Method for analyzing device electrode contact condition
Scanning Joule thermal expansion microscopy technology is used to analyze device electrode contact quality, which solves the problems of low accuracy and high cost of contact resistance evaluation in the existing technology, and achieves efficient contact quality optimization and device performance improvement.
Patent Information
- Application Number
- CN202411520666.X
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-10-29
- Publication Date
- 2025-01-24
AI Technical Summary
The prior art is difficult to effectively evaluate and optimize device electrode contact quality, especially in the case of high contact resistance, and traditional methods have the disadvantages of low accuracy, high cost and inability to analyze specific contact situations.
By using the scanning ear thermal expansion microscope to obtain the high -resolution temperature distribution diagram and surface appearance diagram of the device, analyze the temperature distribution and appearance characteristics of the contact area, combine the variance and average value of the temperature distribution to assess the uniformity of contact, thereby optimizing the quality of contact.
It is possible to test the contact quality in situ of the device, obtain distribution information of contact resistance, bubbles, contaminants and material defects, provide directions for optimizing contact quality, reduce contact resistance and improve device performance.
Smart Images
Figure CN119355301A_ABST
Abstract
Description
Technical Field
[0001] The invention relates to a method for obtaining electrode contact conditions through a surface morphology diagram and a temperature distribution diagram, and in particular to a method for analyzing device electrode contact resistance conditions. Background Art
[0002] The evaluation of contact quality is very important in information electronic devices. Low contact quality can effectively reduce the obstacles to the flow of electrons in the device. Especially for transistors, low contact resistance is the key to whether the device can operate normally. Especially in the process of continuous reduction in chip size, achieving low contact resistance is a huge challenge currently faced. For two-dimensional materials, the defect distribution and contact quality in the material will seriously affect the size of the contact resistance, resulting in device performance degradation or even failure. It is particularly important to select a suitable contact resistance test and evaluation method and obtain the direction of subsequent optimization to reduce the contact resistance.
[0003] Contact resistance is usually measured using electrical testing methods, such as the Kelvin four-wire method and the transmission line model test method. The Kelvin four-wire method uses a constant current source, a voltmeter, and an ammeter for testing. The voltmeter probe is used to test the voltage drop on the material near the electrode contact area. The constant current source provides current and tests the voltage drop between the two electrodes. The voltage drop minus the voltage drop near the electrode is the voltage drop on the contact resistance. This method is simple and convenient to test contact resistance, but its disadvantage is low accuracy. For higher contact resistance, this method is not universal.
[0004] The transmission line model method is a more rigorous test method. It uses the same materials and processes to prepare a group of devices with different electrode spacings, and then tests the change of the overall resistance with the electrode spacing. The resistance when the electrode spacing is 0 is calculated based on the slope, and half of it is the contact resistance value on each electrode. This method is the most commonly used method for researchers at home and abroad to test contact resistance, but there are obvious disadvantages: first, it has high requirements for the preparation process, in which the width and thickness of the material, the electrode spacing, the contact quality, etc. need to be strictly controlled to obtain a set of resistance values with linear regression; second, the test cost is high. In order to test the contact resistance value of the device, it is often necessary to prepare a large number of additional devices for regression analysis of the contact resistance; the parameters of the contact resistance obtained in the end are single, and are often powerless for more complex device structures. The above-mentioned method for testing contact resistance can only obtain the numerical value of the contact resistance, and cannot analyze the specific situation of the contact. Summary of the invention
[0005] In order to solve the shortcomings of the above-mentioned technology, the present invention provides an analysis method for analyzing the contact condition of device electrodes in view of the shortcomings of the existing contact resistance testing method. This method can be used for in-situ testing on the device. While obtaining the contact quality, it can also obtain the distribution information of bubbles, contaminants and impurity defects that cannot be obtained by other methods.
[0006] In order to solve the above technical problems, the technical solution adopted by the present invention is: a method for analyzing the contact condition of device electrodes, which uses the heat generation difference caused by the uneven distribution of resistance during device operation to obtain the contact quality, and specifically includes the following steps: Step S1, obtaining a high-resolution temperature distribution map of the planar device when it is working through a microscope; Step S2, determining the influence of contact resistance on the device by comparing the temperature distribution of the non-contact area and the contact area; The working principle of contact analysis using temperature distribution image is as follows Figure 1 As shown, a simplified schematic diagram of the device ( Figure 1 Left) includes material body resistance 1, contact resistance 2 and electrode 3. For the convenience of analysis, the contact area is equivalent to a model in which many contact resistances and body resistances are arranged alternately. The equivalent circuit diagram is as follows Figure 1 As shown on the right, R1, R2, R3... are the material body resistances, and Ra, Rb, Rc... are the contact resistances.
