Co-axial motorized wafer lift

0001The present invention relates to an apparatus for vertically moving and positioning a workpiece, and more particularly to a motorized lifting apparatus for vertically moving and positioning a semiconductor wafer support pedestal within a processing chamber.

0002In a typical multi-chamber deposition system, a central transfer chamber is surrounded by a plurality of semiconductor processing chambers. A robot is positioned within the central transfer chamber for transferring semiconductor wafers between processing chambers. Process steps carried out within the process chambers include etching, deposition, passivation, etc., where a sealed environment must be maintained in the process chamber to limit the likelihood of contamination and to ensure that various specific processing conditions are provided therein. A valve assembly is positioned between the transfer chamber and each adjacent process chamber to maintain the sealed environment.

0003Within each processing chamber, a pedestal (also commonly termed a susceptor, substrate support or heater) is provided to support the wafer during processing. The pedestal is generally connected to an upper end of a vertical shaft which extends through a lower wall of the process chamber. A bellows assembly sealingly surrounds a portion of the length of the shaft. The lower end of the bellows assembly is typically connected to a base plate, and a vacuum seal is situated between mating surfaces ofthe base plate and lower chamber wall to ensure the existence of a sealed environment within the chamber.

0004The pedestal is typically connected to the vertical shaft by some type of permanent connection, such as welding. At present, the pedestal heater typically wears out much more quickly than the other components of the wafer lift mechanism. Likewise, where a heater is not used, the pedestal surfaces commonly need to be cleaned more frequently than the rest of the system components. On the average, a pedestal will operate for approximately 1500 hours before it must be replaced. In order to replace the pedestal in the currently available systems, it is necessary to break the vacuum seal between the base plate and the lower chamber wall. When the pedestal must be replaced, the entire lift mechanism must be removed and replaced along with the pedestal.

0005The pedestal may be raised or lowered by actuation of an external drive mechanism. Currently, two types of external drive systems are used: servo-motor drive systems and pneumatic drive systems.

0006FIG. <b>1</b> illustrates a typical example of the conventional prior art servo-motor system which has a pedestal <b>10</b> connected to a shaft <b>12</b>. A base plate <b>14</b> surrounds the shaft <b>12</b> and seals the opening in the lower chamber wall <b>20</b>. A bellows assembly <b>16</b> is provided within the chamber, and a bearing <b>18</b> surrounds the shaft <b>12,</b> which slides through the bearing as the pedestal is raised or lowered. The external drive mechanism consists of a motor <b>22</b> which is offset from the longitudinal axis of the lift mechanism shaft <b>12</b>. The motor <b>22</b> can be virtually any type of servo-motor, such as DC, AC and step motors. The motor is connected, and imparts rotary motion, to a motor pulley <b>24.</b> The motor pulley <b>24</b> is connected to a drive pulley <b>26</b> by drive belt <b>28</b>. The drive pulley <b>26</b> threadably engages the lead screw 30 of the shaft 12, such that rotation of the drive pulley <b>26</b> via the drive belt <b>28</b>, causes the pedestal to be raised or lowered. Bearings <b>32, 34</b> are positioned on both sides of the drive pulley <b>26</b> to guide and limit the movement thereof.

0007FIG. <b>2</b> shows an alternative type of prior art servo-motor driven wafer lift mechanism, wherein like reference numerals indicate like components. The external drive mechanism of the servo-motor system shown in FIG. <b>2</b> also consists of a motor <b>36</b> which is offset from the longitudinal axis of the lift mechanism shaft <b>12</b>. A lead screw <b>38</b> protrudes from and is rotatably driven by the motor <b>36</b> and threadably engages a drive nut <b>40.</b> As the lead screw <b>38</b> rotates, the drive nut <b>38</b> moves upwardly or downwardly along the axis of the lead screw, depending upon the direction of rotation. A bearing <b>42</b> surrounds at least a portion of the lead screw <b>38</b> to maintain alignment of the screw with the nut. The drive nut <b>40</b> is connected to the lift mechanism shaft <b>12</b> by a drive arm <b>44</b>, so that vertical movement of the drive nut 40 results in similar vertical movement of the pedestal <b>10</b>.

