| Systems for depositing material onto workpieces in reaction chambers and methods for removing byproducts from reaction chambers -> Monitor Keywords |
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Systems for depositing material onto workpieces in reaction chambers and methods for removing byproducts from reaction chambersRelated Patent Categories: Fluid Handling, Processes, Involving Pressure ControlSystems for depositing material onto workpieces in reaction chambers and methods for removing byproducts from reaction chambers description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20060196538, Systems for depositing material onto workpieces in reaction chambers and methods for removing byproducts from reaction chambers. Brief Patent Description - Full Patent Description - Patent Application Claims
TECHNICAL FIELD [0001] The present invention is related to systems for depositing material onto workpieces in reaction chambers and methods for removing byproducts from reaction chambers. BACKGROUND [0002] Thin film deposition techniques are widely used in the manufacturing of microfeatures to form a coating on a workpiece that closely conforms to the surface topography. The size of the individual components in the workpiece is constantly decreasing, and the number of layers in the workpiece is increasing. As a result, both the density of components and the aspect ratios of depressions (i.e., the ratio of the depth to the size of the opening) are increasing. Thin film deposition techniques accordingly strive to produce highly uniform conformal layers that cover the sidewalls, bottoms, and corners in deep depressions that have very small openings. [0003] One widely used thin film deposition technique is Chemical Vapor Deposition (CVD). In a CVD system, one or more precursors that are capable of reacting to form a solid thin film are mixed while in a gaseous or vaporous state, and then the precursor mixture is presented to the surface of the workpiece. The surface of the workpiece catalyzes the reaction between the precursors to form a solid thin film at the workpiece surface. A common way to catalyze the reaction at the surface of the workpiece is to heat the workpiece to a temperature that causes the reaction. [0004] Although CVD techniques are useful in many applications, they also have several drawbacks. For example, if the precursors are not highly reactive, then a high workpiece temperature is needed to achieve a reasonable deposition rate. Such high temperatures are not typically desirable because heating the workpiece can be detrimental to the structures and other materials already formed on the workpiece. Implanted or doped materials, for example, can migrate within the silicon substrate at higher temperatures. On the other hand, if more reactive precursors are used so that the workpiece temperature can be lower, then reactions may occur prematurely in the gas phase before reaching the substrate. This is undesirable because the film quality and uniformity may suffer, and also because it limits the types of precursors that can be used. [0005] Atomic Layer Deposition (ALD) is another thin film deposition technique. FIGS. 1A and 1B schematically illustrate the basic operation of ALD processes. Referring to FIG. 1A, a layer of gas molecules A coats the surface of a workpiece W. The layer of A molecules is formed by exposing the workpiece W to a precursor gas containing A molecules and then purging the chamber with a purge gas to remove excess A molecules. This process can form a monolayer of A molecules on the surface of the workpiece W because the A molecules at the surface are held in place during the purge cycle by physical adsorption forces at moderate temperatures or chemisorption forces at higher temperatures. Referring to FIG. 1B, the layer of A molecules is then exposed to another precursor gas containing B molecules. The A molecules react with the B molecules to form an extremely thin layer of solid material on the workpiece W. The chamber is then purged again with a purge gas to remove excess B molecules. [0006] FIG. 2 illustrates the stages of one cycle for forming a thin solid layer using ALD techniques. A typical cycle includes (a) exposing the workpiece to the first precursor A, (b) purging excess A molecules, (c) exposing the workpiece to the second precursor B, and then (d) purging excess B molecules. In actual processing, several cycles are repeated to build a thin film on a workpiece having the desired thickness. For example, each cycle may form a layer having a thickness of approximately 0.5-1.0 .ANG., and thus several cycles are required to form a solid layer having a thickness of approximately 60 .ANG.. [0007] FIG. 3 schematically illustrates a single-wafer ALD reactor 10 having a reaction chamber 20 coupled to a gas supply 30 and a vacuum 40. The reactor 10 also includes a heater 50 that supports the workpiece W and a gas dispenser 60 in the reaction chamber 20. The gas dispenser 60 includes a plenum 62 operably coupled to the gas supply 30 and a distributor plate 70 having a plurality of holes 72. In operation, the heater 50 heats the workpiece W to a desired temperature, and the gas supply 30 selectively injects the first precursor A, the purge gas, and the second precursor B, as shown above in FIG. 2. The vacuum 40 maintains a negative pressure in the reaction chamber 20 to draw the gases from the gas dispenser 60 across the workpiece W and then through an outlet of the reaction chamber 20. A trap 80 captures and collects the byproducts from the reaction chamber 20 to prevent fouling of the vacuum 40. [0008] One drawback of ALD processing is that it has a relatively low throughput compared to CVD techniques. For example, each A-purge-B-purge cycle can take several seconds. This results in a total process time of several minutes to form a single thin layer of only 60 .ANG.. In contrast to ALD processing, CVD techniques require only about one minute to form a 60 .ANG. thick layer. The low throughput limits the utility of the ALD technology in its current state because ALD may create a bottleneck in the overall manufacturing process. [0009] Another drawback of both ALD and CVD processing is the downtime required to service or replace the trap. As the trap collects byproducts from the reaction chamber, the byproducts restrict the flow from the reaction chamber 20 to the vacuum 40, and consequently, the pressure in the chamber increases. The increased pressure in the reaction chamber impairs effective removal of the byproducts from the reaction chamber. Accordingly, the trap is cleaned or replaced periodically to avoid significant increases in the pressure in the reaction chamber. Servicing