The led chip preparation method of separate crystal grain vertical structure
Technical field
This invention belongs to field of photoelectric technology, is specifically related to bond organic-matter chemical vapor deposition (MOCVD) growth technology, laser lift-off and falls a kind of power type semiconductor light-emitting diode (LED) chip production method of encapsulation technology.The present invention proposes a kind ofly directly to obtain the method for separate crystal grain led chip by growth, provides the geometric figure design of led chip not to be subjected to the new way of process technology limit behind the led chip, is applicable to obtain preparation novel, great power LED.
Background technology
Usually, LED epitaxial growth on substrate obtains, thereby the preparation of LED is subjected to the restriction of the lattice structure of substrate crystal.The difference of lattice mismatch, thermal coefficient of expansion makes stress accumulation and release in the chip epitaxial loayer in epitaxial growth stage and produces a large amount of dislocations, and on Sapphire Substrate the GaN base LED epitaxial loayer, dislocation density is up to 10 especially
11/ cm
2, fundamentally restricted the further raising of LED power.Aspect photoconduction goes out and since semiconductor refractive index with the air refraction rate variance, suppressed the efficient of light, and the semi-conducting material of exiting surface absorbs and the absorption of metal electrode layer is also very important from the semiconductor outgoing.In addition, the heat dissipation problem of substrate also affects the characteristic of power-type LED widely.More than three aspects become and influence power type semiconductor led chip luminous power principal element.
Back technology---the LED shape and the rate of finished products that the scribing sliver obtains of chip preparation also generally are subjected to the influence of crystal structure on the substrate.On Sapphire Substrate, the GaN base device,, the tube core geometric figure design that helps bright dipping is restricted especially owing to the different shapes that limit chip of sapphire cleavage surface with GaN epitaxial loayer cleavage surface.In addition, use the substrate that is difficult to process, increased the cost of chip preparation.
At present, there are a lot of reports to reduce dislocation density in the epitaxial loayer, improve the result of study of crystal mass, be mainly and select laterally overgrown technology (LEO) and transition zone growing technology.The dislocation density that runs through that the people such as Shuji Nakamura of Japan adopt the epitaxial lateral overgrowth technology will come from substrate has reduced by two orders of magnitude, the LED epitaxial loayer of growing on people's patterned substrate such as Japan KazuyukiTadatomo prepares LED research report, dislocation density is reduced to 1/3rd of conventional growing epitaxial sheet, and the LED luminous power increases nearly five times, and external quantum efficiency reaches 24%; The people such as M.Iwaya of Japan well-known city red rugged brave seminar of university report that low temperature AIN insert layer makes tensile stress obtain discharging, and have obtained that the dim spot density corresponding with dislocation is reduced to 2 * 10 on the epitaxial wafer
7Cm
-2Good result; The multiple buffer layer structure of reports such as people such as T.Wang and C.C.Yang has also provided the etch-pit density corresponding with dislocation and has reached 10
6Cm
-2The result of the order of magnitude shows that crystal mass significantly improves, and obtains the good result that ultraviolet light-emitting diodes (UVLED) power significantly improves.
For the heterogeneous growth of GaN sill, though can improving the mechanism of crystal mass, laterally overgrown technology (LEO) and transition zone growing technology also have many unclear places, can not get rid of that the variation of stress is a key factor in the growth course.
Adopt laser lift-off technique, peel off Sapphire Substrate, the GaN base LED of preparation vertical electrode structure has become a developing direction that merits attention.The Osram company of Japan Ri Ya company and Germany has released the relevant device of this technology.Simultaneously, fall the LED of encapsulating structure, owing to avoided P electrode and P-GaN to absorb, utilization and refractive index are lower than the sapphire face bright dipping of GaN, the verified luminous power that can make obviously improves, even do not peel off Sapphire Substrate, also can significantly improve luminous power more than 1.5 times, the patent US6573537 B1 of propositions such as the result of reports such as the J.J.Wierer of U.S. LumiledsLighting and Daniel Steigerwald shows that the flip-chip light extraction efficiency improves 1.6 times.
