Method for observing section morphology of phase change area in phase change switch in LTCC (Low Temperature Co-Fired Ceramic)

Abstract

The invention discloses a method for observing the section morphology of a phase change area in a phase change switch in LTCC, and belongs to the technical field of phase change device preparation. The method comprises the following steps: firstly preparing a phase change switch on a substrate material and performing surface film pasting, then etching a scratch penetrating through a corresponding area of the phase change switch on the back surface of the substrate material, then performing external force dissociation on a section from the back surface of the substrate, and finally performing scanning electron microscope sample preparation observation. According to the method, the negative influence caused by front diamond cutting or laser cutting when the phase change switch section sample is conventionally prepared is avoided, and the method that the substrate is added, laser scratching is conducted on the back face of the substrate, and then external force dissociation is conducted is adopted, so that it is guaranteed that the section of the obtained section sample is smooth and free of melt; the multi-layer film structure in the phase change area can be rapidly observed through the scanning electron microscope, the experiment cost is reduced, and rapid observation of the section morphology of the phase change area of the phase change switch can be realized without adopting a high-cost and time-consuming method.

Description

Technical Field

[0001] The invention relates to the technical field of phase change device preparation, and in particular to a method for observing the cross-sectional morphology of a phase change region in a phase change switch in LTCC. Background Art

[0002] In terms of phase change device preparation technology, researchers are committed to developing low-cost and high-efficiency methods to manufacture uniform, high-quality phase change films, while exploring how to accurately control the phase change temperature to adapt to different application requirements. In addition, the driving circuit design, thermal management, and integration of phase change switches with existing RF technologies are also research focuses. In order to improve the speed and reliability of the switch, researchers are exploring new structural designs, such as indirect heating structures with heaters placed on top, in order to achieve faster phase change processes and lower energy consumption. In terms of applied research, the reconfigurable characteristics of phase change switches give them great potential in dynamically adjusting RF system parameters, such as applications in reconfigurable filters and antenna arrays.

[0003] Although phase change switches show great potential in RF applications, they still face some technical and engineering challenges. First, the phase change temperature control of phase change materials is a key issue, which requires precise control to adapt to different application environments. Secondly, there are technical difficulties in the large-scale production of high-quality phase change material films, including the thickness uniformity of the films and the recrystallization of the phase change materials, which may affect the performance and reliability of the switch. In addition, the driving circuit design of the phase change switch is also a technical challenge. It is necessary to ensure a fast response while avoiding excessive power consumption and thermal effects, which may limit the service life of the switch. In practical applications, phase change switches also need to be integrated with other RF components, which requires that the switch design must take into account the compatibility and integration with existing technologies.

[0004] Phase change switch devices involve the use of multiple layers of thin films, multiple photolithography masks, and multiple process methods. Deviations in the connection of a certain layer of structure during the preparation process will cause the failure of the entire device. The morphological observation of the device cross section plays an important role in evaluating the failure analysis of the device, but the effective area of ​​the phase change switch is small, usually within 10μm×50μm. Conventional cutting methods such as diamond cutting and laser cutting methods are difficult to obtain the cross section of the central area of ​​the device, and it is impossible to observe the film thickness of the device and the contact between the layers through a scanning electron microscope. Among them, the diamond cutting method can observe the cross section of some areas, but due to the limitations of the cutting tool, the cross section is not smooth enough, and it is difficult to observe the cross section completely. The laser cutting method will cause a large amount of molten material due to the high temperature generated by the laser, and it is difficult to observe effective morphological information through a scanning electron microscope. Therefore, only the focused ion beam (FIB) method can be used to cut the sample, but this method is costly, complicated to operate, and time-consuming, and there are certain requirements for the prepared samples. Summary of the invention

[0005] In order to solve the above technical problems, the purpose of the present invention is to provide a method for observing the cross-sectional morphology of the phase change region in a phase change switch in LTCC, so as to solve the problems of difficult processing, high cost, complex operation and long time consumption of the cross-sectional samples of the phase change region of the existing phase change switch.

[0006] The technical solution of the present invention to solve the above technical problems is as follows:

[0007] A method for observing the cross-sectional morphology of a phase change region in a phase change switch in LTCC, comprising the following steps:

[0008] First, a phase change switch is prepared on the substrate material and a surface film is applied. Then, scratches are etched on the back of the substrate material to penetrate the corresponding area of ​​the phase change switch. Then, an external force dissociation section is performed from the back of the substrate. Finally, a scanning electron microscope sample is prepared for observation.

[0009] Furthermore, in step (1), the substrate material is a P-type silicon wafer with a crystal orientation of (100) and a thickness of 0.50-0.55 mm.