the trap requires that the reactor be shut down, which results in a reduction in throughput. One approach to reduce the downtime of the reactor includes increasing the size of the trap. Although this approach reduces the downtime, a significant need still exists to eliminate the downtime required to service the trap and to maintain a consistent pressure in the reaction chamber. BRIEF DESCRIPTION OF THE DRAWINGS [0010] FIGS. 1A and 1B are schematic cross-sectional views of stages in ALD processing in accordance with the prior art. [0011] FIG. 2 is a graph illustrating a cycle for forming a layer using ALD techniques in accordance with the prior art. [0012] FIG. 3 is a schematic representation of a system including a reactor for depositing material onto a microfeature workpiece in accordance with the prior art. [0013] FIG. 4 is a schematic representation of a system for depositing material onto a microfeature workpiece in accordance with one embodiment of the invention. [0014] FIG. 5 is a schematic representation of a portion of a system for depositing material onto a workpiece in accordance with another embodiment of the invention. [0015] FIG. 6 is a schematic representation of a portion of a system for depositing material onto a workpiece in accordance with another embodiment of the invention. DETAILED DESCRIPTION A. Overview [0016] The following disclosure describes several embodiments of systems for depositing material onto workpieces in reaction chambers and methods for removing byproducts from reaction chambers. Many specific details of the invention are described below with reference to single-wafer reactors for depositing material onto microfeature workpieces, but several embodiments can be used in batch systems for processing a plurality of workpieces simultaneously. Moreover, several embodiments can be used for depositing material onto workpieces other than microfeature workpieces. The term "microfeature workpiece" is used throughout to include substrates upon which and/or in which microelectronic devices, micromechanical devices, data storage elements, read/write components, and other features are fabricated. For example, microfeature workpieces can be semiconductor wafers such as silicon or gallium arsenide wafers, glass substrates, insulative substrates, and many other types of materials. Furthermore, the term "gas" is used throughout to include any form of matter that has no fixed shape and will conform in volume to the space available, which specifically includes vapors (i.e., a gas having a temperature less than the critical temperature so that it may be liquefied or solidified by compression at a constant temperature). Several embodiments in accordance with the invention are set forth in FIGS. 4-6 and the following text to provide a thorough understanding of particular embodiments of the invention. A person skilled in the art will understand, however, that the invention may have additional embodiments, or that the invention may be practiced without several of the details of the embodiments shown in FIGS. 4-6. [0017] One aspect of the invention is directed to systems for depositing material onto workpieces in reaction chambers. In one embodiment, a system includes a gas phase reaction chamber, a first exhaust line coupled to the reaction chamber, first and second traps each in fluid communication with the first exhaust line, and a vacuum pump coupled to the first exhaust line to remove gases from the reaction chamber. The first and second traps are operable independently to individually and/or jointly collect byproducts from the reaction chamber. In one aspect of this embodiment, the first exhaust line includes a first branchline and a second branchline each downstream from the reaction chamber. The first trap can be disposed in the first branchline and the second trap can be disposed in the second branchline. The first and second branchlines can be configured in a parallel arrangement. In another aspect of this embodiment, the system further includes a throttling valve in the second branchline, a pressure monitor, and a controller operably coupled to the throttling valve and the pressure monitor. The pressure monitor can determine the difference between the pressure in the first exhaust line upstream from the first trap and the pressure in the first exhaust line downstream from the first trap. The controller can operate the throttling valve to control the flow of byproducts into the second branchline to maintain the pressure differential in the first exhaust line within a desired range. [0018] In another embodiment, a system includes a gas phase reaction chamber, a first exhaust line coupled to the reaction chamber, a trap in the first exhaust line to collect byproducts from the reaction chamber, and first and second vacuum pumps. The first and second vacuum pumps are each in fluid communication with the first exhaust line and positioned downstream from the trap. The first and second vacuum pumps are operable independently to individually and/or jointly exhaust byproducts from the reaction chamber. In one aspect of this embodiment, the first exhaust line includes a first branchline and a second branchline each downstream from the reaction chamber. The first vacuum pump can be coupled to the first branchline and the second vacuum pump can be coupled to the second branchline. The system can also include a throttling valve in the second branchline to control the pressure in the first exhaust line. [0019] Another aspect of the invention is directed to methods for removing byproducts from a reaction chamber through a first mainline. The first mainline has first and second branchlines downstream from the reaction chamber. In one embodiment, the method includes exhausting byproducts from the reaction chamber through the first mainline and dynamically controlling the flow of byproducts into the second branchline of the first mainline to maintain a pressure differential in the first mainline within a desired range. In one aspect of this embodiment, the method further includes collecting byproducts in a first trap in the first branchline of the first mainline and collecting byproducts in a second trap in the second branchline of the first mainline. In another aspect of this embodiment, the method further includes monitoring the difference between the pressure in the first mainline upstream from the first trap and the pressure in the first mainline downstream from the first trap. In response to the monitored pressure differential, a throttling valve in the second branchline can be regulated to maintain the pressure differential within the desired range. 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