High temperature annealing treatment of silicon carbide crystal

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The most common and mature method for SiC crystal growth is still physical gas phase transport (PVT), which is a gas-phase growth method with high growth temperature and high requirements on raw materials and process parameters. In recent years, a great deal of time and energy have been invested in the development of PVT process at home and abroad, and great breakthroughs have been made in the quality and size of SiC crystals, etc., but there are still tissue defects and microscopic stresses in the crystals. The existence of tissue defects will worsen the performance of SiC based devices, thus affecting the application of the devices, while the existence of stress will make SiC crystal easy to break during the processing stage, thus reducing the yield of SiC chips. Therefore, it is particularly important to reduce the microstructure defects and microstructure stress in SiC crystals, and high temperature annealing treatment can effectively reduce the microstructure stress and eliminate the microstructure defects.

Annealing is a method of heating a material to a certain temperature in a specific atmosphere, holding it for a period of time, and then cooling it at an appropriate rate. It is a very common heat treatment process in the material field. Annealing treatment plays an important role in the post-processing of artificial crystal. For example, after the growth of single crystal Si, sapphire and other crystals are completed, corresponding annealing treatment should be carried out to eliminate the stress and defects in the crystal and improve the crystal quality.

Tissue defect

SiC crystals prepared by PVT method usually have dislocations, micropipes, stacking faults, multitype inclusions and inclusions.

Dislocation is a kind of line defect caused by strain. The dislocation will seriously affect the mechanical and electrical properties. The existence of micropipeline will have a fatal effect on SiC based devices. Even if there is only one micropipeline in high-voltage devices, it will lead to the destruction of devices. The formation mechanism of micropipeline has not yet reached a consensus and is still under study. As shown in the figure below, the dislocation crater on Si surface, in which the large six-square crater is a microtubule; The six-square corrosion pits of medium size are screw dislocation with hexagonal shape, the small six-square corrosion pits are edge dislocation and the oval corrosion pits are surface dislocation.

SiC crystal in a region of stacking order deviated from the original stacking order, resulting in misalignment, resulting in stacking fault. The generation of multitype inclusion is due to the overlap of growth temperature interval of different SiC crystal types, and the good crystallographic compatibility and close free energy among the multitypes. The existence of such defects will destroy the structural integrity of SiC crystal. SiC crystals adsorb some large impurity particles during the growth process, forming Mosaic structure and inclusion defects.

Microscopic stress

Microstress occurs in SiC crystals, on the one hand, due to various defects in SiC crystals, such as the distortion between the above defect tissue and the surrounding normal lattice points, which will generate a stress field around. On the other hand, the non-uniform growth of SiC crystal also produces stress, for example, axial and radial temperature gradient exists in the crucible of SiC crystal growth, which leads to the inconsistent growth rate on the surface of SiC crystal, thus making the surface of SiC crystal grown appear uneven. The stress is likely to cause cracking during the post-processing (rounding, surface grinding, multi-line cutting, etc.), which will greatly reduce the yield of SiC chips.

High temperature annealing treatment of silicon carbide crystal

In the process of PVT growth of SiC single crystal, many defects and stresses will inevitably occur. In order to improve the crystal quality of SiC crystal and reduce the tissue defects and thermal stress, high temperature annealing treatment must be carried out on SiC crystal. This process can be basically divided into three processes of “heating up — heat preservation — cooling down”, which can be repeated several times. Due to the high temperature resistance of SiC crystal, in order to reduce the thermal stress to the maximum extent, the annealing temperature of the chip is relatively high, generally around 1800℃.

The high temperature vacuum horizontal annealing furnace independently developed by SIMUWU consists of high temperature reaction system, heating system, vacuum system and control system. The heating system adopts graphite heating with rated power up to 60KW and maximum working temperature of 2300 ° C, which can keep the temperature field uniform and constant within a large range of working area inside the chamber during the heating process. Temperature measurement system is divided into two kinds, in less than 1600 ℃ when the beta type thermocouple, higher than 1600 ℃ when using infrared thermometer, can control the temperature precision in + / – 1 ℃, the annealing furnace can use different annealing atmosphere, and can adjust the pressure value, through the mechanical pump and molecular pump pumping air into vacuum state, make the high vacuum annealing furnace.

SIMUWU Vacuum Furnace continuously develops and improves the technology, promotes the heat treatment equipment with excellent performance in accordance with the market demand, and provides corresponding technical support to aid the domestic semiconductor market and provide corresponding technical consultation on the heat treatment process of the semiconductor industry.