A method and system for measuring threshold voltage

Abstract

The present invention provides a threshold voltage measurement method and system, comprising: step S1: setting the maximum working voltage and the minimum working voltage of a MOS tube as an upper limit voltage and a lower limit voltage, and executing step S2; step S2: taking the value between the upper limit voltage and the lower limit voltage as a scanning voltage, applying the scanning voltage to the gate of the MOS tube, and obtaining the drain current, and executing step S3; step S3: subtracting the drain current from the target current to obtain a first difference, and when the absolute value of the first difference is less than or equal to the first set value, outputting the scanning voltage as a threshold voltage; when the absolute value of the first difference is greater than the first set value, adjusting the upper limit voltage and the lower limit voltage by judging the magnitude relationship between the drain current and the target current, and returning to step S2. The damage to the MOS tube caused by the application of the maximum working voltage and the minimum working voltage and the shift of the threshold voltage are avoided.

Description

Technical Field

[0001] The present invention relates to the field of semiconductors, and particularly to a method and system for measuring a threshold voltage. Background Art

[0002] With the continuous progress of semiconductor technology, the requirements for integrated circuit manufacturing processes are increasing day by day. However, due to the long manufacturing cycle and extremely high cost of integrated circuits, it is particularly important to improve the production efficiency of manufacturing processes and the yield of products. After a semiconductor device is fabricated and before it is packaged, in order to ensure the yield of the semiconductor device and avoid waste of packaging, it is necessary to detect the electrical performance of the semiconductor device to prevent devices that do not meet the requirements from entering the next process.

[0003] When measuring the electrical properties of current semiconductor devices, the most typical one is the measurement of the threshold voltage. Generally, the input voltage corresponding to the midpoint of the transition region where the output voltage changes sharply with the input voltage in the transfer characteristic curve is called the threshold voltage. The principle of measuring the threshold voltage is that when the gate voltage reaches a certain value, the current between the source and the drain during this period reaches a certain specific value, that is, it is considered that the MOS transistor is turned on, and the gate voltage at this time is the threshold voltage.

[0004] Generally, there are two methods for testing the threshold voltage. One is the linear voltage sweep method, and the other is the dichotomy voltage sweep method. The linear voltage sweep starts from the minimum operating voltage of the semiconductor device and sequentially applies voltages to the maximum operating voltage according to a set voltage step size, and finds the voltage value corresponding to the target current value by measuring the current value at the drain end of the semiconductor device; while the dichotomy voltage sweep method first measures the current values corresponding to the maximum operating voltage, the minimum operating voltage and the intermediate voltage, and compares them with the target current value to determine the interval where the threshold voltage is located, and gradually narrows the voltage range to be measured by a step-by-step approximation method, and finally determines the threshold voltage.

[0005] However, there is a contradiction between the accuracy and the test efficiency in the linear voltage sweep method. If the set voltage step size is made smaller to improve the accuracy, it will be very time-consuming; if the set voltage step size is increased to reduce the test time, the accuracy will be reduced. Relatively speaking, the dichotomy voltage sweep method is more accurate and efficient, but during the test, due to the immaturity of the semiconductor device and its inability to withstand high voltages, device damage may occur; or due to the application of high or low voltages to the semiconductor device, slight erasure or writing may occur, resulting in a shift of the threshold voltage. As Figure 1 shown, slight erasure occurred during the first threshold voltage measurement of the semiconductor device, resulting in a different result for the second threshold voltage measurement compared to the first one. Summary of the Invention

[0006] The object of the present invention is to provide a method and system for measuring a threshold voltage, so as to avoid the problems of device damage and threshold voltage shift caused by the application of the maximum operating voltage or the minimum operating voltage to a semiconductor device.

[0007] To achieve the above object, the present invention provides a method for measuring a threshold voltage, including:

[0008] Step S1: Set the maximum operating voltage and the minimum operating voltage of the MOS transistor as the upper limit voltage and the lower limit voltage, and execute Step S2;

[0009] Step S2: Use the value between the upper limit voltage and the lower limit voltage as the scanning voltage, apply the scanning voltage to the gate of the MOS transistor, and obtain the drain current of the MOS transistor, and execute Step S3;

[0010] Step S3: Subtract the drain current from the target current to obtain a first difference. When the absolute value of the first difference is less than or equal to a first set value, output the scanning voltage as the threshold voltage of the MOS transistor; when the absolute value of the first difference is greater than the first set value, judge the magnitude relationship between the drain current and the target current. When the drain current is greater than the target current, replace the upper limit voltage with the scanning voltage and return to Step S2. When the drain current is less than the target current, replace the lower limit voltage with the scanning voltage and return to Step S2.

