Patent Application
20110104843
1. Field of the Invention
Embodiments of the present invention relate to a method of reducing of the degradation of multiple quantum well in light emitting diodes by utilizing a fast growth rate of chlorine based hydride vapor phase epitaxy for upper p-type gallium nitride layers.
2. Discussion of Related Art
Light emitting diodes (LEDs) are the ultimate light source in lighting technology. The LED technology has flourished for the past few decades. High efficiency, reliability, rugged construction, low power consumption, and durability are among the key factors for the rapid development of the solid-state lighting based on high-brightness visible LEDs. Conventional light sources, such as filament light bulbs or fluorescent lamps depend on either incandescence or discharge in gases. These two processes are accompanied by large energy losses, which are attributed to high temperatures and large Stokes shift characteristics. On the other hand, semiconductors allow an efficient way of light generation. LEDs made of semiconductor materials have the potential of converting electricity to light with near unity efficiency. An example of a typical gallium nitride (GaN) based light emitting diodes (LEDs) is illustrated in
The p-type contact layer 108 and the p-type electron blocking layer 110 are typically formed utilizing a metal organic chemical vapor deposition (MOCVD) process. In order to deposit a high quality single crystalline p-type GaN film by MOCVD, high deposition temperatures, such as greater than 1000° C., and low deposition rates are required. Unfortunately, the exposure of the quantum wells and barrier layers to high temperatures for extended periods of time result in the interdiffusion of indium (In) and gallium (Ga) in the quantum well and barrier layers resulting in the formation of an indium (In) rich indium gallium nitride InGaN precipitates which retard the optical quality of the MQW active layers.
A method of fabricating a light emitting diode. According to embodiments of the present invention an active region comprising a plurality of gallium nitride (GaN) barrier layers and a plurality of indium gallium nitride (InGan) quantum well layers are formed over a substrate. A p-type gallium nitride layer is formed above the active region by a hydride vapor phase epitaxy (HVPE) at a high deposition rate.
The present invention is a method of forming a high quality light emitting diode (LED) having multiple quantum wells (MQW) active layers. The present invention has been described with respect to specific details in order to provide a thorough understanding of the invention. One of ordinary skill in the art will appreciate that the invention can be practiced without these specific details. In other instances, well known semiconductor processes and equipment have not been described in specific detail in order to not unnecessarily obscure the present invention.
The present invention is a method of forming a high quality light emitting diode (LED) having multiple quantum wells (MQW) active layers. According to an embodiment of the present invention, after the formation of the active region of the light emitting diode including a plurality of quantum well layers, such as indium gallium nitride (InGaN) layers and a plurality of barrier layers, such as gallium nitride (GaN) layers, a p-type contact layers, such as a magnesium doped gallium nitride layer (Mg—GaN), is formed on the active region by a chlorine based hydride vapor phase epitaxial (HVPE) deposition process. The use of an HVPE process enables the p-type GaN film to formed at a high growth rate, such as greater than 25 μm/hr, and ideally greater than 100 μm/hr so that the underlying quantum well/barrier layers are exposed to high temperatures for a much shorter time. By decreasing the amount of time that the active region is exposed to high temperatures prevents or reduces indium (In) and gallium (Ga) interdiffusion and therefore the formation of indium (In) rich which indium gallium nitride (InGaN) precipitates which retard the optical quality of the MQW active layers. Additionally, in embodiments of the present invention, a p-type GaN layer is formed by HVPE at a relatively low temperature such as less than or equal to 900 C. In embodiments of the present invention, the upper p-type GaN contact layer is grown by HVPE at a sufficiently high growth rate and/or at sufficiently low deposition temperature to reduce the degree of degradation of the active MQW and thereby increase the internal quantum efficiency (IQE) to enable the formation of high brightness LEDs.
An undoped gallium nitride (GaN) single crystalline or crystalline film 204 is formed on substrate 202. Undoped gallium nitride film 204 can be formed to any suitable thickness. In an embodiment of the present invention, an optional buffer layer 203 may be formed between undoped gallium nitride layer 204 and substrate 202. Buffer layer 203 generally will have a lattice constant between that of undoped gallium nitride layer 204 and substrate 202.
