Patent Publication Number: US-2010112191-A1

Title: Systems and associated methods for depositing materials

Description:
TECHNICAL FIELD 
     The present disclosure is directed toward systems for depositing materials onto microelectronic workpieces and associated methods of operation. 
     BACKGROUND 
     Atomic layer deposition (ALD) is one widely used deposition technique for depositing a material in the manufacture of microelectronic devices.  FIGS. 1A and 1B  schematically illustrate the basic operation of an ALD process. As illustrated in  FIG. 1A , a layer of gas molecules A x  coats a surface of a workpiece W when the workpiece W is exposed to a first precursor. After purging with a purge gas, the workpiece W is then exposed to B y  molecules in a second precursor as shown in  FIG. 1B . The A x  and B y  molecules then react to form a thin solid layer of material on the surface of the workpiece W. 
       FIG. 2  illustrates the stages of one typical cycle for forming a thin film using ALD techniques. The stages include (a) exposing the workpiece to the first precursor containing A x , (b) purging excess A x  molecules with the purge gas, (c) exposing the workpiece to the second precursor containing B y , and then (d) purging excess B y  molecules with the purge gas. Multiple cycles can be repeated to build a thin film having the desired thickness. For example, each cycle may form a film having a thickness of approximately 0.5-1.0 Å, and thus approximately 60-120 cycles are needed to form a film having a thickness of approximately 60 Å. 
     One drawback of the foregoing ALD process is that the first and second precursors tend to mix and react with each other at undesirable times and/or locations as the cycle time decreases. For example, as the purge period in  FIG. 2  decreases, the first precursor may be insufficiently removed before the second precursor is injected. Thus, the first and second precursors can mix apart from the surface of the workpiece and react to form unwanted deposits on various processing components (e.g., vacuum pumps, reaction chambers, etc.) Such unwanted deposits may adversely affect the performance of the ALD process and/or shorten the lifespan of the processing components. Thus, several improvements to ALD processes may be desirable. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A and 1B  are schematic cross-sectional views of stages in atomic layer deposition processing in accordance with the prior art. 
         FIG. 2  is a graph illustrating a cycle for forming a layer using atomic layer deposition in accordance with the prior art. 
         FIG. 3  is a schematic representation of a system for depositing material onto a microelectronic workpiece in accordance with embodiments of the invention. 
         FIG. 4  is a schematic representation of a system having a reactor for depositing material onto a microelectronic workpiece in accordance with embodiments of the invention. 
         FIG. 5  is a flowchart illustrating a method for depositing material onto a microelectronic workpiece in accordance with embodiments of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     Specific details of several embodiments are described below with reference to systems for depositing material onto microelectronic workpieces and associated methods of operation. The term “microelectronic workpiece” is used throughout to include substrates upon which and/or in which microelectronic devices, micromechanical devices, data storage elements, photoelectric elements, and/or other features can be fabricated. For example, microelectronic workpieces can include semiconductor wafers, glass substrates, insulative substrates, and other types of suitable materials having SRAM, DRAM (e.g., DDR/SDRAM), flash-memory (e.g., NAND flash-memory), logic processors, CMOS imagers, CCD imagers, and other types of microelectronic device constructed thereon. The term “gas” is used throughout to include any form of matter that has no fixed shape and is conformable in volume to a space available. Although many of the embodiments are described below with respect to ALD processing systems and methods, other embodiments may include chemical vapor deposition (CVD), and/or other types of deposition systems and methods. Moreover, several embodiments of the ALD processing systems and methods can have different configurations, components, or procedures other than those described in this section. A person of ordinary skill in the art, therefore, will accordingly understand that the invention can have other embodiments with additional features, or that the invention can have other embodiments without several of the features shown and described below in reference to  FIGS. 3 and 4 . 
       FIG. 3  is a schematic representation of a system  100  for depositing material onto a microelectronic workpiece W in accordance with an embodiment of the invention. As illustrated in  FIG. 3 , the system  100  can include a reactor  110  coupled to a gas supply  130  and a vacuum  140  in series. The vacuum  140  can include a vacuum pump (e.g., a liquid-ring pump), a jet (e.g., a steam jet), and/or another suitable vacuum source. In other embodiments, the system  100  can also include gas scrubbers, liquid-gas separators, and/or other suitable processing components. Even though the gas supply  130  is shown in  FIG. 3  as having four gas sources, in certain embodiments, the gas supply  130  can include any desired number of gas sources, which may be more or less than those shown in  FIG. 3 . 
