A method for detecting trap density of MOSFET gate oxide layer

Abstract

The present invention discloses a method for detecting the trap density of a MOSFET gate oxide layer, comprising: 1) testing the threshold voltage and gate oxide layer capacitance of a MOSFET device; 2) subjecting the MOSFET to electron beam irradiation treatment, and testing the threshold voltage of the device after different irradiation doses; 3) when the device threshold voltage does not change with increasing irradiation dose, discontinuing irradiation treatment and recording the final threshold voltage; 4) calculating the change in the gate oxide layer fixed charge based on the change in the MOSFET threshold voltage before and after electron irradiation treatment; and 5) calculating the gate oxide layer trap density based on the change in the gate oxide layer fixed charge and the area of ​​the gate oxide layer. Using the present invention, the gate oxide layer trap density of a MOSFET can be quickly obtained, which is used for analyzing device performance and improving gate oxide layer processes, and has a wide range of applications.

Description

Technical Field

[0001] The invention belongs to the technical field of semiconductors, and in particular relates to a method for detecting trap density of a MOSFET gate oxide layer. Background Art

[0002] The quality of the gate oxide layer significantly impacts MOSFET device performance. Silicon / silicon carbide (SiC) generates charge traps, such as oxygen vacancies, during thermal oxidation. These traps can capture electrons and holes during device operation. Electrons and holes can be injected into the oxide layer from the substrate or gate electrode, and radiation can also generate electron-hole pairs in the oxide layer. These electrons and holes are trapped in the oxide traps, forming a fixed charge in the oxide layer. This fixed charge in the oxide layer can cause the MOSFET threshold voltage to drift, affecting device characteristics and even leading to device failure.

[0003] Therefore, it is more important to fully and effectively detect the trap density of the gate oxide layer and its impact on device characteristics, which has important academic and practical production significance for device performance analysis, life prediction and process improvement.

[0004] The traditional gate oxide accelerated aging test method is a high-temperature gate bias accelerated aging test. Under the stress of high temperature and gate bias voltage, the injected charge in the gate oxide is trapped and forms fixed charge, causing device gate oxide degradation and threshold voltage drift. However, this method has a slow charge injection rate and is time-consuming, making it inefficient for device gate oxide detection and analysis.

[0005] Therefore, there is a need to find a fast and effective testing method to realize the testing method of the gate oxide trap density of MOSFET devices, which is of great significance for detecting and analyzing device performance and improving gate oxide layer process. Summary of the Invention

[0006] The purpose of the present invention is to provide a method for detecting the trap density of a MOSFET gate oxide layer, so as to realize the detection of the trap density of the gate oxide layer of a MOSFET device.

[0007] The present invention is achieved by adopting the following technical solutions:

[0008] A method for detecting trap density of a MOSFET gate oxide layer comprises the following steps:

[0009] 1) Test the threshold voltage and gate oxide capacitance of MOSFET devices: a) Test the transfer characteristics of the device, taking the gate voltage corresponding to the set drain current as the threshold voltage; b) Test the C GS -V GS Characteristic testing to obtain the gate oxide capacitance of the device;

[0010] 2) Electron irradiation treatment of MOSFET devices, and testing the threshold voltage of the devices after different irradiation doses;

[0011] 3) When the device threshold voltage does not change with increasing irradiation dose, the trapped charge in the gate oxide layer reaches saturation, and irradiation treatment is no longer performed. The final threshold voltage is recorded to obtain the change in the MOSFET threshold voltage after electron irradiation treatment;

[0012] 4) The gate oxide fixed charge is calculated based on the change in MOSFET threshold voltage before and after electron irradiation. The gate oxide fixed charge is obtained by the following formula:

[0013] Q t =ΔV th C ox

[0014] where Q t is the fixed charge of the gate oxide layer, △V th is the threshold voltage change, C ox is the gate oxide capacitance;

[0015] 5) The gate oxide fixed charge density is calculated based on the gate oxide fixed charge and the area of ​​the gate oxide. The calculation formula is as follows:

[0016] n t =Q t / qS ox

[0017] where n t is the fixed charge density of the gate oxide, Q t is the fixed charge of the gate oxide layer, q is the elementary charge, S ox is the area of ​​the gate oxide layer;

[0018] The gate oxide trap density is:

[0019] n=n t(max)

[0020] Where n is the gate oxide trap density, n t(max) It is the fixed charge density when the gate oxide traps are completely filled with charge.

[0021] A further improvement of the present invention is that in step 1) a), the drain-source electrode voltage V is set DS =10V for transfer characteristic curve test, and the gate voltage corresponding to the drain current of 1mA is selected as the threshold voltage of the device.

[0022] A further improvement of the present invention is that, in step 1), the initial threshold voltage of the MOSFET device is obtained by testing.

[0023] A further improvement of the present invention is that, in step 1), the types of the MOSFET devices include silicon and silicon carbide MOSFET devices.

[0024] A further improvement of the present invention is that in step 1), the MOSFET device includes a packaged single-tube device, a module and an unpackaged bare-die device.

[0025] A further improvement of the present invention is that in step 2), the ionization effect of electron irradiation in the gate oxide layer of the MOSFET generates electron-hole pairs, which are then captured by traps in the gate oxide layer; the threshold voltage of the MOSFET will drift due to the fixed charge in the gate oxide layer.

[0026] A further improvement of the present invention is that in step 2), the energy of the electron irradiation is 5-15 MeV, and the irradiation dose of the device is gradually increased from 0 in a step range of 1-50 kGy.

[0027] A further improvement of the present invention is that after each irradiation, the threshold voltage of the device is tested and recorded according to step 1).

[0028] The present invention has at least the following beneficial technical effects:

[0029] The present invention provides a method for detecting the trap density of the gate oxide layer of a MOSFET. This method, based on electron irradiation technology, enables testing of the trap density of the gate oxide layer of a MOSFET. The method can be used for analyzing device performance and improving gate oxide processes. This testing method uses electron beam irradiation to generate a large number of electron-hole pairs within the gate oxide layer in a short period of time to fill the oxide traps, enabling rapid testing of the oxide trap density. This method accurately and efficiently detects oxide trap density, facilitating widespread use in science and industry. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 Schematic diagram of the SiC VD-MOSFET device structure tested in Example 1 of the present invention;

[0031] Figure 2 The MOSFET device C tested in Example 1 of the present invention is GS -V GS Characteristic curve diagram;

[0032] Figure 3 3 is a graph showing changes in the threshold voltage and gate oxide layer charge density of the MOSFET device in Example 1 of the present invention as the electron irradiation dose increases.

[0033] Figure 4 Schematic diagram of the SiC U-MOSFET device structure tested in Example 2 of the present invention;

[0034] Figure 5 The MOSFET device C tested in Example 2 of the present invention is GS -V GS Characteristic curve diagram;

[0035] Figure 6 3 is a graph showing changes in the threshold voltage and gate oxide layer charge density of the MOSFET device in Example 2 of the present invention as the electron irradiation dose increases.

[0036] Figure 7 is a schematic diagram of the structure of the Si SJ-MOSFET device tested in Example 3 of the present invention;

[0037] Figure 8 The MOSFET device C tested in Example 3 of the present invention is GS -V GS Characteristic curve diagram;

[0038] Figure 9 3 is a graph showing changes in the threshold voltage and gate oxide layer charge density of the MOSFET device as the electron irradiation dose increases in Example 3 of the present invention. DETAILED DESCRIPTION

[0039] The exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. Although exemplary embodiments of the present disclosure are shown in the accompanying drawings, it should be understood that the present disclosure can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided to enable a more thorough understanding of the present disclosure and to fully convey the scope of the present disclosure to those skilled in the art. It should be noted that, unless there is a conflict, the embodiments of the present disclosure and the features described in the embodiments can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0040] The present invention provides a method for detecting the trap density of a MOSFET gate oxide layer, comprising the following steps:

[0041] 1) Test the threshold voltage and gate oxide capacitance of MOSFET devices: a) Test the transfer characteristics of the device, taking the gate voltage corresponding to the set drain current as the threshold voltage; b) Test the C GS -V GS Characteristic testing to obtain the gate oxide capacitance of the device;

[0042] 2) Electron irradiation treatment of MOSFET devices, and testing the threshold voltage of the devices after different irradiation doses;

