Complementary integrated circuit device equipped with latch-up preventing means

Abstract: A complementary integrated circuit device is disclosed which includes a semiconductor substrate having a first area in which a plurality of first transistors are formed and a second area in which a plurality of second transistors are formed, each of the first transistors being larger in size than each of the second transistors. A guard ring region is formed in the substrate to surround the first area. The guard ring region is supplied with a power voltage via a first conductor line which is formed separately from a second conductor line supplying the power voltage to each of the first transistors.

Description: The present invention relates to a semiconductor integrated circuit device and, more particularly, to a complementary MOS integrated circuit device (called hereinafter "CMOS-IC") including N-channel and P-channel MOS transistors. As well-known in the art, the CMOS-IC includes a parasitic thyristor therein. When carriers are produced to trigger the parasitic thyristor, the thyristor is turned ON to cause a so-called latch-up phenomenon which in turn stops a circuit operation of the CMOS-IC and often destroys the IC. It is also well-known in the art that a noise voltage applied to an lead terminal of the CMOS-IC produces such carriers that trigger the parasitic thyristor. Various countermeasures are provided to prevent the latch-up phenomenon caused by the noise voltage. However, the carriers triggering the parasitic thyristor may be produced by not only the noise voltage, but also by the CMOS-IC itself. More specifically, a MOS transistor produces carriers, electrons or holes, and supplies them to a substrate region thereof in response to a switching operation. In the transistor of a small size, the amount of the produced carries is small, and therefore the carriers are absorbed almost by the substrate region. Substantially no carrier is transferred to other transistors. On the other hand, the transistor having a large size produces a great amount of carriers, so that a part of them is transferred to other transistors. As a result, the parasitic thyristor is turned ON to cause the latch-up phenomenon. A semiconductor device according to the preamble of claim 1 is disclosed WO-A-85/02062. This device comprises a guard ring region to absorb carriers flowing between adjacent to N-channel and P-channel MOS transistors. However, this document has no concern with the problem that carrier absorbtion effect is lowered due to change in biasing voltage in the guard ring region. EP-A-0 169 559 also discloses a guard ring region which surrounds a protective element. This guard ring region serves to absorb carriers injected from the protective element by a noise voltage applied to an input terminal and thus prevent them from reaching an internal circuit. It is an object of the invention to provide a CMOS-IC in which carriers produced by transistors do not cause the occurance of a latch-up phenomenon. Another object of the invention is to provide a CMOS-IC having means for preventing carriers produced by transistors from causing a latch-up phenomenon. These objects are achieved by a semiconductor device as defined in claim 1; claim 2 is related to a development of the invention. Each first transistor is formed in a large size and therefore produces a large amount of carriers in response to aswitching operation thereof. A part of the produced carriers is apt by a substrate region of the first transistor, but the remaining carriers are intended to be transferred to other transistors and/or to the second area. However, the guard ring region is formed to surround the first area. Moreover, the guard ring region is supplied with the power voltage via the third interconnection line formed independently of the first interconnection line, and therefore the voltage of the guard ring region is constant irrespective of a voltage change of the first interconnection line caused by a variation of a current flowing therethrough. Accordingly, the remaining carriers are absorbed into the guard ring region, so that substantially no carriers are transferred to other first transistors and the second area. The occurrence of the latch-up phenomenon is thus prevented. The above and other objects, advantages and features of the present invention will be more apparent from the following description taken in conjunction with the accompanying drawing, in which Fig. 1 is a plan view representative of an IC chip according to an embodiment of the present invention; Fig. 2 is a plan view representative of the IC chip in which second-level conductors are omitted; and first-level conductors specfially, illustrated ; Fig. 3 is a cross sectional view along a line I-I shown in Fig. 1; and Fig. 4 is a cross sectional view along a line II-II shown in Fig. 1. Referring to Fig. 1, a CMOS-IC chip 100 according to an embodiment of the present invention is a microprocessor which includes a clock generator/driver (CD) 20, a central processing unit (CPU) 30, a read only memory (ROM) 40 and a random access memory (RAM) 50, all formed on a single semiconductor substrate 1 of one conductivity type (P-type in this embodiment). The CPU 30, ROM 40 and RAM 50 are interconnected by address/data bus lines (not shown). Each of the blocks 20to 50 includes a great number of N-channel and P-channel MOS transistors which are interconnected to constiute necessary circuits. The CD 20includes an oscillation circuit oscillating by employing a quartz crystal (not shown) to be exterterually connected between terminals X 1 and X 2 and generates two system clocks  1 and  2 having predetermined pulse frequencies. The terminals X 1 and X 2 are connected to the CD 20 via second-level interconnection lines 93 and 94 and first-level interconnection lines 13 and 14 shown in Fig. 2, respectively. A first power voltage of +5 V is supplied to a first power terminal V-1 and a second pwer voltage of a ground potential is supplied