Patent Application
20090194024
1. Field of the Invention
Embodiments of the present invention generally relate to methods and apparatus for chemical vapor deposition (CVD) on a substrate, and, in particular, to a process chamber for use in chemical vapor deposition.
2. Description of the Related Art
Group III-V films are finding greater importance in the development and fabrication of a variety of semiconductor devices, such as short wavelength light emitting diodes (LEDs), laser diodes (LDs), and electronic devices including high power, high frequency, high temperature transistors and integrated circuits. For example, short wavelength (e.g., blue/green to ultraviolet) LEDs are fabricated using the Group Ill-nitride semiconducting material gallium nitride (GaN). It has been observed that short wavelength LEDs fabricated using GaN can provide significantly greater efficiencies and longer operating lifetimes than short wavelength LEDs fabricated using non-nitride semiconducting materials, comprising Group II-VI elements.
One method that has been used for depositing Group III-nitrides, such as GaN, is metal organic chemical vapor deposition (MOCVD). This chemical vapor deposition method is generally performed in a reactor having a temperature controlled environment to assure the stability of a first precursor gas which contains at least one element from Group III, such as gallium (Ga). A second precursor gas, such as ammonia (NH3), provides the nitrogen needed to form a Group III-nitride. The two precursor gases are injected into a processing zone within the reactor where they mix and move towards a heated substrate in the processing zone. A carrier gas may be used to assist in the transport of the precursor gases towards the substrate. The precursors react at the surface of the heated substrate to form a Group III-nitride layer, such as GaN, on the substrate surface. The quality of the film depends in part upon deposition uniformity which, in turn, depends upon uniform flow and mixing of the precursors across the substrate.
As the demand for LEDs, LDs, transistors, and integrated circuits increases, the efficiency of depositing high quality Group-III nitride films takes on greater importance. Therefore, there is a need for an improved deposition apparatus and process that can provide uniform precursor mixing and consistent film quality over larger substrates and larger deposition areas.
The present invention generally relates to methods and apparatus for chemical vapor deposition (CVD) on a substrate, and, in particular, to a process chamber and components for use in chemical vapor deposition.
In one embodiment an apparatus for metal organic chemical vapor deposition on a substrate is provided. The process apparatus comprises a chamber body defining a process volume. A showerhead in a first plane defines a top portion of the process volume. A substrate carrier plate extends across the process volume in a second plane forming an upper process volume between the showerhead and the susceptor plate. A transparent material in a third plane defines a bottom portion of the process volume forming a lower process volume between the substrate carrier plate and the transparent material. A plurality of lamps forms one or more zones located below the transparent material. The plurality of lamps direct radiant heat toward the substrate carrier plate creating one or more radiant heat zones.
In another embodiment a substrate processing apparatus for metal organic chemical vapor deposition is provided. The process apparatus comprises a chamber body defining a process volume. A showerhead in a first plane defines a top portion of the process volume. A substrate carrier plate extends across the process volume in a second plane below the first plane within the process volume. A light shield comprising an angled portion surrounds the periphery of the substrate carrier plate wherein the light shield directs radiant heat toward the substrate carrier plate.
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.
Embodiments of the present invention generally provide a method and apparatus that may be utilized for deposition of Group III-nitride films using MOCVD. Although discussed with reference to MOCVD, embodiments of the present invention are not limited to MOCVD.
With reference to
The carrier plate 114 may rotate about an axis during processing. In one embodiment, the carrier plate 114 may be rotated at about 2 RPM to about 100 RPM. In another embodiment, the carrier plate 114 may be rotated at about 30 RPM. Rotating the carrier plate 114 aids in providing uniform heating of the substrates 140 and uniform exposure of the processing gases to each substrate 140. In one embodiment, the carrier plate 114 is supported by a carrier supporting device comprising a susceptor plate 115. Exemplary substrate support structures that may be adapted to practice the present invention are described in U.S. patent application Ser. No. 11/552,474, filed Oct. 24, 2006, titled SUBSTRATE SUPPORT STRUCTURE WITH RAPID TEMPERATURE CHANGE, which IS incorporated by reference in its entirety.
The lift mechanism 150 will be discussed with respect to
The carrier plate lift mechanism 150 comprises a vertically movable lift tube 152 arranged so as to surround the central shaft 132 of the susceptor support shaft 118, a driving unit (not shown) for moving the lift tube 152 up and down, three lift arms 154 radially extending from the lift tube 152, and lift pins 157 suspended from the bottom surface of the susceptor plate 115 by way of respective throughholes 158 formed so as to penetrate therethrough. When the driving unit is controlled so as to raise the lift tube 152 and lift arms 154 in such a configuration, the lift pins 157 are pushed up by the distal ends of the lift arms 154 whereby the carrier plate 114 rises.
