Abstract:
A system and method for making very small (e.g., 1 millimeter diameter) spherical shaped devices is disclosed. The system includes a supply system for providing predetermined amounts of raw material into a chamber, which is used for melting the raw material. The melted raw material is then provided to a dropper for measuring predetermined amounts of the melted raw material (droplets) and releasing the droplets into a drop tube, where they are cooled and solidified into spherical shaped silicon devices. The system includes a container of silicon powder in which the solidified spherical shaped devices are received from the drop tube, the container including a stirring mechanism for agitating the silicon powder. The system also includes a separating device for separating the powder from the solidified spherical shaped devices after the devices have been received into the container

Description:
BACKGROUND  
         [0001]    The invention relates generally to semiconductor devices, and more particularly, to a system and method for creating three-dimensional semiconductor devices.  
           [0002]    This disclosure claims the benefit of U.S. Ser. No. 60/279,484, filed Mar. 28, 2001.  
           [0003]    In U.S. Pat. No. 5,955,776, which is hereby incorporated by reference, a method and apparatus for manufacturing spherical-shaped semiconductor integrated circuit devices is disclosed. Although certain systems and methods for performing various processing operations are discussed in the above-referenced patent, it is desired to further improve on the operations. For example, in making a p-n junction diode, a first type (e.g. n-type) outer layer is diffused onto a second type (e.g., p-type) spherical shaped semiconductor substrate. It is desired that both the outer layer and the inner substrate are maintained at an appropriate shape, thickness, and diffusion concentration.  
           [0004]    In U.S. patent Ser. Nos. 09/490,650 and 09/489,782, which are hereby incorporated by reference, methods for doping material on a spherical shaped substrate in a non-contact environment are disclosed. These methods can be used to make spherical p-n junction diodes for solar cell applications. It is desired, however, to make uniform sized spherical p-n diodes in a continuous operation (e.g., a single step).  
           [0005]    In U.S. patent Ser. Nos. 09/363,420 and 09/672,566, which are hereby incorporated by reference, methods for making single crystal devices and for making uniformly thick p-n junctions on these devices are disclosed, respectively. It is desired, however, to better automate the production of these devices in a highly manufacturable setting.  
         SUMMARY  
         [0006]    A technical advance is achieved by a new and improved jet system for making spherical shaped devices. In one embodiment, the system includes a supply system for providing predetermined amounts of raw material at a temperature at or above a melting point of the material, and for moving the predetermined amounts of melted raw material without physical contact so that a liquid surface tension of each predetermined amount of melted raw material will cause the material to form into a spherical shape device. The system also includes a container of powder in which the solidified spherical shaped devices are received from the supply system and means for separating the powder from the solidified spherical shaped devices after the devices have been received.  
           [0007]    In another embodiment, the system includes a supply system for providing predetermined amounts of raw material into a chamber, which is used for melting the raw material. The melted raw material is then provided to a dropper for measuring predetermined amounts of the melted raw material (droplets) and releasing the droplets into a drop tube, where they are cooled and solidified into spherical shaped silicon devices. The system includes a container of silicon powder in which the solidified spherical shaped devices are received from the drop tube, the container including a stirring mechanism for agitating the silicon powder. The system also includes a separating device for separating the powder from the solidified spherical shaped devices after the devices have been received into the container. 
       
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0008]    [0008]FIG. 1 is a flow chart of a new and improved processing flow for creating spherical shaped devices according to one embodiment of the present invention.  
         [0009]    [0009]FIG. 2 is a diagram of a feeder device, such as can be used in the processing flow of FIG. 1.  
         [0010]    FIGS.  3 - 4  are diagrams of a dropper device, such as can be used in the processing flow of FIG. 1.  
         [0011]    [0011]FIG. 5 is a diagram of a receiver device, such as can be used in the processing flow of FIG. 1.  
         [0012]    FIGS.  6 - 7  are diagrams of a separator device, such as can be used in the processing flow of FIG. 1. 
     
    
     DETAILED DESCRIPTION  
       [0013]    The present disclosure provides many different embodiments, or examples, for implementing different features of the invention. Specific examples of components, sizes, and arrangements are described below to simplify the present disclosure and are not intended to limit the invention.  
         [0014]    Referring to FIG. 1, the reference numeral  10  designates, in general, one embodiment of a processing flow for making spherical shaped semiconductor devices. The processing flow  10  utilizes a feeder system  12  that provides continuous feeding of raw material and prevents undesired material and/or fluids from entering other components. The feeder system  12  provides the material to a dropper  14 , which is used to make the spherical shaped semiconductor devices. The spherical shaped semiconductor devices are received into a receiver  16 , which include a soft powder-like refractory receiving material, such as quartz. The devices and receiving material are then provided to a separator  18  where the receiving material is separated and recycled.  
         [0015]    The following discussion provides many different embodiments for different systems that can be used in the processing flow  10 . Each of the embodiments are different, but may include similar components that are similarly numbered.  
