A method for preparing a wafer surface metal IO pad

Abstract

The application discloses a kind of preparation methods of wafer surface metal IO pad, belong to semiconductor manufacturing technical field.The method includes the following steps: depositing barrier layer on wafer surface;Metal layer is deposited to form on barrier layer;Mask layer is deposited on metal layer;Etching forms PAD pattern;Local chemical mechanical polishing is carried out to PAD.It is optional, including: S1, wafer pretreatment: provide the semiconductor wafer that has completed front process, clean wafer surface, remove contaminant.The application is sequentially innovated by "TiN-cold AL-dielectric mask", and the low pressure, low speed Touch-up CMP designed specially for finishing appearance is combined, the roughness of aluminum layer is reduced from source, the traditional TiN etching damage is avoided, and high-quality AL PAD top height flat, four around bonding surface smooth transition appearance can be accurately obtained.The method process has strong compatibility, high stability, can significantly improve bonding reliability, and can be applied to surface improvement of other metal pad.

Description

Technical Field

[0001] This invention relates to the field of semiconductor manufacturing technology, specifically to a method for preparing wafer surface metal input / output (IO) pads for heterogeneous integration, and more particularly to a preparation process that can significantly improve the surface morphology and flatness of aluminum (AL) pads and enhance the reliability of package bonding. Background Technology

[0002] In the back-end manufacturing process of semiconductor devices, metal I / O pads (such as AL PAD aluminum pads) are key structures for achieving electrical connections and mechanical bonding between chips and external circuits. Their surface quality, including flatness, roughness, and edge morphology, directly affects the reliability of subsequent wire bonding or flip chip bonding, the stability of electrical connections, and the overall lifespan of the device.

[0003] Currently, the mainstream AL PAD fabrication process in the industry mostly adopts a "TiN / AL / TiN" (titanium nitride / aluminum / titanium nitride) sandwich structure, combined with thermal aluminum deposition technology. However, this traditional process has the following inherent drawbacks: First, during thermal aluminum deposition, aluminum atoms exhibit high surface mobility, which can easily lead to abnormally large grains and a high intrinsic surface roughness (Ra) of the AL layer. This inherent roughness is difficult to completely eliminate in subsequent processes, becoming a potential problem affecting the quality of the bonding interface.

[0004] Secondly, the etching process for the top TiN layer, which serves as both a hard mask and an antioxidant layer, is quite complex. During the dry etching process to remove excess TiN, etching residues are easily generated, causing physical or chemical damage to the surface of the underlying Al layer. This can lead to localized corrosion or micropits in the Al layer, further deteriorating the surface quality.

[0005] Finally, conventional chemical mechanical polishing (CMP) processes used to planarize surfaces typically employ relatively coarse parameters. While pursuing global planarization, it is difficult to precisely control the local flatness of the top region of the AL PAD and the smoothness of the transition between the surrounding sidewalls (i.e., the interface with the dielectric layer). This often leads to defects such as dishing at the PAD edges or scratching on the top, severely reducing the yield of the bonding process.

[0006] Therefore, the industry urgently needs a new fabrication method that can improve the surface quality of AL PADs from the source of the process, achieving high flatness, low roughness and excellent edge morphology, in order to meet the requirements of advanced packaging for high-reliability IO interfaces. Summary of the Invention

[0007] The purpose of this invention is to overcome the shortcomings of existing AL PAD fabrication processes, such as surface roughness, narrow process windows, and susceptibility to edge defects, and to provide a method for fabricating metal I / O pads on wafer surfaces. This method, through innovative process sequence, material selection, and precise morphology control techniques, aims to produce high-quality AL PADs with a flat top, smooth transitions at the perimeter, and extremely low surface roughness, thereby significantly improving the packaging bonding reliability and electrical performance of semiconductor devices.

[0008] To achieve the above objectives, the present invention adopts the following technical solution: A method for preparing a metal I / O pad on a wafer surface includes the following steps: Deposit a barrier layer on the wafer surface; A metal layer is deposited on the barrier layer; Deposit a mask layer on the metal layer; Etching forms the PAD pattern; The PAD was subjected to localized chemical mechanical polishing.