As shown in
The plurality of inner lamps, central lamps, and outer lamps 121A, 121B, 121C may be arranged in concentric zones or other zones (not shown), and each zone may be separately powered allowing for the tuning of deposition rates and growth rates through temperature control. In one embodiment, one or more temperature sensors, such as pyrometers 122A, 122B, 122C, may be disposed within the showerhead assembly 104 to measure substrate 140 and carrier plate 114 temperatures, and the temperature data may be sent to a controller (not shown) which can adjust power to each zone to maintain a predetermined temperature profile across the carrier plate 114. In one embodiment, an inert gas is flown around the pyrometers 122A, 122B, 122C into the processing volume 108 to prevent deposition and condensation from occurring on the pyrometers 122A, 122B, 122C. The pyrometers 122A, 122B, 122C can compensate automatically for changes in emissivity due to deposition on surfaces. Although three pyrometers 122A, 122B, 122C are shown, it should be understood that any numbers of pyrometers may be used, for example, if additional zones of lamps are added it may be desirable to add additional pyrometers to monitor each additional zone. In another embodiment, the power to separate lamp zones may be adjusted to compensate for precursor flow or precursor concentration non-uniformity. For example, if the precursor concentration is lower in a carrier plate 114 region near an outer lamp zone, the power to the outer lamp zone may be adjusted to help compensate for the precursor depletion in this region. Advantages of using lamp heating over resistive heating include a smaller temperature range across the carrier plate 114 surface which improves product yield. The ability of lamps to quickly heat up and quickly cool down increases throughput and also helps create sharp film interfaces.
Other metrology devices, such as a reflectance monitor 123, thermocouples (not shown), 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. In one embodiment, the reflectance monitor 123 is coupled with the showerhead assembly 104 via a central conduit (not shown). Other aspects of the 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 inner, central, and outer lamps 121A, 121B, 121C may heat the substrates 140 to a temperature of about 400 degrees Celsius to about 1200 degrees Celsius. It is to be understood that the invention is not restricted to the use of arrays of inner, central, and outer lamps 121A, 121B, and 121C. Any suitable heating source may be utilized to ensure that the proper temperature is adequately applied to the chamber 102 and substrates 140 therein. For example, in another embodiment, the heating source may comprise resistive heating elements (not shown) which are in thermal contact with the carrier plate 114.
With reference to
In one embodiment, the exhaust ring 120 may be disposed around the periphery of the carrier plate 114 to help prevent deposition from occurring in the lower volume 110 and also help direct exhaust gases from the chamber 102 to exhaust ports 109. In one embodiment, the exhaust ring 120 comprises silicon carbide. The exhaust ring 120 may also comprise alternative materials that absorb electromagnetic energy, such as ceramics.
In one embodiment, the exhaust ring 120 is coupled with an exhaust cylinder 160. In one embodiment, the exhaust cylinder 160 is perpendicular to the exhaust ring 120. The exhaust cylinder 160 helps maintain uniform and equal radial flow from the center outward across the surface of the carrier plate 114 and controls the flow of gas out of process volume 108 and into the annular exhaust channel 105. The exhaust cylinder 160 comprises an annular ring 161 having an inner sidewall 162 and an outer side wall 163 with throughholes or slots 165 extending through the sidewalls and positioned at equal intervals throughout the circumference of the ring 161. In one embodiment, the exhaust cylinder 160 and the exhaust ring 120 comprise a unitary piece. In one embodiment the exhaust ring 120 and the exhaust cylinder 160 comprise separate pieces that may be coupled together using attachment techniques known in the art. With reference to
A gas delivery system 125 may include multiple gas sources, or, depending on the process being run, some of the sources may be liquid sources rather than gases, in which case the gas delivery system may include a liquid injection system or other means (e.g., a bubbler) to vaporize the liquid. The vapor may then be mixed with a carrier gas prior to delivery to the chamber 102. Different gases, such as precursor gases, carrier gases, purge gases, cleaning/etching gases or others may be supplied from the gas delivery system 125 to separate supply lines 131, 135 to the showerhead assembly 104. The supply lines may include shut-off valves and mass flow controllers or other types of controllers to monitor and regulate or shut off the flow of gas in each line. In one embodiment, precursor gas concentration is estimated based on vapor pressure curves and temperature and pressure measured at the location of the gas source. In another embodiment, the gas delivery system 125 includes monitors located downstream of the gas sources which provide a direct measurement of precursor gas concentrations within the system.
