Abstract:
An apparatus and method for applying a fluid spin-on material on a surface of first and second substrates. A spin coating device is configured to dispense the fluid spin-on material to form a first layer on the surface of the first substrate. A metrology tool is configured to measure a first thickness profile of the first layer and generate data representing the first thickness profile. A processing unit is electrically coupled with the metrology tool and is configured to analyze the data received from the metrology unit and to determine a variation in the first thickness profile. The processing unit then determines an adjustment to an operational parameter of the spin coating device predicted to reduce a variation in a second thickness profile of a second layer subsequently formed by the spin coating device on a second substrate.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention is related to semiconductor processing, in particular, to apparatus and methods for applying a layer of a spin-on material on a series of substrates. 
       BACKGROUND OF THE INVENTION 
       [0002]    Lithographic processes are widely used in the manufacture of semiconductor devices and other patterned structures. In track photolithographic processing used in the fabrication of semiconductor devices, the following sorts of processes may be performed in sequence: resist coating that coats a resist solution on a semiconductor wafer to form a resist film, exposure processing to expose a predetermined pattern on the resist film, heat processing to promote a chemical reaction within the resist film after exposure, developing processing to develop the exposed resist film, etc. 
         [0003]    A conventional method that may be used for coating the resist solution on a wafer is a method referred to as spin coating. Spin coating is a method in which the wafer is suction-held on a disk-shaped support member known as a spin chuck. A solution-like resist is dispensed in essentially the center of the wafer, and the spin chuck rotates. Rotating disperses the resist solution supplied to the center of the wafer radially outward by centrifugal force to coat the entire surface of the wafer. 
         [0004]    In order to suitably perform a predetermined track photolithographic process, it is important that the resist film coated on the wafer have a relatively uniform predetermined film thickness. Conventionally, this may be performed by measuring the film thickness of the resist film on the wafer before exposing a predetermined pattern on the resist film. If the allowable non-uniformity of the film thickness is exceeded, a correction is made, based on measurement results, to the rotation speed of the spin chuck in the spin coating device that applied the resist solution. 
         [0005]    Because a flat wafer should be used to accurately measure film thickness, the calibration of the spin coating device is performed before the coating/developing system is put into a production mode. Therefore, conventional practice often requires an engineer highly skilled in the art of photolithography track processing to halt the system that photolithographicly processes the production wafer, introduce the first of a series of test wafers into the photolithographic processing system, form a resist film on the wafer, and then measure the film thickness on the test wafer before pattern exposure. Subsequently, based on the result of measuring film thickness of the resist film on the test wafer, if the allowed non-uniformity for film thickness is exceeded, the process engineer may manually make a correction to the rotational speed of the wafer (rotational speed of the spin chuck), for example, in the spin coating device in the system. The process engineer may then proceed with the measurement process with the next test wafer until either an allowable thickness is attained or a maximum number of test wafers is reached. 
         [0006]    Given the complexity of resist chemistries, variations of casting and processing solvent systems, and the associated processing complexity generated by the shear number of available chemistries, the optimization of a spin-on chemistry for minimal non-uniformity of film thickness often requires an engineer highly skilled in arts of photolithography track processing. However, also given the usual highly symmetric nature of spin coating, the various parameters that affect film thickness uniformity may often be decoupled. Track process engineers call upon knowledge of parameter impact on uniformity of film thickness and a historical knowledge base of past experiences of a given chemistry and its conditions to minimize the non-uniformity. 
         [0007]    What is needed, therefore, is an apparatus and process for assisting an operator of the coating/developing system in optimizing wafer uniformity, which does not require a highly skilled photolithography track processing engineer. 
