Integrated circuit

Abstract: An integrated circuit having a capacitor consisting of an active area originally employable for power supply / GND, a gate insulator layer and a conductive poly crystalline silicon layer produced on a part of the active area originally employable for power supply / GND, the capacitor being employed to exclude external noises from the integrated circuit. It is noted the capacitor is produced on an area which is remained unemployed in the prior art.

Description: This invention relates to an improvement applicable to an integrated circuit. More specifically, this invention relates to an improvement developed for enabling a semicustom integrated circuit particularly a semicustom LSI to exclude external noises particularly noises originated from a power supply, from the semicustom integrated circuit. BACKGROUND OF THE INVENTION An IC or LSI available in the prior art usually has a circuit having a capacitor connected in series with earth, the circuit being arranged between the core domain and the I/O domain of the IC or LSI. The function of the circuit is to prevent external noises from flowing into the major circuits of the IC or LSI and to expel them toward outside of the IC or LSI. A semicustom IC or LSI has a plurality of unit cells arranged in a regular lattice pattern or in a matrix pattern. Fig. 1 illustrates the plan view of the unit cell of a semicustom LSI. In the drawing, the numeral 1 shows a unit cell having a P channel transistor 2 and an N channel transistor 11 therein. The P channel transistor 2 has an N - doped semiconductor layer 3 whose potential is selected to be identical to the substrate potential. The numeral 4 shows an N + active area located in the N - doped semiconductor layer 3. The numeral 5 shows a P semiconductor substrate, the numeral 6 shows an N well produced in the P semiconductor substrate, the numeral 7 shows gates, the numeral 8 shows a P - doped semiconductor layer, the numeral 9 shows a P + active area located in the P - doped semiconductor layer 8, and the numeral 10 shows a VDD line. Incidentally, the N channel transistor 11 has a P - doped semiconductor layer 12 whose potential is selected to be identical to the substrate potential. The numeral 13 shows a P + active area located in the P - doped semiconductor layer 12, the numeral 14 shows an N - doped semiconductor layer, the numeral 15 shows an N + active area, the numeral 16 shows gates and the numeral 17 shows a VSS line. In order to fulfill the foregoing object, the foregoing capacitor is required to have a relatively large amount of capacity. This resultantly requires a large horizontal area on an IC chip. Since improvement in integration is one of the most important requirements for an IC or LSI, the foregoing structure of an IC or LSI is a big drawback which should be removed by all means. From EP-A-0644594 a power supply wiring for a semiconductor device is known wherein a gate oxide film and a gate are formed below a power supply line. By sandwiching the gate oxide film between the gate and an inversion layer below the oxide film, a capacitor is formed constituting a large capacitance bypass capacitor between the power source and the ground reducing power supply noise. JP-A-03-097245 and corresponding English language abstract describes a semiconductor device wherein capacitors are provided on the corner part regions of the gate array device, so as to be connected to power supply and suppressing power supply noise inside the gate array device. JP-A-63-143843 describes a power source wiring for a semiconductor integrated circuit having a large capacitor in the semiconductor substrate directly beneath a metallic power source wiring layer and a grounding wiring layer, wherein the capacitor is connected to the power supply metal wiring. It is thus possible to reduce the fluctuations in the supplied power source voltage. US patent No. 5,307,309 describes a single in-line memory module board provided with a plurality of semiconductor devices which include as part of each memory device a current spike leveling capacitor. The capacitor is on the die side of circuitry connecting the memory device to the board. By connecting the on-chip capacitors of the memory devices in parallel, sufficient capacitance is provided to stabalize the current to all of the memory devices. From JP-A-07-106521 a semiconductor integrated circuit device is known wherein capacitor cells are arranged on a wiring region, using a cell base design technique to insert a bypass capacitor without increasing the chip size. OBJECT AND SUMMARY OF THE INVENTION Accordingly, an object of this invention is to provide an integrated circuit which does not require an additional horizontal area for arranging a capacitor which is employable to expel higher harmonics contained in a noise originated from a power supply (a power supply noise) toward outside of the integrated circuit. The foregoing object can be achieved by any of the following integrated circuits. An integrated circuit in accordance with this invention is defined by claim 1. As is clear from the above, the only structural change applicable to a semicustom IC or LSI available in the prior art for the purpose to produce an integrated circuit in accordance with the first embodiment of this invention is limited to a structural change applicable to a poly crystalline silicon layer which is the bottom layer of a semiconductor IC available in the prior art. It is noted