Patent Application
20130280427
The present invention relates generally to apparatus and methods for chemical processing, and, more particularly, to tube-based reactors for chemical vapor deposition.
Chemical vapor deposition (CVD) is widely used in the semiconductor industry as well as other industries to form non-volatile solid-films on a substrate. In a typical CVD process, a given composition and flow of reactant gases are introduced into a reaction space where they are adsorbed onto a substrate. There, the reactants undergo migration and film-forming chemical reactions. The reaction by-products are then desorbed from the substrate and removed from the reaction space.
Furnace CVD systems (horizontal or vertical) are commonly utilized for CVD. In a typical furnace CVD system, the chemical reactants are flowed through a cylindrical quartz or alumina process tube that houses the substrate. The process tube, in turn, is surrounded by a heating furnace comprising resistance-heated heating elements (e.g., heating coils), which may be separated into zones to improve axial temperature uniformity. When properly designed, furnace CVD systems can achieve temperature uniformities of about one-half degree Centigrade (° C.) up to about 1,200° C.
Nevertheless, despite their widespread use, furnace CVD systems may suffer from several disadvantages. One way to improve throughput in a furnace CVD system, for example, is to increase the diameter of the process tube. However, both manufacturing costs and manufacturing errors increase when increasing process tube size. In addition, the roundness of the process tube may be compromised with greater process tube diameter, which may make it problematic to achieve a reliable vacuum seal with metal end-ports. Finally, the greater the size of the process tube, the more difficult it becomes to manage processing conditions therein.
For the foregoing reasons, there is a need for tube-based CVD systems that increase throughput while maintaining desirable footprint, energy efficiency, and deposition characteristics.
Embodiments of the present invention address the above-identified needs by providing new apparatus for film deposition by CVD, as well as methods for their use. Advantageously, apparatus in accordance with aspects of the invention provide substantially greater throughput than conventional single-tube CVD reactors while not requiring that process tube diameters be substantially increased. At the same time, through the use of compact designs and the use of single heating sources, apparatus in accordance with aspects of the invention do not create a footprint that is substantially larger than a conventional single-tube CVD reactor nor do they consume a substantially greater amount of energy per run.
In accordance with an aspect of the invention, an apparatus for performing film deposition comprises an energy source, a plurality of process tubes, and a gas manifold. The energy source is adapted to direct energy into a cylindrical space. The plurality of process tubes, in turn, pass through this cylindrical space. To perform the film deposition, the gas manifold is operative to introduce a respective gas flow into each of the plurality of process tubes.
In accordance with another aspect of the invention, a method for performing film deposition comprises directing energy into a cylindrical space. A plurality of process tubes pass through this cylindrical space. To perform film deposition, a respective gas flow is introduced into each of the plurality of process tubes.
These and other features, aspects, and advantages of the present invention will become better understood with regard to the following description, appended claims, and accompanying drawings where:
The present invention will be described with reference to illustrative embodiments. For this reason, numerous modifications can be made to these embodiments and the results will still come within the scope of the invention. No limitations with respect to the specific embodiments described herein are intended or should be inferred.
The term “film deposition” as used herein is intended to encompass both what is commonly called film deposition and film growth. Thus, the term “film deposition” would include the forming of films that differ in composition and/or crystallinity from the respective substrates on which they are deposited, as well as the forming of films that substantially match the composition and crystallinity of the respective substrates on which they are deposited.
In the CVD tube reactor 100, each of the process tubes 110-n passes through a cylindrical space 120 that is defined by a heating source 130, an input block 140, and an output block 150. The heating source 130 defines a wall of the cylindrical space 120 and is adapted to direct its energy into the cylindrical space 120. The input block 140 and the output block 150, in contrast, act to define the opposing ends of the cylindrical space 120 and, in doing so, act to trap the heat within the cylindrical space 120. The input block 140 and the output block 150 also act to physically support the process tubes 110-n. Such physical support is accomplished by having each of the input and output blocks 140, 150 define seven respective openings therein through which the process tubes 110-n pass.
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The CVD tube reactor 100 in the present illustrative embodiment is capable of performing film deposition by what is commonly called low-pressure CVD (LPCVD). When performing film deposition by LPCVD, reaction conditions are primarily determined by gas flow rates, pressure, and temperature, with pressure generally being set substantially below atmospheric pressure (e.g., about 0.25-2.0 Torr).
Notably, the gas manifold 180 is operative to determine a different composition for each of the respective gas flows introduced into each of the plurality of process tubes 110-n, while the exhaust manifold 190 is operative to determine a different pressure for each of the plurality of process tubes 110-n. These capabilities allow different process conditions to be independently established in each of the process tubes 110-n during a single run of the CVD tube reactor 100. To facilitate such independent process control, both the gas manifold 180 and the exhaust manifold 190 in the CVD tube reactor 100 are partitioned into sub-portions so that a single process tube 110-n is serviced by a single respective gas manifold sub-portion and a single respective exhaust manifold sub-portion. Such partitioning is further shown in
As indicated above, the gas manifold sub-portion 182-1 shown in
In fact, if independent process control for each of the process tubes 110-n is not required, it may not be necessary to partition the gas manifold 180 and the exhaust manifold 190 in the manner shown in
The various elements of the CVD tube reactor 100 may be formed from largely conventional materials. The process tubes 110-n in the CVD tube reactor 100 may, for example, comprise a material such as, but not limited to, quartz or alumina. At the same time, the input and output blocks 140, 150 may comprise any material having sufficient strength to support the process tubes 110-n and still be capable of withstanding high temperatures. Such materials may include, as just an example, refractory oxide materials such as alumina, which may be stable to temperatures greater than 1800° C. Finally, the input and output ports 160, 170 may comprise a metal such as aluminum or stainless steel, and may be vacuum coupled to the process tubes 110-n utilizing high-temperature o-ring seals formed of an elastomeric material such as perfluoroelastomer. If it is necessary to cool the input and the output ports 160, 170 to maintain the vacuum seal, they may be cooled by circulating cooling water, as is conventional.
