Abstract:
Embodiments of the present invention provide apparatus and method for processing a substrate with increased uniformity. One embodiment of the present invention provides an apparatus for processing a substrate. The apparatus comprises a chamber body defining a processing volume, a substrate support disposed in the processing volume, a showerhead disposed in the processing volume opposite to the substrate support, and a plasma generation assembly configured to ignite a plasma from the processing gases in the processing gas in the processing volume. The showerhead is configured to provide one or more processing gases to the processing volume. The showerhead has two or more distribution zones each independently controllable.

Description:
BACKGROUND 
       [0001]    1. Field 
         [0002]    Embodiments of the present invention generally relate to method and apparatus for processing a semiconductor substrate. More particularly, embodiments of the present invention provide method and apparatus for processing a semiconductor substrate with improved uniformity. 
         [0003]    2. Description of the Related Art 
         [0004]    When processing substrates in a plasma environment, the uniformity of the plasma will affect the uniformity of processing. For example, in an etching process, more material is likely to be removed or etched from the substrate near the center of the substrate as compared to the edge of the substrate when plasma of the processing gases is greater in the area of the chamber corresponding to the center of the substrate. Similarly, if the plasma is greater in the area of the chamber corresponding to the edge of the substrate, more material may be removed or etched from the substrate at the edge of the substrate compared to the center of the substrate 
         [0005]    Non-uniformity in plasma processes can significantly decrease device performance and lead to waste because the deposited layer or etched portion is not consistent across the substrate. 
         [0006]    Excellent process uniformity has become increasingly important as semiconductor devices become continuously more complex. Uniformity is important in both the feature-scale (&lt;1 micron) and the wafer-scale (300 mm). Non-uniformities arise from a variety of reasons, for example variation of concentration of different ingredients of a processing gas, such as etching and passivating species, ion bombardment flux and energy, and temperature within the feature profile and across the wafer. 
         [0007]    One of the non-uniformities observed is CD (critical dimension) bias edge roll-off. CD bias refers to the difference between the critical dimension of a feature before and after processing. CD bias edge roll-off refers to decrease of CD bias toward an edge of a substrate compared to CD bias near a central region of the substrate. 
         [0008]      FIG. 1  schematically illustrates a CD bias edge roll-off of a hard mask etching process in a gate etching application.  FIG. 1  demonstrates a critical dimension from bottom measurement of isolated features across a radius of a substrate after etching. The x-axis of  FIG. 1  indicates a distance from the center of the substrate, and the y-axis indicates a critical dimension measurement. The CD bias edge roll-off is obvious from the decrease of the critical dimension measurement from 110 mm to 150 mm, i.e. towards the edge of the substrate. Additionally,  FIG. 1  also illustrates non-uniformity near a center of the substrate where the critical dimension measurements are lower than a middle section of the substrate. 
         [0009]    Traditionally, non-uniformity during etch, such as the CD bias edge roll-off shown in  FIG. 1 , is controlled by maintaining a temperature gradient across the substrate using heaters in the substrate support. However, in most applications, adjusting the substrate temperature gradient is still an inadequate method to tune the CD bias edge roll-off. 
         [0010]    Therefore, there is a need for apparatus and method for processing a semiconductor substrate with reduced CD bias edge roll-off and other non-uniformity. 
       SUMMARY 
       [0011]    Embodiments of the present invention generally provide apparatus and methods for processing a semiconductor substrate. Particularly, the embodiments of the present invention provide apparatus and method for processing a substrate with increased uniformity. 
         [0012]    One embodiment of the present invention provides an apparatus for processing a substrate comprising a chamber body defining a processing volume, a substrate support disposed in the processing volume, a showerhead disposed in the processing volume opposite to the substrate support, wherein the showerhead is configured to provide one or more processing gases to the processing volume, the showerhead has two or more distribution zones each independently controllable, and a plasma generation assembly configured to ignite a plasma from the processing gases in the processing gas in the processing volume. 
         [0013]    Another embodiment of the present invention provides a method for processing a substrate comprising positioning the substrate on a substrate support disposed in a plasma chamber, flowing a first processing gas towards a top surface of the substrate, flowing a second processing gas towards an edge region of the substrate, wherein the first processing gas and the second processing gas are different, and striking a plasma of the processing gases in the plasma chamber. 
         [0014]    Yet another embodiment of the present invention provides a method for adjusting process uniformity in an etching process comprising positioning a substrate on a substrate support disposed in a plasma chamber, flowing processing gases to the plasma chamber, wherein flowing the processing gases comprises flowing a first processing gas towards a central region of the substrate being processed at a first flow rate, flowing the first processing gas towards a region radially outwards the central region of the substrate at a second flow rate, and flowing a second processing gas towards an edge region of the substrate, and generating a plasma of the processing gases in the plasma chamber. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]    So that the manner in which the above recited features of embodiments of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments. 