     The reactor  110  can include a distributor  160  and a workpiece support  150  in a reaction chamber  120  with an inlet  122  and an outlet  124 . The inlet  122  is coupled to the gas supply  130 . The outlet  124  is coupled to the vacuum  140  via a conduit  125  (e.g., a piece of pipe or tubing). The distributor  160  faces the workpiece support  150 . The distributor  160  can include a plenum  162  at least partially defined by a sidewall  164  and a distributor plate  170  with a plurality of passageways  172 . The workpiece support  150  can include a plate, a vacuum chuck, a mechanical chuck, and/or another suitable supporting component. In certain embodiments, the workpiece support  150  can also include a heating element (not shown) configured to heat the workpiece W to a desired temperature. In other embodiments, the workpiece support  150  can also include other suitable components. 
     The gas supply  130  includes a plurality of gas sources  132 , a valve assembly  133 , and a plurality of gas lines  136  coupling the gas sources  132  individually to the valve assembly  133 . In the illustrated embodiment, the gas sources  132  can include a first gas source  132   a  holding a first precursor gas “A,” a second gas source  132   b  holding a second precursor gas “B,” a third gas source  132   c  holding a purge gas “P,” and a fourth gas source  132   d  holding a catalyst gas “C.” The first and second precursors A and B include constituents that can react to form a solid layer of material on a surface of the microelectronic workpiece W. For example, the first precursor A can include a silicon precursor, and the second precursor B can include an oxidizer that can oxidize the silicon precursor. A suitable silicon precursor includes tris-dimethylaminosilane(((CH 3 ) 2 N) 3 SiH), tetrakis-dimethylaminosilane(((CH 3 ) 2 N) 4 Si), hexachlorodisilane(Si 2 Cl 6 ), chlorosilane(SiCl 4 ), silane(SiH 4 ), and/or other suitable silicon precursor. A suitable oxidizer includes oxygen(O 2 ), ozone(O 3 ), hydrogen peroxide(H 2 O 2 ), nitrous oxide(N 2 O), nitric oxide(NO), dinitrogen pentoxide(N 2 O 5 ), nitrogen dioxide(NO 2 ), water(H 2 O), and/or other suitable oxidizing agent. 
     The purge gas P can include a gas that is generally inert to the reaction chamber  120  and to the workpiece W. For example, the purge gas P can include nitrogen, argon, and/or another suitable inert gas. The catalyst gas C can include compositions selected to increase a rate of reaction between the silicon precursor and the oxidizer. For example, the catalyst gas C can include ammonia(NH 3 ), pyridine(C 5 H 5 N), and/or another suitable catalytic composition. In certain embodiments, the fourth gas source  132   d  may be omitted, and the catalyst gas C may be combined with the first precursor gas A and/or the second precursor gas B. In further embodiments, the catalyst gas C may be omitted from the gas supply  130 . 
     The valve assembly  133  can be configured to selectively allow a gas to flow into the reaction chamber  120  from the gas supply  130 . The valve assembly  133  can include a plurality of valves, a multi-way valve, and/or other suitable flow directing components. For example, in one embodiment, the valve assembly  133  can include four single-path valves (e.g., gate valves) individually coupled to the gas sources  132 . In another embodiment, the valve assembly  133  can include a multipath valve (e.g., a four-way valve) with each path coupled to the gas sources  132  individually. In other embodiments, the valve assembly  133  can include a combination of single-path valves and multipath valves and/or other suitable arrangements. 
     The system  100  can also include a neutralizer source  135  coupled to the outlet  124  of the reaction chamber  120  upstream of the vacuum  140  via the conduit  125  and a neutralizer valve  137  (e.g., a gate valve). The neutralizer source  135  can contain a neutralizing agent “N” selected to reduce a rate of reaction between the first and second precursor gases A and B. In one embodiment, the neutralizing agent N can contain at least one of carbon dioxide(CO 2 ), nitrogen oxide(NO), nitrogen dioxide(NO 2 ), sulfur dioxide(SO 2 ), hydrogen fluoride(HF), hydrogen chloride(HCl), hydrogen iodide(HI), nitrogen trifluoride(NF 3 ), chlorine trifluoride(ClF 3 ), an organic acid (e.g., formic acid or acetic acid), and/or another suitable electrophile. In another embodiment, the neutralizing agent N can include glycol, polyethylene glycol, and/or other hygroscopic substances. In further embodiments, the neutralizing agent N can include both an electrophile, a hygroscopic substance, and/or another suitable composition. 
