Patent Application
20090194026
1. Field of the Invention
Embodiments of the present invention generally relate to the manufacture of compound nitride semiconductor devices, such as light emitting diodes (LEDs), and, more particularly, to a processing system integrating one or more processing chambers that implement hydride vapor phase epitaxial (HVPE) deposition and/or metal-organic chemical vapor deposition (MOCVD) techniques to fabricate such devices.
2. Description of the Related Art
The history of light-emitting diodes (“LEDs”) is sometimes characterized as a “crawl up the spectrum.” This is because the first commercial LEDs produced light in the infrared portion of the spectrum, followed by the development of red LEDs that used GaAsP on a GaAs substrate. This was, in turn, followed by the use of GaP LEDs with improved efficiency that permitted the production of both brighter red LEDs and orange LEDs. Refinements in the use of GaP then permitted the development of green LEDs, with dual GaP chips (one in red and one in green) permitting the generation of yellow light. Further improvements in efficiency in this portion of the spectrum were later enabled through the use of GaAlAsP and InGaAlP materials.
This evolution towards the production of LEDs that provide light at progressively shorter wavelengths has generally been desirable not only for its ability to provide broad spectral coverage but because diode production of short-wavelength light may improve the information storage capacity of optical devices like CD-ROMs. The production of LEDs in the blue, violet, and ultraviolet portions of the spectrum was largely enabled by the development of nitride-based LEDs, particularly through the use of GaN. While some modestly successful efforts had previously been made in the production of blue LEDs using SiC materials, such devices suffered from poor luminescence as a consequence of the fact that their electronic structure has an indirect bandgap.
While the feasibility of using GaN to create photoluminescence in the blue region of the spectrum has been known for decades, there were numerous barriers that impeded their practical fabrication. These barriers included the lack of a suitable substrate on which to grow the GaN structures, generally high thermal requirements for growing GaN that resulted in various thermal-convection problems and a variety of difficulties in efficient p-doping of such materials. The use of sapphire as a substrate was not completely satisfactory because it provides approximately a 15% lattice mismatch with the GaN. Progress has subsequently been made in addressing many aspects of these barriers. For example, the use of a buffer layer of AlN or GaN formed from a metal-organic vapor has been found effective in accommodating the lattice mismatch. Further refinements in the production of Ga—N-based structures has included the use of AlGaN materials to form heterojunctions with GaN and particularly the use of InGaN, which causes the creation of defects that act as quantum wells to emit light efficiently at short wavelengths. Indium-rich regions have a smaller bandgap than surrounding material, and may be distributed throughout the material to provide efficient emission centers.
While some improvements have thus been made in the manufacture of such compound nitride semiconductor devices, it is widely recognized that a number of deficiencies yet exist in current manufacturing processes. Moreover, the high utility of devices that generate light at such wavelengths has caused the production of such devices to be an area of intense interest and activity. In view of these considerations, there is a general need in the art for improved methods and systems for fabricating compound nitride semiconductor devices.
The present invention generally provides an integrated processing system for manufacturing compound nitride semiconductor devices. The processing system comprises one or more walls that form a transfer region that has a robot disposed therein, one or more processing chambers operable to form one or more compound nitride semiconductor layers on a substrate that are in transferable communication with the transfer region, a loadlock chamber in transferable communication with the transfer region, the loadlock chamber having an inlet and an outlet valve to receive at least one substrate into a vacuum environment, and a load station in communication with the loadlock chamber, wherein the load station comprises a conveyor tray movable to convey a carrier plate loaded with one or more substrates into the loadlock chamber.
