Home Case studies Case study graphite crucible for SiC synthesis

Case study: Graphite crucible for SiC synthesis

From mixing to synthesis - One crucible for the entire process

Every detail counts in semiconductor production: the manufacture of silicon carbide (SiC) places particularly high demands on purity, process stability and energy efficiency. Producers and research institutes are therefore constantly working on optimizing their synthesis processes. Not least because the smallest impurities can impair the electrical conductivity of the end product.

Share case study

Background

Silicon carbide is valued in the semiconductor industry as a high-performance material, for example for power electronics and high-temperature applications. One method of SiC production is the direct synthesis process from a stoichiometric powder mixture of silicon and carbon at temperatures above 2000 °C, usually under vacuum or inert gas and in graphite crucibles.
The industry faces typical challenges here: high energy consumption, complex process control and the need to ensure absolute purity. At the same time, the material quality and design of the graphite components used have a significant influence on the success of the synthesis.

Overview

Industry:

Semiconductor manufacturing, technical ceramics

Procedure:

Direct synthesis of silicon carbide (SiC)

Solution:

Customized graphite crucible with integrated cover system and filter inserts

Services:

Consulting, engineering technical documentation, manufacturing

Result:

– Pure SiC end product without impurities

– No powder loss and clean system

– Elimination of the decanting step (more efficient handling)

– Improved process reliability and energy efficiency

The challenge

In a specific application, a research institute in the field of technical ceramics worked with an open synthesis crucible that was operated under vacuum during the process. This regularly led to problems:

Impurities in the end product due to foreign atoms such as iron or boron, which impair the electrical properties of the SiC
Contamination of the system, as powder particles escaped from the open crucible during evacuation and settled in the reactor.
Complex handling, because the powder first had to be mixed in a separate mixing container and then transferred to the synthesis crucible.

These factors led to increased costs, potential rejects and limited process reliability.

The specific task: Optimization of the synthesis crucible

The aim was to develop a graphite crucible that allows both the mixing and synthesis of SiC in a single container – while ensuring the purity of the process.
Graphite Materials was responsible for the engineering from concept development to execution. Together with the customer, we developed a new jar design with an integrated lid system that combines several functions:

Safe evacuation despite the lid: Special filter inserts in the lid allow the pressure to be lowered without powder escaping.
Targeted safety mechanism: If a filter insert becomes clogged during evacuation, any potential crack formation is directed specifically into the lid area. The powder is prevented from escaping into the system.
Increased purity: All crucible components are thermally post-cleaned in order to exclude impurities from metallic foreign atoms.

Process results

By using the new crucible concept, the entire synthesis process could be made significantly more efficient and cleaner. The SiC end product is now produced free of impurities, while the workflow has been simplified and the risk of plant contamination minimized.