CAM unit inspection module and inspection method thereof

Abstract

The present invention relates to a CAM cell inspection module and an inspection method thereof. The CAM cell inspection module is used to inspect a CAM cell in a NAND memory and includes: a read level setting unit, which sets a CAM cell read level based on a pre-stored CAM cell read level table; a special read command execution unit, which executes a special read command based on the set CAM cell read level; and a status inspection unit, which reads data from the CAM cell in response to the special read command and determines whether the status of the CAM cell is passed or failed. Under the special read command, the data read from the CAM cell is only used by the status inspection unit to determine the status of the CAM cell.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor technology, and in particular to a CAM unit inspection module in a NAND memory and an inspection method thereof. Background Art

[0002] NAND memory is a high-capacity storage chip characterized by high density, low manufacturing cost, and fast access speed. It is commonly used in devices such as USB flash drives, solid-state drives, and memory cards. NAND memory typically performs the following three operations: programming, erasing, and reading.

[0003] Figure 1 This is a schematic diagram showing the level distribution of a normal cell in a NAND memory. Figure 1 ERA in the figure indicates an erased cell, which is marked as "1"; PGM indicates a programmed cell, which is marked as "0"; EV indicates an erase verification level; PV indicates a program verification level; and RD indicates a read level.

[0004] like Figure 1 As shown in Figure 1, the voltage level of a programmed cell is higher than PV, while the voltage level of an erased cell is lower than EV. The read voltage level RD lies between PV and EV, reading "0" or "1" data from a NAND memory cell. Sufficient margin should be maintained between the voltage levels of programmed and erased cells to avoid false reads.

[0005] Figure 2 This is a schematic diagram showing the level distribution of the CAM cell in the NAND memory. Figure 1 same, Figure 2 ERA in the figure indicates an erased cell, which is marked as "1"; PGM indicates a programmed cell, which is marked as "0"; EV indicates an erase verification level; PV indicates a program verification level; and RD indicates a read level.

[0006] CAM cells refer to content addressable memory cells in NAND memory. Because NAND memory is non-volatile, configuration and repair information can be stored in internal storage cells without the need for additional fuses typically used in volatile memory. The memory cell area that stores this important content of the device is usually called a CAM cell.

[0007] Specifically, the configuration information stored in the CAM cell includes, for example, operating voltage, programming, reading, and erasing conditions, trim data, etc. The repair information stored in the CAM cell includes, for example, column repair information and block repair information.

[0008] like Figure 2 As shown, in the case of a CAM cell, the width between the program verification level PV and the erase verification level EV is wider than that of a normal cell. This is because retention is particularly important in the case of a CAM cell.

[0009] The CAM cell can store configuration and repair information of the NAND memory device. Therefore, in the case of the CAM cell, the level VT of the programmed cell is higher than that of the normal cell to obtain more margin than the normal cell.

[0010] CAM cells are usually programmed only once, so their voltage level after programming can be higher than that of ordinary cells. Before NAND memory is shipped, CAM cells are programmed, and users cannot program or erase CAM cells afterwards.

[0011] In the prior art, a majority check is usually used to test a CAM unit. Specifically, the CAM unit is tested according to the following steps, namely:

[0012] Step 1: Before shipment, program the CAM unit based on the configuration and repair information;

[0013] Step 2: Power on and read the CAM to read the configuration and repair information and compare them.

[0014] In this test flow, the margin between the program verification level PV and the read level RD cannot be checked. However, in the actual manufacturing process, the programming unit is often shifted to the left, resulting in misreading and frequent user complaints of CAM unit failures.

[0015] Therefore, in order to avoid this situation in the prior art, it is necessary to add an additional test process before or after shipment to perform a margin check.

[0016] Furthermore, the added test process typically uses the CellVt method for margin checking. CellVt is a test mode for scanning the threshold voltage of normal cells, measuring it using an externally specified method. Applying this method to CAM cells is time-consuming and results in very low test efficiency. Summary of the Invention

[0017] In order to solve the above technical problems, the present invention provides a CAM unit inspection module for inspecting CAM units in a NAND memory, which is characterized by comprising:

[0018] a read level setting section configured to set a CAM cell read level based on a pre-stored CAM cell read level table;

[0019] a special read command execution unit configured to execute a special read command based on the set CAM cell read level;

[0020] a status checking unit that reads data from the CAM cell in response to the special read command and determines whether the status of the CAM cell is a pass or a fail,

[0021] Under the special read command, the data of the CAM cell read is only used by the status check unit to determine the status of the CAM cell.

