In PVD processes, crucibles are employed to hold solid metals or compounds, which are then heated to the point of evaporation or sublimation. This allows the vaporized material to condense as a thin film on the substrate. Many molten materials require a crucible liner, and the actual charge capacity of the crucible depends on the liner’s volume.
In CVD processes, the crucible serves to heat and vaporize the precursor material, facilitating its reaction and deposition on the substrate.
In the electroplating field, crucibles are used to melt high-temperature solvents or electroplating solutions.
Crucibles and their liners must be chosen carefully to avoid unwanted chemical reactions at high temperatures. Incompatible crucible materials can corrode or contaminate the melt, which may compromise product quality.
A critical issue in high-temperature processes is the thermal expansion mismatch between the crucible and the molten material. During heating, molten materials typically expand more rapidly than the crucible, exerting pressure on the walls and potentially leading to cracks or deformation. Similarly, during cooling, stress can develop as the material contracts, especially if there is an excessive amount of residual material in the crucible.
Crucible Filling Recommendations
The degree to which a crucible is filled depends on the type of deposition material, and it can vary significantly between sublimating materials, molten materials, and chemical compounds.
Sublimating Materials:Fill the crucible to 90% capacity for optimal performance. In constant-power or temperature evaporation, vapor distribution and rate change as the material is consumed, but sublimating materials (e.g., salts) usually exhibit minimal issues.
Molten Materials/Non-Sublimating Materials:The recommended fill level for non-sublimating materials is 75% of the crucible's capacity. Overfilling can lead to cracks due to the difference in thermal expansion between the crucible and materials like aluminum oxide when reheated.
مركبات كيميائية:For chemical compounds, the best results are typically achieved when the crucible is filled to about 50%, with the material reducing to around 17% during evaporation. If vapor quality (e.g., dissociation, vapor temperature, or rate) is critical, further adjustments may be required to optimize the evaporation process.
To avoid cross-contamination, it is recommended that each crucible is dedicated to heating a single type of material. While some organic compounds can be thoroughly removed with proper cleaning, others may be more difficult to eliminate. The success of cleaning depends on the specific organic compound and the firing temperature.
Alternatively, heating the crucible to temperatures well above the normal evaporation point of the organic materials can allow for self-cleaning by burning off residues.
For custom crucible shapes, pore sizes, materials, or other specialized requirements, please contact us for tailored solutions.