SEMICONDUCTOR INTEGRATED CIRCUIT COMPRISING A SEMICONDUCTOR SUBSTRATE AND INTERCONNECTING LAYERS

Abstract: A semiconductor integrated circuit includes a conven­ tional inner cell region (2) and an outer cell region (4). The outer cell region contains a plurality of outer cells (3;116,117) each comprising circuit elements (R₁-R′₄, Q₁-Q′₉) for achieving a predetermined logic function, in addition to circuit elements for achieving the conventional buffer func­ tion of an outer cell. Two or more adjacent outer cells (116,117) cooperate with each other and act as an indepen­ dent circuit so as to form a macro-cell (118).

Description: This invention relates to a semiconductor integrated circuit (IC), and particularly to an IC of a so-called semicustom type in which prefabricated circuit elements are suitably wired during the IC production processes by using, for example, metal sputtering, in accordance with individual user needs. One type of such an IC is a masterslice gate array large-scale integrated circuit (LSI), comprising a bulk including a plurality of basic cells arranged in a plurality of arrays. The wiring inside each basic cell and between the basic cells can be designed automatically with the aid of a computer to produce many varieties of products from one type of bulk. A typical masterslice gate arrange LSI is disclosed in US-A-4 278 897. Such a circuit is fabricated as follows. Firstly, an inner cell region is located at the centre portion of the surface of a substrate. In this region a plurality of inner cells, each provided with a plurality of circuit elements, is arranged in a plurality of arrays. Secondly, an outer cell region, i.e. an input/output (I/O) buffer cell region, is located close to and along a peripheral portion on the surface of the substrate. In this region, a plurality of outer cells, i.e. I/O cells, each provided with a plurality of circuit elements, is arranged. Each of the I/O cells achieves operation for a level conversion between signals appearing in the inner cells and signals appearing outside the masterslice gate array LSI. Thirdly, at least a first wiring layer and a second wiring layer are provided as multilayers on the substrate for distributing lines between the circuit elements. The circuit elements of the inner cells are suitably connected by lines distributed on the first and second wiring layers so as to create desired logic circuits. Power belts are also distributed on the second wiring layer along and above the I/0 cell region. In the above-mentioned typical masterslice gate array LSI, the I/0 cell region functions only for level conversion. Thus, the efficiency of utilisation of the circuit elements on the LSI chip has not been very high. It is an object of the present invention to improve the efficiency of utilisation of the circuit elements on the LSI chip. According to one aspect of the invention there is provided a semiconductor integrated circuit operatively connected to receive external input signals, comprising a semiconductor substrate having a centre portion and a peripheral portion; wiring formed as a plurality of wiring layers on the semiconductor substrate; an inner cell region formed on the centre portion of the semiconductor substrate and having a plurality of relatively low-power inner cells which are arranged in arrays and are operatively connected to each other by the wiring, each of the inner cells comprising a plurality of circuit elements interconnected by the wiring; and an outer cell region formed on the peripheral portion of the semiconductor substrate in a multilayer structure with part of the wiring, the outer cell region occupying less space than that part of the wiring, and comprising a plurality of relatively high-power outer cells each of which comprises a plurality of circuit elements interconnected by the wiring; characterised in that circuit elements in adjacent outer cells in the outer cell region are selectively connected to each other to form a macrocell which performs a function which is different from the function which other single outer cells can perform, thereby releasing a cell or cells in the inner cell region which would otherwise be required to perform said function. According to another aspect of the invention there is provided a semiconductor integrated circuit comprising a semiconductor substrate having a centre portion and a peripheral portion; first level and second level wiring layers formed on the semiconductor substrate, the second level wiring layer being formed over the first level wiring layer; an inner cell region located at the centre portion of the semiconductor substrate, the inner cell region