[0007] When the contact resistance Ra is smaller than the body resistance R1, due to Joule's law, the heat generated by the device is concentrated in the body resistance R1, while the heat generated by other resistors is small; when the contact resistance Ra is larger than the body resistance R1, the heat generated is concentrated in the contact resistance Ra, and the heat generated by Rb, Rc, etc. decreases exponentially step by step; for contact abnormal points (such as larger Rb) and material defects (such as larger R2) in the contact area, the current flowing through these resistors is lower, which is displayed as a low temperature area on the temperature distribution diagram.
[0008] According to the above principle, the temperature distribution diagram obtained by the analysis test, if the temperature of the contact area is significantly higher than the temperature of the non-contact area, then the contact resistance is large at this time, and the contact quality needs to be further improved; if the temperature of the contact area is lower than the temperature of the non-contact area, then the resistance of the non-contact area is large at this time. (Note: the bright area in the temperature distribution diagram corresponds to high temperature, and the dark area corresponds to low temperature).
[0009] Step S3: After the contact area is enlarged, its surface topography and temperature distribution are tested, and the topography and temperature distribution are compared to obtain information on defects, bubbles and contaminants.
[0010] After the contact area is magnified, a scanning Joule thermal expansion microscope is used to test the surface morphology and temperature distribution image. From step S2, it can be seen that abnormal contact points and material defects will cause low-temperature areas. The morphology of the low-temperature area in the temperature distribution diagram corresponds to the morphology of the position in the surface morphology diagram. If the low-temperature area corresponds to a convex morphology, there are bubbles and contaminants at this interface; if there is no convexity in the corresponding morphology of the low-temperature area, there is a material defect here.
[0011] Step S4: In the temperature distribution diagram of S3, each pixel corresponds to a temperature value, and the temperatures corresponding to all the pixels form a data set. The variance / average value of the temperature data set is used to evaluate the contact uniformity.
[0012] Contact uniformity, that is, whether the temperature distribution is uniform, variance is a parameter commonly used to evaluate uniformity. However, in the present invention, the temperature distribution is affected by the applied voltage, contact resistance and body resistance of the conductive material in addition to the surface contact condition. Using the temperature distribution variance to evaluate contact uniformity is not suitable for comparing different devices. Therefore, the variance divided by the average value is used as the evaluation standard. In actual operation, in order to eliminate the influence of spontaneous temperature changes in the contact area, such as Figure 1 The temperature Ra>Rb>Rc is generated in the area, so the appropriate data processing method is to take the average of the calculated coefficient of variation of each column of pixels in the area as the coefficient of variation of the entire area. (Figure of merit <0.1, typical value 0.05-0.3). When the coefficient of variation is less than 0.1, that is, the temperature change rate is less than 10%, the contact is considered uniform.
[0013] Preferably, in step S1, the microscope is a scanning Joule thermal expansion microscope, which is composed of an atomic force microscope, a lock-in amplifier, and a signal generator, and can simultaneously obtain a surface morphology image and a high-resolution temperature distribution image of the device.
[0014] Scanning Joule thermal expansion microscopy can achieve ultra-high resolution testing of nanoscale temperature distribution and simultaneously obtain device surface morphology images.
[0015] Preferably, in step S2, the temperature distribution of the non-contact area and the contact area are compared according to the temperature distribution diagram obtained in step S1. If the temperature of the contact area is higher than that of the non-contact area, the contact resistance limits the current; otherwise, the resistance of the non-contact area limits the current.
[0016] Preferably, in step S3, the morphology of the corresponding position of the low-temperature area in the temperature distribution diagram in the surface morphology diagram, if the corresponding morphology of the low-temperature area is convex, then there are bubbles and contaminants at this interface; if there is no convexity in the corresponding morphology of the low-temperature area, then there is a material defect at this location.
[0017] Based on the distribution of bubbles, contaminants and material defects obtained through analysis, the best way to optimize contact quality can be obtained. Bubbles and contaminants can be removed through annealing and surface smoothing. If there are many defects, conductive materials with lower defect density can be used to optimize the circuit.
[0018] The contact area with uniform heat generation and no low-temperature areas still needs to be further optimized. The electrode material needs to be replaced to achieve better electron transmission to further reduce the contact resistance.
[0019] Preferably, in step S2, the contact area is an area where the conductive material contacts the electrode, and the non-contact area is an area where the conductive material does not contact the electrode.
[0020] like Figure 2 In the sample shown, the overlapping area between the conductive material (graphene) 2 and the electrode (gold) 1 and the electrode (gold) 3 is the contact area, and the area where the conductive material and the electrode do not overlap is the non-contact area.
[0021] Preferably, the contact types of the contact region include three types of contacts: metal / semiconductor, semiconductor / semiconductor, and metal / metal.