[0022] Optionally, in the CAM cell check module of the present invention, the status check unit determines the status of the CAM cell by checking CRC data appended to the data of the CAM cell.

[0023] Optionally, in the CAM unit inspection module involved in the present invention, the CAM unit read level table is set with multiple read levels for the CAM unit, and adjacent read levels differ by a fixed step size.

[0024] Optionally, in the CAM unit inspection module involved in the present invention, different read levels are set based on the CAM unit read level table, and the status of the CAM unit is determined at different read levels to determine whether the status of the CAM unit is a pass or fail threshold.

[0025] The present invention also provides a CAM unit inspection method for inspecting a CAM unit in a NAND memory, which is characterized by comprising:

[0026] a read level setting step of setting a CAM cell read level based on a pre-stored CAM cell read level table;

[0027] a special read command execution step, in which a special read command is executed based on the set CAM unit read level;

[0028] a status checking step of reading data of the CAM cell in response to the special read command and determining whether the status of the CAM cell is a pass or a fail,

[0029] Under the special read command, the data of the CAM cell read is only used to determine the status of the CAM cell.

[0030] Optionally, in the CAM cell inspection method of the present invention, in the status inspection step, the status of the CAM cell is determined by inspecting CRC data appended to the data of the CAM cell.

[0031] Optionally, in the CAM cell inspection method of the present invention, a plurality of read levels for the CAM cell are set in the CAM cell read level table, and adjacent read levels differ by a fixed step size.

[0032] Optionally, in the CAM unit inspection method involved in the present invention, different read levels are set based on the CAM unit read level table, and the state of the CAM unit is determined at different read levels to determine the read level threshold of whether the state of the CAM unit is passed or failed.

[0033] Optionally, in the CAM unit inspection method involved in the present invention, when the status of the CAM unit is judged to be passed, the read level setting step, the special read command execution step, and the status inspection step are repeated until the status of the CAM unit is judged to be failed, and the read level setting at which the status of the CAM unit is judged to be passed for the last time is used as the read level threshold.

[0034] According to the CAM unit inspection module and inspection method of the present invention, since a special read command is added and executed in the normal CAM unit reading process, the margin of the CAM unit can be inspected without adding additional test processes, which greatly reduces the test time and improves the yield.

[0035] According to the CAM unit inspection module and the inspection method thereof of the present invention, since CRC data is added to the data of the CAM unit, the accuracy of the judgment of the state of the CAM unit is improved, and the precision of the test result is improved.

[0036] In addition, even if the CAM unit is returned due to a fault, the margin of the CAM unit can be checked by the CAM unit inspection module and the inspection method thereof of the present invention, which greatly reduces the test time and improves the yield. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 This is a schematic diagram showing the level distribution of a normal cell in a NAND memory.

[0038] Figure 2 This is a schematic diagram showing the level distribution of the CAM cell in the NAND memory.

[0039] Figure 3 This is a block diagram showing a CAM cell inspection module according to the first embodiment.

[0040] Figure 4 This is a diagram showing an example of a CAM cell read level table according to the first embodiment.

[0041] Figure 5 This is a flowchart showing the steps of the CAM cell inspection method according to the second embodiment. DETAILED DESCRIPTION

[0042] The present invention will be described in more detail below with reference to specific embodiments illustrated in the accompanying drawings. The flowcharts and block diagrams in the accompanying drawings illustrate the architecture, functionality, and operations that may be implemented by systems and methods according to embodiments of the present invention. The accompanying drawings are provided only for the purpose of illustrating preferred embodiments and are not to be construed as limiting the present invention. Throughout the drawings, identical reference symbols are used to represent identical components.

[0043] In addition, by reading the detailed description of the specific embodiments below, the various advantages and benefits of the present invention will become clear to those of ordinary skill in the art. However, it should be understood that the present invention can be implemented in various forms and should not be limited by the various embodiments described herein. The following embodiments are provided to enable a more thorough understanding of the present invention. Unless otherwise specified, technical terms or scientific terms used in the present invention should have the common meanings understood by those skilled in the art to which the present invention belongs.

[0044] Implementation Method 1

[0045] Embodiment 1 of the present invention relates to a CAM cell inspection module for inspecting CAM cells in a NAND memory.

[0046] Figure 3 1 is a schematic block diagram showing the CAM unit inspection module 100 according to the first embodiment. Figure 3 As shown, the CAM cell inspection module 100 includes a read level setting section 101 , a special read command execution section 102 , and a status inspection section 103 .

