Study On Annealing And Copper Substrate Technology Of Blue LED On Silicon Substrate

As the InGaN/GaN leds more and more mature in the epitaxial growth and chip preparation technology,LED is popular in lighting,display and backlight market.Besides the LED cost,people are paying more attention to the yield of LED chip production and the reliability of the chip.As is known to all,it has natural advantages in the size,cost,electric conductivity,heat dissipation performance,development and application on Si substrate LED.Compared with sapphire and SiC substrate,there is a larger mismatch on the lattice constant and the thermal expansion coefficient between GaN and Si substrate,it means that stress modulation is more complex and more important during the preparation of film epitaxial growth and LED chips on silicon substrate.If the stress is not controlled properly,it will seriously affect crystal quality of GaN films on Si substrates,even cause cracking phenomenon.at the same time,the yield and photoelectric properties of LED are strongly influenced by the stress state.In this article,we start from the chip technology of the vertical structure of silicon substrate GaN base LED chips,study the stress change of Si substrate LED chips in the process of annealing and the impact of optical performance under stress.On the other hand,with the popularity of high power LED in lighting,the decline of the internal quantum efficiency caused by high power LED bad heat dissipation performance attracts more and more people's attention.In order to solve this problem,a copper substrate GaN base LED has been developed.the results of the study as follow:1.continuous annealing of GaN film after silicon removed,use HRXRD to measure the stress changes in the process of annealing,use SEM to look the spread of the metal in bonding layer;Stress is released when annealing temperature changes from 160? to 180?.the most close to the standard values at 200?,stress have the best release;Continue to heat,stress value changed little near the standard values.Before annealing,interface of metal in bonding layer is ob-vious;Temperature rise,Ag and In layer diffuse to form alloy;When the temperature reached 200?,the interface of metal in the Bonding layer disappeared,alloy is most fully,release the greatest stress.2.GaN thin film after silicon removed have been cut as 4.04 mm×4.04 mm small squares,choose 9 parts stress similar to annealing respectively,stress changes obviously when annealing temperature at 180?and 260?,measurement results of the lattice constant is most close to stress free status when annealing temperature at 260 ?.Compared with quantum well structure before and after annealing,we found that there is no obvious change of GaN,InGaN,AlGaN,AlN peak position in the quantum well when annealing temperature relatively low.3.The effect of photoelectric performance by stress change during continuous annealing:after 150? annealing and 150? mask growth,chip cut as 3.03 mm×3.03 mm small party for continuous annealing,study the relation between stress and photoelectric.Before annealing the chip in the tensile stress,with the increase of continuous annealing temperature,tensile stress reduces,compressive stress increases.When compressive stress of LED increases,the quantum well QSCE effect intensifies,LED chip light power decrease,wavelength redshift and half peak width.The effect of photoelectric performance by stress change during annealing respectively:after 150? annealing and 150? mask growth,the chip cut into four pieces and take three parts to annealing,annealing temperature is 0?,220? and 260?;The compressive stress of Samples greater,the EQE is lower,compressive stress smaller,EQE higher.4.GaN base LED have been made by electroplating Copper +bonding,analysis the degree of difficulty for making the thin copper and thick copper,campare with three transfer chip in EL and junction temperature.