       SUMMARY OF THE INVENTION 
       [0008]    The invention addresses these and other problems associated with the prior art by providing a method and apparatus for applying a fluid spin-on material on a surface of first and second substrates. A temperature of the first substrate is regulated and a first layer of the spin-on material is applied to the surface of the first substrate. The temperature of the first substrate is elevated to treat the spin-on coating. A first thickness profile of the first layer is then measured to determine a variation in the first thickness profile. An adjustment to an operational parameter that is predicted to reduce the variation in the first thickness profile is automatically determined. The adjustment is then made to the operational parameter to affect a second layer of the spin-on material applied to the surface of the second substrate. The adjustment to the operational parameter is automatically determined by numerically analyzing data received from the a metrology unit configured to measure the first thickness profile and utilizing parameter sensitivities derived from a design of experiment model to determine the adjustment to the operational parameter. 
         [0009]    In an embodiment, the adjustment to the operational parameter is made by generating an electrical signal that represents the adjustment. The electrical signal is communicated to a device that regulates the temperature, applies the spin-on material, or elevates the temperature, and the operational parameter of the device is adjusted to reflect the communicated electrical signal. 
         [0010]    In an alternate embodiment, the adjustment of the operational parameter is made by generating an electrical signal that represents the adjustment. The electrical signal is communicated to a display, which visually indicates the operational parameter and the adjustment to the operational parameter on the display. The operational parameter of a device that regulates the temperature, applies the spin-on material, or elevates the temperature is manually adjusted to reflect the visually indicated adjustment. 
         [0011]    In some embodiments, a second thickness profile of the first layer is measured to determine a variation in the second thickness profile. The adjustment to the operational parameter of a device that regulates temperature, applies the spin-on material, or elevates the temperature is automatically determined to reduce the variation in the second thickness profile. 
         [0012]    These and other advantages and features, which characterize the invention, are set forth in the claims annexed hereto and forming a further part hereof. However, for a better understanding of the invention, and of the advantages and objectives attained through its use, reference should be made to the drawings, and to the accompanying descriptive matter, in which there is described exemplary embodiments of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with a general description of the invention given above, and the detailed description given below, serve to explain the principles of the invention. 
           [0014]      FIG. 1  is a plan view showing the general structure of a coating/developing system used to process substrates in accordance with an embodiment of the invention. 
           [0015]      FIG. 2  is a front view of the coating/developing system in  FIG. 1 . 
           [0016]      FIG. 3  is a rear view of the coating/developing system in  FIG. 1 . 
           [0017]      FIG. 4  is a diagrammatic view of a resist coating unit, a temperature regulation device, and a metrology unit included in the coating/developing system in  FIG. 1 . 
           [0018]      FIG. 5A  is diagrammatic view of a thickness measurement tool of the metrology unit of  FIG. 4  measuring coating thickness along a first diameter of a wafer. 
           [0019]      FIG. 5B  is diagrammatic view similar to  FIG. 5A  in which a coating thickness is measured along a second diameter of the wafer. 
           [0020]      FIG. 6A  is a diagrammatic cross-sectional view of a coating on a wafer in which the coating has a non-uniform thickness. 
           [0021]      FIG. 6B  is a diagrammatic cross-sectional view similar to  FIG. 6A  of another coating having a non-uniform thickness. 
           [0022]      FIG. 7A  is a diagrammatic cross-sectional view of a coating on a wafer in which the coating fails to conform to a wafer specification. 
           [0023]      FIG. 7B  is a graphical representation of a 1-D profile of the thickness of the coating of  FIG. 7A  taken across a diameter of the wafer. 
           [0024]      FIG. 8A  is a diagrammatic cross-sectional view of a coating on a wafer in which the coating thickness is asymmetrical across a diameter of the wafer. 
           [0025]      FIG. 8B  is a graphical representation of 1-D profiles of the thickness of the resist coating of  FIG. 8A  taken across two different diameters of the wafer. 
           [0026]      FIG. 9  is a flow chart showing a process of optimizing coating thickness based on historical tendencies. 
           [0027]      FIG. 10  is a flow chart showing a process of optimizing coating thickness based on a design of experiments. 