[0043] 3) When the device threshold voltage does not change with increasing irradiation dose, the trapped charge in the gate oxide layer reaches saturation, and irradiation treatment is no longer performed. The final threshold voltage is recorded to obtain the change in the MOSFET threshold voltage after electron irradiation treatment;

[0044] 4) The gate oxide fixed charge is calculated based on the change in MOSFET threshold voltage before and after electron irradiation. The gate oxide fixed charge is obtained by the following formula:

[0045] Q t =ΔV th C ox

[0046] where Q t is the fixed charge of the gate oxide layer, △V th is the threshold voltage change, C ox is the gate oxide capacitance;

[0047] 5) The gate oxide fixed charge density is calculated based on the gate oxide fixed charge and the area of ​​the gate oxide. The calculation formula is as follows:

[0048] n t =Q t / qS ox

[0049] where n t is the fixed charge density of the gate oxide, Q t is the fixed charge of the gate oxide layer, q is the elementary charge, S ox is the area of ​​the gate oxide layer;

[0050] The gate oxide trap density is:

[0051] n=n t(max)

[0052] Where n is the gate oxide trap density, n t(max) It is the fixed charge density when the gate oxide traps are completely filled with charge.

[0053] Example 1

[0054] The MOSFET device selected in Example 1 is an N-channel SiC MOSFET single-tube device. The structural diagram of the device is shown in FIG. Figure 1 As shown, the gate oxide layer area of ​​the device is 3mm 2 .

[0055] (1) Test the initial threshold voltage and gate oxide capacitance of the device before electron irradiation: a) Threshold voltage test: The voltage between the drain and source electrodes V DS =10V condition to test the device transfer characteristics, the drain current I DS=1mA when the gate voltage V GS =2.48V, as the initial threshold voltage of the device; b) C GS -V GS Curve (source and drain short-circuited), test results are as follows Figure 2 As shown, take V GS =20V is the capacitance value of the gate oxide layer of the device ox =2277.96pF.

[0056] (2) The device was irradiated with an electron beam of 10 MeV energy at a dose rate of 250 kGy / min. The irradiation dose was gradually increased, and the threshold voltage of the device was tested at total irradiation doses of 1 kGy, 5 kGy, 10 kGy, 50 kGy, 100 kGy, and 200 kGy.

[0057] (3) The threshold voltage of the device decreases with the increase of radiation dose and gradually tends to a stable value. As the radiation dose increases, the threshold voltage of the device tends to a stable value V th =-2.58V.

[0058] (4) Further, the fixed charge Q in the gate oxide layer of the device is calculated t , the specific formula is as follows:

[0059] Q t =ΔV th C ox

[0060] Among them, Q t is the fixed charge of the gate oxide layer, △V th is the threshold voltage change, C ox is the gate oxide capacitance.

[0061] The fixed charge of the gate oxide layer is calculated using the above formula.

[0062] In step (5), the fixed charge density of the gate oxide layer is calculated by the following formula:

[0063] n t =Q t / qS ox

[0064] Among them, n t is the fixed charge density of the gate oxide, Q t is the fixed charge of the gate oxide layer, q is the elementary charge, S ox is the area of ​​the gate oxide layer. The relationship between the fixed charge density of the gate oxide layer and the electron irradiation dose is as follows: Figure 3As shown in the figure, the horizontal axis is the electron irradiation dose, the vertical axis (left) is the change in threshold voltage, and the vertical axis (right) is the fixed charge in the oxide layer. As the irradiation dose increases, the trapped charge in the device gate oxide layer increases, and the device threshold voltage decreases.

[0065] The gate oxide trap density in step (5) is:

[0066] n=n t(max)

[0067] =2.46×10 12 cm -2

[0068] Where n is the gate oxide trap density, n t(max) It is the fixed charge density when the gate oxide traps are completely filled with charge.

[0069] Example 2

[0070] The MOSFET device selected in Example 2 is an N-channel SiC U-MOSFET single-tube device. The structural diagram of the device is shown in FIG. Figure 4 As shown, the gate oxide area of ​​the device is 2.27mm 2 .

