Preparation method of 3-omega electrode of surface conductive or rough sample
By using liquid BCB resin spin-coating and metal evaporation with a stencil mask on conductive or rough samples, the problem of poor electrode preparation was solved, and stable and robust 3ω electrode preparation was achieved, improving the applicability and accuracy of thermal conductivity testing.
Patent Information
- Application Number
- CN202511800317.8
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-12-02
- Publication Date
- 2026-03-20
AI Technical Summary
Existing technologies make it difficult to fabricate 3ω electrodes on conductive or rough samples, leading to current short circuits, poor electrode morphology, and uncertain thermal contact area during testing, which affects the accuracy of 3ω thermal conductivity testing.
A flat insulating layer is formed on the sample surface by spin coating and curing of liquid BCB resin combined with metal evaporation through a perforated mask. The metal electrode is then directly evaporated through the perforated mask, avoiding the use of photoresist.
This technology enables the fabrication of stable and robust 3ω electrodes on conductive or rough samples, improving the applicability and accuracy of 3ω thermal conductivity testing.
Smart Images
Figure CN121702820A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of material thermophysical property testing, specifically a method for preparing a 3ω electrode for samples with conductive or rough surfaces. Background Technology
[0002] Thermal conductivity is an important parameter reflecting the thermal properties of a material. Whether used for heat dissipation or insulation, accurate testing of a material's thermal conductivity is crucial. The 3ω method is widely used for testing the thermal conductivity of various materials due to its adaptability, ease of testing, and low equipment cost.
[0003] However, 3ω requires the fabrication of test electrodes. For samples with conductive surfaces, directly fabricating test electrodes on their surface would cause current to flow through the sample interior during testing, affecting the test results. Therefore, an insulating dielectric layer needs to be grown on the surface. The thermal expansion coefficient of the insulating dielectric commonly used in most semiconductor processes is less than 5 × 10⁻. 6 / ℃ (e.g., the thermal expansion coefficient of Si3N4 is 3~4 × 10⁻) 6 / ℃, the coefficient of thermal expansion of SiO2 is 0.5 - 0.6 × 10⁻ 6 / ℃), while the coefficient of thermal expansion of most common metals and alloys is typically 5 × 10⁻ in the range of room temperature to several hundred degrees Celsius. 6 / °C to 25 × 10⁻ 6 Between / °C (e.g., Cu has a thermal expansion coefficient of 17 × 10⁻) 6 / ℃, the coefficient of thermal expansion of Al is 24×10⁻ 6 Due to the large difference in thermal expansion coefficients (°C), significant stress accumulates within the film. Simultaneously, many metals (such as copper and aluminum) are highly susceptible to oxidation and have poor chemical compatibility with silicon nitride, resulting in inherently poor adhesion when silicon nitride is deposited directly on them. Furthermore, excessively rough surfaces can cause stress concentration, becoming the starting point for peeling. The cumulative effect of these factors makes it easy for general insulating media grown on metals to wrinkle, crack, or even peel off over large areas.
[0004] In addition, for samples with non-conductive but rough surfaces, directly fabricating electrodes on their surfaces will cause the following problems due to their rough surfaces: (1) When preparing metal electrodes by photolithography evaporation, the photoresist is very thin in some places due to its rough surface, and adhesion will occur during peeling, resulting in metal residue in places where metal is not needed, making it difficult to prepare electrode patterns with good morphology. (2) Due to the rough surface, the electrode area may be short-circuited. (3) Due to the rough surface, the electrode has irregular undulations, the thermal contact area cannot be determined, the heat flow distribution is complex, the 3ω temperature rise model is no longer applicable, and it will seriously interfere with the measurement. Summary of the Invention
[0005] To address the aforementioned problems, the present invention aims to provide a method for preparing a 3ω electrode for samples with conductive or rough surfaces, thereby enabling the 3ω thermal conductivity testing method to be used for testing samples with conductive or rough surfaces and improving the applicability of the 3ω electrical method for measuring thermal conductivity.
[0006] The specific technical solution for achieving the objective of this invention is as follows:
[0007] A method for preparing a 3ω electrode from a surface-conductive or rough sample includes the following steps:
[0008] Step 1: Clean the sample to be tested;
[0009] Step 2: Apply liquid BCB resin to the surface of the sample to be tested by spin coating;
[0010] Step 3: Place the sample to be tested coated with liquid BCB resin into a curing oven, purge with nitrogen for protection, and heat to cure the BCB resin.
[0011] Step 4: Fit the perforated mask tightly against the sample to be tested so that the pattern on the mask can be transferred onto the sample.
[0012] Step 5: Fix the fitted perforated mask to the sample to be tested, and place it in a metal evaporation furnace to evaporate the metal;
[0013] Step 6: Separate the sample to be tested from the cutout mask to complete the preparation of the 3ω electrode.
[0014] Compared with the prior art, the beneficial effects of the present invention are as follows:
[0015] The present invention solves the problem of delamination that occurs when growing traditional insulating media such as SiN and SiO2 on the surface of metal samples, based on BCB resin spin coating and curing and metal evaporation through a stencil mask. It also solves the problem that the 3ω electrode morphology is poor when directly preparing rough samples without polishing, which is not conducive to subsequent testing. This makes the 3ω thermal conductivity test method applicable to the testing of conductive or rough samples, and improves the applicability of the 3ω electrical method for measuring thermal conductivity.
[0016] This invention utilizes the curable property of liquid BCB resin after spin coating, forming a flat insulating layer on conductive or rough sample surfaces. This facilitates the subsequent fabrication of 3ω electrodes for testing. Furthermore, the perforated mask and evaporation fixture system designed in this invention avoids the use of photoresist for photolithography and electrode evaporation. The peeling process after photoresist evaporation requires immersion in an organic solution like acetone, which may dissolve the cured BCB and cause the prepared electrode to detach. The perforated mask method, which directly evaporates the metal, ensures a more robust bond between the evaporated metal electrode and the sample.
[0017] The present invention will be further described below with reference to specific embodiments. Attached Figure Description
[0018] Figure 1 This is a schematic diagram of the process for preparing a 3ω electrode for a surface-conductive or rough sample according to the present invention.
[0019] Figure 2 This is a schematic diagram of the hollow mask plate in an embodiment of the present invention.
[0020] Figure 3 This is a top view of a sample with a prepared electrode in an embodiment of the present invention.
[0021] Figure 4 This is a schematic cross-sectional view of the sample with the prepared electrode in an embodiment of the present invention. Detailed Implementation
[0022] Example
[0023] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. The described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.
[0024] As indicated in this application and claims, unless the context clearly indicates otherwise, the words "a," "an," "an," and / or "the" do not specifically refer to the singular and may also include the plural. Generally speaking, the terms "comprising" and "including" only indicate the inclusion of explicitly identified steps and elements, which do not constitute an exclusive list, and the method or apparatus may also include other steps or elements.
[0025] Unless otherwise specifically stated, the relative arrangement, numerical expressions, and values of the components and steps described in these embodiments do not limit the scope of this application. It should also be understood that, for ease of description, the dimensions of the various parts shown in the drawings are not drawn to actual scale. Techniques, methods, and devices known to those skilled in the art may not be discussed in detail, but where appropriate, such techniques, methods, and devices should be considered part of the specification. In all examples shown and discussed herein, any specific values should be interpreted as merely exemplary and not as limitations. Therefore, other examples of exemplary embodiments may have different values. It should be noted that similar reference numerals and letters in the following drawings denote similar items; therefore, once an item is defined in one drawing, it need not be further discussed in subsequent drawings.
[0026] Combination Figure 1A method for preparing a 3ω electrode from a surface-conductive or rough sample includes the following steps:
[0027] Step 1: Clean the sample to be tested. In this embodiment, the sample is placed in acetone solution and sonicated for 5 minutes, then placed in ethanol solution and sonicated for 5 minutes, and then dried with nitrogen.
[0028] In addition, the surface of the sample to be tested in this scheme is rough or conductive, and its surface roughness Ra=1000nm;
[0029] Step 2: Apply liquid BCB resin to the surface of the sample to be tested by spin coating. Bake the sample at 90°C for 2 minutes. Then, place the sample on the coating table and spin coat DOW BCB3022-35 at 3000 rpm for 30 seconds. Bake the sample at 90°C for 2 minutes to make the surface of the sample to be tested flat.
[0030] The liquid BCB resin is prepared by mixing BCB resin and diluent, and the mixing ratio is selected according to the surface roughness.
[0031] In this embodiment, the ratio of BCB resin to diluent is 3:1. When selecting the ratio, the higher the dilution concentration, the smaller the BCB curing thickness and the greater the surface roughness. Therefore, the lower the dilution concentration should be selected.
[0032] Step 3: Place the sample to be tested coated with liquid BCB resin into a curing oven, purge with nitrogen for protection, and heat to cure the BCB resin.
[0033] When heating the test sample coated with liquid BCB resin, a stepped heating process is used, sequentially using the first temperature, the second temperature, the third temperature, and the fourth temperature.
[0034] Because liquid BCB resin contains a large amount of solvent, if the temperature is directly raised from room temperature to a high temperature (such as 250°C), the solvent will evaporate extremely rapidly, especially inside the film.
[0035] Therefore, the first temperature step is set at 80-110°C: at this "safe temperature" plateau, the solvent has ample time to diffuse gently from the interior of the film to the surface and evaporate. This avoids the formation of high-pressure bubbles inside the film due to excessively rapid evaporation, thus eliminating fatal defects such as bubbles, pinholes, and craters.
[0036] The second temperature step is set to, for example, 140-160°C: after most of the solvent has been removed, this slightly higher temperature plateau is used to expel the remaining high-boiling-point solvent and increase the viscosity of the film, making the structure more stable.
[0037] The third temperature step is set at 250℃, which is the final curing temperature of BCB. At this temperature, BCB undergoes a cross-linking reaction to form a three-dimensional network polymer structure.
[0038] The fourth temperature step allows it to slowly decrease to the ambient temperature;
[0039] Specifically, in this embodiment, the first temperature is set between 80-110°C and the stabilization time is between 20 and 30 minutes; the second temperature is set between 140-160°C and the stabilization time is between 30 and 40 minutes; the third temperature is set between 250-300°C and the stabilization time is between 60 and 90 minutes; and the fourth temperature is set between 20-100°C and the stabilization time is between 10 and 30 minutes.
[0040] Step 4: Fit the perforated mask tightly against the sample to be tested so that the pattern on the mask can be transferred onto the sample.
[0041] The hollow mask is made of copper, aluminum or stainless steel with a thickness of ≤0.1mm. The electrode pattern to be prepared is pre-made in the hollow mask. The minimum line width of the electrode pattern is less than 50um, so that the error is controlled within 5%. If the minimum line width is too large, it will cause systematic error.
[0042] After the perforated mask is attached to the sample to be tested, it is fixed using a clamping system, which includes a tray and a fixing system.
[0043] In this embodiment, a perforated mask with electrode patterns, an electrode linewidth of 40 μm, and a length of 1500 μm is tightly bonded to the surface of the sample to be tested. The perforated mask in this embodiment is as follows: Figure 2 As shown.
[0044] Step 5: Use a special evaporation stage clamp to fix the fitted hollow mask to the sample to be tested, and place it in a metal evaporation furnace to evaporate the metal. The metal types from bottom to top are Ti / Au: 20 / 200nm.