[0009] Optional, including: S1. Wafer pretreatment: Provide semiconductor wafers that have completed the front-end process, clean the wafer surface to remove contaminants; S2, Deposit TiN barrier layer: Deposit a TiN thin film as a barrier layer on the clean wafer surface; S3. Cold aluminum deposition to form an Al layer: An Al layer is formed on the TiN barrier layer using a cold aluminum deposition process; S4. Deposit mask layer: Deposit a mask layer on the AL layer; S5. Patterning: The mask layer, TiN barrier layer and part of the AL layer are patterned by photolithography and dry etching processes to form the preliminary structure of AL PAD. S6, Touch-up CMP (Local Chemical Mechanical Polishing): Performs light chemical mechanical polishing on the patterned AL PAD surface at low pressure and low speed; S7. Post-cleaning and drying: The polished wafer is cleaned and dried to obtain the final AL PAD structure.

[0010] Compared with the prior art, the beneficial effects of the present invention include: Surface quality improvement at its source: By adopting the core process sequence of "TiN → cold AL → SiO2", the cold aluminum deposition process is used to suppress AL grain coarsening, thereby reducing the intrinsic roughness of the AL layer from the source. At the same time, by replacing the traditional top-layer TiN with dielectrics such as SiO2 as a mask, the risk of damage to the AL surface caused by TiN etching is avoided.

[0011] Precise morphology control capability: The innovative Touch-up CMP process employs a gentle polishing parameter system with low pressure and low rotation speed designed for specific film structures (TiN / AL / SiO2). This process can precisely remove etching residues and surface micro-protrusions, while effectively avoiding edge collapse and surface scratches that are easily caused by conventional CMP. Ultimately, it achieves an ideal morphology with high flatness on the top of the AL PAD (flatness error ≤15Å) and regular rounded corners (rounded corner radius 50~100Å) around the perimeter.

[0012] Excellent process compatibility and stability: The PVD (Physical Vapor Deposition), PECVD (Chemical Vapor Deposition), dry etching, and CMP processes involved in this invention are all standard processes in semiconductor manufacturing and are fully compatible with existing production lines, requiring no additional dedicated equipment. Through precise matching and synergistic optimization of deposition temperature, gas flow rate, polishing parameters, etc., in each step, the reproducibility and stability of the entire process are significantly improved, and the process defect rate can be controlled below 0.5%.

[0013] Wide range of applications: This method is not only applicable to the preparation of AL PADs, but its core Touch-up CMP morphology control concept and process parameter system can also be applied to the surface improvement of other metal IO pads such as copper (CU) and gold (AU) after adaptation, and has broad industrial promotion value. Attached Figure Description

[0014] Figure 1 This is a process flow diagram of the wafer surface metal I / O pad preparation method in an embodiment of the present invention.

[0015] Figures 2 to 8 This is a schematic cross-sectional view of the process for preparing metal I / O pads on a wafer surface in an embodiment of the present invention.

[0016] Reference numerals: 10-Silicon wafer; 20-Barrier layer; 30-Aluminum layer; 40-Mask layer; 50-Mask pattern; 60-Aluminum pad. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.

[0018] The present invention provides a method for preparing a wafer surface metal I / O pad, comprising the following steps: Deposit a barrier layer on the wafer surface; A metal layer is deposited on the barrier layer; Deposit a mask layer on the metal layer; Etching forms the PAD pattern; The PAD was subjected to localized chemical mechanical polishing.

[0019] Example 1

[0020] This embodiment describes in detail a method for preparing an AL PAD (aluminum pad) using SiO2 (silicon dioxide) as a mask layer. Please refer to [link to relevant documentation]. Figure 1 The steps include: S1: Provide semiconductor wafers for surface cleaning.

[0021] Specifically, such as Figure 2 As shown, a silicon wafer 10 with completed front-end processes, such as transistor manufacturing and metal interconnects, is provided. First, the wafer is placed in a wet cleaning system and cleaned using a standard RCA cleaning process. For example, SPM (H2SO4 / H2O2) sulfuric acid-hydrogen peroxide mixture removes organic contaminants, DHF (diluted hydrofluoric acid) removes the native oxide layer, SC-1 (NH4OH / H2O2 / H2O) ammonia-hydrogen peroxide-water mixture (SC-1 cleaning solution) removes particles, and SC-2 (HCl / H2O2 / H2O) hydrochloric acid-hydrogen peroxide-water mixture (SC-2 cleaning solution) removes metal ions, resulting in a clean, hydrophilic wafer surface. After cleaning, the wafer is dried with high-purity nitrogen gas.

[0022] S2: Deposit a TiN barrier layer 20 on the surface of wafer 10.

[0023] Specifically, such as Figure 3 As shown, the pretreated wafer is transferred to the sputtering chamber of a physical vapor deposition (PVD) device, such as the Endura platform from Applied Materials. A TiN thin film is deposited as a barrier layer 20 using a DC magnetron sputtering process.

