Abstract:
An arrangement for depositing a film at a bevel edge of a substrate in a plasma chamber. The arrangement includes a gas delivery system for supplying gas into the chamber. The arrangement also includes a pair of electrodes including a movable electrode and a stationary electrode, wherein the substrate is disposed on one of the pair of electrodes. The arrangement further includes a gap controller module configured for adjusting an electrode gap between the pair of electrodes to a gap distance configured to prevent plasma formation over a center portion of the substrate. The gap distance is also dimensioned such that a plasma-sustainable condition around the bevel edge of the substrate is formed. The arrangement moreover includes a heater disposed below the substrate and powered by an RE source, wherein the heater is maintained at a chuck temperature conducive for facilitating film deposition on the bevel edge of the substrate.

Description:
PRIORITY CLAIM 
       [0001]    This application is a continuation of a previously filed patent application entitled “METHODS FOR DEPOSITING BEVEL PROTECTIVE FILM”, filed on Oct. 19, 2010 (application Ser. No. 12,907,149) with an Attorney Docket No. P2052/LMRX-P195, which is incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    In the manufacture of semiconductor products, substrates (e.g.. semiconductor waters) are processed by successively depositing, etching, and polishing various layers to create semiconductor devices. More specifically, plasma-enhanced etching, and wafer bonding have often been employed in these processing steps. 
         [0003]    However, etching processes tend to cat away at the substrate edge or bevel, and wafer bonding processes tend to create negative slopes at the wafers&#39; edge or bevel while exposing bonding materials.  FIGS. 1A-B  and  2 A-B show examples of these problems in via etching and in wafer bonding. 
         [0004]      FIGS. 1A and 1B  demonstrate the problem of etching processes eating away at the substrate edge or bevel in a via etch process.  FIG. 1A  shows a substrate  100  and a substrate edge region  102  prior to etching. In  FIG. 1A , mask  106  remains on substrate  100  after etching. Thickness  110  reflects the original thickness of the substrate prior to etching. 
         [0005]      FIG. 1B  shows a substrate edge region  112  after etching. In  FIG. 113 , area  114  represents the area where the substrate edge or bevel turns into black silicon post-etch. Black silicon is a rough part of the original substrate that has been eaten away by the etchant. Thickness  120  of  FIG. 1B  is substantially less than the original thickness of the wafer, substantially increasing the likelihood of bevel collapse. Furthermore, the black silicon area  114  can trap contamination that may pollute the processing steps in the future. 
         [0006]    To address the bevel collapse problem described above in etching or other type of material removal or punch-through processes, thick protective films or anti-etching sacrificial films at the substrate edge or bevel are used to minimize substrate bevel collapse. Another approach of wafer bevel protection utilizes a process kit known as a shadow ring, which is placed on top of bevel area of the wafer or slightly above the wafer. However, the shadow ring oftentimes introduces tilting, and particle issues. Accordingly, this process requires many stages to define the film at the substrate edge. This is problematic especially if the film deposition at the substrate edge or bevel requires separate special equipments. 
         [0007]      FIGS. 2A-B  illustrate an example of the problem in wafer bonding near the edge or bevel.  FIG. 2A  shows lower wafer  202 , upper wafer  204 , and bonding material  206 . The bonding material is typically some type of organic material. In general, a Chemical Mechanical Polish (CMP) is performed after the wafer bonding process.  FIG. 2B  shows the post-CMP bonded wafers. Specifically, region  220  shows that the bonding material is exposed at the edge or bevel of the wafers. Having exposed bonding material can create side defects and other unpredictable effects, Furthermore, region  220  shows a negative slope near the edge or bevel of the wafers. For a variety of reasons, semiconductor manufacturers may prefer positive slope geometries near the edge of a wafer. The negative slope and the exposed bonding material may present other problems such as undercut issues or delamination issues. 
         [0008]    To address the bevel edge negative slope problem. CMP may be employed to shape the edge or bevel back to a positive slope. However, this solution is costly, and does not solve the problem of the exposed bonding material. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    The present invention is illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings and in which like reference numerals refer to similar elements and in which: 
           [0010]      FIG. 1A  is a schematic view of a substrate edge prior to a via etch. 
