Semiconductor silicon wafer thinning process based on chemical mechanical cooperation and multi-step stress management

Abstract

The invention relates to a semiconductor silicon wafer thinning process based on chemical-mechanical coordination and multi-step stress management, which belongs to the technical field of semiconductor manufacturing and comprises the following operation steps: 1, a chemical-mechanical coarse grinding stage: thinning the back surface of a silicon wafer by using a fixed abrasive grinding wheel and a chemical active grinding fluid; and 2, an in-situ stress management relay layer coating and curing stage: coating and curing a polymer film on the back surface of the thinned silicon wafer in situ to serve as a stress management relay layer. And 3, a chemical mechanical accurate grinding and relay layer synchronous removal stage: performing accurate grinding on the silicon wafer covered with the relay layer by using a fine-grained grinding material and a chemical active medium, and synchronously realizing refining of the surface of the silicon wafer and complete removal of the relay layer. By introducing a chemical activation step and a stress management relay layer, pure mechanical removal is converted into chemically-assisted plastic domain removal, and processing stress is actively managed, so that efficient, low-damage and low-stress thinning is realized in a single device or process sequence.

Description

Technical Field

[0001] This invention relates to the field of semiconductor manufacturing technology, and more specifically to a semiconductor silicon wafer thinning process based on chemical-mechanical synergy and multi-step stress management. Background Technology

[0002] As chips evolve towards advanced packaging methods such as 3D stacking, silicon wafers need to be thinned to 100 micrometers or even less than 50 micrometers. Traditional thinning processes mainly rely on purely mechanical grinding, which presents the following inherent challenges: (1) Depth of mechanical damage layer: The rough grinding stage inevitably generates a large number of microcracks, dislocations and fragmentation layers on the surface and subsurface of the silicon wafer. This damage layer must be removed by subsequent polishing (CMP), which not only increases the number of process steps and costs, but also leads to additional material loss.

[0003] (2) Residual stress and warping: Severe mechanical grinding will introduce huge compressive and tensile stresses into the silicon wafer, causing severe warping of the silicon wafer after processing or after release from the carrier, which brings a very high risk of wafer breakage to subsequent transport, cleaning and processing.

[0004] (3) The contradiction between efficiency and quality: Using large-particle abrasives and high-speed grinding to improve efficiency will aggravate damage and stress; while using fine-particle abrasives and slow grinding to pursue quality will result in low efficiency and high cost.

[0005] (4) Process discretization: The steps of rough grinding, fine grinding, polishing, etc. are usually discrete and require switching between different equipment, which increases the production cycle and the risk of interface contamination.

[0006] Using traditional pure water grinding technology, after coarse grinding (#600) to 60μm, the silicon wafer showed obvious warping and a relatively deep damage layer (approximately 5μm). Subsequent offline CMP for a long time is required to achieve a similar surface roughness, and the total breakage rate is several times higher.

[0007] While existing technologies have made improvements to grinding wheels or polishing fluids, most have not been systematically optimized from the perspective of the synergy between chemical reactions and physical processes throughout the entire process chain. As a result, it is difficult to fundamentally suppress the generation of damage and stress while ensuring efficiency. Summary of the Invention

[0008] This invention addresses the shortcomings of existing technologies by providing a semiconductor silicon wafer thinning process based on chemical-mechanical synergy and multi-step stress management. By introducing a chemical activation step and a stress management relay layer, it transforms pure mechanical removal into chemically assisted plastic domain removal and actively manages processing stress, thereby achieving efficient, low-damage, and low-stress thinning within a single device or process sequence.

[0009] The above-mentioned technical problems of the present invention are mainly solved by the following technical solutions: A semiconductor silicon wafer thinning process based on chemical-mechanical synergy and multi-step stress management includes the following steps: Step 1: Chemical mechanical grinding stage, using bonded abrasive wheels and chemically active polishing slurry to thin the back side of the silicon wafer. The chemically active polishing slurry contains abrasive, pH adjuster and oxidant.