[0045] Step 6: After the metal has evaporated in the metal evaporation furnace, remove the special evaporation stage fixture, separate the sample to be tested from the hollow mask, and complete the preparation of the thermal conductivity test electrode.
[0046] Figure 3 This is a top view of a 3ω electrode sample prepared on the surface of spin-coated and cured BCB resin using a perforated mask. Figure 4 A cross-sectional view of its A-A' region. Figure 4 The prepared 3ω electrode sample structure, from top to bottom, consists of a 3ω metal electrode (B), a cured BCB (C), and a sample to be tested with a rough or conductive surface (D).
[0047] This invention utilizes the curable property of liquid BCB resin after spin coating, forming a flat insulating layer on conductive or rough sample surfaces. This facilitates the subsequent fabrication of 3ω electrodes for testing. Furthermore, the hollow mask and evaporation fixture system designed in this invention avoids the use of photoresist for photolithography and electrode evaporation. The photoresist evaporation and subsequent stripping process requires immersion in an organic solution like acetone, which may dissolve the cured BCB and cause the prepared electrode to detach. The hollow mask method of directly evaporating the metal results in a more robust bond between the evaporated metal electrode and the sample.
[0048] The present invention enables the 3ω thermal conductivity test method to be used for testing samples with conductive or rough surfaces, thereby improving the applicability of the 3ω electrical method for measuring thermal conductivity.
[0049] The embodiments described above are merely one implementation method of this application, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.
Claims
1. A method for preparing a 3ω electrode for a sample with a conductive or rough surface, characterized in that, Includes the following steps: Step 1: Clean the sample to be tested; Step 2: Apply liquid BCB resin to the surface of the sample to be tested by spin coating; Step 3: Place the sample to be tested coated with liquid BCB resin into a curing oven, purge with nitrogen for protection, and heat to cure the BCB resin. Step 4: Fit the perforated mask tightly against the sample to be tested so that the pattern on the mask can be transferred onto the sample. Step 5: Fix the fitted perforated mask to the sample to be tested, and place it in a metal evaporation furnace to evaporate the metal; Step 6: Separate the sample to be tested from the cutout mask to complete the preparation of the 3ω electrode.
2. The method for preparing a 3ω electrode for a surface-conductive or rough sample according to claim 1, characterized in that, The surface of the sample to be tested is rough or conductive, and its surface roughness Ra < 2000 nm.
3. The method for preparing a 3ω electrode for a surface-conductive or rough sample according to claim 1, characterized in that, The liquid BCB resin coated in step 2 is prepared by mixing BCB resin and diluent in a specific ratio.
4. The method for preparing a 3ω electrode for a surface-conductive or rough sample according to claim 1, characterized in that, In step 3, when heating the sample coated with liquid BCB resin, a stepped heating process is adopted, using the first temperature, the second temperature, the third temperature and the fourth temperature in sequence. The first temperature is set between 80-110℃ with a stabilization time of 20-30 minutes; the second temperature is set between 140-160℃ with a stabilization time of 30-40 minutes; the third temperature is set between 250-300℃ with a stabilization time of 60-90 minutes; and the fourth temperature is set between 20-100℃ with a stabilization time of 10-30 minutes.
5. The method for preparing a 3ω electrode for a surface-conductive or rough sample according to claim 1, characterized in that, The hollow mask is made of copper, aluminum, or stainless steel, with a thickness of ≤0.1mm.
6. The method for preparing a 3ω electrode for a surface-conductive or rough sample according to claim 5, characterized in that, The perforated mask pre-fabricated the electrode patterns to be prepared.
7. The method for preparing a 3ω electrode for a surface-conductive or rough sample according to claim 1, characterized in that, The perforated mask is attached to the sample to be tested and then fixed in place using a clamping system.
8. The method for preparing a 3ω electrode for a surface-conductive or rough sample according to claim 6, characterized in that, The minimum linewidth of the electrode pattern prefabricated on the hollow mask is less than 50 μm.