       
    
    
     DETAILED DESCRIPTION 
       [0028]    Due to the complexity of resist chemistries, variations of casting and processing solvent systems, and the associated processing complexity generated by the sheer number of available chemistries, the optimization of a spin on chemistry for minimal wafer coating non-uniformity often requires an engineer highly skilled in the arts of photolithography track processing. The track process engineers call upon a knowledge of a parameter impact on wafer uniformity from a historical knowledge base of past experiences of a given chemistry and its conditions to minimize wafer non-uniformity. This knowledge encompasses both the parameters related to the spin on coating process as well as parameters of the coating/developing system that may influence the spin on coating process. 
         [0029]    An exemplary coating/developing system  100 , as shown in  FIG. 1 , may be constituted to integrally connect a cassette station  101 , which transports a cassette typically holding  25  wafers W, for example, into the coating/developing system  100  from outside and which transports a wafer W to the cassette C; an inspection station  102  which performs a predetermined inspection on the wafer W; a processing station  103  with a plurality of types of processing devices disposed in stages to perform predetermined processes in a layered manner in the photolithography step; and an interface unit  104 , provided adjacent to the processing station  103 , for delivering the wafer W to an exposure device (not shown). 
         [0030]    A cassette support stand  105  is provided at the cassette station  101 ; the cassette support stand  105  may freely carry a plurality of cassettes C in a row in the X direction (vertically, in  FIG. 1 ). The cassette station  101  is provided with a wafer transporter  107  able to move on the transport path  106  in the X direction. The wafer transporter  107  may also move freely in the wafer array direction (Z direction; perpendicular) of the wafers W housed in the cassette C and can selectively access the wafer W vertically arrayed in the cassette C. The wafer transporter  107  may rotate around an axis (θ direction) in the particular direction, and may also access the inspection station&#39;s transfer unit  108 . 
         [0031]    A metrology unit  20  may be provided at the inspection station  102  adjacent to the cassette station  101 . The metrology unit  20  is configured to receive the wafer W and detect a condition of a layer carried by the wafer, W. For example, the metrology unit  20  may be configured to measure coating thickness across a diameter of the wafer W. 
         [0032]    The metrology unit  20  may be disposed at the negative X direction side (downward in  FIG. 1 ) of the inspection station  102 , for example. Disposed at the cassette station  101  side of inspection station  102  is the transfer unit  108  for transferring the wafer W from the cassette station  101 . A carrying unit  109  for carrying the wafer W may be provided in the transfer unit  108 . A wafer transporter  111  able to move on a transport path  110  in the X direction may be provided at the positive X direction side (upward in  FIG. 1 ) of the metrology unit  20 . The wafer transporter  110  also may move vertically and rotate freely in the θ direction, and may also access the transfer unit  108  in each processing device in a third processing device group G 3  at the processing station  103  side. 
         [0033]    A processing station  103  adjacent to the inspection station  102  is provided with a plurality of processing devices disposed in stages, such as five processing device groups G 1 -G 5 . The first processing device group G 1  and the second processing device group G 2  are disposed in sequence from the inspection station  102  side, at the negative X direction side (downward in  FIG. 1 ) of the processing station  103 . The third processing device group G 3 , fourth processing device group G 4 , and fifth processing device group G 5  are disposed in sequence from the inspection station  102  side, at the positive X direction side (upward in  FIG. 1 ) of the processing station  103 . A first transport device  112  is provided between the third processing device group G 3  and the fourth processing device group G 4 . The transport device  112  may transport the wafer W to access each device in the first processing device group G 1 , third processing device group G 3 , and fourth processing device group G 4 . A second transport device  113  transports the wafer W and selectively accesses the second processing device group G 2 , fourth processing device group G 4 , and fifth processing device group, G 5 . 
