Abstract:
A system and method for uniform deposition of material layers on wafers in a rotating disk chemical vapor deposition reaction system is provided, wherein a plurality of wafers are rotated on a susceptor at a first rate around a first axis by a first motor, and the plurality of wafers rotate independently exhibiting planetary motion at a second rate through application of a vibrational force from a vibration source in a direction transverse to the first axis of rotation.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    In chemical vapor deposition systems, uniform deposition on wafer surfaces is of prime importance. In a typical chemical vapor deposition system, one or more wafers is placed in a wafer carrier, and the carrier is placed in a reaction chamber for deposition. The wafer carrier may be heated by, for example, placing it on a susceptor, and reaction gases are provided into the reaction chamber via gas inlets, gas showerheads, and the like to initiate the growth of material layers on the wafers. 
         [0002]    In order to improve uniformity of deposition, numerous methods have been employed. For example, various modified gas showerheads, rotating susceptors and wafer carriers, modified wafer carrier shapes, and different reaction chamber shapes, have been proposed or used in order to increase deposition uniformity. While each of these methods has met with varying degrees of success, additional improvement in the uniformity of deposition layer growth on the surface of each wafer is desired. 
         [0003]    Chemical vapor deposition systems in which the wafer carrier is rotated tend to increase deposition uniformity. In systems with wafer carriers holding multiple wafers, some systems have been modified to attempt to rotate the wafer carrier on which the wafers are seated at a first rate, while rotating the wafers around themselves (within their wafer seat) at a second rate, thus creating planetary motion of the wafers in the wafer carrier. Such systems have been suggested using planetary gear systems, motor drivers rotating the wafer carrier and the wafers placed thereon, unusual wafer carrier configurations which cause wafer movement therein, or application of gases to the wafers held in the wafer carrier via gas channels in the wafer carrier in order to induce wafer movement. 
         [0004]    Each of these systems has drawbacks, however. Complex gear and motor systems in the wafer carrier itself may be difficult to maintain because the wafer carrier is subjected to reactant gases, heat, and rotational forces. Thus cleaning the wafer carrier is made more complex, and the usable lifetime of the mechanics of the system may be negatively impacted. 
         [0005]    Similarly, gas channels in the wafer carrier to induce wafer movement, and unusual wafer carrier shapes to induce wafer carrier movement, require additional cleaning and care due to their complexity. More importantly, extra application of gas to the wafer from the wafer carrier, or unusual wafer carrier shapes, might adversely affect the integrity of the wafer structure without substantially improving uniformity of deposition. 
         [0006]    Thus, what is needed is a system to improve deposition without the maintenance, complexity and performance drawbacks of present systems. 
       SUMMARY OF THE INVENTION 
       [0007]    In one embodiment, a wafer treatment system is disclosed, comprising: a reaction chamber, a wafer carrier mounted within the chamber for rotation therein about an axis, the wafer carrier adapted to carry a plurality of wafers, a drive for rotating the wafer carrier around the axis, a vibration source vibrationally coupled to the wafer carrier for transferring an oscillatory force to the carrier substantially transverse to the axis, such that the plurality of wafers placed in the carrier exhibit planetary motion. 
         [0008]    In one embodiment, a method for treating wafers is disclosed, comprising: rotating a wafer carrier at a first rotational rate around an axis, applying an oscillatory force substantially transverse to the axis to the wafer carrier so that a plurality of wafers placed in the wafer carrier exhibit planetary motion, and treating the plurality of wafers. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  provides a side representation of one embodiment of a wafer treatment system of the present invention. 
           [0010]      FIG. 2  provides an overhead representation of one embodiment of a wafer carrier for use with the present invention. 
           [0011]      FIG. 3  provides a cross-sectional representation of one embodiment of a wafer compartment of a wafer carrier for use with the present invention. 
           [0012]      FIG. 4  provides a cross-sectional representation of one embodiment of a wafer compartment of a wafer carrier for use with the present invention. 
           [0013]      FIG. 5  provides a side representation of one embodiment of a wafer treatment system of the present invention. 