0008A primary advantage of the servo-motor system is that it permits incremental adjustment and positioning of the pedestal within the chamber. However, the offset positioning of the servo-motor increases the footprint of the device. In addition, the torque required to provide movement to the pedestal generates a large side load on the bearing in which the shaft slides. Furthermore, the translation of rotary motion from the motor into linear motion of the pedestal through the belt or drive arm results in slow acceleration and movement of the pedestal.

0009A pneumatically driven lift mechanism is shown in FIG. <b>3</b>, wherein like reference numerals also indicate like components. In the typical pneumatic system, an air cylinder <b>46</b> and ram <b>48</b> may be directly connected to the lower end of the shaft <b>12</b> to provide vertical movement of the pedestal <b>10.</b> Positioning of the pedestal in the chamber is provided by stops which are engaged by complementary logs on the ram <b>48</b>, thus defining the ram's <b>48</b> and pedestal's <b>10</b> travel. A disadvantage of the pneumatic system is that it cannot provide incremental movement and positioning ofthe pedestal within the chamber. The air cylinder may provide only an upper position, with the ram fully extended against an upper stop for example, and a lower position, e.g. with the ram fully contracted against a lower stop.

0010The present invention is an apparatus for vertically moving and positioning a workpiece, such as a semiconductor wafer, within a chamber. The present invention overcomes the disadvantages inherent in the prior art by providing a servo-motor drive mechanism which is coaxial with the pedestal drive shaft. This allows for very fast movement and incremental positioning of the pedestal, without side loading on the ram inherent in prior art mechanical systems. The present invention also provides a lift mechanism wherein all or a portion of the pedestal assembly can be removed from the remaining components of the lift mechanism without the need to remove the entire lift mechanism or break the chamber seal where the ram extends through the chamber envelope.

0011The apparatus according to a first aspect of the invention comprises a pedestal for supporting the article within the chamber, a shaft extending downwardly from a lower region of the pedestal, and drive means for providing linear vertical translation of the shaft and pedestal. The drive means is co-axial with and surrounds the shaft proximal to a distal portion thereof. The apparatus may further comprise a bearing surrounding the shaft above the drive means, and/or a bellows assembly surrounding the shaft between the drive means and the pedestal.

0012According to a second aspect of the invention, provided is an apparatus for vertically moving and positioning a workpiece, such as a semiconductor wafer, within a chamber comprising a pedestal for supporting the article within the chamber, a shaft extending downwardly from a lower region of the pedestal, a rotatable hollow shaft motor surrounding the shaft proximal to the distal portion thereof, and a drive flange connected to the shaft motor for drivingly engaging the distal portion of the shaft. The drive flange preferably surrounds the shaft proximal to the distal portion thereof and exhibits threads for rotatably engaging a shaft lead screw formed in the distal portion thereof. The apparatus may further comprise a bearing surrounding the shaft above the drive means, and/or a bellows assembly surrounding the shaft between the drive means and the pedestal.

0013A pair of substantially flat planar plates removably connected to one another may be provided for connecting the bellows assembly to the pedestal. The upper plate is preferably connected to a lower region of the pedestal and the lower plate is preferably connected to the upper end of the shaft. A metal gasket may be positioned between the upper plate and the lower plate. A lower surface of the upper plate and an upper mating surface of the lower plate may each exhibit a knife edge metal seal. The upper plate and lower plate are preferably removably connected to one another by a plurality of bolts:

0014The pedestal may further include a heating element therein for heating and cooling a wafer placed on the surface of the pedestal. According to this aspect, the shaft may be a hollow metal cylinder with a plurality of wires and cooling lines passing therethrough and connected to the heating element. A base plate surrounding the shaft at a position between the drive means and the pedestal may be provided to removably connect the apparatus to a lower wall of the chamber.

