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Q & A about Semiconductor Ceramic

Ceramic Materials used in the Semiconductor Industry

Ceramic Materials used in the Semiconductor Industry

Ceramic materials are used in a variety of harsh processing environments where dimensional stability over a range of high temperatures is required or where chemical and corrosion resistance is required. In addition, they can be adjusted or changed according to resistivity requirements, which makes them very versatile materials. Ceramics used in semiconductor applications have high purity and low trace metal content. This means that they can form process chamber materials or internal process surfaces for CVD, PVD, plasma etching and ion implantation, and their strong dielectric properties are very beneficial. In other applications, characteristics such as high wear resistance, hardness, light weight, strength and resistance are utilized. These materials have such a wide range of properties that modern semiconductor processing cannot be done without them.

Q - What are some of the common ceramic materials used and what beneficial properties do these have?

A - Alumina and yttria are typically used for chamber components, while alumina and aluminium nitride are typically used for electrostatic chucks in chamber interiors. In etching, CVD and PVD processes, they offer excellent dimensional stability alongside the ability to withstand a corrosive environment.

These products are mostly metal oxides, but there are also other advanced technical ceramics including carbides and nitrides. These include materials such as silicon carbide (SiC) and pyrolitic boron nitride (PBN).  SiC manufactured using a Chemical Vapour Deposition (CVD) process yields the highest performance SiC available. This material offers high thermal conductivity and stability in extreme thermal and chemical environments, making it ideal for use as showerheads in etch applications and rings in rapid thermal processing (RTP) applications. PBN is primarily used for crucibles in metal oxide (MOCVD) deposition tools.

Q - Could you explain the need for an ‘end effector’ in wafer processing and the properties this must possess?

A - End effectors constitute the end of the robot arm which handles and moves the semiconductor wafer between positions.  It’s basically the robot’s hand so it is important that it be thermally and dimensionally stable and not contaminate the chamber with particles or chemical contaminants.

Q - What are some of the major benefits of using aluminium oxide ceramics for this application rather than aluminium metal?

A - Ceramic end effectors are used for their stiffness and high strength, meaning the robot arm settles to its final position faster than with aluminium.  Additionally, the robot’s motion itself is faster, optimising positioning accuracy and increasing efficiency.

Q - What aspects need to be considered when choosing a material for a chamber lining for the deposition process?

A - The ceramic material is chosen based on the deposition chemistry to which it will be exposed. For example, if plasma is used, a minimum 99.5% alumina must be used.

The same consideration of gas chemistry is needed for determining the interior materials for plasma etch processes. If an anodised aluminium or alumina chamber is used with fluorinated gases or oxygen plasma then an yttria coating may be used on the anodised aluminium walls to prevent chemical attack.  Yttria has superior erosion resistance and low particulation compared with alumina or thermal spray alumina coating.

Could you explain the benefits and applications of a metal matrix composite (MMC) material?

This is an interesting material, basically alloying ceramics with metals. One current example involves combining aluminium with SiC.  One of the objectives of this technology is to match the thermal coefficient of expansion of alumina where a layer of aluminium/SiC attached to an alumina part increases the thermal conductivity and acts as a heat spreader. Applications are being considered for heated electrostatic chucks, but there are other applications as well.

Another MMC consists of SiC or B4C in a matrix of silicon which combines high strength, oxidation resistance, and high wear resistance and is used in applications such as chemical processing, wear parts and armour. Other options include a zirconia-based material for applications such as orthopaedics and rocket nozzles.

Q - Are there additional uses for monolithic SiC parts?

A - Yes, the integrity of an entirely CVD SiC is required wherever high temperatures are needed in combination with a corrosive chemistry. For chlorine and fluorine etch chambers, the so called ‘shower head’, which distributes the gas uniformly into the plasma process comprises of monolithic CVD SiC. The part needs to be semi-conductive to meet the requirements of the plasma process and currently these parts are being made cost-effectively in monolithic SiC grown to a thickness as high as 11.5 mm.  This is an important milestone thickness needed for some applications.

Q - How can coatings be used to improve the performance of ceramic materials?

A - Several coatings have already been discussed, such as textured ceramic coatings used for particulate contamination control.  For electrostatic chucks, spray alumina coatings are used as the insulator layer over electrodes that have been embedded in a monolithic alumina chuck.  It is the electrical specification of the insulator overlaying the electrodes that produces the electrostatic attractive force that holds the wafer in place in a vacuum process.

A variety of other coatings are also available, each offering different performance attributes. These include an anti-wetting coating boasting strong hydrophobic properties; a 99.9% yttria coating offering strong resistance to plasma; a charge-dissipating titanium magnesium coating whose performance rating can be tailored to the application; and CVD diamond coatings, used on CMP conditioners but also high-wear applications such as pump seals.

Q - Are there other advancements in ceramics, concerning which manufacturers may not yet be aware?

A - Yes. There is also another new technology coming to market for heated electrostatic chucks.  Current technology uses Aluminium Nitride (AlN) heaters which are restricted to operating temperatures below 450˚C. Alumina heaters are showing promise at temperatures up to 800˚C.  This will give process equipment manufacturers new process regimes to operate within. We expect this product for ion implant processes to come to market in the second half of 2014.