         [0034]    Referring now to  FIG. 2 , the first processing device group G 1  stacks liquid processing devices that supply a predetermined liquid spin on material to the wafer W and process it. Devices such as spin coating devices  120 ,  121 , and  122 , which may apply a resist solution to the wafer W and form a resist film, and bottom coating devices  123  and  124 , which form an anti-reflection film that prevents light reflection during exposure processing, may be arranged in five levels in sequence from the bottom. The second processing device group G 2  stacks liquid processing devices such as developing devices  130 - 134 , which supply developing fluid to the wafer W and develop it, in five levels in sequence from the bottom. Also, terminal chambers  140  and  141  are provided at the lowest stages of the first processing device group G 1  and the second processing device group G 2  in order to supply processing liquids to the liquid processing devices in the processing device groups G 1  and G 2 . 
         [0035]    Also, as shown in  FIG. 3 , for example, the third processing device group G 3  stacks temperature regulation device  150 , transition device  151  for transfer of the wafer W, high precision temperature regulation devices  152 - 154 , which regulate the temperature of the wafer W under high precision temperature management, and high temperature heating devices  155 - 158 , which heat the wafer W to high temperature, in nine levels in sequence from the bottom. 
         [0036]    The fourth processing device group G 4  stacks a high precision temperature regulation device  160 , pre-baking devices  161 - 164  for heating the wafer W after resist coating processing, and post-baking devices  165 - 169 , which heat the wafer W after developing, in ten levels in sequence from the bottom. Each of the pre-baking devices  161 - 164  and post-baking devices  165 - 169  includes a hotplate (not shown) for elevating the temperature of the wafer W and the layer on the wafer W. 
         [0037]    The fifth processing device group G 5  stacks a plurality of heating devices that heat the wafer W, such as high precision temperature regulation devices  170 - 173 , and post-exposure baking devices  174 - 179  in ten levels in sequence from the bottom. 
         [0038]    A plurality of processing devices may be disposed at the positive X direction side of the first transport device  112  as shown in  FIG. 1 . Adhesion devices  180  and  181  for making the wafer W hydrophobic and heating devices  119  and  114  for heating the wafer W are stacked in four levels in sequence from the bottom, as shown in  FIG. 3 , for example. A peripheral exposure device  115  for selectively exposing only the edge of the wafer W may be disposed at the positive X direction side of the second transport device  113  as shown in  FIG. 1 . 
         [0039]    Provided in the interface unit  104  are a wafer transporter  117  that moves on a transport path  116  extending in the X direction as shown in  FIG. 1  and a buffer cassette  118 . The wafer transporter  117  can move in the Z direction and can rotate in the θ direction; and can transport the wafer W and access the exposure device (not shown) adjacent to the interface unit  104  and the buffer cassette  118  and the fifth processing device group G 5 . 
         [0040]    Wafers W are coated in the spin coating devices  120 - 122  which may be seen in greater detail in  FIG. 4 . The structure of the spin coating device  120 , for example, may have a chamber wall  11 . A substrate support, which has the form of a spin chuck  14  in the representative embodiment, is disposed inside the chamber wall  11 . The spin chuck  14  has a horizontal upper surface on which the wafer W is supported during processing. A suction port (not shown) may be provided in its upper surface for securing the wafer W to the spin chuck  14  with suction. 
         [0041]    The spin chuck  14  and the wafer W supported by the spin chuck  14  may be rotated at a variable angular velocity by a drive mechanism  15 , which may be a stepper motor, etc. Additionally, a lift drive source, such as a cylinder, may be provided in the drive mechanism  15  so the spin chuck  14  may move vertically relative to the chamber wall  11 . The drive mechanism may operate at two different angular velocities, one for the application of the spin-on material, and one for the reflow of the material on the substrate. 
         [0042]    A dispenser, which has the form of a nozzle  12  in the representative embodiment, is adapted to dispense resist solution onto the wafer, W at a specified rate. The nozzle  12  is coupled to a supply unit  92  configured to control the temperature of and supply specific volume for a flow of a spin-on material, which may comprise a resist solution. A drive mechanism  90  may move the nozzle  12  in the plane of the wafer W, as well as normal to the surface of the wafer W, in order to adjust the position of the nozzle  12  relative to the wafer W. The nozzle  12  and/or the supply unit  92  may include a heater (not shown) for regulating the temperature of the liquid spin-on material. 
