Patent Grant
6936086
The present invention relates to filtering methods for fluid streams, and more specifically, to filters for separating particles from precursor vapor in a thin film deposition system.
Reactor chambers provide a controlled location for chemical processes using introduced vapor. Depending on the process, the vapor is ideally free of particles and droplets to ensure quality. Filters serve to reduce particles and droplets from entering the reactor chambers.
There are many particle filters available for chemical vapor deposition (“CVD”) reactors. CVD reactors are based upon a static flow of precursor vapor and the flow resistance of the filter is not especially important.
Atomic layer deposition (“ALD”), formerly known as atomic layer epitaxy (“ALE”), is a thin film deposition process based on dynamic flows. The ALD process relies on sequential pulsing of two or more precursor vapors over a substrate in a reaction chamber. To increase the productivity of an ALD reactor, it is advantageous to switch the precursor vapors as fast as possible. The films yielded by the ALD technique have exceptional characteristics, such as being pinhole free and possessing almost perfect step coverage.
A key to successful ALD growth is to have the correct precursor vapors pulsed into the reaction chamber sequentially and without overlap. Since the actual pulses are not Delta functions (i.e., do not exhibit instantaneous rise and decay), they will overlap if the second pulse is started before the first is completely decayed. Since both highly reactive precursor vapors are present in the reaction chamber at the same time, this condition leads to non-ALD growth, and typically CVD-type growth, which can lead to film thickness non-uniformity. To prevent this problem, the pulses must be separated in time.
High-resistance elements, such as particle filters, in the flow path from the main precursor switching element to the reaction chamber can result in much longer exponential decays in the precursor pulses. With a poorly designed precursor delivery system, it is common for the purge times, defined as the time between precursor pulses, to be 10 times as long as the pulse itself to prevent overlap of the precursor pulses and achieve good film thickness uniformity. Longer purge times increase processing time, which substantially reduces the overall efficiency of the ALD reactor. To optimize the throughput of a reactor and minimize particle generation, it is, therefore, desirable to create a precursor delivery system that has the fastest possible rise and decay of the precursor pulse.
For most films grown by ALD, particles in or on the film will reduce the manufacturing yield. It is, therefore, important that the precursor source does not emit any particles. This is especially difficult when the precursor exists in powder form at standard temperature and pressure (“STP”). Powdered precursors are changed to vapor by exposing the vapor to high temperatures and low pressure. The resulting vapor contains more contaminant particles than precursors that exist in liquid or solid phase at STP, because it is difficult to eliminate contaminant particles from a powdered mixture.
A typical solution is to add a high efficiency particle filter, which is quite common for CVD systems. These filters can typically block 99.99999% of particles smaller than 0.003 microns. However, such particle filters are very resistive to flow, which leads to long precursor decay times and, therefore, long process times.
U.S. Pat. No. 6,354,241 to Tanaka et al. and U.S. Pat. No. 5,709,753 to Olson et al. disclose filters that rely on sinuous flow paths to capture undesired materials. However, materials captured in the disclosed filters are continuously exposed to the flow and may be drawn back into the flow. Thus, these filters may not provide the required filtering efficacy.
High efficiency particle filters serve well in CVD systems, which rely on static vapor flow, but have limited use with ALD systems due to the dynamic nature of the ALD process. The present inventors have recognized that efficient filters having high flow conductivity are desirable for pulsed precursor vapor delivery systems.
A particle filter for removing particles from a fluid flow provides a flow path with several turns to separate particles with a higher inertia from the accompanying fluid. Traps are positioned in proximity to the turns to capture particles. The turns and traps ensure filter efficiency while maintaining the cross sectional area of the flow path. The turns require high-speed changes of direction, which separates particles from the fluid stream due to higher inertia of the particles. Preferred embodiments involve filtering of particles from precursor vapor in a thin film deposition system.
In one embodiment, the flow path includes a curved spiral with traps in tangential communication with the spiral. Alternatively, the flow path may be a spiral with angled turns. Traps are located before the angled turns to capture particles that are unable to negotiate the turn.
In an alternative embodiment, the filter includes a series of baffles arranged to provide a series of 180-degree turns. Traps are located proximate to the turns to capture particles.