0015According to a third aspect of the present invention a lift mechanism for vertically translating a workpiece, such as a semiconductor wafer, within a chamber is provided comprising a pedestal located within the chamber for supporting the article, a pair of substantially flat planar plates removably connected to one another, and an external drive mechanism. An upper one of the pair of plates is connected to a lower region of the pedestal. A shaft is connected to a lower surface of a lower one of the pair of plates and extends downwardly therefrom through a lower wall of the chamber. The external drive mechanism is connected to a distal end of the shaft. The external drive mechanism may be comprised of a rotatable hollow shaft motor proximal to and surrounding the distal portion of the shaft, and a drive flange connected to the rotatable hollow shaft motor and surrounding the shaft proximal to the distal portion thereof. The drive flange exhibits threads for rotatably engaging a shaft lead screw. The lift mechanism may further include a bearing surrounding said shaft above the rotatable hollow shaft motor, and/or a bellows assembly surrounding the shaft between the rotatable hollow shaft motor and the pair of planar plates. A metal gasket may be provided between the upper plate and lower plate, and a lower surface of the upper plate and an upper mating surface of the lower plate may each exhibit a knife edge metal seal. The upper plate and the lower plate may be removably connected to one another by a plurality of bolts.

0016These and other features, aspects and advantages of the present invention will become better understood by referring to the following detailed description, drawings and claims, wherein examples of the presently preferred embodiments are given for purposes of illustration and disclosure.

0017Figure 1 is a side sectional view of a first prior art wafer lift device.

0018Figure 2 is a side sectional view of a second prior art wafer lift device.

0019Figure 3 is a side sectional view of a third prior art wafer lift device.

0020Figure 4 is a side sectional view of the wafer lift mechanism according to an embodiment of the present invention.

0021Figure 5 is an exploded side sectional view of a portion of the wafer lift mechanism shown in Figure 4.

0022The present invention is best understood by referring to the Drawings in connection with review of this Description. The present invention is an apparatus for vertically moving and positioning a workpiece, such as a semiconductor wafer, within a chamber comprising a pedestal for supporting the article within the chamber, a shaft extending downwardly from a lower region of the pedestal and exhibiting a lead screw at a distal portion thereof, and drive means for providing linear vertical translation of the shaft and pedestal. The drive means is co-axial with, and preferably surrounds the shaft proximal to the distal portion thereof. Alternatively, the drive means may be located coaxially within the hollow shaft. Also provided is a lift mechanism for vertically translating a workpiece, such as a semiconductor wafer, within a chamber comprising a pedestal located within the chamber for supporting the article, upper and lower substantially flat planar plates removably connected to one another, the upper plate being connected to a lower region of the pedestal, a shaft connected to a lower surface of the lower plate and extending downwardly therefrom through a lower wall of the chamber, and an external drive mechanism connected to a distal end of the shaft.

0023FIG. <b>4</b> shows a preferred embodiment ofa wafer heating and lifting mechanism <b>50</b> according to the present invention. The lifting mechanism is shown extending through the lower wall <b>52</b> of a wafer processing chamber <b>54,</b> in which a slot <b>56</b> is provided to insert and remove a semiconductor wafer. A wafer pedestal <b>58</b> is located within the chamber <b>54</b> for supporting a wafer during processing. The wafer pedestal <b>58</b> includes a heater <b>60,</b> which is used to heat the wafer prior to and/or during processing to ensure, for example, better deposition of a target metal onto the surface of the wafer and into vias in the wafer surface. Heating and cooling tubes <b>62</b> are also provided to facilitate heat transfer to and from the heater <b>60</b> located within the wafer pedestal <b>58</b>. For certain applications, it is unnecessary to provide a heater. In such applications, a pedestal is provided without the internal heating apparatus.

0024The wafer pedestal <b>58</b> is connected to the upper end of a drive shaft <b>64</b> by a CONFLAT® assembly <b>66</b>. The drive shaft <b>64</b> is hollow to permit the cooling tubes <b>62,</b> wires and thermocouples to pass therethrough. The CONFLAT® assembly <b>66</b> includes an upper flange or plate <b>68</b> connected to a lower region of the pedestal 58, and a lower flange or plate <b>70</b> connected to the upper end of the hollow drive shaft 64. A gasket <b>72</b> is disposed between the upper and lower plates to provide a seal therebetween. The gasket is preferably formed from a malleable metal, such as aluminum. The upper plate <b>68</b>, gasket <b>72</b> and lower plate <b>70</b> are held together by a plurality of bolts <b>74</b> and nuts <b>76</b> which are positioned along the periphery thereof to removably connect the upper plate to the lower plate. In this way, a pedestal can be removed and a new pedestal installed without removing the entire lift assembly.

