Method for composite etching of electroplating seed gold layer
By combining dry etching with wet etching, the lateral etching problem in wet etching technology was solved, achieving high-precision etching of electroplated gold layers, improving device reliability and yield, and reducing costs.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- SHAANXI INST OF ADVANCED OEIC TECH CO LTD
- Filing Date
- 2025-12-26
- Publication Date
- 2026-05-15
AI Technical Summary
Existing wet etching technology suffers from severe lateral corrosion problems during the etching process of electroplated gold layers, resulting in loss of critical dimensions, deterioration of electrode morphology, corrosion of metal contact layers, and short-circuit risks, which limits the miniaturization and integration of devices.
A combination of dry etching and wet etching is used. Dry etching removes the seed gold layer in the non-electroplated areas. Combined with photoresist and a protective mask layer, anisotropic etching is achieved, and the lateral corrosion of the seed gold layer is controlled.
It significantly reduces lateral corrosion of the metal layer, improves device reliability and yield, reduces costs, reduces the use of toxic chemicals, and enhances process flexibility and precision.
Smart Images
Figure CN122054929A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of semiconductor manufacturing technology, specifically relating to a method for composite etching of electroplated gold layers. Background Technology
[0002] In the fabrication of chips such as lasers, a thick gold layer is typically required. This thick gold layer is generally achieved through electroplating. Before electroplating gold (Au), a seed gold layer needs to be sputtered, usually a TiW / Au composite metal material. After electroplating, the seed gold layer in the non-electroplated areas needs to be etched away.
[0003] Traditional titanium-tungsten-gold (TiW / Au) metal etching primarily employs wet etching processes. Wet etching uses specific chemical solutions, such as potassium iodide solution for gold and hydrogen peroxide solution for TiW. Its advantages include simple equipment, low cost, and high selectivity in etching. However, wet etching is isotropic, leading to severe undercutting, where the etchant corrodes both the vertical and horizontal metal contact layers simultaneously.
[0004] This type of lateral erosion can lead to a series of problems: 1. Critical dimension (CD) loss: The final electrode linewidth is much smaller than the linewidth of the photoresist mask metal pattern, resulting in increased electrode resistance and a large deviation from the design pattern.
[0005] 2. Deterioration of electrode morphology: Side etching can cause uneven electrode edges and "eaves"-like structures, which can easily lead to metal residue, breakage or poor passivation layer coverage in subsequent processes, affecting device reliability and yield.
[0006] 3. Corrosion of the metal contact layer: Lateral corrosion can also cause the underlying metal contact layer to be corroded by chemical liquids, affecting the ohmic contact between the metal and the compound, resulting in a decrease in the reliability of the device; 4. Short circuit risk: For high-density, small-size VCSEL arrays, severe side etching may reduce the spacing between adjacent electrodes or even cause short circuits, limiting the miniaturization and integration of the device.
[0007] Therefore, there is an urgent need for an etching method that can precisely control the size of the gold seed layer metal pattern and reduce lateral corrosion. Summary of the Invention
[0008] The purpose of this invention is to provide a method for composite etching of electroplated gold layers, which solves the shortcomings of existing wet etching technology. By combining dry etching with wet etching, the lateral corrosion problem of the metal layer is significantly reduced.
[0009] The technical solution adopted in this invention is a method for composite etching of electroplated seed gold layers. This method combines dry etching and wet etching to etch the electroplated metal seed gold layer in non-electroplated areas, removing the seed gold layer in the non-electroplated areas. This achieves good anisotropic etching, controls lateral corrosion of the seed gold layer, and improves device reliability. Specifically, it includes the following steps: Step 1: Photolithography pattern is made on the front side of gallium arsenide epitaxial layer by photolithography, photoresist coating, exposure and development process. Then, metal contact layer is deposited by electron beam evaporation, and the photoresist and contact metal layer in non-metallic areas are removed by wet stripping. Finally, metal alloy is formed by RTP high temperature alloying. Step 2: Deposit a layer of SiN based on Step 1. x A protective mask layer (refractive index of the mask layer is 2.0±0.02, and the value of x is in the range of 1.1-1.4) is used. The protective layer can also be other dielectric layers such as silicon oxide to protect the metal contact layer and serve as a silicon nitride mask layer. Mesa mesa etching is performed on the gallium arsenide epitaxial layer to form a Mesa etching mesa, exposing the high aluminum layer on the side of the epitaxial material, and an aluminum oxide confinement layer is formed by wet oxidation process. Step 3: Deposit a second layer of SiN based on Step 2 x A protective mask layer is used to passivate the surface of the wafer, and then a dry etching process is used to create vias to expose the metal contact layer. Step 4: TiW / Au metal is sputtered from the front using a magnetron sputtering device to form a seed gold layer. Photoresist is then spin-coated onto the seed gold layer. Through homogenization, exposure and development, and hardening processes, a photoresist mask with the target electrode pattern is formed. Step 5: Perform selective electroplating of thick gold on the photoresist mask pattern from Step 4; remove the photoresist mask layer after electroplating is complete. Step 6: Remove the seed gold layer in the non-electroplated areas using a combination of dry etching and wet etching.