comprising a plurality of relatively low-power inner cells which are arranged in the form of arrays and are connected by the first and second wiring layers, each of the inner cells comprising a plurality of circuit elements interconnected by the first level wiring layer; and an outer cell region located at the peripheral portion of the semiconductor substrate in a multilayer structure with a third wiring layer, and occupying less space than the third wiring layer, the outer cell region comprising a plurality of relatively high-power outer cells each of which comprises a plurality of circuit elements interconnected by at least the first level wiring layer; characterised in that circuit elements in adjacent outer cells in the outer cell region are selectively connected to each other to form a macro-cell which performs a function which is different from the function which other single outer cells can perform, thereby releasing a cell or cells in the inner cell region which would otherwise be required to perform said function. Embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, wherein: Fig. 1A is a plan view of one example of a known typical IC: Fig. 1B is an enlarged plan view of one corner part of the IC shown in Fig. 1A; Fig. 1C is a reduced plan view used for illustrating power sources located above an I/O cell region (outer cell region) of Fig. 1B; Fig. 2 is a block diagram of one example of a conventional IC; Fig. 3 is a circuit diagram of a first embodiment according to the present invention; Fig. 4 is a symbolic diagram schematically representing the I/O cell (outer cell) of Fig. 3; Fig. 5 is a circuit diagram of a modification of the conventional IC shown in Fig. 2, according to the present invention; Fig. 6 is a circuit diagram of a second embodiment according to the present invention; Fig. 7 is a symbolic diagram schematically representing the I/O cell of Fig. 6; Fig. 8 is a symbolic diagram schematically representing an I/O cell similar to that of Fig. 6; Fig. 9 is a detailed circuit diagram representing the first embodiment of Fig. 3; Fig. 10 is a partial plan view of one example of a conventional IC; Fig. 11 is a circuit diagram of a third embodiment according to the present invention; Fig. 12A is a circuit diagram of a fourth embodiment according to the present invention; Fig. 12B is a circuit diagram of a fifth embodiment according to the present invention; Fig. 13 illustrates six circuit diagrams representing sixth, seventh, eighth, ninth, tenth, and eleventh embodiments, in columns (A) through (F), according to the present invention; Fig. 14 is a detailed circuit diagram representing the circuit of the sixth embodiment shown in column (A) of Fig. 13; and Fig. 15 illustrates a detailed example of the circuit shown in Fig. 11. Figure 1A is a plan view of one example of a typical IC. The circuit is fabricated as a masterslice gate array LSI on a single chip. Figure 1B is an enlarged plan view of one corner part of the IC shown in Fig. 1A. The gate array LSI is comprised as follows. Reference numeral 1 represents an inner cell. A plurality of inner cells are arranged in each array 1-1. A wiring region 2-1, or "channel region", is located between each two pairs of arrays 1-1. The wiring regions 2-1 are used for the computer-aided automatic wiring of lines between two or more corresponding inner cells. Reference numeral 2 represents an inner cell region located at the center of the LSI chip and contains many logic circuits. Reference numeral 4 represents an outer cell region, hereinafter called an I/O cell region. The I/O cell region 4 is located closed to and along the peripheral portion of the LSI chip and at the same time outside the inner cell region 2. The I/O cell region 4 contains a plurality of outer cells, i.e. I/O (buffer) cells 3 which operate as electric interfaces between the inner cells 1 and the external circuits of the LSI chip. That is, the I/O cells 3 achieve operations for level conversions between signals appearing inside and outside the LSI chip. Reference numeral 6 (Fig. 1B) represents a power source. The power source 6 comprises, first, V cc power belts and ground belts 6-1, both located as plane-like belts along the peripheral portion of the LSI chip and at the same time above the I/O cell region 4; second, ground lines 6-2 arranged above the inner cell region 2 in a vertical direction in Fig. 1B and on the second wiring layer; third, V cc power lines 6-3 arranged above the inner cell region 2 in a horizontal direction in Fig. 1B and on the first wiring layer; and, fourth, power source pads 6-4. It should be understood that although the above-mentioned power belts, power