The J.T.Shu in China Taiwan etc. has carried out the method for HVPE island selection growth LED, and the etch-pit density (EPD) of observing the island growth zone is 1-5 * 10
7Cm
-2, illustrate that the island epitaxial growth has obtained good crystal mass, simultaneously the LED profile is made hexagon, make the luminous power of LED be the twice of the square LED of conventional non-island growth.
Therefore, utilization improves growing method, the preparation of encapsulation, vertical stratification LED of combination of crystal mass, is the main direction that improves the LED luminous power.
This invention is on above-mentioned research basis, propose in a kind of different change epitaxial process stress distribution and improve crystal mass to reduce dislocation density, it is the MOCVD island growth, in conjunction with the die shape design and the laser lift-off technique of high light-emitting efficiency, obtain simple, the effective new method of high-power LED chip.
Summary of the invention
The objective of the invention is to propose a kind of die shape design in conjunction with high light-emitting efficiency, by island areas LED epitaxial growth, growth separate crystal grain led chip behind the laser lift-off is packaged into discrete led chip the preparation method of LED vertical stratification, that have high optical power of upper/lower electrode.
Separate crystal grain LED epitaxial loayer, in the island areas epitaxial process, because the improvement of stress distribution, dislocation density reduces in the epitaxial loayer, and crystal mass improves, thereby has improved the LED internal quantum efficiency.
The shape of design island areas, the crystal grain geometry that growth is obtained is polygon, circle that suitable photoconduction goes out, improves the luminous power of LED.
Because the island areas growth helps the release of stress, in the laser lift-off process, reduce the stress that GaN and Sapphire Substrate produce owing to laser irradiation at the interface, reduce the damage in the stripping process, the luminescent spectrum stress that reduces LED before and after peeling off changes and is moved, and obtains high performance LED to guarantee at the bottom of the peeling liner.
Tradition LED preparation method is MOCVD epitaxial growth, electrode preparation, epitaxial wafer attenuate, cuts apart the acquisition chip.The present invention then obtains discrete LED crystal grain when epitaxial growth, only need laser lift-off to remove substrate and electrode preparation, can obtain led chip, technical process such as need not attenuate, cut apart can obtain led chip, compares with conventional LED technology, reduce back technology, reduced cost.
The island areas epitaxial growth that the present invention proposes obtains the method for the vertical stratification LED of separate crystal grain, and technical process is simple, is easy to realize, is the effective way that improves the light-emitting diodes tube efficiency.
This method is peeled off Sapphire Substrate owing to combine laser lift-off technique, be prepared into the led chip of vertical stratification, and the shaped design of chip is circle and polygon, thereby has different significantly with led chip method that the island growth of report such as J.T.Shu obtains.
The preparation method of separate crystal grain vertical structure light-emitting diode of the present invention has following main points:
1. at island areas epitaxial growth separate crystal grain LED epitaxial loayer, be different from conventional full wafer growth and laterally overgrown, growth be limited in certain zone of chip dimension.
2. stress distribution is improved in the growth course, can the thicker epitaxial loayer of growth fraction, and dislocation density reduces in the epitaxial loayer, and crystal mass improves.
3. in the laser lift-off process, island areas growth can reduce the stress that GaN and Sapphire Substrate produce owing to laser irradiation at the interface, reduce the damage in the stripping process, the luminescent spectrum stress that reduces LED before and after peeling off changes and is moved, and obtains high performance LED to guarantee at the bottom of the peeling liner.
4. the geometric figure of island areas is for being fit to polygon and the circle that light is derived from tube core, thereby realized by growth control tube core shape and size, crossed the difficulty of back processes acquisition polygon and circular die, for die preparation provides a new approach.
5. when epitaxial growth, obtain discrete LED crystal grain, only need laser lift-off removal substrate and electrode preparation can obtain led chip, need not sapphire or GaN attenuate, technical process such as cut apart, can obtain led chip, compare with conventional LED technology, reduce the cost of back technology, reduced cost.
According to the preparation method of separate crystal grain vertical structure light-emitting diode of the present invention, concrete technical scheme has two kinds, describes the concrete steps of each technical scheme below in detail:
The preparation method one of the light-emitting diode chip for backlight unit light-emitting diode of separate crystal grain vertical structure, concrete steps are as follows:
1. deposit SiO on Sapphire Substrate
2, and etching SiO
2To limit island growth zone and geometry.The geometry design of vitellarium is gone out polygon and circle for helping photoconduction.