[0010] The invention is further characterized in that, Furthermore, the metal contact layer includes any one or a combination of Ti / Pt / Au, Ni / Ge / Au, and Pd / Ge / Ti / Pt / Au; the structure of the metal contact layer from bottom to top includes an adhesive contact layer, a barrier layer, and a metal wire bonding layer. Furthermore, the TiW thickness in the seed gold layer is 50±10nm, and the Au thickness is 150±20nm; the thickness of the seed gold layer is not limited to the above and can be matched according to the specific process.
[0011] Furthermore, step 6 is detailed below: Step 6.1: Perform wet etching on the seed gold layer to remove the upper seed gold layer (Au) and expose the lower metal titanium-tungsten (TiW). In step 6.1, wet etching is performed using a diluted HF solution or an alkaline hydrogen peroxide solution containing a complexing agent; the HF solution contains HF, H2O2, and H2O; the specific ratio of HF, H2O2, and H2O is not limited.
[0012] Step 6.2: Use dry etching to remove most of the TiW metal. Dry etching uses chlorine, argon, and one or more of other chlorine-based gases, as well as other auxiliary gases. Dry etching can be performed using reactive ion etching (RIE), ion beam etching (IBE), or inductively coupled plasma etching (ICP). Step 6.3: Then, a wet etching process is used, employing hydrogen peroxide (H2O2) solution to wet-etch the remaining small portion of the TiW metal layer.
[0013] Furthermore, if inductively coupled plasma etching (ICP) is used, the Cl2 flow rate is 30±2 sccm, the BCl3 flow rate is 10±2 sccm, the ICP power is 500±5W, the bias power is 100±2 W, the pressure is 5±0.5 mTorr, and the temperature is 40±2°C.
[0014] Furthermore, in step 6.1, optical emission spectroscopy (OES) is used to monitor the disappearance of Au characteristic spectral lines, thereby precisely controlling the etching endpoint.
[0015] Furthermore, the TiW / Au can be replaced with Ti / Au, Cr / Au, Ni / Au, or TaN / Cu.
[0016] The specific type and flow rate of the dry etching gas can be matched to the metal system; similarly, the wet etching solution can be matched to the specific metal type.
[0017] The beneficial effects of this invention are: 1. Significantly improved precision: By locking the pattern boundary through dry etching, the lateral etching amount is reduced to 1 / 5 or even less of the traditional pure wet process, which significantly improves the fidelity of pattern transfer.
[0018] 2. Enhanced yield and reliability: It avoids erosion and metal residue at the root of the electroplated pattern, reduces the risk of short circuits and interface defects, and improves the long-term reliability of the product.
[0019] 3. High process flexibility: The order, formulation and parameters of dry and wet processes can be flexibly adjusted according to different material systems (such as TiW / Au, Cr / Au, TaN / Cu, etc.) and device sensitivity, making it highly adaptable.
[0020] 4. Cost-effectiveness optimization: Although a dry process step is introduced, the overall cost is optimized because it is shorter (the gold seed layer is thinner) and avoids waste caused by low yield.
[0021] 5. Environmentally friendly: It reduces the amount of highly corrosive and toxic wet chemicals used and processed. Attached Figure Description
[0022] Figure 1 This is a morphological image of the electroplated gold seed layer after wet etching and soft baking according to the present invention; Figure 2 This is a cross-sectional view of the device before corrosion. Figure 3 This is a cross-sectional view of the device after wet etching; Figure 4 This is a cross-sectional view of the device after dry and wet etching. Detailed Implementation
[0023] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.