that no change is required for the wirings, and that an area which has not been employed so far is positively employed in the first embodiment of this invention. The gates of the field effect transistors and the electrode of the capacitor can be made of the same material and made via the same gate insulator layer. BRIEF DESCRIPTION OF THE DRAWINGS This invention can be readily understood from the following detailed description presented in conjunction with the following drawings, in which : Fig. 1 is a plan view of a unit cell of a semiconductor LSI available in the prior art, Fig. 2 is a plan view of a unit cell of a semicustom LSI in accordance with the first embodiment of this invention, Fig. 3 is a cross section of Fig. 1, along the A-B line, Fig. 4 is an equivalent circuit diagram of Fig. 3, Fig. 5 is a plan view of a unit cell of a semicustom LSI in accordance with an embodiment not according to this invention, Fig. 6 is an enlarged plan view of the corner (Corner A) of a semicustom LSI in accordance with the embodiment of Fig 5; Fig. 7 is an enlarged plan view of edge B of a semicustom LSI, the edge B being shown in Fig. 6, Fig. 8 is a plan view of a unit cell of a semicustom LSI in accordance with a further embodiment not of this invention, Fig. 9 is an enlarged plan view of the corner (Corner A) of a semicustom LSI in accordance with the embodiment of Fig. 8, Fig. 10 is a more enlarged plan view of the corner (Corner C) of a unit cell of a semicustom LSI of Fig. 8, Fig. 11 is a plan view of a unit cell of a semicustom LSI in accordance with a still further embodiment not of this invention, Fig. 12 is an enlarged plan view of Area D (Power supply ring) of a unit cell of a semicustom LSI in accordance with Fig. 11, Fig. 13 is a plan view of a unit cell of a semicustom LSI in accordance with another embodiment not of this invention, Fig. 14 is an enlarged plan view of the corner of a unit cell of a semicustom LSI in accordance with the embodiment of Fig. 13. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to drawings, a detailed description will be presented below for integrated circuits in accordance with this invention. EMBODIMENT OF THE INVENTION Referring to drawings, an integrated circuit in accordance with the first embodiment of this invention will be described below. Fig. 2 is a plan view of a unit cell of a semicustom LSI in accordance with the first embodiment of this invention. A semicustom LSI has a plurality of the unit cells illustrated in Fig. 2, the plurality of the unit cells being arranged in a regular lattice pattern or in a matrix pattern. One of the plural unit cells is illustrated in Fig. 2. Fig. 3 is a cross section of Fig. 1, along the A-B line and Fig. 4 is an equivalent circuit diagram of Fig. 3. Referring to Figs. 2 through 4, a numeral 20 shows a P channel transistor, a numeral 21 shows a P substrate, the numeral 22 shows an N well, the numeral 24 is an N + active area made in an N - doped semiconductor layer 23, the numeral 25 shows a P - doped semiconductor layer, the numeral 26 shows a P + active area, the numeral 27 shows gates made of conductive poly crystalline silicon and the numeral 28 shows a VDD line. An N channel transistor 30 has an N - doped semiconductor layer 31, a P + active area produced in the P - doped semiconductor layer, an N - doped semiconductor layer 33, an N + active area produced in the N - doped semiconductor area 33, an N + active area 34, a gate 35 made of conductive poly crystalline silicon and a VSS line 36. Poly crystalline silicon layers 43 are produced to cover all the active areas 24 and 32 which are exclusively employed for power supply / GND, to form capacitors each of which consists of the poly crystalline silicon layers 43, the gate insulator 41 and the active area 24 or 32. The poly crystalline silicon layers 43 made of conductive poly crystalline silicon is produced in a step for producing the gates 27 or simultaneously with the gates 27. In other words, the poly crystalline silicon layers 43 is produced on an active area 24 or 32, thereby MIS capacitors described above are produced. In Fig. 3, the numeral 42 shows a field insulator layer. As was described above, capacitors are formed by the P + active area 32, a gate insulator layer 41 and the poly crystalline silicon layer 43 and by the N + active area 24, a gate insulator layer 41 and the poly crystalline silicon layer 43. These capacitors are connected in series by the poly crystalline silicon layer 43 produced on the field insulator layer 42, as shown by an equivalent circuit diagram illustrated in Fig. 4. ' Since the capacitors are formed by combination of the P + active area 32, a gate insulator layer 41 and the poly crystalline silicon layer 43 and of the N + active area 24, a gate insulator layer 41 and the poly crystalline silicon layer 43, no change is required for layer configuration of a semiconductor LSI available in the prior art, to produce a semicustom LSI in accordance with the first embodiment of this invention. Further, since an area which was remained unemployed in the prior art is positively employed in this embodiment of this invention, it is effective to improve the magnitude of integration. In addition, since the dielectric layer 41 of the capacitor is a thin silicon dioxide layer produced by oxidation of silicon in the step for producing the gate insulator layer 41, the capacity of the capacitor is large. FURTHER EMBODIMENT Referring to drawings, an