JP2000131398A - Method for testing nonvolatile semiconductor storage device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a method for testing nonvolatile semiconductor storage devices which is capable of sufficiently securing the reliability of data holding and in which increase in cost due to increase in the number of processes is reduced. SOLUTION: A method for testing nonvolatile semiconductor storage devices is a method for testing data-writable nonvolatile semiconductor devices and provided with a writing process 203 to write data, an aging process to hold the nonvolatile semiconductor storage devices under predetermined aging conditions, and a verifying process 205 to read data, compare it with the data written in the writing process, and verify it. In the method, the aging process includes a coating film growing process 204 for relaxing stress at the time of assembling the nonvolatile semiconductor storage devices.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nonvolatile semiconductor memory device and a method for testing the same, a semiconductor memory device having a sense amplifier, and a semiconductor device. In particular, it is easy to test whether a manufactured semiconductor device has a predetermined performance. The present invention relates to a semiconductor device and a test method therefor.

[0002]

2. Description of the Related Art Semiconductor storage devices (semiconductor memories) such as DRAMs and SRAMs have been widely used. In particular, flash memories have attracted attention as electrically erasable nonvolatile semiconductor memories. A memory cell of a flash memory is composed of one transistor. This transistor is called a memory cell transistor. FIG. 1 shows an example of a memory cell transistor of a flash memory.
It is shown in FIG. (1) is a top view, (2) is a cross-sectional view along AA ', and (3) is a cross-sectional view along BB'. 101 is a P-type silicon (Si) substrate, 102 is a floating gate (FG) made of polysilicon, 103 is a control gate (CG) made of polysilicon capacitively coupled to the FG 102, and 104 and 105 are N-type regions. And functions as a source and a drain. 106 is an oxide film.

As described above, the flash memory
The cell transistor has a structure in which a floating gate is located below the gate of an N-channel MOS transistor. To perform erasing, use CG103
Is open and a high voltage is applied to the source, the charge is removed from the source, and the charge of the FG 102 becomes approximately zero. When an appropriate voltage is applied to the CG 103 in this state, the transistor is turned on. When a high voltage is applied to the CG103 and the drain, an avalanche breakdown phenomenon occurs,
Some of the electrons that have obtained high energy near the drain are FG10
2 captured. This is called writing. When writing is performed, since charges are accumulated in the FG 102, the CG 103
, The transistor does not conduct. Data is made to correspond to whether the transistor is conductive or nonconductive. In this flash memory, information can be written / erased electrically as described above.

FIG. 13 shows a block diagram of a conventional flash memory. In the drawings, the same functional portions are denoted by the same reference numerals, and when some functions are different, alphabetical characters are used. 1 is a command register circuit, 2 is a status register circuit, 3 is an operation logic circuit, 4 is a column address buffer, 5 is a row address buffer, 6 is a block address buffer, and 7 is a write / read
Erasing switching circuit, 8A is data comparator circuit, 9
A is a write / erase timing generating circuit, 10 is a column decoder, 11A is a row decoder, 12 is a block decoder, and 13A is a write / erase timing generator only when a test signal is input by a write / erase test signal input circuit. 9A is forcibly brought into the operating state, and the data comparison of the data comparator circuit 8A is brought into the prohibited state. 14
Is an input / output buffer, 15 is a sense amplifier / write amplifier, 16 is a Y gate, 17A is a memory cell matrix,
Reference numeral 18 denotes an erase source control circuit.

In a flash memory, the voltage applied to each part is different in each mode of reading, writing, and erasing, so that the control operation thereof is complicated. In addition, when the writing and erasing operations are performed, the data of the processed part is lost. In general, an operation called a verify operation for reading and confirming is performed. Conventionally, such an operation has been performed by outputting a predetermined voltage to a terminal of a flash memory from an external device such as a writer. For this reason, a considerable load has been placed on external devices such as a writer for writing / erasing. Therefore, recently, an automatic circuit has been provided in order to simplify the complicated control algorithm, so that a flash memory cell can be programmed / erased only by a simple control command from the outside. It is becoming.

