Semiconductor and template for growing semiconductors

Abstract

A template for a semiconductor device is made by providing an AGN substrate, growing a first layer of Group III nitrides on the substrate, depositing a thin metal layer on the first layer, annealing the metal such as gold so that it agglomerates to form a pattern of islands on the first layer; transferring the pattern into the first layer by etching then removing excess metal; and then depositing a second Group III nitride layer on the first layer. The second layer, through lateral overgrowth, coalesces over the gaps in the island pattern leaving a smooth surface with low defect density. A Group III semiconductor device may then be grown on the template, which may then be removed. Chlorine gas may be used for etching the pattern in the first layer and the remaining gold removed with aqua regia.

Claims

1. A method of making a template for a semiconductor device, said method comprising the steps of: (a) providing a substrate; (b) depositing a first layer on said substrate, said first layer being made of Group III nitrides; (c) depositing a metal layer on said first layer; (d) annealing said metal layer at a temperature not higher than 500 C. for not longer than 15 seconds to form a pattern of islands; (e) transferring said pattern of islands to said first layer; (f) removing said metal layer from said first layer; and then (g) depositing a second layer on said first layer, said second layer being made of Group III nitrides.

2. The method of claim 1, wherein said substrate is made of AlGaN.

3. The method of claim 1, wherein said metal layer is a gold metal layer.

4. The method of claim 3, wherein said metal layer is at most 5000 A thick.

5. The method of claim 1, wherein said temperature is at least 350 C.

6. The method of claim 1, wherein said annealing takes place for at least 10 seconds.

7. The method of claim 1, wherein said annealing takes place in air.

8. The method of claim 1, wherein said transferring step further comprises the steps of: (a) etching said pattern of island into said first layer; and (b) removing said metal layer.

9. The method of claim 8, wherein said etching is reactive ion etching.

10. The method of claim 9, wherein said etching is done with chlorine.

11. The method of claim 8, wherein said metal layer is removed using aqua regia.

12. A method of making a semi-conductor device, said method comprising the steps of: (a) providing a substrate made of AlGaN; (b) growing a template on said substrate, said template made by (i) depositing a first layer on said substrate, said first layer being made of Group III nitrides; (ii) depositing a metal layer on said first layer; (iii) annealing said metal layer at a temperature not higher than 500 C. for not longer than 15 seconds to form a pattern of islands; (iv) transferring said pattern of islands to said first layer; (v) removing said metal layer from said first layer; and then (vi) depositing a second layer on said first layer, said second layer being made of Group III nitrides; and (c) growing a semiconductor device on said second layer, said semi-conductor device being made of Group III nitrides.

13. The method as recited in claim 12, further comprising the step of removing said substrate.

14. The method as recited in claim 13, further comprising the step of removing said template.

15. The method as recited in claim 12, wherein said growing a semiconductor step further comprises the steps of: (a) growing a first conductive layer on said second layer, said first conductive layer being made of Group III nitrides; (b) growing a quantum well on said first conductive layer said quantum well being made of Group III nitrides; and (c) attaching a first conductor to said first conductive layer.

16. The method of claim 15, further comprising the step of growing a second conductive layer on said quantum well, said second conductive layer being a different polarity than said first conductive layer, said second conductive layer being made of Group III nitrides.

17. A template for use with a semiconductor device, said template made by a method comprising the steps of: (a) providing a substrate made of AlGaN; (b) depositing a first layer on said substrate, said first layer being made of Group III nitrides; (c) depositing a layer of gold on said first layer; (d) annealing said gold at a temperature not higher than 500 C. for not longer than 15 seconds to form a pattern of islands; (e) transferring said pattern of islands to said first layer; (f) removing said gold from said first layer; and then (g) depositing a second layer on said first layer, said second layer being made of Group III nitrides.

