Abstract:
Systems for depositing material onto workpieces in reaction chambers and methods for removing byproducts from reaction chambers are disclosed herein. In one embodiment, the 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. It is emphasized that this Abstract is provided to comply with the rules requiring an abstract. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims.

Description:
TECHNICAL FIELD 
   The present invention is related to systems for depositing material onto workpieces in reaction chambers and methods for removing byproducts from reaction chambers. 
   BACKGROUND 
   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. 
   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. 
   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. 
   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. 
     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 Å, and thus several cycles are required to form a solid layer having a thickness of approximately 60 Å. 
     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 . 
   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 Å. In contrast to ALD processing, CVD techniques require only about one minute to form a 60 Å 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. 
   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 
       FIGS. 1A and 1B  are schematic cross-sectional views of stages in ALD processing in accordance with the prior art. 
       FIG. 2  is a graph illustrating a cycle for forming a layer using ALD techniques in accordance with the prior art. 
       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. 
       FIG. 4  is a schematic representation of a system for depositing material onto a microfeature workpiece in accordance with one embodiment of the invention. 
       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. 
       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 
   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 . 
   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. 
   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. 
   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. 
   B. Deposition Systems 
     FIG. 4  is a schematic representation of a system  100  for depositing material onto a microfeature workpiece W in accordance with one embodiment of the invention. In this embodiment, the system  100  includes a reactor  110  having a reaction chamber  120  coupled to a gas supply  130  and a vacuum pump  140 . The reactor  110  also includes a gas distributor  160  coupled to the reaction chamber  120  and the gas supply  130  to dispense gas(es) into the reaction chamber  120  and onto the workpiece W. Byproducts including excess and/or unreacted gas molecules are removed from the reaction chamber  120  by the vacuum pump  140  and injecting a purge gas into the chamber  120 . 
   The gas supply  130  includes a plurality of gas sources  132  (identified individually as  132   a - c ) and a plurality of gas lines  136  coupled to the gas sources  132 . The gas sources  132  can include a first gas source  132   a  for providing a first gas, a second gas source  132   b  for providing a second gas, and a third gas source  132   c  for providing a third gas. The first and second gases can be first and second precursors, respectively. The third gas can be a purge gas. The first and second precursors are the gas and/or vapor phase constituents that react to form the thin, solid layer on the workpiece W. The purge gas can be a suitable type of gas that is compatible with the reaction chamber  120  and the workpiece W. In other embodiments, the gas supply  130  can include a different number of gas sources  132  for applications that require additional precursors or purge gases. In additional embodiments, the gas sources  132  can include one or more etchants for deposition onto a microfeature workpiece during etching. 
   The system  100  of the illustrated embodiment further includes a valve assembly  133  coupled to the gas lines  136  and a controller  134  operably coupled to the valve assembly  133 . The controller  134  generates signals to operate the valve assembly  133  to control the flow of gases into the reaction chamber  120  for ALD and CVD applications. For example, the controller  134  can be programmed to operate the valve assembly  133  to pulse the gases individually through the gas distributor  160  in ALD applications or to mix selected precursors in the gas distributor  160  in CVD applications. More specifically, in one embodiment of an ALD process, the controller  134  directs the valve assembly  133  to dispense a pulse of the first gas (e.g., the first precursor) into the reaction chamber  120 . Next, the controller  134  directs the valve assembly  133  to dispense a pulse of the third gas (e.g., the purge gas) to purge excess molecules of the first gas from the reaction chamber  120 . The controller  134  then directs the valve assembly  133  to dispense a pulse of the second gas (e.g., the second precursor), followed by a pulse of the third gas. In one embodiment of a pulsed CVD process, the controller  134  directs the valve assembly  133  to dispense a pulse of the first and second gases (e.g., the first and second precursors) into the reaction chamber  120 . Next, the controller  134  directs the valve assembly  133  to dispense a pulse of the third gas (e.g., the purge gas) into the reaction chamber  120 . In other embodiments, the controller  134  can dispense the gases in other sequences. 
   In the illustrated embodiment, the reactor  110  also includes a workpiece support  150  to hold the workpiece W in the reaction chamber  120 . In one aspect of this embodiment, the workpiece support  150  can be heated to bring the workpiece W to a desired temperature for catalyzing the reaction between the first gas and the second gas at the surface of the workpiece W. For example, the workpiece support  150  can be a plate with a heating element. The workpiece support  150 , however, may not be heated in other applications. 
   The system  100  further includes an exhaust mainline  170  coupled to the vacuum pump  140  and the reaction chamber  120  to remove byproducts, including excess and/or unreacted gas molecules, from the reaction chamber  120 . The mainline  170  includes an upstream portion  170   a , a downstream portion  170   b , a first branchline  172   a , and a second branchline  172   b . The branchlines  172   a - b  can be configured in a parallel arrangement and coupled to the upstream and downstream portions  170   a - b . Accordingly, discrete byproducts flow through either the first branchline  172   a  or the second branchline  172   b . In this embodiment, the system  100  further includes a first trap  180   a  disposed in the first branchline  172   a  and a second trap  180   b  disposed in the second branchline  172   b . The traps  180   a - b  capture and collect byproducts in the branchlines  172   a - b  to prevent damage to the vacuum pump  140 . In other embodiments, the system can include a different number of branchlines and/or traps. 
