Method for analyzing defect state density of amorphous semiconductor transistor
Through the combination of optical and electrical methods, the defect state density of amorphous semiconductor transistors is analyzed, and the problem of difficult to analyze the defect density near the top of the valence band is solved, and an efficient test solution is provided to support material and process optimization.
Patent Information
- Application Number
- CN202510493129.9
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-04-18
- Publication Date
- 2025-08-12
AI Technical Summary
The prior art is difficult to effectively analyze the defect density near the valence band top of amorphous semiconductor transistors, affecting device reliability analysis.
Using a combination of optical and electrical methods, the transfer characteristic curve of the oxide device is tested under light sources of different wavelengths and intensities, and the defect state density is calculated in combination with the capacitance correction factor.
It realizes rapid analysis of defect state density of amorphous semiconductor transistors, provides material and process optimization basis, and avoids the introduction of complex testing systems.
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Figure CN120468618A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the technical field of semiconductor characterization and testing, and in particular to a method for analyzing defect state density of an amorphous semiconductor transistor. Background Art
[0002] Oxide field-effect transistors, using amorphous oxide materials as their semiconductor layers, offer advantages such as low-temperature integrated fabrication, high-quality, large-scale uniformity, and low cost, making them promising candidates for new DRAM memory devices and CMOS back-end-compatible devices. Unlike traditional silicon-based semiconductor devices, defects in amorphous materials influence the band gap distribution and device performance. These defects are influenced by intrinsic material defects and processing conditions, making analysis of these defects crucial for performance control and integrated fabrication of oxide devices.
[0003] Currently, electrical characterization methods are commonly used to analyze the defect state density of amorphous semiconductor transistors. Single electrical characterization methods can provide a high degree of resolution for defect states near the Fermi level of amorphous materials, but they are less effective for analyzing defect density near the valence band top. Defects near the valence band top are closely related to material and process defects and are highly correlated with device reliability. Therefore, in-depth testing methods are required to characterize and analyze defect characteristics within the band gap, especially near the valence band top.
[0004] In view of this, the present invention is proposed. Summary of the Invention
[0005] The object of the present invention is to provide a method for analyzing the defect state density of an amorphous semiconductor transistor, which can quickly analyze the defect state density in an oxide device, thereby providing an analysis basis for material defects and process optimization in the amorphous semiconductor transistor.
[0006] The present invention provides a method for analyzing the defect state density of an amorphous semiconductor transistor, comprising the following steps:
[0007] S1: Performing a transfer characteristic curve test on the oxide device under light-shielding conditions to obtain an initial transfer characteristic curve;
[0008] S2: Testing the transfer characteristic curve of the oxide device under the illumination condition of a light source having a wavelength of 405-590 nm to obtain the test transfer characteristic curves under different light source wavelengths;
[0009] S3: Compare the initial transfer characteristic curve with the test transfer characteristic curve to obtain the defect state density of the amorphous semiconductor transistor.
[0010] In step S1, the on / off ratio of the oxide device is greater than 10 5 , especially when the on / off ratio is greater than 10 6, and has an off-state region, a subthreshold region, and an on-state region in semi-logarithmic coordinates. Specifically, oxide devices use oxide materials such as IGZO (indium gallium zinc oxide) and IGO (indium gallium oxide) as channel materials. The oxide device has a field-effect transistor structure with a source terminal, a drain terminal, and a gate terminal. In addition, if the oxide device has a top-gate structure, the top gate metal uses a transparent electrode material to facilitate light incidence; if the oxide device has a bottom-gate structure, there are no strict restrictions on the bottom gate material.
[0011] In step S2, the method for testing the transfer characteristic curve includes: placing the oxide device on a test bench, fixing the height of the light source, connecting the test probes to the source, gate and drain ends of the oxide device respectively and connecting them to a semiconductor tester, and then testing the transfer characteristic curve of the oxide device under set illumination conditions.
[0012] Specifically, a ring-shaped light source can be used as the light source. The light source probe should be kept at a certain height relative to the oxide device to ensure a uniform light field within the oxide device. Before testing the transfer characteristic curve, use a light intensity meter to measure the light intensity at the corresponding light source height and record the light intensity.
[0013] In addition, when performing transfer characteristic curve test, V G -5V to 1V; V D 0.05V to 1V, V D For example, 0.1V to 1V; the light source intensity is 0-180mW / cm 2 , for example 45-180 mW / cm 2 .
