Abstract:
An apparatus and method for depositing thin films on the surface of a device such as a spherical shaped devices. The apparatus includes an enclosure containing a plurality of apertures and a conductor coil. The apertures connect to conduits for inputting and outputting the devices as well as injecting and releasing different gases and/or processing constituents. A chamber is formed within the enclosure and is configured to be coaxial with the conductor coil. Devices move through the input conduit where they are preheated by a resistance-type furnace. The preheated devices then move into the chamber where chemical precursors are added and the devices are further heated to a predefined temperature associated with the chemical precursors by radio frequency energy from the conductor coil. At this time, the gases and/or processing constituents react with the heated device thereby growing a thin film on its outer surface.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates generally to semiconductor integrated circuits, and more particularly, to an apparatus and method for fabricating a spherical-shaped semiconductor device. 
     Conventional integrated circuits, or “chips,” are formed from a flat surface semiconductor wafer. The semiconductor wafer is first manufactured in a semiconductor material manufacturing facility and is then provided to a fabrication facility. At the latter facility, several layers are processed onto the semiconductor wafer surface. Once completed, the wafer is then cut into one or more chips and assembled into packages. Although the processed chip includes several layers fabricated thereon, the chip still remains relatively flat. 
     A fabrication facility is relatively expensive due to the enormous effort and expense required for creating flat silicon wafers and chips. For example, manufacturing the wafers requires several high-precision steps including creating rod-form single crystal semiconductor material; precisely cutting ingots from the semiconductor rods; cleaning and drying the cut ingot sections; manufacturing a large single crystal from the ingots by melting them in a quartz crucible; grinding, etching, and cleaning the surface of the crystal; cutting, lapping and polishing wafers from the crystal; and heat processing the wafers. Moreover, the wafers produced by the above processes typically have many defects which are largely attributable to the difficulty in making a single, highly pure crystal due to the above cutting, grinding and cleaning processes as well as due to the impurities, including oxygen, associated with containers used in forming the crystals. These defects become more and more prevalent as the integrated circuits formed on these wafers become smaller. 
     Another major problem associated with modern fabrication facilities for flat chips is that they require extensive and expensive equipment. For example, dust-free clean rooms and precisely-controlled manufacturing and storage areas are necessary to prevent the wafers and chips from defecting and warping. Also, these types of fabrication facilities suffer from a relatively inefficient throughput as well as an inefficient use of the silicon. For example, facilities using in-batch manufacturing, where the wafers are processed by lots, must maintain huge inventories to efficiently utilize all the equipment of the facility. Also, because the wafers are round, and the completed chips are rectangular, the peripheral portion of each wafer cannot be used. 
     Still another problem associated with modern fabrication facilities is that they do not produce chips that are ready to use. Instead, there are many additional steps that must be completed, including cutting and separating the chip from the wafer; assembling the chip to a lead frame which includes wire bonding, plastic or ceramic molding and cutting and forming the leads, positioning the assembled chip onto a printed circuit board; and mounting the assembled chip to the printed circuit board. The cutting and assembly steps introduce many errors and defects due to the precise requirements of such operations. In addition, the positioning and mounting steps are naturally two-dimensional in character, and therefore do not support curved or three dimensional areas. 
     Therefore, due to these and various other problems, only a few companies in the world today can successfully manufacture conventional flat chips. Furthermore, the chips must bear a high price to cover the costs of manufacturing, as well as the return on initial capital and investment. 
     In co-pending U.S. patent application Ser. No. 08/858,004 filed on May 16, 1997, assigned to the same assignee as the present application and hereby incorporated by reference, a method and apparatus for manufacturing spherical-shaped semiconductor integrated circuit devices is disclosed. The present invention is specific to an apparatus and method for efficiently depositing thin films on the surface of the spherical shaped devices. 
     SUMMARY OF THE INVENTION 
     The present invention, accordingly, provides an apparatus and method for efficiently depositing thin films on the surface of a device such as a spherical shaped devices. To this end, one embodiment provides an enclosure containing a plurality of apertures and a conductor coil. The apertures connect to conduits for inputting and outputting the devices as well as injecting and releasing different inert gases and chemical precursors for chemical vapor deposition. A chamber is formed within the enclosure and is configured to be coaxial with the conductor coil. 
     Devices move through the input conduit where they are preheated by a resistance-type furnace. The preheated devices then move into the chamber where the chemical precursors are added for the chemical vapor deposition process. The devices are then further heated to a predefined temperature associated with the chemical precursors, by radio frequency energy from the conductor coil. At this time, the chemical precursors react with the heated device thereby growing a thin film on its outer surface. 
