Abstract:
The present invention is directed to providing a method and system to measure characteristics of a film disposed on a substrate. The method includes identifying a plurality of processing regions on the film; measuring characteristics of a subset of the plurality of processing regions, defining measured characteristics; determining a variation of one of the measured characteristics; and associating a cause of the variations based upon a comparison of the one of the measured characteristics to measured characteristics associated with the remaining processing regions of the subset. The system carries out the aforementioned method.

Description:
BACKGROUND OF THE INVENTION 
     The field of invention relates generally to imprint lithography. More particularly, the present invention is directed measuring characteristics of a films patterned employing imprint lithography processes. 
     Micro-fabrication involves the fabrication of very small structures, e.g., having features on the order of micro-meters or smaller. One area in which micro-fabrication has had a sizeable impact is in the processing of integrated circuits. As the semiconductor processing industry continues to strive for larger production yields while increasing the circuits per unit area formed on a substrate, micro-fabrication becomes increasingly important. Micro-fabrication provides greater process control while allowing increased reduction of the minimum feature dimension of the structures formed. Other areas of development in which micro-fabrication has been employed include biotechnology, optical technology, mechanical systems and the like. 
     Exemplary micro-fabrication technique are disclosed in U.S. Pat. No. 6,334,960 to Willson et al. and by Chou et al. in  Ultrafast and Direct Imprint of Nanostructures in Silicon, Nature , Col. 417, pp. 835–837, June 2002, which is referred to as a laser assisted direct imprinting (LADI) process. Both of these processes involve the use of forming a layer on a substrate by embossing a flowable material with a mold and subsequently solidifying the flowable material to form a patterned layer. 
     As a result of the small size of the features produced by micro-fabrication techniques, process diagnostics become increasingly important to determine the characteristics of films during processing and after processing. Many prior art process control and diagnostic techniques to facilitate determination of film characteristics have been employed in standard semiconductor processing operations. However, many of the existing process control and diagnostic techniques are not suitable for use with the embossing technique employed during micro-fabrication. 
     Thus, a need exists for providing improved process and diagnostic techniques for use with micro-fabrication processes, such as imprint lithography. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to providing a method and system to measure characteristics of a film disposed on a substrate. The method includes identifying a plurality of processing regions on the film; measuring characteristics of a subset of the plurality of processing regions, defining measured characteristics; determining a variation of one of the measured characteristics; and associating a cause of the variations based upon a comparison of the one of the measured characteristics to measured characteristics associated with the remaining processing regions of the subset. The system carries out the aforementioned method. These and other embodiments are discussed more fully below. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a lithographic system in accordance with the present invention; 
         FIG. 2  is a simplified elevation view of a lithographic system shown in  FIG. 1 ; 
         FIG. 3  is a simplified representation of material from which an imprinting layer, shown in  FIG. 2 , is comprised before being polymerized and cross-linked; 
         FIG. 4  is a simplified representation of cross-linked polymer material into which the material shown in  FIG. 3  is transformed after being subjected to radiation; 
         FIG. 5  is a simplified elevation view of a mold spaced-apart from the imprinting layer, shown in  FIG. 1 , after patterning of the imprinting layer; 
         FIG. 6  is a simplified elevation view of an additional imprinting layer positioned atop of the substrate, shown in  FIG. 5 , after the pattern in the first imprinting layer is transferred therein; 
         FIG. 7  is a top down view of the substrate shown in  FIGS. 1 and 2 ; 
         FIG. 8  is a plan view of a sensing system in accordance with the present invention; 
         FIG. 9  is a detailed perspective view of an imprint head shown in  FIG. 1 ; 
         FIG. 10  is a detailed cross-sectional view of a substrate, having a mold thereon, attached to a chucking system, shown in  FIG. 1 ; 
         FIG. 11  is an exploded perspective view of the imprint head shown in  FIG. 9 ; 
         FIG. 12  is a graph showing the mapping of reflected radiation, sensed by the sensing system shown in  FIG. 8 , in a frequency domain in accordance with the present invention; and 
         FIG. 13  is a flow chart showing a process for measuring characteristics of a film in accordance with the present invention; and 
         FIG. 14  is a side view of the imprinting layer shown in  FIG. 5 , having a defect therein. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  depicts a lithographic system  10  in accordance with one embodiment of the present invention that includes a pair of spaced-apart bridge supports  12  having a bridge  14  and a stage support  16  extending therebetween. Bridge  14  and stage support  16  are spaced-apart. Coupled to bridge  14  is an imprint head  18 , which extends from bridge  14  toward stage support  16  and provides movement along the Z-axis. Disposed upon stage support  16  to face imprint head  18  is a motion stage, referred to as a substrate support stack  20 . Substrate support stack  20  is configured to move with respect to stage support  16  along X- and Y-axes. It should be understood that imprint head  18  may provide movement along the X- and Y-axes, as well as the Z-axis, and motion stage  20  may provide movement in the Z-axis, as well as the X- and Y-axes. An exemplary substrate support stack  20  is disclosed in U.S. patent application Ser. No. 10/194,414, filed Jul. 11, 2002, entitled “Step and Repeat Imprint Lithography Systems,” assigned to the assignee of the present invention, and which is incorporated by reference herein in its entirety. A radiation source  22  is coupled to lithographic system  10  to impinge actinic radiation upon substrate support stack  20 . As shown, radiation source  22  is coupled to bridge  14  and includes a power generator  24  connected to radiation source  22 . Operation of lithographic system  10  is typically controlled by a processor  26  that is in data communication therewith. 