[0010] Furthermore, PE blue film is used for surface pasting.

[0011] The beneficial effect of adopting the above-mentioned further technical solution is: by sticking a layer of PE blue film on the front side of the prepared phase change switch sample, the present invention can prevent the front side of the device from being damaged or contaminated when the back side of the substrate is laser-etched, and avoid impurity contamination caused by direct contact with the laser table during processing.

[0012] Furthermore, laser etching is used to etch the scratches.

[0013] Furthermore, the power of laser etching is 8-12 W, the etching speed is 180-220 rad / s, the number of rotations is 4-6 times, and it is repeated 80-120 times.

[0014] Furthermore, the power of laser etching is 10 W, the etching speed is 200 rad / s, the number of rotations is 5 times, and it is repeated 100 times.

[0015] The beneficial effect of adopting the above-mentioned further technical scheme is as follows: the present invention adopts laser etching to perform scratch processing on the back side of the substrate, and can accurately control the etching scratch depth by adjusting the laser power intensity and the action time, thereby ensuring that the cross-sectional morphology of the phase change switch will not be destroyed, and ensuring that the cross-sectional structure of the phase change region of the phase change switch can be successfully prepared by external force dissociation.

[0016] Further, the depth of the scratch is less than the thickness of the substrate material.

[0017] The beneficial effect of adopting the above-mentioned further technical scheme is as follows: the present invention controls the scratch depth of laser etching to be smaller than the thickness of the substrate material, thereby effectively avoiding the damage to the cross-sectional structure of the phase change switch caused by the large amount of molten material generated at the scratch due to the high temperature during laser cutting, and effectively ensures that the cross-sectional sample can be successfully and conveniently processed by external force dissociation from the back of the substrate in the subsequent process.

[0018] Furthermore, the method of external force dissociation section is to fix the sample so that the substrate with the scratch is suspended in the air, and apply external force to make the sample break and fall off along the scratch.

[0019] The beneficial effect of adopting the above-mentioned further technical scheme is as follows: the present invention simultaneously breaks the substrate and the phase change switch by applying external force to the sample after laser etching from the back side of the substrate, thereby avoiding the problem of an insufficiently smooth cross section caused by diamond cutting from the front side in the conventional method or a large amount of molten material accumulation on the cross section caused by laser cutting. The processing method is simple, reduces the cost required for the experiment, and shortens the sample preparation time.

[0020] The present invention has the following beneficial effects:

[0021] The present invention avoids the negative effects of conventionally preparing cross-sectional samples of phase change switches by front diamond cutting or laser cutting, and adopts a method in which a substrate is added to the back of the substrate and then the back is laser scratched and then dissociated by external force, thereby ensuring that the cross-sectional sample obtained is smooth and free of melt, and the multilayer thin film structure in the phase change region can be quickly observed by a scanning electron microscope, thereby reducing the cost required for the experiment, and rapid observation of the cross-sectional morphology of the phase change region of the phase change switch can be achieved without adopting high-cost and time-consuming methods such as FIB. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1A schematic diagram of the cross-sectional structure of a phase change switch obtained in the embodiment;

[0023] Figure 2 The arrangement of the phase change switches on the substrate and the cutting path diagram in Example 1;

[0024] Figure 3 is a schematic diagram of a planar structure of a single folded phase change switch in an embodiment;

[0025] Figure 4 A drawing showing the back cutting path when laser etching scratches in Example 1;

[0026] Figure 5 This is the SEM observation image of the cross-section sample obtained in Example 1;

[0027] Figure 6 This is the SEM observation image of the cross-section sample prepared in Comparative Example 1. DETAILED DESCRIPTION

[0028] The principles and features of the present invention are described below in conjunction with the accompanying drawings. The examples are only used to explain the present invention and are not used to limit the scope of the present invention. If specific conditions are not specified in the embodiments, they are carried out according to normal conditions or conditions recommended by the manufacturer. If the manufacturer is not specified for the reagents or instruments used, they are all conventional products that can be purchased commercially.

[0029] Embodiment 1:

[0030] A method for observing the cross-sectional morphology of a phase change region in a phase change switch in LTCC, comprising the following steps:

[0031] (1) A small P-type silicon wafer with a crystal orientation of (100) and a length × width × height of 10 mm × 15 mm × 0.52 mm is used as a substrate. After cleaning, a heater film is deposited on the substrate. The pattern is transferred by photolithography and etching. Then, a silicon nitride dielectric film is deposited by PECVD technology and then ICP-RIE is used to transfer the pattern. The pattern transfer of the GeTe phase change film is achieved by the lift-off method. The lift-off method is also used to achieve the pattern transfer of the radio frequency metal Au film, and the following is obtained: Figure 1 The phase change switch is shown in the cross-sectional structural diagram, and a layer of PE blue film is attached to the front of the prepared phase change switch to prevent the front of the device from being damaged or contaminated when the back is etched.