         [0043]    A cup  13  bounding a processing space  19  may be provided about the periphery of the spin chuck  14  to capture and collect a majority of the liquid spin-on material ejected from the wafer W by centrifugal forces generated during rotation by the spin chuck  14 . The spin chuck  14  supports and rotates (i.e., spins) the wafer W about its central normal axis relative to the cup  13 , which is stationary. An exhaust port  18  communicates with the processing space  19  bounded by the cup  13 . The processing space  19  is coupled by the exhaust port  18 , which extends through the chamber wall  11 , with a negative pressure-generating device  94 , such as a vacuum pump. Operation of the negative pressure-generating device  94  continuously removes gaseous species at an exhaust rate, including but not limited to vapors released from layer  34  during processing, from the processing space  19  inside cup  13 . The processing space  19  bounded by the cup  13 , which contains a gaseous atmosphere, is also coupled by a drain port  17  with a drain unit  96 , which disposes of liquid spin-on material collected by the cup  13  and drained from the processing space  19  through drain port  17 . 
         [0044]    A controller  16  is electrically connected to the drive mechanism  90 , resist supply unit  92 , exhaust unit  94 , drain unit  96 , and the chuck drive mechanism  15 . The controller  16  is configured to respond to changes in parameters for the various components, which in turn adjust the performance of the spin coating device  120 . The controller  16  may be connected to a processing unit  24 , which is configured to provide the controller  16  with modified parameter information to automatically adjust the performance of the spin coating device  120 . The processing unit  24  may receive input from the metrology unit  20  that is representative of the condition of the layer  34  carried on the wafer W. 
         [0045]    The processing unit  24  may also be electrically connected to a temperature controller  32  for the temperature regulation device  160 . The temperature controller  32  may also be configured to respond to changes in parameters for a chill plate  31 , which in turn affect the coating thicknesses produced by the spin coating device  120 . The chill plate  31  may be electrically connected to the temperature controller  32 , which is in turn connected to the processing unit  14 . A wafer W may be delivered to the temperature regulation device  160  where it is supported above a chill plate  31 . The wafer may be delivered to the temperature regulation device  160  before or after the spin coating device  120 . Operational parameters such as chill plate temperature and chill time may affect the coating thickness of layer  34  across the diameter of the wafer. For example, a wafer temperature that is greater than the temperature of the spin-on material may create a concave profile. Similarly, a wafer temperature that is less than the temperature of the spin-on material may create a convex profile. A chill time that is too short may lead to across wafer thermal non-uniformities causing non-uniform profiles. 
         [0046]    The metrology unit  20 , as shown in  FIG. 4 , may be configured to measure the coating thickness of layer  34  across a diameter of the wafer W. After coating the wafer W in the spin coating device  120 , the wafer W may be transported to a baking device  161  and a temperature regulation device  170  prior to being delivered to the metrology unit  20 . The metrology unit  20  has an outer wall  21 , which may be sealed. The wafer W is delivered to the metrology unit  20  and may be supported on the wafer support  22  during processing. 
         [0047]    A thickness measurement tool  23  of the metrology unit  20  is configured to measure a thickness of the layer  34  on the wafer W in a profile taken, for example, across a diameter of the wafer W. The thickness profile of layer  34  represents point-by-point thickness data mapped as a function of position on a top surface of layer  34 . The data in the thickness profile is generated at a sufficient number of discrete positions to map the layer  34  across the diameter. The data generated by the thickness measurement is then sent to the processing unit  24 , which is connected between the metrology unit  20 , the spin coating device  120  the temperature regulation device  152 , and the baking device  161 . The thickness measurement tool  23  may generate the data by optical digital profiling (ODP) or other techniques understood by a person having ordinary skill in the art. 
