Abstract:
A gas jet deposition method and apparatus includes a plurality of ports to supply plasma to the substrate on which deposition is to occur. A reagent gas is introduced either into the ports or into the expansion chamber. The use of multiple ports results in a much more uniform deposition of material on the substrate. In preferred embodiments, a carrier gas plasma is created using an excitation source such as a microwave power supply.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to the field of thin film deposition generally, and more particularly to gas jet deposition of thin films.  
           [0003]    2. Discussion of the Background  
           [0004]    Depositing thin films of materials (including metals, semiconductors, insulators/dielectrics, organics and inorganics) is required in a wide variety of manufacturing operations. The semiconductor manufacturing industry is one industry in which thin film deposition is especially important. The present invention will therefore be discussed in connection with the semiconductor manufacturing industry, but it should be understood that the present invention is not limited thereto.  
           [0005]    There are several known methods for depositing thin films. One such method is known as gas jet deposition. This method is desirable for many applications because it can be performed at low temperatures (less than 300 degrees Celsius). In gas jet deposition, a carrier gas is excited, typically by applying microwave power to the gas while it is in an applicator, such that a plasma is formed. The applicator feeds a chamber which is maintained at a lower pressure than the applicator. This pressure difference causes gases to exit the applicator at high speeds. A reagent gas is introduced near the exit of the applicator. This gas reacts with the carrier gas to form a deposition material. The deposition material is then deposited on a substrate that is positioned in the flow of the gases exiting from the applicator. An example of such a gas jet deposition system is discussed in U.S. Pat. No. 5,256,205.  
           [0006]    An important problem with known jet deposition systems is that the thin film that is deposited is often not of uniform depth. Uniform depth is important in many applications, including especially the semiconductor manufacturing industry. Known gas jet deposition systems, such as the one described in U.S. Pat. No. 5,256,205, use a single jet in the deposition process. In a single jet, there is typically a greater flow in the center of the jet stream than at the edges of a jet stream due to friction of the gas with the side wall of the jet. This results in the aforementioned non-uniform deposition problem.  
           [0007]    What is needed is a more uniform gas jet deposition technique.  
         SUMMARY OF THE INVENTION  
         [0008]    The present invention meets the foregoing need to a great extent by providing a gas jet deposition method and apparatus in which a plurality of ports supply gas to the substrate on which deposition is to occur. In preferred embodiments, a carrier gas plasma is created using an excitation source such as a microwave power supply. The applicator is in fluid communication with an expansion chamber. The carrier gas plasma, which is at a high pressure, exits the applicator and enters the expansion chamber, which is at a relatively lower pressure. In a wall of the expansion chamber opposite the applicator are formed a plurality of orifices, which are in fluid communication with a deposition chamber. Near the orifices is a reagent gas source which supplies a reagent gas. The carrier gas and the second gas react to form the material that is ultimately deposited. The carrier gas passes through the ports and enters the deposition chamber, which is maintained at a lower pressure than both the expansion chamber and the applicator. The deposition material is eventually deposited on a substrate in the deposition chamber. The use of multiple ports results in a much more uniform deposition of material on the substrate. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]    A more complete appreciation of the invention and many of the attendant advantages and features thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:  
         [0010]    [0010]FIG. 1 is a cross sectional view of a gas jet deposition apparatus according to a first embodiment of the present invention.  
         [0011]    [0011]FIG. 2 is a cross sectional view of a plate from the apparatus of FIG. 1 having a plurality of orifices formed therein.  
         [0012]    [0012]FIG. 3 is a cross sectional view of a gas jet deposition apparatus according to a second embodiment of the present invention.  
         [0013]    [0013]FIGS. 4 a,b  are perspective and cross sectional views, respectively, of a port included in the embodiment of FIG. 3.  
     
    
     DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0014]    The present invention will be discussed with reference to preferred embodiments of gas jet deposition devices. Specific details, such as dimensions of ports and chambers, are set forth in order to provide a thorough understanding of the present invention. The preferred embodiments discussed herein should not be understood to limit the invention. Furthermore, for ease of understanding, certain method steps are delineated as separate steps; however, these steps should not be construed as necessarily distinct nor order dependent in their performance.  
         [0015]    [0015]FIG. 1 illustrates a gas deposition apparatus  100 . The apparatus  100  includes an applicator  110  to which is attached a waveguide  112 . The waveguide  112  is connected to a microwave power supply (not shown in FIG. 1). Microwave energy supplied through the waveguide  112  excites a gas (e.g., nitrogen, to which a second gas such as helium may be added to increase gas diffusivity) in the applicator  110 , thereby forming a plasma. Preferably, a pressure in the applicator  110  is between 0.5 torr and 10 torr.  
         [0016]    The plasma is transported to an expansion chamber  120  through a plurality of channels  122  formed in an expansion chamber lid  121 . The expansion chamber includes a sidewall  123  which typically includes a quartz liner  124 . The pressure in the expansion chamber  120  is less than the pressure in the applicator  110 , and is preferably between 0.1 and 2 torr. This pressure difference causes plasma from the applicator  110  to exit the channels  122  at high speeds (however, unlike the apparatus discussed in U.S. Pat. No. 5,256,205, these speeds are subsonic).  