[0011] Optionally, before executing Step S3, subtract the scanning voltage from the maximum operating voltage and the minimum operating voltage respectively to obtain a second difference and a third difference. If any one of the absolute values of the second difference and the third difference is less than a second set value and the absolute value of the first difference is still greater than the first set value, output an error signal as the threshold voltage of the MOS transistor.

[0012] Optionally, the second set value is less than 0.05V.

[0013] Optionally, in Step S2, subtract the value between the upper limit voltage and the lower limit voltage from the maximum operating voltage and the minimum operating voltage respectively to obtain a fourth difference and a fifth difference, and the absolute values of the fourth difference and the fifth difference are both greater than the second set value.

[0014] Optionally, in Step S2, use the average value between the upper limit voltage and the lower limit voltage as the scanning voltage.

[0015] Optionally, the first set value is 0.1 times to 0.3 times of the target current.

[0016] Optionally, while applying a scanning voltage to the gate of the MOS transistor, a preset voltage is applied to the drain of the MOS transistor, and the source of the MOS transistor is grounded.

[0017] Based on the same inventive concept, the present invention further provides a threshold voltage measurement system, which uses the maximum operating voltage and the minimum operating voltage of the MOS transistor as the upper limit voltage and the lower limit voltage respectively, and includes:

[0018] An electrical signal application unit, which uses the value between the upper limit voltage and the lower limit voltage as the scanning voltage and applies the scanning voltage to the gate of the MOS transistor;

[0019] An electrical signal reading unit, which measures the drain current of the MOS transistor;

[0020] An electrical signal processing unit, which subtracts the drain current from the target current to obtain a first difference. When the absolute value of the first difference is less than or equal to a first set value, the scanning voltage is output as the threshold voltage of the MOS transistor; when the absolute value of the first difference is greater than the first set value, it judges the magnitude relationship between the drain current and the target current. When the drain current is greater than the target current, the upper limit voltage is replaced with the scanning voltage, and the electrical signal application unit is returned to re-apply the scanning voltage to the gate of the MOS transistor. When the drain current is less than the target current, the lower limit voltage is replaced with the scanning voltage, and the electrical signal application unit is returned to re-apply the scanning voltage to the gate of the MOS transistor.

[0021] Optionally, the electrical signal application unit also applies a preset voltage to the drain of the MOS transistor to ground the source of the MOS.

[0022] Optionally, before the absolute value of the first difference and the first set value, it further includes:

[0023] The scanning voltage is subtracted from the maximum operating voltage and the minimum operating voltage respectively to obtain a second difference and a third difference. If any one of the absolute values of the second difference and the third difference is less than a second set value, and the absolute value of the first difference is still greater than the first set value, an error signal is output as the threshold voltage of the MOS transistor.

[0024] The present invention provides a method and system for measuring a threshold voltage. Step S1: Set the maximum operating voltage and the minimum operating voltage of the MOS transistor as the upper limit voltage and the lower limit voltage, and execute step S2; Step S2: Use the value between the upper limit voltage and the lower limit voltage as the scanning voltage, apply the scanning voltage to the gate of the MOS transistor, and obtain the drain current of the MOS transistor, then execute step S3; Step S3: Subtract the drain current from the target current to obtain a first difference. When the absolute value of the first difference is less than or equal to a first set value, output the scanning voltage as the threshold voltage of the MOS transistor; when the absolute value of the first difference is greater than the first set value, determine the magnitude relationship between the drain current and the target current. When the drain current is greater than the target current, replace the upper limit voltage with the scanning voltage and return to step S2. When the drain current is less than the target current, replace the lower limit voltage with the scanning voltage and return to step S2. The present invention can avoid applying the maximum operating voltage and the minimum operating voltage to the MOS transistor during the measurement process. By comparing the relationship between the drain current of the MOS transistor and the target current, the voltage measurement range is gradually reduced, approaching the threshold voltage continuously, and avoiding the damage to the MOS transistor and the shift of the threshold voltage caused by the application of the maximum operating voltage and the minimum operating voltage. Description of the Drawings