     Optionally, the system  100  can include a sensor  151  upstream of the vacuum  140 . The sensor  151  can be configured to monitor a concentration and/or other characteristics of at least one of the first precursor gas A, the second precursor gas B, and/or the catalyst gas C. In one embodiment, the sensor  151  includes a pH monitor. In other embodiments, the sensor  151  can also include a mass spectrometer, a UV-visible spectrometer, an infrared radiation spectrometer, a gas chromatography analyzer, and/or other suitable chemical analyzers. In the illustrated embodiment, the sensor  151  is approximate to the conduit  125 . In other embodiments, the sensor  151  can be approximate to the reaction chamber  120 , the vacuum  140 , and/or other components of the system  100 . 
     The system  100  can also include a controller  142  electrically coupled to the valve assembly  133 , the neutralizer valve  137 , and the optional sensor  151 . The controller  142  can include a logic processor  144  coupled to a computer-readable medium  146  having computer-executable instructions stored therein. The logic processor  144  can include a microprocessor, a digital signal processor, and/or other suitable processing components. The computer-readable medium  146  can include any mechanism that provides (i.e., stores and/or transmits) information in a form accessible by the logic processor  144 . In one embodiment, the computer-readable medium  146  includes volatile and/or nonvolatile media (e.g., read-only memory (ROM); random access memory (RAM); magnetic disk storage media; optical storage media; flash memory devices; etc.) The controller  142  can also include specific hardware components having hard-wired logic (e.g., field-programmable gate arrays) for performing the operations, methods, or processes or with any combination of programmed data processing components and specific hardware components. 
     The computer-executable instructions can be configured to cause the logic processor  144  to perform methods or processes in accordance with embodiments of the system  100 . For example, the computer-executable instructions can cause the logic processor  144  to generate signals for pulsing the individual gases through the reaction chamber  120  in a number of cycles. Each cycle can include a first pulse of the first precursor gas A, a second pulse of the purge gas P, a third pulse of the second precursor gas B, and a fourth pulse of the purge gas P. The computer-executable instructions can also cause the logic processor  144  to inject the neutralizing agent N into an exhaust of the reaction chamber  120  during at least a portion of the deposition process. The computer-executable instructions can also cause the logic processor  144  to monitor a process parameter via the optional sensor  151  and adjust the flow of the neutralizing agent N based on the monitored process parameter. Various operations, methods, or processes performed by the controller  142  are described in more detailed below. 
     During a deposition process, in certain embodiments, the controller  142  can first command the valve assembly  133  to selectively flow the first precursor gas A and the catalyst gas C into the reaction chamber  120  via the inlet  122 . The first precursor gas A and the catalyst gas C then flow into the distributor  160  to be dispensed onto the surface of the microelectronic workpiece W. As a result, a layer of the first precursor gas A and the catalyst gas C can be adsorbed and/or otherwise attached to the surface of the microelectronic workpiece W. The vacuum  140  exhausts excess first precursor gas A and the catalyst gas C from the reaction chamber  120  along a flow path “F.” 
     After a first deposition period (e.g., 10 seconds), the controller  142  can command the valve assembly  133  to stop the flow of the first precursor gas A and the catalyst gas C and start to flow the purge gas P into the reaction chamber  120 . The flow of the purge gas P can continue for a first purge period (e.g., 10 seconds) sufficient to reduce the concentration of the first precursor gas A and the catalyst gas C in the reaction chamber  120  to a desired level. 
     After the first purge period, the controller  142  can then command the valve assembly  133  to selectively flow the second precursor gas B and the catalyst gas C into the reaction chamber  120  via the inlet  122 . The second precursor gas B and the catalyst gas C then flow into the distributor  160  to be dispensed onto the surface of the microelectronic workpiece W. As a result, a layer of the second precursor gas B and the catalyst gas C can be adsorbed and/or otherwise attached to the layer of the first precursor gas A and/or the surface of the microelectronic workpiece W. The vacuum  140  exhausts excess second precursor gas B and the catalyst gas C from the reaction chamber  120  along flow path F. 