           [0016]      FIG. 1  (prior art) schematically illustrates a CD bias edge roll-off of a hard mask etching process in gate etching application. 
           [0017]      FIG. 2  is a schematic sectional side view of a plasma chamber in accordance with one embodiment of the present invention. 
           [0018]      FIG. 3  is a schematic top of a showerhead for a plasma chamber in accordance with one embodiment of the present invention. 
           [0019]      FIGS. 4A-4B  illustrate results of a method for reducing CD bias edge roll-off in accordance with one embodiment of the present invention. 
           [0020]      FIGS. 5A-5B  illustrate results of a method for improving CD bias uniformity across a substrate in accordance with one embodiment of the present invention. 
           [0021]      FIGS. 6A-6B  illustrate effects of adjusted spacing on CD bias uniformity. 
       
    
    
       [0022]    To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that elements disclosed in one embodiment may be beneficially utilized on other embodiments without specific recitation. 
       DETAILED DESCRIPTION 
       [0023]    Embodiments of the present invention generally provide apparatus and method for improving process uniformity. More particularly, the embodiments of the present invention provide apparatus and method for CD bias uniformity and edge roll-off. In one embodiment, a multi-zone showerhead is used for an etching process. In one embodiment, additional passivating gas is supplied to a plasma chamber from an outermost zone of the multi-zone showerhead while processing gas comprising both etching gas and passivating gas is supplied from one or more inner zones of the showerhead. Edge roll-off may be reduced by adjusting the passivating gas provided from the outermost zone of the showerhead. The overall CD bias uniformity may be adjusted by adjusting a ratio of flow rates among one or more inner zones of the showerhead. In another embodiment, the CD bias may be adjusted by adjusting spacing between the substrate and the showerhead. 
         [0024]      FIG. 2  is a schematic sectional side view of a plasma reactor  200  in accordance with one embodiment of the present invention. The plasma reactor  200  comprises a processing chamber  202  configured to process a substrate  204  therein. 
         [0025]    The processing chamber  202  comprises a chamber wall  228 , a chamber bottom  227 , and a chamber lid  229 . The chamber wall  228 , chamber bottom  227 , and the chamber lid  229  define a processing volume  218 . 
         [0026]    A substrate support  206  is disposed in the processing volume  218  configured to support the substrate  204  during processing. The substrate support  206  may move vertically and rotate about a central axis driven by a moving mechanism  262 . In one embodiment, the substrate support  206  may be a conventional electrostatic chuck that actively holds the substrate  204  during processing. 
         [0027]    In one embodiment, the substrate support  206  may be temperature controlled by a temperature controller  261  adapted to cool and heat the substrate support  206  to a desired temperature. The temperature controller  261  may use conventional means, such as embedded resistive heating elements, or fluid cooling channels that are coupled to a heat exchanger. 
         [0028]    A showerhead  208  is disposed in the processing volume  218  through the chamber lid  229 . The shower head  208  is disposed opposite the substrate support  206  and is configured to provide one or more processing gases to the processing volume  218  through a plurality of holes  209 . 
         [0029]    In one embodiment, the showerhead  208  may have multiple zones each configured to deliver processing gases to a certain area of the processing volume  218  and certain area of the substrate  204 . Each of the multiple zones may be independently connected to the gas source  212 , thus, allowing control of gas species and flow rate provided to different areas of the processing volume  218 . 
         [0030]    In one embodiment, the showerhead  208  may have multiple zones arranged in a concentric manner. As shown in  FIG. 2 , the showerhead  208  has an inner zone  230  corresponding to a central region of the substrate support  206 , an edge zone  232  corresponding to an edge region of the substrate support  206 , and a middle zone  231  radially outwards from the inner zone  230  and inwards from the edge zone  232 . Each of the inner zone  230 , middle zone  231  and edge zone  232  is independently connected to the gas source  212 . 
         [0031]    The gas source  212  may be a gas panel with multiple outputs each adapted to output an independent flow of an independent combination of species. A system controller  213  may be used to control flow rate and ratio of species provided from the gas source  212  to the inner zone  230 , middle zone  231  and edge zone  232 . 
         [0032]    During processing, a plasma is generated within the processing volume  218  by a plasma generating assembly to process the substrate  204 . In one embodiment, the plasma generating assembly may include a capacitor having the showerhead  208  and the substrate support  206  as electrodes. In one embodiment, a RF (radio frequency) power source  235  may be connected to the substrate support  206  through an impedance match network  234 , and the showerhead  208  is grounded. A plasma may be generated in the processing volume  218  between the showerhead  208  and the substrate  204  when a RF power is applied to the substrate support  206 . 