           [0014]      FIG. 6  provides a cross-sectional representation of one embodiment of a wafer treatment system of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0015]      FIG. 1  provides a side representation of one embodiment of a wafer treatment system of the present invention. A reaction chamber  100  includes a wafer carrier  110  placed therein. The wafer carrier  110  includes a plurality of wafer compartments  120  in which a plurality of wafers  125  are placed. The wafer carrier  110  is seated on a susceptor  130 , which transmits heat to the wafer carrier  110  from heating elements  140 . The susceptor  130  and wafer carrier  110  are seated on a spindle  150 . Above the wafer carrier, a flange  160  provides one or more reaction gases  165  to the reaction chamber  100  for deposition processes to be performed on the wafers  125 . Reaction gases leave the reaction chamber  100  via exhaust outlets  170 . As shown in more detail in  FIG. 2 , which provides an overhead representation of one embodiment of a wafer carrier for use with the present invention, the first motor  180  provides primary rotation to the spindle  150  and wafer carrier  110  placed thereon. The vibration source  190  provides a transverse vibration force to the spindle  150  and wafer carrier  110 , which is communicated to individual wafers  125 , inducing planetary motion in the wafers  125 . 
         [0016]    In particular, the spindle  150  is rotated by a first motor  180  around a central axis of the spindle (α) at a first rate (β). The spindle  150  communicates the rotation to the susceptor  130  and wafer carrier  110 . 
         [0017]    A vibration source  190 , preferably a piezoelectric motor, is also in physical contact with the spindle  150 . The vibration source  190  communicates an oscillatory vibration (γ) substantially transverse to the central axis (α) of rotation of the spindle  150  and first motor  180 . This transverse vibration (γ) is communicated through the spindle  150  and susceptor  130  to the wafer carrier  110 . At the wafer carrier  110 , the transverse vibration (γ) induces planetary motion of the plurality of wafers  125  held in the wafer compartments  120  of the wafer carrier  110 . This planetary motion is typically exhibited as the rotation of each wafer around its own central axis (δ) at a second rate (ε) distinct from the first wafer carrier  110  central axis (α) and the wafer carrier  110  first rate of rotation (β). 
         [0018]    Preferably, although it is not required, if the spindle  150  extends outside of the reaction chamber  100 , then both the vibration source  190  and the first motor  180  are preferably located outside of the main reaction chamber  100  and communicate their respective rotational and vibrational energy to the wafer carrier  110  in the reaction chamber  100  through the spindle  150  which extends therethrough. 
         [0019]      FIG. 3  provides a cross-sectional representation of one embodiment of a wafer compartment of a wafer carrier  300  for use with the present invention. One wafer carrier  310  for use with the present invention includes a plurality of wafer compartments  320  with sides  330  and a base  340 . The base  340 , in this embodiment, includes vertical dimples  350 . When a wafer  360  is placed therein, the wafer  360  is seated on the vertical dimples  350 . 
         [0020]      FIG. 4  provides a cross-sectional representation of one embodiment of a wafer compartment of a wafer carrier  400  for use with the present invention, with at least a top surface  410  and a bottom surface  415 . The top surface  410  of the wafer carrier  400  includes a plurality of wafer compartments  420  with sides  430  and a base  440 . The base  440  includes a nonlinear surface  450 , such that when a wafer  460  is placed therein, the wafer  450  is not in contact with the entirety of the base  440 , and particularly is not in contact with at least part of the nonlinear surface  450 . 
         [0021]      FIG. 5  provides a side representation of one embodiment of a wafer treatment system of the present invention, where the vibration source  190  itself rotates around said central axis (α) at a third rate (ζ) via a third motor  500 . The vibration source  190  may be placed on a platform  510 , a rotating arm, or another device or mechanism through which it rotates around the spindle  150 . 
         [0022]      FIG. 6  provides a cross-sectional representation of one embodiment of a wafer treatment system of the present invention. A wafer carrier  600  with a top surface  610  and a bottom surface  615  includes a plurality of wafer compartments  620  in the top surface  610  of the wafer carrier  600 . The bottom surface  615  of the wafer carrier  600  is seated on a platform  630 . Each wafer compartments  620  in the wafer carrier  600  includes at least sides  640  and a base  650 . Preferably, the base  650  of the wafer compartments  620  includes a nonlinear surface  660  on which a wafer (not shown) is seated when placed in the wafer compartments  620 . A vibration source  670 , preferably a piezoelectric motor, is placed in vibrational contact with the platform  630 , thereby communicating vibrational energy from the source  670  through the platform  630  to the wafer carrier  600  and any wafers placed therein. 
         [0023]    In one experimental test, vibrations were created using a magnetic bearing feedback system with a standard vacuum pump drive, two radial bearings separated by approximately six inches, an axial bearing and an integral rotary drive. Two frequency generators (Hewlett Packard) were employed to supply independent oscillations to drive the magnetic bearing feedback systems. For testing, 180 mm wafer carriers composed of graphite, molybdenum, and aluminum were employed. The graphite and molybdenum wafer carriers each had a single symmetric ring of six wafer compartments, where each compartment held a two inch diameter wafer. The aluminum carrier held a single two inch diameter wafer. 
         [0024]    Frequency and amplitude were varied on each axis independently, and in combination, with the following results: 
         [0000]    
       