     Referring to both  FIGS. 1 and 2 , included in imprint head  18 , is a chuck  28  to which a template  30  having a mold  32  thereon is mounted. An imprint head  18  and chuck  28  is disclosed in U.S. patent application Ser. No. 10/293,224, entitled “A Chucking System for Modulating Shapes of Substrates” filed Nov. 13, 2002, which is assigned to the assignee of the present invention and incorporated by reference herein, as well as U.S. patent application Ser. No. 10/316,963, entitled “A Method for Modulating Shapes of Substrates” filed Dec. 11, 2002, which is assigned to the assignee of the present invention and incorporated by reference herein. Mold  32  includes a plurality of features defined by a plurality of spaced-apart recessions  34  and protrusions  36 . The plurality of features defines an original pattern that forms the basis of a pattern that is to be transferred into a wafer  38  positioned on motion stage  20 . To that end, imprint head  18  and/or motion stage  20  may vary a distance “d” between mold  32  and wafer  38 . In this manner, the features on mold  32  may be imprinted into a flowable region of wafer  38 , discussed more fully below. Radiation source  22  is located so that mold  32  is positioned between radiation source  22  and wafer  38 . As a result, mold  32  is fabricated from a material that allows it to be substantially transparent to the radiation produced by radiation source  22 . 
     Referring to both  FIGS. 2 and 3 , a flowable region, such as an imprinting layer  40 , is disposed on a portion of a surface  42  that presents a substantially planar profile. A flowable region may be formed using any known technique, such as a hot embossing process disclosed in U.S. Pat. No. 5,772,905, which is incorporated by reference in its entirety herein, or a laser assisted direct imprinting (LADI) process of the type described by Chou et al. in  Ultrafast and Direct Imprint of Nanostructures in Silicon, Nature , Col. 417, pp. 835–837, June 2002. In the present embodiment, however, a flowable region consists of imprinting layer  40  being deposited as a plurality of spaced-apart discrete beads  44  of a material  46  on wafer  38 , discussed more fully below. An exemplary system for depositing beads  44  is disclosed in U.S. patent application Ser. No. 10/191,749, filed Jul. 9, 2002, entitled “System and Method for Dispensing Liquids,” and which is assigned to the assignee of the present invention, and which is incorporated by reference in its entirety herein. Imprinting layer  40  is formed from material  46  that may be selectively polymerized and cross-linked to record the original pattern therein, defining a recorded pattern. An exemplary composition for material  46  is disclosed in U.S. patent application Ser. No. 10/463,396, filed Jun. 16, 2003 and entitled “Method to Reduce Adhesion Between a Conformable Region and a Pattern of a Mold,” which is incorporated by reference in its entirety herein. Material  46  is shown in  FIG. 4  as being cross-linked at points  48 , forming a cross-linked polymer material  50 . 