0025As shown in FIG. <b>5</b>, the CONFLAT® assembly <b>66</b> also includes a circumferential knife edge seal, which includes a knife edge <b>80</b> located in either the upper or lower plate and a corresponding groove <b>78</b> located in the other plate. FIG. <b>5</b> shows a knife blade <b>80</b> extending from a surface of the upper plate <b>68</b> with a corresponding groove <b>78</b> in the mating upper surface of the lower plate <b>70.</b> The knife edge may be reversed, or a plurality of knife edge seals may be present in any configuration to ensure a proper seal between the vacuum environment of the process chamber <b>54</b> and the interior of the lift mechanism <b>50.</b> The knife edge seal deforms the gasket to create such a seal between the two environments.

0026The wafer heating and lifting mechanism <b>50</b> is attached to the lower wall <b>52</b> of the process chamber <b>54</b> by a mounting assembly <b>82.</b> A bearing <b>86</b> surrounds the drive shaft <b>64</b> within the mounting assembly <b>82</b> to facilitate vertical movement of the shaft through the mounting assembly and to compensate for side loads and torque placed on the shaft as it moves up and down. A bellows assembly <b>84</b> surrounds the bearing <b>86</b> and drive shaft in the region of the bearing to separate the process chamber environment from the bearing assembly. A lower flange <b>88</b> is connected to the lower region of the mounting assembly <b>82</b> and sealingly surrounds the drive shaft. The bellows <b>84</b> are attached at an upper end to the lower region of the lower plate <b>70</b> and at a lower end thereof to the lower flange <b>88</b> to completely seal the bearing assembly from the process chamber environment.

0027The drive mechanism <b>90</b> of the wafer heating and lifting apparatus <b>50</b> is co-axial with the hollow drive shaft <b>64</b>. The drive mechanism <b>90</b> includes a drive motor <b>92</b> which surrounds the drive shaft <b>64.</b> The drive motor <b>92</b> is preferably a standard AC, DC or step servo-motor. Alternatively, magnetic or electromagnetic motors may be used depending upon the system requirements. Upon actuation, the drive motor rotates about the drive shaft. The drive motor <b>90</b> is connected to a drive flange <b>94</b> which includes a threaded drive nut <b>96.</b> The threads of the threaded nut <b>96</b> engage threads of a lead screw <b>98</b> portion of the hollow shaft <b>64</b>. As the motor <b>92</b> is activated, the motor, drive flange <b>94</b> and threaded drive nut <b>96</b> rotate about the shaft. The shaft remains fixed in theta, <i>i.e.,</i> against rotation, and as the drive mechanism rotates, the drive shaft moves vertically due to the threaded connection between the lead screw 98 and drive nut <b>96.</b> The shaft may be fixed against rotation by a variety of mechanisms. For example, a longitudinal groove may be formed in the shaft with a projection from a surrounding fixed surface extending into the groove to prevent rotation of the shaft. Rotation of the drive mechanism <b>90</b> is one direction, for example clockwise, results in vertical movement, i.e. upward, of the drive shaft, while rotation of the drive mechanism in the opposite direction, i.e. counterclockwise, results in vertical movement of the drive shaft in the opposite, or downward, direction.

0028In the preferred implementation of the invention, the pedestal <b>58</b> cooperates with a plurality of lift pins (not shown) which extend through apertures in the pedestal <b>58</b> and which are separately actuable to enable placement of the substrate or wafer thereon, and are moveable, with respect to the pedestal <b>58,</b> to enable placement of the substrate on the pedestal or lifting of the substrate off of the pedestal. Alternatively, the invention may be used in conjunction with a lift hoop or lift fingers disposed about the perimeter of the pedestal <b>58</b>, which hoop or fingers are likewise actuable independently of the pedestal <b>58</b> to enable positioning of a substrate thereon by a robot or other mechanism, and placement of the substrate on, or removal of the substrate from, the pedestal <b>58</b> by relative movement of the pedestal and hoop/fingers. The use, structure nd operation of such pins, hoops and fingers are well known expedients to those skilled in the art.

0029The present invention, therefore, is well adapted to carry out the objects and attain the ends and advantages mentioned as well as others inherent therein. While presently preferred embodiments of the invention are given for the purpose of disclosure, numerous changes in the details will readily suggest themselves to those skilled in the art and which are encompassed within the spirit of the invention and the scope of the appended claims.