[0025] Figure 1 Graph showing the results of two measurements when using the dichotomy voltage sweep method;

[0026] Figure 2 Flowchart of a method for measuring a threshold voltage provided in Embodiment 1 of the present invention;

[0027] Figure 3 Schematic diagram of a method for measuring a threshold voltage provided in Embodiment 1 of the present invention;

[0028] Figure 4 Schematic diagram of a method for measuring a threshold voltage provided in Embodiment 1 of the present invention;

[0029] Figure 5 Schematic diagram of a method for measuring a threshold voltage provided in Embodiment 2 of the present invention;

[0030] Among them, the description of the drawings is as follows:

[0031] V max - Maximum operating voltage; V min - Minimum operating voltage; V1, V2, V3, V4, V5, V6 - Scanning voltages. Detailed Description of the Invention

[0032] The specific embodiments of the present invention will be described in more detail below with reference to the schematic diagrams. According to the following description, the advantages and features of the present invention will be clearer. It should be noted that the drawings are all in a very simplified form and use non-precise scales, only for the purpose of facilitating and clearly assisting in explaining the objectives of the embodiments of the present invention.

[0033] In the following text, terms such as "first" and "second" are used to distinguish between similar elements and are not necessarily used to describe a specific order or time sequence. It is understood that, under appropriate circumstances, these terms used in this way can be replaced. Similarly, if the methods described herein include a series of steps, and the steps presented herein are not necessarily the only order in which these steps can be executed, and some of the described steps can be omitted and / or some other steps not described in the text can be added to the method.

[0034] Embodiment 1

[0035] Figure 2 is a flowchart of a method for measuring a threshold voltage provided for this embodiment. As Figure 2 shown, the present invention provides a method for measuring a threshold voltage, including:

[0036] Step S1: Set the maximum operating voltage and the minimum operating voltage of the MOS transistor as the upper limit voltage and the lower limit voltage, and execute Step S2;

[0037] Step S2: Use the value between the upper limit voltage and the lower limit voltage as the scanning voltage, apply the scanning voltage to the gate of the MOS transistor, and obtain the drain current of the MOS transistor, and execute Step S3;

[0038] Step S3: Subtract the drain current from the target current to obtain a first difference. When the absolute value of the first difference is less than or equal to a first set value, output the scanning voltage as the threshold voltage of the MOS transistor; when the absolute value of the first difference is greater than the first set value, judge the magnitude relationship between the drain current and the target current. When the drain current is greater than the target current, replace the upper limit voltage with the scanning voltage and return to Step S2. When the drain current is less than the target current, replace the lower limit voltage with the scanning voltage and return to Step S2.

[0039] Figure 3 is a schematic diagram of a method for measuring a threshold voltage provided for this embodiment. The following combines the attached Figure 3 to describe in more detail the method for measuring a threshold voltage provided for this embodiment, in which the preferred embodiment of the present invention is illustrated.

[0040] It should be understood that the threshold voltage refers to the gate voltage of the MOS transistor when the surface of the MOS device reaches strong inversion, and it is also the voltage value at which the MOS device transitions from the linear region to the saturation region. Generally, the threshold voltage of the NMOS transistor is greater than zero, and the threshold voltage of the PMOS transistor is less than zero. The theoretical distribution range of both the threshold voltage of the NMOS transistor and the threshold voltage of the PMOS transistor is between the maximum operating voltage and the minimum operating voltage of the device.

[0041] As Figure 3 shown, perform step S1, and use the maximum operating voltage V max of the MOS transistor as the upper limit voltage and the minimum operating voltage V min as the lower limit voltage.

[0042] Refer to Figure 2 and Figure 3 , Figure 3 where V t is the threshold voltage. Perform step S1, apply a set voltage to the drain of the MOS transistor, ground the source of the MOS transistor, and the voltage between the source and the drain can be 0.05V - 0.1V, or it can be the operating voltage of the MOS transistor, or different voltage values can be set according to different test requirements.

