CN101667616A - Ultra-thin ohmic contacts for p-type nitride light emitting devices and methods of forming - Google Patents
Ultra-thin ohmic contacts for p-type nitride light emitting devices and methods of forming Download PDFInfo
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- CN101667616A CN101667616A CN200910175001A CN200910175001A CN101667616A CN 101667616 A CN101667616 A CN 101667616A CN 200910175001 A CN200910175001 A CN 200910175001A CN 200910175001 A CN200910175001 A CN 200910175001A CN 101667616 A CN101667616 A CN 101667616A
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Abstract
A semiconductor based Light Emitting Device (LED) can include a p-type nitride layer and a metal ohmic contact, on the p-type nitride layer. The metal ohmic contact can have an average thickness of less than about 25 A and a specific contact resistivity less than about 10<-3> ohm-cm<2>.
Description
The application is to be on July 27th, 2005 applying date, and application number is 200580025279.8, and denomination of invention is divided an application for the application of " being used for ultra-thin ohmic contact of P type nitride-based light emitting device and forming method thereof ".
CROSS-REFERENCE TO RELATED PATENT
The application relates to the U.S. Provisional Patent Application No.60/591 that is entitled as Ultra-Thin Ohmic Contacts for P-Type Nitride Light EmittingDevices that people such as Raffetto submitted on July 27th, 2004,353, and the U.S. Provisional Patent Application No.60/639 that is entitled as Ultra-Thin Ohmic Contacts for P-TypeNitride Light Emitting Devices that submits on December 28th, 2004 of people such as Raffetto, 705, its full content is incorporated herein by reference in this.
Technical field
The present invention relates to semiconductor device, relate more specifically to have the light-emitting device that is formed at the ohmic contact on the III nitride base epitaxial loayer.
Background technology
Light-emitting diode and laser diode are the known solid-state electronic devices that can produce light when applying enough voltage.Light-emitting diode and laser diode are commonly referred to light-emitting device (LED).Light-emitting device generally includes the p-n junction that is formed in the epitaxial loayer, and this outer layer growth is on substrates such as sapphire, silicon, carborundum, GaAs for example.The structure of thin epitaxy layer that the light wavelength that is produced by this LED distributes and depends on the material that forms p-n junction and comprise the active area of this device.
Usually, LED comprises n type substrate, is formed at the n type epitaxial region on this substrate and is formed at p type epitaxial region on the n type epitaxial region.For the ease of device is applied voltage, the anode ohmic contact is formed in the p type district (being generally the p type epitaxial loayer of exposure) of this device, and the negative electrode ohmic contact is formed in the n type district (for example n type epitaxial loayer of substrate or exposure) of this device.
Because be difficult to form the good p type III group nitride material (for example GaN, AlGaN, InGaN, AlInGaN and AlInN) of conduction, the shortage of CURRENT DISTRIBUTION may become the limiting factor that these materials form the LED performance in the p type layer.Therefore, be desirably on the p type layer surf zone as much as possible of exposure and form ohmic contact, thereby guide current is passed the big as far as possible zone of this device active area.Yet, provide big anode contact device performance to be harmful to from some aspect.Usually expectation is extracted light as much as possible from light-emitting diode.Because the anode ohmic contact generally includes metal level, the light that produces in the LED active area can partly absorb in ohmic contact, has reduced total luminous efficiency of this device.
In some devices, may be desirably on the p type layer of exposure and form reflective metal layer, make that can pass the light that p type layer escapes from device usually is reflected back toward in the auto levelizer, passes substrate and is extracted.Yet for example the high reflecting metal of aluminium and silver does not form with the good ohmic of p type nitride material and contacts.Therefore, between p type nitride layer and reflector, provide ohmic contact usually.The absorption that reduces in the ohmic contact becomes the problem of being concerned about in these devices.
Therefore, need ohmic contact structure of improving and the method that on p type nitride material, forms the ohmic contact structure.
Brief summary of the invention
Can be provided for the ultra-thin ohmic contact and the formation method of p type nitride-based light emitting device according to embodiment of the present invention.According to these embodiments, semiconductor-based light-emitting device (LED) can comprise the metal ohmic contact on p type nitride layer and its, wherein this metal ohmic contact average thickness approximately less than
, the specific contact resistivity rate is approximately less than 10
-3Ohm.cm
2This metal ohmic contact can comprise Pt.
In embodiments more according to the present invention, this metal ohmic contact average thickness approximately less than
In embodiments more according to the present invention, this metal ohmic contact average thickness is about
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In embodiments more according to the present invention, this metal ohmic contact average thickness is about
In embodiments more according to the present invention, this metal ohmic contact average thickness approximately less than
In embodiments more according to the present invention, by the auger analysis of this metal ohmic contact is measured, this metal ohmic contact covers about 67% or p type nitride layer still less.In embodiments more according to the present invention, this metal ohmic contact covers the part of p type nitride layer, and the remainder of this p type nitride layer is not covered by the metal ohmic contact.
In embodiments more according to the present invention, this metal ohmic contact average thickness approximately less than
In embodiments more according to the present invention, by the auger analysis of this metal ohmic contact is measured, this metal ohmic contact covers about 47% or p type nitride layer still less.
In embodiments more according to the present invention, under the measurement wavelength of about 350nm, the standardization transmissivity of this metal ohmic contact is about 92%.In embodiments more according to the present invention, this metal ohmic contact covers the part of p type nitride layer, and the remainder of this p type nitride layer is not covered by the metal ohmic contact.
In embodiments more according to the present invention, this metal ohmic contact average thickness approximately less than
In embodiments more according to the present invention, by the auger analysis of this metal ohmic contact is measured, this metal ohmic contact covers about 28% or p type nitride layer still less.