         [0016]    Referring now to FIG. 2, in one embodiment of the feeder system  12 , raw material Si  20  is received in the form of chunks, powder or granules into a receiver  22 . The receiver  22  includes a sensor  24  for detecting the raw material and ensuring a continuous feeding of raw material into the feeder. The flow of the raw material  20  is controlled by two valves  26 ,  28 . In addition, an argon gas is controlled by valves  28  and  30 .  
         [0017]    The feeder  12  is designed to ensure continuous feeding of the raw material  20  into the dropper system  14 , while at the system eliminating ingress of atmosphere into a nozzle (FIG. 3) of the dropper. When the first valve  26  is opened, the raw material  20  will drop into a first tube portion  34 . Thereafter, the first valve  26  is closed and the third valve  30  is opened to introduce Argon through a first pipe  35 . When the second valve  28  is opened the feed will be dropped into the nozzle. The second valve  28  and the third valve  30  are thereafter closed. In one embodiment, the dropper  14  is as disclosed in presently incorporated U.S. patent Ser. No. 09/672,566.  
         [0018]    Referring now to FIGS. 3 and 4, in other embodiments of the feeder system  12 , the flow of the raw material  20  is controlled by two shutters  36 ,  38 . In the embodiment of FIG. 3, a second Argon pipe  39  is also used to introduce Argon to the operation.  
         [0019]    The feeder system  12  provides the raw material  20  to the receiver system  14 , where it proceeds to a chamber  40 . The raw material is melted by a furnace  42  into a liquid state (designated as liquid material  44 ), which in the case of pure silicon is near 1400° C. In some embodiments, such as is shown in FIG. 4, the chamber  40  is attached to a first vibration device  46 , such as a piezo-electric vibrator (PZT). The first PZT  46  encourages the liquid material  44  to move through a first nozzle  47  at a predetermined rate into a second chamber  48 . In addition, a gas (e.g., Argon) may be supplied through a first pipe  35  to apply a pressure to the first chamber  40  and further help control the flow of the liquid material into the second chamber  48 .  
         [0020]    The second chamber  48  receives the liquid material  44  from the first chamber  40  and feeds it into a jet nozzle  50 , that is controlled by a second vibration device  52 . The nozzle  50  and second vibration device  52  can thereby produce liquid droplets  54  of a predetermined size, e.g. about one millimeter. In addition, a gas (e.g., Argon) may be supplied through a second pipe  56  to apply a pressure to the second chamber  48  and further help control the creation of the liquid droplets  54 .  
         [0021]    Referring now to FIG. 5, in one embodiment of the receiver  16 , the liquid droplets  54  can fall, without contact, through a drop tube  70 . The rate at which the droplets move can be controlled, such as through a pressure or a moving fluid through the drop tube  70 . Eventually, the droplets solidify into spheres  72 . The temperature of the spheres  72  is relatively high, such as between 1000°-1300° C. (near the melting point of silicon).  
         [0022]    The solidified spheres  72  are then received into a container  74 . In the present embodiment, the container  74  is a furnace. The furnace  74  includes a powdered refractory material (e.g., quartz powder, silica, or ceramic powder)  76 , which is heated to about 1000°-1300° C. The powder  76  is continually stirred by a quartz mixing rod  78  connected to a motor  80 . The stirring exposes fresh powder  76  to the falling spheres  72 . The powder  76  thereby provides a soft landing for the spheres  72 .  
         [0023]    Referring again to FIG. 1, the separator  18  receives the spheres  72  and powder  76  from the furnace. It is understood that there may be one or more separators  18  to repeatedly separate the powder  76  from the spheres  72 . The spheres  72  can be provided to other downstream processing operations and the powder  76  can be returned to the receiver  16 .  
         [0024]    Referring now to FIG. 6, in one embodiment the separator  18  includes an enclosure  112  having an inlet opening  114  and three outlet openings  116 ,  118 ,  120 . The outlet opening  116  is located diametrically opposite the inlet opening  114 . The enclosure  112  defines two chambers  122 ,  124 . The chamber  122  is a separation chamber for receiving a supply of spheres  72  and powder  76  and the chamber  124  is a reservoir for receiving, storing and expelling the separated powder  76  through the outlet  118 . The chamber  122  and reservoir  124  are connected by a neck portion  128 .  
         [0025]    A vertically extending conduit  130  is coaxially aligned with the chamber  122 , the reservoir  124  and the neck  126 . The conduit  130  supplies a path between the outlet  116  and a separating device  132  located in the separation chamber  122 . For the present embodiment, the separating device  132  is a wire mesh formed into a funnel shape. The wire mesh  132  includes a plurality of openings having a diameter less than one-half the diameter of the sphere  72 . The wire mesh  132  includes an opening  134  that registers with the inlet opening  114  to receive the supply of spheres  72  and powder  76 . The wire mesh  132  also includes an outlet  136  that registers with the conduit  130 .  
         [0026]    Although not shown, a vacuum source is connected to the outlet  120  for providing a negative pressure inside the reservoir  124 , the neck  128 , and the separation chamber  122 . The negative pressure is not strong enough to lift either the spheres  72  or the powder  76 .  