integrated circuit in accordance with an embodiment not of this invention will be described below. Fig. 5 is the plan view of a semicustom LSI, Fig. 6 is an enlarged plan view of the corner (Corner A) of a semicustom LSI in accordance with this embodiment and Fig. 7 is an enlarged plan view of edge B of a semicustom LSI, the edge B being shown in Fig. 6. Referring to Fig. 5, a semicustom LSI in accordance with this embodiment consists of a core domain 51, I/O domains 52, corner (Corner A) 53, a power supply ring 54 which surrounds the core domain 51 and three lines 55 each of which is arranged close to one another and which are made of poly crystalline silicon. Referring to Fig. 6, the three lines 55 arranged close to one another and which are made of poly crystalline silicon are produced in the area remained unemployed in the prior art. It is noted that connection pads 56 to be connected with VDD and connection pads 57 to be connected with GND are utilized for producing the three lines 55. It is further noted that the three lines 55 are arranged to make the space therebetween minimum. The three lines 55 surrounds the core domain 51 and the I/O domains 52. Referring to Fig. 7, the three poly crystalline silicon lines arranged close to one another consists of a first poly crystalline silicon line 55A, a second poly crystalline silicon line 55B and a third poly crystalline silicon line 55C. The numerals 61 and 63 show respectively a line drawn from the pad 56(GND) and the pad 57(VDD). The numerals 62 and 63 show contacts. The numeral 65 shows an N well. A layout system is employed to produce the foregoing circuit structure. VDD / GND cells are arranged in a wiring step. After the VDD cell is arranged by an automatic process, the line 61 drawn from the pad 56(GND) is connected with the second poly crystalline silicon line 55B by the contact 62. After the GND cell is arranged by an automatic process, the line 63 drawn from the pad 57(VDD) is connected with the first poly crystalline silicon line 55A and the third poly crystalline silicon line 55C by the contact 64. The second poly crystalline silicon line 55B is arranged on an N + active area, and the first poly crystalline silicon line 55A and the third poly crystalline silicon line 55C are arranged on a P + active area. Further, an N well electrically separates the area from the substrate. The foregoing layer arrangement is effective to produce a capacitor. In other words, a MIS capacitor is produced by the second poly crystalline silicon line 55B and the lower layers, and fringing capacitors are produced by a combination of the second poly crystalline silicon line 55B and the first poly crystalline silicon line 55A and by a combination of the second poly crystalline silicon line 55B and the third poly crystalline silicon line 55C. As was described above, an integrated circuit in accordance with the embodiment is provided with three poly crystalline silicon lines 55A, 55B and 55C which are produced surrounding the core domain and the I/O domains. This resultantly produces a large amount of MIS capacity and fringing capacity, which can be employed to expel the power supply noise toward out of the integrated circuit. Since the area on which the foregoing three poly crystalline silicon lines are produced is an area remained unemployed along the edges of the integrated circuit available in the prior art, the integrated circuit in accordance with the embodiment turns out to improve the integration for the integrated circuit. FURTHER EMBODIMENT Referring to drawings, an integrated circuit in accordance with a further embodiment not of this invention will be described below. Fig. 8 is a plan view of a semicustom LSI in accordance with the embodiment, Fig. 9 is an enlarged plan view of the corner (Corner A) of a semicustom LSI in accordance with the embodiment and Fig. 10 is a more enlarged plan view of the corner (Corner C) of a semicustom LSI in accordance with the embodiment. Since the overall structure of and the specific structure of the corner (Corner A) of the semicustom LSI of Fig. 8 are identical to those of the semicustom LSI in accordance with the previous embodiment all the members illustrated in Figs. 8 through 10 are allotted numerals identical to those of the corresponding ones of the embodiment of Fig. 8. Thus, eliminated is a detailed description for the general matters of the semicustom LSI in accordance with this embodiment. Referring to Fig. 10, a VDD pad 71 which is a fixed pad is connected with a P + active area 78 by contacts 74 at locations where a wiring 73 surrounds an N well 72. Upper lines 76 are drawn from a GND pad 75 which is a fixed pad and are connected with a poly crystalline silicon layer 77 by contacts 74 and by second through holes (VIA2) 79. The poly crystalline silicon layer 77 is produced on a P + active area 78, and is separated from a substrate by an N well 72. As was described above, an integrated circuit in accordance with the embodiment is provided a poly crystalline silicon line produced at the corners of an integrated circuit, the corners which were remained unemployed in the prior art, are positively utilized to produce capacitors which are employed to exclude external noises from the integrated circuit. FURTHER EMBODIMENT Referring to drawings, an integrated circuit in accordance with a still further embodiment will be described below. Fig. 11 is a plan view of a semicustom LSI and Fig. 12 is an enlarged plan view of