Abstract:
An apparatus and process for atomic layer deposition that minimizes mixing of the chemicals and reactive gases is disclosed. The first precursor and second precursor are only mixed with other chemicals and reactive gases when and where desired by installing and monitoring a dispensing fore-line. Also, independent and dedicated chamber outlets, isolation valves, exhaust fore-lines, and exhaust pumps are provided that are activated for the specific gas when needed.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 09/977,612, filed Oct. 15, 2001, now U.S. Pat. No. 6,461,436. This application is also related to U.S. patent application Ser. No. 10/166,902, filed Jun. 11, 2002, which application is a divisional of U.S. patent application Ser. No. 09/977,612, filed Oct. 15, 2001, now U.S. Pat. No. 6,461,436. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to atomic layer deposition. More specifically, the present invention relates to an apparatus and process for improving the performance of an atomic layer deposition chamber. 
     A method of depositing very thin films is atomic layer deposition (ALD). This method has several advantages over tradition chemical vapor deposition. It can be performed at lower temperatures, uses a wide range of precursors, produces very thin films, inherently obtains 100% step coverage, and can be used to “microengineer” complex film matrices. 
     In ALD, individual precursors are pulsed onto the surface of a wafer in a sequential manner, without mixing the precursors in the gas phase. Each individual precursor reacts with the surface to form an atomic layer in a way that only one layer can form at a time. The surface reaction occurs such that the reaction is complete, and permits no more than one layer at a time to be deposited. This occurs no matter how many molecules are applied to the surface in an overdosing mode. The films are built up by introducing short bursts of gases in rapid cycles. 
     According to recognitions of the present inventors, two problems occur with the ALD method. One problem concerns the diversion of the flow of liquid precursors introduced in a vapor phase. During ALD processing using a liquid delivery system, it is necessary to keep an established flow of the liquid precursor in a vapor phase. In order to keep the flow active, the flow must be diverted to a fore-line of the ALD chamber when the liquid precursor is not needed in the deposition process. When the opposing gas is pulsed, the unreacted chemical is mixed in the fore-line with the diverted chemical and reacts causing a build up in the fore-line. The build up can be severe and clogs the foreline. A second problem concerns the reaction of the gases. Process gases are introduced individually for the ALD process and disposed of through the same fore lines causing the gases or vapors to react with one another. 
     Accordingly, there is a need for an ALD apparatus and process that minimizes clogging of the fore-line of the diverted liquid precursor. There is also a need in the art to control any area that is common to the reactive gases or vapors in a way to minimize any unwanted reaction. 
     BRIEF SUMMARY OF THE INVENTION 
     These needs are met by the present invention wherein an improved ALD apparatus and process are provided. The present invention fulfills the first need of minimizing clogging of the fore-line by providing an ALD apparatus and process that allows separate chemicals to only mix when and where desired by installing and monitoring a second fore-line. The present invention fulfills the second need of minimizing the reaction of the gases in the pump lines, by allowing the reactive gases or vapors to be removed from the process reactor chamber without coming in contact with one another in an area that would create an unwanted reaction of the process gases or vapors. This is accomplished by providing independent and dedicated pumping lines and corresponding isolation valves that are activated for the specific gas when needed. The separate pump lines allow the gas to be exhausted in a manner that minimizes possible unwanted reaction of the reactive gases. Accordingly, it is an object of the present invention to provide an improved ALD apparatus and process using dispensing fore-lines and a second exhaust path in order to prevent clogging of the exhaust fore-line. 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
     The following detailed description of the preferred embodiments of the present invention can be best understood when read in conjunction with the following drawings, where like structure is indicated with like reference numerals and in which: 
     FIG. 1 presents an illustration of an ALD apparatus according to one embodiment of the present invention; 
     FIG. 2 presents an illustration of an ALD apparatus according to another embodiment of the present invention; 
     FIG. 3 presents an illustration of an ALD apparatus according to still another embodiment of the present invention; 
     FIG. 4 presents an illustration of an ALD apparatus according to yet another embodiment of the present invention; and 
     FIG. 5 presents an illustration of an ALD apparatus according to yet another embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION 
     Referring initially to FIG. 1, an ALD apparatus  2  according to one embodiment of the present invention is illustrated. FIG. 1 illustrates an ALD apparatus  2  comprising a process reactor chamber  10 , a first dispensing valve  4 , a second dispensing value  8 , an isolation valve  24 , an exhaust fore-line  22 , an exhaust pump  20 , and a dispensing fore-line  26 . The process reactor chamber  10  includes a first precursor inlet  14 , a second precursor inlet  16 , and a first chamber outlet  17 . The first dispensing valve  4  is coupled to the first precursor inlet  14  of the process reactor chamber  10 . The second dispensing valve  8  is coupled to the second precursor inlet  16  of said process reactor chamber  10 . The isolation valve  24  is directly coupled to the first chamber outlet  17  of the process reactor chamber  10 . The exhaust pump  20  is coupled to the isolation valve  24  by the exhaust fore-line  22 , defining an exhaust path. The dispensing fore-line  26  comprises a first end  25  and a second end  27 . The first end  25  is coupled to the first dispensing valve  4  and the second end  27  is coupled to the exhaust pump  20 . As is illustrated in FIG. 1, no substantial exhaust fore-line exists between the isolation valve  24  and the first chamber outlet  17  because, as is noted above, the isolation valve  24  is directly coupled to the outlet  17 . 
