Abstract:
Systems and methods for depositing material onto a microfeature workpiece in a reaction chamber are disclosed herein. In one embodiment, the system includes a gas supply assembly having a first gas source, a first gas conduit coupled to the first gas source, a first valve assembly, a reaction chamber, and a gas distributor carried by the reaction chamber. The first valve assembly includes first and second valves that are in fluid communication with the first gas conduit. The first and second valves are configured in a parallel arrangement so that the first gas flows through the first valve and/or the second valve. 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  
       [0001]     The present invention is related to systems and methods for depositing material in thin film deposition processes used in the manufacturing of microfeatures.  
       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. The size of workpieces is also increasing to provide more real estate for forming more dies (i.e., chips) on a single workpiece. Many fabricators, for example, are transitioning from 200 mm to 300 mm workpieces, and even larger workpieces will likely be used in the future. 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 or partial layer of gas molecules A x  coats the surface of a workpiece W. The layer of A x  molecules is formed by exposing the workpiece W to a precursor gas containing A x  molecules and then purging the chamber with a purge gas to remove excess A x  molecules. This process can form a monolayer or partial monolayer of A x  molecules on the surface of the workpiece W because the A x  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 x  molecules is then exposed to another precursor gas containing B y  molecules. The A x  molecules react with the B y  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 y  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 x , (b) purging excess A x  molecules, (c) exposing the workpiece to the second precursor B y , and then (d) purging excess B y  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 or partial layer having a thickness of approximately 0.1-1.0 Å, and thus several cycles are required to form a solid layer having a thickness of approximately 60 Å.  
         [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 x , the purge gas, and the second precursor B y , as shown above in  FIG. 2 . The vacuum  40  maintains a negative pressure in the chamber to draw the gases from the gas dispenser  60  across the workpiece W and then through an outlet of the reaction chamber  20 .  
         [0008]     One drawback of ALD processing is that it has a relatively low throughput compared to CVD techniques. For example, each A x -purge-B y -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 of existing ALD techniques limits the utility of the technology in its current state because ALD may be a bottleneck in the overall manufacturing process.  
         [0009]     Another drawback of ALD and pulsed CVD processing is the downtime required to service the valves that control the flow of precursor into the reaction chamber. The flow of each precursor is controlled by a single, quick-action valve that actuates at least once per cycle to provide the precursor to the gas dispenser. For example, the valves can actuate between 100-2000 times to build a single 200 Å thick layer. Accordingly, the high frequency of actuations causes the valves to wear out relatively quickly. Replacing and servicing these valves requires downtime, increases operating costs, and causes an associated reduction in throughput. Therefore, there is a significant need to reduce the downtime for servicing components in CVD and ALD reactors. 
     
    
     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 isometric view of a valve assembly for use in the system shown in  FIG. 4  in accordance with another embodiment of the invention.  
         [0015]      FIG. 6  is a schematic side cross-sectional view of a valve assembly for use in the system shown in  FIG. 4  in accordance with yet another embodiment of the invention. 
     
    
     DETAILED DESCRIPTION  
       [0000]     A. Overview  
         [0016]     The following disclosure describes several embodiments of systems and methods for depositing material onto microfeature workpieces in 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. 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 a system for depositing material onto a microfeature workpiece in a reaction chamber. In one embodiment, the system includes a gas supply assembly having a first gas source, a first gas conduit coupled to the first gas source, a first valve assembly, a reaction chamber, and a gas distributor carried by the reaction chamber. The first valve assembly includes first and second valves that are in fluid communication with the first gas conduit. The first and second valves are configured in a parallel arrangement so that the first gas flows through the first valve and/or the second valve.  
         [0018]     In one aspect of this embodiment, the system further includes a controller configured to operate the first and second valves simultaneously or in an alternating sequence. In another aspect of this embodiment, the first valve assembly further includes first and second gas passageways in fluid communication with the first gas conduit. The first valve can be configured to control the first gas flow through the first passageway, and the second valve can be configured to control the first gas flow through the second passageway. In another aspect of this embodiment, the first valve assembly further includes a third valve in fluid communication with the first gas conduit. The first, second, and third valves can be arranged symmetrically so that the first, second, and third valves are spaced apart from a portion of the gas distributor by at least approximately the same distance.  
         [0019]     In another embodiment, the system includes a gas supply assembly having a first gas source, a first gas conduit coupled to the first gas source, a first valve and a second valve each in fluid communication with the first gas conduit, a reaction chamber, and a gas distributor carried by the reaction chamber. The first and second valves are operable independently to individually and/or jointly provide pulses of the first gas downstream from the first and second valves. The gas distributor is in fluid communication with the first and second valves to receive the pulses of the first gas.  
