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:
CROSS-REFERENCE 
     This invention claims the benefit of U.S. Provisional Patent Application No. 60/178,213 filed on Jan. 26, 2000. 
    
    
     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. Pate. 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 . 
     FIGS. 4-6 are cross-sectional views of apparatuses for use in doping spherical semiconductors according to other embodiments of the present invention. 
    
    
     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 1 μm 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. In this embodiment, the semiconductors  30  would first be oxidized (in a prior, separate step), and then mixed with and submersed in a bed of BN powder. During the process, the BN powder would react and bond with the oxide on the surface of the spherical semiconductors and the transfer of Boron would take place. After the process, the semiconductors  30  would be chemically etched to remove the layer of oxide/powder. The process would be done under a non-oxidizing atmosphere to prevent oxidation of the BN powder, thus allowing it to be reused fro subsequent treatments. 
     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). 
     Referring now to FIG. 4, the reference numeral  150  designates, in general, another embodiment of an apparatus used for the doping of spherical semiconductors. The apparatus  150  includes a chamber  152  having two furnaces  154 ,  156  associated with the chamber. The chamber  152  has an inlet port  158  at one end and an opposing outlet port  160 . The apparatus  150  can be used with the method  100 , as described above. 
     The inlet port  158  is used for allowing a carrier gas  162  to enter the chamber  152 , similar to the carrier gas from the gas source  20  of FIG.  1 . The chamber  152  includes a first boat  164  and a second boat  166 , both similar to the boat  22  of FIG.  1 . 
     The first boat  164  and the first heater  154  are positioned in a first area of the chamber  152 , herein designated as the diffusion zone  168 . The second boat  166  and the second heater  156  are positioned in a second area of the chamber  152 , herein designated as the vaporization zone  170 . Although the diffusion zone  168  and the vaporization zone  170  are illustrated as being in a single, common chamber  152 , in other embodiments, they may be in separate chambers. 
     In the present embodiment, the first boat  164  includes a plurality of spherical semiconductors  30  and the second boat  166  has the dopant mixture  32 . The dopant mixture  32  may be as described in FIG.  3 . However, in the present embodiment, the dopant mixture  32  and the spherical semiconductors  30  are kept separate from each other. In this way, different processing environments can be maintained in the different zones  168 ,  170 . For example, the temperature of the vaporization zone  170  may be higher than that of the diffusion zone  168 . 
     In operation, the dopant material  32  is heated by the heater  156  and vaporizes in the vaporization zone  170 . The carrier  160  moves through the vaporization zone  170  and carries the vaporized dopant into the diffusion zone  168 . At this time, the vaporized dopant comes in uniform contact with the spherical semiconductors  30 . Diffusion may then occur on the semiconductors. Exhaust  172  from the process may be expelled through the outlet  160 . 
     Referring now to FIG. 5, the reference numeral  200  designates, in general, yet another embodiment of an apparatus used for the doping of spherical semiconductors. The apparatus  200  includes a first chamber  202  having a furnace  204 . The chamber  202  has an inlet port  206  at one end connected by a coupling  208  to a second chamber  210 . Opposing the inlet  206  is an outlet port  212 . The apparatus  200  can be used with the method  100 , as described above. 
     The first chamber  202  is connected to a rotating device  214  for rotating the chamber, as illustrated by the arrows  216 . The rotator  214  may be any mechanical means, such as a small motor assembly. The rotation  216  allows a plurality of spherical semiconductors  30  to move inside the first chamber  202 . 
     The second chamber  210  does not have to rotate. Instead, the coupling  208  allows the first and second chambers  202 ,  210  to remain connected while only one rotates. In other embodiments, the second chamber  210  may also rotate. The second chamber  210  also includes a heater  220  and the dopant mixture  32 , such as is described in FIG.  3 . However, like the embodiment of FIG. 4, the dopant mixture  32  and the spherical semiconductors  30  are kept separate from each other. In this way, different processing environments can be maintained in the different chambers  202 ,  210  For example, the temperature of the second chamber  210  may be higher than that of the first chamber  202 . 
     In operation, the dopant material  32  is heated by the heater  220  and vaporizes in the second chamber  210 . A carrier gas  160  moves through the second chamber  210  and associates with the vaporized dopant. The carrier gas and vaporized dopant then move into the first chamber  202 . At this time, the vaporized dopant comes in contact with the spherical semiconductors  30 . Diffusion may then occur on the semiconductors. The rotation  216  of the first chamber  202  helps to encourage uniform contact between the vaporized dopant and the spherical semiconductors  30 . Exhaust  172  from the process may be expelled through the outlet  212 . 
     Referring now to FIG. 6, the reference numeral  250  designates, in general, still another embodiment of an apparatus used for the doping of spherical semiconductors. The apparatus  250  includes a chamber  252  having a furnace  204 . The furnace  204  of FIG. 6 is illustrated as a conductive coil, although many types of heaters can be used. The chamber  252  has an inlet port  256  and an opposing outlet port  258 . The chamber  152  also includes a boat  164 , similar to that shown in FIG. 4, for containing a plurality of spherical semiconductors  30 . The apparatus  250  can be used with the method  100 , as described above. 
     The inlet port  256  of the chamber  252  is connected to a dopant sleeve  260  associated with a heater  262 . The dopant sleeve  260  includes a solid dopant material such as Sb 2 O 3 , P 2 O 5 , B 2 O 3 , BN, P, Sb, or SiP 2 O 7 . The solid dopant material may be similar to the dopant material  32  of FIG.  3 . Like the embodiment of FIG. 4, the dopant material from the sleeve  269  and the spherical semiconductors  30  are kept separate from each other. In this way, different processing environments can be maintained in the different chambers  252 ,  210   
     In operation, the dopant material in the sleeve  260  is heated by the heater  262  and vaporizes. A carrier gas  160  moves through the dopant sleeve  260  and associates with the vaporized dopant. The carrier gas and vaporized dopant then move into the chamber  252 . At this time, the vaporized dopant comes in contact with the spherical semiconductors  30 . Diffusion may then occur on the semiconductors. Exhaust  172  from the process may be expelled through the outlet  258 . 
     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.