2. having SiO
2Growing n-type GaN, LED active layer, p type GaN successively on the substrate of figure; Epitaxial wafer also will carry out conventional P type and activate annealing.
3. on p-GaN, prepare electrode and reflector, electrode metal wants to obtain the good ohmic contact, also will consider simultaneously with the reflector metal that plays the mirror surface effect has good adhesive attraction, to pass through alloy after the deposit and obtain and p-GaN between ohmic contact; Being chosen as reflectivity height, good stability, good adhesiveness being arranged of reflector metal with the ohmic contact layer metal, the metal that ohmic contact is had no adverse effects.
4. utilize metal level to be bonded on Si or the Cu support substrates the above-mentioned P of having electrode LED epitaxial wafer, be placed on and take bubble in the metal level in the vacuum chamber away, guarantee evenly tight contact the in nothing cavity of island growth layer and support substrates surface, support substrates is processed into has the figure of inducing the sliver function.
5. laser lift-off is removed the Sapphire Substrate that is difficult to process.Because GaN and Sapphire Substrate bound fraction are few, can adopt more low-energy laser beam in the laser lift-off, have reduced at stripping process the damage of crystal at the interface.Peel off finish after, need to remove the metal Ga of epi-layer surface.
6. on the n-GaN face, finish the n electrode preparation; Because the requirement of exiting surface, the n electrode will occupy less area as far as possible, designs electrode size usually on the minimum requirements yardstick that guarantees bonding wire.
7. separating the island growth district is the led chip of vertical electrode structure.
The preparation method two of the light-emitting diode chip for backlight unit light-emitting diode of separate crystal grain vertical structure, concrete steps are as follows:
1. deposit SiO on Sapphire Substrate
2, and etching SiO
2To limit island growth zone and geometry.The geometry design of vitellarium is gone out polygon and circle for helping photoconduction.
2. on Sapphire Substrate, use the thick n-GaN epitaxial loayer of hydride gas-phase epitaxy (HVPE) technology growth.
3. use MOCVD technology diauxic growth Si Doped GaN, LED active layer, p type GaN on the substrate that has thick n-GaN island growth layer, epitaxial wafer also will carry out conventional P type and activate annealing.
4. on p-GaN, prepare electrode and reflector, electrode metal wants to obtain the good ohmic contact, also will consider simultaneously with the reflector metal that plays the mirror surface effect has good adhesive attraction, to pass through alloy after the deposit and obtain and p-GaN between ohmic contact; Being chosen as reflectivity height, good stability, good adhesiveness being arranged of reflector metal with the ohmic contact layer metal, the metal that ohmic contact is had no adverse effects.
5. utilize metal level to be bonded on Si or the Cu support substrates the above-mentioned P of having electrode LED epitaxial wafer, be placed on and take bubble in the metal level in the vacuum chamber away, guarantee evenly tight contact the in nothing cavity of island growth layer and support substrates surface, support substrates is processed into has the figure of inducing the sliver function.
6. laser lift-off is removed the Sapphire Substrate that is difficult to process.Because GaN and Sapphire Substrate bound fraction are few, can adopt more low-energy laser beam in the laser lift-off, have reduced at stripping process the damage of crystal at the interface.Peel off finish after, need to remove the metal Ga of epi-layer surface.
7. finish the n electrode preparation on the n-GaN face, because the requirement of exiting surface, the n electrode will occupy less area as far as possible, designs electrode size usually on the minimum requirements yardstick that guarantees bonding wire.
8. separating the island growth district is the led chip of vertical electrode structure.
Above-mentioned two kinds of methods are equally applicable to have in the epitaxial loayer preparation of the LED of AlGaN electronic barrier layer.
Description of drawings
Below in conjunction with accompanying drawing the present invention is illustrated in further detail:
The plane geometric figure structure of Fig. 1 island growth;
Fig. 2 n type electrode plane figure;
Fig. 3 (a)~(g) is a separate crystal grain vertical structure led chip preparation process;
Fig. 4 (a) and (b) illustrate the relation of reflectivity and thickness of Al and Ag respectively.