[0047] The read level setting section 101 sets the CAM cell read level based on a pre-stored CAM cell read level table. Figure 4 FIG. 1 is a diagram showing an example of a CAM unit read level table according to the first embodiment. Figure 4As shown in FIG. 1 , the CAM cell read level table is set with multiple read levels A to H for the CAM cell, and the adjacent read levels differ by a fixed step size alpha. The value of alpha can be flexibly set as needed. For example, when the read level information is set to 3 bits (3 bits), i.e., <2:0>, as shown in FIG. Figure 4 As shown, 000 corresponds to read level A, 001 corresponds to read level B (=A+alpha), 010 corresponds to read level C (=B+alpha), ..., 110 corresponds to read level G (=F+alpha), and 111 corresponds to read level H (=G+alpha). By the method described below, it is possible to determine which of the multiple read levels A to H indicates a failed state of the CAM cell.

[0048] The special read command execution unit 102 executes a special read command based on the CAM cell read level set by the read level setting unit 101. This special read command differs from a command that performs CAM read preparation after power-on. When this special read command is executed, it only initiates a CAM read operation without performing a power-on CAM read. In other words, when this special read command is executed, the data from the CAM cell read performed during the CAM read operation is used only for determining the CAM cell status, which will be described later.

[0049] By introducing the special read command execution unit 102 into the test module of the CAM unit to execute the special read command, the margin of the CAM unit can be checked without adding additional test procedures, which greatly reduces the test time and improves the yield.

[0050] The status check unit 103 is a unit that determines the status of the CAM cell. In response to the special read command from the special read command execution unit 102, the status check unit 103 reads data from the CAM cell by performing a CAM read operation and determines whether the status of the CAM cell is pass or fail.

[0051] Specifically, the CAM cell status is determined by checking the CRC data appended to the CAM cell data. CRC is a commonly used error detection code in digital networks and storage devices. Because CRC is easy to implement in binary hardware, it is widely used.

[0052] In some embodiments, CRC may adopt the following scheme, for example:

[0053] CRC 16:x16+x15+x2+1;

[0054] CRC 32:x32+x26+x23+x22+x16+x12+x11+x10+x8+x7+x5+x4+x2+x+1.

[0055] However, the present invention is not limited thereto and other technologies known in the art may be used.

[0056] In this embodiment, a CRC is incorporated into the CAM cell data. Specifically, CRC data is calculated based on the CAM cell data and appended to the CAM cell data. While the status check unit 103 is reading the CAM cell data through a CAM read operation, the appended CRC data is used to check for errors in the CAM cell data. If an error occurs in the CAM cell data, that is, if the CAM cell status is determined to be a failure, this means that the configuration and repair information in the CAM cell is damaged, and the user will be unable to use the memory device. In this embodiment, by incorporating a CRC into the determination of the CAM cell status and appending the CRC data to the CAM cell data, the accuracy of the CAM cell status determination is improved, thereby enhancing the precision of the test results.

[0057] The status check unit 103 is based on Figure 4 The CAM cell read level table shown is used to set different read levels, and the status of the CAM cell is determined at different read levels to determine whether the status of the CAM cell is a pass or fail threshold. If the CAM cells are located in different pages of the NAND memory, a pass / fail bit is allocated in each CAM cell page. For example, in some embodiments, if two pages are allocated to the CAM cell, 2 bits (2 bits) are allocated for each pass / fail check. If three pages are allocated to the CAM cell, 3 bits (3 bits) are allocated for each pass / fail check. The allocation of pass / fail bits can be set according to actual conditions.

[0058] According to the CAM cell check module 100 of Embodiment 1, by adding and executing a special read command during the normal CAM cell read process, the CAM cell margin can be checked without adding an additional test process, significantly reducing test time and improving yield. Furthermore, by appending CRC data to the CAM cell data, the accuracy of determining the CAM cell status is improved, thereby improving the precision of the test results.

[0059] Implementation Method 2

[0060] The following is based on Figure 5 The CAM cell inspection method according to the second embodiment will be described in detail. Figure 5 This is a flowchart showing the steps of the CAM cell inspection method according to the second embodiment.

[0061] like Figure 5 As shown, the NAND memory is first powered on. In step S100, the CAM unit is started and is ready for reading. In step S101, a reset command is executed to reset the CAM unit. In step S102, a test mode command is executed to enter the CAM unit test mode.

[0062] Next, in step S103 (reading level setting step), the CAM cell reading level is set based on the pre-stored CAM cell reading level table. Figure 4 As shown, a plurality of read levels A to H are set for the CAM cell, and adjacent read levels differ by a fixed step size alpha.