lines, ground belts, and ground lines are located on the first wiring layer and/or the second wiring layer, these members are illustrated in Fig. 1B as if they were located on the same plane. Reference numeral 5 represents signal line pads to be connected to the corresponding I/O cells 3. Figure 1C is a reduced plan view, for illustrating the power sources located above the I/O cell region 4 of Fig. 1B. In Fig. 1C, the V cc power belt 6′-1 is arranged parallel with the ground belt 6″-1 with a small pitch therebetween. The power source pad 6-4 is used for the V cc power belt 6′-1 via through-holes (not shown). It should be understood that in Fig. 1C, the hatchings illustrated in the belts 6′-1 and 6″-1 do not indicate cross-sections as usual, but are merely for distinguishing one location from another. Generally, in gate array LSI chips, the lines connecting circuit elements of the inner cells 1 and I/O cells 3 are arranged primarily in the X direction on the first wiring layer, primarily in the Y direction on the second wiring layer, and down through the holes for connection between the first and second wiring layers. The inner cell region 2 is located at the center of the LSI chip, and the I/O cell region 4 is located between the inner cell region 2 and the signal line pads 5. The power belts 6-1 are provided in the second wiring layer and above the I/O cell region 4. The lines to be arranged between the power belts 6-1 and the inner cell region 2 are formed as the thin ground lines 6-2 and the thin V cc power lines 6-3 of the second and first wiring layers, respectively. Consequently, the configuration of the I/O cell region 4 is mainly restricted by the power belts 6-1. That is, the locations of the I/O cell regions 4 and the power belts 6-1 are usually almost identical to each other. On the other hand, each of the inner cells 1 and the I/O cells 3 is a combination of various kinds of circuit elements, such as transistors, diodes, resistors, and capacitors. In each of these cells, these circuit elements are selectively connected to obtain the desired basic logic circuits. Such cells are called basic cells. The lines to be arranged inside the basic cells are formed in the first wiring layer, while the lines to be arranged between two or more basic cells are formed in the first and second wiring layers. Since the lines to be connected between the inner cells 1 are arranged utilizing the first and second wiring layers, there is considerably high freedom in wiring. However, since the second wiring layer, located above the I/O cell region 4, is already occupied by the power belts 6-1, the lines to be connected between the circuit elements of the I/O cells 3 have to be formed mainly in the first layer. Thus, there is less freedom in wiring with the I/O cells 3 than with the inner cells 1. In addition, the lines for the I/O cell region 4 should be arranged fixedly. Further, the inner cells 1 must be formed as small as possible, in order to obtain high speed operation and high LSI integration. Contrary to this, the I/O cells 3 must be formed relatively large in order to produce high power for driving the loads. Furthermore, the power voltage and threshold voltage applied to the inner cells 1 must be lower than those of the I/O cells 3, in order to attain low power consumption in the inner cells 1. Therefore, the threshold voltage level of the external circuit of the LSI chip must be matched with the lowered threshold voltage level of the inner cells 1 through a level converting operation by the I/O cells 3. As mentioned above, the I/O cells 3 and the inner cells 1 differ in function and size. Accordingly, cells 1 and 3 cannot be treated as identical cells in computer-aided automatic wiring operations. As previously mentioned, the object of the present invention is to maximize the efficiency of utilization of the circuit elements on the LSI chip. One way of doing this is explained immediately below. A second way will be explained later. Along and on the peripheral portion, the power belts 6-1 and the I/O cell region 4 are formed as a multilayer structure. Therefore, the area allotted to the I/O cell region 4 is determined by the area occupied by the power belts 6-1. Accordingly, the area allotted to the I/O cells 3 must be smaller than that of the power belts 6-1. This results in an unused region, that is, an empty region, adjacent to the I/O cell region 4. The higher the integration of the gate array LSI and the larger the width of the power belts 6-1, the greater the area of the empty region. Regarding the input signal for the inner cell region 2, it is usually necessary to employ two inner cells at the output