Next, an n-type gallium nitride (GaN) contact layer 206 is formed on the undoped gallium nitride layer 204. N-type gallium nitride layer can be formed to a thickness between 0.1-4.0 microns and doped to an n-type conductivity between 1×1018-5×1019 atoms/cm3. Any suitable n-type dopants, such as but not limited to Si, Ge, Sn, Pb or any suitable Group IV, Group V, or Group VI element may be utilized.
An active region 208 is formed on the n-type gallium nitride contact layer 206. In an embodiment of the present invention, the active region 208 includes at least a first quantum well 220 and a second quantum well 222 and at least a first barrier layer 224 and a second barrier layer 226. In an embodiment of the present invention, the active region 208 includes a first indium gallium nitride (InGaN) quantum well 220 and a second indium gallium nitride (InGaN) quantum well 222 and a first gallium nitride (GaN) barrier 224 and a second gallium nitride (GaN) barrier 226. In an embodiment of the present invention, the active region 208 includes between 10-20 stacks of barrier layers and wells wherein each stack includes a quantum well layer between 1-5 nanometers thick and a barrier layer between 1-30 nanometers thick.
In an embodiment of the present invention, the quantum well layers and barrier layers of the active region 208 are formed by metal organic chemical vapor deposition (MOCVD) utilizing a relatively low deposition temperature, such as between 750-850° C. to provide a clean sharp interface between the barrier layers and the quantum wells.
A gallium nitride (GaN) film may be formed by MOCVD by providing a metal organic source of gallium, such as trimethylgallium (TMGa) into a chamber along with the nitrogen source, such as ammonia (NH3) in a chamber containing a substrate. A carrier gas, such as N2 may be utilized. The substrate may be heated to a temperature between 700-850° C. which causes the source gases to react and to form a gallium nitride (GaN) film on the substrate. The chamber can be maintained at a pressure between 100 torr to atmospheric pressure while depositing the gallium nitride film.
An indium gallium nitride (InGaN) film may be formed by MOCVD by providing a metal organic source of indium, such as trimethylindium (TMIn) and an organic source of gallium, such as trimethylgallium (TMGa) into a chamber along with a nitrogen source, such as ammonia (NH3) in a chamber containing a substrate. A carrier gas, such as N2 may be utilized. The substrate may be heated to a growth temperature between 700-850° C. which causes the source gases to react and form an indium gallium nitride (InGaN) film on the substrate. The chamber can be maintained at a pressure between 100 torr to atmospheric pressure while depositing the indium gallium nitride (InGaN) film. In an embodiment of the present invention, the indium gallium nitride film has an atomic formula of In1Ga1-xN where 0.05≦x≦0.25. A 20-80% indium atomic ratio in the gas phase with respect to gallium will yield between 5-25% indium in the solid phase.
Next, as shown in
Additionally, in embodiments of the present invention, the p-type aluminum gallium nitride electron blocking layer 210 is also formed by a chlorine based HVPE technique with a high deposition rate and low deposition temperature. It is to be appreciated that since the electron blocking layer is significantly thinner than the p-type contact layer 212, it is not as important to form this film with a high growth rate and low deposition temperature and as is the p-type contact layer 212.
The p-type gallium nitride contact layer 212 and the p-type aluminum gallium nitride layer 210 may be doped to a p-type conductivity level between 1×1017-1×1020 atoms/cm2. The p-type dopants can be any element having two valance electrons, such as but not limited to zinc (Zn), magnesium (Mg), lithium (Li), calcium (Ca), Strontium (Sr), Beryllium (Be) and cadmium (Cd). In an specific embodiment the electron barrier layer 210 is a magnesium doped aluminum gallium nitride layer (Mg—AlGaN) and the p-type contact layer is a magnesium doped gallium nitride (Mg—GaN) layer.