18. A semiconductor device made a method comprising the steps of: (a) providing a substrate made of AlGaN; (b) depositing a first layer on said substrate, said first layer being made of Group III nitrides; (c) depositing a metal layer of gold, palladium, or platinum on said first layer (d) annealing said metal layer at a temperature not higher than 500 C. for not longer than 15 seconds to form a pattern of islands; (e) transferring said pattern of islands to said first layer; (f) removing said metal layer from said first layer; then (g) depositing a second layer on said first layer, said second layer being made of Group III nitrides; and (h) growing a semiconductor device on said second layer.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In the figures,

(2) FIG. 1 is a schematic diagram of a first layer grown on a substrate;

(3) FIG. 2 is a schematic diagram of the first layer of FIG. 1 with a thin metal layer applied to the first layer, according to aspects of the disclosure;

(4) FIG. 3 is a schematic diagram of the thin metal layer after annealing, according to aspects of the disclosure;

(5) FIG. 4A is a detailed view of FIG. 3, FIG. 4B shows the surface of the first layer after ionic etching has transferred the pattern of the annealed metal to the first layer, and FIG. 4C is the surface after chemical etching has removed the remaining metal, according to aspects of the disclosure;

(6) FIG. 5 is a schematic view of the template after growing the second layer, according to aspects of the disclosure;

(7) FIG. 6 is a schematic view of the template after growing a second pair of first and second layers, according to aspects of the disclosure;

(8) FIG. 7 is a schematic view of a light emitting diode grown on the template of FIG. 5, according to aspects of the disclosure; and

(9) FIG. 8 is a schematic view of the light emitting diode of FIG. 7 with the substrate removed.

DETAILED DESCRIPTION

(10) The present process is for making a semiconductor device and a template that supports a semiconductor device, such as a light emitting diode or laser diode and a sensor capable of detecting photons in the 250 A-500 A wavelength range. The present template has higher quality, that is, it has a smoother, flatter epilayer with fewer defects on which to grow a semiconductor device.

(11) The process begins by providing a substrate 10 and growing a first layer 16 on substrate 10. Substrate 10 may be made of a variety of standard substrate materials but a substrate of AlN is preferred over sapphire. First layer 16 is made of Group III nitrides.

(12) Then a layer 22 of metal such as gold, palladium or platinum is deposited directly on first layer 16. Metal layer 22 may be applied to first layer 16 using pulsed vapor deposition or chemical vapor deposition. Any of the following may also be used: aluminum, vanadium, molybdenum, chromium, indium, tin, cobalt, ruthenium, rubidium, silicon, and oxides of these.

(13) Metal layer 22 is thin, for example, 5 A to 5000 A. Metal layer 22 is then annealed for a limited time and at a limited temperature so that it agglomerates. The time and temperature of the annealing step are chosen to be shorter and cooler than those times and temperatures that would adversely affect the Group III composition of first layer 16, namely, a time and temperature that causes the metal to coalesce to form nanoscale islands 24, such as a temperature between 350 C. to 500 C. for a time between 10-15 seconds f or gold. Annealing of metal layer 22 is done in air or in a forming gas such as nitrogen gas or argon. The annealing oven is not preheated and cool down times are on the order of a few minutes.

(14) Annealing metal layer 22 forms islands 24 forms island-like agglomerations in a natural, random pattern dictated by chemical and physical forces among the metal atoms that yield tiny islands with tiny gaps between them, as seen in FIG. 3 and in the detail of 4 A. By islands or island-like, it is meant that the metal atoms cluster and separate, and have various shapes, but their dimensions are on a nanometer scale (10.sup.6 to 10.sup.9 meters with gaps between islands ranging from 20 nm to 200 nm).

(15) The random island-like pattern defined by the annealed metal is then transferred to the surface of the first layer in a two-step etching process, as illustrated in FIGS. 4B and 4C, respectively. The pattern may be transferred to first layer 16 by reactive ion or ICP etching, and is then followed by chemical cleaning to remove the metal of metal layer 22. Etching may be performed using gases such as chlorine, boron tri-chloride, argon, fluorine, silicon hexafluoride, carbon tetra-fluoride, or any combination of the above gases. Reactive ion etching with chorine etches Group III nitrides but is less effective etching metals such as gold, which makes it a good candidate for the present process.

(16) After etching the pattern to transfer it to first layer 16, the remaining metal is removed by chemical etching. Chemical etching can be performed by buffered oxide etching or by dipping the sample in acids such as aqua-regia, sulphuric acid, phosphoric acid, nitric acid or in bases such ammonium hydroxide, potassium hydroxide, hydrogen peroxide or any combination of such acids and bases. Aqua regia is effective in dissolving gold.

(17) At this point, and as shown in FIG. 4C, there is a pattern of tiny islands formed in first layer 16 and no remaining metal.

(18) Now a second layer 28 is grown on first layer 16. Lateral overgrowth will coalesce over the islands transferred to the surface of first layer 16 and eliminate many lattice defects that would otherwise occur readily in the structure of second layer 28. The top surface of second layer 28 will be much smoother than first layer 16 and have a lower defect density than otherwise.

(19) The process of growing a first layer 16, applying a metal layer 22, annealing metal layer 22, transferring the pattern formed by the annealed metal to first layer 16, and then growing second layer 28 on first layer 16, may be repeated to produce a third (patterned) layer 34 and a fourth (smooth) layer 40, and so on. First and second layers 16, 28 comprise a first layer pair 46; third and fourth layers 34, 40, comprise a second layer pair 52. Each layer pair 46, 52, reduces the defect density of the topmost surface and renders that surface a better one for a template 54, that is, one that has a lower defect density on which to build a device 56. Device 56 may be a light emitter, a light emitting diode, an ultraviolet light emitting diode, or a sensor capable of detecting photons.

(20) First and second layers 16, 28, are grown either by metal-organic chemical vapor deposition (MOCVD) or metal-organic vapor phase epitaxy (MOVPE) in a reaction vessel. Either of these processes enables growth of crystalline layers by chemical reaction to create complex multilayer structures. In the present process, first and second layers 16, 28, and the two layers of second layer pair 52 and any other layer pairs may be made of a material with high aluminum content, such as AlGaN, including AlN, AlInGaN and AlInGaBN, particularly for deep ultraviolet light applications, but the rest of Group III Nitride semiconductor materials: GaN, InGaN and InN, are also candidates for the present process of making a template or a semiconductor grown on a template according to an aspect of the disclosure.

(21) As an example of a device 56, a light emitting diode may be grown on the present template 54 by growing a first conductive layer 58, such as an n-layer, followed by a quantum well 64 on the present template, and then a second conductive layer 70, such as a p-layer. A first electrical contact 76 is then attached to first conductive layer 58 and a second electrical contact 82 is attached to second conductive layer 70. For a device 56 that is a sensor, second conductive layer 70 and second electrical contact 82 are omitted. For a device 56 that is an ultraviolet light emitter, the choice of materials for the first and second conductive layers 58, 70, and quantum well 64 must have suitable band gaps.

(22) Although illustrated as single layers, first and second electrically conductive layers 58, 70, may be formed of multiple layers. Each layer of those multiple layers has an elemental composition that may differ from one or more other layers of that electrically conductive layer.

(23) Also, quantum well 64, although also illustrated as a single layer, preferably comprises several layers forming a quantum-well region. For an ultraviolet light emitting diode, quantum well 64 may have an emission spectrum ranging from 190 nm to 369 nm. Such a quantum well 64 may be made of Al.sub.xIn.sub.yGa.sub.1-x-yN wherein 0<x<1, 0<y<1, and 0<x+y<1. Quantum well 64 has a surface 66. A first barrier layer 68 may be placed on surface 66 of quantum well 64, and quantum well 64 may end with a second barrier layer 72. First and second barrier layers 68, 72, may be made of Al.sub.xIn.sub.yGa.sub.1-x-yN wherein 0<x<1, 0<y<1 and 0<x+y<1 and may have band gaps larger than the band gap of quantum well 64. In one aspect of the disclosure, quantum well 64 may comprise layers of Al.sub.xIn.sub.yGa.sub.1-x-yN wherein 0<x<1, 0<y<1, and 0<x+y<1.

(24) In another aspect of the disclosure, quantum well 64 is doped with at least one p-type dopant preferably selected from the group consisting of magnesium, zinc and beryllium. In another aspect of the disclosure, quantum well 64 is doped with at least one n-type and at least one p-type dopant. Quantum well 64 produces ultra-violet photons. In an aspect of the disclosure, the quantum well region emits photons having a wavelength in the range 190 nm<<240 nm. In another aspect of the disclosure, quantum well 64 emits or detects with a wavelength in the range 240 nm280 nm. In another aspect of the disclosure, quantum well 64 emits or detects photons having a wavelength in the range 280 nm<<320 nm. In another aspect of the disclosure, quantum well 64 emits or detects photons with a wavelength in the range 320 nm<<369 nm.

(25) Barrier layers 68, 72, preferably include Al.sub.xIn.sub.yGa.sub.1-x-yN, wherein 0<x<1, 0<y<1 and 0<x+y<1, and the compositions of quantum well 64 and barrier layers 68, 72, may each be different. In one aspect of the disclosure, quantum well 64 is preferably doped with at least one n-type intentional dopant and other intentional dopants selected from the group consisting of silicon, oxygen and indium.

(26) First and third layers 16, 28, may be bound by crystallographic faces with (0001), (1-100), (1011), (1-102), (11-20), (11-22) facets being aspects of the disclosure.

(27) First and third layers 16, 34, may be deposited by controlling the flow of group III (Ga, Al and In) precursors and ammonia (NH3) and the ratio of Group III to Group V

(28) First and third layers 16, 34, preferably have growth rates of about 6 A to about 100 m per hour with at least 0.2 m per hour a particular aspect of the disclosure.

(29) Second and fourth layers 28, 40, are deposited on first and third layers 16, 34, respectively, to produce a smooth top surface for template 54 by controlling the flow of group III precursors (Ga, Al and In) and ammonia (NH3). Second and fourth layers 28, 40, are deposited at a Group V-to-Group III ratio in the range of from 1 to 100000. Second and fourth layers 28, 40, preferably have a growth rate of at least 0.01 m per hour and an R.sub.rms ranging from 1 A to 100 A.

(30) Second and fourth layers 28, 40, are also defined as having at least one surface preferably selected from (001), (110), (101), (102), and (114) facets.

(31) Second layer 28 and fourth layer 40 may be graded layers wherein the composition gradient is changes as a function of thickness so that they are less similar to that of first and third layers 16, 34, and are more similar to the composition of first conductive layer 58.

(32) Each layer of template 54 and device 56 may be made of a Group III-nitride, preferably Al.sub.xIn.sub.yGa.sub.1-x-yN (wherein 0<x<1, 0<y<1 and 0<x+y<1). The precursor sources include a metal-organic source, ammonia, a carrier gas and, optionally, doping sources such as silane, and/or biscyclopentadienyl magnesium. The metal-organic source is preferably trimethyl aluminum, triethyl aluminum, trimethyl gallium, triethyl gallium, trimethyl boron, trimethyl iron, triethyl indium or trimethyl indium. Suitable carrier gases are hydrogen and nitrogen and a combination of hydrogen and nitrogen.

(33) In an alternative configuration and after construction, substrate 10 or all of template 54 may be removed by polishing, etching or lifting-off using a laser. First electrical contact 76 may be applied to the backside first conductive layer 58. Second electrical contact 82 may be attached to an opposing side of second conductive layer 70.

(34) It is an ongoing desire to reduce resistance in a layer, and particularly, at the interface between layers. Resistance at the contact layers is a particular concern since resistance is a source of heat. As current increases, the temperature of the LED increases. Temperature limits the current at which an LED can be operated. With silicon doping, the operating temperature limit is a particular problem. The incorporation of indium in a layer reduces the resistance of a layer. Indium is particularly desirable in doped layers such as silicon-doped or magnesium-doped layers. At a given level of silicon doping, for example, incorporation of indium reduces the resistance thereby decreasing the heat generation which allows for an increase in the current at which the LED can be operated. In a silicon-doped layer, the indium is preferably present in an amount of atoms ranging from 10.sup.15/cm.sup.3 to 10.sup.24/cm.sup.3. In a magnesium doped layer the indium is preferably present in an amount of atoms ranging from 10.sup.15/cm.sup.3 to 10.sup.24/cm.sup.3.

(35) It will be apparent to those skilled in the art of ultraviolet light-emitting diodes and laser diodes that many modifications and substitutions can be made to the method described herein without departing from the spirit and scope of the present disclosure which is specifically set forth in the appended claims.