In a flash memory equipped with such an automatic circuit, a control command is received once from the outside, and all processes are automatically performed internally until the writing / erasing of cells is completed. Therefore, a status register function is generally mounted as a means for externally knowing the state of the device. Once the automatic circuit operates, the state of the internal circuit cannot be known except by reading the status register.

As shown in FIG. 13, in a flash memory, a sense amplifier 15 whose output level changes according to the amount of current flowing through a bit line is used to detect whether each memory cell is conductive or not. This sense amplifier is widely used for a semiconductor memory of a type in which memory cells are arranged in a matrix.
Also used for RAM, EPROM, etc.

FIG. 14 is a diagram showing a conventional example of a sense amplifier. In order to show how the sense amplifier is connected to a memory cell matrix, a Y gate 16, a memory cell matrix 17A, and a column decoder 10 shown in FIG. , Row decoder 11A. In the memory cell matrix 17A, a number of parallel word lines WLi and a number of parallel bit lines BLj are vertically arranged, and transistors corresponding to intersections of the nonvolatile memory cells Cij as shown in FIG. 12 are arranged. ing. The gate of the transistor is connected to a word line, the drain is connected to a bit line, and the source is connected to a common source line SL. A voltage higher than the other is applied to the word line selected from the row decoder 11A, one of the Y gates 16 is turned on by a signal from the column decoder 10, and only the selected bit line is connected to the sense amplifier 151A. Bit line K
BL is connected to the sense amplifier 1 to determine whether the memory cell corresponding to the intersection of the selected word line and bit line is conductive / non-conductive.
51A. This is a read operation. The write operation is almost the same except that the voltage applied to the word line and the bit line is different, but different in that the common bit line KBL is connected to the write amplifier instead of the sense amplifier 151A.

The sense amplifier 151A shown in FIG.
This is called a single-ended sense amplifier, and is widely used because it has a small number of components and is easy and easy to adjust. At the stage when the semiconductor device is manufactured, various tests are performed to determine whether the semiconductor device has a predetermined performance. For example, in the case of a nonvolatile semiconductor memory such as a flash memory, it is tested whether or not the above-described status register operates normally. The status register is for externally knowing the state of the writing and erasing operations by the operation logic circuit, and the value of each bit of the status register indicates whether the writing or erasing has been normally performed, whether the operation has been completed, and the like. Express. Therefore, in order to detect whether or not the status register operates normally, it is necessary to actually perform various operations by the operation logic circuit to cause various states to appear, and to detect whether or not the status register correctly indicates the state. is there.

FIG. 15 is a flowchart showing steps of a conventional status register test for a flash memory.
In step 501, first, whether to operate normally or to cause an abnormality is selected, and the write / erase test signal input circuit 13A in FIG. 13 is set. In response, in step 502, the data comparison in the data comparator circuit 8A is stopped, and the setting is made so that a result of a normal operation or an abnormal operation is obtained regardless of the data to be compared. Step 5
In step 03, a command is input depending on whether the operation is a writing operation or an erasing operation. In step 504, an operation corresponding to the command is started.

At steps 505 and 506, the process waits until the above operation is completed. When the operation is completed, the value of the status register is read at step 507 to confirm that the desired value is obtained. The above is the conventional status register test process. It is the portion of the write / erase timing generation circuit 9A that causes an abnormal operation, and when an abnormality occurs in the memory cell matrix 17A or the sense amplifier / write amplifier 15, However, it is not guaranteed that the status register 2 operates normally.

As a test peculiar to a nonvolatile semiconductor memory such as a flash memory, there is a test for guaranteeing that data is correctly stored even if stored data is held for a long time in a state where the power is turned off. In practice, such a test that has been left for a long time cannot be performed, so that a data retention test is generally performed by an accelerated test called an aging test. The aging test is performed in such a manner that after writing to a predetermined level, the data is held at a temperature higher than usual to give an accelerated stress to data holding, and then a threshold level is detected.

