LED (Light-EmittingDiode, acronym LED) is a light-emitting diode is short, the second half of 2009 , LED market big leap as high-growth emerging industries, is expected by 2015 , LED street lighting industry will exceed 500 billion yuan , of which general lighting industry 160 billion yuan , a large -size LCD TV backlight industry 120 billion yuan , 20 billion yuan automotive lighting industry , general lighting industry 160 billion yuan , landscape , display and other industry 100 billion yuan .
LED industry chain can be divided into three parts, which are upstream of the growth substrate , wafer manufacturing, midstream and downstream chip packaging applications . In the whole industry chain, the core part of the growth substrate and epitaxial wafer manufacturing sectors , both technical content is relatively high, nearly 70% of total industry output value and profits .
LED current industry trends , the international and domestic markets, “National Semiconductor Lighting Project” under the impetus of China’s LED industry initially formed upstream of the substrate material , including LED , LED epitaxial wafers , led chip preparation , LED chips, packaging and application of LED products , including a relatively complete industrial chain .
Known semiconductor light-emitting diodes with high conversion efficiency , long life and other advantages, is considered to be the next generation of light sources and will replace the currently used conventional light sources . However, the performance of light-emitting diodes on the current point of view, to achieve this goal , there are many technical difficulties to be overcome , you need to analyze the material characterization , device analysis technology, and increase research efforts. In the light emitting diode device and the chip package structure of the structure , components, and the interface state analytical techniques optical microscopy, scanning electron microscopy , X-ray spectroscopy , secondary ion mass spectrometry equipment and structure of a device failure analysis, epitaxial process monitoring , improve and enhance the essential analysis tools.
The following briefly describes Zeiss optical microscopy, scanning electron microscopy in the LED production process part of the application .
I. Zeiss optical microscope , scanning electron microscope in the LED substrate material in the upstream ( sapphire material ) specific applications :
A sapphire substrate material introduced
Since sapphire insulation, dielectric loss, high temperature, corrosion . Good thermal conductivity, the mechanical strength is high enough . And can be processed into a flat surface . Transmission band width . It is widely used in industry, national defense , scientific research fields. But also a wide range of uses light-emitting diodes on a good substrate material . In the resulting light-emitting diode is the most promising to become high-brightness light-emitting diodes race sapphire substrate in the next generation of fluorescent light sources are semiconductor light emitting device substrate material . At present these high- brightness light-emitting diodes have been widely used in advertising , traffic lights, instrument lights ; and surgical lights and other fields. With high-brightness light-emitting diode applications increasingly widespread.
LED sapphire (Sapphire) is a single crystal alumina , also known as corundum . Sapphire crystal has excellent optical properties, mechanical properties and chemical stability , high strength, hardness, resistance to erosion, close to 2000 ℃ high temperature in harsh conditions. According to the study suggest that the current can be applied to the LED substrate material only four . As an important technique sapphire crystal , has been in the LED industry to form a more mature fashion and applications .
2, the application
Polarizing microscope using Zeiss exception can be identified sapphire crystal birefringence . In certain cases, by means of the cone of light microscopy, the crystal can be observed interferogram , determine the crystal axis , used in the direction of observation of each wafer is uniform , in order to determine the quality of the substrate .
Second, the Zeiss microscope, scanning electron microscope in the LED epitaxial wafers , LED chips preparation of the application process
1, LED epitaxial wafers Introduction
LED epitaxial film grown basic principle is: on a substrate heated to a suitable temperature the substrate ( mainly sapphires and , Sic, Si) , the gaseous substance in a controlled InGaAlP delivered to the substrate surface , growing single crystal thin film of a specific . LED epitaxial film growth techniques currently used mainly metal organic chemical vapor deposition (MOCVD)
2, LED chip introduced
LED chip, also known as LED light chip is the core component of led lights , but also refers to the PN junction . Its main functions are: electrical energy into light energy , the main material for silicon chips . Semiconductor chip consists of two parts, part of the P -type semiconductor , the hole in it dominates the other side is an N-type semiconductor, here is mainly electronic . But the two semiconductor connected , when between them to form a PN junction . When the current through the wire on the chip when the electron will be pushed to the P region , in the P zone electron hole recombination , and then will be issued in the form of photon energy , which is the principle of LED light . Is the wavelength of the light color of the light , is formed by the PN junction to the materials .
3 , Application:
a) the use of scanning electron microscopy wafer growth after dislocation planes corrosion morphology information ;
Crystal plane dislocations provide corrosion morphology meaning : respective samples of dislocation etch presents an different shapes and crystal and crystal structure of point group is determined , the role of chemical etchant is to destroy the molecules within the crystal , and interatomic bond , the first key to a smaller force is destroyed , thus forming the shape of a particular corrosion spots, so good imaging , has corrosion spots detail perfect presentation, can fully reflect the quality of the crystal growth form .
Improve the quality and reduce the epitaxial material lattice defects is to produce high performance and high reliability LED devices premise , or by other means is irreparable . Clear crystal quality of the LED epitaxial material Reliability of the device , through the epitaxial material quality control , to reduce the defect density materials to improve the crystal quality of the epitaxial layer and improve the reliability of the LED devices .
b) before packaging of the chip testing: surface inspection using an optical microscope to determine if there is mechanical damage and pitting, the chip size and the size of the electrode meets the process requirements , the electrode pattern is complete.
c) LED chip oxide thickness: Detection technologies include color comparison, the edge count , interference, ellipsometry , sculptured needle amplitude and scanning electron microscopy ;
d) Measurement of the chip wafer junction depth : SEM PN junction of the LED chip wafer thickness detection junction depth
e) SEM etching process of the LED street lighting chip surface roughening process research applications: surface roughening techniques to solve because the refractive index of the semiconductor material ( average 3.5 ) is greater than the refractive index of air leaving the angle of incidence greater than the critical angle of total reflection of light can not be the losses caused by the exit . Roughening the surface of the light emitted great randomness requires a lot of experiments to study the roughness scale roughening rate of the light . An LED light from the high refractive index material GaP window layer air enters the low refractive index , the total reflection is generated , and significant loss of the emitted light . Surface roughening method using the total reflection can be suppressed to improve light extraction efficiency. Scanning electron microscope to directly observe the roughened structure of the sample surface , compared to rough surface roughness before and after treatment . SEM large depth of field , rich three-dimensional image can be observed through the roughened surface of three-dimensional island structure .
Third, the Zeiss optical microscopy and scanning electron microscopy analysis of the LED device failure in the finished application .
Scanning electron microscopy and X-ray energy spectrum analyzer can overload caused by thermal power LED stratification and black failure analysis. The results show that , since the light emitting diode of the input current increases , the chip junction temperature rise caused by thermal overload epoxy lens chip and the mismatch between the thermal stress , coupled with expansion of the epoxy material to moisture stress , eventually lead to light-emitting diode chip surface with the epoxy resin at the interface delamination . An epoxy resin in contact with the chip surface material under the action of high temperature aging, after degradation significantly change the internal structure of the epoxy resin , to form a C elemental and oxide deposited on the chip surface, which is the main surface of the chip black reasons .
Source from:http://www.lighting-ledlight.com/
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