A semiconductor integrated circuit having wirings for power supply

Abstract: A semiconductor integrated circuit of standard-cell type or gate-array type includes a plurality of first cells arranged in a plurality of parallel lines, the first cells having first wirings for supplying power, the first wirings being extended over a plurality of the first cells arranged in the same line in a direction of the same line of the first cells, a second cell disposed in the neighbourhood of some of the first cells and having a dimension larger than the first cells, said second cell having second wirings on a periphery thereof to surround circuit portion of the second cell and means for connecting the second wirings with the first wirings in the first cells in the neighbourhood of the second cell.

Description: BACKGROUND OF THE INVENTION Field of the Invention: The present invention relates to a semiconductor integrated circuits (hereinafter, referred to IC's) suited for computer-aided-design, and more particularly to standard-cell type IC's using poly-cells having improved wiring structure for supplying power. PRIOR ART As semi-custom LSI's (Large Scale Integrated cirsuits) designed in accordance with the customer's specification, the standard-cell type IC's using polycells have been widely used. They are designed by a technique similar to the gate-array type semiconductor integrated circuits (hereinafter, simply referred to the gate-array IC's). In the gate-array process, a plurality of blocks of circuit elements and limited number of wirings are preliminarily formed on a semiconductor chip. An electrical circuit in accordance with the customer's specification is then formed by designing a wiring pattern. The wiring pattern to be designed in the later process include wirings for forming a cell of circuit with the circuit elements in each block, wirings for connecting the cells and wirings for supplying power. On the other hand, the standard-cell type IC using polycells, the blocks of circuit elements are used in software program for designing an IC. The wirings for forming the polycells of circuit with the circuit elements and for connecting the polycells are also designed by computor-aided-design. All the masks for producing the standard-cell type IC is designed by the computer-aided-design. In the standard-cell type IC, a plurality of polycells are arranged in lines. The polycells have the same or the substantially same width in a direction perpendicular to the line and arbitrary length in a direction in parallel with the line. The polycells are made of various standardized blocks of circuit elements. The standard-cell type IC's are designed by combining the polycells formed by the standardized blocks. The use of the standardized blocks makes the computor-aided-designe of IC easy, resulted in an improvement of design efficiency. Turning to the design of wirings for power supply, they are designed so as to traverse the polycells and to reach predetermined positions on opposing sides facing the neighbouring polycells. If all the polycells have the same width, the wirings for power supply automatically contact with those in the neighbouring polycells. The cells to be formed in a semiconductor chip, however, may have different dimensions. Cells for specific functions such as RAM (Random Access Memory), ROM (Read-Only Memory), microprocessor, peripheral controller of the microprocessor and PLA (Programable Logic Array) may be included as megacells which have a dimension much larger than the polycells. If the wirings for power supply in the megacells are similarly designed to the polycells, the wirings for power supply differ in position between neighbouring polycell and megacell at their sides facing to each other. Thus, disconnection occurs at contacting sides of those cells having different dimensions. In the prior art, such disconnection was cured by manual correction of wiring pattern. The manual correction spoilt the production efficiency of the computor-aided-design to raise the production cost and to prolong the production period of term. A semiconductor integrated circuit according to the preamble part of the main claim is known from US-A-4 161 662. A similar device is known from IBM TECHNICAL DISCLOSURE BULLETIN, Vol. 27, No. 11, April 1985, pages 6687-6691; USA; "Flexible image for physical layout of circuits". A further similar semiconductor circuit is known from the older application EP-A-0 170 052. This application falls under article 54(3) EPC. SUMMARY OF THE INVENTION It is, therefore, a major object to provide a semiconductor integrated circuit having a structure of wirings for power supply suited for a computer-aided-design and avoiding the possibility of disconnection between cells having different