Most preferred embodiment is described in detail
Below with reference to accompanying drawing of the present invention, more detailed description goes out most preferred embodiment of the present invention.
Be depicted as separate crystal grain vertical structure light-emitting diode chip for backlight unit preparation process as Fig. 3 (a)~(f), 1 expression is Sapphire Substrate or the substrate that has the GaN grown layer among the figure, the 2nd, and SiO
2, the 3rd, LED epitaxial wafer, the 4th, transparency electrode (Ni/Au), the 5th, reflector, the 6th, support substrates (Si or Cu), the 7th, bonding metal (Au-Sn alloy).Describe most preferred embodiment one concrete steps in detail below in conjunction with accompanying drawing:
(a) deposit SiO on Sapphire Substrate 1
22, and etching SiO
22 to limit island growth zone and geometry.The size of growth district is the LED device size, and the geometry of vitellarium goes out polygon and circle for helping photoconduction, among Fig. 1 example rectangle, hexagon and circle;
(b) on the substrate that (a) step obtains, utilization MOCVD technology growth LED epitaxial loayer, and carry out the P type and activate annealing.
(c) evaporation transparency electrode 4 on GaN base LED epitaxial wafer 3p face, structure be Ni (
)/Au (
), 500 ℃ of following alloys 5 minutes in oxygen atmosphere then.
(d) on transparency electrode evaporation Ni (
)/Al (
)/Ni (
)/Au (
) reflector 5.High-reflectivity metal can be Al or Ag in the reflector 5, and corresponding wavelength can be adjusted according to thickness and reflectivity relation.Figure 4 shows that corresponding to different wave length the graph of relation of Al layer thickness and Ag layer thickness and reflectivity.
(e) prepare SiO on Si or the Cu support substrates
2Insulating barrier, evaporation Au-Sn alloy or other can be used for the metal level 7 of bonding, and be placed on and take bubble in the metal level 7 in the vacuum chamber away, guarantee that the island growth layer does not evenly have empty tight the contact with the support substrates surface, is processed into support substrates figure and the structure that can induce sliver.
(f) at about 300 ℃ or lower temperature following LED epitaxial wafer and Si substrate or copper substrate 6 bondings.
(g) shine from sapphire substrate side with the KrF excimer laser, peel off Sapphire Substrate, laser wavelength 248nm, irradiation energy density 400-600mJ/cm
2, scanning frequency is 1Hz; Peel off finish after, need to remove the metal Ga of epi-layer surface.
(h), peel off acquisition n electrode through figure at n-GaN surface evaporating n electrode metal; Be illustrated in figure 3 as n type electrode plane figure, electrode structure is Ti among the figure
/ Al
/
Ti 100~
/ Au
(i) separate the island growth district, then obtain the led chip of high-power vertical electrode structure.Most preferred embodiment two technical schemes are as follows, and the concrete steps of present embodiments are described with reference to figure 3:
(a) deposit SiO on Sapphire Substrate 1
22, and etching SiO
22 to limit island growth zone and geometry.The size of growth district is the LED device size, and the geometry of vitellarium goes out polygon and circle for helping photoconduction, among Fig. 1 example rectangle, hexagon and circle.
(b) on the substrate that in (a) step, obtains, on Sapphire Substrate, use the thick n-GaN epitaxial loayer of hydride gas-phase epitaxy (HVPE) technology growth, obtain the n type GaN substrate of island growth.
(c) on the island GaN substrate that (b) step obtains, utilization MOCVD technology diauxic growth Si Doped GaN, LED active layer, p type GaN, epitaxial wafer also will carry out conventional P type and activate annealing.
(d) evaporation transparency electrode 4 on GaN base LED epitaxial wafer p face, structure be Ni (
)/Au (
), 500 ℃ of following alloys 5 minutes under oxygen then.