to a first ground terminal G-1. The first power voltage is also supplied to second and third power terminals V-2 and V-3 and the second power voltage is also supplied to second and third ground terminals G-2 and G-3. The first power terminal V-1 is connected to CD 20 via a second-level interconnection line 5 to supply the first power voltage to each transistor in the CD 20. The first ground terminal G-1 is also connected to the CD 20 via a second-level interconnection line 6 to supply the ground potential thereto. The system clocks  1 and  2 are supplied to the CPU 30 via first-level interconnection lines 11 and 12 shown in Fig. 2, respectively. The CPU 30 executes a program stored in the ROM 40 in response to the system clocks  1 and  2 . The ROM 40 often stores fixed data in addition to the program. The RAM 50 stores data to be processed by the CPU 30 and processed results from the CPU 30. The CD 20 is required to operate at a very high frequency, generate the system clocks  1 and  2 of a predetermined rate and supply them to the CPU with sufficient driving capability. For this purpose, each of the MOS transistors in the CD 20 is formed in a very large size to have large current ability and is larger than each MOS transistor in the CPU 30, ROM 40 and RAM 50 several hundred times. Therefore, each MOS transistor in the CD 20 produces a great amount of carriers and supplies them to a substrate region thereof in response to a switching operation. Here, the substrate region represents a part of the silicon substrate 1 in which an N-channel MOS transistor is formed or an N-well region in which a P-channel MOS transistor is formed. Since a great amount of carriers are produced, a part of them is not absorbed in the substrate region and may be transferred to other MOS transistors in the CD 20 and/or to CPU 30, ROM 40 and RAM 50. As a result, the latch-up phenomenon occurs to break down the function of the microcomputer chip 100. In order to solve this problem, guard ring regions 3 and 4 are formed in the substrate 1 in accordance with the present invention. The guard ring region 3 is of a P-type and the guard ring region 4 is of an N-type and they completely surround the CD 20. In this embodiment, the P-type guard ring region 3 is formed outside the N-type guard ring region, but can be formed inside it, if desired. Referring to Fig.2, first-level aluminum layers 8, which are provided simultaneously with other first-level interconnection lines are provided on the p-type guard ring region 3 except on portions thereofhover which the first-level interconnection lines 11 to 14 cross via an insulation film, respectively. Similarly, first-level aluminum layers 10 are formed on the N-type guard ring region 4 except on portions thereof over which the interconnection lines 11 to 14 cross via an insulation film, respectively. Turning back to Fig.1, second-level aluminum layers 7 and 9, which are formed simultaneously with other second-level interconnection lines, are provided directly on the layers 8 and 10, respectively, except on portions thereof over which the interconnection lines 5 and 6 cross via an insulation film. The second-level layers 7 and 9 are also provided above the first-level interconnection lines 11, 12, 13 and 14 to bridge the lacked portions 8 and 10. The guard ring regions 3 and 4 and the aluminum layers 7 to 10 are shown in more detail in Fig. 3 which is cross sectional view along a line I-I in Fig. 1. Fig. 3 also shows one P-channel MOS transistor Q 1 and one N-channel MOS transistor Q 2 in the CD 20. The N-type guard ring region 4 is formed simultaneously with an N-well region 52 operating as the substrate region of the transistor Q 1 , and the P-type guard ring region 3 is formed simultaneously with source and drain regions 53 and 54 of the transistor Q 1 . The N-type guard ring region 4 has a contact region 4-1 which is formed simultaneously with source and drain regions 56 and 57 of the transistor Q 2 . The transistors Q 1 and Q 2 have gates 55 and 58 made of polycrystalline silicon. The N-well region 52 has a contact region 521 which is in turn connected to the source region 53 by a first-level interconnection line 60. A contact region 1-1 is formed near the transistor Q 2 and connected to the source region 57 thereof via a first-level interconnection line 61. The drain regions 54 and 56 of the transistors Q 1 and Q 2 are connected to each other by a first-level-unterconnection line 59 which is in turn led out to another transistor. A second-level interconnection line 5-1 connects the line 60 to the line 5 (Fig. 1) to supply the power voltage thereto. The line 61 is connected via a second-level interconnection line 6-1 to the line 6 (Fig. 1) to receive the ground potential. Silicon oxide layers 50 embedded in part in the substrate 1 are formed selectively to isolate the respective regions and transistors, and an insulating layer 51 separates the first-level interconnection lines from the second-level interconnection lines. Turning back to Fig. 1, the aluminum layer 7 is connected via a second-level interconnection line 16 to the first ground terminal G-1, and the aluminum layer 9 is connected to the first power terminal V-1 via a second-level interconnection line 15. Therefore, the P-type guard ring region 3 is supplied with the ground voltage and the N-type guard ring region 4 receives the power voltage. Moreover, the interconnection lines 15 and 16 are formed independently of and separately from the lines 5 and 6. The transistors in the CD 20carry out a switching operation at a high speed to generate the system clocks  1 and  2 , and further currents flowing therethrough are considerably large as mentioned above. For this reason, the potentials on lines 5 and 6 vary due to impedance and/or inductance thereof. If the layers 7 and 9 are respectively connected to the lines 5 and 6, therefore, the voltages of the guard ring regions 3 and 4 are not stabilized, but changed. Since the interconnection lines 15 and 16 are formed