Embodiments of the invention further provide an integrated processing system for manufacturing compound nitride semiconductor devices. The processing system comprises one or more walls that form a transfer region that has a robot disposed therein and a first processing chamber that is in communication with the transfer region. The first processing chamber comprises a substrate support positioned within a processing volume of the first processing chamber, a showerhead defining a top portion of the processing region, and a plurality of lamps forming one or more zones located below the processing region and adapted to direct radiant heat toward the substrate support creating one or more radiant heat zones. The integrated processing system further comprises a loadlock chamber in transferable with the transfer region and a load station in communication with the loadlock chamber, wherein the load station comprises a conveyor tray movable to convey a carrier plate loaded with one or more substrates into the loadlock chamber.
Embodiments of the invention further provide an integrated processing system for manufacturing compound nitride semiconductor devices. The integrated processing system comprises one or more walls that form a transfer region that has a robot disposed therein, one or more metalorganic chemical vapor deposition (MOCVD) chambers operable to form a compound nitride semiconductor layer on a substrate in transferable communication with the transfer region, and one or more hydride vapor phase epitaxy (HVPE) chambers operable to form a compound nitride semiconductor layer on a substrate in transferable communication with the transfer region.
So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.
To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that elements disclosed in one embodiment may be beneficially utilized on other embodiments without specific recitation.
The present invention generally provides an apparatus and method for simultaneously processing substrates using a multi-chamber processing system (e.g. a cluster tool) that has an increased system throughput, increased system reliability, and increased substrate to substrate uniformity. In one embodiment, the processing system is adapted to fabricate compound nitride semiconductor devices in which a substrate is disposed in a HVPE chamber where a first layer is deposited on the substrate and then the substrate is transferred to a MOCVD chamber where a second layer is deposited over the first layer. In one embodiment, the first layer is deposited over the substrate with a thermal chemical-vapor-deposition process using a first group-III element and a nitrogen precursor and the second layer is deposited over the first layer with a thermal chemical-vapor deposition process using a second group-III precursor and a second nitrogen precursor. Although 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. Exemplary systems and chambers that may be adapted to practice the present invention are described in U.S. patent application Ser. No. 11/404,516, filed on Apr. 14, 2006, titled EPITAXIAL GROWTH OF COMPOUND NITRIDE SEMICONDUCTOR STRUCTURES and U.S. patent application Ser. No. 11/429,022, filed on May 5, 2006, titled PARASITIC PARTICLE SUPPRESSION IN GROWTH OF III-V NITRIDE FILMS USING MOCVD AND HVPE, both of which are incorporated by reference in their entireties.
Each processing chamber comprises a chamber body (such as element 112 for the MOCVD chamber 102 and element 114 for the HVPE chamber 104) forming a processing region where a substrate is placed to undergo processing, a chemical delivery module (such as element 116 for the MOCVD chamber 102 and element 118 for the HVPE chamber 104) from which gas precursors are delivered to the chamber body, and an electrical module (such as element 120 for the MOCVD chamber 102 and element 122 for the HVPE chamber 104) that includes the electrical system for each processing chamber of the processing system 100. The MOCVD chamber 102 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 104 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 170 be coupled with the transfer chamber 106. 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 206. For example, each batch of substrates 214 may be transported on a carrier plate 212 that can be placed on the conveyor tray 206. The lid 211 may be selectively opened and closed over the conveyor tray 206 for safety protection when the conveyor tray 206 is driven in movement. In operation, an operator opens the lid 211 to load the carrier plate 212 containing a batch of substrates on the conveyor tray 206. A storage shelf 216 may be provided for storing carrier plates containing substrates to be loaded. The lid 211 is closed, and the conveyor tray 206 is moved through the slit valve 210 into the loadlock chamber 108. The lid 211 may comprise a glass material, such as Plexiglas or a plastic material to facilitate monitoring of operations of the conveyor tray 206.