[0071] (1) Test the initial threshold voltage and gate oxide capacitance of the device before electron irradiation: a) Threshold voltage test: The voltage between the drain and source electrodes V DS =10V condition to test the device transfer characteristics, the drain current I DS =1mA when the gate voltage V GS =3.85V, as the initial threshold voltage of the device; b) C GS -V GS Curve (source and drain short-circuited), test results are as follows Figure 5 As shown, take V GS =20V is the capacitance value of the gate oxide layer of the device ox =1567pF.

[0072] (2) The device was irradiated with an electron beam of 10 MeV energy at a dose rate of 250 kGy / min. The irradiation dose was gradually increased, and the threshold voltage of the device was tested at total irradiation doses of 1 kGy, 5 kGy, 10 kGy, 50 kGy, 100 kGy, and 200 kGy.

[0073] (3) The threshold voltage of the device decreases with the increase of radiation dose and gradually tends to a stable value. As the radiation dose increases, the threshold voltage of the device tends to a stable value V th =-11.36V.

[0074] (4) Further, the fixed charge Q in the gate oxide layer of the device is calculated t , the specific formula is as follows:

[0075] Q t =ΔV th C ox

[0076] Among them, Q t is the fixed charge of the gate oxide layer, △V th is the threshold voltage change, C ox is the gate oxide capacitance.

[0077] The fixed charge of the gate oxide layer is calculated using the above formula.

[0078] In step (5), the fixed charge density of the gate oxide layer is calculated by the following formula:

[0079] n t =Q t / qS ox

[0080] Among them, n t is the fixed charge density of the gate oxide, Q t is the fixed charge of the gate oxide layer, q is the elementary charge, S ox is the area of ​​the gate oxide layer. The relationship between the fixed charge density of the gate oxide layer and the electron irradiation dose is as follows: Figure 6 As shown in the figure, the horizontal axis is the electron irradiation dose, the vertical axis (left) is the change in threshold voltage, and the vertical axis (right) is the fixed charge in the oxide layer. As the irradiation dose increases, the trapped charge in the device gate oxide layer increases, and the device threshold voltage decreases.

[0081] The gate oxide trap density in step (5) is:

[0082] n=n t(max)

[0083] =6.56×10 12 cm -2

[0084] Where n is the gate oxide trap density, n t(max) It is the fixed charge density when the gate oxide traps are completely filled with charge.

[0085] Example 3

[0086] The MOSFET device selected in Example 3 is an N-channel SiSJ-MOSFET single-tube device, and the structural diagram of the device is shown in FIG. Figure 7 As shown, the gate oxide area of ​​the device is 4.12mm 2 .

[0087] (1) Test the initial threshold voltage and gate oxide capacitance of the device before electron irradiation: a) Threshold voltage test: The voltage between the drain and source electrodes V DS =10V condition to test the device transfer characteristics, the drain current I DS =1mA when the gate voltage V GS =2.99V, as the initial threshold voltage of the device; b) C GS -V GS Curve (source and drain short-circuited), test results are as follows Figure 8 As shown, take V GS =20V is the capacitance value of the gate oxide layer of the device ox =2846.78pF.

[0088] (2) The device was irradiated with an electron beam of 10 MeV energy at a dose rate of 250 kGy / min. The irradiation dose was gradually increased, and the threshold voltage of the device was tested at total irradiation doses of 1 kGy, 5 kGy, 10 kGy, 50 kGy, 100 kGy, and 200 kGy.

[0089] (3) The threshold voltage of the device decreases with the increase of radiation dose and gradually tends to a stable value. As the radiation dose increases, the threshold voltage of the device tends to a stable value V th =-8.88V.

[0090] (4) Further, the fixed charge Q in the gate oxide layer of the device is calculated t , the specific formula is as follows:

[0091] Q t =ΔV th C ox

[0092] Among them, Q t is the fixed charge of the gate oxide layer, △V th is the threshold voltage change, C ox is the gate oxide capacitance.

[0093] The fixed charge of the gate oxide layer is calculated using the above formula.

