In order to develop blue high brightness LED, around the world related research staff are committed. While the commercial application shows the III V group elements as potential. In the current commercial LED material and its extension, the red and green light emitting diode epitaxial technique for liquid phase epitaxial growth of most main method, while the yellow, orange light emitting diode at present still with gas phase epitaxial growth techniques of gallium arsenide GaAsP materials.
GaN growth need high temperature to interrupt the NH3 N-H key solution, on the other hand by dynamic simulation also learned that the NH3 and MO Gas will react to produce no volatile byproducts.
LED LED epitaxial wafer process is as follows:
Substrate structure design of buffer layer growth - N GaN layer growth - multiple quantum well light emitting layer of P type GaN layer growth - annealing - Detection ( fluorescence, X ray ) - LED epitaxial wafers
LED epitaxial wafer - design, processing mask - lithography - ion etching N type electrode ( plating, annealing, etching ) - P type electrode ( plating, annealing, etching ) - scribing - chip sorting, grading
Fixed: monocrystalline silicon rods fixed on the working bench.
Slice: monocrystalline silicon rod into precise geometry of thin silicon.
Annealing: duplex thermal oxidation furnace with nitrogen purge, infrared heating to 300~500℃, silicon surface reacts with oxygen to form protective layer of silicon dioxide, silicon surface.
Chamfer: annealed wafer trim into a circular shape, prevent the wafer edge rupture and lattice defects, increase the epitaxial layer and a photoresist layer smoothness.
Classification and detection: to ensure the wafer specifications and quality, to detect.
Grinding: grinding agent to remove slicing and grinding wheel made mark and surface damage layer, effectively improve the silicon wafer curvature, flatness and parallelism.
Cleaning: through organic solvent which dissolves, combined with ultrasonic cleaning technology for removal of organic impurities in silicon surface.
RCA cleaning: cleaning to remove silicon surface through a variety of particulate material and metal ions.
The specific process:
Cleaning: SPM by H2SO4 solution and H2O2 solution according to the proportion of SPM solution, the metal oxide dissolved in the cleaning liquid, and the organic pollutant is oxidized into CO2 and H2O.
DHF: cleaning with hydrofluoric acid with a certain concentration removal from silicon wafer surface in the natural oxide film, and attached to the natural oxide film on the metal is dissolved into the cleaning fluid, while DHF inhibits the formation of an oxide film.
APM: APM cleaning solution by a certain proportion of NH4OH solution, H2O2 solution composition, silicon surface due to oxidation oxide film on H2O2 ( about 6nm in hydrophilic ), the film was NH4OH corrosion, corrosion and oxidation occurs immediately after, repeated, attached to the surface of the silicon wafer particles and metal with corrosion layer and into the cleaning liquid. Cleaning: HPM by HCl solution and H2O2 solution according to the proportion of HPM, the removal of silicon surface sodium, iron, magnesium and zinc.
DHF cleaning: removes a procedure in the silicon surface oxide film. Grinding test: detection after grinding, RCA after cleaning the wafer quality, do not meet the requirements from the new RCA grinding and cleaning.
Corrosion of A/B: through slicing and grinding machining, the wafer surface by processing stress and the formation of the damaged layer, usually by chemical etching to remove. Corrosion of A is corrosive acid, mixed acid solution to remove damage layer, to produce hydrogen fluoride, NOX and waste mixed acid; corrosion B is an alkaline corrosion, using sodium hydroxide solution to remove damage layer, produce waste lye. The part of a program using A silicon corrosion, partly by the corrosion B.
Classified monitoring: the silicon wafer for damage detection, there is damage to the corrosion of silicon.
Rough polishing: use a grinding agent to remove the damaged layer.
Polishing: using grinding agent to improve the silicon surface micro roughness.
Inspection: check whether it meets the requirements of silicon wafers.
Detection: view the silicon surface is clean.
Packaging: monocrystalline silicon polished wafers for packaging.