     In one embodiment, the device moves through the chamber responsive to a process gas flowing in a direction opposite to the direction of the device. In this way, the speed of the device through the chamber can be controlled. 
     Several advantages result from the foregoing. For one, the process gases can treat the spheres in several manners including depositing a thin film on the spheres. Also, the spheres can be continuously introduced into the chamber to facilitate a pipeline production process. Further, the method of the present invention can be carried out in a relatively small space, thereby reducing or eliminating the need for a clean room environment. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 illustrates a chemical vapor deposition processor according to one embodiment of the invention; 
     FIG. 2 is a graph illustrating the relationship of the deposition rate of TEOS according to the inverse temperature; 
     FIG. 3 is a graph illustrating the relationship of the deposition rate of TEOS according to the flowrate of TEOS; 
     FIG. 4 is a graph illustrating the relationship of the deposition rate of TEOS according to the flowrate of ozone; 
     FIG. 5 is a graph illustrating the relationship of the growth rate of Si 3 N 4  according to the inverse temperature; and 
     FIG. 6 is a graph illustrating the relationship of the growth rate of Si 3 N 4  according to the flowrate of SiH 4 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIG. 1, the reference numeral  10  designates, in general, one embodiment of a processor for growing a film on a spherical shaped semiconductor device using chemical vapor deposition (“CVD”). Moreover, multiple processes, such as processing a consecutive sequence of devices, is possible by varying parameters described herein. 
     The processor  10  includes an enclosure  12  in the form of a hollow tube having two inlet openings  12   a ,  12   b , one inlet/outlet opening  12   c , and one outlet opening  12   d . The outlet opening  12   c  is located diametrically opposite the inlet opening  12   a  and the outlet opening  12   d  is located diametrically opposite the inlet opening  12   b.    
     One end of a vertically extending inlet conduit  14  registers with the inlet opening  12   a  to allow a supply of devices and carrier gas to be introduced into the enclosure  12 . An electric furnace  16  surrounds an upstream portion of the conduit  14 , the furnace  16  providing radiant heat inside the conduit. An exhaust conduit  18  registers with the opening  12   d  to allow exhaust fumes to be expelled from the enclosure  12 . A cooling conduit  20  registers with the opening  12   b  and allows a cooling gas to be injected into the enclosure  12 . One end of a discharge conduit  22  registers with the opening  12   c  and allows any devices received through the opening  12   a  to exit the enclosure  12 . The opposite end of the discharge conduit  22  registers with a receiver section  24 , which is further connected with a gas and materials conduit  26  for providing gases and/or other process constituents to the enclosure  12 . 
     Imposed within the enclosure  12  is a processing chamber  30  having a tube portion  32  and a funnel portion  34 . The tube portion  32  registers with and interconnects the funnel portion  34  and the discharge conduit  22 . The chamber  30  is coaxial with a coiled electrical conductor  36  that surrounds the outer surface of the enclosure  12 . The coil  36  is connected to a radio frequency (“RF”) generator  38  for creating an RF current and producing RF heating energy inside the chamber  30 . 
     In operation, a plurality of spherical devices  50 , each of a semiconductor material, are introduced into the conduit  14 . The spherical devices  50  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. Included with the spherical devices  50  is a process gas, such as an argon (Ar) carrier gas with CVD constituents. The process gases serve to float the spherical devices throughout the conduit  12  as well as to provide deposition chemicals. As the spherical devices  50  pass through the conduit  14 , they are preheated to 600-800° C. by the resistance-type furnace  16 . This preheating serves to make the surface of the spherical devices  50  more conductive, and thereby more susceptible to receiving RF energy, which enables film growth to take place on the surface of the spherical devices  50  but not on the walls of the enclosure  12 . 
     The spherical devices  50  exit the conduit  14  at the opening  12   a  and descend down (as shown in the figure) towards the chamber  30 . Once the spherical devices  50  enter the funnel portion  34 , they are directed towards the tube portion  32 . Normally, the spherical devices  50  will be spinning due to rotating momentum. After traversing the interior of the chamber  30 , the spherical devices  50  pass through the outlet opening  12   c , through the discharge conduit  22 , and into the receiver  24 . The introduction and discharge of the spherical devices  50  in this manner is controlled to prevent the accumulation of a relatively large number of spherical devices in the chamber  30  at the same time. 