[0024] Example 1: Composite etching for TiW / Au seed gold layers Substrate: A silicon substrate with a TiW (50±10nm) / Au (150±10nm) gold layer formed on its surface and patterned gold pillars after electroplating is provided; Step 1 - Dry etching of Au: Equipment: Inductively Coupled Plasma (ICP) etching machine.
[0025] Process gas: Cl2 (30±2 sccm) + BCl3 (10±2 sccm).
[0026] Process parameters: ICP power 500 W, bias power 100 W, pressure 5 mTorr, temperature 40°C.
[0027] Endpoint detection: The disappearance of Au characteristic spectral lines is monitored by optical emission spectroscopy (OES).
[0028] Effect: By using dry plasma anisotropic etching to etch the Au layer until the underlying TiW layer is exposed, the Au seed gold layer on the sidewall of the electroplated Au pillar is vertically cut off.
[0029] Step 2 - Wet etching of TiW: Etching solution: diluted HF solution (HF: H2O2: H2O = 1:1:50) Process conditions: room temperature, soaking time 60 seconds, supplemented with megasonic cleaning to enhance the effect and prevent residue.
[0030] Effect: From Figure 1Before optimization, the SEM image (using only wet etching) showed obvious lateral etching; however, when the TiW layer was laterally etched using the HF solution of this invention, the lateral etching undercut was controlled within a very small range (<50nm) because the Au layer above had formed a protective layer. The etching solution caused almost no damage to the electroplated Au and the underlying passivation layer. Example 2 Step 1: Photolithography pattern is made on the front side of gallium arsenide epitaxial layer by photolithography, photoresist coating, exposure and development process. Then, metal contact layer is deposited by electron beam evaporation, and the photoresist and contact metal layer in non-metallic areas are removed by wet stripping. Finally, metal alloy is formed by RTP high temperature alloying. Step 2: Deposit a layer of SiN based on Step 1. x Protective layer, SiN x With a refractive index of 2±0.02 and an N / Si ratio of 1.1-1.4, the metal contact layer is protected. Step 3: On the silicon nitride mask layer, the photolithography process of photoresist / exposure / development is performed again to create the photolithography pattern. Then, the silicon nitride is first etched with gases such as CF4 / O2 using a dry etching method. Then, the gallium arsenide epitaxial layer is etched with Mesa mesa using a photoresist / silicon nitride double mask to form a Mesa etching mesa, exposing the high aluminum layer on the side of the epitaxial material. Then, the aluminum oxide confinement layer is formed by wet oxidation process. Step 4: Based on Step 3, deposit a second SiNx protective layer to passivate the wafer surface and protect the surface and sidewalls. Then, use a dry etching process to create vias to expose the contact metal layer. Step 5: Use a magnetron sputtering device to sputter TiW / Au metal from the front to form a seed gold layer, and spin-coat photoresist on the TiW / Au metal layer. Through the processes of homogenization, exposure and development, and hardening, a photoresist mask with the target electrode pattern is formed. Step 6: Perform selective thick gold plating on the photolithographic mask pattern from Step 5; remove the photoresist mask layer after plating is complete. Step 7: Remove the composite gold layer from the non-electroplated areas.
[0031] Example 3 Based on Example 2, step 6 is as follows: Option 1: Use wet method to remove Au, and dry method + wet method to remove TiW; Step 1, Wet etching: The seed gold layer metal is etched using a potassium iodide (KI) solution with a certain ratio to remove the upper seed gold layer (Au) and expose the lower titanium-tungsten (TiW) metal. Step 2: A dry etching method is used, employing etching gases such as chlorine and argon in varying proportions. This method combines chemical and physical etching techniques to remove most of the TiW metal. This step utilizes plasma dry etching, such as RIE, IBE, or ICP. Dry etching minimizes anisotropic lateral etching, accurately replicating the sidewall morphology of the photoresist pattern and significantly reducing lateral corrosion.
[0032] Step three involves a wet etching process using hydrogen peroxide (H2O2) solution or other highly selective wet etching solutions suitable for TiW etching to wet-etch the remaining small portion of the TiW metal layer. Because the sidewalls of the upper metal layer are etched using a dry etching method, the metal morphology is good, there is no lateral etching, and the coverage of the lower metal layer is good. The wet etching solution, hydrogen peroxide (H2O2), does not etch gold; the solution can only attack the adhesion layer laterally from the TiW layer. This avoids the lateral etching that exposes the TiW metal after etching Au in traditional wet etching, and avoids excessive etching of the seed gold layer, fundamentally solving the under-cut problem. This method avoids the etching damage to the substrate material caused by dry etching, controls the lateral etching caused by isotropic wet etching, avoids erosion and metal residue at the root of the electroplated pattern, reduces the risk of short circuits and interface defects, and keeps the metal size within a safe range.