[0024] The specific process parameters are as follows: High-purity titanium (Ti) was used as the target material, and reactive sputtering was performed in a mixed atmosphere of high-purity argon (Ar) and nitrogen (N2). The Ar gas flow rate was set to 120 sccm, the N2 gas flow rate to 30 sccm, and the chamber pressure maintained at 3 mTorr. The applied sputtering power was 5 kW, and the substrate temperature was maintained at 180°C by controlling the heater on the wafer stage. Under these conditions, the deposition time was approximately 30 seconds, resulting in a dense and uniform TiN barrier layer with a thickness of approximately 70 Å (angstroms). This TiN layer exhibits good conductivity, excellent adhesion, and strong resistance to aluminum diffusion.

[0025] S3: An AL layer 30 is formed on the TiN barrier layer 20 using a cold aluminum deposition process.

[0026] Specifically, such as Figure 4As shown, in the same PVD equipment or another dedicated aluminum sputtering chamber, an aluminum layer is subsequently deposited on the TiN barrier layer without interrupting the vacuum or significantly increasing the temperature. To obtain a fine-grained aluminum film, this step employs a "cold aluminum" deposition process.

[0027] The specific process parameters are as follows: High-purity aluminum (Al) was used as the target material, and sputtering was performed in a high-purity Ar atmosphere. The Ar gas flow rate was set to 200 sccm, and the chamber pressure was maintained at 5 mTorr. The sputtering power was 8 kW. Crucially, by controlling the stage cooling system or using an unheated stage, the substrate temperature was maintained below 50°C (room temperature), thereby effectively suppressing aluminum atom surface migration and grain growth. The deposition time was approximately 60 seconds, forming an aluminum layer with a thickness of approximately 1000 Å. This "cold aluminum" layer has a finer and more uniform grain structure than traditional hot aluminum deposition, and the initial surface roughness is significantly reduced.

[0028] S4: Deposit a mask layer 40 on the AL layer.

[0029] Specifically, such as Figure 5 As shown, a wafer with an aluminum layer 30 deposited is transferred to a plasma-enhanced chemical vapor deposition (PECVD) apparatus. A silicon dioxide (SiO2) thin film is deposited on the surface of the aluminum layer 30 as a mask layer 40 for subsequent etching. In this embodiment, the material of the mask layer is SiO2, and the specific process parameters are as follows: silane (SiH4) and nitrous oxide (N2O) are used as reactant gases, and Ar is used as the carrier gas. The SiH4 flow rate is 200 sccm, the N2O flow rate is 400 sccm, and the Ar gas flow rate is 200 sccm. The chamber pressure is 2 Torr, and the radio frequency (RF) power is 300 W. The substrate temperature is set at 250°C. The deposition time is approximately 40 seconds, forming a SiO2 mask layer 40 with a thickness of approximately 60 nm. This temperature condition ensures good quality of the SiO2 thin film and is far below the recrystallization temperature of aluminum, thus preventing grain coarsening of the underlying aluminum layer.

[0030] S5: Perform photolithography and dry etching to form the AL PAD pattern.

[0031] This step is as follows: Figure 6 , Figure 7 As shown, it includes two sub-steps: photolithography and dry etching.

[0032] (1) Photolithography: such as Figure 6 As shown, positive photoresist is coated on the SiO2 mask layer 130, and exposure is performed using a stepper lithography machine with a mask having a defined AL PAD pattern. After development, a photoresist mask pattern 50 corresponding to the desired AL PAD pattern is formed on the SiO2 surface.

[0033] (2) Dry etching: Using photoresist as a mask, SiO2 is etched first. The wafer is placed in a reactive ion etching (RIE) apparatus, and etching is performed using a mixture of carbon tetrafluoride (CF4) and oxygen (O2). The CF4 flow rate is 50 sccm, the O2 flow rate is 10 sccm, the chamber pressure is 50 mTorr, and the RF power is 300 W. This formulation has a high etching rate for SiO2, while also having a high etching selectivity for the underlying aluminum and photoresist. Etching stops after penetrating the SiO2 mask layer.