FIG. 16 is a flowchart showing the order of an aging test in a conventional semiconductor device manufacturing process. In the procedure of (1) of FIG.
1. An aging test is performed in a final test step 606 performed on a semiconductor device completed as an individual device through a cover film growth step 602, a coating film growth step 603, a probe test step 604, and an assembly step 605. In the final test step 606, first, a predetermined process including writing is performed in the first final test step 607, the aging step 608 holds the data at, for example, 150 ° C. for several tens of hours, and the level of the data written in the second final test step 609. A second final test including measurements such as

As described above, in FIG. 16A, the aging test is performed in an individual state sealed in a package. However, in the aging test as shown in FIG. 16A, since the aging process is performed in the final test stage after the assembly, a sufficient temperature cannot be applied to the assembled plastic package, and the reliability of data retention is low. In order to guarantee the above, it is necessary to lengthen the aging time, and there is a problem that the number of processes increases.

Therefore, FIG. 16 (2) differs from (1) in that an aging test is performed between the cover film growth step 702 and the coating film growth step 706. After writing to a predetermined level in step 703, an acceleration stress for maintaining at 300 ° C. for 1 hour is applied in an aging step 704, and the data level is checked in step 705.

In a semiconductor memory, it is necessary to measure a power supply margin on a high voltage side which can be applied to a memory cell.
However, the slope of the current characteristic of the memory cell decreases as the gate voltage increases. Therefore, in the sense amplifier shown in FIG. 14, when the power supply voltage increases, the sense point shifts, and correct cell comparison cannot be performed. Therefore, it was necessary to add a circuit so that the power supply of the sense amplifier and the power supply of the cell could be separated, and it was also necessary to add a special test for measuring the power supply.

Furthermore, in the semiconductor device, it is necessary to measure the power supply current during operation. However, due to the test process, the power supply current is measured in a state as shown in FIG. You. In FIG. 18, reference numeral 52 denotes a driver circuit, and TP11 and TN11 denote P-channel and N-channel transistors constituting an output circuit.
4 is an output pad, and 57, 58 and 59 are resistors and capacitors constituting a load circuit on the tester side. The measurement condition of the power supply current at the time of operation, which is guaranteed in a catalog or the like, is such that the current flowing to the load is 0 mA, and the current measured with the load circuit connected to the output also measures the charge / discharge current flowing to the load circuit. Therefore, there is a problem that it cannot be measured accurately. Therefore, in order to actually measure the guaranteed value of the catalog, the output pin is removed from the measurement circuit and measured.

[0018]

As described above, the tests in the manufacturing process of the semiconductor device have been described, but each has its own problems. In the test of the status register of the flash memory described with reference to the flowchart of FIG. 15, as described above, only the status register function and the operation of some circuits can be confirmed.

In a memory test, the test time is greatly increased with an increase in the memory capacity, and the test cost is becoming very high as it is. In order to reduce this test cost, it is important to identify defective products in as little time as possible, but it is also necessary to shorten the test time and suppress the increase in test cost by incorporating various tests and incorporating tests. It is. Therefore, in the test of the status register, it is desirable that a comprehensive test is performed not only on the above-described portion but also on a wider portion, and there is a problem that the current test method is insufficient.

In the aging test shown in FIG. 16B, the reliability can be assured because the semiconductor device on the wafer is aged, but there is still a problem that the number of steps is increased. When measuring the power supply margin of a sense amplifier, a test is performed using a circuit that separates the power supply of the sense amplifier and the power supply applied to the gate of the cell. It is necessary to do a good test. However, there is a problem that an increase in cost caused by introducing a test other than the normal test is reflected in the chip cost.