In embodiments more according to the present invention, under the measurement wavelength of about 350nm, the standardization transmissivity of this metal ohmic contact is about 94% to 96%.In embodiments more according to the present invention, this metal ohmic contact average thickness is about
In embodiments more according to the present invention, by the auger analysis of this metal ohmic contact is measured, this metal ohmic contact covers about 13% or p type nitride layer still less.In embodiments more according to the present invention, under the measurement wavelength of about 350nm, the standardization transmissivity of this metal ohmic contact is about greater than 98%.
In embodiments more according to the present invention, this metal ohmic contact can be platinum, rhodium, zinc oxide, palladium, palladium oxide, titanium, nickel/gold, nickel oxide/gold, nickel oxide/platinum and/or titanium/gold.In embodiments more according to the present invention, this LED also can comprise the pad that is positioned on the metal ohmic contact.
In embodiments more according to the present invention, LED can comprise p type nitride layer and the metal ohmic contact on it, and wherein this metal ohmic contact average thickness is about
In embodiments more according to the present invention, LED can comprise p type nitride layer and the metal ohmic contact on it.This metal ohmic contact average thickness is about
, by the auger analysis of this metal ohmic contact is measured, this metal ohmic contact covers about 13% or p type nitride layer still less.
In embodiments more according to the present invention, LED comprises p type nitride layer and the metal ohmic contact on it.This metal ohmic contact can have certain average thickness, and standardization transmissivity greater than 98% is provided provide under the measurement wavelength of about 350nm approximately for it.
In embodiments more according to the present invention, can be provided for forming the method for semiconductor-based light-emitting device (LED) by following steps: on n type substrate, form p type nitride layer, on this p type nitride layer, form the metal ohmic contact, until its have approximately less than
The average thickness peace treaty less than 10
-3Ohm.cm
2The specific contact resistivity rate, and stop to form this metal ohmic contact.
In embodiments more according to the present invention, formation metal ohmic contact can further comprise with given pace accompanies sheet (witness slide) to go up one time period of plated metal on p type nitride layer and in reference, being provided for the metal level with first average thickness of metal ohmic contact, and accompany on the sheet this metal layer thickness indication monitored.If this indication is higher than predetermined indication threshold value, then further with the follow-up time interval and/or subsequent rate plated metal to increase average thickness.If described indication is equal to or less than predetermined indication threshold value, then stop plated metal.
In embodiments more according to the present invention, by measuring transmissivity, sheet resistivity, electric capacity, reflectivity and/or the resonance frequency of metal level, so that the monitoring to the thickness indication to be provided.In embodiments more according to the present invention, further deposit this metal level, surpass predetermined indication threshold value up to this indication.In embodiments more according to the present invention, deposition rate is about per second
Arrive
Description of drawings
Fig. 1 is the cross section view that shows some embodiments of the present invention.
Fig. 2 A and 2B are the top view of LED tube core (dice) with ohmic contact of some embodiments according to the present invention.
Fig. 3 is the cross section view that shows the other embodiment of the present invention.
Fig. 4 is the flow chart that shows the inventive method embodiment.
Fig. 5 is the curve chart of the transmissivity of all thickness platinum film measured on wave-length coverage.
Fig. 6 is the flow chart that shows the other method embodiment of the present invention.
Fig. 7 is the flow chart that shows the other method embodiment of the present invention.
Fig. 8 is the schematic diagram of the film depositing system of some embodiments according to the present invention.
Fig. 9 A and 9B are some embodiments according to the present invention, and average thickness is about
Scanning transmission electron microscope (STEM) image of Pt contact layer.
Figure 10 A and 10B are some embodiments according to the present invention, and average thickness is about
The STEM image of Pt contact layer.
Figure 11 A and 11B are some embodiments according to the present invention, and average thickness is about
The STEM image of Pt contact layer.
Detailed Description Of The Invention
Below with reference to accompanying drawing the present invention is described more all sidedly, embodiment of the present invention wherein shown in the drawings.Embodiment shown in the present invention should not be understood that to be subject to here; On the contrary, provide the purpose of these embodiments to be, make this disclosure become thorough and complete, and will pass on scope of the present invention to those skilled in the art all sidedly.Identical numeral is represented components identical all the time.
In addition, schematically show each layer and the zone shown in the figure.Described the present invention although those skilled in the art it is also understood that in conjunction with the chip of semiconductor wafer and scribing, this chip can be diced into arbitrary dimension.Therefore, the invention is not restricted to relative size shown in the accompanying drawing and spacing.In addition, explain, show illustrated some feature for example layer thickness and characteristic size with exaggerative size for illustrating clear and being convenient to.
Term is only for the purpose of describing specific embodiments as used herein, but not is intended to limit the present invention.Use singulative " " and " being somebody's turn to do " also to comprise plural form at this, unless clear and definite explanation in addition in context.It should also be understood that, when in specification, using, term " comprises " having indicated and has described feature, integral body, step, operation, element and/or form, and do not exist or adds one or more other features, integral body, step, operation, element, composition and/or its combination but do not get rid of.
Be to be understood that, when element or the layer be called as be positioned at another element or the layer " on ", when " connection " or " coupling " arrives another element or layer, this element or layer can be located immediately on this another element or the layer, directly connect or be coupled to another element or the layer, perhaps can have intermediary element.On the contrary, when element be called as " directly " be positioned at another element or layer " on ", there is not intermediary element in " directly connect " or " directly coupling " during to another element or layer.Identical numeral is always represented components identical.As used herein, term " and/or " comprise one or more associations the project of enumerating arbitrarily and all combinations.
