figure 1 designate the same or corresponding parts. Reference numeral 10 designates island patterns of thermoplastic polyimide (hereinafter referred to as thermoplastic polyimide patterns). In the IC device shown in figure 5, the microwave signal transmission path and the DC bias voltage application path are the same as those already described in the first embodiment. The thermoplastic polyimide patterns 10 are disposed on the semiconductor substrate 1 at the both sides of the gate side bias line 61. The magnetic substance layer 9 comprising thermoplastic polyimide containing ferrite grains, or ferrite in the shape of a plate or a bead is disposed across the bias line 61 and adhered to the thermoplastic polyimide patterns 10, whereby it is fixed to the semiconductor substrate 1. While in the above-described first and second embodiments a plate-shaped thermoplastic polyimide layer is employed, in this third embodiment a plurality of island patterns of thermoplastic polyimide are employed. A description is given of the method for fabricating the IC device shown in figure 5. Figure 6 is a plan view illustrating a process step in the fabricating method. In figure 6, the same reference numerals as in figure 5 designate the same or corresponding parts. Initially, the via-holes 3, the MIM capacitor 4, the transistor 7, the electrode pads 21 to 24, the signal transmission lines 51 and 52, and the bias lines 61 and 62 are fabricated on the semiconductor substrate 1. Thereafter, the thermoplastic polyimide patterns 10 are formed on the semiconductor substrate 1 at the both sides of the bias line 61 as shown in figure 6. Then, DC bias voltage is applied to the gate and the drain of the transistor 7 to evaluate the oscillation characteristics of the transistor 7. The magnetic substance 9 which comprises thermoplastic polyimide containing ferrite grains, or ferrite in the shape of a plate or a bead is pressed onto the thermoplastic polyimide patterns 10, and they are heated to adhere the magnetic substance 9 to the polyimide patterns 10, whereby the magnetic substance 9 is fixed to the semiconductor substrate 1. In this way, the IC device shown in figure 5 on which the magnetic substance layer 9 for preventing oscillation of the transistor 7 is disposed across the drain side bias line 62 is fabricated. Also in this third embodiment of the invention, as in the above-described first and second embodiments, since the frequency components of the oscillation of the transistor 7 are absorbed by the magnetic substance layer 9, the oscillation of the transistor 7 is prevented. Further, since the magnetic substance layer 9 is formed on the gate side bias line 61 after the evaluation of the oscillation characteristics of the transistor 7, the shape and the position of the magnetic substance layer 9 can be appropriately selected according to the oscillation characteristics of the transistor 7. Therefore, it is possible to prevent the oscillation of any transistor. Further, the magnetic substance layer 9 is disposed on the bias line 61, and the thermoplastic polyimide patterns 10 are disposed on the minimum regions required for fixing the magnetic substance layer 9 at the both sides of the bias line 61. Therefore, the undesired increase in the chip area of the IC device due to the use of the prior art oscillation preventing circuit 11 shown in figure 7(b) is avoided. Although the magnetic substance layer 9 is disposed on the gate side bias line 61, it may be disposed on the drain side bias line 62 or on both of these bias lines. Alternatively, the magnetic substance and the thermoplastic polyimide patterns according to this embodiment may be disposed on one of the bias lines 61 and 62 while the magnetic substance and the thermoplastic polyimide layer according to the above-described first or second embodiment are disposed on the other bias line. Although a single magnetic substance layer is adhered to the thermoplastic polyimide patterns 10, a plurality of magnetic substance layers may be adhered.

Claims: Method of fabricating an integrated semiconductor device, comprising the following steps: fabricating circuit elements including an active element (7) and a bias line (61, 62) for applying a DC bias voltage to the active element (7) on a substrate (1); forming a thermoplastic material layer (8) on a region of the substrate (1); forming a magnetic substance layer (9) on a region of the substrate (1) including a required region on the bias line (61, 62) by applying a magnetic substance (9) to the thermoplastic material layer (8) and heating the magnetic substance (9) and the thermoplastic material layer (8) to adhere the magnetic substance (9) to the thermoplastic material layer (8); after fabricating the circuit elements, evaluating the oscillation characteristics of the active element (7) by applying a DC bias voltage to the active element (7); and after evaluating the oscillation characteristics of the active element (7), forming the magnetic substance layer (9) in an appropriate shape and on an appropriate position according to the oscillation characteristics of the active element (7) such that the magnetic substance layer (9) absorbs frequency components of an oscillation of the active element (7) to prevent the oscillation of the active element (7). Method according to claim 1, characterized by the following steps: forming the thermoplastic material layer (8) on two regions of the substrate (1) which are opposed each other with the bias line (61, 62) between them; and forming the magnetic substance layer (9) across the bias line (61, 62) by applying a magnetic substance (9) to the thermoplastic material layer (8) and heating the magnetic substance (9) and the thermoplastic material layer (8) to adhere the magnetic substance (9) to the thermoplastic material layer (8). Method according to claim 1, characterized by the step of forming the thermoplastic material layer (8) on a region of the substrate (1) including a required region on the bias line (61, 62). Method according to claim 1, characterized by the following steps: forming a plurality of island patterns of thermoplastic material (10) on two regions of the substrate (1) which are opposed each other with the bias line (61, 62) between them; and forming the magnetic substance layer (9) across the bias line (61, 62) by applying a magnetic substance (9) to the island patterns of thermoplastic material (10) and heating the magnetic substance (9) and the island patterns (10) to adhere the magnetic substance (9) to the island patterns (10). Method according to claim 1, characterized in that the thermoplastic material layer (8) comprises thermoplastic polyimide. Method of claim 1, characterized in that the magnetic substance layer (9) comprises a thermoplastic material containing ferrite grains. Method according to claim 1, characterized in that the magnetic substance layer (9) comprises ferrite. Method according to claim 1, characterized in that the integrated circuit device is a monolithic semiconductor integrated circuit device.

Inventors: GOTO KEI, INOUE AKIRA, MATSUBAYASHI HIROTO, NAKAJIMA YASUHARU, NOTANI YOSHIHIRO, OHTA YUKIO, GOTO, KEI, INOUE, AKIRA, MATSUBAYASHI, HIROTO, NAKAJIMA, YASUHARU, NOTANI, YOSHIHIRO, OHTA, YUKIO
Applicants: MITSUBISHI ELECTRIC CORP, MITSUBISHI DENKI KABUSHIKI KAISHA
Application year: 1996
Main classification: H01L23
IPC codes: H01L21, H01L27, H01L23, H03F1, H03F3, H01P1, H01L29