         [0048]    The processing unit  24  may be composed of a processor  25 , a volatile memory  26 , and a nonvolatile memory  27 . A 1-D profile of the thickness of layer  34  created from the diameter measurement data from the metrology unit  20  may be sent and stored in the volatile memory  26  of the processor unit  24  as the processor  25  determines, by use of an analysis engine, if the diameter measurements are within the wafer specification. More specifically, the processor  25  determines an average thickness and standard deviation from the average thickness based upon the 1-D profile. The processor unit  24  may then adjust operational parameters of the spin coating device  120 , for example, and send the adjustments to the controller  16 . As shown in  FIG. 4 , the processing unit  24  may also be electrically connected to a temperature regulation device  160 . The processing unit  24  may communicate with a temperature controller  32 , which in turn adjusts the temperature of a chill plate  31  in the temperature regulation device  160 . The processing unit  24  may also be electrically connected to other components of the coating/developing system  100 , the heating and baking devices  155 - 158 ,  161 - 169 ,  174 - 179  to adjust operational parameters related to bake or cool time and temperature. 
         [0049]    The processing unit  24  may display instructions to an operator of the coating/developing system  100  directing the operator to make adjustments to these other components, which may have an influence on the spin coating process of the spin coating device  120 . For example, the temperature regulation devices  150 , 152 - 154 , 160 ,  170 - 173  may have operational parameters that may automatically adjust the temperature of the chill plate while other operational parameters may be adjustable by the operator. Similarly, the heating and baking devices  155 - 158 ,  161 - 169 ,  174 - 179 , may have an exhaust port to remove any waste product or impurities produced from the coating  31  on the topside  30  of the wafer W during the heating process. The exhaust port may have an exhaust rate that may adjustable by the operator. 
         [0050]    In order to ensure accurate coating measurements, the thickness measurement tool  23  may measure the thickness of the coating along multiple diameters of the wafer, creating multiple 1-D profiles, as shown in  FIGS. 5A and 5B . In one embodiment, two diameter measurements creating two 1-D profiles  36 ,  38  may be made by the thickness measurement tool  23  of the metrology unit  20 . Both 1-D profiles  36 ,  38  may then be sent to the processing unit  24  for analysis. 
         [0051]    The suction port on the spin chuck  14 , in some embodiments, may act as a heat sink causing a temperature gradient across the wafer W affecting the thickness of the coating on the wafer, as can be seen in the examples in  FIGS. 6A and 6B  in which differences in thickness are exaggerated for purposes of illustration. For example, in  FIG. 6A , the coating  31  deposited on the topside  30  of wafer W is thicker in the regions that correspond spatially to the location of the suction port of the spin chuck  14 , which holds the wafer W in place during the spin coating process. In other cases, the suction port of the spin chuck  14  may have the opposite effect, as shown in  FIG. 6B , where the coating  32  deposited on the topside  30  of wafer W is thinner in the area immediately above the suction port of the spin chuck  14 . 
         [0052]    An exemplary coating that is outside of the wafer specification may be seen in  FIG. 7A . The coating  33  deposited on the topside  30  of wafer W shows a non-uniform coating thickness thicker in the center tapering down and then again slightly thicker toward the edges. The graph shown in  FIG. 7B , illustrates the 1-D profile obtained from the diameter measurement data made by the thickness measurement tool  23  of the metrology unit  20 , which may be sent to the processing unit  24  for analysis. After analysis of the 1-D profile is made by the processing unit  24 , parameters that directly influence the coating thickness may be automatically adjusted by the controller to correct the non-uniformity of the coating across the wafer W. These parameters include, but are not limited to a resist temperature, chill plate temperature, resist dispense rate, angular velocity of the spin chuck, resist dispense volume, dispense time, reflow step time, or reflow step angular velocity. Historical data acquired from previous measurements or parameter sensitivities obtained from a Design of experiment may be used as part of the analysis engine executing in the processing unit  24  to adjust the parameters, optimizing coating thickness on wafer W. 