Although should be appreciated that and utilize first, second grade of term to describe various elements, composition, zone, layer and/or part here, these elements, composition, zone, layer and/or part are not limited to these terms.These terms are only used for an element, composition, zone, layer or part are different from another element, composition, zone, layer or part.Therefore, next said first element, composition, zone, layer or part also can be called second element, composition, zone, layer or part, and do not break away from instruction of the present invention.
In addition, relative terms, for example " bottom " or " bottom " and " top " or " top " this can be used for describing as shown in the figure an element and the relation of another element.Should be appreciated that relative terms is intended to comprise the different orientation of the device except orientation described in the figure.For example, if the device among figure upset, so be described as being positioned at other elements of element D score side be positioned at this element " on " side.Exemplary term " bottom " therefore can comprise " bottom " and " top " two kinds of orientations, depends on the concrete orientation of figure.Similarly, if the upset of the device in diagram, then be described as element " under " or " below " then other elements will be oriented in this element " top ".Exemplary term " under " or " below " therefore can comprise two orientations in above and below.
Employed as the thickness that relates to ohmic contact at this, term " about " is meant
Tolerance within.
Unless otherwise defined, used here all terms (comprising technical term and scientific terminology) have the identical meaning with those skilled in the art's common sense.It should also be understood that, term, defined these terms in common dictionary for example should be interpreted as having the meaning with the contextual aggregatio mentium of correlation technique and this specification, be not construed as meaning desirable or extremely formal form, unless do clearly to limit here.
Describe embodiment of the present invention in this reference section diagram, these are illustrated as the indicative icon of the desirable embodiment of the present invention.Therefore, since for example the change of the shape shown that causes of manufacturing technology and/or tolerance be expected.Therefore, embodiment of the present invention should not be construed as the concrete shape that is limited to zone shown here, but for example comprise owing to make the form variations that causes.For example, the zone that is shown rectangle can have feature that is round, crooked or gradual change usually at its edge, rather than changes to next zone from a discrete region.Therefore, zone shown in the figure is schematically in essence, its shape do not set forth device the zone accurate shape and be not intended to limit the scope of the invention.
Usually with reference to the gallium nitride based light emitting diode on the silicon carbide-based substrate embodiment of the present invention are described.Yet, it will be appreciated by those skilled in the art that and adopt many various combinations of substrate and epitaxial loayer can implement many additive methods of the present invention.For example, combination can comprise AlGaInP diode, the InGaAs diode on the GaAs substrate, the AlGaAs diode on the GaAs substrate, SiC or the sapphire (Al on the GaP substrate
2O
3) SiC diode on the substrate and/or the nitride based diode on gallium nitride, carborundum, aluminium nitride, sapphire, zinc oxide and/or other substrates.
The GaN based illuminating device generally includes insulation, semiconductor or conductive substrates, and for example SiC or sapphire deposit a plurality of GaN base epitaxial loayers on it.This epitaxial loayer includes the source region, and it has p-n junction luminous when being subjected to encouraging.
Although the various LED embodiments in this announcement comprise substrate, those skilled in the art are to be understood that, crystallization epitaxial growth substrate of the epitaxial loayer that comprises LED of having grown on it can be removed, this self-supporting epitaxial loayer can be installed in alternative bearer substrate or inferior mounting on the platform (submount), and the latter can have calorifics, electricity, structure and/or the optical characteristics that is better than initial substrates.The structure that the invention is not restricted to have the crystallization epitaxial growth substrate described here can be used from the structure that the alternative bearer substrate had been removed and be bonded to original growth substrates in conjunction with epitaxial loayer wherein.
The light-emitting device that is used for embodiment of the present invention can be gallium nitride based light emitting diode or the laser of making on silicon carbide substrates, for example by Cree, and Inc.of Durham, the device of NorthCarolina manufacturing and sale.For example, the present invention is suitable for using as United States Patent (USP) 6,740, and 906,6,734,033,6,664,560,6,201,262,6,187,606,6,120,600,5,912,477,5,739,554,5,631,190,5,604,135,5,523,589,5,416,342,5,393,993,5,338,944,5,210,051,5,027,168,4,966,862 and/or 4,918,497 described LED and/or lasers, the disclosure of these patents is incorporated herein by reference in this, as having set forth it fully at this in full.The U.S. Patent application No.10/899 that LED that other are suitable and/or laser are being entitled as " GROUP III NITRIDE BASED LIGHT EMITTING DIODESTRUCTURES WITH A QUANTUM WELL AND SUPERLATTICE; GROUP IIINITRIDE BASED QUANTUM WELL STRUCTURES AND GROUP III NITRIDEBASED SUPERLATTICE STRUCTURES " U.S. Patent application No.2003/0006418 and in being entitled as of submitting on July 27th, 2004 " GROUP III NITRIDE BASED QUANTUMWELL LIGHT EMITTING DEVICE STRUCTURES WITH AN INDIUM CONTAININGCAPPING STRUCTURE ", 791 (AttorneyDocket No.5308-204IP), the U.S. Patent application No.10/881 that is entitled as " LIGHTEMITTING DEVICES HAVING CURRENT BLOCKING STRUCTURES AND METHODSOF FABRICATING LIGHT EMITTING DEVICES HAVING CURRENT BLOCKINGSTRUCTURES " that submits on June 30th, 2004,814 (Attorney Docket No.5308-457), and/or on July 27th, 2004 submit to be entitled as " LIGHT EMITTINGDEVICES HAVING A REFLECTIVE BOND PAD AND METHODS OF FABRICATINGLIGHT EMITTING DEVICES HAVING A REFLECTIVE BOND PAD " U.S. Patent application No.10/899, describe to some extent among 793 (the Attorney Docket No.5308-468), the disclosure of these patents is incorporated herein by reference in this, as having set forth it fully at this in full.
