Patent Publication Number: US-2005126490-A1

Title: Substrate temperature control apparatus

Description:
FIELD OF THE INVENTION  
      The present invention relates to a substrate temperature control apparatus adopted for use on substrates to do diamond coating by plasma and particularly to a substrate temperature control apparatus for reducing warping caused by excessive temperature variations.  
     BACKGROUND OF THE INVENTION  
      Conventional methods for diamond coating on a thick substrate (about 5 mm) that are larger than four inches generally adopt a chemical vapor deposition (CVD) process to develop a diamond film. The plasma will increase the temperature of the substrate surface instantaneously. This will cause a large temperature difference between the surface and bottom side of the substrate, and result in uneven distribution and warping of the substrate.  
      To solve this problem, the earlier approach is adopting a tempering method. However, tempered by heating the plated substrate again could change the structural strength of the surface. Moreover, the common practice does not shut down the plasma when plating of the diamond film is completed. Instead, the energy of the plasma is reduced gradually to alleviate the problem of abrupt dropping of the surface temperature of the substrate. However, after plating of the diamond film is completed, to use the plasma continuously could make the surface characteristics of the substrate uncontrollable, and the desired condition could be not achievable. U.S Pat. No. 5,620,745 discloses a technique which calculates the possible stress that will occur before the substrate is used for diamond coating, then a reverse compression stress or extension stress is applied in advance to match the deformation generated by the diamond coating to reduce warping. But such a practice is too theoretical. In practice, the stress occurred to the substrate in the reaction of high temperature plasma is difficult to calculate. Moreover, a slight change of external environments (such as alterations of temperature and humidity of the atmosphere) will cause stress variations and result in unpredictable effects.  
     SUMMARY OF THE INVENTION  
      In view of the foregoing problems, the present invention aims to provide a substrate temperature control apparatus to reduce excessive instantaneous temperature variations while the substrate is undergoing diamond coating so that the temperature of the substrate is more uniform, thereby to reducing thermal stress and warping.  
      The substrate temperature control apparatus according to the invention includes a holding dock, a temperature sensor, a heater and a cooler. The holding dock is used to hold a substrate. The temperature sensor is used to detect the temperature of the upper surface and the lower surface of the substrate. During the diamond coating process, when the temperature variation is too large, such as at the initial time when the plasma is activated, the temperature of the upper surface rises instantaneously. Then the heater is activated to heat the lower surface of the substrate so that temperature difference between the upper surface and the lower surface is reduced. On the other hand, when the diamond coating is completed, the temperature of the upper surface drops instantaneously. The cooler is used to lower the temperature of the lower surface so temperature difference between the upper surface and lower surface is smaller when the plasma is shut down. Thereby, the substrate temperature is more uniform and thermal stress and warping will be reduced.  
      The foregoing, as well as additional objects, features and advantages of the invention will be more readily apparent from the following detailed description, which proceeds with reference to the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a schematic view of the structure of the invention.  
       FIG. 2  is a schematic view of the entire system for diamond coating according to the invention.  
       FIG. 3  is a fragmentary enlarged view according to  FIG. 2 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      Refer to  FIG. 1  for the substrate temperature control apparatus according to the invention. It includes a holding dock  10 , a temperature sensor  20 , a heater  30  and a cooler  40 . The holding dock  10  has a holding trough  11 . The temperature sensor  20  includes thermal couples  22  and  21  located respectively on the bottom of the holding trough  11  and the surface of the holding dock  10 . The heater  30  and the cooler  40  are located in the holding trough  11 . A substrate  60  for diamond coating, as shown in  FIGS. 2 and 3 , is held in a cover  50  and diamond coating is performed through plasma  70 . The substrate  60  is held in the holding trough  11  of the holding dock  10 . The thermal couples  21  and  22  of the temperature sensor  20  detect respectively the temperature of the upper surface  61  and the lower surface  62  of the substrate  60 . The thermal couple  21  can also use infrared to perform temperature detection.  
      When processed by plasma  70 , the temperature will rise instantaneously (working temperature is about 750° C.-850° C.), especially the temperature of the upper surface  61 , which will rise significantly and result in a great temperature difference with the temperature of the lower surface  62 . Hence the heater  30  is activated to heat the temperature of the lower surface  62 . The heater  30  can include a plurality of electrical heaters  31 ,  32  and  33 . And they can use chrome electric heating wires. Of course, other heating methods can also be adopted.  
      When the diamond coating is completed, and the plasma  70  is shut down, the thermal couples  21  and  22  detect that the temperature of the upper surface  61  drops instantaneously. The cooler  40  is used to cool the temperature of the lower surface  62  of the substrate  60 . The cooler  40  can use a water-cooling approach, and include a plurality of water-cooling channel  41 ,  42  and  43 .  
      On the other hand, based on the temperature difference of the upper surface  61  and lower surface  62  of the substrate  60  detected by the temperature sensor  20 , a pre-determined temperature (such as 0.1° C.) may be set. When the temperature difference exceeds the pre-determined temperature, the heater  30  or cooler  40  is activated to reduce the temperature difference of the upper surface  61  and the lower surface  62  of the substrate  60 . Thus the temperature of the substrate  60  is more uniform, and thermal stress and warping can be reduced.  
      While the preferred embodiments of the invention have been set forth for the purpose of disclosure, modifications of the disclosed embodiments of the invention as well as other embodiments thereof may occur to those skilled in the art. Accordingly, the appended claims are intended to cover all embodiments, which do not depart from the spirit and scope of the invention.