During operation, a carrier plate 212 containing a batch of substrates is loaded on the conveyor tray 206 in the load station 110. The conveyor tray 206 is then moved through the slit valve 210 into the loadlock chamber 108, placing the carrier plate 212 onto the carrier support 244 inside the loadlock chamber 108, and the conveyor tray returns to the load station 110. While the carrier plate 212 is inside the loadlock chamber 108, the loadlock chamber 108 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 130 may transfer the carrier plate 212 to either the MOCVD chamber 102 or, the HVPE chamber 104 to undergo deposition processes. In alternate embodiments, the carrier plate 212 may be transferred and stored in the batch loadlock chamber 109 on standby for processing in either the MOCVD chamber 102 or the HVPE chamber 104. After processing of the batch of substrates is complete, the carrier plate 212 may be transferred to the loadlock chamber 108, and then retrieved by the conveyor tray 206 and returned to the load station 110.
A storage cassette 610 is moveably disposed within the cavity 607 and is coupled with an upper end of a movable member 630. The moveable member 630 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 630 enters the cavity 607 through the bottom 616. The movable member 630 is slidably and sealably disposed through the bottom 616 and is raised and lowered by the platform 687. The platform 687 supports a lower end of the movable member 630 such that the movable member 630 is vertically raised or lowered in conjunction with the raising or lowering of the platform 687. The movable member 630 vertically raises and lowers the storage cassette 610 within the cavity 607 to move the substrates carrier plates 212 across a substrate transfer plane 632 extending through a window 635. The substrate transfer plane 632 is defined by the path along which substrates are moved into and out of the storage cassette 610 by the robot assembly 130.
The storage cassette 610 comprises a plurality of storage shelves 636 supported by a frame 625. Although in one aspect,
The storage shelves 636 are spaced vertically apart and parallel within the storage cassette 610 to define a plurality of storage spaces 622. Each substrate storage space 622 is adapted to store at least one carrier plate 212 therein supported on a plurality of support pins 642. The storage shelves 636 above and below each carrier plate 212 establish the upper and lower boundary of the storage space 622.
In another embodiment, substrate support 640 is not present and the carrier plates 212 rest on brackets 617.
The robot assembly 130 is centrally located within the transfer chamber 106 such that substrates can be transferred into and out of adjacent processing chambers, the loadlock chamber 108, and the batch loadlock chamber 109, and other chambers through slit valves 242, 812, 814, 816, 818, and 820 respectively. The valves enable communication between the processing chambers, the loadlock chamber 108, the batch loadlock chamber 109, and the transfer chamber 106 while also providing vacuum isolation of the environments within each of the chambers to enable a staged vacuum within the system. The robot assembly 130 may comprise a frog-leg mechanism. In certain embodiments, the robot assembly 130 may comprise any variety of known mechanical mechanisms for effecting linear extension into and out of the various process chambers. A blade 810 is coupled with the robot assembly 130. The blade 810 is configured to transfer the carrier plate 212 through the processing systems. In one embodiment, the processing system 100 comprises an automatic center finder (not shown). The automatic center finder allows for the precise location of the carrier plate 212 on the robot assembly 130 to be determined and provided to a controller. Knowing the exact center of the carrier plate 212 allows the computer to adjust for the variable position of each carrier plate 212 on the blade and precisely position each carrier plate 212 in the processing chambers.
A plurality of lamps 930a, 930b may be disposed below the carrier plate 212. 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 930b may include eight lamps, and the outer array of lamps 930a may include twelve lamps. In one embodiment of the invention, the lamps 930a, 930b are each individually powered. In another embodiment, arrays of lamps 930a, 930b may be positioned above or within showerhead assembly 904. It is understood that other arrangements and other numbers of lamps are possible. The arrays of lamps 930a, 930b may be selectively powered to heat the inner and outer areas of the carrier plate 212. In one embodiment, the lamps 930a, 930b 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 980. 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 980 is remotely located with respect to the chamber body 114, 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 930a, 930b may be powered to heat the substrates as well as the source boat 980. The lamps may heat the substrate to a temperature of about 900 degrees Celsius to about 1200 degrees Celsius. In another embodiment, the lamps 930a, 930b maintain a metal source within the source boat 980 at a temperature of about 350 degrees Celsius to about 900 degrees Celsius. 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 930a, 930b 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 906 flow from the showerhead assembly 904 towards the substrate surface. Reaction of the precursor gases 906 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 908 may be maintained at a pressure of about 760 Torr down to about 100 Torr. In one embodiment, the processing volume 908 is maintained at a pressure of about 450 Torr to about 760 Torr. Exemplary embodiments of the showerhead assembly 904 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.