(e) on transparency electrode evaporation Ni (
)/Al (
)/Ni (
)/Au (
) reflector 5.High-reflectivity metal can be Al or Ag in the reflector 5, and corresponding wavelength can be adjusted according to thickness and reflectivity relation.Figure 4 shows that corresponding to different wave length the graph of relation of Al layer thickness and Ag layer thickness and reflectivity.
(f) 1 preparation SiO on Si or the Cu support substrates
2Insulating barrier, evaporation Au-Sn alloy or other can be used for the metal level 7 of bonding, and be placed on and take bubble in the metal level 7 in the vacuum chamber away, guarantee that the island growth layer does not evenly have empty tight the contact with the support substrates surface, is processed into support substrates figure and the structure 6 that can induce sliver.
(g) at about 300 ℃ or more following LED epitaxial wafer of low temperature and Si substrate or copper substrate 6 bondings.
(h) shine from sapphire substrate side with the KrF excimer laser, peel off Sapphire Substrate, laser wavelength 248nm, irradiation energy density 400-600mJ/cm
2, scanning frequency is 1Hz; Peel off finish after, need to remove the metal Ga of epi-layer surface.
(i), peel off acquisition n electrode through figure at n-GaN surface evaporating n electrode metal; Be illustrated in figure 3 as n type electrode plane figure, electrode structure is Ti among the figure
/ Al
/
Ti 100~
/ Au
(j) separate the island growth district, then obtain the led chip of high-power vertical electrode structure.
Two most preferred embodiments in the preparation method's of the light-emitting diode chip for backlight unit of above corresponding two kinds of separate crystal grain vertical structures preparation method, increase the AlGaN electronic barrier layer in the epitaxial growth steps or carry out other growths, to obtain to have the light-emitting diode chip for backlight unit of the separate crystal grain vertical structure of AlGaN electronic barrier layer or other epitaxial structures, all can implement the described technical scheme of preparation method of the light-emitting diode chip for backlight unit of above-mentioned separate crystal grain vertical structure.
The advantage of this invention:
(1) at island areas epitaxial growth separate crystal grain LED epitaxial loayer, be different from conventional full wafer growth and laterally overgrown, growth district is limited in the chip dimension, obtain the high-quality island LED epitaxial loayer of chip size.
(2) stress distribution is improved in the growth course, can the thicker epitaxial loayer of growth fraction, and dislocation density reduces in the epitaxial loayer, and crystal mass improves, and the LED luminous efficiency is improved.
(3) directly on the island graph substrate, implement to grow near technology, realize volume production easily with common GaN-based LED;
(4) in the laser lift-off process, island areas growth can reduce the stress that GaN and Sapphire Substrate produce owing to laser irradiation at the interface, reduce the damage in the stripping process, the luminescent spectrum stress that reduces LED before and after peeling off changes and is moved, and obtains high performance LED to guarantee at the bottom of the peeling liner.
(5) geometric figure of island areas is for being fit to polygon and the circle that light is derived from tube core, thereby realized by growth control tube core shape and size, crossed the difficulty of back processes acquisition polygon and circular die, for die preparation provides a new approach.
(6) when epitaxial growth, obtain discrete LED crystal grain, only need laser lift-off removal substrate and electrode preparation can obtain led chip, need not sapphire or GaN attenuate, technical process such as cut apart, can obtain led chip, compare with conventional LED technology, reduce the cost of back technology, reduced cost.
(7) the Al lamination layer structure of high reflectance is adopted in p type reflector, improves chip light-emitting efficiency.
This invention provides new method to GaN based high-power light-emitting device, and is especially significant to short wavelength's light-emitting diode.Use the LED of this method preparation, having becomes the vertical electrode of main flow potentiality structure, thereby luminous power and thermal characteristic are good, and owing to adopt the die shape (circular, polygon) that helps the light outgoing, luminous power can further improve.Compare with the method for the raising light extraction efficiency of present report, led chip preparation process involved in the present invention is simple, helps realizing industrialization.
Although disclose most preferred embodiment of the present invention and accompanying drawing for the purpose of illustration, it will be appreciated by those skilled in the art that: without departing from the spirit and scope of the invention and the appended claims, various replacements, variation and modification all are possible.Therefore, the present invention should not be limited to most preferred embodiment and the disclosed content of accompanying drawing.