Patent Publication Number: US-2009238985-A1

Title: Systems and methods for deposition

Description:
BACKGROUND OF THE INVENTION 
     Deposition systems, such as sputtering deposition systems, are employed in various industries for depositing thin films of various materials on substrates (e.g., wafers). The industries may include, for example, semiconductor, magnetic storage, optical system, and micro-electromechanical system (MEMS) industries. The materials to be deposited may be, for example, aluminum oxide, zinc oxide, tin oxide, or titanium dioxide. As an example, a deposition system may utilize a plasma source to sputter a target material such that sputtered atoms of the target material (or molecules comprising the sputtered atoms) may attach to a surface of a wafer. 
     Wafer arrangement may be an important consideration in deposition processes and deposition system design. Conventionally, the wafer may be disposed parallel to the target material, i.e., parallel to an imaginary plane containing the long axis of the target material, based on the assumption that the sputtered atoms would generally have travel paths that are orthogonal to both the target material and the wafer. 
     In an example conventional arrangement, the target material may be disposed above the wafer, such that gravity may move sputtered atoms from the target toward the wafer. However, also because of gravity, contaminants, such as flakes of the target material, also may fall onto the wafer. As a result, the yield associated with the deposition process may be undesirable. 
     In another example conventional arrangement, the target material may be disposed below the wafer. Under this arrangement, the movement of the sputtered atoms toward the wafer may be slowed down by gravity. As a result, the deposition rate (or efficiency) for the deposition process may be undesirable. 
     In another example conventional arrangement, both the target material and the wafer may be disposed perpendicular to the ground, or a level plane. Under this arrangement, because of gravity, the sputtered atoms may not approach the wafer in paths orthogonal to the deposition surface of the wafer. As a result, the deposition rate for the deposition process may be undesirable. Further, the deposited thin film may not be sufficiently homogenous. 
     Cooling also may be an important consideration in deposition processes and deposition system design. During a deposition process, the temperature of the wafer may substantially increase such that effective cooling may be required for the wafer. Typically, a deposition system may include a gas inlet to enable a cooling gas, such as helium, to flow in to contact the wafer for absorbing thermal energy from the wafer. The cooling gas that has absorbed thermal energy from the wafer will be heated as a result of the thermal energy transfer. The deposition system may also include a gas outlet to allow the heated cooling gas to leave the wafer. In general, a continuous flow of the cooling gas may be utilized to continuously remove thermal energy from the wafer. Under this conventional arrangement, a significant amount of the cooling gas may be required (and consumed), and therefore substantial cost associated with cooling may be incurred. 
     SUMMARY OF INVENTION 
     An embodiment of the invention relates to a substrate stage system for supporting and cooling a substrate during a deposition process that involves utilizing a target material. The substrate stage system may include a substrate seat made of a thermally conductive material. The substrate stage system may also include a sealing unit coupled with the substrate seat. The sealing unit may define a boundary of a space between the substrate and the substrate seat. The substrate seat may include a gas channel for delivering a gas to the space. The sealing unit may seal the space to inhibit the gas from escaping from the space. The substrate seat may receive heat from the substrate through the gas and may dissipate the heat. 
     The above summary relates to only one of the many embodiments of the invention disclosed herein and is not intended to limit the scope of the invention, which is set forth in the claims herein. These and other features of the present invention will be described in more detail below in the detailed description of the invention and in conjunction with the following figures. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       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: 
         FIG. 1A  illustrates a schematic representation of a deposition system including a substrate stage system in accordance with one or more embodiments of the present invention. 
         FIG. 1B  illustrates a schematic representation of the substrate stage system illustrated in the example of  FIG. 1A  and including a shutter in accordance with one or more embodiments of the present invention. 
         FIG. 2A  illustrates a schematic representation of a deposition system including a substrate stage system with an orientation mechanism in accordance with one or more embodiments of the present invention. 
         FIG. 2B  illustrates a schematic representation of a substrate orientation arrangement for a deposition process in accordance with one or more embodiments of the present invention. 
         FIG. 3  illustrates a schematic representation of a substrate stage system including a gas shower unit in accordance with one or more embodiments of the present invention. 
