Abstract:
A system and method for conserving and/or recycling hydrogen used in processing operations. The present invention can be used with any conventional reactor, which supports semiconductor processes using hydrogen. Hydrogen is pumped into the reactor from a hydrogen gas supply chamber. The hydrogen is used in the reactor as needed to perform the process function. The hydrogen accompanied with other process gases is exhausted from the reactor. The exhausted gases are routed through a scrubber, which is used to separate the hydrogen from the other gases. The other gases are allowed to vent from the system in a typical manner. The hydrogen is then pumped through an H 2  purifier, which cleans the hydrogen gas making the gas once again useable in the semiconductor process.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The invention is generally related to semiconductor processing, and more particularly to methods of hydrogen conservation and recycling in semiconductor processing operations.  
           [0003]    2. Related Art  
           [0004]    There are numerous semiconductor reactors, which are designed to perform various semiconductor processes on semiconductor substrates. Typically, during many of these processes hydrogen gas is employed for various purposes. For example, a method is disclosed in U.S. Pat. No. 5,660,682, for removing undesired material from an integrated circuit. In this method, a flow of argon and hydrogen are energized in a reactor to form a plasma, which reacts with the material to be removed, to form a gaseous product. The gaseous product is then subsequently removed from the reactor. In another example, a method is disclosed in U.S. Pat. No. 5,882,424, for depositing a thin film of Ti or TiN on a substrate by plasma enhanced CVD, which uses H 2  as a preferred process gas.  
           [0005]    Although, these exemplary uses of hydrogen in semiconductor processes are by no means exhaustive, they do suggest the potential advantage of hydrogen use to the semiconductor processing art. Unfortunately, hydrogen tends to be wasted in large amounts from most processing systems. Moreover, the excess hydrogen poses a potential fire and explosion hazard. For this reason, the excess hydrogen is typically burned away in a relatively costly process. Moreover, since hydrogen is itself a relatively expensive gas, processing costs for process including hydrogen may be substantial. Hydrogen is also difficult to store in large amounts in vapor phase do to volume requirements. Thus, hydrogen is typically stored in liquid phase, and converted to vapor phase, requiring large amounts of energy.  
           [0006]    For these reasons, what is needed is a system and method for conserving and/or recycling hydrogen used in semiconductor processing operations, which may reduce hazards, costs, and energy consumption.  
         SUMMARY  
         [0007]    The present invention provides a system and method for conserving and/or recycling hydrogen used in semiconductor processing operations. The present invention can be used with any conventional reactor, which supports semiconductor processes using hydrogen. Alternatively, the present invention can be used with a modified reactor, described in detail below.  
           [0008]    In the present invention, hydrogen is pumped into the reactor from a hydrogen gas supply chamber. The hydrogen is used in the reactor as needed to perform the process function. The hydrogen accompanied with other process gases is exhausted from the reactor. The exhausted gases are routed through a scrubber, which is used to separate the hydrogen from the other gases. The other gases are allowed to vent from the system in a typical manner. The hydrogen is then pumped through an H 2  purifier, which cleans the hydrogen gas making the gas once again useable in the semiconductor process.  
           [0009]    In one aspect of the present invention, a process is provided for recycling a vapor-phase chemical. The method includes introducing vapor-phase chemicals into a reactor with sufficiently supplied energy to cause a reaction in said reactor; exhausting gases resulting from the reaction; separating a first gas from the exhausted gases; purifying the first gas; and thereafter introducing the first gas into the reactor.  
           [0010]    In another aspect of the invention, a system is provided for recycling a vapor phase chemical. The system includes a reactor chamber capable of receiving and exhausting the vapor-phase chemicals. A gas scrubber is also provided, which is capable of receiving the vapor-phase chemicals exhausted from the reactor chamber. The scrubber outputs a first gas; which is directed to a gas purifier capable of purifying the first gas. Once the first gas is purified it is returnable to the reactor chamber.  
           [0011]    Advantageously, the present invention may return between approximately 80% to 90% of the initial hydrogen let into the reactor. Accordingly, if for example, 90% of the hydrogen is returned to the reactor, only 10% of the initial amount needs to be added for subsequent processes. The conservation and recycling of hydrogen used in semiconductor processing operations helps to reduce processing costs. For example, since the hydrogen requirement is reduced, the need to convert large amounts of liquid hydrogen to gaseous hydrogen is removed, which lowers overall energy consumption.  
           [0012]    These and other features and advantages of the present invention will be more readily apparent from the detailed description of the embodiments set forth below taken in conjunction with the accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]    The present invention may be better understood, and its numerous objects, features, and advantages made apparent to those skilled in the art by referencing the accompanying drawings.  
         [0014]    [0014]FIG. 1 is a simplified illustration of a conventional reactor suitable for use with the present invention;  
         [0015]    [0015]FIG. 2 is a schematic illustration of an embodiment of the present invention;  
         [0016]    [0016]FIG. 3 illustrates a flow chart of one embodiment of the process of the present invention; and  
         [0017]    [0017]FIG. 4 is a simplified illustration of an embodiment of a reactor for use with the present invention.  