[0014] Step S2 includes:
[0015] S211: performing a transfer characteristic curve test on the oxide device under an illumination condition of a light source having a wavelength of 480-590 nm to obtain a first test transfer characteristic curve;
[0016] S212: performing a transfer characteristic curve test on the oxide device under an illumination condition of a light source having a wavelength of 405-480 nm to obtain a second test transfer characteristic curve.
[0017] Furthermore, step S2 includes:
[0018] S221: performing a transfer characteristic curve test on the oxide device under an illumination condition of a light source having a wavelength of 531-590 nm to obtain a first test transfer characteristic curve;
[0019] S222: performing a transfer characteristic curve test on the oxide device under an illumination condition of a light source having a wavelength of 480-530 nm to obtain a second test transfer characteristic curve;
[0020] S223: performing a transfer characteristic curve test on the oxide device under an illumination condition of a light source having a wavelength of 440-480 nm to obtain a third test transfer characteristic curve;
[0021] S224: performing a transfer characteristic curve test on the oxide device under an illumination condition of a light source having a wavelength of 405-440 nm to obtain a fourth test transfer characteristic curve.
[0022] It can be understood that the above steps S211 and S212 use different light source wavelengths; the above steps S221, S222, S223, and S224 use different light source wavelengths.
[0023] In addition, step S2 also includes: testing the transfer characteristic curve of the oxide device under the conditions of the same light source wavelength and different light source intensities, and obtaining the test transfer characteristic curves under different light source intensities. Specifically, the light source wavelength can be 455nm, and the light source intensity can be 0-180mW / cm 2 , for example, 36-144 mW / cm 2 .
[0024] In step S3 , the comparison includes at least one of a shift of the subthreshold region and an increase in the magnitude of the off-state current under a semi-logarithmic coordinate.
[0025] Furthermore, if the subthreshold region moves under the semi-logarithmic coordinates, it means that the light source with the corresponding wavelength can excite the defect state in the band gap; if the off-state current changes in magnitude, it means that the light source with the corresponding wavelength can excite the carriers to make a transition from the defect band to the conduction band.
[0026] In step S3, the defect state density of the amorphous semiconductor transistor is obtained by the following formula:
[0027]
[0028] Where: C ox is the oxide layer capacitance, ΔV G V under different lighting conditions G The offset value relative to the dark light result.
[0029] Furthermore, by V D The current increase caused by the increase can be corrected by the additional factor k:
[0030]
[0031] k=f(V D )
[0032] Furthermore, the light source intensity I phThe current increase caused by the increase can be corrected by the additional factor M:
[0033]
[0034] M=f(I ph )
[0035] The implementation of the present invention has at least the following advantages:
[0036] 1. The method of the present invention can perform defect analysis while testing the performance of oxide devices directly after the preparation of amorphous semiconductor transistors, thereby eliminating the need to introduce additional test units in the layout or use complex test systems (such as DLTS), and has the advantages of high convenience and high test efficiency.
[0037] 2. The deep energy level defect state density obtained by the method of the present invention provides an analysis basis for material defects and process optimization in amorphous semiconductor transistors. BRIEF DESCRIPTION OF THE DRAWINGS
[0038] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the specific embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.
[0039] Figure 1 For Example 1, V D =0.1 for IV test results of different light wavelengths;
[0040] Figure 2 For Example 2, V D =1.0 when IV test results of different light wavelengths;
[0041] Figure 3 For Example 3, V D =0.1, IV test results at different light intensities when λ=455nm;
[0042] Figure 4 For control example 1, V D =1.0V, IV test results under no light. DETAILED DESCRIPTION
[0043] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which the present application belongs.
[0044] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular also includes the plural. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, they indicate the presence of features, steps, operations, devices, components and / or combinations thereof.
[0045] The following will clearly and completely describe the technical solutions of the present invention in conjunction with the embodiments. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.
[0046] Example 1
[0047] This example analyzes the defect state density of an IGZO field effect transistor (width-to-length ratio W / L=100 μm / 30 μm) in the following steps:
[0048] 1. Preparation
[0049] Place the IGZO field-effect transistor on the test bench, fix the height of the light source, and use a light intensity meter to measure and record the light source intensity data.