[0010] Nanoscale or microscale abrasives (such as diamond and cerium oxide).

[0011] pH adjuster is used to adjust the grinding slurry to a weakly alkaline environment (pH 8-11), preferably TMAH (tetramethylammonium hydroxide) or KOH.

[0012] Oxidizing agents, such as hydrogen peroxide or permanganate, are used to create a softer, more easily removable chemically modified silica layer on the silicon surface.

[0013] Surfactants ensure the effective removal of the modified layer and reaction products.

[0014] At this stage, mechanical grinding and chemical corrosion work together: the mechanical force of the grinding wheel continuously removes the soft modified layer generated by the chemical liquid, exposing a new silicon surface to continue the reaction. This "chemical-mechanical" coupling effect significantly reduces the required mechanical cutting force, allowing more material removal to occur in the "quasi-plastic domain". This results in efficient material removal while significantly reducing the depth of the subsurface damage layer.

[0015] Step 2: In-situ stress management relay layer coating and curing stage. A polymer film is coated and cured in-situ on the back of the thinned silicon wafer as a stress management relay layer.

[0016] After rough grinding, the silicon wafer remains on the thinning machine and is not unloaded. A transparent, photocurable or thermocurable polymer film is coated in situ on the back of the thinned silicon wafer using an integrated spraying system as a stress management relay layer.

[0017] This intermediate layer material possesses moderate flexibility and high adhesion, with a Young's modulus between that of silicon and subsequent abrasive particles. Its functions include: filling surface microcracks and preventing their propagation under external forces; uniformly dispersing localized stresses applied in subsequent processing steps, acting as a "stress buffer"; and providing additional rigid support overall, effectively suppressing warping of the ultrathin silicon wafer during subsequent processing.

[0018] Step 3: Chemical mechanical grinding and simultaneous removal of the relay layer stage. Fine-grained abrasive and chemically active media are used to grind the silicon wafer covered with the relay layer, so as to simultaneously refine the surface of the silicon wafer and completely remove the relay layer.

[0019] Using finer-grit bonded grinding wheels or polishing pads, and a chemically active polishing slurry with a similar chemical composition but adjusted concentration to that used in the chemical mechanical grinding (CMP) coarse grinding stage, the silicon wafer covered with the relay layer is finely ground. This stage is a simultaneous dual-objective process: the fine grinding process further removes the trace damage layer left by the CMP coarse grinding stage, achieving nanoscale surface roughness. At the same time, mechanical action synchronously and uniformly removes the relay layer.

[0020] Because the relay layer is a flexible polymer, its removal rate is much higher than that of silicon, thus not affecting the final thickness accuracy of the silicon wafer. The result is a final silicon wafer with an ultra-smooth surface, extremely low damage, and effectively released residual stress.

[0021] Preferably, the chemically active grinding fluid is weakly alkaline and contains hydrogen peroxide as an oxidant.

[0022] Preferably, the stress management relay layer in the in-situ stress management relay layer coating and curing stage is a transparent polymer film that is UV-curable or thermosetting.

[0023] Preferably, the chemical mechanical grinding stage, the in-situ stress management intermediate layer coating and curing stage, and the chemical mechanical grinding and intermediate layer simultaneous removal stage are all completed continuously on the same thinning equipment.

[0024] As a preferred option, during the chemical mechanical coarse grinding stage and the chemical mechanical fine grinding and intermediate layer synchronous removal stage, the grinding parameters are controlled in real time by monitoring the spindle load or acoustic emission signal to maintain a stable chemical mechanical synergistic removal state.

[0025] Preferably, a grinding device is used for grinding in the chemical mechanical coarse grinding stage and the chemical mechanical fine grinding and intermediate layer synchronous removal stage; a spraying device is used for intermediate layer coating and a curing device is used for intermediate layer curing in the in-situ stress management intermediate layer coating and curing stage.

