In core semiconductor processes such as etching, thin-film deposition, and ion implantation, the components inside the equipment must operate stably for long periods under extreme plasma environments, high voltages, corrosive gases, and frequent thermal cycling. Advanced ceramic materials such as alumina, aluminum nitride, silicon carbide, and silicon nitride, with their high hardness, high resistivity, excellent plasma erosion resistance, and good thermal matching, have become irreplaceable key materials. However, their high hardness, high brittleness, and low fracture toughness also pose manufacturing challenges. Moreover, as the downstream industry moves toward miniaturization, integration, and multifunctionality, the shape requirements for semiconductor ceramics have evolved from simple plates, blocks, and rods to complex structures such as irregular shapes, porous features, thin walls, and complex curved surfaces. Examples of typical complex-shaped ceramic components required by semiconductor equipment include:
(1) Electrostatic chucks (ESC): containing high-density micro-hole arrays, complex gas channel paths, and micro-bump arrays for uniform wafer support.
(2) Etch chamber insulation components: such as gas showerheads, focus rings, insulating rings, etc., often featuring curved profiles, non-uniform thickness flange structures, a large number of fine micro-holes, and irregular connection grooves.
(3) Precision sensor housings: with thin walls, closed or semi-closed internal cavities, threaded interfaces, and tiny lead holes, etc.
These complex shapes impose stringent requirements on ceramic manufacturing processes that go far beyond conventional structural parts. The following sections analyze the technical challenges and possible solutions in three key stages: forming, sintering, and precision machining.
1. Forming
Forming is the first critical step in producing complex-shaped semiconductor ceramics. Components such as electrostatic chucks, etch chamber insulation parts, and precision sensor housings require uniform internal structure and near-net shape accuracy. Conventional forming methods like dry pressing and slip casting are limited by mold geometry and cannot meet the diverse, individualized demands of complex shapes. Moreover, during forming of complex-shaped green bodies, uneven loading and filling speeds in different regions often lead to non-uniform density distribution, dimensional deviations, delamination, and cracking due to stress concentration during demolding. Currently, the main forming processes suitable for complex-shaped semiconductor ceramics include:
1.1 Gel casting
This process involves injecting a low-viscosity, high-solid-loading ceramic slurry into a mold, adding organic monomers, crosslinkers, and initiators to induce in-situ polymerization and form a green body. It can directly form complex-shaped parts, and the green body exhibits minimal deformation during drying and sintering, resulting in high dimensional accuracy and reduced subsequent machining costs. The in-situ polymerization uniformly disperses and immobilizes ceramic particles in a three-dimensional network, avoiding density gradients caused by particle sedimentation or uneven distribution, making it especially suitable for large-sized, thin-walled complex components.
1.2 Ceramic injection molding (CIM)
CIM is also a near-net shape process. The procedure involves mixing ceramic powder with organic binders and plasticizers to form a feedstock, heating it to a molten state, injecting it under pressure into a metal mold, cooling to solidify, demolding, then debinding and sintering to obtain the final product. Compared to traditional slip casting, CIM uses a plasticized material pressed in a rigid mold, avoiding compositional segregation. Compared to dry pressing, CIM provides more uniform green density due to flow filling, overcoming density, microstructure, and performance inhomogeneities. It is suitable for cost-effective mass production of small, high-performance parts with complex shapes, such as sensor housings and small insulating rings.
1.3 Isostatic pressing
For axisymmetric complex parts like focus rings, isostatic pressing can be used. The powder is sealed in a flexible mold and immersed in a liquid or gaseous medium inside a high-pressure vessel. An external pressurization system (e.g., a hydraulic pump) applies high pressure to the liquid. Because the liquid or gas is incompressible, the pressure is transmitted uniformly to the material surface inside the mold, achieving uniform pressure in all directions and avoiding density unevenness due to pressure gradients.
1.4 3D printing
For parts with extremely complex internal channels (e.g., ESC prototypes with cooling circuits), digital light processing (DLP) or direct ink writing can create interconnected channels impossible with traditional molds. However, this technology is currently limited by lower solid loading of the slurry, resulting in lower sintered density and larger shrinkage.
2. Sintering
Sintering transforms the green body into a dense ceramic, typically accompanied by 15–25% linear shrinkage. For complex-shaped parts, thickness variations cause anisotropic shrinkage. Combined with non-uniform temperature or stress fields, this can degrade feature dimensional accuracy and, more severely, cause warping, cracking, or collapse. Therefore, sintering process optimization focuses on reducing shrinkage rate differences, suppressing abnormal grain growth, homogenizing the temperature field, and minimizing thermal stress. Sintering methods suitable for complex shapes include:
2.1 Hot pressing
Applying uniaxial or isostatic pressure to the green body during sintering provides additional densification driving force, lowers sintering temperature, suppresses abnormal grain growth, and helps maintain complex feature shapes. Suitable for electrostatic chucks and showerheads.