[0050] Connect the test probes to the source, gate, and drain terminals of the IGZO field-effect transistor and connect them to a semiconductor tester. Use the semiconductor tester to test the transfer characteristic curve. The transfer characteristic curve uses Vg as the horizontal axis and the normalized current (Id) as the vertical axis. The test conditions are as follows: V G The test range is -5V to 1V, V D is 0.1V.
[0051] 2. Shading test
[0052] The transfer characteristic curve of the IGZO field effect transistor was tested under light-shielding conditions to obtain an initial transfer characteristic curve (denoted as DARK; VD=0.1).
[0053] 3. Lighting test
[0054] Adjust the light source wavelength to 590nm (2.10eV) and the light source intensity to 60mW / cm 2 , a transfer characteristic curve test was performed on the IGZO field effect transistor to obtain a first transfer characteristic curve (recorded as 590nm; VD=0.1).
[0055] Adjust the light source wavelength to 530nm (2.34eV) and the light source intensity to 45mW / cm 2, the transfer characteristic curve of the IGZO field effect transistor was tested to obtain the second transfer characteristic curve (recorded as 530nm; VD=0.1).
[0056] Adjust the light source wavelength to 455nm (2.73eV) and the light source intensity to 180mW / cm 2 , a transfer characteristic curve test was performed on the IGZO field effect transistor to obtain a third transfer characteristic curve (denoted as 455nm; VD=0.1).
[0057] Adjust the light source wavelength to 405nm (3.06eV) and the light source intensity to 134mW / cm 2 , a transfer characteristic curve test was performed on the IGZO field effect transistor to obtain a fourth transfer characteristic curve (denoted as 405nm; VD=0.1).
[0058] The test results are as follows Figure 1 shown by Figure 1 visible:
[0059] When the device is irradiated with 590nm, the transfer characteristic curve hardly changes, indicating that at the energy corresponding to the 590nm wavelength (2.10eV), there is no corresponding defect state density in the band gap or the wavelength is not sufficient to excite the defect charges.
[0060] When 530nm irradiation is applied to the device, the transfer characteristic curve hardly changes, indicating that at the energy corresponding to the 590nm wavelength (2.10eV), there is no corresponding defect state density in the band gap or the wavelength is not sufficient to excite the defect charges.
[0061] When 455nm radiation is applied to the device, the transfer characteristic curve produces a visible negative shift; at the same time, the off-state current of the transfer characteristic curve has a significant increase.
[0062] When the device is irradiated with 405nm, the transfer characteristic curve shifts significantly in the negative direction, and the off-state current increases by an order of magnitude. This indicates that the energy corresponding to 405-455nm can cause carrier transitions from the valence band to the conduction band.
[0063] Based on the above experimental results, by selecting the reference current I D , and calculate V under different illumination at the response reference current point G Offset value ΔV relative to the dark light result G , the defect state density in different energy level ranges can be calculated by the following formula:
[0064]
[0065] Where: C ox is the oxide layer capacitance, ΔV GV under different lighting conditions G The offset value relative to the dark light result.
[0066] In this embodiment, ss=130mV / dec, C ox =9.38×10 -7 F / cm 2 . Select the reference current I D =1×10 - 11 A, corresponding to V G The deep level defect density in the range of 2.10-2.34 eV is 5.96×10 10 / cm 2 The deep level defect density in the range of 2.34-2.73 eV is 1.17×10 11 / cm 2 The deep level defect density in the range of 2.73-3.06 eV is 1.28×10 12 / cm 2 .
[0067] Example 2
[0068] In this embodiment, under high leakage voltage (V D =1.0V) to test the transfer characteristic curves at different wavelengths. The specific steps refer to Example 1; the test results are as follows Figure 2 shown.
[0069] By comparing Example 1 with Example 2, it can be seen that for the same device and the same defect state density, using a higher drain voltage can improve the defect response to the test under the same illumination and obtain a larger current change. Other experimental results and trends are similar to those of Example 1. In this case, the current increase caused by the increase in VD can be corrected by adding a factor k:
[0070]
[0071] k=f(V D )
[0072] Example 3
[0073] This embodiment is optimized based on the embodiment 1. The optimization includes: selecting a light source wavelength (λ=455nm) at which current changes can be observed, fixing the light source wavelength test conditions, and measuring the transfer characteristic curve under different light source intensities. The test results are shown in FIG. Figure 3 shown.
