Semiconductor integrated circuit having self-diagnosis test function

Abstract: An I/O cell (101) becomes an output state according to a burn-in test mode signal M in a burn-in test and the output of a port output signal setting register (106) is selected in an output signal selecting circuit (105). An instruction for periodically alternately setting "H" and "L" in the port output signal setting register (106) is written in test ROM (103). According to this circuit configuration, in burn-in, "H" and "L" are alternately output from the I/O cell (101) and appropriate stress can be applied to the I/O cell (101).

Description: Background of the Invention The present invention relates to a semiconductor integrated circuit provided with a self-diagnosis test circuit function and the test method of the semiconductor integrated circuit, particularly relates to an effective test circuit for a burn-in test and its test method. Such semiconductor integrated circuits are known from JP 10 115 662 and JP 01 121 945. In a burn-in test which is one of a reliability test of a semiconductor integrated circuit, an internal circuit is operated in a state close to actual operation and stress is applied, however, as a conventional burn-in test was made for a packaged finished product, a method of inputting a required input signal to a pin from an external signal supply unit and operating an internal circuit was taken. However, recently, the technique of wafer level burn-in by which a great many semiconductor integrated circuits can be simultaneously tested is also being established and the need for the test of a semiconductor integrated circuit having a great many pins increases. In the case of a test depending upon external connection, the number of pins which can be used for input is limited, compared with a burn-in test of a conventional type packaged product and therefore, a method of applying stress to a circuit by providing a pseudo-random number generating circuit inside and making scan using the output signal as an input signal including a scan chain is proposed. However, according to the method, appropriate stress cannot be applied to an I/O cell except a pin used for input of an external signal supply unit and a pin from which an output signal of the final section of a scan chain is output. There is a method of providing an output determination circuit to a circuit provided with a scan function and checking whether appropriate stress is applied in a burn-in test or not. However, in a method of operating CPU according to an instruction written in test ROM and applying stress to an asynchronous circuit and a memory cell respectively without a scan function, a case that appropriate stress is not applied because of a malfunction of test ROM and others cannot be discriminated from a case that appropriate stress is applied. Summary of the Invention The invention is made in view of the actual situation and provides a test circuit for a semiconductor integrated circuit and its test method wherein appropriate stress can be applied to all I/O cells only by adding a slight circuit in a test. The invention also provides a test circuit for a semiconductor integrated circuit and its test method wherein it can be further checked whether appropriate stress is applied to an asynchronous circuit and a memory cell respectively without a scan function or not. It is furthermore an object of the invention to provide a semiconductor integrated circuit for which it can be determined whether a test ROM, being part of the semiconductor integrated circuit, is correctly operated to end in a test or not. This object is achieved with the semiconductor integrated circuit according to claim 1. According to such configuration, in the case of a burn-in test, as it can be judged whether stress is actually applied or not after a test process for a long time is finished, the result of the test can be verified. Also, according to this circuit configuration, it can be checked whether stress is correctly applied or not even if CPU is operated and stress is applied to an asynchronous circuit and a memory cell respectively without a scan function according to an instruction written to test ROM. An second aspect of the invention is based upon the semiconductor integrated circuit provided with the self-diagnosis test circuit function according to claim 1 of the invention and is characterized in that even if a flag of the test ROM determination register is fixed because of any cause in a test, the register composed of plural bits is provided so that it can be determined whether test ROM is correctly operated to the end or not. According to this circuit configuration, even if a flag of the test ROM determination register is fixed because of any cause in a test such as a burn-in test, it can be determined whether test ROM is correctly operated to the end or not. A second aspect of the invention is based upon the semiconductor integrated circuit provided with a self-diagnosis test circuit function according to the claim 1 of the invention and is characterized in that a semiconductor integrated circuit is provided with a port signal output setting register that outputs a high level and a low level to all I/O cells. According to such configuration, a self-diagnosis test can be easily made to all I/O cells. Brief Description of the Drawings Fig. 