Abstract:
An apparatus and method for measuring an amount of condensable material which outgas during cure of organic thin films. The apparatus includes a hotplate placed in a chamber having a removeable liner and means for cooling the liner. The method includes: weighing the liner, sequentially placing multiple substrates on said hotplate, and then weighing the liner again.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to the field of characterizing condensable materials which outgas from organic films during heating; more specifically, it relates to an apparatus and a method for characterizing the condensable materials which outgas from organic films during heating. 
       BACKGROUND OF THE INVENTION 
       [0002]    Many organic materials, when formed into a thin layer on a substrate, outgas volatile components that can condense out on processing equipment. This can cause significant maintenance, process defects, and/or process performance degradation particularly in the lithographic processes of the semiconductor industry. Therefore, there is a need to evaluate the volatility of organic materials prior to introduction of the materials into a manufacturing environment. 
       SUMMARY OF THE INVENTION 
       [0003]    A first aspect of the present invention an apparatus, comprising: a chamber having top and sidewalls and open at a bottom, the chamber divided into an upper region and a lower region by a removeable plate, the sidewalls in the lower region covered by a removeable liner, means for introducing and controlling the flow rate of a coolant gas into the upper region of the chamber; a hotplate positioned in the lower region of the chamber, the hotplate controllable to a temperature greater than room temperature; and a first slot in the sidewall in the lower chamber, the first slot aligned with a second slot in the liner, the first and second slots adapted to allow introduction of a substrate into the chamber and placement on the hotplate. 
         [0004]    A second aspect of the present invention is a method, comprising, in the order recited: (a) weighing a plate and a liner to establish a tare weight; (b) providing a chamber having top and sidewalls and open at a bottom; (c) removeably mounting the plate in the chamber, the plate dividing the chamber into an upper region and a lower region; (d) removeably mounting the liner on the sidewalls in the lower region of the chamber; (e) introducing and controlling the flow rate of a coolant gas into the upper region of the chamber; (f) coating a set of substrates with an organic material to generate a set of coated substrates; (g) placing a coated substrate of the set of coated substrates on a hotplate positioned in the lower region of the chamber, the hotplate controlled to a temperature greater than room temperature; (h) after a fixed period of time removing the coated substrate from the hotplate; (i) repeating steps (g) and (h) for each coated substrate of the set of coated substrates; (j) removing the plate and the liner from the chamber; (k) weighing the plate and liner to obtain a post-test weight; and (l) subtracting the tare weight from the post-test weight to determine a weight of material, if any, condensed onto the plate and liner 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0005]    The features of the invention are set forth in the appended claims. The invention itself, however, will be best understood by reference to the following detailed description of an illustrative embodiment when read in conjunction with the accompanying drawings, wherein: 
           [0006]      FIG. 1  is a cross-sectional view through an apparatus for collecting condensable materials from an organic film according to the present invention; and 
           [0007]      FIG. 2  is flowchart of a method for determining the acceptability of an organic material for use in a manufacturing environment using the apparatus of  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0008]      FIG. 1  is a cross-sectional view through an apparatus for collecting condensable materials from an organic film according to the present invention. In  FIG. 1 , an apparatus  100  includes a test chamber  105  and a hotplate  110 . Chamber  105  includes a top  115  and sidewalls  120  and is divided into and upper region  125  and a lower region  130 . A slot  135  in sidewall  120  of chamber  105  allows passing of test substrates (e.g. wafers) in and out of lower region  130 . Upper region  125  is fitted with a cooling gas inlet  140  and an outlet  145 . An upper removable and disposable collection plate  150  separates upper region  125  from lower region  130  of chamber  105 . A removable and disposable sidewall liner  155  lines inner surfaces of sidewalls  120  in lower region  130 . Plate  150  prevents coolant gas from entering lower region  130 . Cooling gas entering lower region  130  of chamber  105  would reduce the amount of condensables collected on plate  150  and liner  155 , by sweeping away the liberated condensables before they contact the plate and liner. A slot  160  in liner  155  of chamber  105  allows passing of test substrates in and out of lower region  130 . In one example, plate  150  and liner  155  have a thickness T equal to between about 0.016 mm and about 0.024 mm. In one example, plate  150  and liner  155  are formed aluminum foil. It is advantageous that plate  150  and  155  be easily (e.g. by hand) compacted for weighing and easily (e.g. by hand) returned to shape for mounting in chamber  105 . 
         [0009]    In  FIG. 1 , a test substrate  165  is shown on a top surface  170  of hotplate  170  and an organic film  175  has been formed on a top surface  180  of substrate  165  prior to placing the substrate into chamber  105 . Organic film  175  is positioned a distance D from plate  150 . In one example, D is between about 20 mm and about 40 mm. In one example, substrate  165  is a silicon wafer. In one example, substrate  165  is a silicon wafer having a diameter of 8 inches. 