         [0018]    The use of the same reference symbols in different drawings indicates similar or identical items.  
         [0019]    Embodiments of the present invention will be described with reference to the aforementioned figures. These figures have been simplified for ease of understanding and describing the embodiments. 
     
    
     DETAILED DESCRIPTION  
       [0020]    The present invention does not specifically concern the process employed to carry out processing operations on a semiconductor substrate or wafer, but rather concerns a system and process for conserving and/or recycling hydrogen, which may be used in the processing operations.  
         [0021]    For ease of understanding and clarity, FIG. 1 is a simplified illustration of a typical processing operation. Apparatus  10  includes a gas delivery showerhead  12  provided in upper wall  14   a  of reactor  14 , which is used for introducing reaction gas, supplied from reaction gas supply mechanism  16 , into the reactor  14 . Showerhead  12  is formed from an electrically conductive material. A voltage of fixed frequency is applied to showerhead  12  through matching circuit  18  from power supply  20 .  
         [0022]    A substrate holder  22  is provided along bottom wall  14   b  of reactor  14 . A plate  24  for fixing a substrate  26  is provided on the substrate mounting surface of substrate holder  22 , facing showerhead  12 . A heater  28  and a thermocouple  30  are provided within substrate holder  22 . The required voltage is supplied from power source  32  to plate  24 . Temperature data obtained by measurement with thermocouple  30  is input to heating control mechanism  34 . Heating control mechanism  34  maintains substrate holder  22  at a desired temperature by applying the required electrical power to heater  28  on the basis of the measured temperature data.  
         [0023]    Typically, a vent  36  connected to an external pump  38  is provided. Hydrogen alone or in combination with other process gases, such as NH 3 , N 2 O, SiF 4 , TiCl 4 , N 2 , Ar, SiH 4 , HCl, and SiCl 4  are introduced from showerhead  12 . The gases are excited in the space between showerhead  12  and substrate holder  22 , by applying electrical power to showerhead  12  by means of power supply  20 , thereby depositing the desired thin film on substrate  24 . The unreacted gas and the product gas in reactor  14  are pumped out of the system through vent  36  by means of pump  38 .  
         [0024]    [0024]FIG. 2 is a schematic illustration of an embodiment of hydrogen conservation/recycling system  40  in accordance with the present invention. System  40  includes any apparatus  10 , which can support a semiconductor process, which includes the use of hydrogen. For example, with no intent to limit the invention thereby, the processes disclosed in U.S. Pat. No. 5,660,682, and U.S. Pat. No. 5,956,616, both of which are herein incorporated by reference for all purposes.  
         [0025]    In one embodiment, reactor  14  of system  40  is operatively coupled to a scrubber  46 , which is used to separate gases vented from reactor  14  via line  44 . In this embodiment, scrubber  46  is used to separate hydrogen from the remaining unreacted or product gases. Once separated or scrubbed of impurities, the hydrogen is returned to the system via line  48 , while the other gases and impurities are exhausted from the system via line  50 . In one embodiment, scrubber  46  may be a dry scrubber. In operation scrubber  46  receives H 2 , product gases and impurities from reactor  14 . Scrubber  46  includes a filtering mechanism that is permeable only to H 2 . An exemplary scrubber  46  is available from Matheson Tri-Gas® of Parsippany, N.J.  
         [0026]    A pump  52  can be added to system  40  to ensure that the separated hydrogen is able to adequately flow through system  40 . In this embodiment, pump  52  can provide approximately 50 psig to 250 psig. An example of a suitable pump  52  is available from KASHIYAMA IND., LTD.  
         [0027]    The separated hydrogen enters an H 2  purifier  56  via line  54 . Purifier  56  “cleans” the separated hydrogen, making the separated hydrogen suitable for reuse in reactor  14 . Hydrogen purifier  56  cleans the separated hydrogen, using any well known technique, for example, using a heated paradium membrane/filter. In one embodiment, as an example with no intent to limit the invention, the effluent from purifier  56  can have a capacity of about 24 SLPM, 50 SCFH.115 V standard, 50/60 Hz and a total impurity level of less than about 0.5 ppm. The operating pressure of purifier  56  can range from between 50 psig and 200 psig. An H 2  purifier  56  of this type is available from Matheson TriGas®, for example, Model 8374V. Once purified, the H 2  gas can be returned to reactor  14  via line  58 .  
         [0028]    Initially, H 2  is added to system  40  from H 2  gas supply  60 . A sensor  62 , may be placed into line  58  to determine the quantity of purified H 2  being re-introduced into reactor  14 . Typically, some processes can require up to approximately about 200 l/min to about 500 l/min of H 2  per operation. Thus, if sensor  62  determines that the delivery rate of H 2  to reactor  14  has dropped below required levels, mass flow meter  64  can be activated allowing additional H 2  to be added to system  40  to maintain the required levels. In a typical operation of system  40 , 80% to 90% of the initial H 2  can be recovered for reuse in reactor  14 .  
