Method for removing passivation layer from probe surface by cathodic reduction electrolysis

Abstract

The application belongs to the field of MEMS probe manufacturing process, and particularly relates to a method for removing a passivation layer on a probe surface by cathodic reduction electrolysis. The method takes the probe as a cathode, and performs electrolysis in an electrolyte with a pH value of 3.0-5.5 until the current is stable, and the passivation layer on the probe surface is reduced to a metal element. The technical scheme provided by the application can accurately protect the morphology of the microstructure of the MEMS probe, especially the micron-level needle tip and needle tail structure. The constant potential cathodic reduction can only reduce the nanoscale passivation layer within the potential window, avoiding isotropic drilling of chemical etching. After removing the passivation layer on the surface, the electrical contact performance of the probe can be improved, the contact impedance can be reduced, and the consistency between the probes can be improved, which is helpful for improving the reliability of wafer testing.

Description

Technical Field

[0001] This invention pertains to MEMS probe manufacturing processes, specifically relating to a method for removing the passivation layer on the probe surface using cathode reduction electrolysis. Background Technology

[0002] In the manufacturing process of MEMS probes, chemical mechanical polishing (CMP) is required to achieve high flatness and precise thickness control. However, MEMS probes have very high requirements for contact impedance during wafer testing, and CMP forms a passivation layer on the surface. This passivation layer is mainly an oxide of the substrate metal. Although the passivation layer is only 3-10 nm thick, it can still block electron tunneling at the microscale, resulting in a significant increase in contact impedance.

[0003] Therefore, it is necessary to remove the passivation layer. The existing methods for removing the passivation layer mainly include the following.

[0004] Wet cleaning: Since the probe structure is at the micrometer level, such as the tip, tail, and arm, traditional wet cleaning methods such as strong acid treatment to remove the passivation layer risk damaging the structure and have poor uniformity. This results in inconsistent removal amounts at different locations of the array MEMS probe.

[0005] Plasma cleaning can remove the passivation layer, but high-energy particle bombardment can change the crystal structure of the tip surface and introduce new defect energy levels.

[0006] In summary, current passivation layer removal processes all have various shortcomings. Summary of the Invention

[0007] This invention provides a method for removing the passivation layer on the probe surface by cathodic reduction electrolysis, thereby overcoming the insurmountable defects in current passivation layer removal processes.

[0008] To solve the above-mentioned technical problems, the present invention provides a method for removing the passivation layer on the probe surface by cathodic reduction electrolysis, which uses the probe as the cathode and performs electrolysis treatment in an electrolyte with a pH value of 3.0-5.5 until the current stabilizes, and the passivation layer on the probe surface is reduced to a metallic element.

[0009] Optionally, the electrolysis treatment lasts for 10-120 seconds, and is maintained for 5-10 seconds after the current stabilizes.

[0010] Optionally, the probe material is selected from nickel-based, nickel-based alloys, copper-based, or copper-based alloys.

[0011] Optionally, the probe is formed by electroplating.

[0012] Optionally, the electrolyte includes a conductive salt and a surfactant.

[0013] The surfactant can inhibit the adhesion of hydrogen bubbles and improve uniformity.

[0014] Optionally, the concentration of the conductive salt is 0.05-0.5 mol / L.

[0015] Optionally, the conductive salt is selected from citric acid or tartaric acid, and the surfactant is selected from Tween-80, fatty alcohol polyoxyethylene ether, or sodium dodecyl sulfate.

[0016] Optionally, in the electrolysis process, the anode is a platinum sheet, platinum-titanium mesh, or graphite, and the reference electrode is a saturated calomel electrode or an Ag / AgCl electrode.

[0017] Optionally, the electrolysis process employs a constant potential mode, applying a potential of -0.4V to -1.2V relative to the reference electrode to the cathode.

[0018] There may be a small amount of dissolved copper ions in the electrolyte. Although the given potential is sufficient for copper deposition, the deposition potential will increase significantly due to the low concentration of copper ions in the solution. However, if the potential is too high, the copper ions in the solution will still be deposited at the cathode, causing phenomena such as dust accumulation on the surface and affecting the surface quality.

[0019] Optionally, the electrolysis temperature is 20-50℃.

[0020] Optionally, during electrolysis, the electrolyte is subjected to ultrasonic vibration.

[0021] Some electrochemical reaction processes may result in hydrogen evolution, which could cause hydrogen embrittlement and affect material properties. Ultrasonic vibration can remove bubbles near the probe microstructure.

[0022] Optionally, after electrolysis, the probe is cleaned and dried, wherein the drying process is carried out in a nitrogen atmosphere to prevent secondary oxidation.

[0023] The technical solution provided by this invention can precisely protect the morphology of MEMS probe microstructures, especially the micron-level tip and tail structures. By using constant potential cathode reduction, the nanoscale passivation layer can be reduced only within the potential window, avoiding the isotropic drilling of chemical etching. After removing the surface passivation layer, the electrical contact performance of the probe can be improved, the contact impedance can be reduced, and the consistency between probes can be improved, which helps to improve the reliability of wafer testing. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0025] The test methods in the following embodiments are as follows:

[0026] Surface oxygen element detection: The surface composition was analyzed by scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS).