         FIG. 4  illustrates a schematic representation of a cross-sectional view of a substrate seat of a substrate stage system in accordance with one or more embodiments of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     The present invention will now be 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. 
     One or more embodiments of the invention relate to an improved substrate stage system for supporting and cooling a substrate during a deposition process. The substrate stage system includes a cooling arrangement that utilizes a confined gas, in contrast with a flowing gas utilized in the prior art, for cooing the substrate. Advantageously, the substrate stage system may substantially reduce consumption of the gas. 
     The substrate stage system may include a substrate seat made of a thermally conductive material. The substrate stage system may also include a sealing unit coupled with the substrate seat. The sealing unit may be configured to define a boundary of a space between the substrate and the substrate seat. The sealing unit may also be configured to seal the space to inhibit the gas from escaping from the space. Accordingly, the gas may be trapped in the space to serve as a thermal conductor. The substrate seat may include at least a gas channel configured to deliver the gas to the space. The gas channel may include an opening configured for both injecting the gas into the space and withdrawing the gas from the space, in contrast with the gas inlet and outlet required for the flowing gas utilized in the prior art. 
     Through the gas, the substrate seat may receive heat from the substrate and subsequently dissipate the heat. In one or more embodiments, the substrate seat may also include at least a cooling channel configured to allow a cooling fluid, e.g., water, to flow through the substrate seat for facilitating/accelerating dissipating heat received from the substrate. 
     The substrate stage system may also include a step unit disposed between the substrate seat and the substrate for maintaining the height of the space. The step unit may be coupled with the substrate seat or may be an integral part of the substrate seat 
     The substrate stage system may also include a pump coupled with the gas channel and a valve coupled with the gas channel. At least one of the pump and the valve may be configured to maintain a constant pressure for the gas during the deposition process, for a controlled heat dissipation rate. 
     The substrate stage system may also include a clamp unit. The sealing unit may be compressible, for biasing the substrate against the clamp unit to secure the substrate in place. 
     The substrate stage system may also include a gas shower unit configured to be disposed between a target material and the substrate during the deposition process. The gas shower unit may include a plurality of distributed gas holes. The distributed gas holes may be configured to provide a process gas in a distributed manner, for substantially homogeneous chemical reaction between the process gas and particles from the target material. 
     The substrate stage system may also include an orientation mechanism coupled with the substrate seat. The orientation mechanism may be configured to orient the substrate seat such that a surface of the substrate is tilted, i.e., at an angle to an imaginary plane containing a vector of gravity, during the deposition process, for optimizing deposition amid the effect of gravity. The angle may be greater than 0 degree and less than 90 degrees. In one or more embodiments, the angle may be at most 10 degrees. 
     The orientation mechanism may also be configured to orient the gas shower unit when orienting the substrate seat, such that a distance between the gas shower unit and the substrate may remain constant. The orientation mechanism may also be configured to rotate the substrate around a diameter of the substrate. Accordingly, additional variables and associated complication for optimizing the deposition process may be avoided. 
     The substrate stage system may also include a shutter coupled with the substrate seat. The shutter may be configured to shield the substrate before and/or after the deposition process, for protecting the substrate from unready or undesirable conditions. The shutter may also be configured to be disposed between the target material and the gas shower unit for preventing the chemical reaction from starting before the deposition process. 
     The substrate stage system may also include a rotation mechanism configured to rotate the substrate seat (without rotating the shutter and the gas shower unit in one or more embodiments) during the deposition process. Accordingly, the substrate may be rotated during the deposition process for improved homogeneity. 
     One or more embodiments of the invention relate to a deposition system for performing deposition on a substrate utilizing a target material. The deposition system may include a chamber, within which the deposition may take place. The deposition system may also include a substrate stage system according to one or more embodiments discussed above. 
