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Today, we will discuss the growth process of LED wafers. In the early days of small integrated circuits, thousands of crystal grains were fabricated on each 6-inch wafer. Now, large VLSIs with sub-micron line widths, each 8-inch crystal. Only one or two hundred large wafers can be completed on the circle. Although wafer manufacturing is investing tens of billions, it is the foundation of all electronics industries.
For the growth of a silicon crystal column, it is first necessary to put a relatively high purity silicon ore into the furnace and add a predetermined metal substance so that the generated silicon crystal column has the required electrical properties, and then all the substances are required. After melting, it will grow into a single crystal silicon crystal column. The following will introduce all the crystal column growth processes:
The main steps of the crystal :
1. Melting (MeltDown)
The process is to heat the bulk polycrystalline silicon placed in the quartz crucible above the melting temperature of 1420 degrees Celsius. The most important parameter in this stage is the position of the crucible and the supply of heat. The large power to melt the polycrystalline silicon, the life of the quartz crucible will be reduced, and if the power is too low, the melting process takes too long, affecting the overall production capacity.
2, neck growth (Neck Growth)
After the temperature of the silicon melt is stabilized, the seed crystal of the direction is gradually injected into the liquid, and then the seed crystal is pulled up, and the diameter is reduced to a certain value (about 6 mm), the diameter is maintained and the length is 10-20 cm, Eliminate the dislocation within the seed crystal. This dislocation-free control is mainly to limit the displacement to the growth of the neck.
3, Crown Growth (Crown Growth)
After the neck is finished, slowly reduce the speed and temperature to gradually increase the diameter of the neck to the desired size.
4, crystal growth (Body Growth)
The fixed ingot diameter is maintained by the adjustment of the pulling speed and the temperature change, so the crucible must be continuously raised to maintain the fixed liquid level, so the radiant heat transmitted from the crucible to the ingot and the liquid surface will gradually increase. This radiant heat source will cause the temperature gradient of the solid interface to gradually decrease, so the pulling speed during the growth phase of the ingot must be gradually reduced to avoid the distortion of the ingot.
5, tail growth (Tail Growth)
When the crystal grows to a fixed (required) length, the diameter of the ingot must be gradually reduced until it is separated from the liquid surface, thereby avoiding the difference between the displacement and the slip surface due to thermal stress.
Cutting:
Once the ingot is grown, it can be cut into pieces, that is, wafers. A wafer, a wafer, is a substrate of a "grain" or a "wafer" of a semiconductor element. From a high-purity silicon crystal ingot that is stretched out, the circular slice is called a wafer ( Epitaxial film).
Epitaxial:
GaAs epitaxy can be divided into LPE (liquid phase epitaxy), MOCVD (organic metal vapor phase epitaxy) and MBE (molecular beam epitaxy) depending on the process. LPE technology is relatively low, mainly used for general light-emitting diodes, while MBE has a higher technical level, easy to grow extremely thin epitaxial, high purity, good flatness, but low mass production capacity, epitaxial growth rate SLOW. In addition to high purity and good flatness, MOCVD has higher mass production capacity and epitaxial growth rate than MBE, so most of them are now produced by MOCVD.
The process begins with placing the GaAs substrate in an expensive organic chemical vapor deposition furnace (MOCVD, also known as an epitaxial furnace), followed by an alkyl compound (methyl or ethylate) vapor of Group III and II metal elements. With a non-metal (V or VI element) hydride (or alkyl) gas, pyrolysis reaction occurs at a high temperature to form a III-V or II-VI compound deposited on the substrate to grow a layer A compound semiconductor epitaxial layer having a thickness of only a few micrometers (1 mm = 1000 μm). A GaAs wafer having an epitaxial layer is also known as an epitaxial wafer. After the epitaxial wafer is processed by the wafer, it can emit a pure color of monochromatic light, such as red or yellow. Different materials, different growth conditions, and different epitaxial layer structures can change the color and brightness of the luminescence. In fact, in a few micrometers thick epitaxial layer, the true luminescence is only a few hundred nanometers (1 micron = 1000 nm) thick quantum well structure.
Reaction formula: Ga(CH3)3 + PH3= GaP+3CH4
(Edit: Xiaotang)
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