         [0053]    Another example of a non-uniform coating may be seen in  FIG. 8A . The layer  34  deposited on the topside  30  of wafer W may be biased toward one side of the wafer such that a 1-D profile from a single diameter measurement may not detect the wafer non-uniformity. As can be seen in the graph in  FIG. 8B , a 1-D profile of one diameter thickness indicates a fairly uniform coating thickness across the diameter where a second 1-D profile illustrates a non-uniformity from one edge of the wafer across the diameter to the second edge of the wafer. One reason to take multiple diameter measurements to create multiple 1-D profiles in some embodiments may be to detect this type of non-uniformity in the wafer. To keep the number of diameter measurements to a minimum, measurements may be taken approximately 90 degrees apart from one another in order to capture non-uniformities across the wafer. 
         [0054]    In addition to the parameters mentioned above, other parameters of the coating/developing system  100  may have an indirect affect on the wafer thickness. These parameters of the coating/developing system  100  may take longer to stabilize and may not be well suited for automatic adjustments. The system parameters may include parameters such as a coater exhaust, hot plate exhaust, temperature, airflow in the cup, humidity or water content in the cup. While some of these parameters may not be able to be adjusted automatically by the processing unit  24  through the controller  16 , in some embodiments, the processing unit  24  may include a display  28  to display instructions directed to an operator of the coating/developing system to adjust the parameter, for example, manually adjusting the humidity with a humidity control device  93  coupled to the processing space  19  in the spin coating device  120 . 
         [0055]    The processor unit  24 , in one embodiment, may utilize a historical database containing data related to the parameters to dial into a best case faster. Given a statistical relevant amount of historical data from a broad selection of chemistries, significant parametric tendencies may be calculated and understood to generate a thickness uniformity model engine. The historical knowledge base may originate from past experiences of a skilled engineer for a given chemistry and its relative parameter sensitivities. This information may be entered into the model engine, which may refine the data during future optimization cycles. If no historical data exists for a given chemistry, the thickness uniformity model engine may use data from similar chemistries to adjust parameters, while building a new knowledge base for the new chemistry to be used in later processing. 
         [0056]      FIG. 9  illustrates one embodiment to optimize coating thickness. A set of input parameters for the controller  16  of the spin coating device  120  may be determined in block  40 . In block  42 , the spin coating process is run on a first wafer. The spin coating process may contain multiple steps that prepare and coat the wafer W. For example, during a single a coating process, the wafer W may be delivered to baking units  155 - 158  for an adhesion step and then sent to a pre-coating chill in temperature regulation devices  152 - 154 . The wafer W may then be delivered to a spin coating device  120 - 122  to receive a coating of liquid spin-on material. The wafer W may then be delivered to a baking unit  161 - 164  for a pre-exposure bake. The pre-exposure bake at least partially cures the spin-on material in the coating or layer of liquid spin-on material. After the bake, the wafer W may be delivered to a temperature regulation device  170 - 173  where the temperature of the wafer W and the layer  34  deposited on the topside  30  of the wafer W are cooled, completing the coating process. After being coated, the wafer is transferred to the metrology unit  20  where, in block  44 , a bare wafer thickness measurement is made in a diameter scan mode. The one-dimensional profile from the bare wafer thickness is sent to the processing unit  24  in block  46  for analysis automatically and without human intervention. If the uniformity of the coating on the wafer W is within the wafer specification (yes branch of decision block  48 ), then the optimized conditions and results of the parameters are reported in block  58 . 
         [0057]    If the uniformity of the coating is not within the wafer specification (no branch of decision block  48 ) then a check for another wafer is performed. If all of the wafers W of the lot, typically 25, have been exhausted (no branch of decision block  50 ), then the parameters in current optimized conditions are reported in block  58 . If another wafer W is available (yes branch of decision block  50 ), then the processing unit  24  determines an adjustment to at least one of the parameters in block  52  and the parameter is adjusted either automatically without human intervention when data is sent to the controller  16  in block  54  or with human intervention when the parameter is one that requires a longer time for stabilization. In the latter case, the processing unit  24  may display instructions on the display  28  directing an operator to adjust the parameter. Another wafer W is then selected and run through the spin coating process in block  56 , which in turn is then sent to the metrology unit  20  for a bare wafer thickness measurement. The process continues until either the uniformity of the coating on the wafer W falls within the wafer specification or the lot of wafers is exhausted. 
