Abstract:
A method for doping crystals is disclosed. The method includes a receiver for receiving semiconductor spheres and doping powder. The semiconductor spheres and dopant powder are then directed to a chamber defined within an enclosure. The chamber maintains a heated, inert atmosphere with which to diffuse the dopant to the semiconductor spheres.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates generally to semiconductor devices, and more particularly, to a method for doping spherical-shaped semiconductors. 
     The doping process involves the controlled introduction of an impurity to a substrate, which produces subtle changes in the electrical resistivity of the material. Such characteristics are necessary for solid-state electronic semiconductor devices, such as the transistor. 
     In the conventional semiconductor industry, a doped silicon substrate is created by adding the doping impurity directly into the melt during the crystal-pulling process. The final crystal is a uniformly doped one, from which wafers may be cut to serve as doped substrates. 
     In the case of spherical semiconductors, the single crystal substrates are not produced from a melt, but rather are made by remelting polycrystalline silicon granules which are grown by gas-phase reaction in a fluidized bed reactor. The random and turbulent nature of the fluidized bed process makes the attainment of sample-to-sample doping uniformity difficult. Therefore, the granules cannot be doped during growth in the fluidized bed, and must be doped by external means. 
     In U.S. Pat. Nos. 5,278,097, 5,995,776, and 5,223,452, methods and apparatuses for doping spherical-shaped semiconductors are disclosed. However, an improved method of doping the spherical shaped semiconductors, which is simpler and more economical, is desired. 
     SUMMARY OF THE INVENTION 
     The present invention, accordingly, provides a method for doping spherical semiconductors. To this end, one embodiment provides a receiver for receiving semiconductor spheres and a dopant powder. The semiconductor spheres and dopant powder are then directed to a chamber defined within an enclosure. The chamber maintains a heated, inert atmosphere with which to diffuse the dopant properties of the dopant powder into the semiconductor spheres. 
     In one embodiment, the method of doping a plurality of spherical shaped semiconductors includes: embedding the plurality of spherical shaped semiconductors in a dopant mixture to produce a powder mixture; heating the powder mixture to produce a plurality of doped spherical shaped semiconductors; cooling the doped spherical shaped semiconductors; removing the doped spherical shaped semiconductors from the powder mixture; and chemically etching the doped spherical shaped semiconductors. 
     In one embodiment, the plurality of spherical shaped semiconductors are made from a commercially available semiconductor material. 
     In one embodiment, the plurality of spherical shaped semiconductors are p-type spherical single crystal substrates. 
     In one embodiment, the plurality of spherical shaped semiconductors are n-type spherical single crystal substrates. 
     In one embodiment, the plurality of spherical shaped semiconductors are oxidized spherical shaped semiconductors. 
     In one embodiment, the dopant mixture is a mixture of a dopant oxide and silicon dioxide. 
     In one embodiment, the dopant mixture is a dopant nitride. 
     In one embodiment, the dopant mixture is a mixture of antimony oxide/silicon dioxide (Sb 2 O 3 SiO 2 ). 
     In one embodiment, the dopant mixture is a mixture of boric oxide/silicon dioxide (B 2 O 3 SiO 2 ). 
     In one embodiment, heating the powder mixture comprises diffusion and/or viscous flow along the surface of the spherical shaped semiconductors. 
     In one embodiment, the dopant mixture is boron nitride (BN). 
     In one embodiment, the method is done in a non-oxidizing environment. 
     In one embodiment, the method further includes melting the doped spherical shaped semiconductors to produce uniformly doped spherical shaped semiconductors and cooling the uniformly doped spherical shaped semiconductors. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cross-sectional view of an apparatus for use in doping spherical semiconductors according to one embodiment of the present invention. 
     FIG. 2 is a flow chart of a method for doping a spherical shaped semiconductor using the apparatus of FIG.  1 . 
     FIG. 3 is a cross-sectional view of the apparatus of FIG. 1 in use during the method of FIG.  2 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The present invention provides a method for doping substrates. The following description provides many different embodiments, or examples, for implementing different features of the invention. Certain techniques and components described in these different embodiments may be combined to form more embodiments. Also, specific examples of components, chemicals, and processes are described to help clarify the invention. These are, of course, merely examples and are not intended to limit the invention from that described in the claims. 
