Method for processing microprobe by using ultrafast laser

Abstract

The invention discloses a method for processing a microprobe by using ultrafast laser, and the method comprises the following steps: laying a base material on a workbench through a micro-adhesion layer which is a polydimethylsiloxane layer; ultrafast picosecond laser is used for machining the base material to form a probe blank, during machining, different machining parameters are used according to different materials of the base material, the machining parameters comprise the wavelength, the pulse width, the repetition frequency, the power, the scanning speed and the single-time machining depth of the laser, and the pulse width ranges from 0.8 ps to 12 ps; the surface roughness of the blank body is reduced through a reactive ion etching process, etching gas of the reactive ion etching process comprises mixed etching gas of CH4 gas, H2 gas and Ar, in the mixed etching gas, the volume ratio of the CH4 gas to the H2 gas is 30: 70, and the flow of the Ar gas is 15 sccm. According to the invention, the problem that the existing processing technology of the microprobe is difficult to meet the comprehensive requirements on precision, efficiency, cost and consistency at the same time is solved.

Description

Technical Field

[0001] This invention relates to the field of probe fabrication technology, and more specifically to a method for fabricating microprobes using ultrafast lasers. Background Technology

[0002] High-density, fine-pitch vertical microprobes used for chip testing are key components connecting chips to testing equipment, and their performance directly determines the accuracy of the test. As chip integration increases and complex structures such as springs are integrated, the feature size of the probes needs to be reduced to 10~30μm, which places extremely high demands on fabrication technology.

[0003] Existing methods for fabricating microprobes include mechanical grinding, electrical discharge machining (EDM), conventional laser processing, and focused ion beam (FIP) processing. These methods have significant limitations. Specifically, mechanical grinding achieves only 50μm-level precision and is prone to introducing stress; EDM is inefficient and produces rough surfaces; conventional laser processing results in a large heat-affected zone, damaging the material; and while FIP offers high precision, it is expensive and inefficient. These technologies struggle to simultaneously meet the comprehensive requirements of microprobes in terms of precision, efficiency, cost, and consistency, thus becoming a technological bottleneck. Summary of the Invention

[0004] To overcome the shortcomings of existing technologies, a method for processing micro probes using ultrafast lasers is provided to address the problem that existing micro probe processing technologies cannot simultaneously meet the comprehensive requirements of accuracy, efficiency, cost, and consistency.

[0005] To achieve the above objectives, a method for processing microprobes using ultrafast lasers is provided, comprising the following steps: The substrate is laid on the worktable through a micro-adhesion layer, wherein the micro-adhesion layer is a polydimethylsiloxane layer; The substrate is processed using an ultrafast picosecond laser to form a probe preform. During processing, different processing parameters are used depending on the material of the substrate. The processing parameters include the laser wavelength, pulse width, repetition frequency, power, scanning speed, and single processing depth. The pulse width is 0.8~12ps. The surface roughness of the preform is reduced by reactive ion etching process. The etching gas in the reactive ion etching process includes CH4 gas, H2 gas and Ar gas, wherein the volume ratio of CH4 gas to H2 gas is 30:70 and the flow rate of Ar gas is 15 sccm.

[0006] Furthermore, when the substrate is a copper-based substrate, the laser used has a wavelength of 1064nm, a pulse width of 8~12ps, a repetition frequency of 500KHz, a power of 30W, a scanning speed of 2000mm / s, and a single processing depth of 5μm. The target thickness is achieved by multiple stacking operations.

[0007] Furthermore, when the substrate is a gold-based substrate, the laser used has a wavelength of 532nm, a pulse width of 0.8~3ps, a repetition frequency of 1000KHz, a power of 20W, a scanning speed of 3000mm / s, and a single processing depth of 3μm.

[0008] Furthermore, when using ultrafast picosecond lasers to process minute features, the power of the laser is reduced to 10-15W, and a multiple-scan method is employed.

[0009] Furthermore, before the substrate is laid on the workbench with a micro-adhesive layer, it is pretreated by sequentially undergoing degreasing, pickling, washing, and drying processes.

[0010] Furthermore, after reducing the surface roughness of the preform using reactive ion etching, the preform undergoes a plating process.

[0011] Furthermore, when the substrate is a copper-based substrate, a photoresist mask is first applied, followed by electroplating of a nickel layer, and preferably electroplating of a gold layer.