A magnesium doped gallium nitride (Mg—GaN) layer can be formed by HYPE by providing a gallium containing precursor, such as gallium chloride (GaCl or GaCl3), a magnesium containing precursor, such as magnesium chloride (MgCl) and a nitrogen containing precursor, such as ammonia (NH3) into a chamber and reacting them together near the surface of the substrate to deposit a magnesium doped gallium nitride (Mg—GaN) film. In an embodiment of the present invention, the gallium containing precursor is formed by providing a source of gallium, and flowing over it a halide or halogen gas to form a gaseous gallium containing precursor. In an embodiment of the present invention, HCl is reacted with a liquid gallium source to form gaseous gallium chloride (GaCl). In another embodiment of the present invention, chlorine gas (Cl2) is reacted with a liquid gallium to form GaCl and GaCl3. Similarly, a magnesium (Mg) containing precursor can be formed by providing a magnesium source and flowing over it a halide or halogen gas to form a magnesium containing precursor. In an embodiment of the present invention, Cl2 is reacted with magnesium (Mg) to form magnesium chloride (MgCl). In an embodiment of the present invention, the chamber is maintained at a pressure between 100 torr and 760 torr during deposition. In one embodiment, the chamber is maintained at a pressure of about 450 torr to about 760 torr while depositing the magnesium doped gallium nitride (Mg—GaN) film. In an embodiment of the present invention, the magnesium doped gallium nitride film is formed at a temperature less than 900° C. and ideally the temperature is between 600-900° C. A high quality single crystalline p-type GaN film can be reasonably formed by HVPE at a growth rate between 5 μm/hr and 100 μm/hr.
In an embodiment of the present invention, one or more magnesium doped gallium nitride (Mg—GaN) barrier layers are formed by HVPE using a magnesium gallium (MgGa) eutectic alloy as the source. HCl or chlorine gas (Cl2) is then reacted with the magnesium gallium (MgGa) eutectic alloy to form gaseous magnesium chloride (MgCl) and gallium chloride (GaCl or GaCl3).
In an embodiment of the present invention a high deposition rate of greater than or equal to 100 μm/hr may be achieved by providing a high Cl2 flow rate of greater than 150 SCCMs over or equal to the gallium source to form gallium trichloride (GaCl3) or gallium chloride (GaCl). Additionally, in an embodiment of the present invention, a high GaCl and/or GaCl3 partial pressure of greater than 100 torr is used to help increase the deposition rate of the p-type gallium nitride film. In an embodiment of the present invention, the temperature of the boat which contains the gallium source is at least 500° C. during deposition to help promote a high deposition rate.
An Mg—AlGaN electron blocking layer can be formed by HVPE in a manner similar to a Mg—GaN layer except that an aluminum (Al) source is also provided.
In an embodiment of the present invention, the LED device is fabricated in a cluster tool having one or more MOCVD chambers and one or more HVPE chambers. In this way, the quantum well layers and the barrier layers can be formed by MOCVD in the MOCVD chambers and the p-type gallium nitride blocking layer, if desired, may be fabricated in the HVPE chambers. An example of a cluster tool which may be used to fabricate an LED device in accordance with the present invention is set forth and described with respect to
Each processing chamber comprises a chamber body (such as element 312 for the MOCVD chamber 302 and element 314 for the HVPE chamber 304) forming a processing region where a substrate is placed to undergo processing, a chemical delivery module (such as element 316 for the MOCVD chamber 302 and element 318 for the HVPE chamber 304) from which gas precursors are delivered to the chamber body, and an electrical module (such as element 320 for the MOCVD chamber 302 and element 322 for the HVPE chamber 304) that includes the electrical system for each processing chamber of the processing system 300. The MOCVD chamber 302 is adapted to perform CVD processes in which metalorganic elements react with metal hydride elements to form thin layers of compound nitride semiconductor materials. The HVPE chamber 304 is adapted to perform HVPE processes in which gaseous metal halides are used to epitaxially grow thick layers of compound nitride semiconductor materials on heated substrates. In alternate embodiments, one or more additional chambers may 370 be coupled with the transfer chamber 306. These additional chambers may include, for example, anneal chambers, clean chambers for cleaning carrier plates, or substrate removal chambers. The structure of the processing system permits substrate transfers to occur in a defined ambient environment, including under vacuum, in the presence of a selected gas, under defined temperature conditions, and the like.
