Patent Publication Number: US-2005133165-A1

Title: Apparatus for the prevention of arcing in a CVD-TiN chamber

Description:
BACKGROUND OF THE INVENTION  
      (1) Technical Field  
      This invention relates generally to semiconductor processes and more particularly to improvements to vapor deposition equipment for the prevention of high energy arcing causing particulate contaminants to settle on semiconductor substrates during deposition of titanium nitride.  
      2. Description of the Prior Art  
      The fabrication of integrated circuit devices is a complex manufacturing process-involving hundreds of steps that must be executed with great precision. In simplified terms, making devices involves three basic operations: deposition, patterning and etching. These and other processes are repeated many times on a silicon base substrate resulting in the buildup of microscopically thin layers of materials. In the process of building these layers, thousands or millions of transistors are created and interconnected. When the process is complete, a single silicon base substrate will contain hundreds of individual devices that are then diced into separate device entities, tested for their electrical properties, packaged and assembled.  
      During the forming of these well-defined integrated circuit structures, it has become increasingly important to construct line widths measuring in the sub micron and nanomicron ranges. Advances in circuit packaging generally include reducing the size of components that form these integrated circuit structures. With smaller circuit components, the value of each unit area on a silicon base substrate becomes higher because the ability to use all of the substrate area for circuit components improves. To properly form an integrated circuit with advanced circuit designs that use higher percentages of the substrate area for smaller components, it is critical that defect counts on a semiconductor substrate be reduced below levels, which were previously acceptable for many circuit designs. For example, minute particles of less than 0.2 microns are unacceptable for many of the current advanced circuit designs. This is because the small particles or defects can damage the integrated circuit by shorting out two or more circuit lines or by cutting or otherwise impairing the operation of these circuits.  
      Thin film deposition techniques occupy an advantageous position among current technologies. The established processes remain efficient for many applications, while newer ones are evolving rapidly based on customer requirements and evolutionary technology. Tools are customized for sophisticated and often difficult applications. This rapid movement involves significant challenges. Manufacturers express an increasing need to deposit films, on larger substrates, that are free from contaminates.  
      Applied Materials, Inc., a leader in making semiconductor equipment, provides an integrated CVD/PVD (chemical and physical vapor deposition) system. The Liner TxZ Centura designed for the metallization of devices with 0.35-micron and under line widths, combines a CVD titanium nitride chamber with a PVD titanium chamber on a Centura/Endura platform. It enables chip producers to deposit sequential layers of Ti and CVD TiN without worrying about the growth of unwanted oxide between processing steps.  
      Referring to  FIGS. 3 and 4 , of the prior art, a significant limitation of existing CVD-TiN (TxZ) processing equipment relates to a conductive strap  26  and isolator rings  23 ,  24 . The conductive strap electrically connects a substrate heater platform  21  to an annular housing  22 , also known as an edge ring. A potential difference build-up between the substrate heater platform and the annular housing  22  generates a spark discharge between a gap separating the inner periphery of the annular housing and the periphery of the heater platform. The spark forms a cloud of particulate contaminate that land on the substrate. This problem has always been a major issue that impacts product quality and throughput.  
     SUMMARY OF THE INVENTION  
      The present invention has been accomplished in view of the above mentioned problems. That is therefore a primary object of the present invention to prevent particulate contaminates from being formed and landing on semiconductor substrates during vapor deposition of TiN in a CVD-TXZ chamber.  
      Another object of the present invention has been to eliminate a spark discharge in the vicinity of the semiconductor substrate.  
      Still another object of the present invention has been to increase CVD-TiN utilization by reducing down time needed for machine maintenance.  
      Yet another object of the present invention has been to improve product quality and throughput during vapor deposition of TiN.  
      These objects have been achieved by a design modification of an conductive strap and isolation rings so that the potential difference is reduced and any cumulative electric charge build-up would pass through the bottom of the isolation rings to the supporting heater surface instead of arching between a gap separating the inner periphery of the annular housing and the outer periphery of the heater platform. The spark discharge generates a cloud of particulate contaminates that land on the substrate surface short circuiting sub-micron conductive circuit lines. 
    