[0012] Furthermore, when the substrate is a gold-based substrate, a photoresist mask is first applied, followed by electroplating of a gold layer.

[0013] Furthermore, the thickness of the polydimethylsiloxane layer is 100–200 μm.

[0014] The beneficial effects of this invention are that the method of using ultrafast laser to process micro probes establishes a correspondence between laser processing parameters (wavelength, pulse width, repetition frequency, power) and processing effects (accuracy, efficiency, surface quality) for different substrates (copper-based, gold-based) and feature size requirements. It utilizes the short pulse width characteristics (0.8~12ps) of ultrafast lasers to reduce the heat-affected zone (≤5μm), avoids substrate melting and stress deformation, and achieves 10μm-level micro-feature processing through the threshold effect, avoiding thermal damage in traditional laser processing and improving processing accuracy.

[0015] The present invention uses an ultrafast laser to process micro probes. The substrate is fixed on the worktable by a micro-adhesive layer, so that the displacement of the substrate during processing is controlled within 1μm. Combined with the coordinated control of a biaxial high-speed galvanometer and a flat field mirror, the processing trajectory is accurately positioned, ensuring that the dimensional error is ≤±1μm. This makes the micro probe accurately positioned and less prone to deformation during processing.

[0016] The method for processing micro probes using ultrafast lasers in this invention employs a CH4 / H2 / Ar mixed gas RIE etching process to achieve precise control of surface roughness (RMS≤0.7nm) while ensuring the perpendicularity of the etching profile. Attached Figure Description

[0017] Other features, objects, and advantages of this application will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings: Figure 1 This is a schematic diagram of the structure of the ultrafast laser processing microprobe system according to an embodiment of the present invention.

[0018] Figure label: 1. Worktable; 2. Control system; 3. Picosecond laser; 4. Beam expander; 5. Reflector; 6. Galvanometer system field lens; 7. Substrate; 8. Micro-adhesion layer. Detailed Implementation

[0019] The present application will now be described in further detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and not intended to limit it. Furthermore, it should be noted that, for ease of description, only the parts relevant to the invention are shown in the accompanying drawings.

[0020] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. This application will now be described in detail with reference to the accompanying drawings and embodiments.

[0021] This invention provides a method for processing microprobes using ultrafast lasers, comprising the following steps: S1. The substrate is laid on the workbench 1 through the micro-adhesion layer 8, which is a polydimethylsiloxane layer.

[0022] In this embodiment, a fixture is mounted on the worktable. A substrate is laid on the fixture. Specifically, the fixture material is quartz glass.

[0023] A 100–200 μm thick layer of polydimethylsiloxane (PDMS) is coated onto the upper surface of the quartz glass to form a micro-adhesion layer. The micro-adhesion layer bonds to the substrate to ensure that no displacement occurs during the fabrication of the microprobe material, with a displacement of ≤1 μm during the fabrication process.

[0024] The substrate is pretreated before being mounted onto the fixture.

[0025] Specifically, the pretreatment steps include: degreasing, pickling, washing, and drying.

[0026] The degreasing process uses an alkaline degreasing solution (50g / L sodium hydroxide + 30g / L sodium carbonate + 20g / L sodium phosphate) at a temperature of 60℃ for 5 minutes.

[0027] The pickling process uses a 5% dilute hydrochloric acid solution and is treated at room temperature for 2 minutes to remove the oxide layer on the substrate surface, ensuring the adhesion of subsequent coatings.

[0028] The washing and drying process involves ultrasonically cleaning the substrate with deionized water (frequency 40KHz, time 3min) and drying it in an 80℃ oven.

[0029] In this embodiment, the substrate is classified into copper-based (beryllium copper, tungsten copper) substrate or gold-based substrate according to its material.

[0030] S2. Ultrafast picosecond laser is used to process the substrate to form a probe blank. During processing, different processing parameters are used depending on the material of the substrate. The processing parameters include the laser wavelength, pulse width, repetition frequency, power, scanning speed and single processing depth. The pulse width is 0.8~12ps.

[0031] In this embodiment, when the substrate is a copper-based substrate, the laser used has a wavelength of 1064nm, a pulse width of 8~12ps, a repetition frequency of 500KHz, a power of 30W, a scanning speed of 2000mm / s, and a single processing depth of 5μm. The target thickness is achieved by multiple stacking operations.