A conduit 129 may receive cleaning/etching gases from a remote plasma source 126. The remote plasma source 126 may receive gases from the gas delivery system 125 via a supply line 124, and a valve 130 may be disposed between the shower head assembly 104 and remote plasma source 126. The valve 130 may be opened to allow a cleaning and/or etching gas or plasma to flow into the shower head assembly 104 via supply line 133 which may be adapted to function as a conduit for a plasma. In another embodiment, cleaning/etching gases may be delivered from the gas delivery system 125 for non-plasma cleaning and/or etching using alternate supply line configurations to shower head assembly 104. In yet another embodiment, the plasma bypasses the shower head assembly 104 and flows directly into the processing volume 108 of the chamber 102 via a conduit (not shown) which traverses the shower head assembly 104.
The remote plasma source 126 may be a radio frequency or microwave plasma source adapted for chamber 102 cleaning and/or substrate 140 etching. Cleaning and/or etching gas may be supplied to the remote plasma source 126 via supply line 124 to produce plasma species which may be sent via conduit 129 and supply line 133 for dispersion through showerhead assembly 104 into chamber 102. Gases for a cleaning application may include fluorine, chlorine or other reactive elements.
In another embodiment, the gas delivery system 125 and remote plasma source 126 may be suitably adapted so that precursor gases may be supplied to the remote plasma source 126 to produce plasma species which may be sent through showerhead assembly 104 to deposit CVD layers, such as III-V films, for example, on substrates 140.
A purge gas (e.g., nitrogen) may be delivered into the chamber 102 from the showerhead assembly 104 and/or from inlet ports or tubes (not shown) disposed below the carrier plate 114 and near the bottom of the chamber body 103. The purge gas enters the lower volume 110 of the chamber 102 and flows upwards past the carrier plate 114 and exhaust ring 120 and into multiple exhaust ports 109 which are disposed around an annular exhaust channel 105. An exhaust conduit 106 connects the annular exhaust channel 105 to a vacuum system 112 which includes a vacuum pump (not shown). The chamber 102 pressure may be controlled using a valve system 107 which controls the rate at which the exhaust gases are drawn from the annular exhaust channel 105.
The showerhead assembly 104 is located near the carrier plate 114 during substrate 140 processing. In one embodiment, the distance from the showerhead assembly 104 to the carrier plate 114 during processing may range from about 4 mm to about 40 mm.
During substrate processing, according to one embodiment of the invention, process gas flows from the showerhead assembly 104 towards the surface of the substrate 140. The process gas may comprise one or more precursor gases as well as carrier gases and dopant gases which may be mixed with the precursor gases. The draw of the annular exhaust channel 105 may affect gas flow so that the process gas flows substantially tangential to the substrates 140 and may be uniformly distributed radially across the deposition surfaces of the substrate 140 deposition surfaces in a laminar flow. The processing volume 108 may be maintained at a pressure of about 760 Torr down to about 80 Torr.
Reaction of process gas precursors at or near the surface of the substrate 140 may deposit various metal nitride layers upon the substrate 140, including GaN, aluminum nitride (AlN), and indium nitride (InN). Multiple metals may also be utilized for the deposition of other compound films such as AlGaN and/or InGaN. Additionally, dopants, such as silicon (Si) or magnesium (Mg), may be added to the films. The films may be doped by adding small amounts of dopant gases during the deposition process. For silicon doping, silane (SiH4) or disilane (Si2H6) gases may be used, for example, and a dopant gas may include Bis(cyclopentadienyl) magnesium (Cp2Mg or (C5H5)2Mg) for magnesium doping.
In one embodiment, a fluorine or chlorine based plasma may be used for etching or cleaning. In other embodiments, halogen gases, such as Cl2, Br, and I2, or halides, such as HCl, HBr, and HI, may be used for non-plasma etching.
In one embodiment, a carrier gas, which may comprise nitrogen gas (N2), hydrogen gas (H2), argon (Ar) gas, another inert gas, or combinations thereof may be mixed with the first and second precursor gases prior to delivery to the showerhead assembly 104.
In one embodiment, the first precursor gas may comprise a Group III precursor, and second precursor gas may comprise a Group V precursor. The Group III precursor may be a metal organic (MO) precursor such as trimethyl gallium (“TMG”), triethyl gallium (TEG), trimethyl aluminum (“TMAI”), and/or trimethyl indium (“TMI”), but other suitable MO precursors may also be used. The Group V precursor may be a nitrogen precursor, such as ammonia (NH3).
An improved deposition apparatus and process that provides uniform precursor flow and mixing while maintaining a uniform temperature over larger substrates and larger deposition areas has been provided. The uniform mixing and heating over larger substrates and/or multiple substrates and larger deposition areas is desirable in order to increase yield and throughput. Further uniform heating and mixing are important factors since they directly affect the cost to produce an electronic device and, thus, a device manufacturer's competitiveness in the market place.
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.