In specific embodiments of the present invention, light-emitting device can comprise the p electrode, and this electrode cremasteric reflex layer passes device with the light that will produce in the active area toward back reflective.Reflection p electrode and dependency structure are at the U.S. Patent Publication No.2003/0123164 that is entitled as " LIGHT EMITTING DIODES INCLUDING SUBSTRATEMODIFICATIONS FOR LIGHT EXTRACTION AND MANUFACTURING METHODSTHEREFOR " and be entitled as among the U.S. Patent Publication No.2003/0168663 of " REFLECTIVEOHMIC CONTACTS FOR SILICON CARBIDE INCLUDING A LAYER CONSISTINGESSENTIALLY OF NICKEL; METHODS OF FABRICATING SAME; AND LIGHTEMITTING DEVICES INCLUDING THE SAME " and describe to some extent, the disclosure of these patents is incorporated herein by reference in this, as having set forth it fully at this in full.
Here, term " ohmic contact " is meant such contact, wherein under nearly all expection operating frequency, impedance between this contact is provided by relational expression impedance=V/I substantially, wherein V is this contact both sides voltage, I is electric current (that is, under all working frequency, basic identical with the impedance that this ohmic contact is associated).For example, in some embodiments according to the present invention, ohmic contact can be that the specific contact resistivity rate is approximately less than 10
-03Ohm.cm
2, and in some embodiments approximately less than 10
-04Ohm.cm
2Contact.Therefore, rectification or the high contact of specific contact resistivity rate, for example the specific contact resistivity rate is greater than about 10
-03Ohm.cm
2Contact be not the ohmic contact of the term indication here.
The inferior of metallic plate, printed circuit board (PCB) or lead frame (all these all are called " the inferior platform that mounts " at this) mounts on the platform can to make substrate for example LED is installed in downwards.Fig. 1 has schematically shown LED 1, comprises n type SiC substrate 10 and active area 12, and this active area 12 comprises n-GaN basic unit 14 and the p-GaN basic unit 16 that is grown on this substrate and is patterned as platform.Metal p electrode 18 is deposited on the p-GaN layer 16 and electricity coupling with it, and the preparation wire-bonded connects 28 pads 20 that are connected on the p electrode 18.Use conductive epoxy resin 26 time to mount platform 24 on the conductive substrates and with the n electrode 22 of this conductive substrates electricity coupling attaches to conduction.Hot curing is with this epoxy resin 26 that hardens, be formed for thus led chip stable and conduction mount platform (mount).The light that produces in active area 12 is upwards advanced and from the device outgoing.Yet the part of the light that is produced can be absorbed (being called ohmic contact 18 at this sometimes) by ohm p electrode 18.
In order to reduce and/or minimize the absorption of 18 pairs of light of p electrode, some embodiments according to the present invention, the thickness of this p electrode can be reduced to
Below.Embodiments more of the present invention provide the ultra-thin p contacting metal that can deposit by mode reproducible, controlled and that can make.In some embodiments, ohmic contact 18 comprises platinum.Ohmic contact 18 can be used other materials.For example, ohmic contact 18 can comprise rhodium, zinc oxide, palladium, palladium oxide, titanium, nickel/gold, nickel oxide/gold, nickel oxide/platinum and/or titanium/gold.In some embodiments, ohmic contact 18 average thicknesss less than
In other embodiment, ohmic contact 18 average thicknesss less than
In some embodiments, ohmic contact 18 average thicknesss can arrive for 13
In other embodiment, ohmic contact 18 average thicknesss can for.
In some embodiments, ohmic contact 18 average thicknesss less than
In some embodiments, ohmic contact 18 average thicknesss less than
, in other embodiment, ohmic contact 18 average thicknesss less than
More in addition in the embodiment, ohmic contact 18 average thicknesss are less than approximately
It will be appreciated by those skilled in the art that less than
Thickness, particularly less than
Thickness can represent the part on surface or inferior individual layer are covered.Therefore, even the gained layer is called " film ", this film may only partly cover the surface of p type GaN layer.In addition, some of this p type GaN layer are not capped part can be characterized by " exposure ", because these parts are not covered (part that for example, is exposed is covered by the metal ohmic contact of inferior individual layer) by the film thicker than metal ohmic contact minimum average thickness.
Therefore, embodiments more of the present invention provide coverage less than 70% contact layer.Other embodiment of the present invention provides coverage less than 50% contact layer.Of the present invention more in addition embodiment provide coverage less than 30% contact layer.Additional embodiment of the present invention provides coverage less than 20% contact layer.Here, when the metal ohmic contact is described as the p type nitride layer that " only " cover particular percentile (for example 70%), be to be understood that, the remainder of this p type nitride layer (for example 30%) is not capped (promptly, be exposed), perhaps covered by this metal ohmic contact part less than the metal ohmic contact average thickness that covers p type nitride layer.In addition, these percentage of coverage should not be construed as and comprise the p type nitride portions (for example excessive p type nitride layer) that is not positioned at metal ohmic contact external margin below.
Can or be used for controllably forming any other appropriate technology of atom level metallic film by electron beam (e-beam) evaporation, form the ohmic contact of some embodiments according to the present invention.For example, suppose to keep enough technology controlling and process, then can form ohmic contact by electroplating.In electron beam evaporation plating, in vacuum chamber, use the high-intensity beams of fusing target region that the source metal target is heated to evaporating point.Controllably with the evaporation metal coat to the epitaxial wafer that places in this cavity.Electron beam evaporation plating and other film deposition methods have been described in the INTRODUCTION TO MICROELECTRONICFABRICATION that R.Jaeger showed (second edition in the 2002) chapter 6.