     Referring to  FIGS. 2 ,  3  and  5 , the pattern recorded in imprinting layer  40  is produced, in part, by mechanical contact with mold  32 . To that end, distance “d” is reduced to allow imprinting beads  44  to come into mechanical contact with mold  32 , spreading beads  44  so as to form imprinting layer  40  with a contiguous formation of material  46  over surface  42 . In one embodiment, distance “d” is reduced to allow sub-portions  52  of imprinting layer  40  to ingress into and fill recessions  34 . 
     To facilitate filling of recessions  34 , material  46  is provided with the requisite properties to completely fill recessions  34 , while covering surface  42  with a contiguous formation of material  46 . In the present embodiment, sub-portions  54  of imprinting layer  40  in superimposition with protrusions  36  remain after the desired, usually minimum, distance “d”, has been reached, leaving sub-portions  52  with a thickness t 1 , and sub-portions  54  with a thickness t 2 . Thicknesses “t 1 ” and “t 2 ” may be any thickness desired, dependent upon the application. 
     Referring to  FIGS. 2 ,  3  and  4 , after a desired distance “d” has been reached, radiation source  22  produces actinic radiation that polymerizes and cross-links material  46 , forming cross-linked polymer material  50 . As a result, the composition of imprinting layer  40  transforms from material  46  to cross-linked polymer material  50 , which is a solid. Specifically, cross-linked polymer material  50  is solidified to provide side  56  of imprinting layer  40  with a shape conforming to a shape of a surface  58  of mold  32 , shown more clearly in  FIG. 5 . After imprinting layer  40  is transformed to consist of cross-linked polymer material  50 , shown in  FIG. 4 , imprint head  18 , shown in  FIG. 2 , is moved to increase distance “d” so that mold  32  and imprinting layer  40  are spaced-apart. 
     Referring to  FIG. 5 , additional processing may be employed to complete the patterning of wafer  38 . For example, wafer  38  and imprinting layer  40  may be etched to transfer the pattern of imprinting layer  40  into wafer  38 , providing a patterned surface  60 , shown in  FIG. 6 . To facilitate etching, the material from which imprinting layer  40  is formed may be varied to define a relative etch rate with respect to wafer  38 , as desired. The relative etch rate of imprinting layer  40  to wafer  38  may be in a range of about 1.5:1 to about 100:1. 
     Referring to  FIGS. 7 and 8 , typically the entire wafer  38  is patterned employing a step-and-repeat process. The step-and-repeat processes includes defining a plurality of regions, shown as, a–l, on wafer  38  in which the original pattern on mold  32  will be recorded. The original pattern on mold  32  may be coextensive with the entire surface of mold  32 , or simply located to a sub-portion thereof. The present invention will be discussed with respect to the original pattern being coextensive with the surface of mold  32  that faces wafer  38 . Proper execution of a step-and-repeat process may include proper alignment of mold  32  with each of regions a–l. To that end, mold  32  includes alignment marks (not shown). One or more of regions a–l includes fiducial marks (not shown). By ensuring that alignment marks (not shown) are properly aligned with fiducial marks (not shown), proper alignment of mold  32  with one of regions a–l in superimposition therewith is ensured. To that end, sensing device  62 , discussed more fully below, may be employed. In this manner, mold  32  is sequentially contacted with each of processing regions a–l to record a pattern thereon. 
     Sensing device  62  may also be employed to facilitate process diagnostics. To that end, sensing device  62  includes a light source  64  and an optical train  66  to focus light upon wafer  38 . Sensing device  62  is configured to focus alignment radiation reflected from regions a–l onto a single focal plane, P, wherein an optical sensor  68  may be positioned. As a result, optical train  66  may be configured to provide wavelength-dependent focal lengths, should it be desired and differing wavelengths of light employed. Light may be produced in any manner known in the art. For example, a single broadband source of light, shown as a light  70 , may produce wavelengths that impinge upon optical train  66 . Optical band-pass filters (not shown) may be disposed between the broadband source and the alignment marks (not shown). 
