In the microscopic world of semiconductor manufacturing, a wafer with a thickness of only 0.7 millimeters and a diameter of 300 millimeters carries the fate of hundreds of billions of transistors. Its manufacturing process is like dancing on the tip of a needle - from lithography exposure to thin film deposition, each step requires nanometer-level positional accuracy, micrometer-level angular consistency, and a zero-pollution transfer environment. Supporting this precise manufacturing chain are a series of "invisible key components": they may be calibrators hidden inside the equipment, or rotating shafts suspended on a gas film; they may be micro-forks made of ceramics, or nanometer-level motion stages driven by piezoelectric ceramics. The coordinated operation of these components constitutes the core code of the "precision genes" of semiconductor equipment. 

I. Wafer Aligner: The "Eyes" and "Brain" of Nanoscale Positioning 

Before the exposure of the photolithography machine, the wafer must be precisely aligned to the nanometer-level position of the mask, a process led by the wafer aligner. The core challenge lies in achieving sub-micron overlay accuracy in the presence of process deformations on the wafer surface (such as photoresist residue, film stress) and temperature fluctuations (±1℃ may cause 0.1μm deformation). 

Modern wafer aligners adopt a composite solution of "multi-wavelength interferometry + piezoelectric ceramic drive". Firstly, multi-wavelength light beams (such as He-Ne laser and infrared laser) are emitted by a laser interferometer and projected onto the reference marks (Alignment Mark) on the wafer surface. The X/Y position, rotation angle (θ), and flatness (Warp) of the wafer are calculated based on the interference fringes of the light. To eliminate the interference of environmental vibrations, the measurement system is usually equipped with an active vibration isolation platform, with an isolation accuracy of up to 0.1 μm/s².

More crucially, the driving part: the micro-motion stage of the aligner adopts a stacked structure of piezoelectric ceramics (PZT), achieving nanometer-level displacement (resolution up to 0.1 nm) through the inverse piezoelectric effect. To avoid mechanical clearance, the PZT drive end adopts a "flexible hinge" design, converting rigid transmission into elastic deformation to ensure motion without backlash. For instance, the wafer aligner of a certain advanced lithography machine can complete the measurement of 9 reference points within 3 seconds, with overlay accuracy stably within 1.5 nm - this is equivalent to finding the intersection point of two fine lines with a spacing of only 0.075 μm within the space of a human hair diameter (about 50 μm). 

II. Air Floatation Rotating Shaft: A Frictionless Rotating "Space Cabin" 

During the wafer exposure or measurement process, the wafer needs to rotate around a vertical axis to achieve multi-angle alignment or uniform process treatment. At this time, the air bearing rotary axis becomes a key execution component. Its core requirements are: rotational accuracy (radial/axial runout) < 0.1 μm, angular velocity fluctuation < 0.001°/s, and it must be able to bear the weight of the wafer (up to approximately 2 kg) without deformation. 

The "suspension" principle of the air-floatation rotating shaft is derived from air bearing technology: by injecting high-pressure air (0.1-0.5 MPa) between the shaft end and the bearing housing, a 0.01-0.05 mm air film is formed, completely separating the metal contact surfaces. This "non-contact support" completely eliminates mechanical friction, and theoretically has an infinite lifespan (only requiring regular filter replacement). However, achieving stable suspension is not simple - the thickness of the air film must be precisely controlled within 5-20 μm; too thin will cause contact wear, while too thick will reduce stiffness due to the compressibility of air.

To enhance dynamic performance, modern air-floatation rotating shafts commonly adopt "active control" technology: integrating high-sensitivity capacitive sensors (resolution 0.01 μm) at the shaft end to monitor radial displacement in real time; the controller adjusts the airway pressure or electromagnetic force (if it is a magnetic levitation-air floatation composite shaft) based on feedback signals, forming a closed-loop control. For instance, in a 300mm wafer rotation test of a certain semiconductor equipment manufacturer's air-floatation rotating shaft, the peak-to-peak radial runout was only 0.03 μm, and there was no performance degradation after continuous operation for 1000 hours, supporting the high-precision requirements of EUV lithography machines for wafer shape. 

III. Ceramic Chip Fork: The "Nanotweezers" for Zero-Pollution Transmission 

The transfer of wafers between different process chambers requires avoiding any particle contamination (particles ≥ 0.1 μm can cause chip failure). At this time, the ceramic fork becomes the preferred tool. Its core requirements are: surface roughness < 0.02 μm (Ra), hardness > HV1500 (to prevent scratching the wafer), and it must also have high-temperature resistance (> 300°C) and corrosion resistance (compatible with HF acid vapor). 

The material selection for ceramic wafer forks is of critical importance. Alumina (Al₂O₃) is widely used due to its low cost and ease of processing, but it has a relatively low fracture toughness (about 3 MPa·m¹/²) and is prone to microcracks due to impacts. Silicon nitride (Si₃N₄), on the other hand, combines high hardness (HV1800) with fracture toughness (6-8 MPa·m¹/²), making it more suitable for high-reliability applications. To further reduce surface energy, ceramic wafer forks need to undergo "mirror polishing + ion beam cleaning" treatment to ensure there are no adsorbed particles.

