Abstract:
A method of adjusting a spacing between a gas distribution member and a substrate support includes forming a layer on a substrate disposed on the substrate support; measuring a thickness of the layer on the substrate; and calculating differences in thickness between a reference location on the substrate and a plurality of remaining locations on the substrate. The method further comprises computing spacing adjustment amounts for the remaining locations relative to the reference location based on the differences in thickness between the reference location and the remaining locations.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     The present application is a Divisional of U.S. patent application Ser. No. 10/618,187 filed Jul. 10, 2003; the disclosure of which is incorporated herein by reference in its entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates generally to semiconductor manufacturing and, more particularly, to a method and an apparatus for achieving a desired thickness uniformity of a layer formed on a substrate. 
     One of the primary steps in the fabrication of modern semiconductor devices is the formation of a thin film on a semiconductor substrate by chemical reaction of gases. Such a deposition process is referred to as chemical vapor deposition (CVD). Conventional thermal CVD processes supply reactive gases to the substrate surface where heat-induced chemical reactions can take place to produce the desired film. Plasma enhanced CVD processes promote the excitation and/or dissociation of the reactant gases by the application of radio frequency (RF) energy to the reaction zone proximate the substrate surface thereby creating a plasma of highly reactive species. The high reactivity of the released species reduces the energy required for a chemical reaction to take place, and thus lowers the required temperature for such CVD processes. 
     The substrate rests on a substrate support during processing in the chamber such as the formation of a layer on the substrate. The substrate support typically is a substrate heater which supports and heats the substrate during substrate processing. The substrate rests above the heater surface of the heater and heat is supplied to the bottom of the substrate. Some substrate heaters are resistively heated, for example, by electrical heating elements such as resistive coils disposed below the heater surface or embedded in a plate having the heater surface. The heat from the substrate heater is the primary source of energy in thermally driven processes such as thermal CVD for depositing layers including undoped silicate glass (USG), doped silicate glass (e.g., borophosphosilicate glass (BPSG)), and the like. 
     The substrate support typically supports the substrate opposite a gas distribution faceplate through which a reactant gas is supplied to the chamber. The faceplate is part of the gas distribution member for supplying one or more gases to the chamber. The gas flow from the faceplate to the substrate affects the uniformity of the layer formed on the substrate, such as the thickness of the layer. 
     BRIEF SUMMARY OF THE INVENTION 
     Embodiments of the present invention are directed to adjusting the spacing between the substrate support and the faceplate of the gas distribution member to achieve improved uniformity of the layer formed on the substrate. The spacing between the substrate support and the faceplate affects the gas flow to the substrate surface and the uniformity of the layer formed on the substrate surface. The spacing between the substrate and the faceplate is typically about 0.2 inch. In some processes, the substrate is placed very close to the faceplate (e.g., spaced by about 0.1 inch or less) to increase film deposition rate. This decrease in spacing renders the film thickness uniformity more sensitive to the uniformity of spacing between the substrate and the faceplate. 
     One embodiment of the present invention is directed to a method of adjusting a spacing between a gas distribution member and a substrate support disposed generally opposite from the gas distribution member, wherein the substrate support is configured to support a substrate on which to form a layer with improved thickness uniformity. The method comprises forming a layer on the substrate disposed on the substrate support; measuring a thickness of the layer on the substrate; and calculating differences in thickness between a reference location on the substrate and a plurality of remaining locations on the substrate. The method further comprises computing spacing adjustment amounts for the remaining locations relative to the reference location based on the differences in thickness between the reference location and the remaining locations. The spacing adjustment amount is positive to increase the spacing between the substrate support at the location and the gas distribution member if the thickness is greater at the location than at the reference location. The spacing adjustment amount is negative to decrease the spacing between the substrate support at the location if the thickness is smaller at the location than at the reference location. 