     Alternatively, a plurality of sources of light (not shown) may be employed, each one of which produces distinct wavelengths of light. Light  70  is focused by optical train  66  to impinge upon regions a–l at one or more regions, shown as region R 1  and region R 2 . Light reflects from regions R 1  and R 2 , shown as a reflected light  72 , and is collected by a collector lens  74 . Collector lens  74  focuses all wavelengths of reflected light  72  onto plane P so that optical sensor  68  detects reflected light  72 . The reflected light contains information concerning characteristics of imprinting layer  40  using well known techniques. For example, characteristics, such as, film thickness, pattern quality, pattern alignment, pattern critical dimension variation and the like may be obtained by light sensed by sensor  68 . The information sensed by sensor  68  is transmitted to processor  26  that quantizes the same to create measurement quantizations. Processor  26  may then compare information received from sensor  68  to a priori information contained in a look up table, for example in memory  106 , to determine whether anomalies are present in imprinting layer  40  of regions a–l. 
     Referring to  FIGS. 1 and 7 , were an anomaly found in the pattern generated in a processing region a–l, the step-and-repeat imprinting process is found to facilitate determining a source of the anomaly. For example, were it found that a substantially similar anomaly was found in each of processing regions a–l, it could be deduced that imprint head  18  was the cause of the anomaly. To determine which subsystem of imprint head  18  contributed to, or caused, the anomaly, the subsystems could be systematically replaced. 
     For example, referring to  FIGS. 9 and 10 , imprint head  18  includes many subsystems, such as head housing  76  to which template  30  is coupled via a chucking system  80  that includes chuck body  28 . Specifically, template  30  includes opposed surfaces  84  and  86  and a periphery surface  88  extending therebetween. Surface  86  faces chucking system  80 , and mold  32  extends from surface  84 . To ensure that fluid from beads  44 , shown in  FIG. 2 , do not spread beyond the area of mold  32 , surface  58  of mold  32  is spaced-apart from surface  84  of template  30  a distance on the order of micron, e.g., 15 microns. A calibration system  90  is coupled to imprint head housing  76 , and chuck body  28  couples template  30  to calibration system  90  vis-à-vis a flexure system  92 . Calibration system  90  facilitates proper orientation alignment between template  30  and wafer  38 , shown in  FIG. 2 , thereby achieving a substantially uniform gap distance, “d”, therebetween. 
     Referring to both  FIGS. 9 and 11 , calibration system  90  includes a plurality of actuators  94 ,  96  and  98  and a base plate  100 . Specifically, actuators  94 ,  96  and  98  are connected between housing  76  and base plate  100 . Flexure system  92  includes flexure springs  102  and flexure ring  104 . Flexure ring  104  is coupled between base plate  100  and flexure springs  102 . Motion of actuators  94 ,  96  and  98  orientates flexure ring  104  that may allow for a coarse calibration of flexure springs  102  and, therefore, chuck body  28  and template  30 . Actuators  94 ,  96  and  98  also facilitate translation of flexure ring  104  to the Z-axis. Flexure springs  102  include a plurality of linear springs that facilitate gimbal-like motion in the X-Y plane so that proper orientation alignment may be achieved between wafer  38  and template  30 , shown in  FIG. 2 . 
     Referring to  FIGS. 1 ,  10  and  11 , to determine whether mold  32  attributed to an anomaly, template  30  would be replaced. Were the anomaly absent, then it could be concluded that mold  32  was the source of the anomaly. Were the anomaly still present, another subsystem of imprint head  18  could be replaced, such as, flexure springs  102 . Were the anomaly found to be absent in patterns of other regions a–l, and then it could be concluded that flexure springs  102  were the source. Were the anomaly still present, the other subsystems could be replaced, such as chuck body  28 , actuators  94 ,  96 , and  98 , flexure ring  104  and the like. 
     Were it observed that the anomaly appeared in only one of processing regions, then it could be deduced that substrate support stack  20  was the cause of the anomaly. As discussed above with respect to imprint head  18 , the subsystems of substrate support stack  20  may be individually replaced to identify the subsystem attributing to the anomaly. 
     It should also be understood, however, that anomalies and their sources may be determined without the use of Step-and-Repeat imprinting, e.g., with whole wafer patterning techniques. To that end, batches of substrates are examined during processing to determine whether anomalies are present on successive substrates. Were it found that a substantially similar anomaly was found in the same region, or a similar anomaly in differing regions, on successive wafers  38 , it could be deduced that mold  32  or chuck  28  was the cause of the defect. This could be verified by replacing mold  32 . Were the anomaly still present, it could be concluded that the cause of the anomaly was chuck  28 . Were the anomaly found not to repeat upon replacement of mold  32 , it could be concluded that mold  32  was the cause of the anomaly. Were it observed that the anomaly appeared on a limited number or one of wafers  38 , then it could be deduced that wafer  38  was the cause of the anomaly. 