By changing the electric current and the energy of electron beam, can control the deposition rate of this technology.In some embodiments, deposition rate maintains low speed, and for example per second 0.1 arrives
Thereby, keep abundant control to thickness.In addition.Accompany the transmission performance of sheet by monitoring the reference that has deposited the ohmic metal film on it simultaneously, can between depositional stage, deposit by controlling diaphragm.It can be sapphire, quartz or any other optical transmission material that can depositing metallic films on it that sheet is accompanied in this reference.Transmission sensitivity to metal thickness depends on the optical wavelength of using in the monitor procedure.That is to say, can improve transmission sensitivity at shorter wavelength.Therefore, in some embodiments, can launch 350nm or short wavelength's the UV light source spectrophotometric supervisory control system of UV for example more, between the film depositional stage or measure sapphire afterwards with reference to the transmission performance of accompanying sheet by adopting.Deposition rate can realize reproducing of thin layer and controllable deposition slowly.
In case after the deposition, ohmic contact 18 provides " deposition " ohm or nonrectifying contact.That is to say,, do not need further to handle or annealing for accurate desirable the electrically contacting with p type GaN layer 16 is provided.Yet, in some cases, may need or expect ohmic contact 18 annealing or carry out other to deposit back technology, thereby improve its ohm property (for example reducing the specific contact resistivity of contact layer).
In some embodiments, the method according to this invention comprises: form n type epitaxial loayer on substrate; On this n type epitaxial loayer, form p type epitaxial loayer, thus the generator precursor construction; This device precursor construction is placed the electron beam evaporation plating system; In this deposition system, place with reference to accompanying sheet; And accompany in this device precursor construction and this reference and to form platinum layer on the sheet, monitor the transmissivity that metal film on the sheet is accompanied in this reference simultaneously.In some embodiments, measure under the wavelength, before dropping to below 98%, stop to deposit this ohmic contact metal layer with reference to the standardization transmissivity of accompanying the metal film on the sheet at 350nm.In other embodiments, measure under the wavelength, before dropping to below 96%, stop to deposit this ohmic contact metal layer with reference to the standardization transmissivity of accompanying the metal film on the sheet at 350nm.In other embodiment, measure under the wavelength at 350nm, before dropping to below 92%, stop to deposit this ohmic contact metal layer with reference to the standardization transmissivity of accompanying the metal film on the sheet.
As shown in Figure 5, be deposited on reference to the standardization transmissivity of accompanying the metal film on the sheet according to the thickness of this film and the optical wavelength of using in measuring change.Change angle, the absorptivity of this metal film is film thickness and the function that passes the light wavelength of this film.Apparent from the curve chart of Fig. 5, for changing, the maximum of the absorptivity of the function of thickness betides the short wavelength.For example, at the 350nm wavelength,
The transmissivity of platinum film is 98 to 100%, and average thickness is
The transmissivity of film be 94 to 96%, average thickness is
The transmissivity of film be about 92%.Short wavelength more, this effect is more remarkable.
Therefore, in some embodiments, can be by adopting in the 350nm or the supervisory control system of the UV light source of short-wave long light-emitting more, the monitoring sapphire is with reference to the transmission performance of accompanying sheet between the film depositional stage.Be formed at the transmissivity of accompanying the metal film on the sheet through calibration reference by in-situ monitoring, can reach predetermined threshold levels in the transmissivity of this metal film before or stop this depositing operation afterwards.Therefore, can highly precisely control the deposition of metal film as thin as a wafer according to an embodiment of the present invention.
In some embodiments, measure under the wavelength, before dropping to below 98%, stop to deposit this ohmic contact with reference to the standardization transmissivity of accompanying this metal film on the sheet at 350nm.In other embodiments, measure under the wavelength, before dropping to below 96%, stop to deposit this ohmic contact with reference to the standardization transmissivity of accompanying the metal film on the sheet at 350nm.In other embodiment, measure under the wavelength at 350nm, before dropping to below 92%, stop to deposit this ohmic contact with reference to the standardization transmissivity of accompanying the metal film on the sheet.
Can adopt additive method to monitor the thickness of the metal film that is deposited.For example, can measure other physics, electricity or the optical characteristics of this film (perhaps having deposited the material of this film on it) that changes according to thickness, and itself and known standard are compared, thereby determine thickness.These characteristics can be including but not limited to sheet resistivity, electric capacity or the reflectivity of this film.In one embodiment, the coated resonant frequency of quartz crystal of deposition material of monitoring in deposition process.The resonance frequency of this crystal is offset pro rata with the thickness of the film that is deposited, and can provide to measure thickness is enough accurate.See INTRODUCTION TOMICROELECTRONIC FABRICATION (second edition in the 2002) chapter 6 that R.Jaeger shows.
In order to promote CURRENT DISTRIBUTION, pad can comprise and strides across one or more CURRENT DISTRIBUTION that ohmic contact partly extends and refer to.Shown in Fig. 2 A and 2B, be formed at pad 20 on the ohmic contact 18 and can comprise and stride across one or more CURRENT DISTRIBUTION that ohmic contact 18 parts extend from pad 20 and refer to 21.CURRENT DISTRIBUTION refers to that 21 can be straight shown in Fig. 2 A, can be crooked shown in Fig. 2 B perhaps.Other configurations also are possible.Although embodiment shown in Fig. 2 A and the 2B comprises four respectively and refers to 21,, can use more or less finger 21 according to the quantity of desired CURRENT DISTRIBUTION.