1 shows the circuit configuration of the main part of a test circuit of a semiconductor integrated circuit in a first example useful for the understanding of the invention; Fig. 2 shows the circuit configuration of the test circuit of the semiconductor integrated circuit in the first example; Fig. 3 shows the circuit configuration of a test circuit of a semiconductor integrated circuit in a second example useful for the understanding of the invention; and Fig. 4 shows the circuit configuration of a test circuit of a semiconductor integrated circuit in an embodiment of the invention. Detailed Description of the Preferred Embodiment Examples and an Embodiment of the invention will be described below with reference to the drawings. (First Example useful for the understanding of the invention) Fig. 1 is a circuit diagram showing a test circuit of a semiconductor integrated circuit in a first example. A semiconductor integrated circuit (chip) 100 has a self-diagnosis test function of an I/O cell 101. The semiconductor integrated circuit includes a CPU 102, a test ROM 103 in which instructions for operating the CPU 102 in a burn-in test mode are written, and a port signal output setting register 106 that outputs "H" and "L" to the I/O cell 101 in a test according to the test ROM 103. As shown in Fig. 1, a reference number 101 denotes an I/O cell wherein the switching of input/output is enabled, 104 denotes a semiconductor integrated circuit (in the following also internal circuit) inside the chip and 105 denotes an output signal selecting circuit. That is, this semiconductor integrated circuit is provided with the I/O cell 101, the switching of the input/output of which is enabled in accordance with a setting of a mode, and the test ROM 103 in which instructions for operating the CPU 102 in a burn-in test mode are written. As for this I/O cell 101, in a normal mode, input signal to the internal circuit 104 is input from an external device or an output signal from the internal circuit 104 is output to an external device. In a burn-in test, the I/O cell 101 becomes an output state according to a burn-in test mode signal M and in the output signal selecting circuit 105, the output of the port output signal setting register 106 is selected. In the test ROM 102, instructions for periodically alternately setting "H" and "L" in the port output signal setting register 106 are written. According to this circuit configuration, in burn-in, "H" and "L" are alternately output from the I/O cell 101 and appropriate stress can be applied to the I/O cell 101. In this circuit configuration described above as shown in Fig. 1, one I/O cell is described. However, as shown in Fig. 2, as all I/O cells on the chip can have the similar configuration. Further, since the port output signal setting register 106 may be common to all the I/O cells, it is enough to provide only one port output signal setting register on the chip. Next, a test process using the semiconductor integrated circuit will be described. Multiple semiconductor wafers on each of which desired semiconductor integrated circuits are mounted are prepared at a predetermined interval and are installed in an oven in high temperature environment of 140° C determined beforehand. In this state, a test instruction signal M is sent to the test ROM 103 to change to a self-diagnosis test mode. Stress is automatically applied to the whole device including all I/O cells by leaving in this state for eight hours. A defective product is selected by burn-in and the burn-in test is completed. As described above, after the test is completed, only nondefective products are shipped. In normal use, the port output signal setting register 106 is not used in this embodiment. However, in normal use, the port output signal setting register 106 may be also used. As described above, according to this example, appropriate stress can be applied to all the I/O cells on the chip in wafer level burn-in by only adding the output signal selecting circuit 105 and the port output signal setting register 106. Also, the output signal selecting circuit 105 and the port output signal setting register 106 respectively used in circuit operation may be also used for a test. Further, the test ROM is also used in normal circuit operation. (Second example useful for the understanding of the invention) Next, a second example will be described. In this example, as shown in Fig. 3, an output signal selecting circuit 105s and a port output signal setting register 106s particularly provided for dedication is effective in addition to the output signal selecting circuit 105 and the port output signal setting register 106 respectively used in normal circuit operation and also used for a test as in the first example. However, the same reference number is allocated to the same component and the description is omitted. As described above, for a part of I/O cells, the degree of the freedom of the circuit configuration increases and a securer and more reliable test can be executed by also using the output signal selecting circuit 105s and the port output signal setting register 106s respectively used in normal circuit operation for a test in addition to the output signal selecting circuit 105 and the port output signal setting register 106 respectively particularly provided for dedication. (Embodiment) Fig. 