[0032] When the substrate is a gold-based substrate, the laser used has a wavelength of 532nm, a pulse width of 0.8~3ps, a repetition frequency of 1000KHz, a power of 20W, a scanning speed of 3000mm / s, and a single processing depth of 3μm.

[0033] When using ultrafast picosecond lasers to process minute features, the laser power is reduced to 10–15W by utilizing the ultrafast laser threshold effect and employing a multi-scan method to achieve feature size processing at the 10μm level.

[0034] Combined Figure 1 As shown, in this embodiment, a system for processing microprobes using ultrafast lasers is constructed, and the substrate is processed using the laser of the system for processing microprobes using ultrafast lasers.

[0035] Specifically, the ultrafast laser processing system for microprobes includes a picosecond laser 3, a beam expander 4, a reflector 5, a galvanometer system, a field mirror 6, a stage 1, and a control system 2.

[0036] Among them, the picosecond laser can switch to output 1064nm or 532nm wavelength laser, with a pulse width adjustment range of 0.8 to 12ps, a repetition frequency that is continuously adjustable from 100 to 2000KHz, and an output power of 10 to 100W.

[0037] The beam expander adopts a Galilean beam expander structure to expand the 3mm beam emitted by the laser to 6mm.

[0038] The galvanometer system uses a dual-axis high-speed galvanometer with a scanning speed of up to 5000 mm / s and a positioning accuracy of ±0.5 μm.

[0039] A field lens with a focal length of 50-60mm is selected, and the diameter of the focused spot is 15-25μm, covering a processing area of ​​15mm×15mm to 25mm×25mm, which can meet the needs of micro probe processing.

[0040] The control system adopts an industrial-grade PC + motion control card architecture, supports the import of various CAD format files such as DXF and STEP, and can realize the coordinated control of laser parameters and processing trajectory.

[0041] During processing, after the CAD design drawings are imported through the control system, trial processing is carried out first. The processing trajectory is calibrated through the vision inspection system before batch processing.

[0042] S3. The surface roughness of the preform is reduced by reactive ion etching process. The etching gas in the reactive ion etching process includes CH4 gas, H2 gas and Ar gas, wherein the volume ratio of CH4 gas to H2 gas is 30:70 and the flow rate of Ar gas is 15 sccm.

[0043] In this embodiment, reactive ion etching (RIE) is used to reduce the surface roughness after laser processing. The etching equipment used is a SENTECH Si500 ICP device, and the working mode is RIE mode.

[0044] The reactive ion etching process parameters were set as follows: RF power 150W, process pressure 75mT, and etching time 2min.

[0045] After being processed by reactive ion etching, the surface roughness of the probe blank is reduced from 100-200 nm (RMS) to ≤0.7 nm (RMS), and the verticality of the etching profile can reach 88°, with no mask undercut phenomenon.

[0046] S4. After reducing the surface roughness of the preform using reactive ion etching, the preform undergoes a plating process.

[0047] When the substrate is copper-based, a photoresist mask is applied first, followed by electroplating of a nickel layer, and preferably electroplating of a gold layer.

[0048] Specifically, the copper-based substrate is first electroplated with a nickel layer. The plating solution is a sulfate system (250 g / L nickel sulfate + 40 g / L nickel chloride + 30 g / L boric acid), and the current density is 2 A / dm³. 2 The temperature is 50℃, and the electroplating time is adjusted according to the thickness of the nickel layer (15 min for 0.5 μm, 60 min for 2 μm). Subsequently, a gold layer was electroplated using a cyanide system (potassium gold cyanide 2g / L + citric acid 30g / L) at a current density of 1A / dm³. 2Temperature 30℃, electroplating time 10-20 min (10 min for 1μm, 20 min for 2μm). When the substrate is a gold-based substrate, a photoresist mask is first applied, followed by electroplating of a gold layer.

[0049] Specifically, the gold-based substrate is directly plated with gold.

[0050] After electroplating, the mask is removed sequentially (using acetone ultrasonic cleaning at a frequency of 40KHz for 5 minutes), washed with water, and dried to finally obtain a uniform nickel-gold composite coating.

[0051] The present invention provides a method for processing micro probes using ultrafast lasers. This method establishes a correlation between laser processing parameters (wavelength, pulse width, repetition frequency, power) and processing effects (precision, efficiency, surface quality) for different substrates (copper-based, gold-based) and feature size requirements. It utilizes the short pulse width (0.8–12 ps) of ultrafast lasers to reduce the heat-affected zone (≤5 μm), avoiding substrate melting and stress deformation. Simultaneously, it achieves 10 μm-level micro-feature processing through a threshold effect, avoiding thermal damage from traditional laser processing and improving processing accuracy.