Fig. 3 shows other LED of some embodiments according to the present invention, and wherein this LED is designed to upside-down mounting (that is, substrate is installed up) is installed.Fig. 3 has schematically shown LED 2, and it has n type SiC substrate 10 and active area 12, and this active area comprises n-GaN basic unit 14 and the p-GaN basic unit 16 that grows on the substrate and be patterned into platform.Metal p electrode 18 be deposited on the p-GaN layer 16 and with its electricity coupling, the wire-bonded connection 28 that preparation is connected with pad 20 on the p electrode 18.Be positioned on the conductive substrates 10 and comprise pad 20, the wire-bonded connection 28 that preparation is connected with this pad 20 with the n electrode 22 of its electricity coupling.In the embodiment of Fig. 3, this LED further comprises reflector 30.On reflector 30, form metal laminated 32, for example above-cited U.S. Patent No. 6,740, metal laminated described in 906, thereby for example provide stop, bonding and/or bonded layer.Whole device is installed to inferior mounting on the platform 24 by scolder 34 subsequently.
In order to reduce or to minimize the light absorption of p electrode 18 and make body 30 reflection that can be reflected of more light, according to the present invention, the thickness of this p electrode is reduced to
Below.In some embodiments, this p electrode comprises platinum.Ohmic contact 18 can be used other materials.For example, ohmic contact 18 can comprise rhodium, zinc oxide, palladium, palladium oxide, titanium, nickel/gold, nickel oxide/gold, nickel oxide/platinum and/or titanium/gold.In some embodiments, ohmic contact 18 average thicknesss less than
In some embodiments, ohmic contact 18 average thicknesss less than
In some embodiments, ohmic contact 18 average thicknesss are 13 to arrive
In other embodiment, ohmic contact 18 average thicknesss are about
In some embodiments, ohmic contact 18 average thicknesss less than
In some embodiments, ohmic contact 18 average thicknesss less than
In other embodiment, ohmic contact 18 average thicknesss less than
More in addition in the embodiment, ohmic contact 18 average thicknesss are about
In some embodiments, ohmic contact 18 average thicknesss less than
, and coverage is less than about 70%.In some embodiments, ohmic contact 18 average thicknesss less than
, and coverage is less than about 50%; In other embodiment, ohmic contact 18 average thicknesss less than
, and coverage is less than about 30%.More in addition in the embodiment, ohmic contact 18 average thicknesss are for approximately
, and coverage is less than about 15%.
Embodiment of the present invention can reduce because the interior optical loss of the LED due to the absorption in the p contacting metal.Need this p contacting metal to have the ohmic contact of minimum voltage drop, but this contacting metal is introduced optical loss usually with formation.Embodiment of the present invention can provide a kind of contact, and it is bonding that it has low optical losses, low contact resistance and good metal-semiconductor, are applicable to adopt reflection or the metal laminated high-brightness nitride LED of transparent p side.By the p contacting metal being reduced to layer (for example, Pt, 1.5 pair as thin as a wafer
), the light that can significantly improve device is exported.For example, in 300 μ m * 300 μ m chips, obtain about 10% light output improvement, in 900 μ m * 900 μ m chips, obtain about 20% improvement.Luminance level improves can to quicken solid state light emitter introduced and is used for for example product of automobile headlamp of general illumination and other dedicated illumination purposes.
Fig. 4 shows method embodiment of the present invention.As shown in Figure 4, the method embodiment can be included in step 100 and make GaN based illuminating device precursor construction.The step of this manufacturing GaN based illuminating device precursor construction can comprise, and is forming n type epitaxial loayer on the substrate and form p type epitaxial loayer on this n type epitaxial loayer.In step 105, this method comprises with this device precursor construction with reference to accompanying sheet to place in the metal film deposition system of electron beam evaporation plating system for example.After the step 110, this method is included in this device precursor construction and depositing metallic films on the sheet is accompanied in reference.Witness mark is accompanied the transmissivity of the metal film on the sheet in step 115.If the film transmissivity is equal to or less than predetermined threshold (judgement frame 120), this technology stops.Otherwise continue depositing metallic films (step 110).
In some embodiments, measure under the wavelength, before dropping to below 98%, stop to deposit this metal ohmic contact with reference to the standardization transmissivity of accompanying the metal film on the sheet at 350nm.In other embodiments, measure under the wavelength, before dropping to below 96%, stop to deposit this metal ohmic contact with reference to the standardization transmissivity of accompanying the metal film on the sheet at 350nm.In other embodiment, measure under the wavelength at 350nm, before dropping to below 92%, stop to deposit this metal ohmic contact with reference to the standardization transmissivity of accompanying the metal film on the sheet.
Embodiments more of the present invention comprise: make GaN base LED precursor construction; Accompany the test substrate of sheet to insert the metal film deposition system with for example reference precursor construction; With set rate depositing metallic films scheduled time on this precursor construction and this test substrate; And the transmissivity of this film on the measurement test substrate.If the transmissivity of this film is then removed this metal film from precursor construction less than predetermined threshold (showing that this metal film is too thick), presoma is put back the film depositing system, and with second scheduled time and/or deposition rate depositing metallic films on this precursor construction.This process can repeat arbitrary number of times, till having deposited acceptable thickness.
As shown in Figure 6, embodiments more of the present invention comprise the step (step 200) of making GaN base LED precursor construction.Precursor construction accompanies sheet or other test substrate to insert film depositing system (step 205) with reference.Subsequently in this precursor construction with reference to accompanying depositing metallic films (step 210) on the sheet.For example witness mark is accompanied the thickness of this film on the sheet by the transmissivity of measuring film subsequently.If this transmissivity less than predetermined threshold (representing that this film is too thick) (step 220), is then removed this metal film (for example by etching) and this precursor construction is put back the film depositing system from this structure.