     The first dispensing valve  4  allows a first precursor  6  to flow into the process reactor chamber  10  through a first precursor inlet  14 . A continuous flow of the first precursor  6  must be maintained. Therefore, the first dispensing valve  4  selectively diverts the direction of the first precursor  6  to the first precursor inlet  14  of the process reactor chamber  10 . When the first precursor  6  is not diverted into the process reactor chamber  10 , it is sent to the exhaust pump  20  via a dispensing fore-line  26 . The dispensing fore-line  26  is used to discard the first precursor  6  when it is not diverted into the first precursor inlet  14 . The dispensing fore-line  26  may be used to isolate the first precursor  6  from other chemicals, precursors, and exhausts that would otherwise mix with the first precursor  6  and potentially cause clogging of the first exhaust fore-line  22 . Thus, the exhaust fore-line  22  remains clean and flow remains stable and consistent. 
     The process reactor chamber  10  comprises a first precursor inlet  14 , a second precursor inlet  16 , a heater  13 , a wafer  11 , and a shower head device  18 . The first precursor inlet  14  and second precursor inlet  16  can share a common opening  12  or alternatively have separate openings. The first precursor inlet  14  may direct the first precursor  6  through a shower head device  18  that distributes the first precursor  6  into the process reactor chamber  10 . Once in the process reactor chamber  10  the first precursor  6  is absorbed onto the surface of a wafer  11 . The wafer rests on a heater  13 . The manner in which absorption of the precursor is achieved is beyond the scope of the present invention and is well known in the art. It may be gleaned from any one of a number of teachings relating to atomic layer deposition. 
     After the first precursor  6  is absorbed onto the wafer  11 , unreacted first precursor is purged out of the process reactor chamber  10  by introducing a purge gas via the purge valve  7  into the chamber outlet  17 . Unreacted first precursor flows directly into the isolation valve  24  where unreacted first precursor is transferred to the exhaust pump  20  via the exhaust fore-line  22 . 
     The first precursor  6  and second precursor  9  are introduced in separate intervals. Once unreacted first precursor is purged from the process reactor chamber  10  through use of the purging valve  7 , the second dispensing valve  8  allows for the introduction of the second precursor  9  into the second precursor inlet  16  and ultimately into the process reactor chamber  10 . The second precursor inlet  16  directs the second precursor  9  through a shower head device  18  that distributes the second precursor  9  into the process reactor chamber  10 . The second precursor  9  then reacts with the layer formed on the wafer  11  from the first precursor  6 , creating a monolayer of film on the wafer  11 . 
     Unreacted second precursor is purged from the process reactor chamber  10 , using the purging valve  7 , into the chamber outlet  17 . Unreacted second precursor flows directly into the isolation valve  24  where unreacted second precursor is transferred to the exhaust pump  20  via the exhaust fore-line  22 . 
     This process of the introduction, reaction, and purging alternating the first precursor  6  with the second precursor  9  is performed at a high rate of speed with continuous successions. 