[0052] The present invention uses an ultrafast laser to process micro probes. The substrate is fixed on the worktable by a micro-adhesive layer, so that the displacement of the substrate during processing is controlled within 1μm. Combined with the coordinated control of a biaxial high-speed galvanometer and a flat field mirror, the processing trajectory is accurately positioned, ensuring that the dimensional error is ≤±1μm. This makes the micro probe accurately positioned and less prone to deformation during processing.

[0053] The method for processing micro probes using ultrafast lasers in this invention employs a CH4 / H2 / Ar mixed gas RIE etching process to achieve precise control of surface roughness (RMS≤0.7nm) while ensuring the perpendicularity of the etching profile.

[0054] The present invention employs a method for processing micro probes using ultrafast lasers, which adopts differentiated plating processes for copper-based and gold-based substrates. Through pretreatment and process parameter optimization, the adhesion of the plating layer is improved (≥50MPa), ensuring that the probe has excellent conductivity and corrosion resistance, thereby improving the surface quality of the micro probe after laser processing and ensuring stable plating adhesion.

[0055] The above description is merely a preferred embodiment of this application and an explanation of the technical principles employed. Those skilled in the art should understand that the scope of the invention involved in this application is not limited to technical solutions formed by specific combinations of the above-described technical features, but should also cover other technical solutions formed by arbitrary combinations of the above-described technical features or their equivalents without departing from the inventive concept. For example, technical solutions formed by substituting the above features with (but not limited to) technical features with similar functions disclosed in this application.

Claims

1. A method for processing microprobes using ultrafast lasers, characterized in that, Includes the following steps: The substrate is laid on the worktable through a micro-adhesion layer, wherein the micro-adhesion layer is a polydimethylsiloxane layer; The substrate is processed using an ultrafast picosecond laser to form a probe preform. During processing, different processing parameters are used depending on the material of the substrate. The processing parameters include the laser wavelength, pulse width, repetition frequency, power, scanning speed, and single processing depth. The pulse width is 0.8~12ps. The surface roughness of the preform is reduced by reactive ion etching process. The etching gas in the reactive ion etching process includes CH4 gas, H2 gas and Ar gas, wherein the volume ratio of CH4 gas to H2 gas is 30:70 and the flow rate of Ar gas is 15 sccm.

2. The method for processing microprobes using ultrafast lasers according to claim 1, characterized in that, When the substrate is a copper-based substrate, the laser used has a wavelength of 1064nm, a pulse width of 8~12ps, a repetition frequency of 500KHz, a power of 30W, a scanning speed of 2000mm / s, and a single processing depth of 5μm. The target thickness is achieved by multiple stacking operations.

3. The method for processing microprobes using ultrafast lasers according to claim 2, characterized in that, When the substrate is a gold-based substrate, the laser used has a wavelength of 532nm, a pulse width of 0.8~3ps, a repetition frequency of 1000KHz, a power of 20W, a scanning speed of 3000mm / s, and a single processing depth of 3μm.

4. The method for processing microprobes using ultrafast lasers according to claim 3, characterized in that, When using ultrafast picosecond lasers to process minute features, the power of the laser is reduced to 10-15W, and a multiple-scan method is employed.

5. The method for processing microprobes using ultrafast lasers according to claim 4, characterized in that, Before the substrate is laid on the workbench with a micro-adhesive layer, it is pretreated by degreasing, pickling, washing and drying in sequence.

6. The method for processing microprobes using ultrafast lasers according to claim 5, characterized in that, After reducing the surface roughness of the preform using reactive ion etching, the preform undergoes a plating process.

7. The method for processing microprobes using ultrafast lasers according to claim 6, characterized in that, When the substrate is a copper-based substrate, a photoresist mask is first applied, followed by electroplating of a nickel layer, preferably a gold layer.

8. The method for processing microprobes using ultrafast lasers according to claim 6, characterized in that, When the substrate is a gold-based substrate, a photoresist mask is first applied, followed by electroplating of a gold layer.

9. The method for processing microprobes using ultrafast lasers according to claim 1, characterized in that, The thickness of the polydimethylsiloxane layer is 100–200 μm.

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