[0032] (2) First input the designed drawing into the laser scribing system, and then use the optical alignment system to Figure 2Then adjust the laser etching power to 10W, the etching speed to 200rad / s, the number of rotations to 5 times, and repeat 100 times, so that laser etching scratches appear on the back of the substrate, and the depth of the scratches does not exceed the thickness of the substrate, so that the front device structure is complete. Figure 3 It is a schematic diagram of the planar structure of a single device. The dotted box is the phase change area to be observed. Figure 4 In accordance with Figure 2 Drawing of the backside of the substrate as the path shown is laser etched.

[0033] (3) Take out the laser-etched sample, use pointed tweezers to pick up the sample along the scratch, suspend the sample with the scratched part horizontally in the air, and then use flat-nosed tweezers to apply external force to make the sample break and fall off along the scratch, thereby obtaining a cross-sectional sample of the phase change region of the phase change switch.

[0034] (4) Prepare the cross-sectional sample obtained in step (3) according to the conventional SEM cross-sectional observation sample preparation method. Use conductive glue to fix the sample on a special mold, spray gold, and then place it in the SEM equipment for morphology observation. The observation results are as follows: Figure 5 As shown, the multilayer film in the center area can be clearly seen. The cross-sectional SEM image of the device in the present invention shows that the thickness of the multilayer film is uniform, and there is no obvious connection failure. It can be seen from the phase change switch structure diagram prepared by the present invention that the thickness of the heater in the present invention is obviously about 254.7nm, while the thickness of the heater generally does not exceed 100nm. An overly thick heater film may affect the use of subsequent devices. The present invention can observe the phenomenon through a scanning electron microscope by processing the cross-sectional sample through a simple method, without the need for a more expensive TEM / FIB method for observation, which greatly reduces the economic cost and time cost of experimental observation.

[0035] Embodiment 2:

[0036] A method for observing the cross-sectional morphology of a phase change region in a phase change switch in LTCC, comprising the following steps:

[0037] (1) A small P-type silicon wafer with a crystal orientation of (100) and a size of 10 mm in length, width, and height (10 mm, 15 mm, and 0.52 mm) was used as a substrate. After cleaning, a heater film was deposited on the substrate. The pattern was transferred using photolithography and etching. Subsequently, a silicon nitride dielectric film was deposited using PECVD technology and then ICP-RIE was used to transfer the pattern. The pattern transfer of the GeTe phase change film was achieved using the lift-off method. The pattern transfer of the radio frequency metal Au film was also achieved using the lift-off method to obtain a phase change switch. A layer of PE blue film was attached to the front of the prepared phase change switch to prevent the front of the device from being damaged or contaminated when the back side was etched.

[0038] (2) First input the designed drawing into the laser scribing system, and then use the optical alignment system to Figure 2 The path shown is aligned, and then the laser etching power is adjusted to 12 W, the etching speed is 180 rad / s, the number of rotations is 5 times, and repeated 100 times, so that laser etched scratches appear on the back of the substrate, and the depth of the scratches does not exceed the thickness of the substrate, so that the front device structure is complete.

[0039] (3) Take out the laser-etched sample, use pointed tweezers to pick up the sample along the scratch, suspend the sample with the scratched part horizontally in the air, and then use flat-nosed tweezers to apply external force to make the sample break and fall off along the scratch, thereby obtaining a cross-sectional sample of the phase change region of the phase change switch.

[0040] (4) The cross-sectional sample obtained in step (3) is prepared according to the conventional method for preparing cross-sectional observation by a scanning electron microscope. The sample is fixed on a special mold using conductive glue and subjected to gold spraying treatment. The sample is then placed in a scanning electron microscope for morphology observation.

[0041] Embodiment 3:

[0042] A method for observing the cross-sectional morphology of a phase change region in a phase change switch in LTCC, comprising the following steps:

[0043] (1) A small P-type silicon wafer with a crystal orientation of (100) and a size of 10 mm in length, width, and height (10 mm, 15 mm, and 0.52 mm) was used as a substrate. After cleaning, a heater film was deposited on the substrate. The pattern was transferred using photolithography and etching. Subsequently, a silicon nitride dielectric film was deposited using PECVD technology and then ICP-RIE was used to transfer the pattern. The pattern transfer of the GeTe phase change film was achieved using the lift-off method. The pattern transfer of the radio frequency metal Au film was also achieved using the lift-off method to obtain a phase change switch. A layer of PE blue film was attached to the front of the prepared phase change switch to prevent the front of the device from being damaged or contaminated when the back side was etched.

