Test method for BTI effect of MOSFET discrete device

Abstract

According to the test method for the BTI effect of the MOSFET discrete device, a Keysight B2902 source meter can provide dual-channel power supply voltage and is connected with a grid electrode, a source electrode and a drain electrode of the MOSFET device. A constant grid bias voltage is applied to the grid during BTI effect test under the control of a computer program of the source meter, and the other two electrodes are grounded; when the threshold voltage of the device under different stress time is tested, the source meter in-situ test can also be used, and the situation that the BTI effect is recovered due to the fact that the interval time between the grid bias voltage and the test is long after the grid bias voltage is removed, and the test result is inaccurate is avoided.

Description

Technical Field

[0001] This invention relates to the field of semiconductor device technology, and specifically to a test method for the BTI effect in discrete MOSFET devices. Background Technology

[0002] Metal-oxide-semiconductor field-effect transistors (MOSFETs), as core power components in modern electronic devices, offer several significant advantages. First, their extremely low drive power simplifies circuit design and reduces energy consumption. Second, MOSFETs boast fast switching speeds (nanosecond levels) and low on-resistance, making them particularly suitable for high-frequency switching circuits and high-efficiency power conversion applications. Furthermore, the structural characteristics of MOSFETs support high integration, are compatible with modern microelectronic processes, and exhibit strong radiation resistance, demonstrating excellent reliability in extreme environments such as aerospace and nuclear power. These advantages make MOSFETs irreplaceable in fields such as new energy, aerospace, power electronics, and high-speed communications.

[0003] Bias temperature instability (BTI) refers to the unavoidable positive / negative drift of the threshold voltage over time in MOSFET devices operating at high temperatures and with gate bias. This drift can reach hundreds of millivolts, severely impacting circuit and device performance. For n-channel MOSFETs, the gate voltage is positive when the device is turned on, resulting in positive bias temperature instability (PBTI), which increases the positive drift of the threshold voltage and increases the overall system conduction losses. For p-channel MOSFETs, the gate voltage is negative when the device is turned on, resulting in negative bias temperature instability (NBTI), which decreases the negative drift of the threshold voltage and makes the device more prone to false turn-on.

[0004] Studies have shown that the BTI effect in MOSFETs is related to oxide layer defects. The main defect types in the MOSFET oxide layer include... Figure 1 As shown, charges are typically categorized into mobile charges, oxide-trapped charges, fixed oxide charges, near-interface oxide-trapped charges, and interface charges. During the oxidation process of Si MOSFET devices, interface defects such as oxygen vacancies and dangling bonds are introduced into the oxide layer. When the device is at high temperature and under gate bias, conductive carriers can easily gain energy from the electric field to overcome the Si / SiO2 interface barrier (3.2 eV). The high temperature activates interface charge defects and near-interface trap charges in the oxide layer, making it easier for carriers that have crossed the barrier to be trapped by these defects. This causes a change in the number of effective carriers when the MOSFET is turned on, resulting in a shift in the threshold voltage.

[0005] According to the "Reliability Characterization Structural Test Method" implemented in 2022 (GJB10489-2022), under certain conditions, a 100 mV drift in the threshold voltage indicates that the device or integrated circuit has experienced the BTI effect. Therefore, in order to further evaluate the BTI effect of MOSFET devices and screen for high-quality and reliable devices, it is crucial to establish effective test and measurement methods for the BTI effect. Summary of the Invention

[0006] In view of this, the present invention provides an experimental testing method for the BTI effect of discrete MOSFET devices.