         [0017]    The plasma exits the expansion chamber  120  through a plurality of ports  132  in an expansion chamber floor  130 . The floor  130  is supported by an adapter ring  133 . Each of the ports  132  in the floor  130  is preferably approximately one inch in diameter. A distance D 1  from the expansion chamber top  121  and the floor  130  is 5-25 cm in preferred embodiments.  
         [0018]    The cross-sectional view of FIG. 2 illustrates the floor  130  in greater detail. Each of the ports  132  has an orifice  134  formed through a sidewall of the port  132  such that each of the ports  132  is in fluid communication with one of a plurality of gas distribution rings  136 . The gas distribution rings  136  are connected to and in fluid communication with a gas supply line  138 . The floor  130  may be made of a material such as aluminum. In order to fabricate the floor  130 , the gas distribution rings  136  and the supply line  138  are formed on an upper surface of an aluminum disc using a router. Next, the ports  132  are formed. Then an orifice  134  is formed in each port  132  to connect the port  132  to a gas distribution ring  136 . Next, a second aluminum disc is placed over the first disc with a metal flux between the first and second discs. The two discs are then placed in a vacuum autoclave and heated until the metal flux melts, thereby binding the two discs together to form the floor  130 .  
         [0019]    The gas supply line  138  is connected to a reagent gas. In this fashion, the reagent gas is mixed with the plasma as it passes through the ports  122 . The plasma and reagent react to form a deposition material. It is possible to form many different deposition materials in this fashion. By way of example, silane reagent gas could be used together with a plasma formed from a nitrogen/helium gas mixture to form a deposition material such as silicon nitride (Si 3 N 4 ). Although the ports  132  are illustrated as having a circular cross-sectional shape in FIGS. 1 and 2, other cross-sectional shapes, including, but not limited to, square, hexagonal, and oval may be used. Furthermore, the pattern of ports  132  may be different from that shown in FIG. 2. For example, in another embodiment, the innermost four ports  132  may be replaced by a single port  132  of the same size so that 3×3 grid of ports  132  is formed. In yet another embodiment, ports  132  in addition to the ports  132  of FIG. 2 are added to the floor  130 .  
         [0020]    Referring now back to FIG. 1, the plasma and reagent gases and products formed by the reaction between the two exit the ports  132  and enter a deposition chamber  140 . Material formed by the reaction (e.g., silicon nitride) is deposited onto a substrate on a platform  152 . Gases and undeposited material are removed through a plurality of vents  159  (only one is shown in FIG. 1) that are provided around the walls of the chamber  150 . The vents  159  are in fluid communication with a pumping port  158 , which is connected to a vacuum pump. It has been discovered that adjusting the height of the platform  152  such that it is just below the vents  159  provides superior performance. The provision of the multiple ports  132  results in an improved uniformity of distribution as compared to single port deposition devices.  
         [0021]    A distance D 2  in FIG. 1, which is the distance between the bottom of floor  130  and the top of platform  152 , is chosen (by adding spacer  142 ) to provide uniform deposition. In preferred embodiments, this distance is between approximately 10 centimeters and approximately 60 centimeters. In some embodiments, the platform  152  is stationary; in other embodiments, the platform is rotated to improve deposition uniformity.  
         [0022]    A second embodiment of the invention is illustrated by the device  200  shown in FIG. 3. In this embodiment, microwave energy from a waveguide  112  energizes a gas in an applicator  110  to create a plasma. The plasma passes through a port  116  in a lid  222  of an expansion chamber  120 . In this embodiment, the reagent gas is drawn from a reservoir  115  into plasma stream through supply tubes  115   a.  The reagent gas and the carrier gas from the applicator  110  are thus combined in the expansion chamber  120  prior to their passage through the floor  230 .  
         [0023]    Inserted into openings  236  in the floor  230  are nozzles  237 , as illustrated in FIG. 4. The nozzle  237  includes a shoulder  237   a  which rests on a corresponding notch in the floor  230  to support the nozzle  237 . A nozzle opening  237   b  is tapered to a nozzle width W. In preferred embodiments, the width W ranges from approximately one-half of an inch to approximately one inch. The nozzles  237  serve the same function as the ports  132  of FIG. 1—namely, the nozzles  237  cause the gases from the expansion chamber  120  to be evenly distributed over the wafer on platform  152 , thereby causing the deposition material to be evenly deposited.  
         [0024]    Other embodiments of the invention that share some of the features of the foregoing embodiments are also possible. For example, the lid  222  of FIG. 3 (which includes the reservoirs  115  and passages  115   a ) could be used to replace the lid  122  in the embodiment of FIG. 1. In such an embodiment, the floor  130  is dramatically simplified by eliminating the gas distribution rings  136 , supply line  138  and orifices  134 . In other words, since the reagent gas is being supplied by the reservoirs in the lid  222 , it is only necessary to form ports  132  in the floor  130 . This simplification would make the use of a material such as quartz for the floor  130  practical economically.  
         [0025]    Obviously, numerous other modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described herein.