[0022] Metal / metal contact is common in mechanical switches because metal has good conductivity, i.e. Figure 1 In this case, R1, R2, and R3 are relatively small. The contact resistance has the greatest impact on this type of contact, and the temperature in the contact area is the highest. It is generally necessary to test the enlarged morphology and temperature distribution diagram of the contact area, and analyze the contact situation based on this to optimize the contact quality. In metal / semiconductor and semiconductor / semiconductor contacts, due to the high resistance of the semiconductor body, that is, Figure 1 R1, R2, and R3 are greater than those in metal / metal contact. Therefore, the highest temperature point may appear in the contact area or the non-contact area. When the highest temperature point appears in the contact area, it is necessary to measure the enlarged morphology and temperature distribution diagram of the contact area and then optimize the contact quality.
[0023] Compared with traditional electrical testing methods, the present invention uses the heat difference caused by the uneven distribution of resistance of semiconductor devices to determine the contact situation. The test only uses a non-conductive atomic force microscope probe to scan the surface of the device (the device to be tested is placed under the microscope for scanning to obtain the corresponding temperature distribution map). This analysis method is convenient and will not damage the device. It does not require complicated testing procedures and can achieve good results for complex device structures. In addition, it can also obtain information on the distribution of bubbles, contaminants, material defects and contact area at the same time and provide further optimization routes. BRIEF DESCRIPTION OF THE DRAWINGS
[0024] Figure 1is a simplified schematic diagram (left) and a circuit schematic diagram (right) of the electrode contact of the present invention; Figure 2 The diagram is a schematic diagram of the structure of the gold / graphene / gold sample of the present invention (left), and a temperature distribution diagram of the test (right); Figure 3 This is a schematic diagram of the testing principle of the scanning Joule thermal expansion microscope of the present invention; Figure 4 1 is an enlarged morphology (left) and temperature (right) distribution diagram of the graphene / gold electrode contact area in Example 1 of the present invention, and the dotted box is the area where the material defects are located; Figure 5 It is the morphology (left) and temperature (right) distribution diagram of the enlarged graphene / gold electrode contact area in Example 2 of the present invention, and the dotted box is the area where the pollutants / bubbles are located.
[0025] Figure 6 It is a temperature distribution diagram of grayscale mapping before (left) and after (right) cleaning of contaminants at the contact interface of gold / graphene / gold sample by the present invention.
[0026] Figure 7 It is the temperature change of contact area and non-contact area extracted from the temperature distribution diagram after optimizing the contact interface of gold / graphene / gold sample. DETAILED DESCRIPTION
[0027] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.
[0028] Example 1 A method for analyzing the contact condition of device electrodes comprises the following steps: S1. Use scanning Joule thermal expansion microscopy to obtain high-resolution temperature distribution images of planar devices during operation ( Figure 2 Right); The working principle of the scanning Joule thermal expansion microscope is as follows Figure 3 As shown, the atomic force microscope probe is used to characterize the material morphology, and the lock-in amplifier is used to obtain the Joule thermal expansion in combination with the atomic force microscope to obtain the temperature distribution map; Figure 3 The figure shows the principle diagram of the temperature test method using scanning Joule thermal expansion microscope. By using this test method to analyze the contact condition of the electrode, the test process is simpler than other methods and more information can be obtained.
[0029] S2, based on the temperature distribution image obtained from the actual test ( Figure 2 Right), in the temperature distribution image, the temperature of the contact area (4) is significantly higher than that of the non-contact area (5). At this time, the contact resistance is large and the surface contact quality needs to be further improved; S3, after the contact area is enlarged, the surface morphology is tested using a scanning Joule thermal expansion microscope (256×256 pixels, Figure 4 Left) and temperature distribution image (256×256 pixels, Figure 4 Right), from step S2, we can know that abnormal contact points and material defects will cause low-temperature areas. Compare the position of the low-temperature area in the temperature distribution image and the position of the protrusion in the surface morphology image; in the dotted line frame, there is no protrusion in the morphology, and the temperature here is low. It is judged that this corresponds to a material defect. It is necessary to reduce the density of this defect by optimizing the device preparation process and selecting a suitable low-defect conductive material.
[0030] S4. The temperature values corresponding to all pixels in the area (256×256 pixels) are used to form a data set. The coefficient of variation (variance / mean) of the temperature set is calculated to be 0.19, which is greater than the optimal value of 0.1, indicating that the contact is relatively uneven and there is room for optimization.