In another embodiment, plates are sequentially disposed within a housing to define a series of chambers. Each plate has an aperture, which provides the only exit from a chamber into a subsequent chamber. Each aperture is nonaligned with adjacent apertures to provide several turns for a flow path.
In yet another embodiment, the filter includes tubes with sealed ends disposed parallel to one another. The tubes have input and output apertures that enable communication between the tubes and provide a series of turns for a flow path. The apertures further define traps adjacent to the sealed ends of the tubes.
Once the particles are separated from the fluid stream, they should be retained or removed so they cannot re-enter the fluid stream. This can be done by modifying the particle traps to include a rough or adhesive surface or to remove particles from the traps by means of a small orifice in the trap that leads to a pump.
Non-exhaustive embodiments are described with reference to the figures, in which:
Reference is now made to the figures in which like reference numerals refer to like elements.
Throughout the specification, reference to “one embodiment” or “an embodiment” means that a particular described feature, structure, or characteristic is included in at least one embodiment. Thus, appearances of the phrases “in one embodiment” or “in an embodiment” or other similar phrases in various places throughout this specification are not necessarily all referring to the same embodiment.
As used herein, the term “in communication” refers not only to components that are directly connected, but also to components that are connected via one or more other components.
Furthermore, the described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. Those skilled in the art will recognize that the invention can be practiced without one or more of the specific details, or with other methods, components, materials, etc. In other instances, well-known structures, materials, or operations are not shown or not described in detail to avoid obscuring aspects of the embodiments.
Referring to
The filter 10 includes a flow path 12 that may be formed in a block 14. The flow path 12 is configured as a continuous spiral in communication with an input 16 and an output 18. The arrows indicate the direction of vapor flow through the flow path 12. The output 18 may be oriented perpendicular to the flow path 12. In application, the flow path 12 provides one-way directional flow of a vapor stream from the input 16 to the output 18. Configured as shown, the flow path 12 is a plane curve that moves around the fixed point of the output 18 while constantly approaching the output 18.
The flow path 12 is in communication with a plurality of tangential particle reservoirs or traps 20. As vapor travels through the flow path 12 the particles have greater inertia than the vapor. As the vapor travels through the curve, the inertia of particles does not allow the particles to follow and the particles are captured in the traps 20 while the vapor continues. Several traps 20 disposed along the flow path 12 provide a highly efficient filter 10 that does not constrain flow. The exact number of traps 20 may vary and depends, in part, on system design limitations.
The filter 10 may be formed from a block 14 of heat-resistant material, such as metal. The material may be aluminum, silicon, titanium, copper, stainless steel or other high thermal conductivity material. In manufacturing, the flow path 12 may be drilled or otherwise machined from the block 14. A lid may then be placed on the block 14 to seal the flow path 12. The filter 10 may be interchangeable in a modular system to facilitate equipment modifications, repair, and replacement. After forming the filter 10, the filter 10 may be coated with Al2O3 or other chemically resistant material to protect the filter 10 from corrosive vapors and/or abrasive particles.
Referring to
The movement around the fixed point may be achieved through angled turns 30. The angled turns 30 of
A trap 32 is disposed before an angled turn 30 such that the trap 32 continues along the direction of the flow path 24 before the angled turn 30. As the vapor stream approaches the turn, the inertia of the particles is greater than that of the vapor. As the vapor stream passes through an angled turn 30, particles continue along the former path of the flow path 24 and into a trap 32. The filter 22 includes several traps 32 to provide high filtering efficiency. The traps 32 do not limit the flow of a vapor stream, which allows for high conductivity.
The turns need not all have the same angle in order to accommodate the flow path. For example, in the embodiment shown in
Referring to
The spiral flow path 38 is comprised entirely of 90-degree angled turns 44. In alternative implementations, the angle of the turns 44 may vary. A trap 46 is disposed prior to an angled turn 44 such that the trap 46 continues along the direction of the flow path 38 before the angled turn 44. As the vapor stream passes through an angled turn 44, particles continue along the former path of the flow path 38 and into a trap 46. Traps 46 may be placed prior to each turn 44 to maximize the efficiency of the filter 36.