[0034] Subsequently, the etching gas was changed, such as... Figure 7 As shown, the TiN layer is etched. Chlorine-based (Cl2 / BCl3) or fluorine-based (SF6) gas chemistry can be used. For example, a mixture of Cl2 (40 sccm) and BCl3 (20 sccm) gas is used at a chamber pressure of 30 mTorr and an RF power of 200 W. After etching through the TiN barrier layer 110, slight over-etching occurs because the underlying aluminum layer 120 also has an etching rate against the chlorine-based plasma, thus forming preliminary grooves at the bottom of the sidewalls of the ALPAD pattern. After etching, residual photoresist is thoroughly removed using oxygen plasma ashing and wet cleaning (such as a sulfuric acid-hydrogen peroxide mixture). At this point, a stacked structure consisting of the remaining SiO2 mask layer, TiN barrier layer, and aluminum layer remains on the wafer, representing the preliminary ALPAD pattern.

[0035] S6: Perform touch-up chemical mechanical polishing on the AL PAD.

[0036] Specifically, such as Figure 8 As shown, a crucial Touch-up CMP (local chemical mechanical polishing) process is performed on the patterned wafer. The purpose of this step is not global planarization, but to precisely remove the residual SiO2 mask layer on top of the AL PAD pattern, and simultaneously perform fine trimming and smoothing on the aluminum layer surface and sidewall transition area.

[0037] The wafer is mounted on a CMP device using a dedicated soft polishing pad. The polishing slurry is a key component; this embodiment uses a mild polishing slurry specifically formulated for aluminum and silicon oxide, containing oxidants and added corrosion inhibitors. More specifically, this embodiment employs the following process parameters and polishing slurry formulation: polishing pressure: 12 kPa; polishing pad rotation speed: 52 r / min; polishing slurry flow rate: 22 ml / min; polishing time: 3.5 min; polishing slurry: a mild polishing slurry containing 2 wt% H2O2 (2% hydrogen peroxide by mass), wherein the colloidal SiO2 particles have a particle size of 30 nm, and specific organic amine corrosion inhibitors are added.

[0038] Under these mild conditions, the polishing process can effectively remove SiO2 residues and perform micro- and uniform finishing on the aluminum surface, eliminating etching damage and naturally forming a smooth edge transition to avoid collapse.

[0039] S7: Clean and dry to obtain an AL PAD with a smooth surface and rounded edges.

[0040] Specifically, after CMP, cleaning and drying steps are performed. First, ultrasonic cleaning is used. The wafer is placed in an ultrasonic cleaner, and the cleaning medium is a mixture of deionized water and anhydrous ethanol at a volume ratio of 3:1, corresponding to claim 9. The specific ultrasonic cleaning parameters are: ultrasonic power set to 100 W, and cleaning time set to 4 minutes. Ultrasonic cleaning can effectively remove residual polishing liquid and particles from the surface. After cleaning, the wafer is rinsed with deionized water, spun dry in a rotary dryer, and finally dried in a low-pressure nitrogen atmosphere to obtain the final high-quality AL PAD aluminum bonding pad 60. Atomic force microscopy (AFM) shows that the surface roughness (Ra) of the AL PAD 150 prepared in this embodiment is less than 0.25 nm. Scanning electron microscopy (SEM) cross-sectional observation shows that its top flatness error is within 10 Å, and it forms a uniform rounded corner with a radius of about 80 Å at the interface with the surrounding dielectric layer 140.

[0041] Example 2

[0042] The difference between this embodiment and Embodiment 1 is that the material of the mask layer 40 in step S4 is replaced with silicon nitride (SiN). Specifically, in a PECVD (plasma-enhanced chemical vapor deposition) apparatus, SiH4 (silane), NH3 (ammonia), and N2 (nitrous oxide) are used as reactant gases to deposit a SiN layer with a thickness of approximately 55 nm as the mask layer at 220°C. In the dry etching step S5, a mixed gas of CHF3 (trifluoromethane) and O2 (oxygen) is used to etch the SiN layer, and the subsequent TiN etching is the same as in Embodiment 1. In the Touch-up CMP step S6, the polishing slurry needs to be adjusted to a formulation with a suitable selectivity ratio for SiN and Al, for example, using a polishing slurry with cerium oxide as the main abrasive, but the core low-pressure (10-15 kPa) and low-speed (50-55 r / min) process concept remains unchanged. Ultimately, an AL PAD with a smooth surface and rounded edges can be obtained, verifying that the "mask layer" in this invention is not limited to SiO2, but can be extended to other dielectric materials, which provides support for the possible interpretation scope of the claims.

[0043] Example 3

[0044] This embodiment focuses on the application and expansion of the method of the present invention in the preparation of copper (CU) PADs. The basic process follows the steps described in claim 1, with the main changes as follows: In step S2, the deposited barrier layer can be a Ta / TaN (tantalum / tantalum nitride) bilayer.