[0026] Preferably, the grinding device uses bonded abrasive wheels and chemically active grinding fluid, employing mechanical grinding to continuously remove the chemically softened surface layer, while fresh grinding fluid continuously reacts with the newly formed surface, forming an efficient "softening-removal" cycle.

[0027] The present invention can achieve the following effects: This invention provides a semiconductor silicon wafer thinning process based on chemical-mechanical synergy and multi-step stress management. Compared with the prior art, by introducing a chemical activation step and a stress management relay layer, pure mechanical removal is transformed into chemically assisted plastic domain removal, and processing stress is actively managed, thereby achieving efficient, low-damage, and low-stress thinning within a single device or process sequence.

[0028] Significantly reduces subsurface damage: Through the synergistic mechanism of "chemical modification-mechanical removal", the material removal mode in the rough grinding stage is changed from brittle fracture to plastic flow, which greatly reduces the generation and propagation of microcracks from the source and can reduce the depth of the damaged layer by more than 50%.

[0029] 2. Active stress management and warp suppression: The innovative in-situ stress management relay layer technology acts like a "built-in stress buffer," effectively absorbing processing stress and supporting the silicon wafer structure, significantly reducing warp during and after processing, and reducing the breakage rate by an order of magnitude.

[0030] 3. Improved process efficiency and integration: Chemical assistance improves material removal rate, while the integration of multi-step processes on a single equipment platform shortens the production cycle and reduces the cleanroom footprint and wafer handling risks.

[0031] 4. Achieving true surface smoothness: The fine grinding stage is carried out under the protection of the stress relay layer, which can more safely and effectively obtain a damage-free ultra-smooth surface, providing an ideal surface for subsequent metallization or bonding processes. Detailed Implementation

[0032] The technical solution of the invention will be further described in detail below through examples.

[0033] Example 1: A semiconductor silicon wafer thinning process based on chemical-mechanical synergy and multi-step stress management, comprising the following steps: Step 1: Chemical Mechanical Grinding Stage. This stage uses bonded abrasive wheels and a chemically active polishing slurry to thin the back side of the silicon wafer. The slurry contains abrasive particles, a pH adjuster, and an oxidizing agent. It is weakly alkaline and contains hydrogen peroxide as an oxidizing agent.

[0034] The hydrogen peroxide in the weakly alkaline polishing slurry reacts with the silicon wafer surface to form a soft silica hydrate layer. The abrasive grains of the bonded abrasive wheel efficiently scrape away this softened oxide layer. As the oxide layer is removed, the fresh silicon surface is exposed and immediately reacts with fresh polishing slurry, forming a continuous, efficient, and low-stress material removal process.

[0035] By monitoring the spindle load (reflecting cutting resistance) or acoustic emission signals (reflecting material fracture and friction state), the system can determine in real time whether the "softening-removal" process is in balance. If the load is too high, it indicates that the mechanical action is too strong and may damage the silicon wafer; if the load is too low, it indicates that the chemical action is too strong or the material removal rate is low. Based on this, the system automatically adjusts parameters such as pressure and speed to maintain the optimal synergy.

[0036] The goal is to efficiently remove most of the silicon material to achieve a thickness close to the target thickness.

[0037] Step 2: In-situ stress management relay layer coating and curing stage. A polymer film is coated and cured in-situ on the back of the thinned silicon wafer as a stress management relay layer. The stress management relay layer is a transparent polymer film that is UV-cured or thermosetting.

[0038] After rough grinding, the silicon wafer does not need to leave the vacuum or processing environment; it is directly coated by the spraying device within the equipment. This avoids pollution, particle adhesion, and secondary damage and efficiency loss caused by handling and cleaning due to atmospheric exposure. Rough grinding inevitably leaves microcracks and residual stress on the silicon wafer surface. This transparent polymer film (rapidly formed via UV or thermosetting equipment) can: Filling scratches: smoothing out the microscopic unevenness of the rough-ground surface, providing an ideal initial plane for subsequent fine grinding.