         [0029]    [0029]FIG. 3 illustrates a flow chart of one embodiment of process  100  of the present invention, which will be described with reference to components identified and described with reference to both FIGS. 1 and 2. As an initial step  110 , substrate  26  is positioned on substrate holder  22  in reactor  14 . Substrate  26  can be heated to a temperature above 200° C.; preferably, to a temperature generally in the range of between about 200° C. to about 500° C., for example 400° C. In this manner, substrate  26  is prepared for receiving a film to be deposited on the upper surface of the substrate. Substrate  26  may be a bare silicon wafer. In alternative embodiments, substrate  26  may be a silicon wafer having a metal barrier and/or etch stop layer of SiNx, Ta(N), TiN, WNx, or the like, thereon.  
         [0030]    Next, process  100  includes the introduction of a flow of H 2  (action  120   a ) and reactant gases (action  120   b ) into reactor  14  as required for a particular process. In one embodiment, in addition to the H 2 , the gases can include, but are not limited to, NH 3 , N 2 O, SiF 4 , SiH 4 , TiCl 4 , N 2 , Ar, HCl, and SiCl 4  introduced via showerhead  12 . The ratios of particular gases to deposit a particular thin film on substrate  26  are determined and selected in accordance with the specific process being conducted in reactor  14 . Alternatively, H 2  can be introduced into reactor  14  to perform a plasma cleaning operation of the substrate.  
         [0031]    In a typical CVD process, as the gases enter reactor  14 , suitable power is applied to begin the processing of the substrate (action  130 ). As is known to those skilled in the art of CVD processing, the power supplied in reactor  14  excites the introduced gases, generating radicals which are deposited on the surface of substrate  36 .  
         [0032]    Once processing of substrate  26  is complete, the unreacted gases and the product gases (hereinafter the “gases”) are exhausted from reactor  14  (action  140 ) through vent  36  using pump system  38 .  
         [0033]    With reference now to the embodiment of FIG. 2, the vented gases are directed to a scrubber  46 . The scrubber separates H 2  from the remainder of the gases (action  150 ). The remaining gas is then exhausted from the recycling system. The separated H 2 , however, is pumped using pump  52  through H 2  purifier  56 . The H 2  is then purified (action  160 ) and returned to reactor  14  for re-use (action  170 ). As necessary, additional H 2  can be added to system  40  to ensure that a predetermined flow rate of H 2  is maintained (action  180 ). In one embodiment, the additional H 2  may be approximately 10% to 20% of the H 2  introduced at the beginning of the process (action  120   a ).  
         [0034]    [0034]FIG. 4 is a simplified illustration of an embodiment of a reactor  200  for use in accordance with the present invention. Reactor  200  includes a tapered shell  202 , being wider at a bottom portion than at a top portion. The taper of shell  202  can have a diameter at the widest portion from between about  6  inches to about 100 inches; preferably between about 10 inches to about 80 inches.  
         [0035]    Reactor  200  also includes a substrate holder or susceptor  204 , which has a tapered shape, which corresponds with the taper of shell  202 . In one embodiment, the clearance between shell  202  and susceptor  204  is between no less than between about 1 mm and 200 mm; for example about 25 mm. Susceptor  204  provides mechanical support for the substrates and are the source of thermal energy for the reaction. Susceptor  204  is non-contaminating to the process and does not react with the process reactants. Preferably, susceptor  204  is made of graphite, which can be coated with approximately 50 to 500 μm of SiC or similar material to make up for the impurity and softness of the graphite. The susceptor is also coated to couple susceptor  204  to the RF field. Substrates are carried on susceptor  204  by a carbon blank shaped to the dimensions of the substrate.  
         [0036]    An induction coil  206  surrounds shell  202  to provide energy for the reaction. The energy is transferred to the substrate via conduction and radiation. In one embodiment, induction coils  206  are formed along the tapered surface of shell  202 . Accordingly, since the distance from the coils to the susceptor surface is evenly maintained, the spacing of induction coils need not be uniform to provide the same uniform heating. Thus, relatively fewer coils may be used in reactor  200 .  
         [0037]    In one embodiment, hydrogen gas is introduced into shell  202  as indicated in FIG. 4 from below susceptor  204 . In this manner, the H 2  gas flows through reactor  200  in the direction indicated by arrows  206 . Hydrogen is carried through shell  200  without the need for forcing the gas through the system. Moreover, the tapered shape of shell  202  and susceptor  204  maintains an even reactant concentration throughout reactor  200 . Thus, there is no partial pressure drop as the reactant courses through reactor  200 . Accordingly, no temperature drops are experienced within reactor  200  and gas consumption/flow requirements for uniform deposition can be made substantially lower.  
         [0038]    While the principles of the invention have been described in connection with specific apparatus, it is to be understood that this description is not a limitation on the scope of the invention.