[0007] A test method for the BTI effect in discrete MOSFET devices includes: Step 1: First, fix the discrete MOSFET device onto the heating stage. Use a CNC platform to control the temperature of the heating stage, thereby controlling the device temperature. Step 2: Connect the three electrodes of the discrete MOSFET device to the three channels of the B2902 source meter: connect the gate to channel one, the drain to channel two, and the source to channel three. Step 3: Set the parameters of the computer online control program: Before conducting the BTI effect test, open the channel parameter setting interface in the software, set the voltage of channel one to a constant, and channel two and channel three to 0V, save the channel parameter settings in this interface, and name it "Program 1 - Gate Stress Application"; After closing the program, reopen a channel parameter setting interface. According to the threshold voltage test method provided in the device datasheet, set the voltage of channel one connected to the gate to be a variable, and the voltage scan range to the voltage range when the device is tested for the threshold voltage. Channel two is connected to the drain and set to a constant voltage. Channel three, which is the ground terminal, is set to 0V. Save the channel parameter settings of this interface and name it "Program 2 - Threshold Voltage Test". Step 4, Initial Threshold Voltage Performance Test: After the temperature of the heating stage is set by CNC and the device temperature stabilizes, open the software, open the saved "Program 2 - Threshold Voltage Test", click run, and the program controls the source table to test the transfer characteristics of the device, thus obtaining the transfer characteristic curve of the MOSFET device, and reading the threshold voltage from the curve. Step 5, BTI effect test: Open "Program 1 - Gate Stress Application", click Run, and record the time. According to the requirements of the test design, determine the time for applying the gate bias voltage. When the time is reached, stop the current program, and then immediately open "Program 2 - Threshold Voltage Test" and run it. Test the transfer characteristic curve of the MOSFET device at this time and read the threshold voltage from the curve. Step 6: After completing step 5, continue to open "Program 1 - Gate Stress Application", click Run, and record the time; this allows for real-time measurement of the threshold voltage change under long-term gate bias stress. Step 7: Calculate the threshold voltage drift Δ caused by the BTI effect. V th : Subtracting the threshold voltage value obtained in step 4 from the threshold voltage value obtained in step 5 gives the threshold voltage drift caused by the BTI effect during the stress time when the gate bias is applied.

[0008] Preferably, the MOSFET device is fixed to the heating platform with screws, so that the heating platform and the MOSFET device are in close contact, which is conducive to heat transfer.

[0009] Ideally, the values ​​of the transfer characteristic curve should be saved as a CSV file for easy import into Origin plotting software.

[0010] Ideally, the wires should not come into contact with the heating platform during the wire connection process to prevent the high temperature from burning the outer layer of the wires and affecting the test results.

[0011] The present invention has the following beneficial effects: This invention discloses a test method for the BTI effect in discrete MOSFET devices. The Keysight B2902 source meter provides dual-channel power supply voltages, connected to the gate, source, and drain of the MOSFET device respectively. During the BTI effect test, a constant gate bias voltage is applied to the gate, while the other two electrodes are grounded, controlled by a computer program on the source meter. When testing the threshold voltage of the device under different stress times, the source meter can also be used for in-situ testing to avoid inaccurate test results due to the BTI effect recovering after a long interval between removing the gate bias voltage and the test. Attached Figure Description

[0012] Figure 1 The types of existing MOSFET oxide layer defects; Figure 2(a) is a schematic diagram of the BTI effect test platform; Figure 2(b) is a schematic diagram of the MSM test method; Figure 3 This shows the wiring configuration of the heating platform and MOSFET electrodes. Figure 4 The transfer characteristic curves of the MOSFET under different stress times (T=150℃, Vg=20V). Detailed Implementation

[0013] The present invention aims to provide an effective test and measurement method for the BTI effect in MOSFET devices.

[0014] The schematic diagram of the constructed test platform is shown in Figure 2(a). The test platform consists of a digital temperature control device, a Keysight B2902 source meter, a computer-aided source meter test program Quick IV Measurement Software, a device placement platform, and other equipment. It can measure the MOSFET threshold voltage in real time under different temperatures and constant gate bias voltages in vacuum or air, thereby observing the BTI effect of the device. The temperature control device has a temperature range of -150~200℃ and an accuracy of ±1℃. The B2902 source meter can provide dual-channel constant output voltage and a ground terminal. The set voltage output from the first channel of the source meter is connected to the gate, and the second channel and the ground terminal are connected to the drain and source of the device, respectively. With the online control program of the instrument, online in-situ testing of the MOSFET threshold voltage can be completed by computer-controlled voltage switching.