[0033] Example 4 Based on Example 2, step 6 is as follows: Option 2: Dry removal of Au, combined with dry and wet removal of TiW; Step 1: Use dry etching methods such as RIE, IBE, ICP, etc. Use gases such as chlorine and argon to etch away all the upper metal Au, and use the OES endpoint monitoring function to set the etching termination point to precisely control the etching endpoint and avoid over-etching affecting other areas of metal. Step 2: Then select the matching menu and use the dry etching method to etch away most of the underlying TiW metal. Step 3: For the remaining small portion of the gold metal, a high-selectivity chemical solution, such as hydrogen peroxide or other chemical solutions that can corrode the matching metal, is used to remove the remaining metal layer by wet etching. This simplifies the process, avoids the etching of the substrate material by dry etching, and controls the lateral etching caused by isotropic wet etching, keeping the lateral etching within a safe range.
[0034] Example 5 Based on Example 2, step 6 is as follows: Option 3: Dry etching of Au and most of TiW in one step, followed by wet etching to remove the remaining small portion of the gold seed layer. Step 1: Use dry etching methods such as RIE, IBE, ICP, etc., and use gases such as chlorine to etch away the first layer of metal and the second layer of metal. Step 2: The remaining small portion of seed gold metal is removed by wet etching using a high-selectivity chemical solution such as hydrogen peroxide or other chemical solutions that can corrode the matching metal. This simplifies the process, avoids the etching of the substrate material by dry etching, and keeps the side etching caused by isotropic wet etching within a safe range.
[0035] like Figure 2 This is a schematic diagram of the cross-sectional structure of the device before etching; the gold seed layer is exposed on the surface in the non-electroplated areas. Figure 1 and Figure 3 The image shown is a cross-sectional view of the device after etching (wet etching, unmodified), showing that the side of the seed gold layer is etched; as shown... Figure 4 The image shown is a cross-sectional view of the device after etching (the improved dry + wet etching method of this invention). The side of the seed gold layer is well protected and no lateral erosion has occurred.
[0036] Example 6 The method for composite etching of electroplated gold seed layer of the present invention includes the following steps: Step 1: Photolithography pattern is made on the front side of gallium arsenide epitaxial layer by photolithography, photoresist coating, exposure and development process. Then, a metal contact layer Ti / Pt / Au is deposited by electron beam evaporation. The photoresist and contact metal layer in the non-metallic area are removed by wet stripping. Finally, a metal alloy is formed by RTP high temperature alloying. Step 2: Deposit a layer of SiN based on Step 1. x A protective mask layer is used to perform Mesa mesa etching on the gallium arsenide epitaxial layer to form a Mesa etching mesa, exposing the high aluminum layer on the side of the epitaxial material, and then forming an aluminum oxide confinement layer using a wet oxidation process. Step 3: Deposit a second layer of SiN based on Step 2 x A protective mask layer is used to passivate the surface of the wafer, and then a dry etching process is used to create vias to expose the metal contact layer. Step 4: Use magnetron sputtering equipment to sputter TiW / Au metal from the front to form a seed gold layer. The thickness of the seed gold layer is selected according to actual needs. Photoresist is then spin-coated on the seed gold layer. Through homogenization, exposure and development, and hardening processes, a photoresist mask with the target electrode pattern is formed. Step 5: Perform selective electroplating of thick gold on the photoresist mask pattern from Step 4; remove the photoresist mask layer after electroplating is complete. Step 6: Remove the gold layer from the non-electroplated areas.
[0037] Step 6.1: Wet etching of the seed gold layer using potassium iodide solution (KI) to remove the upper seed gold layer (Au) and expose the lower titanium-tungsten (TiW) metal layer; optical emission spectroscopy (OES) is used to monitor the disappearance of Au characteristic spectral lines and precisely control the etching endpoint. Step 6.2: Most of the TiW metal is removed by inductively coupled plasma etching (ICP). The ICP process parameters are as follows: Cl2 flow rate of 30 sccm, BCl3 flow rate of 10 sccm, ICP power of 500 W, bias power of 100 W, pressure of 5 mTorr, and temperature of 40°C.