Further, since accurate power supply current cannot be measured in the state of the output circuit shown in FIG. 18, the measurement is performed after removing the output pin from the measurement circuit. It is. The present invention has been made in view of the above problems, and has the following objects. A first object is to realize a non-volatile semiconductor memory device capable of performing a test in which a status register function including an internal automatic circuit, a sense amplifier, and the like are integrated, and improving test efficiency and test accuracy. .

A second object of the present invention is to realize a method of testing a nonvolatile semiconductor memory device in which the reliability of data retention of the nonvolatile semiconductor memory device can be sufficiently ensured and the increase in cost due to an increase in the number of steps is reduced. A third object is to realize a sense amplifier that can obtain an accurate output even when the power supply voltage is changed to a high voltage.

A fourth object is to realize an output circuit capable of performing accurate measurement without removing a load circuit from an output pin when measuring a power supply current.

[0024]

According to a first aspect of the present invention, there is provided a nonvolatile semiconductor memory device comprising: a plurality of word lines and a plurality of bit lines arranged in a grid;
A memory cell matrix in which electrically erasable nonvolatile memory cells whose gates are connected to word lines and whose drains are connected to bit lines are arranged corresponding to intersections of word lines and bit lines; A sense amplifier that detects a current amount different depending on whether a memory cell located at an intersection of a line and a selected bit line is conductive or non-conductive, and outputs a signal corresponding to a logical value “1” or “0” And a write / erase timing circuit for automatically performing timing control necessary for writing data in a memory cell and erasing stored data, and externally accessing the operation state of the device after the operation of the write / erase timing circuit. In a nonvolatile semiconductor memory device having a status register for storing data in an Wherein the output of the sense amplifier when the comprises a dummy cell composed of two rewritable cells that are set to the logical value "1" and "0" respectively.

According to a second aspect of the present invention, a method for testing a data writable nonvolatile semiconductor memory device, which achieves the second object, comprises the steps of: writing data; In a method for testing a nonvolatile semiconductor memory device comprising: an aging step of maintaining the aging condition, and a confirmation step of reading data and comparing the data with data written in the writing step, the aging step includes The method includes a step of growing a coating film for stress reduction at the time of assembling the storage device.

A semiconductor memory device according to a third aspect of the present invention which achieves the third object is a semiconductor memory device having a sense amplifier, wherein the sense amplifiers have different loads which can be switched to be connected. A load resistor having a plurality of load transistors having characteristics is provided. A semiconductor device according to a fourth aspect of the present invention that achieves the fourth object is characterized in that the power supply of the output circuit can be switched between a normal power supply and an independent power supply independent of the normal power supply. .

In the nonvolatile semiconductor memory device according to the first aspect of the present invention, the operation test of the function of the status register is performed in such a manner that a test signal is forcibly applied to a part of the internal automatic circuit as in the prior art. Rather, it is possible to make sure that the write test always looks normal by preparing a dummy cell that is fixed at "0" data and has no data change, and writing "0" data there. It is. Conversely, if a dummy cell with data "1" and no data change is prepared in advance and an operation of writing data "0" is performed, it is possible to make it appear that a failure has occurred in the write test. It is.

Similarly, at the time of erasing, a dummy cell having a fixed data of "1" and having no data change is prepared in advance, and if an erasing operation is performed, a normal operation always appears in the erasing test. It is possible. Conversely, if a dummy cell with a fixed data of “0” and no data change is prepared in advance and an action of erasing it is performed,
In the erase test, it is always possible to make it appear that a defect has occurred.

This makes it possible to confirm the operation of the entire circuit including the internal automatic circuit when the cell is normal, and to confirm the operation of the entire circuit including the automatic circuit when the cell is defective. According to the present invention, in addition to checking the status register function, it is possible to check the operation of the entire circuit including the internal automatic circuit.

In the method for testing a nonvolatile semiconductor memory device according to the second aspect of the present invention, a high temperature can be applied to perform an aging process on a semiconductor device on a wafer, and stress during assembly can be reduced. The holding time at a high temperature in the step of growing a coating film for the purpose is also used for the aging step, so that the test step can be reduced.