         [0027]    For the sake of reference, the pressure at several locations inside the fluid separating processor  18  are identified. A pressure P 1  represents the pressure inside the reservoir  124 ; a pressure P 2  represents the pressure inside the neck  128 ; a pressure P 3  represents the pressure inside the separation chamber  122 ; a pressure P 4  represents the pressure at the conduit  130 ; and a pressure P 5  represents the pressure at the opening  114 . The following comparative relationships exist between the different pressures P: 
         P1&lt;P2  (1) 
         P2&lt;P3 and P5  (2) 
         P4&gt;P3 and P5  (3) 
         [0028]    In operation, the supply of spheres  72  and powder  76  are introduced into the opening  114 . The spheres  72  are preferably of a generally spherical shape and could be of the same type formed according to the technique disclosed in the above-identified and presently incorporated patent application Ser. No. 08/858,004. The powder  76  may be a flow of constituents or liquids or the like. For the sake of example, the powder  76  is a high-viscosity liquid from a previous process.  
         [0029]    When the spheres  72  and powder  76  enter the separation chamber  122 , they contact the wire mesh  134  and are propelled towards the opening  136 . In the preferred embodiment, the pressure P 3  assists this propelling action, but in other embodiments, the momentum of the spheres  72  and powder  76 , or other forces, may so assist.  
         [0030]    As the powder  76  is propelled towards the opening  136 , it flows through the wire mesh  134 . The pressure P 3  helps to draw the powder  76  through the wire mesh  134 . In some embodiments, the (higher) pressure P 4  from the conduit  130  also persuades the powder  76  to move through the wire mesh  134 . In so doing, even highly viscous fluid will be drawn through the wire mesh, despite the wire mesh&#39;s narrow openings. The fluid is then drawn by either gravity or by the pressure P 2 , or both, into the neck  128  and further drawn (by gravity and/or the pressure P 1 ) into the reservoir  124 . It is noted that the reservoir  124  is physically isolated from the interior of the conduit  130  so that none of the powder  76  can enter the conduit. The reservoir  124  maintains a portion of the powder  76  while draining out another portion through the outlet  118 .  
         [0031]    As the spheres  72  move toward the opening  136 , they cannot move through the wire mesh  134 . Instead, the spheres  72  move into the conduit  130  and then exit through the outlet  116 .  
         [0032]    Referring to FIG. 7, in another embodiment, the separator  18  includes an enclosure  142  having an inlet opening  144  and two outlet openings  146 ,  148 . The outlet opening  146  is opposite the inlet opening  144 . The enclosure  142  defines a chamber  152  and a reservoir  154 . The chamber  152  is a separation chamber for receiving a supply of spheres  72  and powder  76  and the reservoir  154  receives and stores and expels the separated powder  76  using the outlet  148 . The chamber  152  and reservoir  154  are connected by a slot  156 .  
         [0033]    A vertically extending conduit  158  is connected at one end  160  of the chamber  152  and passes through the reservoir  154 . The conduit  158  supplies a path between the outlet  146  and an opening  162  at the end  160  of the slot  156 . For the present embodiment, the slot  156  acts as a separation device by providing an opening with a diameter less than the diameter of the sphere  72  (except at the opening  162 ) but sufficiently large to allow the powder  76  to flow there through.  
         [0034]    Although not shown, a vacuum source is connected to the outlet  148  for providing a negative pressure inside the reservoir  154 , the slot  156 , and the separation chamber  152 . Also not shown, a plurality of air inlets may be provided in the chamber  152 . The air inlets may be used to provide a dry, inert gas such as N2 to the chamber.  
         [0035]    For the sake of reference, the pressure at several locations inside the fluid separating processor  18  are identified. A pressure P 10  represents the pressure inside the reservoir  154 ; a pressure P 11  represents the pressure the separation chamber  152 ; and a pressure P 12  represents the pressure at the conduit  158 . The following comparative relationships exist between the different pressures P: 
         P10&lt;P11 and P12  (4) 
         [0036]    In operation, the supply of spheres  72  and powder  76  are introduced into the opening  144 , opposite to the end  160 . When the spheres  72  and powder  76  enter the separation chamber  152 , they contact the slot  156  and are propelled towards the opening  162  at the end  160 .  
         [0037]    The slot  156  is small enough so that a sphere  72  cannot fall into the reservoir  154 , but the powder  76  can. The pressure P 10  and the dry inert air help to draw the powder  76  through the slot  156 . In some embodiments, the pressure P 12  from the conduit  130  may be high to prevent any of the powder  76  from entering the conduit. It is noted that the reservoir  154  is physically isolated from the interior of the conduit  158  so that none of the powder  76  can enter the conduit. The reservoir  154  drains the powder  76  through the outlet  148 .  
         [0038]    It is understood that several variations may be made in the foregoing. For example, different heating steps may be used in different parts of the system  10 . Other modifications, changes and substitutions are also intended in the foregoing disclosure and in some instances some features of the invention will be employed without a corresponding use of other features. Accordingly, it is appropriate that the invention be construed broadly.