[0015] The MSM (Measure-Stress-Measure) testing method is employed. Specifically, during the stress phase, the device's source and drain are grounded, and a constant voltage is applied to the gate to assess the device. After the stress phase, the gate bias is removed, and the measurement phase begins immediately. The threshold voltage is measured by scanning the device's transfer characteristic curve, thus obtaining the threshold voltage drift Δ caused by the BTI effect during the stress phase. V th The changes in the gate signal in the MSM method are shown in Figure 2(b).

[0016] This invention utilizes existing testing equipment to build a test platform capable of performing MOSFET BTI effects, and uses this platform to test the threshold voltage drift of devices during the BTI effect.

[0017] Step 1. First, secure the device to the heating platform. Secure the MOSFET device to the heating platform with screws, ensuring close contact between the platform and the MOSFET device to facilitate heat transfer. Using a CNC platform, the temperature of the heating platform can be controlled, thereby controlling the device temperature.

[0018] Step 2. Connect the wires. Connect the three electrodes of the MOSFET device to the three channels of the B2902 source meter using alligator clips (wires). Connect the gate to channel one, the drain to channel two (channel two is on the back of the source meter), and the source to channel three (ground). During the wire connection process, care must be taken to ensure that the wires do not touch the heating platform to prevent the high temperature from burning the outer layer of the wires and affecting the test results. Figure 3 As shown.

[0019] Step 3. Set the parameters of the Quick IV Measurement Software online control program. Before conducting the BTI effect test, open the channel parameter setting interface in the software. Set the voltage of Channel 1 to a constant (a constant voltage bias applied to the gate during the BTI test), and set Channels 2 and 3 to 0V. Save the channel parameter settings and name it "Program 1 - Gate Stress Application". After closing the program, reopen a channel parameter setting interface. According to the threshold voltage test method provided in the device datasheet, set the voltage of Channel 1 connected to the gate to a variable, and the voltage scan range to the voltage range when the device is testing the threshold voltage (e.g., the gate bias scan range is from 0V to 10V, with a step size of 0.1V). Connect Channel 2 to the drain and set it to a constant voltage (e.g., 0.06V). Set Channel 3, which is the ground terminal, to 0V. Save the channel parameter settings and name it "Program 2 - Threshold Voltage Test". Close the software.

[0020] Step 4. Initial Threshold Voltage Performance Test. Set the temperature of the heating stage using CNC and wait approximately 5 minutes for the device temperature to stabilize. Open the software, open the saved program 2, and click run. The program will control the source table to test the transfer characteristics of the device, thus obtaining the transfer characteristic curve of the MOSFET device. The threshold voltage can be read from the curve. Save the curve values ​​as a CSV file for easy import into Origin plotting software.

[0021] Step 5. BTI Effect Test. Open software program 1, click run, and record the time. Determine the time for applying the gate bias voltage according to the experimental design requirements. Once this time is reached, stop program 1, then immediately open and run program 2. Test the transfer characteristic curve of the MOSFET device at this point. The threshold voltage can be read from the curve. Save the curve values ​​as a CSV file for easy import into Origin plotting software.

[0022] Step 6. After completing Step 5, reopen Program 1, click Run, and record the time. This allows for real-time measurement of the threshold voltage change under prolonged gate bias stress.

[0023] Step 7. Calculate the device threshold voltage drift Δ caused by the BTI effect. V th Subtracting the threshold voltage value obtained in step 4 from the threshold voltage value obtained in step 5 gives the threshold voltage drift caused by the BTI effect during the stress time when the gate bias is applied.

[0024] By setting the above parameters, the BTI effect of MOSFETs can be tested and accurate data can be obtained.

[0025] Example: To verify the effectiveness of this experimental method, a BTI effect test was conducted on a MOSFET device by setting various parameters, and the threshold voltage of the device at different times was tested.

[0026] During the experiment, the device placement platform temperature was set to 150℃, the gate bias voltage was set to 20V, and the stress time for applying the gate bias voltage was 0h, 1h, 6h, 12h, 24h, and 48h, respectively. The transfer characteristic curves of the MOSFET were tested at these predetermined times. According to the device datasheet, the gate voltage corresponding to a drain current of 9.5mA is the threshold voltage.