side of the I/O cell 3, in a case where the logic circuits of the inner cell region 2 require both inverted and non-inverted input signals simultaneously, with respect to the external signal. This is because each I/O cell 3 cannot achieve both buffering and inverting functions. Therefore, one of said two inner cells must be allotted for the buffering function, while the other thereof must be allotted for the inverting function. A more specific explanation follows with reference to Fig. 2. Figure 2 is a block diagram of one example of a conventional IC. In Fig. 2, the signal line pad 5 is connected to an input 9 of a buffer 8 included in the I/O cell 3 contained in the I/O cell region 4. An output 10 of the buffer 8 is connected to both an input 13 of an inverter 11 and an input 14 of a buffer 12. Both the inverter 11 and the buffer 12 are fabricated inside the inner cell region 2. A signal from an output 15 of the inverter 11 is applied to both inputs 18 and 19 of inverters 16 and 17, respectively. A signal from an output 20 of the inverter 12 is applied to both inputs 23 and 24 of inverters 21 and 22, respectively. Outputs 25, 26, 27, and 28 of respective inverters 16, 17, 21, and 22 are connected in a logic circuit group 29 to inputs 30, 31, inputs 32, 33, inputs 34, 35, and inputs 36, 37, respectively. An input signal is applied to the LSI chip through the signal line pad 5 and then applied to the buffer 8 in the I/O cell 3, in which the level of the input signal is converted into the signal level specified for the inner cell region 2. The output signal from the buffer 8 is applied to both buffer 12 and the inverter 11 and thereby both non-inverted and inverted signals, with respect to said input signal, are respectively formed therethrough. These non-inverted and inverted input signals are supplied to the logic circuit group 29 at its inputs 30 through 37. If the logic circuit group 29 thus requires both non-inverted and inverted input signals, the buffer 12 and the inverter 11 must be fabricated by two inner cells 1 inside the inner cell region 2 and between the inputs of the logic circuit group 29 in the region 2 and the buffer 8 in the region 4. As a result, the efficiency of utilization of the inner cells 1 in the inner cell region 2 is reduced due to the presence of such inverter 11 and buffer 12 in the region 2. Conventional gate array LSI′s frequently have inverter 11 and buffer 12 fabricated by using two inner cells 1 between the inputs of the logic circuit group and the buffer 8 in the I/O cell 3. Introducing such a construction fixedly in the inner cell region 2, however, is not preferable in terms of efficiency of utilization of the inner cells 1, because it reduces the high degree of freedom in wiring in the region 2 itself. According to the present invention, the above-mentioned conventional construction for performing logic functions, fixedly existing and using the inner cells 1, is replaced by one using the I/O cells 3. This can easily be done because the region for the I/O cells 3 is increased in proportion to the recent increase of the area to be occupied by the power belts. In other words, the fixed construction for performing logic functions is realized in a region having a relatively low degree'of freedom in wiring, that is, in the region 4. This eliminates the fixed construction for logic functions from the inner cell region 2, having a high degree of freedom in wiring, enabling more variable constructions for other logic functions to be incorporated into this region. Figure 3 is a circuit diagram of a first embodiment according to the present invention. In an I/O cell 40, a buffer 41 for converting the level of signal is fabricated. An input signal is applied through the signal line pad 5 to an input 42 of the buffer 41. The output 43 of the buffer 41 is connected to inputs 46 and 47 of an inverter 44 and a buffer 45, respectively, both located in the same I/O cell 40. Output signals of the I/O cell 40 are produced from outputs 48 and 49 of the inverter 44 and the buffer 45, respectively. Figure 4 is a symbolic diagram schematically representing the I/O cell of Fig. 3. In Fig. 4, a circuit corresponding to that of Fig. 3 is indicated as an output circuit 50 for producing both inverted and non-inverted signals. Figure 5 is a circuit diagram of a modification of the conventional IC shown in Fig. 2, according to the present invention. This modification is made based on the circuits shown in Figs. 3 and 4, representing one example of the present invention. Reference numerals the same as those in Fig. 2 represent the same member. The signal line pad 5 is connected to an input 51 