independently, however, the voltages of the guard ring regions 3 and 4 are not changed and they are constant. In addition, the first-level aluminum layers 8 and 10 are directly connected to the guard ring regions 3 and 4, respectively, along almost entire lengths thereof to decrease the resistances of the regions 3 and 4. Therefore, the voltage drops along the lengths of the guard ring regions 3 and 4 are suppressed. As discussed hereinbefore, since the transistors in the CD 20 are formed in a large size, the source and drain regions 53, 54, 56 and 57 of the transistors Q 1 and Q 2 shown in Fig. 3 have a large area. For this reason, a great amount of carriers are produced by the switching operations of the transistors Q 1 and Q 2 and then supplied to the substrate regions thereof. Since the contact regions 521 and 1-1 are respectively formed near the transistors Q 1 and Q 2 , they have a function of absorbing the carriers therefrom. However, the amount of the produced carriers is very large and the voltages of the contact regions 521 and 1-1 change, so that not all carriers are absorbed. Thus, a part of carriers from the transistors Q 1 and Q 2 are intended to be transferred to other transistors in the CD20 and to the formation areas of the CPU 30, ROM 40 and RAM50. However, the guard ring regions 3 and 4 are formed to surround the CD20 and a constant voltage is supplied to the regions 3 and 4. Accordingly, the guard ring regions absorb undesired carriers which would otherwise move into the substrate 1. Thus, the occurrence of the latch-up phenomenon caused by the carriers from the transistors in the CD 20 is prevented. The microprocessor chip 100 shown in Fig. 1 further has a P-type guard ring region 26 and an N-type guard ring region 21 which are formed along the periphery of the chip 100 to completely surround the CD20, CPU 30, ROM 40 and RAM 50. The microprocessor chip 100 is equipped with a plurality of input/output terminalsto receive data to be processed and to output processed data. In Fig. 1, only four input/output terminals IO1 to IO4 are shown. In addition, a plurality of address output terminals are provided (two terminals A 1 and A 2 are shown in Fig. 1). These terminals IO1 to IO4, A 1 and A 2 are associated to buffer circuits B 1 to B 6 , respectively. Since a load capacitance of each of the terminals IO1 to IO4, A 1 and A 2 is considerably large, each of the buffer circuits B 1 to B 6 is designed to have large driving ability. That is, large sized:transistors are employed in each buffer circuit B. Therefore, the buffer circuits B 1 to B 6 may supply the CD 20, CPU 30, ROM 40, RAM 50 with carriers causing the latch-up phenomenon. In order to absorb such carriers, the guard ring regions 26 and 21 surround the internal circuit blocks 20 to 50 and intervene between the each circuit block and each buffer circuit B. As shown in Figs.2 and 4, first-level aluminum layers 23 and 25 are respectively formed on the guard ring regions 26 and 21 except on portions thereof over which first-level interconnction lines 81 to 86 of the buffer circuits B1 to B6 and the first-level interconnection lines 13 and 14 cross via an insulation film, respectively. The guard ring region 21 has a contact region 21-1. Referring also to Fig.l, a second-level aluminum layer 22 connected to the ground terminals G-1 to G-3 is formed on the layer 23 except on portions thereof over which the second-level interconnection lines connected to the power terminals V-1 to V-3 cross via the insulation film 51. A second-level aluminum layer 24 connected to the power terminals V-1 to V-3 is formed on the layer 25 except on portions thereof over which the second-level interconnection lines connected to the ground terminals G-1 to G-3 cross via the insulation film 51. Therefore, the P-type guard ring region 26 is supplied with the ground voltage and the N-type guard ring region 21 is supplied with the power voltage. Thus, the carriers from the buffer circuits B1 to B6 are absorbed by the guard ring regions 26 and 21 and are not transferred to the internal blocks 20, 30, 40 and 50.

Claims: A complementary semiconductor device comprising a semiconductor substrate (100) having a first area (20) into which a plurality of first N-channel and P-channel transistors are formed and a second area (30, 40, 50) into which a plurality of second N-channel and P-channel transistors are formed, said first transistors being larger in size than said second transistors, a first guard ring region (4) of one conductivity type formed in said semiconductor substrate and surrounding said first area, first and second power terminals (V-1; G-1) formed on said semiconductor substrate, first and second interconnection lines (5; 6) extended respectively from said first and second power terminals to said first area to supply first and second power voltages to said first transistors, characterized in that said device further comprises a second guard ring region (3) of an opposite conductivity type formed in said semiconductor substrate and surrounding said first area, a third interconnection line (15) extended from said first power terminal to said first guard ring region independently of and separately from said first interconnection line to supply said first power voltage to said first guard ring region and a fourth interconnection line (16) extended from said second power terminal to said second guard ring region independently of and separately from said second interconnection line to supply said second power voltage to said second guard ring region. The device as claimed in claim 1, charaterized in that said first transistors constitute a clock driver circuit (20) and said second transistors constitute a central processing unit (30), said clock driver circuit generating and supplying a clock signal to said central processing unit.

Inventors: SUGAWARA YUKARI, SUGAWARA, YUKARI
Applicants: NIPPON ELECTRIC CO, NEC CORPORATION
Application year: 1988
Main classification: H01L27
IPC codes: H01L27, H01L23