[0027] The results are as follows Figure 4 As shown, before the gate bias voltage was applied (stress time 0h), the device's threshold voltage was 1.85V. After a constant bias of 20V was applied to the gate for 1h, the threshold voltage increased to 1.96V. According to the "Reliability Characterization Structural Test Method" (GJB10489-2022), the device had already experienced the BTI effect at this point. After a constant bias of 20V was applied to the gate for 48h, the threshold voltage increased to 2.04V, and the BTI effect became more pronounced. Therefore, the BTI effect of this MOSFET device was successfully tested using this BTI effect test method, and the threshold voltage drift was measured.

[0028] The specific embodiments described above only illustrate the design principles of the present invention. The shapes and names of the components in this description may differ and are not limited. Therefore, those skilled in the art can modify or make equivalent substitutions to the technical solutions described in the foregoing embodiments; and these modifications and substitutions do not depart from the inventive spirit and technical solutions of the present invention, and should all fall within the protection scope of the present invention.

Claims

1. A test method for the BTI effect in discrete MOSFET devices, characterized in that, include: Step 1: First, fix the discrete MOSFET device onto the heating stage. Use a CNC platform to control the temperature of the heating stage, thereby controlling the device temperature. Step 2: Connect the three electrodes of the discrete MOSFET device to the three channels of the B2902 source meter: connect the gate to channel one, the drain to channel two, and the source to channel three. Step 3: Set the parameters of the computer online control program: Before conducting the BTI effect test, open the channel parameter setting interface in the software, set the voltage of channel one to a constant, and channel two and channel three to 0V, save the channel parameter settings in the interface, and name it "Program 1 - Gate Stress Application"; After closing the program, reopen a channel parameter setting interface. According to the threshold voltage test method provided in the device datasheet, set the voltage of channel one connected to the gate to be a variable, and the voltage scan range to the voltage range when the device is tested for the threshold voltage. Channel two is connected to the drain and set to a constant voltage. Channel three, which is the ground terminal, is set to 0V. Save the channel parameter settings of this interface and name it "Program 2 - Threshold Voltage Test". Step 4, Initial Threshold Voltage Performance Test: After the temperature of the heating stage is set by CNC and the device temperature stabilizes, open the software, open the saved "Program 2 - Threshold Voltage Test", click run, and the program controls the source table to test the transfer characteristics of the device, thus obtaining the transfer characteristic curve of the MOSFET device, and reading the threshold voltage from the curve. Step 5, BTI effect test: Open "Program 1 - Gate Stress Application", click Run, and record the time. According to the requirements of the test design, determine the time for applying the gate bias voltage. When the time is reached, stop the current program, and then immediately open "Program 2 - Threshold Voltage Test" and run it. Test the transfer characteristic curve of the MOSFET device at this time, and read the threshold voltage from the curve. Step 6: After completing Step 5, continue to open "Program 1 - Gate Stress Application", click Run, and record the time; This allows for real-time measurement of threshold voltage changes under long-term gate bias stress. Step 7: Calculate the threshold voltage drift Δ caused by the BTI effect. V th : Subtracting the threshold voltage value obtained in step 4 from the threshold voltage value obtained in step 5 gives the threshold voltage drift caused by the BTI effect during the stress time when the gate bias is applied.

2. The experimental testing method for the BTI effect in a MOSFET discrete device as described in claim 1, characterized in that, The MOSFET device is fixed to the heating platform with screws to ensure close contact between the heating platform and the MOSFET device, which is beneficial for heat transfer.

3. The experimental testing method for the BTI effect in a MOSFET discrete device as described in claim 1, characterized in that, Save the values ​​of the transfer characteristic curve as a CSV file for easy import into Origin plotting software.

4. The experimental testing method for the BTI effect of a MOSFET discrete device as described in claim 1, characterized in that, During the wire connection process, the wires should not come into contact with the heating platform to prevent the high temperature from burning the outer layer of the wires and affecting the test results.

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