The flow paths shown in
Referring to
The filter 50 includes a series of baffles aligned to define paths and traps. The filter 50 includes a major baffle 60 that defines a path 62 for a vapor stream. The housing 51 provides an opposing side and also defines the path 62. A minor baffle 64, that is substantially in the same plane as a corresponding major baffle 60, defines a trap 58 to capture particles. The housing 51 also defines the trap 58. The trap 58 continues in the same direction as the path 62. The turns 57 require abrupt directional changes and particle inertia will cause particles to enter traps. As in previous filters, the trap 58 is a dead end to capture and retain particles. As the names indicate, the major baffle 60 has a greater length than the minor baffle 64. Accordingly, the path 62 is longer than a corresponding trap 58.
An aperture 66 separates the major and minor baffles and is nonaligned with a subsequent adjacent aperture. The aperture 66 may also be nonaligned with the input 54 and output 56. The aperture 66 provides the only exit for a vapor stream from the path 62 to a subsequent path. The aperture 66 may be referred to as providing the only flow path exit from the path 62. The flow path is defined as passing from the input 54 to the output 56 in the direction indicated by the arrows. Thus, the vapor stream must pass through the aperture 66 and be subject to a 180-degree angled turn 57.
As the vapor stream enters the filter 50, the vapor stream enters the path 62. The input 54 may be disposed perpendicular to the major baffle 60. The vapor stream continues along the path 62, toward the trap 58, until encountering the aperture 66. Since the vapor has less inertia than the particles, the path of the vapor will tend to bend and travel through the aperture 66. The particles, due to their greater inertia, will tend to continue on their direction and enter the trap 58.
A second major baffle 70 is disposed parallel to the first minor baffle 64, and together the first minor baffle 64 and the second major baffle 70 defines a pocket 72 that serves as a secondary trap to capture particles ejected from the flow path 62 after the flow path has passed through the aperture 66.
A vapor stream passing through the aperture 66 enters a second path 68 that is defined by the second major baffle 70 and the first major baffle 60. The second major baffle 70 is disposed to create a 180-degree turn 57 for the vapor stream. The second major baffle 70 is separated from a second minor baffle 74 by a second aperture 76. The second minor baffle 74 is substantially in the same plane as the second major baffle 70 and defines a second trap 78. The second trap 78 continues in the same direction as the second path 68 to capture particles. The second major baffle 70 is longer than the second minor baffle 74 as the second path 68 is longer than the second trap 78.
The second aperture 76 provides the only exit for a vapor stream passing from the first path 62 to the second path 68. The second aperture 76 is nonaligned with the aperture 66 or a subsequent downstream aperture.
Additional major and minor baffles with separating apertures may be similarly disposed to create a series of 180-degree turns 57 and corresponding traps. Some particles, especially smaller particles, may be able to follow the vapor through one or more apertures without being captured in a trap. Further, while the traps are designed to retain particles, it remains possible for particles collected in a trap to be drawn back into the vapor stream. Accordingly, multiple stages of filtering are used to increase the overall effectiveness of the filter 50.
To increase the chances that a particle will be captured, the velocity of the stream should be as high as possible at the turn 57. The inertia differences that separate particles from the vapor are a function of the velocity of the flow and, in particular, the velocity of the particles. Accordingly, the path leading up to a trap should be as long as space allows, which will allow sufficient room in which to accelerate the particles to a substantial linear velocity before reaching the turn adjacent the trap.
The output 56 may be disposed perpendicular to a final major baffle 77 and is in communication with a final path 79. The number of baffles and turns may vary based on design considerations, but allows for high conductivity while maintaining the efficiency of the filter 50.
The surface of each trap 58, 78 and pocket 72 may be modified to help retain particles in the traps and pockets. For example, one or more of the trap and pocket surfaces may be roughened or have an adhesive coating applied, to cause particles to adhere to the surfaces. The entire flow path may include a rough surface or an adhesive coating as well. In this implementation, particles traveling through the flow path would be collected and retained by the flow path surface.