Substrates for processing may be grouped in batches and transported on the conveyor tray 506. For example, each batch of substrates 514 may be transported on a carrier plate 512 that can be placed on the conveyor tray 506. The lid 511 may be selectively opened and closed over the conveyor tray 506 for safety protection when the conveyor tray 506 is driven in movement. In operation, an operator opens the lid 511 to load the carrier plate 512 containing a batch of substrates on the conveyor tray 506. A storage shelf 516 may be provided for storing carrier plates containing substrates to be loaded. The lid 511 is closed, and the conveyor tray 506 is moved through the slit valve 510 into the loadlock chamber 308. The lid 511 may comprise a glass material, such as Plexiglas or a plastic material to facilitate monitoring of operations of the conveyor tray 506.
During operation, a carrier plate 512 containing a batch of substrates is loaded on the conveyor tray 506 in the load station 310. The conveyor tray 506 is then moved through the slit valve 510 into the loadlock chamber 308, placing the carrier plate 512 onto the carrier support 644 inside the loadlock chamber 308, and the conveyor tray returns to the load station 310. While the carrier plate 512 is inside the loadlock chamber 308, the loadlock chamber 308 is pumped and purged with an inert gas, such as nitrogen, in order to remove any remaining oxygen, water vapor, and other types of contaminants. After the batch of substrates have been conditioned in the loadlock chamber, the robot assembly 330 may transfer the carrier plate 512 to either the MOCVD chamber 302 or, the HVPE chamber 304 to undergo deposition processes. In alternate embodiments, the carrier plate 512 may be transferred and stored in the batch loadlock chamber 309 on standby for processing in either the MOCVD chamber 302 or the HVPE chamber 304. After processing of the batch of substrates is complete, the carrier plate 512 may be transferred to the loadlock chamber 308, and then retrieved by the conveyor tray 506 and returned to the load station 310.
A storage cassette 810 is moveably disposed within the cavity 807 and is coupled with an upper end of a movable member 830. The moveable member 830 is comprised of process resistant materials such as aluminum, steel, nickel, and the like, adapted to withstand process temperatures and generally free of contaminates such as copper. The movable member 830 enters the cavity 807 through the bottom 816. The movable member 830 is slidably and sealably disposed through the bottom 816 and is raised and lowered by the platform 887. The platform 887 supports a lower end of the movable member 830 such that the movable member 830 is vertically raised or lowered in conjunction with the raising or lowering of the platform 887. The movable member 830 vertically raises and lowers the storage cassette 810 within the cavity 807 to move the substrates carrier plates 512 across a substrate transfer plane 832 extending through a window 835. The substrate transfer plane 832 is defined by the path along which substrates are moved into and out of the storage cassette 810 by the robot assembly 330.
The storage cassette 810 comprises a plurality of storage shelves 836 supported by a frame 825. Although in one aspect,
The storage shelves 836 are spaced vertically apart and parallel within the storage cassette 810 to define a plurality of storage spaces 822. Each substrate storage space 822 is adapted to store at least one carrier plate 512 therein supported on a plurality of support pins 842. The storage shelves 836 above and below each carrier plate 512 establish the upper and lower boundary of the storage space 822.
In another embodiment, substrate support 840 is not present and the carrier plates 512 rest on brackets 817.
The robot assembly 330 is centrally located within the transfer chamber 306 such that substrates can be transferred into and out of adjacent processing chambers, the loadlock chamber 308, and the batch loadlock chamber 309, and other chambers through slit valves 642, 1012, 1014, 1016, 1018, and 1020 respectively. The valves enable communication between the processing chambers, the loadlock chamber 308, the batch loadlock chamber 309, and the transfer chamber 306 while also providing vacuum isolation of the environments within each of the chambers to enable a staged vacuum within the system. The robot assembly 330 may comprise a frog-leg mechanism. In certain embodiments, the robot assembly 330 may comprise any variety of known mechanical mechanisms for effecting linear extension into and out of the various process chambers. A blade 1010 is coupled with the robot assembly 330. The blade 1010 is configured to transfer the carrier plate 512 through the processing systems. In one embodiment, the processing system 300 comprises an automatic center finder (not shown). The automatic center finder allows for the precise location of the carrier plate 512 on the robot assembly 330 to be determined and provided to a controller. Knowing the exact center of the carrier plate 512 allows the computer to adjust for the variable position of each carrier plate 512 on the blade and precisely position each carrier plate 512 in the processing chambers.