Since the sense amplifier of the semiconductor memory device according to the third aspect of the present invention includes a plurality of load transistors having different load characteristics, the sense amplifier is switched from the normal operating voltage by switching the connected load transistors according to the power supply voltage. , Accurate cell comparison up to high voltage. The output circuit of the semiconductor device according to the third aspect of the present invention can be switched from a normal power supply to an independent power supply. Therefore, by connecting the power supply of the output Tr to another power supply only at the time of measuring the power supply current, unnecessary current does not flow through the power supply (VCC) of another circuit, and the power supply current during operation can be accurately measured. Moreover, the operation of the device is not affected at all.

[0032]

FIG. 1 is a block diagram of a flash memory according to a first embodiment of the present invention, which corresponds to the conventional example shown in FIG. 13. In FIG. 13 are indicated by the letter A in FIG. 1 is a command register circuit, 2 is a status register circuit, 3 is an operation logic circuit, 4 is a column address buffer, 5 is a row address buffer, 6
Is a block address buffer, 7 is a write / erase switching circuit, 8 is a data comparator circuit, 9 is a write / erase timing generation circuit, 10 is a column decoder, 11 is a row decoder, 12 is a block decoder, 14 is an input / output buffer, 15 Is a sense amplifier / write amplifier, 16 is a Y gate, 17 is a memory cell matrix, and 18 is an erase source control circuit. Reference numeral 19 denotes a test dummy cell selection signal input circuit, and reference numeral 20 denotes a test dummy cell provided in a part of a cell matrix. The test dummy cell is fixed at "0" data and does not change data, or changes data with "1" data. Dummy cells without any problem are prepared.

FIG. 2 is a diagram showing the Y gate 16, the memory cell matrix 17, the erase source control circuit 18, and the test dummy cell in more detail. FIG. 3 is a diagram showing the row decoder 11 in more detail, and FIG. 4 is a diagram showing the details of the test dummy cell selection signal input circuit 19. As shown in FIG. 2, dummy cells D ₁ , D ₂ , D ₃ ,
.. Are ordinary N-channel transistors having no floating gate unlike other memory cells. The gate is connected to the dummy word line DWL, the drain is connected to each bit line BLi, and the source is connected to the common source line SL. ing. The dummy cells D ₁ , D ₂ , D ₃ ,... Can be accessed by selecting a dummy word line DWL and one of bit lines, and depending on whether the dummy cell is conductive or non-conductive, as in the case of a normal memory cell Cij. It is determined whether a current flows or does not flow through the common bit line KBL, and this is detected by the sense amplifier 151. That is, reading of the dummy cell is performed in the same manner as the other memory cells Cij.

The threshold voltage Vth of at least one transistor of the dummy cells D ₁ , D ₂ , D ₃ ,... Is high, and when the dummy cell is read, the transistor is always in a non-conductive state, that is, data “0” is read. Is set to The transistors of the remaining dummy cells are Vt
h is set to be low and data “1” is always read.

The erasing source control circuit 18 turns on the N-channel transistor at the time of reading and writing according to the supplied signal, grounds the common source line SL,
At the time of erasing, the P-channel transistor is turned on, and a high voltage is applied to the common source line SL. The row decoder 11 has the individual decoders indicated by 21 corresponding to the word lines, and applies the voltage VC to the selected word line by decoding the address signal. VC is VCC when reading
And VPP at the time of writing. TS is one of the AND gates forming the decoder, and when selecting a dummy cell, a signal of “L” is applied to this gate, and selection of a normal memory cell Cij is prohibited. Reference numeral 23 denotes a circuit for driving the dummy word line DWL. When a dummy cell is selected, an "L" signal is input, and a voltage VC is applied to the dummy word line DWL.