[0038] Step 6.3: Then, a wet etching process is used, in which hydrogen peroxide solution is used to wet etch the remaining small portion of the TiW metal layer.
Claims
1. A method for electroplating a gold layer and then etching it, characterized in that, The electroplated metal seed layer in non-electroplated areas is etched by combining dry etching and wet etching methods to remove the seed layer in non-electroplated areas, achieving good anisotropic etching and controlling the lateral corrosion of the seed layer.
2. The method for composite etching of electroplated gold layers as described in claim 1, characterized in that, Specifically, the following steps are included: Step 1: Photolithography pattern is made on the front side of gallium arsenide epitaxial layer by photolithography, photoresist coating, exposure and development process. Then, metal contact layer is deposited by electron beam evaporation, and the photoresist and contact metal layer in non-metallic areas are removed by wet stripping. Finally, metal alloy is formed by RTP high temperature alloying. Step 2: Deposit a layer of SiN based on Step 1. x A protective mask layer is used, with x ranging from 1.1 to 1.
4. Mesa mesa etching is performed on the gallium arsenide epitaxial layer to form a Mesa etching mesa, exposing the high aluminum layer on the side of the epitaxial material. An aluminum oxide confinement layer is then formed using a wet oxidation process. Step 3: Deposit a second layer of SiN based on Step 2 x A protective mask layer is used to passivate the surface of the wafer, and then a dry etching process is used to create vias to expose the metal contact layer. Step 4: TiW / Au metal is sputtered from the front using a magnetron sputtering device to form a seed gold layer. Photoresist is then spin-coated onto the seed gold layer. Through homogenization, exposure and development, and hardening processes, a photoresist mask with the target electrode pattern is formed. Step 5: Perform selective electroplating of thick gold on the photoresist mask pattern from Step 4; Remove the photoresist mask layer after electroplating; Step 6: Use a combination of dry etching and wet etching to remove the seed gold layer in the non-electroplated areas.
3. The method for composite etching of electroplated gold seed layer as described in claim 2, characterized in that, The metal contact layer includes any one or a combination of Ti / Pt / Au, Ni / Ge / Au, and Pd / Ge / Ti / Pt / Au.
4. The method for composite etching of electroplated gold seed layer as described in claim 2, characterized in that, The TiW layer has a thickness of 50 nm ± 10 nm, and the Au layer has a thickness of 150 ± 20 nm.
5. The method for composite etching of electroplated gold seed layer as described in claim 4, characterized in that, Step 6 is as follows: Step 6.1: Perform wet etching on the seed gold layer to remove the upper seed gold layer Au and expose the lower metal TiW layer; Step 6.2: Remove most of the TiW metal using a dry etching method. The dry etching method uses one or both of chlorine and argon. Step 6.3: Then, a wet etching process is used, in which hydrogen peroxide solution is used to wet etch the remaining small portion of the TiW metal layer.
6. The method for composite etching of electroplated gold seed layer as described in claim 5, characterized in that, The dry etching described in step 6.2 can be performed using reactive ion etching (RIE), ion beam etching (IBE), or inductively coupled plasma etching (ICP).
7. The method for composite etching of electroplated gold seed layer as described in claim 5, characterized in that, In step 6.1, wet etching uses a diluted HF solution or an alkaline hydrogen peroxide solution containing a complexing agent; the mass ratio of HF, H2O2, and H2O in the HF solution is 1:1:50; in step 6.1, optical emission spectroscopy (OES) is used to monitor the disappearance of Au characteristic spectral lines to precisely control the etching endpoint.
8. The method for composite etching of electroplated gold seed layer as described in claim 6, characterized in that, If inductively coupled plasma etching (ICP) is used, the Cl2 flow rate is 30±2 sccm, the BCl3 flow rate is 10±2 sccm, the ICP power is 500±5 W, the bias power is 100±2 W, the pressure is 5±0.5 mTorr, and the temperature is 40±2°C.
9. The method for composite etching of electroplated gold seed layer as described in claim 4, characterized in that, Step 6 is as follows: Step 6.1: Remove the top layer of metal Au and most of the metal TiW using a dry etching method; Step 6.2: Then use wet etching to remove the remaining TiW metal.
10. The method for composite etching of electroplated gold seed layer as described in claim 2, characterized in that, The TiW / Au can be replaced with Ti / Au, Cr / Au, Ni / Au, or TaN / Cu.