of the output circuit 50 for producing both inverted and non-inverted signals. An inverting output 52 of the circuit 50 is connected to both inverters 16 and 17. A non-inverting output 53 thereof is connected to both inverters 21 and 22. Accordingly, only the inverters 16, 17, 21, 22, and the logic circuit group 29 are formed inside the inner cell region 2. As understood from the circuits shown in Figs. 3, 4, and 5 according to the present invention, the I/O cell 40 can also function to both non-invert and invert a signal. Therefore, the inner cells 1 for fabricating the buffer and inverter used for achieving the same function as mentioned above are not needed in the inner cell region 2. The inverter 44 and the buffer 45 to be fabricated in the I/O cell 40 of Fig. 3 are built as a multilayer construction together with the aforesaid power belts 16-1 (Fig. 1C). At the same time, the inverter 44 and the buffer 45 can be fabricated in the aforementioned empty region located under the power belts and adjacent to the I/O cell region 4. Since the inverter 44 and the buffer 45 are inserted into the empty region, the size of the LSI chip according to the present invention is exactly the same as that of a similar LSI chip of typical type. In addition to this, the efficiency of utilization of the inner cells 1 in the region 2 in the present invention can be increased over that of the typical inner cell region. Further, it is clear that current branches in the inner cell region 2 are also reduced. Figure 6 is a circuit diagram of a second embodiment according to the present invention. In an I/O cell 40′, two inverted signals with respect to an input signal applied thereto can be produced therefrom. That is, the signal line pad 5 is connected to an input 55 of a buffer 54, and an output 56 of the buffer 54 is connected to both inputs 59 and 60 of respective inverters 57 and 58. The output signals of the I/O cell 40′ are produced from outputs 61 and 62 of respective inverters 57 and 58. Figure 7 is a symbolic diagram schematically representing the I/O cell of Fig. 6. In Fig. 7, the circuit corresponding to that of Fig. 6 is indicated as an output circuit 63 for producing two inverted signals. Figure 8 is a symbolic diagram schematically representing an I/O cell similar to that of Fig. 6. In Fig. 8, the circuit corresponding to that of Fig. 6 is indicated as an output circuit 64 for producing two non-inverted signals with respect to an input signal. However, both the inverters 57 and 58 of Fig. 6 are replaced by buffers such as the buffer 45 of Fig. 3. The existence of two inverted or two non-inverted outputs in a single I/O cell allows, for example, twice the load to be driven compared with a similar I/O cell of a conventional type. This is also true in the aforementioned first embodiment. Figure 9 is a detailed circuit diagram representing the first embodiment of Fig. 3. As previously mentioned, the I/O cell 40 contains the buffer 41 for the level conversion, the inverter 44, and also the buffer 45. In Fig. 9, terminals 42, 48, and 49 and circuits 41, 44, and 45 correspond to those shown in Fig. 3. A level conversion part, that is, the buffer 41 of Fig. 3, is comprised of a resistor R₁, diodes Q₂, Q₆, Q₇, and a transistor Q₁. An inversion part, that is the inverter 44 of Fig. 3, is comprised of resistors R₂, R₃, R₄, diodes Q₅, Q₈, Q₉, and transistors Q₃, Q₄. A buffering part, that is, the buffer 45 of Fig. 3, is comprised of resistors R₂′, R₃′, R₄′, diodes Q₅′, Q₈′, Q₉′, and transistors Q₁₁, Q₁₂. The input of the buffer 41 for the level conversion corresponds to the base of the transistor Q₁. The output of the buffer 41 is located at an interconnecting point 70 between the diodes Q₂ and Q₆. Both the inputs of the inverter 44 and the buffer 45 are located at a base 67 of the transistor Q₃. The output of the inverter 44 is located at a point 65 between the diodes Q₅ and Q₈ and is also connected to the transistor Q₄. The output of the buffer 45 is located at a point 73 between the diodes Q₅′ and Q₈′ and is also connected to the transistor Q₁₂. In Fig. 9, the V cc power line 71 for energizing the buffer 41 has a voltage of, for example, 5 V with respect to a ground line 73, while the V cc power line 72 for energizing both the inverter 44 and the buffer 45 has a voltage of, for example, 2.3 V. Therefore, the buffer 41 can achieve the level conversion to different operating voltages. Thus, as mentioned above, some logic circuits, such as an inverter, a buffer, and so on, conventionally fabricated by utilizing the inner cells 1, are fabricated in the present invention by utilizing the I/O cells 3. The efficiency of utilization