[0063] Next, in step S104 (special read command execution step), a special read command is executed based on the set CAM cell read level. This special read command differs from the command that initiates CAM read readiness after power-up. When this special read command is executed, only a CAM read operation is initiated without performing a power-up CAM read. In other words, when this special read command is executed, the data from the CAM cell read through the CAM read operation is used only for determining the CAM cell status, which will be described later.

[0064] Next, in step S105 (status check step), in response to the special read command, the data of the CAM cell is read and the status of the CAM cell is determined to be pass or fail. Specifically, the status of the CAM cell is determined by checking the CRC data attached to the data of the CAM cell. The CRC setting method is as described in Implementation 1 and will not be repeated here.

[0065] If the CAM cell status is determined to be failed in step S105 , the inspection process ends, and the read level at which the CAM cell status was last determined to be passed is set as the read level threshold.

[0066] If the status of the CAM unit is determined to be passed in step S105 , the process returns to step S103 and repeats steps S103 , S104 , and S105 until it is determined to be failed in step S105 .

[0067] According to the CAM cell inspection method of embodiment 2, by adding and executing a special read command during the normal CAM cell read process, the CAM cell margin can be inspected without adding an additional test process, significantly reducing test time and improving yield. Furthermore, by appending CRC data to the CAM cell data, the accuracy of determining the CAM cell status is improved, thereby improving the precision of the test results.

[0068] In addition, even if the CAM unit is returned due to a fault, the CAM unit margin can be checked by the CAM unit inspection module involved in the above-mentioned embodiment 1 and the CAM unit inspection method involved in the above-mentioned embodiment 2, which greatly reduces the test time and improves the yield.

[0069] The above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents; and these modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of this application, and they should all be included in the scope of the claims and description of this application.

[0070] Description of labels

[0071] 100 CAM unit inspection module

[0072] 101 Reading level setting unit

[0073] 102 Special read command execution unit

[0074] 103 Status Inspection Department.

Claims

1. A CAM unit inspection module for inspecting CAM units in a NAND memory, characterized in that: include: a read level setting section configured to set a CAM cell read level based on a pre-stored CAM cell read level table; a special read command execution unit configured to execute a special read command based on the set CAM cell read level; a status checking unit that reads data from the CAM cell in response to the special read command and determines whether the status of the CAM cell is a pass or a fail, Under the special read command, the data of the CAM cell read is only used by the status check unit to determine the status of the CAM cell. The special read command is an instruction dedicated to CAM unit testing, and power-on CAM reading is prohibited during execution.

2. The CAM unit inspection module according to claim 1, wherein: The status check unit determines the status of the CAM cell by checking CRC data added to the data of the CAM cell.

3. The CAM unit inspection module according to claim 1, wherein: The CAM cell read level table is configured with a plurality of read levels for the CAM cell, and adjacent read levels differ from each other by a fixed step size.

4. The CAM unit inspection module according to any one of claims 1 to 3, characterized in that: By setting different read levels based on the CAM cell read level table and determining the state of the CAM cell at the different read levels, a threshold value of whether the state of the CAM cell is pass or fail is determined.

5. A CAM unit inspection method for inspecting a CAM unit in a NAND memory, characterized in that: include: a read level setting step of setting a CAM cell read level based on a pre-stored CAM cell read level table; a special read command execution step, in which a special read command is executed based on the set CAM unit read level; a status checking step of reading data of the CAM cell in response to the special read command and determining whether the status of the CAM cell is a pass or a fail, Under the special read command, the data of the CAM unit read is only used to determine the state of the CAM unit. The special read command is an instruction dedicated to CAM unit testing, and power-on CAM reading is prohibited during execution.

6. The CAM unit inspection method according to claim 5, wherein: In the state checking step, the state of the CAM cell is determined by checking CRC data added to the data of the CAM cell.

7. The CAM unit inspection method according to claim 5, wherein: The CAM cell read level table is configured with a plurality of read levels for the CAM cell, and adjacent read levels differ from each other by a fixed step size.

8. The CAM unit inspection method according to any one of claims 5 to 7, characterized in that: By setting different read levels based on the CAM cell read level table and determining the state of the CAM cell at the different read levels, a read level threshold value for determining whether the state of the CAM cell is pass or fail is determined.

9. The CAM unit inspection method according to claim 8, wherein: When the status of the CAM unit is judged to be passed, the read level setting step, the special read command execution step, and the status checking step are repeated until the status of the CAM unit is judged to be failed, and the read level setting at which the status of the CAM unit is judged to be passed for the last time is used as the read level threshold.

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