FIG. 4 shows a test dummy cell selection signal input circuit. The Add input terminal 31 is one of the address signal input terminals. When an intermediate voltage of about 3 to 4 V is applied thereto, the P-channel transistors TP3 and TP4 are turned on. The state is turned on, TN3 to TN5 are also turned on, the dummy cell select signal becomes "H", and the real cell WL non-selection signal becomes "L". At this time, a dummy cell is selected, and a normal memory mole is not selected.

Next, an operation test of the status register circuit 2 in the first embodiment will be described. FIG. 5 is a flowchart showing the process. When performing an operation test, first, in step 101, a pass mode in which a normal operation is performed or a fail mode in which an operation failure occurs is selected. When a predetermined voltage is applied to the terminal 31 of the test dummy cell selection signal input circuit 19, a dummy selection signal is applied to the row decoder 11, and the word line connected to the dummy cell is selected by the row decoder 11. Step 102
To change the column address to select either a dummy cell which is fixed to "0" data and has no data change or a dummy cell which is previously set to "1" data and has no data change. For example, if it is desired to test the operation state of the status register circuit when the writing of cells is normal in the writing system, a dummy cell fixed to "0" data and having no data change is selected. Then, if a write command is input in step 103 and a normal write operation is performed in step 104, the write must be completed normally.
Therefore, if the operation is completed in steps 105 and 106 and the status register is read in step 107, it can be determined whether the status register circuit in the normal state is operating properly. On the other hand, if it is desired to check the operation of the status register circuit when a failure occurs, it is necessary to execute step 10
In step 2, a dummy cell having no data change with "1" data is selected, and if a normal write operation is performed in this state, the write operation must always end with a failure. It can be determined whether the status register circuit at the time of occurrence is operating properly.

Similarly, when testing the operation state of the status register circuit of the erase system, if it is desired to test the operation state of the status register circuit when erasure is normally performed,
"1" A dummy cell with fixed data and no data change is selected. If a normal erasing operation is performed in this state, the erasing should always be completed normally. Based on this, it can be determined whether the status register circuit at the time of the normal erasing is operating properly. On the other hand, if it is desired to confirm the operation of the status register circuit when an erasure failure occurs, a dummy cell having no data change with “0” data is selected, and if a normal erasure operation is performed in this state, erasure will be performed. Since the processing must be always terminated with a failure, it can be determined based on the result that the status register circuit at the time of occurrence of the erasure failure is operating properly. In this way, the operation of the entire circuit including the automatic circuit when the cell is good and when the cell is defective is checked in the form including the entire circuit of the writing system and the entire system of erasing.

As another modified example, a test signal input for selecting a dummy cell is applied to the column address side, and the row address is changed in this state. Alternatively, the same effect can be expected even if some of the dummy cells having data "1" and having no data change are selected in advance.

FIG. 6 is a flowchart showing steps including an aging test according to the second embodiment of the present invention. In the present embodiment, a wafer is formed in Step 201 and Step 20 is performed.
In step 203, a cover film is grown, and in step 203, a first probe test is performed. At this time, charges are injected into the floating gate. As a result, the cell transistor is turned off, and the output becomes "0". In step 204, a coating film is grown.
Since the temperature is kept high for about an hour, the same result as in the aging step can be obtained. In step 205, a second probe test is performed to confirm that the output is "0" even when reading is performed under conditions having a predetermined margin. This means that the data retention test has been performed.

Thereafter, assembly is performed in step 206, and a final test is performed in step 207. In the final test, after a first final test for performing a predetermined operation test, a burn-in for continuously operating for a predetermined time is performed, and then a second final test for testing the operation is performed again, and the process ends. In the second embodiment, after the coating film growth step in step 204, the second probe test for confirming the retained charge is performed, but this can be performed at the time of the final test.

FIG. 7 is a flowchart of a process in the third embodiment in which the second probe test in the second embodiment is performed in the final test process. The second probe test is omitted from the flowchart of FIG.
The difference is that in the first final test of 07, it is checked whether or not the charge injected in step 303 is retained after the coating film growth step and the assembly step in steps 304 and 305. The third embodiment is advantageous in the process because the second probe test can be omitted.