the edge D (power supply ring line) of the semicustom LSI of Fig. 12. Since the structure of the semiconductor LSI in accordance with this embodiment is identical to that of the embodiment of Fig. 5, all the members illustrated in Figs. 11 and 12 are allotted numerals identical to those of the corresponding ones of Fig. 5. Thus, eliminated is a detailed description for the general matters of the a semicustom LSI in accordance with this embodiment. Referring to Fig. 12, processes employed for the embodiments of Figs. 5 and 8 are employed to produce an active layer 81 under the area of the power supply ring line 54. The active layer 81 is covered by a poly crystalline silicon layer 82, to form a capacity thereby. The numerals 83 and 84 show respectively VDD lines and GND lines. As was described above, a power supply ring line 54 which surrounds the core domain 51 of an integrated circuit, can be employed to arrange a poly crystalline silicon line 55, to form a capacity. In a similar manner as is in the previously described embodiments, a poly crystalline silicon layer can be produced on the I/O domains 52 which are produced on the active layer. This layer configuration is also effective to produce a capacitor. ANOTHER EMBODIMENT Referring to drawings, an integrated circuit in accordance with another embodiment not of this invention will be described below. Fig. 13 is a plan view of semicustom LSI in accordance an embodiment and Fig. 14 is an enlarged plan view of the corner of a semicustom LSI in accordance with the embodiment of Fig. 13. Since the overall structure of the semicustom LSI in accordance with this embodiment is identical to that of the semicustom LSI in accordance with the embodiment of Fig. 5, all the members illustrated in Figs. 13 and 14 are allotted numerals identical to those of the corresponding ones of Fig. 5. Thus, eliminated is a detailed description for the general matters of the semicustom LSI in accordance with this embodiment. Referring to Fig. 14, poly crystalline silicon layers and active regions 92 are arranged in the area where pads 91 are arranged. In this manner, a capacitor can be produced. As was described above, an integrated circuit in accordance with the embodiment positively employs the area remained unemployed in the prior art. The foregoing description has clarified that an integrated circuit which does not require an additional horizontal area for arranging a capacitor which is employable to expel higher harmonics contained in a power supply noise toward outside of the integrated circuit, has successfully been provided by this invention, resultantly enabling the integrated circuit to be appropriately employed for a semicustom LSI. It is particularly emphasized that this invention positively employs the surface area of an integrated circuit which area is remained unemployed in the prior art, specifically for the purpose to produce a capacitor for the ultimate purpose to exclude external noises particularly noises originated from a power supply.

Claims: An integrated circuit having a plurality of unit cells disposed adjacent each other, each of said unit cells comprising: a first field effect transistor (20) of a first conductivity; a first area (24, 23) of a second conductivity, being supplied a first voltage, V DD , during operation; a second field effect transistor (30) of the second conductivity; a second area (32, 31) of the first conductivity, being supplied a second different voltage, V SS , during operation, characterized by a floating conductivity line (43) extended over the first (24, 23) and second (32, 31) areas electrically separated from the first and second voltages; a first insulator layer (41) between the conductive line and the first area (24, 23) such that a first capacitor is formed by the conductive line (43), the first insulator layer (41) and the first area (24, 23); a second insulator layer (41) between the conductive line (43) and the second area (32, 31) such that a second capacitor is formed by the conductive line (43), the second insulator layer (41) and the second area (32, 31). An integrated circuit according to claim 1, wherein the conductive line (43) is formed by a polycrystalline silicon layer. An integrated circuit according to claim 1 or 2, wherein the first and second insulator layers (41) are formed by gate insulators. An integrated circuit according to claim 3, wherein the first and second insulating layers (41) are thin silicon dioxide layers produced by oxidation of silicon in the step of producing the gate insulating layer. An integrated circuit according to one of claims 1 to 4, wherein gates (35) of said first and second transistors (20, 30) and the conductive line (43) are made of the same material and formed over the same insulator layer (41). An integrated circuit according to one of claims 1 to 5, each of said unit cells further comprising a second conductive line (43) extended over the second area (32, 31) and extended over a first area (24, 23) of an adjacent unit cell. An integrated circuit according to claim 6, each of said unit cells further comprising a third conductive line (43) extended over the first area (24, 23) and extended over a second area (32; 31) of another adjacent unit cell.

Inventors: MASUDA HIROHISA, TASHIRO MASAHISA, MASUDA, HIROHISA, TASHIRO, MASAHISA
Applicants: OKI ELECTRIC IND CO LTD, OKI ELECTRIC INDUSTRY CO., LTD.
Application year: 1997
Main classification: H01L27
IPC codes: H01L21, H01L27