A plurality of lamps 1130a, 1130b may be disposed below the carrier plate 512. For many applications, a typical lamp arrangement may comprise banks of lamps above (not shown) and below (as shown) the substrate. One embodiment may incorporate lamps from the sides. In certain embodiments, the lamps may be arranged in concentric circles. For example, the inner array of lamps 1130b may include eight lamps, and the outer array of lamps 1130a may include twelve lamps. In one embodiment of the invention, the lamps 1130a, 1130b are each individually powered. In another embodiment, arrays of lamps 1130a, 1130b may be positioned above or within showerhead assembly 1104. It is understood that other arrangements and other numbers of lamps are possible. The arrays of lamps 1130a, 1130b may be selectively powered to heat the inner and outer areas of the carrier plate 512. In one embodiment, the lamps 1130a, 1130b are collectively powered as inner and outer arrays in which the top and bottom arrays are either collectively powered or separately powered. In yet another embodiment, separate lamps or heating elements may be positioned over and/or under the source boat 1180. It is to be understood that the invention is not restricted to the use of arrays of lamps. Any suitable heating source may be utilized to ensure that the proper temperature is adequately applied to the processing chamber, substrates therein, and a metal source. For example, it is contemplated that a rapid thermal processing lamp system may be utilized such as is described in United States Patent Publication No. 2006/0018639, published Jan. 26, 2006, entitled PROCESSING MULTILAYER SEMICONDUCTORS WITH MULTIPLE HEAT SOURCES, which is incorporated by reference in its entirety.
In yet another embodiment, the source boat 1180 is remotely located with respect to the chamber body 314, as described in U.S. Provisional Patent Application Ser. No. 60/978,040, filed Oct. 5, 2007, titled METHOD FOR DEPOSITING GROUP III/V COMPOUNDS, which is incorporated by reference in its entirety.
One or more lamps 1130a, 1130b may be powered to heat the substrates as well as the source boat 1180. The lamps may heat the substrate to a temperature of about 900° C. to about 1200° C. In another embodiment, the lamps 1130a, 1130b maintain a metal source within the source boat 1180 at a temperature of about 350° C. to about 900° C. A thermocouple may be used to measure the metal source temperature during processing. The temperature measured by the thermocouple may be fed back to a controller that adjusts the heat provided from the heating lamps 1130a, 1130b so that the temperature of the metal source may be controlled or adjusted as necessary.
During the process according to one embodiment of the invention, precursor gases 1106 flow from the showerhead assembly 1104 towards the substrate surface. Reaction of the precursor gases 1106 at or near the substrate surface may deposit various metal nitride layers upon the substrate, including GaN, AlN, and InN. Multiple metals may also be utilized for the deposition of “combination films” such as AlGaN and/or InGaN. The processing volume 1108 may be maintained at a pressure of about 760 torr down to about 100 torr. In one embodiment, the processing volume 1108 is maintained at a pressure of about 450 torr to about 760 torr. Exemplary embodiments of the showerhead assembly 1104 and other aspects of the HVPE chamber are described in U.S. patent application Ser. No. 11/767,520, filed Jun. 24, 2007, entitled HVPE TUBE SHOWERHEAD DESIGN, which is herein incorporated by reference in its entirety. Exemplary embodiments of the HVPE chamber 304 are described in U.S. Patent Application Ser. No. 61/172,630 filed Apr. 24, 2009, entitled HVPE CHAMBER HARDWARE, which is herein incorporated by reference in its entirety.
A lower dome 1219 is disposed at one end of a lower volume 1210, and the carrier plate 512 is disposed at the other end of the lower volume 1210. The carrier plate 512 is shown in process position, but may be moved to a lower position where, for example, the substrates 1240 may be loaded or unloaded. An exhaust ring 1220 may be disposed around the periphery of the carrier plate 512 to help prevent deposition from occurring in the lower volume 1210 and also help direct exhaust gases from the chamber 302 to exhaust ports 1209. The lower dome 1219 may be made of transparent material, such as high-purity quartz, to allow light to pass through for radiant heating of the substrates 1240. The radiant heating may be provided by a plurality of inner lamps 1221A and outer lamps 1221B disposed below the lower dome 1219 and reflectors 1266 may be used to help control the chamber 302 exposure to the radiant energy provided by inner and outer lamps 1221A, 1221B. Additional rings of lamps may also be used for finer temperature control of the substrates 1240.