     For the purposes of describing and defining the present invention, it is noted that the precise mechanism by which the molecules of the first precursor adhere to the surface of the semiconductor substrate is not the subject of the present invention. The mechanism is merely described herein as ‘absorption.’ The generic term ‘absorption’ is intended to cover absorption, adsorption, and any other similar mechanisms by which the precursor may form a monolayer upon the surface of the wafer  11 . 
     The embodiment of the present invention illustrated in FIG. 2 differs from FIG. 1 in that it utilizes a dispensing pump  28 . In this embodiment, the first end  25  of the dispensing fore-line  26  is coupled to the dispensing valve  4 . The second end  27  of the dispensing fore-line  26  is coupled to the dispensing pump  28 . The dispensing pump  28  collects the undiverted first precursor  6  so that the undiverted first precursor  6  is isolated from other chemicals, precursors, and exhausts that would otherwise mix with the first precursor  6  and potentially cause clogging of the first exhaust fore-line  22 . Thus, the exhaust fore-line  22  remains clean and flow remains stable and consistent. 
     The embodiment of FIG. 3 differs from that illustrated in FIG. 2 because the second isolation valve  34 , the second exhaust fore-line  32 , and the second exhaust pump  30  are shown, thus defining a second exhaust path. This second exhaust path is constructed to keep the unreacted first precursor and the unreacted second precursor separate. Thereby, reducing the possibility of mixing and clogging the either of the exhaust fore-lines  22 ,  32 . The second isolation valve  34 , the second exhaust fore-line  32 , and the second exhaust pump  30  operate in a similar manner as the first isolation valve  24 , the first exhaust fore-line  22 , and the first exhaust pump  20 . After the second precursor  9  is absorbed onto the wafer  11 , the unreacted second precursor is purged out of the process reactor chamber  10  by introducing a purge gas via the purge valve  7  into the second chamber outlet  29 . The unreacted second precursor flows directly into the second isolation valve  34  where the unreacted second precursor is transferred to the second exhaust pump  30  via the second exhaust fore-line  32 . 
     The embodiment in FIG. 3 also differs from that illustrated in FIG. 2 because the dispensing fore-line  26  is connected to the first exhaust path. Specifically, the dispensing fore-line  26  is connected to the first exhaust pump  20 . The dispensing valve could alternatively be coupled to the first exhaust fore-line  22  or directly to a dispensing pump  28  as illustrated in FIG.  2 . 
     The embodiment of FIG. 4 differs from that of FIG. 3 because a second dispensing fore-line  36  is provided. The second dispensing fore-line  36  comprises a first end  31  and a second end  33 . The first end  31  is coupled to the second dispensing valve  8  and the second end  33  is coupled to the second exhaust path, specifically the second exhaust fore-line  32 . The second dispensing fore-line  36  can alternatively be directly connected to the second exhaust pump  30 , similar to the embodiment of FIG. 1 or connected to a second dispensing pump, similar to the embodiment of FIG.  2 . The second dispensing pump would operate in a similar manner as the first dispensing pump  28  described above. The second dispensing pump collects the undiverted second precursor  9  so that the undiverted second precursor  9  is isolated from other chemicals, precursors, and exhausts that would otherwise mix with the second precursor  9  and potentially cause clogging of the second exhaust fore-line  32 . Thus, the second exhaust fore-line  32  remains clean and flow remains stable and consistent. 
     The second dispensing fore-line  36  operates in a similar manner as the first dispensing fore-line  26 . The second dispensing fore-fine  36  is used to discard the second precursor  9  when it is not diverted into the second precursor inlet  16 . The second dispensing fore-line  36  may be used to isolate the second precursor  9  from other chemicals, precursors, and exhausts that would otherwise mix with the second precursor  9  and potentially cause clogging of the second exhaust fore-line  32 . Thus, the second exhaust fore-line  32  remains clean and flow remains stable and consistent. 
     FIG. 5 differs from the previous figures because it does not show the first dispensing fore-line  26  or the second dispensing fore-line  36 . Therefore, only the two separate exhaust paths are depicted. 
     Having described the invention in detail and by reference to preferred embodiments thereof, it will be apparent that modifications and variations are possible without departing from the scope of the invention defined in the appended claims. More specifically, although some aspects of the present invention are identified herein as preferred or particularly advantageous, it is contemplated that the present invention is not necessarily limited to these preferred aspects of the invention.