     In accordance with another embodiment of the invention, an apparatus for adjusting a spacing between a gas distribution member and a substrate support comprises a processing chamber including a gas distribution member, and a substrate support disposed in the processing chamber and located generally opposite from the gas distribution member. The substrate support has a substrate support surface configured to support a substrate on which to form a layer. A leveling plate is coupled to the substrate support, the leveling plate including at least three measurement locations to mount a measuring device to measure distances between the leveling plate and a reference surface fixed with respect to the gas distribution member at each of the measurement locations. At least three adjustment members are each coupled between the leveling plate and the reference surface. The at least three adjustment members are disposed at separate adjustment locations distributed over the leveling plate and independently adjustable to change positions of the leveling plate relative to the reference surface, thereby adjusting spacings between the substrate support surface and the gas distribution member at a plurality of corresponding adjustment locations on the substrate support surface to modify a tilt of the substrate support surface with respect to the gas distribution member. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a simplified front elevational view of a substrate support showing a height adjustment mechanism according to an embodiment of the present invention; 
         FIG. 2  is a side elevational view of a portion of the height adjustment mechanism of  FIG. 1  showing slots for a micrometer; 
         FIG. 3  is a side elevational view of a portion of the height adjustment mechanism of  FIG. 1  showing the use of a micrometer for measuring height adjustments; 
         FIG. 4  shows a plot of the deposition rate in thickness per time versus the spacing between the substrate and the faceplate for one semiconductor process; 
         FIG. 5  shows a plot of the deposition rate in thickness per time versus the spacing between the substrate and the faceplate for another semiconductor process; 
         FIG. 6  is a flow diagram of the substrate support leveling method according to an embodiment of the present invention; and 
         FIG. 7  is a thickness map of a layer formed on the substrate in one example. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     As shown in  FIG. 1 , a substrate holder or support  10  is disposed in a processing chamber  12  for processing a substrate  13  to be placed on the substrate support surface  14 . A gas distribution member  16 , which is typically a faceplate having a plurality of apertures for introducing gases, is disposed generally opposite from the substrate support surface  14 . The substrate holder  10  includes a shaft  18  which is supported on a support structure or hub  20  and is slidable with respect to the hub  20  to adjust the spacing between the substrate holder surface  14  and the faceplate  16 . The hub  20  is disposed outside of the chamber  12 . The shaft  18  is movable vertically by an actuator  24 . The tilt of the substrate holder  10  can be defined by the tilt of the hub  20  due to the connection therebetween. The hub  20  is connected to a bracket  28 , which is mounted to a leveling member or leveling plate  30 . Adjustment of the tilt of the substrate holder  10  is made by adjusting the tilt of the leveling plate  30 . 
     The leveling plate  30  is disposed generally parallel to the substrate support surface  14 . At least three adjustment members  34  are coupled between the leveling plate  30  and a reference surface  36 . In the embodiment shown, the reference surface  36  is the bottom surface  36  of the chamber  12 , but it may be some other surface that is fixed with respect to the faceplate  16 . The reference surface  36  may be generally parallel to the faceplate  16 . The adjustment members  34  are connected to the leveling plate  30  at a plurality of adjustment locations  40  distributed over the leveling plate  30 . The adjustment members  34  are independently adjustable to change the spacings between the leveling plate  30  and the reference surface  36  at the adjustment locations  40 . This in turn alters the spacings between the substrate support surface  14  and the faceplate  16  at a plurality of corresponding adjustment locations  42 , thereby adjusting the tilt of the substrate support surface  14  with respect to the faceplate  16 . In the embodiment of  FIG. 1 , the corresponding adjustment locations  42  of the substrate support surface  14  are generally aligned with the adjustment locations  40  of the leveling plate  30 , since the leveling plate  30  is generally parallel to the substrate support surface  14 . In specific embodiments, the corresponding adjustment locations  42  are uniformly distributed around the substrate support surface  14  with respect to the center of the support surface  14 . 
     As more clearly seen in  FIG. 2 , the leveling plate  30  includes a plurality of measurement locations  50  for mounting measurement devices to measure the spacings between the leveling plate  30  and the reference surface  36 . As illustrated in  FIGS. 2 and 3 , the measurement locations  50  include slots for mounting measurement devices  54  which may be micrometers. The micrometers  54  may be temporarily mounted at the measurement locations  50  when the leveling plate  30  is adjusted, and be removed after the adjustments are made. Typically, each measurement location  50  has a corresponding adjustment location  40 , and each measurement location  50  is disposed in close proximity or adjacent to the corresponding adjustment location  40 . For instance, the distance between each measurement location  50  and the corresponding adjustment location  40  is substantially less than the diameter of the substrate  13  (e.g., less than about 10% of the diameter of the substrate). In alternate embodiments, the numbers and proximity of the measurement locations  50  and adjustment locations  40  may vary. 
     The adjustment members  34  each include adjustment screws threadingly coupled to the leveling plate  30  and having ends  58  that bear against the reference surface  36  of the processing chamber  12 . A knurled lock nut  60  is threadingly coupled to each adjustment screw  34  and bears against the bottom surface of the leveling plate  30 . Another knurled lock nut  62  may also be provided to be threadingly coupled to the adjustment screw  34  and to bear against the top surface of the leveling plate  30 . The knurled lock nuts preferably provide sufficiently fine adjustments to achieve the desired accuracy of tilt adjustment of the leveling plate  30  and hence the substrate support surface  14  (e.g., adjustments on the order of about 4 mil). An Allen wrench or the like may be used to turn the knurled lock nuts for adjustment. Of course, other suitable adjustment mechanisms may be used in alternate embodiments. 