           [0011]      FIG. 1B  is a schematic view of a substrate edge post a via etch. 
           [0012]      FIG. 2A  is a schematic view of substrate edges post wafer bonding and prior to a CMP. 
           [0013]      FIG. 2B  is a schematic view of substrate edges post wafer bonding and post-CMP. 
           [0014]      FIG. 3A  shows, in accordance with an embodiment of the invention, a schematic view of substrate edge prior to a via etch using localized film deposition at the substrate edge. 
           [0015]      FIG. 3B  shows, in accordance with an embodiment of the invention, a schematic view of substrate edge post a via etch using, localized film deposition at the substrate edge. 
           [0016]      FIG. 4  shows, in accordance with an embodiment of the invention, a schematic view of substrate edge post wafer bonding and post-CMP using localized film deposition at the substrate edge. 
           [0017]      FIG. 5A  shows, in accordance with an embodiment of the invention, a generic machine for depositing protective film at bevel edge. 
           [0018]      FIG. 5B  shows, in accordance with an embodiment of the invention, a magnified illustration of a ceramic part illustrated in  FIG. 3A . 
           [0019]      FIG. 6  shows, in accordance with an embodiment of the invention, the method steps for creating protective film at bevel edge. 
           [0020]      FIG. 7  shows, in accordance with an embodiment of the invention, a generic machine of  FIG. 3A  plus inductive antennas for in situ cleaning at the bevel edge. 
           [0021]      FIG. 8  shows, in accordance with an embodiment of the invention, the method steps for in situ inductive cleaning, post localized film deposition, 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0022]    The present invention will now he described in detail with reference to a few embodiments thereof as illustrated in the accompanying drawings. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. It will be apparent, however, to one skilled in the art, that the present invention may be practiced without some or all of these specific details. In other instances, well known process steps and/or structures have not been described in detail in order to not unnecessarily obscure the present invention. 
         [0023]    The present invention addresses at least the problems faced in via etching and wafer bonding. The invention relates, in one embodiment, to a method of film deposition using localized plasma to protect the bevel edge of a wafer or wafers in a plasma chamber. The method includes adjusting an electrode gap between a movable electrode and a stationary electrode with a wafer disposed in between. The electrode gap is adjusted to a gap distance configured to prevent plasma formation over a center portion of the wafer, while a plasma-sustainable condition around the wafer&#39;s bevel edge still may be formed. The method also includes flowing deposition gas into the plasma chamber. The method further includes maintaining, using a heater, a chuck temperature that is configured to facilitate film deposition on the bevel edge. The method also includes generating the localized plasma from the deposition gas for depositing a film on the bevel edge. 
         [0024]    The invention relates, in one embodiment, to a method of film deposition using localized plasma to protect the bevel edge of a wafer or wafers. The method includes adjusting the flow of deposition gas into a plasma chamber to a pressure configured to prevent plasma formation over a center portion of the wafer, the pressure also adjusted such that a plasma-sustainable condition around the bevel edge of the wafer is formed after the adjusting. The method also includes maintaining, using a heater, a chuck temperature that is configured to facilitate film deposition on the bevel edge. The method further includes generating the localized plasma from the deposition gas for depositing a film on the bevel edge. 
         [0025]    The invention relates, in one embodiment, to a method of film deposition using localized plasma to protect the bevel edge of a wafer or wafers. The method includes adjusting an electrode gap between a movable electrode and a stationary electrode with the wafer disposed in between. The electrode gap is adjusted to a gap distance configured to prevent plasma formation over a center portion of the wafer, while a plasma-sustainable condition around the bevel edge of the wafer may still be or is formed. The method also includes adjusting the flow of deposition gas into a plasma chamber to a pressure configured to prevent plasma formation over a center portion of the wafer, while a plasma-sustainable condition around the bevel edge of the wafer may still be or is formed. The method further includes maintaining,. using a heater, a chuck temperature that is configured to facilitate film deposition on the bevel edge. The method also includes generating the localized plasma from the deposition gas for depositing a film. on the bevel edge. 