         [0020]     In another embodiment, the system includes a gas supply assembly having a first gas source, a first gas conduit coupled to the first gas source, a valve assembly, a reaction chamber, and a gas distributor carried by the reaction chamber. The valve assembly includes a body with first and second gas passageways, a first valve stem configured to control the flow of the first gas through the first gas passageway, and a second valve stem configured to control the flow of the first gas through the second gas passageway. The first and second gas passageways are in fluid communication with the first gas conduit and are configured in a parallel arrangement.  
         [0021]     Another aspect of the invention is directed to a method of depositing material onto a microfeature workpiece in a reaction chamber. In one embodiment, the method includes flowing a first pulse of a first gas through a first gas conduit and a first valve into the reaction chamber. The method further includes flowing a second pulse of the first gas through the first gas conduit and a second valve into the reaction chamber without flowing the second pulse of the first gas through the first valve. In one aspect of this embodiment, flowing the first pulse of the first gas includes controlling the first valve to dispense the first pulse of the first gas into the reaction chamber, and flowing the second pulse of the first gas includes controlling the second valve to dispense the second pulse of the first gas into the reaction chamber.  
         [0000]     B. Deposition Systems  
         [0022]      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  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.  
         [0023]     The gas supply  130  includes a plurality of gas sources  132  (identified individually as  132   a - c ) and a plurality of upstream main 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.  
         [0024]     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.  
         [0025]     The system  100  of the illustrated embodiment further includes a plurality of valve assemblies  168  (identified individually as  168   a - c ) coupled to the upstream main lines  136  and a plurality of downstream main lines  139  coupled to the valve assemblies  168  and the gas distributor  160 . The valve assemblies  168  can include a plurality of branch lines  137  (identified individually as  137   a - b ) attached to the upstream and downstream main lines  136  and  139  and a plurality of valves  170  (identified individually as  170   a - b ) attached to the branch lines  137 . The branch lines  137  flow the gases from the upstream main lines  136  to the downstream main lines  139 , and the valves  170  control the flow of the gases through the branch lines  137 . In the illustrated embodiment, the first and second valves  170   a - b  are configured in a parallel arrangement, and accordingly, each portion of gas flows through either the first valve  170   a  or the second valve  170   b  of the corresponding valve assembly  168 . In other embodiments, such as those described below with reference to  FIGS. 5 and 6 , the valve assemblies can have a different configuration and/or a different number of valves. For example, several valve assemblies  168  can be combined into a single valve assembly, and/or the valve assemblies  168  can be carried by the reaction chamber  120 .  
         [0026]     The valve assemblies  168  are operated by a controller  142  that generates signals for controlling the flow of gases into the reaction chamber  120  for ALD and CVD applications. For example, the controller  142  can be programmed to operate the valve assemblies  168  to pulse the gases individually through the gas distributor  160  in ALD applications or mix selected precursors in the gas distributor  160  in CVD applications. More specifically, in one embodiment of an ALD process, the controller  142  actuates the first valve  170   a  of a first valve assembly  168   a  to dispense a pulse of the first gas (e.g., the first precursor) into the reaction chamber  120 . Next, the controller  142  actuates the first valve  170   a  of a third valve assembly  168   c  to dispense a pulse of the third gas (e.g., the purge gas) into the reaction chamber  120 . The controller  142  then actuates the first valve  170   a  of a second valve assembly  168   b  to dispense a pulse of the second gas (e.g., the second precursor) into the reaction chamber  120 . Next, the controller  142  actuates the second valve  170   b  of the third valve assembly  168   c  to dispense a pulse of the third gas into the reaction chamber  120 . In the next cycle, the process is repeated except the controller  142  actuates the second valves  170   b  (rather than the first valves  170   a ) of the first and second valve assemblies  168   a - b  to dispense pulses of the first and second gases into the reaction chamber  120 .  
         [0027]     In one embodiment of a pulsed CVD process, the controller  142  actuates the first valves  170   a  of the first and second valve assemblies  168   a - b  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  142  actuates the first valve  170   a  of the third valve assembly  168   c  to dispense a pulse of the third gas (e.g., the purge gas) into the reaction chamber  120 . In the next cycle, the controller  142  actuates the second valves  170   b  (rather than the first valves  170   a ) of the first and second valve assemblies  168   a - b  to dispense a pulse of the first and second gases into the reaction chamber  120 . The controller  142  then actuates the second valve  170   b  of the third valve assembly  168   c  to dispense a pulse of the third gas into the reaction chamber  120 . In other embodiments, the controller  142  can actuate the valves  170  in other sequences.  
         [0028]     One feature of the illustrated embodiment is that each gas source is coupled to a valve assembly with a plurality of valves. By coupling several valves to each gas source, the frequency with which each valve is actuated to dispense gas is reduced. For example, if each gas source is coupled to a valve assembly with two valves, the frequency that each valve is actuated may be reduced by one half. One advantage of this feature is that the life of the valve assembly is extended because the valves do not wear out as quickly. When the valves wear out or otherwise fail, the system is shut down to replace and/or service the valves. Accordingly, the system of the illustrated embodiment reduces the downtime to replace and/or service the valves and thereby increases the throughput.  
         [0029]     In other embodiments, the controller  142  can simultaneously actuate the first and second valves  170   a - b  of a single valve assembly  168  to dispense a portion of the corresponding gas into the reaction chamber  120 . One advantage of this arrangement is that if one valve fails, the other valve in the valve assembly will continue to dispense gas for deposition onto the workpiece W.  
         [0000]     C. Other Valve Assemblies  
         [0030]      FIG. 5  is a schematic isometric view of a valve assembly  268  for use in the system  100  shown in  FIG. 4  in accordance with another embodiment of the invention. The valve assembly  268  includes a plurality of valves  270  (identified individually as  270   a - c ) and a plurality of branch lines  237  (identified individually as  237   a - c ) coupling the valves  270  to the upstream and downstream main lines  136  and  139 . In one aspect of this embodiment, the branch lines  237  and the valves  270  are arranged symmetrically so that the valves  270  provide pulses of gas to the reaction chamber  120  ( FIG. 4 ) at a consistent pressure and with a consistent response time. For example, the branch lines  237  can include a first portion  243  coupled to the upstream main line  136 , a second portion  244  coupled to the first portion  243  and the valve  270 , a third portion  245  coupled to the valve  270 , and a fourth portion  246  coupled to the third portion  245  and the downstream main line  139 . The first portions  243  can be oriented at generally the same angle relative to the upstream main line  136 , and the fourth portions  246  can be oriented at generally the same angle relative to the downstream main line  139 . The second and third portions  244  and  245  can be generally parallel to the upstream and downstream main lines  136  and  139 . Moreover, the portions  243 ,  244 ,  245  and  246  in each branch line  237  can have approximately the same length as the corresponding portions in the other branch lines  237 . In this embodiment, the symmetric arrangement can ensure that each valve  270  provides consistent and uniform pulses of gas to the reaction chamber  120  ( FIG. 4 ). In other embodiments, the valve assembly  268  may have other configurations, including asymmetric arrangements. For example, the valve assembly can include a body with gas passageways, such as in the embodiment described below with reference to  FIG. 6 , or the valve assembly can include a different number of valves.  
         [0031]      FIG. 6  is a schematic side cross-sectional view of a valve assembly  368  for use in the system  100  shown in  FIG. 4  in accordance with another embodiment of the invention. The valve assembly  368  includes a valve body  372  having a first gas passageway  338   a  and a second gas passageway  338   b , a first valve stem  380   a  in the valve body  372 , and a second valve stem  380   b  in the valve body  372 . The valve body  372  includes an inlet  374  configured for attachment to the upstream main line  136  ( FIG. 4 ), an outlet  376  configured for attachment to the downstream main line  139  ( FIG. 4 ), a plurality of valve seats  383 , and a plurality of cavities  378 . The first and second valve stems  380   a - b  include a first portion  381  configured to engage the valve seat  383  and a second portion  382  configured to be received in the cavity  378 . The first and second valve stems  380   a - b  are movable in a direction D between a first position (illustrated by the first valve stem  380   a ) in which the first portion  381  engages the valve seat  383  and a second position (illustrated by the second valve stem  380   b ) in which the second portion  382  is received in the cavity  378 . The position of the first and second valve stems  380   a - b  controls the flow of gas through the gas passageways  338 .  
         [0032]     In operation, a gas flow “F” enters the valve body  372  through the inlet  374  and is split into two separate flows at a junction  347  of the first and second gas passageways  338   a - b . The first and second gas passageways  338   a - b  are configured in a parallel arrangement so that each portion of gas flows through either the first gas passageway  338   a  or the second gas passageway  338   b . When one or both of the valve stems  380   a - b  are in the second position, the gas flows past the valve stems  380   a - b  and exits the valve body  372  through the outlet  376 . In one embodiment, a controller can actuate the valve stems  380  in an alternating sequence so that when one valve stem  380  is in the second position, the other valve stem  380  is in the first position. In other embodiments, a controller can actuate the valve stems  380  simultaneously so that both of the valve stems  380  can be in the second position at the same time. In additional embodiments, the valve assembly  368  can include a different number of valve stems  380  and gas passageways  338 . For example, a valve assembly can include four gas passageways and four valve stems.  
         [0033]     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.