In terms of structural design, the "prongs" of the ceramic wafer fork must precisely match the "notch" or "flat" on the edge of the wafer, with a positioning accuracy of ±5 μm. Some high-end equipment adopts a "double-fork structure": the main fork fixes the central area of the wafer, while the auxiliary fork fixes it through vacuum adsorption, preventing the wafer from sagging due to its own weight (the sagging of a 300mm wafer edge can reach 0.1 μm/mm). This design enables the wafer fork to move smoothly at a speed of 0.1 m/s with an acceleration of less than 1g, ensuring no displacement or tilting of the wafer during the transfer process. 

IV. Precision Motion Stage: A "Nanometer Stage" of Multi-Axis Synergy 

Core processes such as wafer alignment, lithography exposure, and measurement all rely on precision motion stages, whose performance directly determines the process capability of the equipment. The design of precision motion stages needs to balance the three major contradictions of "stiffness - weight - travel": it must be stiff enough to resist external vibrations (such as ground vibration of 0.1 μm/s²), lightweight enough to achieve high-speed movement (acceleration > 1g), and provide millimeter-level or even centimeter-level travel (for example, the X-axis travel of the lithography machine's scanning platform can reach 200mm). 

Modern precision motion stages commonly adopt a "coarse motion + fine motion" composite structure: the coarse motion stage is driven by a linear motor (with a large stroke and strong thrust), while the fine motion stage is driven by piezoelectric ceramics or voice coil motors (with nanometer-level resolution). For instance, in a certain lithography machine's wafer surface topography measurement platform, the coarse motion stage has a stroke of 150mm and a repeat positioning accuracy of ±1μm; the fine motion stage has a stroke of 20mm and a resolution of 0.1nm. Through the cascaded control of "coarse motion - fine motion", nanometer-level positioning is achieved throughout the entire stroke.

To suppress thermal deformation (the motor of the motion stage can cause a temperature rise of 5-10℃, and a steel structure with a thermal expansion coefficient of 11×10⁻⁶/℃ will elongate by 55-110μm), the motion stage needs to integrate temperature sensors (with an accuracy of ±0.1℃) and thermal compensation algorithms: a thermal deformation model is established through finite element simulation, and the thermal drift of each axis is calculated in real time, and the deformation is offset by adjusting the pre-tightening force of the piezoelectric ceramics. Additionally, the application of air static pressure guides (air bearing guides) enables the straightness/flatness of the motion stage to reach 0.1μm/100mm, providing a "super-clean track" for nanometer-level motion. 

V. Wafer Handling Robot: The "Safety Guardian" in Human-Robot Collaboration 

During the "first mile" transfer of wafers from the Front Opening Unified Pod (FOUP) to the process chamber, the wafer handling robot (OHT/EFEM Robot) is responsible for the entire process of "picking up - inspecting - placing". The core challenge lies in precisely grasping the wafer within the 400mm×400mm FOUP (with a positional deviation of less than ±200μm), moving at a speed of 0.5m/s (without causing vibration), and accurately placing the wafer onto the chuck in the process chamber (with an angular deviation of less than ±0.05°). 

The design of the "arm" of the robotic arm needs to balance rigidity and flexibility. The mainstream solution adopts a "redundant degree-of-freedom mechanical arm" (such as a 7-axis articulated arm), which avoids interference with equipment through the coordinated movement of multiple joints. The end effector integrates vacuum suction cups (with a hole diameter of 0.1-0.3mm and a distribution density of >10 per cm²) and force sensors (with a resolution of 0.1N): vacuum adsorption provides the main grasping force (>5N), and the force sensor monitors the contact force in real time to prevent excessive local pressure (>20N may cause breakage) due to wafer warping.

More crucially, the "visual guidance" technology: the robotic arm is equipped with a 3D line laser sensor (with an accuracy of ±5μm), which scans the position and posture of the wafer before grasping. Through visual algorithms (such as ICP registration), the compensation displacement and rotation angle are calculated to upgrade from "blind grasping" to "precise grasping". For example, the EFEM (Equipment Front End Module) robotic arm of a certain manufacturer, in a fully loaded FOUP (25 wafers) environment, has an average wafer picking time of only 8 seconds and a wafer breakage rate of <0.01%, meeting the reliability requirements for 24-hour continuous production. 

Conclusion: Coevolution of Precision Components 

From the nanometer-level positioning of wafer aligners to the frictionless suspension of air-bearing spindles; from the zero-contamination transfer of ceramic wafer forks to the multi-axis coordination of precision motion stages, and then to the intelligent grasping of handling manipulators - although each component has its own specialized function, they form a strong coupling in the "precision ecosystem" of semiconductor manufacturing. Every technological breakthrough they achieve (such as a tenfold improvement in the active control accuracy of air-bearing spindles and a reduction in the surface roughness of ceramic wafer forks to 0.01 μm) is propelling semiconductor processes towards more advanced nodes (such as 2nm and 1nm). 

In the future, with the deep integration of AI algorithms and multi-physics field simulation (such as real-time prediction of the thermo-mechanical-vibration coupling deformation of the motion stage), as well as the application of new materials (such as diamond-coated ceramics and superconducting materials), these "invisible key components" will continue to write the legend of semiconductor precision manufacturing - after all, in the nanometer world, there is no "approximately", only "more precise".