A purge gas (e.g., nitrogen) may be delivered into the chamber 302 from the showerhead assembly 1204 and/or from inlet ports or tubes (not shown) disposed below the carrier plate 512 and near the bottom of the chamber body 312. The purge gas enters the lower volume 1210 of the chamber 302 and flows upwards past the carrier plate 512 and exhaust ring 1220 and into multiple exhaust ports 1209 which are disposed around an annular exhaust channel 1205. An exhaust conduit 1206 connects the annular exhaust channel 1205 to a vacuum system 1212 which includes a vacuum pump (not shown). The chamber 302 pressure may be controlled using a valve system 1207 which controls the rate at which the exhaust gases are drawn from the annular exhaust channel 1205. Other aspects of the MOCVD chamber are described in U.S. patent application Ser. No. 12/023,520, filed Jan. 31, 2008, (attorney docket no. 011977) entitled CVD APPARATUS, which is herein incorporated by reference in its entirety.
Various metrology devices, such as, for example, reflectance monitors, thermocouples, or other temperature devices may also be coupled with the chamber 302. The metrology devices may be used to measure various film properties, such as thickness, roughness, composition, temperature or other properties. These measurements may be used in an automated real-time feedback control loop to control process conditions such as deposition rate and the corresponding thickness. Other aspects of chamber metrology are described in U.S. Patent Application Ser. No. 61/025,252, filed Jan. 31, 2008, (attorney docket no. 011007) entitled CLOSED LOOP MOCVD DEPOSITION CONTROL, which is herein incorporated by reference in its entirety.
The chemical delivery modules 316, 318 supply chemicals to the MOCVD chamber 302 and HVPE chamber 304 respectively. Reactive and carrier gases are supplied from the chemical delivery system through supply lines into a gas mixing box where they are mixed together and delivered to respective showerheads 1204 and 1104. Generally supply lines for each of the gases include shut-off valves that can be used to automatically or manually shut-off the flow of the gas into its associated line, and mass flow controllers or other types of controllers that measure the flow of gas or liquid through the supply lines. Supply lines for each of the gases may also include concentration monitors for monitoring precursor concentrations and providing real time feedback, backpressure regulators may be included to control precursor gas concentrations, valve switching control may be used for quick and accurate valve switching capability, moisture sensors in the gas lines measure water levels and can provide feedback to the system software which in turn can provide warnings/alerts to operators. The gas lines may also be heated to prevent precursors and etchant gases from condensing in the supply lines. Depending upon the process used some of the sources may be liquid rather than gas. When liquid sources are used, the chemical delivery module includes a liquid injection system or other appropriate mechanism (e.g. a bubbler) to vaporize the liquid. Vapor from the liquids is then usually mixed with a carrier gas as would be understood by a person of skill in the art.
While the foregoing embodiments have been described in connection to a processing system that comprises one MOCVD chamber and one HVPE chamber, alternate embodiments may integrate one or more MOCVD and HVPE chambers in the processing system, as shown in
A system controller 360 controls activities and operating parameters of the processing system 300. The system controller 360 includes a computer processor and a computer-readable memory coupled to the processor. The processor executes system control software, such as a computer program stored in memory. Aspects of the processing system and methods of use are further described in U.S. patent application Ser. No. 11/404,516, filed Apr. 14, 2006, entitled EPITAXIAL GROWTH OF COMPOUND NITRIDE STRUCTURES, which is hereby incorporated by reference in its entirety.
The system controller 360 and related control software prioritize tasks and substrate movements based on inputs from the user and various sensors distributed throughout the processing system 300. The system controller 360 and related control software allow for automation of the scheduling/handling functions of the processing system 300 to provide the most efficient use of resources without the need for human intervention. In one aspect, the system controller 360 and related control software adjust the substrate transfer sequence through the processing system 300 based on a calculated optimized throughput or to work around processing chambers that have become inoperable. In another aspect, the scheduling/handling functions pertain to the sequence of processes required for the fabrication of compound nitride structures on substrates, especially for processes that occur in one or more processing chambers. In yet another aspect, the scheduling/handling functions pertain to efficient and automated processing of multiple batches of substrates, whereby a batch of substrates is contained on a carrier. In yet another aspect, the scheduling/handling functions pertain to periodic in-situ cleaning of processing chambers or other maintenance related processes. In yet another aspect, the scheduling/handling functions pertain to temporary storage of substrates in the batch loadlock chamber. In yet another aspect the scheduling/handling functions pertain to transfer of substrates to or from the load station based on operator inputs.