         [0058]    In an alternate embodiment and with reference to  FIG. 10 , the analytical engine in the processing unit  24  may be driven by a design of experiment. A design of experiment (DOE) is a structured, organized method for determining the relationship between factors (spin coating input parameters) affecting a process and the output of that process (film coating thickness on the wafer). Design of experiment techniques analyze the effect of varying several variables simultaneously in order to get the most data with the fewest runs (each run generates the result from and the set values of the variables being studied) while capturing interaction effects between the variables being studied. Designed experiments typically rely on random test runs. The runs may be in a random order to avoid introducing bias into the results. 
         [0059]    DOE may be utilized in the processing unit  24 , as shown in the flow chart in  FIG. 10 . Input parameters for the controller  16  are determined in block  60 . In block  62 , the variable parameter sensitivities are determined using design of experiments. A first wafer W is then run through the spin coating process in block  64 , which may contain steps similar to the spin coating process described for the embodiment in  FIG. 9  above. The pre-exposure bake at least partially cures the spin-on material in the coating or layer of liquid spin-on material. The wafer W is transferred to metrology unit  20  and, in block  66 , a bare wafer thickness measurement is made in the diameter scan mode of the metrology unit. The one-dimensional profile data from the bare wafer thickness measurement is sent to the processing unit  24  for automatic analysis without human intervention in block  68 . If the uniformity of the coating on the wafer W is within the wafer specification (yes branch of decision block  70 ), then the optimized conditions and the results are reported in block  80 . 
         [0060]    If the uniformity of the coating is not within the wafer specification (no branch of decision block  70 ), then a check is made for another wafer W. If another wafer w is not available (no branch of decision block  72 ) because all of the wafers W in the lot have been exhausted, then the optimized conditions and the results at this point are reported in block  80 . If another wafer W is available (yes branch of decision block  72 ), then an adjustment to at least one of the parameter is determined by the parameter sensitivities that are calculated by the design of experiments in block  74 . Adjustments are made to the parameters in block  76 , which are then sent to the controller  16  to be ready for the next spin coating process. The adjustments may be communicated directly to the controller  16  or may be communicated to an observer via display. A new wafer W is selected and run through the spin coating process in block  78  after which it is transferred to the metrology unit  20  for a thickness measurement. The process continues until either a coating with a uniformity that is within the wafer specification is reached or the lot of wafers is exhausted. 
         [0061]    Using an automated process that utilizes either historical data or DOE may allow field engineers who are installing and setting up the coating/developing systems  100  to be able to configure those systems to produce uniform coatings on wafers W in a shorter time frame than has been done traditionally in the past. In addition to the automated parameter adjustments, field engineers may not need to be experts in order to determine which of the coating/developing system  100  parameters to adjust to provide coating uniformity on the wafers W. In this particular illustrated embodiment, the metrology unit  20  was shown to be integrated with the coating/developing system  100 . In other embodiments, the metrology unit may be off-line. Likewise, while historical data stored in a database or design of experiments was used in the analytical engine executing in the processing unit  24 , any numerical methods appropriate for analyzing the one-dimension profile and comparing it against the wafer specification to determine parameter adjustments may be used. 
         [0062]    While the invention has been illustrated by a description of various embodiments and while these embodiments have been described in considerable detail, it is not the intention of the applicants to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art. The invention in its broader aspects is therefore not limited to the specific details, representative apparatus and method, and illustrative examples shown and described. Accordingly, departures may be made from such details without departing from the spirit or scope of applicant&#39;s general inventive concept.