[0031] Example 2 A method for analyzing the contact condition of device electrodes comprises the following steps: S1. Use scanning Joule thermal expansion microscopy to obtain high-resolution temperature distribution images of planar devices during operation ( Figure 2 Right); The working principle of the scanning Joule thermal expansion microscope is as follows Figure 3 As shown, the atomic force microscope probe is used to characterize the material morphology, and the lock-in amplifier is used to obtain the Joule thermal expansion in combination with the atomic force microscope to obtain the temperature distribution map; Figure 3 The figure shows the principle diagram of the temperature test method using scanning Joule thermal expansion microscope. By using this test method to analyze the contact condition of the electrode, the test process is simpler than other methods and more information can be obtained.
[0032] S2, based on the temperature distribution image obtained from the actual test ( Figure 2 Right), in the temperature distribution image, the temperature of the contact area (4) is significantly higher than that of the non-contact area (5). At this time, the contact resistance is large and the surface contact quality needs to be further improved; S3, after the contact area is enlarged, the surface morphology is tested using a scanning Joule thermal expansion microscope (256×256 pixels, Figure 5 Left) and temperature distribution image (256×256 pixels, Figure 5 Right), as can be seen from step S2, contact anomalies and defects will cause low-temperature areas. Comparing the position of the low-temperature area in the temperature distribution image and the convex position in the surface topography image (the position selected by the dotted line in the figure), it is found that the positions are the same, which means that there are bubbles and contaminants on the interface here, resulting in poor contact; S4. Continue to use the atomic force microscope to apply a large force to the probe to remove contaminants and bubbles. Use the scanning Joule thermal expansion microscope to test before removing contaminants and bubbles ( Figure 6 Left) Rear ( Figure 6 Right) The temperature distribution image of the device. The temperature values corresponding to all pixels (256×256 pixels) in the two images are used to form two data sets. The coefficient of variation (variance / mean) of the temperature set is calculated to be 0.285 and 0.13 respectively. The reduction in the coefficient of variation indicates that the sweeping operation reduces the unevenness of the interface heating, and after sweeping away bubbles and contaminants, it is close to the figure of merit of 0.1, achieving good contact uniformity. The temperature distribution of the non-contact area and the contact area was tested by scanning Joule thermal expansion microscopy, and the temperature variation in the area was extracted. Figure 7 As shown, the temperature of the non-contact area of the device after treatment increases significantly, indicating that after the cleaning operation, the contact resistance of the device decreases, causing the current to increase and the heat generated in the non-contact area to increase.
[0033] The above implementation modes are not limitations of the present invention, and the present invention is not limited to the above examples. Changes, modifications, additions or substitutions made by technicians in this technical field within the scope of the technical solution of the present invention also belong to the protection scope of the present invention.
Claims
1. A method for analyzing the contact condition of device electrodes, characterized in that: This method uses the heat generation difference caused by the uneven distribution of resistance during device operation to evaluate the contact quality, and specifically includes the following steps: Step S1, obtaining a high-resolution temperature distribution map of the planar device when it is working through a microscope; Step S2, determining the influence of contact resistance on the device by comparing the temperature distribution of the non-contact area and the contact area; Step S3, after magnifying the contact area, testing its surface topography and temperature distribution, comparing the topography and temperature distribution, and obtaining information on defects, bubbles and contaminants; Step S4: In the temperature distribution diagram of S3, each pixel corresponds to a temperature value, and the temperatures corresponding to all the pixels form a data set. The variance / average value of the temperature data set is used to evaluate the contact uniformity.
2. The method for analyzing the contact condition of device electrodes according to claim 1, characterized in that: In step S1, the microscope is a scanning Joule thermal expansion microscope, which is composed of an atomic force microscope, a lock-in amplifier, and a signal generator, and can simultaneously obtain a surface morphology image and a high-resolution temperature distribution image of the device.
3. The method for analyzing the contact condition of device electrodes according to claim 1, characterized in that: In step S2, the temperature distribution of the non-contact area and the contact area are compared according to the temperature distribution diagram obtained in step S1. If the temperature of the contact area is higher than that of the non-contact area, the contact resistance limits the current; otherwise, the resistance of the non-contact area limits the current.
4. The method for analyzing the contact condition of device electrodes according to claim 1, characterized in that: In step S3, the morphology of the corresponding position of the low temperature area in the temperature distribution diagram in the surface morphology diagram, if the corresponding morphology of the low temperature area is convex, then there are bubbles and contaminants at this interface; if there is no convexity in the corresponding morphology of the low temperature area, then there is a material defect at this location.
5. The method for analyzing the contact condition of device electrodes according to claim 3, characterized in that: In the step S2, the contact area is the area where the conductive material contacts the electrode, and the non-contact area is the area where the conductive material does not contact the electrode.
6. The method for analyzing the contact condition of device electrodes according to claim 5, characterized in that: The contact types of the contact area include metal / semiconductor, semiconductor / semiconductor, and metal / metal.