[0044] (2) First, input the designed drawing into the laser scribing system, align the etching path through the optical alignment system, and then adjust the laser etching power to 8W, the etching speed to 220rad / s, the number of rotations to 5 times, and repeat 100 times, so that laser etching scratches appear on the back of the substrate, and the depth of the scratches does not exceed the thickness of the substrate, so that the front device structure is complete.

[0045] (3) Take out the laser-etched sample, use pointed tweezers to pick up the sample along the scratch, suspend the sample with the scratched part horizontally in the air, and then use flat-nosed tweezers to apply external force to make the sample break and fall off along the scratch, thereby obtaining a cross-sectional sample of the phase change region of the phase change switch.

[0046] (4) The cross-sectional sample obtained in step (3) is prepared according to the conventional method for preparing cross-sectional observation by a scanning electron microscope. The sample is fixed on a special mold using conductive glue and subjected to gold spraying treatment. The sample is then placed in a scanning electron microscope for morphology observation.

[0047] Comparative Example 1:

[0048] A method for observing the cross-sectional morphology of a phase change region in a phase change switch in LTCC, comprising the following steps:

[0049] (1) A small P-type silicon wafer with a crystal orientation of (100) and a length × width × height of 10 mm × 15 mm × 0.52 mm is used as a substrate. After cleaning, a heater film is deposited on the substrate. The pattern is transferred by photolithography and etching. Then, a silicon nitride dielectric film is deposited by PECVD technology and then ICP-RIE is used to transfer the pattern. The pattern transfer of the GeTe phase change film is achieved by the lift-off method. The lift-off method is also used to achieve the pattern transfer of the radio frequency metal Au film, and the following is obtained: Figure 1 A phase change switch shown in cross-sectional schematic.

[0050] (2) The phase change switch obtained in step (1) was frontally cut using a diamond tool dicing machine. The substrate thickness was set to 0.55 mm, the cutting reserve was 0.15 mm, the tool speed was 27000 rad / s, and the dicing speed was 0.3 mm / s to obtain a cross-sectional sample.

[0051] (3) Prepare the cross-sectional sample obtained in step (2) according to the conventional SEM cross-sectional observation sample preparation method. Use conductive glue to fix the sample on a special mold, spray gold, and then place it in the SEM equipment for morphology observation. The observation results are as follows: Figure 6 As shown, it can be seen that although the cross section of the device can be obtained after cutting, there are obviously many impurities in the cross section obtained, which block the various layers of the film, making it impossible to observe the overall morphology in the SEM image, which is not conducive to experimental observation and analysis.

[0052] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for observing the cross-sectional morphology of the phase change region in a phase change switch in LTCC, It is characterized in that The following steps are involved: First, a phase change switch is prepared on the substrate material and a surface film is applied. Then, scratches are etched on the back of the substrate material to penetrate the corresponding area of ​​the phase change switch. Then, an external force dissociation section is performed from the back of the substrate. Finally, a scanning electron microscope sample is prepared for observation.

2. The method for observing the cross-sectional morphology of the phase change region in the phase change switch in LTCC according to claim 1, It is characterized in that In the step (1), the substrate material is a P-type silicon wafer with a crystal orientation of (100) and a thickness of 0.50-0.55 mm.

3. The method for observing the cross-sectional morphology of the phase change region in the phase change switch in LTCC according to claim 1, It is characterized in that Use PE blue film for surface pasting.

4. The method for observing the cross-sectional morphology of the phase change region in the phase change switch in LTCC according to claim 1, It is characterized in that The scratches are etched using laser etching.

5. The method for observing the cross-sectional morphology of the phase change region in the phase change switch in LTCC according to claim 4, It is characterized in that The power of laser etching is 8-12W, the etching speed is 180-220rad / s, the number of rotations is 4-6 times, and it is repeated 80-120 times.

6. The method for observing the cross-sectional morphology of the phase change region in the phase change switch in LTCC according to claim 5, It is characterized in that The power of laser etching was 10 W, the etching speed was 200 rad / s, the number of rotations was 5 times, and it was repeated 100 times.

7. The method for observing the cross-sectional morphology of the phase change region in the phase change switch in LTCC according to claim 1, It is characterized in that The depth of the scratch is less than the thickness of the substrate material.

8. The method for observing the cross-sectional morphology of the phase change region in the phase change switch in LTCC according to claim 1, It is characterized in that The method of external force dissociation section is to fix the sample so that the substrate with scratches is suspended in the air, and apply external force to make the sample break and fall off along the scratches.

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