         [0033]    It should be noted that other configurations of plasma may be applied, for example, a capacitive plasma generator with a RF power source applied to the showerhead  208  and the substrate support  206  is grounded, a capacitive plasma generator using electrodes other than the showerhead  208  and the substrate support  206 , an inductively coupled plasma generator, or a combination of capacitive and inductive plasma generator. Inductive coils may be disposed above the showerhead  208  of the plasma reactor  200  for generating inductively coupled plasma. Exemplary inductive coupled plasma generator may be found in U.S. patent application Ser. No. 11/960,111, entitled “Apparatus and Method for Processing a Substrate Using Inductively Coupled Plasma Technology,” which is incorporated herein by reference. 
         [0034]    The showerhead  208  of the plasma reactor  200  is configured to adjust performance across the substrate  204  by adjusting flow rate and gas species supplied to different regions over the substrate  204 . 
         [0035]      FIG. 3  is a schematic bottom view of the showerhead  208  for the plasma reactor  200  of  FIG. 2 . The showerhead  208  has a substantially circular bottom surface  208   a  configured to be disposed opposite the substrate support  206  in a parallel manner. The plurality of the holes  209  connects with the gas source  212  through different gas passages. In this configuration, the holes  209  are distributed in the inner zone  230 , the middle zone  231  and the edge zone  232 . The holes  209  within each of the zones  230 ,  231 ,  232  are connected respectively to an output of the gas source  212 . 
         [0036]    Even though the showerhead  208  described here has three concentric zones for independent gas control, other arrangements, for example, more or less concentric zones, zones of different shapes, may be used for the same purpose. 
         [0037]    Embodiments of the present invention provide method for improving process uniformity across a substrate. The method comprises one of adjusting flow rates to different regions of a processing chamber, adjusting components in the processing gas supplied to different regions, adjusting spacing between electrodes of a capacitive plasma generator, or combinations thereof. 
         [0038]      FIGS. 4-6  illustrate results from examples of plasma etching processes incorporated with embodiments of the present invention. The examples discussed below are hard mask etching process performed in a capacitive coupled plasma reactor having a showerhead with three zones, similar to the plasma reactor  200  of  FIG. 2 . 
         [0039]    The etching process is generally performed by positioning a substrate to be etched in a plasma chamber, flowing a processing gas into the chamber, and etching the substrate by generating a plasma of the processing gas in the plasma chamber. The processing gas generally comprises an etching gas and a passivating gas mixed in a certain ratio. The processing gas may also comprise a carrier gas. The etching gas may be CF 4 , C 2 F 6 , C 4 F 8 ,Cl 2 , BCl 3 , CCl 4 , NF 3 , SF 6 , HBr, BBr 3 , C 2 F 2 , O 2 , H 2 , CH 4 , COS SO 2 , and combinations thereof, depending on the material to be etched. The passivating gas may comprise CHF 3 , CH 2 F 2 , CH 3 F, SiCl 4 , HBr, and the combinations thereof, depending on the material to be etched and the etching gas used. The carrier gas may be any inert gas, such as Ar, He, N2, and combinations thereof. It is to be appreciated that other suitable etching gases and passivating gases can also be used. 
         [0040]    The examples listed below use a capacitively coupled CF 4 /CHF 3  plasma to etch a silicon nitride hard mask, wherein CF 4  acts as etching gas and CHF 3  acts as passivating gas. The processing gas, CF 4  and CHF 3  in this case, is distributed to the chamber through a tri-zone showerhead. Flow rates, gas ratio, and spacing may be adjusted to adjust CD bias result across the substrate. 
         [0041]    The showerhead used in the examples has three zones. Zone  1  covers a circular region of about 3.36 inch in diameter corresponding to a central region of the substrate being processed. Zone  2  covers a circular region with an inner diameter of about 3.36 inch and an outer diameter of about 7.68 inch. Zone  3  covers a circular region with an inner diameter of about 7.68 inch and an outer diameter of about 12 inch. 
         [0042]    It has been observed that chemical etching processes exhibit a significant loading effect resulting from the depletion of active etching species by reaction with the film being etched. Thus, the etch rate depends on the etchable area either on the feature-scale (microloading) or on the substrate-scale (macroloading). On the feature-scale, microloading is brought about by differences in the feature dimension and pattern density. For example, isolated features etch at a different rate than dense features. Therefore, macroloading and microloading tunability is an essential requisite to a successful etching process. Thus, examples below are performed on both substrates with isolated features and substrates with dense features to examine macroloading and microloading tunability. 
         [0043]      FIGS. 4A-4B  illustrate results of a method for reducing CD bias edge roll-off by supplying additional passivating gas to an edge region of the substrate in accordance with one embodiment of the present invention. 