   In one aspect of this embodiment, the system  100  further includes a throttling valve  190  in the second branchline  172   b , a valve controller  194  operably coupled to the throttling valve  190 , and a pressure monitor  198  operably coupled to the valve controller  194 . The throttling valve  190  and the valve controller  194  regulate the flow of byproducts into the second branchline  172   b , and the pressure monitor  198  determines the pressure difference between the upstream and downstream portions  170   a - b  of the mainline  170 . The throttling valve  190 , the valve controller  194 , and the pressure monitor  198  can operate together to maintain the pressure in the upstream portion  170   a  of the mainline  170  within a desired range. For example, the pressure differential across the first trap  180   a  increases as the first trap  180   a  collects byproducts because the byproducts in the first trap  180   a  obstruct the flow from the reaction chamber  120  to the vacuum pump  140 . The pressure monitor  198  detects this increase in the pressure differential across the first trap  180   a  and sends a signal to the valve controller  194 . In response to the signal, the valve controller  194  at least partially opens the throttling valve  190  to allow some of the flow of byproducts to pass through the second branchline  172   b . The throttling valve  190  is opened sufficiently to reduce the pressure differential in the upstream and downstream portions  170   a - b  of the mainline  170  to within the desired range. In additional embodiments, the system  100  can include a throttling valve in the first branchline  172   a  that is coupled to the valve controller  194 . 
   One feature of this embodiment of the system  100  is that it maintains the pressure differential between the upstream and downstream portions  170   a - b  of the mainline  170  as the traps  180   a - b  collect byproducts. Accordingly, the pressure in the upstream portion  170   a  and the reaction chamber  120  can remain generally consistent. An advantage of this feature is that a consistent pressure in the reaction chamber  120  helps create a consistent flow through the reaction chamber  120 . More specifically, a consistent pressure facilitates the consistent, effective removal of byproducts, including excess and/or unreacted gas molecules, from the reaction chamber  120 . In contrast, the pressure in many prior art reaction chambers increases as the trap collects byproducts that obstruct the exhaust line. This increase in pressure (i.e., decrease in negative pressure) in the prior art reaction chambers impairs consistent, effective removal of the byproducts from the reaction chambers, and consequently, the byproducts may react with incoming gases. 
   In another aspect of the illustrated embodiment, the system  100  can include a plurality of valves  192  (identified individually as  192   a - c ) to selectively isolate the first and/or second traps  180   a - b  for service or replacement. The first branchline  172   a , for example, can include a first valve  192   a  (shown in hidden lines) upstream from the first trap  180   a  and a second valve  192   b  (shown in hidden lines) downstream from the first trap  180   a . The first and second valves  192   a - b  can be closed to allow the first trap  180   a  to be serviced or replaced without interrupting the deposition process of the system  100 . For example, when the first and second valves  192   a - b  are closed, the throttle valve  190  can be opened enough to exhaust the byproducts solely through the second branchline  172   b  of the mainline  170 . The first trap  180   a  can then be replaced with a new trap without shutting down the system  100 . Similarly, the second branchline  172   b  can include a third valve  192   c  (shown in hidden lines) downstream from the second trap  180   b . The throttling valve  190  and the third valve  192   c  can be closed to allow the second trap  180   b  to be serviced or replaced without interrupting the deposition process of the system  100 . In other embodiments, the system  100  may not include the valves  192 . 
   One feature of the illustrated embodiment is that the system  100  does not need to be shut down to replace and/or service the traps  180 . Each trap  180  can be isolated for service or replacement, and while one trap  180  is serviced, the other trap  180  can collect byproducts. An advantage of this feature is that the throughput of the system  100  is increased because the downtime resulting from servicing the traps  180  is reduced or eliminated. 
   C. Other Systems to Remove Byproducts 
     FIG. 5  is a schematic representation of a portion of a system  200  for depositing material onto a workpiece in accordance with another embodiment of the invention. The system  200  can be generally similar to the system  100  described above with reference to  FIG. 4 . For example, the system  200  includes a reaction chamber  120 , a mainline  270  coupled to the reaction chamber  120 , and a trap  180  in the mainline  270  to capture and collect the byproducts from the reaction chamber  120 . The mainline  270  includes a first branchline  272   a  and a second branchline  272   b  each downstream from the trap  180 . The system  200  further includes a first vacuum pump  140   a  coupled to the first branchline  272   a  and a second vacuum pump  140   b  coupled to the second branchline  272   b.    