4 is a circuit diagram showing a test circuit of a semiconductor integrated circuit in an embodiment of the invention. The semiconductor integrated circuit includes a test ROM 203 in which instructions for operating the CPU in a test mode are written, further to the semiconductor integrated circuit in the first example. In the test ROM 203, an instruction for setting a flag in the test ROM determination register is written to final part of the instructions for operating the CPU. Therefore, it can be determined whether the test ROM is correctly operated to the end in a test or not, by outputting the flag to an external terminal. As shown in Fig. 4, a reference number 203 denotes test ROM operated in a burn-in test mode, 207 denotes a register for determining the operation of the test ROM, 208 denotes an output determination circuit for determining a stress applied state and 209 denotes an AND circuit. The other is similar to that in the first example and the same reference number is allocated to the same component. In this embodiment, CPU 102 is operated according to an instruction written to the test ROM 203 in a burn-in test and stress is applied to an asynchronous circuit without a scan function and a memory without a self-diagnosis circuit. To check that the test ROM 203 is correctly operated to the end, the register for determining the test ROM 207 is provided and an instruction for writing a flag "H" to the register for determining the test ROM 207 is written in the end of an instruction to be written to the test ROM 203. This flag is reset only by an external reset signal R to be "L". The flag written to the register is input to the AND circuit 209 together with an output signal from the output determination circuit 208 for determining a stress applied state of a internal circuit 104 including a bistable circuit provided with a scan function, an output signal from the AND circuit 209 is output to an external terminal and it is determined whether the application of stress to the circuit is suitable or not. As described above, according to this embodiment, it can be determined only by adding the test ROM 203 and the register for determining the operation 207 and writing an instruction for writing a flag to the register for determining the operation 207 in the end of an instruction in the test ROM 203 whether the simultaneous application of stress to not only a synchronous circuit provided with a scan function but an asynchronous circuit without a scan function and a memory cell without a self-diagnosis circuit in a burn-in test is suitable or not. Also, since the register for determining the operation 207 is composed by plural bits, it can be determined by inputting the conjunction of all flags to the AND circuit 209 whether the test ROM is correctly operated to the end or not even if any of the flags of the register is fixed to "H" because of any cause in a burn-in test. As described above, it is enabled to execute a securer burn-in test provided with extremely simple configuration. In the embodiment described above, the burn-in test is described, however, the present invention is not limited to the burn-in test and it need scarcely be said that the invention can be also applied to a normal test. Also, in the embodiment described above, the burn-in test in the semiconductor integrated chip is described, however, the invention is not limited to it, can be also applied to a burn-in test at the level of a wafer and batch processing can be also extremely easily executed for a semiconductor integrated circuit provided with multiple pins. As described above, according to the invention, appropriate stress can be applied to all I/O cells in a burn-in test only by adding a slight circuit. Also, it can be checked by extremely simple configuration whether stress is also correctly applied to an asynchronous circuit without a scan function and memory cell or not.

Claims: Semiconductor integrated circuit (100) having a self-diagnosis test function, comprising a test ROM (203) and a CPU (102), wherein instructions for preparing the CPU (102) in a test mode are written in the test ROM (203) and being characterized in that an instruction for setting a flag in the end of the instructions for operating the CPU (102) is written in the test ROM (203); and in that a determination circuit (207) is provided for determining whether the test ROM (203) is correctly operated to the end in a test by outputting the flag to the external terminal. A semiconductor integrated circuit according to claim 1, wherein the determination circuit (207) includes a register composed of plural bits for determining whether the test ROM (203) is correctly operated to the end even if the flag of the test ROM determination register is fixed in a test because of any cause. A semiconductor integrated circuit according to claim 1. wherein the semiconductor integrated circuit (100) includes a plurality of I/O cells (101), and a port signal output setting register (106) outputting "H" and "L" to all the I/O cells (101).

Inventors: HORI SATOSHI, KAWABE ATSUSHI, MIYAZAWA HIDEO, HORI, SATOSHI, KAWABE, ATSUSHI, MIYAZAWA, HIDEO
Applicants: MATSUSHITA ELECTRIC IND CO LTD, MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD.
Application year: 2000
Main classification: G01R31
IPC codes: H01L21, G01R31, G06F11, H01L27, G06F15, G11C29