In other embodiments shown in Figure 7,, can control thickness thus by in this depositing system, test material being carried out calibration operation to determine the appropriate time and the speed of this deposition step.Therefore, some embodiments of the present invention comprise manufacturing GaN base LED precursor construction (step 300); Test substrate is inserted film depositing system (step 305); With predetermined deposition rate depositing metallic films scheduled time (step 310) on this test substrate; And the thickness (step 315) of measuring the gained film.If this thickness within predetermined expected range (step 320), is then inserted film depositing system (step 325) with GaN base LED precursor construction, and with predetermined deposition rate depositing metallic films scheduled time (step 330) on this precursor construction.If thickness is not within preset range, then second test substrate (first test substrate of perhaps clearing up again) is inserted this film depositing system (step 305), on second test substrate, deposit second film with second scheduled time and/or speed.
In other embodiment, when thickness reached threshold level, this supervisory control system can provide signal output to the film depositing system.This film depositing system stops depositing operation in response to the signal output that comes self-monitoring system, thereby the auto-closing circuit controls to depositing operation is provided.Fig. 8 is the indicative icon of film depositing system 50 according to embodiments of the present invention.System 50 comprises vacuum chamber 52, and wherein chip carrier 54 is installed in this chamber.Accompany sheet or test structure 70 to be installed on this chip carrier 54 with reference the wafer 56 of depositing metallic films on it.Vacuum pump system 58 is coupled to vacuum chamber 52, is used for outwards aspirating intracavity gas.Vacuum pump system 58 can comprise a plurality of pumps and measurer (not shown), so that vacuum chamber 52 pressure inside are reduced to less than 10
-3Pa.
Electron beam generator 60 in the vacuum chamber produces electron beam with predetermined power, and with this electron beam pilot source target 64.By electron beam controller 62 controlling electron beam generators 60.When the target 64 of electron beam generator 60 produces beam bombardment source, source material is from 64 evaporations of source target and be deposited on wafer 56 again and with reference to accompanying on the sheet 70., can measure these and compare to determine thickness with reference to physics, electricity or the optical characteristics of accompanying sheet by monitoring, be installed in the thickness that vacuum chamber inside or sensor external 66 are measured the film that is deposited according to the characteristic of Thickness Variation and with itself and known standard.As previously mentioned, this specific character can comprise transmissivity, reflectivity, conductivity, resonance frequency or other characteristics.Transducer 66 is subjected to sensor controller 68 (may be identical with electron beam controller 62 in the practical application) control.Arrived predetermined threshold when transducer 66 detects institute's thickness of deposited film, this supervisory control system can provide signal output to electron beam controller 62, makes electron beam controller stop this depositing operation.Therefore, system 50 provides auto-closing circuit controls to depositing operation according to embodiments of the present invention.
Making thickness as previously mentioned is
,
,
With
Contact layer.Contact layer is Pt.Suppose
Layer is a continuous P t layer.Obtain
,
With
The STEM image of layer.The STEM image is shown in Fig. 9 A, 10A and 11A.The STEM image show from
(Fig. 9 A) (coverage＞＞50%) arrives
The marked change of (Figure 11 A) (coverage＜＜50%) Pt quantity.Pt quantity is being carried out in the quantitative trial, to the STEM image applications a kind of threshold technology, this technology is removed gray scale, makes the pixel value be higher than special value be designated as pure white (Pt), is designated as black less than the pixel value of special value.See Fig. 9 B, 10B and 11B through the image after the thresholding.Although the selection of threshold value is subjective, thresholding image and original image are compared, it seems that this match be consistent.The ratio of black by calculating (no Pt) and white (Pt) can obtain the indication of coverage.Following table 1 shows the analysis of STEM image among Fig. 9 B, 10B and the 11B.
Table 1.STEM analyzes
Also the Pt layer is carried out the Auger surface analysis.The Auger surface analysis the results are shown in table 2.
Table 2. auger analysis
As can be seen from Table 2, suppose
Layer is continuous layer, then by auger analysis,
Layer coverage is about 67%,
Layer coverage is about 47%,
Layer coverage is about 28%,
Layer coverage is about 13%.Therefore, in some embodiments according to the present invention, the average thickness of metal ohmic contact is relevant by the percentage that this metal ohmic contact covers with p shape nitride layer.
In view of the benefit of disclosure of the present invention, under the situation that does not deviate from the spirit and scope of the present invention, those of ordinary skills can carry out many modifications and adjustment.Therefore should be appreciated that, shown in embodiment only for exemplary purposes, shall not be applied to the present invention that restriction is defined by claims.Therefore, claims not only comprise the combination of elements of stating on the literal, also comprise in essentially identical mode to implement essentially identical function to obtain all equivalent elements of essentially identical result.Therefore claim should be understood that to comprise above concrete elaboration and description, notion equivalent and the content that combines basic thought of the present invention.
Claims (23)
1. a semiconductor-based light-emitting device (LED) comprising:
P type nitride layer; And
Metal ohmic contact on the described p type nitride layer, described metal ohmic contact average thickness is about
2. LED as claimed in claim 1, wherein by the auger analysis of described metal ohmic contact is measured, described metal ohmic contact covers approximately the described p type nitride layer less than 13%.
3. a semiconductor-based light-emitting device (LED) comprising:
P type nitride layer; And
Metal ohmic contact on the described p type nitride layer, described metal ohmic contact average thickness is about
And by the auger analysis of described metal ohmic contact is measured, described metal ohmic contact covers approximately the described p type nitride layer less than 13%.