         [0010]    Chamber  105  is mounted to a rotatable arm  190  that is illustrated in the up position, allowing easy access to the interior of chamber  105  to place or remove plate  150  and liner  155  from the chamber. In the down position, arm  190  positions chamber  105  so wafer  165  and an upper portion of hotplate  110  are within lower region  130  of the chamber. Plate  150  and liner  155  may be held in place in chamber  105  by spring clips (not shown). Apparatus  100  may also include a robot (not shown) for moving substrates from a cassette of substrates to hotplate  110  and from hotplate  110  back to the cassette. 
         [0011]    It is advantageous for the shape of chamber  105  and the shapes of plate  150  and liner  155  to conform to the shape of substrate  165 . In the example, that substrate  165  is a circular wafer, chamber  105  would be a cylinder, plate  150  would be disc-shaped and liner  155  would be cut to be rectangular in shape and then formed into a cylinder. It is advantageous for plate  150  and liner  155  to be as light-weight as possible in order to reduce the errors in weighing the small quantities of residuals that will be deposited on the liners during testing. It is advantageous that plate  150  and  155  be easily (e.g. by hand) compacted (reduced in spatial extent, for example, by rolling or folding) for weighing and easily (e.g. by hand) returned to shape for mounting in chamber  105 . 
         [0012]    A condensable is defined as material given off by an organic film when heated above room temperature, the condensable being a solid or non-volatile residue at room temperature. A solvent is defined as material given off by an organic film when heated above room temperature that is a liquid at room temperature. The temperature of the hotplate is adjusted high enough above room temperature so solid condensables are driven off and the cooling gas flow rate is adjusted to maximize the quantity of solid condensables collected and to minimize the amount of liquid solvents collectables that are also driven from the organic film. In one example, hotplate  105  is set for between about 140° C. to about 300° C. and the flow of cooling gas is selected to maintain the temperature of plate  150  at about 35° C. or higher. In one example, hotplate  105  is set for between about 140° C. to about 300° C. and the flow of cooling gas is selected to maintain the temperature of plate  150  above the dew point of the solvent being emitted from organic film  175 . 
         [0013]    Examples of organic thin films include photoresists, anti-reflective coatings, ancillary coatings, and adhesion promoters. Examples of condensables include, but are not limited to sensitizers (material reactive to actinic radiation), photo-acid generators and cross-linking agents. 
         [0014]      FIG. 2  is flowchart of a method for determining the acceptability of an organic material for use in a manufacturing environment using the apparatus of  FIG. 1 . The steps of  FIG. 2  will be described in terms of a circular wafer substrate, but are applicable to almost any shaped substrate. In step  200 , a liner pair (upper and sidewall liners) are conditioned by heating to drive off any materials present that could interact with the condensables collected. In one example, the liners are heated to a temperature of 25° C. higher than the temperature of the hotplate in a nitrogen oven and then hermitically sealed or otherwise stored in a clean inert atmosphere. 
         [0015]    In step  205  a group of wafers of a fixed number (e.g. 50 to 100) are each coated with the same amount of a same material to be tested for condensables. In one example, a milliliter of material is dispensed onto to the top surface of each wafer and the wafer spun to form a thin film of the material on the top surface of the wafer. Optionally, the thickness of the film may be measured and the amount of material dispensed or the spin conditions adjusted to give a predetermined film thickness. 
         [0016]    In step  210  a conditioned liner pair are weighed to determine their tare weight and in step  215 , the weighed conditioned liner pair are installed in the test chamber. 
         [0017]    In step  220 , the first/next wafer of the group of coated wafers is placed on the hotplate. In step  225 , the wafer placed on the hotplate in step  220  is removed after a fixed amount of time. In one example, the fixed amount of time is between about 10 seconds and 1 minute. 
         [0018]    In step  230 , it is determined if there are more wafers in the group of wafers to be processed. If there are more wafers the method loops back to step  220 , otherwise the method proceeds to step  235 . In step  235 , the liners are removed and in step  240 , the liners are weighed. 
         [0019]    In step  245 , the weight of material collected (condensate) on the liners is determined by comparing the weight obtained in step  240  with the tare weigh obtained in step  210 . The weight of material may be compared to a specification to determine the suitability of the material for use in the manufacturing environment. 
         [0020]    Optionally, in step  250 , the composition of the condensate collected on the liners may be determined by chemical analysis. Optionally in step,  255  the wafers are cleaned (e.g. in an oxygen plasma) and stored for reuse. 
         [0021]    Thus the present invention provides an apparatus and method to evaluate the volatility of organic materials prior to introduction of the materials into a manufacturing environment. 
         [0022]    The description of the embodiments of the present invention is given above for the understanding of the present invention. It will be understood that the invention is not limited to the particular embodiments described herein, but is capable of various modifications, rearrangements and substitutions as will now become apparent to those skilled in the art without departing from the scope of the invention. Therefore, it is intended that the following claims cover all such modifications and changes as fall within the true spirit and scope of the invention.