of the inner cells can be increased, because the inner cells which would conventionally be employed for certain logic circuits can be used to create other logic circuits. Therefore, further complicated logic functions can be realized. As previously mentioned the object of the present invention is to increase the efficiency of utilization of the circuit elements on the LSI chip. The reasons for this are derived from two facts. The first way of doing this was explained above. Now, the second way will be explained. Figure 10 is a partial plan view of one example of a conventional IC. In Fig. 10, one of the I/O cells 3 contains, for example, an AND gate 17, an NAND gate 18, and a buffer 19. Two inputs 110 of the AND gate 17 are connected to the corresponding inner cells 1 (the connections are not shown in Fig. 10). The output of the AND gate 17 is connected to a control input 111 which acts as an enable terminal of a tri-state NAND gate 18. The signal line pad 5 is connected, on one hand, to the output 113 of the NAND gate 18, on the other hand, to the input 114 of the buffer 19. Two inputs 115 of the NAND gate 18 and also an output of the buffer 19 are connected to the corresponding inner cells 1 (the connections are not shown in Fig. 10). Further, each I/O cell 3 is connected to the corresponding one of the signal line pads 5. It should be noted that, as shown in Fig. 10, the I/O cells 3 are all independent from each other. Therefore, no logic circuit is constructed by using adjacent I/O cells 3. On the other hand, as previously mentioned, along and on the peripheral portion, the power belts 6-1 and the I/O cell region 4 are formed as a multilayer structure. Therefore, the area allotted to the I/O cell region 4 is determined by the area occupied by the power belts 6-1. Accordingly, the area allotted to the I/O cells 3 must be smaller than that of the power belts 6-1. This results in an unused region, that is, an empty region, adjacent to the I/O cell region 4. The higher the integration of the gate array LSI and the larger the width of the power belts 6-1, the greater the area of the empty region. Further, regarding the input signal for the inner cell region 2, it is usually necessary to employ two inner cells at the output side of the I/O cell 3, in a case where the logic circuits of the inner cell region 2 require both inverted and non-inverted input signals simultaneously, with respect to the external signal. This is because each I/O cell 3 cannot achieve both buffering and inverting functions. Therefore, one of said two inner cells must be allotted for the buffering function, while the other thereof must be allotted for the inverting function. Furthermore, in a case where some logic operation is to be effected on the input signal, for example, a latch function is to be effected on the input signal, a logic circuit for performing this latch function is conventionally formed by using only the inner cells 1. According to the present invention, first, as already mentioned, one or more logic circuits which would conventionally be created by using the inner cells in the inner cell region are created in the I/O cell region by using circuit elements of the I/O cells. Second, as will be explained in detail hereinafter, two or more adjacent I/O cells are connected to create a macro-cell. Thus, a logic circuit for performing complicated logic functions can be constructed, as the macro-cell logic circuit, in the I/O cell region 4. To be more specific, the circuit elements of each I/O cell are connected by lines distributed on at least said first wiring layer, the thus connected two or more adjacent I/O cells are connected with each other by lines distributed on the first wiring layer, and thereby the macrocell logic circuit is constructed. The macro-cell logic circuit is fabricated by using both said circuit elements in the I/O cells and lines connecting therewith distributed on at least said first wiring layer located above the I/O cell region. Figure 11 is a circuit diagram of a third embodiment according to the present invention. In Fig. 11, a 2-input logic output circuit for producing both inverted and non-inverted signals is formed, as the macro-cell logic circuit, by using two adjacent I/O cells 116 and 117. The signal line pads 5-1 and 5-2 are connected with respective inputs 119 and 120 of the 2-input logic output circuit 118. Both inverting output 122 and non-inverting output 121 thereof are connected with the corresponding logic circuit fabricated by I/O cell or I/O cells 1 (the connections are not shown in Fig. 11). Figure 12A is a circuit diagram of a fourth embodiment according to the present