A lower dome 1019 is disposed at one end of a lower volume 1010, and the carrier plate 212 is disposed at the other end of the lower volume 1010. The carrier plate 212 is shown in process position, but may be moved to a lower position where, for example, the substrates 1040 may be loaded or unloaded. An exhaust ring 1020 may be disposed around the periphery of the carrier plate 212 to help prevent deposition from occurring in the lower volume 1010 and also help direct exhaust gases from the chamber 102 to exhaust ports 1009. The lower dome 1019 may be made of transparent material, such as high-purity quartz, to allow light to pass through for radiant heating of the substrates 140. The radiant heating may be provided by a plurality of inner lamps 1021A and outer lamps 1021B disposed below the lower dome 1019 and reflectors 1066 may be used to help control the chamber 102 exposure to the radiant energy provided by inner and outer lamps 1021A, 1021B. Additional rings of lamps may also be used for finer temperature control of the substrates 1040.
A purge gas (e.g., nitrogen) may be delivered into the chamber 102 from the showerhead assembly 1004 and/or from inlet ports or tubes (not shown) disposed below the carrier plate 212 and near the bottom of the chamber body 112. The purge gas enters the lower volume 1010 of the chamber 102 and flows upwards past the carrier plate 212 and exhaust ring 1020 and into multiple exhaust ports 1009 which are disposed around an annular exhaust channel 1005. An exhaust conduit 1006 connects the annular exhaust channel 1005 to a vacuum system 1012 which includes a vacuum pump (not shown). The chamber 102 pressure may be controlled using a valve system 1007 which controls the rate at which the exhaust gases are drawn from the annular exhaust channel 1005. Other aspects of the MOCVD chamber are described in U.S. patent application Ser. No. ______, 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 102. 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. ______, 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 116, 118 supply chemicals to the MOCVD chamber 102 and HVPE chamber 104 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 1004 and 904. 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 160 controls activities and operating parameters of the processing system 100. The system controller 160 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 160 and related control software prioritize tasks and substrate movements based on inputs from the user and various sensors distributed throughout the processing system 100. The system controller 160 and related control software allow for automation of the scheduling/handling functions of the processing system 100 to provide the most efficient use of resources without the need for human intervention. In one aspect, the system controller 160 and related control software adjust the substrate transfer sequence through the processing system 100 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 100 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 100 having at least two processing chambers, such as MOCVD chamber 102 and HVPE chamber 104. The cleaning and deposition of the initial GaN layers is performed in the HVPE chamber 104, with growth of the remaining InGaN, AlGaN, and GaN contact layers being performed in the MOCVD system 102.
The process begins with a carrier plate containing multiple substrates being transferred into the HVPE chamber 104. The HVPE chamber 104 is configured to provide rapid deposition of GaN. A pretreatment process and/or buffer layer is grown over the substrate in the HVPE chamber 104 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 104 and into the MOCVD chamber 102, with the transfer taking place in a high-purity N2 atmosphere via the transfer chamber 106. The MOCVD chamber 102 is adapted to provide highly uniform deposition, perhaps at the expense of overall deposition rate. In the MOCVD chamber 102, 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 102 so that the MOCVD chamber 102 is ready to receive an additional carrier plate containing partially processed substrates from the HVPE chamber 104 or from a different processing chamber. The completed structure may either be transferred to the batch loadlock chamber 109 for storage or may exit the processing system 100 via the loadlock chamber 108 and the load station 110.
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.
While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.