     For example, the anomaly could be a film thickness variation. To that end, any one of a number of film thickness measurements can be employed, such as ellipsometry, scatteromety, broad-band spectrometry and the like. An exemplary technique for measuring film thickness is based on Fast Fourier Transform (FFT) of reflective radiation obtained from a broad-band spectrometer, which is disclosed in U.S. patent application Ser. No. 09/920,341 entitled “Methods For High-Precision Gap Orientation Sensing Between a Transparent Template and Substrate For Imprint Lithography”, which is incorporated by reference herein in its entirety. For multi-layer films, the technique may provide an average thickness of each thin film and its thickness variations by measuring at a predetermined number of sub-portions in one of processing regions a–l, e.g., 1,000 sub-portions. Employing FFT thickness measurement techniques, reflective radiation is digitized/quantized and a wave number obtained. The quantized data is then mapped into the frequency domain processing the same employing an FFT algorithm. In the frequency domain, one or more peaks, shown in  FIG. 12  as p 1  and p 2 , are obtained, one of which may correspond to the film thickness at one of the sub-portions of one of processing regions a–l. For a clearly defined single peak, for example, p 1 , the film thickness (t) may be a function of the frequency around which peak p 1  is centered. This may be derived or determined from a priori information. 
     For example, after obtaining film thickness measurements at several or all of the sub-portions, a mean value is derived from these thickness measurements. Thereafter, each of the film thickness measurements are compared to the mean value. If any one of the thickness measurements vary from the mean more than a predetermined threshold it may be determined that an anomaly with respect to the film thickness measurement in associated processing region a–l is present. Furthermore, the location of the anomaly within the processing region may be ascertained. The actual value of the threshold may be any desired and is typically dependent upon several factors, such as the design tolerance of the pattern, the thickness of the film and the like. Alternatively, it has been found to determine anomalies as a variation from a standard deviation from the mean value. To that end, the standard deviation, either first, second, third standard deviation and the like, from the mean is compared with a predetermined threshold. From the foregoing the film thickness in each of the processing regions a–l may be determined, as well as whether a film thickness anomaly is present. 
     Referring to  FIGS. 1 and 13 , in operation, a plurality of processing regions is identified at step  200 . At step  202  the characteristics of a subset of the plurality of processing regions are measured. The subset may include all of the processing regions a–l. Determined, at step  204  are a variation of one or more of the measured characteristics, using one or more of the measurement techniques mentioned above. In the present example, assume an anomaly was found in processing region b. At step  206 , a cause of the variation in processing region b is determined based upon a comparison with measured characteristics associated with processing regions a and c–l. To facilitate the aforementioned operation, processor  26  is coupled to a memory  106  that stores code to be operated on by processor  26 . The code includes a first subroutine to control the sensing device  62 , shown in  FIG. 8 , to impinge optical radiation on the plurality of processing regions a–l and detect optical radiation reflected therefrom. A second subroutine is included that controls the operations of the sensing device to obtain a predetermined number of measurements in the one of said plurality of processing regions a–l and quantizing the predetermined number of measurements to obtain a mean value, with the first subroutine determining the variation by comparing mean value with a predetermined threshold, which may be established as desired and/or based upon the application. 
     The embodiments of the present invention described above are exemplary. Although the invention has been described with respect to measuring film thickness anomalies, other anomalies may be determined. For example, distortions  99  in the pattern may formed in imprinting layer  40 , shown as a loss of planarity in sub-portion  52  in  FIG. 14 , may be sensed and the cause of the same determined employing the present invention. As a result, the system may be employed to detect anomalies in critical dimension variations of the pattern features, as well as, errors in field-to-field and/or layer-to-layer alignment. With such information adaptive control may be employed to correct/compensate for such anomalies. These measurements may be made either in-situ or post processes. Furthermore, the invention has been discussed with respect to being placed upon an imprint lithography machine. However, the invention may be performed by a separate machine and apart from the imprint lithography process. 
     As a result, many changes and modifications may be made to the disclosure recited above, while remaining within the scope of the invention. Therefore, the scope of the invention should not be limited by the above description, but instead should be determined with reference to the appended claims along with their full scope of equivalents.