Semiconductor wafer glass is a core material for semiconductor products such as integrated circuits, optoelectronic devices, and microelectromechanical systems (MEMS). It possesses excellent light transmittance, insulation, thermal stability, and dimensional accuracy, and is widely used in critical components such as wafer substrates, packaging covers, and optical windows. As semiconductor process nodes continue to shrink, the size of wafer glass gradually increases while its thickness continues to decrease. Its surface is susceptible to damage such as scratches, abrasion, and contamination. Furthermore, during processing such as cutting, grinding, coating, and bonding, it must withstand complex conditions including temperature changes, mechanical stress, and chemical environments. This places increasingly stringent requirements on the protective films used for its surface protection.
The protective film, precisely adhered to the surface of the wafer glass, forms a temporary protective barrier. It effectively isolates external contaminants such as dust, metal particles, and moisture, mitigates mechanical impact and friction damage during processing, and suppresses the risk of device breakdown caused by static electricity accumulation. Simultaneously, it must be adaptable to the specific requirements of different processing techniques and be able to be peeled off without residue or damage after the process is completed. Currently, the rapid development of the semiconductor industry is driving the upgrading of wafer glass towards higher purity, higher flatness, ultra-thinness, and larger sizes. Traditional protective films are no longer sufficient to meet the protection requirements of high-end wafer glass, resulting in problems such as residue, scratches, and poor compatibility, which seriously affect the yield and reliability of semiconductor devices. Therefore, clarifying the core requirements of semiconductor wafer glass for protective films and developing high-performance, highly adaptable protective film materials has become an important support for the high-quality development of the semiconductor industry chain. This article discusses in detail the various requirements of the protective films needed for semiconductor wafer glass, based on its characteristics and processing technology.
1. Core Characteristics and Protection Requirements of Semiconductor Wafer Glass The material characteristics and application scenarios of semiconductor wafer glass determine its core protection requirements for protective films, which is the basis for clarifying the requirements of protective films. Semiconductor wafer glass is mostly made of high-purity quartz glass, borosilicate glass, etc., and has the following key characteristics: First, it has extremely high surface flatness, with roughness typically controlled at the nanometer level. The surface is free of any micro-scratches, dents, or protrusions; otherwise, it will affect the precision of subsequent processes such as coating and photolithography. Second, it has excellent chemical stability, but is still somewhat sensitive to corrosive substances such as fluorides, strong acids, and strong alkalis. Simultaneously, the surface easily adsorbs dust, metal ions, and other contaminants from the air, which can cause malfunctions such as leakage and short circuits in semiconductor devices. Third, it has relatively low mechanical strength, especially ultra-thin wafer glass (thickness <100μm), which has weak impact and wear resistance, making it prone to breakage and chipping during processing and transportation. Fourth, it has excellent insulation properties, but is prone to static electricity. Static electricity accumulation can attract microparticles and may also damage the sensitive structures on the wafer glass surface. Fifth, it has extremely high dimensional accuracy. The dimensional deviation of large-size wafer glass (such as 12 inches and above) must be controlled at the micrometer level, and the bonding of the protective film must avoid stress to prevent warping and deformation of the wafer glass.
Based on the above characteristics, the core protective requirements for protective films on semiconductor wafer glass can be summarized in four points: First, contamination protection, preventing external contaminants such as dust, metal ions, water vapor, and organic matter from adhering to the wafer glass surface; second, damage protection, avoiding scratches, breakage, or chipping of the wafer glass surface caused by mechanical friction, impact, and squeezing during processing and transportation; third, electrostatic protection, suppressing static electricity generated during the bonding and peeling of the protective film to the wafer glass, preventing electrostatic adsorption of contaminants or breakdown of the device structure; and fourth, process compatibility, adapting to the temperature and chemical environment requirements of different processing techniques such as cutting, grinding, coating, photolithography, and bonding, ensuring smooth process execution, and leaving no residue or damage after peeling. These protective requirements directly determine the specific requirements for the protective film in terms of physical properties, chemical properties, cleanliness, and process compatibility.