dimensions. According to the present invention, there is provided a semiconductor integrated circuit comprising a semiconductor chip; a plurality of first cells of partial circuit formed on the semiconductor chip and arranged in a plurality of lines, the first cells having the substantially same width in perpendicular to the lines and arbitrary lengths in parallel to the lines, the first cells having a first wirings for supplying power to the partial circuit, the first wirings being extended over a plurality of the first cells arranged in the same line in a direction of said same line; a second cell of another partial circuit formed on the semiconductor chip and arranged in neighbouring with some of the first cells, the second cell having a width larger than the width of the first cells and a length and having second wirings for supplying power to the other partial circuit, the second wirings being disposed on periphery of the second cell to surround the other partial circuit and connected with the first wirings in the first cells in the neighbourhood of the second cell; and means for connecting the second wiring with the first wirings in the first cells in the neighbourhood of the second cell. The IC of the present invention has the second wirings for power supply on periphery of the second cells having a width larger than the neighbouring first cells. The first wiring for power supply, therefore, can be connected with the second wiring by prolonging straight. This connection may be easily achieved by the computer-aided-design technique which requires only modification of the data for the second wiring pattern of the second cell. Any manual correction of wiring pattern is not required. Thus, an efficiency in designing IC is greatly improved with a slight change of wiring pattern. BRIEF DESCRIPTION OF THE DRAWINGS The above and other objects, features and advantages of the present invention will become more apparent from the following description taken in conjunction with the accompanying drawings, in which: Fig. 1 is a schematic view for explaining the wirings for power supply of the standard-cell type IC in the prior art; Fig. 2 is a schematic partial plan view of the first preferred embodiment according to the present invention; Fig. 3 is a schematic but more-detailed partial plan view of a part in the first preferred embodiment according to the present invention; Fig. 4 is a sectional view for explaining a structure used in the first preferred embodiment according to the present invention; Fig. 5 is a schematic partial plan view of the second preferred embodiment according to the present invention; and Fig. 6 is a schematic partial plan view of the third preferred embodiment according to the present invention. The wirings for supplying power on polycells arranged in a line in the prior art of a standard-cell type IC is shown in Fig. 1. The polycells 1 have the substantially same width or height and arbitrary length determined by functions such as an inverter, an AND gate, an OR gate and a flip-flop. A plurality of polycells are arranged in a line to form a stripe having the substantially uniform width. Wirings 2 and 3 are programed in a software for designing a standard-cell type IC so as to run predetermined levels in a direction of the width. Therefore, the wirings 2 and 3 are automatically connected between neighbouring polycells 1 by arranging polycells in a line. When a megacell having a large dimension and then a large width are combined with the polycells 1, wirings for the power supply between neighbouring polycell and the megacell cannot be connected with each other by the computor-aided-design which is programed so that wiring for the power supply may run on predetermined levels in the width. For avoiding such disconnection of the wirings, a complicated software program for the computer-aided-design or a manual correction of the wirings is required. It is difficult to make such software program commonly applicable to the standard-cell type IC including the megacell having arbitrary dimension. The manual correction of the wirings, therefore, cannot be avoided to lower the efficiency in designing standard-cell type IC's in the prior art. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first preferred embodiment according to the present invention having an improved structure of wirings for power supply is shown in Fig. 2. A plurality of polycells 11 have the substantially same width (or height). A plural number of polycells 11 are arranged in a line to form a stripe having the substantially uniform width. A plural number of stripes of the polycells 11 are disposed in parallel with one another. A megacell 19 having a width of about three times of the width of the polycell 11 is disposed in the parallel arrangement of the stripes of polycells 11. First level wirings 13 for power voltage V DD runs through the stripes of polycells at a predetermined level in the width. First level wirings 12 for power voltage V DD run along peripheries of the megacell 19 in parallel with the stripes of polycells 11 and through the megacell 19 at a one level in the width thereof. Similarly, first level wirings 15 in the polycells 11 and first level wirings 14 in the megacell 19 are formed in parallel with the first level wirings 12 and 13 for supplying power voltage V SS to the polycells 11 and the megacell 19. The first level wirings 12, 13, 14 and 15 directly contact with circuit element in a semi-conductor chip and run thereon through an insulator film in a direction in parallel with the stripe of polycells 11. Second level wirings 16 for supplying power voltage V DD run across the first level wirings 12 to 15 to connect with the first level wirings 12 and 13. Similarly, second level wiring 17 for supplying power voltage V SS run in parallel with the second level wirings 16 to connect with the first level wiring 14 and 15. On the megacell 19, the second level wirings 16 and 17 are disposed on peripheries thereof and on a region thereof in the direction perpendicular to the stripes of polycells 11. The second level wirings 16 and 17 respectively contact with the first level wirings 12 and 13 and the first level wirings 14 and 15 and run on an insulator film disposed on the above-mentioned insulator film on the semiconductor chip. On the periphery of the megacell 19, the first level wirings 12 and 14 and the second level wirings 16 and 17 surround the circuit-element region of the megacell 19 and contact the second level wirings 16 and 17 on the stripes of polycells 11 and the first level wirings 13 and 15 on the stripes of polycells 11. Those connections are achieved by only extending the wirings 16, 17, 13 and 15 on the stripes of polycells 11. The softwave programing to achieve such connection is easy and is commonly applicable to megacells 19 having arbitrary dimension. Any manual correction is not required to obtain a high efficiency in designing standard-cell type IC's. A stripe of polycells 11 is partially shown in Fig. 3. The polycells 11 respectively consist of one or more basic cell patterns 50. The cell pattern 50 includes two P-channel MOS FET's and two N-channel MOS FET's. A P-channel MOS FET is made of a gate electrode 51, a source region 53 and a drain region 54, the other being made of a gate electrode 52, a source region 53 and a drain region 55. An N-channel MOS FET is made of a gate electrode 56, a source region 58 and a drain region 59, the other being made of a gate electrode 57, a source region 58 and a drain region 60. The N-channel MOS FET's are formed in a P-type semiconductor substrate 70, the P-channel MOS FET's being formed in an N-type well-region 71 diffused in the semiconductor substrate 70. Those MOS FET's are wired to form a partial circuit of the standard-cell type IC with first level wirings running in parallel with the stripe of polycells 11 and second level wirings running in perpendicular to the stripe of polycells 11. The first level wirings directly contact with the source and drain regions, but the second level wirings contact with them through the first level wirings. To accomplish this structure, a lower insulator film, the first level wirings, an intermediate insulator film, the second level wirings and an upper insulator film are formed on the semiconductor substrate in this order. Those first and second level wirings also connect MOS FET's in different polycells 11 to form a whole circuit of a standard-cell type IC. Such structure is explanatory shown in Fig. 4 which is drawn only for explaining the concept of the structure and which does not correspond to any actual part of Figs. 2 and 3. The N-type well region 71 is provided in the P-type substrate 70. P-type source and drain regions 53 and 54 are formed in the well-region 71. The gate electrode 51 is formed on a gate insulator film 77 disposed between the source and drain regions 53 and 54. N-type source and drain regions 58 and 59 are formed in the semiconductor substrate 70. The gate electrode 56 is formed on a gate insulator film 78 disposed between the source and drain regions 58 and 59. The semiconductor substrate 70 and the N-well region 71 are covered with a phosphosilicate glass 72 having a thickness of 1 µm. The first level wirings 73 made of aluminum, for example, are evaporated on the phosphosilicate glass 72 and connected with the source and drain regions 53, 54, 58 and 59 through holes in the phosphosilicate glass 72. The thickness of the first level wirings 73 is 0.5 µm, for example. The