The manner of forming the heating source 130, on the other hand, depends to a large degree on whether the walls of the process tubes 110-n are allowed to become relatively hot during processing, or whether, instead, it is desirable to keep the walls of the process tubes 110-n relatively cold during processing. Such a difference determines whether the CVD tube reactor 100 is configured as a “hot-wall” reactor or a “cold-wall” reactor. A cold-wall configuration reduces the rate of film deposition on the sidewalls of the process tubes 110-n, and thereby reduces the need to frequently clean the process tubes 110-n. In either case, several options are available for the heating source 130 that will fall within the scope of the invention. These options include, but are not limited to, resistance heating, radiant heating with high intensity radiation lamps, and electric induction heating. These heating options and other suitable options are described in a number of readily available publications, including A. C. Jones, Chemical Vapour Deposition: Precursors, Processes and Applications, Royal Society of Chemistry, 2009, which is hereby incorporated by reference herein. Whatever heating option is ultimately chosen, the heating source 130 preferably includes a suitable jacket or box (e.g., refractory metal oxide or fibrous refractory metal oxide) that helps to support the heating elements and to both thermally and electrically isolate the heating elements and the cylindrical space 120 from the environment outside the CVD tube reactor 100.
If a hot-wall reactor is acceptable, the heating source 130 may be formed utilizing resistively-heated heating elements that are energized by a voltage/current regulator. In one configuration, such resistively-heated heating elements may comprise, for example, one or more wires that are coiled around the cylindrical space 120 to form what is frequently called a “tube furnace.” If desired, several different coils may be arranged along the longitudinal axis of the cylindrical space 120 to create separately-controllable heating zones that can compensate for reactant depletion effects and so forth. For temperature regulation, signals from thermocouples in the CVD tube reactor 100 may be fed back to the voltage/current regulator so as to maintain a predetermined temperature set point.
If, on the other hand, a cold-wall reactor is desired, the heating source 130 may be configured utilizing high-intensity radiation lamps or radio frequency (rf) induction. To utilize high-intensity radiation lamps, the heating source 130 may be fitted with a multiplicity of radiation lamps (e.g., tungsten filament lamps) driven by a voltage/current regulator. Ideally, the radiation lamps will produce a light spectrum that effectively heats the contents of the process tubes 110-n (e.g., substrates and/or susceptors) by radiant heating while being transmitted through the walls of the process tubes 110-n with little absorption. Reflectors may be incorporated into the heating source 130 to help provide uniform illumination by the radiation lamps. Alternatively, the heating source 130 may be configured with one or more electric coils surrounding the cylindrical space 120 and driven by an rf generator. The electric coils may be configured as tubes capable of circulating a cooling liquid in order to facilitate their cooling. A strong magnetic field formed in the cylindrical space 120 thereby induces induction heating in any electrically conductive elements disposed in the process tubes 110-n (e.g., substrates and/or susceptors). Thermocouples and/or pyrometers may be used to feed back signals indicative of temperature to the voltage/current regulator or rf generator, as appropriate, to again maintain a predetermined temperature set point.
It should be noted that, while the CVD tube reactor 100 comprises seven process tubes 110-n, this number is largely arbitrary and other designs would also come within the scope of the invention.
Embodiments in accordance with aspects of the invention provide a number of advantages over conventional single-tube CVD reactors. In providing more than one process tube within the heated cylindrical space, for example, “multi-tube” CVD tube reactors in accordance with aspects of the invention provide a much greater throughput than conventional single-tube CVD reactors. The CVD tube reactor 100, for example, with its seven process tubes 110-n, may accomplish in a single run what would take a conventional single-tube CVD reactor seven runs to realize. Notably, this increase in throughput is accomplished without the need to increase process tube diameter. Those issues associated with increasing the diameter of a process tube such as process tube defects, vacuum leaks, and poorly controlled processing conditions are thereby avoided. At the same time, through the use of a compact design and single heating source, the multi-tube CVD tube reactors do not create a footprint that is substantially larger than a conventional single-tube CVD reactor nor do they consume a substantially greater amount of energy per run.
In closing, it should again be emphasized that the above-described embodiments of the invention are intended to be illustrative only. Other embodiments can use different types and arrangements of elements for implementing the described functionality. These numerous alternative embodiments within the scope of the appended claims will be apparent to one skilled in the art. For example, the CVD tube reactor 100 described herein is one made suitable for LPCVD film deposition processes, meaning that the exhaust manifold 190 is capable of reducing the respective pressures in the plurality of process tubes 110-n substantially below atmospheric pressure. Nevertheless, this particular configuration is not intended to be a limitation on the scope of the invention. In one or more alternative embodiments of the invention, for example, CVD tube reactors in accordance with aspects of the invention may be configured for film deposition at atmospheric pressure, thereby facilitating atmospheric-pressure CVD (APCVD). Moreover, in one or more other alternative embodiments of the invention, CVD tube reactors falling within the scope of the invention may be fitted with electrodes capable of being energized by sources of rf energy to allow plasma-enhanced CVD (PECVD).
The features disclosed herein may be replaced by alternative features serving the same, equivalent, or similar purposes, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.
Any element in a claim that does not explicitly state “means for” performing a specified function or “step for” performing a specified function is not to be interpreted as a “means for” or “step for” clause as specified in 35 U.S.C. §112, ¶6. In particular, the use of “step of” in the claims herein is not intended to invoke the provisions of 35 U.S.C. §112, ¶6.