2. Core Requirements for Protective Films on Semiconductor Wafer Glass
2.1 Physical Performance Requirements
The physical properties of the protective film are fundamental to effective protection of the wafer glass, directly affecting the protective effect and processing compatibility. These mainly include thickness accuracy, flatness, mechanical strength, adhesive properties, and electrostatic properties.
Thickness accuracy and flatness are among the core physical indicators of the protective film. Semiconductor wafer glass has extremely high surface flatness, requiring the protective film to perfectly adhere to it without bubbles or wrinkles. This necessitates excellent thickness uniformity, with thickness deviation controlled within ±2μm to avoid uneven thickness leading to poor adhesion, bubbles, or stress, which could cause warping or deformation of the wafer glass. Simultaneously, the surface flatness of the protective film must match that of the wafer glass, with a roughness not exceeding half that of the wafer glass surface to prevent protrusions on the protective film surface from scratching the wafer glass surface. Furthermore, the thickness of the protective film needs to be adapted to the thickness of the wafer glass and the processing technology. Ultra-thin wafer glass requires a thinner protective film to reduce the overall thickness after lamination and avoid affecting subsequent processing operations. Protective films used in cutting and grinding processes need to have a certain thickness to provide sufficient mechanical support and prevent wafer glass breakage.
In terms of mechanical strength, the protective film must have good tensile, tear, and abrasion resistance. During wafer glass cutting and grinding, the protective film needs to withstand certain mechanical stress. If the tensile strength is insufficient, it is prone to breakage; if the tear resistance is poor, the protective film will be damaged and lose its protective function; if the abrasion resistance is poor, scratches will easily appear on the protective film surface, which will then transfer to the wafer glass surface, causing damage. Typically, the tensile strength of the protective film needs to be ≥15MPa, the tear strength ≥50N/m, and the surface hardness needs to be moderate—it needs to have a certain degree of abrasion resistance but not be too hard to avoid scratching the wafer glass during lamination and peeling. For protective films used on ultra-thin wafer glass, good flexibility is also required to ensure a tight fit to the curved surface of the wafer glass (if any) during lamination, while avoiding excessive lamination stress.
Adhesive properties are a key performance characteristic of the protective film, directly affecting lamination stability and peel safety. A balance must be achieved between "firm adhesion and residue-free peeling." During the lamination stage, the protective film must possess suitable adhesiveness to adhere tightly to the wafer glass surface without bubbles or lifting. Simultaneously, the adhesiveness must be evenly distributed to avoid insufficient adhesion in some areas leading to weak adhesion, or excessive adhesion in others causing peeling difficulties. Depending on the processing technology, the adhesiveness of the protective film needs precise control: For protective films used in storage and transportation, moderate adhesiveness (10-20 g/in) is required to ensure a firm adhesion and leave no residue upon peeling; for protective films used in cutting and grinding processes, higher adhesiveness (40-100 g/in) is needed to provide sufficient holding force to prevent wafer displacement and scattering during processing, reducing breakage during cutting; while for protective films used in photolithography and coating processes, lower adhesiveness (5-10 g/in) is required to avoid damage to sensitive structures or photoresist layers on the wafer surface during peeling. Furthermore, the adhesiveness of the protective film must have good stability, with changes in adhesiveness not exceeding 10% under different temperature and humidity environments to prevent adhesion failure or peeling residue due to environmental changes. It is worth noting that UV-type protective films need to have high adhesiveness before UV irradiation, and the adhesiveness needs to decrease significantly after irradiation (to below 2-5 g/in) to ensure that the wafer does not scatter or leave residue during pickup. Simultaneously, the UV reaction time needs to be rapid to improve processing efficiency.