     Components of the first and second precursor gases A and B can then react to produce a thin film in the presence of the catalyst gas C. For example, in one embodiment, the first precursor gas A containing hexachlorodisilane can react with the second precursor gas B containing water in the presence of the catalyst gas C containing pyridine to produce a silicon oxide(SiO 2 ) film as follows: 
     
       
         
         
             
             
         
       
     
     In other embodiments, the first and/or second precursor gases A and B can contain other suitable precursor compositions to produce a film of polysilicon(Si), silicon nitride(SiNe), metal (e.g., Cu, Al, W, etc.), and/or another desired material. 
     After a second deposition period (e.g., 10 seconds), the controller  142  can command the valve assembly  133  to stop the flow of the second precursor gas B and the catalyst gas C and again start to flow the purge gas P into the reaction chamber  120 . The flow of the purge gas P can continue for a second purge period (e.g., 10 seconds) sufficient to reduce the concentration of the second precursor gas B and the catalyst gas C in the reaction chamber  120  to a desired level. Then, controller  142  can repeat the deposition cycle by selectively flowing the first precursor gas A and the catalyst gas C into the reaction chamber  120  via the inlet  122  until a desired deposition is achieved on the surface of the microelectronic workpiece W. 
     In any of the foregoing embodiments, the controller  142  can command the neutralizer valve  137  to flow the neutralizing agent N into the conduit  125  during at least a portion of the deposition process. In one embodiment, the flow of the neutralizing agent N can be generally continuous for the entire duration of the deposition process. In other embodiments, the flow of the neutralizing agent N can be based on a temporal relationship between the flow of the first precursor gas A, the second precursor gas B, and/or the purge gas P. For example, the neutralizing agent N can be flowed before, substantially contemporaneous with, or after a delay period (e.g., 10 seconds) following the flowing of the first and second precursor gases A and B into the reaction chamber  120 . 
     In further embodiments, the flow of the neutralizing agent N can be at least in part based on a process parameter of the deposition process. For example, the controller  142  can monitor a concentration of the catalyst gas C in the conduit  125  via the sensor  151 . If the monitored concentration is above a predetermined threshold, the controller  142  can open the neutralizer valve  137  to flow the neutralizing agent N into the conduit  125  at a first rate; or, the controller  142  can either stop the flow of the neutralizing agent N or maintain the flow of the neutralizing agent N at a second rate lower than the first rate. In other examples, the controller  142  can also monitor and control the flow of the neutralizing agent N based on the concentration of the first precursor gas A, the second precursor gas B, the purge gas P, the deposition rate on the conduit  125 , and/or other suitable process parameters. In yet further embodiments, the flow of the neutralizing agent N can be based on a combination of a temporal relationship and a monitored process parameter. 
     The neutralizing agent N can then mix with the first precursor gas A, the second precursor gas B, and the catalyst gas C exiting the reaction chamber  120  upstream of the vacuum  140 . In certain embodiments, the neutralizing agent N can poison the catalyst gas C. For example, the neutralizing agent N can react and/or otherwise combine with the catalyst gas C to at least reduce its catalytic effectiveness. Without being bound by theory, in a particular embodiment, it is believed that a neutralizing agent N containing hydrogen fluoride(HF) can react with a catalyst gas C containing pyridine(C 5 H 5 N) to remove the lone electron pair of pyridine as follows: 
       C 5 H 5 N+HF→C 5 H 6 N + +F −   
     It is also believed that without the lone electron pair, the catalyst gas C is ineffective in facilitating the reaction between the first and second precursor gases A and B. As a consequence, the activation energy of the reaction between the first and second precursor gases A and B increases. Accordingly, the concentration of the catalyst gas C and the rate of reaction between the first and second precursor gases A and B both decrease away from the workpiece support  150  without affecting the deposition of the layer of solid material on the surface of the microelectronic workpiece W. 
     In other embodiments, the neutralizing agent N can also reduce a concentration of the first and/or second precursor gases A and B. For example, the neutralizing agent N can absorb, adsorb, chemically react, and/or otherwise combine with the first and/or second precursor gases A and B. In a particular example, the first and second precursor gases A and B include hexachlorodisilane and water, respectively, and the neutralizing agent N includes glycol that can absorb water. Thus, the concentration of the second precursor gas B can be reduced to decrease the rate of reaction between hexachlorodisilane and water. 