[0039] Stress buffering: As a soft intermediate layer, it can absorb and disperse the stress generated during fine grinding, preventing the microcracks generated in the rough grinding stage from continuing to expand during the fine grinding process.

[0040] Surface protection: Protects the active surface after coarse grinding during the waiting period before fine grinding.

[0041] The goal is to create a temporary protective and buffering layer on the back of the coarsely ground silicon wafer.

[0042] Step 3: Chemical mechanical grinding and simultaneous removal of the relay layer stage. Fine-grained abrasive and chemically active media are used to grind the silicon wafer covered with the relay layer, so as to simultaneously refine the surface of the silicon wafer and completely remove the relay layer.

[0043] Simultaneous removal: Fine grinding is performed using fine-grained abrasives and chemical media. This process simultaneously grinds two materials of different hardness: the upper polymer relay layer and the lower silicon wafer.

[0044] The "soft landing" effect: When fine grinding begins, it primarily acts on the softer intermediate layer. As the intermediate layer is gradually thinned and eventually completely removed, the pressure and chemical environment of the fine grinding process are at a very mild level. At this point, the fine grinding head seamlessly transitions to the final polishing of the silicon wafer surface, avoiding the severe impact and damage that could occur from directly grinding a rough silicon wafer.

[0045] During this stage, the spindle load or acoustic emission signal exhibits a characteristic change: the signal is weaker when grinding the relay layer and strengthens when it comes into contact with the silicon wafer. The control system can accurately capture this transition point and automatically adjust the grinding parameters to achieve a smooth and non-destructive transition from the relay layer to the silicon wafer.

[0046] The goal is to obtain a final mirror-like, ultra-low-damage surface and remove the temporary relay layer.

[0047] The chemical mechanical grinding (CMP) stage, the in-situ stress management intermediate layer coating and curing stage, and the CMP fine grinding and simultaneous intermediate layer removal stage are all continuously completed on the same thinning equipment. In the CMP coarse grinding and CMP fine grinding / simultaneous intermediate layer removal stages, a grinding device is used. This device employs bonded abrasive wheels and chemically active grinding fluid, using mechanical grinding to continuously remove the chemically softened surface layer, while fresh grinding fluid continuously reacts with the newly formed surface, forming an efficient "softening-removal" cycle. In the in-situ stress management intermediate layer coating and curing stage, a spraying device is used for intermediate layer coating, and a curing device is used for intermediate layer curing.

[0048] Example 2: Prepare an 8-inch silicon wafer with a thickness of 775μm, with the goal of thinning it to 50μm.

[0049] Stage S1: The silicon wafer is loaded onto the vacuum chuck of the thinning machine. A diamond grinding wheel with a grit size of #600 is used, and a chemically active polishing slurry (containing 1 wt% diamond micron powder, 2 vol% H2O2, 0.1 M TMAH, pH≈10.5, and a suitable amount of surfactant) is supplied. Rough grinding is performed to a thickness of 60 μm under parameters of 200 N pressure, 2000 rpm spindle speed, and 10 μm / min feed rate. This stage results in a high material removal rate, and due to the chemical softening effect, the spindle motor current is 15% lower than that of pure water grinding, indicating a lower cutting force.

[0050] Performing the S2 stage: After rough grinding, the silicon wafer is rotated on the machine and UV-curable acrylic resin is evenly sprayed onto the back side through an integrated nozzle to form a film of about 5μm thick, which is then cured by UV light.

[0051] Stage S3: Replace with a #3000 diamond grinding wheel and use a special fine-grinding chemical solution (H2O2 concentration reduced to 0.5 vol%, other components adjusted accordingly). Fine grinding is performed at a pressure of 50 N and a spindle speed of 2500 rpm. This process reduces the silicon wafer from 60 μm to the target 50 μm within 10 minutes, simultaneously removing the 5 μm thick polymer relay layer. After fine grinding, the surface roughness Ra < 5 nm, with no visible scratches.