In terms of electrostatic properties, the protective film must possess excellent antistatic capabilities to suppress the generation and accumulation of static electricity. Semiconductor wafer glass is prone to static electricity, which can attract contaminants such as fine dust and metal particles from the air. It may also damage sensitive structures on the wafer glass surface, affecting the performance of semiconductor devices. Therefore, the protective film must have antistatic properties, with a surface resistance controlled within the range of 10⁶-10⁹Ω. The electrostatic voltage generated during bonding and peeling must be ≤500V to avoid static accumulation. Furthermore, the antistatic properties of the protective film must be durable and not fail due to environmental changes during storage and processing. Simultaneously, the antistatic agent must not migrate to the wafer glass surface to avoid contamination.
2.2 Chemical Performance Requirements Semiconductor wafer glass has low sensitivity to chemical substances, but the protective film may chemically react with the wafer glass or release chemicals causing contamination during bonding, processing, and storage. Therefore, the protective film must possess excellent chemical stability and low exudation to meet the chemical protection requirements of the wafer glass.
Firstly, the protective film must possess good chemical stability and not react chemically with the semiconductor wafer glass. The main component of wafer glass is silicon dioxide. The substrate and adhesive layer of the protective film must avoid containing corrosive substances such as fluorides, strong acids, and strong alkalis. Otherwise, they will react with the wafer glass surface, leading to corrosion, discoloration, and increased roughness, affecting the precision of subsequent processes and device performance. Simultaneously, the protective film must be able to withstand the chemical environment during semiconductor processing, such as photoresist and developer in photolithography, and organic solvents and deionized water in cleaning processes, without dissolving, deforming, or aging, ensuring the stability of its protective function. For example, protective films used in wafer glass thinning and dicing processes must have good acid and alkali resistance, able to withstand acid and alkali solutions that may be encountered during processing, without adhesive layer peeling or substrate damage.
Secondly, the protective film must have low leaching properties, not releasing any contaminants. If the substrate and adhesive layer of the protective film contain easily leached substances, such as plasticizers, stabilizers, or residual solvents, these substances will migrate to the wafer glass surface, forming contaminants and causing malfunctions such as leakage and short circuits in semiconductor devices. Therefore, the protective film must strictly control the content of precipitates to ensure no volatile organic compounds (VOCs), no siloxanes, and no metal ions (such as Na⁺, K⁺, etc.) are released. The metal ion content must be controlled at the ppb level to avoid affecting the electrical characteristics of CMOS and capacitor devices. Simultaneously, the adhesive layer of the protective film must possess good stability, leaving no residue after peeling. The residue rate must be controlled below 0.01%, otherwise, the residue will adsorb contaminants or affect the precision of subsequent coating, photolithography, and other processes. Furthermore, the protective film must avoid containing heavy metals, harmful organic pollutants, and other environmental pollutants, meeting the environmental protection requirements of the semiconductor industry.
Additionally, the protective film must possess good temperature resistance to adapt to temperature changes during semiconductor processing. The processing of semiconductor wafer glass (such as coating, bonding, and baking) typically requires operation at specific temperatures, generally ranging from -10℃ to 250℃. The temperature requirements vary depending on the process: back-grinding bonding usually requires 60–120℃, RDL processes can reach 120–200℃, and laser bonding and some temporary bonding/debonding processes can even exceed 250℃. Therefore, the protective film must maintain stable physical and chemical properties within this temperature range, without softening, deformation, aging, or decomposition, while maintaining consistent adhesion to prevent detachment or residue due to temperature changes. For example, protective films used in high-temperature coating processes must have high-temperature resistance (≥200℃), not release harmful substances at high temperatures, and not react with the wafer glass; while protective films used for low-temperature storage must have low-temperature resistance (≤-10℃), without becoming brittle or cracking.
2.3 Cleanliness Requirements The surface cleanliness of semiconductor wafer glass directly determines the yield and reliability of semiconductor devices. Any minute contaminants (such as dust, metal particles, organic matter, etc.) can lead to device failure. Therefore, the protective film must possess extremely high cleanliness, not becoming a source of contamination itself, while effectively blocking external contaminants.