         [0026]      FIG. 3A  illustrates the proposed solution to the via etching problem suggested in  FIGS. 1A and 1B , as applied to a wafer  300  prior to etching. There is also shown a substrate edge area  302 . Hard mask  306  remains on the central region of the wafer, while conformal protective film  308  is deposited on the bevel edge to protect the bevel edge. 
         [0027]      FIG. 3B  illustrates the proposed solution to the via etching problem suggested in  FIGS. 1A and 1B , as applied to a wafer  300  after etching. Here, hard mask  306  remains. The protective film  308  is worn away slightly, protecting the substrate underneath in the bevel edge region  312 . This solves the problem of black silicon forming on the bevel edge, limiting the probability of break off or contaminant trapping. A comparison between  FIG. 3A  and  FIG. 3B  will show that thickness  318  of the substrate edge prior to etching remains approximately the same as thickness  320  of the substrate edge post etching. 
         [0028]      FIG. 4  illustrates the proposed solution to the wafer bonding problem presented in  FIGS. 2A and 213 .  FIG. 4  shows the bonded wafers  400  after the Chemical Mechanical Polish (CMP) process. Lower wafer  402  is bonded by bonding material  406  with upper wafer  414 . Upper wafer  414  is grinded down by CMP, In this situation, most semiconductor manufacturers want to protect the bonding material while creating a positive slope on the edge of the bonded wafers.  FIG. 4  demonstrates how localized conformal film  418  deposited in the bevel edge region  420  may create the desired effects on the edge of the bonded wafers. 
         [0029]      FIG. 5A  illustrates a generalized arrangement for depositing a protective film at the bevel edge of the wafer. Due to the need to deposit a precise conformal film on a challenging bevel edge topology and the need to refrain from depositing elsewhere, specialized equipment is necessary. The arrangement of  FIG. 5A  includes a capacitively coupled chamber  500 . Gas flow control  504  supplies gas or plasma to the edge area of a wafer  502 . Gas flow control  506  supplies gas or plasma to the central area of the wafer  502 . Gas flow may be supplied through liquid gas delivery or vas phase delivery. The two gas flow controls  504  and  506  individually or together may change the differential pressure over the center portion of the wafer as compared to the edge portion of the wafer. The exhaust from the chamber may exit through the exhaust pump  508 . 
         [0030]    Gap  510  represents the distance between the ceramic cover  512  and the wafer  502 . In the present invention, gap  510  is controlled such that the gap is insufficient for plasma formation. For example, a gap no larger than 1 mm cannot sustain plasma formation in sonic cases. The gap itself may be determined empirically based on the particulars of each chamber. Gas supplied by the gas flow controls  504  and  506  is turned into plasma by a RF source  520  that powers heater/chuck  524 . A top electrode  526  is disposed above ceramic cover  512 . Further,  FIG. 5   a  shows wafer  502  disposed above heater/chuck  524 . 
         [0031]    On the edge of the chamber is a grounded upper extended electrode  536  and a grounded lower extended electrode  538 . Liner  540  helps to protect lower extended electrode  538  against deposition. Liner  540  may be formed of a suitable material compatible with the deposition process. RF currents may flow from the heater/chuck  524  through both the upper extended electrode  536  and lower extended electrode  538 , through the chamber wall, and return back to the RF source  520 . Size-controllable ceramic part  550  is disposed next to the heater/chuck  524 . 
         [0032]      FIG. 5B  illustrates the magnified view of the size-controllable ceramic part.  550 . The size of the ceramic part  550  may be adjusted to expose more or less of the under edge of the wafer  502  to the plasma for deposition purpose.  FIG. 5B  illustrates ceramic part  550  and the ceramic cover  512 . If a semiconductor manufacturer wants to deposit more to the backside of the wafer  502  edge, the size of ceramic part  550  may be adjusted. For example, a smaller outer diameter of ceramic part  550  may allow more of the deposition to reach the underside of the bevel edge. The diameter of ceramic cover  512  may also be adjusted to determine the width of the bevel edge film deposition on the upper side of the wafer. For example, a smaller outer diameter of ceramic cover  512  may allow more deposition on the upper outer edge of the bevel. 