FIG. 8 is a flowchart showing a coating film growing step for reference. Step 4 in the figure
The curing step 07 is a step of drying the formed film. Since the film is held at a high temperature of 300 ° C. to 350 ° C. for 60 minutes, the conditions of the aging step are similar, and the coating film growing step and the aging step are shared. It is possible to

FIG. 9 is a diagram showing the configuration of the sense amplifier in the fourth embodiment. Here, the sense amplifier is connected to the common bit line KBL of the flash memory shown in FIG. 2, but is not limited to this and can be used in other semiconductor devices. . In FIG. 9, 41 is a sense amplifier, and 42 is a load Tr in the sense amplifier. The portion 43 is a VCC power supply voltage circuit. The circuit 43 is a general high-voltage detection circuit, and outputs “H” and “L” signals at an output point C based on the difference between the voltage at the power supply terminal D and the voltage at the gate E. However, this time, the voltage VP is input to the gate E, and the level of the voltage VCC is determined based on the voltage VP (here, the voltage VP is fixed to 5 V). According to this, the line A becomes "L" and the line B becomes "H" before and after the VCC voltage is the voltage VP.
When VCC becomes sufficiently higher than VP, line A becomes "H" and line B becomes "L". Further, the output from the circuit 43 is the load transistor TL for the normal voltage of the circuit 41.
1 and a line A and a line B are connected to the gates of the high-voltage load transistor TL2, respectively. At the time of normal voltage, the line A is "L" and the line B is "H".
The normal voltage load transistor TL1 is turned on, the high voltage load transistor TL2 is turned off, and normal comparison is performed. However, when the power supply voltage becomes high to some extent, A
The line becomes "H" and the line B becomes "L", the normal voltage load transistor TL1 is turned off, and the high voltage load transistor TL2 is turned on to prevent the power supply voltage from becoming too high to make accurate comparison impossible. .

FIG. 10 is a diagram showing load characteristics of the sense amplifier of FIG. Load transistor TL1 for normal voltage
And the slope of the characteristic of the high-voltage load transistor TL2 is different, and by switching in the middle, the characteristic of the sense amplifier becomes as shown by the solid line, and can be made to match the change of the judgment level shown in FIG. Accurate comparison can be performed even at high voltage.

FIG. 11 is a diagram showing a configuration of an output circuit of the nonvolatile semiconductor memory according to the fifth embodiment, to which a tester 56 is connected. In the figure, 51 is a sense amplifier, 52
Is an output buffer. An output transistor circuit 53 includes an N-channel transistor TN11 and a P-channel transistor TP11, and an output terminal 54 thereof. Reference numeral 55 denotes a power supply switching circuit of the output transistor circuit 53, which switches between the normal power supply VCC and the high voltage supply VPP. The high voltage source VPP is a power source supplied for writing and erasing and is independent of the normal power source VCC. Reference numeral 60 denotes a switching signal generating circuit for generating a switching signal of the power supply switching circuit 55. When a high voltage is applied to the electrode pad 61, the signal to the power supply switching circuit 55 becomes "H", and the output transistor circuit 53 Is applied.
Thus, the output transistor circuit 53 outputs the tester 5
The current flowing through the load circuit formed by the resistors 57 and 58 and the capacitor 59 formed by the transistor 6 becomes independent of the power supply VCC. In addition, since the charge and discharge of the load circuit are performed as usual, the semiconductor memory operates normally. In this state, the power supply current value is measured.

[0047]

As described above, according to the present invention, a test signal is forcibly applied to a part of an internal automatic circuit as a conventional means for checking the status register function of a flash memory. Eliminating the need to check the status register function reduces the possibility of logic mistakes that can occur when a test signal is forcibly applied to the internal automatic circuit, and further reduces the internal automatic circuit when the cell is normal. It is possible to easily check the operation of the whole circuit including the automatic circuit when the cell is defective, and to check the operation of the entire circuit including the automatic circuit when the cell is defective. Since it is possible to check the operation of the entire circuit, including the circuit, it is possible to improve test efficiency and test accuracy, which greatly contributes to improvement in reliability.