4. LED as claimed in claim 3, wherein under the measurement wavelength of about 350nm, the standardization transmissivity of described metal ohmic contact is approximately greater than 98%.
5. a semiconductor-based light-emitting device (LED) comprising:
P type nitride layer; And
Metal ohmic contact on the described p type nitride layer, described metal ohmic contact has certain average thickness, and standardization transmissivity greater than 98% is provided provide under the measurement wavelength of about 350nm approximately for it.
6. LED as claimed in claim 5, wherein said average thickness is about
7. LED as claimed in claim 5, wherein said metal ohmic contact covers approximately the described p type nitride layer less than 13%, makes the part that is not capped of described p type nitride layer be exposed by described metal ohmic contact.
8. a semiconductor-based light-emitting device (LED) comprising:
N N-type semiconductor N substrate;
N type GaN epitaxial loayer on the described substrate;
P type GaN epitaxial loayer on the described n type GaN epitaxial loayer;
Metal ohmic contact on the described p type GaN epitaxial loayer, described metal ohmic contact average thickness approximately less than
The specific contact resistivity rate is approximately less than 10
-3Ohm.cm
2And
Pad on the described metal ohmic contact.
9. LED as claimed in claim 8, wherein said average thickness is for about
Arrive
10. LED as claimed in claim 8, wherein by the auger analysis of described metal ohmic contact is measured, described metal ohmic contact covers approximately less than 13% to approximately less than 47% p type nitride layer.
11. LED as claimed in claim 8, wherein under the measurement wavelength of about 350nm, the standardization transmissivity of described metal ohmic contact is approximately higher than 92%.
12. LED as claimed in claim 8, wherein said average thickness is for about
Arrive
13. a method that forms semiconductor-based light-emitting device (LED) comprises:
On n type substrate, form p type nitride layer;
Form the metal ohmic contact on described p type nitride layer, measure by the auger analysis to described metal ohmic contact, described metal ohmic contact covers the described p type nitride layer less than 100%; And
Stop to form described metal ohmic contact.
14. method as claimed in claim 13 wherein forms the metal ohmic contact and further comprises:
With given pace on described p type nitride layer and with reference to accompanying one time period of plated metal on the sheet, to be provided for the metal level with first average thickness of described metal ohmic contact;
Monitor described reference and accompany the indication of the above metal layer thickness of sheet;
If described indication is higher than predetermined indication threshold value, then further with the follow-up time interval and/or subsequent rate plated metal to increase average thickness; And
If described indication is approximately equal to or less than predetermined indication threshold value, then stop plated metal.
15. method as claimed in claim 14 is wherein monitored described reference and is accompanied the described metal layer thickness indication on the sheet to comprise transmissivity, sheet resistivity, electric capacity, reflectivity and/or the resonance frequency of measuring described metal level.
16. method as claimed in claim 15, wherein:
Under the measurement wavelength of about 350nm, about 92% transmissivity represent this thickness comprise approximately less than
Average thickness;
Under the measurement wavelength of about 350nm, about transmissivity of 94% to 96% represent this thickness comprise approximately less than
Average thickness; And
Under the measurement wavelength of about 350nm, represent that greater than 98% transmissivity this thickness comprises approximately approximately
Average thickness.
17. method as claimed in claim 14, wherein further plated metal comprises that continuing plated metal surpasses predetermined indication threshold value up to described indication.
18. method as claimed in claim 14, wherein said speed is about per second
Arrive
19. method as claimed in claim 13 wherein forms the metal ohmic contact and further comprises:
With given pace on described p type nitride layer and with reference to accompanying one time period of plated metal on the sheet, to be provided for the metal level with first average thickness of described metal ohmic contact;
Monitor described reference and accompany the indication of the above metal layer thickness of sheet;
If described indication approximates or is higher than predetermined indication threshold value, then stop plated metal; And
If described indication is less than predetermined indication threshold value, then from described p type nitride layer with reference to accompanying sheet to remove described metal level, and with the follow-up time interval and/or subsequent rate at described p type nitride layer with reference to accompanying on the sheet further plated metal.
20. method as claimed in claim 19 further comprises:
Remove after the described metal level, the follow-up time of adjusting the follow-up deposition again of metal at interval and/or subsequent rate up to forming described metal level, makes relevant indication approximate or is higher than described predetermined indication threshold value.
21. method as claimed in claim 13 wherein forms the metal ohmic contact and further comprises:
With given pace one time period of plated metal on first test substrate, so that the first metal layer to be provided;
Monitor the thickness indication of described the first metal layer;
If described indication drops in the thickness tolerance scope of described metal ohmic contact, then with described speed described time period of plated metal on described p type nitride layer, so that the ohmic contact of the metal with described average thickness to be provided;
If described indication is not within described thickness tolerance scope, the plated metal on second test substrate with second speed and/or second time period then is to provide second metal level;
Monitor described second metal layer thickness indication; With
If the indication of described second metal layer thickness drops in the described thickness tolerance scope, the plated metal on described p type nitride layer with second speed and/or second time period then is to provide the ohmic contact of the metal with described average thickness.
22. method as claimed in claim 21, described method further comprises:
Continue the different time period of plated metal with described speed, and monitor formed metal layer thickness, thereby form the described metal level that drops within the described thickness tolerance scope with definite time enough section.
23. the semiconductor-based LED of upside-down mounting comprises:
P type nitride layer;
Metal ohmic contact p electrode on the described p type nitride layer, described metal ohmic contact p electrode average thickness approximately less than
And
Reflector on the described metal ohmic contact p electrode.
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