2.2 Gas pressure sintering
Applying inert gas (e.g., nitrogen) pressure during high-temperature sintering inhibits material decomposition and volatilization, significantly reduces closed porosity, and ensures uniform pressure on the material surface due to the gaseous medium. Suitable for sintering complex-shaped ceramic components.
2.3 Spark plasma sintering (SPS)
During SPS, a pulsed DC current generates instantaneous spark plasma, causing uniform Joule heating and surface activation of individual particles. Because densification across different thicknesses occurs almost simultaneously and the temperature field is extremely uniform, SPS greatly reduces differences in shrinkage rates. However, the current limitation is the chamber size, making it suitable for sensor housings or small insulating parts.
2.4 Microwave sintering
Microwave sintering uses an electromagnetic field to induce polarization of electrons, ions, or dipoles within the material, converting microwave energy into heat through dielectric, conductive, or magnetic losses, achieving uniform volumetric heating. Unlike conventional conductive heating, microwave sintering heats from within, with rapid ramp rates and small temperature gradients, reducing defects like deformation and cracking caused by thermal gradients.
3. Precision Machining
Sintered ceramic components often require grinding, lapping, polishing, and even laser processing to achieve sub-micron dimensional tolerances and nanometer surface roughness for semiconductor-grade applications. However, the high hardness and brittleness of ceramics cause rapid tool wear (grinding wheels, cutting tools) and high machining costs. Moreover, the material is prone to edge chipping, surface microcracks, and subsurface damage under grinding forces. For dense, fine features requiring high edge quality-such as ESC bump arrays and thousands of micro-holes in a showerhead-conventional grinding and lapping methods are often inadequate. They either cause edge chipping due to excessive contact force or cannot uniformly reach inner walls and orifices. As a result, a range of non-contact or low-contact-force ultra-precision machining techniques have been developed for complex-shaped ceramics, including abrasive flow polishing, laser drilling/polishing, magnetorheological fluid polishing, and plasma-assisted polishing.
3.1 Abrasive flow polishing
For showerhead bottom surfaces with hundreds to thousands of micro-holes and deep gas channels on the backside of an ESC, abrasive flow polishing uses a semi-solid, viscoelastic abrasive medium containing ultra-fine abrasives. Driven hydraulically, the medium flows repeatedly through the holes. At the orifice, the medium is squeezed, producing uniform sliding abrasion that removes burrs and forms smooth rounded edges.
3.2 Laser processing and polishing
For micro-holes that are blocked or have shape deviations after sintering, femtosecond or picosecond lasers are used for precise hole correction. Femtosecond lasers have extremely short pulse widths; the energy is absorbed and released so quickly that heat does not diffuse to the surrounding area, resulting in a heat-affected zone below 0.01 μm and hole walls free of microcracks and recast layers. Laser polishing uses low-energy-density laser beams to rapidly scan the ceramic surface, causing a shallow surface melt that achieves high-precision polishing, avoiding surface scratches, deformation, or wear caused by friction and pressure in conventional polishing. It can easily handle complex 3D curved surfaces, microstructures, or localized areas, making it especially suitable for internal cavities of sensor housings that are inaccessible to abrasive tools.
3.3 Magnetorheological fluid polishing
Magnetorheological fluid polishing disperses micron-sized carbonyl iron powder and abrasive particles in a carrier fluid, forming a controllable-viscosity "flexible polishing tool" under a strong magnetic field. When the magnetic field is locally applied to the ceramic workpiece surface, the magnetorheological fluid solidifies rapidly in the polishing zone, and material removal occurs under combined pressure and shear flow. This method offers high surface accuracy and good process controllability, especially suitable for complex curved surfaces, thin walls, inner walls, and other hard-to-reach surfaces, as well as precision machining scenarios requiring high surface integrity and low subsurface damage.
3.4 Plasma-assisted polishing (PAP)
PAP is a polishing method that first modifies the ceramic surface using plasma to form a softer modified layer, followed by gentle abrasive polishing to achieve efficient material removal. It offers high removal efficiency, atomically flat surfaces, and no subsurface damage. By controlling gas flow and electric fields, it can uniformly treat complex curved surfaces, internal cavities, micro-holes, and other areas difficult to access with conventional polishing, achieving all-round processing.