   In one aspect of this embodiment, the system  200  includes a throttling valve  190  in the second branchline  272   b , a valve controller  194  operably coupled to the throttling valve  190 , and a pressure monitor  298  operably coupled to the valve controller  194  to determine the pressure in the mainline  270  downstream from the trap  180 . The throttling valve  190 , the valve controller  194 , and the pressure monitor  298  can operate together to maintain a consistent pressure in the mainline  270  and/or maintain a consistent mass flow rate and/or fluid velocity of byproducts through the mainline  270 . For example, in one embodiment, if the first vacuum pump  140   a  is fouled because the trap  180  fails to capture all the byproducts in the mainline  270 , the pressure in the mainline  270  will increase and the throughput of byproducts through the mainline  270  will decrease. The pressure monitor  298  detects the pressure increase and sends a signal to the valve controller  194 . In response to the signal, the valve controller  194  opens the throttling valve  190  sufficiently to allow the second vacuum pump  140   b  to reduce the pressure in the mainline  270  to a desired range and to increase the throughput of byproducts in the mainline  270  to a consistent level. In other embodiments, the pressure monitor  298  can monitor the pressure differential in the mainline  270  upstream and downstream of the trap  180  (shown in broken line). In this embodiment, if the trap  180  is fouled, the pressure upstream from the trap  180  will increase. The valve controller  194  can accordingly open the valve  190  to reduce the pressure downstream from the trap  180  and thus increase the flow rate across the trap  180 . The system  200  can include a different number of branchlines and vacuum pumps than shown in  FIG. 5 , or the system  200  can include a throttling valve in the first branchline  272   a  in still another embodiment. 
   In one aspect of this embodiment, the first branchline  272   a  can include a valve  192  (shown in hidden lines) to control the flow through the first branchline  272   a . The valve  192  allows the first vacuum pump  140   a  to be serviced or replaced without interrupting the deposition process of the system  200 . For example, when the valve  192  is closed to service or replace the first vacuum pump  140   a , the second vacuum pump  140   b  can continue to remove byproducts from the reaction chamber  120 . 
   One feature of the embodiment illustrated in  FIG. 5  is that the system  200  does not need to be shut down to replace and/or service one of the vacuum pumps  140  because the valves  190  and  192  can isolate the vacuum pump  140 . An advantage of this feature is that the throughput of the system  200  is increased because the downtime for servicing the vacuum pumps  140  is reduced or eliminated. Another feature of this embodiment is that a consistent pressure can be maintained in the mainline  270 , and consequently, byproducts can be removed from the reaction chamber  120  at a consistent rate. An advantage of this feature is that removing byproducts from the reaction chamber  120  at a consistent rate results in a more consistent deposition process and reduces the likelihood that byproducts may recirculate in the reaction chamber  120  and react with incoming gases. 
     FIG. 6  is a schematic representation of a portion of a system  300  for depositing material onto a workpiece in accordance with another embodiment of the invention. The system  300  can be generally similar to the systems  100  and  200  described above with reference to  FIGS. 4 and 5 . For example, the system  300  includes a reaction chamber  120 , a mainline  370  coupled to the reaction chamber  120 , a plurality of traps  180  (identified individually as  180   a - b ) in the mainline  370 , and a plurality of vacuum pumps  140  (identified individually as  140   a - b ) coupled to the mainline  370 . The mainline  370  includes first and second branchlines  372   a - b  configured in a parallel arrangement and third and fourth branchlines  372   c - d  configured in a parallel arrangement downstream from the first and second branchlines  372   a - b . In the illustrated embodiment, a first trap  180   a  is disposed in the first branchline  372   a , a second trap  180   b  is disposed in the second branchline  372   b , a first vacuum pump  140   a  is coupled to the third branchline  372   c , and a second vacuum pump  140   b  is coupled to the fourth branchline  372   d.    
   The system  300  of the illustrated embodiment can further include a first throttling valve  190   a  in the second branchline  372   b , a second throttling valve  190   b  in the fourth branchline  372   d , a valve controller  194  operably coupled to the throttling valves  190   a - b , and a pressure monitor  198  coupled to the valve controller  194 . The pressure monitor  198  monitors the pressure difference between an upstream portion  370   a  of the mainline  370  and a downstream portion  370   b  of the mainline  370 . As described above with reference to  FIG. 4 , the valve controller  194  can regulate the first throttling valve  190   a  to create a desired pressure differential in the upstream and downstream portions  370   a - b  of the mainline  370 . Moreover, as described above with reference to  FIG. 5 , the valve controller  194  can regulate the second throttling valve  190   b  to create a consistent pressure in the mainline  370  if the first vacuum pump  140   a  is fouled. The system  300  can further include a plurality of valves  192  (identified individually as  192   a - d ) to isolate the traps  180   a - b  and/or vacuum pumps  140   a - b  so that the traps  180   a - b  and vacuum pumps  140   a - b  can be serviced or replaced without interrupting the deposition process in the system  300 , as described above with reference to  FIGS. 4 and 5 . In other embodiments, the system can include additional traps, vacuums, and/or branchlines. 
   From the foregoing, it will be appreciated that specific embodiments of the invention have been described herein for purposes of illustration but that various modifications may be made without deviating from the spirit and scope of the invention. Accordingly, the invention is not limited, except as by the appended claims.