[0043] Perform step S2: Use the average value of the upper limit voltage and the lower limit voltage as the scan voltage V1, apply the scan voltage V1 to the gate of the MOS transistor. At this time, the voltage measurement range is [V min , V max , and obtain the drain current of the MOS transistor.

[0044] Perform step S3, subtract the drain current from the target current to obtain a first difference, and compare the relationship between the absolute value of the first difference and a first set value. As Figure 3 shown, if the absolute value of the first difference is greater than the first set value, then judge the magnitude relationship between the drain current and the target current. When the drain current is less than the target current, adjust the upper limit voltage to the scan voltage V1 and return to step S2.

[0045] Among them, the first set value is 0.1 times the target current to 0.3 times the target current. The accuracy of the measured threshold voltage can be improved by adjusting the first set value. At the same time, setting the first set value can avoid the excessive measurement time caused by too many measurement times.

[0046] Furthermore, repeat step S2. At this time, the upper limit voltage is the scan voltage V1, the lower limit voltage is the minimum operating voltage V min , and the voltage measurement range is [Vmin , take the intermediate value of the upper limit voltage and the lower limit voltage as the scanning voltage V2, apply the scanning voltage V2 to the gate of the MOS transistor, and measure the drain current at this time.

[0047] Compare the absolute value of the first difference with the first set value. If Figure 3 as shown, the absolute value of the first difference is greater than the first set value, then judge the magnitude relationship between the drain current and the target current. When the drain current is greater than the target current, adjust the lower limit voltage to the scanning voltage V2. At this time, the voltage measurement range is [V1, V2], and return to step S2.

[0048] Continue to refer to Figure 3 , repeat step S2, gradually narrow the voltage measurement range until the scanning voltage V6 is applied to the MOS transistor. At this time, the obtained drain current is equal to the target current, that is, the absolute value of the first difference is equal to zero. Zero must be less than the first set value, then output the scanning voltage V6 at this time as the threshold voltage of this MOS transistor.

[0049] Furthermore, during the measurement of the voltage threshold, as the voltage measurement range changes, when the absolute value of the first difference is less than or equal to the first set value, output the scanning voltage at this time as the threshold voltage of this MOS transistor, not limited to the case where the drain current is equal to the target current.

[0050] It should be understood that the change of the voltage measurement range depends on the relationship between the drain current and the target current, and does not follow the rule of changing the upper limit voltage once and then changing the lower limit voltage once. For example, Figure 3 during the process from the scanning voltage V3 to the scanning voltage V5, the lower limit voltage was changed twice continuously.

[0051] Before executing step S3, before executing step S3, subtract the scanning voltage from the maximum operating voltage and the minimum operating voltage respectively to obtain a second difference and a third difference. If any one of the absolute values of the second difference and the third difference is less than the second set value, and the absolute value of the first difference is still greater than the first set value, then output the error signal as the threshold voltage of the MOS transistor. Figure 4 is a schematic diagram of a method for measuring the threshold voltage provided by this embodiment. As Figure 4As shown, if after several measurements, until the absolute value of the second difference is less than the second set value, and the absolute value of the first difference is still greater than the first set value, then the error signal is output as the threshold voltage of the MOS transistor. Adding the second set value can avoid damage or threshold voltage shift of the MOS transistor caused by the scanning voltage applied to the MOS transistor being too large or too small, and also avoid entering an infinite loop in measurement when the drain current can never be equal to the target current.

[0052] Among them, the second set value is less than 0.05V.

[0053] Figure 4 Only the case where the scanning voltage is infinitely close to the maximum operating voltage V is exemplified. max It should be understood that when the scanning voltage is infinitely close to the minimum operating voltage V. min The situation is the same as the above case.

[0054] The traditional binary search scanning method applies the maximum operating voltage V, max the minimum operating voltage V, min and the intermediate voltage between the maximum operating voltage V max and the minimum operating voltage V min to the gate of the MOS transistor, and uses the drain currents obtained from three measurements to gradually narrow the voltage measurement range. However, the application of the maximum operating voltage V max and the minimum operating voltage V min will cause problems such as damage and threshold voltage shift to the MOS transistor.