     Referring to FIG. 1, the reference numeral  10  designates, in general, one embodiment of an apparatus used for the doping of spherical semiconductors. The apparatus  10  includes a chamber  12  having a furnace  14  surrounding the chamber. The chamber  12  has an inlet port  16  at one end for connecting to an inlet line  18 . 
     The inlet line  18  is used for allowing a gas source  20  to enter the chamber  12 . The chamber  12  includes a boat  22  which can be held in place by a base  24  which is connected to one or more legs  26 . The boat  22  may be, for example, quartz or alumina. In a preferred embodiment, the boat  22  is quartz. The chamber  12  also includes an outlet line  28  for exhausting the gas source  20 . 
     Referring to FIGS. 2 and 3, a method  100  may be used in conjunction with the apparatus  10 . The method  100  is preferably performed in an inert atmosphere. At step  102 , a plurality of spherical semiconductors  30  is placed in the boat  22 . The spherical semiconductors  30  may be, for example, any commercially available spherical semiconductor material, any oxidized spherical semiconductor material, an n-type spherical single crystal substrate, or a p-type spherical single crystal substrate. In a preferred embodiment, the spherical semiconductors  30  are silicon. 
     At step  104 , a dopant mixture  32  is placed in the boat  22  containing the spherical semiconductors  30 . The spherical semiconductors  30  are embedded within the dopant mixture  32 . The dopant mixture  32  preferably has particles that are approximately less than 1μm in size. The dopant mixture  32  may be, for example, any dopant oxide mixed with silicon dioxide (SiO 2 ) or any dopant nitride. In a preferred embodiment, the dopant mixture  32  is an antimony oxide/silicon dioxide (Sb 2 O 3 /SiO 2 ) mixture. The ratio of the dopant oxide/silicon dioxide mixture is chosen to maximize the viscosity of the dopant mixture  32  and to maximize the amount of the dopant oxide in the dopant mixture  32 . 
     At step  106 , the boat  22  is placed within the chamber  12  and the chamber  12  is subjected to a predetermined thermal cycle. In a preferred embodiment, at the process temperature, antimony oxide is transferred from the dopant mixture  32  to the surface of the spherical semiconductors  30 . This is accomplished by diffusion and/or viscous flow along the surface of the powder particles of the dopant mixture  32  which are in intimate contact with the spherical semiconductors  30 . In a preferred embodiment, elemental antimony is further diffused to a shallow depth into the spherical semiconductors  30 . 
     At step  108 , the boat  22  is cooled and removed from the chamber  12 . The spherical semiconductors  30  are doped with antimony and are removed from the dopant mixture  32 . 
     At step  110 , the spherical semiconductors  30  doped with antimony, are chemically etched to remove any oxide/powder layer. The spherical semiconductors  30  doped with antimony may be chemically etched by any commercially available chemical etching process. 
     In an alternate embodiment, the method  100  further includes melting the spherical semiconductors  30  doped with antimony to produce spherical semiconductors  30  uniformly doped with antimony upon cooling. 
     In an alternate embodiment of the method  100 , the dopant mixture  32  is a boric oxide/silicon dioxide (B 2 O 3 /SiO 2 ) mixture. The spherical semiconductors  30  are doped with boron. 
     In an alternate embodiment of the method  100 , the spherical semiconductors  30  are a p-type spherical single crystal substrate and the dopant mixture  32  is an antimony oxide/silicon dioxide (Sb 2 O 3 /SiO 2 ) mixture. The spherical semiconductors  30  are doped to produce a p-n junction near the surface of the spherical semiconductors  30 . 
     In an alternate embodiment of the method  100 , the spherical semiconductors  30  are an n-type spherical single crystal substrate and the dopant mixture  32  is a boron oxide/silicon dioxide (B 2 O 3 /SiO 2 ) mixture. The spherical semiconductors  30  are doped to produce a p-n junction near the surface of the spherical semiconductors  30 . 
     In an alternate embodiment of the method  100 , the spherical semiconductors  30  are oxidized spherical semiconductors and the dopant mixture  32  is boron nitride (BN). 
     Several advantages result from the above-described embodiments. For one, the spherical semiconductors seldom, if ever, come in physical contact with any other device or any part of the apparatus  10 . 
     It is understood that several variations may be made in the foregoing. For example, different heating mechanisms may be used with the apparatus. 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 appended claims be construed broadly and in a manner consistent with the scope of the invention.