[0094] In step (5), the fixed charge density of the gate oxide layer is calculated by the following formula:

[0095] n t =Q t / qS ox

[0096] Among them, n t is the fixed charge density of the gate oxide, Q t is the fixed charge of the gate oxide layer, q is the elementary charge, Sox is the area of ​​the gate oxide layer. The relationship between the fixed charge density of the gate oxide layer and the electron irradiation dose is as follows: Figure 9 As shown in the figure, the horizontal axis is the electron irradiation dose, the vertical axis (left) is the change in threshold voltage, and the vertical axis (right) is the fixed charge in the oxide layer. As the irradiation dose increases, the trapped charge in the device gate oxide layer increases, and the device threshold voltage decreases.

[0097] The gate oxide trap density in step (5) is:

[0098] n=n t(max)

[0099] =5.12×10 12 cm -2

[0100] Where n is the gate oxide trap density, n t(max) It is the fixed charge density when the gate oxide traps are completely filled with charge.

[0101] The present invention can obtain the gate oxide layer defect density more quickly and can be used for analyzing device performance and improving process.

[0102] The above description is merely a limited embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications made within the spirit and principles of the present invention are within the scope of protection of the present invention.

Claims

1. A method for detecting trap density of a MOSFET gate oxide layer, characterized in that: The following steps are involved: 1) Test the threshold voltage and gate oxide capacitance of MOSFET devices: a) Test the transfer characteristics of the device, taking the gate voltage corresponding to the set drain current as the threshold voltage; b) Test the C GS -V GS Characteristic testing to obtain the gate oxide capacitance of the device; 2) Electron irradiation treatment of MOSFET devices, and testing the threshold voltage of the devices after different irradiation doses; 3) When the device threshold voltage does not change with increasing irradiation dose, the trapped charge in the gate oxide layer reaches saturation, and irradiation treatment is no longer performed. The final threshold voltage is recorded to obtain the change in the MOSFET threshold voltage after electron irradiation treatment; 4) The gate oxide fixed charge is calculated based on the change in MOSFET threshold voltage before and after electron irradiation. The gate oxide fixed charge is obtained by the following formula: Q t =ΔV th C ox where Q t is the fixed charge of the gate oxide layer, △V th is the threshold voltage change, C ox is the gate oxide capacitance; 5) The gate oxide fixed charge density is calculated based on the gate oxide fixed charge and the area of ​​the gate oxide. The calculation formula is as follows: n t =Q t / qS ox where n t is the fixed charge density of the gate oxide, Q t is the fixed charge of the gate oxide layer, q is the elementary charge, S ox is the area of ​​the gate oxide layer; The gate oxide trap density is: n=n t(max) Where n is the gate oxide trap density, n t(max) It is the fixed charge density when the gate oxide traps are completely filled with charge.

2. A method for detecting a MOSFET gate oxide layer trap density according to claim 1, characterized in that, In step 1) a), set the drain-source electrode voltage V DS =10V for transfer characteristic curve test, and the gate voltage corresponding to the drain current of 1mA is selected as the threshold voltage of the device.

3. A method for detecting trap density of a MOSFET gate oxide layer according to claim 1, characterized in that, In step 1), the initial threshold voltage of the MOSFET device is obtained by testing.

4. A method for detecting a MOSFET gate oxide layer trap density according to claim 1, characterized in that, In step 1), the types of the MOSFET devices include silicon and silicon carbide MOSFET devices.

5. A method for detecting trap density of a MOSFET gate oxide layer according to claim 1, characterized in that, In step 1), the MOSFET devices include packaged single-tube devices, modules and unpackaged bare-die devices.

6. A method for detecting trap density of a MOSFET gate oxide layer according to claim 1, characterized in that, In step 2), the ionization effect of electron irradiation in the gate oxide layer of the MOSFET generates electron-hole pairs, which are then captured by traps in the gate oxide layer; the threshold voltage of the MOSFET will drift due to the fixed charge in the gate oxide layer.

7. A method for detecting trap density of a MOSFET gate oxide layer according to claim 1, characterized in that, In step 2), the energy of the electron irradiation is 5-15 MeV, and the irradiation dose of the device is gradually increased from 0 in a step range of 1 to 50 kGy.

8. A method for detecting trap density of a MOSFET gate oxide layer according to claim 7, characterized in that, After each irradiation, the threshold voltage of the device was tested and recorded according to step 1).

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