invention, and Fig. 12B is a circuit diagram of a fifth embodiment according to the present invention. The fourth and fifth embodiments provide the macrocell logic circuits comprised of two I/O cells 3. In Fig. 12A, the two outputs of the logic circuit 118-1 both produce non-inverted signals with respect to the input signal. In Fig. 12B, the two outputs of the logic circuit 118-2 both produce inverted signals with respect to the input signal. Since each of the logic circuits 118-1 and 118-2 has two inputs, two signal line pads 5-1 and 5-2 are necessary. Figure 13 illustrates six circuit diagrams representing sixth, seventh, eighth, ninth, tenth, and eleventh embodiments, in columns (A) through (F), according to the present invention. In the sixth embodiment in column (A) of Fig. 13, the signal line pad 5-1 is connected to the input 124 of a logic circuit 123. The logic circuit 123 has two non-inverting outputs 125 and 126 and two inverting outputs 127 and 128 with respect to the input signal supplied from the pad 5-1. These outputs are connected to the corresponding logic circuit (not shown) formed in the inner cell region 2 (Fig. 10). On the other hand, the output signals from the inner cell region 2 are applied to inputs 130, 131, and 132 of a logic circuit 129. Then, in the logic circuit 129, a predetermined logic operation, for example, an AND logic operation is executed, and the resultant logic output signal is produced therefrom, at its output 133, and supplied to the pad 5-2. The macro-cell logic circuit (123 and 129) is comprised of two I/O cells 3 (Fig. 10), as clarified with reference to Fig. 14 mentioned hereinafter. In the seventh and eighth embodiments shown in columns (B) and (C) of Fig. 13 respectively, logic circuits 134 and 135 produce, at their four outputs, the inverted signals and the non-inverted signals with respect to their input signals. The ninth, tenth, and eleventh embodiments shown respectively in columns (D), (E), and (F) correspond to the sixth, seventh, and eighth embodiments, shown in upper columns (A), (B), and (C), except that the output logic circuits 129, each providing output signals outside the LSI chip, are replaced with logic output circuits 136, each providing an inverted signal with respect to a signal supplied from a corresponding logic circuit in the inner cell region 2 (Fig. 10). Figure 14 is a detailed circuit diagram representing the circuit of the sixth embodiment shown in column (A) of Fig. 13. In Fig. 14, the macro-cell logic circuit 123 having an input 124 from the pad 5-1 is fabricated by using two adjacent I/O cells 3-1 and 3-2. A semi-macro-cell logic circuit 129 can be fabricated by using a part of the I/O cell 3-2. In Fig. 14, the pad 5-3 and the I/O cell 3-3 are used for creating another macro-cell logic circuit. Figure 15 illustrates a detailed example of the circuit shown in Fig. 11. Each of the I/O cells 116 and 117 originally contains circuit elements Q₁ through Q₉, Q₃′ through Q₅′, Q₈′, Q₉′, R₁ through R₄, and R₂′ through R₄′. However, only the circuit elements Q₁, Q₆, and Q₇ of the I/O cell 116, along with all the circuit elements of the I/O cell 117, are necessary to create the macro-cell logic circuit 118 of Fig. 11. The inverting output 121 and the non-inverting output 122 produce output signals OUT₁, and OUT₂, respectively. Since the circuit elements of the I/O cell 116 other than the circuit elements Q₁, Q₆, and Q₇ are not necessary to create the macro-cell logic circuit 118, the lines connected to these non-used circuit elements are cut at a portion P. As apparent from the above, a person skilled in the art can create various kinds of macro-cell logic circuits by combining two or more I/O cells 3. For example, a well-known latch circuit, exclusive OR (EOR) circuit, and exclusive NOR (ENOR) can be created as the macro-cell logic circuit. As mentioned above, according to the present invention, it is also possible to operate the I/O cells as the macro-cell logic circuit, in which a plurality of I/O cells, each having the same pattern as each other, are fixedly connected in advance by lines so as to obtain desired logic functions. Therefore, a large variety of logic circuits can be fabricated in the I/O cell region 4, as compared with that of the identical conventional type LSI chip. This means that the efficiency of utilization of not only the inner cells but also the I/O cells is remarkably increased. In this case, additional circuit elements other than the circuit elements of the I/O cells can be mounted in the aforesaid empty region. Accordingly, in spite of these additional circuit elements, the size of the LSI chip still remains unchanged.