Referring to
Referring to
Referring to
Referring to
An input 100 provides passage through the first end 92 and is in communication with a first chamber 102. Similarly, an output 104 provides passage through the second end 94 and is in communication with a final chamber 106. The input 100 and output 104 may be disposed perpendicular to the surface area of the plates 82, 84. The input 100 and output 104 may be nonaligned with the sequential apertures 82, 86.
The filter 88 may be characterized as providing a three-dimensional flow path, as vapor movement is not primarily confined to two dimensions. A vapor stream must pass through the provided aperture to exit each chamber and undergoes a series of turns. Sequential apertures 82, 86 should be distanced from each other as much as possible to lengthen the flow path and increase the velocity of the vapor stream. As the vapor stream passes through the apertures 82, 86, the particles, having a greater inertia, will continue along their former path and collect in traps of the chambers 98 adjacent the apertures. A series of plates 80, 84 and chambers 98 provide a highly efficient filter without unnecessary flow resistance. The interior surfaces of the chambers 98 may be modified to encourage particle adhesion. For example, the interior surfaces of a chamber 98 may be roughened or coated with an adhesive to retain particles.
In one embodiment (not shown), the plates 80, 84 may be spaced progressively closer to one another along a flow path to sequentially decrease the volumes of the chambers. Accordingly, the first chamber 102 would have a greater volume than the second chamber 108, the subsequent chamber would have a volume less than the second chamber 108, and so forth. The final chamber 106 may be configured with the smallest volume of all the previous chambers. Progressively decreasing the chamber volumes gradually decreases the cross-section of the flow path through the filter 88 and increases the velocity of a vapor stream. An increased vapor stream velocity increases the likelihood of smaller particles being retained in a trap 98. Apertures 82, 86 may also have sequentially decreasing diameters to decrease the cross-section of the flow path.
Referring to
The filter 110 includes tubes 122 that are disposed parallel to one another. Each tube 122 has scaled first and second ends 124, 126 and a first (input) aperture 128 and a second (output) aperture 130 disposed along the length of the tube 122. The apertures 128, 130 allow for a flow path 136 through the tube 122 and define traps 132, 134 within tubes 122. The traps 132, 134 extend from corresponding apertures 128, 130 to the respective second and first sealed ends 126 and 124. As such, each trap 132, 134 is a “dead end” in which particles are captured and retained in a manner similar to previously described embodiments.
Each tube 122 includes a path 137 which may be generally defined as the length of the tube 122 from the first aperture 128 to the second aperture 130. Vapor exiting the path 137 must turn through the output aperture 130 and particles, having a higher inertia than the vapor, continue in the same direction and enter a trap 134.
The tubes 122 are in communication with one another to provide a sinuous flow path that includes a series of paths 137 and turns. Traps 132, 134 are disposed adjacent each aperture 128, 130 to capture particles unable to negotiate a turn. The number of tubes 122 used for a flow path may vary based on system design constraints and desired efficiency of the filter 110.
The first and second apertures 128, 130 provide communication between the tubes 122 in the filter 110 as shown in FIG. 6. Thus, whether an aperture may be characterized as an input or output is relative to the tube since an output for one tube is an input for an adjacent tube.
The last tube in the flow path is defined herein as the output tube 138 and is in communication with or passes through the output 121. The output tube 138 may have an open end 140 to provide an exit for the vapor stream as shown in FIG. 6. Alternatively, the output tube 138 may have one or more output apertures.
In the embodiment shown in
The filter 110 may further include one or more preliminary traps 142 adjacent the input 120. The preliminary traps 142 may be formed by the extending the walls of the tubes 122 beyond their sealed first ends 124. The preliminary traps 142 may be disposed such that incoming vapor stream must turn and pass over the traps 142 before entering into the tubes 122. As in previous embodiments, the preliminary traps 142 and the previously discussed traps 132, 134 may have their interior surface roughened or coated with an adhesive to retain particles. The entire interior surface of the tubes 122 and the output tube 138 may include a rough surface or an adhesive coating to capture and retain particles.
A method of increasing velocity is to decrease the cross section of paths 137. Thus, the tubes 122 may be configured with progressively decreasing cross sectional areas in the direction of a flow path. As is well known, decreasing the cross sectional area of a flow path increases the velocity of a fluid as it travels along the flow path.