[0027] Contact resistance measurement: A miniature ohmmeter is used. The lower part is a gold-plated test block with a standard platform. The upper probe has a precision pressing structure, which can control the displacement distance and contact force. Before the test, the contact gold-plated block is short-circuited for calibration. During the test, the probe is pressed down at a fixed distance, and the resistance is read at this time.

[0028] Example 1: Nickel-based cantilever beam probe

[0029] The probe material is a nickel-cobalt alloy, which is formed by electroplating with a nickel-cobalt electroplating solution and then chemically and mechanically polished to form a NiO / CoO composite passivation layer on the surface, which can detect the presence of oxygen on the surface.

[0030] Electrolyte:

[0031] Citric acid: 0.1 mol / L

[0032] Sodium dodecyl sulfate: 0.03 g / L

[0033] pH: 4.3 (pH adjuster is sulfuric acid or potassium hydroxide).

[0034] Electrolysis parameters:

[0035] The MEMS probe is the cathode, the platinum-titanium mesh is the anode, and Ag / AgCl is the reference electrode.

[0036] Relative to the reference electrode, the cathode potential is controlled at around -0.58V. NiO / CoO is reduced to Ni and Co. During the electrolysis process, the electrolyte is subjected to ultrasonic vibration to avoid hydrogen evolution. After the current stabilizes, the time is extended by 8 seconds, for a total of about 50 seconds. Temperature: 25℃.

[0037] After electrolysis, the probe is cleaned and dried to ensure no water residue remains. The drying process is carried out in a nitrogen atmosphere to prevent secondary oxidation.

[0038] After processing, the probe was observed by SEM. The surface was smooth and flat, no oxygen was detected, the tip and cantilever beam structure were undamaged, and the size was almost unchanged.

[0039] The contact resistance was 1.2Ω before treatment and 0.3Ω after treatment.

[0040] Example 2: Copper-based vertical probe

[0041] The probe material is electroplated copper, which is relatively soft and easily scratched. After chemical mechanical polishing, a double passivation layer of Cu2O and CuO may be formed on the surface, which can detect the presence of oxygen on the surface. The tip has a pyramid-shaped structure with obvious sharp edges.

[0042] Electrolyte:

[0043] Tartaric acid: 0.15 mol / L

[0044] Fatty alcohol polyoxyethylene ether: 0.02 g / L

[0045] pH: 3.5 (pH adjuster is sulfuric acid or potassium hydroxide).

[0046] Electrolysis parameters:

[0047] The MEMS probe is the cathode, the platinum-titanium mesh is the anode, and Ag / AgCl is the reference electrode.

[0048] The cathode potential is controlled at around -0.45V relative to the reference electrode to avoid Cu deposition at the cathode. During electrolysis, the electrolyte is subjected to ultrasonic vibration to prevent hydrogen evolution. After the current stabilizes, the time is extended by 5 seconds, for a total of about 25 seconds. Temperature: 40℃.

[0049] After electrolysis, the probe is cleaned and dried to ensure no water residue remains. The drying process is carried out in a nitrogen atmosphere to prevent secondary oxidation.

[0050] After processing, the probe was observed by SEM. The surface was smooth and flat, no oxygen was detected, the tip was sharp and without rounded corners, and the size was almost unchanged.

[0051] The contact resistance was measured to be 0.6Ω before treatment and 0.2Ω after treatment.

[0052] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein, and these modifications or substitutions 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 removing the passivation layer on the surface of a probe by cathodic reduction electrolysis, characterized in that, Using a probe as the cathode, electrolysis was performed in an electrolyte with a pH of 3.0-5.5 until the current stabilized, and the passivation layer on the probe surface was reduced to a metallic element.

2. The method for removing the passivation layer on the probe surface by cathodic reduction electrolysis according to claim 1, characterized in that, The probe material is selected from nickel-based, nickel-based alloys, copper-based or copper-based alloys.

3. The method for removing the passivation layer on the probe surface by cathodic reduction electrolysis according to claim 1, characterized in that, The electrolyte includes a conductive salt and a surfactant.

4. The method for removing the passivation layer on the probe surface by cathodic reduction electrolysis according to claim 3, characterized in that, The concentration of the conductive salt is 0.05-0.5 mol / L.

5. The method for removing the passivation layer on the probe surface by cathodic reduction electrolysis according to claim 3, characterized in that, The conductive salt is selected from citric acid or tartaric acid, and the surfactant is selected from Tween-80, fatty alcohol polyoxyethylene ether, or sodium dodecyl sulfate.

6. The method for removing the passivation layer on the probe surface by cathodic reduction electrolysis according to claim 1, characterized in that, In the electrolysis process, the anode is a platinum sheet, platinum-titanium mesh, or graphite, and the reference electrode is a saturated calomel electrode or an Ag / AgCl electrode.

7. The method for removing the passivation layer on the probe surface by cathodic reduction electrolysis according to claim 7, characterized in that, The electrolysis process employs a constant potential mode, applying a potential of -0.4V to -1.2V relative to the reference electrode to the cathode.

8. The method for removing the passivation layer on the probe surface by cathodic reduction electrolysis according to claim 1, characterized in that, During the electrolysis process, the electrolyte is subjected to ultrasonic vibration.

9. The method for removing the passivation layer on the probe surface by cathodic reduction electrolysis according to claim 1, characterized in that, After electrolysis, the probe is cleaned and dried in a nitrogen atmosphere to prevent secondary oxidation.