Claims: 1. A semiconductor integrated circuit operatively connected to receive external input signals, comprising a semiconductor substrate having a centre portion and a peripheral portion; wiring formed as a plurality of wiring layers (6-1,6-2,6-3) on the semiconductor substrate; an inner cell region (2) formed on the centre portion of the semiconductor substrate and having a plurality of relatively low-power inner cells (1) which are arranged in arrays and are operatively connected to each other by the wiring, each of the inner cells comprising a plurality of circuit elements interconnected by the wiring; and an outer cell region (4) formed on the peripheral portion of the semiconductor substrate in a multilayer structure with part of the wiring (6-1), the outer cell region occupying less space than that part of the wiring, and comprising a plurality of relatively high-power outer cells (3) each of which comprises a plurality of circuit elements interconnected by the wiring; characterised in that circuit elements in adjacent outer cells in the outer cell region are selectively connected to each other to form a macrocell which performs a function which is different from the function which other single outer cells can perform, thereby releasing a cell or cells in the inner cell region which would otherwise be required to perform said function. 2. A semiconductor integrated circuit comprising a semiconductor substrate having a centre portion and a peripheral portion; first level and second level wiring layers (6-3,6-2) formed on the semiconductor substrate, the second level wiring layer being formed over the first level wiring layer; an inner cell region (2) located at the centre portion of the semiconductor substrate, the inner cell region comprising a plurality of relatively low-power inner cells (1) which are arranged in the form of arrays and are connected by the first and second wiring layers, each of the inner cells comprising a plurality of circuit elements interconnected by the first level wiring layer; and an outer cell region (4) located at the peripheral portion of the semiconductor substrate in a multilayer structure with a third wiring layer (6-1), and occupying less space than the third wiring layer, the outer cell region comprising a plurality of relatively high-power outer cells (3) each of which comprises a plurality of circuit elements interconnected by at least the first level wiring layer; characterised in that circuit elements in adjacent outer cells in the outer cell region are selectively connected to each other to form a macro-cell which performs a function which is different from the function which other single outer cells can perform, thereby releasing a cell or cells in the inner cell region which would otherwise be required to perform said function. 3. A circuit as claimed in claim 2, characterised in that the first level wiring layer (6-3) selectively connects the plurality of circuit elements (41-49) which are included in the same outer cell (40). 4. A circuit as claimed in claim 2 or claim 3, characterised in that the third level wiring layer (6-1) is located on the same level as the second level wiring (6-2). 5. A circuit as claimed in claim 2, characterised in that said macro-cell (40) has one input (5) for receiving an external input signal and also has a plurality of outputs (48,49) for producing output signals therefrom. 6. A circuit as claimed in claim 5, characterised in that the output signals are all non-inverted signals with respect to the external input signal. 7. A circuit as claimed in claim 5, characterised in that the output signals are all inverted signals with respect to the external input signal (5). 8. A circuit as claimed in claim 5, characterised in that the output signals are a mixture of inverted and non-inverted signals with respect to the external input signal (5). 9. A circuit as claimed in any one of claims 1-4, characterised in that the macro-cell includes gate means (134) for receiving a single external input signal and produces a plurality of inverted signals with respect to the single external input signal, the inverted signals being fed to the inner cell region. 10. A circuit as claimed in any one of claims 1-4, characterised in that the macro-cell includes gate means (135) for receiving a single external input signal and produces a plurality of non-inverted signals with respect to the single external input signal, the non-inverted signals being fed to the inner cell region. 11. A circuit as claimed in any one of claims 1-4, characterised in that the macro-cell includes gate means (123) for receiving a single external input signal and produces mixtures of inverted and non-inverted signals with respect to the single external input signal, the inverted and non-inverted signals being fed to the inner cell region. 12. A circuit as claimed in any one of claims 1-4, characterised in that the macro-cell includes a multi-input logic gate (133) cooperating with a plurality of external input signals (130-132), the logic gate operating as a known logic gate such as a multi-input NAND gate, multi-input AND gate, or multi-input latch gate.

Inventors: MITONO, YOSHIHARU, OMICHI, HITOSHI, TANIZAWA, TETSU
Applicants: FUJITSU LIMITED
Application year: 1982
Main classification: H01L23
IPC codes: H01L23, H01L27