    
     DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a CVD-TiN defect ratio chart of the prior art.  
       FIG. 2  shows an annular housing assembly of the prior art and its placement on a heater of the prior art.  
       FIG. 3  illustrates a cut-away perspective of the annular housing assembly connected to the heater of the prior art.  
       FIG. 4  shows an enlarged view of a conductive strap of the prior art.  
       FIG. 5  illustrates an enlarged view of the annular housing assembly connected to the heater of the prior art.  
       FIG. 6  illustrates an enlarged view of a conductive strap according to the invention.  
       FIG. 7  shows an enlarged view of the annular housing assembly connected to the heater according to the invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
      Chipmaking is a complex manufacturing process-involving hundreds of steps that must be executed with great precision. In simplified terms, chipmaking involves three basic operations: deposition, patterning and etching. These and other processes are repeated many times on a silicon base substrate resulting in the buildup of microscopically thin layers of materials. In the process of building these layers, thousands or millions of transistors are created and interconnected. When the process is complete, a single silicon base substrate will contain hundreds of individual chips that are then diced into separate chip entities, tested for their electrical properties, packaged and assembled.  
      In view of the prior art, it is a principle object of the present invention to provide an improved design of a conductive strap and isolation rings contained within the annular housing. The improvement is put into practice so that a potential difference, within an electric field, is reduced in order that any cumulative charge would pass through the bottom of the isolation rings to the supporting heater surface instead of arching between a gap separating the inner periphery of the annular housing and the outer periphery of the heater platform, thereafter, eliminating the cloud of particulate contaminates that land and short circuit the sub-micron circuit lines formed on the semiconductor substrate.  
       FIG. 1  explains a graph  50  of CVD-TiN (TxZ) particle analysis. The source of particles versus the particle counts  52  and percent of particles  53  categorize the analysis. A cumulative percent plot  56  is shown plotted above the bar chart. The mechanical and arcing make up ⅔rds of the overall cumulative percent. As shown by the arcing bar chart  55  in graph  50 , arcing contributes 30% of the overall particle categories and is a close second to the mechanical category  55  that are caused by handling and other mechanical associated particle producers. Particulates caused by arcing have become a major detractor in the CVD-TiN process.  
      Analysis of the process has shown that arcing occurs in the gap area separating the heater and periphery of the annular housing. The reason is that the proximity of the periphery of the annular housing  22  to the outer periphery of the heater  21  creates a path of least resistance whenever a large difference of electric potential between the two is too high and the arc current jumps the gap between the annular housing and heater.  
      Referring now to  FIGS. 2 through 5  of the prior art.  FIG. 2  shows an exploded view of the items making up the annular housing assembly  15 . The annular housing  22 , shown inverted, has a top surface  42 , and a bottom surface  41  with a cylindrical wall  44  extending peripherally below the surfaces. The cylindrical wall encircles and houses a pair of isolator rings  23  and  24 , a first isolator ring  24  separated from the bottom surface  41  of the annular housing with spacer washers  29 , a second isolator ring  23  separated from the bottom of the first isolator ring  24  by a second set of spacer washers  29 . Machine screws  27  are used to secure the pair of isolator rings  23 ,  24  and spacer washers  29  to the annular housing  22 . conductive strap  25  electrically connects the annular housing to the heater to minimize an electrical potential difference. The heater assembly  20 , which includes the annular housing assembly, is best illustrated in  FIGS. 3 and 5 . The annular housing assembly is supported by at least three lift pins  43  extending on the top periphery of heater  21 . The annular housing assembly  15  is placed on heater pins  43  shown in exploded view  16  of  FIG. 2  as well as in  FIG. 3 .  
       FIG. 3  of the prior art, is a perspective cut-away view of the heater assembly  20  to best illustrate the relationship of the semiconductor substrate  10  and the various parts making up the CVD-TiN chamber. The annular housing  22  is shown mounted on heater pins  43 . Isolator rings  23  and  24  are contained within the annular housing and securely held to the bottom of its surface by machine screws  29 . The conductive strap  25  electrically ties heater  21  to annular housing  22 .  
       FIG. 5 , of the prior art, pictorially illustrates the reason arcing occurs during TiN deposition. A build of a potential difference between the annular housing and heater caused by high resistance contact between the conductive strap  25  and its connecting terminal ends. The high resistance contact was attributed to elongated slots  26 . During the heat cycles, changing from room temperature to high process temperatures, thermal contraction and expansion eventually caused contact failure of the small connecting surface. The potential difference  22  becomes too great and the high arc current therefore, discharges to a path of least resistance. This path was found to be between the annular housing  22  and heater  21 . The proximity of substrate  10  to this path shows contaminants landing on the surface of the substrate causing defects to happen in the circuit lines.  FIG. 4  is a view of the conductive strap  25  with the elongated slots  26 .  
       FIG. 7 , of the invention, pictorially illustrates the solution to the problems described in the prior art. The potential difference is minimized between the annular housing  32  and heater  21  by eliminating the high resistance contact between the conductive strap  35  and its connecting terminal ends  36 . The contacting terminal ends were changed to holes. This increases the contact area under the head of the screw. During the heat cycles, the bowed portion of the conductive strap takes up changing from room temperature to high process temperatures, thermal contraction and expansion. The operation of the conductive strap  35  has since proven itself by eliminating particulates on substrate  10  caused by arcing. While the potential difference is minimized and the risk of discharge is reduced, a path of least resistance has been redirected to the underside of isolator ring  34 . Making and using one isolator ring  34  that are twice as thick as that used makes this possible by conventional equipment. This also eliminates the use of spacer washers.  FIG. 6  is a view of the conductive strap  25  showing the terminal ends with holes  36 .  
      In summary, a substrate processing apparatus for processing a semiconductor substrate is disclosed. The apparatus includes a vacuum chamber, and a heater assembly disposed within the vacuum chamber. The heater assembly consists of a heater with a supporting surface and an annular housing supported by the heater. The annular housing has a top surface and a bottom surface and a cylindrical wall extending peripherally below the top surface and the bottom surface. An isolating ring is encircled by the cylindrical wall. The isolating ring is in contact with the bottom surface of the annular housing and the supporting heater surface of the heater. A conductive strap electrically connects the annular housing to the heater through screw holes in place of slots.  
      These and further constructional and operational characteristics of the invention will be more evident from the detailed description given hereafter with reference to the figures of the accompanying drawings which illustrate preferred embodiments and alternatives by way of non-limiting examples.  
      While the invention has been particularly shown and described with reference to the preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made without departing from the spirit and scope of the invention.