[0055] In this embodiment, only a voltage between the maximum operating voltage V max and the minimum operating voltage V min is applied to the MOS transistor, and the obtained drain current is compared with the target current to narrow the voltage measurement range, avoiding applying the maximum operating voltage V max and the minimum operating voltage V min to the MOS transistor, thereby avoiding damage and threshold voltage shift of the MOS transistor.

[0056] Based on the same inventive concept, this embodiment provides a threshold voltage measurement system, which uses the maximum operating voltage and the minimum operating voltage of the MOS transistor as the upper limit voltage and the lower limit voltage respectively, and includes:

[0057] An electric signal application unit applies the scanning voltage, which is a value between the upper limit voltage and the lower limit voltage, to the gate of the MOS transistor; an electric signal reading unit measures the drain current of the MOS transistor; an electric signal processing unit subtracts the drain current from the target current to obtain a first difference. When the absolute value of the first difference is less than or equal to a first set value, the scanning voltage is output as the threshold voltage of the MOS transistor; when the absolute value of the first difference is greater than the first set value, the magnitude relationship between the drain current and the target current is judged. When the drain current is greater than the target current, the upper limit voltage is replaced with the scanning voltage, and the electric signal application unit is returned to re-apply the scanning voltage to the gate of the MOS transistor. When the drain current is less than the target current, the lower limit voltage is replaced with the scanning voltage, and the electric signal application unit is returned to re-apply the scanning voltage to the gate of the MOS transistor.

[0058] The electric signal application unit also applies a preset voltage to the drain of the MOS transistor to ground the source of the MOS.

[0059] Before the electric signal processing unit judges the magnitude relationship between the absolute value of the first difference and the first set value, it further includes: subtracting the scanning voltage from the maximum operating voltage and the minimum operating voltage respectively to obtain a second difference and a third difference. If any one of the absolute values of the second difference and the third difference is less than a second set value, and the absolute value of the first difference is still greater than the first set value, an error signal is output as the threshold voltage of the MOS transistor.

[0060] The threshold voltage measurement system proposed in this embodiment and the threshold voltage measurement method proposed in the above embodiment belong to the same inventive concept. Technical details not described in detail in this embodiment can be referred to in the above embodiment, and this embodiment has the same beneficial effects as the above embodiment.

[0061] Embodiment 2

[0062] Figure 5 As a schematic diagram of a method for measuring the threshold voltage provided in Embodiment 2 of the present invention, as Figure 5 shown, the difference from Embodiment 1 is that in this embodiment, in step S2, the value between the upper limit voltage and the lower limit voltage is used as the scanning voltage. Among them, the values between the upper limit voltage and the lower limit voltage are respectively subtracted from the maximum operating voltage and the minimum operating voltage to obtain a fourth difference and a fifth difference. The absolute values of the fourth difference and the fifth difference are both greater than the second set value, so as to ensure that the maximum operating voltage or the minimum operating voltage is not applied to the MOS transistor.

[0063] In summary, the present invention provides a threshold voltage measurement method and system. Step S1: Set the maximum operating voltage and the minimum operating voltage of the MOS transistor as the upper limit voltage and the lower limit voltage, and execute step S2; Step S2: Use the value between the upper limit voltage and the lower limit voltage as the scanning voltage, apply the scanning voltage to the gate of the MOS transistor, and obtain the drain current of the MOS transistor, and execute step S3; Step S3: Subtract the drain current from the target current to obtain a first difference. When the absolute value of the first difference is less than or equal to a first set value, output the scanning voltage as the threshold voltage of the MOS transistor; When the absolute value of the first difference is greater than the first set value, judge the magnitude relationship between the drain current and the target current. When the drain current is greater than the target current, replace the upper limit voltage with the scanning voltage and return to step S2. When the drain current is less than the target current, replace the lower limit voltage with the scanning voltage and return to step S2. Avoid applying the maximum operating voltage and the minimum operating voltage to the MOS transistor during the measurement process. By comparing the relationship between the drain current of the MOS transistor and the target current, gradually reduce the voltage measurement range and continuously approach the threshold voltage, avoiding damage to the MOS transistor caused by the application of the maximum operating voltage and the minimum operating voltage and the shift of the threshold voltage.