     One or more embodiments of the invention relate to a method for performing deposition on a first surface of a substrate utilizing a target material. The method may include supporting the substrate using a substrate seat. The method may also include tilting the substrate seat such that the first surface of the substrate is at an angle to an imaginary plane containing a vector of gravity. The tilting may enable desirable particles to travel toward the substrate substantially orthogonally to the first surface, for optimizing the deposition. The angle may be greater than 0 degree and less than 90 degrees. For example, the angle may be at most 10 degrees. The method may also include maintaining the angle during the deposition. The method may also include rotating the substrate around a center of the substrate during the deposition, for improving homogeneity of the deposition. 
     The method may also include forming a space between the substrate seat and the substrate. The method may also include filling the space with a gas for transferring heat from the substrate to substrate seat through the gas. The method may also include maintaining a constant pressure for the gas during the deposition, for a controlled heat transfer. 
     The method may also include providing an opening on the substrate seat for both injecting the gas into the space and withdrawing the gas from the space. Accordingly, manufacturing for the substrate seat may be simplified. 
     The features and advantages of the present invention may be better understood with reference to the figures and discussions that follow. 
       FIG. 1A  illustrates a schematic representation of a deposition system  100 , including a substrate stage system  102 , in accordance with one or more embodiments of the present invention. Deposition system  100  may also include a chamber  104 , in which deposition processes may take place. A cut-away view of chamber  104  is shown in the example of  FIG. 1A , such that a schematic representation of substrate stage system  102  may be illustrated. 
     For example, deposition system  100  may be utilized in a deposition process for forming a thin film on a surface of a substrate, such as substrate  114 . The deposition process may involve utilizing a target material  106 , such as a cylindrical block of aluminum. Deposition system  100  may include a plasma source  154  configured to generate a plasma to sputter target material  106 , such that sputtered particles (e.g., atoms) from target material  106  or molecules containing the sputtered atoms may be deposited onto substrate  114 . As an example, plasma source  154  may represent a capacitively coupled plasma source, and an end of target material  106  may be coupled with a DC power source (not shown) for facilitating generating the plasma. 
     Substrate stage system  102  may be configured to support substrate  114  during the deposition process. Substrate stage system  102  may include a shutter  110  configured to shield substrate  114  before and/or after the deposition process. For example, shutter  110  may be configured to shield substrate  114  until sputtered particles from target material  106  (or molecules containing the sputtered atoms) have substantially homogeneously distributed in chamber  104 , before allowing deposition to start on substrate  114 . Accordingly, the sputtered particles or molecules may be deposited on substrate  114  in a homogeneous manner, such that homogeneity of the thin film formed on substrate  114  may be optimized. 
     As another example, shutter  110  may be configured to shield substrate  114  once an optimum thickness for the thin film formed on substrate  114  has been achieved. Accordingly, further deposition that may change the thickness and/or homogeneity of the thin film may be prevented. 
     Deposition system  100  may also include an arm  108  configured to support substrate stage system  102 . In one or more embodiments, arm  108  may be considered part of substrate stage system  102 . 
     Further details of substrate stage system  102  are discussed with reference to  FIG. 1B . 
       FIG. 1B  illustrates a schematic representation of a partial perspective view of substrate stage system  102  that includes shutter  110  in accordance with one or more embodiments of the present invention. Shutter  110  may be made of a corrosion resistant material, such as stainless steel, for durability consideration and for effective protection for substrate  114 . Shutter  110  may include a stiffening structure  136  configured to provide structural stiffness for shutter  110  while minimizing thickness and weight requirements for shutter  110 . 
     Shutter  110  may be configured to rotate around an axis  130  in a covering direction  132  and an uncovering direction  134  to shield and to expose substrate  114 , respectively. Alternatively or additionally, shutter  110  may perform shielding and exposing wafer  114  through translational motions. 
     Shutter  110  may be coupled with a plate  124  through axis  130 . Plate  124  may be coupled, e.g., through one or more components of substrate stage system  102 , with a substrate seat  120  that is configured to support substrate  114  during the deposition process. 
     Substrate seat  120  may also be configured to rotate substrate  114  around a center of substrate  114  during the deposition process, for homogeneous deposition. The rotation may be actuated by a rotation mechanism  140  of substrate stage system  102 . 
     Substrate stage system  102  may also include a gas shower unit  126  supported by plate  124  and coupled with substrate seat  120  through one or more components of substrate stage system  102 , such as plate  124 . Gas shower unit  126  may be configured to be disposed between substrate  114  and target material  106  during the deposition process. Gas shower unit  126  may also be configured to provide a process gas in a homogeneous manner during the deposition process, such that chemical reaction may be facilitated between the process gas and the sputtered particles (from target material  106  illustrated in the example of  FIG. 1A ). Molecules resulted from the chemical reaction may be deposited on substrate  114 . 
     Gas shower unit  126  may be configured to be shielded by shutter  110  before the deposition process, for preventing the chemical reaction from happening too early, e.g., before there are sufficient sputtered particles in chamber  104  illustrated in the example of  FIG. 1A . Shutter  110  may also be configured to shield gas shower unit  126  once the optimum thickness of the thin film has been achieved on substrate  114  or after the deposition process, to prevent further chemical reaction. Advantageously, thickness and homogeneity of the thin film may be optimized. 
     Substrate stage system  102  may also include an orientation mechanism  142  configured to adjust the orientation of wafer  114  with respect to target material  106  (illustrated in the example of  FIG. 1A ) for optimum deposition. Orientation mechanism  142  may be coupled with substrate seat  120  through one or more components, such as arm  108  and feature mount  122 . 
       FIG. 2A  illustrates a schematic representation of a partial top cut-away view of a deposition system  200  in accordance with one or more embodiments of the present invention. Deposition system  200  may be utilized for performing deposition, for example, on a substrate  214  utilizing a target material  206 . Deposition system  200  may include a chamber  204  to contain sputtered particles from target material  206 . Deposition system  200  may also include a substrate stage system  202  configured to support substrate  214  during the deposition process. One or more components of substrate stage system  202  may be disposed inside chamber  204 . 
     Substrate stage system  202  may include a substrate seat  220  for securing substrate  214  in place during the deposition process. Substrate stage system  202  may also include a positioning mechanism  254  coupled with substrate seat  220  and configured to move substrate seat  220  in a direction  232  to place substrate  214  at position  286  for the deposition. 
     Substrate stage system  202  may also include an orientation mechanism  242 , configured to tilt substrate seat  220 , such that substrate  214  may have an optimal orientation during the deposition. Orientation mechanism  242  may be coupled with substrate seat  220  through one or more components, such as arm  208 . Orientation mechanism  242  may be configured to orient/rotate substrate  214  around a diameter  284  of substrate  214  when substrate  214  is in position  286 . Accordingly, a distance D 2  between target material  206  and a central line of substrate  214 , represented by diameter  284 , may remain constant for various orientations of substrate  214 . Given that distance D 2  is maintained constant, the number of variables involved in optimizing the deposition process might be minimized. Therefore, optimizing the deposition process may be simplified. 
     Substrate stage system  202  may also include a rotation mechanism  240 , configured to rotate substrate  214  around the center  282  of substrate  214  when substrate  214  is in position  286  during the deposition. With the rotation, homogeneity of the deposition may be improved. A distance D 1  between target material  206  and center  202  may be maintained constant during the deposition process. With distance D 1  being maintained constant, the number of variables involved in optimizing the deposition process may also be minimized, and the optimization may be simplified. 
       FIG. 2B  illustrates an orientation arrangement for substrate seat  220  and substrate  214  in accordance with one or more embodiments of the present invention. Orientation mechanism  242  (illustrated in the example of  FIG. 2A ) may orient/tilt substrate seat  220  such that substrate  214  is at an angle  272  with respect to an imaginary plane  270  containing a gravity vector  238 . Orienting/tilting substrate seat  220  (and/or substrate  214 ) may represent a process step in a deposition process in one or more embodiments of the invention. 
     Angle  272  may be greater than zero degree such that substrate  214  is not in line with gravity vector  238 . Angle  272  may be less than 90 degrees, such that the surface of substrate  214  for the deposition is not perpendicular to gravity vector  238 . Angle  272  may be configured such that sputtered particles from a target material  206  may approach substrate  214  in a direction  234  that is substantially orthogonal to the surface of substrate  214  for the deposition. Angle  272  may be optimized With gravity and the dynamics of the sputtered particles (and/or molecules containing the sputtered particles) taken into consideration. For example, angle  272  may be at most 10 degrees. As another example, angle  272  may be approximately 10 degrees. 
     With sputtered particles (and/or molecules containing the sputtered particles) approaching substrate  214  in a direction that is substantially orthogonal to the deposition surface, the efficiency for the deposition process may be substantially improved. 
     Given that angle  272  is substantially small, the majority of contaminants, such as flakes from target material  206 , which generally weigh more than the particles or molecules for deposition, may be unlikely to attach to the deposition surface of substrate  214 . Advantageously, the yield associated with the deposition process may be substantially improved. 
       FIG. 3  illustrates a schematic representation of a partial perspective view of a substrate stage system  302  in accordance with one or more embodiments of the present invention. Substrate stage system  302  may include a substrate seat  320  configured to support a substrate, such as substrate  314 . 
     Substrate stage system  302  may also include a gas shower unit  326 , configured to be disposed between substrate  314  (supported by substrate seat  320 ) and a target material (for example, similar to target material  106  illustrated in the example of  FIG. 1A ) during a deposition process. Gas shower unit  326  may be made of a corrosion resistant material, such as stainless steel, for durability and consistent performance. Gas shower unit  326  may include a gas inlet  322  for receiving gas supply and may be coupled with a plate  324  through gas inlet  322 . Plate  324  may be configured to support and stabilize gas shower unit  326  during the deposition process. 
     Gas shower unit  326  may include a plurality of gas holes, such as gas holes  328   a - c,  configured to provide a process gas, such as oxygen, for facilitating chemical reaction between the process gas and sputtered particles from the target material during the deposition process. The gas holes may be distributed along at least a portion of gas shower unit  326  such that the chemical reaction may be substantially homogeneous over the surface of substrate  314  for the deposition. The shape of the portion of gas shower unit  326  may be configured to be similar to the outline of substrate  314 , for uniform supply of the process gas over substrate  314 . For example, if substrate  314  represents a circular wafer, gas shower unit  326  may have a circular ring shape. Advantageously, homogeneity of the thin film formed on substrate  314  may be substantially improved. 
     Substrate stage system  326  may also include an orientation mechanism (not shown) similar to orientation mechanism  242  illustrated in the example of  FIG. 2A . Substrate seat  320  and gas shower unit  326  may be coupled with the orientation mechanism through one or more components of substrate stage system  302 , such as plate  324  and/or arm  308 . The orientation mechanism may be configured to substrate seat  320 , and therefore orient substrate  314 , with respect to the target material, such that the deposition may be optimized, e.g., in efficiency, yield, etc. The orientation mechanism may be configured to also orient gas shower unit  326  when orienting substrate  314 , such that a distance D 3  between substrate  314  and gas shower unit  326  may remain constant. With D 3  being maintained constant, the number of variables involved in optimizing the deposition process may be minimized, and optimizing the deposition process may therefore be simplified. 
       FIG. 4  illustrates a schematic representation of a partial cross-sectional view of a substrate seat  420  of a substrate stage system  402  in a deposition system (for example, similar to deposition system  100  illustrated in the example of  FIG. 1 ) in accordance with one or more embodiments of the present invention. Substrate seat  420  may be configured for supporting and cooling a substrate, such as substrate  414 , during a deposition process. 
     Substrate seat  420  may be made of a thermally conductive material, such as aluminum, for facilitating the cooling. Substrate stage system may also include a sealing unit  458  coupled with substrate seat  420  and configured to define a boundary of a space  456  formed between substrate seat  420  and substrate  414 . The shape of sealing unit  458  may be similar to the outline of substrate  414 . For example, if substrate  414  represents a circular wafer, sealing unit  458  may have a circular ring shape. 
     Substrate seat  420  may include a gas channel  452  configured to deliver a gas, such as helium, to fill space  456 . Gas channel  452  may include an opening  454  for both injecting the gas into space  456  and withdrawing the gas from space  456 . Accordingly, manufacturing of substrate seat  420  may be simplified. Sealing unit  458  may seal space  456 , and therefore the gas may be inhibited from escaping from space  456 . Filling space  456  with the gas and sealing space  456  may represent process steps for the deposition process. 
     Substrate stage system  402  may also include a mass flow control  474  and a valve  472  for controlling the input of the gas into space  456 . Substrate stage system  402  may also include a pump  476 , configured to withdraw the gas from space  456 . Substrate stage system  402  may also include a capacitance manometer  482  for measuring the flow rate of the gas withdrawn from space  456 . Substrate stage system  402  may also include a controller  486  (coupled with capacitance manometer  482 ) for controlling the flow rate of the gas withdrawn from space  456 , for example, by expanding or contracting an orifice  484  disposed in the path of the withdrawn gas, thereby controlling the gas pressure in space  456 . At least one of valve  472 , mass flow control  474 , capacitance manometer  482 , controller  486 , orifice  484 , and pump  476 , may be configured to maintain a constant pressure for the gas in space  456  during the deposition process. 
     During the deposition process, the gas may serve as a thermal conductor between substrate  414  and substrate seat  420  for thermally coupling substrate  414  and substrate seat  420 . Accordingly, substrate seat  420  may receive heat from substrate  414  through the gas and may subsequently dissipate the heat. Heat transfer from substrate  414  to substrate seat  420  may represent a process step in the deposition process. 
     During the deposition process, the amount of the gas that is utilized may be substantially represented by the volume of space  456  (and gas channel  452  and other gas conduits). Since the gas is sealed by sealing unit  458  without substantially flowing out of space  456  during the deposition process, the amount of the gas utilized during the deposition process may be minimized, compared with the prior art arrangement that involves a continuous flow of a cooling gas. Advantageously, cooling cost associated with the deposition process may be reduced. 
     Substrate seat  420  may also include a cooling channel  478  configured to allow a cooling fluid, such as water or water-alcohol mixture, to flow through substrates  420 . The cooling fluid may facilitate and/or accelerate dissipation of the heat. 
     Substrate stage system  402  may also include a step unit  460  configured to contact substrate  414 . Step unit  460  may also be configured to maintain a height H 1  for space  456  between substrate  414  and substrate seat  420 . Step unit  460  may be attached to substrate seat  420  or may be an integral part of substrate seat  420 . 
     Substrate stage system  402  may also include a clamp unit  424  configured to secure substrate  414  in place. In one or more embodiments, sealing unit  458  may be made of a compressible material and may be configured to bias substrate  414  against clamp unit  424  during the deposition process. Accordingly, substrate  414  may remain stable during the deposition process, and the deposition process may be optimized without considering shifting of substrate  414 . 
     As can be appreciated from the foregoing, embodiments of the present invention may eliminate the need for a continuous flow of cooling gas during deposition processes. Advantageously, the cost associated with cooling for deposition processes may be substantially reduced. 
     Embodiments of the invention may also protect substrates when the environment surrounding the substrates is not ready or is not suitable for deposition. Accordingly, homogeneity of thin films formed on the substrates may be optimized. Advantageously, the yield associated with deposition processes may be optimized. 
     Embodiments of the invention may also enable sputtered particles and molecules for deposition to approach surface of substrates in directions that are substantially orthogonal to the surfaces. Advantageously, efficiency for deposition processes may be substantially improved. 
     Embodiments of the present invention may also provide homogeneous chemical reactions between process gases and sputtered particles from target materials over substrates during deposition processes. Advantageously, homogeneity of thin films formed on the substrates may be optimized. 
     While this invention has been described in terms of several embodiments, there are alterations, permutations, and equivalents, which fall within the scope of this invention. It should also be noted that there are many alternative ways of implementing the methods and apparatuses of the present invention. Furthermore, embodiments of the present invention may find utility in other applications. The abstract section is provided herein for convenience and, due to word count limitation, is accordingly written for reading convenience and should not be employed to limit the scope of the claims. It is therefore intended that the following appended claims be interpreted as including all such alterations, permutations, and equivalents as fall within the true spirit and scope of the present invention.