The vapor stream proceeds from tube 150 to 152 to 154 to 156 to 158 and, since the cross section is decreasing, the vapor stream velocity is increasing, thereby increasing the inertia of any particles in the vapor. The decreasing diameters and increasing particle inertia encourage separation of the increasingly smaller particles from the vapor stream as the flow proceeds to the outlet 140.
Referring to
An orifice 164 may have a cross-section that is approximately 1 to 5 percent as large as the cross-sectional area of the vapor flow channel 166. The orifices 164 communicating with a pump improve the ability of the filter 160 to capture and retain particles from a vapor stream 172. The orifices 164 also provide a means for cleaning the traps in-situ, without disassembling the filter 160, to thereby prevent the traps from becoming filled with particles that might otherwise be drawn back into the vapor stream 172. The resistance of the orifices 164 should be high enough so that the majority (e.g., preferably more than 90 percent) of the vapor stream 172 flowing through the filter 160 does not go through an orifice 164, but rather continues to the exit of the filter 160.
To direct the particles toward an orifice 164, a trap 168 may have sidewalls that are tapered toward the orifice 164 in a funnel configuration. In this implementation, particles traveling through the orifice 164 are directed away from the trap 168 down a separate path 170. The particles are permanently removed from the vapor stream 172. Some traps 168 may have tapering configurations while other traps 162 do not. Furthermore, some traps 162 may have orifices 164 while others do not.
In all of the embodiments of the filters shown herein, the interior surfaces exposed to the vapor stream may be coated or passivated to prevent chemical reactions. Otherwise, the precursor vapor stream may react with the surface of the material of which the filter is made. Reactions affect the concentration of a vapor stream and destabilize a precursor delivery system. The coating or passivation may include, for example, oxides such as Al2O3, ZrO2, HfO2, TiO2, Ta2O5, and Nb2O5; nitrides such as AlN, ZrN, HfN, TiN, TaN, and NbN; or carbides such as AlC, ZrC, HfC, TiC, TaC, and NbC; and mixtures thereof.
The high conductivity particle filters described herein provide a flow path with turns and traps to capture particles. The number of turns and traps ensure filter efficiency. The turns preferably involve abrupt high-speed changes of direction, which separates particles from vapor due to higher inertia. The filter's high conductivity offers little flow resistance, thereby speeding up precursor vapor pulse decay. Faster switching times for precursor vapor are possible due to the decreased resistance. Although the filter is described for use in a precursor vapor delivery system, the filter may also be used in a pumping line, a reaction chamber, and other applications.
Depending upon the location of the filter, the preferred dimensions and operating conditions will vary. When the filter is in a precursor delivery system of an ALD system or other thin film deposition system, it may typically operate at a temperature in the range of 120 C to 250 C and at a pressure in the range of 1 to 10 Torr with flows less than 1 standard liter per minute (slm). If the filter is located near a reaction chamber, it may typically operate at a temperature in the range of 200 C to 500 C and at a pressure of 0.5 to 5 Torr at flows in the range of 1 to 10 slm. If the filter is located in the pumping line, it may operate near room temperature at pressures in the range of 0.1 to 10 Torr and at flows in the range of 1 to 10 slm.
While specific embodiments and applications have been illustrated and described, it is to be understood that the invention is not limited to the precise configuration and components disclosed herein. Various modifications, changes, and variations apparent to those skilled in the art may be made in the arrangement, operation, and details of the methods and systems of the embodiments disclosed herein without departing from the spirit and scope of the invention. For example, filters applying the principles of the preferred embodiments can be used in various environments and applications for removing particles from fluids of all types, including gases, liquids, slurries, and mixtures thereof. The scope of the invention should therefore be determined only by the following claims.
This application claims the benefit under 35 U.S.C. § 119(e) of U.S. Provisional Patent Application No. 60/410,067, filed Sep. 11, 2002, titled “Precursor Material Delivery System for Atomic Layer Deposition,” which is incorporated herein by reference.
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| Number | Date | Country | |
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| 20040045889 A1 | Mar 2004 | US |
| Number | Date | Country | |
|---|---|---|---|
| 60410067 | Sep 2002 | US |