The cleanliness of the protective film is mainly reflected in three aspects: First, it must be free of contaminants. The production process of the protective film requires a high-cleanliness production environment (such as a Class 100 or Class 1000 cleanroom), strictly controlling the purity of raw materials such as substrates and adhesive layers to avoid impurities such as dust and metal particles. Simultaneously, the production process must avoid defects such as scratches, stains, and wrinkles on the surface of the protective film. The finished protective film must undergo rigorous cleanliness testing to ensure that there are no visible contaminants on the surface, with the number of microparticles (particle size ≥ 0.5 μm) ≤ 10 particles/m², and the number of metal particles (particle size ≥ 0.1 μm) ≤ 5 particles/m². Secondly, it must prevent dust shedding. The substrate and adhesive layer of the protective film must possess excellent stability, preventing dust or fiber shedding during lamination, peeling, and processing. This avoids dust adhering to the wafer surface and causing contamination. Thirdly, it must have contaminant blocking capabilities. The protective film must have excellent sealing properties, tightly covering the wafer surface after lamination without gaps or air bubbles, effectively blocking contaminants such as dust, moisture, and metal ions from the outside air, preventing them from adhering to the wafer surface.
Furthermore, the packaging of the protective film must meet cleanliness requirements, using high-cleanliness packaging materials (such as dust-free paper and dust-free plastic bags). Secondary contamination must be avoided during packaging. The finished protective film must be sealed and stored in a clean, dry, and contaminant-free environment to prevent contamination during storage. Simultaneously, the surface tension of the protective film must be uniform to prevent uneven surface tension from causing loose adhesion, air bubbles, and subsequent contaminant adsorption. For high-end semiconductor wafer glass, the cleanliness of the protective film must meet the SEMI F57-0301 standard and ISO 14644-1 certification requirements to ensure it meets the production needs of high-end semiconductor devices.
2.4 Process Compatibility Requirements The processing flow of semiconductor wafer glass is complex, encompassing multiple steps such as dicing, grinding, coating, photolithography, bonding, and cleaning. Different processes have different requirements for the protective film; therefore, the protective film must possess good process compatibility to meet the specific needs of different processing techniques and ensure smooth process execution.
In the dicing process, the protective film must have good dicing adaptability, able to tightly adhere to the wafer glass surface, providing sufficient support to prevent wafer glass displacement, chipping, and breakage during dicing. Simultaneously, the dicing process should not generate excessive dust, and the diced edges should be free of residual adhesive and burrs to avoid affecting subsequent chip pick-up processes. For DBG (Dual Cut Grinding) processes involving half-cut dicing followed by post-grinding, the protective film must effectively reduce defects such as back-side chipping, cracks, and chip edge breakage, ensuring the integrity of the die during dicing and preventing any die loss. Furthermore, the protective film must be easy to peel off after dicing, leaving no residue or damage and not affecting subsequent chip packaging.
During the grinding process, the protective film must possess good abrasion and impact resistance, able to withstand the mechanical friction and impact during grinding, preventing abrasive particles from scratching the wafer glass surface. Simultaneously, the protective film must have good sealing properties to prevent grinding fluid and particles from entering between the protective film and the wafer glass, causing contamination or scratches. For wafer back-side thinning processes, the protective film must have good adhesion stability, effectively supporting the ultra-thin wafer glass and reducing wafer warpage caused by stress. After the thinning process, residue-free peeling can be achieved through chemical treatment (such as alkaline solution treatment) or UV exposure, ensuring a clean and undamaged wafer surface after thinning. For example, a temporary protective film prepared using a photocurable liquid phase composition has good fluidity and strong adhesion, can uniformly cover the wafer surface, has good surface flatness after film formation, has little wafer warpage after back grinding, and can be peeled off with NaOH alkaline solution after processing, leaving no residue.