[0064] The above are only the preferred embodiments of the present invention and do not impose any limitation on the present invention. Any person skilled in the art within the technical field, without departing from the technical solution of the present invention, makes any form of equivalent replacement or modification and other changes to the technical solution and technical content disclosed by the present invention, all of which belong to the content of the technical solution of the present invention and are still within the protection scope of the present invention.

Claims

1. A threshold voltage measurement method, characterized in that, comprising: Step S1: Set the maximum operating voltage and the minimum operating voltage of the MOS transistor as the upper limit voltage and the lower limit voltage, and execute Step S2; Step S2: Use the value between the upper limit voltage and the lower limit voltage as the scanning voltage, apply the scanning voltage to the gate of the MOS transistor, and obtain the drain current of the MOS transistor, then execute Step S3. In Step S2, subtract the value between the upper limit voltage and the lower limit voltage from the maximum operating voltage and the minimum operating voltage respectively to obtain a fourth difference and a fifth difference, and the absolute values of the fourth difference and the fifth difference are both greater than a second set value; Step S3: Subtract the drain current from the target current to obtain a first difference. When the absolute value of the first difference is less than or equal to a first set value, output the scanning voltage as the threshold voltage of the MOS transistor; when the absolute value of the first difference is greater than the first set value, judge the magnitude relationship between the drain current and the target current. When the drain current is greater than the target current, replace the upper limit voltage with the scanning voltage and return to Step S2. When the drain current is less than the target current, replace the lower limit voltage with the scanning voltage and return to Step S2; Before executing Step S3, subtract the scanning voltage from the maximum operating voltage and the minimum operating voltage respectively to obtain a second difference and a third difference. If any of the absolute values of the second difference and the third difference is less than the second set value, and the absolute value of the first difference is still greater than the first set value, output an error signal as the threshold voltage of the MOS transistor.

2. The threshold voltage measurement method according to claim 1, characterized in that, the second set value is less than 0.05V.

3. The threshold voltage measurement method according to claim 1, characterized in that, in Step S2, use the average value between the upper limit voltage and the lower limit voltage as the scanning voltage.

4. The threshold voltage measurement method according to claim 1, characterized in that, the first set value is 0.1 times to 0.3 times of the target current.

5. The threshold voltage measurement method according to claim 1, characterized in that, while applying the scanning voltage to the gate of the MOS transistor, apply a preset voltage to the drain of the MOS transistor and ground the source of the MOS transistor.

6. A threshold voltage measurement system, characterized in that, using the maximum operating voltage and the minimum operating voltage of the MOS transistor as the upper limit voltage and the lower limit voltage respectively, comprising: An electrical signal application unit, which uses the value between the upper limit voltage and the lower limit voltage as the scanning voltage and applies the scanning voltage to the gate of the MOS transistor; An electrical signal reading unit, which measures the drain current of the MOS transistor; The electric signal processing unit subtracts the drain current from the target current to obtain a first difference. When the absolute value of the first difference is less than or equal to a first set value, the scanning voltage is output as the threshold voltage of the MOS transistor; when the absolute value of the first difference is greater than the first set value, the magnitude relationship between the drain current and the target current is judged. When the drain current is greater than the target current, the upper limit voltage is replaced with the scanning voltage, and the electric signal applying unit is returned to re-apply the scanning voltage to the gate of the MOS transistor. When the drain current is less than the target current, the lower limit voltage is replaced with the scanning voltage, and the electric signal applying unit is returned to re-apply the scanning voltage to the gate of the MOS transistor; before the absolute value of the first difference and the first set value, it further includes: subtracting the scanning voltage from the maximum operating voltage and the minimum operating voltage respectively to obtain a second difference and a third difference. If any one of the absolute values of the second difference and the third difference is less than a second set value and the absolute value of the first difference is still greater than the first set value, an error signal is output as the threshold voltage of the MOS transistor; the values between the upper limit voltage and the lower limit voltage are subtracted from the maximum operating voltage and the minimum operating voltage respectively to obtain a fourth difference and a fifth difference, and the absolute values of the fourth difference and the fifth difference are both greater than the second set value.

7. The threshold voltage measurement system according to claim 6, wherein, the electric signal applying unit further applies a preset voltage to the drain of the MOS transistor to ground the source of the MOS.

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