       EXAMPLE 1 
       [0044]      FIGS. 4A-4B  illustrate effects of varying passivating gas flow in Zone  3  while the other processing parameters remain the same.  FIG. 4A  shows CD bias results for etching on substrates having isolated features.  FIG. 4B  shows CD bias results for etching on substrates with densely packed features. 
         [0045]    The following illustrates an exemplary etching process with the following parameters:
   Temperature: about 60° C.   Chamber pressure: about 90 mTorr   Spacing: about 2.3 inch (the distance between shower head and substrate being processed, as shown by distance  233  of  FIG. 2 )   RF power: about 500 W and 60 MHz   Flow rates in Zone  1 : 300 sccm of CF 4 , 220 sccm of CHF 3      Flow rates in Zone  2 : 0 sccm of CF 4 , 0 sccm of CHF 3      Flow rates in Zone  3 : 0 sccm of CF 4 , 10/50/100 sccm of CHF 3      
 
         [0053]    As shown in  FIGS. 4A-4B , edge roll-off is reduced by supplying additional passivating gas CHF 3  to Zone  3  for both substrates with isolated features and dense features. Substrates with dense features are more susceptible to edge roll-off. The edge roll-off can be substantially eliminated by flowing 100 sccm passivating gas to Zone  3 . 
         [0054]    Even though only the passivating gas is supplied near the edge region in Example 1, any adjustment to provide additional passivating gas near the edge region may be applied. For example, both etching gas and passivating gas may be supplied to all regions of the substrate, only a higher ratio of passivating gas is supplied near the edge compared to the central region of the substrate. 
         [0055]      FIGS. 5A-5B  illustrate results of a method for improving CD bias uniformity across a substrate by tuning ratio of flow rates among regions of the substrate in accordance with one embodiment of the present invention. 
       EXAMPLE 2 
       [0056]      FIGS. 5A-5B  illustrate effects of varying ratio of flow rates between Zone  1  and Zone  2  while the other processing parameters remain the same.  FIG. 5A  shows CD bias results for etching on substrates having isolated features.  FIG. 5B  shows CD bias results for etching on substrates with densely packed features. 
         [0057]    The following illustrates an exemplary etching process with the following parameters:
   Temperature: about 60° C.   Chamber pressure: about 90 mTorr   Spacing: about 2.3 inch   RF power: about 500 W and 60 MHz   Flow rates in Zone  1 : 300*x sccm of CF 4 , 220*x sccm of CHF 3      Flow rates in Zone  2 : 300*(1−x) sccm of CF 4 , 220*(1−x) sccm of CHF 3 , x=1, 1/3, 1/3.5   Flow rates in Zone  3 : 0 sccm of CF 4 , 100 sccm of CHF 3      
 
         [0065]    As shown in  FIGS. 5A-5B , CD uniformity is improved by adjusting flow ratio of Zone  1  and Zone  2  for both substrates with isolated features and dense features. Thus, CD uniformity may be improved by adjusting ratio of flow rates of processing gas to different regions of a substrate. Particularly, CD uniformity may be improved by adjusting ratio of flow rate along a radius of a substrate being processed. 
       EXAMPLE 3 
       [0066]      FIGS. 6A-6B  illustrate effects of adjusted spacing on CD bias uniformity while the other processing parameters remain the same.  FIG. 6A  shows CD bias results for etching on substrates having isolated features.  FIG. 6B  shows CD bias results for etching on substrates with densely packed features. 
         [0067]    The following illustrates an exemplary etching process with the following parameters:
   Temperature: about 60° C.   Chamber pressure: about 90 mTorr   Spacing: about 2.3 inch/5.0 inch   RF power: about 500 W and 60 MHz   Flow rates in Zone  1 : 86 sccm of CF 4 , 63 sccm of CHF 3      Flow rates in Zone  2 : 214 sccm of CF 4 , 146 sccm of CHF 3      Flow rates in Zone  3 : 0 sccm of CF 4 , 100 sccm of CHF 3      
 
         [0075]      FIGS. 6A-6B  illustrate that CD bias may be changed evenly across the substrate by changing the spacing. Substrates with dense features are less responsive to the change of spacing compared to substrates with isolated features. Edge areas are slightly less responsive to the change of spacing. 
         [0076]    The approaches illustrated in Examples above may be combined to achieve a desired processing profile across a substrate. Additionally, a desired processing profile may be any profiles depending on a process, for example, a uniform profile, an edge weak profile (where edge areas are processed less than central areas), or an edge strong profile (wherein edge areas are processed more than central areas). 
         [0077]    Even though an etching process is described in accordance with embodiments of the present invention, embodiments of the present invention may be applied to improve uniformity across a substrate for any suitable processes, for example deposition and implantation. 
         [0078]    While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.