The following example is provided to illustrate how the general process described in connection with processing system 300 may be used for the fabrication of compound nitride structures. The example refers to a LED structure, with its fabrication being performed using a processing system 300 having at least two processing chambers, such as MOCVD chamber 302 and HVPE chamber 304. The cleaning and deposition of the initial GaN layers is performed in the HVPE chamber 304, with growth of the remaining InGaN, AlGaN, and GaN contact layers being performed in the MOCVD system 302.
The process begins with a carrier plate containing multiple substrates being transferred into the HVPE chamber 304. The HVPE chamber 304 is configured to provide rapid deposition of GaN. A pretreatment process and/or buffer layer is grown over the substrate in the HVPE chamber 304 using HVPE precursor gases. This is followed by growth of a thick n-GaN layer, which in this example is performed using HVPE precursor gases. In another embodiment the pretreatment process and/or buffer layer is grown in the MOCVD chamber and the thick n-GaN layer is grown in the HVPE chamber.
After deposition of the n-GaN layer, the substrate is transferred out of the HVPE chamber 304 and into the MOCVD chamber 302, with the transfer taking place in a high-purity N2 atmosphere via the transfer chamber 306. The MOCVD chamber 302 is adapted to provide highly uniform deposition, perhaps at the expense of overall deposition rate. In the MOCVD chamber 302, the InGaN multi-quantum-well active layer is grown after deposition of a transition GaN layer. This is followed by deposition of the p-AlGaN layer and p-GaN layer. In another embodiment the p-GaN layer is grown in the HVPE chamber.
The completed structure is then transferred out of the MOCVD chamber 302 so that the MOCVD chamber 302 is ready to receive an additional carrier plate containing partially processed substrates from the HVPE chamber 304 or from a different processing chamber. The completed structure may either be transferred to the batch loadlock chamber 309 for storage or may exit the processing system 300 via the loadlock chamber 308 and the load station 310.
Before receiving additional substrates the HVPE chamber and/or MOCVD chamber may be cleaned via an in-situ clean process. The cleaning process may comprise etchant gases which thermally etch deposition from chamber walls and surfaces. In another embodiment, the cleaning process comprises a plasma generated by a remote plasma generator. Exemplary cleaning processes are described in U.S. patent application Ser. No. 11/404,516, filed on Apr. 14, 2006, and U.S. patent application Ser. No. 11/767,520, filed on Jun. 24, 2007, titled HVPE SHOWERHEAD DESIGN, both of which are incorporated by reference in their entireties.
An improved system and method for fabricating compound nitride semiconductor devices has been provided. In conventional manufacturing of compound nitride semiconductor structures, multiple epitaxial deposition steps are performed in a single process reactor, with the substrate not leaving the process reactor until all of the steps have been completed resulting in a long processing time, usually on the order of 4-6 hours. Conventional systems also require that the reactor be manually opened in order to remove and insert additional substrates. After opening the reactor, in many cases, an additional 4 hours of pumping, purging, cleaning, opening, and loading must be performed resulting in a total run time of about 8-10 hours per substrate. The conventional single reactor approach also prevents optimization of the reactor for individual process steps.
The improved system provides for simultaneously processing substrates using a multi-chamber processing system that has an increased system throughput, increased system reliability, and increased substrate to substrate uniformity. The multi-chamber processing system expands the available process window for different compound structures by performing epitaxial growth of different compounds in different processing having structures adapted to enhance those specific procedures. Since the transfer of substrates is automated and performed in a controlled environment, this eliminates the need for opening the reactor and performing a long pumping, purging, cleaning, opening, and loading process.
Thus, a method of reducing the degradation of multi quantum well (MQW) light emitting diodes has been described.
This application claims the benefit of and priority to Provisional Application Ser. No. 61/230,671, filed Jul. 31, 2009 which is hereby incorporated by reference.
| Number | Date | Country | |
|---|---|---|---|
| 61230671 | Jul 2009 | US |
