In the front-end-of-line (FEOL) processes of semiconductor manufacturing, wafers undergo various processing steps, particularly being heated to a specific temperature with strict requirements, as temperature uniformity has a crucial impact on product yield. Additionally, semiconductor equipment must operate in environments where vacuum, plasma, and chemical gases are present, which necessitates the use of ceramic heaters. Ceramic heaters are critical components in semiconductor thin-film deposition equipment, applied in process chambers where they directly contact the wafer, providing stable and uniform process temperatures and enabling high-precision reactions on the wafer surface to form thin films.
Ceramic heaters, due to their involvement with high temperatures, typically use ceramic materials based primarily on aluminum nitride (AlN). This is because aluminum nitride has electrical insulating properties and is an excellent thermal conductivity ceramic material. Additionally, its coefficient of thermal expansion is close to that of silicon, and it possesses excellent plasma resistance, making it highly suitable for use as a component in semiconductor equipment.
Basic structure of the heater
The ceramic heater consists of a ceramic base that supports the wafer and a cylindrical support body on the back that provides support. Inside or on the surface of the ceramic base, there are not only heating elements (heating layer) for heating, but also RF electrodes (RF layer). To achieve rapid heating and cooling, the thickness of the ceramic base needs to be thin, but making it too thin would reduce its rigidity. The support body of the heater is typically made of a material with a coefficient of thermal expansion similar to that of the base, which is why the support body is often made of aluminum nitride. The heater adopts a unique shaft structure to join the bottom, which protects the terminals and wires from the effects of plasma and corrosive chemical gases. The support body is equipped with gas inlet and outlet channels for thermal conduction, ensuring uniform temperature distribution across the heater. The base and the support body are chemically bonded together with a bonding layer.
The ceramic heater base contains embedded resistive heating elements. These elements are formed by using a screen-printing method with conductor paste (such as tungsten, molybdenum, or tantalum) to create spiral or concentric circular circuit patterns. Alternatively, metal wires, metal meshes, or metal foils can also be used. In the screen-printing process, two ceramic plates with the same shape are prepared, and conductor paste is applied to the surface of one of them. The paste is then sintered to form the resistive heating element. The second ceramic plate is then used to sandwich the resistive heating element, completing the process of embedding the resistive element within the base.
When preparing thin films using Plasma-Enhanced Chemical Vapor Deposition (PECVD) equipment, the main factors affecting film uniformity and thickness are the plasma characteristics and process temperature. First, the density and distribution of the plasma directly affect the uniformity of the film and the deposition rate. A uniformly distributed plasma ensures that the reactive gases fully react on the substrate surface, forming a uniform film. The uniformity of the plasma distribution is closely related to the RF Mesh embedded in the heater. Secondly, a specific process temperature ensures excellent thermal uniformity. The ceramic heater ensures that the wafer surface temperature fluctuates within ±1.0%. For example, heaters produced by NGK Insulator in Japan have a temperature fluctuation of less than 0.1%, which is considered an excellent performance indicator.
When manufacturing ceramic heaters, there are also requirements for high purity of aluminum nitride (AlN) materials. Slight changes in composition can alter the color of the heater under certain conditions, and may also change the electrical properties of the heater. Naturally, this also affects the characteristics of the coupled plasma. In addition, the density, thermal conductivity, and bulk resistivity of the aluminum nitride material all influence the performance of the heater.
Literature indicates that the bulk resistivity of the heater at 500°C needs to be within the range of 5.0E+9 to 1.0E+10 Ω·cm, and at temperatures between 600°C and 700°C, the bulk resistivity should be within the range of 1.0E+8 to 1.0E+9 Ω·cm. The bulk resistivity of typical aluminum nitride ceramic heaters tends to decrease rapidly starting from 500°C, which can lead to leakage current.
According to a market research report, the global market size for aluminum nitride ceramic heaters for semiconductors was $33 million in 2022, and it is expected to reach $78.53 million by 2031, with a compound annual growth rate (CAGR) of 10% during the forecast period. Major manufacturers of aluminum nitride ceramic heaters for semiconductors include NGK Insulator, MiCo Ceramics, Boboo Hi-Tech, AMAT, Sumitomo Electric, CoorsTek, Semixicon LLC, and others. In 2023, the top five companies accounted for approximately 91.0% of the market share. In terms of product types, 8-inch heaters currently dominate the market, accounting for about 45.9% of the share. In terms of application, chemical vapor deposition (CVD) equipment is the primary demand source, accounting for approximately 73.7% of the share.