         
               
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                 Carrier Type 
                 Vert. Freq. 
                 Horiz. Freq. 
                 Wafer Rotation 
               
               
                   
               
             
             
               
                 Molybdenum (6) 
                  19 Hz 
                 728 Hz 
                 ~0.3–0.5 Hz 
               
               
                 Graphite (6) 
                  28 Hz 
                 783 Hz 
                 ~0.3–0.5 Hz 
               
               
                 Aluminum (1) 
                 230 Hz 
                 455 Hz 
                     ~1 Hz 
               
               
                 Aluminum (1) 
                 450 Hz 
                 446 Hz 
                     ~1 Hz 
               
               
                   
               
             
          
         
       
     
         [0025]    Vibration frequency was found to have more significant effect than amplitudes. While vibration amplitudes were tested from 50 microns to 200 microns, little change was observed over this range. In contrast, a change of ±1 Hz was found to significantly effect rotation, such that a change of ±2 Hz from the greatest amount of wafer rotation would stop wafer rotation. In experimental setups, secondary rotation of the wafer carrier itself was found to impede wafer rotation above a wafer carrier rotation speed of about 150 RPM for multiple wafer carriers such as the Molybdenum and Graphite wafer carriers tested. For single wafer carriers, independent wafer rotation continued through 1000 RPM, the highest sped tested. In testing, wafers with clean smooth bottom surfaces were found to rotate more freely than those with dirty or pitted bottom surfaces, but textures of the bottom surface of the wafer carrier itself did not appear to have a significant effect on rotation of the wafers. Finally, at very high amplitudes, the wafer carrier itself begins to demonstrate secondary rotation (akin to precession) independent of primary wafer carrier rotation. 
         [0026]    Mixing of process gas at the wafer surface may be advantageously enhanced by enforcing planetary motion of the wafer through vibrational forces. Moreover, planetary motion of a wafer may be enforced by varying vibrational forces over time (rather than constant vibrational forces at the same frequency). In particular, a pattern of vibrations at set intervals, say, for example, a 50 RPM jerk (change in acceleration) in rotational speed at frequent intervals may cause a rotation that would result in advantageous planetary motion of wafers. Similarly, temporarily and briefly reducing wafer carrier rotation speed to below 150 RPM while applying vibrational forces to the wafer carrier may be sufficient for inducing sufficient planetary motion in wafers. 
         [0027]    As shown in  FIGS. 3 and 4 , above, dimples in the edge of the wafer compartments may change the frictional relationship between the wafer and the wafer carrier to assist in bringing about wafer vibration and wafer carrier rotation rates above 150 RPM, and other pocket shapes for the wafer compartment may bring about a similar effect. 
         [0028]    Although the invention herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims.