Patent Publication Number: US-6992892-B2

Title: Method and apparatus for efficient temperature control using a contact volume

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention is generally related to semiconductor processing systems and, more particularly, to temperature control of a substrate using rough contact or micron-size gaps in a substrate holder. 
   2. Discussion of the Background 
   Many processes (e.g., chemical, plasma-induced, etching and deposition) depend significantly on the instantaneous temperature of a substrate (also referred to as a wafer). Thus, the capability to control the temperature of a substrate is an essential characteristic of a semiconductor processing system. Moreover, fast application (in some important cases, periodically) of various processes requiring different temperatures within the same vacuum chamber requires the capability of rapid change and control of the substrate temperature. One method of controlling the temperature of the substrate is by heating or cooling a substrate holder (also referred to as a chuck). Methods to accomplish faster heating or cooling of the substrate holder have been proposed and applied before, but none of the existing methods provide rapid enough temperature control to satisfy the growing requirements of the industry. 
   For example, flowing liquid through channels in the chuck is one method for cooling substrates in existing systems. However, temperature of the liquid is controlled by a chiller, which is usually located at a remote location from the chuck assembly, partially because of its noise and size. However, the chiller unit is often very expensive and is limited in its capabilities for rapid temperature change due to the significant volume of the cooling liquid and to limitations on heating and cooling power provided by the chiller. Moreover, there is an additional time delay for the chuck to reach a desired temperature setting, depending mostly on the size and thermal conductivity of the chuck block. These factors limit how rapidly the substrate can be cooled to a desired temperature. 
   Other methods have also been proposed and used, including the use of an electric heater embedded in a substrate holder to affect heating of the substrate. The embedded heater increases the temperature of the substrate holder, but the cooling thereof is still dependent on cooling liquid controlled by a chiller. Also, the amount of power that can be applied to the embedded heater is limited, as the chuck materials in direct contact with the embedded heater may be permanently damaged. The temperature uniformity on an upper surface of the substrate holder is also an essential factor and further limits the rate of heating. All of these factors place limits on how rapidly a temperature change of a substrate can be accomplished. 
   BRIEF SUMMARY OF THE INVENTION 
   Accordingly, one object of the present invention is to solve or reduce the above-described or other problems with conventional temperature c 
   Another object of the present invention is to provide a method and system for providing faster heating a cooling of a substrate. 
   These and/or other objects of the present invention may be provided by a method and apparatus for rapid temperature change and control of an upper part of a substrate holder that supports a substrate during chemical and/or plasma processing. 
   In accordance with a first aspect of the present invention, a substrate holder for supporting a substrate is provided. The substrate holder includes an exterior supporting surface, a cooling component, a heating component positioned adjacent to the supporting surface and between the supporting surface and the cooling component. A contact volume is positioned between the heating component and the cooling component, and is formed by a first internal surface and a second internal surface. The thermal conductivity between the heating component and the cooling component is increased when the contact volume is provided with a fluid. 
   In accordance with a second aspect of the present invention, a substrate processing system is provided. The system includes a substrate holder for supporting a substrate, including an exterior supporting surface, a cooling component including a cooling fluid, a heating component positioned adjacent to the supporting surface and between the supporting surface and the cooling component, and a contact volume positioned between the heating component and the cooling component, and formed by a first internal surface and a second internal surface. The system also includes a fluid supply unit connected to the contact volume. The fluid supply unit is arranged to supply a fluid to the contact volume and to remove the fluid from the contact volume. 
   In accordance with a third aspect of the present invention, a substrate holder for supporting a substrate is provided. The substrate holder includes an exterior supporting surface, a cooling component, and a heating component positioned adjacent to the supporting surface and between the supporting surface and the cooling component. The substrate holder also includes first means for effectively reducing a thermal mass of the substrate holder to be heated by the heating component and for increasing thermal conductivity between a portion of the substrate holder surrounding the heating component and a portion of the substrate holder surrounding the cooling component. 
   In accordance with a fourth aspect of the present invention, a method for manufacturing a substrate holder is provided. The method includes providing an external supporting surface, polishing a first internal surface and/or a second internal surface, connecting peripheral portions of the first internal surface and of the second internal surface to form a contact volume, and providing a heating component and a cooling component on opposite sides of the contact volume. 
   In accordance with a fifth aspect of the present invention, a method of controlling a temperature of a substrate holder is provided. The method includes increasing the temperature of the substrate holder, the increasing step including activating a heating component, and effectively reducing a thermal mass of the substrate holder to be heated by the heating component. The method also includes decreasing the temperature of the supporting surface, the decreasing step including activating a cooling component, and increasing a thermal conductivity between the heating component and the cooling component. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate presently preferred embodiments of the invention, and together with the general description given above and the detailed description of the preferred embodiments given below, serve to explain the principles of the invention. 
       FIG. 1  is a schematic view a semiconductor processing apparatus in accordance with an exemplary embodiment of the present invention. 
       FIG. 2  is a cross-section view of the substrate holder of  FIG. 1 . 
       FIG. 3  is a schematic view of the contact between two internal rough surfaces inside the substrate holder of  FIG. 1 . 
       FIG. 4  is a schematic view of a contact volume between two internal rough surfaces inside the substrate holder of  FIG. 1  in accordance with a further embodiment of the present invention. 
       FIG. 5  is a schematic view of a contact volume between two internal smooth surfaces inside the substrate holder of  FIG. 1  in accordance with another embodiment of the present invention. 
       FIG. 6  is a plan view of an exemplary single-zone groove pattern on an internal surface of  FIG. 5 . 
       FIG. 7  is a plan view of an exemplary dual-zone groove pattern on an internal surface of  FIG. 5 . 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring now to the drawings, where like reference numeral designations identify the same or corresponding parts throughout the several views, several embodiments of the present invention are next described. 
     FIG. 1  illustrates a semiconductor processing system  1 , which can be used for chemical and/or plasma processing, for example. The processing system  1  includes a vacuum processing chamber  10 , a substrate holder  20  having a supporting surface  22 , and a substrate  30  that is supported by substrate holder  20 . The processing system  1  also includes a pumping system  40  for providing a reduced pressure atmosphere in the processing chamber  10 , an embedded electric heating component  50  fed by a power supply  130 , and an embedded cooling component  60  with channels for a liquid flow controlled by a chiller  120 . A contact volume  90  is provided between the heating component  50  and the cooling component  60 . A fluid supply unit  140  is provided to supply and remove a fluid  92  from the contact volume  90  via the conduit  98  to facilitate heating and cooling of the substrate holder  20 . As a non-limiting example, the fluid  92  can be helium (He) gas or, alternatively, any other fluid capable of rapidly and significantly increasing or decreasing the heat conductivity across contact volume  90 . 
     FIG. 2  shows additional details of the substrate holder  20  in relation to the substrate  20 . As seen in this figure, the helium backside flow  70  is provided from a He supply (not shown) for enhanced thermal conductivity between the substrate holder  20  and the substrate  30 . The enhanced thermal conductivity ensures that rapid temperature control of the supporting surface  22 , which includes or is directly adjacent to the heating component  50 , leads to rapid temperature control of the substrate  30 . Grooves on the surface  22  can also be used for faster He gas distribution. As also seen in  FIG. 2 , the cooling component  60  includes a plurality of channels  62  arranged to contain liquid flow controlled by the chiller  120 , and the substrate holder  20  can include an electrostatic clamping electrode  80  and a corresponding DC power supply and connecting elements required to provide electrostatic clamping of substrate  30  to substrate holder  20 . 
   It is to be understood that the system shown in  FIGS. 1 and 2  is exemplary only and that other elements may be included. For example, the processing system  1  can also include a RF power supply and an RF power feed, pins for placing and removing the wafer, a thermal sensor, and any other elements known in the art. The processing system  1  can also include process gas lines entering the vacuum chamber  10 , and a second electrode (for a capacitively-coupled-type system) or an RF coil (for an inductively-coupled-type system), for exciting the gas in the vacuum chamber  10  into a plasma. 
     FIG. 3  shows the details of the contact volume  90  according to one embodiment of the present invention. As seen in  FIG. 3 , the contact volume  90  is provided between an upper internal surface  93  and a lower internal surface  96  of substrate holder  20 . In this example, the contact volume  90  is arranged as a rough contact between two rough surfaces  93  and  96 . As shown in  FIGS. 1 and 2 , each of surfaces  93  and  96  has a surface area substantially equal to the operating surface areas of heating component  50  and cooling component  60 . Alternatively, the surface areas of the surfaces  93  and  96  can be greater or smaller than the surface areas of the heating component  50  and the cooling component  60 , but the resulting contact volume  90  should be of a size facilitating rapid heating and cooling of the supporting surface  22 . Also, preferably, the supporting surface  22 , an operating surface of the cooling component  60 , an operating surface of the heating component  50 , the upper surface  93 , and the lower surface  96  can be substantially parallel to one another, although they need not be. For purposes of this document, “substantially equal” and “substantially parallel” respectively refer to a condition where any deviations from complete equality or complete parallelism are within a permitted range as recognized in the art. The preparation steps for obtaining the rough surface areas of the surfaces  93  and  96  can be as follows or, alternatively, by any other method known in the art for surface roughening. 
   First, the surfaces  93  and  96  are both polished everywhere in an area defined by radius R, where R is the full radius of the substrate holder (or through the full size, if it is not circular). Then, some techniques for surface roughening (e.g., sand blasting) are applied to an inner area of the surfaces defined by a radius R 1  (in the case of circular geometry), where R 1  is a radius slightly less than R, so only a relatively small periphery strip  95  is left as polished. Then, the upper and lower blocks corresponding to the upper surface  93  and the lower surface  96  are connected, which results in good mechanical contact at the periphery strip  95 , while leaving the contact volume  90  as being a rough contact of the surfaces  93  and  96 . 
   The idea of the rough contact is to significantly reduce the heat conductivity across contact volume  90 , while keeping surfaces  93  and  96  very close (i.e., within a range of a few microns; preferably, in the range of 1–20 microns) to each other. In the  FIG. 3  embodiment, surfaces  93  and  96  can be in contact with each other at some areas including surface irregularities, but are in most places separated. With this configuration, the thermal conductivity across contact volume  90  is reduced by an order of magnitude or more. 
   As described above, the example shown in  FIG. 3  illustrates a contact volume  90  that is formed by two surfaces  93  and  96  that have each been polished and subsequently roughened. In an alternative embodiment, only one of the surfaces  93  and  96  is roughened, such that the contact volume is formed by a polished surface on one side and a roughened surface on the opposite side. In this configuration, a rough contact is still achieved. 
   As another alternative to the embodiment illustrated in  FIG. 3 , the contact volume  90  can be formed by the upper surface  93  and the lower surface  96  such that these surfaces to not contact each other at all. This configuration is shown in  FIG. 4 , where the surfaces  93  and  96  are separated from each other by a small amount of space, i.e., where the distance across the contact volume  90  between the surfaces  93  and  96  is a few microns. Preferably, the distance across the contact volume  90  is between 1 micron and 50 microns, and, more preferably, between 1 micron and 20 microns. The surfaces  93  and  96  can be roughened (as shown in  FIG. 4 ) to increase the surface area and modify interaction of fluid  92  with the surfaces  93  and  96 . As shown in the further alternative embodiment of  FIG. 5 , the surfaces  93  and  96  can both be smooth, while separated by a small amount of space, as in the embodiment of  FIG. 4 . In both of these examples, the distance across the contact volume  90  between the surfaces  93  and  96  should be dimensioned such that the thermal conductivity of the contact volume  90  can be changed dramatically and in a controllable fashion by the introduction and evacuation of the fluid  92 . In the example of using pressurized He gas as the fluid  92 , this distance is preferably between 1 micron and 50 microns, and, more preferably, between 1 micron and 20 microns. 
     FIG. 6  illustrates a single-zone groove system including ports  105  and grooves  115 , the combination of which is provided to improve rapid distribution of the fluid  92  within the contact volume  90 . Ports  105  can be positioned on the upper surface  93  (as shown in  FIG. 6 ) and/or the lower surface  96 . The fluid  92  is supplied to the contact volume  90  through the conduit  98  and through ports  105 . Grooves  115  can also be positioned on the upper surface  93  (e.g., the smooth upper surface  93  of the embodiment shown in phantom in  FIG. 5 ) and/or on the lower surface  96 . When grooves  115  are positioned in both surfaces  93  and  96 , they can be identically configured and aligned opposite to each other or shifted relative to each other. Alternatively, each set of grooves  115  can be differently configured such that they do not align when surfaces  93  and  96  are brought together. Grooves  115  can have a width of about 0.2 mm to 2.0 mm and a depth of the same dimension range. Thermal conductivity within the contact volume  90  depends on the pressure of the fluid  92  in a zone (e.g. area) covered by grooves  115 , a condition that allows thermal conductivity profile control, and therefore temperature profile control over surfaces  93  and  96 . 
   Alternatively to the single-zone system shown in  FIG. 6 ,  FIG. 7  illustrates a dual-zone system in which a first zone  94   a  includes and is formed by inner grooves  115  and inner ports  105 , and a second zone  94   b  includes and is formed by outer grooves  116  and outer ports  106 . The inner grooves  115  govern the pressure, thermal conductivity, and temperature in the first zone  94   a  of the substrate holder, while the outer grooves  116  govern these conditions in the second zone  94   b . Grooves  115  do not connect with grooves  116  at any point on the surface  93 , creating a configuration that facilitates separate control of different zones of a contact volume. Further, a multi-zone groove system (not shown) can be provided, in which case a separate set of fluid ports is provided to each zone and different gas pressures can be used for different zones. Moreover, grooves  115  and ports  105  can alternatively be configured in any other manner to obtain a desired fluid distribution in contact volume  90 . For example, a 3-zone contact volume can include inner grooves, mid-radius grooves, and outer grooves, with independently controlled pressures of fluid  92 . 
   The various embodiments of the present invention can be operated as follows. During a heating phase, the heating component  50  is powered, while the fluid  92  is evacuated from the contact volume  90  and transferred into the fluid supply unit  140 . In this way, the heat conductivity across the contact volume  90  is greatly decreased such that the contact volume  90  acts as a heat barrier. That is, the evacuation step effectively separates the portion of the substrate holder  20  directly surrounding the cooling component  60  from the portion of the substrate holder  20  directly surrounding the heating component  50 . Thus, the mass of the substrate holder  20  to be heated by the heating component  50  is effectively reduced to only the portion of the substrate holder  20  directly over and surrounding the heating component  50 , allowing rapid heating of the supporting surface  22  and the wafer  30 . Alternative to the use of the heating component  50 , heating can be provided by an external heat flux, such as heat flux from plasma generated in the vacuum chamber  10 . 
   In the cooling phase, the heating component  50  is turned off, the fluid  92  is supplied to the contact volume  90  from the fluid supply unit  140 , and the cooling component  60  is activated. When the contact volume  90  is filled with the fluid  92 , the heat conductivity across the contact volume  90  is significantly increased, thus providing rapid cooling of the supporting surface  22  and the wafer  30  by the cooling component  60 . The small peripheral area  95  ( FIGS. 3–5 ) prevents the fluid  92  from flowing out of the contact volume  90 . In some situations, the polished area  95  can be absent, such that the whole areas of the surfaces  93  and  96  are rough. In such situations, either leakage of the fluid  92  from the contact volume  90  can be tolerated or a sealing component (e.g., an o-ring) is used to prevent leakage of the fluid  92 . 
   The present invention can be effectively applied in various systems where efficient temperature control or rapid temperature control is of importance. Such systems include, but are not limited to, systems using plasma processing, non-plasma processing, chemical processing, etching, deposition, film-forming, or ashing. The present invention can also be applied to a plasma processing apparatus for a target object other than a semiconductor wafer, e.g., an LCD glass substrate, or similar device. 
   It will be appreciated by those skilled in the art that the present invention can be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The presently disclosed embodiments are therefore considered in all respects to be illustrative and not restricted. The scope of the invention is indicated by the appended claims rather than the foregoing description and all changes that come within the meaning and range and equivalence thereof are intended to be embraced therein.