         [0033]    Ceramic cover  512  and the top electrode  526  are movable (e.g., up and down) using a robot arm, a bellow, a belt, or other methods in order to allow for gap control. This mechanism is controlled by gap controller circuitry. The gap controller serves to control plasma formation in between the wafer and the top electrode of the chamber. The gap controller also assists in the insertion and the removal of the wafer to and from the plasma chamber. The actual mechanical movement to control the gap may be accomplished by a mechanical actuator, or by bellows, or by a belt-type gear, or the like. 
         [0034]      FIG. 6  shows, in accordance with an embodiment of the invention, the method steps for creating a protective film at the bevel edge. At a first step  652 , the silicon wafer is placed within the chamber via a robot arm mechanism At step  654 , the gap between the upper ceramic cover and the wafer is adjusted to a plasma-inhibiting gap distance to ensure that plasma will not form over the center portion of the water. In an embodiment of the invention, the center portion of the wafer is the portion of the wafer with etched features, or is the part intended to have etched features. In another embodiment of the invention, the center portion of the wafer is the portion of the wafer that is substantially flat. 
         [0035]    At step  656 , liquid or gas phase deposition gas is flowed into the plasma chamber, creating a pressure differential between the center portion of the chamber and the edge portion of the chamber. In an embodiment of the invention, the pressure differential is controlled by multiple gas inlets into the center and the edge portion of the plasma chamber, in an embodiment of the invention, the pressure differential and the specified electrode gap may sustain plasma in the vicinity of the edge region of the wafer, but not in the region between the center portion of the wafer and the upper electrode, The exact pressure differential and electrode gap may be pre-determined through testing, or may be determined real-time by a feedback control system capable of detecting. whether plasma is formed over the center portion of the wafer. The deposition gas used may be a precursor for a dielectric film, a conductor film, an organic film, or any other film used in the semiconductor industry. 
         [0036]    At step  658 , RF-power to the heater and/or the chuck is turned on. At this stage, film deposition plasma should have formed on the bevel edge of the wafer. The heater temperature is controlled, for example, to minimize adhesion stress. At step  660 , RF power and gas flow are turned off. At step  662 , the electrode gap above the wafer is enlarged to facilitate wafer removal. At step  664 , the wafer is removed by the robot arm mechanism. 
         [0037]      FIG. 7  shows, in accordance with an embodiment of the invention, a generalized implementation of  FIG. 3A  plus inductive antennas for in situ cleaning at the bevel edge. The ability to perform in-situ cleaning is an important advantage in improving output. Gap  710  may be adjusted to optimize for cleaning. Localized plasma may be created by RF source  722  energizing coil  724 . In an embodiment, electrode  726  is formed of aluminum. Grounded upper and lower extended electrodes  736  and  738  typically are made from aluminum as well in one or more embodiments. Other materials may also be used for various electrodes. 
         [0038]      FIG. 8  shows, in accordance with an embodiment of the invention, the method steps for in situ inductive cleaning, post localized film deposition. The combination of in-situ inductive cleaning (which creates high density cleaning plasma) in a substantially capacitive chamber provides many advantages. At a first step  852 , the electrode gap above the wafer in the plasma chamber is adjusted to provide space for wafer removal. At step  854 , the electrode gap is adjusted again to a gap distance to govern how much of the cleaning plasma will encroach on the center portion of the plasma chamber. At step  856 , the etchant cleaning gas flows into the plasma chamber. At step  858 , the Transformer-Coupled Plasma (TCP) inductor coils are powered on for a certain period, of time to allow for the cleaning plasma to form and use the cleaning plasma to clean the plasma chamber. At step  860 , the etchant cleaning gas is allowed to exhaust. 
         [0039]    Advantages of the invention include the prevention of bevel collapse and the formation of black silicon on substrate edges during an etching process. Additional advantages include sealing off bonding materials post a wafer-bonding process. This conformal edge film deposition process further allows users to create a positive slope on the edges of two bonded wafers. 
         [0040]    Having disclosed exemplary embodiments and the best mode, modifications and variations may be made to the disclosed embodiments while remaining within the subject and spirit of the invention a defined by the following claims.