     Several embodiments of the system  100  can have improved deposition efficiency and/or components with longer lifespans than in conventional systems. The inventors have recognized that as the cycle time decreases in an ALD process, the first and second precursor gases A and B can coexist in the exhaust of the reaction chamber  120 . As a result, the first and second precursor gases A and B can react to deposit an unwanted layer of solid material (e.g., SiO 2 ) on internal components of the vacuum  140  and/or other processing components downstream of the workpiece support  150 . Such unwanted deposition can adversely affect the performance of the system  100  by reducing a suction head of the vacuum  140  and/or shortening the lifespan of the vacuum  140 . As a result, by flowing the neutralizing agent N into the exhaust upstream of the vacuum  140 , the rate of reaction between the first and second precursor gases A and B can be reduced. The reduced reaction rate can at least reduce solid deposition on internal components of the vacuum  140 , and thus prolong its life. 
     Although the system  100  is illustrated in  FIG. 3  as being configured to process a single microelectronic workpiece W, in other embodiments, the system  100  may be configured to process multiple microelectronic workpieces, e.g., by having a wafer boat designed to carry multiple microelectronic workpieces. In other embodiments, the first precursor gas A, the second precursor gas B, and the catalyst gas C can be flowed into the reaction chamber  120  individually. For example, a flow of the catalyst gas C can follow a flow of the first precursor gas A and/or the second precursor gas B. In further embodiments, the flow of the catalyst gas C can be omitted, or the catalyst gas C can be combined with the first and/or second precursor gases A and B in the first and second gas sources  132   a  and  132   b , respectively. 
     Even though the system  100  illustrated in  FIG. 3  has the neutralizer source  135  coupled to the conduit  125 , in other embodiments, the neutralizer source  135  can also be coupled directly to the reaction chamber  120 . For example, as illustrated in  FIG. 4 , the reaction chamber  120  can include an outlet plenum  163  between the workpiece support  150  and the outlet  124 , and the neutralizer valve  137  can couple the neutralizer source  135  to the outlet plenum  163 . In other embodiments, the neutralizer source  135  can also be coupled to the vacuum  140  and/or other processing components of the system  100 . 
     Several embodiments of a deposition process  200  are illustrated in  FIG. 5 . Even though the embodiments of the deposition process  200  are discussed below with reference to the system  100  of  FIG. 3 , one skilled in the art will understand that certain embodiments of the deposition process  200  can also be practiced in systems with different and/or additional process components. 
     As shown in  FIG. 5 , the deposition process  200  can include deposition stages  202  in which a first precursor gas and a second precursor gas are sequentially or alternatively injected into a reaction chamber with purging stages therebetween. For example, the deposition stages  202  can include sequentially flowing the first precursor gas into the reaction chamber  120  ( FIG. 3 ) for a first deposition period to contact the surface of the microelectronic workpiece W (stage  204 ), purging the reaction chamber for a first purge period (stage  206 ), flowing the second precursor gas for a second deposition period to contact the surface of the microelectronic workpiece W (stage  208 ), and purging the reaction chamber for a second purge period (stage  210 ). In certain embodiments, the deposition stages  202  can also include flowing a catalyst gas into the reaction chamber  120  with the first and/or second precursor gases. In other embodiments, the deposition stages  202  can also include flowing the catalyst gas before flowing the first and second precursor gases. In further embodiments, the catalyst gas can be omitted. 
     The deposition process  200  can also include an injection stage  212  in which a neutralizing agent is injected into the reaction chamber away from the surface of the microelectronic workpiece W. The neutralizing agent is selected to reduce a rate of reaction between the first and second precursor gases, as described above with reference to  FIG. 3 . In the illustrated embodiment, the injection stage  212  is generally contemporaneous with the deposition stages  202 . In other embodiments, the injection stage  212  can have an on-delay and/or an off-delay from the deposition stages  202 . In further embodiments, the injection stage  212  can correspond with only a limited number of deposition stages  202 . In one example, the injection stage  212  corresponds only with the purging of the reaction chamber  120  at stages  206  and  210 . In other examples, the injection stage  212  corresponds with the flowing of the first and second precursor gases at stages  204  and  208 . 
     The deposition process  200  can include a decision block  214  to determine whether the process should continue. Conditions for continuing the process can include an insufficient deposition on the surface of the microelectronic workpiece W, and/or other suitable conditions. If the process continues, the process reverts to flowing the first precursor gas at stage  204  and injecting the neutralizing agent at stage  212 ; otherwise, the process ends. 
     From the foregoing description, 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 invention. For example, many of the elements of one embodiment may be combined with other embodiments in addition to or in lieu of the elements of the other embodiments. Accordingly, the invention is not limited except as by the appended claims.