Ion Implantation in Semiconductor Manufacturing - Using Graphite and Refractory Metals to Improve System Reliability

Ion implantation is a complex and sensitive process and is used in the manufacture of semiconductors. For successful operation, beam purity and process stability are important. Here, graphite and refractory metal parts play a critical role. On the whole, the total cost of maintaining the system can be reduced when conventional materials are substituted with higher quality materials and process specific alloys.

During the implantation process, dopant ions are accelerated and implanted within a monocrystalline silicon substrate to manipulate its bulk properties. Arsenic, boron, phosphorous, germanium and germanium are some of the typical dopant materials.

The ion beam’s direction, energy, and uniformity must be repeatable over several process changes and should not vary even if it remains in continuous operation for many hours. Component shape and material properties impact process stability and life. This means, the longer the components maintain their shape and material properties, the more stable and repeatable the process will be.

In the implanter system, a number of components remain in contact with the ion beam and process gases over extended periods of time. However, strong chemical and electro-mechanical forces inside the system can promote re-deposition, erosion, and transport of component materials along the beamline. When material is lost from such components, it can affect the process accuracy and result in equipment failures. Such events can cost thousands of dollars to high volume factories.

Graphite and Refractory Metals

Materials like graphite and refractory metals are mainly utilized in ion implanter beamlines. The thermal, chemical, electrical, and mechanical properties of these materials are essential in improving the service life of the system.

One must be familiar with these material properties so as to select the right material for each replacement part. Materials experts at PLANSEE have more than nine decades of expertise in the field of refractory metals and more than three decades of experience with graphite and ion implantation processes. PLANSEE enhances both the design of OEM parts and the materials used in them.

Three Graphite Quality Classes

To meet the different demands in anion implanter, PLANSEE provides three different but perfectly matched quality classes. These graphite quality classes comprise Aperture Graphite, Purified Structural Graphite, and Specialty Graphite. These materials differ by hardness, strength and particle size.

Purified Structural Graphite has a particle size of 5-10 ^m and is utilized where the beam will not contact the material under normal operating conditions. For instance, it is employed in mounting frames and covers.

Aperture Graphite has a particle size of ~5 µm and is mainly used for apertures. It is 50% harder and stronger than Purified Structural Graphite. Aperture Graphite is also homogeneous. In applications where material loss is unavoidable, the homogeneity of this graphite ensures that such loss is more uniform when compared to Purified Structural Graphite.

Specialty Graphite has an ultra-fine particle size of 1-2 µm and has excellent homogeneity. This material is around 50% harder and stronger than Aperture Graphite and is utilized for extraction optics and in mass resolution applications.

PLANSEE aperture with high quality graphite insert

Figure 1. PLANSEE aperture with high quality graphite insert

In addition to different hardness, strength and particle size, these graphite quality classes also differ in terms of their electrical, chemical, and mechanical properties. Certain Specialty Graphites have smooth surfaces and exhibit good electrical conductivity. They can reduce glitching effects in extraction aperture systems and also ensure a uniform distribution of temperature in an ion source. All three graphite quality classes posses a high degree of purity.

Combination of Graphites Saves Costs

Only few suppliers of graphite implanter components meet PLANSEE's rigorous quality requirements. PLANSEE ensures transparency when dealing with a sensitive process like ion implantation and clearly defines what material is used for which component.

PLANSEE relies on a combination of graphites to save costs and deliver high-quality products to its customers. For instance, standard quality graphite is used for peripheral parts, while premium- quality graphite is employed for the most sensitive parts.

Dr. Thomas Werninghaus shows the PLANSEE Advanced Standard Single Mount G2 Aperture.

Figure 2. Dr. Thomas Werninghaus shows the PLANSEE Advanced Standard Single Mount G2 Aperture.

PLANSEE’s extensive experience in the properties of graphite proves useful in engineering and manufacturing fields, where the most intricate geometrical shapes can be produced or where complex, multi-part assemblies can be simplified to ease installation and cut down component costs.

Halogen Cycling

A research team at PLANSEE also develops new alloys and composite materials in order to improve component life and implanter performance. One particular composite material called tungsten lanthanum-oxide (WL) is being used by many PLANSEE customers to reduce the effects of halogen cycling in the ion source.

Ion source chamber with WL

Figure 3. Ion source chamber with WL

Conclusion

PLANSEE develops a wide range of replacement parts from graphite, molybdenum, tungsten, tantalum, and ceramics for ion implantation and other semiconductor applications. PLANSEE offers innovative solutions that help extend the service life of systems, allow simplified handling, and reduce maintenance costs.

This information has been sourced, reviewed and adapted from materials provided by PLANSEE.

For more information on this source, please visit PLANSEE.

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