[0045] In step S3, a copper layer is deposited instead of cold aluminum deposition using electrochemical plating (ECP) or PVD processes.

[0046] In step S4, SiO2 or SiN is deposited as a mask layer.

[0047] In step S6, a Touch-up CMP polishing slurry specifically designed for copper and dielectric layers, containing oxidants and corrosion inhibitors, is used. However, gentle polishing parameters of low pressure (10-15 kPa) and low rotation speed (50-55 r / min) are applied to precisely finish the copper surface while removing mask residue, avoiding dish defects and corrosion. Results demonstrate that this Touch-up CMP method effectively improves the surface morphology of copper pads, enhancing their electromigration reliability and bonding performance. The polishing slurry and process parameters in Example 1 are applicable.

[0048] It should be noted that the above embodiments are merely preferred embodiments of the present invention and do not limit the scope of the patent. Any equivalent structural or procedural transformations made based on the description and drawings of this invention, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of this invention. For example, specific parameters such as temperature, pressure, flow rate, and thickness in each step can be reasonably adjusted within the range described in the invention; the mask layer material can also be other suitable media; cold aluminum deposition can also be replaced by other techniques capable of achieving fine-grained aluminum deposition (such as low-temperature crystal growth). These variations and improvements based on the core concept of this invention should all be considered to fall within the protection scope of this invention.

[0049] Benefiting from the teachings presented in the foregoing description and the accompanying drawings, those skilled in the art will conceive of many modifications and other embodiments of the invention set forth herein. Therefore, it should be understood that the invention is not limited to the specific embodiments disclosed, and that modifications and other embodiments are intended to be included within the scope of the appended claims. Although specific terminology is used herein, it is used only in a general and descriptive sense and is not intended to be limiting.

Claims

1. A method for preparing a metal I / O pad on a wafer surface, characterized in that, Includes the following steps: Deposit a barrier layer on the wafer surface; A metal layer is deposited on the barrier layer; Deposit a mask layer on the metal layer; Etching forms the PAD pattern; The PAD was subjected to localized chemical mechanical polishing.

2. The preparation method according to claim 1, characterized in that, Step S1: Provide a semiconductor wafer and perform surface cleaning; Step S2: Deposit a TiN barrier layer on the wafer surface; Step S3: An Al layer is formed on the TiN barrier layer using a cold aluminum deposition process; Step S4: Deposit a mask layer on the AL layer; Step S5: Perform photolithography and dry etching to form an AL PAD pattern; Step S6: Perform localized chemical mechanical polishing on the AL PAD; Step S7: Clean and dry to obtain an AL PAD with a smooth surface and rounded edges.

3. The preparation method according to claim 2, characterized in that, The TiN barrier layer is deposited at a temperature of 150~200℃ and a thickness of 50~100Å, using a magnetron sputtering process with an argon flow rate of 100~150sccm and a target-substrate distance of 18~22cm.

4. The preparation method according to claim 3, characterized in that, The cold aluminum deposition process employs magnetron sputtering, with a deposition temperature ranging from room temperature to 100°C and an AL layer thickness of 500~2000 Å.

5. The preparation method according to claim 3, characterized in that, The mask layer is made of SiO2, and the deposition temperature of the SiO2 mask layer is 200~300℃, the thickness is 50~100nm, and the PVD or PECVD process is used. The flow rate of the argon protective gas is 150~250sccm.

6. The preparation method according to claim 5, characterized in that, The dry etching process employs reactive ion etching, sequentially etching the SiO2 layer and the TiN layer, with the etching gas consisting of a mixture of CF4 and O2.

7. The preparation method according to claim 1, characterized in that, The deposited barrier layer is a Ta / TaN bilayer; Copper layers are deposited using electrochemical plating (ECP) or PVD processes; SiO2 or SiN is deposited as a mask layer.

8. The preparation method according to claim 1, characterized in that, The localized chemical mechanical polishing uses a mild polishing slurry containing an oxidant and a corrosion inhibitor.

9. The preparation method according to claim 1, characterized in that, The process parameters for the localized chemical mechanical polishing include: Polishing pressure: 10~15KPa; Polishing disc rotation speed: 50~55 r / min; Polishing fluid flow rate: 20~25ml / min; Polishing time: 2~5 minutes; The polishing slurry is a mild polishing slurry containing 2% H2O2, with SiO2 particles having a diameter of 20~40nm, and corrosion inhibitors are added.

10. The preparation method according to claim 1, characterized in that, The cleaning in step S7 is performed using ultrasonic cleaning, and the cleaning medium is a mixture of deionized water and ethanol.

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