In addition, since a test for guaranteeing the reliability of data retention of a nonvolatile semiconductor memory such as a flash memory can be reliably performed without increasing the number of steps, manufacturing costs can be reduced. Further, the value of the cell at a high voltage can be read out by a simple circuit device without performing a special test.

Furthermore, the power supply current during operation can be easily and accurately measured without modification of the device.

[Brief description of the drawings]

FIG. 1 is a block diagram of a first embodiment of the present invention.

FIG. 2 is a diagram showing a cell configuration of the first embodiment.

FIG. 3 is a diagram illustrating a configuration of a row decoder according to the first embodiment.

FIG. 4 is a diagram showing a configuration of a test dummy cell selection signal input circuit of the first embodiment.

FIG. 5 is a flowchart showing a status register test process in the first embodiment.

FIG. 6 is a flowchart showing steps including an aging test of the second embodiment.

FIG. 7 is a flowchart showing steps including an aging test of a seventh embodiment.

FIG. 8 is a flowchart showing a coating film growing step.

FIG. 9 is a diagram illustrating a configuration of a sense amplifier according to a fourth embodiment.

FIG. 10 is a diagram illustrating characteristics of a sense amplifier according to a fourth embodiment.

FIG. 11 is a diagram showing a configuration of a fifth embodiment.

FIG. 12 is a diagram of a memory cell structure of a flash memory.

FIG. 13 is a block diagram showing a configuration of a conventional flash memory.

FIG. 14 is a diagram showing a conventional example of a sense amplifier.

FIG. 15 is a flowchart showing a conventional status register test process.

FIG. 16 is a flowchart showing steps including a conventional aging test.

FIG. 17 is a diagram showing a change in a determination level of a sense amplifier with respect to a gate voltage of a memory cell transistor.

FIG. 18 is a diagram showing a conventional configuration when testing a power supply current of a semiconductor device.

[Explanation of symbols]

 2 Status register 3 Operation logic circuit 10 Column decoder 11 Row decoder 15 Sense amplifier / write amplifier 16 Y gate 17 Memory cell matrix 18 Erase source control circuit 19 Dummy cell selection signal circuit for test 20 Test dummy cell

Continued on the front page (72) Inventor Hisaka Watanabe 1015 Uedanaka, Nakahara-ku, Kawasaki City, Kanagawa Prefecture Inside Fujitsu Limited (72) Inventor Yasushi Yasushi 1015 Uedanaka, Nakahara-ku Nakagawa-ku, Kawasaki City, Kanagawa Prefecture Fujitsu Limited

Claims (4)

[Claims] 1. A method for testing a nonvolatile semiconductor memory device to which data can be written, comprising: a writing step of writing data; an aging step of maintaining the nonvolatile semiconductor memory device under a predetermined aging condition; A method for testing a nonvolatile semiconductor memory device, comprising: a step of reading and comparing with data written in the writing step; and a step of reducing stress during assembly of the nonvolatile semiconductor memory device. A method for testing a nonvolatile semiconductor memory device, comprising a film growing step. 2. The nonvolatile semiconductor memory device according to claim 1, wherein said writing step and said confirming step are performed by bringing a stylus into contact with said nonvolatile semiconductor memory device on a semiconductor wafer. Test method. 3. The writing step is performed by bringing a stylus into contact with the nonvolatile semiconductor memory device on a semiconductor wafer, and the checking step is performed in a final test step after the nonvolatile semiconductor memory device is assembled. 2. The method for testing a nonvolatile semiconductor memory device according to claim 1, wherein the method is performed. 4. The method for testing a nonvolatile semiconductor memory device according to claim 1, wherein said nonvolatile semiconductor memory device is assembled into a plastic package during assembly.