     Experiments have demonstrated that the deposition rate of the layer on a substrate  13  can be correlated to the spacing between the substrate  13  and the faceplate  16 , and hence the uniformity of the thickness of the layer formed on the substrate  13  can be adjusted by changing the tilt of the substrate support surface  14  on which the substrate  13  rests. Experimental results for two sets of tests are shown in  FIGS. 4 and 5 . 
     In  FIG. 4 , BPSG films were formed on substrates while varying the spacing between the substrate and the faceplate. The films were deposited using He, TEOS, TEB, TEPO as process gases at a temperature of about 550° C. and a pressure of about 200 Torr.  FIG. 4  plots the deposition rate in thickness per time (Å/min) versus the spacing (mils). As the spacing increases, the deposition rate decreases by about 27.953 Å/min, which is the slope of the line that is used to compute a correlation factor for the particular process. 
     In  FIG. 5 , BPSG films were formed on substrates while varying the spacing between the substrate and the faceplate. The films were deposited using He, TEOS, TEB, TEPO as process gases at a temperature of about 550° C. and a pressure of about 200 Torr. As the spacing increases, the deposition rate decreases by about 23.169 Å/min, which is the slope of the line that is used to computer a correlation factor for the particular process. The relatively small difference in the results obtained for  FIG. 4  and  FIG. 5  may be attributed to the variability of the leveling mechanism, liquid flow variations, fab temperatures, and the like. 
     A three point counter-tilt procedure will now be described for adjusting the tilt of the substrate support surface to improve uniformity based on the correlation between deposition rate and spacing between the substrate and the faceplate that has been established for the particular type of process involved. As shown in the flow diagram  100  of  FIG. 6 , a layer is formed on the substrate after positioning the substrate support at a desired spacing from the faceplate (step  102 ). The thickness of the layer is measured in step  104 , which may be done in situ.  FIG. 7  shows an example of a thickness map  90  having 49 points to generate a thickness profile of the layer on the substrate. Three points  92 ,  94 ,  96  on the substrate correspond in location to the three measurement locations  50  on the leveling plate  30  for making spacing measurements using the micrometers  54  as illustrated in  FIG. 3 . The three points  92 ,  94 ,  96  are typically close to the edge of the substrate, and angularly spaced generally uniformly with respect to the center of the substrate. For example, the three points  92 ,  94 ,  96  are spaced about 120° apart with respect to the center of the substrate, and are each spaced from the edge of the substrate by a distance that is less than about 10% of the radius of the substrate. 
     Referring to  FIG. 6 , the next step  106  is to calculate the thickness differences among the three points. For instance, the point  92  is selected as a reference location and the thickness differences are calculated between the reference point  92  and the other points  94 ,  96  at the remaining locations. In step  108 , the thickness differences (between the points  94  and  92  and between the points  96  and  92 ) are divided by the deposition time to obtain the deposition rate differentials between the reference point  92  and the remaining points  94 ,  96 . A previously determined correlation factor is then used to convert the deposition rate differentials into spacing adjustments at the remaining points  94 ,  96  to improve the uniformity (step  110 ). The spacing adjustment is positive to increase the spacing between the substrate support at the remaining point and the faceplate if the thickness is greater at that remaining point than at the reference point  92 . Conversely, the spacing adjustment is negative to decrease the spacing between the substrate support at the remaining point and the faceplate if the thickness is smaller at that remaining point than at the reference point  92 . In step  112 , the spacing adjustments are made, and the substrate support is calibrated for forming layers of improved uniformity for the particular process selected. 
     The correlation factor is proportional to the slope of a plot of deposition rate versus spacing such as those shown in  FIGS. 4 and 5 . That is, the correlation factor is proportional to a ratio of change in spacing divided by deposition thickness rate of the layer. Typically, the correlation factor will not be equal to the slope, but will need to be modified to account for the difference between the three point counter-tilt procedure and the spacing adjustments used to obtain the slope of the plot. To obtain the plot, the substrate is moved up or down without tilting. In the three point counter-tilt procedure, however, the spacing at one of the remaining points is adjusted with respect to the reference point to tilt the substrate. Thus, the correlation factor will equal to the slope of the plot multiplied by a correction factor or constant, which may be determined empirically by conducting a number of experiments to determine the correction factor to achieve film thickness uniformity. 
     Various experiments were conducted to confirm the repeatability of the three point counter-tilt procedure to achieve improvement in thickness uniformity in the layer formed on the substrate for particular semiconductor processes. 
     The above-described arrangements of apparatus and methods are merely illustrative of applications of the principles of this invention and many other embodiments and modifications may be made without departing from the spirit and scope of the invention as defined in the claims. For instance, the number of measurement locations may be more than three. The scope of the invention should, therefore, be determined not with reference to the above description, but instead should be determined with reference to the appended claims along with their full scope of equivalents.