     During this flow of the spherical devices  50  through the chamber  30 , one or more gases, including chemical vapor deposition constituents (collectively CVD precursors  60 ), are introduced from the gas and materials conduit  26 , through the discharge conduit  22 , and into the chamber  30 . In addition, another process gas, such as Ar or N 2 , is introduced into the discharge conduit  26  and the chamber  30 . The Ar or N 2  gas introduced through the discharge conduit  26  mainly serves to float the spherical devices  50  towards the receiver  24 , thereby controlling the rate of descent of the spherical devices through the chamber  30 . 
     During the passage of the Ar gas and CVD precursors  60  through the tube portion  32  of the chamber  30 , the coil  36  is activated by the RF generator  38 . The coil  36  thereby applies the RF energy to the spherical devices  50 . The RF energy is concentrated in the center of the enclosure  12  and hence the center of the coaxial tube portion  32 . As a result, the enclosure  12  is not heated to a great extent and, is further cooled by cooling gas flowing from the cooling conduit  20  through the opening  12   b . The RF generator  38  produces the RF energy at a frequency of more than 10 kHz, which produces a relatively high temperature of about 600-1200° C. It is understood that this frequency and temperature does not generate inductively coupled plasma. 
     The chamber  30  now includes the CVD precursors  60 , the high amount of RF energy, and the plurality of spherical devices  50  moving therethrough. The CVD precursors  60 , in combination with the RF energy from the coil  36 , grow a thin film on the outer surface of the spherical devices  50 . The preheating of the spherical devices  50  makes their outer surface more conductive, which facilitates the deposition. The deposition rate can be controlled by the RF energy from the coil  36  and the descent rate of the spherical devices  50 . 
     A preferred embodiment for an efficient method for depositing SiO 2  films on the surface of spherical shaped devices at a much faster speed will now be described. An inert gas, such as Ar or N 2 , flows through a liquid Tretraethaloxisilane (TEOS) bubbler, which is within the discharge conduit  26 , and delivers TEOS vapor into CVD chamber  30 . Ozone, a CVD precursor  60 , is generated in an ozone generator and is also sent to the CVD chamber  30  via the discharge conduit  26  to catalyze a CVD reaction. The gas stream of TEOS vapor, ozone and carrier gas flows upward and provides suspension to the spherical device. SiO 2  films are formed on the device surface by the chemical reaction of TEOS at a temperature of about 360° C. As shown in FIG. 2, the film growth rate increases as the deposition temperature goes up from 300° C. to 360° C., reaches its highest level at 360° C. and then decreases as the deposition temperature goes up from 360° C. to 400° C. 
     The TEOS delivery rate also has a direct influence on the film growth rate, as shown in FIG.  3 . As seen in the figure, the SiO 2  growth rate improves almost linearly with the TEOS delivery rate. At optimized conditions, the TEOS deposition rate is about one magnitude higher than the conventional semiconductor process. 
     FIG. 4 shows the effect of the ozone flow rate on the film growth rate. The film growth rate increases very quickly as the Ozone flow rate is raised from 2 standard cubic centimeters per minute (sccm) to 100 sccm. As more Ozone is delivered to the system, the film growth rate decreases from 5000 Å/min to 1000 Å/min. 
     A preferred embodiment for efficiently depositing Si 3 N 4  films on the surface of a spherical shaped device at a much faster speed will now be described. A gas stream of inert gas (i.e. N 2  or Ar), SiH 4  and NH 3  flows through the discharge conduit  26  and provides the spherical device with suspension and rotation. Uniform Si 3 N 4  film can be deposited on the device surface at high speed by chemical reaction of SiH 4  with NH 3  at a temperature of about 750° C. 
     Now referring to FIG. 5, at the deposition temperature of about 675° C. to 815° C., the film growth rate shows an exponential increase with the temperature, which may indicate that the overall film growth rate is controlled by the surface reaction. As the deposition temperature enhances, the film deposition rate shows almost no dependence with the temperature in the range of 815° C. to 900° C. However, the Si 3 N 4  growth rate then decreases when the deposition temperature exceeds 900° C. 
     In addition, as shown in FIG. 6, the film growth rate shows a linear increase with the SiH 4  delivery rate. 
     It is understood that several variations may be made in the foregoing. For example, the invention is not limited to the specific orientation of the various inlet and outlet conduits relative to the processor  10  described above. Thus the spherical devices  50  and the gases can travel in a direction through the chamber  30  other than a vertical and horizontal direction, respectively, as described above. Also the shape of the chamber  30  can be changed to facilitate different requirements. Other modifications, changes and substitutions are 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.