[0074] By comparing the IV test results under different light source intensities, we can see that for the same device and the same defect state density, using a higher light source intensity improves the defect response to the test under the same light source wavelength conditions and obtains a larger current change. Other experimental results and trends are similar to those in Example 1. ph The current increment caused by the increase can be corrected by the additional factor M:
[0075]
[0076] M=f(I ph )
[0077] Comparative Example 1
[0078] The defect state density of the IGZO field effect transistor of Example 1 was analyzed by a single electrical characterization method, and the device transfer characteristics were tested under dark conditions. The test results are as follows: Figure 4 shown.
[0079] The subthreshold swing (ss) of the device is extracted in the subthreshold region, and the shallow energy level surface defect state density is calculated using the following formula:
[0080]
[0081] Where: C ox is the oxide layer capacitance, q is the basic charge, k is the Boltzmann constant, and T is the thermodynamic temperature. In this comparative example, ss = 130mV / dec, C ox =9.38×10 -7 F / cm 2 , we can get the shallow energy level D it =1.27×10 13 / cm 2 .
[0082] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention 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. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.
Claims
1. A method for analyzing defect state density of an amorphous semiconductor transistor, characterized in that: The steps include: S1: Performing a transfer characteristic curve test on the oxide device under light-shielding conditions to obtain an initial transfer characteristic curve; S2: Testing the transfer characteristic curve of the oxide device under the illumination condition of a light source having a wavelength of 405-590 nm to obtain the test transfer characteristic curves under different light source wavelengths; S3: Compare the initial transfer characteristic curve with the test transfer characteristic curve to obtain the defect state density of the amorphous semiconductor transistor.
2. The method according to claim 1, characterized in that In step S1, the on / off ratio of the oxide device is greater than 10 5 , and has an off-state region, a subthreshold region and an on-state region in the semi-logarithmic coordinates.
3. The method according to claim 1, characterized in that In step S2, the method for testing the transfer characteristic curve includes: placing the oxide device on a test bench, fixing the height of the light source, connecting the test probes to the source, gate and drain ends of the oxide device respectively and connecting them to a semiconductor tester, and then testing the transfer characteristic curve of the oxide device under set illumination conditions.
4. The method according to claim 1, wherein In step S2, when the transfer characteristic curve test is performed, V G -5V to 1V, V D 0.05V to 1V.
5. The method according to claim 1, wherein Step S2 includes: S211: performing a transfer characteristic curve test on the oxide device under an illumination condition of a light source having a wavelength of 480-590 nm to obtain a first test transfer characteristic curve; S212: performing a transfer characteristic curve test on the oxide device under an illumination condition of a light source having a wavelength of 405-480 nm to obtain a second test transfer characteristic curve.
6. The method according to claim 1, characterized in that Step S2 includes: S221: performing a transfer characteristic curve test on the oxide device under an illumination condition of a light source having a wavelength of 531-590 nm to obtain a first test transfer characteristic curve; S222: performing a transfer characteristic curve test on the oxide device under an illumination condition of a light source having a wavelength of 480-530 nm to obtain a second test transfer characteristic curve; S223: performing a transfer characteristic curve test on the oxide device under an illumination condition of a light source having a wavelength of 440-480 nm to obtain a third test transfer characteristic curve; S224: performing a transfer characteristic curve test on the oxide device under an illumination condition of a light source having a wavelength of 405-440 nm to obtain a fourth test transfer characteristic curve.
7. The method according to claim 1, characterized in that Step S2 also includes: performing a transfer characteristic curve test on the oxide device under the conditions of illumination with the same light source wavelength and different light source intensities, to obtain the test transfer characteristic curves under different light source intensities.
8. The method according to claim 1, characterized in that In step S3 , the comparison includes at least one of a shift of the subthreshold region and an increase in the magnitude of the off-state current under a semi-logarithmic coordinate.
9. The method according to claim 8, characterized in that If the subthreshold region moves under the semi-logarithmic coordinates, it means that the light source with the corresponding wavelength can excite the defect state in the band gap; if the off-state current increases by an order of magnitude, it means that the light source with the corresponding wavelength can excite the transition of charge from the defect band to the conduction band.
10. The method according to claim 1, characterized in that In step S3, the defect state density of the amorphous semiconductor transistor is obtained by the following formula: Where: C ox is the oxide layer capacitance, ΔV G V under different lighting conditions G The offset value relative to the dark light result.