first level wirings 73 runs in parallel with the stripe of polycells 11. A silicon oxide film 74 having a thickness of 1 µm covers the first level wirings 73. The second level wirings 75 having a thickness of 1 µm and made of aluminum, for example, are deposited on the silicon oxide film 74 and connected with the first level wirings 73 through holes in the silicon oxide film 74. The second level wirings 75 runs in perpendicular to the stripe of polycells 11. Silicon nitride film 76 having a thickness of 1 µm covers whole structure except for bonding pads (not shown) as a surface passivation film. Fig. 5 shows a peripheral portion of the megacell 19 according to the second preferred embodiment which is modified to improve the connection between wirings on the periphery of the megacell 19 and wirings on the polycell 11. This second embodiment has two first level wirings 12 and 14 for supplying power voltages V DD and V SS on the central part of the megacell 19. In accordance with position of the wirings 12 and 14, there happens a case where one or two of the wirings 12 and 14 forms straight lines with the first level wirings 13 and 15 on the polycells 11. When the wirings 12 for the power voltage V DD forms the straight line with the wirings 15 for the power voltage V SS and/or the wirings 14 for the power voltage V SS forms the straight line with the wirings 13 for the power voltage V DD , the above-mentioned first embodiment has a possibility that any one of the wirings forming a straight line cannot be connected with the second level wirings 15 or 17 on the periphery of the megacell 19, because those wirings 12 to 15 are made of the same first level wirings. The second preferred embodiment has additional second level wirings 18 to form three parallel wirings 16, 17 and 18 on the periphery of the megacell 19. The first level wiring 14 connects with the second level wiring 18. The first level wirings 12 and 13 connect with the second level wiring 16. The first level wiring 15 connects with the second level wiring 17. The second embodiment resolved the problem by the additional wiring 17 and requires no difficulty in the software program. The third preferred embodiment shown in Fig. 6 is another resolusion for the same problem. The first level wiring 13 turns perpendicularly by use of a second:level wiring 20 and then connects with the second level wiring 16. This embodiment use only two second level wirings 16 and 17 on the periphery of the megacell 19 to save area. The present invention can be applicable to the gate-array IC in which macrocell has wirings for power supply on the periphery thereof, similarly to the regacell in the standard-cell type IC. Furthermore, the functions of the first and second level wirings for supplying power voltages may be interchanged. The first and second level wirings respectively have wirings for supplying a high power voltage and a low power voltage or a high or low power voltage and a grounding potential.

Claims: A semiconductor integrated circuit comprising: a semiconductor chip ; a plurality of first cells (11) of partial circuits formed on said semiconductor chip and arranged in a plurality of parallel lines, said first cells having the substantially same width in a direction perpendicular to said lines, said first cells having a plurality of first wirings (13,15,16, 17) for supplying power to said partial circuits, said plurality of first wirings consisting of a first level of first wirings (13,15) in a direction parallel with said plurality of lines and a second level of first wirings (16,17) intersecting with said first level of first wirings; a second cell (19) of another partial circuit formed on said semiconductor chip and arranged so as to neighbor with some of said first cells, said second cell having a width larger than said width of said first cells and having second wirings (12,14,16,17) for supplying said power to said other partial circuit; and means for connecting said first wirings in said first cells in the neighborhood of said second cell with said second wirings: characterized in that said second wirings (12,14,16,17) are disposed on the inside periphery of said second cell (19) along sides of the same to encircle said other partial circuit in said second cell and said first wirings (13,15, 16,17) in said first cells (11) in the neighborhood of said second cell are connected with said second wirings by being linearly extended over said first cells in the neighbor-hood.

Inventors: ITO SOICHI C O NEC CORPORATION, MABUCHI YOSHIHIRO C O NEC CORP, ITO, SOICHI C/O NEC CORPORATION, MABUCHI, YOSHIHIRO C/O NEC CORPORATION
Applicants: NIPPON ELECTRIC CO, NEC CORPORATION
Application year: 1987
Main classification: H01L27
IPC codes: H01L23, H01L27, H01L21