[0052] In summary, this semiconductor silicon wafer thinning process based on chemical-mechanical synergy and multi-step stress management transforms pure mechanical removal into chemically assisted plastic domain removal by introducing a chemical activation step and a stress management relay layer, and actively manages processing stress, thereby achieving efficient, low-damage, and low-stress thinning within a single device or process sequence.

[0053] The core of this semiconductor silicon wafer thinning process lies in building a closed-loop, integrated, and intelligent processing system. It does not simply connect the three steps in series, but rather organically integrates rough grinding, stress management, and fine grinding through "in-situ" operation and "synchronous" removal, aiming to achieve efficient, low-damage, and high-flatness silicon wafer thinning.

[0054] Deep synergy between chemistry and mechanics: It is not just about chemical assistance to mechanics, but about forming a dynamic "softening-removal" cycle that maximizes material removal efficiency while minimizing mechanical damage.

[0055] Innovative active stress management: The introduction of the concept of a "stress management relay layer" transforms stress from passively being absorbed to actively buffering and releasing it, which is key to preventing thin silicon wafers from breaking and warping.

[0056] The entire process is integrated: coarse grinding, coating, curing and fine grinding are completed continuously in the same equipment, which completely breaks the equipment barriers of traditional processes and realizes "one-stop" processing.

[0057] Intelligent control based on real-time feedback: By using sensor signals to monitor and adjust process parameters in real time, the stability and repeatability of the entire process are ensured, which is a manifestation of the process moving from "automation" to "intelligence".

[0058] The above description is only a specific embodiment of the present invention, but the structural features of the present invention are not limited thereto. Any changes or modifications made by those skilled in the art within the scope of the present invention are covered by the patent scope of the present invention.

Claims

1. A semiconductor silicon wafer thinning process based on chemical mechanical synergy and multi-step stress management, characterized by The method comprises the following steps: First step: chemical mechanical rough grinding stage, using fixed abrasive grinding wheel and chemical active polishing liquid to thin the back surface of the silicon wafer, the chemical active polishing liquid contains abrasive, pH regulator and oxidant; Second step: in-situ stress management relay layer coating and curing stage, coating and curing a layer of polymer film as stress management relay layer on the back surface of the thinned silicon wafer in-situ; Third step: chemical mechanical fine grinding and relay layer synchronous removal stage, using fine abrasive and chemical active medium to fine grind the silicon wafer covered with the relay layer, and synchronously realizing the fine grinding of the surface of the silicon wafer and the complete removal of the relay layer.

2. The process of claim 1, wherein: The chemical active polishing liquid is weak alkaline and contains hydrogen peroxide as oxidant.

3. The process of claim 1, wherein: The stress management relay layer in the in-situ stress management relay layer coating and curing stage is a transparent polymer film which is ultraviolet cured or heat cured.

4. The process of claim 1, wherein: The chemical mechanical rough grinding stage, the in-situ stress management relay layer coating and curing stage and the chemical mechanical fine grinding and relay layer synchronous removal stage are continuously completed on the same thinning equipment.

5. The process of claim 1, wherein: In the chemical mechanical rough grinding stage and the chemical mechanical fine grinding and relay layer synchronous removal stage, the grinding parameters are controlled in real time through monitoring the spindle load or acoustic emission signal to maintain the stable chemical mechanical cooperative removal state.

6. The process of claim 1, wherein: In the chemical mechanical rough grinding stage and the chemical mechanical fine grinding and relay layer synchronous removal stage, the grinding device is used for grinding; In the in-situ stress management relay layer coating and curing stage, the spraying device is used for coating the relay layer and the curing device is used for curing the relay layer.

7. The process of claim 6, wherein the process further comprises: The grinding device uses fixed abrasive grinding wheel and chemical active polishing liquid, and the mechanical grinding continuously removes the chemically softened surface layer, while the fresh polishing liquid continuously reacts with the new surface to form an efficient "softening-removal" cycle.